Ischemic stroke remains a leading cause of mortality and disability worldwide, but efforts to develop efficacious neuroprotective therapy face ongoing challenges. Efferocytosis, the phagocytic clearance of dying cells, by microglia is crucial for limiting neuroinflammation and promoting stroke resolution. Extracellular cold-inducible RNA-binding protein (eCIRP) is an inflammatory mediator which impairs macrophage bacterial phagocytosis in sepsis and radiation injury, but its role in microglial efferocytosis in ischemic stroke has not yet been studied. Using a transient middle cerebral artery occlusion (tMCAO) model of ischemic stroke, we demonstrate that eCIRP is released into the cerebrospinal fluid and microglial expression of crucial efferocytic receptor MerTK decreases in tMCAO mice. CIRP deficiency significantly improved neurological deficit, MerTK expression and microglial efferocytosis in tMCAO mice. Utilizing tMCAO, hippocampal injections, and primary microglia, we show that eCIRP induces pro-inflammatory micro-RNA 155 (miR-155) via TLR4, which suppresses its target pro-efferocytic transcription factor MAF bZIP (MafB), downregulating MerTK and microglial efferocytosis. Pharmacological blockade of eCIRP-TLR4 interaction using small peptide C23 attenuates miR-155 induction, restores MerTK expression, rescues microglial efferocytosis, and improves outcomes in tMCAO mice. We show that eCIRP causes microglial efferocytic dysfunction in ischemic stroke via TLR4/miR-155/MafB axis. These findings uncover a previously unknown pathway through which eCIRP signaling impairs neuroprotective function in microglia and suggest that targeting eCIRP may promote functional recovery after stroke.
Lapin et al. (Thu,) studied this question.