Morbidity and mortality from atherosclerosis are associated with complicated atherosclerotic lesions due to plaque rupture and severe hemispheric neurological symptoms. However, a group of atherosclerotic patients remain asymptomatic because of plaque stability. It is not known if and how the stable and unstable plaques are different biochemically, and how the immune system regulates plaque stability. The studies over the past several years in our laboratory suggest that insulin-like growth factor-1 (IGF-1) is a potent chemoattractant for monocytes, and possess strong mitogenic and anti-apoptotic activity for vascular smooth muscle cells (VSMCs). Furthermore, we have shown that in stable plaques there is increased density of VSMCs and decreased number of macrophages and T-lymphocytes, whereas reverse is true with unstable plaques. We propose the hypothesis that decreased expression and activity of IGF-1 receptors (IGF-1R) on VSMCs due to cytokines released by proliferating and activated T-lymphocytes (IFN-gamma) and macrophages (IL-12 and IL-18) leads to apoptosis resulting in the instability of atherosclerotic plaques observed in symptomatic patients. To these ends the Specific Aims of this application in the carotid plaque VSMCs of both symptomatic and asymptomatic patients are:
Specific Aim 1 : We will examine IGF-l-induced survival of plaque VSMCs of both symptomatic and asymptomatic patients in the presence and absence of human atheroma-associated cytokines (11-12, IL-18 and IFN-gamma) using TUNEL, annexin V labeling, time-lapse videomicroscopy, and caspase 3 activity. For comparison, VSMCs from normal carotid artery will be run in parallel.
Specific Aim 2 : We will examine the underlying mechanisms of cytokine-induced decrease in IGF-l-induced survival of VSMCs. We will assess the effect of cytokines on IGF-1R and IGFBPs in VSMCs of symptomatic and asymptomatic carotid plaques.
Specific Aim 3 : We will investigate the role of FoxO family of forkhead transcription factors, specifically FKHR (FoxO1) and FKHR-L1 (FoxO3), and cyclin-dependent kinase inhibitor p27kip1 and Bim, a pro-apoptotic proteinof Bcl-2 family in IGF-l-induced survival of VSMCs from symptomatic and asymptomatic carotid plaques. A better understanding of the pathophysiology of carotid stenosis and regulatory role of IGF-1 receptors in the stability of plaques will provide opportunities to develop a more precise and cost-effective treatment.
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