EFFECTS OF LAMINAR SHEAR STRESS ON MITOCHONDRIAL DNA INTEGRITY IN ENDOTHELIAL CELLS

Abstract

Purpose/hypothesis: Regular practice of exercise is the most effective non-pharmacological intervention that improves vascular health, which is thought to be mediated by a repeated exposure of vessel walls to increased hemodynamic shear stress (SS). Mitochondria have been shown to be essential cellular structures responsible for a wide variety of vascular functions, and its impairment is often associated with cardiovascular disease. However, researches on vascular mitochondrial adaptations to SS are in a very early stage and many questions remain unresolved. The objective of this study is to investigate the effect of exercise preconditioning on endothelial mitochondria in an angiotensin (Ang) II-induced hypertension model. It was hypothesized that exercise preconditioning prevents Ang II induced-hypertensive phenotypes by improving mitochondrial homeostasis in the endothelium. Methods: High-magnitude laminar SS (LSS) (20 dyne/cm2) was applied to human aortic endothelial cells (HAECs) using a cone-and-plate shear apparatus for 48 hours. Either LSS-preconditioned or static flow-situated HAECs were incubated with Ang II. In in vivo experiments, C57BL/6J mice were singly housed with or without a voluntary running wheel for 7 weeks. Ang II or saline was infused in a constant rate using an implantable osmotic pump for the last 2 weeks of the experimental period. Mitochondrial membrane potential (ÄØm) and mitoROS production were measured using fluorochrome molecular probe-based microscopic techniques, and mtDNA damage was assessed by a long amplicon quantitative PCR (LA-QPCR) method. Results: In HAECs, LSS preconditioning attenuated Ang II-induced mitochondrial dysfunction, which was evidenced by decreased mitoROS generation, increased ÄØm, and reduced mtDNA damage. Likewise, in aortic tissues, Ang II-induced mitochondrial phenotypic changes (i.e. mitoROS production, mtDNA damage and ÄØm reduction) were significantly reduced in exercise-preconditioned mice compared to sedentary controls. Moreover, Ang II-induced blood pressure elevation was completely blocked in exercise preconditioned animals. Conclusion: Taken together, high-magnitude LSS improves endothelial function by enhancing mtDNA integrity and mitochondrial function. These findings further support the idea that aerobic exercise is a prominent life-style modification strategy to prevent hypertension by targeting dysfunctional mitochondria in the vessel wall.