Biology subjects

Kovacs, G. G.

Publications and source records attributed to Kovacs, G. G..

13 recordsLinked to original sources

bioRxiv2026

Differently sized soluble α-synuclein species from multiple system atrophy and Lewy body disease brains display different seeding propensities

Different conformations, or strains, of -synuclein (-syn) aggregates are believed to be responsible for the distinct seeding propensities, propagation profiles, and clinical presentations in Lewy body diseases (LBD) and multiple system atrophy (MSA). While biochemical properties and strain differences of insoluble deposits have been extensively characterized, the understanding of what influence soluble -syn species may have on these processes is limited to a small number of studies focusing on complex mixtures of soluble species or on a single - synucleinopathy. Given that soluble oligomers are considered highly pathologically relevant, we isolated and characterized the biochemical, seeding, and toxicity properties of size-fractionated soluble -syn species from MSA and LBD brains, comparing them to species from control brains without known neurological disease (Ctrl). We observed that levels of differently sized oligomers phosphorylated at Ser129, as well as soluble large oligomers (>450 kDa), were increased in LBD compared to both MSA and Ctrl brains. Nevertheless, species derived from MSA brain exhibited seeding activity across the spectrum of -syn species (oligomers, monomers, and truncated forms) in the seed amplification assay, whereas only oligomeric species (>150 kDa) from LBD cases were seeding-prone. In the HEK293 -syn (A53T)-YFP biosensor line, as well as in murine primary neurons, only large oligomers (>450 kDa) from MSA cases induced seeding and aggregation of -syn. Taken together, our study suggests that soluble -syn species derived from MSA and LBD brains show different biochemical, aggregation and seeding patterns, presumably due to strain variations of the respective oligomers. Our findings provide novel insight into the pathogenesis of different -synucleinopathies, which may guide us in the development of targeted therapeutics.

neuroscience↗

bioRxiv2026

Microvascular pathology of proteotoxic endothelial signature characterizes Progressive Supranuclear Palsy

Cerebrovascular pathology is increasingly implicated in neurodegenerative diseases, yet its pathomechanistic contribution remains poorly defined. Building on prior evidence of dysregulated iron and oxygen homeostasis in early-affected brain regions of progressive supranuclear palsy (PSP), we hypothesized that brain microvascular alterations may play an etiological role in select neurodegenerative proteinopathies. First, we conducted a systematic neuropathological evaluation of 178 brains from the University Health Network Neurodegenerative Brain Collection, including Alzheimers disease-related neuropathologic change (ADNC; n=30), Lewy body disease with high or intermediate ADNC (n=38) and low ADNC (n=16), multiple system atrophy (MSA; n=14), PSP (n=39), frontotemporal lobar degeneration with TDP-43 proteinopathy (FTLD-TDP; n=10), and controls (n=31). Arteriolosclerosis, microinfarction, and calcification were assessed in the basal ganglia and frontal cortex. Iron burden was correlated by quantification of Perls staining in MSA and PSP, where vessel pathology was most severe. Single-nucleus RNA-sequencing (snRNA-seq) of frontal cortex tissue from control (n=5) and PSP (n=8) cases with varying arteriolosclerosis severity was performed to characterize the vascular transcriptome, with validation against an independent snRNA-seq evaluation of PSP (n= 11), Picks disease (n=9), AD (n=10), and control (n=10) brains. Histological analysis revealed disease-specific involvement of microvascular pathology in neurodegenerative diseases, identifying PSP to demonstrate most prominent and widespread vessel wall thickening across regions examined. Regression analysis using demographic, APOE and MAPT genetic risk status, and neuropathological features of cases corroborated the distinct association with PSP pathology. Elevated iron load in early affected regions of MSA and PSP brains correlated with greater vessel wall thickening, suggesting a possible pathomechanistic relationship between the two disease physiologies. snRNA-seq analysis of vascular transcriptome identified robust upregulation of heat shock proteins and hypoxia-related genes in PSP endothelial cells and pericytes across both datasets. Importantly, we found the proteotoxic signature to be strongly associated with higher vessel scores in PSP cases, linking microvascular morphology to endothelial dysfunction. Our comprehensive neuropathological evaluation coupled with correlative snRNA-seq analysis establish PSP-specific arteriolar thickening associated with endothelial proteotoxic state as a candidate pathogenic mechanism. The cerebral arteriolar unit represents a compelling therapeutic target for disease modification in PSP.

