NSUN6 promotes neuronal axon regeneration after traumatic brain injury by enhancing HMGB1 expression via m5C modification

Traumatic brain injury (TBI) often results in neurofunctional impairments that can be mitigated by promoting axonal regeneration. NOP2/Sun RNA methyltransferase 6 (NSUN6), a 5-methylcytosine (m5C) methyltransferase, has been implicated in TBI recovery. This study investigated the role and mechanism of NSUN6 in axonal regeneration following TBI. C57BL/6 mice were used to establish a controlled cortical impact (CCI) model. Hematoxylin and eosin (H&E) staining and quantitative real-time PCR (qRT-PCR) were performed to assess axonal injury and regeneration and NSUN6 expression in brain tissues, respectively. Pearson correlation analysis evaluated the relationship between NSUN6 expression and axonal regeneration. Neurological function was assessed using modified neurological severity scores (mNSS) and balance beam tests. Primary cortical neurons were isolated to establish a stretch injury model, and the effect of NSUN6 on axonal regeneration was evaluated by detecting GAP-43 and βIII-tubulin expression. Mechanisms were explored using Methylated RNA immunoprecipitation (MeRIP), RNA immunoprecipitation (RIP), and dual luciferase assays. Results indicated that NSUN6 expression increased over time after TBI and was positively correlated with axonal regeneration. NSUN6 overexpression promoted axonal regeneration in the stretch injury model and upregulated HMGB1 expression by enhancing m5C methylation. HMGB1 knockdown inhibited axonal regeneration induced by NSUN6 overexpression. Additionally, NSUN6 overexpression improved neurological function and axonal regeneration in TBI mice. In conclusion, NSUN6 promotes axonal regeneration following TBI by enhancing HMGB1 expression through m5C methylation, providing a potential target for TBI therapeutics.