The overall goal of this proposal is to gain new understanding into the mechanisms of atherosclerosis. The specific objective is to investigate how platelet-derived growth factor (PDGF) regulates glucose transport and insulin receptor signaling to influence phenotypic changes in vascular smooth muscle cells (VSMCs). The development of vascular complications in nondiabetic and diabetic patients correlates closely with increased VSMC glucose metabolism and dysregulated insulin signaling. Preliminary studies reveal that PDGF-induced VSMC proliferation is accompanied by enhanced glucose uptake through glucose transporters (GLUTs) and impaired insulin receptor signaling. Serine phosphorylation or downregulation of insulin receptor substrates (IRS-1/2) by PDGF attenuates insulin-induced IRS-associated phosphoinositide 3-kinase (PI 3-kinase) activity. We therefore hypothesize that PDGF contributes to vascular proliferative disease by altering glucose transport and insulin receptor signaling in VSMCs.
Specific Aim 1 will determine the mechanism by which PDGF alters VSMC glucose transport and insulin signaling and its functional consequences in the glycolytic, proliferative, and contractile phenotype.
This aim will use human aortic VSMCs to determine the differential effects of PDGF and insulin on glucose uptake, glycolysis, GLUT-1/GLUT-4 expression and translocation, IRS- 1/2 expression and phosphorylation, and the key signaling events/SRF transcription factor that regulate glycolytic, proliferative, and contractile phenotype. Constitutive overexpression and gene-silencing strategies will be employed to elucidate the distinct roles of GLUT isoforms and IRS isoforms in regulating VSMC phenotype.
Specific Aim 2 will determine the mechanism by which systemic insulin resistance and/or GLUT4 deficiency alter injury-induced neointimal growth and PDGF- vs insulin-induced glucose transport.
This aim will employ femoral arterial injury model in high-fat fed mice and GLUT4-null mice, to determine the roles of endogenous PDGF and glucose transporters toward neointimal growth, and the effects of intravenous PDGF vs insulin on neointimal glucose metabolism.
Specific Aim 3 will determine the mechanism by which diabetes alters VSMC glucose transport and insulin signaling and its functional consequences in conduit vessel neointimal growth and vasoconstriction.
This aim will utilize venous vs arterial grafts from nondiabetic and diabetic patients to determine how diabetes alters the chronic effects of PDGF (vs insulin) on VSMC glucose transport, IRS-1/2 signaling, and phenotypic changes. In addition, this aim will determine how diabetes alters the acute effects of vasoactive agonist, serotonin (vs insulin) on smooth muscle glucose uptake and contractility. Together, these studies will provide a better understanding of dysregulated glucose transport and metabolism that contribute to exaggerated VSMC growth and increased vasoreactivity in insulin-resistant states. The rationale for the proposed studies is that it will provide new insights into treatment strategies to ameliorate restenosis after angioplasty and stenotic complications in nondiabetic and diabetic patients.
Abnormal increases in glucose transport and metabolism in vascular smooth muscle cells (VSMCs) are implicated in the development of vascular proliferative diseases such as atherosclerosis, restenosis after angioplasty, vein graft stenosis, and vasospasm. The proposed studies investigate the detrimental effects of platelet-derived growth factor (PDGF) toward increased glucose uptake and impaired insulin receptor signaling in VSMCs. Strategies to inhibit PDGF receptor signaling may prevent dysregulated glucose metabolism and insulin signaling to improve vascular function in nondiabetic and diabetic patients.
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