AGE DEPENDENT CONTROL OF VASCULAR SMOOTH MYOCYTE GROWTH

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Aging is a major risk for atherosclerosis. Abnormal proliferation of vascular smooth muscle cells (VSMCs) is an integral part of atherosclerotic plaque formation. Recent studies performed in my laboratory have shown the temporally and spatially coordinated induction of cdk2 and its regulatory subunits, cyclins E and A, after angioplasty in the rat carotid artery. Expression of these factors was also seen in proliferating VSMCs within human restenotic lesions, suggesting that induction of cdks and cyclins may contribute to pathological VSMC growth in injured human arteries. Induction of the cdk inhibitor p27, through suppression of cdk2 activity and transcriptional repression of cyclin A gene expression, might limit VSMC growth at late time points after angioplasty, and adenovirus- mediated overexpression of p27 after angioplasty reduced intimal lesion formation. We have also shown that elements within the -209 to +79 cyclin E and -79 to +100 cyclin A promoter regions confer cell cycle- dependent transcriptional control in VSMCs. Previous studies by others have demonstrated that the proliferative response of VSMCs to balloon angioplasty is enhanced in aged rats, suggesting that age-related increased VSMC growth kinetics might contribute-to the increasing prevalence and severity of atherosclerosis seen with aging. The broad objective of this Proposal is to elucidate age-dependent changes in the cell-cycle machinery in VSMCs that may contribute to enhanced atherosclerosis with aging. The investigations outlined in Specific Aim I will characterize the kinetics of expression and activity of cell-cycle regulatory factors after angioplasty in young and old rats. The studies outlined in Specific Aim 2 will elucidate age-related changes in the transcriptional regulation of cyclin E and A gene expression in VSMCs. Investigations outlined in Specific Aim 3 will assess the relevance of p27 to VSMC growth and intimal lesion formation in young and old animals. These studies will include gain-of function experiments using an adenovirus vector directing the overproduction of p27, and loss-of function studies using p27-deficient mice. These studies should yield valuable mechanistic insights into the cell-cycle regulatory networks underlying age-related increased VSMC proliferation and, ultimately, enhanced intimal lesion formation seen with aging.