Astrocytes In Progressive Supranuclear Palsy Research Articles

Imaging of Reactive Astrogliosis by Positron Emission Tomography.

Many neurodegenerative diseases are neuropathologically characterized by neuronal loss, gliosis, and the deposition of misfolded proteins such as β-amyloid (Aβ) plaques and tau tangles in Alzheimer’s disease (AD). In postmortem AD brains, reactive astrocytes and activated microglia are observed surrounding Aβ plaques and tau tangles. These activated glial cells secrete pro-inflammatory cytokines and reactive oxygen species, which may contribute to neurodegeneration. Therefore, in vivo imaging of glial response by positron emission tomography (PET) combined with Aβ and tau PET would provide new insights to better understand the disease process, as well as aid in the differential diagnosis, and monitoring glial response disease-specific therapeutics. There are two promising targets proposed for imaging reactive astrogliosis: monoamine oxidase-B (MAO-B) and imidazoline2 binding site (I2BS), which are predominantly expressed in the mitochondrial membranes of astrocytes and are upregulated in various neurodegenerative conditions. PET tracers targeting these two MAO-B and I2BS have been evaluated in humans. [18F]THK-5351, which was originally designed to target tau aggregates in AD, showed high affinity for MAO-B and clearly visualized reactive astrocytes in progressive supranuclear palsy (PSP). However, the lack of selectivity of [18F]THK-5351 binding to both MAO-B and tau, severely limits its clinical utility as a biomarker. Recently, [18F]SMBT-1 was developed as a selective and reversible MAO-B PET tracer via compound optimization of [18F]THK-5351. In this review, we summarize the strategy underlying molecular imaging of reactive astrogliosis and clinical studies using MAO-B and I2BS PET tracers.

Immunohistochemical Study of Mitochondrial Ferritin in the Midbrain of Patients with Progressive Supranuclear Palsy.

Mitochondrial ferritin (FtMt) is a novel ferritin that is localized in the mitochondria. FtMt expression is low in the liver and spleen, and high in the heart, testis, and brain. We previously detected FtMt in dopaminergic neurons in the substantia nigra pars compacta (SNc) in human and monkey midbrains. We investigated the localization and expression of FtMt in the midbrain of patients with progressive supranuclear palsy (PSP) and controls using a monoclonal antibody (C65-2) against human FtMt. FtMt immunoreactivity was weakly detected in neuromelanin-containing neurons in the SNc and ventral tegmental area (VTA) of control cases compared with PSP, which exhibited a remarkable increase in FtMt immunoreactivity. Preincubation of C65-2 with the immunizing FtMt peptide significantly reduced the staining, indicating the specificity of C65-2. Several puncta were observed outside the neurons of PSP, in contrast with the control cases. Double immunofluorescence histochemistry for FtMt and tyrosine hydroxylase (TH), glial fibrillary acidic protein, and Iba1 showed localization of FtMt in dopaminergic neurons, microglia, and astrocytes in PSP. Furthermore, FtMt immunoreactivity was detected in a few TH-negative neurons. In the SNc and VTA, FtMt immunoreactivity colocalized with phosphorylated tau immunoreactivity. Our results indicate that FtMt is involved in the pathology of PSP. Clarifying the involvement of FtMt in PSP is of great interest.

Contribution of the astrocytic tau pathology to synapse loss in progressive supranuclear palsy and corticobasal degeneration.

