Human urotensin-II potentiates the mitogenic effect of mildly oxidized low-density lipoprotein on vascular smooth muscle cells: comparison with other vasoactive agents and hydrogen peroxide.

Human urotensin-II (U-II) is the most potent vasoactive peptide identified to date, and may be involved in hypertension and atherosclerosis. We investigated the effects of the interactions between U-II or other vasoactive agents and mildly oxidized low-density lipoprotein (mox-LDL) or hydrogen peroxide (H2O2) on the induction of vascular smooth muscle cell (VSMC) proliferation. Growth-arrested rabbit VSMCs were incubated with vasoactive agents (U-II, endothelin-1, angiotensin-II, serotonin, or thromboxane-A2) in the presence or absence of mox-LDL or H2O2. [3H]Thymidine incorporation into DNA was measured as an index of VSMC proliferation. On interaction with mox-LDL or H2O2, U-II induced the greatest increase in [3H]thymidine incorporation among these vasoactive agents. A low concentration of U-II (10 nmol/l) enhanced the potential mitogenic effect of low concentrations of mox-LDL (120 to 337%) and H2O2 (177 to 226%). U-II at 50 nmol/l showed the maximal mitogenic effect (161%), which was abolished by G protein inactivator (GDP-beta-S), c-Src tyrosine kinase inhibitor (radicicol), protein kinase C (PKC) inhibitor (Ro31-8220), extracellular signal-regulated kinase (ERK) kinase inhibitor (PD98059), or Rho kinase inhibitor (Y27632). Mox-LDL at 5 microg/ml showed the maximal mitogenic effect (211%), which was inhibited by free radical scavenger (catalase), intracellular and extracellular antioxidants (N-acetylcysteine and probucol), nicotinamide adenine dinucleotide phosphate oxidase inhibitor (diphenylene iodonium), or c-Jun N-terminal kinase (JNK) inhibitor (SP600125). These results suggested that U-II acts in synergy with mox-LDL in inducing VSMC DNA synthesis at the highest rate among these vasoactive agents. Activation of the G protein/c-Src/PKC/ERK and Rho kinase pathways by U-II together with the redox-sensitive JNK pathway by mox-LDL may explain the synergistic interaction between these agents.     

Lysophosphatidylcholine potentiates the mitogenic effect of various vasoactive compounds on rabbit aortic smooth muscle cells

We examined the mechanism of action of lysophosphatidylcholine (lyso-PC), which is suggested to be involved in the pathogenesis of atherosclerosis and inflamatory disorders, and its interaction with well-known vasoactive compounds such as hydrogen peroxide (H2O2), thromboxane A2 (TX-A2), serotonin (5-HT), angiotensin II (Ang-II), endothelin-1 (ET-1), or urotensin II (U-II) on VSMC proliferation. Growth-arrested rabbit VSMCs were incubated with given concentrations of lyso-PC with H202, TX-A2, 5-HT, Ang-II, ET-1, or U-II. [3H]Thymidine incorporation into DNA was measured as an index of VSMC proliferation. Lyso-PC induced a maximal effect on [3H]thymidine incorporation at a concentration of 15 microM (156%), and its effect was significantly inhibited by the phospholipase C inhibitor U73122 (10 microM), the intracellular antioxidant NAC (400 microM), and the NADPH oxidase inhibitor diphenylene iodonium (1 microM), but not by the MAPK kinase inhibitor (10 microM). H2O2, TX-A2, 5-HT, Ang-II, ET-1, or U-II also stimulated [3H]thymidine incorporation in a dose-dependent manner. A non-mitogenic concentration of lyso-PC (5 microM) significantly potentiated the effect of low concentrations of H2O2 (0.1 microM, 110 to 222%), TX-A2 (5 microM, 120 to 202%), 5-HT (5 microM, 182 to 259%), Ang-II (0.5 microM, 167 to 304%), ET-1 (0.01 microM, 139 to 297%), or U-II (0.025 microM, 120 to 332%) on [3H]thymidine incorporation. The results suggest that lyso-PC acts synergistically with the vasoactive compounds H2O2, TX-A2, 5-HT, Ang-II, ET-1, or U-II in inducing VSMC proliferation, which may play an important role in the progression of atherosclerosis.     

