Gomes, Cláudio Emanuel MoreiraMoreira, Guilherme G.2025-06-062025-04-162025-02-04http://hdl.handle.net/10400.5/101426Alzheimer's disease (AD), the foremost cause of dementia, is characterized by persistent neuroinflammation and amyloid- and tau protein aggregation. Notably, S100 proteins are upregulated in neurodegenerative conditions, including AD, where they localize in proximity to amyloid plaques and neurons with tau-containing neurofibrillary tangles (NFTs). This dissertation examines the role of S100B in modulating tau aggregation during the early stages of AD. Our findings reveal that S100B colocalizes with microtubule-bound tau and interacts dynamically with tau in a calcium-dependent manner, specifically targeting aggregation-prone segments within the repeat region. As a holdase-type chaperone, S100B inhibits tau aggregation at substoichiometric concentrations by suppressing secondary nucleation pathways, as confirmed through seeding assays and direct observation of S100B's interaction with tau oligomers and fibrils. Furthermore, S100B, consistent with its extracellular chaperone function, effectively inhibits proteopathic tau seeding. In exploring tau liquid-liquid phase separation (LLPS), identified as an early event in tau aggregation, we demonstrate that S100B inhibits tau condensation in a calcium-dependent manner, shifting the phase boundary to higher PEG concentrations. S100B integrates into tau droplets, stabilizing tau and reducing the formation of toxic aggregates, preserving the liquid-like properties of tau droplets. Additionally, S100B’s capacity to buffer Zn²⁺, mitigates Zn²⁺-induced tau LLPS. In subsequent investigations, we assessed the inhibitory effects of various S100 proteins on K18 aggregation. S100B and S100A1 were identified as the most potent inhibitors, while other S100 proteins demonstrated varying inhibition levels. Kinetic analyses revealed distinct preferences: S100B and S100A1 predominantly inhibited secondary aggregation pathways, while S100A9 targeted primary pathways. NMR studies mapped tau-binding regions for S100A1 across tau’s repeat domain, whereas S100A9 interacted with the PHF6 segment and the C-terminal region. S100A1 reduced the seeding activity of pre-formed K18 fibrils in tau-RD biosensor cells, whereas S100A9 was ineffective. These findings underscore the neuroprotective role of S100 proteins, particularly S100B, in tauopathies.engAlzheimer's diseaseProtein aggregationTauS100B proteinMolecular chaperoneDoença de AlzheimerAgregação proteicaProteína S100BChaperona moleculardoctoral thesis101764073