Phosphorylated Tau Pathology Research Articles

HnRNP A1, hnRNP A2B1, and hnRNP K are dysregulated in tauopathies, but do not colocalize with tau pathology.

Tau interacts with multiple heterogeneous nuclear ribonucleoproteins (hnRNPs)-a family of RNA binding proteins that regulate multiple known cellular functions, including mRNA splicing, mRNA transport, and translation regulation. We have previously demonstrated particularly significant interactions between phosphorylated tau and three hnRNPs (hnRNP A1, hnRNP A2B1, and hnRNP K). Although multiple hnRNPs have been previously implicated in tauopathies, knowledge of whether these hnRNPs colocalize with tau aggregates or show cellular mislocalization in disease is limited. Here, we performed a neuropathological study examining the colocalization between hnRNP A1, hnRNP A2B1, hnRNP K, and phosphorylated tau in two brain regions (hippocampus and frontal cortex) in six disease groups (Alzheimer's disease, mild cognitive impairment, progressive supranuclear palsy, corticobasal degeneration, Pick's disease, and controls). Contrary to expectations, hnRNP A1, hnRNP A2B1, and hnRNP K did not colocalize with AT8-immunoreactive phosphorylated tau pathology in any of the tauopathies examined. However, we did observe significant cellular mislocalization of hnRNP A1, hnRNP A2B1 and hnRNP K in tauopathies, with unique patterns of mislocalization observed for each hnRNP. These data point to broad dysregulation of hnRNP A1, A2B1 and K across tauopathies with implications for disease processes and RNA regulation.

β-Amyloid species production and tau phosphorylation in iPSC-neurons with reference to neuropathologically characterized matched donor brains.

A basic assumption underlying induced pluripotent stem cell (iPSC) models of neurodegeneration is that disease-relevant pathologies present in brain tissue are also represented in donor-matched cells differentiated from iPSCs. However, few studies have tested this hypothesis in matched iPSCs and neuropathologically characterized donated brain tissues. To address this, we assessed iPSC-neuron production of β-amyloid (Aβ) Aβ40, Aβ42, and Aβ43 in 24 iPSC lines matched to donor brains with primary neuropathologic diagnoses of sporadic AD (sAD), familial AD (fAD), control, and other neurodegenerative disorders. Our results demonstrate a positive correlation between Aβ43 production by fAD iPSC-neurons and Aβ43 accumulation in matched brain tissues but do not reveal a substantial correlation in soluble Aβ species between control or sAD iPSC-neurons and matched brains. However, we found that the ApoE4 genotype is associated with increased Aβ production by AD iPSC-neurons. Pathologic tau phosphorylation was found to be increased in AD and fAD iPSC-neurons compared to controls and positively correlated with the relative abundance of longer-length Aβ species produced by these cells. Taken together, our results demonstrate that sAD-predisposing genetic factors influence iPSC-neuron phenotypes and that these cells are capturing disease-relevant and patient-specific components of the amyloid cascade.

Amygdala TDP-43 pathology is associated with behavioural dysfunction and ferritin accumulation in amyotrophic lateral sclerosis.

Cognitive and behavioural symptoms associated with amyotrophic lateral sclerosis and frontotemporal spectrum disorders (ALSFTSD) are thought to be driven, at least in part, by the pathological accumulation of TDP-43. Here we examine post-mortem tissue from six brain regions associated with cognitive and behavioural symptoms in a cohort of 30 people with sporadic ALS (sALS), a proportion of which underwent standardized neuropsychological behavioural assessment as part of the Edinburgh Cognitive ALS Screen (ECAS). Overall, the behavioural screen performed as part of the ECAS predicted accumulation of pathological phosphorylated TDP-43 (pTDP-43) with 100% specificity and 86% sensitivity in behaviour-associated brain regions. Notably, of these regions, pathology in the amygdala was the most predictive correlate of behavioural dysfunction in sALS. In the amygdala of sALS patients, we show variation in morphology, cell type predominance, and severity of pTDP-43 pathology. Further, we demonstrate that the presence and severity of intra-neuronal pTDP-43 pathology, but not astroglial pathology, or phosphorylated Tau pathology, is associated with behavioural dysfunction. Cases were also evaluated using a TDP-43 aptamer (TDP-43APT), which revealed that pathology was not only associated with behavioural symptoms, but also with ferritin levels, a measure of brain iron. Intra-neuronal pTDP-43 and cytoplasmic TDP-43APT pathology in the amygdala is associated with behavioural symptoms in sALS. TDP-43APT staining intensity is also associated with increased ferritin, regardless of behavioural phenotype, suggesting that ferritin increases may occur upstream of clinical manifestation, in line with early TDP-43APT pathology, representing a potential region-specific imaging biomarker of early disease in ALS.

