Recombinant RANKL protects against brain injury in intracerebral haemorrhage by regulating microglial phenotypes via the STAT3 pathway

Background Intracerebral haemorrhage (ICH) is a severe stroke subtype with high morbidity and mortality, where inflammation plays a crucial role. Recent studies suggest that the RANKL/RANK pathway is involved in stroke pathophysiology. This study investigated the effects of recombinant RANKL on microglial polarization after ICH.Methods In vitro, BV2 cells were stimulated with erythrocyte lysis (ELS) to assess cell viability, migration, and microglial phenotype markers. Stattic was used to block STAT3 pathway, and microglial markers were measured by RT-qPCR. In vivo, ICH rats were treated with RANKL or OPG. Neurological deficits and brain injury were evaluated. Immunohistochemistry analysed microglial activation and M1/M2 marker expression.Results Recombinant RANKL enhanced BV2 cell migration induced by ELS and shifted microglial polarization towards M2, with reduced M1 marker expression. The increase in M2 markers was inhibited by Stattic, which blocks STAT3 signalling. In vivo, RANKL-treated rats showed reduced brain edema and improved neurobehavioral outcomes after ICH. RANKL treatment promoted M2 polarization of microglia/macrophages and inhibited M1 polarization following ICH.Conclusions RANKL plays a key role in ICH by promoting microglia M2 polarization and inhibiting M1 polarization.