pathology↗

bioRxiv2026

Protein folding stress shapes microglial phenotype in progressive supranuclear palsy

Microglia play a pivotal role in neurodegeneration, yet their response to tau pathology remains incompletely understood. Through single-nucleus RNA sequencing of A{beta} plaque-free frontal cortex from 4R tauopathy progressive supranuclear palsy (PSP) brains, we reveal a distinct transcriptional reprogramming of homeostatic microglia. PSP microglia exhibit pronounced protein-folding and ER-stress signatures, elevated homeostatic and MHC class II gene expression, and attenuated cytoskeletal, motility, and interferon-related programs, accompanied by reduced inferred intercellular communication. Neuropathological analysis corroborates a shift toward highly ramified morphologies and increased MHC class II positivity in PSP cortex. In HMC3 cells, pharmacological induction of protein-folding stress recapitulates this phenotype, driving homeostatic gene upregulation and morphological transition to process-bearing forms. We define this protein-folding-stress-associated microglial (PSAM) state as a PSP-linked phenotype mechanistically distinct from disease-associated microglia (DAM), highlighting ER stress as a key driver of microglial remodeling in tauopathies.

neuroscience↗

bioRxiv2025

Investigation of the HLA locus in autopsy-confirmed progressive supranuclear palsy

ObjectivesProgressive supranuclear palsy (PSP) is a neurodegenerative disease showing pathological tau accumulation in subcortical neurons and glial cells. The human leukocyte antigen (HLA) locus on chromosome 6 is a polymorphic region with complex linkage patterns that has been implicated in several autoimmune and neurological disorders. The HLA locus has not been systematically examined in PSP. It is unclear whether tau and HLA can interact to induce an autoimmune disease mechanism. MethodsWe evaluated an autopsy confirmed PSP cohort (n=44) and compared allele/haplotype frequencies to those of the reference group of a local deceased Canadian donor pool. We performed HLA/Tau peptide binding prediction and modelling of HLA Class II and Tau Peptide interactions. FindingsOdds ratio was 2.94 (95% CI 1.01 to 8.55; p=0.047) for DQB1*06:01 allele, and 2.59 (95% CI 1.39 to 4.83; p=0.0025) for the narcolepsy associated haplotype (DRB1*15:01DQB1*06:02). One patient with 4 repeat tau PSP type pathology was a carrier of the IgLON5-associated haplotype (DRB1*10:01DQB1*05:01). HLA/Tau peptide binding prediction and modelling of HLA Class II/Tau Peptide interactions revealed strong binding tau peptides but not the PSP protofilament fold for alleles DQA1*01:02DQB1*06:02 and DQA1*01:03DQB1*06:01. ConclusionOur study suggests that epitopes within the tau peptide may bind to HLA alleles that are found in a subset of PSP patients supporting the notion of an autoimmune pathophysiological component. These findings have implications for subtyping and stratifying patients for therapies, including those targeting immune modulation.

