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

Effect of novel GPCR ligands on blood pressure and vascular homeostasis

Maintenance of normal blood pressure under conditions of drug treatment is a measure of system-wide neuro-hormonal controls and electrolyte/fluid volume homeostasis in the body. With increased interest in designing and evaluating novel drugs that may functionally select or allosterically modulate specific GPCR signaling pathways, techniques that allow us to measure acute and long-term effects on blood pressure are very important. Therefore, this chapter describes techniques to measure acute and long-term impact of novel GPCR ligands on blood pressure regulation. We will use the angiotensin type 1 receptor, a powerful blood pressure regulating GPCR, in detailing the methodology. Normal blood pressure maintenance depends upon dynamic modulation of angiotensin type 1 receptor activity by the hormone peptide angiotensin II. Chronic activation of angiotensin type 1 receptor creates hypertension and related cardiovascular disease states which are treated with angiotensin type 1 receptor blockers (ARBs). Thus, a prototype for evaluation of blood pressure control under experimental evaluation of novel drugs.

Immunomodulatory properties of captopril, an ACE inhibitor, on LPS-induced lung inflammation and fibrosis as well as oxidative stress

BACKGROUND

The role of angiotensin converting enzyme inhibitors on the inflammation process has been demonstrated previously. In the present study, the effects of captopril on lung injury induced by lipopolysaccharide (LPS) were investigated.

METHODS

Control, LPS, 12.5, 25 and 50 mg/kg captopril-treated before LPS administration and captopril 50 mg/kg before saline administration groups of rats were studied. Total and percentage of differential WBC, the levels of MDA, total thiol groups, the activities of SOD and CAT, the levels of IFN-γ, PGE2, TGF-β1 and IL-4 in the BALF were evaluated.

RESULTS

MDA concentration in LPS groups treated with all captopril concentrations, total WBC in LPS + Cap50, percent of neutrophils in LPS + Cap25 and LPS + Cap50, levels of IFN-γ, PGE2, TGF-β1 in LPS + Cap50 and IFN-γ/IL-4 ratio in LPS + Cap25 and LPS + Cap50 were significantly decreased but total thiol groups and activity of SOD in LPS + Cap25 and LPS + Cap50, percent of lymphocyte, CAT activity and concentration of IL-4 only in LPS + Cap50 group were increased in comparison to the LPS group (p < 0.05 to p < 0.001).

CONCLUSION

Captopril dose dependently improved oxidant-antioxidant biomarkers, the imbalance between pro-inflammatory and anti-inflammatory cytokines and showed specific immunomodulatory effect on Th1/Th2 balance in the BALF of lung injury induced by LPS.

The ACE2/Angiotensin-(1-7)/MAS Axis of the Renin-Angiotensin System: Focus on Angiotensin-(1-7)

The renin-angiotensin system (RAS) is a key player in the control of the cardiovascular system and hydroelectrolyte balance, with an influence on organs and functions throughout the body. The classical view of this system saw it as a sequence of many enzymatic steps that culminate in the production of a single biologically active metabolite, the octapeptide angiotensin (ANG) II, by the angiotensin converting enzyme (ACE). The past two decades have revealed new functions for some of the intermediate products, beyond their roles as substrates along the classical route. They may be processed in alternative ways by enzymes such as the ACE homolog ACE2. One effect is to establish a second axis through ACE2/ANG-(1-7)/MAS, whose end point is the metabolite ANG-(1-7). ACE2 and other enzymes can form ANG-(1-7) directly or indirectly from either the decapeptide ANG I or from ANG II. In many cases, this second axis appears to counteract or modulate the effects of the classical axis. ANG-(1-7) itself acts on the receptor MAS to influence a range of mechanisms in the heart, kidney, brain, and other tissues. This review highlights the current knowledge about the roles of ANG-(1-7) in physiology and disease, with particular emphasis on the brain.

Differential effects of angiotensin II type I receptor blockers on reducing intraocular pressure and TGFβ signaling in the mouse retina

PURPOSE

Angiotensin II type 1 receptor blockers (ARBs) have been investigated for their neuroprotective and intraocular pressure (IOP) lowering effects in treating glaucoma, but the reports have been inconsistent possibly because different compounds and models have been used. Here we selected three ARBs for head-to-head comparisons of their effects on IOP and transforming growth factor β (TGFβ) signaling, which is believed to play an important role in glaucoma pathogenesis.

METHODS

Three ARBs (losartan, irbesartan or telmisartan) or vehicle controls were administered via chow to C57BL/6J mice for up to 7 days. Drug concentrations in the eye, brain, and plasma were evaluated by liquid chromatography mass spectrometry. Cohorts of mice were randomly assigned to different treatments. IOP and blood pressure were measured before and after ARB treatment. Effects of ARBs on TGFβ signaling in the retina were evaluated by phosphorylated Smad2 (pSmad2) immunohistochemistry.

RESULTS

Physiologically relevant concentrations of losartan, irbesartan and telmisartan were detected in eye, brain and plasma after drug administration (n = 11 mice/treatment). Blood pressure was significantly reduced by all ARBs compared to vehicle-fed controls (all p-values < 0.001, n = 8-15 mice/treatment). Compared to vehicle control, IOP was significantly reduced by irbesartan (p = 0.030) and telmisartan (p = 0.019), but not by losartan (n = 14-17 mice/treatment). Constitutive pSmad2 fluorescence observed in retinal ganglion cells was significantly reduced by telmisartan (p = 0.034), but not by losartan or irbesartan (n = 3-4 mice/treatment).

CONCLUSIONS

Administration via chow is an effective delivery method for ARBs, as evidenced by lowered blood pressure. ARBs vary in their abilities to lower IOP or reduce TGFβ signaling. Considering the significant roles of IOP and TGFβ in glaucoma pathogenesis, specific ARBs with dual effects, such as telmisartan, may be more effective than other ARBs for treating glaucoma.

Chronic administration of the angiotensin type 2 receptor agonist C21 improves insulin sensitivity in C57BL/6 mice

The renin-angiotensin system modulates insulin action. Angiotensin type 1 receptor exerts a deleterious effect, whereas the angiotensin type 2 receptor (AT2R) appears to have beneficial effects providing protection against insulin resistance and type 2 diabetes. To further explore the role of the AT2R on insulin action and glucose homeostasis, in this study we administered C57Bl/6 mice with the synthetic agonist of the AT2R C21 for 12 weeks (1 mg/kg per day; ip). Vehicle-treated animals were used as control. Metabolic parameters, glucose, and insulin tolerance, in vivo insulin signaling in main insulin-target tissues as well as adipose tissue levels of adiponectin, and TNF-α were assessed. C21-treated animals displayed decreased glycemia together with unaltered insulinemia, increased insulin sensitivity, and increased glucose tolerance compared to nontreated controls. This was accompanied by a significant decrease in adipocytes size in epididymal adipose tissue and significant increases in both adiponectin and UCP-1 expression in this tissue. C21-treated mice showed an increase in both basal Akt and ERK1/2 phosphorylation levels in the liver, and increased insulin-stimulated Akt activation in adipose tissue. This positive modulation of insulin action induced by C21 appeared not to involve the insulin receptor. In C21-treated mice, adipose tissue and skeletal muscle became unresponsive to insulin in terms of ERK1/2 phosphorylation levels. Present data show that chronic pharmacological activation of AT2R with C21 increases insulin sensitivity in mice and indicate that the AT2R has a physiological role in the conservation of insulin action.

