AT2 receptor and vascular smooth muscle cell differentiation in vascular development

Unveiling the intricacies of chronic kidney disease: From ocular manifestations to therapeutic frontiers

BACKGROUND

Shared anatomical, histological and physiological pathways between the kidney and the eye are well documented, demonstrating that ocular manifestations serve as valuable prognostic indicators in chronic kidney disease (CKD), providing insights into disease severity and progression. Through non-invasive imaging modalities such as retinal fundus photography, early retinal microvascular alterations indicative of CKD progression can be detected, enabling timely intervention and risk stratification. However, the conclusions drawn from the review primarily demonstrate a strong or independent association between glaucoma or retinopathy and CKD.

RESULTS AND CONCLUSION

Multiple shared pathophysiological events have been implicated in the pathogenesis in the alterations at eye and kidney including renin-angiotensin-aldosterone system. Patients with CKD are more likely to experience glaucoma, age-related macular degeneration, cataracts, uremic optic neuropathy and retinopathy. To establish the role of ocular manifestations in predicting CKD progression, it is crucial to address the limitations of correlation and explore the underlying causality with further research on common disease pathogenesis. Additionally, specific methods for risk stratification based on retinal changes, the effectiveness of timely interventions, and the development of predictive tools combining ocular and renal data are of utmost importance research topics to enlighten the bidirectional causality.

Ginsenoside Rh1 Inhibits Angiotensin II-Induced Vascular Smooth Muscle Cell Migration and Proliferation through Suppression of the ROS-Mediated ERK1/2/p90RSK/KLF4 Signaling Pathway

Vascular smooth muscle cell (VSMC) proliferation and migration play key roles in the progression of atherosclerosis and restenosis. A variety of ginsenosides exert various cardiovascular benefits. However, whether and how ginsenoside Rh1 (Rh1) inhibits VSMC dysfunction remain unclear. Here, we investigated the inhibitory effects of Rh1 on rat aortic smooth muscle cell (RASMC) migration and proliferation induced by angiotensin II (Ang II) and the underlying mechanisms. Cell proliferation and migration were evaluated using sulforhodamine B and wound-healing assay. The molecular mechanisms were investigated using Western blotting, quantitative reverse-transcription polymerase chain reaction analysis, immunofluorescence staining, and luciferase assay. Reactive oxygen species (ROS) production was measured using dihydroethidium and MitoSOX staining. We found that Rh1 dose-dependently suppressed Ang II-induced cell proliferation and migration. Concomitantly, Ang II increased protein levels of osteopontin, vimentin, MMP2, MMP9, PCNA, and cyclin D1, while these were reduced by Rh1 pretreatment. Notably, Ang II enhanced both the protein expression and promoter activity of KLF4, a key regulator of phenotypic switching, whereas pretreatment with Rh1 reversed these effects. Mechanistically, the effects of Rh1 on VSMC proliferation and migration were found to be associated with inhibition of ERK1/2/p90RSK signaling. Furthermore, the inhibitory effects of Rh1 were accompanied by inhibition of ROS production. In conclusion, Rh1 inhibited the Ang II-induced migration and proliferation of RASMCs by suppressing the ROS-mediated ERK1/2/p90RSK signaling pathway.

Angiotensin-(1-9) prevents vascular remodeling by decreasing vascular smooth muscle cell dedifferentiation through a FoxO1-dependent mechanism

The renin-angiotensin system, one of the main regulators of vascular function, controls vasoconstriction, inflammation and vascular remodeling. Antagonistic actions of the counter-regulatory renin-angiotensin system, which include vasodilation, anti-proliferative, anti-inflammatory and anti-remodeling effects, have also been described. However, little is known about the direct effects of angiotensin-(1-9), a peptide of the counter-regulatory renin-angiotensin system, on vascular smooth muscle cells. Here, we studied the anti-vascular remodeling effects of angiotensin-(1-9), with special focus on the control of vascular smooth muscle cell phenotype. Angiotensin-(1-9) decreased blood pressure and aorta media thickness in spontaneously hypertensive rats. Reduction of media thickness was associated with decreased vascular smooth muscle cell proliferation. In the A7r5 VSMC cell line and in primary cultures of rat aorta smooth muscle cells, angiotensin-(1-9) did not modify basal proliferation. However, angiotensin-(1-9) inhibited proliferation, migration and contractile protein decrease induced by platelet derived growth factor-BB. Moreover, angiotensin-(1-9) reduced Akt and FoxO1 phosphorylation at 30 min, followed by an increase of total FoxO1 protein content. Angiotensin-(1-9) effects were blocked by the AT2R antagonist PD123319, Akt-Myr overexpression and FoxO1 siRNA. These data suggest that angiotensin-(1-9) inhibits vascular smooth muscle cell dedifferentiation by an AT2R/Akt/FoxO1-dependent mechanism.

Ablation of angiotensin type 2 receptor prevents endothelial nitric oxide synthase glutathionylation and nitration in ischaemic abductor muscle of diabetic mice

Peripheral artery disease is a severe complication of diabetes. We have reported that the deletion of angiotensin type 2 receptor in diabetic mice promoted vascular angiogenesis in the ischaemic muscle 4 weeks following ischaemia. However, the angiotensin type 2 receptor deletion beneficial effects occurred 2 weeks post surgery suggesting that angiotensin type 2 receptor may regulate other pro-angiogenic signalling pathways during the early phases of ischaemia. Nondiabetic and diabetic angiotensin type 2 receptor-deficient mice (Agtr2^-/Y) underwent femoral artery ligation after 2 months of diabetes. Blood perfusion was measured every week up to 2 weeks post surgery. Expression of vascular endothelial growth factor, vascular endothelial growth factor receptor and endothelial nitric oxide synthase expression and activity were evaluated. Blood flow reperfusion in the ischaemic muscle of diabetic Agtr2^+/Y mice was recovered at 35% as compared to a 68% recovery in diabetic Agtr2^-/Y mice. The expression of vascular endothelial growth factor and its receptors was diminished in diabetic Agtr2^+/Y mice, an observation not seen in diabetic Agtr2^-/Y mice. Interestingly, Agtr2^-/Y mice were protected from diabetes-induced glutathionylation, nitration and decreased endothelial nitric oxide synthase expression, which correlated with reduced endothelial cell death and enhanced vascular density in diabetic ischaemic muscle. In conclusion, our results suggest that the deletion of angiotensin type 2 receptor promotes blood flow reperfusion in diabetes by favouring endothelial cell survival and function.

