Extracellular calcium sensing in rat aortic vascular smooth muscle cells

Extracellular calcium (Ca(2+)(o)) can act as a first messenger in many cell types through a G protein-coupled receptor, calcium-sensing receptor (CaR). It is still debated whether the CaR is expressed in vascular smooth muscle cells (VSMCs). Here, we report the expression of CaR mRNA and protein in rat aortic VSMCs and show that Ca(2+)(o) stimulates proliferation of the cells. The effects of Ca(2+)(o) were attenuated by pre-treatment with MAPK kinase 1 (MEK1) inhibitor, as well as an allosteric modulator, NPS 2390. Furthermore, stimulation of the VSMCs with Ca(2+)(o)-induced phosphorylation of ERK1/2, but surprisingly did not cause inositol phosphate accumulation. We were not able to conclusively state that the CaR mediates Ca(2+)(o)-induced cell proliferation. Rather, an additional calcium-sensing mechanism may exist. Our findings may be of importance with regard to atherosclerosis, an inflammatory disease characterized by abnormal proliferation of VSMCs and high local levels of calcium.     

Endothelin-1 induces the expression of C-reactive protein in rat vascular smooth muscle cells

Numerous studies have shown that both vasoconstrictive peptide endothelin-1 (ET-1) and inflammatory marker C-reactive protein (CRP) are implicated in the inflammatory process of atherosclerosis. The purpose of the present study was to observe effect of ET-1 on CRP production and the molecular mechanisms in rat vascular smooth muscle cells (VSMCs). The results showed that ET-1 was capable of stimulating VSMCs to produce CRP both in protein and in mRNA levels in vitro and in vivo. ET_A receptor antagonist BQ123, but not ET_B receptor antagonist BQ788, inhibited CRP production in VSMCs. In addition, ET-1 was able to elicit reactive oxygen species (ROS) generation and mitogen-activated protein kinase (MAPK) activation, and antioxidant pyrrolidine dithiocarbamate and p38MAPK inhibitor SB203580 inhibited ET-1-induced CRP expression. The results demonstrate that ET-1 induces CPR production in VSMCs via ET_A receptor followed by ROS and MAPK signal pathway, which may contribute to better understanding of the role of ET-1 in inflammatory activation of the vessel wall during atherogenesis.     

Caveolin-1 sensitizes vascular smooth muscle cells to mildly oxidized LDL-induced apoptosis

Oxidized low-density lipoprotein (oxLDL)-induced apoptosis of vascular cells may participate to plaque instability and rupture. Caveolin-1 has emerged as an important regulator of several signal transduction pathways and processes that play a role in atherosclerosis. In this study we examined the potential role of caveolin-1 in the regulation of oxLDL-induced Ca²⁺ signaling and apoptosis in vascular smooth muscle cells (VSMC). Cells expressing caveolin-1 were more susceptible to oxLDL-induced apoptosis, and this was correlated with enhanced Ca²⁺ entry and pro-apoptotic events. Moreover, caveolin-1 silencing by small interfering RNA decreased the level of apoptotic cells after oxLDL treatment. These findings provide new insights about the potential role of caveolin-1 in the regulation of oxLDL-induced apoptosis in vascular cells and its contribution to the instability of the plaque.     

Posttranslational nitrotyrosination of alpha-tubulin induces cell cycle arrest and inhibits proliferation of vascular smooth muscle cells

Hyperproliferation of vascular smooth muscle cells is a hallmark of atherosclerosis and related vascular complications. Microtubules are important for many aspects of mammalian cell responses including growth, migration and signaling. alpha-Tubulin, a component of the microtubule cytoskeleton, is unique amongst cellular proteins in that it undergoes a reversible posttranslational modification whereby the C-terminal tyrosine residue is removed (Glu-tubulin) and re-added (Tyr-tubulin). Whereas the reversible detyrosination/tyrosination cycle of alpha-tubulin has been implicated in regulating various aspects of cell biology, the precise function of this posttranslational modification has remained poorly characterized. Herein, we provide evidence suggesting that alpha-tubulin detyrosination is a required event in the proliferation of vascular smooth muscle cells. Proliferation of rat aortic smooth muscle cells in response to serum was temporally associated with the detyrosination of alpha-tubulin, but not acetylation of alpha-tubulin; Glu-tubulin reached maximal levels between 12 and 18h following cell cycle initiation. Inclusion of 3-nitro-l-tyrosine (NO(2)Tyr) in the culture medium resulted in the selective nitrotyrosination of alpha-tubulin, that was paralleled by decreased elaboration of Glu-tubulin, decreased expression of cyclins A and E, decreased association of the microtubule plus-end binding protein EB1, and inhibited cell proliferation. Nitrotyrosination of alpha-tubulin did not induce necrotic or apoptotic death of rat aortic smooth muscle cells, but instead led to cell cycle arrest at the G(1)/S boundary coincident with decreased DNA synthesis. Collectively, these results suggest that the C-terminus of alpha-tubulin and its detyrosination are functionally important as a molecular switch that regulates cell cycle progression in vascular smooth muscle cells.     

