Angiotensin II responses of vascular smooth muscle cells from hypertensive rats: enhancement at the level of p42 and p44 mitogen activated protein kinase

Defining the roles of arrestin2 and arrestin3 in vasoconstrictor receptor desensitization in hypertension

Prolonged vasoconstrictor-stimulated phospholipase C activity can induce arterial constriction, hypertension, and smooth muscle hypertrophy/hyperplasia. Arrestin proteins are recruited by agonist-occupied G protein-coupled receptors to terminate signaling and counteract changes in vascular tone. Here we determine whether the development of hypertension affects arrestin expression in resistance arteries and how such changes alter arterial contractile signaling and function. Arrestin2/3 expression was increased in mesenteric arteries of 12-wk-old spontaneously hypertensive rats (SHR) compared with normotensive Wistar-Kyoto (WKY) controls, while no differences in arrestin expression were observed between 6-wk-old SHR and WKY animals. In mesenteric artery myography experiments, high extracellular K(+)-stimulated contractions were increased in both 6- and 12-wk-old SHR animals. Concentration-response experiments for uridine 5'-triphosphate (UTP) acting through P2Y receptors displayed a leftward shift in 12-wk, but not 6-wk-old animals. Desensitization of UTP-stimulated vessel contractions was increased in 12-wk-old (but not 6-wk-old) SHR animals. Dual IP3/Ca(2+) imaging in mesenteric arterial cells showed that desensitization of UTP and endothelin-1 (ET1) responses was enhanced in 12-wk-old (but not 6-wk-old) SHR compared with WKY rats. siRNA-mediated depletion of arrestin2 for UTP and arrestin3 for ET1, reversed the desensitization of PLC signaling. In conclusion, arrestin2 and 3 expression is elevated in resistance arteries during the emergence of the early hypertensive phenotype, which underlies an enhanced ability to desensitize vasoconstrictor signaling and vessel contraction. Such regulatory changes may act to compensate for increased vasoconstrictor-induced vessel contraction.

The vascular relaxing effects of sevoflurane and isoflurane are more important in hypertensive than in normotensive rats

PURPOSE

The vascular response to anesthetics is altered in hypertensive patients since the functional and structural integrities of vascular smooth muscle and endothelium are deranged. The effects of anesthetics on angiotensin II (Ang II)-induced changes in vascular tone are not well understood. We investigated the effects of sevoflurane and isoflurane on Ang II-induced vasoconstriction in spontaneously hypertensive rats (SHR).

METHODS

The dose-dependent effects of sevoflurane and isoflurane on the Ang II-induced contraction of aortic rings, in the presence and absence of an intact endothelium, were investigated in normotensive Wistar-Kyoto rats (WKY) and SHR and compared using isometric force transducers.

RESULTS

Ang II (10(-9)-10(-6) M) induced a similar transient phasic contraction of endothelium-intact rings from the two rat strains in a dose-dependent manner. Removal of the endothelium augmented the Ang II-elicited phasic contraction, to a greater extent in the SHR group than in the WKY group. Sevoflurane and isoflurane (1-3 minimum alveolar concentration) concentration-dependently inhibited the Ang II-induced contraction of endothelium-intact rings from WKY; an effect that was greatly enhanced following removal of the endothelium. A greater degree of attenuation of the Ang II-induced contraction of both endothelium-intact and -denuded rings by the two anesthetics was observed in the SHR group. The inhibitory effects of isoflurane on the Ang II-induced contraction of aortic rings from both strains appeared to be stronger than that of sevoflurane at equipotent concentrations.

CONCLUSION

Our finding that the inhibitory effects of isoflurane and sevoflurane on Ang II-induced vasoconstriction are enhanced in SHR may, at least in part, account for the anesthesia-induced systemic hypotension frequently seen in hypertensive patients.

Non-canonical signalling and roles of the vasoactive peptides angiotensins and kinins

GPCRs (G-protein-coupled receptors) are among the most important targets for drug discovery due to their ubiquitous expression and participation in cellular events under both healthy and disease conditions. These receptors can be activated by a plethora of ligands, such as ions, odorants, small ligands and peptides, including angiotensins and kinins, which are vasoactive peptides that are classically involved in the pathophysiology of cardiovascular events. These peptides and their corresponding GPCRs have been reported to play roles in other systems and under pathophysiological conditions, such as cancer, central nervous system disorders, metabolic dysfunction and bone resorption. More recently, new mechanisms have been described for the functional regulation of GPCRs, including the transactivation of other signal transduction receptors and the activation of G-protein-independent pathways. The existence of such alternative mechanisms for signal transduction and the discovery of agonists that can preferentially trigger one signalling pathway over other pathways (called biased agonists) have opened new perspectives for the discovery and development of drugs with a higher specificity of action and, therefore, fewer side effects. The present review summarizes the current knowledge on the non-canonical signalling and roles of angiotensins and kinins.

