Role of extracellular signal-regulated kinases in angiotensin II-stimulated contraction of smooth muscle cells from human resistance arteries

Regulation of vascular angiotensin II type 1 and type 2 receptor and angiotensin-(1-7)/MasR signaling in normal and hypertensive pregnancy

Normal pregnancy (Norm-Preg) is associated with a slight reduction in blood pressure (BP) and decreased BP response to vasoconstrictor stimuli such as angiotensin II (Ang II), although the renin-angiotensin-aldosterone system (RAAS) is upregulated. Preeclampsia (PE) is a complication of pregnancy manifested as hypertension-in-pregnancy (HTN-Preg), and dysregulation of angiotensin biosynthesis and signaling have been implicated. Ang II activates vascular Ang II type-1 receptor (AT1R) and Ang II type-2 receptor (AT2R), while angiotensin-(1-7) promotes Ang-(1-7)/MasR signaling. The role of AT1R in vasoconstriction and the activated cellular mechanisms are well-characterized. The sensitivity of vascular AT1R to Ang II and consequent activation of vasoconstrictor mechanisms decrease during Norm-Preg, but dramatically increase in HTN-Preg. Placental ischemia in late pregnancy could also initiate the release of AT1R agonistic autoantibodies (AT1AA) with significant impact on endothelial dysfunction and activation of contraction pathways in vascular smooth muscle including [Ca2+]c and protein kinase C. On the other hand, the role of AT2R and Ang-(1-7)/MasR in vascular relaxation, particularly during Norm-Preg and PE, is less clear. During Norm-Preg, increases in the expression/activity of vascular AT2R and Ang-(1-7)/MasR promote the production of endothelium-derived relaxing factors such as nitric oxide (NO), prostacyclin and endothelium-derived hyperpolarizing factor leading to generalized vasodilation. Aortic segments of Preg rats show prominent endothelial AT2R staining and increased relaxation and NO production in response to AT2R agonist CGP42112A, and treatment with AT2R antagonist PD123319 enhances phenylephrine-induced contraction. Decreased vascular AT2R and Ang-(1-7)/MasR expression and receptor-mediated mechanisms of vascular relaxation have been suggested in HTN-Preg animal models, but their role in human PE needs further testing. Changes in angiotensin-converting enzyme-2 (ACE2) have been observed in COVID-19 patients, and whether ACE2 influences the course of COVID-19 viral infection/immunity in Norm-Preg and PE is an intriguing area for research.

Antiaging effect of inotodiol on oxidative stress in human dermal fibroblasts

Oxidative damage is one of the major causes of human skin aging. Inotodiol is a lanostane triterpenoid that demonstrates antiviral, anticancer, and anti-inflammatory activities. Previous studies have reported that inotodiol also has antiallergic effects. However, whether inotodiol inhibits oxidative stress-induced human skin aging is not known. Stimulation of human dermal fibroblast cells with hydrogen peroxide is related to skin aging. Inotodiol inhibited the expression of mitogen-activated protein kinase (MAPK) and NADPH Oxidase 5 (NOX5). Moreover, inotodiol effectively decreased nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), as well as nitric oxide (NO), reactive oxygen species (ROS), cyclooxygenase-2 (COX-2), and cytokines such as IL-1β, IL-6, and TNF-α. Based on our results, inotodiol protects human dermal fibroblast by preventing MAPK-NOX5 and NF-κB activation and attenuates the expression of aging genes. Inotodiol may therefore be considered a potential candidate for developing natural antiaging products, because it protects the human skin from oxidative stress-induced skin aging by inhibiting the MAPK-NOX5 and NF-κB signaling pathways.

Protein kinases in cardiovascular diseases

ABSTRACT

Cardiovascular disease (CVD) remains the leading cause of death worldwide. Therefore, exploring the mechanism of CVDs and critical regulatory factors is of great significance for promoting heart repair, reversing cardiac remodeling, and reducing adverse cardiovascular events. Recently, significant progress has been made in understanding the function of protein kinases and their interactions with other regulatory proteins in myocardial biology. Protein kinases are positioned as critical regulators at the intersection of multiple signals and coordinate nearly every aspect of myocardial responses, regulating contractility, metabolism, transcription, and cellular death. Equally, reconstructing the disrupted protein kinases regulatory network will help reverse pathological progress and stimulate cardiac repair. This review summarizes recent researches concerning the function of protein kinases in CVDs, discusses their promising clinical applications, and explores potential targets for future treatments.

Antibodies against Angiotensin II Type 1 and Endothelin 1 Type A Receptors in Cardiovascular Pathologies

Angiotensin II receptor type 1 (AT1R) and endothelin-1 receptor type A (ETAR) are G-protein-coupled receptors (GPCRs) expressed on the surface of a great variety of cells: immune cells, vascular smooth cells, endothelial cells, and fibroblasts express ETAR and AT1R, which are activated by endothelin 1 (ET1) and angiotensin II (AngII), respectively. Certain autoantibodies are specific for these receptors and can regulate their function, thus being known as functional autoantibodies. The function of these antibodies is similar to that of natural ligands, and it involves not only vasoconstriction, but also the secretion of proinflammatory cytokines (such as interleukin-6 (IL6), IL8 and TNF-α), collagen production by fibroblasts, and reactive oxygen species (ROS) release by fibroblasts and neutrophils. The role of autoantibodies against AT1R and ETAR (AT1R-AAs and ETAR-AAs, respectively) is well described in the pathogenesis of many medical conditions (e.g., systemic sclerosis (SSc) and SSc-associated pulmonary hypertension, cystic fibrosis, and allograft dysfunction), but their implications in cardiovascular diseases are still unclear. This review summarizes the current evidence regarding the effects of AT1R-AAs and ETAR-AAs in cardiovascular pathologies, highlighting their roles in heart transplantation and mechanical circulatory support, preeclampsia, and acute coronary syndromes.

Angiotensin II type 1 receptor is involved in hypertension and vascular alterations caused by environmental toxicant hexachlorobenzene

Environmental hexachlorobenzene (HCB) increases blood pressure (BP) in female rats, causing alterations in arterial structure and function. Here we study the role of Angiotensin II receptor type 1 (AT1) in HCB-induced hypertension through the use of AT1 antagonist losartan. HCB-treated male rats showed a 22.7% increase in BP which was prevented by losartan. Losartan blocked HCB-induced changes in arterial morphology (decreased aorta cell number and increased wall thickness). Losartan also prevented HCB-induced alterations in artery relaxation by acetylcholine and nitroprusside but not the reduction in the maximum contraction by phenylephrine. Losartan rescued arterial molecular alterations caused by HCB (i.e. an increase in TGF-β1 and AT1 expression and a decrease in eNOS expression and nitrite levels) and reduced hydrogen sulfide plasma concentration. In conclusion: in this work we demonstrate that AT1 activity is involved in HCB effects on the vascular system leading to hypertension.

ROCK (RhoA/Rho Kinase) in Cardiovascular-Renal Pathophysiology: A Review of New Advancements

Rho-associated, coiled-coil containing kinases (ROCK) were originally identified as effectors of the RhoA small GTPase and found to belong to the AGC family of serine/threonine kinases. They were shown to be downstream effectors of RhoA and RhoC activation. They signal via phosphorylation of proteins such as MYPT-1, thereby regulating many key cellular functions including proliferation, motility and viability and the RhoA/ROCK signaling has been shown to be deeply involved in arterial hypertension, cardiovascular–renal remodeling, hypertensive nephropathy and posttransplant hypertension. Given the deep involvement of ROCK in cardiovascular–renal pathophysiology and the interaction of ROCK signaling with other signaling pathways, the reports of trials on the clinical beneficial effects of ROCK’s pharmacologic targeting are growing. In this current review, we provide a brief survey of the current understanding of ROCK-signaling pathways, also integrating with the more novel data that overall support a relevant role of ROCK for the cardiovascular–renal physiology and pathophysiology.