Oxidized low-density lipoproteins potentiate the mitogenic effect of 5-hydroxytryptamine on vascular smooth muscle cells

Considerable attention has been focused on both highly oxidized low-density lipoprotein (ox-LDL) and mildly oxidized LDL (mox-LDL) as important risk factors for cardiovascular disease. Further, 5-hydroxytryptamine (5-HT) appears to play a crucial role in the development of atherosclerotic plaque. We assessed the interaction of oxidatively modified LDL and its major oxidative components, ie, hydrogen peroxide (H2O2), lysophosphatidylcholine (LPC), and 4-hydroxy-2-nonenal (HNE) with 5-HT on DNA synthesis in vascular smooth muscle cells (VSMCs). Growth-arrested rabbit VSMCs were incubated in serum-free medium with native LDL, mox-LDL, ox-LDL (all 50 ng/mL), H2O2 (0.5 microM), LPC (1 microM), or HNE (0.1 microM) for 24 hours followed by 5-HT (5 microM) for another 24 hours. DNA synthesis in VSMCs was measured by [3H]thymidine incorporation. Significant effects on [3H]thymidine incorporation were observed in VSMCs incubated with mox-LDL (129%), ox-LDL (129%), H2O2 (119%), LPC (115%), HNE (127%), or 5-HT (183%) in contrast with native LDL (113%). The mitogenic effect of 5-HT was potentiated by mox-LDL, ox-LDL, H2O2, LPC, or HNE (183 to 365%, 274%, 304%, 339%, or 273%, respectively) but not by native LDL (240%). The mitogen-activated protein kinase (MAPK) kinase inhibitor PD98059 (10 microM) significantly inhibited the mitogenic effect of 5-HT but did not influence the effects of mox-LDL, ox-LDL, H2O2, LPC, or HNE. The intracellular antioxidant N-acetylcysteine (400 microM) significantly inhibited the mitogenic effects of mox-LDL, ox-LDL, H2O2, LPC, and HNE but not that of 5-HT. Our results suggest that mox-LDL, ox-LDL, and their major components H2O2, LPC, and HNE act synergistically with 5-HT in inducing VSMC DNA synthesis via MAPK and redox-sensitive pathways, contributing to the development of atherosclerotic plaque.     

Heparin-binding EGF-like growth factor induces expression of lectin-like oxidized LDL receptor-1 in vascular smooth muscle cells

Receptor-mediated endocytosis of oxidized LDL (Ox-LDL) has been implicated in lipid accumulation and vascular cell dysfunction. Lectin-like Ox-LDL receptor-1 (LOX-1) is highly inducible by proinflammatory cytokines, as well as angiotensin II and Ox-LDL in vitro. LOX-1 is expressed in macrophages and smooth muscle cells accumulated in the intima of advanced atherosclerotic plaques in vivo. Here we show that heparin-binding epidermal growth factor-like growth factor (HB-EGF), a potent mitogen for vascular smooth muscle cells, induces LOX-1 expression in cultured bovine aortic smooth muscle cells. HB-EGF (1-100 ng/ml) induced LOX-1 expression, which was peaked between 8 and 16 h after HB-EGF stimulation. HB-EGF-induced expression of LOX-1 was suppressed by ZD1839, an inhibitor of EGF receptor phosphorylation. Both MEK and p38 mitogen-activated protein kinase (MAPK) inhibitors significantly blocked LOX-1 upregulation induced by HB-EGF. Phosphatidylinositol 3-kinase (PI3K) inhibitors also blocked HB-EGF-induced LOX-1 expression. HB-EGF induced phosphorylation of ERK, p38 MAPK and Akt, which were suppressed by ZD1839. Upregulated expression of LOX-1 was associated with enhanced uptake of DiI-labeled Ox-LDL in smooth muscle cells. Taken together, HB-EGF can also act as an inducer of LOX-1 expression and play an integral role in foam cell transformation, cellular dysfunction, and proliferation of smooth muscle cells in atherogenesis.     