Identification of Pre-symptomatic Gene Signatures That Predict Resilience to Cognitive Decline in the Genetically Diverse AD-BXD Model

Across the population, individuals exhibit a wide variation of susceptibility or resilience to developing Alzheimer’s disease (AD). Identifying specific factors that promote resilience would provide insight into disease mechanisms and nominate potential targets for therapeutic intervention. Here, we use transcriptome profiling to identify gene networks present in the pre-symptomatic AD mouse brain relating to neuroinflammation, brain vasculature, extracellular matrix organization, and synaptic signaling that predict cognitive performance at an advanced age. We highlight putative drivers of these observed relationships, including Itgb2, Fcgr2b, Slc6a14, and Gper1, which represent prime targets through which to promote resilience prior to overt symptom onset. In addition, we identify a genomic region on chromosome 2 containing variants that directly modulate resilience network expression. Overall, work here highlights new potential drivers of resilience to AD and contributes significantly to our understanding of early, potentially causal, disease mechanisms.

Age-related differences in the cutaneous vascular response to exogenous angiotensin II

Angiotensin II (ANG II) is locally produced in human skin and contributes to the reflex vasoconstriction (VC) response in aged but not young skin. We hypothesized that the exogenous ANG II-mediated VC response would be greater in older adults and would be affected by inhibition of adrenoreceptor or ANG II type II receptor (AT₂R) pathways. Three microdialysis (MD) fibers were placed in the forearm skin of 11 young (26 ± 3 yr) and 11 older (68 ± 4 yr) individuals for perfusion of 1) Ringer solution (control), 2) adrenoreceptor blockade with yohimbine + propranolol, and 3) AT₂R inhibition with PD-123319. ANG II was then added to the perfusates at eight graded dose concentrations ranging from 10^-10 to 10^-3 M. Laser Doppler flux was measured at each MD site, and cutaneous vascular conductance (CVC) was calculated as CVC =  laser Doppler flux/mean arterial pressure and normalized to baseline CVC values collected before ANG II perfusion (%ΔCVC_baseline). At the control site, older adults (-34 ± 4%ΔCVC_baseline) exhibited a greater peak VC compared with young adults (-22 ± 2%ΔCVC_baseline, P < 0.05), which was attenuated with adrenoreceptor blockade. Young skin exhibited a vasodilation in response to lower ANG II doses that was inhibited with AT₂R inhibition. AT₂R inhibition also increased the VC response to higher ANG II doses such that young skin responded similarly to older skin. These results indicate that ANG II has a greater VC influence in older than young individuals. Furthermore, ANG II may be affecting multiple targets, including adrenergic and AT₂R pathways. NEW & NOTEWORTHY Intradermal perfusion of successive doses of angiotensin II (ANG II) revealed a role for ANG II type II receptors and dose-dependent, ANG II-mediated vasodilation in young but not older adults. In contrast, older adults exhibited greater vasoconstriction for a given dose of ANG II. The increased vasoconstriction in older adults was subsequently blunted with adrenoreceptor blockade, which indicates an interaction between ANG II and adrenergic signaling pathways in the cutaneous microcirculation.

Angiotensin II type 2 receptor (AT2R) in renal and cardiovascular disease

Angiotensin II (Ang II) is well-considered to be the principal effector of the renin-angiotensin system (RAS), which binds with strong affinity to the angiotensin II type 1 (AT1R) and type 2 (AT2R) receptor subtype. However, activation of both receptors is likely to stimulate different signalling mechanisms/pathways and produce distinct biological responses. The haemodynamic and non-haemodynamic effects of Ang II, including its ability to regulate blood pressure, maintain water-electrolyte balance and promote vasoconstriction and cellular growth are well-documented to be mediated primarily by the AT1R. However, its biological and functional effects mediated through the AT2R subtype are still poorly understood. Recent studies have emphasized that activation of the AT2R regulates tissue and organ development and provides in certain context a potential counter-regulatory mechanism against AT1R-mediated actions. Thus, this review will focus on providing insights into the biological role of the AT2R, in particular its actions within the renal and cardiovascular system.

Salt, Angiotensin II, Superoxide, and Endothelial Function

Proper function of the vascular endothelium is essential for cardiovascular health, in large part due to its antiproliferative, antihypertrophic, and anti-inflammatory properties. Crucial to the protective role of the endothelium is the production and liberation of nitric oxide (NO), which not only acts as a potent vasodilator, but also reduces levels of reactive oxygen species, including superoxide anion (O2•-). Superoxide anion is highly injurious to the vasculature because it not only scavenges NO molecules, but has other damaging effects, including direct oxidative disruption of normal signaling mechanisms in the endothelium and vascular smooth muscle cells. The renin-angiotensin system plays a crucial role in the maintenance of normal blood pressure. This function is mediated via the peptide hormone angiotensin II (ANG II), which maintains normal blood volume by regulating Na+ excretion. However, elevation of ANG II above normal levels increases O2•- production, promotes oxidative stress and endothelial dysfunction, and plays a major role in multiple disease conditions. Elevated dietary salt intake also leads to oxidant stress and endothelial dysfunction, but these occur in the face of salt-induced ANG II suppression and reduced levels of circulating ANG II. While the effects of abnormally high levels of ANG II have been extensively studied, far less is known regarding the mechanisms of oxidant stress and endothelial dysfunction occurring in response to chronic exposure to abnormally low levels of ANG II. The current article focuses on the mechanisms and consequences of this less well understood relationship among salt, superoxide, and endothelial function.

International Union of Basic and Clinical Pharmacology. XCIX. Angiotensin Receptors: Interpreters of Pathophysiological Angiotensinergic Stimuli [corrected]

The renin angiotensin system (RAS) produced hormone peptides regulate many vital body functions. Dysfunctional signaling by receptors for RAS peptides leads to pathologic states. Nearly half of humanity today would likely benefit from modern drugs targeting these receptors. The receptors for RAS peptides consist of three G-protein-coupled receptors—the angiotensin II type 1 receptor (AT1 receptor), the angiotensin II type 2 receptor (AT2 receptor), the MAS receptor—and a type II trans-membrane zinc protein—the candidate angiotensin IV receptor (AngIV binding site). The prorenin receptor is a relatively new contender for consideration, but is not included here because the role of prorenin receptor as an independent endocrine mediator is presently unclear. The full spectrum of biologic characteristics of these receptors is still evolving, but there is evidence establishing unique roles of each receptor in cardiovascular, hemodynamic, neurologic, renal, and endothelial functions, as well as in cell proliferation, survival, matrix-cell interaction, and inflammation. Therapeutic agents targeted to these receptors are either in active use in clinical intervention of major common diseases or under evaluation for repurposing in many other disorders. Broad-spectrum influence these receptors produce in complex pathophysiological context in our body highlights their role as precise interpreters of distinctive angiotensinergic peptide cues. This review article summarizes findings published in the last 15 years on the structure, pharmacology, signaling, physiology, and disease states related to angiotensin receptors. We also discuss the challenges the pharmacologist presently faces in formally accepting newer members as established angiotensin receptors and emphasize necessary future developments.