Distinct patterns of plaque and microglia glycosylation in Alzheimer's disease.

Glycosylation is the most common form of post-translational modification in the brain. Aberrant glycosylation has been observed in cerebrospinal fluid and brain tissue of Alzheimer's disease (AD) cases, including dysregulation of terminal sialic acid (SA) modifications. While alterations in sialylation have been identified in AD, the localization of SA modifications on cellular or aggregate-associated glycans is largely unknown because of limited spatial resolution of commonly utilized methods. The present study aims to overcome these limitations with novel combinations of histologic techniques to characterize the sialylation landscape of O- and N-linked glycans in autopsy-confirmed AD post-mortem brain tissue. Sialylated glycans facilitate important cellular functions including cell-to-cell interaction, cell migration, cell adhesion, immune regulation, and membrane excitability. Previous studies have not investigated both N- and O-linked sialylated glycans in neurodegeneration. In this study, the location and distribution of sialylated glycans were evaluated in three brain regions (frontal cortex, hippocampus, and cerebellum) from 10 AD cases using quantitative digital pathology techniques. Notably, we found significantly greater N-sialylation of the Aβ plaque microenvironment compared with O-sialylation. Plaque-associated microglia displayed the most intense N-sialylation proximal to plaque pathology. Further analyses revealed distinct differences in the levels of N- and O-sialylation between cored and diffuse Aβ plaque morphologies. Interestingly, phosphorylated tau pathology led to a slight increase in N-sialylation and no influence of O-sialylation in these AD brains. Confirming our previous observations in mice with novel histologic approach, these findings support microglia sialylation appears to have a relationship with AD protein aggregates while providing potential targets for therapeutic strategies.

Association of reactive astrogliosis and microglial activation with tau pathology in Alzheimer’s disease

AbstractBackgroundGlial contributions to Alzheimer’s disease (AD) etiology and progression have been increasingly recognized. Experimental and clinical evidence suggests that both microglial activation and astrocyte reactivity have pivotal roles in the progression of tau pathology. However, it remains to be elucidated how microglia and astrocytes complement each other in AD pathogenesis. Here, we tested the associations between reactive astrogliosis and microglial activation with tau phosphorylation and aggregation in individuals across the aging and AD spectrum.MethodWe studied 95 participants (14 cognitively unimpaired [CU] young, 46 CU elderly, and 35 cognitively impaired [CI]) from the Translational Biomarkers in Aging and Dementia (TRIAD) cohort. Individuals had available positron emission tomography (PET) for Aβ ([18F]AZD4694), tau tangles ([18F]MK6240), and microglial activation ([11C]PBR28). We further assessed reactive astrogliosis (plasma glial fibrillary acidic protein [GFAP]) and pathological tau phosphorylation (plasma phosphorylated tau [p‐tau] at threonine 231, 181, and 217).ResultDemographic characteristics of the study population are reported in Table 1. Regression analyses revealed that reactive astrogliosis and microglial activation were synergistically associated with higher plasma phosphorylated tau levels independently of Aβ pathology in CU but not CI individuals (Figure 1A). On the other hand, no interactive effects of reactive astrogliosis and microglial activation on tau‐PET burden were observed in either CU or CI individuals (Figure 1B). Similar findings were observed in sensitivity analyses excluding CU young participants.ConclusionOur results suggest that reactive astrocytes and activated microglia have Aβ‐independent synergistic effects on the early progression of AD pathophysiology by contributing to tau phosphorylation but not tau aggregation. These findings can help to better understand the complementary roles of glial cells in neurodegenerative diseases, as well as provide insights for the development novel therapeutic strategies for AD targeting the interplay between astrocyte and microglial reactivity.

