Evidence that angiotensin II, endothelins and nitric oxide regulate mitogen-activated protein kinase activity in rat aorta

Identifying S-nitrosylated proteins and unraveling S-nitrosoglutathione reductase-modulated sodic alkaline stress tolerance in Solanum lycopersicum L

S-nitrosylation, regulated by S-nitrosoglutathione reductase (GSNOR), is considered as an important route for nitric oxide (NO)-modulated stress tolerance in plants. However, genetic evidence for the GSNOR-mediated integrated regulation of S-nitrosylation and plant stress response remains elusive until now. In the present study, we used a site-specific nitrosoproteomic approach to identify 334 endogenously S-nitrosylated proteins with 425 S-nitrosylated sites from the wild type (WT) and GSNOR-knockdown (G) tomato plants under both control (C) and sodic alkaline stress (S) conditions. In detail, the results revealed 68, 92, 54 and 56 up-regulated, as well as 10, 36, 14 and 10 down-regulated S-nitrosylated proteins in G-C/WT-C, G-S/WT-S, WT-S/WT-C, and G-S/G-C, which is the first dataset for S-nitrosylated proteins in Solanaceae. These S-nitrosylated proteins are involved in a wide range of various metabolic, cellular and catalytic processes. Based on this data, proteins involving in NO homeostasis control, signaling of Ca²⁺, ethylene and MAPK, reactive oxygen species (ROS) scavenging, osmotic regulation, as well as energy support pathway have been identified and selected as the key and sensitive targets that were regulated by GSNOR-modulated S-nitrosylation in response to sodic alkaline stress. Taken together, GSNOR is actively involved in the regulation of sodic alkaline stress tolerance by S-nitrosylation. And the present study provided valuable resources and new clues for the study of S-nitrosylation-regulated metabolism in tomato plants.

Enhanced expression of Gqα and PLC-β1 proteins contributes to vascular smooth muscle cell hypertrophy in SHR: role of endogenous angiotensin II and endothelin-1

Vascular Gqα signaling has been shown to contribute to cardiac hypertrophy. In addition, angiotensin II (ANG II) was shown to induce vascular smooth muscle cell (VSMC) hypertrophy through Gqα signaling; however, the studies on the role of Gqα and PLC-β1 proteins in VSMC hypertrophy in animal model are lacking. The present study was therefore undertaken to examine the role of Gqα/PLC-β1 proteins and the signaling pathways in VSMC hypertrophy using spontaneously hypertensive rats (SHR). VSMC from 16-wk-old SHR and not from 12-wk-old SHR exhibited enhanced levels of Gqα/PLC-β1 proteins compared with age-matched Wistar-Kyoto (WKY) rats as determined by Western blotting. However, protein synthesis as determined by [3H]leucine incorporation was significantly enhanced in VSMC from both 12- and 16-wk-old SHR compared with VSMC from age-matched WKY rats. Furthermore, the knockdown of Gqα/PLC-β1 in VSMC from 16-wk-old SHR by antisense and small interfering RNA resulted in attenuation of protein synthesis. In addition, the enhanced expression of Gqα/PLC-β1 proteins, enhanced phosphorylation of ERK1/2, and enhanced protein synthesis in VSMC from SHR were attenuated by the ANG II AT1 and endothelin-1 (ET-1) ETA receptor antagonists losartan and BQ123, respectively, but not by the ETB receptor antagonist BQ788. In addition, PD98059 decreased the enhanced expression of Gqα/PLC-β1 and protein synthesis in VSMC from SHR. These results suggest that the enhanced levels of endogenous ANG II and ET-1 through the activation of AT1 and ETA receptors, respectively, and MAP kinase signaling, enhanced the expression of Gqα/PLC-β1 proteins in VSMC from 16-wk-old SHR and result in VSMC hypertrophy.

