Acute hypertension activates mitogen-activated protein kinases in arterial wall

Mitogen-activated protein kinase activation by hydrogen peroxide is mediated through tyrosine kinase-dependent, protein kinase C-independent pathways in vascular smooth muscle cells: upregulation in spontaneously hypertensive rats

OBJECTIVE

To investigate the putative molecular mechanisms underlying mitogen-activated protein (MAP) kinase activation by hydrogen peroxide (H(2)O(2)) in vascular smooth muscle cells (VSMC) and to evaluate whether H(2)O(2)-induced actions are altered in VSMC from spontaneously hypertensive rats (SHR).

METHOD

VSMC from mesenteric arteries of Wistar-Kyoto rats (WKY) and SHR were stimulated with H(2)O(2) (2-30 min). The phosphorylation of extracellular signal-regulated kinases (ERK)1/2 and p38MAP kinase was determined by immunoblotting. The involvement of tyrosine kinase and protein kinase C (PKC) was evaluated using pharmacological inhibitors, tyrphostin (A23 and A9) and GF109203X, respectively. The role of receptor tyrosine kinases (RTK) was assessed with AG1478, AG1296 and AG1024, selective inhibitors of epidermal growth factor receptor, platelet-derived growth factor receptor and insulin-like growth factor receptor, respectively. Non-receptor tyrosine kinases (NRTK) were studied using AG490 (JAK2 inhibitor) and PP2 (Src inhibitor).

RESULTS

H(2)O(2) stimulated phosphorylation of ERK1/2 and p38MAP kinase in a time-dependent manner. This increase was significantly greater in SHR versus WKY (P < 0.01). The activation of MAP kinases was unaffected by GF109203X but was decreased by tyrphostins (P < 0.01). The inhibition of NRTK attenuated H(2)O(2)-mediated phosphorylation of ERK1/2 (P < 0.001) but not of p38MAP kinase, whereas Src and JAK2 inhibition significantly decreased phosphorylation of both MAP kinases (P < 0.01).

CONCLUSION

These data indicate that H(2)O(2) increases ERK1/2 and p38MAP kinase activation through tyrosine kinase-dependent, PKC-independent mechanisms. Whereas ERK1/2 is regulated by both RTK and NRTK, p38MAP kinase is regulated by NRTK. Our findings identify an important role for tyrosine kinases, but not PKC, in H(2)O(2)-induced phosphorylation of ERK1/2 and p38MAP kinase in VSMC. The upregulation of these processes may contribute to enhanced redox-dependent MAP kinase signaling in SHR VSMC.

Reactive oxygen species as mediators of calcium signaling by angiotensin II: implications in vascular physiology and pathophysiology

Reactive oxygen species (ROS), including superoxide anion, hydrogen peroxide, and hydroxyl radical, and reactive nitrogen species, such as nitric oxide and peroxynitrite, are biologically relevant O2 derivatives increasingly being recognized as important in vascular biology through their oxidation/reduction (redox) potential. All vascular cell types produce ROS primarily via membrane-associated NAD(P)H oxidase. ROS influence vascular function by modulating contraction/dilation, cell growth, apoptosis/anoikis, migration, inflammation, and fibrosis. An imbalance in redox state where prooxidants overwhelm antioxidant capacity results in oxidative stress. Oxidative excess and associated oxidative damage are mediators of altered vascular tone and structural remodeling in many cardiovascular diseases. ROS elicit these effects by influencing intracellular signaling events. In addition to modulating protein tyrosine kinases, protein phosphatases, mitogen-activated protein kinases, and transcription factors, ROS are important regulators of intracellular Ca2+ homeostasis and RhoA/Rho kinase signaling. ROS increase vascular [Ca2+]i by stimulating inositol trisphosphate-mediated Ca2+ mobilization, by increasing cytosolic Ca2+ accumulation through sarcoplasmic/endoplasmic reticulum Ca2+-ATPase inhibition, and by stimulating Ca2+ influx through Ca2+ channels. Increased ROS generation enhances Ca2+ signaling and up-regulates RhoA/Rho kinase, thereby altering vascular contractility and tone. The present review discusses the importance of ROS in angiotensin II signaling in vascular biology and focuses specifically on the role of oxidative stress in Ca2+ signaling in the vasculature.

Arterial hemodynamics and mechanical properties after circulatory intervention in the chick embryo

Altered blood pressure and flow impact cardiac function during morphogenesis. How the arterial system supports cardiac morphogenesis after circulatory disruptions is not well characterized. We manipulated arterial flow via left atrial ligation (LAL) or arterial load via right vitelline artery ligation (VAL) in Hamburger-Hamilton (HH) stage 21 chick embryos. Embryos were reincubated for 1 h (HH21), 14 h (HH24) or 30 h (HH27). At each stage we measured simultaneous dorsal aortic blood pressure and flow, and calculated arterial compliance, impedance and hydraulic power. LAL acutely reduced stroke volume (Vs), cardiac output (Q) and hydraulic power. Arterial pressure was preserved by a compensatory increase in characteristic impedance and decrease in compliance. Impedance parameters and compliance normalized by HH24 and all parameters normalized by HH27. VAL acutely increased arterial resistance. Embryos maintained arterial pressure by decreasing Vs and Q. These parameters remained altered through HH27. In summary, despite the intervention, compensatory alterations in Vs and arterial resistance maintained arterial pressure and fraction of oscillatory power within a narrow range. These results suggest that the maintenance of arterial pressure and circulatory energy efficiency, but not arterial flow, is critical to embryogenesis.

Mitogen-activated protein kinase expression and activation does not differentiate benign from malignant mesothelial cells

BACKGROUND

In vitro studies of malignant mesothelioma (MM) cells have suggested activation of mitogen-activated protein kinase (MAPK) in response to asbestos exposure. The objective of this study was to investigate protein expression (level) and phosphorylation status (activity) of the extracellular-regulated kinase (ERK), the c-Jun amino-terminal kinase (JNK), and the high-osmolarity glycerol response kinase (p38) in vivo through the analysis of fresh frozen reactive mesothelium (RM) and MM specimens.

METHODS

MAPK levels were analyzed in 36 fresh-frozen MM specimens (32 effusions, 4 biopsies) and in 14 RM specimens (all effusions) using immunoblotting with antibodies detecting the total (pan-) and activated (phospho-) fraction (p-) of ERK, JNK, and p38. Values for pan-MAPK and p-MAPK expression and the p-MAPK/pan-MAPK ratio in MM and RM specimens were compared. Results were corroborated using immunocytochemistry for p-ERK, p-JNK, and p-38 in selected specimens.

RESULTS

Pan-ERK, pan-JNK, and pan-p38 expression was found frequently in both MM specimens (35 of 36 specimens) and RM specimens (14 of 14 specimens) using immunoblotting, with comparable findings for activated p-p38 (34 of 36 MM specimens, 13 of 14 RM specimens). Activation of p-ERK (27 of 36 MM specimens, 10 of 14 RM specimens) and p-JNK (25 of 36 MM specimens, 10 of 14 RM specimens) was less frequent. Pan-ERK (P = 0.016), pan-JNK (P = 0.004), pan-p38 (P = 0.012), and p-ERK (P = 0.02) expression levels were higher in MM specimens from female patients. Pan-p38 expression levels also were higher in peritoneal MM specimens (P = 0.019). MM and RM showed similar MAPK expression, activation, and activation ratios (Mann-Whitney test; P > 0.05). Immunocytochemistry localized MAPK to MM and RM cells.

CONCLUSIONS

The current results provided the first evidence of in vivo activation of MAPK in clinical MM and RM. The similar values in these two cell types suggest that MAPK may not be involved in the transformation of benign to malignant mesothelium, thus bringing into question the validity of using MAPKs as molecular therapeutic targets in patients with MM.

Stretch-induced Raf-1 activation in mesangial cells requires actin cytoskeletal integrity

Glomerular capillary hypertension is a determinant of glomerulosclerosis and is modelled in vitro by exposure of mesangial cells to cyclic mechanical strain. In response to strain, Erk is activated and mediates extracellular matrix accumulation and mesangial cell proliferation. Erk activation is dependent on an intact cytoskeleton. Since Raf-1 lies upstream of Erk in response to numerous stimuli, and since its activation is dependent on membrane recruitment, we postulated that the cytoskeleton was essential for Raf-1 membrane recruitment and Erk activation. Primary rat mesangial cells (passages 8-20) were stretched at 1 Hz and 27 kPa. Raf-1 was both phosphorylated on serine-338 (S338) and activated within 2 min of strain. The Raf-1 inhibitor, GW5074, dose-dependently blocked strain-induced Erk activation and Raf-1 phosphorylation. Although phosphatidylinositol-3-kinase (PI3-K) may mediate Raf-1 activation, PI3-K inhibition with wortmannin or LY294002 had no effect on stretch-induced Raf-1 activation. Cytoskeletal disruption with cytochalasin D and the Rho-kinase inhibitor, Y-27632, however, blocked both Raf-1 phosphorylation and activation. Furthermore, membrane localization of Raf-1 was increased by strain and prevented by cytoskeletal disruption. Thus, strain leads to rapid membrane localization, S338 phosphorylation, and activation of Raf-1. These events are independent of PI3-K, but require Rho-kinase activation and an intact actin cytoskeleton.