Crystal structure of the human angiotensin II type 2 receptor bound to an angiotensin II analog

Angiotensin II (AngII) plays a central role in regulating human blood pressure, which is mainly mediated by interactions between AngII and the G-protein-coupled receptors (GPCRs) AngII type 1 receptor (AT₁R) and AngII type 2 receptor (AT₂R). We have solved the crystal structure of human AT₂R binding the peptide ligand [Sar¹, Ile⁸]AngII and its specific antibody at 3.2-Å resolution. [Sar¹, Ile⁸]AngII interacts with both the 'core' binding domain, where the small-molecule ligands of AT₁R and AT₂R bind, and the 'extended' binding domain, which is equivalent to the allosteric modulator binding site of muscarinic acetylcholine receptor. We generated an antibody fragment to stabilize the extended binding domain that functions as a positive allosteric modulator. We also identified a signature positively charged cluster, which is conserved among peptide-binding receptors, to locate C termini at the bottom of the binding pocket. The reported results should help with designing ligands for angiotensin receptors and possibly to other peptide GPCRs.

Neuroprotection via AT2 receptor agonists in ischemic stroke

Stroke is a devastating disease that afflicts millions of people each year worldwide. Ischemic stroke, which accounts for ~88% of cases, occurs when blood supply to the brain is decreased, often because of thromboembolism or atherosclerotic occlusion. This deprives the brain of oxygen and nutrients, causing immediate, irreversible necrosis within the core of the ischemic area, but more delayed and potentially reversible neuronal damage in the surrounding brain tissue, the penumbra. The only currently approved therapies for ischemic stroke, the thrombolytic agent recombinant tissue plasminogen activator (rtPA) and the endovascular clot retrieval/destruction processes, are aimed at restoring blood flow to the infarcted area, but are only available for a minority of patients and are not able in most cases to completely restore neurological deficits. Consequently, there remains a need for agents that will protect neurones against death following ischemic stroke. Here, we evaluate angiotensin II (Ang II) type 2 (AT2) receptor agonists as a possible therapeutic target for this disease. We first provide an overview of stroke epidemiology, pathophysiology, and currently approved therapies. We next review the large amount of preclinical evidence, accumulated over the past decade and a half, which indicates that AT2 receptor agonists exert significant neuroprotective effects in various animal models, and discuss the potential mechanisms involved. Finally, after discussing the challenges of delivering blood–brain barrier (BBB) impermeable AT2 receptor agonists to the infarcted areas of the brain, we summarize the evidence for and against the development of these agents as a promising therapeutic strategy for ischemic stroke.

Angiotensin II Promotes KV7.4 Channels Degradation Through Reduced Interaction With HSP90 (Heat Shock Protein 90)

Voltage-gated K_v7.4 channels have been implicated in vascular smooth muscle cells' activity because they modulate basal arterial contractility, mediate responses to endogenous vasorelaxants, and are downregulated in several arterial beds in different models of hypertension. Angiotensin II (Ang II) is a key player in hypertension that affects the expression of several classes of ion channels. In this study, we evaluated the effects of Ang II on the expression and function of vascular K_v7.4. Western blot and quantitative polymerase chain reaction revealed that in whole rat mesenteric artery, Ang II incubation for 1 to 7 hours decreased K_v7.4 protein expression without reducing transcript levels. Moreover, Ang II decreased XE991 (K_v7)-sensitive currents and attenuated membrane potential hyperpolarization and relaxation induced by the K_v7 activator ML213. Ang II also reduced K_v7.4 staining at the plasma membrane of vascular smooth muscle cells. Proteasome inhibition with MG132 prevented Ang II-induced decrease of K_v7.4 levels and counteracted the functional impairment of ML213-induced relaxation in myography experiments. Proximity ligation assays showed that Ang II impaired the interaction of K_v7.4 with the molecular chaperone HSP90 (heat shock protein 90), enhanced the interaction of K_v7.4 with the E3 ubiquitin ligase CHIP (C terminus of Hsp70-interacting protein), and increased K_v7.4 ubiquitination. Similar alterations were found in mesenteric vascular smooth muscle cells isolated from Ang II-infused mice. The effect of Ang II was emulated by 17-AAG (17-demethoxy-17-(2-propenylamino) geldanamycin) that inhibits HSP90 interactions with client proteins. These results show that Ang II downregulates K_v7.4 by altering protein stability through a decrease of its interaction with HSP90. This leads to the recruitment of CHIP and K_v7.4 ubiquitination and degradation via the proteasome.

Novel mechanisms of G-protein-coupled receptors functions: AT1 angiotensin receptor acts as a signaling hub and focal point of receptor cross-talk

AT₁ angiotensin receptor (AT₁R), a prototypical G protein-coupled receptor (GPCR), is the main receptor, which mediates the effects of the renin-angiotensin system (RAS). AT₁R plays a crucial role in the regulation of blood pressure and salt-water homeostasis, and in the development of pathological conditions, such as hypertension, heart failure, cardiovascular remodeling, renal fibrosis, inflammation, and metabolic disorders. Stimulation of AT₁R leads to pleiotropic signal transduction pathways generating arrays of complex cellular responses. Growing amount of evidence shows that AT₁R is a versatile GPCR, which has multiple unique faces with distinct conformations and signaling properties providing new opportunities for functionally selective pharmacological targeting of the receptor. Biased ligands of AT₁R have been developed to selectively activate the β-arrestin pathway, which may have therapeutic benefits compared to the conventional angiotensin converting enzyme inhibitors and angiotensin receptor blockers. In this review, we provide a summary about the most recent findings and novel aspects of the AT₁R function, signaling, regulation, dimerization or oligomerization and its cross-talk with other receptors, including epidermal growth factor (EGF) receptor, adrenergic receptors and CB₁ cannabinoid receptor. Better understanding of the mechanisms and structural aspects of AT₁R activation and cross-talk can lead to the development of novel type of drugs for the treatment of cardiovascular and other diseases.

Chemical Diversity in the G Protein-Coupled Receptor Superfamily

G protein-coupled receptors (GPCRs) are the largest family of cell signaling transmembrane proteins that can be modulated by a plethora of chemical compounds. Systematic cheminformatics analysis of structurally and pharmacologically characterized GPCR ligands shows that cocrystallized GPCR ligands cover a significant part of chemical ligand space, despite their limited number. Many GPCR ligands and substructures interact with multiple receptors, providing a basis for polypharmacological ligand design. Experimentally determined GPCR structures represent a variety of binding sites and receptor-ligand interactions that can be translated to chemically similar ligands for which structural data are lacking. This integration of structural, pharmacological, and chemical information on GPCR-ligand interactions enables the extension of the structural GPCR-ligand interactome and the structure-based design of novel modulators of GPCR function.

Role of Lipotoxicity and Contribution of the Renin-Angiotensin System in the Development of Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) is a common and significant condition associated with hyperandrogenism, infertility, low quality of life, and metabolic comorbidities. One possible explanation of PCOS development is cellular dysfunction induced by nonesterified fatty acids (NEFAs), that is, lipotoxicity, which could explain both the hyperandrogenemia and insulin resistance that characterize women with PCOS. The literature suggests that androgen biosynthesis may be induced by overexposure of androgen-secreting tissues to NEFA and/or defective NEFA metabolism, leading to lipotoxic effects. Indeed, lipotoxicity could trigger androgenic hyperresponsiveness to insulin, LH, and ACTH. In most PCOS women, lipotoxicity also causes insulin resistance, inducing compensatory hyperinsulinemia, and may thus further increase hyperandrogenemia. Many approaches aimed at insulin sensitization also reduce lipotoxicity and have been shown to treat PCOS hyperandrogenemia. Furthermore, our group and others found that angiotensin II type 2 receptor (AT2R) activation is able to improve lipotoxicity. We provided evidence, using C21/M24, that AT2R activation improves adipocytes' size and insulin sensitivity in an insulin-resistant rat model, as well as androgen levels in a PCOS obese rat model. Taken together, these findings point toward the important role of lipotoxicity in PCOS development and of the RAS system as a new target for the treatment of PCOS.

