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 beta 3 is higher than in descending arteries. In the advanced atherosclerosis lesion, we found an inverse correlation between the level of integrin beta 3 and apoptosis (deoxynucleotidyltransferase- mediated dUTP nick end labeling-positive). We also found an increase in integrin alpha V beta 3 (but not integrin beta 1) expression in VSMC that are subjected to cyclic stretch. VSMC subjected to stretch as well as VSMC with forced expression of alpha V beta 3 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 beta 3 as well as VSMC isolated from integrin beta 3 knock-out mice. Disruption of the cytoskeleton abolished the protective effect of stretch or alpha V beta 3 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 beta 1 or integrin beta 3 prevented its down-regulation. In the arteries of integrin beta 3 null mice, there were lower levels of PINCH-1 and ILK-1. Moreover, deletion of integrin beta 3 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 alpha V beta 3 integrin expression, stabilization of PINCH-1, and remodeling of the cytoskeleton.