Published online before print July 16, 2009, doi: 10.1161/ATVBAHA.109.191965
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
© 2009 American Heart Association, Inc.
Cell Biology/Signaling |
Sphingosine-1-Phosphate Receptor-2 Regulates Expression of Smooth Muscle Alpha-Actin After Arterial Injury
From the Departments of Surgery (A.D.G., J.D., G.D.) and Pathology (A.D.G., T.S., W.M.M., M.A.R.) University of Washington, Seattle.
Correspondence to Guenter Daum, PhD, Research Associate Professor, University of Washington, Department of Surgery, Box 358050, 815 Mercer Street, Seattle, WA 98109. E-mail daum{at}u.washington.edu
Objective— This study tests the hypothesis that S1P2R regulates expression of SMC differentiation genes after arterial injury.
Methods and Results— Carotid ligation injury was performed in wild-type and S1P2R-null mice. At various time points after injury, expression of multiple SMC differentiation genes, myocardin, and S1P receptors (S1P1R, S1P2R, and S1P3R) was measured by quantitative PCR. These experiments demonstrate that at day 7 after injury, S1P2R specifically regulates expression of smooth muscle 
-actin (SMA) and that this is not mediated by changes in expression of myocardin or any of the S1PRs. In vitro studies using carotid SMCs prepared from wild-type and S1P2R-null mice show that S1P stimulates expression of all SMC-differentiation genes tested, but S1P2R significantly regulates expression of SMA and SM22 only. Chromatin immunoprecipitation assays suggest that S1P-induced recruitment of serum response factor to the SMA promoter and enhancer largely depends on S1P2R. S1P-stimulated SMA expression requires S1P2R-dependent activation of RhoA and mobilization of calcium from intracellular stores. Chelation of calcium does not affect the activation of RhoA by S1P, whereas blockade of Rho by C3 exotoxin partially inhibits the mobilization of calcium by S1P.
Conclusions— The results of this study support the hypothesis that S1P2R regulates expression of SMA after injury. We further conclude that transcriptional regulation of SMA by S1P in vitro requires S1P2R-dependent activation of RhoA and mobilization of calcium from intracellular calcium stores.
At day 7 after injury, S1P2R-null carotid arteries express less SMA compared to wild-type carotid arteries, which may contribute to the extensive neointimal growth observed in S1P2R-null mice. In vitro, S1P-induced SMA expression requires S1P2R-dependent activation of Rho and mobilization of calcium from intracellular stores.
Key Words: sphingosine-1-phosphate • S1P2R • smooth muscle actin • Rho • calcium
Related Article:
Arterioscler Thromb Vasc Biol 2009 29: 1439-1443.