How Structure, Mechanics, and Function of the Vasculature Contribute to Blood Pressure Elevation in Hypertension

Large conduit arteries and the microcirculation participate in the mechanisms of elevation of blood pressure (BP). Large vessels play roles predominantly in older subjects, with stiffening progressing after middle age leading to increases in systolic BP found in most humans with aging. Systolic BP elevation and increased pulsatility penetrate deeper into the distal vasculature, leading to microcirculatory injury, remodelling, and associated endothelial dysfunction. The result is target organ damage in the heart, brain, and kidney. In younger individuals genetically predisposed to high BP, increased salt intake or other exogenous or endogenous risk factors for hypertension, including overweight and excess alcohol intake, lead to enhanced sympathetic activity and vasoconstriction. Enhanced vasoconstrictor responses and myogenic tone become persistent when embedded in an increased extracellular matrix, resulting in remodelling of resistance arteries with a narrowed lumen and increased media-lumen ratio. Stimulation of the renin-angiotensin-aldosterone and endothelin systems and inflammatory and immune activation, to which gut microbiome dysbiosis may contribute as a result of salt intake, also participate in the injury and remodelling of the microcirculation and endothelial dysfunction. Inflammation of perivascular fat and loss of anticontractile factors play roles as well in microvessel remodelling. Exaggerated myogenic tone leads to closure of terminal arterioles, collapse of capillaries and venules, functional rarefaction, and eventually to anatomic rarefaction, compromising tissue perfusion. The remodelling of the microcirculation raises resistance to flow, and accordingly raises BP in a feedback process that over years results in stiffening of conduit arteries and systo-diastolic or predominantly systolic hypertension and, more rarely, predominantly diastolic hypertension. Thus, at different stages of life and the evolution of hypertension, large vessels and the microcirculation interact to contribute to BP elevation.

AT1 Receptor Antagonism Improves Structural, Functional, and Biomechanical Properties in Resistance Arteries in a Rodent Chronic Kidney Disease Model

BACKGROUND

The renin-angiotensin system, in particular Angiotensin II (AngII), plays a significant role in the pathogenesis of hypertension in chronic kidney disease (CKD). Effects of chronic AT1 receptor antagonism were investigated in a genetic hypertensive rat model of CKD, the Lewis polycystic kidney (LPK) rat.

METHODS

Mixed-sex LPK and Lewis control rats (total n = 31) were split between treated (valsartan 60 mg/kg/day p.o. from 4 to 18 weeks) and vehicle groups. Animals were assessed for systolic blood pressure and urine biochemistry, and after euthanasia, blood collected for urea and creatinine analysis, confirming the hypertensive and renal phenotype. Mesenteric resistance vasculature was assessed using pressure myography and histology.

RESULTS

Valsartan treatment improved vascular structure in LPK rats, increasing internal and external diameter values and reducing wall thickness (untreated vs. treated LPK: 53.19 ± 3.29 vs. 33.93 ± 2.17 μm) and wall-lumen ratios (untreated vs. treated LPK: 0.52 ± 0.09 vs. 0.16 ± 0.01, all P < 0.0001). Endothelium dysfunction, as measured by maximal response to acetylcholine (Rmax), was normalized with treatment (untreated vs. treated LPK: 69.56 ± 4.34 vs. 103.05 ± 4.13, P < 0.05), increasing the relative contributions of nitric oxide and endothelium-derived hyperpolarization to vasorelaxation while downregulating the prostanoid contribution. Biomechanical properties also improved with treatment, as indicated by an increase in compliance, decrease in intrinsic stiffness and alterations in the artery wall composition, which included decreases in collagen density and collagen/elastin ratio.

CONCLUSIONS

Our results highlight the importance of AngII as a driver of resistance vessel structural, functional, and biomechanical dysfunction and provide insight as to how AT1 receptor blockade exerts therapeutic efficacy in CKD.

Impaired Ca2+ handling in resistance arteries from genetically obese Zucker rats: Role of the PI3K, ERK1/2 and PKC signaling pathways

The impact of obesity on vascular smooth muscle (VSM) Ca²⁺ handling and vasoconstriction, and its regulation by the phosphatidylinositol 3-kinase (PI3K), mitogen activated protein kinase (MAPK) and protein kinase C (PKC) were assessed in mesenteric arteries (MA) from obese Zucker rats (OZR). Simultaneous measurements of intracellular Ca²⁺ ([Ca²⁺]_i) and tension were performed in MA from OZR and compared to lean Zucker rats (LZR), and the effects of selective inhibitors of PI3K, ERK-MAPK kinase and PKC were assessed on the functional responses of VSM voltage-dependent L-type Ca²⁺ channels (Ca_V1.2). Increases in [Ca²⁺]_i induced by α₁-adrenoceptor activation and high K⁺ depolarization were not different in arteries from LZR and OZR although vasoconstriction was enhanced in OZR. Blockade of the ryanodine receptor (RyR) and of Ca²⁺ release from the sarcoplasmic reticulum (SR) markedly reduced depolarization-induced Ca²⁺ responses in arteries from lean but not obese rats, suggesting impaired Ca²⁺-induced Ca²⁺ release (CICR) from SR in arteries from OZR. Enhanced Ca²⁺ influx after treatment with ryanodine was abolished by nifedipine and coupled to up-regulation of Ca_V1.2 channels in arteries from OZR. Increased activation of ERK-MAPK and up-regulation of PI3Kδ, PKCβ and δ isoforms were associated to larger inhibitory effects of PI3K, MAPK and PKC blockers on VSM L-type channel Ca²⁺ entry in OZR. Changes in arterial Ca²⁺ handling in obesity involve SR Ca²⁺ store dysfunction and enhanced VSM Ca²⁺ entry through L-type channels, linked to a compensatory up-regulation of Ca_V1.2 proteins and increased activity of the ERK-MAPK, PI3Kδ and PKCβ and δ, signaling pathways.

Angiotensin, transforming growth factor β and aortic dilatation in Marfan syndrome: Of mice and humans

Marfan syndrome is consequent upon mutations in FBN1, which encodes the extracellular matrix microfibrillar protein fibrillin-1. The phenotype is characterised by development of thoracic aortic aneurysm. Current understanding of the pathogenesis of aneurysms in Marfan syndrome focuses upon abnormal vascular smooth muscle cell signalling through the transforming growth factor beta (TGFβ) pathway. Angiotensin II (Ang II) can directly induce aortic dilatation and also influence TGFβ synthesis and signalling. It has been hypothesised that antagonism of Ang II signalling may protect against aortic dilatation in Marfan syndrome. Experimental studies have been supportive of this hypothesis, however results from multiple clinical trials are conflicting. This paper examines current knowledge about the interactions of Ang II and TGFβ signalling in the vasculature, and critically interprets the experimental and clinical findings against these signalling interactions.

Are the innate and adaptive immune systems setting hypertension on fire?

Hypertension is the most common chronic cardiovascular disease and is associated with several pathological states, being an important cause of morbidity and mortality around the world. Low-grade inflammation plays a key role in hypertension and the innate and adaptive immune systems seem to contribute to hypertension development and maintenance. Hypertension is associated with vascular inflammation, increased vascular cytokines levels and infiltration of immune cells in the vasculature, kidneys and heart. However, the mechanisms that trigger inflammation and immune system activation in hypertension are completely unknown. Cells from the innate immune system express pattern recognition receptors (PRR), which detect conserved pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs) that induce innate effector mechanisms to produce endogenous signals, such as inflammatory cytokines and chemokines, to alert the host about danger. Additionally, antigen-presenting cells (APC) act as sentinels that are activated by PAMPs and DAMPs to sense the presence of the antigen/neoantigen, which ensues the adaptive immune system activation. In this context, different lymphocyte types are activated and contribute to inflammation and end-organ damage in hypertension. This review will focus on experimental and clinical evidence demonstrating the contribution of the innate and adaptive immune systems to the development of hypertension.

Fibroblast Angiotensin II Type 1a Receptors Contribute to Angiotensin II-Induced Medial Hyperplasia in the Ascending Aorta

OBJECTIVE

Angiotensin II (Ang II) infusion causes aortic medial thickening via stimulation of angiotensin II type 1a (AT1a) receptors. The purpose of this study was to determine the cellular loci of AT1a receptors that mediate this Ang II-induced aortic pathology.