Angiotensin II AT2 Receptors Contribute to Regulate the Sympathoadrenal and Hormonal Reaction to Stress Stimuli

Angiotensin II, through AT1 receptor stimulation, mediates multiple cardiovascular, metabolic, and behavioral functions including the response to stressors. Conversely, the function of Angiotensin II AT2 receptors has not been totally clarified. In adult rodents, AT2 receptor distribution is very limited but it is particularly high in the adrenal medulla. Recent results strongly indicate that AT2 receptors contribute to the regulation of the response to stress stimuli. This occurs in association with AT1 receptors, both receptor types reciprocally influencing their expression and therefore their function. AT2 receptors appear to influence the response to many types of stressors and in all components of the hypothalamic-pituitary-adrenal axis. The molecular mechanisms involved in AT2 receptor activation, the complex interactions with AT1 receptors, and additional factors participating in the control of AT2 receptor regulation and activity in response to stressors are only partially understood. Further research is necessary to close this knowledge gap and to clarify whether AT2 receptor activation may carry the potential of a major translational advance.

Protective Angiotensin Type 2 Receptors in the Brain and Hypertension

PURPOSE OF REVIEW

The goal of this review is to assess the evidence that activation of angiotensin type 2 receptors (AT2R) in the brain can lower blood pressure and possibly constitute an endogenous anti-hypertensive mechanism.

RECENT FINDINGS

Recent studies that detail the location of AT2R in the brain, particularly within or near cardiovascular control centers, mesh well with findings from pharmacological and gene transfer studies which demonstrate that activation of central AT2R can influence cardiovascular regulation. Collectively, these studies indicate that selective activation of brain AT2R causes moderate decreases in blood pressure in normal animals and more profound anti-hypertensive effects, along with restoration of baroreflex function, in rodent models of neurogenic hypertension. These findings have opened the door to studies that can (i) assess the role of specific AT2R neuron populations in depressing blood pressure, (ii) determine the relevance of such mechanisms, and (iii) investigate interactions between AT2R and depressor angiotensin-(1-7)/Mas mechanisms in the brain.

Connective tissue growth factor dependent collagen gene expression induced by MAS agonist AR234960 in human cardiac fibroblasts

Perspectives on whether the functions of MAS, a G protein-coupled receptor, are beneficial or deleterious in the heart remain controversial. MAS gene knockout reduces coronary vasodilatation leading to ischemic injury. G protein signaling activated by MAS has been implicated in progression of adaptive cardiac hypertrophy to heart failure and fibrosis. In the present study, we observed increased expression of MAS, connective tissue growth factor (CTGF) and collagen genes in failing (HF) human heart samples when compared to non-failing (NF). Expression levels of MAS are correlated with CTGF in HF and NF leading to our hypothesis that MAS controls CTGF production and the ensuing expression of collagen genes. In support of this hypothesis we show that the non-peptide MAS agonist AR234960 increases both mRNA and protein levels of CTGF via ERK1/2 signaling in HEK293-MAS cells and adult human cardiac fibroblasts. MAS-mediated CTGF expression can be specifically blocked by MAS inverse agonist AR244555 and also by MEK1 inhibition. Expression of CTGF gene was essential for MAS-mediated up-regulation of different collagen subtype genes in HEK293-MAS cells and human cardiac fibroblasts. Knockdown of CTGF by RNAi disrupted collagen gene regulation by the MAS-agonist. Our data indicate that CTGF mediates the profibrotic effects of MAS in cardiac fibroblasts. Blocking MAS-CTGF-collagen pathway should be considered for pharmacological intervention for HF.

Divergent Spatiotemporal Interaction of Angiotensin Receptor Blocking Drugs with Angiotensin Type 1 Receptor

Crystal structures of the human angiotensin II type 1 receptor (AT₁R) complex with the antihypertensive agent ZD7155 (PDB id: 4YAY ) and the blood pressure medication Benicar (PDB id: 4ZUD ) showed that binding poses of both antagonists are similar. This finding implies that clinically used angiotensin receptor blocking (ARB) drugs may interact in a similar fashion. However, clinically observed differences in pharmacological and therapeutic efficacies of ARBs lead to the question of whether the dynamic interactions of AT₁R with ARBs vary. To address this, we performed induced-fit docking (IFD) of eight clinically used ARBs to AT₁R followed by 200 ns molecular dynamic (MD) simulation. The experimental K_i values for ARBs correlated remarkably well with calculated free energy with R² = 0.95 and 0.70 for AT₁R-ARB models generated respectively by IFD and MD simulation. The eight ARB-AT₁R complexes share a common set of binding residues. In addition, MD simulation results validated by mutagenesis data discovered distinctive spatiotemporal interactions that display unique bonding between an individual ARB and AT₁R. These findings provide a reasonably broader picture reconciling the structure-based observations with clinical studies reporting efficacy variations for ARBs. The unique differences unraveled for ARBs in this study will be useful for structure-based design of the next generation of more potent and selective ARBs.

Nitric oxide bioavailability dysfunction involves in atherosclerosis

The pathological characteristics of atherosclerosis (AS) include lipid accumulation, fibrosis formation and atherosclerotic plaque produced in artery intima, which leads to vascular sclerosis, lumen stenosis and irritates the ischemic changes of corresponding organs. Endothelial dysfunction was closely associated with AS. Nitric oxide (NO) is a multifunctional signaling molecule involved in the maintenance of metabolic and cardiovascular homeostasis. NO is also a potent endogenous vasodilator and enters for the key processes that suppresses the formation vascular lesion even AS. NO bioavailability indicates the production and utilization of endothelial NO in organisms, its decrease is related to oxidative stress, lipid infiltration, the expressions of some inflammatory factors and the alteration of vascular tone, which plays an important role in endothelial dysfunction. The enhancement of arginase activity and the increase in asymmetric dimethylarginine and hyperhomocysteinemia levels all contribute to AS by intervening NO bioavailability in human beings. Diabetes mellitus, obesity, chronic kidney disease and smoking, etc., also participate in AS by influencing NO bioavailability and NO level. Here, we reviewed the relationship between NO bioavailability and AS according the newest literatures.

Early intervention by Captopril does not improve wound healing of partial thickness burn wounds in a rat model

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Inhibition of the Renin Angiotensin System does not influence the inflammatory reaction in the burn wounds.

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Inhibition of the Renin Angiotensin System early during burn wound healing does not improve the process.

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Inhibition of the Renin Angiotensin System early during burn wound healing does not reduce scar formation.

The Renin Angiotensin System is involved in fibrotic pathologies in various organs such as heart, kidney and liver. Inhibition of this system by angiotensin converting enzyme antagonists, such as Captopril, has been shown beneficial effects on these pathologies. Captopril reduced the inflammatory reaction but also directly influenced the fibrotic process.

Prolonged and excessive inflammatory response is a major cause of hypertrophic scar formation in burns. We therefore evaluated the effect of Captopril on the healing of partial thickness burn wounds in a rat model.

Partial thickness contact burns were inflicted on the dorsum of the rats. The rats received either systemic or local treatment with Captopril. The inflammatory reaction and wound healing (scar) parameters were investigated and compared to control animals.

In this study we could not detect positive effects of either administration route with Captopril on the inflammatory reaction, nor on wound healing parameters. The local treatment showed reduced wound closure in comparison to the systemic treatment and the control group.

