Liquid-Liquid Phase Separation of Tau Driven by Hydrophobic Interaction Facilitates Fibrillization of Tau.
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ABSTRACT:
SUBMITTER: Lin Y
PROVIDER: S-EPMC7855949 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:The transition of tau proteins from its soluble physiological conformation to the pathological aggregate forms found in Alzheimer's disease and related dementias, is poorly understood. Therefore, understanding the process that modulates the formation of toxic tau oligomers and their conversion to putative neuroprotective neurofibrillary tangles will lead to better therapeutic strategies. We previously identified that EFhd2 is associated with aggregated tau species in AD brains and the coiled-coil domain in EFhd2 mediates the interaction with tau. To further characterize the association between EFhd2 and tau, we examined whether EFhd2 could affect the liquid-liquid phase separation properties of tau under molecular crowding conditions. We demonstrate that EFhd2 alters tau liquid phase behavior in a calcium and coiled-coil domain dependent manner. Co-incubation of EFhd2 and tau in the absence of calcium leads to the formation of solid-like structures containing both proteins, while in the presence of calcium these two proteins phase separate together into liquid droplets. EFhd2's coiled-coil domain is necessary to alter tau's liquid phase separation, indicating that protein-protein interaction is required. The results demonstrate that EFhd2 affects the liquid-liquid phase separation of tau proteins in vitro, suggesting that EFhd2 modulates the structural dynamics of tau proteins.
| S-EPMC6700279 | biostudies-literature
Project description:The transition between soluble intrinsically disordered tau protein and aggregated tau in neurofibrillary tangles in Alzheimer's disease is unknown. Here, we propose that soluble tau species can undergo liquid-liquid phase separation (LLPS) under cellular conditions and that phase-separated tau droplets can serve as an intermediate toward tau aggregate formation. We demonstrate that phosphorylated or mutant aggregation prone recombinant tau undergoes LLPS, as does high molecular weight soluble phospho-tau isolated from human Alzheimer brain. Droplet-like tau can also be observed in neurons and other cells. We found that tau droplets become gel-like in minutes, and over days start to spontaneously form thioflavin-S-positive tau aggregates that are competent of seeding cellular tau aggregation. Since analogous LLPS observations have been made for FUS, hnRNPA1, and TDP43, which aggregate in the context of amyotrophic lateral sclerosis, we suggest that LLPS represents a biophysical process with a role in multiple different neurodegenerative diseases.
| S-EPMC5881631 | biostudies-literature
Project description:Tau is a microtubule-associated protein that plays a major role in Alzheimer's disease (AD) and other tauopathies. Recent reports indicate that, in the presence of crowding agents, tau can undergo liquid-liquid phase separation (LLPS), forming highly dynamic liquid droplets. Here, using recombinantly expressed proteins, turbidimetry, fluorescence microscopy imaging, and fluorescence recovery after photobleaching (FRAP) assays, we show that the divalent transition metal zinc strongly promotes this process, shifting the equilibrium phase boundary to lower protein or crowding agent concentrations. We observed no tau LLPS-promoting effect for any other divalent transition metal ions tested, including Mn2+, Fe2+, Co2+, Ni2+, and Cu2+ We also demonstrate that multiple zinc-binding sites on tau are involved in the LLPS-promoting effect and provide insights into the mechanism of this process. Zinc concentration is highly elevated in AD brains, and this metal ion is believed to be an important player in the pathogenesis of this disease. Thus, the present findings bring a new dimension to understanding the relationship between zinc homeostasis and the pathogenic process in AD and related neurodegenerative disorders.
