The contribution of Nox4 to NADPH oxidase activity in mouse vascular smooth muscle

OBJECTIVE: NADPH oxidases are important sources of reactive oxygen species (ROS) in the vasculature. In phagocytic cells, the catalytic subunit of NADPH oxidase is a glycoprotein, gp91phox. However, vascular smooth muscle cells (VSMCs), which show prominent NADPH oxidase activity, lack gp91phox. Hence, we examined the role of Nox4, a gp91phox homologue, in superoxide production in mouse-cultured VSMCs. METHODS AND RESULTS: Incubation of VSMCs with NADPH increased ROS production whether detected by lucigenin-enhanced chemiluminescence or dichlorofluorescein. Superoxide production was inhibited by the NADPH oxidase inhibitors, diphenyleneiodonium and apocynin, but not by inhibitors of other potential sources of superoxide. In unstimulated VSMCs, phosphorothioate antisense oligonucleotides against Nox4 down-regulated mRNA expression of the subunit by 65% and attenuated superoxide production by 41% without affecting Nox1 expression. Interleukin-1beta (IL-beta) thrombin and platelet-derived growth factor (PDGF) also reduced Nox4 mRNA expression after 3 h without affecting Nox1 levels. Of these stimuli, only IL-beta reduced superoxide, but this effect was more rapid (< or =30 min) than its actions on Nox4. CONCLUSIONS: Under resting conditions, NADPH oxidase activity in VSMCs is largely dependent upon Nox4 expression. Proinflammatory mediators down-regulated Nox4 but did not affect Nox1 expression, so other factors must compensate to regulate superoxide production.     

NADPH氧化酶对培养的小鼠血管平滑肌细胞Toll样受体4介导的炎症表型的影响

目的 探讨NADPH氧化酶对培养的小鼠血管平滑肌细胞(vascular smooth muscle cell,VSMC)Toll样受体4(Toll-like receptor 4,TLR4)介导的炎症表型中的作用.方法 分别采用NADPH氧化酶激动剂血小板衍生生长因子-BB(platelet-derived growth factor-BB,PDGF-BB)和抑制剂夹竹桃麻素(apocynin)处理培养的C57BL/6J和TLR4-/-小鼠胸主动脉VSMC.分别采用荧光探针二氯荧光素双醋酸盐染色法检测VSMC内活性氧(reactive oxygen species,ROS)含量,酶联免疫吸附法检测VSMC白细胞介素(interleukin,IL)-6、IL-1β和肿瘤坏死因子-α(tumor necrosis factor-o,TNF-α)表达,四甲基偶氮唑蓝染色法和Boyden小室检测VSMC的增殖和迁移.结果 PDGF-BB处理可显著增高C57BL/6J和TLR4-/-VSMC内ROS含量,而夹竹桃麻素可抑制ROS生成.PDGF-BB处理可使C57BL/6J VSMC IL-6[(52.69±3.49)ng/ml对(35.04±2.74) ng/ml,P=0.001]、IL-1β[(79.68±2.33) ng/ml对(62.38±0.54)ng/ml,P=0.000]和TNF-α[(218.35±5.42)ng/ml对(124.74±4.59) ng/ml,P=0.000]表达显著上调,增殖(1.69±0.53对1.04±0.40,P=0.000)和迁移(42.ll±4.05对1.69±0.53,P=0.000)能力均显著增强,而夹竹桃麻素预处理则可显著抑制VSMC IL-6[(42.11±4.05) ng/ml对(52.69±3.49) ng/ml,P=0.010]、IL-1β[(67.57± 1.36)ng/ml对(79.68±2.33) ng/ml,P=0.000]和TNF-α[(156.18±6.98) ng/ml对(218.35±5.42) ng/ml,P=0.000]表达以及增殖(1.23±0.42对1.69± 0.53,P=0.000)和迁移(42.11±4.05对52.69±3.49,P=0.000).TLR4-/-VSMC经PDGF-BB和夹竹桃麻素处理后,IL-6、IL-1β和TNF-α表达以及增殖和迁移能力均无显著变化.结论 NADPH氧化酶衍生的ROS参与了TLR4介导的VSMC炎症表型以及增殖和迁移,可能是其影响动脉粥样硬化发生和发展的重要机制.     

