Microglial P2Y₆ calcium signaling promotes phagocytosis and shapes neuroimmune responses in epileptogenesis

Microglial calcium signaling is rare in a baseline state but strongly engaged during early epilepsy development. The mechanism(s) governing microglial calcium signaling are not known. By developing an in vivo uridine diphosphate (UDP) fluorescent sensor, GRAB_UDP1.0, we discovered that UDP release is a conserved response to seizures and excitotoxicity across brain regions. UDP can signal through the microglial-enriched P2Y₆ receptor to increase calcium activity during epileptogenesis. P2Y₆ calcium activity is associated with lysosome biogenesis and enhanced production of NF-κB-related cytokines. In the hippocampus, knockout of the P2Y₆ receptor prevents microglia from fully engulfing neurons. Attenuating microglial calcium signaling through calcium extruder (“CalEx”) expression recapitulates multiple features of P2Y₆ knockout, including reduced lysosome biogenesis and phagocytic interactions. Ultimately, P2Y₆ knockout mice retain more CA3 neurons and better cognitive task performance during epileptogenesis. Our results demonstrate that P2Y₆ signaling impacts multiple aspects of myeloid cell immune function during epileptogenesis.