Understanding the mechanistic basis of chronic aberrant regulation of SREBP-1c and its downstream lipogenic enzyme targets in chronic hyperinsulinemic states has been a focus of research in our laboratory. Specifically, we have been studying the insulin-responsive cis-acting elements of the rat SREBP-1c promoter and have found that its full response requires participation of multiple cis-acting sites that bind to LXR1, NF-Y, Sp1 and SREBP-1c itself. As a logical extension of our ongoing studies we now propose to examine the molecular mechanisms by which polyunsaturated fatty acids (PUFA), specifically n-3 PUFA, reduce transcription of SREBP-1c, thereby effectively mitigating the effect of insulin to induce lipogenic enzyme expression and hepatic lipid overproduction in hyperinsulinemic states. To systematically examine the cellular and molecular mechanisms by which n-3 PUFA mitigate induction of SREBP-1c gene expression we propose a three- pronged hypothesis: (i) n-3 PUFA modulate the interaction of LXR1 with transcription factors (Sp1, SREBP- 1c), co-activators (SRC-1, CBP), and co-repressors (NcoR, SMRT, HDAC), (ii) n-3 PUFA alter binding and/or metabolism of endogenous ligands of LXR1 and (iii) the full complement of nuclear factors and their posttranslational modifications that modulate SREBP-1c promoter by insulin and PUFA remain to be defined. POTENTIAL IMPACT ON VETERAN'S HEALTH CARE: The prevalence of obesity and Type II Diabetes is extraordinarily high among veterans receiving health care within the VA Health Care System. The dyslipidemia that accompanies these disorders is a significant risk factor for atherosclerotic vascular disease which is also highly prevalent in the VA population. The combined effects of vascular complications of obesity and Type II Diabetes in the Veteran population results in significant morbidity and mortality among Veterans. Further, providing care related to these complications entails significant cost to the VA Health Care System. Effective treatment modalities for the dyslipidemia that accompanies obesity, Type II Diabetes, and Metabolic Syndrome, primarily hypertriglyceridemia and low HDLC, are needed. Research such as the proposed studies that examines the molecular mechanisms underlying dyslipidemia in hyperinsulinemic states will provide needed information for development of new, effective treatments.

Public Health Relevance

Both obesity and adult onset (Type II) diabetes increase the risk of heart attack and stroke. Risk factors for heart disease in such individuals include increased blood sugar, increased blood pressure, increased levels of blood fat, specifically triglyceride, and decreased levels of "good" cholesterol (HDL). We are studying the underlying mechanisms by which the hormone insulin increases blood triglyceride levels in individuals who are overweight or have type II diabetes. Such individuals have high insulin levels. Our hypothesis is that insulin increases production of fat (triglyceride) in such individuals by increasing levels of a protein called sterol regulatorybinding-protein-1c or SREBP-1c. We are examining the ability of highly unsaturated fatty acids (Polyunsaturated Fatty Acids or PUFA) derived from fish oil to reduce fat production in the liver by decreasing levels of SREBP-1c. Understanding how PUFA causes this will lead to more effective treatments for high triglyceride levels in individuals with obesity and type II diabetes to reduce risk of heart attack and stroke.

National Institute of Health (NIH)
Veterans Affairs (VA)
Non-HHS Research Projects (I01)
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Endocriniology A (ENDA)
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Memphis VA Medical Center
United States
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