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Microglial Tau Undergoes Phosphorylation-Independent Modification after Ischemia
Abstract
Tau2 is a phosphorylation-independent antibody that immunolabels neurofibrillary tangles (NFTs) of Alzheimer type and microglia around ischemic foci on formalin-fixed, paraffin-embedded sections. We found that copresence of polyethyleneglycol-p-isooctylphenyl ether (Triton X-100; TX) with tau2 abolished its immunoreactivity (IR) in these microglia but not its IR on NFTs. Tau2-immunoreactive bands, exclusively retrieved in Tris-soluble fraction of brain homogenates from ischemic foci, normal human and bovine brains, were of similar electrophoretic mobility, indicating that tau2 IR in these microglia is unrelated to hyperphosphorylation of tau. These tau2-immunoreactive bands except those from bovine brain were abolished in the copresence of TX. This was not due to washing out of tau, because similar immunoreactive bands were detectable with another antitau antibody even under a higher concentration of TX and because washing after TX exposure restored similar tau2 IR both on immunohistochemistry and immunoblot. These findings are explained if tau, modified after ischemia, undergoes a reversible conformational change on TX exposure. Because conformation at Ser101 of bovine tau is crucial for its affinity to tau2, this Ser-like conformation mimicked by its human counterpart Pro may represent pathological modification of tau shared by microglia around ischemic foci and NFTs. Relative resistance of tau2 epitope in NFTs to TX exposure suggests that tau woven into NFTs confers additional stability to this pathological modification on tau2 epitope. Susceptibility of tau2 epitope to TX, seen in these microglia, is shared with glial cytoplasmic inclusions and will show its conformational state to be different from that in NFTs.
... Historical studies have shown a strong accumulation of the tau protein in neurons, astrocytes, and oligodendrocytes in the hippocampus, thalamus, and cortex in both experimental [39][40][41][42][43][44] and post-ischemic brain injuries in humans [45][46][47][48][49]. The tau protein was also accumulated in microglia in ischemic penumbra [47][48][49]. ...
... Historical studies have shown a strong accumulation of the tau protein in neurons, astrocytes, and oligodendrocytes in the hippocampus, thalamus, and cortex in both experimental [39][40][41][42][43][44] and post-ischemic brain injuries in humans [45][46][47][48][49]. The tau protein was also accumulated in microglia in ischemic penumbra [47][48][49]. The above observations indicate that some neurons show changes in the tau protein after brain ischemia with reperfusion [41], which may indicate the main pathological phase of the development of ischemic processes in these cells [43]. ...
... The functions of the tau protein are controlled by a multifaceted system of post-translational changes such as glycation, phosphorylation, acetylation, nitration, isomerization, O-GlcNAcylation, sumoylation, and truncation [72][73][74], suggesting that the tau protein plays an important role in both the physiology and pathology of the brain [75]. The modified structure of the tau protein is one of the most neurotoxic proteins accumulated in neuronal and neuroglial cells post-ischemia in humans and animals [27,28,33,34,36,47,63,69,70]. According to previous studies, the stages of the dysfunctional tau protein differ in different ischemic brain models such as dephosphorylation [32,41,42,64,66,76,77], re-phosphorylation [32,66], hyperphosphorylation [32,49,60,62,63], and the development of neurofibrillary tangles [69][70][71] (Table 2) ( Figure 1). ...
Recent data suggest that post-ischemic brain neurodegeneration in humans and animals is associated with the modified tau protein in a manner typical of Alzheimer’s disease neuropathology. Pathological changes in the tau protein, at the gene and protein level due to cerebral ischemia, can lead to the development of Alzheimer’s disease-type neuropathology and dementia. Some studies have shown increased tau protein staining and gene expression in neurons following ischemia-reperfusion brain injury. Recent studies have found the tau protein to be associated with oxidative stress, apoptosis, autophagy, excitotoxicity, neuroinflammation, blood-brain barrier permeability, mitochondrial dysfunction, and impaired neuronal function. In this review, we discuss the interrelationship of these phenomena with post-ischemic changes in the tau protein in the brain. The tau protein may be at the intersection of many pathological mechanisms due to severe neuropathological changes in the brain following ischemia. The data indicate that an episode of cerebral ischemia activates the damage and death of neurons in the hippocampus in a tau protein-dependent manner, thus determining a novel and important mechanism for the survival and/or death of neuronal cells following ischemia. In this review, we update our understanding of proteomic and genomic changes in the tau protein in post-ischemic brain injury and present the relationship between the modified tau protein and post-ischemic neuropathology and present a positive correlation between the modified tau protein and a post-ischemic neuropathology that has characteristics of Alzheimer’s disease-type neurodegeneration.
... Initial tau protein staining was presented in both neural and glial cells in the hippocampus, cortex and thalamus in both experimental and human brain ischemia [59,[64][65][66][67][68][69][70][71]. Tau protein was also observed in microglia after focal ischemia of the brain in ischemic penumbra [57,71]. ...
... Initial tau protein staining was presented in both neural and glial cells in the hippocampus, cortex and thalamus in both experimental and human brain ischemia [59,[64][65][66][67][68][69][70][71]. Tau protein was also observed in microglia after focal ischemia of the brain in ischemic penumbra [57,71]. The data presented indicate that some neurons show changes in the tau protein after ischemia-reperfusion brain injury [67], which may be related to the main neuropathological stage of ischemic processes in these cells [69]. ...
... During the death of neurons in the CA1 region of the hippocampus after transient cerebral ischemia in the gerbil, hyperphosphorylation of serine 199/202 tau protein was regulated by GSK3, MAP kinase and CDK5 activity (Table 1) [58]. In addition, it was observed that the microglial tau protein is phosphorylated after ischemic brain damage in humans (Table 1) [71]. Current research indicates that after transient focal and global ischemia of the brain with reperfusion, modifications of the hyperphosphorylation of tau protein are similar to those occurring in Alzheimer's disease and predominate in cortical neurons and are accompanied by apoptosis ( Figure 2) [49,55,57,87]. ...
Recent evidence suggests that transient ischemia of the brain with reperfusion in humans and animals is associated with the neuronal accumulation of neurotoxic molecules associated with Alzheimer’s disease, such as all parts of the amyloid protein precursor and modified tau protein. Pathological changes in the amyloid protein precursor and tau protein at the protein and gene level due to ischemia may lead to dementia of the Alzheimer’s disease type after ischemic brain injury. Some studies have demonstrated increased tau protein immunoreactivity in neuronal cells after brain ischemia-reperfusion injury. Recent research has presented many new tau protein functions, such as neural activity control, iron export, protection of genomic DNA integrity, neurogenesis and long-term depression. This review discusses the potential mechanisms of tau protein in the brain after ischemia, including oxidative stress, apoptosis, autophagy, excitotoxicity, neurological inflammation, endothelium, angiogenesis and mitochondrial dysfunction. In addition, attention was paid to the role of tau protein in damage to the neurovascular unit. Tau protein may be at the intersection of many regulatory mechanisms in the event of major neuropathological changes in ischemic stroke. Data show that brain ischemia activates neuronal changes and death in the hippocampus in a manner dependent on tau protein, thus determining a new and important way to regulate the survival and/or death of post-ischemic neurons. Meanwhile, the association between tau protein and ischemic stroke has not been well discussed. In this review, we aim to update the knowledge about the proteomic and genomic changes in tau protein following ischemia-reperfusion injury and the connection between dysfunctional tau protein and ischemic stroke pathology. Finally we present the positive correlation between tau protein dysfunction and the development of sporadic Alzheimer’s disease type of neurodegeneration.
... Early studies have shown that tau protein staining in neurons and glia is present in the hippocampus, thalamus, and cerebral cortex in the human brain after ischemia (61)(62)(63). The modified tau protein was also observed in microglial cells (63). ...
... Early studies have shown that tau protein staining in neurons and glia is present in the hippocampus, thalamus, and cerebral cortex in the human brain after ischemia (61)(62)(63). The modified tau protein was also observed in microglial cells (63). It was noted that microglial cells' tau protein passes independent of phosphorylation modification following cerebral ischemia with recirculation in humans (63). ...
... The modified tau protein was also observed in microglial cells (63). It was noted that microglial cells' tau protein passes independent of phosphorylation modification following cerebral ischemia with recirculation in humans (63). Finally, in one of the studies, many neurofibrillary tangle-bearing neurons were observed in the nucleus basalis of Meynert ipsilateral to a massive focal cerebral infarction (23). ...
ABSTRACT Ischemic brain damage is associated with the deposition of folding proteins, such as all fragments of the amyloid protein precursor and tau protein, in the intra- and extracellular spaces of neurons. In this chapter, we summarize the protein changes associated with Alzheimer’s disease and their gene expression (amyloid protein precursor and tau protein) after cerebral ischemia and their role in the ischemic etiology of Alzheimer’s disease. Recent advances in understanding the ischemic etiology of Alzheimer’s disease have revealed dysregulation of amyloid protein precursors, β-secretase, presenilin 1 and 2, autophagy, mitophagy, apoptosis, and tau protein genes after ischemic brain injury. However, reduced expression of mRNA of the α-secretase in cerebral ischemia causes neurons to be less resistant to injury. In this chapter, we present the latest evidence that Alzheimer’s disease-related proteins and their genes play a key role in brain damage with ischemia-reperfusion and that ischemic episode is an essential and leading provider of Alzheimer’s disease development. Understanding the underlying processes of linking Alzheimer’s disease-related proteins and their genes in brain ischemia injury with the risk of developing Alzheimer’s disease will provide the most significant goals for therapeutic development to date.
... However, the expression of the significant growth of the tau protein gene was noted 7-30 days post-ischemia (Table 1) [31]. Increased accumulation of tau protein in neuronal cells, astrocytes and oligodendrocytes in the cortex, hippocampus and thalamus has been established in experimental studies [32][33][34][35][36][37] as well as in human brains after ischemia [38][39][40]. Accumulating tau protein was also visible in the microglia in the focal brain ischemia penumbra [40][41][42][43]. Observations indicate that brain cells accumulate the tau protein as a result of ischemia [35], which indicates a significant phase in the development of pathological ischemic processes in the brain tissue [36]. ...
... Increased accumulation of tau protein in neuronal cells, astrocytes and oligodendrocytes in the cortex, hippocampus and thalamus has been established in experimental studies [32][33][34][35][36][37] as well as in human brains after ischemia [38][39][40]. Accumulating tau protein was also visible in the microglia in the focal brain ischemia penumbra [40][41][42][43]. Observations indicate that brain cells accumulate the tau protein as a result of ischemia [35], which indicates a significant phase in the development of pathological ischemic processes in the brain tissue [36]. ...
Cerebral ischemia in humans and animals is a life-threatening neuropathological event and leads to the development of dementia with the Alzheimer’s disease phenotype [...]