Position of Src tyrosine kinases in the interaction between angiotensin II and endothelin in in vivo vascular protein synthesis

OBJECTIVES

Endothelin is a necessary intermediate in the trophic action of angiotensin II during hypertension-induced resistance artery remodeling in vivo. Since Src tyrosine kinases can be activated by both agonists, we studied their role in the trophic action of angiotensin II, endothelin and their interaction in rat small mesenteric arteries.

METHODS AND RESULTS

Twenty-six hour infusion of high-dose angiotensin II (400 ng/kg per min) or endothelin (5 pmol/kg per min) via osmotic pumps significantly enhanced vascular protein synthesis in vivo. When angiotensin II was used as the trophic stimulus, treatment with a Src tyrosine kinase inhibitor (PP2, 0.5 mg/kg, starting at 21 h of the 26-h stimulation) produced a significant attenuation of extracellular regulated kinase 1 (ERK 1) phosphorylation and of protein synthesis. However, PP2 administered at 21 h or throughout the 26-h infusion did not abrogate the elevation of protein synthesis induced by endothelin. Moreover, endothelin did not enhance the phosphorylation of ERK 1/2 in small mesenteric arteries. We confirmed that angiotensin II stimulated the expression of prepro-endothelin mRNA in small mesenteric arteries in a Src-dependent manner, as the response was inhibited by PP2. To support the specific inhibitory activity of PP2 on Src tyrosine kinases in vivo, angiotensin II-induced phosphorylation of cortactin, a Src-specific substrate, was inhibited by PP2.

CONCLUSION

Src tyrosine kinases represent an important signaling element in angiotensin II-induced endothelin production in small arteries in vivo. However, Src tyrosine kinases did not appear to contribute to the trophic signaling of endothelin, suggesting that they lie upstream of endothelin in the angiotensin II-endothelin-protein synthesis cascade.

Effects of aging on pressure-induced MAPK activation in the rat aorta

With increasing age, the cardiovascular system experiences substantial alterations in cellular morphology and function. Whilst the factors regulating these changes are unknown, the mitogen-activated protein kinase (MAPK) pathways have emerged as critical components for mediating numerous cellular responses including control of cell growth, differentiation and adaptation. Here we compare the expression, basal activation and the ability of increased pressure to activate the MAPK pathways in adult (6-month-old), aged (30-month-old) and very aged (36-month-old) Fischer 344xBrown Norway F1 hybrid rats. Histochemical analysis demonstrated an age-related increase in tunica media thickness of approximately 11 and 21% in aortae from aged and very aged animals, respectively. Western blot analysis of the MAPK family extracellular signal-regulated kinase (ERK 1/2), p38, and c-Jun NH2 -terminal kinase (JNK) MAPKs showed differential expression and activation among these proteins with age. Expression of ERK 1/2, p38, and JNK were unchanged, slightly increased (10+/-17.5%) or significantly increased (72.3+/-27%), respectively, in very aged aortae. In contrast, basal activation levels of these proteins were reduced (-26.2+/-7.4%), markedly increased (97.0+/-16.8%), and slightly increased (14.4+/-4.5%), respectively, in very aged compared with 6-month rat aortae. An acute increase of aortic intraluminal pressure (200 mmHg) indicated that ERK 1/2 regulation differed from p38 or JNK. Pressure loading-induced phosphorylation of ERK1/2 was unchanged or increased with aging while p38 and JNK phosphorylation was attenuated (P<0.01). These observations confirm previous conclusions that MAPK proteins are regulated mechanically and expand these studies to suggest that MAPK expression and the control of activation are changed with aging.

Recommendations for Blood Pressure Measurement in Humans and Experimental Animals

In experimental animals, as in humans, techniques for measuring blood pressure (BP) have improved considerably over the past decade. In this document, we present recommendations for measuring BP in experimental animals with the goal of helping investigators select optimal methods for BP monitoring in the research laboratory. The advantages and disadvantages of various BP measurement methods are discussed and specific recommendations are provided for selecting the optimal technique depending on the study objective. Although indirect techniques that permit only sporadic measurements of BP may be suitable for some purposes, methods for directly measuring BP are generally preferred because of their ability to monitor the highly dynamic nature of BP in a comprehensive fashion. Selection of the methods to be used should ultimately be guided by the study objectives to insure that the techniques chosen are appropriate for the experimental questions being explored.

Differential Regulation of Vascular Focal Adhesion Kinase by Steady Stretch and Pulsatility

Background— In vivo tensile strain in arteries comprises 2 components: steady stretch and pulsatile stretch. However, little attention has been paid to the differential transduction of these stimuli in whole vessels.

Methods and Results— Using rabbit aortas maintained in organ culture for 24 hours, we found that focal adhesion kinase (FAK) was strongly activated by high intraluminal pressure (150 mm Hg), as evidenced by increased phosphorylation ( P <0.01) of tyrosine residues Tyr-397 (3.06±0.17-fold), Tyr-407 (3.71±0.65-fold), Tyr-861 (1.92±0.33-fold), and Tyr-925 (2.41±0.39-fold), compared with 80 mm Hg controls. Immunohistochemistry showed positive staining for these phosphotyrosines in the endothelium and innermost smooth muscle cell layers. Total FAK phosphorylation was reduced in vessels at 150 mm Hg by treatment with the Src family kinase inhibitor PP2 or with the integrin–extracellular matrix interaction–blocking RGD peptide, attaining 1.75±0.22-fold and 2.00±0.19-fold, respectively ( P <0.05), compared with 3.07±0.38-fold ( P <0.001) in untreated vessels. PP2 prevented phosphorylation of Tyr-407 and Tyr-925, whereas RGD peptide abolished phosphorylation of Tyr-397 and Tyr-407. PP2 and RGD peptide also inhibited high pressure–induced binding of FAK with the effector Grb2 and blocked activation of extracellular regulated kinase (ERK) 1/2 in vessels at 150 mm Hg. In contrast, 10% cyclic stretch in aortas did not induce significant FAK phosphorylation relative to nonpulsatile controls. Furthermore, although ERK1/2 was activated in vessels exposed to pulsatility, it was not blocked by PP2 or RGD peptide treatment.

Conclusions— Our results demonstrate that (1) steady and cyclic modes of stretch are transduced differently in the aorta, the former implicating FAK, the latter not, and (2) Src and integrins are involved in steady pressure–induced FAK.

Fluvastatin Prevents Vascular Hyperplasia by Inhibiting Phenotype Modulation and Proliferation Through Extracellular Signal-Regulated Kinase 1 and 2 and p38 Mitogen-Activated Protein Kinase Inactivation in Organ-Cultured Artery

OBJECTIVE

We examined the inhibitory mechanisms of fluvastatin on FBS-induced vascular hypertrophy assessed by organ-cultured rat tail artery.

METHODS AND RESULTS

After 5 days of culture with 10% FBS, hyperplastic morphological changes in the media layer were induced. Treatment with 1 mumol/L fluvastatin significantly inhibited these changes. In the FBS-cultured arteries, the protein expression ratio of alpha-actin/beta-actin was significantly decreased, indicating the change to synthetic phenotype. Fluvastatin restored the decreased expression ratio, and the addition of mevalonate (100 mumol/L) suppressed this recovery. In accordance with the synthetic morphological changes, the absolute force of contractions induced by stimuli was decreased. Fluvastatin treatment also restored the decreased contractility, and the addition of mevalonate suppressed this recovery. In the arteries cultured with FBS, extracellular signal-regulated kinase 1 and 2 (ERK1/2) and p38 mitogen-activated protein kinase (p38MAPK) phosphorylation were significantly increased. Fluvastatin inhibited these phosphorylations, and mevalonate prevented the action of fluvastatin.

