KDM4A promotes microglial pyroptosis and neuropathic pain via the MEG3/SMURF2/HES1 axis

Neuropathic pain (NP) is a refractory clinical disorder in which microglial pyroptosis plays a crucial role, yet the epigenetic regulation by lysine demethylase 4A (KDM4A) remains unclear. In this study, chronic constriction injury (CCI) rat models were established, and KDM4A was knocked down to evaluate its effects on paw withdrawal mechanical threshold (PWMT), paw withdrawal thermal latency (PWTL), histopathological changes, and NLR family pyrin domain containing 3 (NLRP3)/ionized calcium-binding adapter molecule 1 (Iba1) expression. In vitro, lipopolysaccharide (LPS)-treated BV2 microglial cells were used as an inflammatory model. We found that KDM4A and the long non-coding RNA maternally expressed gene 3 (MEG3) were highly expressed in NP rats. KDM4A inhibition ameliorated CCI-induced symptoms and suppressed microglial pyroptosis in vitro. Mechanistically, chromatin immunoprecipitation (ChIP) assays revealed that KDM4A promoted MEG3 expression by removing histone H3 lysine 9 di-/trimethylation (H3K9me2/3) modifications at the MEG3 promoter. RNA immunoprecipitation (RIP) and co-immunoprecipitation (Co-IP) assays further demonstrated that MEG3 at least partially recruited the E3 ubiquitin ligase SMAD specific E3 ubiquitin protein ligase 2 (SMURF2) to bind hairy and enhancer of split 1 (HES1), promoting HES1 ubiquitination and degradation. Rescue experiments confirmed that overexpression of MEG3 or SMURF2 partially reversed the inhibitory effect of KDM4A knockdown on microglial pyroptosis in vitro. In conclusion, KDM4A facilitates microglial pyroptosis and aggravates pain responses in NP rats through the MEG3/SMURF2/HES1 axis in a manner at least partially dependent on SMURF2, providing novel insights into the epigenetic regulation of NP.