... For example, voluntary aerobic training improved non-spatial memory more significantly in males than females; whereas forced aerobic training improved hippocampal dependent learning and memory in females more than males (Barha et al. 2017). Females had a greater increase in brain-derived neurotrophic factor (Lindsay et al. 2019;Branyan and Sohrabji 2020;Roth et al. 2020;Saklayen 2018;Benjamin et al. 2017) Age effects (Lindsay et al. 2019;Branyan and Sohrabji 2020;Roth et al. 2020;Saklayen 2018;Maaijwee et al. 2014;Putaala et al. 2009;Kappelle et al. 1994 Kokmen et al. 1996;Khan et al. 2016;Pohjasvaara et al. 1998;Madureira et al. 2001;Yang et al. 2006;Leys et al. 2005;Ali et al. 1996;Dewar and Dawson 1995;Irving et al. 1997;Uchihara et al. 2004;Ishibashi et al. 2006;Kiryk et al. 2011;Block and Schwarz 1997;Davis et al. 1986) Sex difference (Khattab et al. 2020;Wang et al. 2014;Anstey et al. 2021;Scheyer et al. 2018;Dufouil et al. 2014;Pendlebury and Rothwell 2009;Podcasy and Epperson 2016;Poynter et al. 2009;Gall et al. 2012;Bushnell and McCullough 2014;Bushnell et al. 2014) Age effects (Wang et al. 2014) Post-stroke mental health and mood/personality changes General (Carota and Bogousslavsky 2012;Lees et al. 2012a;Turner et al. 2019;Naess et al. 2012;Das and Rajanikant 2018;Gorelick et al. 2016;Hadidi et al. 2009;Lai et al. 2002;El Husseini et al. 2012;Gao et al. 2017;Kim et al. 2017;Tsai et al. 2011;Karaiskos et al. 2012;Niedermaier et al. 2004;Paolucci 2017;Stone et al. 2004;Rabat et al. 2021;Suñer-Soler et al. 2012Huang et al. 2017;Ebrahimi et al. 2018;Esse et al. 2011;Shah and Cole 2010;Larsson et al. 2016;Osama et al. 2018;Widar et al. 2002;Tang et al. 2013;Scuteri et al. 2020) (continued) (BNDF) after aerobic training when compared to males which could result in increased neuroprotection (Barha et al. 2017;Alcantara et al. 2018). These studies suggest that exercise programs could further be tailored based on sex (i.e., voluntary or forced) to best improve individual cognitive benefit rather than assuming aerobic exercise in general is enough. ...
... Ischemia has also been shown to increase the expression and activity of β-secretase, an enzyme critical to the conversion of amyloid precursor protein to pathological β-amyloid (Wen et al. 2004). Tau protein expression is increased in astrocytes, oligodendrocytes, and microglia following ischemia (Dewar and Dawson 1995;Irving et al. 1997;Uchihara et al. 2004). Increased deposition of amyloidogenic proteins and neuronal expression of apolipoprotein E is also increased after stroke in human brains (Jendroska et al. 1995;Qi et al. 2007). ...
Stroke is the fifth leading cause of death and as healthcare intervention improves, the number of stroke survivors has also increased. Furthermore, there exists a subgroup of younger adults, who suffer stroke and survive. Given the overall improved survival rate, bettering our understanding of long-term stroke outcomes is critical. In this review we will explore the causes and challenges of known long-term consequences of stroke and if present, their corresponding sex differences in both old and young survivors. We have separated these long-term post-stroke consequences into three categories: mobility and muscle weakness, memory and cognitive deficits, and mental health and mood. Lastly, we discuss the potential of common preclinical stroke models to contribute to our understanding of long-term outcomes following stroke.
... After ischemia and global brain recirculation, the tau protein is phosphorylated and slowly accumulates (71). Transient focal cerebral ischemia with 1 day of reperfusion induces local hyperphosphorylation (regions of injury) of the tau protein (72,73). Current research indicates that after ischemia, hyperphosphorylated tau protein accumulates in cortical neuronal cells and is accompanied by apoptosis (72,74). ...
... A prospective study revealed that tau levels in both plasma and CSF were closely related not only to stroke severity assessed using the National Institutes of Health Stroke Scale but also to long-term outcomes (83). In particular, the study of autopsy specimens of the brains from patients with cerebral infarction showed an increase in tau immunoreactivity and tau deposition in the ischemic area (73,84). However, the tau protein has been detected in the serum of ~40% of patients with stroke (78,79). ...
The cytoskeleton is the main intracellular structure that determines the morphology of neurons and maintains their integrity. Therefore, disruption of its structure and function may underlie several neurodegenerative diseases. This review summarizes the current literature on the tau protein, microtubule-associated protein 2 (MAP2) and neurofilaments as common denominators in pathological conditions such as Alzheimer's disease (AD), cerebral ischemia, and multiple sclerosis (MS). Insights obtained from experimental models using biochemical and immunocytochemical techniques highlight that changes in these proteins may be potentially used as protein targets in clinical settings, which provides novel opportunities for the detection, monitoring and treatment of patients with these neurodegenerative diseases.
... A common appearance of immunoreactive tau protein neurons and neuroglial cells was found in human and experimental post-ischemic hippocampus, thalamus, and cortex [58,90,[118][119][120][121][122][123][124][125]. Some neurons were also labeled with tau protein antibodies after cerebral ischemia in humans due to cardiac arrest with 1 month survival [113]. ...
... Some neurons were also labeled with tau protein antibodies after cerebral ischemia in humans due to cardiac arrest with 1 month survival [113]. After focal cerebral ischemia, tau protein staining was also noted in microglia [125]. The evidence presented indicates that some neuronal cells show changes in tau protein during post-ischemic brain injury [121] that may be associated with the degree of development of ischemic neuron death (Figure 2) [124]. ...
Post-ischemic brain damage is associated with the deposition of folding proteins such as the amyloid and tau protein in the intra- and extracellular spaces of brain tissue. In this review, we summarize the protein changes associated with Alzheimer’s disease and their gene expression (amyloid protein precursor and tau protein) after ischemia-reperfusion brain injury and their role in the post-ischemic injury. Recent advances in understanding the post-ischemic neuropathology have revealed dysregulation of amyloid protein precursor, α-secretase, β-secretase, presenilin 1 and 2, and tau protein genes after ischemic brain injury. However, reduced expression of the α-secretase in post-ischemic brain causes neurons to be less resistant to injury. In this review, we present the latest evidence that proteins associated with Alzheimer’s disease and their genes play a key role in progressive brain damage due to ischemia and reperfusion, and that an ischemic episode is an essential and leading supplier of proteins and genes associated with Alzheimer’s disease in post-ischemic brain. Understanding the underlying processes of linking Alzheimer’s disease-related proteins and their genes in post-ischemic brain injury with the risk of developing Alzheimer’s disease will provide the most significant goals for therapeutic development to date.
... Another study provided evidence that staining of tau protein PHF-1 epitope phosphorylation declined to 6%, immediately following brain ischemia, and then it returned near to the normal value during few hours of reperfusion and consequently increased above normal level over next 7 days, signifying a strong hyperphosphorylation phenomenon [134]. Another group has demonstrated that microglia tau protein undergoes phosphorylation independent modification following brain ischemia [135]. ...
... An increase in full-length tau protein staining in oligodendrocytes was evident following focal ischemic brain injury [128]. The pathological modification of tau protein by microglia around ischemic foci was also demonstrated [135]. The accumulation of tau protein in neuronal cell bodies throughout the ischemic hippocampus has been shown, too [127]. ...
There are evidences for the influence of Alzheimer's proteins on postischemic brain injury. We present here an overview of the published evidence underpinning the relationships between β-amyloid peptide, hyperphosphorylated tau protein, presenilins, apolipoproteins, secretases and neuronal survival/death decisions after ischemia and development of postischemic dementia. The interactions of above molecules and their influence and contribution to final ischemic brain degeneration resulting in dementia of Alzheimer phenotype are reviewed. Generation and deposition of β-amyloid peptide and tau protein pathology are essential factors involved in Alzheimer's disease development as well as in postischemic brain dementia. Postischemic injuries demonstrate that ischemia may stimulate pathological amyloid precursor protein processing by upregulation of β- and γ-secretases and therefore are capable of establishing a vicious cycle. Functional postischemic brain recovery is always delayed and incomplete by an injury-related increase in the amount of the neurotoxic C-terminal of amyloid precursor protein and β-amyloid peptide. Finally, we present here the concept that Alzheimer's proteins can contribute to and/or precipitate postischemic brain neurodegeneration including dementia with Alzheimer's phenotype.
... Increased tau protein immunoreactivity in neuronal and neuroglial cells, mainly in the hippocampus, brain cortex, and thalamus, has been demonstrated in animals and also in humans post-ischemia [48,49,[70][71][72][73][74][75][76][77][78]. Data indicate that neuronal and neuroglial cells store tau protein during and after experimental ischemia [73], which indicates the progression of pathological phenomena in the ischemic brain related to tau protein [76]. ...
Recent evidence indicates that experimental brain ischemia leads to dementia with an Alzheimer’s disease-like type phenotype and genotype. Based on the above evidence, it was hypothesized that brain ischemia may contribute to the development of Alzheimer’s disease. Brain ischemia and Alzheimer’s disease are two diseases characterized by similar changes in the hippocampus that are closely related to memory impairment. Following brain ischemia in animals and humans, the presence of amyloid plaques in the extracellular space and intracellular neurofibrillary tangles was revealed. The phenomenon of tau protein hyperphosphorylation is a similar pathological feature of both post-ischemic brain injury and Alzheimer’s disease. In Alzheimer’s disease, the phosphorylated Thr231 motif in tau protein has two distinct trans and cis conformations and is the primary site of tau protein phosphorylation in the pre-entanglement cascade and acts as an early precursor of tau protein neuropathology in the form of neurofibrillary tangles. Based on the latest publication, we present a similar mechanism of the formation of neurofibrillary tangles after brain ischemia as in Alzheimer’s disease, established on trans- and cis-phosphorylation of tau protein, which ultimately influences the development of tauopathy.
... Studies of ischemic brains in animals and humans have documented the accumulation of tau protein in neurons and glial cells in the hippocampus, cortex, and thalamus [83,[115][116][117][118][119][120][121]. An increase in soluble tau protein in brain tissue using microdialysis in an ischemic brain is also shown [122]. ...
Recent years have seen remarkable progress in research into free radicals oxidative stress, particularly in the context of post-ischemic recirculation brain injury. Oxidative stress in post-ischemic tissues violates the integrity of the genome, causing DNA damage, death of neuronal, glial and vascular cells, and impaired neurological outcome after brain ischemia. Indeed, it is now known that DNA damage and repair play a key role in post-stroke white and gray matter remodeling, and restoring the integrity of the blood-brain barrier. This review will present one of the newly characterized mechanisms that emerged with genomic and proteomic development that led to brain ischemia to a new level of post-ischemic neuropathological mechanisms, such as the presence of amyloid plaques and the development of neurofibrillary tangles, which further exacerbate oxidative stress. Finally, we hypothesize that modified amyloid and the tau protein, along with the oxidative stress generated, are new key elements in the vicious circle important in the development of post-ischemic neurodegeneration in a type of Alzheimer’s disease proteinopathy.
... The major component of NFT is hyperphosphorylated tau protein, which may have a critical role in the progression of AD (42). It is observed in neurons, astrocytes, microglial cells, and oligodendrocytes after ischemia in both the hippocampus and cortex (51)(52)(53)(54). Hyperphosphorylated tau protein is deposited as paired helical filaments in brain tissue (55), leading to neuronal apoptosis (56), followed by memory dysfunction (55). ...
