Angiotensin AT1 Receptor Research Articles

Intracerebroventricular infusion of angiotensin AT2 receptor agonist novokinin aggravates some diabetes-mellitus-induced alterations in Wistar rats.

Cumulative data suggest the significant role of the renin-angiotensin system in the development of the pathological consequences of diabetes mellitus (DM). Newly synthesized AT2 receptor agonists gained importance as a target for creating new antihypertensives. The aim of the present work was to study the effects of peptide AT2 agonist novokinin, infused intracerebroventricularly, on the consequences of the streptozotocin-induced type 1 DM (T1DM) in Wistar rats. Food and water consumption, body mass, urine excretion (metabolic cages), motor activity (open-field test), anxiety (elevated plus maze), nociception (paw pressure analgesimeter test), spatial memory (T-maze alternation test), and plasma levels of glucose and corticosterone (ELISA) were assessed 2 weeks after the T1DM induction. Novokinin increased water and food consumption, as well as urine output, and reduced mass gain in the control rats. Diabetic rats demonstrated hyperalgesia, increased level of plasma corticosterone, decreased motor and exploratory activity, and impaired spatial memory. Novokinin infusion increased water intake, diuresis, and mortality rate, decreased food intake, exacerbated diabetes-induced hyperalgesia, and provoked anxiety-like behavior but improved spatial memory in diabetic rats. These initial data suggest that angiotensin AT2 receptors participate in the pathogenesis of T1DM-induced complications in the function of the nervous system.

Modulating Role of Ang1-7 in Control of Blood Pressure and Renal Function in AngII-infused Hypertensive Rats.

Indirect evidence suggests that angiotensin 1-7 (Ang1-7) may counterbalance prohypertensive actions of angiotensin II (AngII), via activation of vascular and/or renal tubular receptors to cause vasodilation and natriuresis/diuresis. We examined if Ang1-7 would attenuate the development of hypertension, renal vasoconstriction, and decreased natriuresis in AngII-infused rats and evaluated the mechanisms involved. AngII, alone or with Ang1-7, was infused to conscious Sprague-Dawley rats for 13 days and systolic blood pressure (SBP) and renal excretion were repeatedly determined. In anesthetized rats, acute actions of Ang1-7 and effects of blockade of angiotensin AT1 or Mas receptors (candesartan or A-779) were studied. Chronic AngII infusion increased SBP from 143 ± 4 to 195 ± 6 mm Hg. With Ang1-7 co-infused, SBP increased from 133 ± 5 to 161 ± 5 mm Hg (increase reduced, P < 0.002); concurrent increases in urine flow (V) and sodium excretion (UNaV) were greater. In anesthetized normotensive or AngII-induced hypertensive rats, Ang1-7 infusion transiently increased mean arterial pressure (MABP), transiently decreased renal blood flow (RBF), and caused increases in UNaV and V. In normotensive rats, candesartan prevented the Ang1-7-induced increases in MABP and UNaV and the decrease in RBF. In anesthetized normotensive, rats intravenous A-779 increased MABP (114 ± 5 to 120 ± 5 mm Hg, P < 0.03) and urine flow. Surprisingly, these changes were not observed with A-779 applied during background Ang1-7 infusion. The results suggest that in AngII-dependent hypertension, Ang1-7 deficit contributes to sodium and fluid retention and thereby to BP elevation; a correction by Ang1-7 infusion seems mediated by AT1 and not Mas receptors.

Hypoxia preconditioning promotes cardiac stem cell survival and cardiogenic differentiation in vitro involving activation of the HIF-1\u03b1/apelin/APJ axis

