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Stroke Induces Ependymal Cell Transformation into Radial Glia in the Subventricular Zone of the Adult Rodent Brain
Abstract
Adult ependymal cells are postmitotic and highly differentiated. Radial glial cells are neurogenic precursors. Here, we show that stroke acutely stimulated adult ependymal cell proliferation, and dividing ependymal cells of the lateral ventricle had genotype, phenotype, and morphology of radial glial cells in the rat. The majority of radial glial cells exhibited symmetrical division about the cell cleavage plane, and a radial fiber was maintained throughout each stage of cell mitosis. Increases of radial glial cells parallel expansion of neural progenitors in the subventricular zone (SVZ). Furthermore, after stroke radial glial cells derived from the SVZ supported neuron migration. These results indicate that adult ependymal cells divide and transform into radial glial cells after stroke, which could function as neural progenitor cells to generate new neurons and act as scaffolds to support neuroblast migration towards the ischemic boundary region.
... Although E1 cells do not act as neural stem cells under physiological conditions (Capela & Temple, 2002;Chiasson, Tropepe, Morshead, & van der Kooy, 1999), their ability to do so in physiopathological conditions is less clear. Some studies suggest that E1 cells may proliferate and contribute to neurogenesis (Carlen et al., 2009;Gleason, Fallon, Guerra, Liu, & Bryant, 2008;Johansson et al., 1999;Zhang et al., 2007), while others indicate that forebrain E cells are terminally differentiated (Luo et al., 2008;Young et al., 2013). ...
... In line with others, we did not find evidence for proliferating E1 cells at any time point using short and long term EdU pulse labeling (Capela & Temple, 2002;Del Carmen Gomez-Roldan et al., 2008;Spassky et al., 2005;Young et al., 2013). These data contrast with other investigators reporting that E1 cells might act as NSCs under pathological conditions (Batiz et al., 2011;Carlen et al., 2009;Johansson et al., 1999;Zhang et al., 2007). This discrepancy could result from the difficulty to discriminate between the ependymal cells and astrocytes or from the fact that different types or degree of insults differentially affect the ependyma causing either denudation or preservation (Chojnacki, Mak, & Weiss, 2009). ...
... This discrepancy could result from the difficulty to discriminate between the ependymal cells and astrocytes or from the fact that different types or degree of insults differentially affect the ependyma causing either denudation or preservation (Chojnacki, Mak, & Weiss, 2009). Indeed ependymal denudation is generally associated with either E1 cell proliferation (Carlen et al., 2009;Johansson et al., 1999;Zhang et al., 2007) or differentiation of SVZ astrocytes into E1 cells (Luo et al., 2008) to regenerate the depleted structure. By contrast, in situations of ependymal preservation when restoration of the ependymal pool is not required, E1 cells remain quiescent and undergo subtle changes to preserve the ependymal function (Young et al., 2013). ...
Ependymal cells (E1/E2) and ciliated B1cells confer a unique pinwheel architecture to the ventricular surface of the subventricular zone (SVZ), and their cilia act as sensors to ventricular changes during development and aging. While several studies showed that forebrain demyelination reactivates the SVZ triggering proliferation, ectopic migration, and oligodendrogenesis for myelin repair, the potential role of ciliated cells in this process was not investigated. Using conventional and lateral wall whole mount preparation immunohistochemistry in addition to electron microscopy in a forebrain-targeted model of experimental autoimmune encephalomyelitis (tEAE), we show an early decrease in numbers of pinwheels, B1 cells, and E2 cells. These changes were transient and simultaneous to tEAE-induced SVZ stem cell proliferation. The early drop in B1/E2 cell numbers was followed by B1/E2 cell recovery. While E1 cell division and ependymal ribbon disruption were never observed, E1 cells showed important morphological modifications reflected by their enlargement, extended cytoskeleton, and reinforced cell-cell junction complexes overtime, possibly reflecting protective mechanisms against ventricular insults. Finally, tEAE disrupted motile cilia planar cell polarity and cilia orientation in ependymal cells. Therefore, significant ventricular modifications in ciliated cells occur early in response to tEAE suggesting a role for these cells in SVZ stem cell signalling not only during development/aging but also during inflammatory demyelination. These observations may have major implications for understanding pathophysiology of and designing therapeutic approaches for inflammatory demyelinating diseases such as MS.
... Until recently, only two brain niches, the subventricular zone (SVZ) of the anterolateral ventricle and the subgranular zone (SGZ) of the hippocampal dentate gyrus, were thought to be capable of generating new neurons throughout adult life (Alvarez-Buylla and Lim, 2004;Doetsch et al., 1999aDoetsch et al., , 1999bDoetsch, 2003aDoetsch, , 2003bLie et al., 2004;Ming and Song, 2005). However, in the last decade, there has been mounting evidence to show widespread neurogenesis and gliogenesis in the adult brain, particularly after injury (Barnabé-Heider et al., 2010;Carlén et al., 2009;Decimo et al., 2012;Lin et al., 2015;Lindvall and Kokaia, 2008;Robins et al., 2013) or other inductive stimuli (Bennett et al., 2009;Cunningham et al., 2012;Decimo et al., 2011;Kokoeva et al., 2007Kokoeva et al., , 2005; Lee et al., 2012aLee et al., , 2012bMigaud et al., 2010;Pencea et al., 2001b;Sanin et al., 2013;Suh et al., 2007;Sundholm-Peters et al., 2004;Xu et al., 2005;Zhang et al., 2007). This review will focus on the role of classic and novel niches in brain homeostasis and in their response to injury. ...
... Uniformly, these studies show a marked but transient amplification of proliferating subependemal NSCs in the SVZ and SGZ, capable of migrating towards the injury and differentiating into new neurons (Barkho et al., 2006;Brazel et al., , 2005Haas et al., 2005;Kokaia and Lindvall, 2003;Ohira et al., 2009;Romanko et al., 2004;Thored et al., 2006;Yamashita et al., 2006). In similar fashion, ependymal cells in the SVZ which are not involved in constituitive neurogenesis in the healthy brain, transform into proliferating radial glial progenitors, further contributing to the reparative response to stroke (Zhang et al., 2007). In spite of this vigorous stem cell response to injury, the progenitor cell pool arising from subependymal and ependymal stem cells depletes in the SVZ over time after ischemic injury (Brazel and Rao, 2004;Carlén et al., 2009;Levison et al., 2001;Romanko et al., 2004). ...
... Moreover, because of the significant up-amplification of NSCs after stroke, proliferating subependymal NSCs in 3V ( Fig. 2B-D) and 4V (Fig. 2G) niches, predominantly on the side of the injury, were additionally detected for the first time . Also as widely reported previously (Barnabé-Heider et al., 2010;Carlén et al., 2009;Ekdahl et al., 2009;Lindvall and Kokaia, 2008;Robins et al., 2013), enhanced proliferation of ependymal tanycytes lining the mid-level 3V was also observed ipsilaterally after stroke (Fig. 2D, E) or other inductive stimuli (Lee et al., 2012a(Lee et al., , 2012bMigaud et al., 2010;Sundholm-Peters et al., 2004;Xu et al., 2005;Zhang et al., 2007). It is unlikely that stem cells in these novel ventricular locations have migrated there from more classic niche sites since virally-labeled SVZ NSCs do not appear in the 3V or 4V niches after MCAO . ...
Neural stem cells (NSCs) critical for the continued production of new neurons and glia are sequestered in distinct areas of the brain called stem cell niches. Until recently, only two forebrain sites, the subventricular zone (SVZ) of the anterolateral ventricle and the subgranular zone (SGZ) of the hippocampus, have been recognized adult stem cell niches (Alvarez-Buylla and Lim, 2004; Doetsch et al., 1999a, 1999b; Doetsch, 2003a, 2003b; Lie et al., 2004; Ming and Song, 2005). Nonetheless, the last decade has been witness to a growing literature suggesting that in fact the adult brain contains stem cell niches along the entire extent of the ventricular system. These niches are capable of widespread neurogenesis and gliogenesis, particularly after injury (Barnabé-Heider et al., 2010; Carlén et al., 2009; Decimo et al., 2012; Lin et al., 2015; Lindvall and Kokaia, 2008; Robins et al., 2013) or other inductive stimuli (Bennett et al., 2009; Cunningham et al., 2012; Decimo et al., 2011; Kokoeva et al., 2007, 2005; Lee et al., 2012; Migaud et al., 2010; Pencea et al., 2001b; Sanin et al., 2013; Suh et al., 2007; Sundholm-Peters et al., 2004; Xu et al., 2005; Zhang et al., 2007). This review focuses on the role of these novel and classic brain niches in maintaining adult neurogenesis and gliogenesis in response to normal physiological and injury-related pathological cues.
Copyright © 2015. Published by Elsevier B.V.
... After that, whole mounts were incubated with secondary antibodies for an additional 48 h. The following primary antibodies were used in the present studies: mouse anti-acetylated tubulin (1:1000, Sigma-Aldrich), rabbit anti-ctubulin Three dimensional images were acquired using Zeiss two-photon microscopy (Zeiss LSM 510 NLO) [17,20]. The images were taken from the apical surface down to the basal whole mount with 0.5 or 1 mm interval at Z axis under a 406 or 636 objective, with total 20 or 50 mm in thickness. ...
... Non-overlap fields (9)(10)(11)(12) were acquired from anterior-dorsal (AD), anterior-ventral (AV) and posterior dorsal (PD) of a whole mount [1,19]. The density of immunoreactive cells in each image was measured according to our published protocol [17,20]. The data are presented as the average of imaged fields. ...
... Using rat brain coronal sections, we previously showed that stroke induced ependymal cell proliferation based on their cellular morphology and their radial glial phenotype [20]. In the present study, using whole-mount preparations of the lateral ventricle wall in combination with molecular markers and cytoarchitecture to characterize ependymal cells, we did not find any BrdU + ependymal cells on the ventricular surface beyond 30 days of stroke onset. ...
The unique cellular and vascular architecture of the adult ventricular-subventricular zone (V/SVZ) neurogenic niche plays an important role in regulating neural stem cell function. However, the in vivo identification of neural stem cells and their relationship to blood vessels within this niche in response to stroke remain largely unknown. Using whole-mount preparation of the lateral ventricle wall, we examined the architecture of neural stem cells and blood vessels in the V/SVZ of adult mouse over the course of 3 months after onset of focal cerebral ischemia. Stroke substantially increased the number of glial fibrillary acidic protein (GFAP) positive neural stem cells that are in contact with the cerebrospinal fluid (CSF) via their apical processes at the center of pinwheel structures formed by ependymal cells residing in the lateral ventricle. Long basal processes of these cells extended to blood vessels beneath the ependymal layer. Moreover, stroke increased V/SVZ endothelial cell proliferation from 2% in non-ischemic mice to 12 and 15% at 7 and 14 days after stroke, respectively. Vascular volume in the V/SVZ was augmented from 3% of the total volume prior to stroke to 6% at 90 days after stroke. Stroke-increased angiogenesis was closely associated with neuroblasts that expanded to nearly encompass the entire lateral ventricular wall in the V/SVZ. These data indicate that stroke induces long-term alterations of the neural stem cell and vascular architecture of the adult V/SVZ neurogenic niche. These post-stroke structural changes may provide insight into neural stem cell mediation of stroke-induced neurogenesis through the interaction of neural stem cells with proteins in the CSF and their sub-ependymal neurovascular interaction.
... Although ependymal cells in the adult are quiescent, several evidences suggest that they may behave as NSC under specific circumstances. First, forebrain ependymal cells acquire radial glial cell features under certain conditions such as nervous tissue injury (Namiki and Tator 1999), stroke (Carlen et al. 2009;Zhang et al. 2007), carcinogenic transformation (Taylor et al. 2005), Notch1 cell signalling blockade (Carlen et al. 2009), and exposure to growth factors (Gregg and Weiss 2003). Second, a hallmark of all stem cells is the asymmetric cell division, a feature that has also been observed in ependymal cells after brain injury (Gleason et al. 2008). ...
... Second, a hallmark of all stem cells is the asymmetric cell division, a feature that has also been observed in ependymal cells after brain injury (Gleason et al. 2008). Third, it has been demonstrated that ependymal cells can proliferate under certain conditions such as injury of the nervous system (Gleason et al. 2008;Meletis et al. 2008;Cizkova et al. 2009;Moreno-Manzano et al. 2009) and stroke (Carlen et al. 2009;Li et al. 2002;Zhang et al. 2005Zhang et al. , 2007, rendering a progeny consisting of neurons (Carlen et al. 2009) or astrocytes and oligodendrocytes (Meletis et al. 2008). ...
... However, the occasional presence of cells positive for both CD133 and Ki67 in the ependymal layer would argue against such postmitotic character (Coskun et al. 2008). In addition, in certain circumstances, such as stroke or injury of the nervous system, ependymal cells express radial glial cell markers (Carlen et al. 2009;Gregg and Weiss 2003;Taylor et al. 2005;Zhang et al. 2007) or can even proliferate (Gleason et al. 2008;Cizkova et al. 2009;Moreno-Manzano et al. 2009;Li et al. 2002;Zhang et al. 2005Zhang et al. , 2007 and give rise to neurons (Carlen et al. 2009) or oligodendrocytes (Meletis et al. 2008). Such capacity of dedifferentiation and proliferation has been specifically described in the ependymal cells of the spinal cord (Cizkova et al. 2009;Meletis et al. 2008;Danilov et al. 2006;Namiki and Tator 1999;Moreno-Manzano et al. 2009;Attar et al. 2005). ...
Ependymal cells form an epithelium lining the ventricular cavities of the vertebrate brain. Numerous methods to obtain primary culture ependymal cells have been developed. Most of them use foetal or neonatal rat brain and the few that utilize adult brain hardly achieve purity. Here, we describe a simple and novel method to obtain a pure non-adherent ependymal cell culture from explants of the striatal and septal walls of the lateral ventricles. The combination of a low incubation temperature followed by a gentle enzymatic digestion allows the detachment of most of the ependymal cells from the ventricular wall in a period of 6 h. Along with ependymal cells, a low percentage (less than 6 %) of non-ependymal cells also detaches. However, they do not survive under two restrictive culture conditions: (1) a simple medium (alpha-MEM with glucose) without any supplement; and (2) a low density of 1 cell/µl. This purification method strategy does not require cell labelling with antibodies and cell sorting, which makes it a simpler and cheaper procedure than other methods previously described. After a period of 48 h, only ependymal cells survive such conditions, revealing the remarkable survival capacity of ependymal cells. Ependymal cells can be maintained in culture for up to 7-10 days, with the best survival rates obtained in Neurobasal supplemented with B27 among the tested media. After 7 days in culture, ependymal cells lose most of the cilia and therefore the mobility, while acquiring radial glial cell markers (GFAP, BLBP, GLAST). This interesting fact might indicate a reprogramming of the cell identity.
... It has also been reported that MCAO elicits a proliferative response of NSCs in ventricular zones caudal to the lateral ventricles that includes the third and fourth ventricles (Lin et al. 2015). Lastly, in addition to canonical GFAP + SVZ astrocytes, ependymal stem cells of the SVZ are reported to act as an additional, but temporary, neurogenic reservoir 14 days after stroke (Zhang et al. 2007). However, these SVZ-derived ependymal stem cells are seemingly restricted to a neuronal lineage, with negligible contribution to the formation of the glial scar formation. ...
... However, these SVZ-derived ependymal stem cells are seemingly restricted to a neuronal lineage, with negligible contribution to the formation of the glial scar formation. Rather, they are rapidly depleted due to lack of the capacity for self-renewal that is retained by SVZ astrocytes (Zhang et al. 2007). ...
Glial scars are a common pathological occurrence in a variety of central nervous system (CNS) diseases and injuries. They are caused after severe damage and consist of reactive glia that form a barrier around the damaged tissue that leads to a non-permissive microenvironment which prevents proper endogenous regeneration. While there are a number of therapies that are able to address some components of disease, there are none that provide regenerative properties. Within the past decade, neural stem cells (NSCs) have been heavily studied due to their potent anti-inflammatory and reparative capabilities in disease and injury. Exogenously applied NSCs have been found to aid in glial scar healing by reducing inflammation and providing cell replacement. However, endogenous NSCs have also been found to contribute to the reactive environment by different means. Further understanding how NSCs can be leveraged to aid in the resolution of the glial scar is imperative in the use of these cells as regenerative therapies. To do so, humanised 3D model systems have been developed to study the development and maintenance of the glial scar. Herein, we explore the current work on endogenous and exogenous NSCs in the glial scar as well as the novel 3D stem cell–based technologies being used to model this pathology in a dish.
... Other cellular types such as ependymal cells proliferation are induced by ischemia. In a rat stroke study, Zhang et al (Zhang et al., 2007) reported that ependymal cells lining the lateral ventricle wall were transformed into radial glia cells and were surrounded by type-C (progenitors) and type-A (neuroblasts) cells in SVZ. Several molecules and mechanisms are implicated in neural stem progenitor cells (NPCs) regulation. ...
... Radial glia is distributed in both SVZ and striatum after stroke and probably guides migrating neuroblasts (Zhang et al., 2007). Blood vessels are also involved in this process, neuroblasts were located in large number in physical proximity to endothelial cells in the peri-infarct cortex in the presence of vascular remodeling (angiogenesis) (Thored et al., 2007). ...