Neuropeptides: metabolism to bioactive fragments and the pharmacology of their receptors

The proteolytic processing of neuropeptides has an important regulatory function and the peptide fragments resulting from the enzymatic degradation often exert essential physiological roles. The proteolytic processing generates, not only biologically inactive fragments, but also bioactive fragments that modulate or even counteract the response of their parent peptides. Frequently, these peptide fragments interact with receptors that are not recognized by the parent peptides. This review discusses tachykinins, opioid peptides, angiotensins, bradykinins, and neuropeptide Y that are present in the central nervous system and their processing to bioactive degradation products. These well-known neuropeptide systems have been selected since they provide illustrative examples that proteolytic degradation of parent peptides can lead to bioactive metabolites with different biological activities as compared to their parent peptides. For example, substance P, dynorphin A, angiotensin I and II, bradykinin, and neuropeptide Y are all degraded to bioactive fragments with pharmacological profiles that differ considerably from those of the parent peptides. The review discusses a selection of the large number of drug-like molecules that act as agonists or antagonists at receptors of neuropeptides. It focuses in particular on the efforts to identify selective drug-like agonists and antagonists mimicking the effects of the endogenous peptide fragments formed. As exemplified in this review, many common neuropeptides are degraded to a variety of smaller fragments but many of the fragments generated have not yet been examined in detail with regard to their potential biological activities. Since these bioactive fragments contain a small number of amino acid residues, they provide an ideal starting point for the development of drug-like substances with ability to mimic the effects of the degradation products. Thus, these substances could provide a rich source of new pharmaceuticals. However, as discussed herein relatively few examples have so far been disclosed of successful attempts to create bioavailable, drug-like agonists or antagonists, starting from the structure of endogenous peptide fragments and applying procedures relying on stepwise manipulations and simplifications of the peptide structures.

Can proteomics yield insight into aging aorta?

The aging aorta exhibits structural and physiological changes that are reflected in the proteome of its component cells types. The advance in proteomic technologies has made it possible to analyze the quantity of proteins associated with the natural history of aortic aging. These alterations reflect the molecular and cellular mechanisms of aging and could provide an opportunity to predict vascular health. This paper focuses on whether discoveries stemming from the application of proteomic approaches of the intact aging aorta or vascular smooth muscle cells can provide useful insights. Although there have been limited studies to date, a number of interesting proteins have been identified that are closely associated with aging in the rat aorta. Such proteins, including milk fat globule-EGF factor 8, matrix metalloproteinase type-2, and vitronectin, could be used as indicators of vascular health, or even explored as therapeutic targets for aging-related vascular diseases.

Effect of angiotensin II type 2 receptor-interacting protein on adipose tissue function via modulation of macrophage polarization

We demonstrated that angiotensin II type 2 (AT₂) receptor-interacting protein (ATIP) 1 ameliorates inflammation-mediated vascular remodeling independent of the AT₂ receptor, leading us to explore the possibility of whether ATIP1 could exert anti-inflammatory effects and play a role in other pathophysiological conditions. We examined the possible anti-inflammatory effects of ATIP1 in adipose tissue associated with amelioration of insulin resistance. In mice fed a high-cholesterol diet, adipose tissue macrophage (ATM) infiltration and M1-to-M2 ratio were decreased in ATIP1 transgenic mice (ATIP1-Tg) compared with wild-type mice (WT), with decreased expression of inflammatory cytokines such as tumor necrosis factor-α and monocyte chemoattractant protein-1 in white adipose tissue (WAT), but an increase in interleukin-10, an anti-inflammatory cytokine. Moreover, 2-[³H]deoxy-d-glucose (2-[³H]DG) uptake was significantly increased in ATIP1-Tg compared with WT. Next, we examined the roles of ATIP1 in BM-derived hematopoietic cells, employing chimeric mice produced by BM transplantation into irradiated type 2 diabetic mice with obesity, KKAy, as recipients. ATM infiltration and M1-to-M2 ratio were decreased in ATIP1 chimera (ATIP1-tg as BM donor), with improvement of insulin-mediated 2-[³H]DG uptake and amelioration of inflammation in WAT. Moreover, serum adiponectin concentration in ATIP1 chimera was significantly higher than that in WT chimera (WT as BM donor) and KKAy chimera (KKAy as BM donor). These results indicate that ATIP1 could exert anti-inflammatory effects in adipose tissue via macrophage polarization associated with improvement of insulin resistance, and ATIP1 in hematopoietic cells may contribute to these beneficial effects on adipose tissue functions in type 2 diabetes.

Impact of taurine supplementation on blood pressure in gestational protein-restricted offspring: Effect on the medial solitary tract nucleus cell numbers, angiotensin receptors, and renal sodium handling

OBJECTIVE

The current study considers changes of the postnatal brainstem cell number and angiotensin receptors by maternal protein restriction (LP) and LP taurine supplementation (LPT), and its impact on arterial hypertension development in adult life.

METHODS AND RESULTS

The brain tissue studies were performed by immunoblotting, immunohistochemistry, and isotropic fractionator analysis. The current study shows that elevated blood pressure associated with decreased fractional urinary sodium excretion (FENa) in adult LP offspring was reverted by diet taurine supplementation. Also, that 12-day-old LP pups present a reduction of 21% of brainstem neuron counts, and, immunohistochemistry demonstrates a decreased expression of type 1 angiotensin II receptors (AT1R) in the entire medial solitary tract nuclei (nTS) of 16-week-old LP rats compared to age-matched NP and LPT offspring. Conversely, the immunostained type 2 AngII (AT2R) receptors in 16-week-old LP nTS were unchanged.

CONCLUSION

The present investigation shows a decreased FENa that occurs despite unchanged creatinine clearance. It is plausible to hypothesize an association of decreased postnatal nTS cell number, AT1R/AT2R ratio and FENa with the higher blood pressure levels found in taurine-deficient progeny (LP) compared with age-matched NP and LPT offspring.

Discovery of inhibitors of insulin-regulated aminopeptidase as cognitive enhancers

The hexapeptide angiotensin IV (Ang IV) is a metabolite of angiotensin II (Ang II) and plays a central role in the brain. It was reported more than two decades ago that intracerebroventricular injection of Ang IV improved memory and learning in the rat. Several hypotheses have been put forward to explain the positive effects of Ang IV and related analogues on cognition. It has been proposed that the insulin-regulated aminopeptidase (IRAP) is the main target of Ang IV. This paper discusses progress in the discovery of inhibitors of IRAP as potential enhancers of cognitive functions. Very potent inhibitors of the protease have been synthesised, but pharmacokinetic issues (including problems associated with crossing the blood-brain barrier) remain to be solved. The paper also briefly presents an overview of the status in the discovery of inhibitors of ACE and renin, and of AT1R antagonists and AT2R agonists, in order to enable other discovery processes within the RAS system to be compared. The paper focuses on the relationship between binding affinities/inhibition capacity and the structures of the ligands that interact with the target proteins.