ABSRACT Progressive accumulation of misfolded amyloid and tau protein in intracellular and extracellular spaces is the most crucial etiopathological feature of brain ischemia, synaptic damage, or neural communication impairment. Clinical data suggest that dietary intake of curcumin enhances neurogenesis and offers neuroprotection. Curcumin is a natural polyphenolic compound with diverse and attractive biological properties. It may prevent aging-associated changes in cellular proteins, such as β-amyloid peptide and tau protein, that lead to protein insolubility and aggregation after ischemic brain damage. Therefore, curcumin seems to be a promising supplementary agent against neurodegeneration development after brain ischemia. The aim of this chapter is to highlight our current understanding of the neuroprotective role of curcumin in cerebral ischemia-reperfusion injury. The limitations and adverse events of curcumin are also presented.
... LPS-induced activation of microglia could exacerbate major neuropathological changes in AD, such as the formation of neurofibrillary tangles [40,41]. In addition to neurons, tau protein was also observed in microglia [42][43][44][45][46]. Tau protein was a kind of microtubule-related proteins. ...
As a new target protein for Alzheimer's disease (AD), the triggering receptor expressed on myeloid Cells 2 (TREM2) was expressed on the surface of microglia, which was shown to regulate neuroinflammation, be associated with a variety of neuropathologic, and regarded as a potential indicator for monitoring AD. In this study, a novel recognition system based on surface plasmon resonance (SPR) for the TREM2 target spot was established coupled with quadrupole time-of-flight tandem mass spectrometry (UPLC-MS), in order to screen the active ingredients targeting TREM2 from Datura metel seeds. The results showed that four lignan-amides were discovered as candidate compounds by SPR biosensor-UPLC/MS recognition analysis. According to the guidance of the active ingredients discovered by the system, the lignin-amides from Datura metel seeds (LDS) were preliminarily identified as containing 27 lignan-amides, which were enriched compositions by the HP-20 of Datura metel seeds. Meanwhile, the anti-inflammatory activity of LDS was evaluated in BV2 microglia induced by LPS. Our experimental results demonstrated that LDS could reduce NO release in LPS-treated BV2 microglia cells and significantly reduce the expression of the proteins of inducible Nitric Oxide Synthase (iNOS), cyclooxygenase 2 (COX-2), microtubule-associated protein tau (Tau), and ionized calcium-binding adapter molecule 1 (IBA-1). Accordingly, LDS might increase the expression of TREM2/DNAX-activating protein of 12 kDa (DAP12) and suppress the Toll-like receptor SX4 (TLR4) pathway and Recombinant NLR Family, Pyrin Domain Containing Protein 3 (NLRP3)/cysteinyl aspartate specific proteinase-1 (Caspase-1) inflammasome expression by LDS in LPS-induced BV2 microglial cells. Then, the inhibitory release of inflammatory factors Interleukin 1 beta (IL-1β), Interleukin 6 (IL-6), and Tumor necrosis factor-alpha (TNFα) inflammatory cytokines were detected to inhibit neuroinflammatory responses. The present results propose that LDS has potential as an anti-neuroinflammatory agent against microglia-mediated neuroinflammatory disorders.
... Strong neuronal staining of tau protein was found following ischemia in the hippocampus and the brain cortex (Dewar et al., 1993(Dewar et al., , 1994Geddes et al., 1994;Sinigaglia-Coimbra et al., 2002). Also, tau protein staining was documented in post-ischemic microglia, astrocytes, and oligodendrocytes ( Dewar and Dawson, 1995;Irving et al., 1997;Uchihara et al., 2004;Majd et al., 2016;Fujii et al., 2017). Evidence shows that after ischemia, the hyperphosphorylated tau protein dominates in neuronal cells and goes along with apoptosis (Wen et al., 2004b,c;Wen et al., 2007;Majd et al., 2016;Fujii et al., 2017;Basurto-Islas et al., 2018). ...
Transient ischemic brain injury causes massive neuronal death in the hippocampus of both humans and animals. This was accompanied by progressive atrophy of the hippocampus, brain cortex, and white matter lesions. Furthermore, it has been noted that neurodegenerative processes after an episode of ischemia-reperfusion in the brain can continue well-beyond the acute stage. Rarefaction of white matter was significantly increased in animals at 2 years following ischemia. Some rats that survived 2 years after ischemia developed severe brain atrophy with dementia. The profile of post-ischemic brain neurodegeneration shares a commonality with neurodegeneration in Alzheimer's disease. Furthermore, post-ischemic brain injury is associated with the deposition of folding proteins, such as amyloid and tau protein, in the intracellular and extracellular space. Recent studies on post-ischemic brain neurodegeneration have revealed the dysregulation of Alzheimer's disease-associated genes such as amyloid protein precursor, α-secretase, β-secretase, presenilin 1, presenilin 2, and tau protein. The latest data demonstrate that Alzheimer's disease-related proteins and their genes play a key role in the development of post-ischemic brain neurodegeneration with full-blown dementia in disease types such as Alzheimer's. Ongoing interest in the study of brain ischemia has provided evidence showing that ischemia may be involved in the development of the genotype and phenotype of Alzheimer's disease, suggesting that brain ischemia can be considered as a useful model for understanding the mechanisms responsible for the initiation of Alzheimer's disease.
... After cerebral ischemia, strong immunostaining of tau protein was found in neurons, astrocytes and oligodendrocytes in both the hippocampus and brain cortex (Dewar et al., 1993, Dewar et al., 1994, Geddes et al., 1994, Dewar, Dawson 1995, Irving et al., 1997, Sinigaglia-Coimbra et al., 2002. Moreover, the modified tau protein was also found in microglia cells on ischemic penumbra (Uchihara et al., 2004, Majd et al., 2016, Fujii Complimentary Contributor Copy et al., 2017. Another research demonstrates that the tau protein itself blocks the movement of organelles, neurofilaments and the amyloid protein precursor vesicles on the path from the neuron body to the axons and dendrites, leading to the deposition of the amyloid protein precursor in the body of the neurons (Stamer et al., 2002). ...
Alzheimer`s disease (AD) is the most common and incurable form of dementia. The present AD treatments produce only an uncertain amelioration of symptoms. Research on AD has particularly focused on the central nervous system. Though, some systemic and peripheral abnormalities are now clearly understood that are associated to AD. Current research on these alterations that leads to AD are becoming further defined more evidently. Two microscopic features contribute for the depiction of the disease, the amyloid plaques and neurofibrillary tangles. All these aspects are accountable for the deliberate and gradual weakening of memory that disturb the cognitive control, language, thinking and personality. For the diagnosis of AD, some neuropsychological tests are being performed in various spheres of cognitive functions. To date, cholinesterase inhibitors are used as a drug for the treatment of AD, because these are the individual drugs that have depicted substantial enhancements in the cognitive functions of AD patients. Despite the efficacy of cholinesterase inhibitors, the degeneration of neurons is continuing even while being treated an AD patient. For this cause, further biochemical pathways related to pathophysiology of AD have been revealed as an alternative for the treatment of these conditions such as hindrance of glycogen synthase kinase-3β and β-secretase. The present chapter aims to conduct a review of the pathophysiology, symptoms, epidemiology, analysis and treatment of AD.
... Recent studies on spontaneous old rat models and transgenic mice models of AD showed a protective effect of aerobic exercise on tau phosphorylation and related tau kinases [15,27,28]. Although previous investigations with rat stroke models showed increased level of hyperphosphorylation of tau [29][30][31][32], there have been only a few studies evaluating the effect of aerobic training on tau phosphorylation and related proteins after stroke so far. One study of old P301 transgenic mice showed that 12 weeks of treadmill training had a beneficial effect on tauopathy [15]. ...
Although Alzheimer’s disease (AD)-like pathology is frequently found in patients with post-stroke dementia, little is known about the effects of aerobic exercise on the modifications of tau and related proteins. Therefore, we evaluated the effects of aerobic exercise on the phosphorylation and acetylation of tau and the expressions of tau-related proteins, after middle cerebral artery occlusion (MCAO) stroke. Twenty-four Sprague–Dawley rats with MCAO infarction were used in this study. The rehabilitation group (RG) received treadmill training 40 min/day for 12 weeks, whereas the sedentary group (SG) did not receive any type of training. Functional tests, such as the single pellet reaching task, rotarod, and radial arm maze tests, were performed monthly for 3 months. In ipsilateral cortices in the RG and SG groups, level of Ac-tau was lower in the RG, whereas levels of p-tauS396, p-tauS262, and p-tauS202/T205 were not significantly lower in the RG. Level of phosphorylated glycogen synthase kinase 3-beta Tyr 216 (p-GSK3βY216) was lower in the RG, but levels of p-AMPK and phosphorylated glycogen synthase kinase 3-beta Ser 9 (p-GSK3βS9) were not significantly lower. Levels of COX-2 and BDNF were not significantly different between the two groups, while SIRT1 significantly decreased in ipsilateral cortices in RG. In addition, aerobic training also improved motor, balance, and memory functions. Rehabilitation with aerobic exercise inhibited tau modification, especially tau acetylation, following infarction in the rat MCAO model, which was accompanied with the improvement of motor and cognitive functions.
... Massive staining of tau protein at neurons was found in the ischemic hippocampus and brain cortex [52,77,78]. Tau protein staining was also noted in astrocytes, microglia and oligodendrocytes, postischemia [31,33,[79][80][81]. The above observations indicated that neuronal and neuroglial cells display abnormalities in tau protein after an ischemic brain episode [79], which may illustrate a prime pathological stage of the ischemic processes in these cells [80]. ...
Current evidence indicates that postischemic brain injury is associated with the accumulation of folding proteins, such as amyloid and tau protein, in the intra- and extracellular spaces of neuronal cells. In this review, we summarize protein changes associated with Alzheimer’s disease and their gene expression (amyloid protein precursor and tau protein) after brain ischemia, and their roles in the postischemic period. Recent advances in understanding the postischemic mechanisms in development of neurodegeneration have revealed dysregulation of amyloid protein precursor, α-, β- and γ-secretase and tau protein genes. Reduced expression of the α-secretase gene after brain ischemia with recirculation causes neuronal cells to be less resistant to injury. We present the latest data that Alzheimer’s disease-related proteins and their genes play a crucial role in postischemic neurodegeneration. Understanding the underlying processes of linking Alzheimer’s disease-related proteins and their genes in development of postischemic neurodegeneration will provide the most significant goals to date for therapeutic development.
... Intensive staining of tau protein in neurons, astrocytes, microglial cells, and oligodendrocytes after ischemia was observed in both the hippocampus and cortex [64,[88][89][90][91][92][93][94][95][96]. Another study showed that the tau protein can inhibit the transport of the amyloid protein precursor in axons and dendrites, which leads to the deposition of the amyloid protein precursor in the body of a neuronal cell [97]. ...
Currently available pharmacological treatment of post-ischemia-reperfusion brain injury has limited effectiveness. This review provides an assessment of the current state of neurodegeneration treatment due to ischemia-reperfusion brain injury and focuses on the role of curcumin in the diet. The purpose of this review was to provide a comprehensive overview of what was published about the benefits of curcumin influence on post-ischemic brain damage. Some data on the clinical benefits of curcumin treatment of post-ischemic brain in terms of clinical symptoms and adverse reactions have been reviewed. The data in this review contributes to a better understanding of the potential benefits of curcumin in the treatment of neurodegenerative changes after ischemia and informs scientists, clinicians, and patients, as well as their families and caregivers about the possibilities of such treatment. Due to the pleotropic properties of curcumin, including anti-amyloid, anti-tau protein hyperphosphorylation, anti-inflammatory, anti-apoptotic, and neuroprotective action, as well as increasing neuronal lifespan and promoting neurogenesis, curcumin is a promising candidate for the treatment of post-ischemic neurodegeneration with misfolded proteins accumulation. In this way, it may gain interest as a potential therapy to prevent the development of neurodegenerative changes after cerebral ischemia. In addition, it is a safe substance and inexpensive, easily accessible, and can effectively penetrate the blood–brain barrier and neuronal membranes. In conclusion, the evidence available in a review of the literature on the therapeutic potential of curcumin provides helpful insight into the potential clinical utility of curcumin in the treatment of neurological neurodegenerative diseases with misfolded proteins. Therefore, curcumin may be a promising supplementary agent against development of neurodegeneration after brain ischemia in the future. Indeed, there is a rational scientific basis for the use of curcumin for the prophylaxis and treatment of post-ischemic neurodegeneration.