Role of NADPH oxidase 4 in lipopolysaccharide-induced proinflammatory responses by human aortic endothelial cells

OBJECTIVE: We investigated the role of NADPH oxidase 4 (Nox4) on lipopolysaccharide (LPS)-induced proinflammatory responses by human aortic endothelial cells (HAECs). METHODS AND RESULTS: Yeast two-hybrid and glutathione-S-transferase pull-down assays indicated that the cytosolic Toll/IL-1R region of Toll-like receptor 4 (TLR4) (amino acids 739-769) is the responsible domain for interaction with the COOH terminal of Nox4 (amino acids 451-530). Consistently, overexpression of the COOH-terminal region of Nox4 inhibited nuclear factor-kappaB activation in response to LPS. Downregulation of Nox4 by transfection of siRNA specific to Nox4 in HAECs resulted in a failure to induce reactive oxygen species (ROS) generation and subsequent expression of intercellular adhesion molecule-1 (ICAM-1) and chemokines such as IL-8 and monocyte chemoattractant protein-1 (MCP-1) in response to LPS. Furthermore, transient transfection of endothelial cells with Nox4 siRNA led to a decrease in migration and adhesion of monocytes in response to LPS by 36% and 52%, respectively. CONCLUSIONS: Nox4 plays a central role in LPS-induced proinflammatory responses by endothelial cells in an ROS-dependent manner.     

Angiotensin II-induced C-reactive protein generation: inflammatory role of vascular smooth muscle cells in atherosclerosis

BACKGROUND: As the major target of Angiotensin II (Ang II) in the vessel wall, vascular smooth muscle cells (VSMCs) are a tentative source to produce C-reactive protein (CRP). However, it is largely unknown if Ang II is capable of inducing CRP production in VSMCs. METHODS AND RESULTS: Ang II induced a concentration-dependent release of CRP in cultured rat VSMCs as measured by sandwich ELISA. Real-time PCR revealed that Ang II significantly upregulated CRP mRNA level in vitro. Ang II-induced CRP generation in aortic VSMCs was also investigated using double-labeled fluorescent immunohistochemistry and in situ hybridization in subchronic Ang II administration in rats. Losartan but not PD123319 markedly blocked the Ang II-induced CRP production in cultured VSMCs, suggesting that such effect was mediated via Ang II type 1 receptor. Further, Western blotting analysis showed that mitogen-activated protein kinase (MAPK) activation was obligatory in Ang II-induced CRP production, since specific MAPK inhibitor PD098059 almost abolished the action. CONCLUSIONS: We identified that Ang II is capable of inducing CRP generation in VSMCs, in which Ang II type 1 receptor followed by MAPK signal pathway is involved. It strengthened the role of Ang II-induced CRP production by VSMCs in the inflammatory process in atherosclerosis.     

Role of smooth muscle Nox4-based NADPH oxidase in neointimal hyperplasia

Elevated levels of reactive oxygen species (ROS) in the vascular wall play a key role in the development of neointimal hyperplasia. Nox4-based NADPH oxidase is a major ROS generating enzyme in the vasculature, but its roles in neointimal hyperplasia remain unclear.ObjectiveOur purpose was to investigate the role of smooth muscle cell (SMC) Nox4 in neointimal hyperplasia.Approach and resultsMice overexpressing a human Nox4 mutant form, carrying a P437H dominant negative mutation (Nox4DN) and driven by SM22α promoter, to achieve specific expression in SMC, were generated in a FVB/N genetic background. After wire injury-induced endothelial denudation, Nox4DN had significantly decreased neointima formation compared with non-transgenic littermate controls (NTg). ROS production, serum-induced proliferation and migration, were significantly decreased in aortic SMCs isolated from Nox4DN compared with NTg. Both mRNA and protein levels of thrombospondin 1 (TSP1) were significantly downregulated in Nox4DN SMCs. Downregulation of TSP1 by siRNA decreased cell proliferation and migration in SMCs. Similar to Nox4DN, downregulation of Nox4 by siRNA significantly decreased TSP1 expression level, cell proliferation and migration in SMCs.ConclusionsDownregulation of smooth muscle Nox4 inhibits neointimal hyperplasia by suppressing TSP1, which in part can account for inhibition of SMC proliferation and migration.     

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.     