BackgroundCardiac stem cells (CSCs) transplantation has been regarded as an optimal therapeutic approach for cardiovascular disease. However, inferior survival and low differentiation efficiency of these cells in the local infarct site reduce their therapeutic efficacy. In this study, we investigated the influence of hypoxia preconditioning (HP) on CSCs survival and cardiogenic differentiation in vitro and explored the relevant mechanism.MethodsCSCs were obtained from Sprague–Dawley rats and cells of the third passage were cultured in vitro and exposed to hypoxia (1% O2). Cells survival and apoptosis were evaluated by MTS assay and flow cytometry respectively. Cardiogenic differentiation was induced by using 5-azacytidine for another 24 h after the cells experienced HP. Normoxia (20% O2) was used as a negative control during the whole process. Cardiogenic differentiation was assessed 2 weeks after the induction. Relevant molecules were examined after HP and during the differentiation process. Anti-hypoxia-inducible factor-1α (HIF-1α) small interfering RNA (siRNA), anti-apelin siRNA, and anti-putative receptor protein related to the angiotensin receptor AT1 (APJ) siRNA were transfected in order to block their expression, and relevant downstream molecules were detected.ResultsCompared with the normoxia group, the hypoxia group presented more rapid growth at time points of 12 and 24 h (p < 0.01). Cells exhibited the highest proliferation rate at the time point of 24 h (p < 0.01). The cell apoptosis rate significantly declined after 24 h of hypoxia exposure (p < 0.01). Expression levels of HIF-1α, apelin, and APJ were all enhanced after HP. The percentage of apelin, α-SA, and cTnT positive cells was greatly increased in the HP group after 2 weeks of induction. The protein level of α-SA and cTnT was also significantly elevated at 7 and 14 days (p < 0.01). HIF-1α, apelin, and APJ were all increased at different time points during the cardiogenic differentiation process (p < 0.01). Knockdown of HIF-1α, apelin or APJ by siRNAs resulted in a significant reduction of α-SA and cTnT. HIF-1α blockage caused a remarkable decrease of apelin and APJ (p < 0.01). Expression levels of apelin and APJ were depressed after the inhibition of apelin (p < 0.01).ConclusionHP could effectively promote CSCs survival and cardiogenic differentiation in vitro, and this procedure involved activation of the HIF-1α/apelin/APJ axis. This study provided a new perspective for exploring novel strategies to enhance CSCs transplantation efficiency.

Abstract P237: The At2 Receptor Agonist, C21, Can Also Stimulate Mas and Mrgd Receptors

Background: It is well accepted that Compound 21 (C21) is a highly selective non-peptide angiotensin AT2 receptor agonist. C21 as well as angiotensin (Ang)-(1-7) have cardiovascular protective effects and are opponents of the often detrimental Ang II within the renin-angiotensin system. Since the chemical structure of C21 is similar to the Mas receptor specific non-peptidic agonist AVE0991, and we could recently show that the AT2 receptor blocker, PD123319, can also block the effects of Ang-(1-7) at its natural receptors, Mas and MrgD, we tested whether C21 is also not AT2-specific but can stimulate the two Ang-(1-7) receptors, too. Methods and Results: Using cAMP as readout in receptor-transfected HEK293 cells, we generated pharmacological proof that Mas (EC 50 = 1.995 x 10 -12 M) and MrgD (EC 50 = 2.958 x 10 -9 M) are functional receptors for C21, whereby the three receptor blockers, A779, D-Pro7-Ang-(1-7), and PD123319 showed receptor-specific effects towards C21 signalling. Furthermore, C21 elevated the cAMP concentration in primary cells such as mesangial cells (EC 50 = 1.12 x 10 -6 M). However, significant increase in cAMP levels, but not in PKA activity, was still detectable in mesangial cells isolated from AT2-deficient mice, but completely blunted in Mas/MrgD-double knockouts. Finally, in silico modelling was performed to illustrate the structural similarities and differences between C21, AVE0991, and Ang-(1-7). Conclusions: Our results identify C21 as not being a specific AT2 receptor agonist but also interacting with the two Ang-(1-7) receptors, Mas and MrgD. Therefore, the partial overlap in beneficial effects of Ang-(1-7) and C21 might be based on the stimulation of the same receptors under specific pathophysiological circumstances. This also enforces the revisit of such publications which concluded on AT2 function by only using C21.

OP.7C.05] ANGIOTENSIN AT2 RECEPTOR AGONIST, COMPOUND 21, PREVENTS ABDOMINAL AORTIC ANEURYSM PROGRESSION AND THE DECREASE OF AORTIC WALL DISTENSIBILITY IN THE RAT

