Renin-angiotensin System Cascade Research Articles

Emerging roles of the renin-angiotensin system in select oral diseases.

The renin-angiotensin system (RAS) plays essential roles in cardiovascular and renal function regulation. Recent studies have shown that the RAS components are widely expressed in oral tissues, but their roles in oral diseases remain underexplored. This review aims to summarize the effects of the RAS in select oral diseases including oral squamous cells carcinoma (OSCC), periodontitis, oral submucous fibrosis (OSF), and ageusia/dysgeusia. Data searches were performed using PubMed, Web of Science and Scopus through July 2024. A narrative overview of current literature was undertaken to synthesize the contexts with elaboration and summary. In OSCC, ACE/Ang II/AT1R promotes OSCC by inducing angiogenesis, cell proliferation and invasiveness. Conversely, ACE/Ang II/AT2R and ACE2/Ang (1-7)/MasR inhibit OSCC progressions. In periodontitis, ACE/Ang II/AT1R upregulates inflammatory cytokines and promotes osteoclast differentiation factor RANKL, whereas ACE2/Ang (1-7)/MasR exerts opposite effects by preventing inflammation and alveolar bone loss. In OSF, Ang (1-7) counters the profibrotic and proinflammatory action of Ang II. In dysgeusia, Ang II suppresses salt taste responses and enhances sweet taste sensitivities, while Ang (1-7) exhibits opposite effects. The RAS cascade plays crucial roles in OSCC, periodontitis, OSF and ageusia/dysgeusia. The imbalanced RAS may aggravate the progression of these diseases.

Angiotensin II Type I Receptor (AT1R): The Gate towards COVID-19-Associated Diseases.

The binding of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike glycoprotein to its cellular receptor, the angiotensin-converting enzyme 2 (ACE2), causes its downregulation, which subsequently leads to the dysregulation of the renin–angiotensin system (RAS) in favor of the ACE–angiotensin II (Ang II)–angiotensin II type I receptor (AT1R) axis. AT1R has a major role in RAS by being involved in several physiological events including blood pressure control and electrolyte balance. Following SARS-CoV-2 infection, pathogenic episodes generated by the vasoconstriction, proinflammatory, profibrotic, and prooxidative consequences of the Ang II–AT1R axis activation are accompanied by a hyperinflammatory state (cytokine storm) and an acute respiratory distress syndrome (ARDS). AT1R, a member of the G protein-coupled receptor (GPCR) family, modulates Ang II deleterious effects through the activation of multiple downstream signaling pathways, among which are MAP kinases (ERK 1/2, JNK, p38MAPK), receptor tyrosine kinases (PDGF, EGFR, insulin receptor), and nonreceptor tyrosine kinases (Src, JAK/STAT, focal adhesion kinase (FAK)), and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. COVID-19 is well known for generating respiratory symptoms, but because ACE2 is expressed in various body tissues, several extrapulmonary pathologies are also manifested, including neurologic disorders, vasculature and myocardial complications, kidney injury, gastrointestinal symptoms, hepatic injury, hyperglycemia, and dermatologic complications. Therefore, the development of drugs based on RAS blockers, such as angiotensin II receptor blockers (ARBs), that inhibit the damaging axis of the RAS cascade may become one of the most promising approaches for the treatment of COVID-19 in the near future. We herein review the general features of AT1R, with a special focus on the receptor-mediated activation of the different downstream signaling pathways leading to specific cellular responses. In addition, we provide the latest insights into the roles of AT1R in COVID-19 outcomes in different systems of the human body, as well as the role of ARBs as tentative pharmacological agents to treat COVID-19.

Genetic deletion of Mas receptor in FVB/N mice impairs cardiac use of glucose and lipids

Angiotensin-(1−7) is a biologically active product of the renin-angiotensin system cascade and exerts inhibitory effects on inflammation, vascular and cellular growth mechanisms signaling through the G protein-coupled Mas receptor. The major purpose of the present study was to investigate the use of glucose and fatty acids by cardiac tissue in Mas knockout mice models. Serum levels of glucose, lipids, and insulin were measured in Mas-deficient and wild-type FVB/N mice. To investigate the cardiac use of lipids, the lipoprotein lipase, the gene expression of peroxisome proliferator-activated receptor alpha; carnitine palmitoyltransferase I and acyl-CoA oxidase were evaluated. To investigate the cardiac use of glucose, the insulin signaling through Akt/GLUT4 pathway, glucose-6-phosphate (G-6-P) and fructose-6-phosphate (F-6-P) glycolytic intermediates, in addition to ATP, lactate and the glycogen content were measured. Despite normal body weight, cholesterol and insulin, Mas-Knockout mice presented hyperglycemia and hypertriglyceridemia, impaired insulin signaling, through reduced phosphorylation of AKT and decreased translocation of GLUT4 in response to insulin, with subsequent decrease of the cardiac G-6-P and F-6-P. Lactate production and glycogen content were not altered in Mas-KO hearts. Mas-KO presented reduced cardiac lipoprotein lipase activity and decreased translocation of CD36 in response to insulin. The expression of peroxisome proliferator-activated receptor alpha and carnitine palmitoyltransferase I genes were lower in Mas-KO animals compared to wild-type animals. The ATP content of Mas-KO hearts was smaller than in wild-type. The present results suggest that genetic deletion of Mas produced a devastating effect on cardiac use of glucose and lipids, leading to lower energy efficiency in the heart.

