Aging is associated with the appearance of smooth muscle cells in the intimal layer of arteries and the deposition of an increased amount of connective tissue, including collagen and glycosaminoglycans in the arterial wall. Following injury to the endothelium, smooth muscle cell proliferation is increased in the vascular structures of aged rats. This suggests the hypothesis that aging is associated with a change in the regulation of smooth muscle cell proliferation and connective tissue production rather than a primary alteration in proliferative capacity itself. We propose to study the control mechanisms which regulate smooth muscle cell proliferation and connective tissue production as a function of age. We will determine the effect of important regulatory molecules such as platelet-derived growth factor (PDGF), bradykinin, epidermal growth factor and insulin on rat aortic smooth muscle cells, in vitro. Specifically, we will determine the effect of these growth factors on cell proliferation, protein accumulation, including collagen, glycosaminoglycan accumulation and prostaglandin (PG) synthesis. We will determine the relation between growth factor-induced connective tissue accumulation and growth factor-induced cell proliferation as a function of age. We will also assess whether aging interferes with PG-induced inhibition of smooth muscle cell proliferation as well as that induced by heparin-like molecules. The activation of proliferation and PG synthesis by growth factors involves phospholipases. We will examine age-related changes in phospholipase activity by using growth factors that activate predominately cell division (PDGF) or activate both PG production and cell division (bradykinin). In these studies, we will employ smooth muscle cells obtained by enzymatic dissociation. These cells will be used in primary or early passage only. Vascular smooth muscle cells obtained by this methodology closely resemble smooth muscle cells, in vivo. It is expected that these studies will provide new insights into age-related vascular alterations that contribute to cardiovascular diseases in humans.