CONCLUSIONS

These results suggest that fluvastatin inhibits vascular smooth muscle phenotype modulation to synthetic phenotype and proliferation by inhibiting the local metabolic pathway of cholesterol in smooth muscle cells, which inhibits hyperplastic changes in the vascular wall. The antihyperplastic actions by statins may be induced by inhibiting the ERK1/2 and p38MAPK activities, possibly through inhibition of prenylated Ras. We examined the inhibitory mechanisms of fluvastatin on FBS-induced vascular hypertrophy assessed by organ-cultured artery. Results suggest that fluvastatin inhibits vascular smooth muscle phenotype modulation and proliferation by inhibiting the ERK1/2 and p38MAPK activities through depletion of mevalonate in smooth muscle cells, resulting in inhibiting vascular hyperplastic changes.

Recommendations for Blood Pressure Measurement in Humans and Experimental Animals

In experimental animals, as in humans, techniques for measuring blood pressure (BP) have improved considerably over the past decade. In this document, we present recommendations for measuring BP in experimental animals with the goal of helping investigators select optimal methods for BP monitoring in the research laboratory. The advantages and disadvantages of various BP measurement methods are discussed and specific recommendations are provided for selecting the optimal technique depending on the study objective. Although indirect techniques that permit only sporadic measurements of BP may be suitable for some purposes, methods for directly measuring BP are generally preferred because of their ability to monitor the highly dynamic nature of BP in a comprehensive fashion. Selection of the methods to be used should ultimately be guided by the study objectives to insure that the techniques chosen are appropriate for the experimental questions being explored.

Time-dependent transition of tempol-sensitive reduction of blood pressure in angiotensin II-induced hypertension

OBJECTIVE

Reactive oxygen species (ROS) participate in the intracellular signalling of angiotensin II. However, the mechanisms of the interaction of ROS with hypertension and mitogen-activated protein kinase (MAPK) in vivo have remained unclear. Angiotensin II infusion provokes sustained hypertension accompanied with enhancement of ROS production; initially hypertension is non-sensitive to ROS, but thereafter becomes sensitive. We examined the time-dependent transition of ROS-sensitive vasoconstriction during angiotensin II infusion and also ROS sensitivity to cardiovascular MAPK activation in acutely and chronically angiotensin II-infused rats.

METHODS AND RESULTS

During infusion of a pressor dose of angiotensin II to conscious Sprague-Dawley rats, tempol, a superoxide dismutase mimetic, was administered at 10 min, some 1, 3, 6, 12 and 24 h after the start of infusion. The magnitude of the reduction in blood pressure by tempol was initially negligible, but gradually enlarged, and reached a maximum of 96% of delta increase by angiotensin II at 12 h. However, even after sensitization to tempol, superimposed angiotensin II enabled an increase of blood pressure under tempol treatment. In chronically angiotensin II-infused rats, superimposed angiotensin II exhibited tempol quenchable MAPK activation.

CONCLUSIONS

These results indicate that the mechanisms of angiotensin II-induced vasoconstriction may shift from being non-sensitive to ROS to sensitive within 12 h; nevertheless, both ROS non-sensitive vasoconstriction and ROS-sensitive MAPK activation by angiotensin II, which are both seen in the acute phase of infusion, are restored in the late maintaining phase of prolonged angiotensin II infusion.

Pathophysiology of hypertensive renal damage: implications for therapy

Unlike the majority of patients with uncomplicated hypertension in whom minimal renal damage develops in the absence of severe blood pressure (BP) elevations, patients with diabetic and nondiabetic chronic kidney disease (CKD) exhibit an increased vulnerability to even moderate BP elevations. Investigations in experimental animal models have revealed that this enhanced susceptibility is a consequence of an impairment of the renal autoregulatory mechanisms that normally attenuate the transmission of elevated systemic pressures to the glomeruli in uncomplicated hypertension. The markedly lower BP threshold for renal damage and the steeper slope of relationship between BP and renal damage in such states necessitates that BP be lowered into the normotensive range to prevent progressive renal damage. When BP is accurately measured using radiotelemetry in animal models, the renal protection provided by renin-angiotensin system (RAS) blockade is proportional to the BP reduction with little evidence of BP-independent protection. A critical evaluation of the clinical data also suggests that the BP-independent renoprotection by RAS blockade has been overemphasized and that achieving lower BP targets is more important than the selection of antihypertensive regimens. However, achievement of such BP goals is difficult in CKD patients without aggressive diuresis, because of their proclivity for salt retention. The effectiveness of RAS blockers in lowering BP in patients who have been adequately treated with diuretics, along with their potassium-sparing and magnesium-sparing effects, provides a more compelling rationale for the use of RAS blockade in the treatment of CKD patients than any putative BP-independent renoprotective superiority.

TNFalpha-induced ATF3 expression is bidirectionally regulated by the JNK and ERK pathways in vascular endothelial cells

ATF3 (Activating transcription factor 3), a member of the CREB/ATF family, can be induced by stress and growth factors in mammalian cells, and is thought to play an important role in the cardiovascular system. However, little is currently known about how the induction of ATF3 is regulated, except that the JNK pathway is involved. Here, we investigated the differential roles of the MAPK pathways involved in TNFalpha (tumour necrosis factor alpha)-induced ATF3 expression in vascular endothelial cells. In human umbilical vein endothelial cells, the expression of constitutively active MKK7 (MAPK kinase 7) increased the number of ATF3-positive cells, and dominant negative MKK7 suppressed the TNFalpha-induced expression of ATF3, indicating a requirement for the JNK pathway. In contrast, the expression of constitutively active or dominant negative MEK1/2 (MAPK/ERK kinase 1/2) suppressed or enhanced TNFalpha-mediated induction of ATF3, respectively. In support of this, the MEK1/2 specific inhibitor U0126 enhanced the expression of ATF3 induced by TNFalpha. Furthermore, the ERK pathway inhibits the TNFalpha-mediated induction of ATF3 mRNA, but not its stability, suggesting the involvement of ERK activity in the transcriptional regulation of the ATF3 gene. Our results suggest that TNFalpha-induced ATF3 gene expression is bidirectionally regulated by the JNK and ERK pathways in vascular endothelial cells.

Stretch of the vascular wall induces smooth muscle differentiation by promoting actin polymerization

Stretch of the vascular wall by the intraluminal blood pressure stimulates protein synthesis and contributes to the maintenance of the smooth muscle contractile phenotype. The expression of most smooth muscle specific genes has been shown to be regulated by serum response factor and stimulated by increased actin polymerization. Hence we hypothesized that stretch-induced differentiation is promoted by actin polymerization. Intact mouse portal veins were cultured under longitudinal stress and compared with unstretched controls. In unstretched veins the rates of synthesis of several proteins associated with the contractile/cytoskeletal system (alpha-actin, calponin, SM22alpha, tropomyosin, and desmin) were dramatically lower than in stretched veins, whereas other proteins (beta-actin and heat shock proteins) were synthesized at similar rates. The cytoskeletal proteins gamma-actin and vimentin were weakly stretch-sensitive. Inhibition of Rho-associated kinase by culture of stretched veins with Y-27632 produced similar but weaker effects compared with the absence of mechanical stress. Induction of actin polymerization by jasplakinolide increased SM22alpha synthesis in unstretched veins to the level in stretched veins. Stretch stimulated Rho activity and phosphorylation of the actin-severing protein cofilin-2, although both effects were slow in onset (Rho-GTP, >15 min; cofilin-P, >1 h). Cofilin-2 phosphorylation of stretched veins was inhibited by Y-27632. The F/G-actin ratio after 24 h of culture was significantly greater in stretched than in unstretched veins, as shown by both ultracentrifugation and confocal imaging with phalloidin/DNase I labeling. The results show that stretch of the vascular wall stimulates increased actin polymerization, activating synthesis of smooth muscle-specific proteins. The effect is partially, but probably not completely, mediated via Rho-associated kinase and cofilin downstream of Rho.

Increased insulin receptor substrate 1 serine phosphorylation and stress-activated protein kinase/c-Jun N-terminal kinase activation associated with vascular insulin resistance in spontaneously hypertensive rats

Insulin resistance is associated with cardiovascular disease. Impaired insulin receptor substrate (IRS)-mediated signal transduction is a major contributor to insulin resistance. Recently, IRS-1 phosphorylation at serine 307 by stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK) has been highlighted as a molecular event that causes insulin resistance. We investigated IRS-1-mediated insulin signaling, IRS-1 phosphorylation at serine 307, and SAPK/JNK activation status in the aorta of spontaneously hypertensive rats (SHR) by immunoprecipitation and immunoblotting. Insulin-stimulated tyrosine phosphorylation of insulin receptor and IRS-1 in SHR was decreased to 55% (P<0.01) and 40% (P<0.01) of the levels in Wistar-Kyoto rats (WKY), respectively. Insulin-stimulated IRS-1-associated phosphatidylinositol 3-kinase activation in SHR was reduced to 28% of the level in WKY (P<0.0001). Immunoblot analysis revealed that phosphorylated IRS-1 at serine 307 in SHR was increased to 261% (P<0.001) of the level in WKY. Phosphorylated (activated) SAPK/JNK in SHR was increased to 223% of the level in WKY (P<0.01). Serine-phosphorylated IRS-1 that was immunoprecipitated from the aorta of SHR was capable of inhibiting in vitro tyrosine phosphorylation by recombinant insulin receptor compared with WKY-derived IRS-1. These findings demonstrate that insulin resistance in the aorta of SHR was associated with elevated IRS-1 phosphorylation at serine 307 and increased SAPK/JNK activation. The present study suggests that increased SAPK/JNK activation may play an important role in the pathogenesis of vascular insulin resistance via inhibitory serine phosphorylation of IRS-1.