... A recent prospective study proved that tau levels were closely related to not only stroke severity as assessed by NIHSS, but also longterm outcomes both in plasma and CSF [126]. Notably, the study of autopsied brains from patients with cerebral infarction found that an increase of tau immunoreactivity and deposition of tau in ischemic area, but tau deposits were not organized into fibrils or more solid inclusions indicating that tau epitope was secondary to ischemic damage [127,128]. Nevertheless, tau can be detected in the serum of approximately 40% of stroke patients [121,122]. Present studies have not proven why tau could not be detected in the blood of all stroke patients. ...
Tau is a protein mainly expressed in adult human brain. It plays important roles both in neurodegenerative diseases and stroke. Stroke is an important cause of adult death and disability, ischemic stroke almost account for 80% in all cases. Abundant studies have proven that the increase of dysfunctional tau may act as a vital factor in pathological changes after ischemic stroke. However, the relationship between tau and ischemic stroke remains ununified. Based on present studies, we firstly introduced the structure and biological function of tau protein. Secondly, we summarized the potential regulatory mechanisms of tau protein in the process of ischemic stroke. Thirdly, we discussed about the findings in therapeutic researches of ischemic stroke. This review may be helpful in implementing new therapies for ischemic stroke and may be beneficial for the clinical and experimental studies.
... Moreover, an increase of tau protein staining was found in astrocytes and oligodendrocytes, following ischemia [106,107]. Pathologically modified tau protein was also observed in microglia around the ischemic focus [108]. These results indicate that only some neurons display changes in tau protein postischemia [106], which may reflect an early pathological state of the ischemic mechanisms in these cells [107]. ...
The study of sporadic Alzheimer's disease etiology, now more than ever, needs an infusion of new concepts. Despite ongoing interest in Alzheimer's disease, the basis of this entity is not yet clear. At present, the best-established and accepted "culprit" in Alzheimer's disease pathology by most scientists is the amyloid, as the main molecular factor responsible for neurodegeneration in this disease. Abnormal upregulation of amyloid production or a disturbed clearance mechanism may lead to pathological accumulation of amyloid in brain according to the "amyloid hypothesis." We will critically review these observations and highlight inconsistencies between the predictions of the "amyloid hypothesis" and the published data. There is still controversy over the role of amyloid in the pathological process. A question arises whether amyloid is responsible for the neurodegeneration or if it accumulates because of the neurodegeneration. Recent evidence suggests that the pathophysiology and neuropathology of Alzheimer's disease comprises more than amyloid accumulation, tau protein pathology and finally brain atrophy with dementia. Nowadays, a handful of researchers share a newly emerged view that the ischemic episodes of brain best describe the pathogenic cascade, which eventually leads to neuronal loss, especially in hippocampus, with amyloid accumulation, tau protein pathology and irreversible dementia of Alzheimer type. The most persuasive evidences come from investigations of ischemically damaged brains of patients and from experimental ischemic brain studies that mimic Alzheimer-type dementia. This review attempts to depict what we know and do not know about the triggering factor of the Alzheimer's disease, focusing on the possibility that the initial pathological trigger involves ischemic episodes and ischemia-induced gene dysregulation. The resulting brain ischemia dysregulates additionally expression of amyloid precursor protein and amyloid-processing enzyme genes that, in addition, ultimately compromise brain functions, leading over time to the complex alterations that characterize advanced sporadic Alzheimer's disease. The identification of the genes involved in Alzheimer's disease induced by ischemia will enable to further define the events leading to sporadic Alzheimer's disease-related abnormalities. Additionally, knowledge gained from the above investigations should facilitate the elaboration of the effective treatment and/or prevention of Alzheimer's disease.
... In contrast, ischemia also induces the production of intracellular βamyloid peptide what was shown by immunocytochemical investigation [14,22,74,77,80]. Oligomeric β-amyloid peptide is toxic [12] and initiates a series of events in ischemic brain including the hyperphosphorylation of tau protein that results in severe neurons [11,20], microglia [99], and oligodendrocytes [100] pathology. In addition to this, a recent research showed that, in the early stages of amyloid pathology, microplaques develop rapidly and locally, which could damage neighboring axons and dendrites within a few days [101], which eventually causes retrograde neuronal death. ...
Amyloid precursor protein cleavage through β- and γ-secretases produces β-amyloid peptide, which is believed to be responsible for death of neurons and dementia in Alzheimer's disease. Levels of β- and γ-secretase are increased in sensitive areas of the Alzheimer's disease brain, but the mechanism of this process is unknown. In this review, we prove that brain ischemia generates expression and activity of both β- and γ-secretases. These secretases are induced in association with oxidative stress following brain ischemia. Data suggest that ischemia promotes overproduction and aggregation of β-amyloid peptide in brain, which is toxic for ischemic neuronal cells. In our review, we demonstrated the role of brain ischemia as a molecular link between the β- and the γ-secretase activities and provided a molecular explanation of the possible neuropathogenesis of sporadic Alzheimer's disease.
... Tau proteins increase in cerebral spinal fluid as a result of cerebral ischemia in surgery patients, 36 and are found in pathologic brain specimens after cerebral ischemia. 37 Certain genetic factors, such as having the ApoE-e4 allele can predispose to tau deposition with mild head trauma. 38,39 A recent study showed that multiple blows to the head of lessthan-concussive force leads to a release of neurofilament proteins into the cerebral spinal fluid similar to that found in minor brain infarctions. ...
Three adolescent football players who had ischemic stroke associated with football practice and play are described. The literature on stroke associated with childhood sports and football in particular is reviewed, and the multiple mechanisms by which football can contribute to ischemic stroke are discussed.
... Although some cortical neurons showed labeling for phospho-tau we found strong labeling of perivascular activated microglia, particularly in the thalamic region that is affected with a high frequency of capillary amyloid. Although expression of phospho-tau is largely expected in neurons in neurodegenerative conditions, in mice activated microglia have been reported to express and accumulate tau protein following episodes of ischemic injury 11 . Whether this finding microglial phospho-tau presentation is restricted to Tg-SwDI/ NOS2 −/− mice or also observed in human cases of CAA type-1 remains to be further evaluated. ...
Cerebral amyloid angiopathy Type 1 is characterized by amyloid β protein deposition along cerebral capillaries and is accompanied by perivascular neuroinflammation and accumulation of phospho-tau protein. Tg-SwDI mice recapitulate capillary amyloid deposition and associated neuroinflammation but lack accumulation of perivascular phospho-tau protein.
Tg-SwDI mice were bred onto a nitric oxide synthase 2 gene knockout background and aged for 1 year. Brains were harvested and analyzed using immunohistochemical and quantitative stereological methods to determine the extent of capillary amyloid deposition, perivascular activated microglia, and cell-specific accumulation of phospho-tau protein. Similar methods were also used to compare Tg-SwDI/NOS2(-/-) and human cerebral amyloid angiopathy Type 1 brain tissues.
The absence of nitric oxide synthase 2 gene had no effect on the regional pattern or frequency of capillary cerebral amyloid angiopathy or the numbers of perivascular activated microglia in Tg-SwDI mice. On the other hand, Tg-SwDI/NOS2(-/-) mice accumulated phospho-tau protein in perivascular neurons and activated microglia. Tg-SwDI/NOS2(-/-) mice exhibited a very similar distribution of capillary amyloid, activated microglia, and perivascular phospho-tau protein as seen in human cerebral amyloid angiopathy Type 1.
These findings indicate that Tg-SwDI/NOS2(-/-) mice more fully recapitulate the pathological changes observed with capillary amyloid in human cerebral amyloid angiopathy Type 1.
... Moreover, an increase of tau staining was found within glial cells and oligodendrocytes after focal brain ischemia (Dewar and Dawson, 1995;Irving et al., 1997). Pathologically modified tau protein was observed in microglial cells around the ischemic focus (Uchihara et al., 2004). These results indicate that only some neuronal cells display alterations in tau protein after ischemic brain injury (Dewar and Dawson, 1995), which may reflect an early pathological phase of the ischemic mechanisms in these cells (Fig. 5;Irving et al., 1997). ...
There is increasing evidence for influence of Alzheimer's proteins and neuropathology on ischemic brain injury. This review investigates the relationships between beta-amyloid peptide, apolipoproteins, presenilins, tau protein, alpha-synuclein, inflammation factors, and neuronal survival/death decisions in brain following ischemic episode. The interactions of these molecules and influence on beta-amyloid peptide synthesis and contribution to ischemic brain degeneration and finally to dementia are reviewed. Generation and deposition of beta-amyloid peptide and tau protein pathology are important key players involved in mechanisms in ischemic neurodegeneration as well as in Alzheimer's disease. Current evidence suggests that inflammatory process represents next component, which significantly contribute to degeneration progression. Although inflammation was initially thought to arise secondary to ischemic neurodegeneration, recent studies present that inflammatory mediators may stimulate amyloid precursor protein metabolism by upregulation of beta-secretase and therefore are able to establish a vicious cycle. Functional brain recovery after ischemic lesion was delayed and incomplete by an injury-related increase in the amount of the neurotoxic C-terminal of amyloid precursor protein and beta-amyloid peptide. Moreover, ischemic neurodegeneration is strongly accelerated with aging, too. New therapeutic alternatives targeting these proteins and repairing related neuronal changes are under development for the treatment of ischemic brain consequences including memory loss prevention.
... At 12 h after ischemic insult, we found that GAL immunoreactivity was significantly increased in all areas of the hippocampus, especially in CA1 pyramidal cells without increase of h-actin. The maintenance of h-actin level after ischemic insult may imply that the post-translational modification did not occur in this time period [31]. ...
In the present study, we investigated chronological changes of galanin (GAL), well known as the potassium channel opener, immunoreactivity and GAL protein level in the hippocampus of the gerbil at the various times after 5 min transient forebrain ischemia. In the sham-operated group, weak GAL immunoreactivity was found in non-pyramidal cells. At 12 h after ischemia-reperfusion, the number of GAL-immunoreactive neurons and GAL immunoreactivity were significantly increased in the hippocampus compared to 3 h after ischemic insult, especially in the hippocampal CA1 region. Thereafter the number of GAL-immunoreactive neurons and GAL immunoreactivity decrease time-dependently in the hippocampus. Four days after transient ischemia, GAL immunoreactivity was low as compared with the sham-operated group. At this time point after ischemic insult, GAL immunoreactivity was shown in microglia in the CA1 region because delayed neuronal death happened in the CA1 pyramidal cells. The result of Western blot showed the pattern of GAL expression similar to that of immunohistochemical data. These results suggest that the early increase of GAL in the CA1 pyramidal cells may be associated with the reduction of the excitotoxic damage, that long-lasting enhanced expression of endogenous GAL at 12 h-2 days after ischemia may be associated with efflux of potassium ion into the extracellular space, and that GAL expression in microglia 4 days after ischemia may be associated with reduction of ischemic damage.
