Laminar shear stress stimulates vascular smooth muscle cell apoptosis via the Akt pathway.
Vascular smooth muscle cells (SMC) may be directly exposed to blood flow after an endothelial-denuding injury. It is not known whether direct exposure of SMC to shear stress reduces SMC turnover and contributes to the low rate of restenosis after most vascular interventions. This study examines if laminar shear stress inhibits SMC proliferation or stimulates apoptosis. Bovine aortic SMC were exposed to arterial magnitudes of laminar shear stress (11 dynes/cm(2)) for up to 24 h and compared to control SMC (0 dynes/cm(2)). SMC density was assessed by cell counting, DNA synthesis by (3)[H]-thymidine incorporation, and apoptosis by TUNEL staining. Akt, caspase, bax, and bcl-2 phosphorylation were assessed by Western blotting; caspase activity was also measured with an in vitro assay. Analysis of variance was used to compare groups. SMC exposed to laminar shear stress had a 38% decrease in cell number (n = 4, P = 0.03), 54% reduction in (3)[H]-thymidine incorporation (n = 3, P = 0.003), and 15-fold increase in TUNEL staining (n = 4, P < 0.0001). Akt phosphorylation was reduced by 67% (n = 3, P < 0.0001), whereas bax/bcl-2 phosphorylation was increased by 1.8-fold (n = 3, P = 0.01). Caspase-3 activity was increased threefold (n = 5, P = 0.03). Pretreatment of cells with ZVAD-fmk or wortmannin resulted in 42% increased cell retention (n = 3, P < 0.01) and a fourfold increase in apoptosis (n = 3, P < 0.04), respectively. Cells transduced with constitutively-active Akt had twofold decreased apoptosis (n = 3, P < 0.002). SMC exposed to laminar shear stress have decreased proliferation and increased apoptosis, mediated by the Akt pathway. These results suggest that augmentation of SMC apoptosis may be an alternative strategy to inhibit restenosis after vascular injury.
Fitzgerald
Tamara N
TN
Department of Surgery, Yale University School of Medicine, New Haven, Connecticut 06519, USA.
Shepherd
Benjamin R
BR
Asada
Hidenori
H
Teso
Desarom
D
Muto
Akihito
A
Fancher
Tiffany
T
Pimiento
Jose M
JM
Maloney
Stephen P
SP
Dardik
Alan
A
D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D002417:Cattle; D049109:Cell Proliferation; D002478:Cells, Cultured; D006439:Hemodynamics; D006801:Humans; D020287:In Situ Nick-End Labeling; D009131:Muscle, Smooth, Vascular / Q000166:cytology*; D032389:Myocytes, Smooth Muscle / Q000166:cytology / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism*; D033081:Shear Strength; D015398:Signal Transduction / Q000502:physiology*; D013314:Stress, Mechanical
D051057:Proto-Oncogene Proteins c-akt