Differential response of vascular smooth muscle cells to oxidized LDL in mouse strains with different atherosclerosis susceptibility

Oxidized low-density lipoprotein (LDL) has numerous atherogenic properties, including induction of inflammatory genes, and vascular smooth muscle cells (VSMC) are involved in the development of atherosclerosis. In this study, we examined whether variations of VSMC in the capacity to oxidize LDL or in response to minimally modified LDL (MM-LDL) constitute a genetic component in atherosclerosis. VSMC were isolated from the aorta of two inbred mouse strains C57BL/6J (B6) and C3H, which differ markedly in susceptibility to atherosclerosis. LDL oxidation was assessed by measuring thiobarbituric acid-reactive substance (TBARS) production. Responses to MM-LDL were evaluated by examining the expression of inflammatory genes involved atherosclerosis, including monocyte chemotactic protein-1 (MCP-1) and vascular cell adhesion molecule-1 (VCAM-1), and an oxidant stress gene, heme oxygenase-1 (HO-1). VSMC from the two strains exhibited a comparable ability to transform native LDL to oxidized LDL, whereas their response to MM-LDL differed markedly. MM-LDL resulted in dramatic induction of MCP-1, VCAM-1, and HO-1 mRNAs in the cells from B6 mice but exerted little effect in cells from C3H mice. MCP-1 and soluble VCAM-1 protein levels in conditioned media were measured by ELISA. B6 cells produced significantly more MCP-1 and VCAM-1 proteins in response to MM-LDL than C3H cells. These data suggest that variation in the response of VSMC to oxidized LDL may contribute to the difference between B6 and C3H mice in atherosclerosis susceptibility.     

Lysophosphatidylcholine induces apoptotic and non-apoptotic death in vascular smooth muscle cells: in comparison with oxidized LDL

Oxidized low-density lipoprotein (oxLDL) plays a key role in the development of atherogenesis, partly by causing injury to vascular cells. However, different preparations of LDL, methods of oxidation, and/or active components often produce cellular effects of various degrees. To explore the quantitative relationship between dose and level of oxidation of the oxLDL utilized, we employed combinations of different levels of oxidation and concentrations of oxLDL to induce cell death in cultured vascular smooth muscle cells (VSMC). We also examined the effect of lysophosphatidylcholine (lysoPC), a putative active component of oxLDL, on VSMCs by determining, in parallel with a cytotoxicity test (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay), DNA fragmentation ([3H]thymidine release), and flow cytometric analyses. We found that oxLDL caused cytotoxicity in an oxidative level- and dose-dependent manner, lysoPC also caused dose-dependent cytotoxicity with or without serum. Fragmentation of DNA was observed in both oxLDL- and lysoPC-treated VSMCs. Furthermore, lysoPC-induced DNA ladder was also demonstrated by gel electrophoresis at a concentration of 25 micromol/l or higher. Flow cytometric analysis yielded similar results for oxLDL- and lysoPC-treated VSMC; namely, an accumulation in the fraction of cells in G(0)/G(1) phase with a reciprocal change in S-phase fraction. Membrane phosphatidylserine exposure, detected by annexin V staining, provided additional evidence that lysoPC induced significant apoptosis in VSMC. Taken together, the degree of oxLDL-induced cytotoxicity/apoptosis of VSMC depended on combined effects of oxLDL concentration and oxidative level. Moreover, lysoPC also elicited a dose-dependent apoptosis in addition to cytotoxicity.     

LDL receptor-related protein mediates uptake of aggregated LDL in human vascular smooth muscle cells

Foam cell formation is a key event in the onset and progression of atherosclerotic lesions. We have previously reported that internalization of aggregated low density lipoproteins (agLDLs) by vascular smooth muscle cells (VSMCs) produces cholesteryl ester (CE) accumulation in these cells. The aim of this study was to analyze whether the low density lipoprotein receptor-related protein (LRP) mediates the uptake of agLDL by VSMCs. First, immunocytochemistry and fluorescence microscopic analysis with the use of anti-LRP antibodies indicated that there was a high expression of LRP in VSMCs. Confocal microscopic analysis with the use of agLDLs labeled with fluorochrome 1,1'-dioctadecyl-3,3,3', 3'-tetramethylindocarbocyanine and anti-LRP antibodies showed the colocalization of agLDL and LRP. The second approach was to analyze the effect of LRP ligands on agLDL internalization; lactoferrin strongly inhibited CE accumulation from agLDLs (85.0+/-5.7% at 25 microg/mL) by impairing agLDL binding. Coincubation of agLDL with anti-LRP antibodies decreased in a dose-dependent manner agLDL-derived CE accumulation (from 20% at 12.5 microg/mL to 80% at 50 microg/mL). The third approach was to evaluate whether antisense LRP oligodeoxynucleotides were able to block agLDL internalization. Treatment of VSMCs with 5 micromol/L antisense LRP oligodeoxynucleotides reduced agLDL-derived CE accumulation by 84+/-2%. In conclusion, these results from immunologic, biochemical, and molecular interventions demonstrate that LRP mediates the binding and internalization of agLDL in human VSMCs. Because LRP is highly expressed in VSMCs and the uptake of 1 LDL aggregate amounts to the deposition of several hundreds of LDL particles, the uptake of agLDL through LRP could have a crucial role for lipid deposition in VSMCs.     