Aggregation of misfolded microtubule associated protein tau into abnormal intracellular inclusions defines a class of neurodegenerative diseases known as tauopathies. The consistent spatiotemporal progression of tau pathology in Alzheimer’s disease (AD) led to the hypothesis that tau aggregates spread in the brain via bioactive tau “seeds” underlying advancing disease course. Recent studies implicate microglia, the resident immune cells of the central nervous system, in both negative and positive regulation of tau pathology. Polymorphisms in genes that alter microglial function are associated with the development of AD and other tauopathies. Experimental manipulation of microglia function can alter tau pathology and microglia-mediated neuroinflammatory cascades can exacerbate tau pathology. Microglia also exert protective functions by mitigating tau spread: microglia internalize tau seeds and have the capacity to degrade them. However, when microglia fail to degrade these tau seeds there are deleterious consequences, including secretion of exosomes containing tau that can spread to neurons. This review explores the intersection of microglia and tau from the perspective of neuropathology, neuroimaging, genetics, transcriptomics, and molecular biology. As tau-targeted therapies such as anti-tau antibodies advance through clinical trials, it is critical to understand the interaction between tau and microglia.
Brain ischemia comprises blood-brain barrier, glial, and neuronal cells. The blood-brain barrier controls permeability of different substances and the composition of the neuronal cells 'milieu', which is required for their physiological functioning. Recent evidence indicates that brain ischemia itself and ischemic blood-brain barrier dysfunction is associated with the accumulation of neurotoxic molecules within brain tissue, e.g., different parts of amyloid-β protein precursor and changed pathologically tau protein. All these changes due to ischemia can initiate and progress neurodegeneration of the Alzheimer's disease-type. This review presents brain ischemia and ischemic blood-brain barrier as a trigger for tau protein alterations. Thus, we hypothesize that the changes in pattern of phosphorylation of tau protein are critical to microtubule function especially in neurons, and contribute to the neurodegeneration following brain ischemia-reperfusion episodes with Alzheimer's disease phenotype.
Clinical, neuroimaging and neuropathological studies have confirmed overlap between Alzheimer's disease (AD) and vascular dementia (VaD). Classical neuropathological changes of AD (plaques and tangles) can be present in VaD. We review neuroimaging, biochemical and animal studies to consider the role of tau protein in ischemic injury and VaD pathogenesis. The evidence comes largely from transgenic animal studies that confirm that tau transgenes influence cerebral vasculature. Clinicobiochemical studies in the cerebrospinal fluid (CSF) have, similarly, confirmed alterations in both total and phosphorylated tau protein in VaD. These data suggest that tau protein not only serves as a potential diagnostic tool for differential diagnosis of VaD from other types of dementia, but may also be a therapeutic target in ischemic stroke.
This chapter describes pick body disease on the basis of the presence of specific microscopic lesions, argyrophilic intraneuronal Pick bodies (PiBs) and ballooned neurons. Failure to identify a specific cause of the disease led to a speculation that the cortical atrophy of Pick's disease is accentuated in “primary atrophic centers,” macroscopically evident as Pick's atrophy. The chapter describes that in the majority of cases, “primary atrophic centers” are roughly in parallel with phylogenetically new areas, where myelination of the white matter occurs relatively late after birth. The chapter emphasizes that recent advances clarified molecular events related to the nature or mechanism, probably closer to the ultimate cause of PiBD and related conditions. “Pick bodies” are not always homogeneous from both biochemical and morphological viewpoints and await a reasonable definition. Moreover, the reported molecular events around PiBs are not yet sufficient to explain the localization, the extent of lesions or regional differences in brainswith PiBs, which have an actual relevance to the diagnosis and care of the patients. Because these two different aspects are of the same origin, partly shared with other degenerative processes, multidisciplinary approaches to PiBD will strengthen the understanding of this disease.
One of the challenges in neuropathology is to clarify how molecules, functional carriers of uni-dimensional sequence of amino acid or nucleic acid, behave to engender disease-specific pathological processes in complex three-dimensional (3D) structures such as the human brain in an ordered chronological sequence (four-dimensional extension as a whole). Along with expanding molecular explanations for brain diseases, parallel and independent hypotheses based on morphological observations are particularly useful and necessary for reasonable understanding of the brain and its dysfunction. For example, with classical methods such as silver impregnations, it is possible to differentiate underlying molecular pathologies (three-repeat tau/Campbell-Switzer vs. four-repeat tau/Gallyas silver impregnation) for improved histological diagnosis. Innovations with 3D reconstruction not only provide more realistic reproduction of the targets but also allow quantitative measurement on a 3D basis (3D volumetry). Contrary to the prevailing impression that pathological deposits are generally toxic to cells, quantification demonstrated possible countertoxic potentials of ubiquitin-positive intranuclear inclusions in CAG-repeat disorders on a two-dimensional basis and of glial cytoplasmic inclusions of multiple system atrophy on 3D volumetry. Furthermore, 3D extension of neurites around target lesions is now traceable in relation to the relevant clinical consequences. This neurite neuropathology may pave the way for early specific diagnosis of neurodegenerative disorders, as established through (123) I-metaiodobenzylguanidine cardiac scintigraphy for Parkinson disease, aiming at therapeutic intervention before depletion of mother neurons is feasible. For appropriate translation of sequence biology into the frame of human neuropathology, it is necessary to expand further the morphological dimensions so that comprehensive understanding of these disorders leads to specific diagnosis and treatment as early as possible.
Stroke is associated with high mortality and major disability burdens worldwide, but there are few effective and widely available therapies. Tau plays an important role in promoting microtubule assembly and stabilizing microtubule networks with phosphorylation regulating these functions. Based on the "ischemia-reperfusion theory" of Alzheimer's disease, some previous studies have focused on the relationship of tau and Alzheimer lesions in experimental brain ischemia. Thus, we hypothesize that the alterations in phosphorylation of tau are critical to microtubule dynamics and metabolism, and contribute to the pathophysiologic mechanisms during brain ischemia and/or reperfusion processes. We infer that regulation of phosphorylation of tau may be considered as a potential new therapeutic target in ischemic stroke.
The tau deposits found in neurodegenerative diseases are classified based on their isoforms, that is, 3-repeat (3R) tau and 4-repeat (4R) tau. These isoforms are distinguishable using the antibodies RD3 and RD4, respectively, and Gallyas (Gal) and Campbell-Switzer (CS) silver staining methods, respectively. Tau is also deposited in cerebral infarcts. To characterize the tau profile in these lesions, 21 brains from autopsied patients with cerebral infarcts were analyzed using immunohistochemistry with RD3, RD4, and the anti-paired helical filament antibody AT8 and with Gal and CS staining; all of these techniques identify Alzheimer disease-type neurofibrillary tangles. Fluorescence labeling followed by silver staining in mirror-section pairs was also used to compare the staining patterns. Neurons in and around ischemic foci exhibited the 4R-tau epitope until 34 days postinfarction; argyrophilia with Gal staining persisted longer. The 4R-tau/Gal-positive neurons were negative for 3R-tau and AT8 epitopes and lacked fibrillary structures and argyrophilia by CS staining; they are, therefore, distinct from neurons with neurofibrillary tangles. Positivity for 4R tau/Gal and negativity for 3R tau/CS were also seen in astrocytes and microglia around infarcts. Although this staining profile is characteristic of degenerative processes with 4R-tau deposition, lack of AT8 immunoreactivity and of fibrillary structures in neurons, astrocytes, and microglia indicates that selective 4R-tau deposition represents a stage without tau phosphorylation or fibril formation in cerebral infarcts.
Tau2 antibody recognizes a phosphorylation-independent epitope that is pathologically modified as tau protein is phosphorylated to form neurofibrillary tangles of Alzheimer's disease (AD). Similar modification of tau2 epitope can be induced even in the absence phosphorylation of tau, as we first demonstrated in ischemic foci and in glial cytoplasmic inclusions (GCIs) of multiple system atrophy. This modification of tau2 epitope is distinguishable from those observed in degenerative tauopathies because (1) it is a conformational change, which is reversible upon exposure to a detergent; (2) it shows an absence of fibrils composed of phosphorylated tau protein; and (3) it is characterized by the lack of immunohistochemical labeling by anti-tau antibodies other than tau2. In this study, we expanded this observation to inflammatory foci of different pathologies (human immunodeficiency virus encephalopathy, progressive multifocal leukoencephalopathy or multiple sclerosis) by examining formalin-fixed, paraffin-embedded sections immunostained with a panel of anti-tau antibodies. It was found that tau2 was the only anti-tau antibody that immunolabeled microglia/macrophages in these lesions, and this immunoreactivity was reversibly diminished upon exposure to a detergent. Exclusive apparition of tau2 immunoreactivity in these cells without neurofibrillary pathology may be a secondary event shared with ischemic foci and GCIs. It is, however, related to a unique conformational state of tau, possibly grouped under the name of "tautwopathy", that may represent an initial stage of tau deposition distinct from degenerative tauopathies characterized by fibrils composed of phosphorylated tau protein.
We report the case of a 54-year-old woman with mental retardation who developed frontotemporal dementia and amyotrophic lateral sclerosis (ALS) in the presenium. She presented with dementia at age 48, and motor neuron signs developed at age 53. She had no family history of dementia or ALS. Postmortem examination disclosed histopathological features of ALS, including pyramidal tract degeneration, mild loss of motor neurons, and many Bunina bodies immunoreactive for cystatin C, but not ubiquitin-positive inclusions. Unusual features of this case included severe neuronal loss in the substantia nigra and medial globus pallidus. The subthalamic nucleus, limbic system, and cerebral cortex were well preserved. In addition, neurofibrillary tangles (NFTs) were found in the frontal, temporal, insular, and cingulate cortices, nucleus basalis of Meynert, and locus coeruleus, and to a lesser degree, in the dentate nucleus, cerebellum, hippocampus, and amygdala. No ballooned neurons, tufted astrocytes, or astrocytic plaques were found. Tau immunostaining demonstrated many pretangles rather than NFTs and glial lesions resembling astrocytic plaques in the frontal and temporal cortices. This glial tau pathology predominantly developed in the middle to deep layers in the primary motor cortex, and was frequently associated with the walls of blood vessels. NFTs were immunolabeled with 3-repeat and 4-repeat specific antibodies against tau, respectively. Although the pathophysiological relationship between tau pathology and the selective involvement of motor neurons, substantia nigra, and globus pallidus was unclear, we considered that it might be more than coincidental.
Alzheimer's disease (AD) is the leading cause of dementia. Although the etiology of AD remains controversial, the amyloid hypothesis suggests that beta-amyloid (Abeta) peptides may contribute to brain dysfunction, and microglial activation has become increasingly regarded as a potential contributor to disease pathogenesis. Microglial activation is characterized by morphological changes and by production of various effectors, and activated neuroinflammation concurrent with increased oxidative stress may contribute to damage to neurons. However, recently there has been a recognition that microglia may also play a neuroprotective role through their release of neurotrophic factors and through phagocytosis of Abeta. Thus, there is growing consensus that a favorable combination of diminished microglia-mediated neuroinflammation and enhanced Abeta clearance may be critical in AD therapy. In this review, we will discuss the role of microglial activation in AD and how pharmacologic manipulation of microglia might bear upon the treatment of AD.