Angiotensin II type 2 receptor agonists: where should they be applied?

INTRODUCTION

Angiotensin II, the active endproduct of the renin-angiotensin system (RAS), exerts its effects via angiotensin II type 1 and type 2 (AT(1), AT(2)) receptors. AT(1) receptors mediate all well-known effects of angiotensin II, ranging from vasoconstriction to tissue remodeling. Thus, to treat cardiovascular disease, RAS blockade aims at preventing angiotensin II-AT(1) receptor interaction. Yet RAS blockade is often accompanied by rises in angiotensin II, which may exert beneficial effects via AT(2) receptors.

AREAS COVERED

This review summarizes our current knowledge on AT(2) receptors, describing their location, function(s), endogenous agonist(s) and intracellular signaling cascades. It discusses the beneficial effects obtained with C21, a recently developed AT(2) receptor agonist. Important questions that are addressed are do these receptors truly antagonize AT(1) receptor-mediated effects? What about their role in the diseased state and their heterodimerization with other receptors?

EXPERT OPINION

The general view that AT(2) receptors exclusively exert beneficial effects has been challenged, and in pathological models, their function sometimes mimics that of AT(1) receptors, for example, inducing vasoconstriction and cardiac hypertrophy. Yet given its upregulation in various pathological conditions, the AT(2) receptor remains a promising target for treatment, allowing effects beyond blood pressure-lowering, for example, in stroke, aneurysm formation, inflammation and myocardial fibrosis.

Angiotensin II-induced aortic ring constriction is mediated by phosphatidylinositol 3-kinase/L-type calcium channel signaling pathway

Angiotensin II (AngII) is a crucial hormone that affects vasoconstriction and exerts hypertrophic effects on vascular smooth muscle cells. Here, we showed that phosphatidylinositol 3-kinase-dependent calcium mobilization plays pivotal roles in AngII-induced vascular constriction. Stimulation of rat aortic vascular smooth muscle cell (RASMC)-embedded collagen gel with AngII rapidly induced contraction. AngII-induced collagen gel contraction was blocked by pretreatment with a phosphatidylinositol 3-kinase (PI3K) inhibitor (LY294002) whereas ERK inhibitor (PD98059) was not effective. AngII-induced collagen gel contraction was significantly blocked by extracellular calcium depletion by EGTA or by nifedipine which is an L-type calcium channel blocker. In addition, AngII-induced calcium mobilization was also blocked by nifedipine and EGTA, whereas intracellular calcium store-depletion by thapsigargin was not effective. Finally, pretreatment of rat aortic ring with LY294002 and nifedipine significantly reduced AngII-induced constriction. Given these results, we suggest that PI3K-dependent activation of L-type calcium channels might be involved in AngII-induced vascular constriction.

New Alzheimer amyloid beta responsive genes identified in human neuroblastoma cells by hierarchical clustering

Alzheimer's disease (AD) is characterized by neuronal degeneration and cell loss. Aβ₄₂, in contrast to Aβ₄₀, is thought to be the pathogenic form triggering the pathological cascade in AD. In order to unravel overall gene regulation we monitored the transcriptomic responses to increased or decreased Aβ₄₀ and Aβ₄₂ levels, generated and derived from its precursor C99 (C-terminal fragment of APP comprising 99 amino acids) in human neuroblastoma cells. We identified fourteen differentially expressed transcripts by hierarchical clustering and discussed their involvement in AD. These fourteen transcripts were grouped into two main clusters each showing distinct differential expression patterns depending on Aβ₄₀ and Aβ₄₂ levels. Among these transcripts we discovered an unexpected inverse and strong differential expression of neurogenin 2 (NEUROG2) and KIAA0125 in all examined cell clones. C99-overexpression had a similar effect on NEUROG2 and KIAA0125 expression as a decreased Aβ₄₂/Aβ₄₀ ratio. Importantly however, an increased Aβ₄₂/Aβ₄₀ ratio, which is typical of AD, had an inverse expression pattern of NEUROG2 and KIAA0125: An increased Aβ₄₂/Aβ₄₀ ratio up-regulated NEUROG2, but down-regulated KIAA0125, whereas the opposite regulation pattern was observed for a decreased Aβ₄₂/Aβ₄₀ ratio. We discuss the possibilities that the so far uncharacterized KIAA0125 might be a counter player of NEUROG2 and that KIAA0125 could be involved in neurogenesis, due to the involvement of NEUROG2 in developmental neural processes.

Detection of fetal cells in the maternal kidney during gestation in the mouse

It has been reported that fetal cells migrate into maternal blood and organs. Since these fetal chimeric cells could be involved in maternal allogeneic tolerance to the fetus, the fetal chimeric cells might be implicated in maternal-fetal immunology and development of maternal autoimmune diseases. However, the mechanism and role of fetal microchimerism remains unclear. We aimed to describe the mechanism by which fetal cells become associated with maternal organs during pregnancy, using a mouse fetal microchimerism model. Non-obese diabetic/severe combined immunodeficiency (NOD/SCID) female mice, which are useful for tracking the behavior of fetal cells in the maternal body, were mated with transgenic males expressing enhanced green fluorescent protein (GFP), and the presence of GFP-positive cells were examined in peripheral blood and organs of pregnant mothers. By flow cytometry, we showed that 0.95 +/- 0.48% of mononuclear cells detected in the maternal peripheral blood were GFP-positive, and thus of fetal origin, during the first gestational week. This value decreased to 0.10 +/- 0.13% during the third gestational week (p < 0.05). GFP-positive cells were detected in the extraglomerular mesangial region and among the epithelial cells of the proximal renal tubule of the maternal kidney. These GFP-positive cells also expressed angiotensin II receptor subtype 2 (AT2), which is known to participate in regulating organogenesis and vasoreactivity. Fetal cells expressing AT2 may therefore be involved in the regulation of vascular tone in the maternal kidney. These observations suggest that fetal cells could influence maternal renal function through activation of the AT2 signaling.

