In the early stages of nonalcoholic fatty liver disease (NAFLD), triglycerides accumulate in hepatocytes. Diacylglycerol acyltransferase 2 (DGAT2) catalyzes the final step in hepatocyte triglyceride biosynthesis. DGAT2 antisense oligonucleotide (ASO) treatment improved hepatic steatosis dramatically in a previous study of obese mice. According to the 2-hit hypothesis for progression of NAFLD, hepatic steatosis is a risk factor for nonalcoholic steatohepatitis (NASH) and fibrosis. To evaluate this hypothesis, we inhibited DGAT2 in a mouse model of NASH induced by a diet deficient in methionine and choline (MCD). Six-week-old genetically obese and diabetic male db/db mice were fed either the control or the MCD diet for 4 or 8 weeks. The MCD diet group was treated with either 25 mg/kg DGAT2 ASO or saline intraperitoneally twice weekly. Hepatic steatosis, injury, fibrosis, markers of lipid peroxidation/oxidant stress, and systemic insulin sensitivity were evaluated. Hepatic steatosis, necroinflammation, and fibrosis were increased in saline-treated MCD diet-fed mice compared to controls. Treating MCD diet-fed mice with DGAT2 ASO for 4 and 8 weeks decreased hepatic steatosis, but increased hepatic free fatty acids, cytochrome P4502E1, markers of lipid peroxidation/oxidant stress, lobular necroinflammation, and fibrosis. Progression of liver damage occurred despite reduced hepatic expression of tumor necrosis factor alpha, increased serum adiponectin, and striking improvement in systemic insulin sensitivity. Conclusion: Results from this mouse model would suggest accumulation of triglycerides may be a protective mechanism to prevent progressive liver damage in NAFLD. (HEPATOLOGY 2007;45:1366-1374 N onalcoholic fatty liver disease (NAFLD) is one of the most common liver diseases in the world. 1-3 Clinically, the most common disorder associated with NAFLD is insulin resistance. 4 Accumulation of triglycerides in hepatocytes is the hallmark of NAFLD. Recent studies have demonstrated that acyl-coenzyme A:diacylglycerol acyltransferase 2 (DGAT2) plays an important role in hepatocyte triglyceride synthesis and hepatic steatosis. 5,6 Triglyceride synthesis is increased in the fatty livers that accompany obesity and type 2 diabetes in humans and mice. 7 According to the 2-hit hypothesis for NAFLD progression, hepatic steatosis is a risk factor for nonalcoholic steatohepatitis (NASH) and fibrosis. 8,9 In a previous study, knocking down DGAT2 in the livers of mice with diet-induced obesity (DIO) and diabetes successfully prevented hepatic steatosis. 10 Because only mild NASH and little fibrosis develop in mice with DIO, however, that model is not helpful for determining if inhibiting steatosis prevents progression of NAFLD to more advanced stages of liver damage (i.e., NASH and liver fibrosis).To address this question, we studied a recently described model of progressive obesity-related NASH in db/db mice. 11,12 Db/db mice spontaneously develop obe- Gastroenterology, Snyderman GSRB I, Suite 1073, 595 LaSalle Street, Box 3256,...

In bile duct-ligated (BDL) rodents, as in humans with chronic cholangiopathies, biliary obstruction triggers proliferation of bile ductular cells that are surrounded by fibrosis produced by adjacent myofibroblastic cells in the hepatic mesenchyme. The proximity of the myofibroblasts and cholangiocytes suggests that mesenchymal-epithelial crosstalk promotes the fibroproliferative response to cholestatic liver injury. Studying BDL mice, we found that bile duct obstruction induces activity of the Hedgehog (Hh) pathway, a system that regulates the viability and differentiation of various progenitors during embryogenesis. After BDL, many bile ductular cells and fibroblastic-appearing cells in the portal stroma express Hh ligands, receptor and/or target genes. Transwell cocultures of an immature cholangiocyte line that expresses the Hh receptor, Patched (Ptc), with liver myofibroblastic cells demonstrated that both cell types produced Hh ligands that enhanced each other's viability and proliferation. Further support for the concept that Hh signaling modulates the response to BDL was generated by studying PtcLacZ mice, which have an impaired ability to constrain Hh signaling due to a heterozygous deficiency of Ptc. After BDL, PtcLacZ mice upregulated fibrosis gene expression earlier than wild-type controls and manifested an unusually intense ductular reaction, more expanded fibrotic portal areas, and a greater number of lobular necrotic foci. Our findings reveal that adult livers resurrect developmental signaling systems, such as the Hh pathway, to guide remodeling of the biliary epithelia and stroma after cholestatic injury.

Background/Aims-Factors released during liver injury, such as platelet derived growth factor-BB (PDGF) promote accumulation of myofibroblastic hepatic stellate cells (MFB) that drive the pathogenesis of cirrhosis. The Hedgehog (Hh) pathway regulates remodeling of other injured tissues. This study evaluates the hypothesis that autocrine production of Sonic hedgehog (Shh) promotes MFB growth.