The elderly at risk: aldosterone as modulator of the immune response to SARS-CoV-2 infection.

The elderly population is the most susceptible to SARS-CoV-2 infection and develops the worst clinical phenotype with severe pneumonia and cardiac complications. Older COVID-19 patients are also at higher risk of sudden death, mainly attributable to electrolyte disorders and to an uncontrolled inflammatory response. After the identification of ACE 2 as the receptor of SARS-CoV-2 in human cells, several research studies have focused on the role of the activation of Renin Angiotensin System in COVID-19 clinical course. In the present opinion paper, we discuss the role of hyperaldosteronism in the increasing risk of cardiac complications in COVID-19 older patients. In particular, we focus on the immunoregulatory activity of aldosterone, as the last mediator of the Renin Angiotensin System cascade, in activating the innate and adaptive immune response related to SARS-CoV-2 infection in the elderly. Aldosterone may stimulate dendritic cells and the recruitment of monocytes/macrophages in the endothelium of coronary vessels, favoring the production of pro-inflammatory mediators and T-cells response. Higher basal levels of aldosterone together with SARS-CoV-2-induced production may explain the unfavorable course of COVID-19 in the elderly.

Sex differences exist in brain renin-angiotensin system-regulating aminopeptidase activities in transplacental ethyl-nitrosourea-induced gliomas

IntroductionThe renin angiotensin system (RAS) is emerging as an important target for the treatment of glioma. We had described that the local RAS is involved in vivo in tumor growth in the rat model of experimental C6 glioma implanted at the subcutaneous region, through the modification of several proteolytic regulatory enzymes of aminopeptidase type. MethodsWe analyze RAS-regulating aminopeptidase activities in plasma and brain tissue of control male and female rats and rats with transplacental ethylnitrosourea-induced gliomas. ResultsNo differences were found either the mean total number of tumors per animal or the tumor volume between male and female animals. However, we have found increased levels in aspartyl aminopeptidase in both males and females and of aminopeptidase B only in males. On the contrary, decreased levels were found in aminopeptidase N and insulin-regulated aminopeptidase activities in both males and females, whereas aminopeptidase A only decreased in females. Decreased levels of aminopeptidase N, aminopeptidase B and insulin-regulated aminopeptidase were also shown in plasma of only female rats. ConclusionsUnder the complexity of RAS cascade, the changes found suggest the predominant actions of angiotensin III against a decreased action of angiotensin II and angiotensin IV. We conclude that angiotensin peptides are involved in tumor growth in this rat model of glioma and that their role in tumor growth can be analyzed through their corresponding proteolytic regulatory enzymes, which make them new and attractive therapeutic targets beyond the use or angiotensin converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARBs).

Insights on SARS-CoV-2 Molecular Interactions With the Renin-Angiotensin System.

The emergence of SARS-CoV-2/human/Wuhan/X1/2019, a virus belonging to the species Severe acute respiratory syndrome-related coronavirus, and the recognition of Coronavirus Disease 2019 (COVID-19) as a pandemic have highly increased the scientific research regarding the pathogenesis of COVID-19. The Renin Angiotensin System (RAS) seems to be involved in COVID-19 natural course, since studies suggest the membrane-bound Angiotensin-converting enzyme 2 (ACE2) works as SARS-CoV-2 cellular receptor. Besides the efforts of the scientific community to understand the virus’ molecular interactions with human cells, few studies summarize what has been so far discovered about SARS-CoV-2 signaling mechanisms and its interactions with RAS molecules. This review aims to discuss possible SARS-CoV-2 intracellular signaling pathways, cell entry mechanism and the possible consequences of the interaction with RAS components, including Angiotensin II (Ang II), Angiotensin-(1-7) [Ang-(1-7)], Angiotensin-converting enzyme (ACE), ACE2, Angiotensin II receptor type-1 (AT1), and Mas Receptor. We also discuss ongoing clinical trials and treatment based on RAS cascade intervention. Data were obtained independently by the two authors who carried out a search in the PubMed, Embase, LILACS, Cochrane, Scopus, SciELO and the National Institute of Health databases using Medical Subject Heading terms as “SARS-CoV-2,” “COVID-19,” “Renin Angiotensin System,” “ACE2,” “Angiotensin II,” “Angiotensin-(1-7),” and “AT1 receptor.” Similarly to other members of Coronaviridae family, the molecular interactions between the pathogen and the membrane-bound ACE2 are based on the cleavage of the spike glycoprotein (S) in two subunits. Following the binding of the S1 receptor-binding domain (RBD) to ACE2, transmembrane protease/serine subfamily 2 (TMPRSS2) cleaves the S2 domain to facilitate membrane fusion. It is very likely that SARS-CoV-2 cell entry results in downregulation of membrane-bound ACE2, an enzyme that converts Ang II into Ang-(1-7). This mechanism can result in lung injury and vasoconstriction. In addition, Ang II activates pro-inflammatory cascades when binding to the AT1 Receptor. On the other hand, Ang-(1-7) promotes anti-inflammatory effects through its interactions with the Mas Receptor. These molecules might be possible therapeutic targets for treating COVID-19. Thus, the understanding of SARS-CoV-2 intracellular pathways and interactions with the RAS may clarify COVID-19 physiopathology and open perspectives for new treatments and strategies.