Downregulation of Angiotensin II-Induced 12-Lipoxygenase Expression and Cell Proliferation in Vascular Smooth Muscle Cells from Spontaneously Hypertensive Rats by CCL5

Angiotensin II (Ang II) plays an important role in vascular hypertension. The role of the chemokine CCL5 on Ang II-induced activities in vascular smooth muscle cells (VSMCs) has not been studied. In this study, we elucidated the effect of CCL5 on Ang II-induced 12-lipoxygenase (LO) expression and cell proliferation in spontaneously hypertensive rats (SHR) VSMCs. CCL5 decreased Ang II-induced 12-LO mRNA expression and protein production, and it increased Ang II type 2 (AT(2)) receptor expression in SHR VSMCs. The inhibitory effect of CCL5 on Ang II-induced 12-LO mRNA expression was mediated through the AT(2) receptor. Although treatment of CCL5 alone induced SHR VSMCs proliferation, CCL5 inhibited Ang II-induced VSMCs proliferation and PD123,319, an AT(2) receptor antagonist, blocked the inhibitory effect of CCL5 on Ang II-induced VSMCs proliferation. Phosphorylation of p38 was detected in VSMCs treated with Ang II or CCL5 alone. But, decrease of p38 phosphorylation was detected in VSMCs treated with Ang II and CCL5 simultaneously (Ang II/CCL5) and PD123,319 increased p38 phosphorylation in VSMCs treated with Ang II/CCL5. Therefore, these results suggest that the inhibitory effect of CCL5 on Ang II-induced VSMCs proliferation is mediated by the AT(2) receptor via p38 inactivation, and CCL5 may play a beneficial role in Ang II-induced vascular hypertension.

A role for PYK2 in ANG II-dependent regulation of the PHAS-1-eIF4E complex by multiple signaling cascades in vascular smooth muscle

Regulation of the PHAS-1-eukaryotic initiation factor-4E (eIF4E) complex is the rate-limiting step in the initiation of protein synthesis. This study characterized the upstream signaling pathways that mediate ANG II-dependent phosphorylation of PHAS-1 and eIF4E in vascular smooth muscle. ANG II-dependent PHAS-1 phosphorylation was maximal at 10 min (2.47 +/- 0.3 fold vs. control). This effect was completely blocked by the specific inhibitors of phosphatidylinositol 3-kinase (PI3-kinase, LY-294002), mammalian target of rapamycin, and extracellular signal-regulated kinase 1/2 (ERK1/2, U-0126) or by a recombinant adenovirus encoding dominant-negative Akt. PHAS-1 phosphorylation was followed by dissociation of eIF4E. Increased ANG II-induced eIF4E phosphorylation was observed at 45 min (2.63 +/- 0.5 fold vs. control), was maximal at 90 min (3.38 +/- 0.3 fold vs. control), and was sustained at 2 h. This effect was blocked by inhibitors of the ERK1/2 and p38 mitogen-activated protein (MAP) kinase pathways, but not by PI3-kinase inhibition, and was dependent on PKC, intracellular Ca2+, and tyrosine kinases. Downregulation of proline-rich tyrosine kinase 2 (PYK2) by antisense oligonucleotides led to a near-complete inhibition of PHAS-1 and eIF4E phosphorylation in response to ANG II. Therefore, PYK2 represents a proximal signaling intermediate that regulates ANG II-induced vascular smooth muscle cell protein synthesis via regulation of the PHAS-1-eIF4E complex.

Structural determinants for the activation mechanism of the angiotensin II type 1 receptor differ for phosphoinositide hydrolysis and mitogen-activated protein kinase pathways