APPROACH AND RESULTS

Saline or Ang II was infused into AT1a receptor floxed mice expressing Cre under control of cell-specific promoters. Initially, AT1a receptors were depleted in aortic smooth muscle cell and endothelium by expressing Cre under control of SM22 and Tie2 promoters, respectively. Deletion of AT1a receptors in either cell type had no effect on Ang II-induced medial thickening. To determine whether this effect was related to neural stimulation, AT1a receptors were depleted using an enolase 2-driven Cre. Depletion of AT1a receptors in neural cells attenuated Ang II-induced medial thickening of the ascending, but not descending aorta. Lineage tracking studies, using ROSA26-LacZ, demonstrated that enolase 2 was also expressed in adventitial cells adjacent to the region of attenuated thickening. To determine whether adventitial fibroblasts contributed to this attenuation, AT1a receptors in fibroblasts were depleted using S100A4 driven Cre. Similar to enolase 2-Cre, Ang II-induced medial thickening was attenuated in the ascending, but not the descending aorta. Lineage tracking demonstrated an increase of S100A4-LacZ positive cells in the media of the ascending region during Ang II infusion.

CONCLUSIONS

AT1a receptor depletion in fibroblasts attenuates Ang II-induced medial hyperplasia in the ascending aorta.

Angiotensin II and vascular injury

Vascular injury, characterized by endothelial dysfunction, structural remodelling, inflammation and fibrosis, plays an important role in cardiovascular diseases. Cellular processes underlying this include altered vascular smooth muscle cell (VSMC) growth/apoptosis, fibrosis, increased contractility and vascular calcification. Associated with these events is VSMC differentiation and phenotypic switching from a contractile to a proliferative/secretory phenotype. Inflammation, associated with macrophage infiltration and increased expression of redox-sensitive pro-inflammatory genes, also contributes to vascular remodelling. Among the many factors involved in vascular injury is Ang II. Ang II, previously thought to be the sole biologically active downstream peptide of the renin-angiotensin system (RAS), is converted to smaller peptides, [Ang III, Ang IV, Ang-(1-7)], that are functional and that modulate vascular tone and structure. The actions of Ang II are mediated via signalling pathways activated upon binding to AT1R and AT2R. AT1R activation induces effects through PLC-IP3-DAG, MAP kinases, tyrosine kinases, tyrosine phosphatases and RhoA/Rho kinase. Ang II elicits many of its (patho)physiological actions by stimulating reactive oxygen species (ROS) generation through activation of vascular NAD(P)H oxidase (Nox). ROS in turn influence redox-sensitive signalling molecules. Here we discuss the role of Ang II in vascular injury, focusing on molecular mechanisms and cellular processes. Implications in vascular remodelling, inflammation, calcification and atherosclerosis are highlighted.

Upregulation of ERK1/2-eNOS via AT2 receptors decreases the contractile response to angiotensin II in resistance mesenteric arteries from obese rats

It has been clearly established that mitogen-activated protein kinases (MAPKS) are important mediators of angiotensin II (Ang II) signaling via AT1 receptors in the vasculature. However, evidence for a role of these kinases in changes of Ang II-induced vasoconstriction in obesity is still lacking. Here we sought to determine whether vascular MAPKs are differentially activated by Ang II in obese animals. The role of AT2 receptors was also evaluated. Male monosodium glutamate-induced obese (obese) and non-obese Wistar rats (control) were used. The circulating concentrations of Ang I and Ang II, determined by HPLC, were increased in obese rats. Ang II-induced isometric contraction was decreased in endothelium-intact resistance mesenteric arteries from obese compared with control rats and exhibited a retarded AT1 receptor antagonist response. Blocking of AT2 receptors and inhibition of either endothelial nitric oxide synthase (eNOS) or extracellular signal-regulated protein kinases 1 and 2 (ERK1/2) restored Ang II-induced contraction in obese rats. Western blot analysis revealed increased protein expression of AT2 receptors in arteries from obese rats. Basal and Ang II-induced ERK1/2 phosphorylation was also increased in obese rats. Blockade of either AT1 or AT2 receptors corrected the increased ERK1/2 phosphorylation in arteries from obese rats to levels observed in control preparations. Phosphorylation of eNOS was increased in obese rats. Incubation with the ERK1/2 inhibitor before Ang II stimulation did not affect eNOS phosphorylation in control rats; however, it corrected the increased phosphorylation of eNOS in obese rats. These results clearly demonstrate that enhanced AT2 receptor and ERK1/2-induced, NO-mediated vasodilation reduces Ang II-induced contraction in an endothelium-dependent manner in obese rats.

Amplification of AngII-dependent cell contraction by glyoxal: implication of cell mechanical properties and actomyosin activity

Glyoxal (GO), a highly reactive metabolite of glucose, is associated with diabetic vascular complications via the formation of advanced glycation end-products. Considering its ability to react with proteins' amino acids and its crosslinking potential, we suggest that GO affects cellular mechanical functions such as contractility. Therefore, we tested the effects of GO on cellular contractile response following AngII stimulation of human embryonic kidney cells over-expressing the AT1 receptor (HEK 293 AT1aR). Prior to cell stimulation with AngII, cells exposed to GO exhibited carboxymethyllysine-adduct formation and an increase in cellular stiffness, which could be prevented by pre-treatment with aminoguanidine. The time-dependent cellular contractile response to AngII was measured by monitoring cell membrane displacement by atomic force atomic force microscopy (AFM) and by quantifying myosin light chain phosphorylation (p-MLC) via immunoblotting. Interestingly, short-term GO exposure increased by 2.6 times the amplitude of cell contraction induced by AngII and this was also associated with a sustained rise in p-MLC. This increased response to AngII induced by GO appears to be linked to its glycation potential, as aminoguanidine pre-treatment prevented this increased cellular mechanical response. Our results also suggest that GO could have an impact on ROCK activity, as ROCK inhibition with Y-27632 blocked the enhanced contractile response (p = 0.011) measured under GO conditions. Together, these results indicate that GO enhances the cellular response to AngII and modifies cellular mechanical properties via a mechanism that relies on its glycation potential and on the activation of the ROCK-dependent pathway.

Toll-like receptors and damage-associated molecular patterns: novel links between inflammation and hypertension

Low-grade systemic inflammation is a common manifestation of hypertension; however, the exact mechanisms that initiate this pathophysiological response, thereby contributing to further increases in blood pressure, are not well understood. Aberrant vascular inflammation and reactivity via activation of the innate immune system may be the first step in the pathogenesis of hypertension. One of the functions of the innate immune system is to recognize and respond to danger. Danger signals can arise from not only pathogenic stimuli but also endogenous molecules released following cell injury and/or death [damage-associated molecular patterns (DAMPs)]. In the short-term, activation of the innate immune system is beneficial in the vasculature by providing cytoprotective mechanisms and facilitating tissue repair following injury or infection. However, sustained or excessive immune system activation, such as in autoimmune diseases, may be deleterious and can lead to maladaptive, irreversible changes to vascular structure and function. An initial source of DAMPs that enter the circulation to activate the innate immune system could arise from modest elevations in peripheral vascular resistance. These stimuli could subsequently lead to ischemic- or pressure-induced events aggravating further cell injury and/or death, providing more DAMPs for innate immune system activation. This review will address and critically evaluate the current literature on the role of the innate immune system in hypertension pathogenesis. The role of Toll-like receptor activation on somatic cells of the vasculature in response to the release of DAMPs and the consequences of this activation on inflammation, vasoreactivity, and vascular remodeling will be specifically discussed.

