Obesity, insulin resistance, diabetes and hyperlipidemia are leading causes of cardiovascular pathology and mortality. SIRT1, a mammalian ortholog of silent information regulator 2 (Sir2), is an NAD-dependent deacetylase mediates the effects of caloric restriction to expend lifespan. The energy sensor AMP-activated protein kinase (AMPK) and its upstream kinase, LKB1, have been implicated in the therapeutic effect of metformin, an anti-diabetic drug used worldwide. My recent studies and others indicate that both master metabolic regulators, SIRT1 and AMP-activated protein kinase (AMPK), are activated by polyphenols including resveratrol present in red wine. However, If and how SIRT1 is linked to AMPK signaling, lipid metabolism and atherosclerosis remains elusive. I have established in vitro hepatocyte models and in vivo models of type 1 and type 2 diabetic LDL receptor-deficient (LDLR-/-) mice to provide new evidence that 1) polyphenols strongly prevent the inhibition of AMPK, and upregulation of acetyl-CoA carboxylase (ACC) and regulatory element binding protein (SREBP), two key downstream effectors of AMPK, and reduce hepatic lipid accumulation, thereby attenuating diabetic hyperlipidemia and atherosclerosis;2) the stimulation of AMPK and lipid-lowering action of polyphenols are abrogated by inhibition of SIRT1 or AMPK in vitro;3) hepatocyte overexpression of SIRT1 stimulates AMPK, downregulates SREBP function and lowers lipids in vitro and in vivo. The CENTRAL HYPOTHESIS of this proposal is that SIRT1 activation by polyphenols functions as a novel upstream regulator of LKB1/AMPK signaling to modulate hepatocyte lipid metabolism and has potential therapeutic implications in the hyperlipidemia and atherosclerosis caused by diabetes. In my three SPECIFIC AIMS, I will test the hypothesis that 1) SIRT1 activation by polyphenols regulates AMPK activity via a mechanism underlying deacetylation of LKB1;2) polyphenols and SIRT1, via LKB1/AMPK signaling, control ACC and SREBP and their lipid metabolic consequences in hepatocytes in vitro;and 3) the in vivo integrated function of SIRT1 and LKB1/AMPK has been implicated in the development of hyperlipidemia and atherosclerosis in diabetes and in the protective effect of polyphenols against metabolic disease. Innovative aspects of the application include: new insights into the molecular mechanism for the function of SIRT1 as a novel upstream signaling of LKB1/AMPK pathway to control lipid metabolism, and the new concept that SIRT1, via LKB1/AMPK/SREBP signaling, regulates lipid metabolism and atherosclerosis in diabetes. Thus, the proposed studies will emphasize targeting SIRT1/LKB1/AMPK as a new therapeutic avenue to benefit hyperlipidemia and atherosclerosis in diabetes and age-related metabolic disorder.
Although caloric restriction (CR) extends the lifespan and delays the onset of age-related diseases such as diabetes, current trends in unlikelihood that patient with obesity and diabetes would be willing or able to maintain a calorie-restricted diet. This situation gives rise to an important question: "what agents can mimic the beneficial effect of CR?". Ongoing work will employ both in vitro hepatocyte model and in vivo type 2 diabetic mouse models to determine how polyphenols including resveratrol, which is present in red wine and polyphenol-rich fruits, and mimics the beneficial effect of CR, protects against hyperlipidemia and accelerated atherosclerosis in diabetes through activation of the longevity factor SIRT1 and the energy sensor AMPK signaling. Activation of SIRT1/AMPK signaling will provide new therapeutic targets for intervention of diabetes and its vascular complications.
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