As the leading cause of disability in adulthood, stroke remains an important subject of study because no effective treatments except by rehabilitation are currently available after the first hours. The acute phase therapy reperfusion is conditinated to a rapid detection and management. For this reason, just around 10% of patients benefit of this. The application of new brain imaging techniques can be relevant for the comprehension of acute stroke mechanism and for a more accurate identification of candidates for acute phase reperfusion therapies. In our first study in a rat model of ischemic stroke (by occlusion of middle cerebral artery, MCAo) we characterized the microvascular, hemodynamic and local saturation in oxygen (StO2) alterations in the acute phase (around one hour after stroke onset), using multiparametric MRI. We demonstrated the potential of StO2 MRI map for detecting the ischemic core without the inclusion of any reversible ischemic damage.Therapeutic approaches that can be applied beyond acute phase are urgently needed. Most evidences suggest that cell therapies have the potential to reduce post-stroke disability through neuroprotection and brain remodelling mechanism. Despite of beneficial effects were demonstrated, some issues need to be addressed, such as the important loss of grafted cells reported when cells are administrated into infarct cavity. We evaluated an innovating biomaterial hydrogel in vivo and their potential to promote long term protection of grafted cells. In a pilot study, we demonstrated that hyaluronic acid-based hydrogel (HA) HyStemTM-HP (Sigma-Aldrich, France) presented a long lasting (over 28 days) in healthy brain suggesting to be a good candidate for cell therapy.When co-administrated by intracerebral route combined with human Mesenchymal Stem Cells (hMSC from bone marrow) seven days after MCAo, the HAhydrogel promoted an increase of hMSC survival and improved angiogenic process. In the immunohistological study, RECA1+ (vessel endothelial cells makers) were increased. Collagen-IV+ cells (vessel basal membrane) were also increased. Post stroke angiogenesis is a key process for brain recovery. No difference in lesion volume was detected among the ischemic groups by in vivo MRI. Despite the pro-angiogenic beneficial effect, neither hMSC+HA nor hMSC alone were able to improve functional results 3 weeks after intracerebral injection (assessed by modified neurological severity score (mNSS), and adhesive removal test).
... Greater cell plasticity appears to occur on more severe injury, such as TBI and stroke. For instance, ependymal cells have been observed to change their morphology radial glial-like shape after stroke (Zhang et al. 2007). Normally, quiescent ependymal cells activate and generate both astrocytes and neuroblasts suggesting that they might act as a reservoir stem-cell population (Zhang et al. 2007;Carlen et al. 2009). ...
... For instance, ependymal cells have been observed to change their morphology radial glial-like shape after stroke (Zhang et al. 2007). Normally, quiescent ependymal cells activate and generate both astrocytes and neuroblasts suggesting that they might act as a reservoir stem-cell population (Zhang et al. 2007;Carlen et al. 2009). Astrocytes represent a second cell population displaying enhanced cell plasticity after injury. ...
Aided by advances in technology, recent studies of neural precursor identity and regulation have revealed various cell types as contributors to ongoing cell genesis in the adult mammalian brain. Here, we use stem-cell biology as a framework to highlight the diversity of adult neural precursor populations and emphasize their hierarchy, organization, and plasticity under physiological and pathological conditions.
... Interestingly, Zhang et al. (2007a) found that the ependymal cells lining the lateral ventricular wall also proliferate acutely and transiently after stroke. The ependymal cells were transformed into radial glia cells, and were surrounded by type-C ( progenitors) and type-A (neuroblasts) cells in the SVZ. ...
... The new neuroblasts exhibit distinct migratory behaviors and can divide on their way through the striatum toward the damage (Zhang et al. 2007b). Radial glia, which are distributed both in the SVZ and the ischemic striatum after stroke, are probably involved in guiding the migrating neuroblasts, as evidenced by both in vivo and in vitro data (Zhang et al. 2007a). There is also a close association between the newly formed neurons and the vasculature when they migrate toward the damaged area. ...
Abulk of experimental evidence supports the idea that the stroke-damaged adult brain makes an attempt to repair itself by producing new neurons also in areas where neurogenesis does not normally occur (e.g., the striatum and cerebral cortex). Knowledge about mechanisms regulating the different steps of neurogenesis after stroke is rapidly increasing but still incomplete. The functional consequences of stroke-induced neurogenesis and the level of integration of the new neurons into existing neural circuitries are poorly understood. To have a substantial impact on the recovery after stroke, this potential mechanism for self-repair needs to be enhanced, primarily by increasing the survival and differentiation of the generated neuroblasts. Moreover, for efficient repair, optimization of neurogenesis most likely needs to be combined with promotion of other endogenous neuroregenerative responses (e.g., protection and sprouting of remaining mature neurons, transplantation of neural stem/progenitor cells [NSPC]–derived neurons and glia cells, and modulation of inflammation). © 2015 Cold Spring Harbor Laboratory Press; all rights reserved.
... Indeed, we found a dramatic and sustained rise in NSC proliferation in the SVZ and CVOs after focal stroke. These findings are consistent with several recent reports showing similar increases in the SVZ and SGZ of the MCAO-lesioned rat (Zhang et al., 2001(Zhang et al., , 2007Thored et al., 2006;Wang et al., 2011;Sanin et al., 2013), and significantly, in ischemic patients (Sanin et al., 2013). Importantly, the increase in proliferating cells could not be attributed to the infiltration of proliferating immune cells (T-cell, neutrophil) after stroke although there was a rise in dividing IBA-1+ (nestin negative) macrophages/microglia on the ischemic side. ...
... The second group of cells was composed of ependymal cells with long processes projecting away from the ventricular wall. These cells known as tanycytes have been described previously both in the quiescent brain (Chiasson et al., 1999;Spassky et al., 2005) and after injury Carlén et al., 2009;Barnabé-Heider et al., 2010;Robins et al., 2013) or other inductive cues (Sundholm-Peters et al., 2004;Xu et al., 2005;Zhang et al., 2007;Migaud et al., 2010;Lee et al., 2012). Lying between these two groups of cells, we noted a transitional zone composed of a mixture of dividing subependymal and ependymal cells. ...
Previous studies have established the subventricular (SVZ) and subgranular (SGZ) zones as sites of neurogenesis in the adult forebrain (Doetsch et al., 1999a; Doetsch, 2003a). Work from our laboratory further indicated that midline structures known as circumventricular organs (CVOs) also serve as adult neural stem cell (NSC) niches (Bennett et al., 2009, 2010). In the quiescent rat brain, NSC proliferation remains low in all of these sites. Therefore, we recently examined whether ischemic stroke injury (MCAO) or sustained intraventricular infusion of the mitogen bFGF could trigger an up-regulation in NSC proliferation, inducing neurogenesis and gliogenesis. Our data show that both stroke and bFGF induce a dramatic and long-lasting (14day) rise in the proliferation (BrdU+) of nestin+Sox2+GFAP+ NSCs capable of differentiating into Olig2+ glial progenitors, GFAP+nestin- astrocyte progenitors and Dcx+neurons in the SVZ and CVOs. Moreover, because of the up-surge in NSC number, it was possible to detect for the first time several novel stem cell niches along the third (3V) and fourth (4V) ventricles. Importantly, a common feature of all brain niches was a rich vasculature with a blood-brain-barrier (BBB) that was highly permeable to systemically injected sodium fluorescein. These data indicate that stem cell niches are more extensive than once believed and exist at multiple sites along the entire ventricular system, consistent with the potential for widespread neurogenesis and gliogenesis in the adult brain, particularly after injury. We further suggest that because of their leaky BBB, stem cell niches are well-positioned to respond to systemic injury-related cues which may be important for stem-cell mediated brain repair.
Copyright © 2014. Published by Elsevier Inc.
... 4A, C, M). These results are in accordance with a previous study that used a different model, and found an increase in RGLCs around the LV of adult rats a few days after focal ischemia (Zhang et al., 2007). We observed a similar increase in the number of RGLCs in the BCCL animals treated with BMMCs (BCCL + BMMC: 42.73 ± 4.55; n = 6), but there was no difference in the number of RGLCs in the sham + BMMC animals compared with the sham animals (sham + BMMC: 28.29 ± 1.29; n = 4 vs sham: 27.88 ± 1.98) (Figs. ...
... In 2007, Zhang and co-workers demonstrated that ependymal cells proliferate and transform into RGLCs 1-2 days after a stroke. Seven days after injury, fewer RGLCs were observed (Zhang et al., 2007). These findings concord with our observation that after BCCL, the number of RGLCs increased temporarily. ...
... To confirm ependymal GFAP expression, we examined coronal sections and used vimentin as a marker of ependymal cells. Seven days post stroke, vimentin+ ependymal cells expressed GFAP (Fig. 5O,P) and some extended basal processes into the SVZ (Fig. 5Q) (Zhang et al. 2007). The number of vimentin+ ependymal processes, which extend into the SVZ, increased post stroke (20.1 ± 1.8) compared with controls (5.6 ± 1.0; P < 0.0001; Fig. 5R). ...
... We did not find proliferating ependymal cells 7-and 14-days after stroke, using pulse and long-term BrdU labeling, respectively. This contrasts with post stroke rat ependymal cells that incorporated BrdU and expressed the mitotic radial glia marker phosphorylated vimentin (Zhang et al. 2007). There may be interspecies differences, alternatively ependymal cells may have divided so rarely that even our cumulative labeling was insufficient. ...
Subventricular zone (SVZ) astrocytes and ependymal cells are both derived from radial glia and may have similar gliotic reactions
after stroke. Diminishing SVZ neurogenesis worsens outcomes in mice, yet the effects of stroke on SVZ astrocytes and ependymal
cells are poorly understood. We used mouse experimental stroke to determine if SVZ astrocytes and ependymal cells assume similar
phenotypes and if stroke impacts their functions. Using lateral ventricular wall whole mount preparations, we show that stroke
caused SVZ reactive astrocytosis, disrupting the neuroblast migratory scaffold. Also, SVZ vascular density and neural proliferation
increased but apoptosis did not. In contrast to other reports, ependymal denudation and cell division was never observed.
Remarkably, however, ependymal cells assumed features of reactive astrocytes post stroke, robustly expressing de novo glial
fibrillary acidic protein, enlargening and extending long processes. Unexpectedly, stroke disrupted motile cilia planar cell
polarity in ependymal cells. This suggested ciliary function was affected and indeed ventricular surface flow was slower and
more turbulent post stroke. Together, these results demonstrate that in response to stroke there is significant SVZ reorganization
with implications for both pathophysiology and therapeutic strategies.
... After stroke, ependymal cells showed nonstemness [80]. Ependymal cells expressed robust levels of GFAP in the brain ipsilateral to the lesion and exhibited the phenotype and morphology of radial glia and reactive astrocytes at 7 and 14 days after stroke [76,81]. Ependymal cells in the forebrain generate neuroblasts and astrocytes, which are regulated by Notch signalling. ...
Ependymal cells are indispensable components of the central nervous system (CNS). They originate from neuroepithelial cells of the neural plate and show heterogeneity, with at least three types that are localized in different locations of the CNS. As glial cells in the CNS, accumulating evidence demonstrates that ependymal cells play key roles in mammalian CNS development and normal physiological processes by controlling the production and flow of cerebrospinal fluid (CSF), brain metabolism, and waste clearance. Ependymal cells have been attached to great importance by neuroscientists because of their potential to participate in CNS disease progression. Recent studies have demonstrated that ependymal cells participate in the development and progression of various neurological diseases, such as spinal cord injury and hydrocephalus, raising the possibility that they may serve as a potential therapeutic target for the disease. This review focuses on the function of ependymal cells in the developmental CNS as well as in the CNS after injury and discusses the underlying mechanisms of controlling the functions of ependymal cells.
... On the other hand, in response to ischemia stroke, reactive astrocytes produce various neurotrophic factors including BDNF [67], FGF2 [68], and glial-derived neurotrophic factor [69,70] to protect neurons, thus contributing to the restoration of central nervous system homeostasis. Furthermore, it has been proposed that these astrocytes may support neuroblasts migrating to the infarcted brain area [12,71]. Activated astrocytes, however, also release inflammatory cytokines that induce neural tissue damage, and the formation of glial scarring can impede neuronal reconnection and extension [62]. ...
Rationale: Previous work has indicated that continuous theta-burst stimulation (cTBS), a modality of transcranial magnetic stimulation (TMS), may provide neuroprotection and improve neurological function after stroke by preserving the blood-brain barrier, altering glial polarization phenotypes, and supporting peri-infarct angiogenesis. The present study was performed to examine whether cTBS, a noninvasive neurostimulation technique, promotes neurogenesis in a photothrombotic (PT) stroke rat model and contributes to functional recovery.
Methods: Beginning 3 h or 1 week after the induction of PT stroke, once-daily 5-min cTBS treatments were applied to the infarcted hemisphere for 6 days. Samples were collected 6 days, 22 days, and 35 days after PT stroke. Fluorescent labeling, Western blotting, and behavioral tests were performed accordingly.
Results: We found that cTBS therapy significantly expanded the pool of neural progenitor cells (NPCs) and newly generated immature neurons in the cortical peri-infarct region after PT stroke. Likewise, the amount of DCX-positive immature neurons in the peri-infarct area was markedly elevated by cTBS. Application of cTBS strikingly diminished the PT-induced loss of NPCs and newly-formed neurons. In addition, the amount of newly generated mature neurons in the peri-infarct zone was significantly promoted by cTBS. Intriguingly, cTBS reduced reactive gliogenesis significantly while promoting oligodendrogenesis and preserving myelination. Mechanistic studies uncovered that cTBS upregulated brain-derived neurotrophic factor (BDNF) and fibroblast growth factor 2 (FGF2). Finally, cTBS-treated animals displayed improved motor functions. To be noted, temozolomide (TMZ), a drug that has been previously used to suppress neurogenesis, could reverse the beneficial effects of cTBS.
Conclusions: Our findings provide new insight into the mechanism by which cTBS promotes functional recovery from stroke. We demonstrated that cTBS effectively enhances and sustains neurogenesis after PT stroke. Both early and delayed cTBS treatment could improve the survival of newly generated neurons and functional recovery, and inhibition of neurogenesis could reverse these therapeutic benefits. Mechanistically, cTBS was effective in upregulating the release of neurotrophic factors, protecting NPC and immature neurons, as well as suppressing excessive gliogenesis.
... It would therefore be helpful to elucidate the mechanisms of this blood vessel-independent neuronal migration. Previous studies have suggested that neuroblast migration is supported by astrocytes and radial glia-like cells following brain injury (Szele et al., 1996;Zhang et al. 2007;Saha et al. 2013). It is thus important to examine if these cells function as migratory scaffolds for SEZ-derived neuroblasts. ...
In the adult mammalian brain, neural stem cells (NSCs) reside in two neurogenic regions, the walls of the lateral ventricles and the subgranular zone of the hippocampus, which generate new neurons for the olfactory bulb and dentate gyrus, respectively. These adult NSCs retain their self‐renewal ability and capacity to differentiate into neurons and glia as demonstrated by in vitro studies. However, their contribution to tissue repair in disease and injury is limited, lending credence to the claim by prominent neuropathologist Ramón y Cajal that “once development was ended, the founts of growth and regeneration of the axons and dendrites dried up irrevocably”. However, recent progress toward understanding the fundamental biology of adult NSCs and their role in pathological conditions has provided new insight into the potential therapeutic utility of endogenous NSCs. In this short review, we highlight two topics: the altered behavior of NSCs after brain damage and the dysfunction of NSCs and oligodendrocyte precursor cells, another type of undifferentiated cell in the adult brain, in mood affective disorders.
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... These findings are in agreement with reports using other hNSCs [49,63]. Ekdahl et al. [63] also attributed the decreased neurogenesis to inflammation; however, increased proliferation in the SVZ has also been noted at relatively early time points after injury in the adult brain [48,64,65]. The study by Stroemer et al. [33] suggested that at 3 months poststroke, an inflammatory mechanism may operate to suppress cell proliferation and that an anti-inflammatory influence may be exerted by CTX at an early stage postimplantation to counteract the effects of MCAo. ...
Preclinical studies suggest that stem cell therapy (SCT) may improve post-stroke recovery, and clinical trials investigating safety are ongoing. However, knowledge about patients' attitudes to SCT in stroke is limited. We evaluated the knowledge and attitudes to this therapeutic approach as well as possible factors influencing this among stroke patients potentially suitable for SCT. Consecutive first-ever acute ischemic stroke patients aged 20-75 years with NIH stroke scale scores 1-18 were included. Exclusion criteria were severe comorbidities or infratentorial stroke. Clinical follow-up after 3-5 years assessed severity of residual stroke symptoms, cognitive function, functional status, patient-reported outcome, comorbidity, and after receiving standardized information, the participants also completed an 8-item questionnaire on knowledge and attitudes about SCT. The relations between clinical variables and positive attitude to SCT were assessed with logistic regression analyses. Of 108 patients included at baseline, 84 participated at follow-up and completed the questionnaire. In total, 12% had prior knowledge of SCT. When informed, 63% were positive towards it and 36% reported willingness to participate in SCT trials. Only 5-8% expressed ethical considerations regarding different stem cell sources. Positive attitudes to SCT were associated with male gender (OR: 3.74; 95% CI: 1.45-9.61; p<0.01) and better patient-reported outcome (OR: 1.02; 95% CI: 1.00-1.04; p<0.05). In conclusion, stroke patients had limited prior knowledge of SCT, yet attitudes were positive among the majority after receiving standardized and neutral information. Gender and degree of stroke recovery may influence attitudes to SCT, indicating a need for targeted information to improve knowledge about SCT.
