Obese and diabetic <i>db</i>/<i>db</i> mice develop marked liver fibrosis in a model of nonalcoholic steatohepatitis: role of short-form leptin receptors and osteopontin

Abstract

Obesity and type 2 diabetes are associated with nonalcoholic steatohepatitis (NASH), but an obese/diabetic animal model that mimics human NASH remains undefined. We examined the induction of steatohepatitis and liver fibrosis in obese and type 2 diabetic db/ db mice in a nutritional model of NASH and determined the relationship of the expressions of osteopontin (OPN) and leptin receptors to the pathogenesis of NASH. db/ db mice and the corresponding lean and nondiabetic db/ m mice were fed a diet deficient in methionine and choline (MCD diet) or control diet for 4 wk. Leptin-deficient obese and diabetic ob/ ob mice fed similar diets were used for comparison. MCD diet-fed db/ db mice exhibited significantly greater histological inflammation and higher serum alanine aminotransferase levels than db/ m and ob/ ob mice. Trichrome staining showed marked pericellular fibrosis in MCD diet-fed db/ db mice but no significant fibrosis in db/ m or ob/ ob mice. Collagen I mRNA expression was increased 10-fold in db/ db mice, 4-fold in db/ m mice, and was unchanged in ob/ ob mice. mRNA expressions of OPN, TNF-α, TGF-β, and short-form leptin receptors (Ob-Ra) were significantly increased in db/ db mice compared with db/ m or ob/ ob mice. Parallel increases in OPN and Ob-Ra protein levels were observed in db/ db mice. Cultured hepatocytes expressed only Ob-Ra, and leptin stimulated OPN mRNA and protein expression in these cells. In conclusion, our results demonstrate the development of an obese/diabetic experimental model for NASH in db/ db mice and suggest an important role for Ob-Ra and OPN in the pathogenesis of NASH.