Amiloride sensitive activation of S6 kinase by angiotensin II in cultured vascular smooth muscle cells

Angiotensin II was shown to activate S6-kinase in cultured vascular smooth muscle cells (VSMC) in a dose- (10(-9)-10(-6) M) and time-dependent manner. Pretreatment of quiescent cells with 12-O-Tetradecanoylphorbol-13-acetate had no effect on the activation levels of the kinase at the hormone levels used. However, stimulation of S6-kinase activity by angiotensin II was markedly inhibited by the inclusion of amiloride hydrochloride in serum-free medium during activation procedures. Angiotensin was not mitogenic for VSMC at even the highest doses used (10(-6) M). These findings support the notion that raised intracellular pH results in the activation of protein synthesis in quiescent cells.     

Activation of mitogen-activated protein kinase by oxidized low-density lipoprotein in canine cultured vascular smooth muscle cells

Oxidized low-density lipoprotein (OX-LDL) contributes significantly to the development of atherosclerosis. However, the mechanisms of OX-LDL-induced vascular smooth muscle cell (VSMC) proliferation are not completely understood. Therefore, we investigated the effect of OX-LDL on cell proliferation associated with a specific pattern of mitogen-activated protein kinase (MAPK) by [3H]thymidine incorporation and p42/p44 MAPK phosphorylation in canine cultured VSMCs. OX-LDL-induced [3H]thymidine incorporation and p42/p44 MAPK phosphorylation in a time- and concentration-dependent manner in VSMCs. Pretreatment of these cells with pertussis toxin (PTX) for 24 hours attenuated the OX-LDL-induced [3H]thymidine incorporation and p42/p44 MAPK phosphorylation, indicating that these responses were mediated through a receptor coupled to a PTX-sensitive G protein. In cells pretreated with PMA for 24 h and with either the PKC inhibitor staurosporine or the tyrosine kinase inhibitor genistein for 1h, substantially reduced the [3H]thymidine incorporation and p42/p44 MAPK phosphorylation in response to OX-LDL. Removal of Ca(2+) by addition of BAPTA/AM plus EGTA significantly inhibited OX-LDL-induced [3H]thymidine incorporation and p42/p44 MAPK phosphorylation, indicating the requirement of Ca(2+) for these responses. OX-LDL-induced [3H]thymidine incorporation and p42/p44 MAPK phosphorylation was completely inhibited by PD98059 (an inhibitor of MEK1/2) and SB203580 (an inhibitor of p38 MAPK). Furthermore, we also showed that overexpression of dominant negative mutants of Ras (RasN17) and Raf (Raf-301) completely suppressed MEK1/2 and p42/p44 MAPK activation induced by OX-LDL and PDGF-BB, indicating that Ras and Raf may be required for activation of these kinases. Taken together, these results suggest that the mitogenic effect of OX-LDL is mediated through a PTX-sensitive G-protein-coupled receptor that involves the activation o Ras/Raf/MEK/MAPK pathway similar to those of PDGF-BB in canine cultured VSMCs.     

Activation of phospholipase A2 by endothelin in cultured vascular smooth muscle cells

The ability of endothelin to promote phospholipid hydrolysis has been studied in myo-[2-3H]-inositol-, [3H]-arachidonic acid- or methyl-[3H]choline chloride-prelabelled cultured vascular smooth muscle cells (VSMC) from rat and bovine thoracic aortae and human omental vessels. The biochemical responses to endothelin were comparable between the different VSMC isolates. Endothelin promoted the accumulation of glycerolphospho[3H]inositol and concomitant loss of [3H]-inositol label from phosphatidylinositol. Exposure of [3H]choline-labelled VSMC to endothelin resulted in a loss of radioactivity from phosphatidylcholine that was inversely parallelled by an increase in water-soluble [3H]-choline metabolites. In [3H]-arachidonic acid ([3H]-AA)-labelled VSMC, endothelin induced extracellular release of [3H]-AA which derived from both phosphatidylcholine and phosphatidylinositol. Half-maximally effective concentrations of endothelin for all these responses were approximately 2-7 nM and did not vary between VSMC types. Endothelin-induced release of [3H]-AA into VSMC medium-overlay was inhibited by quinacrine and nordihydroguaiaretic acid but not by neomycin or indomethacin. The data herein implicate activation of phospholipase A2 by endothelin with subsequent metabolism of arachidonic acid via the lipoxygenase pathway.     