Association of reactive astrogliosis and microglial activation with tau pathology in Alzheimer’s disease

AbstractBackgroundGlial contributions to Alzheimer’s disease (AD) etiology and progression have been increasingly recognized. Experimental and clinical evidence suggests that both microglial activation and astrocyte reactivity have pivotal roles in the progression of tau pathology. However, it remains to be elucidated how microglia and astrocytes complement each other in AD pathogenesis. Here, we tested the associations between reactive astrogliosis and microglial activation with tau phosphorylation and aggregation in individuals across the aging and AD spectrum.MethodWe studied 95 participants (14 cognitively unimpaired [CU] young, 46 CU elderly, and 35 cognitively impaired [CI]) from the Translational Biomarkers in Aging and Dementia (TRIAD) cohort. Individuals had available positron emission tomography (PET) for Aß ([18F]AZD4694), tau tangles ([18F]MK6240), and microglial activation ([11C]PBR28). We further assessed reactive astrogliosis (plasma glial fibrillary acidic protein [GFAP]) and pathological tau phosphorylation (plasma phosphorylated tau [p‐tau] at threonine 231, 181, and 217).ResultDemographic characteristics of the study population are reported in Table 1. Regression analyses revealed that reactive astrogliosis and microglial activation were synergistically associated with higher plasma phosphorylated tau levels independently of Aß pathology in CU but not CI individuals (Figure 1A). On the other hand, no interactive effects of reactive astrogliosis and microglial activation on tau‐PET burden were observed in either CU or CI individuals (Figure 1B). Similar findings were observed in sensitivity analyses excluding CU young participants.ConclusionOur results suggest that reactive astrocytes and activated microglia have Aß‐independent synergistic effects on the early progression of AD pathophysiology by contributing to tau phosphorylation but not tau aggregation. These findings can help to better understand the complementary roles of glial cells in neurodegenerative diseases, as well as provide insights for the development novel therapeutic strategies for AD targeting the interplay between astrocyte and microglial reactivity.

Plasma biomarkers in relation to spatial distribution of Alzheimer’s disease neuropathology

AbstractBackgroundThe clinical utility of plasma biomarkers will in part be based on the information they convey regarding the distribution of neuropathology, especially beyond the information provided by demographics. We examined the associations of plasma biomarkers with cerebral amyloid and tau pathology determined by positron emission tomography (PET).MethodIn the Baltimore Longitudinal Study of Aging, plasma Aß42/Aß40, glial fibrillary acidic protein (GFAP), and neurofilament light chain (NfL) concentrations were measured using Quanterix Simoa assays. Plasma concentrations of phosphorylated tau at threonine 181 (p‐tau181) and at 231 (p‐tau231) were measured using in‐house Simoa assays at University of Gothenburg. Using voxelwise linear regression models, we investigated cross‐sectional associations of plasma biomarkers with brain fibrillar amyloid and phosphorylated tau pathology as measured by PET with 11C‐Pittsburgh compound B (PiB) conducted on a GE Advance scanner (N = 189) and 18F‐flortaucipir (FTP) conducted on a Siemens High Resolution Research Tomograph (N = 107), respectively. In addition to unadjusted analyses, we conducted analyses adjusting for age, sex, and race. Results were corrected for multiple comparisons using permutation test‐based threshold‐free cluster enhancement (TFCE).ResultLower plasma Aß42/Aß40 was associated with higher PiB distribution volume ratio (DVR) in the unadjusted model, but not in the adjusted model (Figure 1). The remaining plasma biomarkers exhibited statistically significant positive associations with PiB DVR in both unadjusted and adjusted models. The plasma biomarker with the strongest and most widespread association with PiB DVR was p‐tau231 (Figure 2). Both p‐tau biomarkers exhibited statistically significant associations with FTP standardized uptake value ratio (SUVR) in both unadjusted and adjusted models. Aß42/Aß40, GFAP, and NfL did not exhibit statistically significant associations with FTP SUVR. Associations of p‐tau biomarkers with PiB DVR were stronger and more widespread than with FTP SUVR. We did not find any statistically significant associations when we repeated the analyses separately by binary PiB group.ConclusionPlasma biomarkers convey information beyond age, sex, and race in relation to the cerebral distribution of amyloid, and to a lesser extent, tau. The smaller sample size of our FTP PET study might in part explain the weaker associations we observed with FTP SUVR compared to PiB DVR.

Antisense oligonucleotide-based targeting of Tau-tubulin kinase 1 prevents hippocampal accumulation of phosphorylated tau in PS19 tauopathy mice

Tau tubulin kinase-1 (TTBK1), a neuron-specific tau kinase, is highly expressed in the entorhinal cortex and hippocampal regions, where early tau pathology evolves in Alzheimer’s disease (AD). The protein expression level of TTBK1 is elevated in the cortex brain tissues with AD patients compared to the control subjects. We therefore hypothesized that antisense oligonucleotide (ASO) based targeting Ttbk1 could prevent the accumulation of phosphorylated tau, thereby delaying the development of tau pathology in AD. Here we show that in vivo administration of ASO targeting mouse Ttbk1 (ASO-Ttbk1) specifically suppressed the expression of Ttbk1 without affecting Ttbk2 expression in the temporal cortex of PS19 tau transgenic mice. Central administration of ASO-Ttbk1 in PS19 mice significantly reduced the expression level of representative phosphor-tau epitopes relevant to AD at 8 weeks post-dose, including pT231, pT181, and pS396 in the sarkosyl soluble and insoluble fractions isolated from hippocampal tissues as determined by ELISA and pS422 in soluble fractions as determined by western blotting. Immunofluorescence demonstrated that ASO-Ttbk1 significantly reduced pS422 phosphorylated tau intensity in mossy fibers region of the dentate gyrus in PS19 mice. RNA-sequence analysis of the temporal cortex tissue revealed significant enrichment of interferon-gamma and complement pathways and increased expression of antigen presenting molecules (Cd86, Cd74, and H2-Aa) in PS19 mice treated with ASO-Ttbk1, suggesting its potential effect on microglial phenotype although neurotoxic effect was absent. These data suggest that TTBK1 is an attractive therapeutic target to suppress TTBK1 without compromising TTBK2 expression and pathological tau phosphorylation in the early stages of AD.

Correspondence of mean apparent propagator MRI metrics with phosphorylated tau and astrogliosis in chronic traumatic encephalopathy.

Chronic traumatic encephalopathy is a neurodegenerative disease that is diagnosed and staged based on the localization and extent of phosphorylated tau pathology. Although its identification remains the primary diagnostic criteria to distinguish chronic traumatic encephalopathy from other tauopathies, the hyperphosphorylated tau that accumulates in neurofibrillary tangles in cortical grey matter and perivascular regions is often accompanied by concomitant pathology such as astrogliosis. Mean apparent propagator MRI is a clinically feasible diffusion MRI method that is suitable to characterize microstructure of complex biological media efficiently and comprehensively. We performed quantitative correlations between propagator metrics and underlying phosphorylated tau and astroglial pathology in a cross-sectional study of 10 ex vivo human tissue specimens with 'high chronic traumatic encephalopathy' at 0.25 mm isotropic voxels. Linear mixed effects analysis of regions of interest showed significant relationships of phosphorylated tau with propagator-estimated non-Gaussianity in cortical grey matter (P = 0.002) and of astrogliosis with propagator anisotropy in superficial cortical white matter (P = 0.0009). The positive correlation between phosphorylated tau and non-Gaussianity was found to be modest but significant (R2 = 0.44, P = 6.0 × 10-5) using linear regression. We developed an unsupervised clustering algorithm with non-Gaussianity and propagator anisotropy as inputs, which was able to identify voxels in superficial cortical white matter that corresponded to astrocytes that were accumulated at the grey-white matter interface. Our results suggest that mean apparent propagator MRI at high spatial resolution provides a means to not only identify phosphorylated tau pathology but also detect regions with astrocytic pathology and may therefore prove diagnostically valuable in the evaluation of concomitant pathology in cortical tissue with complex microstructure.

Amisulpride Decreases Tau Protein Hyperphosphorylation in the Brain of OXYS Rats.

In this study, OXYS rats of three ages (1, 3, and 6 months), a proven model of Alzheimer's disease (AD), at various stages of disease progression were used to thoroughly study the effects of amisulpride on behavior and tau protein phosphorylation. With the growing number of patients with AD, the problem of finding a cure is very acute. Neurodegeneration in AD has various causes, one of which is hyperphosphorylation of tau protein. This study aimed to investigate whether amisulpride would affect pathological tau phosphorylation in AD. We assessed the influence of chronic administration of amisulpride (3 weeks, 3 mg/kg per day, intraperitoneally)-a 5-HT7 receptor inverse agonist-on behavior and tau hyperphosphorylation in OXYS rats (at ages of 1, 3, and 6 months). Chronic administration of amisulpride dramatically decreased tau phosphorylation in the frontal cortex and hippocampus of 3-month-old OXYS rats. Additionally, in 1- and 3-month-old rats' hippocampi, amisulpride diminished the mRNA level of the Cdk5 gene encoding one of the main tau kinases involved in the 5-HT7 receptor-induced effect on tau phosphorylation. Thus, We found that chronic administration of amisulpride could reduce pathological tau hyperphosphorylation while reducing anxiety. We propose amisulpride to have therapeutic potential against AD and that it can be the most effective in the early stages of the disease.

