Pharmacological inhibition of HDAC1-mediated histone delactylation at the Gria1 promoter promotes SPP1 expression and microglial M2 polarization to alleviate traumatic brain injury

Our previous study demonstrated that HDAC1 knockdown alleviates traumatic brain injury (TBI), although underlying mechanisms remain unclear. Given the importance of microglial polarization in brain repair and its association with protein lactylation, this study investigated whether neuroprotective effects of HDAC1 inhibition in TBI are mediated through regulation of microglial polarization. In vivo TBI models, in vitro microglial cultures, immunofluorescence, CUT&Tag-seq and RNA-seq were employed to investigate the role of HDAC1 in TBI and its effects on microglial polarization and histone lactylation. Following TBI, microglia exhibited a predominant M1 phenotype with elevated HDAC1 expression, reduced histone lactylation, and altered expression of CD86 and CD206. Pharmacological inhibition of HDAC1, particularly with suberoylanilide hydroxamic acid (SAHA), or lactate supplementation restored histone lactylation and promoted M2 polarization. CUT&Tag-seq and qRT-PCR revealed that HDAC1 inhibition increased histone lactylation at the Gria1 promoter, leading to Gria1 upregulation in microglia. Hyperlactylated genes were enriched in neuroactive ligand-receptor interaction pathway. Overexpression of Gria1 in BV2 cells promoted M2 polarization, characterized by increased CD206 and decreased CD86 expression, which was further enhanced by HDAC1 inhibition or lactate treatment. RNA-seq identified SPP1 as a key downstream effector of Gria1 involved in immune and inflammatory responses. Knockdown of SPP1 suppressed CD206 and abolished the M2 polarization induced by Gria1 overexpression and HDAC1 inhibition. In a mouse TBI model, SAHA improved neurological recovery, reduced cortical lesions, upregulated Gria1 and SPP1, increased CD206, decreased CD86, and attenuated microglial activation. Collectively, pharmacological inhibition of HDAC1-mediated histone delactylation at the Gria1 promoter enhances Gria1-dependent SPP1 expression, thereby promoting microglial M2 polarization and attenuating neuroinflammation after TBI.