Reversible conformational change of tau2 epitope on exposure to detergent in glial cytoplasmic inclusions of multiple system atrophy

Identification of high-performing antibodies for the reliable detection of Tau proteoforms by Western blotting and immunohistochemistry

Antibodies are essential research tools whose performance directly impacts research conclusions and reproducibility. Owing to its central role in Alzheimer's disease and other dementias, hundreds of distinct antibody clones have been developed against the microtubule-associated protein Tau and its multiple proteoforms. Despite this breadth of offer, limited understanding of their performance and poor antibody selectivity have hindered research progress. Here, we validate a large panel of Tau antibodies by Western blot (79 reagents) and immunohistochemistry (35 reagents). We address the reagents' ability to detect the target proteoform, selectivity, the impact of protein phosphorylation on antibody binding and performance in human brain samples. While most antibodies detected Tau at high levels, many failed to detect it at lower, endogenous levels. By WB, non-selective binding to other proteins affected over half of the antibodies tested, with several cross-reacting with the related MAP2 protein, whereas the "oligomeric Tau" T22 antibody reacted with monomeric Tau by WB, thus calling into question its specificity to Tau oligomers. Despite the presumption that "total" Tau antibodies are agnostic to post-translational modifications, we found that phosphorylation partially inhibits binding for many such antibodies, including the popular Tau-5 clone. We further combine high-sensitivity reagents, mass-spectrometry proteomics and cDNA sequencing to demonstrate that presumptive Tau "knockout" human cells continue to express residual protein arising through exon skipping, providing evidence of previously unappreciated gene plasticity. Finally, probing of human brain samples with a large panel of antibodies revealed the presence of C-term-truncated versions of all main Tau brain isoforms in both control and tauopathy donors. Ultimately, we identify a validated panel of Tau antibodies that can be employed in Western blotting and/or immunohistochemistry to reliably detect even low levels of Tau expression with high selectivity. This work represents an extensive resource that will enable the re-interpretation of published data, improve reproducibility in Tau research, and overall accelerate scientific progress.

Role of VAPB and vesicular profiles in α-synuclein aggregates in multiple system atrophy

The pathological hallmark of multiple system atrophy (MSA) is fibrillary aggregates of α‐synuclein (α‐Syn) in the cytoplasm and nucleus of both oligodendrocytes and neurons. In neurons, α‐Syn localizes to the cytosolic and membrane compartments, including the synaptic vesicles, mitochondria, and endoplasmic reticulum (ER). α‐Syn binds to vesicle‐associated membrane protein‐binding protein B (VAPB) in the ER membrane. Overexpression of wild‐type and familial Parkinson's disease mutant α‐Syn perturbs the association between the ER and mitochondria, leading to ER stress and ultimately neurodegeneration. We examined brains from MSA patients (n = 7) and control subjects (n = 5) using immunohistochemistry and immunoelectron microscopy with antibodies against VAPB and phosphorylated α‐Syn. In controls, the cytoplasm of neurons and glial cells was positive for VAPB, whereas in MSA lesions VAPB immunoreactivity was decreased. The proportion of VAPB‐negative neurons in the pontine nucleus was significantly higher in MSA (13.6%) than in controls (0.6%). The incidence of cytoplasmic inclusions in VAPB‐negative neurons was significantly higher (42.2%) than that in VAPB‐positive neurons (3.6%); 67.2% of inclusion‐bearing oligodendrocytes and 51.1% of inclusion‐containing neurons were negative for VAPB. Immunoelectron microscopy revealed that α‐Syn and VAPB were localized to granulofilamentous structures in the cytoplasm of oligodendrocytes and neurons. Many vesicular structures labeled with anti‐α‐Syn were also observed within the granulofilamentous structures in the cytoplasm and nucleus of both oligodendrocytes and neurons. These findings suggest that, in MSA, reduction of VAPB is involved in the disease process and that vesicular structures are associated with inclusion formation.