Involvement of endogenous nitric oxide in angiotensin II-induced activation of vascular mitogen-activated protein kinases

Angiotensin II (ANG II) is a powerful activator of mitogen-activated protein (MAP) kinase cascades in cardiovascular tissues through a redox-sensitive mechanism. Nitric oxide (NO) is considered to antagonize the vasoconstrictive and proarteriosclerotic actions of ANG II. However, the role of endogenous NO in ANG II-induced redox-sensitive signal transduction is not yet clear. In this study using catheterized, conscious rats, we found that acute intravenous administration of NG-nitro-l-arginine methyl ester (l-NAME; 5 mg/kg) enhanced phosphorylation of aortic MAP kinases extracellular signal regulated kinase (ERK) 1/2 and p38, which were suppressed only partially by a superoxide dismutase mimetic (Tempol), whereas ANG II-induced MAP kinase phosphorylation was markedly suppressed by Tempol. FK409, a NO donor, had little effect on vascular MAP kinase phosphorylation. On the other hand, acute exposure to a vasoconstrictor dose of ANG II (200 ng·kg−1·min−1 iv) failed to enhance phosphorylation of aortic MAP kinases in the chronically l-NAME-treated rats, whereas the vasoconstrictor effect of ANG II was not affected by l-NAME treatment. Furthermore, three different inhibitors of NO synthase suppressed, in a dose-dependent manner, ANG II-induced MAP kinase phosphorylation in rat vascular smooth muscle cells, which was closely linked to superoxide generation in cells. These results indicate the involvement of endogenous NO synthase in ANG II-induced signaling pathways, leading to activation of MAP kinase, and that NO may have dual effects on the vascular MAP kinase activation associated with redox sensitivity.

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.

Essential role of protein kinase G and decreased cytoplasmic Ca2+ levels in NO-induced inhibition of rat aortic smooth muscle cell motility

Hyperinsulinemia is a major risk factor for the development of vascular disease. We have reported that insulin increases the motility of vascular smooth muscle cells via a hydrogen peroxide-mediated mechanism and that nitric oxide (NO) attenuates insulin-induced motility via a cGMP-mediated mechanism. Events downstream of cGMP elevation have not yet been investigated. The aim of our study was to test the hypothesis that antimotogenic effects of NO and cGMP in cultured rat aortic smooth muscle cells are mediated via PKG, followed by reduction of cytoplasmic Ca(2+) levels and increased protein tyrosine phosphatase-proline, glutamate, serine, and threonine activity, leading to suppression of agonist-induced elevation of hydrogen peroxide levels and cell motility. Treatment of primary cultures with adenovirus expressing PKG-1alpha mimicked NO-induced inhibition of insulin-elicited hydrogen peroxide elevation and cell motility, whereas treatment with the pharmacological PKG inhibitor Rp-8-bromo-3',5'-cyclic monophosphorothioate (Rp-8-Br-cGMPS) rescued the stimulatory effects of insulin that were suppressed by NO donor. Treatment of cells with insulin failed to increase cytoplasmic Ca(2+) levels, whereas NO donor decreased cytoplasmic Ca(2+) levels in the presence or absence of insulin. Treatment of cells with the Ca(2+) chelator BAPTA mimicked the effects of PKG and the NO donor and increased the activity of PTP-PEST. Finally, treatment with a dominant negative allele of PTP-PEST reversed the inhibitory effect of BAPTA on cell motility and hydrogen peroxide elevation. We conclude that NO-induced inhibition of cell motility occurs via PKG-mediated reduction of basal cytoplasmic Ca(2+) levels, followed by increased PTP-PEST activity, leading to decreased hydrogen peroxide levels and reduced cell motility.

Force-independent expression of c-fos mRNA by endothelin-1 in rat intact small mesenteric arteries

AIM

Wall stress-independent signalling pathways were studied for endothelin-1 (ET-1)-induced c-fos expression in rat intact mesenteric small arteries.

METHODS

Arteries were kept unmounted in Krebs buffer, equilibrated for 1 h and stimulated with vasoactive substances for 15-60 min. The c-fos mRNA expression was determined by real-time polymerase chain reaction.