immunology↗

bioRxiv2024

Lewy-MSA hybrid fold drives distinct neuronal a-synuclein pathology

The ordered assembly of -synuclein protein into filaments encoded by SNCA characterizes neurodegenerative diseases called synucleinopathies. Lewy body disease (LBD) shows predominantly neuronal -synuclein pathology and multiple system atrophy (MSA) predominantly oligodendrocytic -synuclein pathology affecting subcortical brain structures. Based on cryo-electron microscopy, it was reported that structures of -synuclein filaments from LBD differ from MSA and juvenile onset synucleinopathy (JOS) caused by a 21-nucleotide duplication in the second exon of one allele of SNCA gene 1-3. Importantly, a rare subtype of MSA, called atypical MSA4 shows abundant neuronal argyrophilic -synuclein inclusions in the limbic system. Current concepts indicate that disease entities are characterized by unique protofilament folds. Here we demonstrate that in addition to the MSA fold, -synuclein can form a new Lewy-MSA hybrid fold in the same brain region, leading to the atypical histopathological form of MSA. Distinct biochemical characteristics of -synuclein, as demonstrated by protease-sensitivity digestion assay, seed amplification assays (SAAs) and conformational stability assay (CSA), are also linked to cytopathological differences (e.g. neuronal or oligodendroglial). We expand the current structure-based classification of -synucleinopathies and propose that cell-specific protein pathologies can be associated with distinct filament folds.

pathology↗

bioRxiv2023

Single-nucleus multiomic atlas of frontal cortex in amyotrophic lateral sclerosis with a deep learning-based decoding of alternative polyadenylation mechanisms

Amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD) are two age-related and fatal neurodegenerative disorders that lie on a shared disease spectrum. While both disorders involve complex interactions between neuronal and glial cells, the specific cell-type alterations and their contributions to disease pathophysiology remain incompletely understood. Here, we applied single-nucleus RNA sequencing of the orbitofrontal cortex, a region affected in ALS-FTLD, to map cell-type specific transcriptional signatures in C9orf72-related ALS (with and without FTLD) and sporadic ALS cases. Our findings reveal disease- and cell-type-specific transcriptional changes, with neurons exhibiting the most pronounced alterations, primarily affecting mitochondrial function, protein homeostasis, and chromatin remodeling. A comparison with independent datasets from different cortical regions of C9orf72 and sporadic ALS cases showed concordance in several pathways, with neuronal STMN2 and NEFL showing consistent up-regulation between brain regions and disease subtypes. We also interrogated alternative polyadenylation (APA) as an additional layer of transcriptional regulation, demonstrating that APA events are not correlated with identified gene expression changes. To interpret these events, we developed APA-Net, a deep learning model that integrates transcript sequences with RNA-binding protein expression profiles, revealing cell type-specific patterns of APA regulation. Our atlas illuminates cell type-specific pathomechanisms of ALS/FTLD, providing a valuable resource for further investigation.

neuroscience↗

bioRxiv2023

4R-Tau seeding activity unravels molecular subtypes in patients with Progressive Supranuclear Palsy

Progressive Supranuclear palsy (PSP) is a 4-repeat (4-R) tauopathy. We hypothesized that the molecular diversity of tau could explain the heterogeneity seen in PSP disease progression. To test this hypothesis, we performed an extensive biochemical characterisation of the high molecular weight tau species (HMW-Tau) in 20 different brain regions of 25 PSP patients. We found a correlation between the HMW-Tau species and tau seeding capacity in the primary motor cortex, where we confirmed that an elevated 4R-Tau seeding activity correlates with a shorter disease duration. To identify factors that contribute to these differences, we performed proteomic and spatial transcriptomic analysis that revealed key mechanistic pathways, in particular those involving the immune system, that defined patients demonstrating high and low tau seeding capacity. These observations suggest that differences in the tau seeding activity may contribute to the considerable heterogeneity seen in disease progression of patients suffering from PSP.