... In addition to the uncommitted precursor cells, some ependymal cells are also able to act as NSCs in the adult brain [83,84]. For instance, forebrain ventricular CD133-positive ependymal cells show NSCs characteristics in response to brain injury [85,86]. Further, tanycytes in the adult hypothalamus and Adult Brain Neurogenesis and Gliogenesis ependymal lining of the third ventricle function as multipotential progenitor cells [87,88]. ...
The subgranular zone (SGZ) and subventricular zone (SVZ) are developmental remnants of the germinal regions of the brain, hence they retain the ability to generate neuronal progenitor cells in adult life. Neurogenesis in adult brain has an adaptive function because newly produced neurons can integrate into and modify existing neuronal circuits. In contrast to the SGZ and SVZ, other brain regions have a lower capacity to produce new neurons, and this usually occurs via parenchymal and periventricular cell genesis. Compared to neurogenesis, gliogenesis occurs more prevalently in the adult mammalian brain. Under certain circumstances, interaction occurs between neurogenesis and gliogenesis, facilitating glial cells to transform into neuronal lineage. Therefore, modulating the balance between neurogenesis and gliogenesis may present a new perspective for neurorestoration, especially in diseases associated with altered neurogenesis and/or gliogenesis, cell loss, or disturbed homeostasis of cellular constitution. The present review discusses important neuroanatomical features of adult neurogenesis and gliogenesis, aiming to explore how these processes could be modulated toward functional repair of the adult brain.
... Moreover, there are serious disturbances such as cerebral ischemia and stroke where glia are not capable of regulating pH, extracellular K + and glutamate. This disturbed homeostasis and water exchange lead to the release of cytotoxic molecules during edema of the brain due to accumulation of water in glia and, as a result, cause neuronal death [315][316][317][318][319]. Study of brain injury [316,320] and certain chemical effects on the brain has shown that they lead to a breach of glial metabolism [7] and to brain swelling and inflammation. ...
The roles of glia and polyamines (PA) in brain function and dysfunction are highlighted in this review. We emphasize that PA accumulation preferentially in glia, but not in neurons, is clearly evolutionarily determined; it is found throughout the brain, retina, peripheral nervous system, and in glial-neuronal co-cultures of multiple species, including man. This phenomenon raises key questions: (i) What are the mechanisms that underlie such uneven distribution, accumulation and release from glia? (ii) What are the consequences of PA fluxes within the brain on neuronal function? (iii) What are the roles of PAs in brain disorders and diseases? This review includes suggestions on the roles of PAs, such as putrescine (PT), spermidine (SPD), spermine (SPM) and their derivatives as novel glio-transmitters in brain since PA affect many neuronal and glial receptors, channels and transporters. Polyamines hitherto have been neglected, although it is evident that these molecules are key elements for normal brain function and their metabolic disorders, apparently, cause the development of many pathological syndromes and diseases. The study of endogenous PA allows one to put forward the basic principles of scientific research on glio-neuronal interactions and clinical therapies, which are based on the exclusivity of glial cells in terms of accumulation of PA and PA-dependent functions.
... Vimentin is a highly expressed intermediate filament protein in radial glia during brain development, and whose expression decreases during adulthood, persisting mainly in radial-like glial cells located near brain ventricles. Vimentin+/GFAP+ radial processes were observed here extending projections from the lateral ventricle wall across the striatum, suggesting that they belong to radial-like astrocytes which persisted during development or which were produced during adulthood by the de-differentiation of mature astrocytes ( Hunter and Hatten 1995;Zhou et al. 2001) or by the transformation of ependimal cells ( Zhang et al. 2007). The vimentin immunoreactivity of these processes markedly increased after the DAergic denervation, a fact that in this study was not associated with the proliferation of astrocytes or the formation of glial scars observed for this protein in previous studies ( Zhu et al. 2007;Herrmann et al. 2008). ...
Increasing evidence suggests that the dopaminergic degeneration which characterizes Parkinson's disease starts in the striatal dopamine terminals and progresses retrogradely to the body of dopamine cells in the substantia nigra. The role of striatal astrocytes in the striatal initiation of the dopaminergic degeneration is little known. This work was aimed at studying the astrocytic response to the dopaminergic denervation of the striatum. The injection of 6‐hydroxydopamine (25 μg) in the lateral ventricle of adult Sprague–Dawley rats induced a fast (4 h) and selective (unaccompanied by unspecific lesions of striatal tissue or microgliosis) degeneration of the dopaminergic innervation of the striatum which was followed by a selective astrocytosis unaccompanied by microgliosis. This astrocytosis was severe and had a specific profile which included some (e.g. up‐regulation of glial fibrillary acidic protein, GS , S100β, NDRG 2, vimentin) but not all (e.g. astrocytic proliferation or differentiation from NG 2 cells, astrocytic scars, microgliosis) the characteristics observed after the non‐selective lesion of the striatum. This astrocytosis is similar to those observed in the parkinsonian striatum and, because it is was unaccompanied by changes in other striatal cells (e.g. by microgliosis), it may be suitable to study the role of striatal astrocytes during the dopaminergic denervation which characterizes the first stages of Parkinson's disease.
image The dopaminergic denervation of the striatum induced a severe astrogliosis with a specific profile which included some (e.g. up‐regulation of GFAP , GS , S100β, NDRG 2, vimentin) but not all (e.g. astrocytic proliferation or differentiation from NG 2 cells, astrocytic scars, microgliosis) the characteristics observed after the non‐selective striatal lesions. This response may help to understand the role of striatal astrocytes during the dopaminergic denervation which characterizes the first stages of PD .
Cover Image for this issue: doi: 10.1111/jnc.13336 .
... Кроме того, существуют серьезные расстройства при ишемии мозга и инсульте, когда глия не способна регулировать рН, внеклеточный K + и глутамат. При этом нарушается гомеостаз и водообмен, что приводит к высвобождению цитотоксических молекул, отеку мозга за счет накопления воды в глии и, как результат, смерти нейронов [315][316][317][318][319]. Изучение чрепномозговых травм [316,320] и определенных химических воздействий на головной мозг показало, что они приводят к нарушению глиального метаболизма [7], отеку мозга и воспалению. ...
В обзоре рассматривается роль глии в регуляции полиаминами (ПА) нейронных взаимодействий вмозге. Мы акцентируем внимание на том, что аккумулирование ПА в глии является эволюционнодетерминированным. При рассмотрении данных, полученных на многих видах животных, включаячеловека, выявляется, что из двух основных популяций клеток в нервной системе – нейроны и гли-альные клетки (глия) – ПА аккумулируются почти исключительно в глии. При этом в головноммозге, сетчатке глаза, периферической нервной системе различных животных и глиально-нейро-нальных культурах синтез ПА, особенно спермидина (СПД) и спермина (СПМ), осуществляется нево всех, но только в нескольких нейронах и отсутствует в глии. Аккумулирование ПА в глиальныхклетках требует существования путей транспортировки от мест его синтеза или из кровотока. По-скольку полиамины и их производные регулируют активность многих рецепторов, каналов и транс-портеров в клетках мозга, локализация ПА в глиальных клетках вызывает ряд вопросов. (1) Каковымеханизмы, лежащие в основе такого неравномерного распределения, накопления ПА в глии и ихосвобождения? (2) Каковы последствия ПА потоков внутри мозга для функционирования нейро-нов? (3) Какова роль ПА при функциональных патологиях мозга и в развитии нервно-психическихзаболеваний? Этот обзор предлагает рассматривать ПА – такие, как путресцин (ПТ), спермидин(СПД), спермин (СПМ) и их производные – в качестве новых глиотрансмиттеров мозга. В исследо-ваниях по глиальной тематике полиаминам до сих пор не уделялось достаточного внимания, хотяочевидно, что эти молекулы являются ключевыми элементами для нормального функционирова-ния мозга, а нарушения их обмена, по-видимому, вызывают развитие многих патологических син-дромов и заболеваний. Изучение эндогенных ПА позволяет выдвинуть основные принципы науч-ных исследований глио-нейронного взаимодействия и клинической терапии, которые основаны наисключительности глиальных клеток в плане аккумулирования ПА и управления ПА-зависимых функций.
Глия и глиальные полиамины. Роль в функционировании мозга в норме и патологии. Available from: https://www.researchgate.net/publication/295100495_Glia_i_glialnye_poliaminy_Rol_v_funkcionirovanii_mozga_v_norme_i_patologii [accessed Jun 29 2018].
... However, doubt concerning the origin of these new neurons emerged when it was shown that the CD133 antigen was also present on a subtype of astrocytes that contact the ventricle (Mirzadeh et al., 2008), suggesting that CD133 þ progenitors may, in fact, be astrocytes rather than ependymal cells. In contrast, recent studies have converged to show that ependymal cells may act as primary precursor cells after brain injury in the adult brain (Gleason et al., 2008;Zhang et al., 2007). Genetic fate mapping showed that FoxJ1 þ ependymal cells do not self-renew to maintain their population after stroke, but are consumed as they give rise to neuroblasts and astrocytes (Carlen et al., 2009). ...
... In the ischemic striatum the number of astrocytes is increased after stroke, and the long processes of astrocytes form a network linking the SVZ and the ischemic striatum (Teramoto et al., 2003). These astrocytes may contribute to guiding neuroblasts migrating to the infarcted brain area (Parent et al., 2002;Zhang et al., 2007b). ...
Astrocytes are the most abundant cell type within the central nervous system. They play essential roles in maintaining normal brain function, as they are a critical structural and functional part of the tripartite synapses and the neurovascular unit, and communicate with neurons, oligodendrocytes and endothelial cells. After an ischemic stroke, astrocytes perform multiple functions both detrimental and beneficial, for neuronal survival during the acute phase. Aspects of the astrocytic inflammatory response to stroke may aggravate the ischemic lesion, but astrocytes also provide benefit for neuroprotection, by limiting lesion extension via anti-excitotoxicity effects and releasing neurotrophins. Similarly, during the late recovery phase after stroke, the glial scar may obstruct axonal regeneration and subsequently reduce the functional outcome; however, astrocytes also contribute to angiogenesis, neurogenesis, synaptogenesis, and axonal remodeling, and thereby promote neurological recovery. Thus, the pivotal involvement of astrocytes in normal brain function and responses to an ischemic lesion designates them as excellent therapeutic targets to improve functional outcome following stroke. In this review, we will focus on functions of astrocytes and astrocyte-mediated events during stroke and recovery. We will provide an overview of approaches on how to reduce the detrimental effects and amplify the beneficial effects of astrocytes on neuroprotection and on neurorestoration post stroke, which may lead to novel and clinically relevant therapies for stroke.
... However, it was shown by several studies that ependymal cells do not seem to be the actual neural stem cells (Capela and Temple, 2002;Doetsch et al., 1999a;Spassky et al., 2005). Though, after injury E-cells are able to transform into radial glial-like cells and function as adult neural stem cells (Coskun et al., 2008;Johansson et al., 1999;Zhang et al., 2007). Since ependymal cells show no self-renewal and thus lack an important characteristic of stem cells, these cells may rather constitute a reservoir that can be activated upon injury (Carlen et al., 2009). ...
Compared to the adult mammalian brain, the brain of the adult zebrafish Danio rerio exhibits a very high proliferative and regenerative potential. The adult mammalian brain in contrast has a very limited neurogenic capacity mainly restricted to two zones, the subventricular zone of the lateral telencephalic ventricles and the subgranular zone of the dentate gyrus of the hippocampus. In contrast, the zebrafish brain harbours 16 proliferation zones distributed all over the brain. The zebrafish has thus become a model for the study of adult neurogenesis and regeneration of nervous tissue. I characterized the expression of the two transcription factors p53 and p73 in the adult zebrafish brain. Both p53 and p73 were shown to play crucial roles in mammalian adult neurogenesis: p53 suppresses the self-renewal of adult neural stem cells and is involved in apoptotic death of neurons following damage. p73 is relevant for the survival of neurons, self-renewal and maintenance of neural stem cells as well as differentiation of precursor cells. It was thus of interest whether these genes have similar roles in the adult zebrafish brain.
I established a detailed map of the expression pattern of p53 and p73 mRNA and p53 protein in the adult zebrafish brain. p53 and p73 mRNA expression overlaps in many regions including neurogenic zones. The p53 protein is expressed in most of these regions indicating that the mRNA expression reflects the protein expression. The p53 protein is expressed in mature neurons, Type I cells (non-dividing radial glial cells) and Type IIIa and Type IIIb cells (neuroblasts) in the adult zebrafish telencephalon. In cells of the oligodendrocyte lineage and in Type II cells (dividing radial glial cells) an expression of the p53 protein is not detectable. After stab injury of the adult zebrafish telencephalon both p53 and p73 genes are up-regulated. p53 is up-regulated in Type I cells. In contrast to the uninjured brain, p53 is expressed in cells of the oligodendrocyte lineage following injury. Furthermore, target genes of p53 are up-regulated and apoptosis is induced after stab injury. These results suggest a role for p53 in constitutive and regenerative neurogenesis. However, tp53M214K mutant zebrafish do not show any phenotype. The structurally related p73 is expressed in a very similar pattern as p53 in the uninjured and injured zebrafish brain. Therefore, redundancy between p53 and p73 may occlude the manifestation of a phenotype in the p53 mutant. Taken together, the analysis of expression of both p53 and p73 in the adult zebrafish brain suggests a role of these genes during constitutive and regenerative neurogenesis. The future elucidation of the precise function of the two genes in these processes requires, however, double mutant analysis.
... Stroke increases proliferation and migration of neural progenitor cells within the SVZ towards injured brain regions [70,71], where they have the ability to differentiate into either neurons or astrocytes based on the local microenvironment [69,72,73]. Treatments that aim to improve brain regeneration must therefore avoid negatively influencing this process [23]. ...
Long term survival and success of transplanted stem cells to facilitate recovery from brain injury may involve prolonged use of immunosuppressive agents such as cyclosporine A (CsA). The effect of immunosuppression on overall stroke outcome, in particular endogenous regeneration, is yet to be determined. This study examined the effects of Cyclosporine A (CsA) treatment on brain remodeling events after stroke. Cyclosporine A (10 mg/kg, n=8) or vehicle (2.6% ethanol; 1% castor oil in saline, n=8) was administered prior to endothelin-1induced middle cerebral artery vasoconstriction in conscious rats, and everyday thereafter for up to 7 days. Treatment with Cyclosporine A significantly attenuated the development of neurological deficits compared to vehicle controls (48hr; P<0.05) but had no effect on infarct volume, activation of microglia/macrophages or critical regenerative responses within the neurogenic niche by 7 days. Treatment with Cyclosporine A did however significantly reduce astrogliosis, in particularly the number of severely diffuse astrocytes present in regions bordering the infarct (P<0.05). Conversely the number of astrocytes (P<0.05) with a pro-survival phenotype were increased with Cyclosporine A treatment. This study suggests that the benefits of Cyclosporine A treatment are not associated with reduced infarct volume but rather retained astrocyte support for preservation of neurotransmission.
... Stroke increases proliferation and migration of neural progenitor cells within the SVZ towards injured brain regions [70,71], where they have the ability to differentiate into either neurons or astrocytes based on the local microenvironment [69,72,73]. Treatments that aim to improve brain regeneration must therefore avoid negatively influencing this process [23]. ...
... Interestingly, besides GFAP 1 SVZ astrocytes, SVZ ependymal cells represent an additional, but temporary, neurogenic reservoir after stroke. SVZ ependymal cells normally do not proliferate, but transiently increase their proliferation following ischemia (Zhang et al., 2007b). These reactive SVZ ependymal cells temporarily regain neurogenic competence to produce new neurons following stroke (Carl en et al., 2009); importantly, however, they lack the self-renewal capacity of SVZ astrocytes and are rapidly depleted. ...
Stroke and spinal cord injury (SCI) are among the most frequent causes of central nervous system (CNS) dysfunction, affecting millions of people worldwide each year. The personal and financial costs for affected individuals, their families, and the broader communities are enormous. Although the mammalian CNS exhibits little spontaneous regeneration and self-repair, recent discoveries have revealed that subpopulations of glial cells in the adult forebrain subventricular zone and the spinal cord ependymal zone possess neural stem cell properties. These endogenous neural stem cells react to stroke and SCI by contributing a significant number of new neural cells to formation of the glial scar. These findings have raised hopes that new therapeutic strategies can be designed based on appropriate modulation of endogenous neural stem cell responses to CNS injury. Here, we review the responses of forebrain and spinal cord neural stem cells to stroke and SCI, the role of these responses in restricting injury-induced tissue loss, and the possibility of directing these responses to promote anatomical and functional repair of the CNS. GLIA 2015.
© 2015 Wiley Periodicals, Inc.
... 151,[217][218][219] In addition, there are severe disorders such as ischemia and stroke where reactive gliosis and an inability to regulate pH, K + -buffering, glutamate homeostasis and water exchange were found to result in the release of cytotoxic molecules, glial swelling and neuronal death. [220][221][222][223][224] The study of both physical 221,225 and chemical brain trauma resulting in the depression of glial metabolism 65 or reconstitution following brain edema and inflammation 226,227 showed that reactive glia no longer were supporting neurons. ...