A modern understanding of the traditional and nontraditional biological functions of angiotensin-converting enzyme

Angiotensin-converting enzyme (ACE) is a zinc-dependent peptidase responsible for converting angiotensin I into the vasoconstrictor angiotensin II. However, ACE is a relatively nonspecific peptidase that is capable of cleaving a wide range of substrates. Because of this, ACE and its peptide substrates and products affect many physiologic processes, including blood pressure control, hematopoiesis, reproduction, renal development, renal function, and the immune response. The defining feature of ACE is that it is composed of two homologous and independently catalytic domains, the result of an ancient gene duplication, and ACE-like genes are widely distributed in nature. The two ACE catalytic domains contribute to the wide substrate diversity of ACE and, by extension, the physiologic impact of the enzyme. Several studies suggest that the two catalytic domains have different biologic functions. Recently, the X-ray crystal structure of ACE has elucidated some of the structural differences between the two ACE domains. This is important now that ACE domain-specific inhibitors have been synthesized and characterized. Once widely available, these reagents will undoubtedly be powerful tools for probing the physiologic actions of each ACE domain. In turn, this knowledge should allow clinicians to envision new therapies for diseases not currently treated with ACE inhibitors.

Beta adrenergic overstimulation impaired vascular contractility via actin-cytoskeleton disorganization in rabbit cerebral artery

Background and Purpose

Beta adrenergic overstimulation may increase the vascular damage and stroke. However, the underlying mechanisms of beta adrenergic overstimulation in cerebrovascular dysfunctions are not well known. We investigated the possible cerebrovascular dysfunction response to isoproterenol induced beta-adrenergic overstimulation (ISO) in rabbit cerebral arteries (CAs).

Methods

ISO was induced in six weeks aged male New Zealand white rabbit (0.8–1.0 kg) by 7-days isoproterenol injection (300 μg/kg/day). We investigated the alteration of protein expression in ISO treated CAs using 2DE proteomics and western blot analysis. Systemic properties of 2DE proteomics result were analyzed using bioinformatics software. ROS generation and following DNA damage were assessed to evaluate deteriorative effect of ISO on CAs. Intracellular Ca²⁺ level change and vascular contractile response to vasoactive drug, angiotensin II (Ang II), were assessed to evaluate functional alteration of ISO treated CAs. Ang II-induced ROS generation was assessed to evaluated involvement of ROS generation in CA contractility.

Results

Proteomic analysis revealed remarkably decreased expression of cytoskeleton organizing proteins (e.g. actin related protein 1A and 2, α-actin, capping protein Z beta, and vimentin) and anti-oxidative stress proteins (e.g. heat shock protein 9A and stress-induced-phosphoprotein 1) in ISO-CAs. As a cause of dysregulation of actin-cytoskeleton organization, we found decreased level of RhoA and ROCK1, which are major regulators of actin-cytoskeleton organization. As functional consequences of proteomic alteration, we found the decreased transient Ca²⁺ efflux and constriction response to angiotensin II and high K⁺ in ISO-CAs. ISO also increased basal ROS generation and induced oxidative damage in CA; however, it decreased the Ang II-induced ROS generation rate. These results indicate that ISO disrupted actin cytoskeleton proteome network through down-regulation of RhoA/ROCK1 proteins and increased oxidative damage, which consequently led to contractile dysfunction in CA.

Angiotensin II-aldosterone interaction in human coronary microarteries involves GPR30, EGFR, and endothelial NO synthase

AIMS

The aim of this study was to investigate the aldosterone-angiotensin (Ang) II interaction in human coronary microarteries (HCMAs).

METHODS AND RESULTS

HCMAs, obtained from 75 heart-beating organ donors, were mounted in myographs and exposed to Ang II, either directly or following a 30-min pre-incubation with aldosterone, 17β-oestradiol, hydrocortisone, the p38 mitogen-activated protein kinase (MAPK) inhibitor SB203580, the extracellular regulated kinase 1/2 (ERK1/2) inhibitor PD98059, the GPR30 antagonist G15, or the epidermal growth factor receptor (EGFR) antagonist AG1478. Ang II constricted HCMAs in a concentration-dependent manner. All steroids, at nanomolar levels, potentiated Ang II and G15 prevented this effect. The potentiation disappeared or was reversed into Ang II antagonism at micromolar steroid levels. NO synthase (NOS) inhibition prevented the latter antagonism in the case of 17β-oestradiol, whereas both aldosterone and 17β-oestradiol at micro- (but not nano-) molar levels induced endothelial NOS phosphorylation in human umbilical vein endothelial cells. AG1478, but not SB203580 or PD98059, abolished the Ang II-induced contraction in the presence of aldosterone or 17β-oestradiol, and none of these drugs affected Ang II alone.

CONCLUSION

Steroids including aldosterone affect Ang II-induced vasoconstriction in a biphasic manner. Potentiation occurs at nanomolar steroid levels and depends on GPR30 and EGFR transactivation. At micromolar steroid levels, this potentiation either disappears (aldosterone and hydrocortisone) or is reversed into an inhibition (17β-oestradiol), and this is due to the endothelial NOS activation that occurs at such concentrations.

Preventing intimal thickening of vein grafts in vein artery bypass using STAT-3 siRNA

BACKGROUND

Proliferation and migration of vascular smooth muscle cells (VSMCs) play a key role in neointimal formation which leads to restenosis of vein graft in venous bypass. STAT-3 is a transcription factor associated with cell proliferation. We hypothesized that silencing of STAT-3 by siRNA will inhibit proliferation of VSMCs and attenuate intimal thickening.

METHODS

Rat VSMCs were isolated and cultured in vitro by applying tissue piece inoculation methods. VSMCs were transfected with STAT 3 siRNA using lipofectamine 2000. In vitro proliferation of VSMC was quantified by the MTT assay, while in vivo assessment was performed in a venous transplantation model. In vivo delivery of STAT-3 siRNA plasmid or scramble plasmid was performed by admixing with liposomes 2000 and transfected into the vein graft by bioprotein gel applied onto the adventitia. Rat jugular vein-carotid artery bypass was performed. On day 3 and7 after grafting, the vein grafts were extracted, and analyzed morphologically by haematoxylin eosin (H&E), and assessed by immunohistochemistry for expression of Ki-67 and proliferating cell nuclear antigen (PCNA). Western-blot and reverse transcriptase polymerase chain reaction (RT-PCR) were used to detect the protein and mRNA expression in vivo and in vitro. Cell apoptosis in vein grafts was detected by TUNEL assay.

RESULTS

MTT assay shows that the proliferation of VSMCs in the STAT-3 siRNA treated group was inhibited. On day 7 after operation, a reduced number of Ki-67 and PCNA positive cells were observed in the neointima of the vein graft in the STAT-3 siRNA treated group as compared to the scramble control. The PCNA index in the control group (31.3 ± 4.7) was higher than that in the STAT-3 siRNA treated group (23.3 ± 2.8) (P < 0.05) on 7d. The neointima in the experimental group(0.45 ± 0.04 μm) was thinner than that in the control group(0.86 ± 0.05 μm) (P < 0.05).Compared with the control group, the protein and mRNA levels in the experimental group in vivo and in vitro decreased significantly. Down regulation of STAT-3 with siRNA resulted in a reduced expression of Bcl-2 and cyclin D1. However, apoptotic cells were not obviously found in all grafts on day 3 and 7 post surgery.

CONCLUSIONS

The STAT-3 siRNA can inhibit the proliferation of VSMCs in vivo and in vitro and attenuate neointimal formation.

Angiotensin II and the vascular phenotype in hypertension

Hypertension is associated with vascular changes characterised by remodelling, endothelial dysfunction and hyperreactivity. Cellular processes underlying these perturbations include altered vascular smooth muscle cell growth and apoptosis, fibrosis, hypercontractility and calcification. Inflammation, associated with macrophage infiltration and increased expression of redox-sensitive pro-inflammatory genes, also contributes to vascular remodelling. Many of these features occur with ageing, and the vascular phenotype in hypertension is considered a phenomenon of ‘premature vascular ageing’. Among the many factors involved in the hypertensive vascular phenotype, angiotensin II (Ang II) is especially important. Ang II, previously thought to be the sole effector of the renin–angiotensin system (RAS), is converted to smaller peptides [Ang III, Ang IV, Ang-(1-7)] that are biologically active in the vascular system. Another new component of the RAS is the (pro)renin receptor, which signals through Ang-II-independent mechanisms and might influence vascular function. Ang II mediates effects through complex signalling pathways on binding to its G-protein-coupled receptors (GPCRs) AT1R and AT2R. These receptors are regulated by the GPCR-interacting proteins ATRAP, ARAP1 and ATIP. AT1R activation induces effects through the phospholipase C pathway, mitogen-activated protein kinases, tyrosine kinases/phosphatases, RhoA/Rhokinase and NAD(P)H-oxidase-derived reactive oxygen species. Here we focus on recent developments and new research trends related to Ang II and the RAS and involvement in the hypertensive vascular phenotype.