While the mechanism whereby the angiotensin II type 1 receptor (AT(1) receptor) activates its classical effector phospholipase C-beta (PLC-beta) has largely been elucidated, there is little consensus on how this receptor activates a more recently identified effector, the p42/44 mitogen-activated protein kinases (p42/44(MAPK)). Using transfected COS-1 cells, we investigated the activation of this signaling pathway at the receptor level itself. Previous mutational studies that relied on phosphoinositide turnover as an index of receptor activation have indicated that key residues in the second and seventh transmembrane domains participate in AT(1) receptor activation mechanisms. Thus, we introduced a variety of mutations-AT(1)[D74N], AT(1)[Y292F], AT(1)[N295S], and AT(1)[AT(2) TM7], which is composed of a chimeric substitution of the AT(1) seventh transmembrane domain with its AT(2) counterpart. These mutations that strongly diminished the receptor's ability to activate PLC-beta had little to no effect on its ability to activate p42/44(MAPK), which not only suggests that p42/44(MAPK) does not exclusively lie downstream of the G-protein G(q)/PLC-beta pathway but also indicates that more than one activation state may exist for the AT(1) receptor. The failure of a protein kinase C inhibitor to block AT(1) receptor activation of p42/44(MAPK) further corroborated evidence that the receptor's activation of p42/44(MAPK) is largely independent of the G(q)/PLC-beta/PKC pathway. Taken together, the experimental evidence strongly suggests that the mechanism whereby the AT(1) receptor activates p42/44(MAPK) is fundamentally different from that for PLC-beta, even at the level of the receptor itself.

Antisense to epidermal growth factor receptor prevents the development of left ventricular hypertrophy

We previously demonstrated that left ventricular hypertrophy (LVH) induced by angiotensin II infusion requires epidermal growth factor receptor (EGFR) activation to mediate the mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) pathway. To test whether the EGFR-mediated MAPK/ERK activation plays an important role in development and maintenance of LVH in spontaneously hypertensive rats (SHR), we investigated the effects of antisense oligodeoxynucleotide to EGFR (EGFR-AS) on LVH and blood pressure in young and adult SHR. EGFR-AS, sense oligonucleotide to EGFR (EGFR-S; 1.5 mg/kg), or vehicle control (5% dextrose) with liposome was injected once a week for 2 months in 5- or 13-week-old SHR. The effect of EGFR-AS on the expression of EGFR and phosphorylated ERK in the heart were examined by Western blots. After treatment, EGFR-AS significantly (P<0.05) decreased left ventricular weight/body weight and blood pressure in young SHR compared with EGFR-S or control-treated rats. In adult SHR, EGFR-AS did not affect left ventricular weight/body weight and blood pressure. EGFR and phosphorylated ERK significantly declined from 5 to 20 weeks (P<0.05). EGFR-AS, but not EGFR-S, significantly (P<0.05) decreased the expression of EGFR and phosphorylated ERK in young SHR, but had no significant effect in adult SHR. These results suggests that EGFR-mediated ERK activation is critically important for LVH in young SHR. This may be related to the high levels of EGFR and phosphorylated ERK in young SHR, suggesting a critical role of the EGFR-activated ERK pathway in cardiovascular development but not in the maintenance of established LVH in adult SHR.

Effects of low dietary magnesium intake on development of hypertension in stroke-prone spontaneously hypertensive rats: role of reactive oxygen species

OBJECTIVES

To investigate whether low dietary Mg2+ intake influences the development of hypertension in stroke-prone spontaneously hypertensive rats (spSHRs) and whether these effects are associated with vascular functional and structural changes, and to assess the role of reactive oxygen species and the activation of vascular mitogen-activated protein (MAP) kinases in these processes.

METHODS

Six-week-old male spSHRs (n = 18) were divided into three groups: control (normal chow, 0.21% Mg2+ ), low Mg2+ group (Mg2+ -free diet), and high Mg2+ group (Mg2+ -rich diet, 0.75%). Systolic blood pressure (SBP) was assessed weekly for 16 weeks. In a second series of experiments, 6-week-old spSHRs (n = 18) were divided into three groups and studied weekly for 7 weeks: control group, low Mg2+ group, and low Mg2+ group receiving the superoxide dismutase mimetic, tempol (1 mmol/l).

RESULTS

The low Mg2+ diet caused an initial decrease in SBP followed, 5 weeks later, by an exacerbated development of hypertension. This was associated with a transient reduction in the plasma concentrations of substances associated with the thiobarbituric acid reaction (markers of oxidative stress), which increased rapidly 2 weeks later. In the low Mg2+ group, acetylcholine-induced vasodilatation was decreased compared with that in controls ( P<0.05). The media : lumen ratio was greater in rats receiving a low Mg2+ diet than in those fed a high Mg2+ diet ( P<0.05). Mg2+ depletion was associated with increased vascular superoxide anion compared with that in Mg2+ -supplemented rats (1.2 0.24 compared with 0.65 0.1 nmol/min per mg). Phosphorylation of MAP kinases was increased two- to threefold in Mg2+ -deficient rats. Tempol prevented the progression of hypertension and normalized the vascular changes in rats fed a low Mg2+ diet.