This review focuses on the roles of glia and polyamines (PAs) in brain function and dysfunction, highlighting how PAs are one of the principal differences between glia and neurons. The novel role of PAs, such as putrescine, spermidine, and spermine and their precursors and derivatives, is discussed. However, PAs have not yet been a focus of much glial research. They affect many neuronal and glial receptors, channels, and transporters. They are therefore key elements in the development of many diseases and syndromes, thus forming the rationale for PA-focused and glia-focused therapy for these conditions.
Copyright © 2014 Elsevier Inc. All rights reserved.
... Yet, the controversy over whether ependymal cells can function as stem cells continues. New experiments suggest that, under normal conditions, ependymal cells do not divide, but that these cells may be activated during injury to begin proliferating and function as progenitor cells (Zhang et al., 2007). Given that some type B cells normally touch the ventricle through a thin process (Doetsch et al., 1999a), it is possible that, following injury, some of these cells expand this apical process and become more exposed to the ventricle. ...
Neurogenesis continues throughout adulthood in the vertebrate brain. New neurons originate from endogenous neural stem cells which could have important applications for brain repair. In rodents, the adult subventricular zone (SVZ) generates thousands of neuroblasts daily, which migrate to the olfactory bulb (OB) and differentiate into interneurons. Recent findings indicate that the neurotrophin Brain-Derived Neurotrophic Factor (BDNF) can enhance adult SVZ neurogenesis, but the mechanism by which it acts is unknown. In my thesis, I analyzed the role of BDNF and its receptor TrkB in adult SVZ neurogenesis. I found that BDNF protein is present and that TrkB is the most prominent neurotrophin receptor in the mouse SVZ, though only the truncated, kinase-negative isoform (TrkB-TR) was detected. TrkB-TR is expressed in SVZ astrocytes and ependymal cells, but not in neuroblasts. Though TrkB mutants have reduced SVZ proliferation and survival and fewer new OB neurons, grafting SVZ cells from TrkB knockout mice (TrkB-KO) into the SVZ of wild-type mice (WT) showed that neuroblasts are generated and migrate to the OB in the absence of TrkB. With the exception of dopaminergic periglomerular cells, OB interneurons derived from TrkB-KO and WT grafts displayed similar survival, molecular and morphological properties. To study the effect of BDNF on SVZ neurogenesis, I infused this neurotrophin into the lateral ventricle of adult rats and mice. After 14 days of infusion, SVZ proliferation was reduced in both species. However, the neuronal output of the SVZ was differentially affected: BDNF infusions decreased the number of new neurons in the rat OB but had no effect in the mouse. Interestingly, rats and mice also differ in their expression of the neurotrophin receptor, p75. In the rat, I detected p75 receptor in many putative type C cells (SVZ intermediate progenitors) and in some neuroblasts, whereas mice had very few p75+ cells. This is the first study to report such effects, as other laboratories had reported that BDNF increased SVZ neurogenesis. Overall, my results indicate that TrkB is not essential for the production and maturation of most SVZ interneurons and do not support the current view that delivering BDNF to the SVZ can enhance adult neurogenesis. Rather, TrkB-TR in ependyma and glial tubes may form a protective barrier, shielding SVZ progenitors and neuroblasts from an activation of p75 by BDNF. My work should promote new studies on how neurotrophins affect adult neurogenesis and the survival of new neurons before therapeutic applications can be designed.
In addition to the research described above, I developed techniques based on reverse transcription and polymerase chain reaction (RT-PCR) to study gene expression in single SVZ cells. I report on encouraging preliminary results, showing that it is possible to detect multiple gene products from a single cell. In the future, this method can be applied to characterize molecular heterogeneity within each cell type of the SVZ (type B astrocytes, type C intermediate progenitors and type A neuroblasts). This type of analysis will likely reveal more subclasses within type B, C and A cells, and will help to characterize differences between neurogenic and non-neurogenic astrocytes and between cells of different regions of the SVZ.
... The SVZ is situated within the lateral walls of the lateral ventricles and is composed of four main cell types: ciliated ependymal cells (type E), slowly proliferating stem cells (type B), transient amplifying progenitors (type C) and proliferating neuroblasts (type A; Mirzadeh et al., 2008). After an ischemic stroke that involves the striatum, the number of type A and C cells in the SVZ is persistently increased, while type B and E cells undergo a period of transient proliferation (Zhang et al., 2004(Zhang et al., , 2007. Increases in mitotic activity within the SVZ appear to peak between 7 and 10 days, subsequently decrease during weeks 3-5 post-stroke, and thereafter continues at lower levels over the course of the following year (Arvidsson et al., 2002;Parent et al., 2002;Thored et al., 2006). ...
After an ischemic stroke, neural precursor cells (NPCs) proliferate within major germinal niches of the brain. Endogenous NPCs subsequently migrate toward the ischemic lesion where they promote tissue remodeling and neural repair. Unfortunately, this restorative process is generally insufficient and thus unable to support a full recovery of lost neurolog-ical functions. Supported by solid experimental and preclinical data, the transplantation of exogenous NPCs has emerged as a potential tool for stroke treatment. Transplanted NPCs are thought to act mainly via trophic and immune modulatory effects, thereby complement-ing the restorative responses initially executed by the endogenous NPC population. Recent studies have attempted to elucidate how the therapeutic properties of transplanted NPCs vary depending on the route of transplantation. Systemic NPC delivery leads to potent immune modulatory actions, which prevent secondary neuronal degeneration, reduces glial scar formation, diminishes oxidative stress and stabilizes blood–brain barrier integrity. On the contrary, local stem cell delivery allows for the accumulation of large numbers of transplanted NPCs in the brain, thus achieving high levels of locally available tissue trophic factors, which may better induce a strong endogenous NPC proliferative response. Herein we describe the diverse capabilities of exogenous (systemically vs. locally transplanted) NPCs in enhancing the endogenous neurogenic response after stroke, and how the route of transplantation may affect migration, survival, bystander effects and integration of the cellular graft. It is the authors' claim that understanding these aspects will be of pivotal importance in discerning how transplanted NPCs exert their therapeutic effects in stroke.
... Within the SVZ, stroke selectively increases the number of type A and C cells [186], yet there is also data to suggest that type B cells undergo a period of transient symmetric division after stroke [187]. Ependymal cells bordering the SVZ have also been noted to proliferate transiently after ischemic stroke [188]. Mitotic activity appears to peak during between 7-10 days post ischemia then returns to baseline levels between the 3-5th week [160, 175, 187,189190191. ...
“Once development was ended, the fonts of growth and regeneration of the axons and dendrites dried up irrevocably. In the adult centers, the nerve paths are something fixed, and immutable: everything may die, nothing may be regenerated.”-Santiago Ramon y Cajal
Identification of NSC in vivo is clearly complicated and relies on the analysis of cell morphology, mitotic activity, and gene and protein expression. Commonly used NSC markers include nestin, glial fibrillary acidic protein (GFAP), Musashi 1/2, and the Shy-related high mobility group box transcription factor 2 (Sox2) [20-23]. Nestin is a class VI intermediate filament linked to mitotically active cells in the CNS [20, 24]. GFAP is expressed in multipotent ependymal cells, radial glia, and also in mature astrocytes [21]. Musashi 1 and 2 expression can be found in embryonic neuroepithelial cells [22] while Sox2 is found primarily in undifferentiated cells that possess self-renewal capabilities [23]. As noted above, NSC can exist in either a quiescent or mitotically active state. Quiescent cells have been shown to express Sox2 and FoxO3A, and are further demarcated by a prolonged retention of bromodeoxyuridine (BrdU) [24-28]. Dividing cells, on the other hand, show a rapid turnover of BrdU and simultaneously contain various markers of cell-cycle entry/progression: Mcm-2, Ki67, cyclin D1 and E (G1 phase), cyclin A (S phase), cytoplasmic cyclin B1 (G2 phase), and phosphohistone H3 (M phase) [10, 29]. Fate restricted precursor cells have traditionally been recognized via the expression of doublecortin (DCX) and the polysialylated-neural adhesion molecule (PSA-NCAM) [30, 31].
"I say all the most acute, most powerful, and most deadly diseases, and those which are most difficult to be understood by the inexperienced, fall upon the brain."-Hippocrates
“As long as our brain is a mystery, the universe, the reflection of the structure of the brain will also be a mystery.”-Santiago Ramón y Cajal
... In the present study larger infarct volumes also correlated with an increase in the number of radial glial cells generated within the SVZ 7 days post-stroke. Radial glial cells retain neural stem celllike properties and are capable of migrating from the SVZ towards the damaged brain where they can differentiate into either neurons or astrocytes based on the microenvironment [50,53,54]. Our results demonstrate that an increase in the number of SVZ derived radial glial cells 7 days post-stroke appear to be extending towards cortical and striatal penumbral regions of animals with larger infarcts (Figure S1A-C). ...
The extent of stroke damage in patients affects the range of subsequent pathophysiological responses that influence recovery. Here we investigate the effect of lesion size on development of new blood vessels as well as inflammation and scar formation and cellular responses within the subventricular zone (SVZ) following transient focal ischemia in rats (n = 34). Endothelin-1-induced stroke resulted in neurological deficits detected between 1 and 7 days (P<0.001), but significant recovery was observed beyond this time. MCID image analysis revealed varying degrees of damage in the ipsilateral cortex and striatum with infarct volumes ranging from 0.76-77 mm3 after 14 days, where larger infarct volumes correlated with greater functional deficits up to 7 days (r = 0.53, P<0.05). Point counting of blood vessels within consistent sample regions revealed that increased vessel numbers correlated significantly with larger infarct volumes 14 days post-stroke in the core cortical infarct (r = 0.81, P<0.0001), core striatal infarct (r = 0.91, P<0.005) and surrounding border zones (r = 0.66, P<0.005; and r = 0.73, P<0.05). Cell proliferation within the SVZ also increased with infarct size (P<0.01) with a greater number of Nestin/GFAP positive cells observed extending towards the border zone in rats with larger infarcts. Lesion size correlated with both increased microglia and astrocyte activation, with severely diffuse astrocyte transition, the formation of the glial scar being more pronounced in rats with larger infarcts. Thus stroke severity affects cell proliferation within the SVZ in response to injury, which may ultimately make a further contribution to glial scar formation, an important factor to consider when developing treatment strategies that promote neurogenesis.
... The cellular source of newly generated neuronal cells during both constitutive and injury-induced neurogenesis is apparently a multipotent cell population with phenotypic traits of glial cells [1], [7], [12], [13]. Interestingly, the ependymal cells lining the ventricle system – previously proposed to act as neural stem cells [9]– represent rather a quiescent and/or latent reservoir of neurogenic cells that could be activated in response to injury, transforming to radial glial cells and giving rise to astrocytes and neuroblasts [14]–[17]. The self-renewing ability of these cells in vivo is very likely disabled [16]. ...
Background:
In mammals, embryonic neural progenitors as well as adult neural stem cells can be prospectively isolated based on the cell surface expression of prominin-1 (CD133), a plasma membrane glycoprotein. In contrast, characterization of neural progenitors in non-mammalian vertebrates endowed with significant constitutive neurogenesis and inherent self-repair ability is hampered by the lack of suitable cell surface markers. Here, we have investigated whether prominin-1-orthologues of the major non-mammalian vertebrate model organisms show any degree of conservation as for their association with neurogenic geminative zones within the central nervous system (CNS) as they do in mammals or associated with activated neural progenitors during provoked neurogenesis in the regenerating CNS.
Methods:
We have recently identified prominin-1 orthologues from zebrafish, axolotl and chicken. The spatial distribution of prominin-1-positive cells--in comparison to those of mice--was mapped in the intact brain in these organisms by non-radioactive in situ hybridization combined with detection of proliferating neural progenitors, marked either by proliferating cell nuclear antigen or 5-bromo-deoxyuridine. Furthermore, distribution of prominin-1 transcripts was investigated in the regenerating spinal cord of injured axolotl.
Results:
Remarkably, a conserved association of prominin-1 with germinative zones of the CNS was uncovered as manifested in a significant co-localization with cell proliferation markers during normal constitutive neurogenesis in all species investigated. Moreover, an enhanced expression of prominin-1 became evident associated with provoked, compensatory neurogenesis during the epimorphic regeneration of the axolotl spinal cord. Interestingly, significant prominin-1-expressing cell populations were also detected at distinct extraventricular (parenchymal) locations in the CNS of all vertebrate species being suggestive of further, non-neurogenic neural function(s).
Conclusion/interpretation:
Collectively, our work provides the first data set describing a comparative analysis of prominin-1-positive progenitor cells across species establishing a framework for further functional characterization in the context of regeneration.
... Stroke results in increased neuroblast formation in the adult ventricle wall and generation of mature striatal neurons and also induces ependymal cells to regain radial glial features 31 . Parent et al 32 demonstrated that SvZ neurogenesis increased from Day 10 to day 21 after mCAO for 90 minutes, and chains of neuroblasts extended from SvZ to the peri-infarct striatum in rats. ...
Objective and background:
FOXJ1 is a member of the Forkhead/winged-helix (Fox) family of transcription factors, which is required for the differentiation of the cells acting as adult neural stem cells which participate in neurogenesis and give rise to neurons, astrocytes, oligodendrocytes. The expression pattern of FOXJ1 in the brain after cerebral ischemia has so far not been described. In the current study, we investigated the expression pattern of FOXJ1 in the rat brain after cerebral ischemia by animal model.
Methods:
We performed a middle cerebral artery occlusion (MCAO) model in adult rats and investigated the expression of FOXJ1 in the brain by Western blotting and immunochemistry; double immunofluorescence staining was used to analyze FOXJ1's co-expression with Ki67.
Results:
Western blot analysis showed that the expression of FOXJ1 was lower than normal and sham-operated brain after cerebral ischemia, but the level of FOXJ1 gradually increased from Day 1 to Day 14. Immuohistochemical staining suggested that the immunostaining of FOXJ1 deposited strongly in the ipsilateral and contralateral hemisphere in the cortical penumbra (CP). There was no FOXJ1 expression in the ischemic core (IC). The positive cells in the cortical penumbra might migrate to the ischemic core. In addition, double immunofluorescence staining revealed that FOXJ1 was co-expressed with mAP-2 and gFAP, and Ki67 had the colocalization with NeuN, GFAP, and FOXJ1.
Conclusions:
All our findings suggest that FOXJ1 plays an important role on neuronal production and neurogenesis in the adult brain after cerebral ischemia.
... Despite stroke injury being focal, the neuronal degeneration in stroke is not selective but involves different neuronal populations, including glial and endothelial cells, and disrupts various anatomical pathways, including both white and grey matter that need to be restored. In contrast, most experimental studies are conducted using a middle cerebral artery stroke model that presents mostly the striatum and, in a minor part, cortex damage, and only a few authors investigated cell therapy for cortex infarcts (Zhang et al. 2007). Thus, there are not any conclusive results on the possibility of restoring cortical damage and thereby memory and behavioural functions. ...
Sleep-disordered breathing (SDB) occupies a leading position in the structure of sleep impairments and concomitant brain damage. This review analyzes results from experimental studies and addresses the roles of astrocyte, microcyte, and oligodendrocyte glia as the main mediators of brain damaged in SDB at the cellular level. In particular, the review discusses the roles of molecules expressed by glial cells and mediating oxidative damage (NADP oxidase), inflammation (hypoxia-inducible factor-1, inducible nitric oxide synthase, pro- and anti-inflammatory cytokines), and sympathetic hyperactivation.
Objective:
The association between boule (BOLL) and endothelin receptor type A (BEDNRA) loci and intracranial aneurysm (IA) formation has been reported via genome-wide association studies (GWASs). We sought to identify genome-wide interactions involving BOLL and BEDNRA loci for IA in a Korean adult cohort.
Methods:
Genome-wide pairwise interaction analyses of BOLL and BEDNRA involving 250 patients with IA and 296 controls were performed using the additive effect model after adjusting for confounding factors.
Results:
Among 512,575 single-nucleotide polymorphisms (SNPs), 23 and 11 common SNPs suggested a genome-wide interaction threshold (p < 1.25×10-8) involving rs700651 (BOLL) and rs6841581 (BEDNRA). Rather than singe SNP effect of BOLL or BEDNRA on IA development, they showed a synergistic effect on IA formation via multifactorial pair-wise interactions. The rs1105980 of PTCH1 gene showed the most significant interaction with rs700651 (natural log-transformed odds ratio, lnOR = 1.53, p = 6.41×10-11). The rs74585958 of RYK gene interacted strongly with rs6841581 (lnOR = -19.91, p = 1.64×10-9). Although, there was no direct interaction between BOLL and BEDNRA variants, two BEDNRA-interacting gene variants of TNIK (rs11925024 and rs1231) and FTO (rs9302654), and one BOLL-interacting METTL4 gene variant (rs549315) exhibited marginal interaction with BOLL gene.
Conclusion:
BOLL or BEDNRA may have a synergistic effect on IA formation via multifactorial pair-wise interactions.
Sleep-disordered breathing (SDB) is one of the most prevalent sleep-wake disorders and is associated with brain damage. In this review, we describe the role of astroglia, microglia and oligodendroglia as the main cellular mediators of brain damage in SDB based on the results of experimental studies. Specifically, we describe the role of the molecules that are expressed by glia and mediate oxidative stress (NADPH-oxidase), inflammation (hypoxia-inducible factor-1, inducible nitric oxide synthase, pro- and anti-inflammatory cytokines) and sympathetic hyperactivation (ATP, lactate).
