[Show abstract][Hide abstract] ABSTRACT: Although the spectrum of white matter injury (WMI) in preterm infants is shifting from cystic necrotic lesions to milder forms, the factors that contribute to this changing spectrum are unclear. We hypothesized that recurrent hypoxia-ischemia (rHI) will exacerbate the spectrum of WMI defined by markers of inflammation and molecules related to the extracellular matrix (hyaluronan (HA) and the PH20 hyaluronidase) that regulate maturation of the oligodendrocyte (OL) lineage after WMI.
PLoS ONE 11/2014; 9(11):e112800. · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: CD44 is a transmembrane receptor for the glycosaminoglycan hyaluronan, a component of the extracellular matrix. CD44 is expressed by neural stem/progenitor cells, astrocytes, and some neurons but its function in the central nervous system is unknown. To determine the role of CD44 in brain function, we behaviorally analyzed CD44-null (KO) and wild-type (WT) mice. KO mice showed increased activity levels in the light-dark test and a trend towards increased activity in the open field. In addition, KO mice showed impaired hippocampus-dependent spatial memory retention in the probe trial following the first hidden-platform training day in the Morris water maze: WT mice showed spatial memory retention and spent more time in the target quadrant than any other quadrant, while KO mice did not. Although there were no genotype differences in swim speeds during the water maze training sessions with the visible or hidden platform, sensorimotor impairments were seen in other behavioral tests. In the inclined screen and balance beam tests, KO mice moved less than WT mice. In the wire hang test, KO mice also fell off of the wire faster than WT mice. In contrast, there was no genotype difference when emotional learning and memory were assessed in the passive avoidance test. These data support an important role for CD44 in locomotor and sensorimotor functions, and in spatial memory retention.
Behavioural Brain Research 09/2014; · 3.39 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Inflammatory demyelinating diseases like multiple sclerosis are characterized by mononuclear cell infiltration into the central nervous system. The glycosaminoglycan hyaluronan and its receptor, CD44, are implicated in the initiation and progression of a mouse model of multiple sclerosis, experimental autoimmune encephalomyelitis (EAE). Digestion of hyaluronan tethered to brain vascular endothelial cells by a hyaluronidase blocks the slow rolling of lymphocytes along activated brain vascular endothelial cells and delays the onset of EAE. These effects could be due to the elimination of hyaluronan or the generation of hyaluronan digestion products that influence lymphocytes or endothelial cells. Here, we found that hyaluronan dodecasaccharides impaired activated lymphocyte slow rolling on brain vascular endothelial cells when applied to lymphocytes but not to the endothelial cells. The effects of hyaluronan dodecasaccharides on lymphocyte rolling were independent of CD44 and a receptor for degraded hyaluronan, toll-like receptor-4. Subcutaneous injection of hyaluronan dodecasaccharides or tetrasaccharides delayed the onset of EAE in a manner similar to subcutaneous injection of hyaluronidase. Hyaluronan oligosaccharides can therefore act directly on lymphocytes to modulate the onset of inflammatory demyelinating disease.
Matrix biology: journal of the International Society for Matrix Biology 01/2013; · 3.56 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Multiple Sclerosis (MS) is an inflammatory demyelinating disease characterized by sensory, motor, and cognitive impairments. Apolipoprotein E (apoE) plays an important role in cholesterol and lipid metabolism in the brain and in susceptibility to cognitive impairment and pathology following brain injury. Studies in mice with a mild form of experimental autoimmune encephalomyelitis (EAE), an MS animal model, support only protective roles for apoE in MS. We examined behavioral and cognitive changes prior to onset of clinical disease and the onset and progression of a more severe form of EAE in female Apoe(-/-) and C57Bl/6 wild-type mice. Apoe(-/-) mice had a later day of onset, a later day of peak symptoms and disease severity, and a lower cumulative disease index compared to wild type mice. Apoe(-/-) mice also showed decreased CD4+ cell invasion following EAE induction compared to wild type mice, and less spinal cord demyelination at 17 but not 30 days following EAE induction. In contrast, EAE-challenged Apoe(-/-) mice showed reduced exploratory activity, rotorod performance, and impaired contextual fear conditioning compared to wild type animals. These data indicate paradoxical effects of apoE on EAE-induced behavioral and cognitive changes and the onset and progression of clinical disease.