Hesperetin, a bioflavonoid, inhibits rat aortic vascular smooth muscle cells proliferation by arresting cell cycle

Diet can be one of the most important factors that influence risks for cardiovascular diseases. Hesperetin, a flavonoid present in grapefruits and oranges, is one candidate that may benefit the cardiovascular system. In this study, we have investigated the effect of hesperetin on the platelet-derived growth factor (PDGF)-BB-induced proliferation of primary cultured rat aortic vascular smooth muscle cells (VSMCs). Hesperetin significantly inhibited 50 ng/ml PDGF-BB-induced rat aortic VSMCs proliferation and [(3)H]-thymidine incorporation into DNA at concentrations of 5, 25, 50, and 100 microM. In accordance with these findings, hesperetin revealed blocking of the PDGF-BB-inducible progression through G(0)/G(1) to S phase of the cell cycle in synchronized cells. Western blot showed that hesperetin inhibited not only phosphorylation of retinoblastoma protein (pRb) and expressions of cyclin A, cyclin D, cyclin E, cyclin-dependent kinase 2 (CDK2) as well as proliferating cell nuclear antigen (PCNA) protein, but also downregulation of cyclin-dependent kinase inhibitor (CKI) p27(kip1), while did not affect CKI p21(cip1), p16(INK4), p53, and CDK4 expressions as well as early signaling transductions such as PDGF beta-receptor, extracellular signal-regulated kinase (ERK) 1/2, Akt, p38, and JNK phosphorylation. These results suggest that hesperetin inhibits PDGF-BB-induced rat aortic VSMCs proliferation via G(0)/G(1) arrest in association with modulation of the expression or activation of cell-cycle regulatory proteins, which may contribute to the beneficial effect of grapefruits and oranges on cardiovascular system.     

Cannabinoid CB1 receptor inhibition decreases vascular smooth muscle migration and proliferation

Vascular smooth muscle proliferation and migration triggered by inflammatory stimuli and chemoattractants such as platelet-derived growth factor (PDGF) are key events in the development and progression of atherosclerosis and restenosis. Cannabinoids may modulate cell proliferation and migration in various cell types through cannabinoid receptors. Here we investigated the effects of CB₁ receptor antagonist rimonabant (SR141716A), which has recently been shown to have anti-atherosclerotic effects both in mice and humans, on PDGF-induced proliferation, migration, and signal transduction of human coronary artery smooth muscle cells (HCASMCs). PDGF induced Ras and ERK 1/2 activation, while increasing proliferation and migration of HCASMCs, which were dose dependently attenuated by CB₁ antagonist, rimonabant. These findings suggest that in addition to improving plasma lipid alterations and decreasing inflammatory cell migration and inflammatory response, CB₁ antagonists may exert beneficial effects in atherosclerosis and restenosis by decreasing vascular smooth muscle proliferation and migration.     

ERK1/2 mediates PDGF-BB stimulated vascular smooth muscle cell proliferation and migration on laminin-5

During restenosis following arterial injury, vascular smooth muscle cells (VSMCs) form a neointimal layer in arteries by changing from a differentiated, contractile phenotype to a dedifferentiated, migratory, and proliferative phenotype. Several growth factors, cytokines, and extracellular matrix components released following injury have been implicated in these phenotypic changes. We have recently detected the expression of laminin-5, an ECM protein found predominantly in epithelial tissues, in the arterial vasculature. Here we report that ln-5 expression by VSMC is upregulated by platelet-derived growth factor (PDGF-BB), epidermal growth factor, basic fibroblast growth factor, and transforming growth factor-beta1. Adhesion to ln-5 specifically enhances PDGF-BB-stimulated VSMC proliferation and migration. PD98059, a specific inhibitor of the ERK1/2 members of the Mitogen Activated Protein kinase family, increases both VSMC adhesion to ln-5 and blocks PDGF-BB-stimulated VSMC migration on ln-5. These results suggest that adhesion to ln-5 mediates a PDGF-BB-stimulated VSMC response to vascular injury via an ERK1/2 signaling pathway.     