Astrocyte reactivity influences amyloid-β effects on tau pathology in preclinical Alzheimer’s disease

An unresolved question for the understanding of Alzheimer’s disease (AD) pathophysiology is why a significant percentage of amyloid-β (Aβ)-positive cognitively unimpaired (CU) individuals do not develop detectable downstream tau pathology and, consequently, clinical deterioration. In vitro evidence suggests that reactive astrocytes unleash Aβ effects in pathological tau phosphorylation. Here, in a biomarker study across three cohorts (n = 1,016), we tested whether astrocyte reactivity modulates the association of Aβ with tau phosphorylation in CU individuals. We found that Aβ was associated with increased plasma phosphorylated tau only in individuals positive for astrocyte reactivity (Ast+). Cross-sectional and longitudinal tau–positron emission tomography analyses revealed an AD-like pattern of tau tangle accumulation as a function of Aβ only in CU Ast+ individuals. Our findings suggest astrocyte reactivity as an important upstream event linking Aβ with initial tau pathology, which may have implications for the biological definition of preclinical AD and for selecting CU individuals for clinical trials.

Zika virus infection of mature neurons from immunocompetent mice generates a disease-associated microglia and a tauopathy-like phenotype in link with a delayed interferon beta response

BackgroundZika virus (ZIKV) infection at postnatal or adult age can lead to neurological disorders associated with cognitive defects. Yet, how mature neurons respond to ZIKV remains substantially unexplored.MethodsThe impact of ZIKV infection on mature neurons and microglia was analyzed at the molecular and cellular levels, in vitro using immunocompetent primary cultured neurons and microglia, and in vivo in the brain of adult immunocompetent mice following intracranial ZIKV inoculation. We have used C57BL/6 and the genetically diverse Collaborative Cross mouse strains, displaying a broad range of susceptibility to ZIKV infection, to question the correlation between the effects induced by ZIKV infection on neurons and microglia and the in vivo susceptibility to ZIKV.ResultsAs a result of a delayed induction of interferon beta (IFNB) expression and response, infected neurons displayed an inability to stop ZIKV replication, a trait that was further increased in neurons from susceptible mice. Alongside with an enhanced expression of ZIKV RNA, we observed in vivo, in the brain of susceptible mice, an increased level of active Iba1-expressing microglial cells occasionally engulfing neurons and displaying a gene expression profile close to the molecular signature of disease-associated microglia (DAM). In vivo as well as in vitro, only neurons and not microglial cells were identified as infected, raising the question of the mechanisms underlying microglia activation following brain ZIKV infection. Treatment of primary cultured microglia with conditioned media from ZIKV-infected neurons demonstrated that type-I interferons (IFNs-I) secreted by neurons late after infection activate non-infected microglial cells. In addition, ZIKV infection induced pathological phosphorylation of Tau (pTau) protein, a hallmark of neurodegenerative tauopathies, in vitro and in vivo with clusters of neurons displaying pTau surrounded by active microglial cells.ConclusionsWe show that ZIKV-infected mature neurons display an inability to stop viral replication in link with a delayed IFNB expression and response, while signaling microglia for activation through IFNs-I secreted at late times post-infection. In the brain of ZIKV-infected susceptible mice, uninfected microglial cells adopt an active morphology and a DAM expression profile, surrounding and sometimes engulfing neurons while ZIKV-infected neurons accumulate pTau, overall reflecting a tauopathy-like phenotype.

Tau promotes oxidative stress-associated cycling neurons in S phase as a pro-survival mechanism: Possible implication for Alzheimer’s disease

Multiple lines of evidence have linked oxidative stress, tau pathology and neuronal cell cycle re-activation to Alzheimer’s disease (AD). While a prevailing idea is that oxidative stress-induced neuronal cell cycle reactivation acts as an upstream trigger for pathological tau phosphorylation, others have identified tau as an inducer of cell cycle abnormalities in both mitotic and postmitotic conditions. In addition, nuclear hypophosphorylated tau has been identified as a key player in the DNA damage response to oxidative stress. Whether and to what extent these observations are causally linked remains unclear. Using immunofluorescence, fluorescence-activated nucleus sorting and single-nucleus sequencing, we report an oxidative stress-associated accumulation of nuclear hypophosphorylated tau in a subpopulation of cycling neurons confined in S phase in AD brains, near amyloid plaques. Tau downregulation in murine neurons revealed an essential role for tau to promote cell cycle progression to S phase and prevent apoptosis in response to oxidative stress. Our results suggest that tau holds oxidative stress-associated cycling neurons in S phase to escape cell death. Together, this study proposes a tau-dependent protective effect of neuronal cell cycle reactivation in AD brains and challenges the current view that the neuronal cell cycle is an early mediator of tau pathology.

