Suppression of growth factor expression and human vascular smooth muscle cell growth by small interfering RNA targeting EGR-1

Smooth muscle cell (SMC) proliferation and migration are key processes that occur in the reparative response to injury after percutaneous coronary intervention and in failed bypass grafts for the treatment of atherosclerosis. In the present study, we generated novel synthetic small interfering RNA (siRNA) molecules targeting the coding region of human early growth response-1 (EGR-1) mRNA that attenuate the expression of EGR-1 and that of fibroblast growth factor-2 (FGF-2) and granulocyte-colony stimulating factor (G-CSF). These agents suppressed SMC proliferation in a dose-dependent and non-toxic manner and blocked SMC regrowth from the wound edge following mechanical injury in vitro. In contrast, the scrambled counterpart did not inhibit SMC proliferation, EGR-1 protein expression or SMC regrowth after injury. These findings demonstrate that EGR-1 siRNA can serve as inhibitors of SMC proliferation and wound repair suggesting that these agents may potentially be useful in the control of vascular proliferative disorders.     

Carotenoids inhibit DNA synthesis in human aortic smooth muscle cells

Quiescent, serum-starved human aortic smooth muscle cells were restimulated with 20% foetal calf serum in Dulbecco's modified Eagle medium, in the presence and absence of beta-carotene, canthaxanthin, zeaxanthin, lycopene, lutein or beta-cryptoxanthin, at final concentrations up to 23 microM. Concentration-dependent inhibition of DNA synthesis, measured by [methyl-3H]thymidine incorporation, was observed for the carotenoids, except for canthaxanthin and lutein which had no effect. Lycopene was the most potent of the carotenoids tested. The results suggest that antiproliferative effects of dietary carotenoids might be of significance in vivo.     

Tyk2 mediates effects of urokinase on human vascular smooth muscle cell growth

The urokinase (uPA)/uPA receptor (uPAR) system plays a role in the response of the vessel wall to injury, presumably by modulating vascular smooth muscle cell (VSMC) functional behaviour. The Jak/Stat signaling pathway has been implicated to mediate the uPA/uPAR-directed cell migration and proliferation in VSMC. We have therefore investigated the underlying molecular mechanisms, which remained not completely understood. In particular, we aimed at identification of the kinase involved in the signaling cascade leading to Stat1 phosphorylation by uPA and its impact on VSMC growth. We performed expression in VSMC of kinase-deficient mutant forms of the Janus kinases Jak1 and Tyk2 and used different cell culture models imitating the response to vascular injury. We provide evidence that Tyk2, but not Jak1, mediates uPA-induced Stat1 phosphorylation and VSMC growth inhibition and suggest a novel function for Tyk2 as an important modulator of the uPA-directed VSMC functional behaviour at the place of injury.     

Cks1 mediates vascular smooth muscle cell polyploidization

Vascular smooth muscle cells (VSMC) at capacitance arteries of hypertensive individuals and animals undergo dramatic polyploidization that contributes toward their hypertrophic phenotype. We report here the identification of a defective mitotic spindle cell cycle checkpoint in VSMC isolated from capacitance arteries of pre-hypertensive rats. These cells demonstrated a high predisposition to polyploidization in culture and failed to maintain cyclin B protein levels in response to colcemid, a mitotic inhibitor. Furthermore, this altered mitotic spindle checkpoint status was associated with the overexpression of Cks1, a Cdc2 adapter protein that promotes cyclin B degradation. Cks1 up-regulation, cyclin B down-regulation, and VSMC polyploidization were evidenced at the smooth muscle of capacitance arteries of genetically hypertensive and Goldblatt-operated rats. In addition, angiotensin II infusion dramatically increased Cks1 protein levels at capacitance arteries of normotensive rats, and angiotensin II treatment of isolated VSMC abrogated their ability to down-regulate Cks1 and maintain cyclin B protein expression in response to colcemid. Finally, transduction of VSMC from normotensive animals with a retrovirus that drives the expression of Cks1 was sufficient to alter their mitotic spindle cell cycle checkpoint status and promote unscheduled cyclin B metabolism, cell cycle re-entry, and polyploidization. These data demonstrate that Cks1 regulates cyclin B metabolism and ploidy in VSMC and may contribute to the understanding of the phenomena of VSMC polyploidization during hypertension.     

