Biology subjects

Tsoi, P. S.

Publications and source records attributed to Tsoi, P. S..

4 recordsLinked to original sources

bioRxiv2025

Modulation of biomolecular aggregate morphology and condensate infectivity

Neurodegenerative diseases are characterized by pathological aggregates exhibiting distinct morphologies, such as neurofibrillary tangles and dense circular Lewy body-like structures in Alzheimers disease, and round hyaline gel-like inclusions and skein-like filaments in amyotrophic lateral sclerosis. However, the mechanisms driving the formation of these diverse morphological structures remain poorly understood. Employing advanced microscopy, including fluorescence lifetime imaging, we investigated condensate aging and aggregation mechanisms of the prion-like domain of hnRNPA1 (A1PrD), a ribonucleoprotein implicated in both disorders. Using a simplified system across various salt and RNA conditions, we demonstrate that homotypic and heterotypic interactions between A1PrD and RNA significantly influence aggregate morphology and amyloid fibril formation, yielding diverse structures including thin fibrils, solid gels, and filamentous starburst aggregates. By tracking aggregate morphogenesis, we observed shifts in fluorescence lifetimes that reflect differences in condensate microenvironments, highlighting distinct homotypic and heterotypic interaction dynamics. Our findings indicate that amyloid fibril formation can initiate within fluid condensates or at the interfaces of solid gels. Moreover, early amyloid-rich fluid starbursts demonstrated the capability to fuse with or recruit younger amyloid-poor droplets, exemplifying prion-like infectivity and accelerating fibril formation. Collectively, our study provides evidence that the interplay between solution composition and the kinetic balance of liquid-liquid phase separation, gelation, and fibrillation contributes to the diverse pathological aggregate morphologies observed in neurodegenerative diseases.

biochemistry↗

bioRxiv2025

Tubulin transforms Tau and -synuclein condensates from pathological to physiological

Proteins phase-separate to form condensates that partition and concentrate biomolecules into membraneless compartments. These condensates can exhibit dichotomous behaviors in biology by supporting cellular physiology or instigating pathological protein aggregation1-3. Tau and - synuclein (Syn) are neuronal proteins that form heterotypic (Tau:Syn) condensates associated with both physiological and pathological processes. Tau and Syn functionally regulate microtubules8-12, but are also known to misfold and co-deposit in aggregates linked to various neurodegenerative diseases4,5,6,7, which highlights the paradoxically ambivalent effect of Tau:Syn condensation in health and disease. Here, we show that tubulin modulates Tau:Syn condensates by promoting microtubule interactions, competitively inhibiting the formation of homotypic and heterotypic pathological oligomers. In the absence of tubulin, Tau-driven protein condensation accelerates the formation of toxic Tau:Syn heterodimers and amyloid fibrils. However, tubulin partitioning into Tau:Syn condensates modulates protein interactions, promotes microtubule polymerization, and prevents Tau and Syn oligomerization and aggregation. We distinguished distinct Tau and Syn structural states adopted in tubulin-absent (pathological) and tubulin-rich (physiological) condensates, correlating compact conformations with aggregation and extended conformations with function. Furthermore, using various neuronal cell models, we showed that loss of stable microtubules, which occurs in Alzheimers disease and Parkinsons disease patients13,14, results in pathological oligomer formation and loss of neurites, and that functional condensation using an inducible optogenetic Tau construct resulted in microtubule stablization. Our results identify that tubulin is a critical modulator in switching Tau:Syn pathological condensates to physiological, mechanistically relating the loss of stable microtubules with disease progression. Tubulin restoration strategies and Tau-mediated microtubule stabilization can be potential therapies targeting both Tau-specific and Tau/Syn mixed pathologies.

biophysics↗

bioRxiv2025

Citrullination of TDP-43 is a key post-translation modification associated with structural and functional changes and progressive pathology in TDP-43 mouse models and human proteinopathies

TAR DNA-binding protein 43 (TDP-43) pathology is associated with a spectrum of clinical dementias including limbic-predominant age-related TDP-43 encephalopathy neuropathological changes (LATE-NC). Post-translational modifications (PTM) are linked to TDP-43 toxic gain-of-function and cytoplasmic aggregation1-3. Phosphorylation remains the most investigated PTM and a standard criterion for determining pathology progression and clinical subclassification in TDP-43 proteinopathies4-7. However, full spectrum of PTMs on TDP-43 structure and biology remain unknown. Utilizing mass-spectrometry analysis we identified citrullination as a novel and irreversible "bona-fide" PTM of TDP-43 protein. We recognized peptidyl arginine deiminase 2 and 4 (PAD2 and PAD4) to mediate the conversion of arginine (R) to citrulline (citR) in vitro and demonstrated increased PAD2 and PAD4 expression and TDP-43 citrullination in a human wildtype TDP-43 mouse model (Tg (Thy1-TARDBP4). Transmission electron microscopy imaging analysis revealed citrullination induced vast structural changes while ThT analysis demonstrated altered aggregation kinetics of citrullinated (citR) TDP-43 protein. We further provided mechanistic evidence on reduced electrostatic and pi-pi interactions of citR TDP-43 Low Complexity Domain (LCD) with RNA, favoring liquid-solid phase separation and condensate formation. Generation and validation of several citR TDP-43 specific antibodies against several TDP-43 epitopes revealed epitope and domain-specific effects of citrullination on TDP-43 solubility in vivo. Importantly, we found distinct reactivities of citR TDP-43 antibodies shedding light into the contribution of epitope-specific properties of human citR TDP-43 to novel pathological citR TDP-43 assemblies in human brain tissue from LATE-NC, with or without comorbid Alzheimers disease neuropathologic changes (ADNC). These findings provided a unique look into the temporal citR TDP-43 signatures, and the potential clinical relevance associated with progression of pure LATE-NC and comorbid ADNC + LATE-NC. Collectively, these data reveal the existence of irreversible TDP-43 citrullination at targeted sites via induced PAD2/PAD4 activities, presenting a critical step in TDP-43 proteinopathy.

neuroscience↗

bioRxiv2017

The N-terminal domain of ALS-linked TDP-43 assembles without misfolding

TDP-43 forms inclusions in several neurodegenerative diseases, and both its N- and C-terminal domains are implicated in this process. We show that the folded TDP-43 N-terminal domain oligomerizes under physiological conditions and propose that, in full-length TDP-43, association between folded N-terminal domains enhances the propensity of the intrinsically unfolded C-terminal domains to drive pathological aggregation.

biophysics↗