Activation of multiple signal transduction pathways by endothelin in cultured human vascular smooth muscle cells

Cellular responses to the vasoconstrictor peptide, endothelin, have been investigated in quiescent cultured human vascular smooth muscle cells (hVSMC). Endothelin caused intracellular alkalinization and activation of the protein synthetic enzyme S6-kinase, but such responses were not associated with any mitogenic effects of endothelin on hVSMC. In myo-[3H]inositol-prelabelled hVSMC endothelin elicited a rapid increase in inositol bis- and tris-phosphates and concomitant hydrolysis of polyphosphoinositol lipids. In [3H]arachidonate-prelabelled hVSMC endothelin promoted production of diacylglycerol, the early kinetics of which parallelled polyphosphoinositol lipid hydrolysis. Such phospholipase C activation by endothelin was sustained in hVSMC with accumulation of inositol polyphosphates being markedly protracted and the decay of diacylglycerol slow. Endothelin promoted extracellular release of [3H]arachidonate-labelled material from hVSMC which derived via deacylation of both phosphatidylinositol and phosphatidylcholine. This process was inhibited by phospholipase A2 and lipoxygenase inhibitors, but insensitive to phospholipase C and cyclooxygenase inhibitors. Endothelin-induced activation of phospholipase C and phospholipase A2 signal transduction pathways (EC50 approximately 5-8 nM for both) in hVSMC apparently proceed in an independent parallel manner rather than a sequential one.     

Heparin increases mRNA levels of thrombospondin but not fibronectin in human vascular smooth muscle cells

The effects of heparin (180 micrograms/ml) on steady state mRNA levels for fibronectin, thrombospondin, actin and collagen types I and III were investigated in human umbilical artery smooth muscle cells. Heparin caused a 120% increase in thrombospondin mRNA levels and a 60% and 180% increase in the mRNA levels of procollagen chains alpha 2(I) and alpha 1(III), respectively. No change in fibronectin or actin mRNA levels resulted from heparin treatment. We reported earlier (Biochem. Biophys. Res. Comm. 148:1264, 1987) that heparin increases smooth muscle cell synthesis of both fibronectin and thrombospondin. These data show that heparin coordinately regulates thrombospondin mRNA and protein levels. The heparin induced increase in fibronectin biosynthesis apparently reflects control at the translational or post-translational level.     

Intercellular communication in cultured human vascular smooth muscle cells

Intercellular communication through gap junction channelsplays a fundamental role in regulating vascular myocyte tone. We investigated gap junction channel expression and activity in myocytes from the physiologically distinct vasculature of the human internal mammary artery (IMA, conduit vessel) and saphenous vein (SV,capacitance vessel). Northern and Western blots documented the presenceof connexin43 (Cx43) in frozen tissues and cultured cells from both vessels. Northern blots also confirmed the presence of Cx40 mRNA incultured IMA and SV myocytes. Dual whole cell patch-clamp experiments revealed that macroscopic junctional conductance was voltage dependent and characteristic of that observed for Cx43. In the majority ofrecords, in both vessels, single-channel activity was dominated by amain-state conductance of 120 pS, with subconducting events comprisingless than 10% of the amplitude histograms. However, some recordsshowed "atypical" unitary events that had a conductance similar toCx40 (~140-160 pS), but gating behavior like that of Cx43. Assuch, it is conceivable that the presence and coexpression of Cx40 andCx43 in IMA and SV myocytes may result in heteromeric channelformation. Nonetheless, in terms of gating, Cx43-like behavior clearly dominates.

     

Vasoconstrictor-induced protein-tyrosine phosphorylation in cultured vascular smooth muscle cells

In cultured rat aortic smooth muscle cells, angiotensin II induced tyrosine phosphorylation of at least 9 proteins with molecular masses of 190, 117, 105, 82, 79, 77, 73, 45 and 40 kDa in time- and dose-dependent manners. Other vasoconstrictors such as [Arg]vasopressin, 5-hydroxytryptamine and norepinephrine induced the tyrosine phosphorylation of the same set of proteins as angiotensin II. The tyrosine phosphorylation of these proteins was mimicked by the protein kinase C-activating phorbol ester, phorbol 12 myristate 13-acetate, and the Ca2+ ionophore, ionomycin. These results demonstrate that the vasoconstrictors stimulate the tyrosine phosphorylation of several proteins in vascular smooth muscle cells and suggest that the tyrosine phosphorylation reactions are the events distal to the activation of protein kinase C and Ca2+ mobilization in the intracellular signalling pathways of the vasoconstrictors.     

