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.