Cyclic strain activates the pro-survival Akt protein kinase in bovine aortic smooth muscle cells

Background. Pulsatile pressure induced by the beating heart causes cylic strain on arterial endothelial cells and smooth muscle cells (SMCs). This study examined whether Akt, a serine/threonine protein kinase known to promote cell survival by inhibiting apoptosis, is activated by cylic strain in hotline aortic SMCs. Methods. Bovine aortic SMCs were cultured on flexible-bottomed membranes and then serum-starved for 24 to 36 hours. The cells were then exposed to 150-mm Hg repetitive deformations, which created an average of 10% strain on the monolayer SMCs at a frequency of 60 cycles/minute for 0 (negative control) and 30 minutes. Platelet-derived growth factor (PDGF)-stimulated SMGs were used as positive controls. Phosphorylation of Akt was determined by means of Western blot analysis. An apoptosis assay (TUNEL) was also performed on SMCs exposed to cyclic strain. Results. Akt phosphorylation was significantly increased over that of the negative control after 30 minutes of cyclic strain and in the PDGF group. Cyclic strain did not increase the prevalence of apoptosis in SMCs over the control. Conclusions. Cyclic strain activated the pro-survival Akt kinase. The pro-survival function was supported by the fact that cyclic strain did not increase apoptosis in bovine aortic SMCs. This experiment suggests that cyclic strain may induce arterial wall thickening by tipping the balance toward arterial SMC Proliferation through the inhibition of apoptosis.