Hepatic insulin resistance is associated with increased apoptosis and fibrogenesis in nonalcoholic steatohepatitis and chronic hepatitis C

Background & Aims

We aimed to elucidate whether hepatic insulin resistance may contribute to hepatocyte apoptosis and fibrogenesis in nonalcoholic fatty liver disease (NAFLD) and in chronic hepatitis C virus (HCV) infection.

Methods

Twenty-seven nonalcoholic steatosis (NAST), 24 nonalcoholic steatohepatitis (NASH), 71 HCV, and 29 patients with histological normal liver (NL) were studied. Real-time PCR, the TUNEL assay, and Western blots were used to assess insulin-signaling molecules, hepatocyte apoptosis, antiapoptotic mediators, active caspase 3, and type I collagen in liver biopsies. HCV core-transfected human hepatocytes were used as an in vitro model.

Results

In NAFLD patients, hepatic levels of insulin receptor substrate (IRS) 1, IRS2 2, the p85α subunit of phosphatidylinositol 3-kinase (p85α), phosphorylated protein kinase B (pAkt), phosphorylated forkhead box-containing protein O subfamily-1 (FoxO), and phosphorylated 5′ adenosine monophosphate-activated protein kinase (pAMPK) as well as the antiapoptotic mediators B-cell lymphoma 2 protein (Bcl-2) and myeloid cell leukemia protein-1 (Mcl-1) were significantly lower in NASH than in NAST and NL. Furthermore, hepatocyte apoptosis and increased active caspase 3 were only present in NASH. In HCV patients, hepatic insulin signaling was markedly impaired, regardless of viral genotype and the presence of steatosis paralleled with enhanced apoptosis. In cultured human hepatocytes, HCV core protein decreased pAkt and increased phosphorylation of c-Jun N-terminal kinase (JNK). This effect was more pronounced in lipid-loaded hepatocytes.

Conclusions

Hepatic insulin signaling is impaired in NASH and HCV patients, and downregulation of insulin-sensitive targets is associated with increased apoptosis and fibrogenesis in both conditions. JNK might be a target for HCV-induced insulin resistance.

Abbreviations: Akt, protein kinase B, AMPK, 5′ adenosine monophosphate-activated protein kinase, AST, aspartate aminotransferase, ALT, alanine aminotransferase, Bcl-2, B-cell lymphoma 2 protein, CHL, Chang human liver cells, DGAT, diglycerol acyltransferase, ECHS1, enoyl-CoA hydratase, ECM, extracellular matrix, FoxO1, forkhead box-containing protein O subfamily-1, HCV, hepatitis C virus, HOMA, homeostatic model assessment, HSC, hepatic stellate cell, IR, insulin resistance, IRS, insulin receptor substrate, JNK, c-Jun N-terminal kinase, Mcl-1, myeloid cell leukemia protein-1, NAFLD, nonalcoholic fatty liver disease, NASH, nonalcoholic esteatohepatitis, NAST, nonalcoholic steatosis, NF-κB, nuclear factor kappa B, NL, normal liver, PNPLA3, patatin-like phospholipase domain containing 3, PI3K, phosphatidylinositol 3-kinase, qPCR, quantitative real-time polymerase chain reaction, TNF, tumor necrosis factor, TRAIL, tumor necrosis factor-related apoptosis-inducing ligand, TUNEL, terminal deoxynucleotidyltransferase-mediated dUTP nick-end labelling

Keywords: Insulin resistance, Nonalcoholic fatty liver disease, Hepatitis C virus, Apoptosis, Fibrogenesis