| S-EPMC7196643 | biostudies-literature
Project description:Formation of membrane-less organelles via liquid-liquid phase separation is one way cells meet the biological requirement for spatiotemporal regulation of cellular components and reactions. Recently, tau, a protein known for its involvement in Alzheimer's disease and other tauopathies, was found to undergo liquid-liquid phase separation making it one of several proteins associated with neurodegenerative diseases to do so. Here, we demonstrate that tau forms dynamic liquid droplets in vitro at physiological protein levels upon molecular crowding in buffers that resemble physiological conditions. Tau droplet formation is significantly enhanced by disease-associated modifications, including the AT8 phospho-epitope and the P301L tau mutation linked to an inherited tauopathy. Moreover, tau droplet dynamics are significantly reduced by these modified forms of tau. Extended phase separation promoted a time-dependent adoption of toxic conformations and oligomerization, but not filamentous aggregation. P301L tau protein showed the greatest oligomer formation following extended phase separation. These findings suggest that phase separation of tau may facilitate the formation of non-filamentous pathogenic tau conformations.
| S-EPMC7272632 | biostudies-literature
Project description:In Parkinson's disease with dementia, up to 50% of patients develop a high number of tau-containing neurofibrillary tangles. Tau-based pathologies may thus act synergistically with the α-synuclein pathology to confer a worse prognosis. A better understanding of the relationship between the two distinct pathologies is therefore required. Liquid-liquid phase separation (LLPS) of proteins has recently been shown to be important for protein aggregation involved in amyotrophic lateral sclerosis, whereas tau phase separation has been linked to Alzheimer's disease. We therefore investigated the interaction of α-synuclein with tau and its consequences on tau LLPS. We find α-synuclein to have a low propensity for both, self-coacervation and RNA-mediated LLPS at pH 7.4. However, full-length but not carboxy-terminally truncated α-synuclein efficiently partitions into tau/RNA droplets. We further demonstrate that Cdk2-phosphorylation promotes the concentration of tau into RNA-induced droplets, but at the same time decreases the amount of α-synuclein inside the droplets. NMR spectroscopy reveals that the interaction of the carboxy-terminal domain of α-synuclein with the proline-rich region P2 of tau is required for the recruitment of α-synuclein into tau droplets. The combined data suggest that the concentration of α-synuclein into tau-associated condensates can contribute to synergistic aSyn/tau pathologies.
| S-EPMC8197422 | biostudies-literature
Project description:The nucleus of eukaryotic cells harbors active and out of equilibrium environments conducive to diverse gene regulatory processes. On a molecular scale, gene regulatory processes take place within hierarchically compartmentalized sub-nuclear bodies. While the impact of nuclear structure on gene regulation is widely appreciated, it has remained much less clear whether and how gene regulation is impacting nuclear order itself. Recently, the liquid-liquid phase separation emerged as a fundamental mechanism driving the formation of biomolecular condensates, including membrane-less organelles, chromatin territories, and transcriptional domains. The transience and environmental sensitivity of biomolecular condensation are strongly suggestive of kinetic gene-regulatory control of phase separation. To better understand kinetic aspects controlling biomolecular phase-separation, we have constructed a minimalist model of the reactive nucleoplasm. The model is based on the Cahn-Hilliard formulation of ternary protein-RNA-nucleoplasm components coupled to non-equilibrium and spatially dependent gene expression. We find a broad range of kinetic regimes through an extensive set of simulations where the interplay of phase separation and reactive timescales can generate heterogeneous multi-modal gene expression patterns. Furthermore, the significance of this finding is that heterogeneity of gene expression is linked directly with the heterogeneity of length-scales in phase-separated condensates.
| S-EPMC8201646 | biostudies-literature
Project description:The liquid-liquid phase separation (LLPS) of Tau has been postulated to play a role in modulating the aggregation property of Tau, a process known to be critically associated with the pathology of a broad range of neurodegenerative diseases including Alzheimer's Disease. Tau can undergo LLPS by homotypic interaction through self-coacervation (SC) or by heterotypic association through complex-coacervation (CC) between Tau and binding partners such as RNA. What is unclear is in what way the formation mechanisms for self and complex coacervation of Tau are similar or different, and the addition of a binding partner to Tau alters the properties of LLPS and Tau. A combination of in vitro experimental and computational study reveals that the primary driving force for both Tau CC and SC is electrostatic interactions between Tau-RNA or Tau-Tau macromolecules. The liquid condensates formed by the complex coacervation of Tau and RNA have distinctly higher micro-viscosity and greater thermal stability than that formed by the SC of Tau. Our study shows that subtle changes in solution conditions, including molecular crowding and the presence of binding partners, can lead to the formation of different types of Tau condensates with distinct micro-viscosity that can coexist as persistent and immiscible entities in solution. We speculate that the formation, rheological properties and stability of Tau droplets can be readily tuned by cellular factors, and that liquid condensation of Tau can alter the conformational equilibrium of Tau.