Objective: We studied the effects of selective AT2 receptor agonist, compound 21, (C21) treatment on experimental abdominal aortic aneurysm (AAA) formation in rats. Design and method: AAA was induced by perfusion of isolated aortic segments with elastase in normotensive Wistar rats. Treatment with C21 (0.03 mg/kg daily) was started after operation and continued for 14 days. Sham operated animals and vehicle-treated animals after aneurysm induction (AI) served as controls. Aortic diameter and blood velocities were measured infrarenally before and on days 7 and 14 post operation via ultrasound biomicroscopy. Analysis of pulse propagation velocity (PPV) and distensibility was performed using the Vevo Vasc® software. Hemodynamic parameters were measured via tail cuff and intraventricular Samba catheter. Aortic tissue expressions of MMP9, IL6, IL1beta, NFkappaB and MLKL as well as serum cytokines were analysed. Results: On day 14 post AI, infrarenal aortic diameter of AAA group was increased 1,55-fold compared to sham operated animals (2.65 mm ± 0.05, n = 8 vs. 1.7 mm ± 0.068, n = 6; p < 0.0001). C21 significantly decreased aortic diameter by 20% on day 7 post AI and by 28% on day 14 compared to vehicle-treated animals (1.9 mm ± 0.06, vs. 2.65 mm ± 0.06; p < 0.0001). Left ventricle parameters and blood pressure were not influenced by AI nor by additional treatment with C21. AI significantly reduced infrarenal blood velocity, distensibility and increased PPV. All these pathological effects were significantly ameliorated in C21 treated rats (p < 0, 0001; p < 0, 0001; p = 0, 0205; 2-wayANOVA). Treatment with C21 also reduced the expression of inflammatory markers IL1 beta, NF kappa B, protease MMP9 and MLKL, the marker of necroptotic cell death in the aortic media. Moreover, C21 reduced the increase of TGF-beta1 in serum (p = 0, 0055). Conclusions: The angiotensin AT2 receptor agonist, C21, prevents abdominal aortic aneurysm progression in the rat without affecting blood pressure or left ventricle parameters. C21 also prevents the decline of infrarenal aortic blood velocity, reduces the decrease of aortic wall distensibility at aneurysm site and the AAA-induced increase of inflammatory and necroptotic markers.

Abstract P430: Soluble Epoxide Hydrolase Inhibition Augments Ras Blockade Renoprotection in 5/6 Nephrectomized Ren-2 Transgenic Hypertensive Rats With Chronic Kidney Disease

Rationale and Objective: We showed recently that increasing kidney tissue epoxyeicosatrienoic acids (EETs) by blocking soluble epoxide hydrolase (sEH) and thereby blocking EETs degradation to inactive dihydroxyeicosatrienoic acids (DHETEs) substantially attenuated the progression of chronic kidney disease (CKD) in Ren-2 transgenic hypertensive rats (TGR) subjected to 5/6 renal mass reduction (5/6 NX). In this study we examined if in this model addition of sEH inhibition to the complex (dual) renin-angiotensin system (RAS) blockade would bring additional renoprotective effects in already established CKD. Methods: TGR aged 9 weeks underwent 5/6 NX and then were left untreated for 6 weeks to develop CKD. Then dual RAS blockade : ACE inhibition (trandolapril) + angiotensin AT 1 receptor blockade (losartan) was instituted, alone or combined with sEH inhibition (c-AUCB, 3 mg/l in drinking water). During the 60 weeks’ follow-up period albuminuria and urinary creatinine excretion was repeatedly determined. The following experimental groups were investigated: ; 1) sham-operated TGR; 2) Untreated 5/6 NX TGR; 3) 5/6 NX TGR + RAS blockade ; 4) 5/6 NX TGR + RAS + sEH blockade. Sham-operated transgene-negative normotensive Hannover-Sprague Dawley (HanSD) rats served as basic controls. In separate groups renal glomerular and tubulointerstitial injury was assessed, and effects of two weeks’ treatments on systolic blood pressure (SBP, measured by telemetry) and on kidney ANG II, ANG 1-7, EETs and DHETEs levels were determined. Results: All untreated TGR died by week 14 after 5/6 NX. RAS blockade increased the final survival rate to 23%, normalized SBP (116 ± 3 vs. 198 ± 3 mmHg, p&lt;0.0015), reduced albuminuria (46 ± 5 vs. 102 ± 12 mg/24 h, p&lt;0.001) and intrarenal ANG II (27 ± 8 vs. 189 ± 14 fmol/g p&lt;0.0015) and did not alter kidney EETs/DHETEs ratio. After addition of sEH blockade kidney EETs/DHETEs ratio increased to 2.89 ± 0.42 (p&lt;0.001 vs. 5/6 NX TGR treated with RAS blockade), the final survival rate increased to 42% and indices of renal glomerular and tubulointerstial injury improved. Conclusion: Addition of sEH blockade to the RAS blockade brings additional renoprotective effects on the CKD progression in 5/6 NX TGR, even when applied in the advanced phase of the disease.