Development of fetal brain renin-angiotensin system and hypertension programmed in fetal origins

Since the concept of fetal origins of adult diseases was introduced in 1980s, the development of the renin-angiotensin system (RAS) in normal and abnormal patterns has attracted attention. Recent studies have shown the importance of the fetal RAS in both prenatal and postnatal development. This review focuses on the functional development of the fetal brain RAS, and ontogeny of local brain RAS components in utero. The central RAS plays an important role in the control of fetal cardiovascular responses, body fluid balance, and neuroendocrine regulation. Recent progress has been made in demonstrating that altered fetal RAS development as a consequence of environmental insults may impact on "programming" of hypertension later in life. Given that the central RAS is of equal importance to the peripheral RAS in cardiovascular regulation, studies on the fetal brain RAS development in normal and abnormal patterns could shed light on "programming" mechanisms of adult cardiovascular diseases in fetal origins.

AT2 receptors: functional relevance in cardiovascular disease

The renin angiotensin system (RAS) is intricately involved in normal cardiovascular homeostasis. Excessive stimulation by the octapeptide angiotensin II contributes to a range of cardiovascular pathologies and diseases via angiotensin type 1 receptor (AT1R) activation. On the other hand, tElsevier Inc.he angiotensin type 2 receptor (AT2R) is thought to counter-regulate AT1R function. In this review, we describe the enhanced expression and function of AT2R in various cardiovascular disease settings. In addition, we illustrate that the RAS consists of a family of angiotensin peptides that exert cardiovascular effects that are often distinct from those of Ang II. During cardiovascular disease, there is likely to be an increased functional importance of AT2R, stimulated by Ang II, or even shorter angiotensin peptide fragments, to limit AT1R-mediated overactivity and cardiovascular pathologies.

The renin-angiotensin system in conscious newborn sheep: metabolic clearance rate and activity

The role of the renin-angiotensin system (RAS) in regulating newborn mean arterial blood pressure (MAP) and tissue blood flow remains unclear. Although postnatal MAP increases, vascular responsiveness to infused angiotensin II (ANG II) is unchanged, possibly reflecting increased metabolic clearance rate of ANG II (MCR(ANG II)). To address this, we examined MAP, heart rate, plasma ANG II and renin activity (PRA), and MCR(ANG II) in conscious postnatal sheep (n = 9, 5-35 d old) before and during continuous systemic ANG II infusions to measure MCR (ANG II). Postnatal MAP increased (p < 0.02), whereas plasma ANG II decreased from 942 +/- 230 (SEM) to 471 +/- 152 and 240 +/- 70 pg/mL at <10 d, 10-20 d, and 21-35 d postnatally (p = 0.05), respectively. Despite high plasma ANG II, PRA remained elevated, averaging 6.70 +/- 1.1 ng/mL.h throughout the postnatal period, but decreased 35% (p = 0.01) during ANG II infusions. MCR(ANG II) decreased approximately sixfold after birth and averaged 115 mL/min.kg during the first month. Circulating ANG II is markedly increased after birth, reflecting placental removal, high fetal MCR(ANG II), and enhanced RAS activity. Although circulating ANG II decreases as MAP increases, MCR(ANG II) is unchanged, suggesting decreased ANG II production. Persistent vascular smooth muscle (VSM) AT2 receptor subtype (AT2R) expression after birth may modify the hypertensive effects of ANG II postnatally.

Renal Angiotensin receptor type 1 and 2 upregulation in intrauterine growth restriction of newborn piglets

Epidemiological and experimental studies suggest that intrauterine growth restriction (IUGR) is associated with abnormalities in kidney development which is thought to be linked with alterations causing adult cardiovascular diseases. The renin-angiotensin system (RAS) plays an important role in the development of renal vascular and tubular structures, and is known to be altered by experimentally induced IUGR. These experimental models of IGUR have been criticized because they may have a more severe impact on intrauterine development than that which is normally encountered in humans. Therefore, we asked whether naturally occurring small-for-gestational-age newborn piglets exhibit features of altered RAS activity. We investigated the regional renal expression of angiotensin II type 1 (AT1) and AT2 receptors in normal-weight and IUGR piglets. The AT1 receptor mRNA expression was markedly enhanced in IUGR piglets, in the renal cortex by 64% and in the renal medulla by 52% (p < 0.05, compared with normal littermates). In contrast, mRNA expression for the AT2 receptor was similar in both the normal-weight and IUGR piglets. A significantly higher AT1 receptor protein expression was found in the IUGR piglets (p < 0.05) in the glomeruli, in the proximal and distal tubules, as well as in the collecting ducts by immunohistochemistry. Furthermore, AT2 receptor protein expression was significantly higher in the IUGR piglets (p < 0.05) in the subcapsular nephrogenic zone and in the distal tubules and collecting ducts. Thus, IUGR is accompanied by an upregulation of angiotensin II receptor expression in the kidneys of newborn piglets. This may indicate an alteration of the RAS in newborns suffering from naturally occurring IUGR.

Physiology of Local Renin-Angiotensin Systems

Since the first identification of renin by Tigerstedt and Bergmann in 1898, the renin-angiotensin system (RAS) has been extensively studied. The current view of the system is characterized by an increased complexity, as evidenced by the discovery of new functional components and pathways of the RAS. In recent years, the pathophysiological implications of the system have been the main focus of attention, and inhibitors of the RAS such as angiotensin-converting enzyme (ACE) inhibitors and angiotensin (ANG) II receptor blockers have become important clinical tools in the treatment of cardiovascular and renal diseases such as hypertension, heart failure, and diabetic nephropathy. Nevertheless, the tissue RAS also plays an important role in mediating diverse physiological functions. These focus not only on the classical actions of ANG on the cardiovascular system, namely, the maintenance of cardiovascular homeostasis, but also on other functions. Recently, the research efforts studying these noncardiovascular effects of the RAS have intensified, and a large body of data are now available to support the existence of numerous organ-based RAS exerting diverse physiological effects. ANG II has direct effects at the cellular level and can influence, for example, cell growth and differentiation, but also may play a role as a mediator of apoptosis. These universal paracrine and autocrine actions may be important in many organ systems and can mediate important physiological stimuli. Transgenic overexpression and knock-out strategies of RAS genes in animals have also shown a central functional role of the RAS in prenatal development. Taken together, these findings may become increasingly important in the study of organ physiology but also for a fresh look at the implications of these findings for organ pathophysiology.

Mass-dependent signaling between G protein coupled receptors

The present study provides evidence that G protein coupled receptor (GPCR) signaling pathways participate in an interactive signaling network governed by the principles of mass action. Using an inducible thromboxane A2 receptor (TPR)/platelet activating factor receptor (PAFR) co-expressing cell model, TPR or PAFR expression was independently up-regulated. Immunostaining and radioligand binding experiments demonstrated that this receptor up-regulation resulted in increased GPCR:G protein mass ratios. This increase in mass ratio impacted both TPR and PAFR ligand affinity. Specifically, up-regulating TPR expression not only decreased TPR ligand affinity, but also decreased the ligand affinity of PAFRs. A similar effect on ligand affinities was observed when PAFRs were up-regulated. In addition, increasing the GPCR:G protein mass ratio for TPRs led to desensitization of the calcium mobilization response to PAFR activation, and increasing PAFR mass desensitized the TPR-mediated calcium response. Finally, it was observed that an increased TPR:G protein mass ratio was associated with a shift in the TPR signaling response, and revealed an additional TPR signaling pathway through G(S). Collectively, these results describe a novel mechanism, i.e., mass-dependent GPCR signaling, by which cells can modulate their GPCR signaling pathways and signaling priorities.