Activation of mitogen-activated protein kinase pathways by cyclic GMP and cyclic GMP-dependent protein kinase in contractile vascular smooth muscle cells

Vascular smooth muscle cells (VSMC) exist in either a contractile or a synthetic phenotype in vitro and in vivo. The molecular mechanisms regulating phenotypic modulation are unknown. Previous studies have suggested that the serine/threonine protein kinase mediator of nitric oxide (NO) and cyclic GMP (cGMP) signaling, the cGMP-dependent protein kinase (PKG) promotes modulation to the contractile phenotype in cultured rat aortic smooth muscle cells (RASMC). Because of the potential importance of the mitogen-activated protein kinase (MAP kinase) pathways in VSMC proliferation and phenotypic modulation, the effects of PKG expression in PKG-deficient and PKG-expressing adult RASMC on MAP kinases were examined. In PKG-expressing adult RASMC, 8-para-chlorophenylthio-cGMP activated extracellular signal- regulated kinases (ERK1/2) and c-Jun N-terminal kinase (JNK). The major effect of PKG activation was increased activation by MAP kinase kinase (MEK). The cAMP analog, 8-Br-cAMP inhibited ERK1/2 activation in PKG-deficient and PKG-expressing RASMC but had no effect on JNK activity. The effects of PKG on ERK and JNK activity were additive with those of platelet-derived growth factor (PDGF), suggesting that PKG activates MEK through a pathway not used by PDGF. The stimulatory effects of cGMP on ERK and JNK activation were also observed in low-passaged, contractile RASMC still expressing endogenous PKG, suggesting that the effects of PKG expression were not artifacts of cell transfections. These results suggest that in contractile adult RASMC, NO-cGMP signaling increases MAP kinase activity. Increased activation of these MAP kinase pathways may be one mechanism by which cGMP and PKG activation mediate c-fos induction and increased proliferation of contractile adult RASMC.     

Interleukin-6 stimulates c-myc expression and proliferation of cultured vascular smooth muscle cells

The effects of interleukin-6 (IL-6), a cytokine recently found to be secreted by monocytes and macrophages, on c-myc expression and proliferation of cultured vascular smooth muscle cells (VSMC) were investigated. Treatment with IL-6 caused rapid increase in the c-myc mRNA level of VSMC. It also stimulated DNA synthesis and proliferation of the cells significantly and dose-dependently at concentrations of more than 10 U/ml. These results suggest that IL-6 may be important in the proliferation of VSMC, which is a key event in the development of arteriosclerosis, as a factor mediating immune cell-VSMC interaction.     

Endothelin stimulates diacylglycerol accumulation and activates protein kinase C in cultured vascular smooth muscle cells

Endothelin, a novel peptide isolated from the conditioned medium of endothelial cells, causes a slow, sustained contraction of vascular smooth muscle, but its mechanism of action remains unclear. To determine whether the diacylglycerol/protein kinase C signalling pathway is stimulated by endothelin, we exposed cultured rat aortic smooth muscle cells to endothelin and measured diacylglycerol accumulation and protein kinase C-dependent protein phosphorylation. Endothelin stimulated a dose-dependent, biphasic increase in diacylglycerol, which was sustained for at least 20 min. This peptide also induced a prolonged phosphorylation of an acidic protein with a molecular weight of 76,000, which was detectable by 30 s and sustained for at least 20 min. This phosphorylation could be mimicked by phorbol 12-myristate 13-acetate, but not by ionomycin, and was markedly reduced when protein kinase C was down-regulated by a 24-h pretreatment with phorbol 12,13-dibutyrate. These results suggest that endothelin causes a robust stimulation of the diacylglycerol/protein kinase C pathway in cultured vascular smooth muscle cells, and that this mechanism may contribute importantly to the physiologic events stimulated by endothelin in intact blood vessels, including slow, tonic contraction and Ca2+ influx.     