Carbon monoxide inhibits apoptosis in vascular smooth muscle cells

OBJECTIVE: Carbon monoxide (CO) is generated from vascular smooth muscle cells via the degradation of heme by the enzyme heme oxygenase-1. Since smooth muscle cell apoptosis is associated with numerous vascular disorders, we investigated whether CO regulates apoptosis in vascular smooth muscle. METHODS AND RESULTS: Treatment of cultured rat aortic smooth muscle cells with a combination of cytokines (interleukin-1beta, 5 ng/ml; tumor necrosis factor-alpha, 20 ng/ml; interferon-gamma, 200 U/ml) for 48 h stimulated apoptosis, as demonstrated by DNA laddering, annexin V binding, and caspase-3 activation. However, the exogenous administration of CO inhibited cytokine-mediated apoptosis. The antiapoptotic action of CO was partially dependent on the activation of soluble guanylate cyclase and was associated with the inhibition of mitochondrial cytochrome c release and with the suppression of p53 expression. Incubation of smooth muscle cells with the cytokines also resulted in a pronounced increase in heme oxygenase-1 protein after 24 h of stimulation. The addition of the heme oxygenase inhibitor, zinc protoporphyrin-IX, or the CO scavenger, hemoglobin, stimulated apoptosis following 24 h of cytokine exposure. CONCLUSIONS: These results demonstrate that CO, either administered exogenously or endogenously derived from heme oxygenase-1 activity, inhibits vascular smooth muscle cell apoptosis. The ability of CO to block smooth muscle cell apoptosis may play an important role in blocking lesion formation at sites of vascular injury.     

Atorvastatin inhibits myocardin expression in vascular smooth muscle cells

Atorvastatin (ATV), an inhibitor of 3-hydroxy-3-methylglutaryl-coenzyme A reductase, is widely prescribed as a lipid-lowering drug. It also inhibits the RhoA-Rho-associated kinase pathway in vascular smooth muscle (SM) cells and critically inhibits SM function. Myocardin is a coactivator of serum response factor, which upregulates SM contractile proteins. The RhoA-Rho-associated kinase pathway, which directly triggers SM contraction, also increases myocardin gene expression. Therefore, we investigated whether ATV inhibits myocardin gene expression in SM cells. In mice injected with ATV (IP 20 μg/g per day) for 5 days, myocardin gene expression was significantly downregulated in aortic and carotid arterial tissues with decreased expression of myocardin target genes SM α-actin and SM22. Correspondingly, the contractility of aortic rings in mice treated with ATV or the Rho-associated kinase inhibitor Y-27632 was reduced in response to treatment with either KCl or phenylephrine. In cultured mouse and human aortic SM cells, KCl treatment stimulated the expression of myocardin, SM α-actin, and SM22. These stimulatory effects were prevented by ATV treatment. ATV-induced inhibition of myocardin expression was prevented by pretreatment with either mevalonate or geranylgeranylpyrophosphate but not farnesylpyrophosphate. Treatment with Y-27632 mimicked ATV effects on the gene expression of myocardin, SM α-actin, and SM22, further suggesting a role for the RhoA-Rho-associated kinase pathway in ATV effects. Furthermore, ATV treatment inhibited RhoA membrane translocation and activation; these effects were prevented by pretreatment with mevalonate. We conclude that ATV inhibits myocardin gene expression in vivo and in vitro, suggesting a novel mechanism for ATV inhibition of vascular contraction.     

