Abstract 452: Cyclic Strain Induces Osteopontin Expression in Vascular Smooth Muscle via a Hydrogen Peroxide--Dependent Mechanism

Abstract

Introduction: Vascular inflammation, a hallmark of hypertension, is associated with increased cyclic strain on the vessel wall. Reactive oxygen species (ROS), such as superoxide and hydrogen peroxide, are known to play an important role in the progression of cardiovascular inflammation. However, the underlying molecular mechanisms of ROS modulation of vascular inflammation through increased cyclic strain remain largely unknown. Objective: In this study, we sought to determine whether cyclical strain induces an increase in osteopontin (OPN), a pro-inflammatory protein, in a hydrogen peroxide dependent manner using an in vitro cell system. Methods: Rat aortic smooth muscle cells were seeded on collagen-I coated, flexible bottomed six-well plates and cyclically stretched at 10% elongation in a biaxial stretch bioreactor. Following stretch, cells were harvested and protein, mRNA, and hydrogen peroxide levels were measured via Western Blotting, quantitative real-time PCR, and Amplex Red assay, respectively. Results: Preliminary results indicate that cyclic strain promotes a 16% ± 6 increase in hydrogen peroxide levels compared to non-stretched cells at 8 hours. In addition, elevated expression of OPN protein was observed with 24 hours of stretch (195% ± 16). Increased OPN mRNA was also observed with 12 hours of stretch (39% ± 15). Finally, OPN expression was blunted when cells were simultaneously stretched for 24 hours with 200U/mL PEG-Catalase (a H2O2 scavenger) suggesting that the stretch induced increase in OPN expression is mediated by hydrogen peroxide (49%±14 decrease in cells stretched with PEG-Catalase versus non- PEG-Catalase treated but stretched cells) Conclusion: These data support that increased cyclical mechanical stretch, as experienced by the vascular wall under hypertensive conditions, increases osteopontin expression, via a hydrogen peroxide-mediated pathway.