Early Captopril treatment of burn wounds did not show the beneficial effects that were reported for fibrotic disorders in other tissues. To influence the fibrotic response Captopril treatment at a later time point, e.g. during the remodeling phase, might still have beneficial effects.

Ang-(1-7) is an endogenous β-arrestin-biased agonist of the AT1 receptor with protective action in cardiac hypertrophy

The renin-angiotensin system (RAS) plays a key role in the control of vasoconstriction as well as sodium and fluid retention mediated mainly by angiotensin (Ang) II acting at the AT₁ receptor (AT1R). Ang-(1-7) is another RAS peptide, identified as the endogenous ligand of the Mas receptor and known to counterbalance many of the deleterious effects of AngII. AT1R signaling triggered by β-arrestin-biased agonists has been associated to cardioprotection. Because position 8 in AngII is important for G protein activation, we hypothesized that Ang-(1-7) could be an endogenous β-arrestin-biased agonist of the AT1R. Here we show that Ang-(1-7) binds to the AT1R without activating Gq, but triggering β-arrestins 1 and 2 recruitment and activation. Using an in vivo model of cardiac hypertrophy, we show that Ang-(1-7) significantly attenuates heart hypertrophy by reducing both heart weight and ventricular wall thickness and the increased end-diastolic pressure. Whereas neither the single blockade of AT₁ or Mas receptors with their respective antagonists prevented the cardioprotective action of Ang1-7, combination of the two antagonists partially impaired the effect of Ang-(1-7). Taken together, these data indicate that Ang-(1-7) mediates at least part of its cardioprotective effects by acting as an endogenous β-arrestin-biased agonist at the AT1R.

Anti-fibrotic Potential of AT2 Receptor Agonists

There are a number of therapeutic targets to treat organ fibrosis that are under investigation in preclinical models. There is increasing evidence that stimulation of the angiotensin II type 2 receptor (AT₂R) is a novel anti-fibrotic strategy and we have reviewed the published in vivo preclinical data relating to the effects of compound 21 (C21), which is the only nonpeptide AT₂R agonist that is currently available for use in chronic preclinical studies. In particular, the differential influence of AT₂R on extracellular matrix status in various preclinical fibrotic models is discussed. Collectively, these studies demonstrate that pharmacological AT₂R stimulation using C21 decreases organ fibrosis, which has been most studied in the setting of cardiovascular and renal disease. In addition, AT₂R-mediated anti-inflammatory effects may contribute to the beneficial AT₂R-mediated anti-fibrotic effects seen in preclinical models.

Validation of commercial Mas receptor antibodies for utilization in Western Blotting, immunofluorescence and immunohistochemistry studies

Mas receptor (MasR) is a G protein-coupled receptor proposed as a candidate for mediating the angiotensin (Ang)-converting enzyme 2-Ang (1-7) protective axis of renin-angiotensin system. Because the role of this receptor is not definitively clarified, determination of MasR tissue distribution and expression levels constitutes a critical knowledge to fully understanding its function. Commercially available antibodies have been widely employed for MasR protein localization and quantification, but they have not been adequately validated. In this study, we carried on an exhaustive evaluation of four commercial MasR antibodies, following previously established criteria. Western Blotting (WB) and immunohistochemistry studies starting from hearts and kidneys from wild type (WT) mice revealed that antibodies raised against different MasR domains yielded different patterns of reactivity. Furthermore, staining patterns appeared identical in samples from MasR knockout (MasR-KO) mice. We verified by polymerase chain reaction analysis that the MasR-KO mice used were truly deficient in this receptor as MAS transcripts were undetectable in either heart or kidney from this animal model. In addition, we evaluated the ability of the antibodies to detect the human c-myc-tagged MasR overexpressed in human embryonic kidney cells. Three antibodies were capable of detecting the MasR either by WB or by immunofluorescence, reproducing the patterns obtained with an anti c-myc antibody. In conclusion, although three of the selected antibodies were able to detect MasR protein at high expression levels observed in a transfected cell line, they failed to detect this receptor in mice tissues at physiological expression levels. As a consequence, validated antibodies that can recognize and detect the MasR at physiological levels are still lacking.

GNAQ TT(-695/-694)GC Polymorphism Is Associated with Increased Gq Expression, Vascular Reactivity, and Myocardial Injury after Coronary Artery Bypass Surgery

BACKGROUND

Angiotensin II receptor type 1-mediated activation of the α-subunit of the heterotrimeric Gq protein evokes increased vasoconstriction and may promote hypertrophy-induced myocardial damage. The authors recently identified a TT(-695/-694)GC polymorphism in the human Gq promoter, the GC allele being associated with an increased prevalence of cardiac hypertrophy. In this article, the authors tested whether the TT(-695/-694)GC polymorphism is associated with differences in (1) myocardial Gq protein expression, (2) vascular reactivity, and (3) myocardial damage after coronary artery bypass grafting.

METHODS

Gq protein expression was measured in right atrial muscle from 55 patients undergoing coronary artery bypass grafting as were skin perfusion changes (n = 18; laser Doppler imaging), saphenous vein ring vascular reactivity (n = 50, organ bath) in response to angiotensin II, and myocardial damage (227 patients undergoing coronary artery bypass grafting), as assessed by postoperative cardiac troponin I concentration.

RESULTS

Myocardial Gq expression was greater in GC/GC genotypes (GC/GC vs.

TT/TT

1.27-fold change; P = 0.006). Skin perfusion after intradermal angiotensin II injection decreased only in GC/GC genotypes (P = 0.0002). Saphenous vein rings exposed to increasing angiotensin II concentrations showed an almost doubled maximum contraction in GC/GC compared with individuals with the TT/TT genotype (P = 0.022). In patients undergoing coronary artery bypass grafting, baseline cardiac ejection fraction was different (GC/GC: 55 ± 13%; GC/TT: 54 ± 14%; TT/TT: 48 ± 15%; P = 0.037) and postoperative peak cardiac troponin I was greater in patients with the GC/GC (11.5 ± 13.8 ng/ml) than in patients with the GC/TT (9.2 ± 9.2 ng/ml) or patients with the TT/TT genotype (6.6 ± 4.8 ng/ml, P = 0.015).

CONCLUSIONS

The GC/GC genotype of the TT(-695/-694)GC polymorphism is associated with increased Gq protein expression, augmented angiotensin II receptor type 1-related vasoconstriction, and increased myocardial injury after coronary artery bypass grafting, highlighting the impact of Gq genotype variation.

The renin-angiotensin system: a possible new target for depression

Depression remains a debilitating condition with an uncertain aetiology. Recently, attention has been given to the renin-angiotensin system. In the central nervous system, angiotensin II may be important in multiple pathways related to neurodevelopment and regulation of the stress response. Studies of drugs targeting the renin-angiotensin system have yielded promising results. Here, we review the potential beneficial effects of angiotensin blockers in depression and their mechanisms of action. Drugs blocking the angiotensin system have efficacy in several animal models of depression. While no randomised clinical trials were found, case reports and observational studies showed that angiotensin-converting enzyme inhibitors or angiotensin receptor blockers had positive effects on depression, whereas other antihypertensive agents did not. Drugs targeting the renin-angiotensin system act on inflammatory pathways implicated in depression. Both preclinical and clinical data suggest that these drugs possess antidepressant properties. In light of these results, angiotensin system-blocking agents offer new horizons in mood disorder treatment.

Is Entresto good for the brain?