Cerebral white matter tau-positive granular glial pathology as a characteristic pathological feature in long survivors of multiple system atrophy

INTRODUCTION

It is unclear whether tau-positive granular glial pathology is a characteristic feature of MSA. We aimed to analyse the prevalence and significance of tau-positive granular glial pathology in MSA.

METHODS

Fourteen MSA cases were clinicopathologically investigated, focusing on tau-positive granular glial pathology in the frontal and temporal white matter and putamen.

RESULTS

In five MSA cases, the temporal white matter showed AT8-positive granular glial pathology; this pathology was detected in the frontal white matter in three cases. AT8-positive granular glia in the white matter were associated with long disease duration with long-term tube feeding and/or long-term tracheotomy. Alpha-synuclein-positive glial cytoplasmic inclusion intensity was not associated with AT8-positive granular glial pathology. The tau isoform of AT8-positive granular glia in the cerebral white matter exhibited three-repeat, not four-repeat, tau. Ten MSA patients showed tau-positive granular glial pathology in the putamen; the tau isoform was predominantly three-repeat tau and four-repeat tau in cases with disease duration ≥13 years and < 13 years, respectively.

CONCLUSIONS

Tau-positive granular glia in the putamen is a characteristic pathological feature of MSA. Tau-positive granular glia appear in the cerebral white matter in MSA patients and are associated with long disease duration with long-term tube feeding and/or long-term tracheotomy.

Multiple System Atrophy: An Oligodendroglioneural Synucleinopathy1

Multiple system atrophy (MSA) is an orphan, fatal, adult-onset neurodegenerative disorder of uncertain etiology that is clinically characterized by various combinations of parkinsonism, cerebellar, autonomic, and motor dysfunction. MSA is an α-synucleinopathy with specific glioneuronal degeneration involving striatonigral, olivopontocerebellar, and autonomic nervous systems but also other parts of the central and peripheral nervous systems. The major clinical variants correlate with the morphologic phenotypes of striatonigral degeneration (MSA-P) and olivopontocerebellar atrophy (MSA-C). While our knowledge of the molecular pathogenesis of this devastating disease is still incomplete, updated consensus criteria and combined fluid and imaging biomarkers have increased its diagnostic accuracy. The neuropathologic hallmark of this unique proteinopathy is the deposition of aberrant α-synuclein in both glia (mainly oligodendroglia) and neurons forming glial and neuronal cytoplasmic inclusions that cause cell dysfunction and demise. In addition, there is widespread demyelination, the pathogenesis of which is not fully understood. The pathogenesis of MSA is characterized by propagation of misfolded α-synuclein from neurons to oligodendroglia and cell-to-cell spreading in a "prion-like" manner, oxidative stress, proteasomal and mitochondrial dysfunction, dysregulation of myelin lipids, decreased neurotrophic factors, neuroinflammation, and energy failure. The combination of these mechanisms finally results in a system-specific pattern of neurodegeneration and a multisystem involvement that are specific for MSA. Despite several pharmacological approaches in MSA models, addressing these pathogenic mechanisms, no effective neuroprotective nor disease-modifying therapeutic strategies are currently available. Multidisciplinary research to elucidate the genetic and molecular background of the deleterious cycle of noxious processes, to develop reliable biomarkers and targets for effective treatment of this hitherto incurable disorder is urgently needed.

Fluorescence and autoradiographic evaluation of tau PET ligand PBB3 to α-synuclein pathology

BACKGROUND

The tau PET ligand 2-((1E,3E)-4-(6-([¹¹ C]methylamino)pyridin-3-yl)buta-1,3-dienyl)benzo[d]thiazol-6-ol ([¹¹ C]PBB3) binds to a wide range of tau pathology; however, binding property of PBB3 to non-tau inclusions remains unknown. To clarify whether [¹¹ C]PBB3 binds to α-synuclein pathology, reactivity of PBB3 was assessed by in vitro fluorescence and autoradiographic labeling of brain sections from α-synucleinopathies patients.

