Shear Stress Increases Sirtuin‐1 Expression to Mediate Shear‐Induced Autophagy in Endothelial Cells

Abstract

Blood flow‐induced shear stress acted on endothelial cells (ECs) is essential for normal vascular function. Autophagy represents a homeostatic mechanism crucial for cell survival. The conversion of non‐lipidated form LC3‐I to autophagosome‐membrane‐associated lipidated form LC3‐II is an indicator of autophagic activity. Sirtuins (SIRT1‐7), a family of NAD+‐dependent deacetylase, mediate adaptive responses to wide spectrum of stresses. Earlier studies showed that Sirtuin 1 (SIRT1) participated in the process of autophagy. In our current study, we demonstrate that shear stress to ECs increases autophagy and SIRT1 participates in this shear stress‐induced autophagy. Human endothelial cells (ECs) were subjected to shear stress (5 or 12 dynes/cm2) in a well‐defined parallel plate flow chamber system. Shear stress increased SIRT1 expression. Shear flow also enhanced NAD+/NADH ratio that is essential for Sirtuins activities. Shear stress stimulated autophagy as demonstrated by 1) an increase of LC3‐II/LC3‐I ratio 2) a decrease of P62 level and 3) an increase of RFP‐LC3 puncta numbers in sheared ECs. Shear‐induced autophagy is shown as time‐dependent but shear force‐independent manner. Interestingly, ECs treated with Sirtuins activator (SRT1720) also increased autophagy. Furthermore, shear stress to ECs with SIRT1 knockdown by SiRNA attenuated autophagy indicating that shear stress‐induced autophagy is mediated at least partially through SIRT1. Furthermore, ECs treated with ROS scavenger (NAC) decreased shear‐induced autophagy indicating ROS play a role in shear‐induced autophagy. In conclusion, ECs under shear stress increase SIRT1 expression to promote autophagy and thus enhances endothelial homeostasis.