Aging and arteriosclerosis. Cell cycle kinetics of young and old arterial smooth muscle cells.

Intimal cell proliferation is a "hallmark" of atherosclerosis. Myointimal hyperplasia in arteries has been shown to be dependent on age after vascular endothelial denudation and injury associated with vascular transplantation. Because myointimal thickening is greater in aged rats than in younger rats, and aortic segments from old rats transplanted into young syngeneic recipients have a greater myointimal proliferative response to injury than its host environment, the authors examined the cell cycle distributions of old and young rat arterial smooth muscle cells (SMCs) by flow-cytometric analysis. They observed that there is an apparent age-dependent variation in the cell cycle distribution. Moreover, old SMCs have a greater percentage of their population in the S phase and not G2/M, compared with young SMCs; and there is a decrease in the percentage of old cells in the G0/G1 phase as compared with young SMCs. These differences may reflect the cellular changes observed during myointimal hyperplasia following vascular injury. It is concluded that our data support the hypothesis that the proliferation of SMCs is dependent, in part, on those processes related to aging as well as to the phenotypic state of the cell.