Reduced proliferation of aged human vascular smooth muscle cells-role of oxygen-derived free radicals and BubR1 expression

Background: Aging is a risk factor for atherosclerosis. Recent studies suggest cell cycle events as well as reactive oxygen species (ROS) contribute to vascular cell dysfunction associated with aging. Mice expressing low levels of the spindle assembly checkpoint protein BubR1 develop aging-associated vascular changes at a young age, including decreased smooth muscle cells and increased reactive oxygen species (ROS) production. This study was designed to determine the effect of aging and production of oxygen-derived free radicals on expression of BubR1. Materials and Methods: To assess cell proliferation capacity, human aortic smooth muscle cells (hAoSMC) derived from a young group (17-30 y) or an aged group (57-62 y) were cultured, and cell numbers were directly counted in using a Neubauer chamber. RT-PCR assay was used to evaluate BubR1 expression in cultured hAoSMC stimulated with Angiotensin II or H₂O₂. Results: No significant difference in BubR1 expression or hAoSMC proliferative ability was demonstrated at passage 5, but both were significantly decreased at passage 8 in the aged hAoSMC. Angiotensin II and H₂O₂ up-regulated BubR1 expression in young hAoSMC, and the up-regulation was abrogated by a p38 MAPK inhibitor or an inhibitor of the NADH/NADPH oxidase. siRNA against BubR1 reduced proliferative activity and increased ROS production in hAoSMC. Conclusions: These findings demonstrate BubR1 mRNA expression decreases along with proliferation in aged hAoSMC. Aging-related loss of BubR1 and subsequent impairment of reactivity to ROS may explain reduced proliferative capacity of aged smooth muscle cells.