尾加压素增加血管平滑肌细胞粘着斑激酶的含量和活力

在体外培养的血管平滑肌细胞上,采用蛋白印迹杂交免疫沉淀的方法,研究尾加压素Ⅱ（ＵⅡ）与粘着斑激酶（ＦＡＫ）介导的信号传导之间的关系。结果表明,ＵⅡ在１０＾－８、１０＾－７和１０＾－６ｍｏｌ／Ｌ的深度时,可分别使ＦＡＫ活力增加２．２、３．０４和０．７３倍。加入ＵⅡ在（１０＾０７ｍｏｌ／Ｌ）５ｍｉｎ后,ＦＡＫ活力增加９５％,但与对照组相比无显著性差异（Ｐ〉０．０５０,刺激１０ｍｉｎ后,ＦＡＫ活力升高３     

Expression of smooth muscle and nonmuscle myosin heavy chains in cultured vascular smooth muscle cells

We explored the hypothesis that discrepancies in the literature concerning the nature of myosin expression in cultured smooth muscle cells are due to the appearance of a new form of myosin heavy chain (MHC) in vitro. Previously, we used a very porous sodium dodecyl sulfate gel electrophoresis system to detect two MHCs in intact smooth muscles (SM1 and SM2) which differ by less than 2% in molecular weight (Rovner, A. S., Thompson, M. M., and Murphy, R. A. (1986) Am. J. Physiol. 250, C861-C870). Myosin-containing homogenates of rat aorta cells in primary culture were electrophoresed on this gel system, and Western blots were performed using smooth muscle-specific and nonmuscle-specific myosin antibodies. Subconfluent, rapidly proliferating cultures contained a form of heavy chain not found in rat aorta cells in vivo (NM) with electrophoretic mobility and antigenicity identical to the single unique heavy chain seen in nonmuscle cells. Moreover, these cultures expressed almost none of the smooth muscle heavy chains. In contrast, postconfluent growth-arrested cultures expressed increased levels of the two smooth muscle heavy chains, along with large amounts of NM. Analysis of cultures pulsed with [35S] methionine indicated that subconfluent cells were synthesizing almost exclusively NM, whereas postconfluent cells synthesized SM1 and SM2 as well as larger amounts of NM. Similar patterns of MHC content and synthesis were found in subconfluent and postconfluent passaged cells. These results show that cultured vascular smooth muscle cells undergo differential expression of smooth muscle- and nonmuscle-specific MHC forms with changes in their growth state, which appear to parallel changes in expression of the smooth muscle and nonmuscle forms of actin (Owens, G. K., Loeb, A., Gordon, D., and Thompson, M. M. (1986) J. Cell Biol. 102, 343-352). The reappearance of the smooth muscle MHCs in postconfluent cells suggests that density-related growth arrest promotes cytodifferentiation, but the continued expression of the nonmuscle MHC form in these smooth muscle cells indicates that other factors are required to induce the fully differentiated state while in culture.     

Activation of heparin cofactor II by fibroblasts and vascular smooth muscle cells

Inhibition of thrombin by heparin cofactor II (HCII) is accelerated by dermatan sulfate, heparan sulfate, and heparin. Purified HCII or defibrinated plasma was incubated with washed confluent cell monolayers, 125I-thrombin was added, and the rate of formation of covalent 125I-thrombin-inhibitor complexes was determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography. Fibroblasts and porcine aortic smooth muscle cells accelerated inhibition of thrombin by HCII 2.3-7.5-fold but had no effect on other thrombin inhibitors in plasma. Human umbilical vein endothelial cells and mouse macrophage-derived cells did not accelerate the thrombin-HCII reaction. IMR-90 normal human fetal lung fibroblasts treated with heparinase or heparitinase accelerated the thrombin-HCII reaction to the same degree as untreated cells. In contrast, treatment with chondroitinase ABC almost totally abolished the ability of these cells to activate HCII while chondroitinase AC had little or no effect, suggesting that dermatan sulfate was responsible for the activity observed. [35S]Sulfate-labeled proteoglycans were isolated from IMR-90 fibroblast monolayers and conditioned medium and fractionated into two peaks on Sepharose CL-2B. The lower Mr proteoglycans contained 74-76% dermatan sulfate and were 11-25 times more active with HCII than the higher Mr proteoglycans which contained 68-97% heparan sulfate. The activity of the lower Mr proteoglycans decreased 70-90% by degradation of the dermatan sulfate component with chondroitinase ABC. These results confirm that dermatan sulfate proteoglycans are primarily responsible for activation of HCII by IMR-90 fibroblasts. We suggest that HCII may inhibit thrombin when plasma is exposed to vascular smooth muscle cells or fibroblasts.     