CONCLUSIONS

Chronic Mg2+ deficiency leads to development of severe hypertension, endothelial dysfunction and vascular remodelling. These processes are associated with oxidative stress and upregulation of redox-dependent MAP kinases. Tempol normalized vascular changes and attenuated the development of hypertension. Our findings suggest that reactive oxygen species play an important part in vascular processes that are associated with progression of hypertension in Mg2+ -deficient spSHRs.

Chronic administration of a tyrosine kinase inhibitor restores functional and morphological changes of the basilar artery during chronic hypertension

OBJECTIVE

Activation of tyrosine kinase appears to play an important role in pathogenesis of cardiovascular disease during chronic hypertension. In the present study, we tested the hypothesis that long-term treatment with an inhibitor of tyrosine kinase would have beneficial effects on hypertension-induced morphological and functional changes of the cerebral artery.

METHODS

Male spontaneously hypertensive rats (SHR; 4 months old) were fed normal rat chow, or that containing an inhibitor of tyrosine kinase, genistein (1 mg/kg chow). Normotensive Wistar-Kyoto (WKY) rats were also fed either of the chows. After feeding the rats for 2 months, we measured wall thickness, diameter of the basilar artery and its dilator responses to acetylcholine (ACh); Y-26763, an opener of ATP-sensitive potassium channels; and Y-27632, an inhibitor of Rho-associated kinase.

RESULTS

Treatment with genistein did not cause significant changes in physiological variables, including mean arterial pressure in either strain. In control SHR, the wall thickness of the basilar artery was greater than that of WKY rats. Genistein treatment reduced the wall thickness significantly in SHR. Vasodilator responses induced by ACh and Y-26763 were markedly attenuated in SHR compared to WKY rats, and treatment of SHR with genistein significantly improved the vasodilatation. Dilatation of the artery in response to Y-27632 was enhanced in SHR compared to WKY rats and treatment of SHR with genistein did not affect the enhanced vasodilator responses to Y-27632.

CONCLUSIONS

Chronic treatment with genistein may be a novel approach to prevent cerebrovascular disorders.

Tyrosine kinases regulate intracellular calcium during alpha(2)-adrenergic contraction in rat aorta

We have demonstrated enhanced contractile sensitivity to the alpha(2)-adrenoreceptor (alpha(2)-AR) agonist UK-14304 in arteries from rats made hypertensive with chronic nitric oxide synthase (NOS) inhibition (LHR) compared with arteries from normotensive rats (NR); additionally, this contraction requires Ca(2+) entry. We hypothesized that tyrosine kinases augment alpha(2)-AR contraction in LHR arteries by increasing Ca(2+). The tyrosine kinase inhibitor tyrphostin 23 significantly attenuated UK-14304 contraction of denuded thoracic aortic rings from NR and LHR. However, tyrphostin 23 did not alter UK-14304 contraction in ionomycin-permeabilized aorta, which indicates that tyrosine kinases regulate intracellular Ca(2+) concentration. The Src family inhibitor PP1 and the epidermal growth factor receptor kinase inhibitor AG-1478 did not alter alpha(2)-AR contraction, whereas the mitogen-activated protein kinase extracellular signal-regulated kinase kinase inhibitor PD-98059 attenuated the contraction. Contraction to CaCl(2) in ionomycin-permeabilized LHR rings was greater than in NR rings. UK-14304 augmented CaCl(2) contraction in ionomycin-permeabilized rings from both groups but to a greater extent in LHR aorta. Together, these data suggest that alpha(2)-AR stimulates contraction via two pathways. One, which is enhanced with NOS inhibition hypertension, activates Ca(2+) sensitivity and is independent of tyrosine kinases. The other is tyrosine kinase dependent and regulates intracellular Ca(2+) concentration.

Inhibition of mitogen-activated protein/extracellular signal-regulated kinase improves endothelial function and attenuates Ang II-induced contractility of mesenteric resistance arteries from spontaneously hypertensive rats

OBJECTIVES

Extracellular signal-regulated kinases (ERK1/2) modulate vascular smooth muscle cell (VSMC) growth and contractility, important factors in blood pressure regulation. In the present in vivo study, we investigated whether short-term inhibition of ERK1/2-dependent signaling pathways influences vascular function and blood pressure (BP) in spontaneously hypertensive rats (SHR).

METHODS

SHR and Wistar-Kyoto (WKY) rats were injected subcutaneously with either PD98059, selective MEK1/2 inhibitor (20 mg/kg), or vehicle. BP was measured by telemetry. Rats were killed 24 h after injection and small mesenteric arteries mounted as pressurized systems for morphometric analysis and assessment of endothelial function and angiotensin II (Ang II)-induced contractility. ERK1/2 phosphorylation was measured by Western blots, using protein extracts from mesenteric arteries, aorta, heart and kidneys.

