Histone H4 lysine 5 lactylation: A key regulator of immune metabolism in microglia during ischemic stroke

Histone lactylation is associated with neurological disorders and the state of reactive microglia. However, the impact of elevated lactate levels, generated through glycolysis under hypoxic conditions, on the status and functionality of reactive microglia in the context of ischemic stroke (IS) remains inadequately understood. Immunofluorescence, Western blot and co-immunoprecipitation were performed to identify the histone lactylation modification sites in microglia after IS. CUT&Tag and RNA sequencing data were used to clarify the target genes of H4K5la in microglia after cerebral ischemia. The influence of H4K5la on microglial functions was assessed through Nile Red staining, ELISA, free fatty acid assays, and energy metabolism kits. TTC, behavioral observation, HE and Nissl staining were used to study the impact of exogenous lactate on IS outcomes. Immunofluorescence, Western blot, co-immunoprecipitation, ELISA and qPCR were conducted to explore the upstream regulator of H4K5la and pro-inflammatory gene expression in microglia following IS.H4K5 lactylation level was elevated in microglia and boosted transcription of immunometabolic genes such as HK1, Fads2, and Pla2g4a. This was linked to higher ECAR, lower OCR, impaired FAO, and a reduced ATP/ADP ratio, resulting in more lipid accumulation and increased pro-inflammatory cytokine expression after IS. Exogenous lactate also increased H4K5la levels, indicating that glycolysis-driven lactate enhances histone lactylation. GCN5 was an upstream regulatory factor in modulating microglia histone lactylation and subsequent immune metabolism gene expression after IS. This study reveals the role and mechanism of H4K5la in microglia immunometabolic dysfunction, identifying a new therapeutic target for IS treatment.