Addition of an angiotensin receptor blocker to full-dose ACE-inhibition: controversial or common sense?

Both angiotensin-converting enzyme (ACE)-inhibitors and angiotensin receptor blockers (ARBs) interfere with the activity of the renin-angiotensin system (RAS) in a different way. Theoretically, one might expect beneficial effects when they are used in combination, as a more complete suppression of the RAS can be achieved. But can this additional effect still be seen in patients on full-dose ACE-inhibition? Several controlled trials demonstrated that combination therapy can have additional benefits in hypertensive patients, in chronic heart failure patients, and in both diabetic and non-diabetic nephropathy patients. However, the clinical benefit was not always as pronounced as expected and not every patient will benefit from dual blockade of the RAS. There is some evidence of a less pronounced effect of combination therapy when a full dose of the ACE-inhibitor is given. However, it is well known that ACE-inhibitors cannot completely suppress the formation of angiotensin II, in particular, when the RAS is activated. Indeed, clinical trials indicated that add-on therapy with an ARB was especially of use when the RAS remained activated despite full-dose ACE-inhibitor treatment. In summary, combination of a full-dose ACE-inhibitor and an ARB can be a rational choice in selected patients.

Angiotensin II type 2 receptor-mediated vasodilation. Focus on bradykinin, NO and endothelium-derived hyperpolarizing factor(s)

Angiotensin (Ang) II type 1 (AT(1)) receptors account for the majority of the cardiovascular effects Ang II, including vasoconstriction and growth stimulation. Recent evidence, mainly obtained in animals, suggests that Ang II type 2 (AT(2)) receptors counteract some or all of these effects. This review summarizes the current knowledge on the vasodilator effects induced by AT(2) receptors in humans and animals, focussing not only on the mediators of this effect, but also on the modulatory role of age, gender, and endothelial function. It is concluded that AT(2) receptor-mediated vasodilation most likely depends on the bradykinin-bradykinin type 2 (B(2)) receptor-NO-cGMP pathway, although evidence for a direct link between AT(2) and B(2) receptors is currently lacking. If indeed B(2) receptors are involved, this would imply that, in addition to NO, also the wide range of non-NO 'endothelium-derived hyperpolarizing factors' (EDHFs) that is released following B(2) receptor activation (e.g., K(+), cytochrome P450 products from arachidonic acid, H(2)O(2) and S-nitrososothiols), could contribute to AT(2) receptor-induced vasodilation.

Temporal and spatial characterization of cellular constituents during neointimal hyperplasia after vascular injury: Potential contribution of bone-marrow-derived progenitors to arterial remodeling

BACKGROUND

Exuberant smooth muscle cells (SMCs) hyperplasia is the major cause of postangioplasty restenosis. We suggested that circulating smooth muscle progenitor cells might contribute to lesion formation after vascular injury.

METHODS

We extensively investigated the cellular constituents during neointimal formation after mechanical vascular injury.

RESULTS

A large wire was inserted into the mouse femoral artery, causing complete endothelial denudation and marked enlargement of the lumen with massive apoptosis of medial SMCs. At 2 h, the injured artery remained dilated with a thin media containing very few cells. A scanning electron microscopy showed fibrin and platelet deposition at the luminal side. One week after the injury, CD45-positive hematopoietic cells accumulated at the luminal side. Those CD45-positive cells gradually disappeared, whereas neointimal hyperplasia was formed with alpha-smooth muscle actin (SMA) positive cells. Bone marrow cells and peripheral mononuclear cells differentiated into alpha-SMA-positive cells in the presence of PDGF and basic FGF. Moreover, in bone marrow chimeric mice, bone-marrow-derived cells substantially contributed to neointimal hyperplasia after wire injury.

CONCLUSION

These results suggest that early accumulation of hematopoietic cells may play a role in the pathogenesis of SMC hyperplasia under certain circumstances.

Vessel-specific regulation of angiotensin II receptor subtypes during ovine development

Umbilical and systemic responses to angiotensin II differ in term fetal sheep, and peripheral vascular responses are attenuated or absent before and after birth. These observations may reflect developmental differences in angiotensin II receptor (AT) subtypes in vascular smooth muscle (VSM). Studies of AT subtype ontogeny and regulation are generally limited to the aorta, which may not be extrapolated to other arteries, and neither is completely described during ovine development. We therefore characterized VSM AT subtype expression and regulation throughout an extended period of development in umbilical and carotid artery and aorta from fetal (85-146 d gestation), postnatal (5-23 d), and adult sheep, measuring AT(1) and AT(2) mRNA and protein and performing immunohistochemistry. Parallel increases in umbilical AT(1) mRNA and protein began early in gestation and continued to term, and although AT(2) mRNA was unchanged, protein levels decreased >90% at term. Fetal carotid AT(1) mRNA was <40% of adult values and unchanged before birth; however, AT(1) protein rose >2-fold at term. After birth, AT(1) mRNA increased to 85% of adult values and was associated with another 2-fold rise in protein. In contrast, carotid AT(2) mRNA and protein fell in parallel throughout development and were barely detectable in the newborn and the adult. Immunostaining was consistent with observations in both arteries. A third pattern occurred in aortic VSM. The ontogeny of AT subtype expression and regulation is vessel specific, with changes in umbilical VSM beginning very early in development. Although the mechanisms that regulate mRNA and protein expression are unclear, these changes parallel differences in VSM maturation and function and local blood flow.

The angiotensin II type 1 receptor blocker valsartan attenuates graft vasculopathy

OBJECTIVE

Transplant arteriosclerosis remains the major cause of graft failure after cardiac transplantation. Here, we investigated the effects of the angiotensin II type 1 receptor blocker valsartan on the development of transplant arteriosclerosis in a murine model of cardiac transplantation.

METHODS

Hearts from DBA/2 (H-2(d)) mice were heterotopically transplanted into B10.D2 (H-2(d)) mice. Recipients were treated with oral administration of valsartan (10 mg/kg/day) or vehicle.