neuroscience↗

bioRxiv2023

Neuronal SNCA transcription during Lewy body formation

BackgroundMisfolded -synuclein (-syn) is believed to contribute to neurodegeneration in Lewy body disease (LBD) based on considerable evidence including a gene-dosage effect observed in relation to point mutations and multiplication of SNCA in familial Parkinsons disease. A contradictory concept proposes early loss of the physiological -syn as the major driver of neurodegeneration. There is a paucity of data on SNCA transcripts in various -syn immunoreactive cytopathologies. MethodsSNCA transcripts in neurons without and with various -syn immunoreactive cytopathologies in the substantia nigra and amygdala in LBD (n = 5) were evaluated using RNAscope combined with immunofluorescence for disease-associated -syn. Single-nucleus RNA sequencing was performed to elucidate cell-type specific SNCA expression in non-diseased frontal cortex (n = 3). ResultsSNCA transcripts in neurons with punctate -syn immunoreactivity were preserved both in the substantia nigra and amygdala but were reduced in neurons with compact -syn inclusions. Only single SNCA transcripts were detected in astrocytes with or without -syn immunoreactivity in the amygdala. Single-nucleus RNA sequencing revealed that excitatory and inhibitory neurons, oligodendrocyte progenitor cells, oligodendrocytes, and homeostatic microglia expressed SNCA transcripts, while expression was largely absent in astrocytes and microglia. ConclusionsThe preserved cellular SNCA expression in the more abundant non-Lewy body type -syn cytopathologies provides a pool for local protein production that can aggregate and serve as a seed for misfolded -syn. Successful segregation of disease-associated -syn is associated with the exhaustion of SNCA production in the terminal cytopathology, the Lewy body. Our observations support a therapeutic strategy incorporating a finely tuned dual approach targeting the elimination of misfolded -syn along with the reduction of the SNCA transcription to avoid feeding of pathological -syn seeding.

pathology↗

bioRxiv2021

Age-dependent formation of TMEM106B amyloid filaments in human brain

Many age-dependent neurodegenerative diseases, like Alzheimers and Parkinsons, are characterised by abundant inclusions of amyloid filaments. Filamentous inclusions of the proteins tau, amyloid-{beta} (A{beta}), -synuclein and TDP-43 are the most common. Here, we used electron cryo-microscopy (cryo-EM) structure determination to show that residues 120-254 of the lysosomal type II transmembrane protein 106B (TMEM106B) also form amyloid filaments in the human brain. We solved cryo-EM structures of TMEM106B filaments from the brains of 22 individuals with neurodegenerative conditions, including sporadic and inherited tauopathies, A{beta}-amyloidoses, synucleinopathies and TDP-43opathies, as well as from the brains of two neurologically normal individuals. We observed three different TMEM106B folds, with no clear relationship between folds and diseases. The presence of TMEM106B filaments correlated with that of a 29 kDa sarkosyl-insoluble fragment of the protein on Western blots. The presence of TMEM106B filaments in the brains of older, but not younger, neurologically normal individuals indicates that they form in an age-dependent manner.

neuroscience↗

bioRxiv2021

Cryo-EM Structures of Amyloid-β 42 Filaments from Human Brain

Filament assembly of amyloid-{beta} peptides ending at residue 42 (A{beta}42) is a central event in Alzheimers disease. We report the cryo-EM structures of A{beta}42 filaments from brain. Two structurally related S-shaped protofilament folds give rise to two types of filaments. Type I filaments were found mostly in the brains of individuals with sporadic Alzheimers disease and Type II filaments in individuals with familial Alzheimers disease and other conditions. The structures of A{beta}42 filaments from brain differ from those of filaments assembled in vitro. By contrast, in AppNL-F knock-in mice, A{beta}42 deposits were made of Type II filaments. Knowledge of A{beta}42 filament structures from human brain may lead to the development of inhibitors of assembly and improved imaging agents.

neuroscience↗

bioRxiv2021

A novel approach to evaluate alpha-synuclein seeding shows a wide heterogeneity in multiple system atrophy

Several in vitro and in vivo findings have consistently shown that -synuclein derived from multiple system atrophy (MSA) subjects has more seeding capacity than Parkinsons disease-derived -synuclein. However, reliable detection of -synuclein derived from MSA using seeded amplification assays, such as the Real-Time Quaking-induced Conversion, has remained challenging. Here we demonstrate that the interaction of the Thioflavin T dye with -synuclein from MSA and Parkinsons disease patients can be modulated by the type of salt, pH, and ionic strength used to generate strain-specific reaction buffers. Employing this novel approach, we have generated a streamlined Real-Time Quaking-induced Conversion assay capable of categorizing MSA brains according to their -synuclein seeding behavior, and to unravel a previously unrecognized heterogeneity in seeding activity between different brain regions of a given individual that goes beyond immunohistochemical observations and provide a framework for future molecular subtyping of MSA.