A bioluminescence resonance energy transfer 2 (BRET2) assay for monitoring seven transmembrane receptor and insulin receptor crosstalk

The angiotensin AT1 receptor is a seven transmembrane (7TM) receptor, which mediates the regulation of blood pressure. Activation of angiotensin AT1 receptor may lead to impaired insulin signaling indicating crosstalk between angiotensin AT1 receptor and insulin receptor signaling pathways. To elucidate the molecular mechanisms behind this crosstalk, we applied the BRET2 technique to monitor the effect of angiotensin II on the interaction between Rluc8 tagged insulin receptor and GFP2 tagged insulin receptor substrates 1, 4, 5 (IRS1, IRS4, IRS5) and Src homology 2 domain-containing protein (Shc). We demonstrate that angiotensin II reduces the interaction between insulin receptor and IRS1 and IRS4, respectively, while the interaction with Shc is unaffected, and this effect is dependent on Gαq activation. Activation of other Gαq-coupled 7TM receptors led to a similar reduction in insulin receptor and IRS4 interactions whereas Gαs- and Gαi-coupled 7TM receptors had no effect. Furthermore, we used a panel of kinase inhibitors to show that angiotensin II engages different pathways when regulating insulin receptor interactions with IRS1 and IRS4. Angiotensin II inhibited the interaction between insulin receptor and IRS1 through activation of ERK1/2, while the interaction between insulin receptor and IRS4 was partially inhibited through protein kinase C dependent mechanisms. We conclude that the crosstalk between angiotensin AT1 receptor and insulin receptor signaling shows a high degree of specificity, and involves Gαq protein, and activation of distinct kinases. Thus, the BRET2 technique can be used as a platform for studying molecular mechanisms of crosstalk between insulin receptor and 7TM receptors.

The benefit of angiotensin AT1 receptor blockers for early treatment of hypertensive patients.

ESC guidelines for management of arterial hypertension allow one to choose among five classes of antihypertensive drugs indiscriminately. They are based on the principle that in the management of hypertensive patients, it is fundamental to reduce blood pressure (BP), independently of the utilized drug. However, it has been demonstrated that the renin-angiotensin system (RAS) plays a relevant role in the hypertensive-derived development and progression of organ damage. Thus, antihypertensive drugs interfering with the RAS should be preferred in preventing and reducing target organ damage. The availability of two classes of drugs, ACE-inhibitors and angiotensin AT1 receptor blockers (ARBs), both interfering with the RAS, makes the choice between them difficult. Both pharmacological strategies offer an effective BP control, and a substantial improvement of prognosis in different associated pathologies. Regarding cardiovascular prevention, ACE-inhibitors have an extensive scientific literature regarding utility in high-risk patients. Nevertheless, there is evidence to support the concept that in the early phases of organ tissue damage, the RAS is activated, but the ACE pathway producing angiotensin II is not always employed. Accordingly, ACE-inhibitors appear to be less effective, whereas ARBs have a greater beneficial action in the initial stages of atherosclerotic disease. Moreover, patients undergoing ARBs therapy show a substantially lower risk of therapy discontinuation when compared to those treated with ACE-inhibitors, because of a better tolerability. In conclusion, ACE-inhibitors should be used in patients who have already developed organ damage, but tolerate this drug well, while ARBs should be the first choice in naïve hypertensive patients without organ damage or at the initial stages of disease.

Azilsartan Medoxomil, an Angiotensin II Receptor Antagonist for the Treatment of Hypertension.