RESULTS

Stimulation with fetal bovine serum (FBS), phorbol 12-myristate 13-acetate (PMA) and ET-1 caused about a doubling of c-fos mRNA. The ET-1-induced c-fos expression was steady (15-60 min) and was inhibited by the inhibitor of the ET(A) receptor, BQ-123. Platelet-derived growth factor-B, angiotensin II and U46619 did not cause increased c-fos mRNA levels. The broad specificity inhibitor staurosporine inhibited the response to ET-1, but inhibitors of Rho-A kinase and phosphatidylinositol 3-kinase had no effect. However, inhibitors to tyrosine kinases, the MAP kinases [extracellular signal-regulated kinase 1/2 (ERK1/2), c-Jun amino-terminal kinase, p38], and to conventional protein kinase C showed no inhibition. Consistent with these findings, ET-1 did not cause activation of ERK1/2, a finding also seen in vessels held under pressure. In contrast, ET-1-induced c-fos expression was inhibited by the calcium chelator BAPTA, suggesting a role for intracellular calcium. This possibility was supported by the finding that raising the extracellular K(+) concentration caused increased expression of c-fos in a concentration-dependent manner.

CONCLUSION

The results suggest that in the absence of wall stress, ET-1 is able to induce increased expression of c-fos independent of traditional growth pathways, such as MAP kinase. The mechanism appears to be calcium-dependent.

Nitric oxide attenuates insulin- or IGF-I-stimulated aortic smooth muscle cell motility by decreasing H2O2 levels: essential role of cGMP

Insulin and insulin-like growth factor I (IGF-I) both play important roles in vascular remodeling. Moreover, nitric oxide (NO) is well established as a counterregulatory agent that opposes the actions of several vascular agonists, in part by decreasing smooth muscle motility. We tested the hypothesis that NO blocks insulin or IGF-I-induced rat aortic smooth muscle cell motility via a mechanism involving the attenuation of agonist-induced elevation of hydrogen peroxide levels and cGMP as mediator. Insulin or IGF-I induced an increase of hydrogen peroxide levels and cell motility. Both effects were blocked by catalase or diphenyleneiodonium, indicating that hydrogen peroxide elevation is necessary for induction of cell motility. Two NO donors mimicked the effects of catalase, indicating that NO decreases cell motility by suppressing agonist-induced elevation of hydrogen peroxide. A cGMP analogue mimicked the effect of NO, whereas a guanyl cyclase inhibitor blocked the effect of NO on hydrogen peroxide levels, indicating that elevation of cGMP is both necessary and sufficient to account for the reduction of hydrogen peroxide levels. A NO donor as well as a cGMP analogue attenuated insulin-stimulated NADPH activity, indicating that NO decreases hydrogen peroxide levels by inhibiting the generation of superoxide, via a cGMP-mediated mechanism. Finally, exogenous hydrogen peroxide increased cell motility and reversed the inhibitory effect of cGMP. These results support the view that NO plays an antioxidant role via reduction of hydrogen peroxide in cultured rat aortic smooth muscle cells and that this effect is both necessary and sufficient to account for its capacity to decrease cell motility.

Regulation of gene expression by cyclic GMP

Cyclic GMP, produced in response to nitric oxide and natriuretic peptides, is a key regulator of vascular smooth muscle cell contractility, growth, and differentiation, and is implicated in opposing the pathophysiology of hypertension, cardiac hypertrophy, atherosclerosis, and vascular injury/restenosis. cGMP regulates gene expression both positively and negatively at transcriptional as well as at posttranscriptional levels. cGMP-regulated transcription factors include the cAMP-response element binding protein CREB, the serum response factor SRF, and the nuclear factor of activated T cells NF/AT. cGMP can regulate CREB directly, through phosphorylation by cGMP-dependent protein kinase, or indirectly, through activation of mitogen-activated protein kinase pathways; regulation of SRF and NF/AT by cGMP is indirect, through modulation of RhoA and calcineurin signaling, respectively. Downregulation of the RNA-binding protein HuR by cGMP leads to destabilization of guanylate cyclase mRNA, but this posttranscriptional mechanism may affect many more cGMP-regulated genes. In this review, we discuss the role of cGMP-regulated gene expression in (patho)physiological processes most relevant to the cardiovascular system, such as regulation of vascular tone, cardiac hypertrophy, phenotypic modulation of vascular smooth muscle cells, and regulation of cell proliferation and apoptosis.

