Lactate modulates microglial M2 polarization <i>via</i> H3K9 lactylation in ischemic stroke

Abstract Background and Objectives Ischemic stroke triggers pathological neuroinflammation primarily mediated by microglial activation. However, the epigenetic impact of lactate, a metabolite that accumulates during cerebral ischemia, on this process has not been comprehensively investigated. This study aimed to determine whether lactate influences microglial polarization through histone lactylation during prolonged cerebral ischemia. Methods In vitro models using lactate-treated BV-2 microglia and in vivo models of transient middle cerebral artery occlusion (MCAO) mice were established. Analyses were conducted at 4 to 12 h post-occlusion. Our comprehensive analysis included H3K9la-targeted CUT&amp; Tag sequencing, Nrf2 promoter-specific ChIP-qPCR, flow cytometry for polarization markers, cytokine enzyme-linked immunosorbent assays (ELISAs), and neuronal viability assays. Results Under ischemic conditions, lactate markedly increased H3K9 lactylation, with selective enrichment at Nrf2 promoters. This epigenetic modification resulted in a phenotypic shift toward anti-inflammatory M2 states in microglia, both in vitro and in vivo . Mechanistically, H3K9la activated the Nrf2/HO-1 pathway, effectively suppressing nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) signaling and significantly reducing pro-inflammatory cytokine secretion. Importantly, conditioned medium derived from lactate-treated microglia mitigated the neurotoxic efects induced by microglia to some extent. Conclusion Our findings suggest that lactate confers neuroprotection via epigenetic activation of Nrf2 via H3K9la, thereby polarizing microglia towards inflammation-resolving states. This finding uncovers a novel metabolic-epigenetic target for therapeutic intervention in ischemic stroke.