The main stay pharmacotherapy for heart failure (HF) is targeted towards rennin-angiotensin-aldosterone (RAAS) and neprilysin pathways (NP). Both therapeutic strategies decreases morbidity and mortality but also carry considerable adverse effects. This review of the literature highlights the new generation of HF drug, sacubitril-valsartan (SV), trade name Entresto (researched as LCZ696, Novartis) which simultaneously blocks RAAS and NP. This dual action of angiotensin receptors blocker and neprilysin inhibitor (NPi) has improved HF prognosis and it is an evolution in the management of HF. Although the initial follow-up of patients treated with SV has yielded promising results, there are concerns regarding potential side effects especially an increase in the risk of Alzheimer’s disease (AD) and young onset of AD. NPi interferes with the breakdown and clearing of beta-amyloid peptides, the plaques seen in AD, raising concern for AD in SV patients. On the other hand, hypertension and cardiovascular diseases are established risk factors for AD which can be decreased by SV therapy. It is therefore essential that SV treated patients are followed up over an extended period of time to detect any adverse cognitive changes.

Structure and Function of Peptide-Binding G Protein-Coupled Receptors

G protein-coupled receptors (GPCRs) are the largest family of cell surface receptors and are important human drug targets. Of the 826 human GPCRs, 118 of them recognize endogenous peptide or protein ligands, and 30 of the 118 are targeted by approved drug molecules, including the very high-profile class B glucagon-like peptide 1 receptor. In this review, we analyze the 21 experimentally determined three-dimensional structures of the known peptide-binding GPCRs in relation to the endogenous peptides and drug molecules that modulate their cell signaling processes. Our integrated analyses reveal that half of the marketed drugs and most of the drugs in clinical trials that interact with peptide GPCRs are small molecules with a wide range of binding modes distinct from those of large peptide ligands. As we continue to collect additional data on these receptors from orthogonal approaches, including nuclear magnetic resonance and electron microscopy, we are beginning to understand how these receptors interact with their ligands at the molecular level and how improving the pharmacology of GPCR signal transduction requires us to study these receptors using multiple biophysical techniques.

AT2 receptors in cardiovascular and renal diseases

The renin-angiotensin system (RAS) plays an important role in the initiation and progression of cardiovascular and renal diseases. These actions mediated by AT1 receptor (AT1R) are well established and led to development of selective AT1R blockers (ARBs). In contrast, there is scientific evidence that AT2 receptor (AT2R) mediates effects different from and often opposing those of the AT1R. Meagrely expressed in healthy tissue the AT2R is upregulated in injuries providing an endogenous protection to inflammatory, oxidative and apoptotic processes. Interestingly the beneficial effects mediated by AT2R can be further enhanced by pharmacological intervention using the recently developed AT2R agonists. This review article summarizes our current knowledge about regulation, signalling and effects mediated by AT2R in health and disease, with emphasis on cardiac and renal systems. At the end a novel concept of natural protective systems will be introduced and discussed as an attractive target in drug development.

Brain renin-angiotensin system in the pathophysiology of cardiovascular diseases

Cardiovascular diseases (CVD) are among the main causes of death globally and in this context hypertension represents one of the key risk factors for developing a CVD. It is well established that the peripheral renin-angiotensin system (RAS) plays an important role in regulating blood pressure (BP). All components of the classic RAS can also be found in the brain but, in contrast to the peripheral RAS, how the endogenous RAS is involved in modulating cardiovascular effects in the brain is not fully understood yet. It is a complex system that may work differently in diverse areas of the brain and is linked to the peripheral system by the circumventricular organs (CVO), which do not have a blood brain barrier (BBB). In this review, we focus on the brain angiotensin peptides, their interactions with each other, and the consequences in the central nervous system (CNS) concerning cardiovascular control. Additionally, we present potential drug targets in the brain RAS for the treatment of hypertension.

Genetic Interference With Endothelial PPAR-γ (Peroxisome Proliferator-Activated Receptor-γ) Augments Effects of Angiotensin II While Impairing Responses to Angiotensin 1-7

Pharmacological activation of PPAR-γ (peroxisome proliferator-activated receptor-γ) protects the vasculature. Much less is known on the cell-specific impact of PPAR-γ when driven by endogenous ligands. Recently, we found that endothelial PPAR-γ protects against angiotensin II-induced endothelial dysfunction. Here, we explored that concept further examining whether effects were sex dependent along with underlying mechanisms. We studied mice expressing a human dominant-negative mutation in PPAR-γ driven by the endothelial-specific vascular cadherin promoter (E-V290M), using nontransgenic littermates as controls. Acetylcholine (an endothelium-dependent agonist) produced similar relaxation of carotid arteries from nontransgenic and E-V290M mice. Incubation of isolated arteries with angiotensin II (1 nmol/L) overnight had no effect in nontransgenic, but reduced responses to acetylcholine by about 50% in male and female E-V290M mice (P<0.05). Endothelial function in E-V290M mice was restored to normal by inhibitors of superoxide (tempol), NADPH oxidase (VAS-2870), Rho kinase (Y-27632), ROCK2 (SLX-2119), NF-κB (nuclear factor-kappa B essential modulator-binding domain peptide), or interleukin-6 (neutralizing antibody). In addition, we hypothesized that PPAR-γ may influence the angiotensin 1-7 arm of the renin-angiotensin system. In the basilar artery, dilation to angiotensin 1-7 was selectively reduced in E-V290M mice by >50% (P<0.05), an effect reversed by Y-27632. Thus, effects of angiotensin II are augmented by interference with endothelial PPAR-γ through sex-independent mechanisms, involving oxidant-inflammatory signaling and ROCK2 (Rho kinase). The study also provides the first evidence that endothelial PPAR-γ interacts with angiotensin 1-7 responses. These critical roles for endothelial PPAR-γ have implications for pathophysiology and therapeutic approaches for vascular disease.

Current topics in angiotensin II type 1 receptor research: Focus on inverse agonism, receptor dimerization and biased agonism

Although the octapeptide hormone angiotensin II (Ang II) regulates cardiovascular and renal homeostasis through the Ang II type 1 receptor (AT1R), overstimulation of AT1R causes various human diseases, such as hypertension and cardiac hypertrophy. Therefore, AT1R blockers (ARBs) have been widely used as therapeutic drugs for these diseases. Recent basic research and clinical studies have resulted in the discovery of interesting phenomena associated with AT1R function. For example, ligand-independent activation of AT1R by mechanical stress and agonistic autoantibodies, as well as via receptor mutations, has been shown to decrease the inverse agonistic efficacy of ARBs, though the molecular mechanisms of such phenomena had remained elusive until recently. Furthermore, although AT1R is believed to exist as a monomer, recent studies have demonstrated that AT1R can homodimerize and heterodimerize with other G-protein coupled receptors (GPCR), altering the receptor signaling properties. Therefore, formation of both AT1R homodimers and AT1R-GPCR heterodimer may be involved in the pathogenesis of human disease states, such as atherosclerosis and preeclampsia. Finally, biased AT1R ligands that can preferentially activate the β-arrestin-mediated signaling pathway have been discovered. Such β-arrestin-biased AT1R ligands may be better therapeutic drugs for cardiovascular diseases. New findings on AT1R described herein could provide a conceptual framework for application of ARBs in the treatment of diseases, as well as for novel drug development. Since AT1R is an extensively studied member of the GPCR superfamily encoded in the human genome, this review is relevant for understanding the functions of other members of this superfamily.

