Diabetes is a progression factor for hepatic fibrosis in a high fat fed mouse obesity model of non-alcoholic steatohepatitis

Background & Aims While type 2 diabetes is an independent risk factor for worsening of human non-alcoholic steatohepatitis (NASH) in clinical studies, it has not been systematically reported in any model whether diabetes exacerbates NASH. The study aim was to determine if diabetes causes NASH progression in a mouse model of diet induced obesity. Methods C57BL/6 mice were fed a high fat diet (HFD: 45% kcal fat) or standard chow (CHOW: 12% kcal fat) for 20 weeks and some animals (HFD + DM or CHOW + DM) were also rendered diabetic by low dose streptozotocin for the final 5 weeks, to model type 2 diabetes. Serum assays included circulating insulin, triglyceride, ALT and AST, glucose, and ultrasensitive CRP and results of insulin tolerance tests. Intrahepatic lipid, triglyceride, macrophage infiltration, and fibrosis were determined. Fibrosis markers collagen-I, collagen-III, CTGF, TIMP-1, and FAP were assessed by qPCR and CTGF and collagen-I by immunostaining. Results HFD mice were obese, insulin resistant and hyperinsulinaemic, with NASH features of elevated intrahepatic lipid and macrophages, but without fibrosis. In contrast, the HFD + DM mice exhibited fibrosis in addition to these NASH features. By ANOVA, Sirius red staining at perisinusoidal, portal tract and central vein sites, collagen-I, collagen-III, FAP, and TIMP-1 transcripts and collagen-I and CTGF protein were each significantly increased in HFD + DM, compared with CHOW alone. In a further experiment, insulin treatment protected against fibrosis and CRP increases in HFD + DM, showing that diabetes, not streptozotocin, causes the fibrosis. Conclusions This novel model indicates that diet-induced NASH fibrosis is exacerbated by diabetes and attenuated by insulin therapy. While type 2 diabetes is an independent risk factor for worsening of human non-alcoholic steatohepatitis (NASH) in clinical studies, it has not been systematically reported in any model whether diabetes exacerbates NASH. The study aim was to determine if diabetes causes NASH progression in a mouse model of diet induced obesity. C57BL/6 mice were fed a high fat diet (HFD: 45% kcal fat) or standard chow (CHOW: 12% kcal fat) for 20 weeks and some animals (HFD + DM or CHOW + DM) were also rendered diabetic by low dose streptozotocin for the final 5 weeks, to model type 2 diabetes. Serum assays included circulating insulin, triglyceride, ALT and AST, glucose, and ultrasensitive CRP and results of insulin tolerance tests. Intrahepatic lipid, triglyceride, macrophage infiltration, and fibrosis were determined. Fibrosis markers collagen-I, collagen-III, CTGF, TIMP-1, and FAP were assessed by qPCR and CTGF and collagen-I by immunostaining. HFD mice were obese, insulin resistant and hyperinsulinaemic, with NASH features of elevated intrahepatic lipid and macrophages, but without fibrosis. In contrast, the HFD + DM mice exhibited fibrosis in addition to these NASH features. By ANOVA, Sirius red staining at perisinusoidal, portal tract and central vein sites, collagen-I, collagen-III, FAP, and TIMP-1 transcripts and collagen-I and CTGF protein were each significantly increased in HFD + DM, compared with CHOW alone. In a further experiment, insulin treatment protected against fibrosis and CRP increases in HFD + DM, showing that diabetes, not streptozotocin, causes the fibrosis. This novel model indicates that diet-induced NASH fibrosis is exacerbated by diabetes and attenuated by insulin therapy.