Azilsartan (AZL) medoxomil was approved by the United States Food and Drug Administration in 2011 for the treatment of hypertension and has shown promising results both in blood pressure (BP) reduction and in tolerability, but has not yet been taken into practice to the same extent as other angiotensin II receptor blockers (ARBs) that have been on the market for a longer period. AZL antagonizes the AT1 receptor for angiotensin II (ANG II), whereas angiotensin-converting enzyme inhibitors block the conversion of angiotensin I to ANG II, but not alternative routes of formation of ANG II. The bioavailability of AZL is about 60% and it has a tmax of 1.5-3hr and a half-life of approximately 11hr. With its IC50 of 7.4nM after 5hr of drug washout in radioligand assays, AZL has a tighter and longer-lasting binding to the AT1 receptor by several orders of magnitude than other ARBs, which might lead to a more effective reduction in BP. Clinical studies have revealed that AZL doses of 40 and 80mg/day reduce BP significantly better than maximal clinical doses of valsartan or olmesartan, while being well tolerated and exhibiting a spectrum of adverse effects comparable to those of other ARBs. These properties of AZL might lower the risk of cardiovascular disease and thereby reduce mortality rates. However, the existing mortality studies have not found this correlation, which should be further investigated.

Functions of AT1 and AT2 angiotensin receptors in the paraventricular nucleus of the rat, correlating single-unit and cardiovascular responses

The paraventricular hypothalamic nucleus (PVN) is a complex structure with both neuroendocrine and autonomic functions including cardiovascular control. The PVN contains angiotensin II (AngII) immunoreactive cells, fibers, as well as AT1 and AT2 receptors of AngII. We microinjected AngII into the PVN of normotensive anesthetized rats and simultaneously recorded blood pressure, heart rate (HR) and single-unit responses. The roles of AT1 and AT2 receptors in these responses were also evaluated. Microinjection of AngII into the PVN produced a short excitatory single-unit response and two types of pressor responses: short duration with a decrease in HR and long with an increase in HR. Microinjection of losartan, an AT1 antagonist, into the PVN produced two response types, attenuation and augmentation of the pressor and firing rate responses to AngII. Microinjection of PD123319, an AT2 antagonist, into the PVN greatly attenuated pressor and single-unit response to AngII, indicating that the pressor response was mediated through AT2 receptors too. In conclusion, microinjection of AngII into the PVN stimulates neurons resulting in an increase in firing rate and consequently produces a short or long pressor response. These responses were mediated through AT1 and AT2 receptors; however, AT1 receptor may produce inhibition too. The results suggest that AngII of the PVN may be a neurotransmitter playing a role in arterial pressure regulation.

Treatment with salvianolic acid B restores endothelial function in angiotensin II-induced hypertensive mice

Salvianolic acid B (Sal B) is one of the most abundant phenolic acids derived from the root of Danshen with potent anti-oxidative properties. The present study examined the vasoprotective effect of Sal B in hypertensive mice induced by angiotensin II (Ang II). Sal B (25mg/kg/day) was administered via oral gavage for 11days to Ang II (1.2mg/kg/day)-infused C57BL/6J mice (8–10weeks old). The vascular reactivity (both endothelium-dependent relaxations and contractions) in mouse arteries was examined by wire myography. The production of reactive oxygen species (ROS), protein level and localization of angiotensin AT1 receptors and the proteins involved in ROS formation were evaluated using dihydroethidium (DHE) fluorescence, lucigenin-enhanced chemiluminescence, immunohistochemistry and Western blotting, respectively. The changes of ROS generating proteins were also assessed in vitro in human umbilical vein endothelial cells (HUVECs) exposed to Ang II with and without co-treatment with Sal B (0.1–10nM). Oral administration of Sal B reversed the Ang II-induced elevation of arterial systolic blood pressure in mice, augmented the impaired endothelium-dependent relaxations and attenuated the exaggerated endothelium-dependent contractions in both aortas and renal arteries of Ang II-infused mice. In addition, Sal B treatment normalized the elevated levels of AT1 receptors, NADPH oxidase subunits (NOx-2 and NOx-4) and nitrotyrosine in arteries of Ang II-infused mice or in Ang II-treated HUVECs. In summary, the present study provided additional evidence demonstrating that Sal B treatment for 11days reverses the impaired endothelial function and with a marked inhibition of AT1 receptor-dependent vascular oxidative stress. This vasoprotective and anti-oxidative action of Sal B most likely contributes to the anti-hypertensive action of the plant-derived compound.

