USP7 alleviates neuronal inflammation and apoptosis in spinal cord injury via deubiquitinating NRF1/KLF7 axis

BackgroundUbiquitin-specific protease 7 (USP7) has been found to be associated with motor function recovery after spinal cord injury (SCI). Therefore, its role and mechanism in SCI process need further exploration.MethodsSCI rat models were established via performing laminectomy at the T9-T11 spinal vertebrae and cutting spinal cord tissues. SCI cell models were constructed by inducing PC12 cells with lipopolysaccharide (LPS). The protein levels of USP7, nuclear respiratory factor 1 (NRF1), Kr & uuml;ppel-like factor 7 (KLF7) and apoptosis-related markers were detected by western blot. Cell viability and apoptosis were tested by cell counting kit-8 assay and flow cytometry. The contents of inflammatory factors were examined using ELISA. The interaction between NRF1 and USP7 or KLF7 was analyzed by co-immunoprecipitation assay, chromatin immunoprecipitation assay and dual-luciferase reporter assay, respectively.ResultsUSP7 was downregulated in SCI rat models and LPS-induced PC12 cells. Overexpressed USP7 promoted viability, while repressed apoptosis and inflammation in LPS-induced PC12 cells. USP7 could stabilize NRF1 protein expression via deubiquitination, and NRF1 knockdown reversed the protective effect of USP7 against LPS-induced PC12 cell injury. NRF1 is bound to KLF7 promoter to enhance its transcription. NRF1 overexpression inhibited LPS-induced PC12 cell inflammation and apoptosis via increasing KLF7 expression.ConclusionUSP7 alleviated inflammation and apoptosis in LPS-induced PC12 cells via NRF1/KLF7 axis, indicating that targeting of USP7/NRF1/KLF7 axis might be a promising treatment strategy for SCI.