Association of boule ( BOLL ) and endothelin receptor type A ( EDNRA ) loci with intracranial aneurysm (IA) formation has been reported via genome-wide association studies. However, the underlying genome-wide interactions have yet to be reported. We sought to identify genome-wide interactions involving BOLL and EDNRA loci for IA. Genome-wide interaction analyses of BOLL and EDNRA involving 250 IA patients and 296 controls were performed under an additive effect model. Subsequent gene expression analyses were conducted using transcripts per million (TPM). A total of 23 and 11 SNPs suggested a genome-wide threshold ( p < 1.25×10 ⁻⁸ ) interacting with rs700651 ( BOLL ) and rs6841581 ( EDNRA ), respectively. The rs1105980 ( PTCH1 ) showed the most significant interaction with rs700651 ( p = 6.41×10 ⁻¹¹ ). The rs74585958 ( RYK ) interacted strongly with rs6841581 ( p = 1.64×10 ⁻⁹ ). The BOLL -interacting CXCR4 was highly overexpressed in whole blood (TPM = 419.8) and CCDC3 was overexpressed in all artery-related tissues (TPM = 315.4 to 473.9). EDNRA -interacting EIF4H showed a comprehensively elevated expression across all tissues and cells (TPM = 85.8 to 372.0). Genome-wide interaction study shows that BOLL and EDNRA may contribute to IA formation by interacting with multiple genes in cardio-metabolic pathway. Our findings may provide insight into the functional relevant to IA susceptibility.
Neurons generated in the postnatal V-SVZ form chainlike aggregates and migrate rapidly within a glial tube for a long distance toward the olfactory bulb. These morphological features are not observed during the embryonic period, suggesting that the chain formation and glial tube have roles specific to the neuronal migration in the postnatal brain. Neuronal migration in the postnatal brain may be affected by changes in the physiological condition of the brain, such as neuronal activity, development, and aging. Furthermore, recent evidence suggests that neuronal migration also depends on nonneural systems such as immune and vascular systems. Further analyses of the spatiotemporal interactions between migrating neurons and other cell types, and identification of the molecules mediating these interactions will be necessary to understand the regulatory mechanisms of neuronal migration in the postnatal brain. Neuronal migration in the postnatal brain appears to be a remarkable strategy for modifying postnatal brain functions, and not just a delivery system of newborn neurons from the germinal zone to their destination. Further studies aimed at clarifying the adaptive potential of migrating neurons in the postnatal brain are needed to establish novel strategies for endogenous neuronal regeneration.
It is well documented that adult neural stem cells (NSCs) residing in the subventricular zone (SVZ) and the subgranular zone (SGZ) are induced to proliferate and differentiate into new neurons after injury such as stroke and hypoxia. However, the role of injury‐related cues in driving this process and the means by which they communicate with NSCs remains largely unknown. Recently, the coupling of neurogenesis and angiogenesis and the extensive close contact between vascular cells and other niche cells, known as the neurovascular unit (NVU), has attracted interest. Further facilitating communication between blood and NSCs is a permeable blood‐brain‐barrier (BBB) present in most niches, making vascular cells a potential conduit between systemic signals, such as vascular endothelial growth factor (VEGF), and NSCs in the niche, which could play an important role in regulating neurogenesis. We show that the leaky BBB in stem cell niches of the intact and stroke brain can respond to circulating VEGF165 to drive induction of the notch ligand DLL4 (one of the most important cues in angiogenesis) in Endothelial cells (ECs), pericytes, and further induce significant proliferation and neurogenesis of stem cells. © AlphaMed Press 2018
Chronic disability after stroke represents a major unmet neurological need. ReNeuron's development of a human neural stem cell (hNSC) therapy for chronic disability after stroke is progressing through early clinical studies. A Phase I trial has recently been published, showing no safety concerns and some promising signs of efficacy. A single arm Phase II multicenter trial in patients with stable upper limb paresis has recently completed recruitment. The hNSCs administrated are from a manufactured, conditionally immortalized hNSC line (ReNeuron's CTX0E03 or CTX), generated with c-mycERTAM technology. This technology has enabled CTX to be manufactured at large scale under cGMP conditions, ensuring sufficient supply to meets demands of research, clinical development and eventually the market. CTX has key pro-angiogenic, pro-neurogenic and immunomodulatory characteristics that are mechanistically important in functional recovery post stroke. This review covers the progress of CTX cell therapy from its laboratory origins to the clinic, concluding with a look in to the later stage clinical future.
Recent experimental evidence obtained mainly in rodents has indicated that the stroke-damaged adult brain makes an attempt to repair itself by producing new neurons from its own neural stem cells. Here, we summarize the current status of this research with an emphasis on how, in the future, optimization of this potential self-repair mechanism could become of therapeutical value to promote functional restoration after stroke. Currently, our knowledge about the mechanisms regulating the different steps of neurogenesis after stroke is incomplete. Despite a lot of circumstantial evidence, we also do not know if stroke-induced neurogenesis contributes to functional improvement and to what extent the new neurons are integrated into existing neural circuitries. It is highly likely that, in order to have a substantial impact on the recovery after stroke, neurogenesis has to be markedly enhanced. Based on available data, this should primarily be achieved by increasing the survival and differentiation of the generated neuroblasts. Moreover, for maximum functional recovery, optimization of neurogenesis most likely needs to be combined with stimulation of other endogenous neuroregenerative responses, e.g., protection and sprouting of remaining mature neurons, and transplantation of stem cell-derived neurons and glia cells.
Neurogenesis is a process that includes not only generation of new neurons from neural stem and progenitor cells, but functional integration of these new born neurons into cortical circuits as well. The subventricular zone of the lateral ventricles and the subgranular zone of the dentate gyrus in the hippocampus are the sites of active adult neurogenesis in most mammals, while other central nervous system (CNS) regions exhibit extremely limited or nonexistent neurogenic capacity. However, after pathological stimulation, such as ischemic brain insult, neurogenesis can appear even in those areas that were previously considered nonneurogenic, such as the striatum and cerebral cortex. Brain ischemia also has strong effect on both the subventricular and the subgranular zone, potently stimulating progenitor proliferation in these areas, which is then followed by migration of newborn neurons to damaged sites. Recent studies also show that brain ischemia can lead to long term potentiation of proliferative processes in these two neurogenic zones. This effect is most likely mediated by microglial cells, the main effector cells in postischemic inflammatory processes, which when chronically activated can become beneficial and support the different steps in neurogenesis. Increased EGF-1 microglial expression in the subventricular zone mitigates apoptosis and promotes proliferation and differentiation of neural progenitors. Microglial release of stromal cell-derived factor 1a and its binding to the CXC4 receptor highly expressed by progenitor cells is involved in migration. Finally, the release of neurotrophic factors like brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor supports survival of newly integrated neurons. The discovery of active adult neurogenesis opens new possibilities for repair of the adult CNS after injury or neurodegenerative diseases by using cell replacement therapy or boosting the brains innate regenerative potential. However, it has been shown that approximately 80 % of striatal neurons generated after brain ischemia die during the first 2 weeks after their formation, which is probably due to the pathological environment of the ischemic brain tissue encountering these newborn neurons. Therefore, further investigation of the influence of the neuroinflammatory environment on the neurogenic niche will contribute to better understanding of the CNS regenerative capabilities under neurodegenerative circumstances, and finding more successful ways of using adult neurogenesis as a therapeutic approach.
New neurons are continuously generated throughout life in the subgranular zone in the dentate gyrus of the mammalian hippocampus and in the subventricular zone of the lateral ventricles. With the aid of new methodologies, significant progress has been made in the characterization of endogenous stem cells (ependymal cells) and their development in the adult spinal cord. Recent studies have shed light on essential extrinsic and intrinsic molecular mechanisms that govern sequential steps of neurogenesis in the adult spinal cord. This review discusses the occurrence, origin, and specific makers of ependymal cells; the factors regulating neurogenesis of multipotent ependymal cells; and the implications of ependymal cells in the repair of spinal cord injuries. © 2014 Wiley Periodicals, Inc.
Cellular mechanisms of regeneration after the white matter injury are difficult to study because of severe, inflammatory response to massively damaged myelin. Myelin-lacking CNS of the adult Long Evans Shaker (LES) rat supplies a model where neuroregeneration can be studied conveniently. The crush site in the dorsal spinal column in LES rats implanted with the normal rat choroid plexus was studied under the light and electron microscopy at 5 time points 3-56 days post-op. While the crush injury in normal rats resulted in severe inflammation active beyond 8 weeks, the same injury in LES rats resulted in a brief inflammation that resolved before day 7 post-op. In a clear fluid-filled crush cavity, ependymal cells from the implanted choroid plexus encased multiple regenerating axons, apparently guided them across the crush cavity and participated in establishing of a zone of neuroregeneration, morphologically similar to the white matter, at the interface of the crush cavity and the surrounding tissue of the spinal cord. Axons that were not encased by implanted cells failed to cross the crush cavity and persisted as markedly swollen end bulbs filled with organelles. At 8 weeks post-op, a large proportion of axons in the zone of neuroregeneration became myelinated by Schwann cells, likely originating from dorsal nerve roots or by oligodendrocytes that formed thin sheaths with a major dense line and likely originated from the implanted choroid plexus. The LES rat can serve as a convenient model to study mechanisms of neuroregeneration including axonal regeneration in the adult CNS injury.
Ependymal cells in the lateral ventricular wall are considered to be post-mitotic but can give rise to neuroblasts and astrocytes after stroke in adult mice due to insult-induced suppression of Notch signaling. The transcription factor FoxJ1, which has been used to characterize mouse ependymal cells, is also expressed by a subset of astrocytes. Cells expressing FoxJ1, which drives the expression of motile cilia, contribute to early postnatal neurogenesis in mouse olfactory bulb. The distribution and progeny of FoxJ1-expressing cells in rat forebrain are unknown. Here we show using immunohistochemistry that the overall majority of FoxJ1-expressing cells in the lateral ventricular wall of adult rats are ependymal cells with a minor population being astrocytes. To allow for long-term fate mapping of FoxJ1-derived cells, we used the piggyBac system for in vivo gene transfer with electroporation. Using this method, we found that FoxJ1-expressing cells, presumably the astrocytes, give rise to neuroblasts and mature neurons in the olfactory bulb both in intact and stroke-damaged brain of adult rats. No significant contribution of FoxJ1-derived cells to stroke-induced striatal neurogenesis was detected. These data indicate that in the adult rat brain, FoxJ1-expressing cells contribute to the formation of new neurons in the olfactory bulb but are not involved in the cellular repair after stroke.
MicroRNAs (miRNAs) regulate dendritogenesis and plasticity. However, the biological function of miRNAs in axons has not been extensively investigated. Here, using rat primary cortical neurons cultured in a microfluidic chamber, we found that the distal axons of the neurons expressed the miR-17-92 cluster, and proteins that regulate production and activity of mature miRNAs, Dicer and Argonaute 2, respectively, were present in the distal axons. Overexpression of the miR-17-92 cluster in cortical neurons substantially increased axonal outgrowth, whereas distal axonal attenuation of endogenous miR-19a, a key miRNA of the miR-17-92 cluster, with the miRNA hairpin inhibitor suppressed axonal outgrowth. Moreover, overexpression of the miR-17-92 cluster reduced phosphatase and tensin homolog (PTEN) proteins and elevated phosphorylated mammalian target of rapamycin (mTOR) in the distal axons. In contrast, distal axonal attenuation of miR-19a increased PTEN proteins and inactivated mTOR in the axons, but did not affect these protein levels in the cell bodies. Overexpression of PTEN and attenuation of endogenous PTEN prevailed over the enhancement and inhibitory effects of the miR-19a on axonal outgrowth, respectively. Axonal application of LY294002, a phosphoinositide3-kinase inhibitor, or rapamycin, an mTOR inhibitor, abolished axonal outgrowth enhanced by overexpression of the miR-17-92 cluster. Collectively, these findings demonstrate that axonal alteration of miR-17-92 cluster expression regulates axonal outgrowth and that local modulation of PTEN protein levels by miR-19a likely contributes to the axonal outgrowth.
Neurogenesis is the process by which cells divide, migrate, and subsequently differentiate into a neuronal phenotype. Significant rates of neurogenesis persist into adulthood in two brain regions, the subgranular zone of the dentate gyrus and the subventricular zone of the lateral ventricles. Cells of the subventricular zone divide and migrate via the rostral migratory stream to the olfactory bulb where they differentiate into granule and periglomerular cells. With the discovery of large-scale neurogenesis in the adult brain, there have been significant efforts to identify the mechanisms that control this process as well as the role of these cells in neuronal functioning. Although many questions remain unanswered, new insights appear daily about adult neurogenesis, regulatory mechanisms, and the fates of the progeny. In this review we highlight the main studies investigating factors that regulate neurogenesis in the subventricular zone, neuronal migration to the olfactory bulb, neuronal integration into the existing bulbar network and shortly discuss the functional meaning of this process.
For a long time it was believed that the adult mammalian brain was completely unable to regenerate after insults. However, recent advances in the field of stem cell biology, including the identification of adult neural stem cells (NSCs) and evidence regarding a continuous production of neurons throughout life in the dentate gyrus (DG) and the subventricular zone of the lateral ventricles (SVZ), have provided new hopes for the development of novel therapeutic strategies to induce regeneration in the damaged brain. Moreover, proofs have accumulated this last decade that endogenous stem/progenitor cells of the adult brain have an intrinsic capacity to respond to brain disorders. Here, we first briefly summarize our current knowledge related to adult neurogenesis before focusing on the behaviour of adult neural stem/progenitors cells following stroke and seizure, and describe some of the molecular cues involved in the response of these cells to injury. In the second part, we outline the consequences of three main neurodegenerative disorders on adult neurogenesis and we discuss the potential therapeutic implication of adult neural stem/progenitors cells during the course of these diseases.
Stroke-induced neurogenesis originates from a neural stem cell (NSC) niche in subventricular zone (SVZ). In mice, NSCs are concentrated in a so-called "neurogenic spot" in the lateral angle area of SVZ. We aimed to identify the "neurogenic spot" in the rat SVZ and to characterize the cellular changes in the ependymal cell compartment in this area at different time points after middle cerebral artery occlusion. The majority of ependymal cells outlining the ventricular wall did not proliferate, and their numbers in the "neurogenic spot" declined at 6 and 16weeks after stroke. Cells with the ultrastructural properties of ependymal cells were detected in the adjacent striatum. The number of these ectopic ependymal cells (EE cells) correlated positively with the magnitude of lateral ventricular enlargement and negatively with the ependymal cell number in the "neurogenic spot". EE cells were found along blood vessels, accumulated in the pericyst regions, and participated in scar formation but did not incorporate BrdU. We provide the first evidence for the occurrence of EE cells in the ischemic striatum following stroke.
Presence of neural stem cells in adult mammalian brains, including human, has been clearly demonstrated by several studies. The functional significance of adult neurogenesis is slowly emerging as new data indicate the sensitivity of this event to several “every day” external stimuli such as physical activity, learning, enriched environment, aging, stress and drugs. In addition, neurogenesis appears to be instrumental for task performance involving complex cognitive functions.
Despite the growing body of evidence on the functional significance of NSC and despite the bulk of data concerning the molecular and cellular properties of NSCs and their niches, several critical questions are still open.
In this work we review the literature describing i) old and new sites where NSC niche have been found in the CNS; ii) the intrinsic factors regulating the NSC potential; iii) the extrinsic factors that form the niche microenvironment. Moreover, we analyse NSC niche activation in iv) physiological and v) pathological conditions.
Given the not static nature of NSCs that continuously change phenotype in response to environmental clues, a unique “identity card” for NSC identification is still lacking. Moreover, the multiple location of NSC niches that increase in diseases, leaves open the question of whether and how these structures communicate throughout long distance. We propose a model where all the NSC niches in the CNS may be connected in a functional network using the threads of the meningeal net as tracks.
Sonic hedgehog (Shh) signaling controls many aspects of ontogeny, orchestrating congruent growth and patterning. During brain development, Shh regulates early ventral patterning while later on it is critical for the regulation of precursor proliferation in the dorsal brain, namely in the neocortex, tectum and cerebellum. We have recently shown that Shh also controls the behavior of cells with stem cell properties in the mouse embryonic neocortex, and additional studies have implicated it in the control of cell proliferation in the adult ventral forebrain and in the hippocampus. However, it remains unclear whether it regulates adult stem cell lineages in an equivalent manner. Similarly, it is not known which cells respond to Shh signaling in stem cell niches. Here we demonstrate that Shh is required for cell proliferation in the mouse forebrain's subventricular zone (SVZ) stem cell niche and for the production of new olfactory interneurons in vivo. We identify two populations of Gli1+ Shh signaling responding cells: GFAP+ SVZ stem cells and
To study neuronal migration, migrating granule neurons in microcultures prepared from early postnatal cerebellum have been analyzed with time-lapse, video-enhanced differential interference contrast microscopy. The morphology of migrating neurons resembles the elongated forms of migrating neurons described both in vivo and in vitro (Rakic, 1971; Hatten et al., 1984). The neuron closely apposes its soma along the glial fiber and extends a thickened leading process in the direction of migration. This leading tip is highly motile, with several filopodial extensions. Intracellular vesicular structures extend from the nucleus into the leading process of migrating neurons in vitro. Quantitation of the motions of migrating neurons revealed a saltatory pattern of advance along the glial fiber. Periods of cell soma movement at the rate of 56 +/- 26 micron/hr along the glial fiber are punctuated by periods during which the cell soma slows to a complete stop. The overall rate of migration is 33 +/- 20 micron/hr. The growing tip of the leading process rapidly extends and retracts, resulting in a net advance along the glial fiber. However, the periods of the extension and retraction of the leading process growing tip are not synchronized with the motions of the cell soma.