Preparations of dispersed paired helical filaments (PHFs) from the brains of Alzheimer's disease and Down's syndrome patients display on gels three principal bands corresponding to abnormally modified forms of the microtubule-associated protein tau. Interpretation of the pattern is difficult because there are six tau isoforms in normal brain and phosphorylation changes their mobility. By enzymatic dephosphorylation at high temperature, we have shifted the three abnormal bands obtained from dispersed PHFs to align with the six nonphosphorylated tau isoforms. By using antibodies specific for some of the inserts that distinguish the various isoforms and label PHFs, we have established a correspondence between PHFs, abnormal bands, and isoforms. This identification of isoforms is a necessary step in unravelling the molecular pathogenesis of PHFs.
Previous studies in gerbils have shown that cytoskeletal disruption and a loss of the dendritic microtubule-associated protein, MAP2, may occur after short periods of transient global ischemia. tau, a predominantly axonal microtubule-associated protein, has not been examined following ischemia. We compared neuronal damage with alterations in MAP2, tau, and 72-kD heat shock protein (HSP72) immunostaining at various reperfusion times following 20 min of ischemia in the rat four-vessel occlusion model. tau accumulated in neuronal cell bodies throughout the hippocampal formation 30 min to 2 h after the ischemic insult. Perikaryal tau immunostaining was transient in most regions, but persisted in polymorphic hilar neurons. This was accompanied by a loss of immunostaining in the target of many hilar neurons, the inner molecular layer of the dentate gyrus. The same neuronal populations that exhibited increased tau immunostaining of perikarya later displayed an induction of HSP72 immunoreactivity. In contrast, loss of MAP2 immunostaining was not consistently observed before neuronal death and did not correspond to HSP72 induction. The altered tau immunostaining is not the direct result of excitotoxic insult, as intrahippocampal injection of kainic acid did not cause the somal accumulation of tau, but did cause disruption of MAP2 immunostaining. Taken together, the results suggest that the somal accumulation of tau is an early, sensitive, and selective marker of ischemic insult.
The epitope on tau protein recognized by the monoclonal antibody Alz50 was defined through internal deletion mutagenesis and quantified by affinity measurements. The epitope is discontinuous and requires both a previously identified N-terminal segment and the microtubule binding region for efficient binding of Alz50. The interaction between these regions is consistent with an intramolecular reaction mechanism, suggesting that Alz50 binding depends on the conformation of individual tau monomers. The results suggest that tau adopts a distinct conformation when polymerized into filaments and that this conformation is recognized selectively by Alz50.
The defining neuropathological characteristics of Alzheimer's disease are abundant filamentous tau lesions and deposits of fibrillar amyloid beta peptides. Prominent filamentous tau inclusions and brain degeneration in the absence of beta-amyloid deposits are also hallmarks of neurodegenerative tauopathies exemplified by sporadic corticobasal degeneration, progressive supranuclear palsy, and Pick's disease, as well as by hereditary frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17). Because multiple tau gene mutations are pathogenic for FTDP-17 and tau polymorphisms appear to be genetic risk factors for sporadic progressive supranuclear palsy and corticobasal degeneration, tau abnormalities are linked directly to the etiology and pathogenesis of neurodegenerative disease. Indeed, emerging data support the hypothesis that different tau gene mutations are pathogenic because they impair tau functions, promote tau fibrillization, or perturb tau gene splicing, thereby leading to formation of biochemically and structurally distinct aggregates of tau. Nonetheless, different members of the same kindred often exhibit diverse FTDP-17 syndromes, which suggests that additional genetic or epigenetic factors influence the phenotypic manifestations of neurodegenerative tauopathies. Although these and other hypothetical mechanisms of neurodegenerative tauopathies remain to be tested and validated, transgenic models are increasingly available for this purpose, and they will accelerate discovery of more effective therapies for neurodegenerative tauopathies and related disorders, including Alzheimer's disease.
The microtubule-associated protein τ plays an important role in the dynamics of microtubule assembly necessary for axonal growth and neurite plasticity. Ischemia disrupts the neuronal cytoskeleton both by promoting proteolysis of its components and by affecting kinase and phosphatase activities that alter its assembly. In this study the effect of ischemia and reperfusion on the expression and phosphorylation of τ was examined in a reversible model of spinal cord ischemia in rabbits. τ was found to be dephosphorylated in response to ischemia with a time course that closely matched the production of permanent paraplegia. Dephosphorylation of τ was limited to the caudal lumbar spinal cord. In a similar manner, Ca2+/calmodulin-dependent kinase II activity was reduced only in the ischemic region. Thus, dephosphorylation of τ is an early marker of ischemia as is the rapid loss of Ca2+/calmodulin-dependent kinase II activity, τ, however, was rephosphorylated rapidly during reperfusion at site(s) that cause a reduction in its electrophoretic mobility regardless of the neurological outcome. Alterations in phosphorylation or degradation of τ may affect microtubule stability, possibly contributing to disruption of axonal transport but also facilitating neurite plasticity in a regenerative response.
The effect of transient cerebral ischemia on phosphorylation of the microtubule-associated protein (MAP) τ was investigated
using the rat four-vessel occlusion model. Phosphorylation of τ is proposed to regulate its binding to microtubules, influencing
the dynamics of microtubule assembly necessary for axonal growth and neurite plasticity. In this study, τ was rapidly dephosphorylated
during ischemia in the hippocampus, neocortex, and striatum. Dephosphorylation of τ was observed within 5 min of occlusion
and increased after 15 min in all three brain regions, regardless of their relative vulnerability to the insult. Thus, dephosphorylation
of τ is an early marker of ischemia and precedes the occlusion time required to cause extensive neuronal cell death in this
model. On restoration of blood flow for a little as 15 min, τ was phosphorylated at a site(s) that causes a reduction in its
electrophoretic mobility. The dephosphorylation/phosphorylation of τ may alter its distribution between axon and cell body,
and affect its susceptibility to proteolysis. These changes would be expected to influence microtubule stability, possibly
contributing to disruption of axonal transport, but also allowing neurite remodeling in a regenerative response.
We have determined the epitope for Tau 2, a monoclonal antibody that intensely stained tangles, plaque neurites, and curly fibers in the tissue section, and strongly labeled bovine tau, but only very weakly labeled human tau on the blot. The epitope has been localized to Ala95 through Ala108 of bovine tau. Ser101 is critical for Tau 2 reactivities; the replacement of Ser by Pro, which is found in rat, mouse, and human tau, brings about very weak Tau 2 reactivities. The strong Tau 2 staining of tangles and its effective absorption with a synthetic Ser peptide (Ala95 through Ala108) suggest that the tau in paired helical filaments takes a Ser conformation, rather than a Pro conformation, in its amino-terminal portion.
A modified form of the microtubule-associated protein Tau is the major component of the paired helical filaments (PHF) found in Alzheimer's disease. The characterization of these posttranslational Tau modifications is hindered by the lack of sufficient PHF-Tau-specific markers. Here we describe several monoclonal antibodies, prepared by immunization with PHF, two of which showed a selective specificity for PHF-Tau without cross-reactivity with normal Tau. Epitope recognition by these two monoclonals was sensitive to alkaline phosphatase treatment. In Western blotting these monoclonal antibodies reacted specifically with the abnormally phosphorylated epitopes on Alzheimer's disease-associated PHF-Tau. One of the new antibodies can be used for the construction of a sandwich enzyme-linked immunosorbent assay for the specific detection of PHF-Tau without cross-reactivity to normal Tau proteins.
Monoclonal antibody Tau 2 was raised against bovine tau protein, was reported to recognize a conformational epitope, and stained tau was found in neurofibrillary tangles of Alzheimer's disease, but not normal human tau. We synthesized tetradeka peptides corresponding to the original bovine sequence, its serine-->proline substituted analog, the genuine human sequence of this region, and the bovine epitope phosphorylated on the crucial serine. The secondary structure of the peptides was determined by circular dichroism. It was found that only the original bovine epitope showed a tendency to form the beta-pleated sheets characteristic of the neurofibrillary tangles. The spectra of the human peptide, its analog, and the phosphorylated bovine sequence were very similar, featuring a weak, helical beta-turn character. Eventual phosphorylation of epitopes of this otherwise heavily phosphorylated protein may overcome inter-species conformational gaps.
Putative Alzheimer disease (AD)-specific proteins (A68) were purified to homogeneity and shown to be major subunits of one
form of paired helical filaments (PHFs). The amino acid sequence and immunological data indicate that the backbone of A68
is indistinguishable from that of the protein tau (tau), but A68 could be distinguished from normal human tau by the degree
to which A68 was phosphorylated and by the specific residues in A68 that served as phosphate acceptors. The larger apparent
relative molecular mass (Mr) of A68, compared to normal human tau, was attributed to abnormal phosphorylation of A68 because
enzymatic dephosphorylation of A68 reduced its Mr to close to that of normal tau. Moreover, the LysSerProVal motif in normal
human tau appeared to be an abnormal phosphorylation site in A68 because the Ser in this motif was a phosphate acceptor site
in A68, but not in normal human tau. Thus, the major subunits of a class of PHFs are A68 proteins and the excessive or inappropriate
phosphorylation of normal tau may change its apparent Mr, thus transforming tau into A68.
Six hours after heat shocking 2- to 3-month-old male and female Sprague-Dawley rats at 42 degrees C for 15 min, we analyzed tau protein immunoreactivity in SDS extracts of cerebrums and peripheral nerves by using immunoblot analysis and immunohistochemistry with the anti-tau monoclonal antibody Tau-1, which recognizes a phosphate-dependent non-phosphorylated epitope, and with 125I-labeled protein A. In the cerebral extracts, we found altered phosphorylation of tau in heat-shocked females, characterized by a marked reduction in the amount of nonphosphorylated tau, a doubling of the ratio of total (phosphorylated plus nonphosphorylated) tau to nonphosphorylated tau, and the appearance of the slowest moving phosphorylated tau polypeptide (68 kDa). Similar, but milder, changes were observed in male rats. These changes progressively increased in females from 3 to 6 h after heat shocking. In contrast, both phosphorylated tau and nonphosphorylated tau were reduced in peripheral nerves after heat shocking. In immunoblots of SDS extracts from Alzheimer disease-affected brain, the two slowest moving phosphorylated tau polypeptides (62 kDa and 66 kDa, respectively) were detected by Tau-1 after dephosphorylation and by Tau-2 (an anti-tau-monoclonal antibody that recognizes a phosphate-independent epitope) without prior dephosphorylation only in regions that contained tau immunoreactivity in histologic preparations. In addition, quantitative immunoblot analysis of cortex and the underlying white matter with Tau-1 and 125I-labeled protein A showed that the amount of phosphorylated tau progressively increased in the Alzheimer disease-affected cerebral cortex, while concurrently a proportionally lesser amount of tau entered the white matter axons. The similar findings for the rat heat-shock model and Alzheimer disease suggest that life stressors may play a role in the etiopathogenesis of Alzheimer disease.