凝血酶及凝血因子Xa诱导血管平滑肌细胞中植物凝集素样氧化型低密度脂蛋白受体-1表达的实验研究

目的研究血管平滑肌细胞中凝血酶及凝血因子xa对新型的氧化型低密度脂蛋白的清道夫受体,即植物凝集素样氧化型低密度脂蛋白受体-1（LOX-1）表达的影响。方法培养的牛主动脉平滑肌细胞,予凝血酶及凝血因子xa刺激后,用鼠抗LOX-1单克隆抗体,对细胞裂解液和浓缩的培养基进行Western blot分析,观察LOX-1表达的变化。结果在凝血酶2．0U／ml及凝血因子Xa 50 nmol／L时,可观察到细胞膜结合型LOX-1表达明显增加。凝血酶3．0U／ml和凝血因子Xa100nmol／L刺激14h后,细胞培养基中可溶型LOX-1表达明显升高。对平滑肌细胞给予1．0U／ml凝血酶及100nmol／L凝血因子xa刺激,4h后LOX-1表达开始增加,12h后达高峰。AGl478是表皮生长因子受体相关酪氨酸激酶抑制剂。用指定浓度AGl478预刺激后,再予凝血酶和凝血因子xa,然后对细胞裂解液进行Western blot分析。AGl478可显著抑制凝血酶及凝血因子xa导致的LOX-1表达增加。结论凝血酶及凝血因子Xa可诱导LOX-1表达增加,此作用由表皮生长因子受体介导。     

Vitamin C protects human vascular smooth muscle cells against apoptosis induced by moderately oxidized LDL containing high levels of lipid hydroperoxides.

Vascular cell death is a key feature of atherosclerotic lesions and may contribute to the plaque "necrotic" core, cap rupture, and thrombosis. Oxidatively modified low-density lipoproteins (LDLs) are implicated in the pathogenesis of atherosclerosis, and dietary antioxidants are thought to protect the vasculature against LDL-induced cytotoxicity. Because LDL oxidative modification may vary within atherosclerotic lesions, we examined the effects of defined, oxidatively modified LDL species on human arterial smooth muscle cell apoptosis and the cytoprotective effects of vitamin C. Moderately oxidized LDL (0 to 300 microg protein/mL), which has the highest content of lipid hydroperoxides, induced smooth muscle cell apoptosis within 6 hours, whereas native LDL and mildly and highly oxidized LDL had no effect. Moderately oxidized LDL increased cellular DNA fragmentation, release of fragmented DNA into the culture medium, and annexin V binding and decreased mitochondrial dehydrogenase activity and expression of the antiapoptotic mediator Bcl-x(L). Treatment of cells with native LDL together with the lipid hydroperoxide 13(S)-hydroperoxyoctadeca-9Z,11E-dienoic acid (HPODE, 200 micromol/L, 6 to 24 hours) also induced apoptotic cell death. Pretreatment of smooth muscle cells with vitamin C (0 to 100 micromol/L, 24 hours) attenuated the cytotoxicity and apoptosis induced by both moderately oxidized LDL and HPODE. Our findings suggest that moderately oxidized LDL, with its high lipid hydroperoxide content, rather than mildly or highly oxidized LDL, causes apoptosis of human smooth muscle cells and that vitamin C supplementation may provide protection against plaque instability in advanced atherosclerosis.     

Rosuvastatin inhibits human airway smooth muscle cells mitogenic response to eicosanoid contractile agents

BackgroundThe concept of permanent narrowing of the airways resulting from chronic inflammation and fibrosis is called remodeling and is a common feature of asthma and chronic obstructive pulmonary disease (COPD). The eicosanoid contractile agents thromboxane A₂ (TxA₂) and cysteinyl-leukotriene D₄ (LTD₄) are among the recognized mitogens for human airway smooth muscle (ASM) cells. Statins are known to possess anti-inflammatory and immunomodulatory properties that are independent on their cholesterol-lowering effects and may result in clinical lung benefits. Rosuvastatin is the last agent of the lipid-lowering drugs to be introduced and experimental evidence indicates that it possess favorable pleiotropic effects in the cardiovascular and nervous systems. Yet, no data is available in the literature regarding its effects on human airway remodeling. The present study was aimed at examining the effect of rosuvastatin and the involvement of prenylated proteins in the response of human ASM cells to serum, epidermal growth factor (EGF) and eicosanoid contractile mitogens that activate TxA₂ prostanoid and LTD₄ receptors.MethodsCell growth was assessed by nuclear incorporation of [³H]thymidine in human ASM cells serum-starved and then stimulated for 48 h in MEM plus 0.1% BSA containing mitogens in the absence and presence of modulators of the mevalonate and prenylation pathways.ResultsWe found that rosuvastatin dose-dependently inhibited serum-, EGF-, the TxA₂ stable analog U46619-, and LTD₄-induced human ASM cells growth. All these effects were prevented by pretreatment with mevalonate. Addition of the prenylation substrates farnesol and geranylgeraniol reversed the effect of rosuvastatin on EGF and U46619, respectively. Interestingly, only mevalonate showed restoration of cell growth following rosuvastatin treatment in LTD₄ and LTD₄ plus EGF treated cells, suggesting a possible involvement of both farnesylated and geranylgeranylated proteins in the cysteinyl-LT-induced cell growth.ConclusionsThe hydrophilic statin rosuvastatin exerts direct effects on human ASM cells mitogenic response in vitro by inhibiting prenylation of signaling proteins, likely small G proteins. These findings are consistent with previous observed involvement of small GTPase signaling in EGF- and U46619-induced human airway proliferation and corroborate the recent interest in the potential clinical benefits of statins in asthma/COPD.     