Primary 4‐repeat tauopathies with frontotemporal lobar degeneration (FTLD) like Progressive Supranuclear Palsy (PSP) or Corticobasal Degeneration (CBD) show diverse cellular pathology in various brain regions. Besides shared characteristics of neuronal and oligodendroglial cytoplasmic inclusions of accumulated hyperphosphorylated tau protein (pTau), astrocytes in PSP and CBD contain pathognomonic pTau aggregates — hence, lending the designation tufted astrocytes (TA) or astrocytic plaques (AP), respectively. pTau toxicity is most commonly assigned to neurons, whereas the implications of astrocytic pTau for maintaining neurotransmission within the tripartite synapse of human brains is not well understood. We performed immunofluorescent synapse labeling and automated puncta quantification in the medial frontal gyrus (MFG) and striatal regions from PSP and CBD postmortem samples to capture morphometric synaptic alterations. This approach indicated general synaptic losses of both, excitatory and inhibitory bipartite synapses in the frontal cortex of PSP cases, whereas in CBD lower synapse densities were only related to astrocytic plaques. In contrast to tufted astrocytes in PSP, affected astrocytes in CBD could not preserve synaptic integrity within their spatial domains, when compared to non‐affected internal astrocytes or astrocytes in healthy controls. These findings suggest a pTau pathology‐associated role of astrocytes in maintaining connections within neuronal circuits, considered as the microscopic substrate of cognitive dysfunction in CBD. By contrasting astrocytic‐synaptic associations in both diseases, we hereby highlight astrocytic pTau as an important subject of prospective research and as a potential cellular target for therapeutic approaches in the primary tauopathies PSP and CBD.

Tau Ser208 phosphorylation promotes aggregation and reveals neuropathologic diversity in Alzheimer\u2019s disease and other tauopathies

Tau protein abnormally aggregates in tauopathies, a diverse group of neurologic diseases that includes Alzheimer’s disease (AD). In early stages of disease, tau becomes hyperphosphorylated and mislocalized, which can contribute to its aggregation and toxicity. We demonstrate that tau phosphorylation at Ser208 (pSer208) promotes microtubule dysfunction and tau aggregation in cultured cells. Comparative assessment of the epitopes recognized by antibodies AT8, CP13, and 7F2 demonstrates that CP13 and 7F2 are specific for tau phosphorylation at Ser202 and Thr205, respectively, independently of the phosphorylation state of adjacent phosphorylation sites. Supporting the involvement of pSer208 in tau pathology, a novel monoclonal antibody 3G12 specific for tau phosphorylation at Ser208 revealed strong reactivity of tau inclusions in the brains of PS19 and rTg4510 transgenic mouse models of tauopathy. 3G12 also labelled neurofibrillary tangles in brains of patients with AD but revealed differential staining compared to CP13 and 7F2 for other types of tau pathologies such as in neuropil threads and neuritic plaques in AD, tufted astrocytes in progressive supranuclear palsy and astrocytic plaques in corticobasal degeneration. These results support the hypothesis that tau phosphorylation at Ser208 strongly contributes to unique types of tau aggregation and may be a reliable marker for the presence of mature neurofibrillary tangles.

Colocalization of BRCA1 with Tau Aggregates in Human Tauopathies.

The mechanism of neuronal dysfunction via tau aggregation in tauopathy patients is controversial. In Alzheimer’s disease (AD), we previously reported mislocalization of the DNA repair nuclear protein BRCA1, its coaggregation with tau, and the possible importance of the subsequent DNA repair dysfunction. However, whether this dysfunction in BRCA1 also occurs in other tauopathies is unknown. The aim of this study was to evaluate whether BRCA1 colocalizes with tau aggregates in the cytoplasm in the brains of the patients with tauopathy. We evaluated four AD, two Pick’s disease (PiD), three progressive supranuclear palsy (PSP), three corticobasal degeneration (CBD), four normal control, and four disease control autopsy brains. Immunohistochemistry was performed using antibodies against BRCA1 and phosphorylated tau (AT8). Colocalization was confirmed by immunofluorescence double staining. Colocalization of BRCA1 with tau aggregates was observed in neurofibrillary tangles and neuropil threads in AD, pick bodies in PiD, and globose neurofibrillary tangles and glial coiled bodies in PSP. However, only partial colocalization was observed in tuft-shaped astrocytes in PSP, and no colocalization was observed in CBD. Mislocalization of BRCA1 was not observed in disease controls. BRCA1 was mislocalized to the cytoplasm and colocalized with tau aggregates in not only AD but also in PiD and PSP. Mislocalization of BRCA1 by tau aggregates may be involved in the pathogenesis of PiD and PSP.