RESULTS

BP was higher (P < 0.01) in SHR than in WKY rats. PD98059 did not influence BP in either group. Endothelial-dependent relaxation (acetylcholine-induced), which was impaired in SHR, was improved by PD98059 (P < 0.05). Ang II increased contraction, with greater responses in SHR (Emax = 25 +/- 4%) than WKY (Emax = 9 +/- 3%) (P < 0.01). PD98059 reduced Ang II-induced contraction in SHR (Emax = 5.8 +/- 0.4%) and WKY (Emax = 4 +/- 0.4%). Vascular structure was unaltered by PD98059. Vascular and renal ERK1/2 phosphorylation, which was higher in SHR than WKY, was decreased by PD98059 in SHR.

CONCLUSION

Short-term treatment with PD98059 improves endothelial function and vascular contractility without influencing BP in SHR. These findings provide evidence that vascular ERK1/2 activity is upregulated and that MEK1/2-sensitive signaling pathways play an important role in the regulation of vascular function in SHR. Acute inhibition of MEK1/2 does not alter blood pressure despite improved endothelial function and reduced arterial reactivity to Ang II.

Altered PYK2 phosphorylation by ANG II in hypertensive vascular smooth muscle

Vascular smooth muscle cells (VSMC) from spontaneously hypertensive rats (SHR) exhibit increased cell growth compared with normotensive Wistar-Kyoto rats (WKY). ANG II stimulates growth via G(q)-protein-coupled signaling that involves changes in cytosolic intracellular Ca(2+) concentration ([Ca(2+)](i)) and activation of protein kinase C (PKC) and mitogen-activated protein kinases. This study examines the role of the proline-rich tyrosine kinase 2 (PYK2) in hypertensive VSMC. Basal PYK2 phosphorylation in SHR VSMC was increased compared with WKY (0.44 +/- 0.02 vs. 0.20 +/- 0.02-fold). ANG II-induced activation of PYK2 in SHR VSMC was of greater magnitude (2.2 +/- 0.2-fold in SHR; 1.4 +/- 0.1-fold in WKY) and occurred more rapidly (peak activation at 2 min in SHR vs. 5 min in WKY). This effect was blocked by pretreatment with the [Ca(2+)](i) chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid or the PKC inhibitor chelerythrine. Basal and ANG II-stimulated c-Fos expression was increased in SHR versus WKY VSMC. PYK2 downregulation with antisense oligonucleotides blocked ANG II-induced c-Fos expression. Increased PYK2 activation may be altered signaling cascades that regulate cell growth in hypertensive VSMC.

Differential ANG II-induced growth activation pathways in mesenteric artery smooth muscle cells from SHR

Angiotensin II-induced growth signaling mechanisms were investigated in vascular smooth muscle cells (VSMCs) from mesenteric arteries of spontaneously hypertensive (SHR) and Wistar-Kyoto rats (WKY). In WKY, angiotensin II significantly increased protein synthesis ([(3)H]leucine incorporation) but not DNA synthesis ([(3)H]thymidine incorporation). In SHR, angiotensin II increased protein and DNA synthesis. VSMCs from both strains expressed angiotensin type 1 (AT(1)) and type 2 (AT(2)) receptors. Losartan (an AT(1) receptor antagonist) but not PD-123319 (an AT(2) receptor antagonist) attenuated angiotensin II-stimulated protein synthesis in WKY VSMCs. In SHR, losartan and PD-123319 partially inhibited angiotensin II-induced VSMC proliferation. The mitogen-activated protein kinase or extracellular signal-regulated protein kinase (ERK) kinase inhibitor PD-98059 blocked VSMC growth responses to angiotensin II in both strains. Angiotensin II increased ERK1/2 activation more in SHR than WKY, an effect inhibited by losartan but not PD-123319. LY-294002 [a phosphatidylinositol-3 (PI3) kinase inhibitor] blocked angiotensin II-stimulated ERK1/2 activation in SHR but not in WKY, whereas bisindolylmaleimide [a protein kinase C (PKC) inhibitor] was ineffective. In conclusion, angiotensin II stimulates VSMC proliferation via AT(1) and AT(2) receptors in SHR. In WKY, angiotensin II induces VSMC hypertrophy via AT(1) receptors. ERK1/2-dependent pathways regulated by intracellular Ca(2+) but not PKC mediate these effects. In SHR VSMCs, PI3 kinase plays a role in augmented angiotensin II-induced ERK1/2 phosphorylation. These angiotensin II-mediated signaling events could contribute to vascular remodeling in SHR.