Epidermal growth factor receptor trans-activation mediates the tonic and fibrogenic effects of endothelin in the aortic wall of transgenic mice

Vascular remodeling and rearrangement of the extracellular matrix formation are among the major adaptive mechanisms in response to a chronic blood pressure increase. Vasoactive peptides, such as endothelin, participate in hypertension-associated vascular fibrosis by stimulating collagen I formation and increasing contractility of arterial wall. In the present study, we tested the hypothesis that activation of the epidermal growth factor (EGF) receptor pathway mediates these events. Experiments were performed in transgenic mice harboring the luciferase gene under the control of the collagen I-alpha2 chain promoter. Endothelin induced a rapid phosphorylation of the mitogen-activated protein kinase (MAPK)/ERK and increased collagen I gene activity in freshly isolated aortas. This effect of endothelin was totally inhibited by an endothelin receptor antagonist, an EGF receptor phosphorylation inhibitor, and a blocker of the MAPK/ERK cascade. In parallel experiments, inhibition of EGF receptor phosphorylation decreased the endothelin-induced pressor effect in isolated aortic rings and in anesthetized animals in vivo. In addition, the endothelin-induced increase of blood pressure was blunted in the waved-2 mice, a strain expressing functionally impaired EGF receptors. Our results provide the first evidence that the EGF receptor mediates at least two of the major actions of endothelin in the vascular tissue: contractility and fibrogenesis.

AT1 Receptor Expression in Glomeruli from NO-Deficient Rats

Chronic inhibition of nitric oxide synthase promotes renin-dependent hypertension and renal injury. The present study examines how renal angiotensin II receptors are expressed in this model. N(G)-nitro-L-arginine methyl ester (L-NAME) was given orally to rats for 1 month and was associated or not with captopril during the 4 last days of the administration. 125I-[Sar1, Ile8]-Ang II binding, AT1)mRNA and cytosolic calcium were studied in isolated glomeruli from L-NAME and control rats and in cultured mesangial cells from normal rats. Renal injury was marked in rats receiving L-NAME. Type I angiotensin II (AT1) receptor number and mRNA expression were decreased (p < 0.05) in glomeruli isolated from L-NAME-treated rats compared with controls, unless they received captopril in combination. The low level of AT1 receptor expression was associated with an attenuated rise of cytosolic calcium in response to angiotensin II. Angiotensin-converting enzyme activity in glomeruli and angiotensin II concentration in renal cortex were increased (p < 0.05) in rats receiving L-NAME alone, whereas aminopeptidase A activity was not modified. To better discriminate between the direct and indirect effects of nitric oxide deficiency, rat mesangial cells were exposed or not for 24 h to S-nitroso-N-acetyl penicillamine, a nitric oxide donor. Angiotensin II binding, AT1 mRNA expression and calcium response to angiotensin II were decreased in presence of the nitric oxide donor (p < 0.01). These results suggest that the decrease of AT1 receptor expression after 1 month of L-NAME treatment does not depend on a direct effect of nitric oxide deficiency but results from the high local angiotensin II concentration due to the stimulated angiotensin-converting enzyme activity. They also show that the renin-angiotensin dependence of this model of hypertension does not result from the overexpression of AT1 receptors.

Altered mitogen-activated protein kinase activation in vascular smooth muscle cells from spontaneously hypertensive rats

1. We previously reported that activation function of mitogen-activated protein kinases (MAPK) is enhanced in aorta strips from both prehypertensive and hypertensive spontaneously hypertensive rats (SHR) and that this enhancement of MAPK activation results from enhanced MAPK activation reactivity to angiotensin (Ang) II in SHR aorta strips. 2. The purpose of the present study was to examine whether the enhanced function of the vascular angiotensin system observed in SHR aorta strips results from genetic alterations of vascular smooth muscle cells from SHR. 3. Basal MAPK activity was within normal limits in cells from 4-week-old SHR, whereas enzyme activity was enhanced in 9-week-old SHR compared with age-matched Wistar-Kyoto (WKY) rats. 4. Mitogen-activated protein kinase activation reactivity to AngII and endothelin-1 was enhanced in 9-week-old SHR cells but not in 4-week-old SHR cells. The enhancement of basal MAPK activity in 9-week-old SHR cells was abolished by a combination of the angiotensin AT(1) receptor antagonist losartan and the endothelin receptor antagonist BQ123. 5. These findings suggest that MAPK activation function in 4-week-old SHR cells is not enhanced. Thus, it appears that factors outside vascular smooth muscle cells are needed for the enhanced MAPK activation observed in 4-week-old SHR aorta strips. In 9-week-old SHR, MAPK activation function is enhanced in cells themselves and this function may, at least in part, contribute to the enhanced MAPK activation observed in SHR aorta strips.