RESULTS

Morphometrical analysis of the cardiac allografts harvested at 30 days revealed that valsartan significantly reduced the development of coronary atherosclerosis (intima/media ratio: 0.39 +/- 0.05 vs. 0.66 +/- 0.08, P < 0.01). At two weeks after transplantation, there was no significant difference between the two groups in expression of adhesion molecules and cytokines. Valsartan significantly reduced the number of peripheral mononuclear cells that differentiated into smooth muscle-like cells in the presence of basic fibroblast growth factor and platelet-derived growth factor BB (18.0 +/- 1.5 vs. 30.3 +/- 4.4 cells/HPF, P = 0.01).

CONCLUSIONS

These results suggest that angiotensin II plays a role in the pathogenesis of transplant arteriosclerosis and that blockade of angiotensin II type 1 receptor might be effective as a prophylactic therapy for transplant arteriosclerosis along with conventional immunosuppressive drugs.

ANG II type 2 receptor regulates smooth muscle growth and force generation in late fetal mouse development

Although evidence from culture studies implicates the angiotensin II (ANG II) type 2 receptor (AT(2)R) in the regulation of growth and differentiation of arterial smooth muscle (SM) cells (SMC), the lack of its expression in adult arteries has precluded direct investigation of its role in vivo. The goal of the present study was to determine the role of AT(2)R in the control of fetal SMC growth, contractility, and differentiation during vascular development. Determination of isometric tension in fetal aortas showed potentiated ANG II-induced contraction by treatment with the selective AT(2)R antagonist PD-123319, demonstrating the presence of functional AT(2)Rs that mediate reduced force development in vascular SMC. In direct contrast to numerous cell culture studies, proliferation indexes were decreased rather than increased in aortic SMC of fetal homozygous AT(2)R knockout compared with wild-type or heterozygous knockout mice. Experiments using SMC tissues from heterozygous female AT(2)R knockout mice, which are naturally occurring chimeras for AT(2)R expression, showed that AT(2)R mRNA expression was exactly 50% of that of wild type. This indicated that loss of AT(2)R expression did not confer a selective advantage or disadvantage for SMC lineage determination and expansion. Real time RT-PCR analyses showed no significant difference in expression of SM-alpha-actin, SM myosin heavy chain, and myocardin in various SM tissues from all three genotypes, suggesting that knockout of AT(2)R had no effect on subsequent SMC differentiation. Taken together, results indicate that functional AT(2)R are expressed in fetal aorta and mediate reduced force development but do not significantly contribute to regulation of SMC differentiation.

Cyclic AMP-independent involvement of Rap1/B-Raf in the angiotensin II AT2 receptor signaling pathway in NG108-15 cells

The angiotensin II (Ang II) type 2 (AT(2)) receptor is an atypical seven-transmembrane domain receptor. Controversy surrounding this receptor concerns both the nature of the second messengers produced as well as its associated signaling mechanisms. Using the neuronal cell line NG108-15, we have reported previously that activation of the AT(2) receptor induced morphological differentiation in a p21(ras)-independent, but p42/p44(mapk)-dependent mechanism. The activation of p42/p44(mapk) was delayed, sustained, and had been shown to be essential for neurite elongation. In the present report, we demonstrate that activation of the AT(2) receptor rapidly, but transiently, activated the Rap1/B-Raf complex of signaling proteins. In RapN17- and Rap1GAP-transfected cells, the effects induced by Ang II were abolished, demonstrating that activation of these proteins was responsible for the observed p42/p44(mapk) phosphorylation and for morphological differentiation. To assess whether cAMP was involved in the activation of Rap1/B-Raf and neuronal differentiation induced by Ang II, NG108-15 cells were treated with stimulators or inhibitors of the cAMP pathway. We found that dibutyryl cAMP and forskolin did not stimulate Rap1 or p42/p44(mapk) activity. Furthermore, adding H-89, an inhibitor of protein kinase A, or Rp-8-Br-cAMP-S, an inactive cAMP analog, failed to impair p42/p44(mapk) activity and neurite outgrowth induced by Ang II. The present observations clearly indicate that cAMP, a well known stimulus of neuronal differentiation, did not participate in the AT(2) receptor signaling pathways in the NG108-15 cells. Therefore, the AT(2) receptor of Ang II activates the signaling modules of Rap1/B-Raf and p42/p44(mapk) via a cAMP-independent pathway to induce morphological differentiation of NG108-15 cells.

ANG II AT(1) and AT(2) receptors in developing kidney of normal microswine

To identify an appropriate model of human renin-angiotensin system (RAS) involvement in fetal origins of adult disease, we quantitated renal ANG II AT(1) and AT(2) receptors (AT1R and AT2R, respectively) in fetal (90-day gestation, n = 14), neonatal (3-wk, n = 5), and adult (6-mo, n = 8) microswine by autoradiography ((125)I-labeled [Sar(1)Ile(8)]ANG II+cold CGP-42112 for AT1R, (125)I-CGP-42112 for AT2R) and by whole kidney radioligand binding. The developmental pattern of renal AT1R in microswine, like many species, exhibited a 10-fold increase postnatally (P < 0.001), with maximal postnatal density in glomeruli and lower density AT1R in extraglomerular cortical and outer medullary sites. With aging, postnatal AT1R glomerular profiles increased in size (P < 0.001) and fractional area occupied (P < 0.04), with no change in the number per unit area. Cortical levels of AT2R by autoradiography fell with age from congruent with 5,000 fmol/g in fetal kidneys to congruent with 60 and 20% of fetal levels in neonatal and adult cortex, respectively (P < 0.0001). The pattern of AT2R binding in postnatal pig kidney mimicked that described in human and simian, but not rodent, species: dense AT2R confined to discrete cortical structures, including pre- and juxtaglomerular, but not intraglomerular, vasculature. Our results provide a quantitative assessment of ANG II receptors in developing pig kidney and document the concordance of pigs and primates in developmental regulation of renal AT1R and AT2R.

Microvascular angiogenesis and the renin-angiotensin system

The renin-angiotensin system is one of the major regulatory mechanisms essential for maintaining cardiovascular homeostasis. Angiotensin II is a multifunctional hormone that plays a key role in regulating this system. The importance of the renin-angiotensin system in controlling sodium homeostasis and vascular resistance is well established, however, in the past decade, much attention has been focused on the importance of angiotensin II as a regulator of microvessel density, acting through the AT1 and AT2 receptors. In this review, we discuss the connections between the renin-angiotensin system and other growth factor pathways known to be involved in pathologic and physiologic angiogenesis and rarefaction.

