OTUB1 alleviates NASH through inhibition of the TRAF6‐ASK1 signaling pathways

Abstract Background and Aims NAFLD is considered as the hepatic manifestation of the metabolic syndrome, which includes insulin resistance, obesity and hyperlipidemia. NASH is a progressive stage of NAFLD with severe hepatic steatosis, hepatocyte death, inflammation, and fibrosis. Currently, no pharmacological interventions specifically tailored for NASH are approved. Ovarian tumor domain, ubiquitin aldehyde binding 1 (OTUB1), the founding member of deubiquitinases, regulates many metabolism‐associated signaling pathways. However, the role of OTUB1 in NASH is unclarified. Methods and Results We demonstrated that mice with Otub1 deficiency exhibited aggravated high‐fat diet–induced and high‐fat high‐cholesterol (HFHC) diet–induced hyperinsulinemia and liver steatosis. Notably, hepatocyte‐specific overexpression of Otub1 markedly alleviated HFHC diet–induced hepatic steatosis, inflammatory responses, and liver fibrosis. Mechanistically, we identified apoptosis signal–regulating kinase 1 (ASK1) as a key candidate target of OTUB1 through RNA‐sequencing analysis and immunoblot analysis. Through immunoprecipitation–mass spectrometry analysis, we further found that OTUB1 directly bound to tumor necrosis factor receptor–associated factor 6 (TRAF6) and suppressed its lysine 63–linked polyubiquitination, thus inhibiting the activation of ASK1 and its downstream pathway. Conclusions OTUB1 is a key suppressor of NASH that inhibits polyubiquitinations of TRAF6 and attenuated TRAF6‐mediated ASK1 activation. Targeting the OTUB1‐TRAF6‐ASK1 axis may be a promising therapeutic strategy for NASH.