Oscillatory shear stress increases smooth muscle cell proliferation and Akt phosphorylation.
OBJECTIVE
Hemodynamic forces affect smooth muscle cell (SMC) proliferation and migration both in vitro and in vivo. However, the effects of oscillatory shear stress (SS) on SMC proliferation and signal transduction pathways that control survival are not well described.


METHODS
Bovine aortic SMC were exposed to arterial levels of oscillatory SS (14 dyne/cm(2)) with an orbital shaker; control cells were exposed to static conditions (0 dyne/cm(2)). Cell number and (3)[H]thymidine incorporation were measured after 1, 3, or 5 days of SS. Activation of the Akt pathway was assessed with the Western blot technique. Specificity of the phosphatidylinositol 3-kinase (PI3K) pathway was determined with the Western blot technique with the inhibitors LY294002 (10 micromol/L) or wortmannin (25 nmol/L).


RESULTS
Arterial levels of oscillatory SS increased SMC cell number by 20.1 +/- 3.7% and (3)[H]thymidine incorporation by 33.4% +/- 6.8% at 5 days. To identify whether SS increased activity of the SMC survival pathway, Akt activation was measured. SMC exposed to SS demonstrated increased Akt phosphorylation compared with control cells, with maximal phosphorylation at 60 minutes. Both PI3K inhibitors specifically inhibited the increase in Akt phosphorylation in SMC exposed to oscillatory SS.


CONCLUSIONS
SMC directly respond to oscillatory SS by increasing DNA synthesis, proliferation, and activation of the PI3K-Akt signal transduction pathway. These results suggest a mechanism of SMC survival and proliferation in response to endothelial-denuding arterial injury.
Haga
Masae
M
Department of Surgery, Section of Vascular Surgery, Yale University School of Medicine, 333 Cedar St, FMB 137, New Haven, CT 06520-8062, USA.
Yamashita
Akimasa
A
Paszkowiak
Jacek
J
Sumpio
Bauer E
BE
Dardik
Alan
A
D000818:Animals; D002417:Cattle; D002468:Cell Physiological Phenomena; D004195:Disease Models, Animal; D006439:Hemodynamics / Q000502:physiology; D066298:In Vitro Techniques; D032389:Myocytes, Smooth Muscle / Q000502:physiology*; D009991:Oscillometry; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000502:physiology*; D011518:Proto-Oncogene Proteins / Q000502:physiology*; D051057:Proto-Oncogene Proteins c-akt; D033081:Shear Strength; D015398:Signal Transduction / Q000502:physiology*; D013312:Stress, Physiological / Q000503:physiopathology*; D014652:Vascular Diseases / Q000503:physiopathology*
D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt