“
“Accumulation of cytoplasmic triacylglycerol (TG) underlies hepatic steatosis, a major cause of cirrhosis. The pathways of cytoplasmic TG metabolism are not well known in hepatocytes, but evidence suggests an important role in lipolysis for

adipose triglyceride lipase (ATGL). We created mice with liver-specific inactivation of Pnpla2, the ATGL gene. These ATGLLKO mice had severe progressive periportal macrovesicular and pericentral microvesicular hepatic steatosis (73, 150, and 226 μmol TG/g liver at 4, 8, and 12 months, respectively). However, plasma levels of glucose, TG, and cholesterol were similar to those of controls. Fasting 3-hydroxybutyrate level was normal, but in thin sections of liver, beta oxidation of palmitate was Selleck Apoptosis Compound Library decreased by one-third in ATGLLKO mice compared with controls. Tests of very low-density lipoprotein production, glucose, and insulin tolerance and gluconeogenesis from pyruvate were normal. Plasma alanine aminotransferase levels were elevated in ATGLLKO mice, but histological estimates of inflammation and fibrosis and messenger RNA (mRNA) levels of tumor necrosis factor-α and interleukin-6 were similar to or lower than those in controls. ATGLLKO cholangiocytes also showed cytoplasmic lipid droplets,

demonstrating that ATGL is also a major lipase in cholangiocytes. There was a 50-fold reduction of hepatic diacylglycerol Ku-0059436 research buy acyltransferase 2 mRNA level and a 2.7-fold increase of lipolysosomes in hepatocytes (P < 0.001), suggesting reduced TG synthesis and increased lysosomal degradation of TG as potential compensatory mechanisms. Conclusion: Compared with the hepatic steatosis of obesity and diabetes, steatosis in ATGL deficiency is well tolerated metabolically. ATGLLKO mice will be useful for studying the pathophysiology of hepatic steatosis. (HEPATOLOGY 2011;) Nonalcoholic fatty liver is the most common chronic liver disease in the United States. Beginning as hepatic steatosis, it leads to fibrosis, cirrhosis,

and hepatocarcinoma.1-5 Excessive energy consumption is a major cause of hepatic steatosis. In mouse studies,6, 7 fatty liver is typically induced by high fat and/or carbohydrate intake, dietary methionine restriction, or hormonal or MCE immunological manipulation. Under these conditions, cytoplasmic triacylglycerol (TG) metabolism in the liver is not specifically modified. Instead, hepatic steatosis is one finding among several that occur in response to these systemic external stresses. Despite the medical importance of hepatic steatosis, the pathways of cytoplasmic TG synthesis and degradation in hepatocytes remain unclear. They are best known in white adipose tissue.8, 9 TG synthesis and lipolysis are distinct pathways. Adipose triglyceride lipase (ATGL), a lipid droplet surface protein,10 is physiologically the main TG lipase of adipose tissue.11 Hormone-sensitive lipase (HSL) is the main diacylglycerol hydrolase.