Pharmacology Biochemistry and Behavior 11/2012; · 2.82 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: OBJECTIVE: Oligodendrocyte progenitor cells (OPCs) recruited to demyelinating lesions often fail to mature into oligodendrocytes (OLs) that remyelinate spared axons. The glycosaminoglycan hyaluronan (HA) accumulates in demyelinating lesions and has been implicated in the failure of OPC maturation and remyelination. We tested the hypothesis that OPCs in demyelinating lesions express a specific hyaluronidase, and that digestion products of this enzyme inhibit OPC maturation. METHODS: Mouse OPCs grown in vitro were analyzed for hyaluronidase expression and activity. Gain of function studies were used to define the hyaluronidases that blocked OPC maturation. Mouse and human demyelinating lesions were assessed for hyaluronidase expression. Digestion products from different hyaluronidases and a hyaluronidase inhibitor were tested for their effects on OPC maturation and functional remyelination in vivo. RESULTS: OPCs demonstrated hyaluronidase activity in vitro and expressed multiple hyaluronidases, including HYAL1, HYAL2, and PH20. HA digestion by PH20 but not other hyaluronidases inhibited OPC maturation into OLs. In contrast, inhibiting HA synthesis did not influence OPC maturation. PH20 expression was elevated in OPCs and reactive astrocytes in both rodent and human demyelinating lesions. HA digestion products generated by the PH20 hyaluronidase but not another hyaluronidase inhibited remyelination following lysolecithin-induced demyelination. Inhibition of hyaluronidase activity lead to increased OPC maturation and promoted increased conduction velocities through lesions. INTERPRETATION: We determined that PH20 is elevated in demyelinating lesions and that increased PH20 expression is sufficient to inhibit OPC maturation and remyelination. Pharmacological inhibition of PH20 may therefore be an effective way to promote remyelination in multiple sclerosis and related conditions. ANN NEUROL 2013;
Annals of Neurology 10/2012; · 11.91 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Shiverer-immunodeficient (Shi-id) mice demonstrate defective myelination in the central nervous system (CNS) and significant ataxia by 2 to 3 weeks of life. Expanded, banked human neural stem cells (HuCNS-SCs) were transplanted into three sites in the brains of neonatal or juvenile Shi-id mice, which were asymptomatic or showed advanced hypomyelination, respectively. In both groups of mice, HuCNS-SCs engrafted and underwent preferential differentiation into oligodendrocytes. These oligodendrocytes generated compact myelin with normalized nodal organization, ultrastructure, and axon conduction velocities. Myelination was equivalent in neonatal and juvenile mice by quantitative histopathology and high-field ex vivo magnetic resonance imaging, which, through fractional anisotropy, revealed CNS myelination 5 to 7 weeks after HuCNS-SC transplantation. Transplanted HuCNS-SCs generated functional myelin in the CNS, even in animals with severe symptomatic hypomyelination, suggesting that this strategy may be useful for treating dysmyelinating diseases.
Science translational medicine 10/2012; 4(155):155ra136. · 14.41 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The extravasation of lymphocytes across central nervous system (CNS) vascular endothelium is a key step in inflammatory demyelinating diseases including multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE). The glycosaminoglycan hyaluronan (HA) and its receptor, CD44, have been implicated in this process but their precise roles are unclear. We find that CD44(-/-) mice have a delayed onset of EAE compared with wild type animals. Using an in vitro lymphocyte rolling assay, we find that fewer slow rolling (<1 μm/s) wild type (WT) activated lymphocytes interact with CD44(-/-) brain vascular endothelial cells (ECs) than with WT ECs. We also find that CD44(-/-) ECs fail to anchor HA to their surfaces, and that slow rolling lymphocyte interactions with WT ECs are inhibited when the ECs are treated with a pegylated form of the PH20 hyaluronidase (PEG-PH20). Subcutaneous injection of PEG-PH20 delays the onset of EAE symptoms by ∼1 day and transiently ameliorates symptoms for 2 days following disease onset. These improved symptoms correspond histologically to degradation of HA in the lumen of CNS blood vessels, decreased demyelination, and impaired CD4(+) T-cell extravasation. Collectively these data suggest that HA tethered to CD44 on CNS ECs is critical for the extravasation of activated T cells into the CNS providing new insight into the mechanisms promoting inflammatory demyelinating disease.