Differential regulation of Nox1, Nox2 and Nox4 in vascular smooth muscle cells from WKY and SHR

The functional significance and regulation of NAD(P)H oxidase (Nox) isoforms by angiotensin II (Ang II) and endothelin-1 (ET-1) in vascular smooth muscle cells (VSMCs) from normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR) was studied. Expression of Nox1, Nox2, and Nox4 (gene and protein) and NAD(P)H oxidase activity were increased in SHR. Basal NAD(P)H oxidase activity was blocked by GKT136901 (Nox1/4 inhibitor) and by Nox1 siRNA in WKY cells and by siNOX1 and siNOX2 in SHR. Whereas Ang II increased expression of all Noxes in WKY, only Nox1 was influenced in SHR. Ang II-induced NAD(P)H activity was inhibited by siNOX1 in WKY and by siNOX1 and siNOX2 in SHR. ET-1 upregulated Nox expression only in WKY and increased NAD(P)H oxidase activity, an effect inhibited by siNOX1 and siNOX2. Nox1 co-localized with Nox2 but not with Nox4, implicating association between Nox1 and Nox2 but not between Nox1 and Nox4. These data highlight the complexity of Nox biology in VSMCs, emphasising that more than one Nox member, alone or in association, may be involved in NAD(P)H oxidase-mediated •O(2)(-) production. Nox1 regulation by Ang II, but not by ET-1, may be important in •O(2)(-) formation in VSMCs from SHR.

Molecular regulation of NADPH oxidase 5 via the MAPK pathway

The mechanisms controlling the activity of NADPH oxidase 5 (Nox5) are unique in that they are independent of the protein: protein interactions that coordinate the activation of other Nox isoforms. Instead, the primary driving force for Nox5 activity is calcium. However, in a previous study we reported that the protein kinase C (PKC)-agonist PMA could induce a sustained activation of Nox5 that was independent of calcium changes. This apparent calcium-independent activation was found to be mediated by the PKC-dependent phosphorylation of specific serine and threonine residues on Nox5 which increased the calcium sensitivity of the enzyme and enabled activation at resting levels of calcium. However, the specific kinase(s) mediating the phosphorylation and activation of Nox5 are not known. As PKC can activate the MEK/ERK1/2 signaling pathway, we hypothesized that Nox5 is activated by the coordinated phosphorylation of both MAPK and PKC pathways. The inhibition of MEK1 using PD-98059 and U-0126 significantly reduced the phosphorylation and activity of Nox5 in response to PMA but not to the calcium-mobilizing stimulus ionomycin. Dominant negative MEK1 and knockdown of endogenous MEK1/2 using a specific small interfering RNA also inhibited Nox5 activity in response to PMA. The mutation of S498 to a nonphosphorylatable residue and to a lesser degree T494 blocked the ability of ERK to stimulate Nox5 activity. However, a constitutively active form of MEK1 failed to increase Nox5 activity in the absence of PMA stimulation. These results suggest that the MEK/ERK1/2 pathway is necessary but not sufficient to regulate the PMA-dependent activation of Nox5.

Involvement of YC-1 in extracellular signal-regulated kinase action in rat cremasteric muscle

Objectives

The nitric oxide (NO)–soluble guanylate cyclase (sGC) signalling pathway is attributed to the prevention of ischaemia–reperfusion (I/R)-induced leucocyte–endothelium adhesive interactions. YC-1 (3-(5′-hydroxymethyl-2′-furyl)-1-benzylindazole), a NO-independent sGC activator, has been shown to exert cardiovascular benefits, but its action on leucocyte–endothelium interactions remains unknown. In this study, the direct effect and the underlying mechanism of the anti-adhesive action of YC-1 have been examined in cremasteric microcirculation.

Methods

Rat cremaster muscle was subjected to 4 h pudic-epigastric artery ischaemia followed by 2 h reperfusion and intravital microscopy was used to observe leucocyte–endothelium interaction and to quantify functional capillaries in rat cremaster muscle flaps.

Key findings

The values for leucocyte rolling, adhering and transmigrating were 5.5-, 6.9- and 8.8-fold greater, respectively, in I/R than in sham-control animals. YC-1 treatment rescued functional capillary density and reduced leucocyte rolling, adhering and transmigrating in I/R injured cremaster muscles to levels observed in sham-controls. Interestingly, these effects were completely blocked by the MEK (extracellular signal-regulated kinase (ERK) kinase) inhibitor (PD98059) but not by sGC or protein kinase C inhibitors. Cotreatment of PD98059 with YC-1 caused a 3.3-, 7.5- and 8.3-fold increase in the values for leucocyte rolling, adhering and transmigrating, respectively, in postcapillary venules of I/R-injured cremaster muscle.

Conclusions

This study has indicated that the anti-adhesive and functional capillary density rescue properties of YC-1 were mediated predominantly by the activation of ERK but not sGC, although YC-1 was identified to be a sGC activator. A better understanding of the action of YC-1 on the microvasculature may help shed light on its therapeutic potential for cardiovascular disease.

Extracellular signal-regulated kinase 1/2 plays a pro-life role in experimental brain stem death via MAPK signal-interacting kinase at rostral ventrolateral medulla

BACKGROUND

As the origin of a life-and-death signal detected from systemic arterial pressure, which sequentially increases (pro-life) and decreases (pro-death) to reflect progressive dysfunction of central cardiovascular regulation during the advancement towards brain stem death in critically ill patients, the rostral ventrolateral medulla (RVLM) is a suitable neural substrate for mechanistic delineation of this fatal phenomenon. The present study assessed the hypothesis that extracellular signal-regulated kinase 1/2 (ERK1/2), a member of the mitogen-activated protein kinases (MAPKs) that is important for cell survival and is activated specifically by MAPK kinase 1/2 (MEK1/2), plays a pro-life role in RVLM during brain stem death. We further delineated the participation of MAPK signal-interacting kinase (MNK), a novel substrate of ERK in this process.

METHODS

An experimental model of brain stem death that employed microinjection of the organophosphate insecticide mevinphos (Mev; 10 nmol) bilaterally into RVLM of Sprague-Dawley rats was used, in conjunction with cardiovascular, pharmacological and biochemical evaluations.

RESULTS

Results from ELISA showed that whereas the total ERK1/2 was not affected, augmented phosphorylation of ERK1/2 at Thr202 and Tyr204 in RVLM occurred preferentially during the pro-life phase of experimental brain stem death. Furthermore, pretreatment by microinjection into the bilateral RVLM of a specific ERK2 inhibitor, ERK activation inhibitor peptide II (1 nmol); a specific MEK1/2 inhibitor, U0126 (5 pmol); or a specific MNK1/2 inhibitor, CGP57380 (5 pmol) exacerbated the hypotension and blunted the augmented life-and-death signals exhibited during the pro-life phase. Those pretreatments also blocked the upregulated nitric oxide synthase I (NOS I)/protein kinase G (PKG) signaling, the pro-life cascade that sustains central cardiovascular regulatory functions during experimental brain stem death.

CONCLUSIONS

Our results demonstrated that activation of MEK1/2, ERK1/2 and MNK1/2 in RVLM plays a preferential pro-life role by sustaining the central cardiovascular regulatory machinery during brain stem death via upregulation of NOS I/PKG signaling cascade in RVLM.

