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Membrane trafficking pathways mediate key microglial activities such as cell migration, cytokine secretion, and phagocytosis. However, the underlying molecular mechanism remains poorly understood. Previously, we found that synaptotagmin‐11 (Syt11), a non‐Ca2+‐binding Syt associated with Parkinson's disease (PD) and schizophrenia, inhibits cytokine release and phagocytosis in primary microglia. Here we reported the in vivo function of Syt11 in microglial immune responses using an inducible microglia‐specific Syt11‐conditional‐knockout (cKO) mouse strain. Syt11‐cKO resulted in activation of microglia and elevated mRNA levels of IL‐6, TNF‐α, IL‐1β, and iNOS in various brain regions under both resting state and LPS‐induced acute inflammation state in adult mice. In a PD mouse model generated by microinjection of preformed α‐synuclein fibrils into the striatum, a reduced number of microglia migrated toward the injection sites and an enhanced phagocytosis of α‐synuclein fibrils by microglia were found in Syt11‐cKO mice. To understand the molecular mechanism of Syt11 function, we identified its direct binding proteins vps10p‐tail‐interactor‐1a (vti1a) and vti1b. The linker domain of Syt11 interacted with both proteins and a peptide derived from it competitively inhibited the interaction of Syt11 with vti1a/vti1b in vitro and in cells. Importantly, application of this peptide induced more cytokine secretion in wild‐type microglia upon LPS treatment, phenocopying defects in Syt11 knockdown cells. Altogether, we propose that Syt11 inhibits microglial activation in vivo and regulates cytokine secretion through interactions with vti1a and vti1b. [ABSTRACT FROM AUTHOR]

Caveolae play crucial roles in intracellular membrane trafficking and mechanosensation. In this study, we report that synaptotagmin‐11 (Syt11), a synaptotagmin isoform associated with Parkinson's disease and schizophrenia, regulates both caveolae‐mediated endocytosis and the caveolar response to mechanical stimuli in astrocytes. Syt11‐knockout (KO) accelerated caveolae‐mediated endocytosis. Interestingly, the caveolar structures on the cell surface were markedly fewer in the absence of Syt11. Caveolar disassembly in response to hypoosmotic stimuli and astrocyte swelling were both impaired in Syt11‐KO astrocytes. Live imaging revealed that Syt11 left caveolar structures before cavin1 during hypoosmotic stress and returned earlier than cavin1 after isoosmotic recovery. Chronic hypoosmotic stress led to proteasome‐mediated Syt11 degradation. In addition, Syt11‐KO increased the turnover of cavin1 and EH domain‐containing protein 2 (EHD2), accompanied by compromised membrane integrity, suggesting a mechanoprotective role of Syt11. Direct interactions between Syt11 and cavin1 and EHD2, but not caveolin‐1, are found. Altogether, we propose that Syt11 stabilizes caveolar structures on the cell surface of astrocytes and regulates caveolar functions under physiological and pathological conditions through cavin1 and EHD2. [ABSTRACT FROM AUTHOR]