METHOD

Of 10 pure Lewy body disease and 120 multiple system atrophy (MSA) cases in the Mayo Clinic brain bank, we selected 3 Lewy body disease and 4 MSA cases with a range of α-synuclein severity based on the quantitative analysis of α-synuclein burden. PBB3 fluorescence labeling, double or single immunostaining for α-synuclein and phospho-tau, Prussian blue staining, and in vitro autoradiography with [¹¹ C]PBB3 were performed for these selected samples.

RESULTS

PBB3 fluorescence labeled various α-synuclein lesions including Lewy bodies, Lewy neurites, spheroids, glial cytoplasmic inclusions, and neuronal cytoplasmic inclusions. Meanwhile, autoradiographic labeling with [¹¹ C]PBB3 at 10 nM demonstrated no significant binding in Lewy body disease cases. In contrast, significant autoradiographic binding of [¹¹ C]PBB3 to the striatopallidal fibers was found in 2 MSA cases, which had high densities of glial cytoplasmic inclusions without tau or iron deposits in this region.

CONCLUSIONS

Given that the maximum concentration of [¹¹ C]PBB3 in human PET scans is approximately 10 nM, the present data imply that α-synuclein pathology in Lewy body disease is undetectable by [¹¹ C]PBB3-PET, whereas those in a subset of MSA cases with high densities of glial cytoplasmic inclusions could be captured by this radioligand. © 2017 International Parkinson and Movement Disorder Society.

Tau-positive glial cytoplasmic granules in multiple system atrophy

Multiple system atrophy (MSA) is a sporadic neurodegenerative disease that is pathologically characterized by the filamentous aggregation of α-synuclein. We report a case of MSA showing unusual neuropathological findings and review six autopsied cases of MSA. The patient progressively developed parkinsonism and ataxia for the 9 years prior to her death at the age of 72 years. Neuropathological examinations revealed neuronal loss restricted to the olivopontocerebellar and striatonigral region, which was more severe in the putamen. Staining with anti-α-synuclein antibody demonstrated widespread occurrence of glial cytoplasmic inclusions, which mainly accumulated in oligodendroglial cells and corresponded closely to the degree of disease progression. In addition, tau-positive granules were detected within the glial cytoplasm in the neurodegenerative region, which was especially prominent in the putamen and internal capsule. Tau accumulation was also clearly recognized by staining with specific antibodies against three-repeat or four-repeat tau. The glia that demonstrated deposition of tau-positive granules were distinguished from α-synuclein-positive oligodendroglia by double immunohistochemical staining. These characteristic glial accumulations of tau were also present in all six cases of MSA. These results indicate that tau-positive granules in glia are common findings in MSA and that tau aggregation might be another pathway to neurodegeneration in MSA.

Papp-Lantos inclusions and the pathogenesis of multiple system atrophy: an update

Multiple systemic atrophy (MSA) is a progressive, adult-onset neurodegenerative disorder of undetermined aetiology characterized by a distinctive oligodendrogliopathy with argyrophilic glial cytoplasmic inclusions (GCIs) and selective neurodegeneration. GCIs or Papp-Lantos inclusions, described more than 20 years ago, are now accepted as the hallmarks for the definite neuropathological diagnosis of MSA and suggested to play a central role in the pathogenesis of this disorder. GCIs are composed of hyperphosphorylated alpha-synuclein (alphaSyn), ubiquitin, LRRK2 (leucin-rich repeat serine/threonine-protein) and many other proteins, suggesting that MSA represents an invariable synucleinopathy of non-neuronal type, a specific form of proteinopathies. The origin of alphaSyn deposition in GCIs is not yet fully understood, but recent findings of dysregulation in the metabolism of myelin basic protein (MBP) and p25alpha, a central nervous system-specific protein, also called TPPP (tubulin polymerization promoting protein), strengthened the working model of MSA as a primary glial disorder and may explain frequent alterations of myelin in MSA. However, it is unknown whether these changes represent an early event or myelin dysregulation occurs further downstream in MSA pathogenesis. The association between polymorphisms at the SNCA gene locus and the risk for developing MSA also points to a primary role of alphaSyn in its pathogenesis, while in a MBP promoter-driven alphaSyn transgenic mouse model gliosis accompanied the neurodegenerative process originating in oligodendrocytes. Because alphaSyn represents a major component in both oligodendroglial and neuronal inclusions in MSA, some authors suggested both a primary oligodendrogliopathy and a neuronal synucleinopathy, but current biomolecular data and animal models support a crucial role of the Papp-Lantos inclusions and of aberrant alphaSyn accumulation as their main constituent, causing oligodendroglial pathology, myelin disruption and, finally, neuronal degeneration in MSA. The relationship between oligodendrocytes involved by Papp-Lantos inclusions and those in degenerating neurons in the course of MSA needs further elucidation.