Angiotensin receptors: signaling, vascular pathophysiology, and interactions with ceramide

Angiotensin II (ANG II) is a pleiotropic vasoactive peptide that binds to two distinct receptors: the ANG II type 1 (AT(1)) and type 2 (AT(2)) receptors. Activation of the renin-angiotensin system (RAS) results in vascular hypertrophy, vasoconstriction, salt and water retention, and hypertension. These effects are mediated predominantly by AT(1) receptors. Paradoxically, other ANG II-mediated effects, including cell death, vasodilation, and natriuresis, are mediated by AT(2) receptor activation. Our understanding of ANG II signaling mechanisms remains incomplete. AT(1) receptor activation triggers a variety of intracellular systems, including tyrosine kinase-induced protein phosphorylation, production of arachidonic acid metabolites, alteration of reactive oxidant species activities, and fluxes in intracellular Ca(2+) concentrations. AT(2) receptor activation leads to stimulation of bradykinin, nitric oxide production, and prostaglandin metabolism, which are, in large part, opposite to the effects of the AT(1) receptor. The signaling pathways of ANG II receptor activation are a focus of intense investigative effort. We critically appraise the literature on the signaling mechanisms whereby AT(1) and AT(2) receptors elicit their respective actions. We also consider the recently reported interaction between ANG II and ceramide, a lipid second messenger that mediates cytokine receptor activation. Finally, we discuss the potential physiological cross talk that may be operative between the angiotensin receptor subtypes in relation to health and cardiovascular disease. This may be clinically relevant, inasmuch as inhibitors of the RAS are increasingly used in treatment of hypertension and coronary heart disease, where activation of the RAS is recognized.

Angiotensin II modulates calponin gene expression in rat vascular smooth muscle cells in vivo

OBJECTIVES

It has been shown that angiotensin II (Ang II) induces the expression of calponin, a 34 kD actin-binding protein, in vascular smooth muscle cells in vitro. The aim of this study was to investigate whether Ang II can modulate calponin gene expression in rat aorta in vivo.

DESIGN

Aortic calponin gene expression was studied after chronic exogenous Ang II administration and in Goldblatt hypertension.

METHODS

To investigate the effect of Ang II administration, Sprague Dawley rats were treated for 6 days with a continuous infusion of Ang II (200 ng/kg per min) or saline by osmotic minipumps. The effect of endogenous Ang II on aortic calponin mRNA expression was studied in Goldblatt hypertensive rats with (2K1C model), or without (1K1C model) activation of the renin-angiotensin system. In particular, calponin gene expression in 2K1C rats was studied both at 1 week (2K1C-HR, high renin) and 4 weeks after the onset of hypertension, when plasma renin activity (PRA) was returned to normal values (2K1C-NR, normal renin). Systolic blood pressure (SBP) was measured twice a week. At the end of the experimental period, PRA was measured by radioimmunoassay, and aortic calponin gene expression was measured by Northern hybridization.

RESULTS

SBP was significantly higher (P < 0.01), whereas PRA was suppressed (P < 0.01), in Ang II versus saline-treated rats. Northern hybridization showed that the aortic calponin gene expression significantly increased (2.5-fold) in Ang II-treated rats (P = 0.01). In Goldblatt hypertensive rats, SBP was significantly higher in 2K1C-HR (P < 0.01), 2K1C-NR (P < 0.01) and 1K1C (P < 0.01) rats compared with the corresponding sham-treated rats. Activation of the renin-angiotensin system was present only in 2K1C-HR rats (P < 0.01), and Northern analysis showed that aortic calponin mRNA expression was significantly increased (2.2-fold) in this group of rats only (P < 0.01).

CONCLUSIONS

Our data demonstrate that both exogenous and endogenous Ang II increase calponin gene expression in aortic smooth muscle cells, independently of the hemodynamic effect of Ang II.

G-protein-coupled-receptor activation of the smooth muscle calponin gene

A hallmark of cultured smooth muscle cells (SMCs) is the rapid down-regulation of several lineage-restricted genes that define their in vivo differentiated phenotype. Identifying factors that maintain an SMC differentiated phenotype has important implications in understanding the molecular underpinnings governing SMC differentiation and their subversion to an altered phenotype in various disease settings. Here, we show that several G-protein coupled receptors [alpha-thrombin, lysophosphatidic acid and angiotensin II (AII)] increase the expression of smooth muscle calponin (SM-Calp) in rat and human SMC. The increase in SM-Calp protein appears to be selective for G-protein-coupled receptors as epidermal growth factor was without effect. Studies using AII showed a 30-fold increase in SM-Calp protein, which was dose- and time-dependent and mediated by the angiotensin receptor-1 (AT1 receptor). The increase in SM-Calp protein with AII was attributable to transcriptional activation of SM-Calp based on increases in steady-state SM-Calp mRNA, increases in SM-Calp promoter activity and complete abrogation of protein induction with actinomycin D. To examine the potential role of extracellular signal-regulated kinase (Erk1/2), protein kinase B, p38 mitogen-activated protein kinase and protein kinase C in AII-induced SM-Calp, inhibitors to each of the signalling pathways were used. None of these signalling molecules appears to be crucial for AII-induced SM-Calp expression, although Erk1/2 may be partially involved. These results identify SM-Calp as a target of AII-mediated signalling, and suggest that the SMC response to AII may incorporate a novel activity of SM-Calp.

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

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

Angiotensin II type 2 receptors: signalling and pathophysiological role

The signalling mechanisms and biological significance of the angiotensin II type 2 receptor have long been unknown. In recent years, studies, first in cell culture models but now increasingly also in vivo, have shed some light on the molecular events occurring after a stimulation of the receptor with its ligand as well as on its physiological effects and its significance for pathophysiological processes. There is increasing evidence that the angiotensin II type 2 receptor is involved in different pathophysiological processes, such as myocardial infarction, heart and kidney failure, and stroke.

Transgenic mouse models of angiotensin receptor subtype function in the cardiovascular system

Angiotensin II mediates is biological actions via different subtypes of G protein-coupled receptors, termed AT(1) and AT(2) receptors. In rodents, two AT(1) receptors have been identified, AT(1A) and AT(1B), whereas in humans a single AT(1) receptor exists. Recently, a number of transgenic animal models have been generated which overexpress or lack functional angiotensin II receptor subtypes. This review focuses on the physiological significance of angiotensin II receptor subtype diversity in the cardiovascular system. In the mouse, AT(1A) receptors are the major regulators of cardiovascular homeostasis by determining vascular tone and natriuresis. In addition, AT(1A) receptors mediate growth-stimulating signals in vascular and cardiac myocytes. AT(1B) receptors participate in blood pressure regulation, and their functions become apparent when the AT(1A) receptor gene is deleted. Deletion of the mouse gene for the AT(2) receptor subtype led to hypersensitivity to pressor and antinatriuretic effects of angiotensin II in vivo, suggesting that the AT(2) receptor subtype counteracts some of the biological effects of AT(1) receptor signalling.