Differential TM4SF5-mediated SIRT1 modulation and metabolic signaling in nonalcoholic steatohepatitis progression.

Nonalcoholic fatty liver disease is a chronic condition involving steatosis, steatohepatitis and fibrosis, and its progression remains unclear. Although the tetraspanin transmembrane 4 L six family member 5 (TM4SF5) is involved in hepatic fibrosis and cancer, its role in nonalcoholic steatohepatitis (NASH) progression is unknown. We investigated the contribution of TM4SF5 to liver pathology using transgenic and KO mice, diet- or drug-treated mice, in vitro primary cells, and in human tissue. TM4SF5-overexpressing mice exhibited nonalcoholic steatosis and NASH in an age-dependent manner. Initially, TM4SF5-positive hepatocytes and liver tissue exhibited lipid accumulation, decreased Sirtuin 1 (SIRT1), increased sterol regulatory-element binding proteins (SREBPs) and inactive STAT3 via suppressor of cytokine signaling (SOCS)1/3 upregulation. In older mice, TM4SF5 promoted inflammatory factor induction, SIRT1 expression and STAT3 activity, but did not change SOCS or SREBP levels, leading to active STAT3-mediated ECM production for NASH progression. A TM4SF5-associated increase in chemokines promoted SIRT1 expression and progression to NASH with fibrosis. Suppression of the chemokine CCL20 reduced immune cell infiltration and ECM production. Liver tissue from high-fat diet- or CCl4 -treated mice and human patients exhibited TM4SF5-dependent steatotic or steatohepatitic livers with links between TM4SF5-mediated SIRT1 modulation and SREBP or SOCS/STAT3 signaling axes. TM4SF5-mediated STAT3 activation in fibrotic NASH livers increased collagen I and laminin γ2. Both collagen I α1 and laminin γ2 suppression resulted in reduced SIRT1 and active STAT3, but no change in SREBP1 or SOCS, and abolished CCl4 -mediated mouse liver damage. TM4SF5-mediated signaling pathways that involve SIRT1, SREBPs and SOCS/STAT3 promoted progression to NASH. Therefore, TM4SF5 and its downstream effectors may be promising therapeutic targets to treat nonalcoholic fatty liver disease.