P2Y2 receptor mediates dying cell removal via inflammatory activated microglia

Microglial removal of dying cells plays a beneficial role in maintaining homeostasis in the CNS, whereas under some pathological conditions, inflammatory microglia can cause excessive clearance, leading to neuronal death. However, the mechanisms underlying dying cell removal by inflammatory microglia remain poorly understood. In this study, we performed live imaging to examine the purinergic regulation of dying cell removal by inflammatory activated microglia. Lipopolysaccharide (LPS) stimulation induces rapid death of primary rat microglia, and the surviving microglia actively remove dying cells. The nonselective P2 receptor antagonist, suramin, inhibited dying cell removal to the same degree as that of the selective P2Y2 antagonist, AR-C118925. This inhibition was more potent in LPS-stimulated microglia than in non-stimulated ones. LPS stimulation elicited distribution of the P2Y2 receptor on the leading edge of the plasma membrane and then induced drastic upregulation of P2Y2 receptor mRNA expression in microglia. LPS stimulation caused upregulation of the dying cell-sensing inflammatory Axl phagocytic receptor, which was suppressed by blocking the P2Y2 receptor and its downstream signaling effector, proline-rich tyrosine kinase (Pyk2). Together, these results indicate that inflammatory stimuli may activate the P2Y2 receptor, thereby mediating dying cell removal, at least partially, through upregulating phagocytic Axl in microglia.