Cardiovascular pathologies in diabetic patients are caused by the acceleration of atherosclerosis. Abnormalities such as hyperlipidemia, insulin resistance and hyperglycemia are important risk factors for cardiovascular disease (CVD) in diabetes. Clinical studies such as DCCT/EDIC, ACCORD, and ADVANCE showed that intensive glycemic control lowers the risk for CVD in type 1 but not type 2 diabetic patients suggesting that insulin resistance at the vascular wall could be very important in the development of CVD complications in type 2 DM. Previously, we have proposed a novel concept that "selective" inhibition of insulin's anti-atherogenic actions mediated by the activation of IRS/PI3K/Akt pathways could be a major cause of cardiovascular complications in diabetes. We showed that diabetes or insulin resistance will inhibit insulin's signaling via IRS-1/PI3K/Akt pathway but may enhance insulin's actions through MAPK pathways, thus causing "selective insulin resistance". Recently, we have obtained the first definitive in vivo evidence to show that insulin has "anti-atherogenic" actions in the endothelium, since mice with deletion of both insulin receptors in the endothelial cells (EC) and apolipoprotein E (apoE-/-) exhibited significantly more atherosclerosis (2X) than apoE-/- single gene deletion mice in parallel with a 50% reduction in Akt/eNOS activation. We have also reported that hyperglycemia and free fatty acids (FFA) can activate protein kinase C (PKC), specifically the 21/2 and 4 isoforms, and induce "selective insulin resistance" in the microvessels or arteries of diabetic or insulin resistant animals. We also showed that "selective insulin resistance" also exists in the myocardium of diabetic or insulin resistant rodents, which could be responsible for the decreases in VEGF expression and collateral vessel formation in the heart observed in these conditions. Thus, our hypothesis suggests that abnormal metabolites of diabetes, resulting from insulin deficiency or resistance, will activate PKC 2 and 4 isoforms, inhibit the IRS-1/PI3K/Akt pathway of insulin signaling via PI3K and resulting in the loss of insulin's "anti-atherogenic" and angiogenic actions. Thus, we are proposing to: (1) Determine whether enhancing insulin's actions at IRS1/2 step by overexpressing IRS-1 in the endothelium will improve endothelial function and decrease atherosclerosis in apoE-/- mice. (2) Identify the role of phospho-Thr86 of p85/PI3K in causing selective insulin resistance in EC and correlate the changes of phospho-Thr86/p85 with vascular insulin resistance and PKC activation in vivo. Evaluate the effect of PKC22 and 4 activation and changes in phosphorylation and function of PI10/PI3K and Akt1/2 as additional targets of PKC to inhibit insulin's signaling in EC. (3) Evaluate the effect of overexpressing PKC22 and 4 isoforms targeted to endothelial cells to cause "selective insulin resistance" and accelerate atherosclerosis when crossbred with apoE-/- mice.
Heart diseases are the major causes of death among diabetic patients. We have found that insulin normally has several actions that can prevent atherosclerosis, which are lost when diabetes develops. We have proposed studies, which could provide explanations and potential interventions, such as the use of inhibitor of an enzyme, PKC, that can improve insulin's effect on the heart and the blood vessels, and decrease the risk of cardiovascular deaths in diabetic patients.
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