Non-cell autonomous downregulation of the purinergic receptor P2Y1R promotes neuroprotection after ischemic injury

Current ischemic stroke treatments largely focus on exogenous means of neural repair, with endogenous mechanisms being less understood. Here, we examine the cellular and molecular foundation of an endogenous neuroprotective mechanism using the in vitro stroke model oxygen–glucose deprivation (OGD). We demonstrate that after OGD, dying cortical neurons release ATP to activate microglia. There is a simultaneous increase in microglial release of B-NGF and IL-2, increased TrkA receptor expression on astrocytes, and a consequent downregulation in astrocyte P2Y1 receptors (P2Y1R), resulting in a decline in neuronal intracellular calcium levels and enhanced neuronal survival. This neuroprotective effect is mimicked when P2Y1R expression is directly knocked out in astrocytes or when exogenous microglial activators IL2 or NGF are added in place of microglia. Conversely, these neuroprotective effects are prevented by blockade of microglial activation or inhibition of TrkA or IL-2 receptors. Pharmacological buffering of intracellular Ca 2+ with BAPTA-AM recapitulated the neuroprotective effect, whereas NMDA receptor blockade with Dizocilpine maleate did not, indicating that neuronal survival is mediated by reduced intracellular Ca 2+ accumulation through an NMDA receptor–independent mechanism. Together, these results suggest the downregulation of P2Y1R in astrocytes by activated microglia is a critical endogenous neuroprotective mechanism after ischemic injury. By understanding these inherent non-cell autonomous mechanisms and their molecular mediators, it may be possible to improve intrinsic neuroprotection and recovery from stroke.