Non-alcoholic fatty liver disease (NAFLD) is a complication of metabolic syndrome and represents a spectrum of progressive liver pathologies, from simple steatosis to inflammatory non-alcoholic steatohepatitis (NASH). An estimated 25% of the American population has NAFLD and it is projected to dramatically in- crease within the next decade following the upward trend of the obesity epidemic. Activation of the metabolic regulator sirtuin-1 (SirT1), an NAD+-dependent class III histone deacetylase, can improve NAFLD. SirT1 is believed to activate beneficial metabolic processes similar to those triggered by caloric restriction and is an important regulator of hepatic lipid metabolism. Conversely, inhibition of SirT1 can promote NAFLD, as seen in mice with metabolic syndrome. In my laboratory, we have found that reversible oxidative protein adducts, including glutathione (GSH) inhibit SirT1 under these conditions. Glutaredoxin-1 (Glrx) is a thioltransferase that preferentialy removes protein GSH-adducts. Chow fed Glrx knockout mice Glrx-/-, develop obesity, hyperlipidemia, and fatty liver, which progresses to NASH upon high fat, high sucrose feeding. In these mice, upregulation of hepatic lipid synthesis was concomitant with inhibition of SirT1 by reversible glutathione adducts. Reconstitution of Glrx in the liver of Glrx-/- mice restored SirT1 activity, reversing fatty liver. To determine whether the metabolic consequences of Glrx-deficiency were truly mediated by SirT1, we overexpressed a novel, oxidant-resistant SirT1 triple cysteine mutant (C67S, C318S, C613S) in Glrx-deficient cells. Expression of our constitutively active SirT1 suppressed lipid synthesis. My central hypothesis is that the redox-regulation of Glrx and SirT1 is instrumental for hepatic lipid homeostasis. Sustained GSH-protein adducts caused by oxidative stress perturb hepatic lipid metabolism, lea ding to lipid accumulation in the liver and plasma, and eventually to metabolic syndrome. Similar effects are caused by Glrx ablation, which sustains oxidative inhibition of SirT1 promoting hepatic lipid accumulation. Based on my hypothesis and data I will study the following specific aims: #1: To determine the novel role of Glrx in regulating hepatic lipid metabolism. #2: To determine the role of SirT1 GSH adducts in regulating hepatic lipid metabolism. #3: To determine the extent to which Glrx or oxidant-resistant SirT1 mutant reverses NASH in mice with metabolic syndrome.
Fatty liver disease often occurs with obesity, diabetes and metabolic disease and is projected to dramatically increase following the upward trend of the obesity epidemic. Unexpectedly, a specific genetic mouse model to study the regulation of liver protein function by oxidants develops a build-up of fat in the blood and liver. Thus, we will use this mouse model to investigate what role oxidants play in the development of fatty liver disease and if the build-up of fats can be stopped by gene therapy.
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