Antioxidant effect of adrenomedullin on angiotensin II-induced reactive oxygen species generation in vascular smooth muscle cells

Recent adrenomedullin (AM) gene-targeting studies have proposed a novel concept that AM plays a protective role against oxidative stress in vivo. The present study was undertaken to explore the underlying molecular mechanism of the putative antioxidant action of AM against angiotensin II (Ang II)induced reactive oxygen species (ROS) generation in rat vascular smooth muscle cells (VSMCs). Intracellular ROS levels were measured by dichlorofluoroscein fluorescence. Redox-sensitive c-Jun amino-terminal kinase (JNK) and ERK1/2 activation and gene expression induced by Ang II in VSMCs were also studied. AM dose-relatedly (10(-8)-10(-7) m) inhibited intracellular ROS generation stimulated by Ang II (10(-7) m), as mimicked by dibutyl-cAMP, the effect of which was inhibited by the pretreatment with N-(2-[p-bromocinnamylamino]ethyl)-5-isoquinolinesulfonamide hydrochloride, a protein kinase A inhibitor, and calcitonin gene-related peptide(8-37), an AM/calcitonin gene-related peptide receptor antagonist. Ang II induced JNK and ERK1/2 activation via a redox-sensitive manner, whereas AM inhibited JNK, but not ERK1/2, activation by Ang II. Furthermore, AM inhibited Ang II-induced redox-sensitive gene expression (plasminogen activator inhibitor-1 and monocyte chemoattractant protein-1) in the same manner as N-acetyl-l-cysteine, a potent antioxidant. AM also inhibited Ang II-induced up-regulation of Nox1, a critical membrane-bound component of reduced nicotinamide adenine dinucleotide phosphate oxidase in VSMCs, in the same degree as N-acetyl-l-cysteine. Our study demonstrates for the first time that AM directly inhibits intracellular ROS generation via an AM receptor-mediated and c-AMP-protein kinase A-dependent mechanism in VSMCs and that AM with its potent antioxidant action inhibits redox-sensitive JNK activation and gene expression induced by Ang II. These data suggest that AM plays a protective role as an endogenous antioxidant in Ang II-induced vascular injury.     

芦丁抑制氧化低密度脂蛋白诱导的血管平滑肌细胞增殖

目的:探讨芦丁在氧化低密度脂蛋白(ox-LDL)诱导的血管平滑肌细胞(VSMC)增殖中的作用。方法:制备ox-LDL,采用贴壁法分离培养C57BL/6J小鼠的VSMC,将细胞分为对照组、芦丁组、ox-LDL组和芦丁+ox-LDL组,MTT法检测各组VSMC细胞增殖活性,Western blot检测VSMC中磷酸化细胞外信号调节激酶(p-ERK)的表达情况。结果:芦丁组与对照组细胞增殖活性及p-ERK蛋白表达水平均无明显差异(P均0.05);ox-LDL组细胞增殖活性及p-ERK蛋白表达水平均显著高于对照组(P均0.05);与ox-LDL组相比,芦丁+ox-LDL组细胞增殖活性及p-ERK蛋白表达水平均明显降低(P均0.05)。结论:芦丁可能通过抑制ERK信号通路,抑制ox-LDL诱导的VSMC的增殖。     

Aldosterone and angiotensin II synergistically induce mitogenic response in vascular smooth muscle cells