During the development of the mammalian brain, neuronal precursors migrate to their final destination from their site of birth
in the ventricular and subventricular zones (VZ and SVZ, respectively). SVZ cells in the walls of the lateral ventricle continue
to proliferate in the brain of adult mice and can generate neurons in vitro, but their fate in vivo is unknown. Here SVZ cells
from adult mice that carry a neuronal-specific transgene were grafted into the brain of adult recipients. In addition, the
fate of endogenous SVZ cells was examined by microinjection of tritiated thymidine or a vital dye that labeled a discrete
population of SVZ cells. Grafted and endogenous SVZ cells in the lateral ventricle of adult mice migrate long distances and
differentiate into neurons in the olfactory bulb.
Cytogenesis is the critical determinant of the total number of neurons that contribute to the formation of the cerebral cortex and the rate at which the cells are produced. Two distinct cell populations constitute the proliferative population, a pseudostratified ventricular epithelium (PVE) lying within the ventricular zone (VZ) at the margin of the ventricle, and a secondary proliferative population that is intermixed with the PVE within the VZ but also is distributed through the overlying subventricular and intermediate zones of the cerebral wall. The present analysis, based upon cumulative S-phase labeling of the proliferative cells with 5-bromo-2'-deoxyuridine, is principally concerned with the PVE of the gestational-day-14 (E14) murine cerebral wall. It has immediate but also more far reaching general objectives. The most immediate objective, essential to the design and interpretation of later experiments, is to provide estimates of critical parameters of cytogenesis for the PVE. The growth fraction is virtually 100%. The lengths of the overall cell cycle, S-, G2+M-m, and G1-phases are 15.1 hr, 3.8 hr, 2 hr, and 9.3 hr, respectively. The PVE is homogeneous with respect to cell cycle length. For methodological considerations, these estimates are more accurate than estimates of the same parameters obtained in earlier analyses based upon S-phase labeling with tritiated thymidine. It is particularly with respect to a shorter length of S-phase determined here that the present values are different from those obtained with thymidine. At a more innovative level, the temporal and spatial resolution of nuclear movement made possible by the methods developed here will allow, in a way not previously attempted, a fine-grained tracking of nuclear movement as cells execute the successive stages of the cell cycle or exit the cycle subsequent to mitosis. Such observations are pertinent to our understanding of the regulatory mechanisms of neocortical histogenesis and the cell biological mechanisms that govern the proliferative cycle of the ventricular epithelium itself. It is known that the velocity of nuclear movement in the PVE is maximum in G2 (fourfold increase from S-phase) and minimum in M and early G1.(ABSTRACT TRUNCATED AT 400 WORDS)
The adult mammalian subventricular zone (SVZ) contains stem cells that give rise to neurons and glia. In vivo, SVZ progeny migrate 3-8 mm to the olfactory bulb, where they form neurons. We show here that the SVZ of the lateral wall of the lateral ventricles in adult mice is composed of neuroblasts, glial cells, and a novel putative precursor cell. The topographical organization of these cells suggests how neurogenesis and migration are integrated in this region. Type A cells had the ultrastructure of migrating neuronal precursors. These cells were arranged as chains parallel to the walls of the ventricle and were polysialylated neural adhesion cell molecule- (PSA-NCAM), TuJ1- (beta-tubulin), and nestin-positive but GFAP- and vimentin-negative. Chains of Type A cells were ensheathed by two ultrastructurally distinct astrocytes (Type B1 and B2) that were GFAP-, vimentin-, and nestin-positive but PSA-NCAM- and TuJ1-negative. Type A and B2 (but not B1) cells incorporated [3H]thymidine. The most actively dividing cell in the SVZ corresponded to Type C cells, which had immature ultrastructural characteristics and were nestin-positive but negative to the other markers. Type C cells formed focal clusters closely associated with chains of Type A cells. Whereas Type C cells were present throughout the SVZ, they were not found in the rostral migratory stream that links the SVZ with the olfactory bulb. These results suggest that chains of migrating neuroblasts in the SVZ may be derived from Type C cells. Our results provide a topographical model for the adult SVZ and should serve as a basis for the in vivo identification of stem cells in the adult mammalian brain.
Cells within the ventricular zone (VZ) of developing neocortex are coupled together into clusters by gap junction channels. The specific role of clustering in cortical neurogenesis is unknown; however, clustering provides a means for spatially restricted local interactions between subsets of precursors and other cells within the VZ. In the present study, we have used a combination of 5-bromo-2'-deoxyuridine (BrDU) pulse labeling, intracellular biocytin labeling, and immunocytochemistry to determine when in the cell cycle VZ cells couple and uncouple from clusters and to determine what cell types within the VZ are coupled to clusters. Our results indicate that clusters contain radial glia and neural precursors but do not contain differentiating or migrating neurons. In early neurogenesis, all precursors in S and G2 phases of the cell cycle are coupled, and approximately half of the cells in G1 are coupled. In late neurogenesis, however, over half of the cells in both G1 and S phases are not coupled to VZ clusters, whereas all cells in G2 are coupled to clusters. Increased uncoupling in S phase during late neurogenesis may contribute to the greater percentage of VZ cells exiting the cell cycle at this time. Consistent with this hypothesis, we found that pharmacologically uncoupling VZ cells with octanol decreases the percentage of VZ cells that enter S phase. These results demonstrate that cell clustering in the VZ is restricted to neural precursors and radial glia, is dynamic through the cell cycle, and may play a role in regulating neurogenesis.
The glutamate transporter GLAST is localized on the cell membrane of mature astrocytes and is also expressed in the ventricular zone of developing brains. To characterize and follow the GLAST-expressing cells during development, we examined the mouse spinal cord by in situ hybridization and immunohistochemistry. At embryonic day (E) 11 and E13, cells expressing GLAST mRNA were present only in the ventricular zone, where GLAST immunoreactivity was associated with most of the cell bodies of neuroepithelial cells. In addition, GLAST immunoreactivity was detected in radial processes running through the mantle and marginal zones. From this characteristic cytology, GLAST-expressing cells at early stages were judged to be radial glia cells. At E15, cells expressing GLAST mRNA first appeared in the mantle zone, and GLAST-immunopositive punctate or reticular protrusions were formed along the radial processes. From E18 to postnatal day (P) 7, GLAST mRNA or its immunoreactivity gradually decreased from the ventricular zone and disappeared from radial processes, whereas cells with GLAST mRNA spread all over the mantle zone and GLAST-immunopositive punctate/reticular protrusions predominated in the neuropils. At P7, GLAST-expressing cells were immunopositive for glial fibrillary acidic protein, an intermediate filament specific to astrocytes. Therefore, the glutamate transporter GLAST is expressed from radial glia through astrocytes during spinal cord development. Furthermore, the distinct changes in the cell position and morphology suggest that both the migration and transformation of radial glia cells begin in the spinal cord between E13 and E15, when the active stage of neuronal migration is over.
The adult derivatives of the embryonic forebrain germinal zones consist of two morphologically distinct cell layers surrounding the lateral ventricles: the ependyma and the subependyma. Cell cycle analyses have revealed that at least two proliferating populations exist in this region, one that is constitutively proliferating and one that is relatively quiescent and thought to include the endogenous adult neural stem cells. Earlier studies demonstrated that specific dissection of the region surrounding the lateral ventricles was necessary for the in vitro isolation of multipotent, self-renewing neural stem cells. However, in these studies, the ependymal layer was not physically separated from the subependymal layer to identify the specific adult laminar localization of the neural stem cells around the lateral ventricles. To determine which cellular compartment in the adult forebrain contained the neural stem cells, we isolated and cultured the ependyma separately from the subependyma and tested for the presence of neural stem cells using the in vitro neurosphere assay. We demonstrate that the ependymal cells can proliferate in vitro to form sphere-like structures. However, the ependymal cells generating spheres do not have the ability to self-renew (proliferate to form secondary spheres after dissociation) nor to produce neurons, but rather only seem to generate glial fibrillary acidic protein-positive ependymal cells when plated under differentiation conditions in culture. On the other hand, a subpopulation of subependymal cells do possess the self-renewing and multipotential characteristics of neural stem cells. Therefore, the adult forebrain neural stem cell resides within the subependymal compartment.
The neocortex of the adult brain consists of neurons and glia that are generated by precursor cells of the embryonic ventricular zone. In general, glia are generated after neurons during development, but radial glia are an exception to this rule. Radial glia are generated before neurogenesis and guide neuronal migration. Radial glia are mitotically active throughout neurogenesis, and disappear or become astrocytes when neuronal migration is complete. Although the lineage relationships of cortical neurons and glia have been explored, the clonal relationship of radial glia to other cortical cells remains unknown. It has been suggested that radial glia may be neuronal precursors, but this has not been demonstrated in vivo. We have used a retroviral vector encoding enhanced green fluorescent protein to label precursor cells in vivo and have examined clones 1-3 days later using morphological, immunohistochemical and electrophysiological techniques. Here we show that clones consist of mitotic radial glia and postmitotic neurons, and that neurons migrate along clonally related radial glia. Time-lapse images show that proliferative radial glia generate neurons. Our results support the concept that a lineage relationship between neurons and proliferative radial glia may underlie the radial organization of neocortex.
For many years, it was assumed that neurons and glia in the central nervous system were produced from two distinct precursor pools that diverged early during embryonic development. This theory was partially based on the idea that neurogenesis and gliogenesis occurred during different periods of development, and that neurogenesis ceased perinatally. However, there is now abundant evidence that neural stem cells persist in the adult brain and support ongoing neurogenesis in restricted regions of the central nervous system. Surprisingly, these stem cells have the characteristics of fully differentiated glia. Neuroepithelial stem cells in the embryonic neural tube do not show glial characteristics, raising questions about the putative lineage from embryonic to adult stem cells. In the developing brain, radial glia have long been known to produce cortical astrocytes, but recent data indicate that radial glia might also divide asymmetrically to produce cortical neurons. Here we review these new developments and propose that the stem cells in the central nervous system are contained within the neuroepithelial --> radial glia --> astrocyte lineage.
The adult mammalian central nervous system (CNS) contains a population of neural stem cells (NSCs) with properties said to include the generation of non-neural progeny. However, the precise identity, location and potential of the NSC in situ remain unclear. We purified NSCs from the adult mouse brain by flow cytometry, and directly examined the cells' properties. Here we show that one type of NSC, which expresses the protein nestin but only low levels of PNA-binding and HSA proteins, is found in both ependymal and subventricular zones and accounts for about 63% of the total NSC activity. Furthermore, the selective depletion of the population of this stem cell in querkopf mutant mice (which are deficient in production of olfactory neurons) suggests that it acts as a major functional stem cell in vivo. Most freshly isolated NSCs, when co-cultured with a muscle cell line, rapidly differentiated in vitro into myocytes that contain myosin heavy chain (MyHC). This demonstrates that a predominant, functional type of stem cell exists in the periventricular region of the adult brain with the intrinsic ability to generate neural and non-neural cells.
In the adult brain, new neurons are continuously generated in the subventricular zone and dentate gyrus, but it is unknown whether these neurons can replace those lost following damage or disease. Here we show that stroke, caused by transient middle cerebral artery occlusion in adult rats, leads to a marked increase of cell proliferation in the subventricular zone. Stroke-generated new neurons, as well as neuroblasts probably already formed before the insult, migrate into the severely damaged area of the striatum, where they express markers of developing and mature, striatal medium-sized spiny neurons. Thus, stroke induces differentiation of new neurons into the phenotype of most of the neurons destroyed by the ischemic lesion. Here we show that the adult brain has the capacity for self-repair after insults causing extensive neuronal death. If the new neurons are functional and their formation can be stimulated, a novel therapeutic strategy might be developed for stroke in humans.
Although thrombolysis with tissue plasminogen activator (tPA) is a stroke therapy approved by the US Food and Drug Administration, its efficacy may be limited by neurotoxic side effects. Recently, proteolytic damage involving matrix metalloproteinases (MMPs) have been implicated. In experimental embolic stroke models, MMP inhibitors decreased cerebral hemorrhage and injury after treatment with tPA. MMPs comprise a family of zinc endopeptidases that can modify several components of the extracellular matrix. In particular, the gelatinases MMP-2 and MMP-9 can degrade neurovascular matrix integrity. MMP-9 promotes neuronal death by disrupting cell-matrix interactions, and MMP-9 knockout mice have reduced blood-brain barrier leakage and infarction after cerebral ischemia. Hence it is possible that tPA upregulates MMPs in the brain, and that subsequent matrix degradation causes brain injury. Here we show that tPA upregulates MMP-9 in cell culture and in vivo. MMP-9 levels were lower in tPA knockouts compared with wild-type mice after focal cerebral ischemia. In human cerebral microvascular endothelial cells, MMP-9 was upregulated when recombinant tPA was added. RNA interference (RNAi) suggested that this response was mediated by the low-density lipoprotein receptor-related protein (LRP), which avidly binds tPA and possesses signaling properties. Targeting the tPA-LRP signaling pathway in brain may offer new approaches for decreasing neurotoxicity and improving stroke therapy.
Radial glial cells (RGCs), a transient cell population present only in the developing CNS, function both as precursor cells and as scaffolds to support neuron migration. Their cellular origin, however, is not understood. In the present study, we tested the hypothesis that functional RGCs can be generated by multipotent neural stem cells. Embryonic forebrain neural stem cells were studied in vitro to identify putative signals that promote the generation and differentiation of functional RGCs, determined by their ability to support neuronal migration. Epidermal growth factor receptor signaling was sufficient to regulate both the generation and differentiation of morphologically, antigenically, and functionally defined RGCs. In contrast, fibroblast growth factor-2 promoted the generation of RGCs but was unable to support their differentiation. Although RGCs are not normally present in the adult brain, epidermal growth factor stimulated adult forebrain neural stem cells to generate RGCs in vitro and functional RGCs within the adult forebrain subependyma in vivo. Surprisingly, epidermal growth factor receptor signaling also promoted adult forebrain ependymal cells to dedifferentiate and adopt a radial morphology in vivo. These results suggest that neural stem cells can give rise to RGCs and that RGC-guided neuronal migration can be recapitulated in the adult CNS.
The orientation of mitotic cleavage regulates neurogenesis during neural development. We examined the orientation of mitotic cleavage of dividing progenitor cells in the subventricular zone (SVZ) of adult rats subjected to stroke. In nonstroke rats, 55% of dividing cells were oriented horizontally, whereas 40% were oriented vertically. Horizontal and vertical cleavage orientations produce asymmetric and symmetric divisions, respectively. Four days after stroke, the number of dividing cells increased twofold, whereas the proportion of symmetric dividing cells significantly (p < 0.01) increased from 40% before stroke to 60%. Fourteen days after stroke, the percentage of symmetric dividing cells was 47%. Stroke-increased numbers of dividing cells in M-phase were confirmed by immuostaining. In nonstroke rats, 37 and 33% of symmetric and asymmetric dividing cells, respectively, exhibited a neuronal marker (TuJ1). Four days after stroke, rats exhibited a significant (p < 0.05) augmentation of the frequency (47%) of neuronal distribution showing TuJ1 immunoreactivity in cells with symmetric division but not cells with asymmetric division (33%). Numb immunoreactivity was detected in SVZ cells of nonstroke rats. Stroke did not change Numb distribution. Our data suggest that neurons are produced by both asymmetric and symmetric cell divisions in the adult SVZ, and the transient increases in symmetric division and neuronal differentiation may result in stroke-induced neurogenesis.
Neural stem cells with the characteristics of astrocytes persist in the subventricular zone (SVZ) of the juvenile and adult brain. These cells generate large numbers of new neurons that migrate through the rostral migratory stream to the olfactory bulb. The developmental origin of adult neural stem cells is not known. Here, we describe a lox–Cre-based technique to specifically and permanently label a restricted population of striatal radial glia in newborn mice. Within the first few days after labeling, these radial glial cells gave rise to neurons, oligodendrocytes, and astrocytes, including astrocytes in the SVZ. Remarkably, the rostral migratory stream contained labeled migratory neuroblasts at all ages examined, including 150-day-old mice. Labeling dividing cells with the S-phase marker BrdUrd showed that new neurons continue to be produced in the adult by precursors ultimately derived from radial glia. Furthermore, both radial glia in neonates and radial glia-derived cells in the adult lateral ventricular wall generated self-renewing, multipotent neurospheres. These results demonstrate that radial glial cells not only serve as progenitors for many neurons and glial cells soon after birth but also give rise to adult SVZ stem cells that continue to produce neurons throughout adult life. This study identifies and provides a method to genetically modify the lineage that links neonatal and adult neural stem cells.