Патологические состояния, ассоциированные с белком тау:механизмы развития и возможные биологические мишени для фармакологической коррекции тау-протеинопатии (обзор)

Background: The pathological process associated with the pathogenic aggregation of tau is called taupathy. The same term is often used to refer to a group of neurodegenerative diseases, an important pathogenetic component of which is the aggregation of tau. A violation in the expression of the MART gene leads to changes in the physicochemical properties of the protein. Modern strategies for the search for therapeutic agents to modulate tau-proteinopathy are aimed at creating drugs that suppress the formation of pathogenic forms of protein and its aggregation, but at the same time do not disrupt the metabolism of normal intracellular tau and its function in stabilizing microtubules. The aim of the study:To consider possible biological targets of pathological conditions associated with tau protein and to identify ways of pharmacological correction of tau proteinopath. Materials and methods:We analyzed the literature on the main mechanisms of pathological conditions associated with tau protein and possible biological targets for pharmacological correction of tau-proteinopathy published over the last 10 years. Results: Modern strategies for the search for therapeutic agents to modulate tau-proteinopathy, including Alzheimer's disease, are aimed at creating drugs that suppress the formation of pathogenic forms of tau and its aggregation, but do not disrupt the metabolism of normal intracellular tau protein and its function in stabilizing microtubules. In this regard, the search for therapeutic agents capable of correcting tau-proteinopathy has significantly intensified. Conclusion: There are several approaches to the treatment and prevention of tau-proteinopathy. Stabilization of the microtubule structure, reduction of the activity of full-sized and hyperphosphorylated tau, regulation of pathological phosphorylation of tau, prevention of protein aggregation, inhibition of abnormal aggregation, prevention of oligomerization, inhibition of accumulation inside the cell, specific inhibition of purinoreceptor P2RX7, regulation of AMPA receptors, blocking penetration into cells and transmission of pathogenic protein.

Associations of phosphorylated tau pathology with whole-hemisphere ex vivo morphometry in 7 tesla MRI.

Neurodegenerative disorders are associated with different pathologies that often co-occur but cannot be measured specifically with in vivo methods. Thirty-three brain hemispheres from donors with an Alzheimer's disease (AD) spectrum diagnosis underwent T2-weighted magnetic resonance imaging (MRI). Gray matter thickness was paired with histopathology from the closest anatomic region in the contralateral hemisphere. Partial Spearman correlation of phosphorylated tau and cortical thickness with TAR DNA-binding protein 43 (TDP-43) and α-synuclein scores, age, sex, and postmortem interval as covariates showed significant relationships in entorhinal and primary visual cortices, temporal pole, and insular and posterior cingulate gyri. Linear models including Braak stages, TDP-43 and α-synuclein scores, age, sex, and postmortem interval showed significant correlation between Braak stage and thickness in the parahippocampal gyrus, entorhinal cortex, and Broadman area 35. We demonstrated an association of measures of AD pathology with tissue loss in several AD regions despite a limited range of pathology in these cases. Neurodegenerative disorders are associated with co-occurring pathologies that cannot be measured specifically with in vivo methods. Identification of the topographic patterns of these pathologies in structural magnetic resonance imaging (MRI) may provide probabilistic biomarkers. We demonstrated the correlation of the specific patterns of tissue loss from ex vivo brain MRI with underlying pathologies detected in postmortem brain hemispheres in patients with Alzheimer's disease (AD) spectrum disorders. The results provide insight into the interpretation of in vivo structural MRI studies in patients with AD spectrum disorders.

