Laminar shear stress stimulates vascular smooth muscle cell apoptosis via the Akt pathway

Abstract

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.

Interstitial flow promotes vascular fibroblast, myofibroblast, and smooth muscle cell motility in 3-D collagen I via upregulation of MMP-1

“…Rat aortic SMCs and adventitial FBs and MFBs were obtained as previously described (7,8). Cells (passages [3][4][5] were first suspended in rat-tail collagen I (BD Science) gels (cell density, 2.5 ϫ 10 5 cells/ml; and final gel concentration, 4 mg/ml). Then, 200 l of gel were loaded into each 12-well cell culture insert with 8-m pore-size membrane (BD Science), the edge of which had been precoated with 50 l of 4 mg/ml of cell-free collagen without serum to prevent the gel from later contracting and detaching during cell spreading (Fig.…”

Tissue factor pathway inhibitor-2 is induced by fluid shear stress in vascular smooth muscle cells and affects cell proliferation and survival

“…Although FSS has previously been shown to inhibit SMC proliferation 11 and induce Akt-mediated apoptosis, 12 SMCs have been assumed to respond mainly to stretch forces, and detailed information on the effect of FSS on SMC molecular processes is lacking. 13 Here, we investigated the effect of FSS on SMC gene expression and function.…”

Shear enhances thrombopoiesis and formation of microparticles that induce megakaryocytic differentiation of stem cells

“…For example, shear stress is an important differentiation signal for embryonic stem cells, 9,10 endothelial progenitor cells circulating in peripheral blood, [11][12][13] and mesenchymal stem cells. 14,15 Many cellular processes are affected by shear forces, including the cell cycle, 11,16,17 migration, 17,18 apoptosis, [19][20][21][22] and differentiation. 11,23 In this study, we probed the role of shear stress on Mk maturation by examining its impact on DNA synthesis, polyploidization, phosphatidylserine (PS) exposure, caspase-3 activation and the generation of PPTs, platelet-like particles (PLPs), and Mk-derived microparticles (MkMPs).…”