LILRB4 Attenuates Ischemic Brain Injury by Inhibiting Microglial Necroptosis via a RIPK3-Dependent Mechanism

Microglia are central mediators of neuroinflammation following ischemic stroke. Our previous multi-omics data revealed significant upregulation of leukocyte immunoglobulin-like receptor subfamily B member 4 (LILRB4) in microglia after transient middle cerebral artery occlusion (tMCAO), but its functional role remains unclear. This study demonstrates that LILRB4 expression peaks at 3 days post-tMCAO and is predominantly localized to microglia. Microglia-specific Lilrb4 knockout (Lilrb4-cKO) displayed worse neurological functions, larger infarct volumes, and more significant microglial activation. Transcriptomic analysis in vitro and functional experiments further revealed that microglial LILRB4 knockdown promoted the release of proinflammatory factors and enhanced necroptosis. Mechanistically, deletion of LILRB4 mainly drives receptor-interacting protein 3 (RIPK3) and mixed lineage kinase domain-like (MLKL) expression and phosphorylation, without affecting receptor-interacting protein 1 (RIPK1). Pharmacologic inhibition of RIPK3 can relieve the brain damage caused by LILRB4 knockout after stroke. Additional analysis showed that LILRB4 negatively regulates the stimulator of interferon genes (STING)/RIPK3 axis to limit microglial necroptosis. STING suppression blocked the hyperactivation of RIPK3 induced by LILRB4 deficiency. In conclusion, LILRB4 attenuates ischemic brain injury by suppressing STING/RIPK3-mediated microglial necroptosis and neuroinflammation, emphasizing its significance as a potential neuroprotective therapy.