Interaction between aldosterone (Aldo) and angiotensin II (Ang II) in the cardiovascular system has been highlighted; however, its detailed signaling mechanism is poorly understood. Here, we examined the cross-talk of growth-promoting signaling between Aldo and Ang II in vascular smooth muscle cells (VSMC). Treatment with a lower dose of Aldo (10(-12) mol/L) and with a lower dose of Ang II (10(-10) mol/L) significantly enhanced DNA synthesis, whereas Aldo or Ang II alone at these doses did not affect VSMC proliferation. This effect of a combination of Aldo and Ang II was markedly inhibited by a selective AT1 receptor blocker, olmesartan, a mineralocorticoid receptor antagonist, spironolactone, an MEK inhibitor, PD98059, or an EGF receptor tyrosine kinase inhibitor, AG1478. Treatment with Aldo together with Ang II, even at noneffective doses, respectively, synergistically increased extracellular signal-regulated kinase (ERK) activation, reaching 2 peaks at 10 to 15 minutes and 2 to 4 hours. The early ERK peak was effectively blocked by olmesartan or an EGF receptor kinase inhibitor, AG1478, but not by spironolactone, whereas the late ERK peak was completely inhibited by not only olmesartan, but also spironolactone. Combined treatment with Aldo and Ang II attenuated mitogen-activated protein kinase phosphatase-1 (MKP-1) expression and increased Ki-ras2A expression. The late ERK peak was not observed in VSMC treated with Ki-ras2A-siRNA. Interestingly, the decrease in MKP-1 expression and the increase in Ki-ras2A expression were restored by PD98059 or AG1478. These results suggest that Aldo exerts a synergistic mitogenic effect with Ang II and support the notion that blockade of both Aldo and Ang II could be more effective to prevent vascular remodeling.     

Mitogenic activity of oxidized lipoprotein (a) on human vascular smooth muscle cells

Although oxidized lipoproteins may play an important role in the progression of atherosclerosis, no report has mentioned the significance of oxidized lipoprotein (a) (Lp[a]) in the pathogenesis of cardiovascular disease. Initially, we compared the mitogenic actions of Lp(a) and oxidized Lp(a) on human vascular smooth muscle cells (VSMC). Lp(a) significantly stimulated the growth of human VSMC in a dose-dependent manner, whereas oxidized Lp(a) showed a stronger stimulatory action on VSMC growth than native Lp(a). Interestingly, antioxidants probucol and fluvastatin inhibited the oxidation of Lp(a). Moreover, the stimulatory effect of oxidized Lp(a) on human VSMC growth was significantly inhibited by probucol. Finally, we elucidated the molecular mechanisms of how Lp(a) stimulated the growth of VSMC. Extracellular signal-regulated kinase (ERK), as those controlled by kinases, modulate critical cellular functions such as cell growth, differentiation, and apoptosis, was transiently phosphorylated by oxidized Lp(a) as well as native Lp(a) from 5 minutes, and the phosphorylation disappeared within 30 minutes. The degree of ERK phosphorylation by oxidized Lp(a) was much higher than that by native Lp(a). Administration of a specific inhibitor of MEK, PD 98059, significantly attenuated VSMC growth induced by native Lp(a) or oxidized Lp(a) in a dose-dependent manner (P<0.01). The current study demonstrated that oxidized Lp(a) is more potent than native Lp(a) in stimulating VSMC growth. Oxidized Lp(a) may play an important role in the pathogenesis of vascular disease.     

Overexpression of human catalase gene decreases oxidized lipid-induced cytotoxicity in vascular smooth muscle cells.

Reactive oxygen metabolites such as hydrogen peroxide (H(2)O(2)) and oxidized fatty acids are proinflammatory and are involved in the pathophysiology of various diseases including atherosclerosis. The effects of these oxidants could be inhibited by the external addition of an antioxidant, suggesting the promotion or propagation of further oxidation. In this study, we describe the stable overexpression of human catalase in smooth muscle cells and the resistance of these cells to cytotoxicity induced not only by the addition of H(2)O(2) but also by the addition of 13-hydroperoxyoctadecadienoic acid (13-HPODE). The results pose an intriguing possibility of the generation of H(2)O(2) from a peroxidized fatty acid. Accordingly, incubation of cells with both 13-HPODE and 13-hydroxyoctadecadienoic acid resulted in the generation of intracellular H(2)O(2). To explain the observed results by which catalase could overcome the effects of 13-HPODE, we propose that oxidized fatty acids are degraded in the cellular peroxisomes, resulting in the generation of H(2)O(2). In other words, the cellular effects of peroxidized fatty acids could be attributed to the generation of H(2)O(2).