Tau R2 and R3 are essential regions for tau aggregation, seeding and propagation

Tauopathies are characterised by intracellular deposits of fibrillar tau tangles. However, the interneuronal spread of pathological tau species precedes the development of major tau burdens. Two amyloid motifs, VQIINK in repeat 2 and VQIVYK in repeat 3, of tau repeat domain, assemble into β-sheet-rich fibrils on their own but alone do not form seed-competent fibrils. In contrast, the entire R3 region self-aggregates and forms seed-competent fibrils. Our study aimed to identify the minimal regions in the tau repeat domain that define seeding and its impact on intracellular tau phosphorylation and aggregation. Using peptides of individual repeats, we show that R2, like R3, forms seed-competent fibrils when assembled in the presence of heparin. However, R3, but not R2, forms seed-competent fibrils when assembled without heparin, even though both R2 and R3 have identical N-terminal hexapeptide and cysteine residue sequences. Moreover, cysteine to alanine substitution in R3 abrogates its self-aggregation and seeding potency. Tau RD P301S biosensor cells and Tau P301L (0N4R)-expressing HEK293 cells seeded with R2 and R3 fibrils show the induction of pathological phosphorylation of tau at Ser262/Ser396/Ser404 positions and oligomerisation of native tau. Protein fractions of biosensor cells seeded with R2 and R3 fibrils reseed endogenous tau aggregation when introduced into a fresh set of biosensor cells. Our findings suggest that R3 may be the minimal region for pathological seed generation under physiological conditions, whereas R2 might need polyanionic cofactors to generate pathogenic seeds. Lastly, R2 and R3 fibrils induce template-induced misfolding and pathological hyperphosphorylation of intracellular tau, making intracellular tau seed-competent.

Structural (dys)connectivity associates with cholinergic cell density in Alzheimer's disease.

Cognitive deficits in Alzheimer’s disease, specifically amnestic (memory dominant) deficits, are associated with cholinergic degeneration in the basal forebrain. The cholinergic nucleus within the basal forebrain, the nucleus basalis of Meynert, exhibits local atrophy and reduced cortical tract integrity on MRI, and reveals amyloid-β and phosphorylated-tau pathology at autopsy. To understand the pathophysiology of nucleus basalis of Meynert atrophy and its neocortical projections in Alzheimer’s disease, we used a combined post-mortem in situ MRI and histopathology approach. A total of 19 Alzheimer’s disease (10 amnestic and nine non-amnestic) and nine non-neurological control donors underwent 3 T T1-weighted MRI for anatomical delineation and volume assessment of the nucleus basalis of Meynert, and diffusion-weighted imaging for microstructural assessment of the nucleus and its projections. At subsequent brain autopsy, tissue dissection and immunohistochemistry were performed for amyloid-β, phosphorylated-tau and choline acetyltransferase. Compared to controls, we observed an MRI-derived volume reduction and altered microstructural integrity of the nucleus basalis of Meynert in Alzheimer’s disease donors. Furthermore, decreased cholinergic cell density was associated with reduced integrity of the nucleus and its tracts to the temporal lobe, specifically to the temporal pole of the superior temporal gyrus, and the parahippocampal gyrus. Exploratory post hoc subgroup analyses indicated that cholinergic cell density could be associated with cortical tract alterations in amnestic Alzheimer’s disease donors only. Our study illustrates that in Alzheimer’s disease, cholinergic degeneration in the nucleus basalis of Meynert may contribute to damaged cortical projections, specifically to the temporal lobe, leading to cognitive deterioration.

Seizure activity triggers tau hyperphosphorylation and amyloidogenic pathways.