PDI via Keap1/Nrf2 pathway Regulates Redox Balance, Renal AT1 Receptor Function and Blood Pressure

Oxidative stress is reported to play a vital role in the regulation of renal angiotensin AT1 receptor (AT1R) function and blood pressure (BP). This indicates that redox balance is crucial for normal AT1R function and BP. We tested a hypothesis that Protein Disulfide Isomerase (PDI), an enzyme that has diverse biological activity, via Keap1/Nrf2 pathway, regulates cellular redox homeostasis, AT1R function and blood pressure. To test the hypothesis, we treated adult Sprague Dawley (SD) rats with bacitracin, a PDI inhibitor for 14 days and determined various parameters. We found that bacitracin treated compared to vehicle treated rats, showed higher blood pressure. This was associated with greater diuresis and natriursis in response to AT1R blocker candesartan in bacitracin treated rats, indicating higher AT1R function in these rats. Moreover, bacitracin treated rats had higher oxidative stress and renal injury, as determined by measuring oxidative stress markers: urinary 8‐isoprostane, renal protein carbonyls and renal nitrotyrosine levels as well as urinary kidney injury molecule‐1 levels, respectively. This was associated with reduced antioxidant capacity and impaired Nrf2 transcription factor activity, involved in maintaining antioxidant capacity. Further, Kelch like ECH associated protein 1 (keap1) levels, an endogenous repressor of Nrf2, and tyrosine 216 phosphorylated GSK3β protein, which causes Nrf2 nuclear export were higher in bacitracin treated rats. Moreover, Nuclear Nrf2 levels in human kidney 2 cells treated with bacitracin also decreased compared to control cells. These data suggest that PDI via keap1/Nrf2 pathway regulates redox balance, AT1R function and BP in SD rats.Support or Funding InformationNIH/NIA, AG039856

The Role of Cyclooxygenase Enzymes in the Effects of Losartan and Lisinopril on the Contractions of Rat Thoracic Aorta.

It was suggested that prostaglandins which are synthesized by cyclooxygenase (COX) enzymes contribute to the actions of angiotensin-converting enzyme (ACE) inhibition and angiotensin AT1 receptor antagonism and there is an interaction between ACE signaling pathway and COX enzymes. We aim to investigate the role of COX enzymes in the effects of losartan, an angiotensin II (Ang II) receptor antagonist or lisinopril, an ACE inhibitor, on the contractions of rat thoracic aorta in isolated tissue bath. Responses of losartan (10-6, 10-5, 10-4 M), lisinopril (10-6, 10-5, 10-4 M), and non-selective COX inhibitor dipyrone (10-4, 7 × 10-4, 2 × 10-3 M) alone to the contractions induced by phenylephrine (Phe) (10-7 M), potassium chloride (KCl) (6 × 10-2 M), Ang II (10-8 M) and responses of losartan or lisinopril in combination with dipyrone to the contractions induced by Phe or KCl were recorded. When used alone, dipyrone and losartan inhibited Phe, KCl, and Ang II-induced contractions, whereas lisinopril inhibited only Phe and Ang II-induced contractions. Inhibition of COX enzymes (COX-3, COX-3 + COX-1, COX-1+ COX-2 + COX-3 by dipyrone 10-4, 7 × 10-4, 2 × 10-3 M, respectively) augmented the relaxant effects of losartan or lisinopril. Also, dipyrone potentiated the effect of lisinopril on KCl-induced contractions. We suggest that dipyrone increases the smooth-muscle relaxing effects of losartan or lisinopril and that COX enzyme inhibition may have a role in the enhancement of this relaxation.

Inflammation, Autoimmunity, and Hypertension: The Essential Role of Tissue Transglutaminase.

Inflammatory cytokines cause hypertension when introduced into animals. Additional evidence indicates that cytokines induce the production of autoantibodies that activate the AT1 angiotensin receptor (AT1R). Extensive evidence shows that these autoantibodies, termed AT1-AA, contribute to hypertension. We review here recent studies showing that cytokine-induced hypertension and AT1-AA production require the ubiquitous enzyme, tissue transglutaminase (TG2). We consider 3 mechanisms by which TG2 may contribute to hypertension. (i) One involves the posttranslational modification (PTM) of AT1Rs at a glutamine residue that is present in the epitope sequence (AFHYESQ) recognized by AT1-AA. (ii) Another mechanism by which TG2 may contribute to hypertension is by PTM of AT1Rs at glutamine 315. Modification at this glutamine prevents ubiquitination-dependent proteasome degradation and allows AT1Rs to accumulate. Increased AT1R abundance is likely to account for increased sensitivity to Ang II activation and in this way contribute to hypertension. (iii) The increased TG2 produced as a result of elevated inflammatory cytokines is likely to contribute to vascular stiffness by modification of intracellular contractile proteins or by crosslinking vascular proteins in the extracellular matrix. This process, termed inward remodeling, results in reduced vascular lumen, vascular stiffness, and increased blood pressure. Based on the literature reviewed here, we hypothesize that TG2 is an essential participant in cytokine-induced hypertension. From this perspective, selective TG2 inhibitors have the potential to be pharmacologic weapons in the fight against hypertension.