The vasoprotective axes of the renin-angiotensin system: Physiological relevance and therapeutic implications in cardiovascular, hypertensive and kidney diseases

The renin-angiotensin system (RAS) is undisputedly one of the most prominent endocrine (tissue-to-tissue), paracrine (cell-to-cell) and intracrine (intracellular/nuclear) vasoactive systems in the physiological regulation of neural, cardiovascular, blood pressure, and kidney function. The importance of the RAS in the development and pathogenesis of cardiovascular, hypertensive and kidney diseases has now been firmly established in clinical trials and practice using renin inhibitors, angiotensin-converting enzyme (ACE) inhibitors, type 1 (AT₁) angiotensin II (ANG II) receptor blockers (ARBs), or aldosterone receptor antagonists as major therapeutic drugs. The major mechanisms of actions for these RAS inhibitors or receptor blockers are mediated primarily by blocking the detrimental effects of the classic angiotensinogen/renin/ACE/ANG II/AT₁/aldosterone axis. However, the RAS has expanded from this classic axis to include several other complex biochemical and physiological axes, which are derived from the metabolism of this classic axis. Currently, at least five axes of the RAS have been described, with each having its key substrate, enzyme, effector peptide, receptor, and/or downstream signaling pathways. These include the classic angiotensinogen/renin/ACE/ANG II/AT₁ receptor, the ANG II/APA/ANG III/AT₂/NO/cGMP, the ANG I/ANG II/ACE2/ANG (1-7)/Mas receptor, the prorenin/renin/prorenin receptor (PRR or Atp6ap2)/MAP kinases ERK1/2/V-ATPase, and the ANG III/APN/ANG IV/IRAP/AT₄ receptor axes. Since the roles and therapeutic implications of the classic angiotensinogen/renin/ACE/ANG II/AT₁ receptor axis have been extensively reviewed, this article will focus primarily on reviewing the roles and therapeutic implications of the vasoprotective axes of the RAS in cardiovascular, hypertensive and kidney diseases.

Alamandine reduces leptin expression through the c-Src/p38 MAP kinase pathway in adipose tissue

Objective

Obesity is associated with an increased risk of diabetes mellitus, hypertension, and renal dysfunction. Angiotensin 1–7 and alamandine are heptameric renin angiotensin system peptide hormones. Further, alamandine levels increase with renal dysfunction. In the cardiovascular system, angiotensin 1–7 and alamandine produce similar improvements and counterbalance angiotensin II in regulating vascular function. We aimed to determine whether the effect of alamandine on leptin expression and secretion in adipocytes was similar to that of angiotensin 1–7.

Approach and results

We studied isolated peri-renal visceral adipose tissue and peri-renal isolated visceral adipocytes from male Wistar rats. Angiotensin II from 0.01 to 10nM had no effect on leptin expression. Angiotensin 1–7 (1 nM) increased leptin secretion and expression, whereas alamandine (1 nM) decreased leptin secretion and expression in adipose tissue and isolated adipocytes and reduced blood leptin levels in vivo. These effects were mediated by Gq, c-Src, p38 mitogen-activated protein, and IκB activation. Additionally, alamandine induced nitric oxide expression via inducible nitric oxidase synthase and plasminogen activator inhibitor 1 expression in adipose tissue and isolated adipocytes.

Conclusions

Angiotensin 1–7 and alamandine produced opposing effects on leptin expression and secretion in adipose tissue. This result suggests that the action of Mas (angiotensin 1–7 receptor) and Mas-related G-protein coupled receptor D in adipocytes exhibited opposing actions similar to angiotensin II type 1 and type 2 receptors.

AT1 receptor signaling pathways in the cardiovascular system

The importance of the renin angiotensin aldosterone system in cardiovascular physiology and pathophysiology has been well described whereas the detailed molecular mechanisms remain elusive. The angiotensin II type 1 receptor (AT1 receptor) is one of the key players in the renin angiotensin aldosterone system. The AT1 receptor promotes various intracellular signaling pathways resulting in hypertension, endothelial dysfunction, vascular remodeling and end organ damage. Accumulating evidence shows the complex picture of AT1 receptor-mediated signaling; AT1 receptor-mediated heterotrimeric G protein-dependent signaling, transactivation of growth factor receptors, NADPH oxidase and ROS signaling, G protein-independent signaling, including the β-arrestin signals and interaction with several AT1 receptor interacting proteins. In addition, there is functional cross-talk between the AT1 receptor signaling pathway and other signaling pathways. In this review, we will summarize an up to date overview of essential AT1 receptor signaling events and their functional significances in the cardiovascular system.

Chemical Composition and Hypotensive Effect of Campomanesia xanthocarpa

Campomanesia xanthocarpa is known in Brazil as Guabiroba and is popularly used for various diseases, such as inflammatory, renal, and digestive diseases and dyslipidemia. The aim of the study was to analyze the chemical composition and investigate the effects of aqueous extract of C. xanthocarpa on the blood pressure of normotensive rats, analyzing the possible action mechanism using experimental and in silico procedures. The extract was evaluated for total phenolic compounds and total flavonoid content. The chemical components were determined by HPLC analyses. Systolic and diastolic blood pressure and heart rate were measured with extract and drugs administration. The leaves of C. xanthocarpa presented the relevant content of phenolics and flavonoids, and we suggested the presence of chlorogenic acid, gallic acid, quercetin, and theobromine. The acute administration of aqueous extract of C. xanthocarpa has a dose-dependent hypotensive effect in normotensive rats, suggesting that the action mechanism may be mediated through the renin-angiotensin system by AT1 receptor blockade and sympathetic autonomic response. Docking studies showed models that indicated an interaction between chlorogenic acid and quercetin with the AT1 receptor (AT1R) active site. The findings of these docking studies suggest the potential of C. xanthocarpa constituents for use as preventive agents for blood pressure.

Significance of angiotensin 1-7 coupling with MAS1 receptor and other GPCRs to the renin-angiotensin system: IUPHAR Review 22

Angiotensins are a group of hormonal peptides and include angiotensin II and angiotensin 1-7 produced by the renin angiotensin system. The biology, pharmacology and biochemistry of the receptors for angiotensins were extensively reviewed recently. In the review, the receptor nomenclature committee was not emphatic on designating MAS1 as the angiotensin 1-7 receptor on the basis of lack of classical G protein signalling and desensitization in response to angiotensin 1-7, as well as a lack of consensus on confirmatory ligand pharmacological analyses. A review of recent publications (2013-2016) on the rapidly progressing research on angiotensin 1-7 revealed that MAS1 and two additional receptors can function as 'angiotensin 1-7 receptors', and this deserves further consideration. In this review we have summarized the information on angiotensin 1-7 receptors and their crosstalk with classical angiotensin II receptors in the context of the functions of the renin angiotensin system. It was concluded that the receptors for angiotensin II and angiotensin 1-7 make up a sophisticated cross-regulated signalling network that modulates the endogenous protective and pathogenic facets of the renin angiotensin system.

Angiotensin II activates CaV 1.2 Ca2+ channels through β-arrestin2 and casein kinase 2 in mouse immature cardiomyocytes

KEY POINTS

Angiotensin II (AngII) is crucial in cardiovascular regulation in perinatal mammalians. Here we show that AngII increases twitch Ca²⁺ transients of mouse immature but not mature cardiomyocytes by robustly activating Ca_V 1.2 L-type Ca²⁺ channels through a novel signalling pathway involving angiotensin type 1 (AT₁ ) receptors, β-arrestin2 and casein kinase 2. A β-arrestin-biased AT₁ receptor agonist, TRV027, was as effective as AngII in activating L-type Ca²⁺ channels. Our results help understand the molecular mechanism by which AngII regulates the perinatal circulation and also suggest that β-arrestin-biased AT₁ receptor agonists may be valuable therapeutics for paediatric heart failure.