Although epilepsies and neurodegenerative disorders show pathophysiological similarities, their direct functional associations are unclear. Here, we tested the hypothesis that experimental seizures can induce tau hyperphosphorylation and amyloidogenic modifications over time, with intersections with neuroinflammation. We used a model of mesial temporal lobe epilepsy (MTLE) where unilateral intrahippocampal injection of kainic acid (KA) in C57BL/6mice elicits epileptogenesis and spontaneous focal seizures. We used a model of generalized status epilepticus (SE) obtained by intraperitoneal KA injection in C57BL/6mice. We performed analyses and cross-comparisons according to a schedule of 72 h, 1 week, and 8 weeks after KA injection. In experimental MTLE, we show AT100, PHF1, and CP13 tau hyperphosphorylation during epileptogenesis (72h-1week) and long-term (8weeks) during spontaneous seizures in the ipsilateral hippocampi, the epileptogenic zone. These pathological modifications extended to the contralateral hippocampus, a seizure propagating zone with no histological lesion or sclerosis. Two kinases, Cdk5 and GSK3β, implicated in the pathological phosphorylation of tau, were activated. In this MTLE model, the induction of the amyloidogenic pathway (APP, C99, BACE1) was prominent and long-lasting in the epileptogenic zone. These Alzheimer's disease (AD)-relevant markers, established during seizure progression and recurrence, reciprocated an enduring glial (GFAP, Iba1) inflammation and the inadequate activation of the endogenous, anti-inflammatory, glucocorticoid receptor system. By contrast, a generalized SE episode provoked a predominantly transient induction of tau hyperphosphorylation and amyloidogenic markers in the hippocampus, along with resolving inflammation. Finally, we identified overlapping profiles of long-term hippocampal tau hyperphosphorylation by comparing MTLE to J20mice, the latter a model relevant to AD. MTLE and a generalized SE prompt persistent and varying tau hyperphosphorylation or amyloidogenic modifications in the hippocampus. In MTLE, an AD-relevant molecular trajectory intertwines with neuroinflammation, spatiotemporally involving epileptogenic and nonlesional seizure propagating zones.

Disrupting the Balance of Protein Quality Control Protein UBQLN2 Accelerates Tau Proteinopathy.

Tau protein accumulation drives toxicity in several neurodegenerative disorders. To better understand the pathways regulating tau homeostasis in disease, we investigated the role of ubiquilins (UBQLNs)-a class of proteins linked to ubiquitin-mediated protein quality control (PQC) and various neurodegenerative diseases-in regulating tau. Cell-based assays identified UBQLN2 as the primary brain-expressed UBQLN to regulate tau. UBQLN2 efficiently lowered wild-type tau levels regardless of aggregation, suggesting that UBQLN2 interacts with and regulates tau protein under normal conditions or early in disease. Moreover, UBQLN2 itself proved to be prone to accumulation as insoluble protein in male and female tau transgenic mice and the human tauopathy progressive supranuclear palsy. Genetic manipulation of UBQLN2 in a tauopathy mouse model demonstrated that a physiological UBQLN2 balance is required for tau homeostasis. UBQLN2 overexpression exacerbated phosphorylated tau pathology and toxicity in mice expressing P301S mutant tau, whereas P301S mice lacking UBQLN2 showed significantly reduced phosphorylated tau. Further studies support the view that an imbalance of UBQLN2 perturbs ubiquitin-dependent PQC and autophagy. We conclude that changes in UBQLN2 levels, whether because of pathogenic mutations or secondary to disease states, such as tauopathy, contribute to proteostatic imbalances that exacerbate neurodegeneration.SIGNIFICANCE STATEMENT We defined a role for the protein quality control protein Ubiquilin-2 (UBQLN2), in age-related neurodegenerative tauopathies. This group of disorders is characterized by the accumulation of tau protein aggregates, which differ when UBQLN2 levels are altered. Given the lack of effective disease-modifying therapies for tauopathies and the function of UBQLN2 in handling various disease-linked proteins, we explored the role of UBQLN2 in regulating tau. We found that UBQLN2 reduced tau levels in cell models but behaved differently in mouse brain, where it accelerated mutant tau pathology and tau-mediated toxicity. A better understanding of the diverse functions of regulatory proteins like UBQLN2 can elucidate some of the causative factors in neurodegenerative disease and outline new routes to therapeutic intervention.

TRPV1-Mediated Microglial Autophagy Attenuates Alzheimer's Disease-Associated Pathology and Cognitive Decline.

Autophagy is a major regulator of the ageing process of the central nervous system and neurodegeneration. Autophagy dysfunction has been implicated in the pathogenesis of Alzheimer’s disease (AD). TRPV1 was reported to regulate autophagy to protect against foam cell formation and reduce the release of inflammatory factors in atherosclerosis. In this study, pharmacological activation of TRPV1 with the TRPV1 agonist capsaicin induced autophagy in a TRPV1-dependent manner in both primary microglia and BV2 cells. TRPV1-mediated autophagy regulated glycolysis and oxidative phosphorylation by controlling the expression of genes required for aerobic glycolysis and mitochondrial respiration in primary microglia. TRPV1 agonist capsaicin decreased amyloid and phosphorylated tau pathology and reversed memory deficits by promoting microglia activation, metabolism, and autophagy in 3xTg mice. These results indicate that TRPV1 was a potential therapeutic target for AD, which suggests that capsaicin should be further assessed as a possible treatment for AD.