Existence of two membrane-bound acetylcholinesterases in the honey bee head

Two acetylcholinesterase (EC 3.1.1.7) membrane forms AChE(m1) and AChE(m2), have been characterised in the honey bee head. They can be differentiated by their ionic properties: AChE(m1) is eluted at 220 mM NaCl whereas AChE(m2) is eluted at 350 mM NaCl in anion exchange chromatography. They also present different thermal stabilities. Previous processing such as sedimentation, phase separation, and extraction procedures do not affect the presence of the two forms. Unlike AChE(m1), AChE(m2) presents reversible chromatographic elution properties, with a shift between 350 to 220 mM NaCl, depending on detergent conditions. Purification by affinity chromatography does not abolish the shift of the AChE(m2) elution. The similar chromatographic behaviour of soluble AChE strongly suggests that the occurrence of the two membrane forms is not due to the membrane anchor. The two forms have similar sensitivities to eserine and BW284C51. They exhibit similar electrophoretic mobilities and present molecular masses of 66 kDa in SDS-PAGE and a sensitivity to phosphatidylinositol-specific phospholipase C in non-denaturing conditions, thus revealing the presence of a glycosyl-phosphatidylinositol anchor. We assume that bee AChE occurs in two distinct conformational states whose AChE(m2) apparent state is reversibly modulated by the Triton X-100 detergent into AChE(m1).

Silver diagnosis in neuropathology: principles, practice and revised interpretation

Silver-staining methods are helpful for histological identification of pathological deposits. In spite of some ambiguities regarding their mechanism and interpretation, they are widely used for histopathological diagnosis. In this review, four major silver-staining methods, modified Bielschowsky, Bodian, Gallyas (GAL) and Campbell–Switzer (CS) methods, are outlined with respect to their principles, basic protocols and interpretations, thereby providing neuropathologists, technicians and neuroscientists with a common basis for comparing findings and identifying the issues that still need to be clarified. Some consider “argyrophilia” to be a homogeneous phenomenon irrespective of the lesion and the method. Thus, they seek to explain the differences among the methods by pointing to their different sensitivities in detecting lesions (quantitative difference). Comparative studies, however, have demonstrated that argyrophilia is heterogeneous and dependent not only on the method but also on the lesion (qualitative difference). Each staining method has its own lesion-dependent specificity and, within this specificity, its own sensitivity. This “method- and lesion-dependent” nature of argyrophilia enables operational sorting of disease-specific lesions based on their silver-staining profiles, which may potentially represent some disease-specific aspects. Furthermore, comparisons between immunohistochemical and biochemical data have revealed an empirical correlation between GAL+/CS-deposits and 4-repeat (4R) tau (corticobasal degeneration, progressive supranuclear palsy and argyrophilic grains) and its complementary reversal between GAL-/CS+deposits and 3-repeat (3R) tau (Pick bodies). Deposits containing both 3R and 4R tau (neurofibrillary tangles of Alzheimer type) are GAL+/CS+. Although no molecular explanations, other than these empiric correlations, are currently available, these distinctive features, especially when combined with immunohistochemistry, are useful because silver-staining methods and immunoreactions are complementary to each other.

