Abstract 151: Plasminogen Activator Inhibitor-1 Stimulates Smooth Muscle Senescence and Atherosclerosis Formation

Abstract

Cell senescence, which is characterized by loss of replicative capacity and secretion of inflammatory mediators, was recently shown to play a causal role in atherosclerosis. Plasminogen activator inhibitor-1 (PAI-1), a serine protease inhibitor that regulates fibrinolysis, cell migration, and cell proliferation, promotes cell senescence. This study tested the hypotheses that 1) PAI-1 stimulates vascular smooth muscle cell (SMC) senescence and 2) pharmacologic PAI-1 inhibition attenuates senescence of SMCs and atherosclerotic plaques. Human coronary artery SMCs were grown in culture and treated with recombinant PAI-1 and PAI-039 (tiplaxtinin), a specific pharmacological inhibitor of PAI-1. SMCs were scored for the presence of senescence-associated β-galactosidase (SA-βgal), an enzyme whose expression is specifically upregulated in senescent cells. PAI-1 (10 μg/mL) significantly increased SMC senescence (28.3±1.2% senescent cells, n=6) compared to vehicle control (14.3±1.4%, n=7, p <0.05). PAI-039 (25 μM) significantly decreased PAI-1-induced SMC senescence (19.1±1.1%, n=5, p <0.05 vs PAI-1-treated cells). To examine the significance of our findings in vivo, we studied the effects of PAI-039 on cell senescence in aortas of ldlr -/- mice fed a western diet (WD) with or without PAI-039 (5 mg/g of diet). After twelve weeks of WD aortas were harvested and SA-βgal activity was measured in intact specimens with FDG substrate. SA-βgal activity was significantly less in ldrl -/- mice fed WD containing PAI-039 (366±64 FU/mg, n=7) compared to controls (591±82 FU/mg, n=7, p<0.05) . The decrease in senescence was associated with a statistically significant reduction in atherosclerosis formation, assessed by quantitative Oil Red O imaging. In summary, SMC senescence is stimulated by PAI-1 and down-regulated by PAI-039, a specific PAI-1 inhibitor. PAI-039 also significantly inhibited cell senescence in aortas of ldlr -/- mice fed WD. These results suggest that PAI-1 is an important mediator of SMC senescence and that pharmacologic targeting of PAI-1 is an effective strategy to inhibit vascular senescence and atherogenesis in vivo.