ABSTRACT

Angiotensin II (AngII), the main effector peptide of the renin-angiotensin system, plays important roles in cardiovascular regulation in the perinatal period. Despite the well-known stimulatory effect of AngII on vascular contraction, little is known about regulation of contraction of the immature heart by AngII. Here we found that AngII significantly increased the peak amplitude of twitch Ca²⁺ transients by robustly activating L-type Ca_V 1.2 Ca²⁺ (Ca_V 1.2) channels in mouse immature but not mature cardiomyocytes. This response to AngII was mediated by AT₁ receptors and β-arrestin2. A β-arrestin-biased AT₁ receptor agonist was as effective as AngII in activating Ca_V 1.2 channels. Src-family tyrosine kinases (SFKs) and casein kinase 2α'β (CK2α'β) were sequentially activated when AngII activated Ca_V 1.2 channels. A cyclin-dependent kinase inhibitor, p27^Kip1 (p27), inhibited CK2α'β, and AngII removed this inhibitory effect through phosphorylating tyrosine 88 of p27 via SFKs in cardiomyocytes. In a human embryonic kidney cell line, tsA201 cells, overexpression of CK2α'β but not c-Src directly activated recombinant Ca_V 1.2 channels composed of C-terminally truncated α_1C , the distal C-terminus of α_1C , β_2C and α₂ δ₁ subunits, by phosphorylating threonine 1704 located at the interface between the proximal and the distal C-terminus of Ca_V 1.2α_1C subunits. Co-immunoprecipitation revealed that Ca_V 1.2 channels, CK2α'β and p27 formed a macromolecular complex. Therefore, stimulation of AT₁ receptors by AngII activates Ca_V 1.2 channels through β-arrestin2 and CK2α'β, thereby probably exerting a positive inotropic effect in the immature heart. Our results also indicated that β-arrestin-biased AT₁ receptor agonists may be used as valuable therapeutics for paediatric heart failure in the future.

Structural basis for selectivity and diversity in angiotensin II receptors

Angiotensin II receptors, AT₁R and AT₂R, serve as key components of the renin-angiotensin-aldosterone system. While AT₁R plays a central role in the regulation of blood pressure, the function of AT₂R is enigmatic with a variety of reported effects. To elucidate the mechanisms for the functional diversity and ligand selectivity between these receptors, we report crystal structures of the human AT₂R bound to an AT₂R-selective and an AT₁R/AT₂R-dual ligand, respectively, capturing the receptor in an active-like conformation. Unexpectedly, helix VIII was found in a non-canonical position, stabilizing the active-like state, but at the same time preventing the recruitment of G proteins/β-arrestins, in agreement with the lack of signaling responses in standard cellular assays. Structure-activity relationship, docking and mutagenesis studies revealed the interactions critical for ligand binding and selectivity. Our results thus provide insights into the structural basis for distinct functions of the angiotensin receptors, and may guide the design of novel selective ligands.

Microvascular vasodilator properties of the angiotensin II type 2 receptor in a mouse model of type 1 diabetes

Diabetes Mellitus is associated with severe cardiovascular disorders involving the renin-angiotensin system, mainly through activation of the angiotensin II type 1 receptor (AT1R). Although the type 2 receptor (AT2R) opposes the effects of AT1R, with vasodilator and anti-trophic properties, its role in diabetes is debatable. Thus we investigated AT2R-mediated dilatation in a model of type 1 diabetes induced by streptozotocin in 5-month-old male mice lacking AT2R (AT2R^−/y). Glucose tolerance was reduced and markers of inflammation and oxidative stress (cyclooxygenase-2, gp91phox p22phox and p67phox) were increased in AT2R^−/y mice compared to wild-type (WT) animals. Streptozotocin-induced hyperglycaemia was higher in AT2R^−/y than in WT mice. Arterial gp91phox and MnSOD expression levels in addition to blood 8-isoprostane and creatinine were further increased in diabetic AT2R^−/y mice compared to diabetic WT mice. AT2R-dependent dilatation in both isolated mesenteric resistance arteries and perfused kidneys was greater in diabetic mice than in non-diabetic animals. Thus, in type 1 diabetes, AT2R may reduce glycaemia and display anti-oxidant and/or anti-inflammatory properties in association with greater vasodilatation in mesenteric arteries and in the renal vasculature, a major target of diabetes. Therefore AT2R might represent a new therapeutic target in diabetes.

Angiotensin AT1A receptors on leptin receptor-expressing cells control resting metabolism

Leptin contributes to the control of resting metabolic rate (RMR) and blood pressure (BP) through its actions in the arcuate nucleus (ARC). The renin-angiotensin system (RAS) and angiotensin AT1 receptors within the brain are also involved in the control of RMR and BP, but whether this regulation overlaps with leptin's actions is unclear. Here, we have demonstrated the selective requirement of the AT1A receptor in leptin-mediated control of RMR. We observed that AT1A receptors colocalized with leptin receptors (LEPRs) in the ARC. Cellular coexpression of AT1A and LEPR was almost exclusive to the ARC and occurred primarily within neurons expressing agouti-related peptide (AgRP). Mice lacking the AT1A receptor specifically in LEPR-expressing cells failed to show an increase in RMR in response to a high-fat diet and deoxycorticosterone acetate-salt (DOCA-salt) treatments, but BP control remained intact. Accordingly, loss of RMR control was recapitulated in mice lacking AT1A in AgRP-expressing cells. We conclude that angiotensin activates divergent mechanisms to control BP and RMR and that the brain RAS functions as a major integrator for RMR control through its actions at leptin-sensitive AgRP cells of the ARC.

Cerebral Vascular Disease and Neurovascular Injury in Ischemic Stroke

The consequences of cerebrovascular disease are among the leading health issues worldwide. Large and small cerebral vessel disease can trigger stroke and contribute to the vascular component of other forms of neurological dysfunction and degeneration. Both forms of vascular disease are driven by diverse risk factors, with hypertension as the leading contributor. Despite the importance of neurovascular disease and subsequent injury after ischemic events, fundamental knowledge in these areas lag behind our current understanding of neuroprotection and vascular biology in general. The goal of this review is to address select key structural and functional changes in the vasculature that promote hypoperfusion and ischemia, while also affecting the extent of injury and effectiveness of therapy. In addition, as damage to the blood-brain barrier is one of the major consequences of ischemia, we discuss cellular and molecular mechanisms underlying ischemia-induced changes in blood-brain barrier integrity and function, including alterations in endothelial cells and the contribution of pericytes, immune cells, and matrix metalloproteinases. Identification of cell types, pathways, and molecules that control vascular changes before and after ischemia may result in novel approaches to slow the progression of cerebrovascular disease and lessen both the frequency and impact of ischemic events.

Chronic blockade of the AT2 receptor with PD123319 impairs insulin signaling in C57BL/6 mice

The renin-angiotensin system modulates insulin action. Angiotensin type 1 receptor exerts a deleterious effects while the angiotensin type 2 receptor (AT2R) appears to have beneficial effects providing protection against insulin resistance and type 2 diabetes. Although recent reports indicate that agonism of AT2R ameliorates diabetes and insulin resistance, the phenotype of AT2R-knockout mice seems to be controversial relating this aspect. Thus, in this study we have explored the role of AT2R in the control of insulin action. To that end, C57Bl/6 mice were administered the synthetic AT2R antagonist PD123319 for 21days (10mg/kg/day ip); vehicle treated animals were used as control. Glucose tolerance, metabolic parameters, in vivo insulin signaling in main insulin-target tissues as well as levels of adiponectin, TNF-α, MCP-1 and IL-6 in adipose tissue were assessed. AT2R blockade with PD123319 induced a marginal effect on glucose homeostasis but an important reduction in the insulin-induced phosphorylation of the insulin receptor and Akt in both liver and adipose tissue. Insulin signaling in skeletal muscle remained unaltered after treatment with PD123319, which could explain the minimal effect on glucose homeostasis induced by PD123319. Our current results reinforce the notion that the AT2R has a physiological role in the conservation of insulin action.