RNA interference targeting alpha8 integrin attenuates smooth muscle cell growth

alpha8 integrin gene silencing has been shown to result in the stress fibre disassembly. Stress fibres are required for cell adhesion to promote passage through cell cycle. Thus, we hypothesized that alpha8 integrin gene silencing might affect vascular smooth muscle cell (VSMC) growth. Short interference RNA (siRNA) targeting alpha8 integrin in rat VSMCs resulted in reduced DNA synthesis. Moreover, siRNA-alpha8 integrin prevented thrombin-induced proliferation. RhoA plays a critical role in regulating VSMC growth. alpha8 integrin co-immunoprecipitated with RhoA and siRNA-alpha8 reduced membrane associated RhoA. Our data suggest that alpha8 integrin expression is critical for VSMC growth, which has potential implications in postangioplasty neointimal hyperplasia.     

Uniaxial strain upregulates matrix-degrading enzymes produced by human vascular smooth muscle cells

Arteries remodel in response to environmental changes. We investigated whether mechanical strain modulates production of matrix metalloproteinase (MMP)-2 and -9 by cultured vascular smooth muscle cells (SMC). MMP-2 and MMP-9 expression were tested using human saphenous vein SMC cultured on silicone membranes at rest or subjected to physiological levels (5%) of stationary or cyclical (1 Hz) uniaxial strain. Compared with control, stationary strain significantly increased MMP-2 mRNA levels at all time points, whereas cyclic strain decreased it after 48 h. Both secreted and cell-associated pro-MMP-2 levels were increased by stationary strain at all times (P < 0.01), whereas cyclic strain decreased secreted levels after 48 h (P < 0.02). MMP-9 mRNA levels and pro-MMP-9 protein were increased after 48 h of stationary stretch (P < 0.01) compared with both no strain and cyclic strain. Our study indicates that vascular SMC show a selective response to different types of strain. We suggest that local increases in stationary mechanical strain resulting from stenting, hypertension, or atherosclerosis may lead to enhanced matrix degradation by SMC.     

Regulation of vascular smooth muscle cell growth by aldose reductase

Aldose reductase (AR) is a broad-specificity aldo-keto reductase with wide species and tissue distribution. The enzyme has been implicated in the development of pleiotropic complications of long-term diabetes. However, the euglycemic function of the enzyme remains unclear. To examine its potential role in cell growth, changes in AR mRNA and protein were measured in human aortic smooth muscle cells exposed in culture to serum or thrombin. Stimulation by these mitogens led to an increase in the abundance of AR mRNA and protein. Furthermore, inhibition of the AR by tolrestat and sorbinil diminished DNA synthesis and cell proliferation in response to serum. Immunohistochemical staining with anti-AR antibodies revealed no significant expression of AR in the smooth muscle cells of rat carotid arteries. However, 10 and 21 days after balloon injury, intense staining was associated with the proliferating cells of the neointima. Treatment of these animals with 40 mg/kg/day sorbinil diminished the ratio of neointima to the media. Together, these observations suggest that, in vascular smooth muscle cells (VSMC), AR is a growth-responsive gene product and that inhibition of AR prevents VSMC growth and decreases intimal hyperplasia and restenosis.     

New DNA enzyme targeting Egr-1 mRNA inhibits vascular smooth muscle proliferation and regrowth after injury.

Early growth response factor-1 (Egr-1) binds to the promoters of many genes whose products influence cell movement and replication in the artery wall. Here we targeted Egr-1 using a new class of DNA-based enzyme that specifically cleaved Egr-1 mRNA, blocked induction of Egr-1 protein, and inhibited cell proliferation and wound repair in culture. The DNA enzyme also inhibited Egr-1 induction and neointima formation after balloon injury to the rat carotid artery wall. These findings demonstrate the utility of DNA enzymes as biological tools to delineate the specific functions of a given gene, and implicate catalytic nucleic acid molecules composed entirely of DNA as potential therapeutic agents.     

Ether-linked diglycerides inhibit vascular smooth muscle cell growth via decreased MAPK and PI3K/Akt signaling

Diglycerides (DGs) are phospholipid-derived second messengers that regulate PKC-dependent signaling pathways. Distinct species of DGs are generated from inflammatory cytokines and growth factors. Growth factors increase diacyl- but not ether-linked DG species, whereas inflammatory cytokines predominately generate alkyl, acyl- and alkenyl, acyl-linked DG species in rat mesenchymal cells. These DG species have been shown to differentially regulate protein kinase C (PKC) isotypes. Ester-linked diacylglycerols activate PKC-epsilon and cellular proliferation in contrast to ether-linked DGs, which lead to growth arrest through the inactivation of PKC-epsilon. It is now hypothesized that ether-linked DGs inhibit mitogenesis through the inactivation of ERK and/or Akt signaling cascades. We demonstrate that cell-permeable ether-linked DGs reduce vascular smooth muscle cell growth by inhibiting platelet-derived growth factor-stimulated ERK in a PKC-epsilon-dependent manner. This inhibition is specific to the ERK pathway, since ether-linked DGs do not affect growth factor-induced activation of other family members of the MAPKs, including p38 MAPK and c-Jun NH(2)-terminal kinases. We also demonstrate that ether-linked DGs reduce prosurvival phosphatidylinositol 3-kinase (PI3K)/Akt signaling, independent of PKC-epsilon, by diminishing an interaction between the subunits of PI3K and not by affecting protein phosphatase 2A or lipid (phosphatase and tensin homologue deleted in chromosome 10) phosphatases. Taken together, our studies identify ether-linked DGs as potential adjuvant therapies to limit vascular smooth muscle migration and mitogenesis in atherosclerotic and restenotic models.     

