Mechanical stretch inhibits oxidized low density lipoprotein-induced apoptosis in vascular smooth muscle cells by up-regulating integrin αVβ3 and stablization of PINCH-1

To determine the mechanisms involved in regulating the balance between apoptosis and survival in vascular smooth muscle cells (VSMC), we studied anti-apoptotic stimuli that can counteract pro-apoptotic events in the process of early atherosclerotic lesions formation. Such a process involves VSMC accumulation even in the presence of oxidized low density lipoprotein (Ox-LDL). In the arch of the aorta, we find that integrin β3 is higher than in descending arteries. In the advanced atherosclerosis lesion, we found an inverse correlation between the level of integrin β3 and apoptosis (deoxynucleotidyltransferase-mediated dUTP nick end labeling-positive). We also found an increase in integrin αVβ3 (but not integrin β1) expression in VSMC that are subjected to cyclic stretch. VSMC subjected to stretch as well as VSMC with forced expression of αVβ3 were demonstrated to be resistant to Ox-LDL-induced cytoskeleton disruption and apoptosis. The anti-apoptotic effect of stretch was abolished by treatment of VSMC with small interfering RNA against integrin β3 as well as VSMC isolated from integrin β3 knock-out mice. Disruption of the cytoskeleton abolished the protective effect of stretch or αVβ3 overexpression on Ox-LDL-induced activation of Bax and apoptosis. We also demonstrated that stretch-mediated protection of Ox-LDL-induced apoptosis involved stabilization of PINCH-1; Ox-LDL decreased the level of PINCH-1, but the application of mechanical stretch or overexpression of either integrin β1 or integrin β3 prevented its down-regulation. In the arteries of integrin β3 null mice, there were lower levels of PINCH-1 and ILK-1. Moreover, deletion of integrin β3 in VSMC abolished the stretch protective effect on PINCH-1. Small interfering RNA-mediated knockdown of PINCH-1 disrupted the cytoskeleton and caused apoptosis of VSMC. These findings provided experimental evidence that mechanical stretch acted as a survival factor in the arches of aortas. Furthermore, mechanical stretch prevented VSMC from apoptosis via a mechanism that involves αVβ3 integrin expression, stabilization of PINCH-1, and remodeling of the cytoskeleton.