Synergistic effect of mechanical stretch and angiotensin II on superoxide production via NADPH oxidase in vascular smooth muscle cells

OBJECTIVE: Mechanical forces and angiotensin II influence the structure and function of vascular cells, and play an important role in reactive oxygen species production. In this study, we examined the effects of mechanical stretch and angiotensin II on the expression of p22-phox and Nox-1, essential membrane components of NADPH oxidase, and superoxide production in rat vascular smooth muscle cells (VSMCs). METHODS AND RESULTS: Neither a stretch force nor angiotensin II alone altered p22-phox and Nox-1 expression in VSMCs. Combined stimulation markedly increased p22-phox and Nox-1 mRNA, however, which was associated with increased NADPH oxidase activity, superoxide production and total 8-iso-prostaglandin F2alpha concentration. The increases in p22-phox mRNA levels induced by a stretch force in combination with angiotensin II were prevented by treatment with an angiotensin type I (AT1) receptor antagonist, RNH-6270 (100 nmol/l). Protein expression of the AT1 receptor was upregulated by a stretch force. CONCLUSIONS: These data indicate that mechanical stretch and angiotensin II synergistically increase NADPH oxidase expression in VSMCs, and suggest that part of this mechanism is mediated through an upregulation of the AT1 receptor induced by mechanical stretch. The combined effects of mechanical strain and angiotensin II might promote vascular damage through the production of superoxide in a hypertensive state.     

Activation of NADPH oxidase 1 increases intracellular calcium and migration of smooth muscle cells

Redox-dependent migration and proliferation of vascular smooth muscle cells (SMCs) are central events in the development of vascular proliferative diseases; however, the underlying intracellular signaling mechanisms are not fully understood. We tested the hypothesis that activation of Nox1 NADPH oxidase modulates intracellular calcium ([Ca(2+)](i)) levels. Using cultured SMCs from wild-type and Nox1 null mice, we confirmed that thrombin-dependent generation of reactive oxygen species requires Nox1. Thrombin rapidly increased [Ca(2+)](i), as measured by fura-2 fluorescence ratio imaging, in wild-type but not Nox1 null SMCs. The increase in [Ca(2+)](i) in wild-type SMCs was inhibited by antisense to Nox1 and restored by expression of Nox1 in Nox1 null SMCs. Investigation into potential mechanisms by which Nox1 modulates [Ca(2+)](i) showed that thrombin-induced inositol triphosphate generation and thapsigargin-induced intracellular calcium mobilization were similar in wild-type and Nox1 null SMCs. To examine the effects of Nox1 on Ca(2+) entry, cells were either bathed in Ca(2+)-free medium or exposed to dihydropyridines to block L-type Ca(2+) channel activity. Treatment with nifedipine or removal of extracellular Ca(2+) reduced the thrombin-mediated increase of [Ca(2+)](i) in wild-type SMCs, whereas the response in Nox1 null SMCs was unchanged. Sodium vanadate, an inhibitor of protein tyrosine phosphatases, restored the thrombin-induced increase of [Ca(2+)](i) in Nox1 null SMCs. Migration of SMCs was impaired with deficiency of Nox1 and restored with expression of Nox1 or the addition of sodium vanadate. In summary, we conclude that Nox1 NADPH oxidase modulates Ca(2+) mobilization in SMCs, in part through regulation of Ca(2+) influx, to thereby promote cell migration.     

溶血磷脂酸受体3介导溶血磷脂酸诱导的血管平滑肌细胞表型转化

目的探讨溶血磷脂酸(LPA)受体在LPA诱导的血管平滑肌细胞(VSMC)表型转化中的作用及相关信号传导通路。方法培养SD大鼠分化表型VSMC,培养液加胰岛素样生长因子(IGF-1)为IGF-1组,加溶剂载体为空白组,以不同浓度水平LPA(0.1～10μmol/L)刺激,依次为LPA 0.1组、LPA 1组和LPA 10组,并在LPA(1μmol/L)条件下,以LPA受体1,3拮抗剂二辛烷甘油焦磷酸盐(DGPP 8:0)为DGPP 1组,RT-PCR法检测平滑肌肌动蛋白α(SMA-α)和骨桥蛋白mRNA表达,Western blot法检测p38分裂原活化蛋白激酶(p38MAPK),细胞外信号调节激酶(ERK)及其磷酸化蛋白水平。结果与空白组和IGF-1组比较,LPA 0.1组、LPA 1组和LPA 10组呈剂量依赖促进骨桥蛋白mRNA表达上升,SMA-αmR NA表达下降(P<0.01);与空白组比较,LPA 1组p38MAPK和ERK激活(P<0.01),DGPP 1组p38MAPK和ERK无明显变化(P>0.05)。结论与Gq蛋白偶联的LPA受体3介导了LPA诱导的VSMC表型转化,阻滞上述通路有可能成为控制与动脉粥样硬化和再狭窄等血管疾病相关的VSMC表型转化潜在的治疗干预靶点。