OTUD7B inhibited hepatic injury from NAFLD by inhibiting K48-linked ubiquitination and degradation of β-catenin

Abstract

Non-alcoholic fatty liver disease (NAFLD) is the prevalent liver disease. Ovarian tumor domain-containing 7B (OTUD7B) is a deubiquitinating enzyme and its role in NAFLD remains unclear. In high-fat diet (HFD)-induced NAFLD mouse model and palmitic acid (PA)-treated HepG2 cells, OTUD7B expression was decreased. Adenoviral overexpression of OTUD7B in mice resulted in reduced body weight and liver injury, with decreased serum aminotransferase (ALT) and aspartate aminotransferase (AST) levels. OTUD7B overexpression attenuated hepatic lipid deposition (serum TG, TC, LDL-C, HDLC, and FFA levels), which might be through the suppression of lipogenesis and β-oxidation-related genes. The contents of hepatic inflammatory factors (TNF-α, IL-6, and IL-1β) were decreased following OTUD7B overexpression in NAFLD mice. A mechanism study indicated that the protective effect of OTUD7B overexpression might be associated with β-catenin signal activation. OTUD7B overexpression promoted PA-induced β-catenin activity in TopFlash assay, and increased total β-catenin and c-myc levels in cells. The increase in β-catenin levels was contributed to the stabilization via inhibiting K48-linked ubiquitination and proteasomal degradation by OTUD7B. NR4A2 role in NASH has been proved. NR4A2 ChIP-seq and RNA-seq data excluded transcriptional regulation of NR4A2 to OTUD7B, and it was experimentally evidenced that NR4A2 bound to OTUD7B promoter region and positively transcriptionally regulate OTUD7B expression. In summary, OTUD7B overexpression ameliorated hepatic inflammation and steatosis in NAFLD. The possible mechanism of OTUD7B might be through the inhibition of β-catenin degradation by removing K48-linked ubiquitination, which might be regulated by NR4A2.