Shear Stress Regulates Endothelial Microparticle Release
Rationale: Endothelial activation and apoptosis release membrane-shed microparticles (EMP) that emerge as important biological effectors.
Objective: As laminar shear stress (SS) is a major physiological regulator of endothelial survival, we tested the hypothesis that SS regulates EMP release.
Methods and Results: EMP levels were quantified by flow cytometry in medium of endothelial cells subjected to low or high SS (2 and 20 dyne/cm2). EMP levels augmented with time in low- compared to high-SS conditions. This effect was sensitive to ERK1/2 and ROCK inhibitors, but unaffected by caspase inhibitors. Low SS-stimulated EMP release was associated with increased endothelial ROCK and ERK1/2 activities and cytoskeletal reorganization. Over-expression of constitutively active RhoA stimulated EMP release under high SS. We also examined the effect of nitric oxide (NO) in mediating SS effects. L-NAME, but not D-NAME, increased high SS-induced EMP levels by 3-fold, whereas the NO donor SNAP decreased it. L-NAME and SNAP did not affect ROCK and ERK1/2 activities. Then, we investigated NO effect on membrane remodeling as microparticle release is abolished in ABCA1-deficient cells. ABCA1 expression, which was greater under low SS than under high SS, was augmented by L-NAME under high SS and decreased by SNAP under low SS conditions.
Conclusions: Altogether, these results demonstrate that sustained atheroprone low SS stimulates EMP release through activation of ROCK and ERK1/2 pathways, whereas atheroprotective high SS limits EMP release in a NO-dependent regulation of ABCA1 expression and of cytoskeletal reorganization. These findings therefore identify endothelial SS as a physiological regulator of microparticle release.
- Received December 21, 2012.
- Revision received March 25, 2013.
- Accepted March 27, 2013.