Angiotensin II activates the GFAT promoter in mesangial cells

Expression of glutamine:fructose-6-phosphate amidotransferase (GFAT), the rate-limiting enzyme for glucose entry into the hexosamine pathway, is transcriptionally regulated. Immunohistochemical studies of human kidney biopsies demonstrate increased GFAT expression in diabetic glomeruli, but the mechanism responsible for this overexpression is unknown. Given the role of ANG II in diabetic kidney disease, we chose to study the effect of ANG II on GFAT promoter activity in mesangial cells (MC). Exposure of MC to ANG II (10(-7) M) increased GFAT promoter activity (2.5-fold), mRNA (3-fold), and protein (1.6-fold). ANG II-mediated GFAT promoter activation was inhibited by the ANG II type I receptor antagonist candesartan (10(-8) M) but was unaffected by the ANG II type II receptor antagonist PD-123319 (10(-8) M). The intracellular calcium chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (10(-6) M), protein kinase C (PKC) inhibitors bisindoylmaleimide-4 (10(-6) M) and calphostin C (10(-7) M), protein tyrosine kinase (PTK) inhibitor genistein (10(-4) M), Src family kinase inhibitor PP2 (2.5 x 10(-7) M), p42/44 mitogen-activated protein kinase (MAPK) inhibitor PD-98059 (10(-5) M), and the epidermal growth factor (EGF) inhibitor AG-1478 all attenuated GFAT promoter activation by ANG II. We conclude that the GFAT promoter is activated by ANG II via the AT1 receptor. Promoter activation is calcium dependent and PKC dependent but also involves PTK signaling pathways including Src, the EGF receptor, and p42/44 MAPK.

Src is an important mediator of extracellular signal-regulated kinase 1/2-dependent growth signaling by angiotensin II in smooth muscle cells from resistance arteries of hypertensive patients

The role of c-Src in growth signaling by angiotensin (Ang) II was investigated in vascular smooth muscle cells (VSMCs) from arteries of hypertensive patients. c-Src and extracellular signal-regulated kinase 1/2 (ERK1/2) activity, proto-oncogene expression, activating protein-1 (AP-1) DNA-binding activity, and DNA and protein synthesis were studied in Ang II-stimulated VSMCs derived from small peripheral resistance arteries of normotensive subjects (NTs, n=5) and age-matched untreated hypertensive patients (HTs, n=10). Ang II type 1 (AT(1)) and type 2 (AT(2)) receptor status was also assessed. Ang II dose-dependently increased the synthesis of DNA and protein, with enhanced effects in VSMCs from HTs. PD 098,059, a selective inhibitor of the ERK1/2 pathway, attenuated Ang II-stimulated growth in HTs. The effects of PD 098,059 were greater in HTs than in NTs. In NTs, Ang II transiently increased ERK1/2 phosphorylation, whereas in HTs, Ang II-stimulated actions were augmented and sustained. PP2, a selective Src inhibitor, reduced ERK1/2 activity and normalized ERK1/2 responses in HTs. Ang II-induced c-Src phosphorylation was 2- to 3-fold greater in HTs than in NTs. In HTs but not NTs, kinase activation was followed by overexpression of c-fos and enhanced AP-1 DNA-binding activity. PD 098,059 and PP2 attenuated these responses. AT(1) receptor expression was similar in NTs and HTs. In HT cells transfected with c-fos antisense oligodeoxynucleotide, Ang II-stimulated growth was reduced compared with sense oligodeoxynucleotide. Our findings suggest that augmented Ang II-stimulated VSMC growth is mediated via hyperactivation of c-Src-regulated ERK1/2-dependent pathways, leading to overexpression of c-fos mRNA and enhanced AP-1 DNA-binding activity. Because AT(1) receptor expression was unaltered in HTs, increased Ang II signaling may be a postreceptor phenomenon. These data define a signal transduction pathway whereby Ang II mediates exaggerated growth in VSMCs from HTs.

Differential activation of extracellular signal-regulated protein kinase 1/2 and p38 mitogen activated-protein kinase by AT1 receptors in vascular smooth muscle cells from Wistar-Kyoto rats and spontaneously hypertensive rats

OBJECTIVES

The present study investigates effects of angiotensin II on activation of extracellular signal-regulated protein kinase (ERK) 1/2, p38 mitogen activated-protein kinase (p38MAPK) and c-Jun amino terminal kinase (JNK) in vascular smooth muscle cells from spontaneously hypertensive rats (SHR).