Redox-dependent signalling by angiotensin II and vascular remodelling in hypertension

1. Hypertension is associated with structural alterations of resistance arteries, a process known as remodelling (increased media-to-lumen ratio). 2. At the cellular level, vascular remodelling involves changes in vascular smooth muscle cell (VSMC) growth, cell migration, inflammation and fibrosis. These processes are mediated via multiple factors, of which angiotensin (Ang) II appears to be one of the most important in hypertension. 3. Angiotensin II signalling, via AT1 receptors, is upregulated in VSMC from resistance arteries of hypertensive patients and rats. This is associated with hyperactivation of vascular NADPH oxidase, leading to increased generation of reactive oxygen species (ROS), particularly O2- and H2O2. 4. Reactive oxygen species function as important intracellular second messengers to activate many downstream signalling molecules, such as mitogen-activated protein kinase, protein tyrosine phosphatases, protein tyrosine kinases and transcription factors. Activation of these signalling cascades leads to VSMC growth and migration, modulation of endothelial function, expression of pro-inflammatory mediators and modification of extracellular matrix. 5. Furthermore, ROS increase intracellular free Ca2+ concentration ([Ca2+]i), a major determinant of vascular reactivity. 6. All these processes play major roles in vascular injury associated with hypertension. Accordingly, ROS and the signalling pathways that they modulate provide new targets to regress vascular remodelling, reduce peripheral resistance and prevent hypertensive end-organ damage. 7. In the present review, we discuss the role of ROS as second messengers in AngII signalling and focus on the implications of these events in the processes underlying vascular remodelling in hypertension.

Angiotensin II and endothelin-1 regulate MAP kinases through different redox-dependent mechanisms in human vascular smooth muscle cells

OBJECTIVE

The role of reactive oxygen species (ROS) in mitogen-activated protein kinase (MAPK) signaling by angiotensin (Ang) II and endothelin-1 (ET-1) in human vascular smooth muscle cells (VSMC) was investigated.

DESIGN

VSMCs were derived from resistance arteries from healthy subjects. MAPK activity was assessed using phospho-specific antibodies. ROS generation was measured by CMH2DCFDA fluorescence and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity by lucigenin chemiluminescence.

RESULTS

Ang II and ET-1 increased MAPK phosphorylation (P < 0.01). Pre-treatment with Tiron and Tempol, *O2 scavengers, attenuated agonist-stimulated phosphorylation of p38MAPK, c-Jun N-terminal kinases (JNK) and ERK5, but not of ERK1/2 (extracellular signal-regulated kinases). Apocynin and diphenylene iodinium (DPI), NAD(P)H oxidase inhibitors, decreased Ang II-induced responses 60-70%. ET-1-mediated MAPK phosphorylation was unaffected by apocynin but was reduced (> 50%) by thenoyltrifluoroacetone (TIFT) and carboxyl cyanide-m-chlorophenylhydrazone (CCCP), mitochondrial inhibitors. Allopurinol and N-nitro-l-arginine methyl ester (l-NAME), xanthine oxidase and nitric oxide synthase (NOS) inhibitors, respectively, did not influence MAPK activation. Intracellular ROS generation, was increased by Ang II and ET-1 (P < 0.01). DPI inhibited Ang II- but not ET-1-mediated ROS production. Expression of p22phox and p47phox and activation of NAD(P)H oxidase were increased by Ang II but not by ET-1. CCCP and TIFT significantly attenuated ET-1-mediated ROS formation (P < 0.05), without influencing Ang II effects.

CONCLUSIONS

Ang II activates p38MAPK, JNK and ERK5 primarily through NAD(P)H oxidase-generated ROS. ET-1 stimulates these kinases via redox-sensitive processes that involve mitochondrial-derived ROS. These data suggest that redox-dependent activation of MAPKs by Ang II and ET-1 occur through distinct ROS-generating systems that could contribute to differential signaling by these agonists in VSMCs.

Translocation of caveolin regulates stretch-induced ERK activity in vascular smooth muscle cells

Mechanical stress contributes to vascular disease related to hypertension. Activation of ERK is key to mediating cellular proliferation and vascular remodeling in response to stretch stress. However, the mechanism by which stretch mediates ERK activation in the vascular tissue is still unclear. Caveolin, a major component of a flasklike invaginated caveolae, acts as an adaptor protein for an integrin-mediated signaling pathway. We found that cyclic stretch transiently induced translocation of caveolin from caveolae to noncaveolar membrane sites in vascular smooth muscle cells (VSMCs). This translocation of caveolin was determined by detergent solubility, sucrose gradient fractionation, and immunocytochemistry. Cyclic stretch induced ERK activation; the activity peaked at 5 min (the early phase), decreased gradually, but persisted up to 120 min (the late phase). Disruption of caveolae by methyl-beta-cyclodextrin, decreasing the caveolar caveolin and accumulating the noncaveolar caveolin, enhanced ERK activation in both the early and late phases. When endogenous caveolins were downregulated, however, the late-phase ERK activation was subsided completely. Caveolin, which was translocated to noncaveolar sites in response to stretch, is associated with beta1-integrins as well as with Fyn and Shc, components required for ERK activation. Taken together, caveolin in caveolae may keep ERK inactive, but when caveolin is translocated to noncaveolar sites in response to stretch stress, caveolin mediates stretch-induced ERK activation through an association with beta1-integrins/Fyn/Shc. We suggest that stretch-induced translocation of caveolin to noncaveolar sites plays an important role in mediating stretch-induced ERK activation in VSMCs.

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.

Alpha1-adrenergic signaling mechanisms in contraction of resistance arteries

Our goal in this review is to provide a comprehensive, integrated view of the numerous signaling pathways that are activated by alpha(1)-adrenoceptors and control actin-myosin interactions (i.e., crossbridge cycling and force generation) in mammalian arterial smooth muscle. These signaling pathways may be categorized broadly as leading either to thick (myosin) filament regulation or to thin (actin) filament regulation. Thick filament regulation encompasses both "Ca(2+) activation" and "Ca(2+)-sensitization" as it involves both activation of myosin light chain kinase (MLCK) by Ca(2+)-calmodulin and regulation of myosin light chain phosphatase (MLCP) activity. With respect to Ca(2+) activation, adrenergically induced Ca(2+) transients in individual smooth muscle cells of intact arteries are now being shown by high resolution imaging to be sarcoplasmic reticulum-dependent asynchronous propagating Ca(2+) waves. These waves differ from the spatially uniform increases in [Ca(2+)] previously assumed. Similarly, imaging during adrenergic activation has revealed the dynamic translocation, to membranes and other subcellular sites, of protein kinases (e.g., Ca(2+)-activated protein kinases, PKCs) that are involved in regulation of MLCP and thus in "Ca(2+) sensitization" of contraction. Thin filament regulation includes the possible disinhibition of actin-myosin interactions by phosphorylation of CaD, possibly by mitogen-activated protein (MAP) kinases that are also translocated during adrenergic activation. An hypothesis for the mechanisms of adrenergic activation of small arteries is advanced. This involves asynchronous Ca(2+) waves in individual SMC, synchronous Ca(2+) oscillations (at high levels of adrenergic activation), Ca(2+) sparks, "Ca(2+)-sensitization" by PKC and Rho-associated kinase (ROK), and thin filament mechanisms.