• neurogenesis
• oligodendrocytes
• subependyma
Migration toward pathology is the first critical step in stem cell engagement during regeneration. Neural stem cells (NSCs) migrate through the parenchyma along nonstereotypical routes in a precise directed manner across great distances to injury sites in the CNS, where they might engage niches harboring local transiently expressed reparative signals. The molecular mechanisms for NSC mobilization have not been identified. Because NSCs seem to home similarly to pathologic sites derived from disparate etiologies, we hypothesized that the inflammatory response itself, a characteristic common to all, guides the behavior of potentially reparative cells. As proof of concept, we show that human NSCs migrate in vivo (including from the contralateral hemisphere) toward an infarcted area (a representative CNS injury), where local astrocytes and endothelium up-regulate the inflammatory chemoattractant stromal cell-derived factor 1alpha (SDF-1alpha). NSCs express CXC chemokine receptor 4 (CXCR4), the cognate receptor for SDF-1alpha. Exposure of SDF-1alpha to quiescent NSCs enhances proliferation, promotes chain migration and transmigration, and activates intracellular molecular pathways mediating engagement. CXCR4 blockade abrogates their pathology-directed chain migration, a developmentally relevant mode of tangential migration that, if recapitulated, could explain homing along nonstereotypical paths. Our data implicate SDF-1alpha/CXCR4, representative of the inflammatory milieu characterizing many pathologies, as a pathway that activates NSC molecular programs during injury and suggest that inflammation may be viewed not simply as playing an adverse role but also as providing stimuli that recruit cells with a regenerative homeostasis-promoting capacity. CXCR4 expression within germinal zones suggests that NSC homing after injury and migration during development may invoke similar mechanisms.
Ependymal cells on the walls of brain ventricles play essential roles in the transport of CSF and in brain homeostasis. It has been suggested that ependymal cells also function as stem cells. However, the proliferative capacity of mature ependymal cells remains controversial, and the developmental origin of these cells is not known. Using confocal or electron microscopy (EM) of adult mice that received bromodeoxyuridine (BrdU) or [3H]thymidine for several weeks, we found no evidence that ependymal cells proliferate. In contrast, ependymal cells were labeled by BrdU administration during embryonic development. The majority of them are born between embryonic day 14 (E14) and E16. Interestingly, we found that the maturation of ependymal cells and the formation of cilia occur significantly later, during the first postnatal week. We analyzed the early postnatal ventricular zone at the EM and found a subpopulation of radial glia in various stages of transformation into ependymal cells. These cells often had deuterosomes. To directly test whether radial glia give rise to ependymal cells, we used a Cre-lox recombination strategy to genetically tag radial glia in the neonatal brain and follow their progeny. We found that some radial glia in the lateral ventricular wall transform to give rise to mature ependymal cells. This work identifies the time of birth and early stages in the maturation of ependymal cells and demonstrates that these cells are derived from radial glia. Our results indicate that ependymal cells are born in the embryonic and early postnatal brain and that they do not divide after differentiation. The postmitotic nature of ependymal cells strongly suggests that these cells do not function as neural stem cells in the adult.
In the adult rodent, stroke induces an increase in endogenous neural progenitor cell (NPC) proliferation in the subventricular zone (SVZ) and neuroblasts migrate towards the ischemic boundary. We investigated the role of stromal cell-derived factor 1alpha (SDF-1alpha) in mediating NPC migration after stroke. We found that cultured NPCs harvested from the normal adult SVZ, when they were overlaid onto stroke brain slices, exhibited significantly (P<0.01) increased migration (67.2+/-25.2 microm) compared with the migration on normal brain slices (29.5+/-29.5 microm). Immunohistochemistry showed that CXCR 4, a receptor of SDF-1alpha, is expressed in the NPCs and migrating neuroblasts in stroke brain. Blocking SDF-1alpha by a neutralizing antibody against CXCR 4 significantly attenuated stroke-enhanced NPC migration. ELISA analysis revealed that SDF-1alpha levels significantly increased (P<0.01) in the stroke hemisphere (43.6+/-6.5 pg/mg) when compared with the normal brain (25.2+/-1.9 pg/mg). Blind-well chamber assays showed that SDF-1alpha enhanced NPC migration in a dose-dependent manner with maximum migration at a dose of 500 ng/mL. In addition, SDF-1alpha induced directionally selective migration. These findings show that SDF-1alpha generated in the stroke hemisphere may guide NPC migration towards the ischemic boundary via binding to its receptor CXCR 4 in the NPC. Thus, our data indicate that SDF-1alpha/CXCR 4 is important for mediating specific migration of NPCs to the site of ischemic damaged neurons.
Radial glial cells play a major guidance role for migrating neurons during central nervous system (CNS) histogenesis but also play many other crucial roles in early brain development. Being among the earliest cells to differentiate in the early CNS, they provide support for neuronal migration during embryonic brain development; provide instructive and neurotrophic signals required for the survival, proliferation, and differentiation of neurons; and may be multipotential progenitor cells that give rise to various cell types, including neurons. Radial glial cells constitute a major cell type of the developing brain in numerous nonmammalian and mammalian vertebrates, increasing in complexity in parallel with the organization of the nervous tissue they help to build. In mammalian species, these cells transdifferentiate into astrocytes when neuronal migration is completed, whereas, in nonmammalian species, they persist into adulthood as a radial component of astroglia. Thus, our perception of radial glia may have to change from that of path-defining cells to that of specialized precursor cells transiently fulfilling a guidance role during brain histogenesis. In that respect, their apparent change of phenotype from radial fiber to astrocyte probably constitutes one of the most common transdifferentiation events in mammalian development. J. Neurosci. Res. 61:357–363, 2000. © 2000 Wiley-Liss, Inc.
Astroglial cells are the most frequent cell type in the adult mammalian brain, and the number and range of their diverse functions are still increasing. One of their most striking roles is their function as adult neural stem cells and contribution to neurogenesis. This chapter discusses first the role of the ubiquitous glial cell type in the developing nervous system, the radial glial cells. Radial glial cells share several features with neuroepithelial cells, but also with astrocytes in the mature brain, which led to the name “radial glia.” At the end of neurogenesis in the mammalian brain, radial glial cells disappear, and a subset of them transforms into astroglial cells. Interestingly, only some astrocytes maintain their neurogenic potential and continue to generate neurons throughout life. We discuss the current knowledge about the differences between the adult astroglial cells that remain neurogenic and act as neural stem cells and the majority of other astroglial cells that have apparently lost the capacity to generate neurons. Additionally, we review the changes in glial cells upon brain lesion, their dedifferentiation and recapitulation of radial glial properties, and the conditions under which reactive glia may reinitiate some neurogenic potential. Given that the astroglial cells are not only the most frequent cell type in an adult mammalian brain, but also the key cell type in the wound reaction of the brain to injury, it is essential to further understand their heterogeneity and molecular specification, with the final aim of using this unique source for neuronal replacement. Therefore, one of the key advances in the field of neurobiology is the discovery that astroglial cells can generate neurons not only during development, but also throughout adult life and potentially even after brain lesion.
A survey of the literature shows that proliferation of ependyma occurs largely during the embryonic and early postnatal periods of development in most species. Differentiation of these cells proceeds along particular regional and temporal gradients as does the expression of various cytoskeletal (vimentin, cytokeratins, glial fibrillary acidic protein) and secretory proteins (S-100). Turnover declines significantly postnatally, and only low levels of residual activity persist into adulthood under normal conditions. Although the reported response of ependyma to injury is somewhat equivocal, only limited regenerative capacity appears to exist and to varying degrees in different regions of the neuraxis. Proliferation has been most often observed in response to spinal cord injury. Indeed, the ependyma plays a significant role in the initiation and maintenance of the regenerative processes in the spinal cord of inframammalian vertebrates. In the human, however, ependyma appears never to regenerate at any age nor re-express cytoskeletal proteins characteristic of immature cells. The functions of ependyma including tanycytes, a specialized form of ependymal cell that persists into adulthood within circumscribed regions of the nervous system, are still largely speculative. Fetal unlike mature ependyma is believed to be secretory and is believed to play a role in neurogenesis, neuronal differentiation/axonal guidance, transport, and support. In the adult brain, mature ependyma is not merely an inert lining but may regulate the transport of ions, small molecules, and water between the cerebrospinal fluid and neuropil and serve an important barrier function that protects neural tissue from potentially harmful substances by mechanisms that are still incompletely understood.
Coronal sections of the cerebral wall from developing ferrets (newborn to adult) were double‐stained with antibodies to vimentin and glial fibrillary acidic protein (GFAP). At birth, the dominant glial population was radial glia and these cells labeled only for vimentin. A small population of immature astrocytes in the cortical plate was double labeled for GFAP and vimentin. In successive days, the number of vimentin‐positive radial glia gradually decreased and they disappeared entirely at about 21 days. During this same period, the double‐stained astrocytes increased in number and were distributed throughout the cortical plate and intermediate zone. After 6 weeks of age the astrocytes were mostly confined to the developing white matter. Around this time they gradually lost their vimentin staining, and in the adult no vimentin‐positive elements were seen except at the ependymal surface.
In newborn ferrets single radial glial cells were also visualized by applying the carbocyanine dye DiI onto the pial surface of fixed brains. While most radial glia extended from the ventricular zone to the pial surface, a substantial fraction of them had lost their contact to the ventricular zone. Their somata were displaced into the subventricular zone and lower portion of the intermdiate zone.
The possibility that radial glia transform into astrocytes was directly tested by injecting fluorescent dyes under the pial surface of newborn ferrets at a time when virtually no GFAP‐positive astrocytes are present. The tracer, which was taken up in the upper portion of the cortical plate, stained the radial glial cell somata in the ventricular zone in a similar way as the dye DiI did in the fixed brains. As the radial glial cells disappeared at successively longer survival times, the tracer was ultimately found within newly formed GFAP‐positive astrocytes. These results provide strong support for the hypothesis that radial glia cells are the immature form of astrocytes (Choi and Lapham: Brain Res. 148: 295–311, ′78; Schmechel and Rakic: Anat. Embryol. (Berl.) 156: 115–152, ′79), and also show that, at least in the ferret cortex, the transformation is accompanied by a change in the expression of intermediate filament protein.
The subventricular zone of the postnatal forebrain produces mainly glia, although it supports limited neurogenesis. To determine whether the subventricular zone is positionally specified, the phenotype and destination of the progeny of subventricular zone cells along the anterior-posterior axis of the lateral ventricles were analyzed. A retroviral lineage tracer containing the E. coli reporter gene lacZ was injected into different parts of the subventricular zone of neonatal rat pups, and at various times thereafter, the expression of beta-galactosidase was detected histochemically or immunohistochemically in the descendants of infected cells. A discrete region of the anterior part of the subventricular zone (SVZa) generated an immense number of neurons that differentiated into granule cells and periglomerular cells of the olfactory bulb-the two major types of interneurons. Thus, the SVZa appears to constitute a specialized source of neuronal progenitor cells. To reach the olfactory bulb, neurons arising in the SVZa migrate several millimeters along a highly restricted route. Guidance cues must be involved to prohibit widespread dispersion of these migrating neurons.
We developed a new model of embolic cerebral ischemia in the rat which provides a reproducible and predictable infarct volume within the territory supplied by the middle cerebral artery (MCA). The MCA was occluded by an embolus in Wistar rats (n = 71). An additional three non-embolized rats were used as a control. Cerebral blood flow (CBF) was measured by means of laser Doppler flowmetry (LDF) and perfusion weighted imaging (PWI) before and after embolization. The evolution of the lesion was monitored by diffusion weighted imaging (DWI). Cerebral vascular perfusion patterns were examined using laser scanning confocal microscopy. Infarct volumes were measured on hematoxylin and eosin (H&E) stained coronal sections. The lodgment of the clot at the origin of the MCA and the ischemic cell damage were examined using light microscopy. Regional CBF in the ipsilateral parietal cortex decreased to 43 +/- 4.1% (P < 0.05) of preischemic levels (n = 10). Confocal microscopic examination revealed a reduction of cerebral plasma perfusion in the ipsilateral MCA territory (n = 6). MRI measurements showed a reduction in CBF and a hyperintensity DWI encompassing the territory supplied by the MCA (n = 4). An embolus was found in all rats at 24 h after embolization. The infarct volume as a percentage of the contralateral hemisphere was 32.5 +/- 3.31% at 24 h (n = 20), 33.0 +/- 3.6% at 48 h (n = 13), and 34.5 +/- 4.74% at 168 h (n = 12) after embolization. This model of embolic focal cerebral ischemia results in ischemic cell damage and provides a reproducible and predictable infarct volume. This model is relevant to thromboembolic stroke in humans and may be useful in documenting the safety and efficacy of fibrinolytic intervention and in investigating therapies complementary to antithrombotic therapy.
Although accumulating data reveal patterns of proliferation, migration, and differentiation of neuronal lineage cells in the developing brain, gliogenesis in the brain has not been well elucidated. In the rat brain, vimentin is selectively expressed in radial glia and in their progeny, not in oligodendrocytes or neurons from embryonic day 15 (E15) until postnatal day 15 (P15). Here we examined mitotic radial glial lineage cells in the rat brain E17-P7, using the monoclonal antibody 4A4, which recognizes vimentin phosphorylated by a mitosis-specific kinase, cdc2 kinase. In the neocortex, mainly radial glia in the ventricular zone, but not their progeny, underwent cell division. In contrast, not only radial glia but also various types of radial glial progeny including Bergmann glia continued to proliferate in the cerebellum. Radial glia in the neocortex divided horizontally, obliquely, and vertically against the ventricular surface. The percentage of the vertical division increased with progress in the stage of development, concurrently with the decrease of the population of horizontal divisions. Thus, the monoclonal antibody 4A4 provides an useful tool to label mitotic glia in the developing brain and revealed different patterns of gliogenesis in the neocortex and cerebellum. A possibility is discussed that the dynamics of mitotic orientation observed here may be related to the change of the pattern of gliogenesis during development.
New neurons are continuously added in specific regions of the adult mammalian central nervous system. These neurons are derived from multipotent stem cells whose identity has been enigmatic. In this work, we present evidence that ependymal cells are neural stem cells. Ependymal cells give rise to a rapidly proliferating cell type that generates neurons that migrate to the olfactory bulb. In response to spinal cord injury, ependymal cell proliferation increases dramatically to generate migratory cells that differentiate to astrocytes and participate in scar formation. These data demonstrate that ependymal cells are neural stem cells and identify a novel process in the response to central nervous system injury.
Neural stem cells reside in the subventricular zone (SVZ) of the adult mammalian brain. This germinal region, which continually generates new neurons destined for the olfactory bulb, is composed of four cell types: migrating neuroblasts, immature precursors, astrocytes, and ependymal cells. Here we show that SVZ astrocytes, and not ependymal cells, remain labeled with proliferation markers after long survivals in adult mice. After elimination of immature precursors and neuroblasts by an antimitotic treatment, SVZ astrocytes divide to generate immature precursors and neuroblasts. Furthermore, in untreated mice, SVZ astrocytes specifically infected with a retrovirus give rise to new neurons in the olfactory bulb. Finally, we show that SVZ astrocytes give rise to cells that grow into multipotent neurospheres in vitro. We conclude that SVZ astrocytes act as neural stem cells in both the normal and regenerating brain.
Radial glial cells play a major guidance role for migrating neurons during central nervous system (CNS) histogenesis but also play many other crucial roles in early brain development. Being among the earliest cells to differentiate in the early CNS, they provide support for neuronal migration during embryonic brain development; provide instructive and neurotrophic signals required for the survival, proliferation, and differentiation of neurons; and may be multipotential progenitor cells that give rise to various cell types, including neurons. Radial glial cells constitute a major cell type of the developing brain in numerous nonmammalian and mammalian vertebrates, increasing in complexity in parallel with the organization of the nervous tissue they help to build. In mammalian species, these cells transdifferentiate into astrocytes when neuronal migration is completed, whereas, in nonmammalian species, they persist into adulthood as a radial component of astroglia. Thus, our perception of radial glia may have to change from that of path-defining cells to that of specialized precursor cells transiently fulfilling a guidance role during brain histogenesis. In that respect, their apparent change of phenotype from radial fiber to astrocyte probably constitutes one of the most common transdifferentiation events in mammalian development.
The role of radial glial cells as guides for migrating neurons is well established, whereas their role as precursor cells is less understood. Here we examined the composition of radial glial cells and their proliferation in the mouse telencephalon during development. We found that almost all radial glial cells proliferate throughout neurogenesis. They consist of three distinct subsets identified by immunostaining for the antigens RC2, the astrocyte-specific glutamate transporter (GLAST), and the brain-lipid-binding protein (BLBP). In addition, RC2, GLAST, and BLBP antisera label precursor cells with different morphologies and thereby cover almost the entire progenitor pool in the developing cerebral cortex. The subsets identified by differential expression of these antigens differ also in their transcription factor expression and cell cycle characteristics. Moreover, the content of BLBP seems correlated to the fate of the progeny. BLBP-negative precursors are detected only during neurogenesis and persist into postnatal stages solely in the rostral migratory stream, a region of ongoing neurogenesis. In contrast, an enriched population of multipotential cells, neurosphere cultures derived from the adult or embryonic telencephalon, is immunoreactive for RC2, GLAST, and BLBP. Taken together, we have identified novel, functionally distinct subsets of CNS precursor cells.