Paired helical filaments (PHFs) are prominent components of Alzheimer disease (AD) neurofibrillary tangles (NFTs). Rather than isolating NFTs, we selected for PHF populations that can be extracted from AD brain homogenates. About 50% of PHF immunoreactivity can be obtained in 27,200 x g supernatants following homogenization in buffers containing 0.8 M NaCl. We further enriched for PHFs by taking advantage of their insolubility in the presence of zwitterionic detergents and 2-mercaptoethanol, removal of aggregates by filtration through 0.45-microns filters, and sucrose density centrifugation. PHF-enriched fractions contained two to five proteins of 57-68 kDa that displayed the same antigenic properties as PHFs. Since the 57- to 68-kDa PHF proteins are antigenically related to tau proteins, they are similar to the tau proteins previously observed in NFTs. However, further analysis revealed that PHF-associated tau can be distinguished from normal, soluble tau by PHF antibodies that do not recognize human adult tau and by one- and two-dimensional PAGE.
The monoclonal antibody, Tau-1, which had previously been used to localize tau to the axonal compartment in brain has been reutilized for light and electron microscopic immunohistochemistry following phosphatase treatment of tissue. We report here that a significant quantity of tau in the central nervous system is phosphorylated in situ at or near the Tau-1 epitope, preventing the binding of the Tau-1 antibody. Upon removal of this/these phosphate group(s), however, Tau-1 was observed in the somatodendritic compartment of neurons as well as in axons. Furthermore, intense staining was also observed in astrocytes and in perineuronal glial cells. This immunoreactivity was present along the lengths of microtubules and on ribosomes (polysomes). Treatment of immunoblots of extracts of whole cerebral cortex with phosphatase confirmed the immunohistochemical results in that a 50-65% increase in Tau-1 binding to the tau region of the blot was noted. Moreover, a novel monoclonal antibody, Tau-2, was also used in these experiments. This antibody binds only to tau and localizes along microtubules in axons, somata, dendrites, and astrocytes and on ribosomes (polysomes) without phosphatase pretreatment.
The author has used two monoclonal antibodies against tau, Tau-1 and Tau-2, to study at the light microscopic level the morphology, evolution, and distribution of tau immunoreactivity in 21 cases with dementia of the Alzheimer type (DAT) with clinical histories of dementia ranging from 6 months to 10-15 years. They included four cases with Alzheimer's disease (AD), 14 cases with senile dementia of the Alzheimer type (SDAT), and three demented patients with Down's Syndrome (DS). The morphology and distribution of tau immunoreactivity was similar in all three forms of DAT, but the rapidity of evolution, as judged by the duration of dementia and the amount of immunoreactivity, was most severe in DS with dementia and least severe in SDAT. Excessive tau immunoreactivity, as compared with controls which were negative, was present in both astrocytes and vulnerable neurons. Tau-2-positive astrocytes were present throughout the brain and even in regions with no neuronal vulnerability. In evolving cases, several regions that in full-blown cases showed neuronal involvement contained only labeled astrocytes. The neurofibrillary tangles in neuronal involvement contained only labeled astrocytes. The neurofibrillary tangles in neuronal perikarya, the neurites in senile plaques, and an abundance of abnormal neurites found diffusely in the neuropil were intensely stained. In addition, stained granules (ribosomes) were present in both astrocytes and vulnerable neurons. The senile plaques frequently developed around and, on serial sectioning, were almost constantly associated with blood vessels. The amyloid core in senile plaques and the congophilic vessels were unstained. In cases with the shortest duration of dementia, tau immunoreactivity in neurons was found only in the amygdala, the subiculum, the Sommer's sector, the nucleus raphe dorsalis, locus ceruleus, and nucleus basalis of Meynert. In evolving cases, the depths of sulci were more severely affected than the crests of gyri, and the temporoparietal association cortex was more severely involved than the frontal cortex, but, in advanced cases, the depths of sulci, the crests of gyri, and the entire association cortex were equally affected.(ABSTRACT TRUNCATED AT 400 WORDS)
Immunohistochemistry of formalin-fixed human Alzheimer's disease (AD) tissue using an anti-tau antibody (Tau-1) reveals staining of neurofibrillary tangles (NFTs) and neuritic plaques (NPs), whereas normal axonal staining is less apparent. In this study, we used a combined biochemical and histochemical approach to assess effects of formalin on immunoreactivity of AD tau. Nitrocellulose blots were treated with fixative to mimic conditions used with tissue sections, a method that might be generally useful for assessing antigen sensitivity to different fixatives. A progressive decrease in Tau-1 immunoreactivity of the tau bands on a Western blot was observed with increasing times of formalin fixation. Phosphatase-digested blots demonstrated an increase in Tau-1 immunoreactivity compared to control blots. These results mimic the phosphatase-sensitive Tau-1 immunohistochemical staining of formalin-fixed AD tissue slices previously reported. Fixation of AD tissue with periodate-lysine-paraformaldehyde (PLP) preserves axonal tau antigenicity. Phosphatase digestion of PLP-fixed AD tissue enhances Tau-1 immunoreactivity of NFTs and NPs but does not alter axonal staining. These results indicate that axonal form(s) of tau are more sensitive to formalin fixation than pathology-associated tau. In addition, a modification of AD tau in pathological structures may protect it from the effects of formalin with regard to Tau-1 antigenicity.
A monoclonal antibody was prepared against pooled homogenates of brain tissue from patients with Alzheimer's disease. This
antibody recognizes an antigen present in much higher concentration in certain brain regions of Alzheimer patients than in
normal brain. The antigen appears to be a protein present in neurons involved in the formation of neuritic plaques and neurofibrillary
tangles, and in some morphologically normal neurons in sections from Alzheimer brains. Partial purification and Western blot
analysis revealed the antigen from Alzheimer brain to be a single protein with a molecular weight of 68,000. Application of
the same purification procedure to normal brain tissue results in the detection of small amounts of a protein of lower molecular
weight.
Tau-like immunoreactivity is known to develop in neurons under some experimental conditions simulating ischemia. The purpose of this study is to investigate the expression of tau-like immunoreactivity in the human brain after ischemic insult.
A series of autopsied human brains with or without ischemic lesion were investigated with immunohistochemistry (Alz-50, anti-tau, and anti-ubiquitin) and with silver-staining methods (Gallyas and Bodian methods).
Punctate immunoreactivity to Alz-50 was visualized in the cytoplasm not only of the neurons in and around the ischemic lesion but also of the neurons free from classic ischemic changes around the necrosis. Some of the neurons around the ischemic lesion were stained by the Gallyas method. Immunostaining with anti-tau and anti-ubiquitin antibodies and the conventional Bodian method failed to visualize these neurons.
The widespread appearance of Alz-50 immunoreactive neurons during the ischemic process signifies that tau-related proteins may be related to ischemic necrosis, but the lack of neurofibrillary tangles morphologically distinguishes ischemic development of tau-related proteins from the neurofibrillary degeneration in Alzheimer's disease.
The present immunohistochemical study determined the relationship between ApoE and the expression of the cytoskeletal protein tau (Tau2) and paired helical filaments (PHF), within the magnocellular neurons of the nucleus basalis of Meynert and layer II stellate neurons of the entorhinal cortex in Alzheimer's disease (AD). Although nearly all ApoE immunoreactive perikarya within these two brain regions were PHF immunoreactive, not all PHF and Tau2 containing neurons stained for ApoE in AD. Moreover, more Tau2-immunostained neurons, as compared to PHF, were ApoE immunonegative. This was particularly evident in a population of control subjects which exhibited AD-like pathology intermediate between the AD and normal aged individuals. Thus, neurons within the nucleus basalis of Meynert and entorhinal cortex layer II stellate exhibit evidence of cytoskeletal pathology prior to displaying ApoE. These observations suggest that (1) ApoE plays a secondary role in NFT formation or (2) this protein is accumulated within these neurons in response to reparative process(es) induced by NFT-associated neuronal damage.
An anti-tau monoclonal antibody tau-2 was demonstrated to react with the cells which characteristically appeared in the subcortical nuclei of certain neurodegenerative disorders. These cells had rod-like cell bodies and elongated processes, whose morphology was consistent with that of reactive microglia (tau-2 positive microglia-like cells; TPMC). TPMC were diffusely scattered in the subcortical nuclei, especially the putamen, irrelevant to focal tissue injury such as infarcts and amyloid deposits. TPMC were positively immunostained with anti-ferritin antibody, but negatively with LN3, anti-GFAP, other kinds of anti-tau and anti-neurofilament antibodies. TPMC were found in some cases of Alzheimer type dementia and diffuse Lewy body disease, but not in the cases of Parkinson's disease, Pick's disease and control without neurological disorder. Similar microglia-like cells were found around infarctic foci and amyloid cores of senile plaques, regardless of the disorder. They were, however, different from TPMC in that they were positively immunostained with LN3.
Breakdown of the cytoskeleton may be involved in the evolution of ischaemic brain damage and alterations in microtubule-associated proteins may play an important role in this process. In the present study, tau, a microtubule-associated protein predominantly located in axons, was examined after 2 or 6 h of focal cerebral ischaemia in the rat. Immunohistochemistry revealed increased Tau1 staining in the neuropil, some perikarya and in glial cells throughout the dorsolateral caudate nucleus and ventrolateral neocortex in the ipsilateral hemisphere at both 2 and 6 h after occlusion of the middle cerebral artery. Contrastingly, immunostaining of another tau antibody, TP70, was unchanged in the neuropil, but was increased specifically in glial cells in these regions. Immunoblotting revealed the presence of additional tau bands in tissue extracts of the caudate nucleus and ventrolateral neocortex ipsilateral to the occluded middle cerebral artery as detected by both tau antibodies after either 2 or 6 h. The results suggest that tau is dephosphorylated and/or degraded in axons and some neuronal perikarya in response to focal cerebral ischaemia. In contrast to the response in neurons, increased immunoreactivity of both tau antibodies in glial cells indicates a differential response of neuronal and glial tau to focal cerebral ischaemia.
Tau from Alzheimer's disease (AD) paired helical filaments (PHF-tau) is phosphorylated at sites not found in autopsy-derived adult tau from normal human brains, and this suggested that PHF-tau is abnormally phosphorylated. To explore this hypothesis, we examined human adult tau from brain biopsies and demonstrated that biopsy-derived tau is phosphorylated at most sites thought to be abnormally phosphorylated in PHF-tau. These sites also were phosphorylated in autopsy-derived human fetal tau and rapidly processed rat tau. The hypophosphorylation of autopsy-derived adult human tau is due to rapid dephosphorylation postmortem, and protein phosphatases 2A (PP2A) and 2B (PP2B) in human brain biopsies dephosphorylate tau in a site-specific manner. The down-regulation of phosphatases (i.e., PP2A and PP2B) in the AD brain could lead to the generation of maximally phosphorylated PHF-tau that does not bind microtubules and aggregates as PHFs in neurofibrillary tangles and dystrophic neurites.
The effects of permanent focal cerebral ischaemia on Alz-50 and ubiquitin antibody immunohistochemical staining were investigated in vivo in the cat. Alz-50 and ubiquitin antibody staining was compared to the distribution of ischaemic cell damage. Six hours following permanent occlusion of one middle cerebral artery, Alz-50 immunoreactivity was present in neurones in the ipsilateral ischaemic cerebral cortex and caudate nucleus but not in any region of the contralateral hemisphere or in sham-operated cats. Only a proportion of neurones were stained with Alz-50 and these did not have the shrunken, pyknotic appearance characteristic of irreversible ischaemic cell damage. Ubiquitin immunoreactivity was also increased in the ischaemic hemisphere, again only a proportion of neurones were stained. The Alz-50 antibody recognises the microtubule-associated protein tau and stains neurofibrillary tangles as well as neurones vulnerable to neurofibrillary change in tissue sections of Alzheimer brain. The results indicate that there are changes in tau protein in response to an ischaemic insult, but only in some neurones, which may reflect an early stage of the degenerative process. Increased ubiquitin immunoreactivity may be a response to the presence of abnormal proteins, including tau, which are induced by an ischaemic challenge.