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.

Crosstalk between angiotensin and the nonamyloidogenic pathway of Alzheimer's amyloid precursor protein

The association between hypertension and an increased risk for Alzheimer's disease (AD) and dementia is well established. Many data suggest that modulation of the renin-angiotensin system may be meaningful for the prevention and therapy of neurodegenerative disorders, in particular AD. Proteolytic cleavage of the amyloid precursor protein (APP) by α-secretase precludes formation of neurotoxic Aβ peptides and is expected to counteract the development of AD. An established approach for the up-regulation of α-secretase cleavage is the activation of G protein-coupled receptors (GPCRs). Therefore, our study aimed to analyze whether stimulation of angiotensin AT1 or AT2 receptors stably expressed in HEK cells influence the nonamyloidogenic pathway of APP processing. Treatment of both receptors with angiotensin II clearly showed that only activation of the AT1 receptor increased several fold the α-secretase-mediated shedding of APP. This effect was completely abolished by treatment with the AT1 receptor-specific antagonist telmisartan. Using the BIM-46187 inhibitor, we demonstrate that the Gαq protein-mediated pathway is involved in this stimulation process. Stimulation of AT1 receptors with the β-arrestin-biased agonist SII was ineffective regarding α-secretase-mediated APP shedding. This result discloses that only the G protein-dependent pathway is involved in the Ang II-induced APP shedding. Blocking of Gβγ subunits by the inhibitor gallein completely prevented constitutive and Ang II-induced APP shedding. Our findings provide evidence that induction of APP shedding via Ang II/AT1 receptor stimulation is effected by G protein activation with Gβγ subunits playing important roles.

Stimulation of AT1 Angiotensin Receptors Activates CaV1.2 L-Type Ca2+ Channels through Beta-Arrestin2 and Casein Kinase 2 in Immature Cardiomyocytes

Angiotensin II (AngII) plays important roles in cardiovascular regulation in the perinatal period. Here, we examined the effect of AngII on cardiac CaV1.2 L-type Ca2+ channels. As assessed in the whole-cell configuration of the patch-clamp method, 2-hour treatment of AngII (3 μM) doubled the activity of CaV1.2 channels in mouse neonatal ventricular cardiomyocytes (NVCM) and an atrial myocyte line HL-1, but not in adult ventricular cardiomyocytes (AVCM). An AT1 receptor antagonist, candesartan (10 μM) and knockdown of β-arrestin2, but not an AT2 receptor antagonist, PD123319 (3 μM) or knockdown of β-arrestin1 or Gq/11 significantly suppressed the AngII-mediated activation of CaV1.2 channels in HL-1 cardiomyocytes. To elucidate possible involvement of protein kinases in this system, we examined the effects of array of kinase inhibitors in NVCM. Then, we found that a casein kinase 2 (CK2) inhibitor, quinalizarin (3 μM) almost completely inhibited the AngII-mediated activation of CaV1.2 channels. Knockdown of CK2α, α’ or β subunit in HL-1 cardiomyocytes indicated requirement of CK2 α’ and β but not α in this response. Immunoblotting revealed that the expression levels of CK2α’ was 7 and 4.5 times higher in NVCM and HL-1 cardiomyocytes than in AVCM, respectively. In tsA201 cells, overexpression of CK2α’β significantly increased the activity of recombinant CaV1.2 channels composed of C-terminally truncated α1C, the distal C-terminus of α1C, β2C and α2δ1 subunits; however, it failed to activate CaV1.2 channels containing α1C whose threonine 1704 was substituted with alanine. These results indicate that stimulation of AT1 receptors activates CaV1.2 L-type Ca2+ channels through β-arrestin2 and casein kinase 2 in immature but not adult cardiomyocytes. This response may play an important role in cardiovascular regulation in the perinatal period.