Progenitor cells in the subventricular zone of the lateral ventricle and in the dentate gyrus of the hippocampus can proliferate throughout the life of the animal. To examine the proliferation and fate of progenitor cells in the subventricular zone and dentate gyrus after focal cerebral ischemia, we measured the temporal and spatial profiles of proliferation of cells and the phenotypic fate of proliferating cells in ischemic brain in a model of embolic middle cerebral artery occlusion in the adult rat. Proliferating cells were labeled by injection of bromodeoxyuridine (BrdU) in a pulse or a cumulative protocol. To determine the temporal profile of proliferating cells, ischemic rats were injected with BrdU every 4 h for 12 h on the day preceding death. Rats were killed 2-14 days after ischemia. We observed significant increases in numbers of proliferating cells in the ipsilateral cortex and subventricular zone 2-14 days with a peak at 7 days after ischemia compared with the control group. To maximize labeling of proliferating cells, a single daily injection of BrdU was administered over a 14-day period starting the day after ischemia. Rats were killed either 2 h or 28 days after the last injection of BrdU. A significant increase in numbers of BrdU immunoreactive cells in the subventricular zone was coincident with a significant increase in numbers of BrdU immunoreactive cells in the olfactory bulb 14 days after ischemia and numbers of BrdU immunoreactive cells did not significantly increase in the dentate gyrus. However, 28 days after the last labeling, the number of BrdU labeled cells decreased by 90% compared with number at 14 days. Clusters of BrdU labeled cells were present in the cortex distal to the infarction. Numerous cells immunostained for the polysialylated form of the neuronal cell adhesion molecule were detected in the ipsilateral subventricular zone. Only 6% of BrdU labeled cells exhibited glial fibrillary acidic protein immunoreactivity in the cortex and subcortex and no BrdU labeled cells expressed neuronal protein markers (neural nuclear protein and microtubule associated protein-2). From these data we suggest that focal cerebral ischemia induces transient and regional specific increases in cell proliferation in the ipsilateral hemisphere and that proliferating progenitor cells may exist in the adult cortex.
Recent studies demonstrated the neuronogenic role of radial glial cells (RGCs) in the rodent. To reveal the fate of radial glial processes, we intensively monitored divisions of RGCs in DiI-labeled slices from the embryonic day 14 mouse cortex. During RGC division, each pia-connected fiber becomes thin but is neither lost nor divided; it is inherited asymmetrically by one daughter cell. In divisions that produce a neuron and a progenitor, the neuron inherits the pial fiber, also grows a thick ventricular process for several hours, and is therefore indistinguishable from the progenitor RGC. The ventricular process in the radial glial-like neuron ("radial neuron") then collapses, leading to ascent of the neuron by using the "recycled" radial fiber.
The persistence of neurogenesis in the forebrain subventricular zone (SVZ) of adult mammals suggests that the mature brain maintains the potential for neuronal replacement after injury. We examined whether focal ischemic injury in adult rat would increase SVZ neurogenesis and direct migration and neuronal differentiation of endogenous precursors in damaged regions. Focal stroke was induced in adult rats by 90-minute right middle cerebral artery occlusion (tMCAO). Cell proliferation and neurogenesis were assessed with bromodeoxyuridine (BrdU) labeling and immunostaining for cell type-specific markers. Brains examined 10-21 days after stroke showed markedly increased SVZ neurogenesis and chains of neuroblasts extending from the SVZ to the peri-infarct striatum. Many BrdU-labeled cells persisted in the striatum and cortex adjacent to infarcts, but at 35 days after tMCAO only BrdU-labeled cells in the neostriatum expressed neuronal markers. Newly generated cells in the injured neostriatum expressed markers of medium spiny neurons, which characterize most neostriatal neurons lost after tMCAO. These findings indicate that focal ischemic injury increases SVZ neurogenesis and directs neuroblast migration to sites of damage. Moreover, neuroblasts in the injured neostriatum appear to differentiate into a region-appropriate phenotype, which suggests that the mature brain is capable of replacing some neurons lost after ischemic injury.
Radial glial cells play at least two crucial roles in cortical development: neuronal production in the ventricular zone (VZ) and the subsequent guidance of neuronal migration. There is evidence that radial glia-like cells are present not only during development but in the adult mammalian brain as well. In addition, radial glial cells appear to be neurogenic in the central nervous system of a number of vertebrate species. We demonstrate here that most dividing progenitor cells in the embryonic human VZ express radial glial proteins. Furthermore, we provide evidence that radial glial cells maintain a vimentin-positive radial fiber throughout each stage of cell division. Asymmetric inheritance of this fiber may be an important factor in determining how neuronal progeny will migrate into the developing cortical plate. Although radial glial cells have traditionally been characterized by their role in guiding migration, their role as neuronal progenitors may represent their defining characteristic throughout the vertebrate CNS.
Pathological processes, including cerebral ischemia, can enhance neurogenesis in the adult brain, but the fate of the newborn neurons that are produced and their role in brain repair are obscure. To determine if ischemia-induced neuronal proliferation is associated with migration of nascent neurons toward ischemic lesions, we mapped the migration of cells labeled by cell proliferation markers and antibodies against neuronal marker proteins, for up to 2 weeks after a 90-min episode of focal cerebral ischemia caused by occlusion of the middle cerebral artery. Doublecortin-immunoreactive cells in the rostral subventricular zone, but not the dentate gyrus, migrated into the ischemic penumbra of the adjacent striatum and, via the rostral migratory stream and lateral cortical stream, into the penumbra of ischemic cortex. These results indicate that after cerebral ischemia, new neurons are directed toward sites of brain injury, where they might be in a position to participate in brain repair and functional recovery.
Radial glial cells function during CNS development as neural progenitors, although their precise contribution to neurogenesis remains controversial. Recent work has argued that regional differences may exist regarding the neurogenic potential of radial glia. Here, we show that the vast majority of neurons in all brain regions derive from radial glia. Cre/loxP fate mapping and clonal analysis demonstrate that radial glia throughout the CNS serve as neuronal progenitors and that radial glia within different regions of the CNS pass through their neurogenic stage of development at distinct time points. Thus, radial glial populations within different CNS regions are not heterogeneous with regard to their potential to generate neurons versus glia.
Stroke increases neurogenesis. The authors investigated whether neural stem cells or progenitor cells in the adult subventricular zone (SVZ) of rats contribute to stroke-induced increase in neurogenesis. After induction of stroke in rats, the numbers of cells immunoreactive to doublecortin, a marker for immature neurons, increased in the ipsilateral SVZ and striatum. Infusion of an antimitotic agent (cytosine-beta-D-arabiofuranoside, Ara-C) onto the ipsilateral cortex eliminated more than 98% of actively proliferating cells in the SVZ and doublecortin-positive cells in the ipsilateral striatum. However, doublecortin-positive cells rapidly replenished after antimitotic agent depletion of actively proliferating cells. Depleting the numbers of actively proliferating cells in vivo had no effect on the numbers of neurospheres formed in vitro, yet the numbers of neurospheres derived from stroke rats significantly (P<0.05) increased. Neurospheres derived from stroke rats self-renewed and differentiated into neurons and glia. In addition, doublecortin-positive cells generated in the SVZ migrated in a chainlike structure toward ischemic striatum. These findings indicate that in the adult stroke brain, increases in recruitment of neural stem cells contribute to stroke-induced neurogenesis, and that newly generated neurons migrate from the SVZ to the ischemic striatum.
During development radial glia (RG) are neurogenic, provide a substrate for migration, and transform into astrocytes. Cells in the RG lineage are functionally and biochemically heterogeneous in subregions of the brain. In the subventricular zone (SVZ) of the adult, astrocyte-like cells exhibit stem cell properties. During examination of the response of SVZ astrocytes to brain injury in adult mice, we serendipitously found a population of cells in the walls of the ventral lateral ventricle (LV) that were morphologically similar to RG. The cells expressed vimentin, glial fibrillary acidic protein (GFAP), intermediate filament proteins expressed by neural progenitor cells, RG and astrocytes. These RG-like cells had long processes extending ventrally into the nucleus accumbens, ventromedial striatum, ventrolateral septum, and the bed nucleus of the stria terminalis. The RG-like cell processes were associated with a high density of doublecortin-positive cells. Lesioning the cerebral cortex did not change the expression of vimentin and GFAP in RG-like cells, nor did it alter their morphology. To study the ontogeny of these cells, we examined the expression of molecules associated with RG during development: vimentin, astrocyte-specific glutamate transporter (GLAST), and brain lipid-binding protein (BLBP). As expected, vimentin was expressed in RG in the ventral LV embryonically (E16, E19) and during the first postnatal week (P0, P7). At P14, P21, P28 as well as in the adult (8-12 weeks), the ventral portion of the LV retained vimentin immunopositive RG-like cells, whereas RG largely disappeared in the dorsal two-thirds of the LV. GLAST and BLBP were expressed in RG of the ventral LV embryonically and through P7. In contrast to vimentin, at later stages BLBP and GLAST were found in RG-like cell somata but not in their processes. Our results show that cells expressing vimentin and GFAP (in the radial glia-astrocyte lineage) are heterogeneous dorsoventrally in the walls of the LV. The results suggest that not all RG in the ventral LV complete the transformation into astrocytes and that the ventral SVZ may be functionally dissimilar from the rest of the SVZ.
Nomen est omen—radial glial cells were, and are still, defined as cells with a radial morphology and glial characteristics. Like neuroepithelial cells, they stretch from the apical surface—the ventricular lumen—to the basement membrane at the pial surface. As both cell types are then “radial” (Figure 1), the defining and discriminating criterion between these two cell types is the “glial” adjective. Indeed, radial glial cells have cellular and molecular characteristics of astroglia, one of the two major macroglial cell types in the adult brain. Radial glial cells and astroglia contain glycogen granules and other ultrastructural characteristics of astrocytes, in contrast to neuroepithelial cells (for recent reviews and references to the corresponding original publications, see Mori et al., 2005). Furthermore, radial glial cells also express the astrocyte-specific glutamate transporter GLAST, S100β, glutamine synthase (GS), vimentin, and tenascin-C (TN-C), and, in certain species, GFAP (Mori et al., 2005). These molecules are all absent in neuroepithelial cells, but present in mature (GLAST, S100β, GS) or reactive astrocytes (S100β, GS, GFAP, vimentin, TN-C). Importantly, the so-called type B cells, which are astrocytes acting as neural stem cells in the adult subependymal zone, also express the same set of molecules (GLAST, S100β, GS, GFAP, vimentin, TN-C; Alvarez-Buylla et al., 2001 and Mori et al., 2005). As a matter of fact, no molecule has been identified so far that would discriminate across species between astrocytes and radial glial cells. Thus, these cells are truly distinct from neuroepithelial cells and are as “astrocytic” as can be assessed by molecular and ultrastructural criteria.
Congenital heart disease (CHD) is a devastating complex of diseases resulting from defects of development. It affects more than 1 of every 100 live births and is responsible for most prenatal losses (1,2). Additionally, 3 per 1000 live births require an intervention (catheter based or surgical) during the first year of life. Despite its prevalence and severity, the causes of CHD are largely unknown. A clear molecular mechanism has been identified in only a small number of instances. In most of these situations, there is a vast gap between identifying the causative gene and understanding the mechanism by which structural or functional defects occur. Indeed, the ability to identify potential disease targets now far outstrips the capacity to test these hypotheses and define their mecha- nisms. What are the obstacles to unraveling the molecular controls of heart morphogenesis, and are there real-time solutions? Presently, there is an acceleration of significant discovery that should reshape our understanding of congenital cardiac disorders. These advances include the description of an increasing number of gene-targeted mouse models of human cardiac disease; the availability of nearly complete genome sequence informa- tion for multiple organisms, including human beings; and increasingly sophisti- cated bioinformatics tools with which to use these data. The manipulation of gene expression is now possible not only in mouse models, where homologous recombination can be used to inactivate or modify a gene, but in organisms like zebrafish and Xenopus (frogs), where newer techniques can be used to ana- lyze gene expression rapidly and efficiently. Increasingly, investigators are using
The effects of statins on gene expression of cerebral endothelial cells (ECs) in vivo have not been investigated after stroke. We developed a rapid double immunofluorescent staining protocol with antibodies against von Willebrand factor (a marker for endothelium) and glial fibrillary acidic protein (a marker for astrocytes) for laser capture microdissection to isolate single ECs in brain tissue of the rat. Using this protocol in combination with real-time PCR, we found that stroke significantly increased mRNA levels of protease-activated receptor 1 (PAR-1) and tissue factor (TF) in ECs isolated from ischemic cerebral microvessels compared with nonischemic vessels. Treatment of embolic stroke with recombinant human tissue plasminogen activator (rht-PA) 4 h after stroke further elevated PAR-1 mRNA levels nearly 1000-fold in the core and 500-fold in the boundary above the nonstroke group 30 h after stroke, while TF mRNA levels were elevated approximately 10 fold above the nonstroke group. Furthermore, stroke significantly increased matrix metalloproteinase (MMP) 2 and 9 mRNA levels in the ischemic core and boundary regions 6 and 30 h after stroke. Treatment with rht-PA-upregulated MMP2 expression in the ischemic boundary and core. Atorvastatin completely blocked rht-PA upregulation of the above genes, when atorvastatin in combination with rht-PA was administered 4 h after stroke. Monotherapy of atorvastatin 4 h after stroke did not significantly reduce expression of genes examined in the present study. These data provide evidence that atorvastatin reduces exogenous tPA-aggravated cerebral endothelial genes that mediate thrombosis and blood-brain barrier permeability, which could contribute to the beneficial effects of statins on thrombolytic treatment of acute stroke.
A critical determinant of proliferation of progenitor cells is the duration of the cell division cycle. Stroke increases proliferation of progenitor cells in the subventricular zone (SVZ). Using cumulative and single S-phase labeling with 5-bromo-2'-deoxyuridine, we examined cell cycle kinetics of neural progenitor cells in the SVZ after stroke. In nonstroke rats, 20% of the SVZ cell population was proliferating. However, stroke significantly increased dividing cells up to 31% and these cells had a cell cycle length (T(C)) of 15.3 h, significantly (P < 0.05) shorter than the 19 h Tc in nonstroke SVZ cells. Few terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end labeling-positive cells were detected in the SVZ cells of nonstroke and stroke groups, suggesting that the majority of dividing cells in the SVZ do not undergo apoptosis. Cell cycle phase analysis revealed that stroke substantially shortened the length of the G1 phase (9.6 h) compared with the G1 phase of 12.6 h in nonstroke SVZ cells (P < 0.03). This reduction in G1 contributes to stroke-induced reduction of T(C) because no significant changes were detected on the length of S, G2 and M phases between two groups. Furthermore, compared with progenitor cells in nonstroke SVZ (10%), a greater proportion (14%) of progenitor cells in stroke SVZ reentered the cell cycle after mitosis (P < 0.05). These results show that an increase in proliferating progenitor cells in the SVZ contributes to stroke-induced neurogenesis and this increase is regulated by shortening the length of the cell cycle, decreasing the G1 phase and increasing cell cycle reentry.
Nestin is a protein that is thought to be expressed in neural stem cells; however, there is a paucity of data on nestin expression in vivo, and little is known of the relationship between nestin and mitotically active cell populations in the subventricular zones (SVZ). In this study, the subventricular zone of the third ventricle contained a high proportion of cells that expressed nestin, while there were significantly fewer cells that expressed nestin in the SVZ of the lateral ventricles. In contrast, bromodeoxyuridine (BrdU) immunoreactivity was the diametric opposite, being higher in the SVZ of the lateral ventricle than in the SVZ of the third ventricle. Morphological and anatomical evidence suggests that nestin-expressing cells in these two areas may be different cell types. In a separate set of experiments, an acute localized lesion was induced adjacent to one of the ventricles. While the number of BrdU cells and Ki-67 cells in the SVZs increased with this manipulation, the number of nestin-expressing cells did not change significantly. These data indicate that the expression of nestin does not correlate with mitotic activity in cells of the SVZs under either normal or inflammatory conditions. It is hypothesized that nestin-expressing cells in the SVZs may give way to transit amplifying cells that in turn give way to immature neurons or glia. These transit-amplifying cells may have a much higher rate of mitosis than nestin-positive cells and may react to neural damage by increasing their rate of proliferation.
Development of glial cells in the cerebral wall of ferrets: direct tracing of their transformation from radial glia into astrocytes Lipoprotein receptor-mediated induction of matrix metalloproteinase by tissue plasminogen activator
- X Wang
- Sr Lee
- K Arai
- K Tsuji
- Gw Rebeck
- Lo
J Neurosci 13:820–33 Voigt T (1989) Development of glial cells in the cerebral wall of ferrets: direct tracing of their transformation from radial glia into astrocytes. J Comp Neurol 289:74–88 Wang X, Lee SR, Arai K, Tsuji K, Rebeck GW, Lo EH (2003) Lipoprotein receptor-mediated induction of matrix metalloproteinase by tissue plasminogen activator
Neuronal replacement from endogenous precursors in the adult brain after stroke
- A Arvidsson
- T Collin
- D Kirik
- Z Kokaia
- O Lindvall
Arvidsson A, Collin T, Kirik D, Kokaia Z, Lindvall O
(2002) Neuronal replacement from endogenous precursors in the adult brain after stroke. Nat Med 8:963–70
Rat forebrain neurogenesis and striatal neuron replacement after focal stroke
- Jm Parent
- Zs Vexler
- C Gong
- N Derugin
- Dm Ferriero
Parent JM, Vexler ZS, Gong C, Derugin N, Ferriero DM
(2002) Rat forebrain neurogenesis and striatal neuron
replacement after focal stroke. Ann Neurol 52:802–13