RGS4 controls renal blood flow and inhibits cyclosporine-mediated nephrotoxicity

Calcineurin inhibitors (CNI) are powerful immunomodulatory agents that produce marked renal dysfunction due in part to endothelin-1-mediated reductions in renal blood flow. Ligand-stimulated Gq protein signaling promotes the contraction of smooth muscle cells via phospholipase Cbeta-mediated stimulation of cytosolic calcium release. RGS4 is a GTPase activating protein that promotes the deactivation of Gq and Gi family members. To investigate the role of G protein-mediated signaling in the pathogenesis of CNI-mediated renal injury, we used mice deficient for RGS4 (rgs4(-/-)). Compared to congenic wild type control animals, rgs4(-/-) mice were intolerant of the CNI, cyclosporine (CyA), rapidly developing fatal renal failure. Rgs4(-/-) mice exhibited markedly reduced renal blood flow after CyA treatment when compared to congenic wild type control mice as measured by magnetic resonance imaging (MRI). Hypoperfusion was reversed by coadministration of CyA with the endothelin antagonist, bosentan. The MAPK/ERK pathway was activated by cyclosporine administration and was inhibited by cotreatment with bosentan. These results show that endothelin-1-mediated Gq protein signaling plays a key role in the pathogenesis of vasoconstrictive renal injury and that RGS4 antagonizes the deleterious effects of excess endothelin receptor activation in the kidney.

Hydrogen peroxide down-regulates inositol 1,4,5-trisphosphate receptor content through proteasome activation

Hydrogen peroxide (H(2)O(2)) is implicated in the regulation of signaling pathways leading to changes in vascular smooth muscle function. Contractile effects produced by H(2)O(2) are due to the phosphorylation of myosin light chain kinase triggered by increases in intracellular calcium (Ca(2+)) from intracellular stores or influx of extracellular Ca(2+). One mechanism for mobilizing such stores involves the phosphoinositide pathway. Inositol 1,4,5-trisphosphate (IP(3)) mobilizes intracellular Ca(2+) by binding to a family of receptors (IP(3)Rs) on the endoplasmic-sarcoplasmic reticulum that act as ligand-gated Ca(2+) channels. IP(3)Rs can be rapidly ubiquitinated and degraded by the proteasome, causing a decrease in cellular IP(3)R content. In this study we show that IP(3)R(1) and IP(3)R(3) are down-regulated when vascular smooth muscle cells (VSMC) are stimulated by H(2)O(2), through an increase in proteasome activity. Moreover, we demonstrate that the decrease in IP(3)R by H(2)O(2) is accompanied by a reduction in calcium efflux induced by IP(3) in VSMC. Also, we observed that angiotensin II (ANGII) induces a decrease in IP(3)R by activation of NADPH oxidase and that preincubation with H(2)O(2) decreases ANGII-mediated calcium efflux and planar cell surface area in VSMC. The decreased IP(3) receptor content observed in cells was also found in aortic rings, which exhibited a decreased ANGII-dependent contraction after treatment with H(2)O(2). Altogether, these results suggest that H(2)O(2) mediates IP(3)R down-regulation via proteasome activity.

NADPH oxidase 1 deficiency alters caveolin phosphorylation and angiotensin II-receptor localization in vascular smooth muscle

The superoxide-generating NADPH oxidase NOX1 is thought to be involved in signaling by the angiotensin II-receptor AT1R. However, underlying signaling steps are poorly understood. In this study, we investigated the effect of AngII on aortic smooth muscle from wild-type and NOX1-deficient mice. NOX1-deficient cells showed decreased basal ROS generation and did not produce ROS in response to AngII. Unexpectedly, AngII-dependent Ca(2+) signaling was markedly decreased in NOX1-deficient cells. Immunostaining demonstrated that AT1R was localized on the plasma membrane in wild-type, but intracellularly in NOX1-deficient cells. Immunohistochemistry and immunoblotting showed a decreased expression of AT1R in the aorta of NOX1-deficient mice. To investigate the basis of the abnormal AT1R targeting, we studied caveolin expression and phosphorylation. The amounts of total caveolin and of caveolae were not different in NOX1-deficient mice, but a marked decrease occurred in the phosphorylated form of caveolin. Exogenous H(2)O(2) or transfection of a NOX1 plasmid restored AngII responses in NOX1-deficient cells. Based on these findings, we propose that NOX1-derived reactive oxygen species regulate cell-surface expression of AT1R through mechanisms including caveolin phosphorylation. The lack cell-surface AT1R expression in smooth muscle could be involved in the decreased blood pressure in NOX1-deficient mice.

Valsartan improves endothelial dysfunction in hypertension: a randomized, double-blind study

Endothelial dysfunction can predict cardiac outcomes in hypertension and reversing this abnormality has become an attractive therapeutic objective. We tested the hypothesis that blocking the angiotensin type 1 (AT₁) receptor with valsartan in comparison with amlodipine would lead to an improvement in forearm resistance artery endothelial dysfunction. In total, 25 hypertensive subjects (mean age 60 years, SD 8) with a mean daytime ambulatory blood pressure (BP) of 154 (10)/97 (6) mmHg were randomized following a 3-week placebo run-in period to a double-blind, crossover trial of 16-week treatment periods with either valsartan or amlodipine, separated by a 3-week washout period. Intra-arterial infusions of acetylcholine (ACh) and N^G-monomethyl-L-arginine (L-NMMA) were used to assess stimulated and basal endothelium-dependent nitric oxide (NO) release, respectively. Coinfusion of ACh and L-NMMA was employed to investigate the existence of an NO-independent vasodilatory pathway. Valsartan and amlodipine each lowered the clinical BP to the same extent (139 [7]/87 [6] and 139 [11]/89 [4] mmHg, respectively). The vasodilatory response to ACh was significantly increased with valsartan (maximal percentage change in forearm blood flow (max. ΔFBF%) 301 [47] vs. 185 [34], mean [SEM]; P < 0.05) as compared with placebo, but remained unchanged with amlodipine. Both valsartan and amlodipine similarly increased the vasoconstrictive response to L-NMMA (max. ΔFBF%–43 [5], −42 [5], respectively, vs. –26 [3] baseline; P < 0.001). The vasodilatory response after coinfusion of ACh and L-NMMA was significantly (P < 0.05) enhanced only with valsartan. Valsartan reserved peripheral endothelial dysfunction through both NO-dependent and -independent pathways, while for the same degree of BP control, amlodipine had only a partial effect on NO bioactivity.

NADPH oxidases and angiotensin II receptor signaling

Over the last decade many studies have demonstrated the importance of reactive oxygen species (ROS) production by NADPH oxidases in angiotensin II (Ang II) signaling, as well as a role for ROS in the development of different diseases in which Ang II is a central component. In this review, we summarize the mechanism of activation of NADPH oxidases by Ang II and describe the molecular targets of ROS in Ang II signaling in the vasculature, kidney and brain. We also discuss the effects of genetic manipulation of NADPH oxidase function on the physiology and pathophysiology of the renin-angiotensin system.

Regulation of the novel Mg2+ transporter transient receptor potential melastatin 7 (TRPM7) cation channel by bradykinin in vascular smooth muscle cells

BACKGROUND

Transient receptor potential melastatin 7 (TRPM7) channels have been identified in the vasculature. However, their regulation and function remain unclear.

METHODS

Here, we tested the hypothesis that bradykinin and its second messenger cAMP upregulate TRPM7, which stimulates activation of annexin-1 (TRPM7 substrate) and increases transmembrane Mg2+ transport and vascular smooth muscle cell (VSMC) migration. Human and rat VSMCs were studied. TRPM7 phosphorylation was assessed by immunoprecipitation:immunoblotting using antiphospho-serine/threonine and anti-TRPM7 antibodies. [Mg2+]i was measured by mag-fura-2. TRPM7 was downregulated by small interfering RNA and 2-aminoethoxydiphenyl borate. Annexin-1 activity was assessed by cytosol-to-membrane translocation. Cell migration and invasion, functional responses to bradykinin, were assessed in transwell chambers.

