Atherosclerosis and its complications occur earlier and are more severe in patients with the metabolic syndrome and type 2 diabetes. Heart disease is the leading cause of death among diabetics. The mechanisms by which insulin resistance and hyperglycemia accelerate atherosclerosis are not clear, nor are the sites at which these metabolic abnormalities promote atherogenesis known. The PI has developed models of tissue-specific insulin resistance and established a signaling cascade by which insulin regulates gene expression via the forkhead transcription factor FoxO1. The proposed PPG represents an ideal venue to integrate the Pi's experience in insulin action and models of insulin resistance with the expertise of the Tall and Tabas laboratories in studies of hepatic lipoprotein turnover, macrophage cell biology and atherosclerosis. This project has two Specific Aims:
Aim 1 will investigate mechanism of FoxO1-dependent atherogenic dyslipidemia in liver. The PI will test the hypothesis that hepatic insulin resistance acts through FoxO1 to promote an atherogenic lipid profile, with increased VLDL ApoB secretion. The proposed experiments will investigate the effects of increased FoxOI-dependent transcription on triglyceride synthesis, FFA oxidation and lipoprotein turnover. In vivo studies will address whether FoxOI can modulate the susceptibilty to atherosclerosis and the role of hyperglycemia on FoxOI activity.
Aim 2 will examine the role of FoxO1/3 in the induction of Unfolded Protein Response (UPR) by cholesterol loading of macrophages. Cholesterol loading and SRA ligation induce macrophage UPR. As shown in preliminary studies by Drs. Tall and Tabas, insulin resistance in the macrophage increases susceptibility to cholesterol-induced apoptosis. This process is associated with increased CD36, SRA and CHOP expression, as well as decreased AKT and FoxO phosphorylation. The PI will generate FoxO1/3-deficient macrophages to examine the effect of altered FoxOI/3 expression on cholesterol-induced UPR and atherosclerosis. The PI will use RNA profiling of FoxOI/3-deficient macrophage to map the FoxO transcriptional targets and integrate this information with the functional analysis of macrophage FoxO1/3 in the Tabas and Tall projects. The upshot of these investigations is to provide new approaches to the therapy of lipid abnormalities in insulin resistance and type 2 diabetes based on the modulation of FoxO activity in liver and macrophages.
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