neuroscience↗

bioRxiv2021

Predictors of cognitive impairment in primary age-related tauopathy: an autopsy study

Primary age-related tauopathy (PART) is a form of Alzheimer-type neurofibrillary degeneration occurring in the absence of amyloid-beta (A{beta}) plaques. While PART shares some features with Alzheimer disease (AD), such as progressive accumulation of neurofibrillary tangle pathology in the medial temporal lobe and other brain regions, it does not progress extensively to neocortical regions. Given this restricted pathoanatomical pattern and variable symptomatology, there is a need to reexamine and improve upon how PART is neuropathologically assessed and staged. We performed a retrospective autopsy study in a collection (n=174) of post-mortem PART brains and used logistic regression to determine the extent to which a set of clinical and neuropathological features predict cognitive impairment. We compared Braak staging, which focuses on hierarchical neuroanatomical progression of AD tau and A{beta} pathology, with quantitative assessments of neurofibrillary burden using computer-derived positive pixel counts on digitized whole slide images of sections stained immunohistochemically with antibodies targeting abnormal hyperphosphorylated tau (p-tau) in the entorhinal region and hippocampus. We also assessed other factors affecting cognition, including aging-related tau astrogliopathy (ARTAG) and atrophy. We found no association between Braak stage and cognitive impairment when controlling for age (p=0.76). In contrast, p-tau burden was significantly correlated with cognitive impairment even when adjusting for age (p=0.03). The strongest correlate of cognitive impairment was cerebrovascular disease, a well-known risk factor (p<0.0001), but other features including ARTAG (p=0.03) and hippocampal atrophy (p=0.04) were also associated. In contrast, sex, APOE, psychiatric illness, education, argyrophilic grains, and incidental Lewy bodies were not. These findings support the hypothesis that comorbid pathologies contribute to cognitive impairment in subjects with PART. Quantitative approaches beyond Braak staging are critical for advancing our understanding of the extent to which age-related tauopathy changes impact cognitive function.

pathology↗

bioRxiv2021

Structure-based Classification of Tauopathies

Ordered assembly of the tau protein into filaments characterizes multiple neurodegenerative diseases, which are called tauopathies. We previously reported that by electron cryo-microscopy (cryo-EM), tau filament structures from Alzheimers disease (1,2), chronic traumatic encephalopathy (CTE) (3), Picks disease (4) and corticobasal degeneration (CBD) (5) are distinct. Here we show that the structures of tau filaments from typical and atypical progressive supranuclear palsy (PSP), the most common tauopathy after Alzheimers disease, define a previously unknown, three-layered fold. Moreover, the tau filament structures from globular glial tauopathy (GGT, Types I and II) are similar to those from PSP. The tau filament fold of argyrophilic grain disease (AGD) differs from the above and resembles the four-layered CBD fold. The majority of tau filaments from aging-related tau astrogliopathy (ARTAG) also have the AGD fold. Surprisingly, tau protofilament structures from inherited cases with mutations +3/+16 in intron 10 of MAPT, the microtubule-associated protein tau gene, are identical to those from AGD, suggesting that a relative overproduction of four-repeat tau can give rise to the AGD fold. Finally, tau filament structures from cases of familial British dementia (FBD) and familial Danish dementia (FDD) are the same as those from Alzheimers disease and primary age-related tauopathy (PART). These structures provide the basis for a classification of tauopathies that also allows identification of new entities, as we show here for a case diagnosed as PSP, but with abundant spherical 4R tau inclusions in limbic and other brain areas. The structures of the tau fold of this new disease (Limbic-predominant Neuronal inclusion body 4R Tauopathy, LNT) were intermediate between those of GGT and PSP.

neuroscience↗