The angiotensin type 2 receptor and the kidney.

Angiotensin II is a main regulator of kidney function. Renal actions mediated by the angiotensin AT1 receptor have been well known for many years. In contrast, several details of angiotensin AT2 receptor actions in kidney physiology and pathophysiology were only described very recently. These findings are reviewed in this article. Regarding the role of the angiotensin AT2 receptor in kidney physiology, a major recent finding was that the AT2 receptor-mediated inhibition of Na-H exchanger-3 and Na/K-ATPase in the renal proximal tubules is caused by internalisation of these transporters, thus reducing reabsorption and increasing natriuresis/diuresis. Regarding renal pathology, several studies demonstrated an attenuation of renal injury caused by diabetes or by obesity with or without high-salt diet through anti-inflammatory, antifibrotic, and antioxidative mechanisms. Generally, AT2 receptor expression seems increased and AT2 receptor-mediated effects stronger in female and obese animals. The recent findings about the role of the angiotensin AT2 receptor in renal health and disease strongly suggest that pharmacological targeting of this receptor with selective agonists is a promising therapeutic strategy for inducing diuresis/natriuresis (also additive to established diuretics) and for the treatment of diabetic nephropathy or kidney disease of other pathogenesis.

Sacubitril and valsartan fixed combination to reduce heart failure events in post-acute myocardial infarction patients.

Heart failure is a term used to define a constellation of symptoms and signs that are commonly attributed to the inability of the heart to produce a cardiac output that meets the demands of the body. It remains a deadly disease, affecting between 1-2% of the population, and is more common in the elderly, with around 6-10% of patients over 65 suffering from the condition. Sacubitril/valsartan (LCZ-696) is a combined neprilysin inhibitor and angiotensin AT1 receptor blocker approved in recent years for the treatment of chronic heart failure with reduced ejection fraction. In an area where there have been limited pharmacological advances in the last 10 years, this drug was a game changer and a much welcomed addition to contemporary heart failure therapy. It is currently being studied in patients with heart failure with preserved ejection fraction and for the reduction of heart failure events post-acute myocardial infarction. Results from the ongoing PARADISE-MI study are awaited by the global cardiology community with great interest.

Matrix Metalloproteinases in Normal Pregnancy and Preeclampsia.

Normal pregnancy is associated with marked hemodynamic and uterine changes that allow adequate uteroplacental blood flow and uterine expansion for the growing fetus. These pregnancy-associated changes involve significant uteroplacental and vascular remodeling. Matrix metalloproteinases (MMPs) are important regulators of vascular and uterine remodeling. Increases in MMP-2 and MMP-9 have been implicated in vasodilation, placentation, and uterine expansion during normal pregnancy. The increases in MMPs could be induced by the increased production of estrogen and progesterone during pregnancy. MMP expression/activity may be altered during complications of pregnancy. Decreased vascular MMP-2 and MMP-9 may lead to decreased vasodilation, increased vasoconstriction, hypertensive pregnancy, and preeclampsia. Abnormal expression of uteroplacental integrins, cytokines, and MMPs may lead to decreased maternal tolerance, apoptosis of invasive trophoblast cells, inadequate remodeling of spiral arteries, and reduced uterine perfusion pressure (RUPP). RUPP may cause imbalance between the antiangiogenic factors soluble fms-like tyrosine kinase-1 and soluble endoglin and the proangiogenic vascular endothelial growth factor and placental growth factor, or stimulate the release of inflammatory cytokines, hypoxia-inducible factor, reactive oxygen species, and angiotensin AT1 receptor agonistic autoantibodies. These circulating factors could target MMPs in the extracellular matrix as well as endothelial and vascular smooth muscle cells, causing generalized vascular dysfunction, increased vasoconstriction and hypertension in pregnancy. MMP activity can also be altered by endogenous tissue inhibitors of metalloproteinases (TIMPs) and changes in the MMP/TIMP ratio. In addition to their vascular effects, decreases in expression/activity of MMP-2 and MMP-9 in the uterus could impede uterine growth and expansion and lead to premature labor. Understanding the role of MMPs in uteroplacental and vascular remodeling and function could help design new approaches for prediction and management of preeclampsia and premature labor.