A Microglia-Astrocyte Signaling Axis Regulates Astrocyte Piezo1 Expression and Inflammatory Responses.

Structural tissue alterations in numerous brain disorders can initiate mechanosensory signaling pathways and influence neuropathology. Astrocytes are highly mechanosensitive cells that play essential roles in maintaining brain homeostasis; however, the molecular mechanisms underlying astrocyte mechanosensation during pathological conditions remain largely unexplored. In this study, we investigated how the expression of the mechanosensitive ion channel Piezo1 in astrocytes is modulated by inflammatory triggers. We found that direct exposure of primary astrocyte cultures to inflammatory stimuli, including lipopolysaccharide (LPS) or oligomeric amyloid-β (oAβ), had minimal impact on astrocytic Piezo1 expression. In contrast, when LPS or oAβ were applied to primary microglia cultures, Piezo1 expression was increased in microglia, and conditioned media from these microglia cultures significantly upregulated Piezo1 expression in astrocytes. We further identified that microglia released pro-inflammatory cytokines (IL-1α, IL-1β, and TNF-α) that can directly enhance Piezo1 expression and Piezo1-mediated Ca2+ signaling in both rodent and human astrocytes. Microglial depletion in 5xFAD mice consistently and substantially reduced astrocytic Piezo1 expression in vivo, supporting the physiological relevance of this microglia-astrocyte signaling axis during pathology. Activation of Piezo1 with Yoda2 did not alter astrocytic inflammatory gene expression under basal conditions but reduced TNF-α, CCL2, and C3 expression following cytokine pretreatment. Conversely, Piezo1 knockdown increased GFAP expression at baseline and enhanced pro-inflammatory gene expression under cytokine stimulation, indirectly promoting microglial activation. These findings demonstrate that astrocytic Piezo1 expression is regulated by microglia-derived inflammatory signals and plays a context-dependent role in modulating astrocyte reactivity and neuroinflammatory responses.