METHODS

Vascular smooth muscle cells (VSMC) from mesenteric arteries of Wistar-Kyoto (WKY) rats and SHR were studied. Angiotensin II-induced phosphorylation of ERK1/2, JNK and p38MAPK were assessed by Western blot analysis. c-fos mRNA expression by angiotensin II was determined by reverse transcriptase-polymerase chain reaction in the absence and presence of PD98059, selective inhibitor of ERK1/2-dependent pathways and SB202190, selective p38MAPK inhibitor.

RESULTS

Angiotensin II increased phosphorylation of ERK1/2 and p38MAPK, but not JNK. Responses were significantly increased in SHR compared with WKY. Irbesartan, AT1 receptor antagonist, but not PD123319, AT2 receptor blocker, abolished angiotensin II-induced effects. PP2, selective Src inhibitor, decreased angiotensin II-mediated activation of MAP kinases. Angiotensin II increased c-fos mRNA expression in SHR and had a small stimulatory effect in WKY. These actions were inhibited by PD98059, whereas SB202190 had no effect.

CONCLUSIONS

Angiotensin II-induced activation of vascular ERK1/2 and p38MAPK is increased in SHR. These effects are mediated via AT1 receptors, which activate Src-dependent pathways. Overexpression of c-fos mRNA in SHR is due to ERK1/2-dependent, p38MAPK-independent pathways. Our results suggest that angiotensin II activates numerous MAP kinases in VSMCs and that differential activation of these kinases may be important in altered growth signaling in VSMCs from SHR.

ANG II potentiates mitogenic effect of norepinephrine in vascular muscle cells: role of FGF-2

We examined the possible cooperation between norepinephrine (NE) and ANG II on proliferation of cultured vascular smooth muscle cells (VSMCs) and the involved cellular mechanisms. Nanomolar NE concentrations stimulated VSMC proliferation through a prazosin-sensitive effect. The pretreatment of cells with 100 nM ANG II for 24 h significantly potentiated the NE-induced VSMC proliferation; this potentiating effect of ANG II was blocked by losartan but was unaffected by the AT(2) receptor antagonist PD-123177. ANG II pretreatment also potentiated the increase in inositol phosphate turnover and upregulated the cell expression of fibroblast growth factor (FGF-2) induced by NE. Anti-FGF-2 neutralizing antibodies prevented the potentiating effect of ANG II on NE-induced cell growth. Both ANG II and NE stimulated extracellular signal-related kinase (ERK1) activation, but an ANG II potentiation of the effect of NE on ERK1 activity was not detectable. Moreover, ANG II significantly increased protein synthesis but did not potentiate the hypertrophic effect of NE. These findings demonstrate that ANG II and NE cooperate in promoting VSMC growth and that FGF-2 upregulation is involved in this effect.

Clotrimazole inhibits smooth muscle cell proliferation and has a vasodilator effect on resistance arteries

Clotrimazole (CLT) is a drug known to interfere with cellular calcium homeostasis, which in turn is reported to intervene in cell proliferation and in the reactivity of small blood vessels. Experiments were designed to test the influence of CLT on the proliferative and vasorelaxant effect of bradykinin (BK) and on calcium homeostasis in smooth muscle cells (SMC). To this purpose two model systems were employed: (i) cultured human smooth muscle cells (HSMC), and (ii) isolated resistance arteries maintained in an organ bath. The effect of various concentrations of CLT (2-15 microM) on BK-induced proliferation of HSMC was quantitated by spectrometry following [3H]-thymidine incorporation, and intracellular calcium [Ca+]i was determined by spectrofluorimetry using Fura 2-AM assay. In other experiments the roles of BK receptor (AB2) and of thapsigargin were assessed. The reactivity of the resistance arteries was measured by the myograph technique, and the effects of BK, CLT, and NO synthase blocker, L-NAME were evaluated. The results showed that 10 microM CLT: (i) inhibits the BK-induced proliferation of HSMC by 45-50%: (ii) prevents the rise of [Ca2+]i induced by BK (120.8 +/- 12.4 nM vs. 235.8 +/- 34.1 nM), an cffect similar to that of "classic" L-type calcium channels blockers: (iii) reduces the release of Ca2+ entry induced by thapsigargin suggesting a possible inhibition of the capacitative Ca2+ entry. Organ bath assays showed that CLT enhanced the BK-induced relaxation of the resistance arteries by an endothelium NO-independent pathway. Together, these data suggest that the mechanism of action of CLT on SMC implies mainly a modification of intracellular calcium homeostasis, with a minor contribution of BK B2 receptors. These new distinctive features of CLT effects suggest the potential use of this drug in the therapy of cardiovascular diseases associated with SMC increased proliferation and impeded relaxation in small arteries, such as atherosclerosis and restenosis.