Journal of Biological Chemistry 08/2012; 287(40):33237-51. · 4.60 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The major form of magnetic resonance imaging-defined white matter injury (WMI) comprises diffuse lesions where the burden of small necrotic foci (microscopic necrosis) is poorly defined. We hypothesized that myelination failure associated with diffuse WMI involves an aberrant injury response linked to arrested preoligodendrocyte (preOL) maturation in reactive astrocyte-rich lesions.
A retrospective autopsy series (1983-2000) was selected for cases with diffuse WMI and analyzed relative to prospectively collected contemporary cases (2003-2010). Controls were age- and region-matched to address regional variation in preOL maturation. Successive oligodendrocyte stages were analyzed with lineage-specific markers. Microscopic necrosis was quantified with microglial markers. Axon injury markers defined the burden of axonopathy. Extracellular matrix remodeling was defined by detection of hyaluronic acid (HA), an inhibitor of preOL maturation, and the HA receptor, CD44.
In the contemporary case series, diffuse WMI was accompanied by a significant reduction in the burden of microscopic necrosis and axonopathy. Diffuse astrogliosis extended into the lesion surround with elevated HA and astrocyte-expressed CD44. The total population of OL lineage stages was significantly increased in lesions. This increase coincided with significant expansion of the preOL pool.
Although these data confirm that microscopic necrosis occurs in contemporary cases, the markedly decreased burden supports that it does not contribute substantially to myelination failure. The primary mechanism of myelination failure involves a disrupted cellular response whereby preOLs fail to differentiate in diffuse astrogliotic lesions. PreOL maturation arrest converts chronic WMI to a more immature state related to the burden of astrogliosis.
Annals of Neurology 01/2012; 71(1):93-109. · 11.91 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The cognitive decline associated with normal aging was long believed to be due primarily to decreased synaptic density and neuron loss. Recent studies in both humans and non-human primates have challenged this idea, pointing instead to disturbances in white matter (WM) including myelin damage. Here, we review both cross-sectional and longitudinal studies in humans and non-human primates that collectively support the hypothesis that WM disturbances increase with age starting at middle age in humans, that these disturbances contribute to age-related cognitive decline, and that age-related WM changes may occur as a result of free radical damage, degenerative changes in cells in the oligodendrocyte lineage, and changes in microenvironments within WM.
[Show abstract][Hide abstract] ABSTRACT: The cellular and molecular mechanisms underlying magnetic resonance imaging-defined white matter (WM) changes associated with age-related cognitive decline remain poorly defined. We tested the hypothesis that WM lesions in older adults, defined by diffusion tensor imaging (DTI), arise in the setting of vascular brain injury (VBI) and are characterized by increased free radical injury and aberrant oligodendrocyte lineage (OL) cell response to injury.
We undertook a multimodal analysis of prefrontal cortex (PFC) WM from 25 autopsies derived from a population-based cohort where VBI and Alzheimer disease (AD) frequently coincide. Ex vivo high field strength DTI measurements of fractional anisotropy (FA), apparent diffusion coefficient, and axial and radial (D(⊥) ) diffusivity were measured at high magnetic field strength (11.7T) and analyzed relative to quantitative in vivo biomarkers of free radical injury, an OL-specific marker Olig2, and histologic evaluation of hyaluronan (HA), an inhibitor of OL maturation.
Coincident AD and VBI showed significant association with lower FA and a robust relationship between decreasing FA and increasing D(⊥) . Free radical injury to docosahexaenoate and adrenate in PFC WM was significantly elevated in cases with VBI independent of AD, and was inversely correlated with FA. Similarly, increased density of Olig2-immunoreactive cells in PFC WM was significantly associated with VBI independent of AD and colocalized with regions enriched in HA.
DTI-defined PFC WM lesions in older individuals are characterized by free radical injury to myelin and neuroaxonal elements that coincides with pronounced expansion of the pool of OL cells in HA-rich regions.
