Microglia calcium signals drive fine process retraction and promote susceptibility to status epilepticus.

Microglia, the resident macrophages of the central nervous system, continuously survey the parenchyma with their highly motile processes. While calcium (Ca2+) signaling is a potential regulator of this process, the intrinsic mechanisms controlling process dynamics remain poorly defined. Here, we characterized microglial Ca2+ signals evoked by purinergic receptor activation both in vitro and in situ. In cultured microglia, UDP/UTP-induced P2Y6 receptor activation evoked robust Ca2+ signals with a sustained component mediated by store-operated Ca2+ entry (SOCE). In contrast, Ca2+ signals induced by P2Y6 and P2Y12/P2Y13 receptor activation in acutely isolated microglia or in situ microglia were dominated by intracellular store release, with minimal SOCE contribution. Functionally, Ca2+ signaling induced by P2Y6 activation or store depletion suppressed dorsal ruffling-an F-actin-dependent process-in cultured microglia. In brain slices, these Ca2+ signals triggered the retraction of fine processes and reduced process surveillance, while chemogenetic activation of Ca2+ signaling in vivo similarly decreased process complexity. Crucially, this microglial structural remodeling was associated with exacerbated status epilepticus. Thus, our study demonstrates that microglial Ca2+ signals act as a potent suppressor of process dynamics, thereby regulating neuronal excitability.