The endothelin system in human saphenous vein graft disease

Saphenous vein graft stenosis is a significant clinical complication for coronary artery bypass patients. Endothelin-1, a peptide synthesised by vascular endothelial cells, is the most potent known vasoconstrictor and has mitogenic properties. Recent advances in our knowledge of endothelin-1 synthesis and endothelin receptor expression and function in normal and atherosclerotic human saphenous vein imply a role for the peptide in the progression of vein graft failure. Manipulation of the endothelin system, by selective receptor antagonism or inhibition of the specific endothelin-converting enzymes may, therefore, represent a novel therapeutic target for treating vein graft disease.

Mitogen-activated protein kinase activity regulation role of angiotensin and endothelin systems in vascular smooth muscle cells

To examine whether angiotensin II and endothelins produced in vascular smooth muscle cells can play roles in the regulation of mitogen-activated protein (MAP) kinase activity in vascular smooth muscle cells, we measured the activity of MAP kinases in cultured vascular smooth muscle cells, and determined effects of renin-angiotensin and endothelin systems activators and inhibitors. Angiotensin II and endothelin-1 produced an activation of MAP kinase activity in vascular smooth muscle cells, whereas the angiotensin receptor antagonist, losartan and the endothelin receptor antagonist, cyclo (D-alpha-aspartyl-L-prolyl-D-valyl-L-leucyl-D-tryptophyl, BQ123) inhibited the enzyme activity. MAP kinase activity in vascular smooth muscle cells was also inhibited either by the renin inhibitor pepstatin A or by the angiotensin-converting enzyme inhibitor captopril. The degree of the inhibition of MAP kinase activity by pepstatin A, captopril and losartan was almost the same. Renin produced a considerable increase in MAP kinase activity and the renin-induced MAP kinase activation was inhibited by pepstatin A. The endothelin precursor big endothelin-1 produced an increase of MAP kinase activity in vascular smooth muscle cells, whereas the endothelin-converting enzyme inhibitor phosphoramidon inhibited the enzyme activity. These findings suggest that functional renin-angiotensin system and endothelin system are present in vascular smooth muscle cells and these systems tonically serve to increase MAP kinase activity. It appears that renin or renin-like substances play the determining role in the regulation of renin-angiotensin system in vascular smooth muscle cells.

Angiotensin II activates collagen I gene through a mechanism involving the MAP/ER kinase pathway

Vascular remodeling and rearrangement of the extracellular matrix formation are among the major adaptive mechanisms to chronic increase in blood pressure. In previous studies we have found that angiotensin II (Ang II) participates in the hypertension-associated aortic and renal vascular fibrosis by stimulating collagen type I formation. The purpose of the present study was to gain insight into the molecular events that lead from the Ang II receptor to collagen I gene activation. To this end, we used a novel strain of transgenic mice harboring the luciferase gene under the control of the collagen I-alpha(2) chain promoter [procolalpha(2)(I)]. Ang II produced an early (1 hour) 2- to 3-fold stimulation of procolalpha(2)(I) activity in freshly isolated aortas and renal cortical slices (P:<0. 01) followed by similar increase in procolalpha(2)(I) mRNA aortic levels. This effect of Ang II was inhibited by AT1-receptor antagonism (candesartan) and blockade of the MAPK/ERK cascade (PD98059); in contrast, inhibition of the P38 kinase pathway (SB202190) and blockade of the release of the transcription factor NFkappaB (PDTC) did not have any effect in the Ang II-induced activation of the collagen I gene. In addition, Ang II induced a rapid (5 minutes) increase of the MAPK/ERK activity that was accompanied by increased expression (3-fold) of the c-fos proto-oncogene. This increase of c-fos mRNA expression was blocked by PD98059; in addition, curcumin, a blocker of the transcriptional factor AP-1, canceled the effect of Ang II on the collagen I gene. Decorin, a scavenger of the active form of transforming growth factor-beta (TGF-beta), canceled the Ang II effect on collagen I gene, whereas inhibition of the MAPK/ERK pathway had no effect on the TGF-beta-induced activation of procolalpha(2)(I). These data indicate that the cellular events after AT1 receptor stimulation and leading to activation of collagen I gene expression require activation of both the MAPK/ERK and TGF-beta signaling pathways.

