Astragaloside IV alleviates neuroinflammation in cerebral ischemia-reperfusion injury by inhibiting HTR2B-mediated microglial M1 polarization

This study aims to elucidate the mechanism by which astragaloside IV (AS-IV) mitigates cerebral ischemia-reperfusion injury (CIRI), with a focus on serotonin receptor 2B (HTR2B)-mediated microglial polarization and neuroinflammation. In vivo, CIRI was induced in rats via middle cerebral artery occlusion-reperfusion (MCAO/R). Rats received AS-IV or HTR2B overexpression vector. In vitro, highly aggressive proliferating immortalized (HAPI) microglia were polarized to M1 with lipopolysaccharide (LPS), followed by AS-IV treatment and co-culture with neuron-like PC12 cells. Neurological function was scored using the Longa scale. Infarct volume and histopathology were assessed by TTC and HE staining, respectively. Levels of inflammatory cytokines in rat brain tissues and HAPI cells were quantified by enzyme-linked immunosorbent assay (ELISA). The viability of HAPI and PC12 cells was assessed using cell counting kit-8 (CCK-8). PC12 apoptosis was evaluated via terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) staining. CIRI rats exhibited significant neurological deficits, enlarged infarct area, and pronounced neuronal damage, which were markedly alleviated by AS-IV treatment. AS-IV also inhibited HTR2B expression and reduced pro-inflammatory cytokine release in both in vivo and in vitro models. In HAPI-PC12 co-culture system, AS-IV reversed LPS-induced microglial activation, restoring PC12 viability and reducing apoptosis. HTR2B overexpression abolished neuroprotective effects of AS-IV, promoting microglial M1 polarization and exacerbating neuroinflammation. AS-IV protects against CIRI by downregulating HTR2B and inhibiting microglial M1 polarization. These findings identify the HTR2B-microglial axis as a promising therapeutic target for ischemic stroke.