Nonalcoholic fatty liver disease (NAFLD) has become the most common chronic liver diseases worldwide. The advantage stage of NAFLD, nonalcoholic steatohepatitis (NASH), has been recognized as the leading cause of end-stage liver injury without FDA-approved therapeutic strategy. Glutathione S-transferase Mu 2 (GSTM2) is a phase II detoxification enzyme. However, the roles of GSTM2 in NASH has not been elucidated yet.Multiple RNA-seq analyses were used to identify hepatic GSTM2 expression in NASH. In vitro and in vivo gain- or loss-of-function approaches were used to investigate the role and molecular mechanism of GSTM2 in NASH.We identified glutathione S-transferase Mu 2 (GSTM2) as a sensitive responder and effective suppressor of NASH progression. GSTM2 was significantly downregulated during NASH progression. Hepatocyte GSTM2 deficiency markedly aggravated insulin resistance, hepatic steatosis, inflammation and fibrosis induced by a high-fat diet and a high-fat/high-cholesterol diet. Mechanistically, GSTM2 sustained MAPK pathway by directly interacting with apoptosis signal-regulating kinase 1 (ASK1). Furthermore, GSTM2 directly bound to the amino-terminal (N-terminal) region of ASK1 and inhibited ASK1 N-terminal dimerization to subsequently repress ASK1 phosphorylation and the activation of its downstream JNK/p38 signaling pathway under metabolic dysfunctional condition.These data demonstrated that hepatocyte GSTM2 was an endogenous suppressor protecting against NASH progression by blocking ASK1 N-terminal dimerization and phosphorylation. This study paved a new way for the development of therapeutic strategy for NASH by activating GSTM2.The GSTM2 has a major role in regulating NASH development. We identified that GSTM2 could exert beneficial effects as an endogenous suppressor of ASK1 dimerization and its downstream ASK1-JNK/p38 signaling activation. Targeting GSTM2 is a promising therapeutic strategy for the treatment of NASH.IIT-2021-277.Copyright © 2021. Published by Elsevier B.V.