Different activation of vascular mitogen-activated protein kinases in spontaneously and DOCA-salt hypertensive rats

Regulation mechanisms of the activity of vascular mitogen-activated protein (MAP) kinases, enzymes believed to be involved in the pathway for cell proliferation, may be altered in hypertension. To examine whether vascular MAP kinase activation mechanisms are altered in hypertension, we measured the activity of MAP kinases in rat aorta strips from spontaneously hypertensive rats (SHR) and from deoxycorticosterone acetate (DOCA)-salt hypertensive rats, and examined whether vascular angiotensin and endothelin systems are responsible for the alteration of MAP kinase activation in these hypertensive models. Endothelium-denuded aorta strips were incubated at 37 degrees C in medium. MAP kinase activity after incubation was increased in rat aorta strips. The MAP kinase activation was greater in 9- and 15-week-old SHR aorta strips than in age-matched Wistar Kyoto rats (WKY) aorta strips. Similarly, MAP kinase activation was enhanced in aorta strips from DOCA-salt hypertensive rats. In aorta strips from these kinds of rats, the angiotensin receptor antagonist, losartan, and the endothelin receptor antagonist, cyclo (D-alpha-aspartyl-L-prolyl-D-valyl-L-leucyl-D-tryptophyl) (BQ123), inhibited the MAP kinase activation. The losartan-induced, but not BQ123-induced, inhibition of MAP kinase activation was enhanced in 15-week-old SHR aorta strips, whereas the BQ123-induced, but not losartan-induced, inhibition of MAP kinase activation was enhanced in DOCA-salt hypertensive rat aorta strips. Angiotensin II-induced MAP kinase activation was enhanced in 15-week-old SHR aorta strips, whereas it was depressed in DOCA-salt hypertensive rat aorta strips. These results indicate that MAP kinase activation function is enhanced in aorta strips from both kinds of hypertensive rats. It appears that the enhancement of MAP kinase activation results partly from enhanced vascular angiotensin system in SHR and from enhanced vascular endothelin system in DOCA-salt hypertensive rats.

Apolipoprotein E inhibition of vascular smooth muscle cell proliferation but not the inhibition of migration is mediated through activation of inducible nitric oxide synthase

Initial experiments revealed that low concentrations of apolipoprotein (apo) E (0.1 to 5 microg/mL) were effective in inhibiting platelet-derived growth factor (PDGF)-directed smooth muscle cell (SMC) migration by 60% to 80%. In contrast, higher concentrations of apoE, at 25 and 50 microg/mL, were necessary to achieve similar inhibition of PDGF-induced SMC proliferation. The potential role of nitric oxide (NO) in mediating the inhibitory effects of apoE was explored. Results showed that, although 0.1 to 5 microg/mL of apoE had no effect on NO production by SMCs, physiological concentrations of apoE (25 to 50 microg/mL) enhanced NO synthesis by 2-fold in a dose-dependent manner (P<0.001). Reverse transcription-polymerase chain reaction amplification of RNA obtained from control and apoE-treated SMCs demonstrated a direct role of apoE in activating inducible nitric oxide synthase (iNOS) gene expression. The apoE-induced nitric oxide production was significantly reduced by coincubation of the cells with aminoguanidine or N(G)-monomethyl-L-arginine (P<0.05) or with antisense iNOS oligodeoxynucleotides (P<0.01). Moreover, the inhibition of iNOS was shown to overcome apoE suppression of PDGF-induced vascular SMC proliferation. However, apoE suppression of PDGF-directed SMC migration was not affected by these treatments. Taken together, these results document that apoE exerts its inhibitory effects on cell proliferation via activation of iNOS. However, apoE inhibition of cell migration is mediated by a mechanism independent of iNOS activation.