Activation of MAPKs in proximal tubule cells from spontaneously hypertensive and control Wistar-Kyoto rats

The aim of this study was to test the hypothesis that differences exist in the activity and/or expression of mitogen-activated protein kinases (MAPKs) between spontaneously hypertensive rats (SHR) and control Wistar-Kyoto rats (WKY) and that these differences may account for the enhanced activity of the Na(+)/H(+) exchanger (NHE) previously observed in the renal proximal tubule of SHR. Therefore, the activities of c-jun N-terminal kinase(1) (JNK(1)), extracellular signal-regulated kinase(1/2) (ERK(1/2)), and p38 were investigated. A reduced amount of ERK(1) and JNK(1) protein was found in renal cortex specimens of SHR as compared with WKY; however, their activities were the same. To study the cellular basis of this difference, immortalized proximal tubule cell lines were grown on Millicell-CM filter inserts where the cell lines organize as polarized monolayers with separate access to apical and basolateral compartments. Although basal JNK(1) and ERK(1/2) activities were not significantly different between WKY and SHR cells, anisomycin stimulated JNK(1) activity in WKY cells more than in SHR cells (eg, at 15 minutes 300% versus 30%, respectively). Similarly, angiotensin II increased JNK(1) and ERK(1/2) activity in a time- and concentration-dependent manner in WKY cells but not in SHR cells. Western blot analyses showed a deficit in JNK(1) and ERK(1) protein in SHR (0.25 and 0.5, respectively, of the levels in WKY cells), although ERK(2) and p38 protein levels were the same. These observations suggest that, although angiotensin II activates MAPKs and MAPKs have been shown to regulate NHE, this regulatory pathway is unlikely to account for the increased activity of NHE in the proximal tubular epithelium of SHR.

Evidence that P2Y4 nucleotide receptors are involved in the regulation of rat aortic smooth muscle cells by UTP and ATP

1. Previous studies have shown that ATP and UTP are able to stimulate phospholipase C (PLC) and proliferation in cultured aortic smooth muscle cells. Here we set out to characterize the receptor responsible, and investigate a possible role for p42 and p44 mitogen activated protein kinase (MAPK) in the proliferative response. 2. The phospholipase C response of spontaneously hypertensive rat (SHR) derived aortic smooth muscle cells in culture showed that the response to ATP was partial compared to the response to UTP. 3. Further studies characterized the responses of the SHR derived cells. UTP was the only full agonist with the SHR cells; UDP gave a partial response while ADP, 2-methythio-ATP and alpha,beta-methylene ATP were essentially ineffective. The response to UDP was almost lost in the presence of hexokinase, consistent with this being due to extracellular conversion to UTP. These observations are inconsistent with the response being mediated by either P2Y1 or P2Y6 receptors. 4. When increasing concentrations of ATP were present with a maximally effective concentration of UTP, the size of the response diminished, consistent with UTP and ATP acting at a single population of receptors for which ATP was a partial agonist. This is inconsistent with a response mainly at P2Y2 receptors. 5. 1321N1 cells transfected with human P2Y4 receptors gave a similar agonist response profile, with ATP being partial compared to UTP, loss of response to UDP with hexokinase treatment, and with the response to UTP diminishing in the presence of increasing concentrations of ATP. 6. Use of the reverse transcriptase-polymerase chain reaction confirmed the presence of mRNA encoding P2Y4 receptors in SHR derived vascular smooth muscle cells. Transcripts for P2Y2, P2Y4 and P2Y6 receptors, but not P2Y1 receptors, were detected. 7. Stimulation of SHR derived cells with UTP enhanced the tyrosine phosphorylation of both p42 and p44 MAPK, and the incorporation of [3H]-thymidine into DNA. Both these responses were diminished in the presence of an inhibitor of activation of MAPK. 8 These results lead to the conclusion that in SHR derived cultured aortic smooth muscle cells, PLC responses to extracellular UTP and ATP are predominantly at P2Y4 receptors, and suggest that these receptors are coupled to mitogenesis via p42/p44 MAPK.

The regulation of vascular function by P2 receptors: multiple sites and multiple receptors

Although the effects of nucleotides in the cardiovascular system have been known for almost 70 years, it is only in the past few years that some of the P2 receptors at which they act have been cloned and characterized. It is now clear that the control of cardiovascular function by nucleotides is complex, involving multiple receptors and multiple effects in the different cell types of importance. In this review Mike Boarder and Susanna Hourani summarize the P2 receptors that are present in endothelial cells, platelets, smooth muscle and nerves, the signalling pathways that they activate and the responses that are produced. They also discuss the important role of nucleotides in the interactions between the different cell types, and the implications of this in vascular disease.