Endothelin stimulates phospholipase C in cultured vascular smooth muscle cells

Cultured vascular smooth muscle cells from bovine and rat thoracic aortae and from human omental vessels have been examined for cellular responses to endothelin. In myo-[3H]-inositol-prelabelled cells endothelin induced a rapid (within 30 sec) and protracted increase of [3H]-inositol content in inositol bis- and tris-phosphates. Concomitantly, significant polyphosphoinositide hydrolysis occurred within 30 sec. Accumulation of [3H]-inositol monophosphate and hydrolysis of phosphatidylinositol were delayed. In cells prelabelled with [3H]-arachidonic acid endothelin promoted rapid production of [3H]-diacylglycerol which decayed slowly toward control values after reaching maximum levels (1-2 min). Half-maximally effective concentrations of endothelin for all these cellular responses were comparable (approximately 3-7 nM) and not significantly different between the vascular cell isolates. The involvement of the phospholipase C-signal transduction pathway in mediating endothelin-induced vasoconstriction is invoked.     

Activation of MAPK by modified low-density lipoproteins in vascular smooth muscle cells.

A high concentration of circulating low-density lipoproteins (LDL) is a major risk factor for atherosclerosis. Native LDL and LDL modified by glycation and/or oxidation are increased in diabetic individuals. LDL directly stimulate vascular smooth muscle cell (VSMC) proliferation; however, the mechanisms remain undefined. The extracellular signal-regulated kinase (ERK) pathway mediates changes in cell function and growth. Therefore, we examined the cellular effects of native and modified LDL on ERK phosphorylation in VSMC. Addition of native, mildly modified (oxidized, glycated, glycoxidized) and highly modified (highly oxidized, highly glycoxidized) LDL at 25 microg/ml to rat VSMC for 5 min induced a fivefold increase in ERK phosphorylation. To elucidate the signal transduction pathway by which LDL phosphorylate ERK, we examined the roles of the Ca(2+)/calmodulin pathway, protein kinase C (PKC), src kinase, and mitogen-activated protein kinase kinase (MEK). Treatment of VSMC with the intracellular Ca(2+) chelator EGTA-AM (50 micromol/l) significantly increased ERK phosphorylation induced by native and mildly modified LDL, whereas chelation of extracellular Ca(2+) by EGTA (3 mmol/l) significantly reduced LDL-induced ERK phosphorylation. The calmodulin inhibitor N-(6-aminohexyl)-1-naphthalenesulfonamide (40 micromol/l) significantly decreased ERK phosphorylation induced by all types of LDL. Downregulation of PKC with phorbol myristate acetate (5 micromol/l) markedly reduced LDL-induced ERK phosphorylation. Pretreatment of VSMC with a cell-permeable MEK inhibitor (PD-98059, 40 micromol/l) significantly decreased ERK phosphorylation in response to native and modified LDL. These findings indicate that native and mildly and highly modified LDL utilize similar signaling pathways to phosphorylate ERK and implicate a role for Ca(2+)/calmodulin, PKC, and MEK. These results suggest a potential link between modified LDL, vascular function, and the development of atherosclerosis in diabetes.     

Functional angiotensin II receptors in cultured vascular smooth muscle cells

To study cellular mechanisms influencing vascular reactivity, vascular smooth muscle cells (VSMC) were obtained by enzymatic dissociation of the rat mesenteric artery, a highly reactive, resistance-type blood vessel, and established in primary culture. Cellular binding sites for the vasoconstrictor hormone angiotensin II (AII) were identified and characterized using the radioligand 125I-angiotensin II. Freshly isolated VSMC, and VSMC maintained in primary culture for up to 3 wk, exhibited rapid, saturable, and specific 125I-AII binding similar to that seen with homogenates of the intact rat mesenteric artery. In 7-d primary cultures, Scatchard analysis indicated a single class of high-affinity binding sites with an equilibrium dissociation constant (Kd) of 2.8 +/- 0.2 nM and a total binding capacity of 81.5 +/- 5.0 fmol/mg protein (equivalent to 4.5 x 10(4) sites per cell). Angiotensin analogues and antagonists inhibited 125I-AII binding to cultured VSMC in a potency series similar to that observed for the vascular AII receptor in vivo. Nanomolar concentrations of native AII elicited a rapid, reversible, contractile response, in a variable proportion of cells, that was inhibited by pretreatment with the competitive antagonist Sar1,Ile8-AII. Transmission electron microscopy showed an apparent loss of thick (12-18 nm Diam) myofilaments and increased synthetic activity, but these manifestations of phenotypic modulation were not correlated with loss of 125I-AII binding sites or hormonal responsiveness. Primary cultures of enzymatically dissociated rat mesenteric artery VSMC thus may provide a useful in vitro system to study cellular mechanisms involved in receptor activation-response coupling, receptor regulation, and the maintenance of differentiation in vascular smooth muscle.     