Level of PICALM, a key component of clathrin-mediated endocytosis, is correlated with levels of phosphotau and autophagy-related proteins and is associated with tau inclusions in AD, PSP and Pick disease

Single nucleotide polymorphisms in PICALM, a key component of clathrin-mediated endocytosis machinery, have been identified as genetic susceptibility loci for late onset Alzheimer's disease (LOAD). We previously reported that PICALM protein levels were decreased in AD brains and that PICALM was co-localised with neurofibrillary tangles in LOAD, familial AD with PSEN1 mutations and Down syndrome. In the present study, we analysed PICALM expression, cell localisation and association with pathological cellular inclusions in other tauopathies and in non-tau related neurodegenerative diseases. We observed that PICALM was associated with neuronal tau pathology in Pick disease and in progressive supranuclear palsy (PSP) and co-localised with both 3R and 4R tau positive inclusions unlike in corticobasal degeneration (CBD) or in frontotemporal lobar degeneration (FTLD)-MAPT P301L. PICALM immunoreactivities were not detected in tau-positive tufted astrocytes in PSP, astrocytic plaques in CBD, Lewy bodies in Lewy body disease, diffuse type (LBD) and in TDP-43-positive inclusions in FTLD. In the frontal cortex in tauopathies, the ratio of insoluble to soluble PICALM was increased while the level of soluble PICALM was decreased and was inversely correlated with the level of phosphotau. PICALM decrease was also significantly correlated with increased LC3-II and decreased Beclin-1 levels in tauopathies and in non-tau related neurodegenerative diseases. These results suggest that there is a close relationship between abnormal PICALM processing, tau pathology and impairment of autophagy in human neurodegenerative diseases.

A proteomic study identifies different levels of light chain ferritin in corticobasal degeneration and progressive supranuclear palsy

Clinical and pathological evidence supports the notion that corticobasal degeneration (CBD) and progressive supranuclear palsy (PSP) are distinct, but overlapping neurodegenerative tauopathies. Although both disorders are characterized by abnormal accumulation of 4-repeat tau, they display distinct proteolytic profiles of tau species and they have distinct astrocytic lesions, astrocytic plaques in CBD and tufted astrocytes in PSP. To investigate other differences between these two disorders at the molecular level, we compared the profiles of proteins from caudate nucleus of CBD and PSP by quantitative two-dimensional difference gel electrophoresis. Twenty-one protein spots differentially expressed in CBD and PSP were dissected for mass spectrometry (MS). One of the spots was identified by MS to contain light chain (LC) ferritin. Western blot analysis verified the presence of LC ferritin in this spot and showed that this protein was two-fold higher in caudate of CBD than that of PSP samples. These results were confirmed by LC ferritin immunohistochemistry. Co-labeling of caudate nucleus with tau and LC ferritin antibodies showed the presence of LC ferritin immunoreactivity in astrocytic plaques of CBD, but minimal labeling of tufted astrocytes in PSP. This difference did not reflect the extent of gliosis. Analysis of other brain regions in CBD and PSP showed no difference in LC ferritin levels. Together the data suggest that LC ferritin is a unique marker of astrocytic lesions in CBD, adding further support to the notion that CBD and PSP are distinct clinicopathologic entities.

Neuropathology of Frontotemporal Lobar Degeneration-Tau (FTLD-Tau)