Angiotensin II mediates pressure loading-induced mitogen-activated protein kinase activation in isolated rat aorta

Vascular hypertrophy occurs during chronic hypertension and contributes to the elevation of peripheral vascular resistance in hypertension. In this study, we examined whether acute pressure overloading of the vascular wall produces activation of mitogen-activated protein (MAP) kinases, enzymes believed to be involved in the pathway for cell proliferation, in isolated perfused rat aortae, and examined whether the mechanical overloading-induced MAP kinase activation is mediated via the vascular angiotensin system. Aortae were perfused with Tyrode solution. Increases in perfusion pressure caused a pressure-dependent increase in MAP kinase activity in endothelium-intact aortae and in endothelium-denuded aortae. The increase in MAP kinase activity induced by pressure loading was inhibited by the angiotensin receptor antagonist, losartan, the renin inhibitor, pepstatin A, and the angiotensin-converting enzyme inhibitor, captopril. Ca(2+) depletion and the Ca(2+) channel antagonist, nifedipine, did not affect the pressure loading-induced MAP kinase activation. The results of the present study suggest that pressure loading of the vascular wall per se can activate MAP kinases in the vasculature and that the MAP kinase activation is mediated at least partly via the vascular angiotensin system. It seems unlikely that the pressure loading-induced increase in MAP kinase activity is mainly mediated via increases in Ca(2+) influx in vascular cells.

Vascular mitogen-activated protein kinase activity is enhanced via angiotensin system in spontaneously hypertensive rats

The vascular structural remodeling function may be altered in genetically hypertensive animals, spontaneously hypertensive rats (SHR). To examine this possibility, we measured the activity of mitogen-activated protein (MAP) kinases, enzymes believed to be involved in the pathway for cell proliferation, in rat aorta strips, and examined whether the endothelium removal-induced MAP kinase activation function is altered in SHR and whether vascular angiotensin and endothelin systems are responsible for the alteration of MAP kinase activation in SHR. Male 4-week-old SHR and age-matched Wistar Kyoto rats (WKY) supplied by Charles River Japan were used. Endothelium-denuded aorta strips were incubated at 37 degrees C in medium. MAP kinase activity after incubation was time-dependently increased in strips from SHR and WKY. MAP kinase activation was greater in SHR than in WKY aorta strips. Similarly, MAP kinase activation was enhanced in aorta strips from 4-week-old SHR and stroke prone SHR supplied by the Diseases Model Cooperative Research Association (Kyoto, Japan). In aorta strips from SHR and WKY, the angiotensin receptor antagonist, losartan, and the endothelin receptor antagonist, cyclo (D-alpha-aspartyl-L-prolyl-D-valyl-L-leucyl-D-tryptophyl)(BQ123), caused concentration-dependent inhibition of MAP kinase activation. The losartan-induced but not BQ123-induced inhibition of MAP kinase activation was greater in SHR than in WKY aorta strips. Angiotensin II caused a concentration-dependent increase in MAP kinase activity and the angiotensin II-induced MAP kinase activation was greater in SHR than in WKY aorta strips. These results indicate that endothelium removal-induced MAP kinase activation is enhanced in aorta strips from young SHR, suggesting that vascular structural remodeling function may be enhanced in SHR. It appears that the enhancement of MAP kinase activation results, at least in part, from enhanced function of vascular angiotensin system in SHR.

Local renin-angiotensin system and mitogen-activated protein kinase activation in rat aorta

We previously reported that endogenous angiotensin II is released to cause mitogen-activated protein (MAP) kinase stimulation in the media portion of the vasculature. In this study, we examined whether a functional renin-angiotensin system is indeed present within the media of the vasculature. In rat aortic strips, endothelium removal produced an increase of MAP kinase activity. The MAP kinase activation was inhibited either by the renin inhibitor pepstatin A or by the angiotensin-converting enzyme inhibitor captopril. The degree of the inhibition of the MAP kinase activation by pepstatin A, captopril and the angiotensin receptor antagonist losartan was almost the same. Pepstatin A inhibited MAP kinase activation induced by renin but not by angiotensin I and angiotensin II. Captopril inhibited the MAP kinase activation induced by angiotensin I but not by angiotensin II. In nephrectomized rat aortic strips, endothelium removal also produced an increase in MAP kinase activity, but the MAP kinase activation was considerably small and minimally inhibited by losartan. Nephrectomy produced a marked decrease in plasma renin activity. These findings suggest that an apparently fully intact and functional renin-angiotensin system is present in the media of the rat vasculature and this system serves to increase MAP kinase activity. It appears that renin plays the determining role in the regulation of angiotensin generation also in the media and the major source of the renin is renin of kidney origin.