Targeting of ubiquitination and degradation of KLF15 by E3 ubiquitin ligase KBTBD7 regulates LPS-induced septic brain injury in microglia

Septic brain injury is a serious disease of the central nervous system that involves inflammation. Kelch repeat and BTB domain containing 7 (KBTBD7), an E3 ubiquitin ligase, is demonstrated to facilitate the pathological changes of various diseases, but its impact on septic brain injury is unclear. In this study, a rat model of septic brain injury was induced by cecal ligation and puncture (CLP). The neurobehavioral score and survival rate of CLP group were worse than those of sham group. In addition, CLP was found to evoke microglia activation, increase inflammation, induce the activation of NLRP3 inflammasome and NF-κB signaling pathway, and upregulate KBTBD7 expression. Immunofluorescence revealed strong positive KBTBD7 staining in CLP rat microglia. Furthermore, primary microglia were exposed to lipopolysaccharide (LPS) to explore the role and mechanism of KBTBD7. The results showed that KBTBD7 expression was increased in LPS-treated microglia. Knockdown of KBTBD7 markedly inhibited LPS-induced proinflammatory cytokine release, as well as the activation of NLRP3 inflammasome and NF-κB signaling pathway. The downstream molecular mechanism of KBTBD7 was then mined. Notably, co-immunoprecipitation (co-IP) results confirmed that KBTBD7 was a novel interacting protein of KLF transcription factor 15 (KLF15) and acted as an E3 ubiquitin ligase that catalyzed the ubiquitination degradation of KLF15 through the ubiquitin-proteasome system. Moreover, recovery experiment data suggested that KLF15 knockdown abolished the anti-inflammatory role of KBTBD7 knockdown in microglia, implying that KLF15 influenced the function of KBTBD7. Taken together, our results reveal a novel KBTBD7-KLF15 signal transduction pathway involved in septic brain injury and provide a potential therapeutic strategy for its treatment.