RESULTS

Bradykinin increased expression of TRPM7 and annexin-1. TRPM7 was rapidly (5 min) phosphorylated on serine/threonine but not on tyrosine residues by bradykinin. [Mg2+]i was increased in bradykinin-stimulated cells (0.53 versus 0.68 mmol/l, basal versus bradykinin, P < 0.01). Annexin-1 activation was increased by bradykinin and inhibited by 2-aminoethoxydiphenyl borate. Although Hoe 140 (B2 receptor antagonist), U-73122 (phospholipase C inhibitor), 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (c-Src inhibitor) and chelerythrine (protein kinase C inhibitor) blocked bradykinin actions, dibutyryl-c-AMP was without effect. In small interfering RNA-transfected and in 2-aminoethoxydiphenyl borate-treated cells, bradykinin-induced Mg2+ influx and VSMC migration were reduced.

CONCLUSION

Our results demonstrate that bradykinin regulates TRPM7 and its downstream target annexin-1 through phospholipase C-dependent, protein kinase C-dependent and c-Src-dependent and cAMP-independent pathways; effects are mediated through bradykinin type 2 receptor; and bradykinin regulates VSMC [Mg2+]i and migration through TRPM7. These data identify TRPM7/annexin-1/Mg2+ as a novel pathway in bradykinin signaling.

Increased vascular angiotensin type 2 receptor expression and NOS-mediated mechanisms of vascular relaxation in pregnant rats

Normal pregnancy is associated with reduced blood pressure (BP) and decreased pressor response to vasoconstrictors, even though the renin-angiotensin system is upregulated. Angiotensin II (ANG II) activates both angiotensin type 1 receptors (AT(1)Rs) and angiotensin type 2 receptors (AT(2)Rs). Although the role of the AT(1)R in vascular contraction is well documented, the role of the AT(2)R in vascular relaxation, particularly during pregnancy, is less clear. It was hypothesized that the decreased BP and vasoconstriction during pregnancy was, at least in part, due to changes in AT(2)R amount, distribution, and/or postreceptor mechanisms of vascular relaxation. To test this hypothesis, systolic BP was measured in virgin and pregnant (day 19) Sprague-Dawley rats. Isometric contraction/relaxation was measured in isolated aortic rings, and nitric oxide (NO) production was measured using 4-amino-5-methylamino-2',7'-difluorescein fluorescence. AT(1)R and AT(2)R mRNA expression and protein amount were measured in tissue homogenates using real-time RT-PCR and Western blots, and their local distribution was visualized in cryosections using immunohistochemistry and immunofluorescence. BP was lower in pregnant than virgin rats. Phenylephrine (Phe) caused concentration-dependent contraction that was reduced in the aorta of pregnant compared with virgin rats. Treatment with the AT(2)R antagonist PD-123319 caused greater enhancement of Phe contraction, and the AT(2)R agonist CGP-42112A caused greater relaxation of Phe contraction in the aorta of pregnant than virgin rats. ANG II plus the AT(1)R blocker losartan induced greater NO production in the aorta of pregnant than virgin rats. RT-PCR revealed increased mRNA expression of vascular endothelial NO synthase (eNOS), little change in AT(1)Rs, and increased AT(2)Rs in pregnant compared with virgin rats. Western blots revealed an increased protein amount of activated phospho-eNOS, little change in AT(1)Rs, and increased AT(2)Rs in pregnant compared with virgin rats. Immunohistochemistry and immunofluorescence analysis in aortic sections of virgin rats revealed abundant AT(1)R staining in tunica media that largely colocalized with actin in vascular smooth muscle and less AT(2)Rs mainly in the tunica intima and endothelium. In pregnant rats, AT(1)R staining in the smooth muscle layer and adventitia was reduced, and endothelial AT(2)R staining was enhanced. These data suggest an enhanced AT(2)R-mediated vascular relaxation pathway involving increased expression/activity of endothelial AT(2)Rs and increased postreceptor activated phospho-eNOS, which may contribute to the decreased BP during pregnancy.

[Ca2+]i and PKC-alpha are involved in the inhibitory effects of Ib, a novel nonpeptide AngiotensinII subtype AT1 receptor antagonist, on AngiotensinII-induced vascular contraction in vitro

The vasoactive peptide AngiotensinII (AngII) is an important factor in the cardiovascular system, exerting most of its effects through AngII receptor type 1 (AT1). Ib, a new nonpeptide AT1 receptor antagonist, has been observed to play a positive role in the treatment of hypertension in preclinical tests. In this study, the inhibitory effects of Ib on AngII-induced vascular contraction in vitro were investigated, and its molecular mechanisms were further explored. In endothelium-denuded aortic rings from rabbits, Ib produced a rightward shift in the concentration-response curve for AngII with a decrease in the maximal contractile response and the pD2' was 7.29. In vascular smooth muscle cells (VSMCs), the specific binding of [125I]AngII to AT1 receptors was inhibited by Ib in a concentration-dependent manner with IC50 value of 0.96nM. Ib could inhibit both AngII-induced Ca2+ mobilization from internal stores and Ca2+ influx. Moreover, the translocation of PKC-alpha stimulated by AngII was inhibited by Ib. Thus, the inhibitory effects of Ib might be related with the depression on AngII-induced increase in [Ca2+]i and translocation of PKC-alpha through blocking AT1 receptors.

Impaired extracellular matrix degradation in aortic vessels of cirrhotic rats

BACKGROUND/AIMS

Thinning of the vascular wall occurs in conductance vessels of cirrhotic rats. Increased nitric oxide synthase (NOS) activity has been involved in the pathogenesis of this phenomenon. Therefore, we assessed the NO-regulated cell signaling pathways participating in vascular remodeling in cirrhosis.

METHODS

Aortas were obtained from 15 control and 15 cirrhotic rats. Phosphorylated p38 MAPK and ERK1/2 were used to evaluate the activation of cell MAPK signaling pathways. Extracellular matrix (ECM) turnover was estimated by measuring matrix metalloproteinases (MMPs) activity and protein expression of collagen IV, MMP-2, MMP-9 and tissue inhibitor of MMPs (TIMP)-2. Thereafter, 12 control and 12 cirrhotic rats received Nomega-nitro-L-arginine-methyl-ester or vehicle daily for 11 weeks.

RESULTS

Cirrhotic vessels showed a reduction in ERK1/2 phosphorylation, lower MMP activity, decreased MMPs expression and higher collagen IV and TIMP-2 abundance, compared to control rats. Chronic NOS inhibition normalized ERK1/2 phosphorylation and MMPs activity, increased MMPs abundance and decreased TIMP-2 expression in cirrhotic rats.

CONCLUSIONS

Vascular remodeling in cirrhotic rats is mediated by down-regulation of cell growth and impaired ERK1/2 activation and subsequent imbalance of ECM turnover. These results further stress the importance of vascular NO overactivity in the reduction of vascular wall thickness in cirrhosis.

Early aging and anatomic heterogeneity determine cyclooxygenase-mediated vasoconstriction to angiotensin II in mice

We previously reported that angiotensin II (AngII)-induced vasoconstriction involves activation of cyclooxygenase (COX) in murine aorta and carotid artery. The aim of this study was to investigate the roles of early aging and COX in AngII-induced vasoconstriction in different vascular beds. Aortic, carotid, renal, and femoral artery rings of 19- and 34-week-old C57BL/6 mice were pretreated with the nitric oxide synthase inhibitor L-NAME (300 micromol/L) to exclude effects of NO. Contractions to AngII (100 nmol/L) were recorded in the presence or absence of meclofenamate (10 micromol/L), a nonselective COX inhibitor. The results indicate a pronounced heterogeneity in the vascular responsiveness to AngII. Renal and femoral artery rings showed stronger contractions than aorta or carotid artery (P < 0.01 for both). In all vessels of young animals COX inhibition with meclofenamate only partially blocked vasoconstriction to AngII, whereas contractions were completely abolished in the aorta and carotid artery of older mice (P < 0.05 vs untreated for both). These data demonstrate that COX determines AngII-induced vasoconstriction in the mouse aorta and carotid artery during the early physiological aging process, independent of endothelial NO bioactivity. AngII-induced vasoconstriction in vessels more distal to the heart such as femoral and renal arteries is only in part mediated by COX-dependent mechanisms that remain unaffected by early aging.

