Endothelial cell apoptosis in high wall shear stress and wall shear stress gradient environments
Kaluvala, Shashikanth R.
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Vascular diseases like cerebral aneurysms and atherosclerosis are leading causes of mortality worldwide, and account for over 860,000 deaths annually in the United States. The vessel wall is an integrated organ composed of endothelial, smooth-muscle, and fibroblast cells that are active with their function defined by the complex interactions between them. These interactions are integrated signals sent through intercellular communication that are influenced by the local production of mediators such as NO, eNOS, VGEF. These mediators are capable of modifying the structure as well as the function of the vasculature. In addition, the mechanical stimuli generated by blood flow such as wall shear stress, wall shear stress gradient and systemic pressure are known to be major contributing factors in the functioning and maintenance of the endothelial cell (EC) monolayer. Understanding how these mechanical forces affect vessel health is critical to future vascular disease treatment. To this point, most in vitro research on endothelial cells focuses on low (15-30 dyn/cm 2 ) to normal shear stress environments rather than on the high shear stress and complex impinging flow environments seen at the apices of bifurcations, where intracranial aneurysms usually form. This study aims at elucidating the EC programmed cell death (apoptosis) response to elevated wall shear stress (WSS), high rate of wall shear stress gradient (WSSG) and the combined effect of WSS and WSSG. For this purpose, a confluent EC monolayer was subjected to flow under a wide range of WSS values, from 15 to 100 dyn/cm 2 with negligible gradient, using a tapered chamber and under a T-shaped impingement chamber that mimics the in vivo arterial bifurcations with varying WSS and WSSG values. The flow experiments were run as steady-state, laminar flow for 24 hrs at a constant pressure of 100 mmHg. Apoptosis was examined using TUNEL labeling assay. In the tapered chamber, the percentage of apoptosis was higher at the regions with physiological WSS magnitudes of 15-30 dyn/cm 2 than at regions with high WSS values (>50 dyn/cm 2 ). And, in the impingement chamber the statistical analysis of the data shows that there is a significant effect of WSSG and the combined effect of WSS and WSSG in increasing the percentage of apoptotic cells. These results demonstrate that high WSS (>50 dyn/cm 2 ) does not damage the EC’s but rather suppresses the apoptotic levels but, acts otherwise when combined together with the WSSG. Although further studies are needed, these results provide insight that will allow better understanding of the molecular mechanisms involved in the regulation of the vascular tone and vascular remodeling at high WSS and WSSG environments.