Matrix metalloproteinases (MMP), EMMPRIN (extracellular matrix metalloproteinase inducer) and mitogen-activated protein kinases (MAPK): co-expression in metastatic serous ovarian carcinoma

Activation or suppression of intracellular signaling via the mitogen-activated protein kinase (MAPK) family has been linked to expression of matrix metalloproteinases (MMP) in experimental models, but this association has not been demonstrated in clinical material. The objective of this study was to investigate the possible association between expression and activity of MMP, expression of the MMP inducer EMMPRIN, and the expression (level) and phosphorylation status (activity) of the extracellular-regulated kinase (ERK), c-Jun amino-terminal kinase (JNK) and high osmolarity glycerol response kinase (p38) in effusions from patients diagnosed with serous ovarian carcinoma. MAPK level and activity were studied in 55 effusions using immunoblotting. MMP-1, MMP-2, MMP-9 and EMMPRIN expression was studied using immunocytochemistry (ICC) and mRNA in situ hybridization (ISH). The gelatinolytic activity of MMP-2 and MMP-9 was measured by zymography. ERK and phospho-ERK (p-ERK) were detected in 54/55 (98%) and 50/55 (91%) specimens, respectively. JNK and p-JNK were detected in 53/55 (96%) and 38/55 (69%) specimens, respectively. p38 was expressed in 54/55 (98%) specimens, and its phosphorylated form was found in 51/55 (92%). MMP-2 mRNA expression (P = 0.048), protein expression (P = 0.046) and gelatinolytic activity (P = 0.039) correlated with ERK phosphorylative activity. MMP-2 activity also correlated with p38 activity (P = 0.017). MMP-9 protein expression correlated with phosphorylation of p38 (P = 0.046), but enzyme activity showed inverse relationship with both p-ERK (P = 0.05) and p-p38 (P = 0.033) expression. EMMPRIN expression correlated with MMP-1 (P < 0.001), MMP-2 (P = 0.042) and MMP-9 (P = 0.029) expression, as well as with ERK activity (P = 0.001). Our results present the first evidence of a possible link between MAPK signaling and MMP expression and activity in vivo. These data may expand our understanding regarding the mechanisms by which MMP synthesis is regulated in effusions and possibly affect treatment strategies for this form of malignancy.

ROS during the acute phase of Ang II hypertension participates in cardiovascular MAPK activation but not vasoconstriction

The relations among hypertensive response, oxidative stress, and mitogen-activated protein kinase (MAPK) in cardiovascular tissues have not been fully established. We investigated the involvement of reactive oxygen species on changes in the hemodynamics and cardiovascular MAPKs activities induced by acutely administered angiotensin II (Ang II) in conscious normotensive rats with or without treatment with a superoxide dismutase mimetic, 4-hydroxy-2,2,6,6-tetramethyl piperidinoxyl (tempol). Intravenous infusion of a pressor dose of Ang II rapidly increased mean arterial blood pressure (MBP) by 53+/-5 mm Hg. After a 30-minute treatment with Ang II, phosphorylated MAPKs (ERK1/2, JNK, p38) as well as thiobarbital reactive substances (T-BARS) were increased in the aorta and cardiac left ventricle. Tempol had no significant effect on the elevation of MBP elicited by Ang II; however, it dose-dependently suppressed the augmented phosphorylation of cardiovascular MAPKs and increased T-BARS levels in plasma and tissues induced by Ang II. An acutely administered pressor dose of phenylephrine, an alpha-adrenoceptor agonist, also showed tempol-sensitive cardiovascular MAPK activation and tempol-insensitive blood pressure elevation. These in vivo data indicate that acute administration of Ang II or phenylephrine provoked an increase in oxidative stress in the cardiovascular tissues leading to the activation of MAPKs, whether it was mediated by pressure overload or the direct action of these vasoconstrictors, and that oxidative stress might not have a major contribution to the acute hypertensive responses elicited by the vasoconstrictors.

Mechanical stress-activated PKCdelta regulates smooth muscle cell migration

Vascular smooth muscle cells (SMCs) are exposed to altered mechanical stress that may contribute to SMC migration in the development of atherosclerosis. Signal transduction pathways in SMCs activated by mechanical stress that instigate cell migration are undefined. Herein, we provide evidence that mechanical stress enhances SMC migration, which is mediated, at least in part, by protein kinase C (PKC)delta. When rat SMCs cultivated on a flexible membrane were subjected to cyclic strain stress (60 cycles/min, 5, 15, or 20% elongation), PKCdelta was translocated to the Triton-insoluble fraction, whereas PKCalpha was translocated to the membrane, which was confirmed by PKC kinase assays. Immunofluorescence and actin staining revealed a cytoskeleton translocation of PKCdelta in SMCs stimulated by cyclic strain. PKCdelta-deficient SMCs cultivated from PKCdelta-/- mice showed an abnormal cytoskeleton structure, which was related to a diminished phosphorylation of paxillin, focal adhesion kinase, and vinculin in response to mechanical stress. Mechanical stress enhanced SMC migration, which was diminished in PKCdelta-/- SMCs. Taken together, our data demonstrated that mechanical stress activates PKCdelta translocation to the cytoskeleton, which is related to decreased SMC migration and indicates that PKCdelta is a key signal transducer between mechanical stress and cell migration.

Mitogen-activated protein kinases (MAPK) as predictors of clinical outcome in serous ovarian carcinoma in effusions

OBJECTIVE

The objective was to investigate the expression (level) and phosphorylation status (activity) of the extracellular-regulated kinase (ERK), c-Jun amino-terminal kinase (JNK), and high-osmolarity glycerol response kinase (p38), their role in the biology of ovarian carcinoma, and their correlation with chemotherapy response.

METHODS

Sixty-four fresh-frozen effusions from patients diagnosed with serous ovarian carcinoma were studied using immunoblotting. Results were analyzed for possible association with expression of proliferation and apoptosis markers, patient age, disease stage, tumor grade, histological grade, chemotherapy status, and survival.

RESULTS

p38 level correlated with younger age (P = 0.004), while that of JNK correlated with better tumor differentiation (P = 0.009). Higher expression of Pan-JNK (P = 0.018) and higher p-ERK activity (P = 0.014) were seen in postchemotherapy specimens, specifically related to treatment by platinum agents. pan-JNK expression was higher in specimens treated with both platinum agents (P = 0.038) and paclitaxel (P = 0.033). In univariate survival analysis, the level of pan-ERK (P = 0.002), pan-JNK (P = 0.045), and pan-p38 (P = 0.016), as well as p-ERK activity (P = 0.014) correlated with better overall survival. In Cox multivariate survival analysis, pan-ERK (P = 0.001), pan-p38 (P = 0.017), and p-ERK (P = 0.041) retained their predictive value.

CONCLUSIONS

Our results present the first evidence of in vivo involvement of MAPKs in the clinical course of ovarian cancer and the possible effect of chemotherapy on intracellular signaling in this disease. The improved prognosis associated with expression and phosphorylation of all three mitogen-activated protein kinase families highlights the unique properties of cancer cells in effusions and may expand our understanding of the biology of ovarian carcinoma at this site, possibly affecting treatment strategies for this malignancy.

ERK1/2-mediated vasoconstriction normalizes wall stress in small mesenteric arteries during NOS inhibition in vivo

As in essential hypertension, chronic nitric-oxide synthase (NOS) inhibition leads to hypertrophic remodeling in conduit and muscular arteries and inward eutrophic remodeling in small resistance arteries with activation of extracellular signal-regulated kinases 1 and 2 (ERK1/2) in both vessel types. The authors tested the hypothesis that this remodeling heterogeneity could be related to distinct vasoreactivity patterns in small and larger arteries, with a vessel-specific function of ERK1/2 signaling. Using intravital microscopy in rats we have demonstrated that acute NOS inhibition (l-NA injection, 100 mg/kg) produced vasoconstriction of small mesenteric arteries. Consequently, the calculated in vivo wall stress was not significantly modified, despite the local rise in pressure. This could explain the lack of vascular protein synthesis elevation in vivo, an early index of hypertrophy. Inhibition of ERK1/2 activation with PD98059 blunted mesenteric artery contractions. Femoral arteries did not contract and were thus submitted to an enhanced wall stress and underwent hypertrophic remodeling in chronic conditions. In conclusion, the heterogeneous vascular remodeling in the l-NAME model is associated with a heterogeneous vasoconstriction response to acute NOS inhibition. Indeed, in contrast to larger arteries, l-NA-induced vasoconstriction in small arteries normalized wall stress and prevented early signs of hypertrophy. The results also suggest that ERK1/2 is a signaling element in NOS inhibition-induced vasoconstriction of small arteries in vivo.

Cholesterol dependence of vascular ERK1/2 activation and growth in response to stretch: role of endothelin-1

OBJECTIVE

Stretch-induced growth of the vascular wall plays a role in hypertension and neointima formation. Its signal pathways involve integrins, cytoskeleton, membrane receptors, and ion channels, some of which are organized in cholesterol-rich, membrane domains such as lipid rafts or caveolae. This study tested the role of rafts/caveolae in stretch-induced vascular growth by manipulation of membrane cholesterol contents.