Induction of heme oxygenase-1 is involved in anti-proliferative effects of paclitaxel on rat vascular smooth muscle cells

In this study, we evaluated the possibility that the anti-proliferative effects of paclitaxel on vascular smooth muscle cells (VSMCs) of the rat might be due to the induction of HO-1 gene expression. Treatment of the cells with paclitaxel resulted in marked time- and dose-dependent inductions of HO-1 mRNA, followed by corresponding increases in HO-1 protein expression and HO enzymatic activities. Furthermore, paclitaxel rapidly activated the JNK, ERK, and p38 mitogen-activated protein kinase pathways. A specific inhibitor of JNK, SP600125, abolished paclitaxel-induced HO-1 mRNA expression, whereas PD98059, a specific inhibitor of ERK, and SB203580, a specific inhibitor of p38, had no significant effect. Finally, the suppression of platelet-derived growth factor induced VSMC proliferation was abolished by the HO inhibitor, ZnPP, as well as by the CO scavenger, hemoglobin. These results demonstrated that paclitaxel induces the expression of HO-1 via the JNK pathway in VSMC and that HO-1 expression might be responsible for the anti-proliferative effect of paclitaxel on VSMC.     

ERK1/2 activation by angiotensin II inhibits insulin-induced glucose uptake in vascular smooth muscle cells

Clinical evidence suggests a relationship between hypertension and insulin resistance, and cross-talk between angiotensin II (Ang II) and insulin signaling pathways may take place. We now report the effect of Ang II on insulin-induced glucose uptake and its intracellular mechanisms in vascular smooth muscle cells (VSMC). We examined the translocation of glucose transporter-4 (GLUT-4) and glucose uptake in rat aortic smooth muscle cells (RASMC). Mitogen-activated protein (MAP) kinases and Akt activities, and phosphorylation of insulin receptor substrate-1 (IRS-1) at the serine and tyrosine residues were measured by immunoprecipitation and immunoblotting. As a result, Ang II inhibited insulin-induced GLUT-4 translocation from cytoplasm to the plasma membrane in RASMC. Ang II induced extracellular signal-regulated kinase (ERK) 1/2 and c-Jun N-terminal kinase (JNK) activation and IRS-1 phosphorylation at Ser³⁰⁷ and Ser⁶¹⁶. Ang II-induced Ser³⁰⁷ and Ser⁶¹⁶ phophorylation of IRS-1 was inhibited by a MEK inhibitor, PD98059, and a JNK inhibitor, SP600125. Ang II inhibition of insulin-stimulated IRS-1 tyrosyl phophorylation and Akt activation were reversed by PD98059 but not by SP600125. Ang II inhibited insulin-induced glucose uptake, which was also reversed by PD98059 but not by SP600125. It is shown that Ang II-induced ERK1/2 activation inhibits insulin-dependent glucose uptake through serine phophorylation of IRS-1 in RASMC.     

The ascochlorin derivative, AS-6, inhibits TNF-alpha-induced adhesion molecule and chemokine expression in rat vascular smooth muscle cells

Vascular inflammation induced by the proinflammatory cytokine/NF-kappaB pathway is one of the key mechanisms in the development of atherosclerosis. Peroxisome proliferators-activated receptor-gamma (PPARgamma) plays an important role in the prevention of arterial inflammation and formation of atherogenesis. Herein we examine the effects of a newly identified synthetic PPARgamma ligand, ascochlorin-6 (AS-6), on TNF-alpha-stimulated NF-kappaB activity and inflammatory molecule expression in vascular smooth muscle cells (VSMCs). AS-6 successfully inhibited TNF-alpha-stimulated NF-kappaB activity and inflammatory molecule expression, including vascular cell adhesion molecule-1 (VCAM-1), monocyte chemotactic protein-1 (MCP-1), and fractalkine (CX3CL1). Transient transfection with an [NF-kappaB]x4 luciferase reporter construct showed that AS-6 inhibition of TNF-alpha-stimulated NF-kappaB activation was PPARgamma-dependent. The effects of AS-6 on TNF-alpha-stimulated VCAM-1 and CX3CL1 expression were abolished in cells transfected with an adenovirus expressing dominant-negative PPARgamma and in cells treated with a PPARgamma specific inhibitor, GW9662, confirming again that the anti-inflammatory effect of AS-6 was PPARgamma-dependent. The inhibitory effects of AS-6 on TNF-alpha-stimulated inflammatory gene expression and NF-kappaB activation were more potent than those of rosiglitazone and pioglitazone. This study shows that AS-6 reduces the inflammatory response to TNF-alpha in VSMCs. The data suggest the possibility that AS-6 can be used to prevent the development and progression of atherosclerosis.     