Role of 15-hydroxyeicosatetraenoic acid in phosphorylation of ERK1/2 and caldesmon in pulmonary arterial smooth muscle cells

We have reported that 15-hydroxyeicosatetraenoic acid (15-HETE) induces pulmonary artery (PA) contraction in rats exposed to hypoxia by activating extracellular signal-regulated kinase 1/2 (ERK1/2). In this study, we investigated the characteristics of 15-HETE mediating phosphorylation of ERK1/2 and caldesmon in rat pulmonary arterial smooth muscle cells (PASMCs). Our data showed that 15-HETE upregulated ERK1/2 phosphorylation in a dose-dependent manner, which could be blocked by ERK pathway inhibitors U0126 and PD98059. ERK1/2 phosphorylation was attenuated by inhibiting endogenous 15-HETE formation with lipoxygenase inhibitor, cinnamyl 3,4-dihydroxy-[alpha]-cyanocinnamate (CDC), in both normoxic and hypoxic PASMCs. ERK1/2 phosphorylation in response to 15-HETE was detected in cytosol as well as in nucleus and phosphorylatd ERK1/2 partly translocated into nucleus, which could be blocked by PD98059. In addition, caldesmon was phosphorylated in 15-HETE-stimulated cells; this could be inhibited by PD98059. These data demonstrated that 15-HETE is associated with ERK1/2 activation and caldesmon phosphorylation in PASMCs and that 15-HETE is at least partly involved in mediating activation of hypoxia-initiated ERK pathway, possibly leading to hypoxic pulmonary vasoconstriction.

Angiotensin II cell signaling: physiological and pathological effects in the cardiovascular system

The renin-angiotensin system is a central component of the physiological and pathological responses of cardiovascular system. Its primary effector hormone, angiotensin II (ANG II), not only mediates immediate physiological effects of vasoconstriction and blood pressure regulation, but is also implicated in inflammation, endothelial dysfunction, atherosclerosis, hypertension, and congestive heart failure. The myriad effects of ANG II depend on time (acute vs. chronic) and on the cells/tissues upon which it acts. In addition to inducing G protein- and non-G protein-related signaling pathways, ANG II, via AT(1) receptors, carries out its functions via MAP kinases (ERK 1/2, JNK, p38MAPK), receptor tyrosine kinases [PDGF, EGFR, insulin receptor], and nonreceptor tyrosine kinases [Src, JAK/STAT, focal adhesion kinase (FAK)]. AT(1)R-mediated NAD(P)H oxidase activation leads to generation of reactive oxygen species, widely implicated in vascular inflammation and fibrosis. ANG II also promotes the association of scaffolding proteins, such as paxillin, talin, and p130Cas, leading to focal adhesion and extracellular matrix formation. These signaling cascades lead to contraction, smooth muscle cell growth, hypertrophy, and cell migration, events that contribute to normal vascular function, and to disease progression. This review focuses on the structure and function of AT(1) receptors and the major signaling mechanisms by which angiotensin influences cardiovascular physiology and pathology.

Saga of Renin-Angiotensin System and Calcium Channels in Hypertensive Diabetics: Does it Have a Therapeutic Edge?

Current understanding of the genesis of diabetic vascular disease suggests that vascular complications, such as atherosclerosis and hypertension, are associated with changes in structural and functional parameters. Experimental and epidemiological data suggest that activation of the renin-angiotensin-aldosterone system plays an important role in the development of micro- and macro-vascular complications. Most of the negative cardiovascular actions of angiotensin II are mediated through AT1 receptors, whereas the AT2 receptors mediate largely beneficial effects. Hence, compared to angiotensin converting enzyme inhibitors (ACEIs), selective AT1 receptor blockers (ARBs) should provide additional end organ protection via AT2 receptors activation. Although ACEIs are useful therapeutically, they are being currently displaced by ARBs. Enhanced calcium ion channel activity is reported in vascular smooth muscles from diabetic animal models. Clinical benefits of calcium channel blockers (CCBs) in diabetic hypertensive patients are controversial, but there is increasing experimental evidence for the beneficial effects of dihydropyridine-type CCBs. Although the treatment of hypertension in diabetics reduces cardiovascular and microvascular complications, the ideal strategy for treating hypertension in diabetics has not been well defined and warrants a combination approach. Only limited clinical data regarding the use of ARBs in combination with CCBs in diabetics are available. The experimental data suggest that combination of a CCB and an AT1 receptor blocker, or a hypothetical dual blocker of AT1 receptors as well as of calcium channels would be an ideal regimen. There is, however, no conclusive clinical evidence to support the combined use of these drugs. This review highlights the available experimental data that support the therapeutic benefits of this combination.

Blockade of the renin-angiotensin-aldosterone system: a key therapeutic strategy to reduce renal and cardiovascular events in patients with diabetes

Diabetes (particularly type 2 diabetes) represents a global health problem of epidemic proportions. Individuals with diabetes are not only more likely to develop hypertension, dyslipidemia, and obesity, but are also at a significantly higher risk for coronary heart disease, peripheral vascular disease, and stroke. Angiotensin II plays a key pathophysiological role in the progression of diabetic renal disease, and blockade of the renin-angiotensin system with angiotensin-converting enzyme inhibitors (ACEi) or angiotensin II antagonists has therefore become an important therapeutic strategy to reduce renal and cardiovascular events in patients with diabetes. Several studies have demonstrated the effects of angiotensin II antagonists on the reduction of albuminuria and the progression of renal disease from microalbuminuria to macroalbuminuria. More importantly, several endpoint trials have shown that the antiproteinuric effects of losartan and irbesartan translate into cardiovascular and renoprotective benefits beyond blood pressure lowering, thereby delaying the need for dialysis or kidney transplantation by several years. These and other studies indicate that angiotensin II antagonists not only improve survival and quality of life of patients with diabetic nephropathy, but also have the potential to reduce the substantial healthcare burden associated with managing these patients. ACEi also appear to exert similar beneficial effects in diabetic patients, but whether clinically significant differences in renoprotection or mortality exist between angiotensin II antagonists and ACEi in patients with type 2 diabetes remains to be fully investigated in appropriate head-to-head studies.

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.

Tyrosine kinase and mitogen-activated protein kinase/extracellularly regulated kinase differentially regulate intracellular calcium concentration responses to angiotensin II/III and bradykinin in rat cortical thick ascending limb

The cortical thick ascending limb (CTAL) coexpresses angiotensin (Ang) II/Ang III receptor type 1A (AT(1A)-R) and bradykinin (BK) receptor type 2 (B2-R). In several cell types, these two receptors share the same signaling pathways, although their physiological functions are often opposite. In CTAL, little is known about the intracellular transduction events leading to the final physiological response induced by these two peptides. We investigated and compared in this segment the action of Ang II/III and BK on intracellular calcium concentration ([Ca2+]i) response and metabolic CO2 production, an index of Na+ transport, by using inhibitors of protein kinase C (bisindolylmaleimide), Src tyrosine kinase (herbimycin A and PP2), and MAPK/ERK (PD98059 and UO126). Ang II/III and BK (10(-7) mol/liter) released Ca2+ from the same intracellular pools but activated different Ca2+ entry pathways. Ang II/III- or BK-induced [Ca2+]i increases were similarly potentiated by bisindolylmaleimide. Herbimycin A and PP2 decreased similarly the [Ca2+]i responses induced by Ang II/III and BK. In contrast, PD98059 and UO126 affected the effects of BK to a larger extent than those of Ang II/III. Especially, the Ca2+ influx induced by BK was more strongly inhibited than that induced by Ang II/III in the presence of both compounds. The Na+ transport was inhibited by BK and stimulated by Ang II/III. The inhibitory action of BK on Na+ transport was blocked by UO126, whereas the stimulatory response of Ang II/III was potentiated by UO126 but blocked by bisindolylmaleimide. These data suggest that the inhibitory effect of BK on Na+ transport seems to be directly mediated by an increase in Ca2+ influx dependent on MAPK/ERK pathway activation. In contrast, the stimulatory effect of Ang II/III on Na+ transport is more complex and involves PKC and MAPK/ERK pathways.