Annals of Neurology 09/2011; 70(3):465-76. · 11.91 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The glycosaminoglycan hyaluronan (HA) accumulates in central nervous system lesions where it limits astrogliosis but also inhibits oligodendrocyte progenitor cell (OPC) maturation. The role of hyaluronan in normative brain aging has not been previously investigated. Here, we tested the hypothesis that HA accumulates in the aging nonhuman primate brain. We found that HA levels significantly increase with age in the gray matter of rhesus macaques. HA accumulation was linked to age-related increases in the transcription of HA synthase-1 (HAS1) expressed by reactive astrocytes but not changes in the expression of other HAS genes or hyaluronidases. HA accumulation was accompanied by increased expression of CD44, a transmembrane HA receptor. Areas of gray matter with elevated HA in older animals demonstrated increased numbers of olig2(+) OPCs, consistent with the notion that HA may influence OPC expansion or maturation. Collectively, these data indicate that HAS1 and CD44 are transcriptionally upregulated in astrocytes during normative aging and are linked to HA accumulation in gray matter.
Neurobiology of aging 08/2011; 33(4):830.e13-24. · 5.94 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: CNS myelination disturbances commonly occur in chronic white matter lesions in neurodevelopmental and adult neurological disorders. Recent studies support that myelination failure can involve a disrupted cellular repair mechanism where oligodendrocyte (OL) progenitor cells (OPCs) proliferate in lesions with diffuse astrogliosis, but fail to fully differentiate to mature myelinating OLs. There are no in vitro models that reproduce these features of myelination failure.
Forebrain coronal slices from postnatal day (P) 0.5/1 rat pups were cultured for 1, 5, or 9 days in vitro (DIV). Slices rapidly exhibited diffuse astrogliosis and accumulation of the extracellular matrix glycosaminoglycan hyaluronan (HA), an inhibitor of OPC differentiation and re-myelination. At 1 DIV ~1.5% of Olig2+ OLs displayed caspase-3 activation, which increased to ~11.5% by 9 DIV. At 1 DIV the density of PDGFRα+ and PDGFRα+/Ki67+ OPCs were significantly elevated compared to 0 DIV (P < 0.01). Despite this proliferative response, at 9 DIV ~60% of white matter OLs were late progenitors (preOLs), compared to ~7% in the postnatal day 10 rat (P < 0.0001), consistent with preOL maturation arrest. Addition of HA to slices significantly decreased the density of MBP+ OLs at 9 DIV compared to controls (217 ± 16 vs. 328 ± 17 cells/mm2, respectively; P = 0.0003), supporting an inhibitory role of HA in OL lineage progression in chronic lesions.
Diffuse white matter astrogliosis and early OPC proliferation with impaired OL maturation were reproduced in this model of myelination failure. This system may be used to define mechanisms of OPC maturation arrest and myelination failure related to astrogliosis and HA accumulation.
[Show abstract][Hide abstract] ABSTRACT: Fxyd1 encodes a trans-membrane protein that modulates Na(+) ,K(+) -ATPase activity and is a substrate for multiple protein kinases. Fxyd1 expression is repressed by methyl CpG-binding protein 2 (Mecp2) in the frontal cortex (FC) but not in the cerebellum (CB) of the mouse brain. Consistently with these observations, FXYD1 mRNA abundance is increased in the FC of Rett syndrome (RTT) patients with MECP2 mutations. Because Fxyd1 is implicated in the regulation of neuronal excitability, understanding how Fxyd1 expression is controlled is important. Here we report that basal expression of Fxyd1a and Fxyd1b, the two main alternatively spliced forms of Fxyd1 mRNA, is lower in the FC than in the CB. This difference is accompanied by increased Mecp2 recruitment to the promoter region of these two Fxyd1 mRNA forms. DNA methylation of both promoters is more frequent in the FC than in the CB, and in both cases the most frequently methylated CpG dinucleotides are adjacent to [A/T](4) sequences required for high-affinity Mecp2 binding. Consistently with these features of epigenetic silencing, histone 3 acetylated at lysines 9 and 14 (H3K9/14ac) and histone 3 methylated at lysine 4 (H3K4me3), both activating histone marks, were associated with the Fxyd1 promoter to a lesser degree in the FC than in the CB. These results indicate that differential Fxyd1 expression in these two brain regions is, at least in part, regulated by an epigenetic mechanism involving increased DNA methylation of the two alternative Fxyd1 promoters, enhanced Mecp2 recruitment, and reduced association of activating histones.
Journal of Neuroscience Research 03/2011; 89(6):840-51. · 2.73 Impact Factor