A clinically and pathologically heterogeneous type of frontotemporal lobar degeneration has abnormal tau pathology in neurons and glia (FTLD-tau). Familial FTLD-tau is usually due to mutations in the tau gene (MAPT). Even FTLD-tau determined by MAPT mutations has clinical and pathologic heterogeneity. Tauopathies are subclassified according to the predominant species of tau that accumulates, with respect to alternative splicing of MAPT, with tau proteins containing three (3R) or four repeats (4R) of ~32 amino acids in the microtubule binding domain. In Pick's disease (PiD), 3R tau predominates, whereas 4R tau is characteristic of corticobasal degeneration (CBD) and progressive supranuclear palsy (PSP). Depending upon the specific mutation in MAPT, familial FTLD-tau can have 3R, 4R or a combination of 3R and 4R tau. PiD is the least common FTLD-tau characterized by neuronal Pick bodies in a stereotypic neuroanatomical distribution. PSP and CBD are more common than PiD and have extensive clinical and pathologic overlap, with no distinctive clinical syndrome or biomarker that permits their differentiation. Diagnosis rests upon postmortem examination of the brain and demonstration of globose tangles, oligodendroglial coiled bodies and tufted astrocytes in PSP or threads, pretangles and astrocytic plaques in CBD. The anatomical distribution of tau pathology determines the clinical presentation of PSP and CBD, as well as PiD. The basis for this selective cortical vulnerability in FTLD-tau is unknown.

Sporadic four-repeat tauopathy with frontotemporal lobar degeneration, Parkinsonism, and motor neuron disease: a distinct clinicopathological and biochemical disease entity

Tau is the pathological protein in several neurodegenerative disorders classified as frontotemporal lobar degeneration (FTLD), including corticobasal degeneration (CBD) and progressive supranuclear palsy (PSP). We report an unusual tauopathy in three Japanese patients presenting with Parkinsonism and motor neuron disease (neuroimaging revealed frontotemporal cerebral atrophy in two patients who were examined). At autopsy, all cases showed FTLD with the most severe neuronal loss and gliosis evident in the premotor and precentral gyri. Although less severe, such changes were also observed in other brain regions, including the basal ganglia and substantia nigra. In the spinal cord, loss of anterior horn cells and degeneration of the corticospinal tract were evident. In addition, the affected regions exhibited neuronal cytoplasmic inclusions resembling neurofibrillary tangles. Immunostaining using antibodies against hyperphosphorylated tau and 4-repeat tau revealed widespread occurrence of neuronal and glial cytoplasmic inclusions in the central nervous system; the astrocytic tau lesions were unique, and different in morphology from astrocytic plaques in CBD, or tufted astrocytes in PSP. However, immunoblotting of frozen brain samples available in two cases revealed predominantly 4R tau, with the approximately 37-kDa and 33-kDa low-molecular mass tau fragments characteristic of CBD and PSP, respectively. No mutations were found in the tau gene in either of the two cases. Based on these clinicopathological, biochemical, and genetic findings, we consider that the present three patients form a distinct 4R tauopathy associated with sporadic FTLD.

Anti-tau phospho-specific Ser262 antibody recognizes a variety of abnormal hyper-phosphorylated tau deposits in tauopathies including Pick bodies and argyrophilic grains.

The rabbit polyclonal anti-tau phospho-specific Ser262 antibody (577814 Calbiochem) recognizes disease-specific band patterns on Western blots of sarkosyl-insoluble fractions in Alzheimer's disease (AD), progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), argyrophilic grain disease (AGD) and Pick's disease (PiD): four bands of 74/72, 68, 64 and 60 kDa in AD, two bands of 68 and 64 kDa in PSP, CBD and AGD, and two bands of 64 and 60 kDa in PiD. Moreover, anti-tau phospho-specific Ser262 decorates neurons with neurofibrillary tangles, neurons with pre-tangles, dystrophic neurites of senile plaques, neuropil threads, Pick bodies, argyrophilic grains, and coiled bodies. Achromatic neurons in CBD, ballooned neurons in AGD, tufted astrocytes in PSP, astrocytic plaques in CBD and tau-containing astrocytes in AGD are not immunostained with the anti-tau phospho-specific Ser262 antibody. The lack of phospho-specific Ser262 immunoreactivity in tau-containing inclusions in astrocytes suggests different kinase equipment and activation in comparing neurons and astrocytes in tauopathies. Pick bodies in PiD and grains in AGD are weakly, or not all, immunostained in tissue samples with long post-mortem delays, although Ser262 is preserved in brain homogenates corresponding to the same time points processed for Western blot. This indicates postmortem modifications of tau in Pick bodies and argyrophilic grains, but not in other tau-containing inclusions, including paired helical filaments and coiled bodies, and suggests differences in tau conformation, particularly that involving phospho-tau Ser262 among tauopathies. However, it is important to note that phosphorylation of tau at Ser262 does occur in Pick bodies and argyrophilic grains, and this may have important consequences in reducing the capacity of binding phospho-tau to microtubules in these inclusions.

