Dual‐Specificity Phosphatase 9 Protects Against Nonalcoholic Fatty Liver Disease in Mice Through ASK1 Suppression

Nonalcoholic fatty liver disease (NAFLD), ranging from nonalcoholic fatty liver to nonalcoholic steatohepatitis (NASH), is the leading cause of chronic liver diseases. Until now, no medications for NAFLD have been approved by relevant governmental agencies. Dual‐specificity phosphatase 9 (Dusp9) is a member of the DUSP protein family. Dusp9 is expressed in insulin‐sensitive tissues, and its expression may be modified with the development of insulin resistance (IR). However, the molecular targets and mechanisms of Dusp9 action on NAFLD and NASH remain poorly understood. In this study, using conditional liver‐specific Dusp9‐knockout (Dusp9‐CKO) mice and Dusp9‐transgenic mice, we showed that Dusp9 was a key suppressor of high‐fat diet–induced hepatic steatosis and inflammatory responses and that Dusp9 deficiency aggravated high‐fat high‐cholesterol diet–induced liver fibrosis. Dusp9 was shown to exert its effects by blocking apoptosis signal–regulating kinase 1 (ASK1) phosphorylation and the subsequent activation of p38 and c‐Jun NH2‐terminal kinase signaling. Conclusion: Hepatocyte Dusp9 prevents NAFLD and NASH progression in mice, including lipid accumulation, glucose metabolism disorders, and enhanced inflammation and liver fibrosis, in an ASK1‐dependent manner; these findings suggest that Dusp9 may be a promising therapeutic target for the treatment of NAFLD and NASH.