HDAC1 dysregulation promotes pro-inflammatory microglial activation and aggravates post-stroke neuroinflammation.

BACKGROUND: Histone deacetylase 1 (HDAC1) is a key epigenetic regulator involved in DNA repair and neuronal survival. While HDAC1 downregulation has been implicated in ischemic brain injury, its role in regulating microglial functional shift and neuroinflammation remains unclear. This study aimed to investigate how HDAC1 dysfunction influences microglial activation states and contributes to neuroinflammatory processes in ischemic stroke. METHODS: Using a rat model of endothelin-1-induced focal cerebral ischemia, HDAC1 knockdown was achieved via stereotactic co-injection of HDAC1 siRNA. Immunofluorescence, Western blotting, ELISA, and oxidative stress assays were performed to assess neuroinflammation, microglial polarization, and related signalling pathways. In parallel, HDAC1 was silenced in HMC3 human microglial cells, with or without IFN-γ stimulation, to evaluate transcriptional responses associated with pro-inflammatory activation. Finally, HDAC1 was selectively reactivated in vivo and in vitro using Compound 5104434 to assess behavioural, neuroinflammatory and mechanistic effects after ischaemic or inflammatory injury. RESULTS: HDAC1 knockdown in vivo led to a pronounced shift towards a pro-inflammatory microglial activation, evidenced by increased CD86 expression, along with elevated levels of IL-1β, IL-6, TNF-α, ROS, LDH and MMP activity. T-cell infiltration was also significantly enhanced. In vitro, HDAC1 deficiency sensitized microglia to IFN-γ, further amplifying the expression of pro-inflammatory genes. Mechanistically, HDAC1 knockdown activated the NF-κB pathway and its downstream effectors MAP3K8, AP-1 and SAT1, while IFN-γ stimulation predominantly drove STAT3 phosphorylation. Notably, pNF-κB was upregulated even in the absence of exogenous stimulation, indicating that HDAC1 intrinsically suppresses pro-inflammatory signalling. HDAC1 enzymatic reactivation by compound 5104434 promotes functional recovery and suppresses NF-κB-driven microglial activation after stroke. CONCLUSION: HDAC1 acts as a key repressor of NF-κB-driven pro-inflammatory microglial activation and neuroinflammation in stroke. Its loss exacerbates inflammatory cascades, immune cell infiltration, and neuronal injury, underscoring HDAC1 as a potential therapeutic target for limiting secondary brain damage after ischaemic stroke.