| S-EPMC8197434 | biostudies-literature
Project description:Tau protein in vitro can undergo liquid-liquid phase separation (LLPS); however, observations of this phase transition in living cells are limited. To investigate protein state transitions in living cells, we attached Cry2 to Tau and studied the contribution of each domain that drives the Tau cluster in living cells. Surprisingly, the proline-rich domain (PRD), not the microtubule binding domain (MTBD), drives LLPS and does so under the control of its phosphorylation state. Readily observable, PRD-derived cytoplasmic condensates underwent fusion and fluorescence recovery after photobleaching consistent with the PRD LLPS in vitro. Simulations demonstrated that the charge properties of the PRD predicted phase separation. Tau PRD formed heterotypic condensates with EB1, a regulator of plus-end microtubule dynamic instability. The specific domain properties of the MTBD and PRD serve distinct but mutually complementary roles that use LLPS in a cellular context to implement emergent functionalities that scale their relationship from binding α-beta tubulin heterodimers to the larger proportions of microtubules.
| S-EPMC7594490 | biostudies-literature
Project description:Recent studies have indicated that tau, a protein involved in Alzheimer's disease and other neurodegenerative disorders, has a propensity to undergo liquid-liquid phase separation (LLPS). However, the mechanism of this process remains unknown. Here, we demonstrate that tau LLPS is largely driven by intermolecular electrostatic interactions between the negatively charged N-terminal and positively charged middle/C-terminal regions, whereas hydrophobic interactions play a surprisingly small role. Furthermore, our results reveal that, in contrast to previous suggestions, phosphorylation is not required for tau LLPS. These findings provide a foundation for understanding the mechanism by which phosphorylation and other posttranslational modifications could modulate tau LLPS in the context of specific physiological functions as well as pathological interactions.
| S-EPMC6643045 | biostudies-literature
Project description:Intraneuronal neurofibrillary tangles composed of Tau aggregates have been widely accepted as an important pathological hallmark of Alzheimer's disease. A current therapeutic avenue for treating Alzheimer's disease is aimed at inhibiting Tau accumulation with small molecules such as natural flavonoids. Liquid-liquid phase separation (LLPS) of Tau can lead to its aggregation, and Tau aggregates can then be degraded by autophagy. However, it is unclear whether natural flavonoids modulate the formation of phase-separated Tau droplets or promote autophagy and Tau clearance. Here, using confocal microscopy and fluorescence recovery after photobleaching assays, we report that a natural antioxidant flavonoid compound myricetin slows LLPS of full-length human Tau, shifting the equilibrium phase boundary to a higher protein concentration. This natural flavonoid also significantly inhibits pathological phosphorylation and abnormal aggregation of Tau in neuronal cells, and blocks mitochondrial damage and apoptosis induced by Tau aggregation. Importantly, using co-immunoprecipitation and Western blotting, we show that treatment of cells with myricetin stabilizes the interaction between Tau and autophagy-related protein 5 (ATG5) to promote clearance of phosphorylated Tau to indirectly limit its aggregation. Consistently, this natural flavonoid inhibits mTOR pathway, activates ATG5-dependent Tau autophagy, and almost completely suppresses Tau toxicity in neuronal cells. Collectively, these results demonstrate how LLPS and abnormal aggregation of Tau are inhibited by natural flavonoids, bridging the gap between Tau LLPS and aggregation in neuronal cells, and also establish that myricetin could act as an ATG5-dependent autophagic activator to ameliorate the pathogenesis of Alzheimer's disease.
| S-EPMC8551527 | biostudies-literature