Cellular pathology in multiple system atrophy

Multiple system atrophy (MSA) is a sporadic, adult-onset neurodegenerative disease, which is characterized by striatonigral degeneration, olivopontocerebellar atrophy, and preganglionic autonomic lesions in any combination. The histological hallmark is the presence of argyrophilic fibrillary inclusions in the oligodendrocytes, referred to as glial cytoplasmic inclusions (GCIs). Fibrillary inclusions are also found in the neuronal somata, axons, and nucleus. Neuronal cytoplasmic inclusions are frequently found in the pontine and inferior olivary nuclei. Since the discovery of alpha-synuclein as a major component of glial and neuronal inclusions in MSA, two neurodegenerative processes have been considered in this disease: one is due to the widespread occurrence of GCIs associated with oligodendroglia-myelin degeneration (oligodendrogliopathy) in the central nervous system, and the other is due to the filamentous aggregation of alpha-synuclein in the neurons in several brain regions. These two degenerative processes might synergistically cause neuronal depletion in MSA.

Progressive accumulation of ubiquitin and disappearance of alpha-synuclein epitope in multiple system atrophy-associated glial cytoplasmic inclusions: triple fluorescence study combined with Gallyas-Braak method

Alpha-synuclein (alphaS) and ubiquitin (Ub) are shared constituents of glial cytoplasmic inclusions (GCIs) and Lewy bodies (LBs), both composed of fibrillary structures. Staining profiles of GCIs were investigated with triple immunofluorescence involving immunostaining for alphaS and Ub, both amplified with catalyzed reporter deposition, and a fluorochrome, thiazin red (TR) that has an affinity to fibrillary structures. After observation for the triple-fluorescent images, the sections were subsequently stained with the Gallyas-Braak method. Sections of putamen, cerebellar white matter and motor cortex from patients suffering from multiple system atrophy (MSA) with varying duration of the disease (4-15 years) were quantified for these staining profiles of Gallyas-positive GCIs. Although most of GCIs were positive for Ub and variably positive for alphaS, they were consistently negative for TR. The result was opposite in LBs in Lewy body disease with variable affinity to TR, suggesting that the construction of GCIs is different from that of LBs. These four staining features (alphaS, Ub, TR and Gallyas) alone failed to exhibit apparent correlation with disease duration, lesion site or severity of degeneration as reported previously. The fraction of alphaS-negative and Ub-positive GCIs, however, linearly increased along the disease progression, while that of alphaS-positive and Ub-negative GCIs decreased in contrast. This reciprocal change suggests that alphaS immunoreactivity in GCIs is being replaced by Ub immunoreactivity during the disease progression, which resulted in the ultimate predominance of alphaS-negative and Ub-positive GCIs in the most advanced case. Interestingly, this predominance of alphaS-negative and Ub-positive GCIs was a feature of motor cortex, where degeneration usually remains mild in spite of robust appearance of Gallyas-positive GCIs. Another fraction, alphaS-positive and Ub-positive GCIs were frequent in cerebellar white matter, suggesting that GCI evolution is heterogeneous and dependent also on area examined. Progressive accumulation of Ub with concomitant disappearance of alphaS epitope and their colocalization, partly shared with LBs, may represent a process of GCI formation, possibly linked to an aspect of degeneration in MSA.

The role of alpha-synuclein in the pathogenesis of multiple system atrophy

The discovery of glial cytoplasmic inclusions (GCIs) in 1989 helped to define multiple system atrophy (MSA) as a clinicopathological entity, and drew attention to the prominent role played by these inclusions in the pathogenesis of the disorder. Subsequently, GCIs were shown to be highly positive for alpha-synuclein, a neuronal protein that is normally absent in oligodendroglia except during embryonic development. The source of oligodendroglial alpha-synuclein aggregation in MSA is unknown. Since genetic overexpression has been excluded, active uptake from dying neurons remains a possibility. The similar topography of oligodendroglial and neuronal pathology in MSA suggests a fundamental disturbance of the functional unit between oligodendroglia, axon, and neuron. Transgenic MSA mouse models are now available to determine these aspects of cellular disturbance experimentally.

Exclusive induction of tau2 epitope in microglia/macrophages in inflammatory lesions-tautwopathy distinct from degenerative tauopathies

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.

Microglial tau undergoes phosphorylation-independent modification after ischemia

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.