METHODS AND RESULTS

Growth and protein synthesis were induced by mechanical stretch of rat portal veins in vitro. Sucrose gradient centrifugation showed stretch-induced tyrosine phosphorylation primarily in fractions containing caveolin-1. Disruption of membrane caveolae with use of methyl-beta-cyclodextrin (mbetacd) reduced weight gain, protein synthesis, and DNA synthesis to levels in unstretched, control veins. These effects were partially reversed by restoration of cellular cholesterol contents. Inhibited growth was associated with abolished activation of extracellular signal-regulated kinase (ERK) 1/2 in response to stretch and endothelin-1 (ET-1) but not to angiotensin II. Inhibition of ET-1 type A (ETA) receptors by RF139317 or endothelin-converting enzyme by phosphoramidone abolished stretch-induced ERK1/2 activation, which was, however, unaffected by removal of the endothelium.

CONCLUSIONS

Stretch-induced growth signaling in vascular smooth muscle depends on cholesterol-rich, membrane microdomains by a mechanism involving ETA receptors that respond to endogenous ET-1 production.

Pressure-induced vascular activation of nuclear factor-kappaB: role in cell survival

The effects of mechanical factors on nuclear factor (NF)-kappaB activation and its potential functional roles have been very little explored in the intact vessel. Thus, we chose to study the regulation of NF-kappaB by intraluminal pressure using an organ culture model of mouse carotid arteries maintained at 80 or 150 mm Hg during 24 hours. Gel shift analysis revealed an increase in the DNA-binding capacity of NF-kappaB in vessels at high pressure compared with vessels at normal pressure (304+/-49%; P<0.001). This coincided with reduced levels of the endogenous NF-kappaB inhibitor IkappaBalpha in arteries at 150 mm Hg (52+/-7%; P<0.001), as detected by Western blot. To study the functional role of the pressure-induced activation of NF-kappaB, we evaluated the rate of apoptosis (TUNEL method) in carotid arteries cultured with or without an inhibitor peptide blocking nuclear translocation of NF-kappaB. No apoptosis was detected in control arteries either at 80 or 150 mm Hg. However, in the presence of the NF-kappaB inhibitor peptide, we observed apoptosis in vessels at 80 mm Hg (5+/-1%; P<0.001 versus untreated controls), which was markedly increased in vessels at 150 mm Hg (14+/-2%; P<0.001). These results were corroborated by immunohistochemical analysis showing positive staining for cleaved caspase 3 in vessels at 80 mm Hg treated with the NF-kappaB inhibitor peptide, which was additionally enhanced in treated vessels at 150 mm Hg. Our findings demonstrate that high intraluminal pressure activates NF-kappaB in arteries. Moreover, the activation of NF-kappaB seems to play a key role in preventing apoptosis in vascular cells, especially when vessels are exposed to high intraluminal pressure.

Stretch-induced contractile differentiation of vascular smooth muscle: sensitivity to actin polymerization inhibitors

Signaling mechanisms for stretch-dependent growth and differentiation of vascular smooth muscle were investigated in mechanically loaded rat portal veins in organ culture. Stretch-dependent protein synthesis was found to depend on endogenous release of angiotensin II. Autoradiography after [(35)S]methionine incorporation revealed stretch-dependent synthesis of several proteins, of which SM22 and actin were particularly prominent. Inhibition of RhoA activity by cell-permeant C3 toxin increased tissue mechanical compliance and reduced stretch-dependent extracellular signal-regulated kinase (ERK)1/2 activation, growth, and synthesis of actin and SM22, suggesting a role of the actin cytoskeleton. In contrast, inhibition of Rho-associated kinase by Y-27632 did not reduce ERK1/2 phosphorylation or actin and SM22 synthesis and did not affect tissue mechanical compliance but still inhibited overall growth. The actin polymerization inhibitors latrunculin B and cytochalasin D both inhibited growth and caused increased tissue compliance. Whereas latrunculin B concentration-dependently reduced actin and SM22 synthesis, cytochalasin D did so at low (10(-8) M) but not at high (10(-6) M) concentration. The results show that stretch stabilizes the contractile smooth muscle phenotype. Stretch-dependent differentiation marker expression requires an intact cytoskeleton for stretch sensing, control of protein expression via the level of unpolymerized G-actin, or both.

Oscillatory shear stress increases smooth muscle cell proliferation and Akt phosphorylation

PURPOSE

Hemodynamic forces affect smooth muscle cell (SMC) proliferation and migration both in vitro and in vivo. However, the effects of oscillatory shear stress (SS) on SMC proliferation and signal transduction pathways that control survival are not well described.

METHODS

Bovine aortic SMC were exposed to arterial levels of oscillatory SS (14 dyne/cm(2)) with an orbital shaker; control cells were exposed to static conditions (0 dyne/cm(2)). Cell number and (3)[H]thymidine incorporation were measured after 1, 3, or 5 days of SS. Activation of the Akt pathway was assessed with the Western blot technique. Specificity of the phosphatidylinositol 3-kinase (PI3K) pathway was determined with the Western blot technique with the inhibitors LY294002 (10 micromol/L) or wortmannin (25 nmol/L).

RESULTS

Arterial levels of oscillatory SS increased SMC cell number by 20.1 +/- 3.7% and (3)[H]thymidine incorporation by 33.4% +/- 6.8% at 5 days. To identify whether SS increased activity of the SMC survival pathway, Akt activation was measured. SMC exposed to SS demonstrated increased Akt phosphorylation compared with control cells, with maximal phosphorylation at 60 minutes. Both PI3K inhibitors specifically inhibited the increase in Akt phosphorylation in SMC exposed to oscillatory SS.

CONCLUSION

SMC directly respond to oscillatory SS by increasing DNA synthesis, proliferation, and activation of the PI3K-Akt signal transduction pathway. These results suggest a mechanism of SMC survival and proliferation in response to endothelial-denuding arterial injury.

Cellular mechanics and gene expression in blood vessels

Blood vessels are permanently subjected to mechanical forces in the form of stretch, encompassing cyclic mechanical strain due to the pulsatile nature of blood flow, and shear stress. Alterations in stretch or shear stress invariably produce transformations in the vessel wall that will aim to accommodate the new conditions and to ultimately restore basal levels of tensile stress and shear stress. Vascular cells are equipped with numerous receptors that allow them to detect and respond to the mechanical forces generated by pressure and shear stress. The cytoskeleton and other structural components have an established role in mechanotransduction, being able to transmit and modulate tension within the cell via focal adhesion sites, integrins, cellular junctions and the extracellular matrix. Beyond the structural modifications incurred, mechanical forces can also initiate complex signal transduction cascades leading to functional changes within the cell. Many intracellular pathways, including the MAP kinase cascade, are activated by flow or stretch and initiate, via sequential phosphorylations, the activation of transcription factors and subsequent gene expression.

Role of JNK, p38, and ERK in platelet-derived growth factor-induced vascular proliferation, migration, and gene expression

OBJECTIVE

We investigated the comparative roles of mitogen-activated protein (MAP) kinases, including c-Jun NH2-terminal kinase (JNK), extracellular signal-regulated kinase (ERK), and p38, in vascular smooth muscle cell (VSMC) proliferation, migration, and gene expression.

METHODS AND RESULTS

VSMCs were infected with recombinant adenovirus containing dominant-negative mutants of ERK, p38, and JNK (Ad-DN-ERK, Ad-DN-p38, and Ad-DN-JNK, respectively) to specifically inhibit the respective MAP kinases and then stimulated with platelet-derived growth factor (PDGF)-BB. Ad-DN-ERK attenuated PDGF-BB-induced VSMC proliferation more potently than Ad-DN-p38 or Ad-DN-JNK, indicating the dominant role of ERK in VSMC proliferation. Ad-DN-ERK, Ad-DN-p38, and Ad-DN-JNK similarly inhibited PDGF-induced VSMC migration. Ad-DN-ERK and Ad-DN-JNK suppressed PDGF-BB-induced downregulation of cyclin-dependent kinase inhibitor p27Kip1, whereas Ad-DN-p38 decreased PDGF-BB-induced upregulation of p21Cip1. Ad-DN-ERK inhibited PDGF-BB-induced plasminogen activator inhibitor type-1 (PAI-1), monocyte chemoattractant protein-1, and transforming growth factor-beta1 expressions, Ad-DN-p38 blocked monocyte chemoattractant protein-1 and transforming growth factor-beta1 expression but not PAI-1, whereas Ad-DN-JNK suppressed only PAI-1 expression. Moreover, in vivo gene transfer of Ad-DN-p38 to rat carotid artery caused the inhibition of intimal hyperplasia by balloon injury, indicating the involvement of p38 in vascular remodeling in vivo.

CONCLUSIONS

We propose that these 3 MAP kinases participate in vascular diseases via differential molecular mechanisms and are new therapeutic targets for treatment of vascular diseases.