Using seven independent antibodies against the amino terminal to the carboxyl terminal sequence of tau, we biochemically analyzed and compared the neuropathogenesis of two Alzheimer's disease brains from the viewpoint of abnormal processing on tau, the major constituent of paired helical filaments. One showed typical Alzheimer's disease with senile plaques and intracellular neurofibrillary tangles. The other showed advanced Alzheimer's disease with senile plaques and virtually the sole of ghost tangles without intracellular neurofibrillary tangles. We confirmed the previous observation that the carboxyl thirds of tau are tightly associated with paired helical filaments isolated in the presence of SDS. We found that biochemically, ghost tangles were abnormally phosphorylated and lacked the final carboxyl terminal sequence as well as the amino half of tau, unlike intracellular tangles. From these biochemical results taken together with the current evidence for ubiquitin in ghost tangles, we concluded that ghost tangles were extensively processed and irreversibly transformed into highly insoluble extracellular deposits.
Tau immunohistochemistry was performed on post-mortem brain tissue from patients who died following head injury or stroke and from neurologically normal controls. Tau-positive oligodendrocytes were detected with three different tau antibodies in head injured or stroke patients, but not in control cases. Tau-positive oligodendrocytes were detected 2 h following head injury indicating that accumulation of tau may be an acute response of these cells to brain injury. The mechanisms underlying accumulation of tau in oligodendrocytes after acute brain injury may be similar to those which occur in chronic neurodegenerative conditions such as progressive supranuclear palsy (PSP) and multi-system atrophy (MSA).
Glial inclusions containing the microtubule-associated protein tau are present in a variety of chronic neurodegenerative conditions. We now report a rapid and time-dependent increase of tau immunoreactivity within oligodendrocytes after focal cerebral ischemia in the rat. The number of tau positive oligodendrocytes in the ipsilateral subcortical white matter increased six- to eightfold by 40 minutes after permanent middle cerebral artery occlusion (MCAO). Tau was detected using antibodies that label both the N- and C-terminal of the protein, suggesting accumulation of full-length protein within these cells. Pretreatment with the spin trap agent alpha-phenyl-tert-butyl-nitrone (PBN)(100mg/kg) reduced the number of tau-positive oligodendrocytes by 55% in the subcortical white matter of the ischemic hemisphere compared with untreated animals at 40 minutes after MCAO. In contrast, pretreatment with glutamate receptor antagonists MK-801 (0.5 mg/kg) or 2,3-dihydroxy-6-nitro-7-sulpfamoyl-benzo(f)quinoxaline (NBQX) (2 x 30 mg/kg), failed to reduce the number of tau-positive oligodendrocytes after 40 minutes of ischemia. The results indicate that oligodendrocytes respond rapidly to an ischemic challenge and that free radical-mediated mechanisms are involved in the cascade leading to increased tau immunoreactivity.
Tau is a microtubule-associated protein which is regulated by phosphorylation. Highly phosphorylated tau does not bind microtubules and is the main component of the paired helical filaments seen in Alzheimer's and related neurodegenerative diseases. Recent reports suggested that patterns of tau phosphorylation changed following ischemia and/or reperfusion in vivo. We used an in vitro model employing rat and human neocortical slices to investigate changes in tau phosphorylation which accompany oxygen and glucose deprivation. Western blotting with polyclonal and phosphorylation-sensitive Tau-1 monoclonal antisera was used to monitor changes in tau which accompanied conditions of oxygen and glucose deprivation and reestablishment of these nutrients. In vitro hypoglycemia/hypoxia caused tau to undergo significant dephosphorylation in both rat and human neocortical slices after 30 and 60 min of deprivation. This dephosphorylation was confirmed using immunoprecipitation experiments after radiolabeling tau and other proteins with 32Pi. Okadaic acid, a phosphatase inhibitor, was able to prevent tau dephosphorylation in both control and ischemic slices. Lubeluzole, a benzothiazole derivative with in vivo neuroprotective activity, did not significantly alter patterns of tau phosphorylation. Restoration of oxygen and glucose following varied periods of in vitro hypoxia/hypoglycemia (15-60 min) led to an apparent recovery in phosphorylated tau. These data suggest that tau undergoes a rapid, but reversible dephosphorylation following brief periods of in vitro hypoxia/hypoglycemia in brain slices and that changes in tau phosphorylation help determine the extent of recovery following oxygen and glucose deprivation.
The effect of transient cerebral ischemia on phosphorylation of the microtubule-associated protein (MAP) tau was investigated using the rat four-vessel occlusion model. Phosphorylation of tau is proposed to regulate its binding to microtubules, influencing the dynamics of microtubule assembly necessary for axonal growth and neurite plasticity. In this study, tau was rapidly dephosphorylated during ischemia in the hippocampus, neocortex, and striatum. Dephosphorylation of tau was observed within 5 min of occlusion and increased after 15 min in all three brain regions, regardless of their relative vulnerability to the insult. Thus, dephosphorylation of tau is an early marker of ischemia and precedes the occlusion time required to cause extensive neuronal cell death in this model. On restoration of blood flow for a little as 15 min, tau was phosphorylated at a site(s) that causes a reduction in its electrophoretic mobility. The dephosphorylation/phosphorylation of tau may alter its distribution between axon and cell body, and affect its susceptibility to proteolysis. These changes would be expected to influence microtubule stability, possibly contributing to disruption of axonal transport, but also allowing neurite remodeling in a regenerative response.
To describe the clinical features, neuropathology, and genetic studies in a family with autosomal dominant frontotemporal dementia (FTD).
Clinical Pick's disease, or FTD with parkinsonism, has been described in several families linked to chromosome 17 (FTDP-17). Most of these have shown tau protein mutations. The clinical and pathologic variations in these families resemble the spectrum of sporadic FTD or "Pick complex."
Clinical and behavioral analysis of the affected members with extensive histochemical and neuropathologic description of three cases, genetic analysis of three clinically affected members and seven at risk members to assess linkage to chromosome 17, and sequencing of the tau gene in two patients were performed.
The clinical pattern shows a highly stereotypic disinhibition dementia with late extrapyramidal features, progressive mutism, and terminal dysphagia in three generations of affected individuals. Neuropathology showed frontotemporal atrophy, and microscopically tau- and synuclein-negative and ubiquitin-positive neuronal inclusions, in the background of superficial cortical spongiosis, neuronal loss, and gliosis. Tau expression was restricted to oligodendroglia. All exons and surrounding introns of the tau gene were sequenced, and no mutation or disease-related polymorphisms were detected in either of two affected pedigree members.
This family with autosomal dominant frontotemporal dementia (FTD) shows no tau expression in neurons. The ubiquitin-positive, tau-negative inclusions have been described before in FTD with and without motor neuron disease, but not in a familial form. The clinical and some pathologic features are similar to those of several of the families included in descriptions of FTD with parkinsonism linked to chromosome 17, but the linkage to tau has been excluded. The defect in this family, however, could be functionally related to tau mutations.
Appearance of tau epitopes in ischemic foci was investigated immunohistochemically on a series of autopsied human brains using a panel of anti-tau antibodies. While neurons were immunopositive for Alz-50, microglia and oligodendroglia around ischemic foci abundantly contained tau-2 immunoreactivity. Some astrocytes contained tau-2 immunoreactive granules in their cytoplasm. This difference suggests that neurons and glia react differently to an ischemic insult by exhibiting different tau epitopes. Immunohistochemical visualization tau-2 epitope represents its conformational change, as was reported with neurofibrillary tangles of Alzheimer type. Lack of argyrophilia in any of these tau-immunoreactive cells distinguishes them from tau-immunoreactive structures seen in various neurodegenerative disorders.
Corticobasal degeneration (CBD) and progressive supranuclear palsy (PSP) are sporadic neurodegenerative diseases with intracytoplasmic aggregates of the microtubule-associated protein, tau, in neurons and glial cells. Immunoblot analysis of detergent-insoluble brain extracts of patients with CBD and PSP shows distinctive patterns of tau fragments. These results suggest differing intracellular processing of aggregated tau in these two diseases despite an identical composition of tau isoforms. Such biochemical differences may be related to the neuropathological features of these diseases.
Attempts at classification of fronto-temporal dementias have not yet been completely successful. We report ten cases of sporadic fronto-temporal dementia (FTD) with ubiquitin-positive neuronal inclusions in cortex or in motor neurons in brain stem or spinal cord, which may contribute to the classification of FTD. Marked variation in clinical presentation as well as in pathological findings was the rule in all cases. Dementia was a prominent feature. Only one case had clinical features suggestive of motor neuron disease. Three of four younger onset cases displayed an especially severe atrophy of the temporal lobes, the basal ganglia and the substantia nigra. This contrasted with the other seven cases in which the fronto-temporal atrophy and changes in basal ganglia and substantia nigra were variable and sometimes mild. In addition to the presence of ubiquitin-reactive, but tau-and silver impregnation-negative neuronal inclusions, all cases demonstrated tau 2-positive glial inclusions, similar to those recently reported in three motor neuron disease cases with dementia. The glial inclusions were not visible with antibody to tau 1. Reaction with antibody to alpha-synuclein was invariably negative. If the combination of ubiquitin-positive neuronal and tau 2-positive glial inclusions is found to be consistently present in FTD of motor neuron type, this feature will provide a firmer basis for this diagnosis than previously available.
Tau-like immunoreactivity (IR) on glial cytoplasmic inclusions (GCIs) of multiple system atrophy (MSA) was investigated with a panel of anti-tau antibodies and we found that tau2, one of the phosphorylation-independent antibodies, preferentially immunolabeled GCIs. Co-presence (0.03%) of polyethyleneglycol- p-isooctylphenyl ether (Triton X-100, TX) with tau2, however, abolished this IR on GCIs, but did not abolish tau2 IR on neurofibrillary tangles (NFTs). Tau2-immunoreactive bands on immunoblot of brain homogenates from MSA brains were retrieved mainly in a TRIS-saline-soluble fraction, as reported in normal brains. This was in contrast to SDS-soluble fractions from brain with Down's syndrome, which contained tau2-immunoreactive bands of higher molecular weight. It indicates that the appearance of tau2 IR on GCIs is not related to hyperphosphorylation of tau. These tau2-immunoreactive bands, except those from bovine brain, were similarly abolished in the presence of TX (0.06%), and repeated washing after exposure to TX restored the tau2 IR on immunohistochemistry and on immunoblot. These findings can be explained if the modified tau2 epitope undergoes a reversible conformational change on exposure to TX, which is reversible after washing. Because the conformation centered at Ser101 of bovine tau is crucial for its affinity to tau2, the Ser-like conformation mimicked by its human counterpart Pro may represent pathological modification of tau shared by GCIs and NFTs. The relative resistance of tau2 epitope on NFTs on exposure to TX suggests that tau woven into NFTs confers additional stability to the pathological conformation of tau2 epitope. The conformation of the tau2 epitope in GCIs is not as stable as in NFTs, suggesting that tau proteins are not the principal constituents of the fibrillary structures of GCIs, even though they were immunodecorated with tau2. The difference in the susceptibility of the tau2 epitope to TX may distinguish its conformational states, which are variously represented according to disease conditions.