Regulation of vascular smooth muscle cell growth by aldose reductase

Aldose reductase (AR) is a broad-specificity aldo-keto reductase with wide species and tissue distribution. The enzyme has been implicated in the development of pleiotropic complications of long-term diabetes. However, the euglycemic function of the enzyme remains unclear. To examine its potential role in cell growth, changes in AR mRNA and protein were measured in human aortic smooth muscle cells exposed in culture to serum or thrombin. Stimulation by these mitogens led to an increase in the abundance of AR mRNA and protein. Furthermore, inhibition of the AR by tolrestat and sorbinil diminished DNA synthesis and cell proliferation in response to serum. Immunohistochemical staining with anti-AR antibodies revealed no significant expression of AR in the smooth muscle cells of rat carotid arteries. However, 10 and 21 days after balloon injury, intense staining was associated with the proliferating cells of the neointima. Treatment of these animals with 40 mg/kg/day sorbinil diminished the ratio of neointima to the media. Together, these observations suggest that, in vascular smooth muscle cells (VSMC), AR is a growth-responsive gene product and that inhibition of AR prevents VSMC growth and decreases intimal hyperplasia and restenosis.     

Locked nucleic acid containing antisense oligonucleotides enhance inhibition of HIV-1 genome dimerization and inhibit virus replication

We have evaluated antisense design and efficacy of locked nucleic acid (LNA) and DNA oligonucleotide (ON) mix-mers targeting the conserved HIV-1 dimerization initiation site (DIS). LNA is a high affinity nucleotide analog, nuclease resistant and elicits minimal toxicity. We show that inclusion of LNA bases in antisense ONs augments the interference of HIV-1 genome dimerization. We also demonstrate the concomitant RNase H activation by six consecutive DNA bases in an LNA/DNA mix-mer. We show ON uptake via receptor-mediated transfection of a human T-cell line in which the mix-mers subsequently inhibit replication of a clinical HIV-1 isolate. Thus, the technique of LNA/DNA mix-mer antisense ONs targeting the conserved HIV-1 DIS region may provide a strategy to prevent HIV-1 assembly in the clinic.     

Uric acid stimulates vascular smooth muscle cell proliferation by increasing platelet-derived growth factor A-chain expression

Recent data suggest that uric acid is generated locally in the vessel wall by the action of xanthine oxidase. This enzyme, activated during ischemia/reperfusion by proteolytic conversion of xanthine dehydrogenase, catalyzes the oxidation of xanthine, thereby generating free radicals and uric acid. Because of the potential role of ischemia/reperfusion in vascular disease, we studied the effects of uric acid on rat aortic vascular smooth muscle cell (VSMC) growth. Uric acid stimulated VSMC DNA synthesis, as measured by [3H]thymidine incorporation, in a concentration-dependent manner with half-maximal activity at 150 microM. Maximal induction of DNA synthesis by uric acid (250 microM) was approximately 70% of 10% calf serum and equal to 10 ng/ml platelet-derived growth factor (PDGF) AB or 20 ng/ml fibroblast growth factor. Neither uric acid precursors (xanthine and hypoxanthine) nor antioxidants (ascorbic acid, glutathione, and alpha-tocopherol) were mitogenic for VSMC. Uric acid was mitogenic for VSMC but not for fibroblasts or renal epithelial cells. The time course for uric acid stimulation of VSMC growth was slower than serum, suggesting induction of an autocrine growth mechanism. Exposure of quiescent VSMC to uric acid stimulated accumulation of PDGF A-chain mRNA (greater than 5-fold at 8 h) and secretion of PDGF-like material in conditioned medium (greater than 10-fold at 24 h). Uric acid-induced [3H]thymidine incorporation was markedly inhibited by incubation with anti-PDGF A-chain polyclonal antibodies. Thus uric acid stimulates VSMC growth via an autocrine mechanism involving PDGF A-chain. These findings suggest that generation of uric acid during ischemia/reperfusion contributes to atherogenesis and intimal proliferation following arterial injury.