Recent advances in intracellular signalling in hypertension

PURPOSE OF REVIEW

Transmission of external signals from the cell surface to the internal cellular environment occurs via tightly controlled complex transduction pathways. Alterations in these highly regulated signalling cascades in vascular smooth cells may play a fundamental role in the structural, mechanical and functional abnormalities that underlie vascular pathological processes in hypertension. The present review focuses on recent developments relating to two novel signalling pathways: angiotensin II signalling through tyrosine kinases; and oxidative stress and redox-dependent signal transduction. These pathways are emerging as critical mediators of hypertensive vascular disease because they influence multiple cellular responses that are involved in structural remodelling, vascular inflammation and altered tone.

RECENT FINDINGS

A recent advance in the field of angiotensin II signalling was the demonstration that, in addition to its vasoconstrictor properties, angiotensin II has potent mitogenic-like and proinflammatory-like characteristics. These actions are mediated through phosphorylation of both nonreceptor tyrosine kinases and receptor tyrosine kinases. It is also becoming increasingly apparent that many signalling events that underlie abnormal vascular function in hypertension are influenced by changes in intracellular redox status. In particular, increased bioavailability of reactive oxygen species (oxidative stress) stimulates growth-signalling pathways, induces expression of proinflammatory genes, alters contraction-excitation coupling and impairs endothelial function.

SUMMARY

A better understanding of the molecular pathways that regulate vascular smooth muscle cell function will provide further insights into the pathophysiological mechanisms that contribute to vascular changes and end-organ damage associated with high blood pressure, and could permit identification of potential novel therapeutic targets in the prevention and management of hypertension.

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.

c-Jun N-terminal kinase activation mediates downregulation of connexin43 in cardiomyocytes

Loss of gap junctions and impaired intercellular communication are characteristic features of pathological remodeling in heart failure as a result of stress or injury, yet the underlying regulatory mechanism has not been identified. Here, we report that in cultured myocytes, rapid loss of the gap junction protein connexin43 (Cx43) occurs in conjunction with the activation of c-Jun N-terminal kinase (JNK), a stress-activated protein kinase, on stress stimulation. To investigate the specific role of JNK activation in the regulation of connexin in cardiomyocytes, an activated mutant of mitogen-activated protein kinase kinase 7 (mutant D), a JNK-specific upstream activator, was expressed in myocytes by adenovirus-mediated gene transfer. JNK activation in infected cardiomyocytes resulted in significant reduction of Cx43 expression at both mRNA and protein levels and impaired cell-cell communication. To evaluate the role of JNK in the regulation of Cx43 expression and gap junction structure in vivo, a Cre-LoxP-mediated gene-switch system was used to establish a transgenic animal model with targeted activation of JNK in ventricular myocardium. The transgenic hearts exhibited significant downregulation of Cx43 expression and loss of gap junctions in myocardium that may contribute to the cardiac dysfunction and premature death phenotype. Our report represents the first evidence, both in vitro and in vivo, implicating JNK as an important mediator of stress-induced Cx43 downregulation and impaired intercellular communication in the failing heart.

Increased expression of phosphorylated c-Jun amino-terminal kinase and phosphorylated c-Jun in human cerebral aneurysms: role of the c-Jun amino-terminal kinase/c-Jun pathway in apoptosis of vascular walls

OBJECTIVE

Vascular remodeling via apoptotic mechanisms is an important factor in vascular diseases. c-Jun amino-terminal kinase (JNK) is a member of the mitogen-activated protein kinase family and initiates apoptosis mainly via phosphorylation of the c-Jun transcription factor. We performed this study to clarify the roles of the JNK/c-Jun pathway and apoptosis in the pathogenesis of cerebral aneurysms.

METHODS

Cerebral aneurysms from 12 patients and control vessels from 5 patients were studied. We analyzed the expression of phosphorylated JNK and phosphorylated c-Jun in cerebral aneurysms by using immunohistochemical methods.

RESULTS

Immunoreactivity for phosphorylated JNK and phosphorylated c-Jun was increased in the vascular walls of the cerebral aneurysms studied. Immunoreactivity for single-stranded deoxyribonucleic acid (a marker of deoxyribonucleic acid damage) was also increased in aneurysmal tissue, compared with control vessels, and was colocalized with that for phosphorylated JNK and phosphorylated c-Jun in smooth muscle cells.

CONCLUSION

These observations may lead to better understanding of the role of the JNK/c-Jun pathway in the development of cerebral aneurysms and to new strategies for treatment.

Repeated fasting stress causes activation of mitogen-activated protein kinases (ERK/JNK) in rat liver

Mitogen-activated protein kinases (MAPK)-signaling pathways play key roles in cytoplasmic-nuclear signal transmission in response to various extracellular stimuli. In this study, we investigated the effect of repeated fasting stress on activation of the 3 members of the MAPK family, the extracellular signal-regulated kinase (ERK), the c-Jun NH(2)-terminal kinase (JNK), and the p38 mitogen-activated protein kinase (p38 kinase), in rat liver. Immunecomplex kinase assays showed that ERK and JNK were significantly activated in the liver extract from fasted rats whereas p38 kinase showed no activation. In an immunohistochemical study, the phosphorylated and activated form of ERK (p-ERK) was abundantly expressed in pericentral hepatocytes of fasted liver compared with those of the control. On the other hand, the phosphorylated and activated form of JNK (p-JNK) was highly expressed in irregular-shaped cells along the sinusoidal lining of fasted liver. A double immunofluorescent study to identify p-JNK immunoreactive cells revealed them to be Kupffer cells, which are the resident hepatic macrophages. In conclusion, ERK and JNK are selectively activated in distinct cell types of rat liver by repeated fasting stress.

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.

Cyclic stretch activates ERK1/2 via G proteins and EGFR in alveolar epithelial cells

Mechanical stimuli are transduced into intracellular signals in lung alveolar epithelial cells (AEC). We studied whether mitogen-activated protein kinase (MAPK) pathways are activated during cyclic stretch of AEC. Cyclic stretch induced a rapid (within 5 min) increase in extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation in AEC. The inhibition of Na(+), L-type Ca(2+) and stretch-activated ion channels with amiloride, nifedipine, and gadolinium did not prevent the stretch-induced ERK1/2 activation. The inhibition of Grb2-SOS interaction with an SH3 binding sequence peptide, Ras with a farnesyl transferase inhibitor, and Raf-1 with forskolin did not affect the stretch-induced ERK1/2 phosphorylation. Moreover, cyclic stretch did not increase Ras activity, suggesting that stretch-induced ERK1/2 activation is independent of the classical receptor tyrosine kinase-MAPK pathway. Pertussis toxin and two specific epidermal growth factor receptor (EGFR) inhibitors (AG-1478 and PD-153035) prevented the stretch-induced ERK1/2 activation. Accordingly, in primary AEC, cyclic stretch activates ERK1/2 via G proteins and EGFR, in Na(+) and Ca(2+) influxes and Grb2-SOS-, Ras-, and Raf-1-independent pathways.

Mechanisms of signal transduction activated by sublytic assembly of terminal complement complexes on nucleated cells

The sublytic assembly of C5b-7, C5b-8, and C5b-9, activates membrane phospholipases through heterotrimeric G proteins and stimulates a variety of cellular activities including prostanoids, leukotrienes, and cytokines synthesis. Activation of mitotic signaling through Ras, Raf-1, ERK1, and phosphatidylinositol-3 kinase (PI3-K) was induced in B lymphocytes, endothelial, and smooth muscle cells. PI3-K activation by C5b-9 induced STAT3 phosphorylation and translocation from cytoplasm to nucleus. This complex signaling mechanism is directly involved in many biological functions such as endo- and exocytosis, cell cycle progression, activation of transcription, and protein synthesis. The key role of this signaling pathway is reflected on cell survival and proliferation in acute and chronic inflammation where complement activation is an ubiquitous event.

Dominant negative c-jun gene transfer inhibits vascular smooth muscle cell proliferation and neointimal hyperplasia in rats

We previously reported that activator protein-1 (AP-1), containing c-Jun, is rapidly activated in balloon-injured artery. Therefore, we examined the role of c-Jun in vascular smooth muscle cell (SMC) proliferation, by using in vitro and in vivo gene transfer techniques. (1) Serum (2%) stimulation significantly increased AP-1 DNA binding activity in aortic SMCs, followed by the increase in both 3H-thymidine incorporation and cell number. Aortic SMCs were infected with recombinant adenovirus containing TAM67, a dominant negative c-Jun lacking transactivation domain of wild c-Jun (Ad-DN-c-Jun), to specifically inhibit AP-1. Ad-DN-c-Jun significantly inhibited serum-induced SMC proliferation, by inhibiting the entrance of SMC into S phase. (2) The effect of DN-c-Jun was examined on balloon injury-induced intimal hyperplasia in rats. Before balloon injury, DN-c-Jun was transfected into rat carotid artery using the hemagglutinating virus of Japan-liposome method. In vivo transfection of DN-c-Jun significantly inhibited vascular SMC proliferation in the intima and the media and subsequently prevented intimal thickening at 14 days after balloon injury. We obtained the first evidence that DN-c-Jun gene transfer prevented vascular SMC proliferation in vitro and in vivo, and c-Jun was involved in balloon injury-induced intimal hyperplasia. Thus, AP-1 seems to be the new therapeutic target for treatment of vascular diseases.