Long-term neprilysin inhibition - implications for ARNIs

Neprilysin has a major role in both the generation and degradation of bioactive peptides. LCZ696 (valsartan/sacubitril, Entresto), the first of the new ARNI (dual-acting angiotensin-receptor-neprilysin inhibitor) drug class, contains equimolar amounts of valsartan, an angiotensin-receptor blocker, and sacubitril, a prodrug for the neprilysin inhibitor LBQ657. LCZ696 reduced blood pressure more than valsartan alone in patients with hypertension. In the PARADIGM-HF study, LCZ696 was superior to the angiotensin-converting enzyme inhibitor enalapril for the treatment of heart failure with reduced ejection fraction, and LCZ696 was approved by the FDA for this purpose in 2015. This approval was the first for chronic neprilysin inhibition. The many peptides metabolized by neprilysin suggest many potential consequences of chronic neprilysin inhibitor therapy, both beneficial and adverse. Moreover, LBQ657 might inhibit enzymes other than neprilysin. Chronic neprilysin inhibition might have an effect on angio-oedema, bronchial reactivity, inflammation, and cancer, and might predispose to polyneuropathy. Additionally, inhibition of neprilysin metabolism of amyloid-β peptides might have an effect on Alzheimer disease, age-related macular degeneration, and cerebral amyloid angiopathy. Much of the evidence for possible adverse consequences of chronic neprilysin inhibition comes from studies in animal models, and the relevance of this evidence to humans is unknown. This Review summarizes current knowledge of neprilysin function and possible consequences of chronic neprilysin inhibition that indicate a need for vigilance in the use of neprilysin inhibitor therapy.

High sucrose intake during gestation increases angiotensin II type 1 receptor-mediated vascular contractility associated with epigenetic alterations in aged offspring rats

Accruing evidence have confirmed that the fetal programming in response to adverse environmental in utero factors plays essential roles in the pathogenesis of hypertension in later life. High sugar intake has been accepted worldwide in everyday life diet and becomes the critical public health issue. Our previous studies indicated that intake of high sucrose (HS) during pregnancy could change the vascular reactivity and dipsogenic behavior closely associated with abnormal renin-angiotensin system (RAS), to increase the risk of hypertension in adult offspring. In the present study, we tested the hypothesis that maternal HS intake in pregnancy may further deteriorate the Ang II-induced cardiovascular responses in the aged offspring. HS intake was provided to pregnant rats throughout the gestation. Blood pressure (BP) in conscious state and vascular contractility in vitro were measured in 22-month-old aged offspring rats. In addition, mRNA and protein expressions and epigenetic changes of Ang II type 1 receptor (AT₁R) gene in blood vessels were determined with the methods of real-time RT-PCR, Western blotting, and Chromatin Immunoprecipitation Assay (CHIP). Results showed that, in the aged offspring, maternal HS intake during gestation would cause the elevation of basal BP which could be diminished by losartan. Although the circulatory Ang II was not changed, levels of local Ang II were significantly increased in blood vessels. In addition, prenatal HS exposure would significantly enhance the AT₁R-mediated vasoconstrictions in both aorta and mesenteric arteries of the aged offspring. Moreover, in the aged offspring of prenatal HS exposure, mRNA and protein expressions of AT₁R gene in both large and small blood vessels were significantly increased, which should be closely associated with the changes of epigenetic mechanisms such as histone modifications. Collectively, we proposed that maternal HS intake during gestation would cause abnormal BP responses mediated via the enhancement of vascular RAS, together with the increased expression of AT₁R gene related to the its epigenetic changes, which would actually lead to the overt phenotype of hypertension in the aged offspring.

Caveolin-1 Deletion Prevents Hypertensive Vascular Remodeling Induced by Angiotensin II

It has been proposed that membrane microdomains, caveolae, in vascular cells are critical for signal transduction and downstream functions induced by angiotensin II (AngII). We have tested our hypothesis that caveolin-1 (Cav1), a major structural protein of vascular caveolae, plays a critical role in the development of vascular remodeling by AngII via regulation of epidermal growth factor receptor and vascular endothelial adhesion molecule-1. Cav1^-/- and control Cav^+/+ mice were infused with AngII for 2 weeks to induce vascular remodeling and hypertension. On AngII infusion, histological assessments demonstrated medial hypertrophy and perivascular fibrosis of aorta and coronary and renal arteries in Cav1^+/+ mice compared with sham-operated Cav1^+/+ mice. AngII-infused Cav1^+/+ mice also showed a phenotype of cardiac hypertrophy with increased heart weight to body weight ratio compared with control Cav1^+/+ mice. In contrast, Cav1^-/- mice infused with AngII showed attenuation of vascular remodeling but not cardiac hypertrophy. Similar levels of AngII-induced hypertension were found in both Cav1^+/+ and Cav1^-/- mice as assessed by telemetry. In Cav1^+/+ mice, AngII enhanced tyrosine-phosphorylated epidermal growth factor receptor staining in the aorta, which was attenuated in Cav1^-/- mice infused with AngII. Enhanced Cav1 and vascular endothelial adhesion molecule-1 expression was also observed in aorta from AngII-infused Cav1^+/+ mice but not in Cav1^-/- aorta. Experiments with vascular cells further provided a potential mechanism for our in vivo findings. These data suggest that Cav1, and presumably caveolae, in vascular smooth muscle and the endothelium plays a critical role in vascular remodeling and inflammation independent of blood pressure or cardiac hypertrophy regulation.

Involvement of Type 1 Angiontensin II Receptor (AT1) in Cardiovascular Changes Induced by Chronic Emotional Stress: Comparison between Homotypic and Heterotypic Stressors

Consistent evidence has shown an important role of emotional stress in pathogenesis of cardiovascular diseases. Additionally, studies in animal models have demonstrated that daily exposure to different stressor (heterotypic stressor) evokes more severe changes than those resulting from repeated exposure to the same aversive stimulus (homotypic stressor), possibly due to the habituation process upon repeated exposure to the same stressor. Despite these pieces of evidence, the mechanisms involved in the stress-evoked cardiovascular dysfunction are poorly understood. Therefore, the present study investigated the involvement of angiotensin II (Ang II) acting on the type 1 Ang II receptor (AT₁) in the cardiovascular dysfunctions evoked by both homotypic and heterotypic chronic emotional stresses in rats. For this purpose, we compared the effect of the chronic treatment with the AT₁ receptor antagonist losartan (30 mg/kg/day, p.o.) on the cardiovascular and autonomic changes evoked by the heterotypic stressor chronic variable stress (CVS) and the homotypic stressor repeated restraint stress (RRS). RRS increased the sympathetic tone to the heart and decreased the cardiac parasympathetic activity, whereas CVS decreased the cardiac parasympathetic activity. Additionally, both stressors impaired the baroreflex function. Alterations in the autonomic activity and the baroreflex impairment were inhibited by losartan treatment. Additionally, CVS reduced the body weight and increased the circulating corticosterone; however, these effects were not affected by losartan. In conclusion, these findings indicate the involvement of angiotensin II/AT₁ receptors in the autonomic changes evoked by both homotypic and heterotypic chronic stressors. Moreover, the present results provide evidence that the increase in the circulating corticosterone and body weight reduction evoked by heterotypic stressors are independent of AT₁ receptors.