Inhibition of calcium transients in cultured vascular smooth muscle cells by pertussis toxin

Effects of pertussis toxin on Ca2+ transients in rat arterial smooth muscle cells in primary culture were monitored, using quin 2-microfluorometry. In the presence or the absence of extracellular Ca2+, norepinephrine, histamine, caffeine and high extracellular K+ induced elevations in cytosolic Ca2+ concentration. Cytosolic Ca2+ elevations induced by norepinephrine and histamine were inhibited by pretreatment of the cells with pertussis toxin, time- and dose-dependently. However, elevations induced by caffeine and K+-depolarization were unaffected by the pretreatment with this toxin. Thus, it is suggested that GTP binding protein, a pertussis toxin substrate and involved in the receptor-mediated cytosolic Ca2+ transients, is not involved in transient elevations in cytosolic Ca2+ induced by caffeine and K+-depolarization in cultured vascular smooth muscle cells.     

Protein tyrosine kinase activity in cultured vascular smooth muscle cells (VSMC) from rat aorta

• 1.1. Protein tyrosine kinase (PTK) activities were detected in both cytosolic and particulate fractions of cultured vascular smooth muscle cells by using poly (Glu: Tyr; 4:1) as an exogenous substrate.
• 2.2. The percent distribution of the enzyme activity between these two fractions was 70 and 30 respectively.
• 3.3. The particulate and not the cytosolic enzyme activity was stimulated by about 4-fold in the presence of non-ionic detergent, Triton X-100 (0.5% v/v).
• 4.4. The PTK activity in both the fractions was absolutely dependent on the presence of divalent cations such as Mg²⁺ and Mn²⁺ which were equipotent in the activation of the enzyme.These data indicate that PTK activity is expressed in cultured VSMC and provide a basis for further studies to examine a possible role of PTKs in growth and proliferation of VSMC.

     

Effect of TNF on triacylglycerol in cultured vascular smooth muscle cells

Smooth muscle cells (SMC) isolated from bovine aorta or human saphenous vein were cultured and used to study the putative effect of recombinant human tumor necrosis factor (TNF) on lipid metabolism in vascular cells. Addition of TNF to the culture medium for 24-48 h resulted in an increase of [3H]oleic acid uptake and esterification into lipids. The effect could be seen already with 0.3 ng/ml and was maximal with 30 ng/ml. The effect of TNF was mainly on the incorporation of [3H]oleic acid into triacylglycerol which increased by 140% in the bovine cells. There was also a significant increase in [3H]cholesteryl ester. In the human SMC there was a 40% increase in [3H]oleic acid into total lipids, while the rise in [3H]triacylglycerol ranged between 60-90%. TNF did not modulate cellular triacyglycerol synthesis in cultured mouse peritoneal macrophages. Since TNF was shown to be synthesized and secreted not only by macrophages but also by smooth muscle cells, it could play an autocrine role in lipid metabolism during development of atherosclerotic lesions. The cellular population of the lesions, i.e., predominance of macrophages or smooth muscle cells, could determine the relative proportion of triacylglycerol accumulation.     

Fluid shear stress-induced alignment of cultured vascular smooth muscle cells

The study objectives were to quantify the time- and magnitude-dependence of flow-induced alignment in vascular smooth muscle cells (SMC) and to identify pathways related to the orientation process. Using an intensity gradient method, we demonstrated that SMC aligned in the direction perpendicular to applied shear stress, which contrasts with parallel alignment of endothelial cells under flow SMC alignment varied with the magnitude of and exposure time to shear stress and is a continuous process that is dependent on calcium and cycloskeleton based mechanisms. A clear understanding and control of flow-induced SMC alignment will have implications for vascular tissue engineering.