Smooth muscle cell response to mechanical injury involves intracellular calcium release and ERK1/ERK2 phosphorylation

We have investigated possible signaling pathways coupled to injury-induced ERK1/2 activation and the subsequent initiation of vascular rat smooth muscle cell migration and proliferation. Aortic smooth muscle cells were cultured to confluency and subjected to in vitro injury under serum-free conditions. In fluo-4-loaded cells, injury induced a rapid wave of intracellular Ca(2+) release that propagated about 200 microm in radius from the injured zone, reached a peak in about 20 s, and subsided to the baseline within 2 min. The wave was abolished by prior treatment with the sarcoplasmic reticulum ATPase inhibitor thapsigargin, but not by omission of extracellular Ca(2+). ERK1/2 activation reached a peak at 10 min after injury and was inhibited by the MEK1 inhibitor PD98059, as well as by thapsigargin, fluphenazine, genistein, and the Src inhibitor PP2. These inhibitors also reduced [(3)H]thymidine incorporation and migration of cells into the injured area determined at 48 h after injury. These results show that mechanical injury to vascular smooth muscle cells induces a Ca(2+) wave which is dependent on intracellular Ca(2+) release. Furthermore, the injury activates ERK1/2 phosphorylation as well as cell migration and replication.

Involvement of Rho-kinase and the actin filament network in angiotensin II-induced contraction and extracellular signal-regulated kinase activity in intact rat mesenteric resistance arteries

We have previously shown that angiotensin II (Ang II) and pressure increase extracellular signal-regulated kinase (ERK) 1/2 activity synergistically in intact, pressurized resistance arteries in vitro. However, the mechanisms by which pressure and Ang II activate ERK1/2 in intact resistance arteries remain to be determined. The purpose of the present study was to investigate the involvement of Rho-kinase and the actin filament network in Ang II- and pressure-induced ERK1/2 activation, as well as in the contractile response induced by Ang II. Mesenteric resistance arteries (200 to 300 microm) were isolated, mounted in an arteriograph, and stimulated by pressure, Ang II, or both. Activation of ERK1/2 was then measured by an in-gel assay. In mesenteric resistance arteries maintained at 70 mm Hg, Ang II (0.1 micromol/L) induced contraction (29+/-1.4% of phenylephrine, 10 micromol/L-induced contraction) and significantly increased ERK1/2 activity. Selective inhibition of Rho-kinase by Y-27632 (10 micromol/L) and selective disruption of the actin filament network by cytochalasin B (10 micromol/L) both decreased the Ang II-induced contraction by 78+/-1.2% and 87+/-1.9%, respectively, and significantly diminished ERK1/2 activity. In the absence of Ang II, increasing intraluminal pressure from 0 to 70 or 120 mm Hg increased ERK1/2 activity. ERK1/2 activity at 120 mm Hg was similar to that observed at 70 mm Hg in the presence of Ang II. Pressure-induced ERK1/2 activation was markedly attenuated by cytochalasin B but not by Y-27632. These results indicate that whereas pressure-induced ERK1/2 activation requires an intact actin filament network, but not Rho-kinase, the activation of ERK1/2 and the contraction induced by Ang II require both Rho-kinase and an intact actin filament network in isolated, intact mesenteric resistance arteries.

Gene transfer of dominant-negative mutants of extracellular signal-regulated kinase and c-Jun NH2-terminal kinase prevents neointimal formation in balloon-injured rat artery

We previously reported that extracellular signal-regulated kinase (ERK) and c-Jun NH2-terminal kinase (JNK), belonging to mitogen-activated protein kinases, are rapidly activated in balloon-injured artery. Therefore, we examined the role of these kinase activations in neointimal formation by using an in vivo gene transfer technique. We made the dominant-negative mutants of ERK (DN-ERK) and JNK (DN-JNK) to specifically inhibit endogenous ERK and JNK activation, respectively. Before balloon injury, these mutants were transfected into rat carotid artery using the hemagglutinating virus of Japan liposome method. In vivo transfection of DN-ERK and DN-JNK significantly suppressed the activation of ERK and JNK, respectively, after balloon injury, confirming successful expression of the transfected genes. Neointimal formation at 14 and 28 days after injury was prevented by gene transfer of DN-ERK or DN-JNK. Furthermore, bromodeoxyuridine labeling index and total cell-counting analysis at 7 days showed that either DN-ERK or DN-JNK remarkably suppressed smooth muscle cell (SMC) proliferation in both the intima and the media after injury. Gene transfer of wild-type ERK (W-ERK) or JNK (W-JNK) significantly enhanced neointimal hyperplasia at 14 days after injury. Furthermore, DN-ERK and DN-JNK significantly suppressed serum-induced SMC proliferation in vitro. We obtained the first evidence that in vivo gene transfer of DN-ERK or DN-JNK prevented neointimal formation in balloon-injured artery by inhibiting SMC proliferation. Thus, ERK and JNK activation triggers SMC proliferation, leading to neointimal formation. These kinases may be the new therapeutic targets for prevention of vascular diseases.

Src tyrosine kinases and extracellular signal-regulated kinase 1/2 mitogen-activated protein kinases mediate pressure-induced c-fos expression in cannulated rat mesenteric small arteries

Chronic hypertension is associated with remodeling of small arteries. There is evidence that the high pressure itself may cause these structural changes, but the responsible mechanisms are not clearly defined. Previously we showed that pressure-induced c-fos expression in intact cannulated rat mesenteric small arteries was inhibited by genistein, a general tyrosine kinase inhibitor. The purpose of this study was to further unravel the underlying signal transduction mechanisms, and we particularly tested the involvement of src tyrosine kinases and extracellular signal-regulated kinase (ERK). Rat mesenteric small arteries were cannulated in a dual-vessel chamber. After a 60-minute equilibration period, the pressure in 1 artery was increased to 140 mm Hg, while the other artery remained at 90 mm Hg. Semiquantitative reverse transcriptase-polymerase chain reaction was used to determine c-fos expression, and Western blotting was used to examine levels of ERK phosphorylation. The involvement of src and ERK was tested with the inhibitors herbimycin A (1 micromol/L), PP1 (10 micromol/L), PP2 (10 micromol/L), and PD98059 (30 micromol/L). One-hour exposure to 140 mm Hg increased the c-fos/cyclophilin ratio 3.6-fold, from 0.29+/-0.07 to 1.06+/-0.25. All the tested inhibitors suppressed the pressure-induced increase of c-fos expression. A 5-minute exposure period to 140 mm Hg increased ERK phosphorylation, and this was abolished in the presence of PP1. The results suggest that pressure-induced c-fos expression in intact cannulated rat mesenteric small arteries may be mediated, at least in part, by src tyrosine kinases and ERK.

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.

Immunohistochemical study of the phosphorylated and activated form of c-Jun NH2-terminal kinase in human aorta

c-Jun NH2-terminal kinase is a key enzyme mediating the cellular response to a variety of extracellular stimuli. In the present study, we performed immunohistochemical studies of the expression of the phosphorylated form of the kinase in 51 human aortas of various ages. The phosphorylated kinase immunoreactivity was strongly detected in vascular smooth muscle cells of the medial vessel layer of atherosclerotic lesions from adults. Immunoreactivity was also strongly detected in similar cells of the intima. On the other hand, immunoreactive phosphorylated kinase was only weakly defected in the medial vascular smooth muscle cells of non-atherosclerotic lesions from adults. We also investigated the expression of the phosphorylated kinase in infant aortas. In contrast to its weak immunoreactivity in adult non-atherosclerotic lesions, the kinase immunoreactivity was detected in high amounts in vascular smooth muscle cells of non-atherosclerotic lesions from infants. Thus, the abundant expression of the phosphorylated kinase in these cells in atherosclerotic lesions of adults and non-atherosclerotic lesions of infants suggests that the activation of c-Jun NH2-terminal kinase may be an important element initiating the proliferation of vascular smooth muscle cells during atherogenesis and aortic development.