Astrocytes expressing hyperphosphorylated tau protein without glial fibrillary tangles in argyrophilic grain disease.

Argyrophilic grain disease (AgD), a frequent type of late onset dementia, is characterized by the occurrence of Gallyas-stained neuropil grains in the hippocampus, entorhinal cortex, amygdala and hypothalamus. High numbers of neurons containing hyperphosphorylated tau protein, but devoid of tangles, are encountered in areas rich in argyrophilic grains (ArGs). A third type of change consists of slender argyrophilic and tau-immunoreactive cytoplasmic inclusions in white matter oligodendrocytes, the coiled bodies. We now extend earlier studies on glial pathology in AgD (20 cases) and compare the results with glial changes in old age (10 cases) and Alzheimer's disease (AD; 7 cases). Numerous non-argyrophilic, non-neuronal tau-positive stellate cells in the amygdala and anterior entorhinal cortex were consistently found in all of the 20 AgD cases but not in AD cases. Double-labelling experiments performed on paraffin sections with phosphorylation-dependent anti-tau antibody AT8, anti-glial fibrillary acidic protein and anti-CD44, revealed coexpression of these markers in stellate cells. The high expression of CD44 indicate that they probably correspond to reactive astrocytes. Unlike astrocytic plaques in corticobasal degeneration (CBD), where AT8 reactivity is accumulating in distal astrocytic processes, tau reactivity in AgD was found in all astrocytic cell compartments. The absence of glial fibrillary tangles further distinguished tau-labelled astrocytes in AgD from astrocytic plaques in CBD and tufted astrocytes in progressive supranuclear palsy (PSP). In contrast to AD and aged non-demented control cases tau-positive non-argyrophilic astrocytes represent a consistent finding in anterior limbic structures in AgD. Our findings point to a more widespread pathology of the glial cell population in AgD than previously supposed, and will be of further help in differentiating AgD from other neurodegenerative disorders, including AD, PSP, CBD and Pick's disease.

Inducible nitric oxide synthase (iNOS)-like immunoreactivity in argyrophilic, tau-positive astrocytes in progressive supranuclear palsy.

The immunoreactivity to the free radical-related enzymes, nitric oxide synthase (NOS) and superoxide dismutase (SOD), was examined in brain tissue in progressive supranuclear palsy (PSP). To determine the relationship between the immunoexpression of these enzymes and tau-positive, argyrophilic cytoplasmic inclusions, which are constantly present in PSP brains, double-label immunohistochemistry was applied. We demonstrated for the first time that strong inducible NOS-like immunoreactivity (iNOS-ir) was detected in tau-positive astrocytes that bore tufts of abnormal fibers (TAF), but not in oligodendrocytes containing argyrophilic/tau-positive coiled bodies nor in microglia. No brain NOS-ir was detected in neurons with neurofibrillary tangles. MnSOD-ir was also detected in tau-positive astrocytes and oligodendrocytes. Nitrotyrosine-ir of variable intensity was observed in astrocytes, oligodendrocytes and neurons. Our results indicate: (1) that TAF-bearing astrocytes may be a major source of excessive NO in PSP brains; (2) that after the induction of iNOS by unknown stimulating factors, TAF-bearing astrocytes produce an excessive amount of NO that exceeds the detoxification capability of SOD; and (3) that peroxynitrite and excessive NO, both cytotoxic, may be present in astrocytes, oligodendrocytes and neurons. Although the precise relationship between NO production and neuronal cell death in PSP remained uncertain, based on the specificity of TAF for PSP brains, our results indicated a possible mechanism of NO-mediated cytotoxicity that may contribute to the neuronal and glial cell damage followed by abnormal tau accumulation in this disease.