Abstract
BackgroundHepatospecific deletion of PTEN results in constitutive activation of Akt and increased lipogenesis. In mice, the addition of a high fat diet (HFD) downregulates lipogenesis. The aim of this study was to determine the effects of a HFD on hepatocellular damage induced by deletion of PTEN.Methods12 Week old male flox/flox hepatospecific PTEN mice (PTENf/f) or Alb-Cre controls were fed a HFD composed of 45% fat-derived calories (from corn oil) or a normal chow. Animals were then analyzed for hepatocellular damage, oxidative stress and expression of enzymes involved in fatty acid metabolism.ResultsIn the Alb-Cre animals, the addition of a HFD resulted in a significant increase in liver triglycerides and altered REDOX capacity as evidenced by increased GPX activity, decreased GST activity and decreased hepatic concentrations of GSSG. In addition, SCD2, ACLY and FASN were all downregulated by the addition of HFD. Furthermore, expression of PPARα and PPARα-dependent proteins Cyp4a and ACSL1 were upregulated. In the PTENf/f mice, HFD resulted in significant increased in ALT, serum triglycerides and decreased REDOX capacity. Although expression of fatty acid synthetic enzymes was elevated in the chow fed PTENf/f group, the addition of HFD resulted in SCD2, ACLY and FASN downregulation. Compared to the Alb-Cre HFD group, expression of PGC1α, PPARα and its downstream targets ACSL and Cyp4a were upregulated in PTENf/f mice.ConclusionsThese data suggest that during conditions of constitutive Akt activation and increased steatosis, the addition of a HFD enhances hepatocellular damage due to increased CD36 expression and altered REDOX status. In addition, this work indicates HFD-induced hepatocellular damage occurs in part, independently of Akt signaling.
Highlights
Non-alcoholic fatty liver disease (NAFLD) is a leading cause of liver disease in the United States today
In a subset of NAFLD patients, symptoms progress to nonalcoholic steatohepatitis (NASH) and in this inflammatory environment a further subset will progress to fibrosis and cirrhosis [1,2,3,4]
To validate the penetrance of the Alb-Cre promoter, lysates were prepared from Chow and high fat diet (HFD) fed Alb-Cre and PTENf/f livers and Western blotted for PTEN, pSer473Akt and total Akt
Summary
Non-alcoholic fatty liver disease (NAFLD) is a leading cause of liver disease in the United States today. A common phenotype of NAFLD is an environment characterized by pronounced hepatic lipid accumulation and enhanced oxidative stress. In a subset of NAFLD patients, symptoms progress to nonalcoholic steatohepatitis (NASH) and in this inflammatory environment a further subset will progress to fibrosis and cirrhosis [1,2,3,4]. Many animal models of NAFLD utilize a long term feeding of a diet high in polyunsaturated fatty acids to induce hepatocellular steatosis. Additional hepatic insults such as cholesterol or oxidized low density lipoproteins are added as well [5,6,7]. In. Hepatospecific deletion of PTEN results in constitutive activation of Akt and increased lipogenesis. The addition of a high fat diet (HFD) downregulates lipogenesis.
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