Targeting GPR84 ameliorates ischemic stroke by enhancing microglial efferocytosis via STAT6 activation

Acute disruption of cerebral blood flow rapidly induces neuronal injury and perturbs immune homeostasis within the central nervous system. As the primary immune regulators in the post-stroke brain, microglia orchestrate inflammatory responses and tissue repair. Enhancing their efferocytic capacity to clear apoptotic cells has thus emerged as a promising neuroprotective strategy. G protein-coupled receptor 84 (GPR84), which is predominantly expressed in innate immune cells, has been implicated in inflammatory responses; however, its role in cerebral ischemia remains poorly elucidated. This study investigates the clinical relevance of GPR84 in stroke and evaluates its therapeutic potential in experimental stroke models. ELISA analysis revealed a positive correlation between elevated peripheral blood GPR84 levels and NIHSS scores in patients with acute ischemic stroke. Integrated bioinformatics data, combined with Western blot and immunofluorescence assays, demonstrated upregulated GPR84 expression in microglia within the ischemic hemisphere. Besides, GPR84 levels in mouse peripheral blood exhibited parallel temporal dynamics with brain tissue levels throughout the first week post-transient middle cerebral artery occlusion (tMCAO). In vivo, GPR84 knockdown enhanced microglial efferocytosis, attenuated neuroinflammation, and improved short-term neurological outcomes after tMCAO. In vitro experiments using immunofluorescence and flow cytometry confirmed that GPR84 knockdown or treatment with the specific inhibitor GLPG1205 (10 µM) enhanced the efferocytosis capacity and induced a shift toward an anti-inflammatory phenotype in microglia subjected to OGD/R, which was associated with the activation of STAT6 signaling. Furthermore, administration of GLPG1205 (30 mg/kg/day) alleviated neurological deficits in tMCAO mice. GPR84 in microglia plays a critical role in the immune responses after ischemic stroke. GPR84 knockdown attenuated post-stroke brain injury by enhancing microglial efferocytosis and suppressing neuroinflammation. Pharmacological inhibition of GPR84 with GLPG1205 likewise exhibited therapeutic potential in experimental stroke models, although further studies are warranted to optimize its dosing regimen and clarify its detailed mechanisms of action.