CREG inhibits migration of human vascular smooth muscle cells by mediating IGF-II endocytosis

We previously determined that the cellular repressor of E1A-stimulated genes, (CREG) plays a role in the maintenance of the mature phenotype of vascular smooth muscle cells (SMCs). This study aimed to identify the role of CREG in modulating the migration of SMCs. Recombinant virus-mediated CREG expression inhibited the cellular migration of cultured SMCs associated with down-regulated activity of matrix metalloproteinase-9 (MMP-9). In contrast, CREG knockdown via the retroviral transfer of short hairpin RNAs promoted cellular migration. Enzyme-linked immunosorbent assay and endocytosis analysis revealed that CREG knockdown attenuated the internalization and increased secretion of insulin-like growth factor (IGF)-II. Western blot analysis demonstrated that both phosphoinositide 3-kinase (PI3K) and phosphatase Akt were enhanced in CREG knockdown SMCs. Furthermore, the effect of CREG knockdown on SMC migration was abrogated in a dose-dependent manner by the addition of either IGF-II neutralizing antibody or the PI3K inhibitor, LY294002. These results indicate that the CREG knockdown-mediated increase in IGF-II secretion promoted cellular migration in SMCs via the PI3K/Akt signal pathway. Additionally, blockage of IGF-II binding to the mannose-6-phosphate/IGF-II receptor (M6P/IGF2R) by IGF2R antibody or recombinant IGF2R fragment attenuated the endocytosis of IGF-II in cells overexpressing CREG. This indicates that M6P/IGF2R is involved in the regulation of CREG-mediated IGF-II endocytosis. In summary, these data demonstrate for the first time that CREG plays a critical role in the inhibition of SMC migration, as well as maintaining SMCs in a mature phenotype. These results may provide a new therapeutic target for vascular disease associated with neointimal hyperplasia.     

Overexpression of heme oxygenase-1 protects smooth muscle cells against oxidative injury and inhibits cell proliferation

To investigate whether the expression of exogenous heme oxygenase-1 (HO-1) gene within vascular smooth muscle cells (VSMC) could protect the cells from free radical attack and inhibit cell proliferation, we established an in vitro transfection of human HO-1 gene into rat VSMC mediated by a retroviral vector. The results showed that the profound expression of HO-1 protein as well as HO activity was 1.8- and 2.0-fold increased respectively in the transfected cells compared to the non-transfected ones. The treatment of VSMC with different concentrations of H2O2 led to the remarkable cell damage as indicated by survival rate and LDH leakage. However, the resistance of the HO-1 transfected VSMC against H2O2 was significantly raised. This protective effect was dramatically diminished when the transfected VSMC were pretreated with ZnPP-IX, a specific inhibitor of HO, for 24 h. In addition, we found that the growth potential of the transfected cells was significantly inhibited directly by increased activity of H     

Enhancement of sphingosine 1-phosphate-induced migration of vascular endothelial cells and smooth muscle cells by an EDG-5 antagonist

Sphingosine 1-phosphate (Sph-1-P), a bioactive lysophospholipid capable of inducing a wide spectrum of biological responses, acts as an intercellular mediator, through interaction with the endothelial differentiation gene (EDG)/S1P family of G protein-coupled receptors. In this study, the effects of JTE-013, a specific antagonist of the migration-inhibitory receptor EDG-5, on Sph-1-P-elicited responses were examined in human umbilical vein endothelial cells (HUVECs) and vascular smooth muscle cells (SMCs), which expressed EDG-5 protein weakly and abundantly, respectively. This pyrazolopyridine compound reversed the inhibitory effect of Sph-1-P on SMC migration and further enhanced Sph-1-P-stimulated HUVEC migration. In contrast, its effect on Sph-1-P-induced intracellular Ca(2+) mobilization was marginal. Our results indicate that specific regulation of Sph-1-P-modulated migration responses in vascular cells can be achieved by EDG-5 antagonists and that manipulation of Sph-1-P biological activities by each EDG antagonist may lead to a therapeutical application to control vascular diseases.