Interaction Between Coronavirus S-Protein and Human ACE2: Hints for Exploring Efficient Therapeutic Targets to Treat COVID-19.

With the global expansion of coronavirus disease 2019 (COVID-19) and the declaration of its outbreak as a Public Health Emergency of International Concern by the World Health Organization, there is an urgent need for vaccines and medicines to prevent and treat COVID-19. The responsible pathogen for the disease is the newly severe acute respiratory syndrome coronavirus (SARS-CoV) 2 belonging to the same family of viruses SARS-CoV and Middle East respiratory syndrome coronavirus that originally are zoonotic and have been associated with severe illness during the outbreaks in 2003 and 2012, respectively. The virulence of coronavirus strains is mainly associated with variations in surface proteins mediating cellular entry of the virus, which can help in finding effective therapeutic targets. In this review, we seek evidence showing the role of coronavirus spike protein (S-protein) and its potential cellular receptor, angiotensin-converting enzyme 2 (ACE2), during infection of coronaviruses, including the newly SARS-CoV-2 and its similar strain SARS-CoV. This review also discusses the therapeutic effect of inhibiting the renin-angiotensin system cascade, a target of ACE2, in patients having coronavirus with cardiovascular disease.

Development of a novel murine heart failure model overexpressing human renin and angiotensinogen.

Renin is the rate‐limiting enzyme of the renin–angiotensin system cascade, which drives the pathophysiological progression of heart failure. Species differences in the amino acid sequence of the catalytic domain of renin limit evaluations of the potency and efficacy of human renin inhibitors in animal models, and a high dose of inhibitors is usually needed to show its organ‐protective effects in rodents. In the present study, we developed a novel murine heart failure model (triple‐tg) to enable us to evaluate the cardioprotective effect of renin inhibitors at more relevant doses for humans, by cross‐breeding calsequestrin transgenic (CSQ‐tg) mice with human renin and human angiotensinogen double‐transgenic mice. The triple‐tg mice exhibited increased plasma renin activity, worsened cardiac hypertrophy, and higher mortality compared to CSQ‐tg mice. Triple‐tg mice treated with 10 mg·kg−1 of TAK‐272 (imarikiren/SCO‐272), an orally active direct renin inhibitor, exhibited improvements in heart failure phenotypes, such as cardiac hypertrophy and survival rate; however, a dose of 300 mg·kg−1 was required to improve symptoms in CSQ‐tg mice. Our results suggest that this newly generated triple‐tg heart failure model is useful to evaluate the cardioprotective effects of human renin inhibitors at clinically relevant doses, thereby minimizing the concerns of off‐target effects related to much higher drug exposure than that achieved in clinical study.

Differential Effects of Doxazosin on Renin-Angiotensin-System- Regulating Aminopeptidase Activities in Neuroblastoma and Glioma Tumoral Cells.

It has been described that doxazosin, an antihypertensive drug, also promotes glioblastoma cells death by inhibiting cell proliferation, arresting cell cycle and inducing apoptosis. Doxazosin has also demonstrated several modulator effects on renin-angiotensin system (RAS)- regulating aminopeptidase activities, which are highly involved in tumor growth in experimental glioma. Therefore, it remains to elucidate if the anti-tumoral effects of doxazosin could also be mediated by the proteolytic regulatory components of the RAS. To analyze the effects of doxazosin on cell growth and on RAS-regulating proteolytic regulatory aspartyl aminopeptidase (ASAP), aminopeptidase A (APA), aminopeptidase N (APN), aminopeptidase B (APB) and insulin-regulated aminopeptidase (IRAP) specific activities in the human neuroblastoma NB69 and astroglioma U373-MG tumoral cell lines. Human neuroblastoma NB69 and astroglioma U373-MG cell lines were treated with doxazosin 50-500 μM for 24h or 48h. The effects on cell growth and on RAS-regulating aminopeptidase specific activities were analyzed. Doxazosin treatments promote a concentration-dependent inhibition on cell growth in both NB69 and U373-MG cells, being NB69 cells more sensitive to the drug than U373-MG cells. However, its effects on RAS-regulating aminopeptidase specific activities depend on the concentration used, the duration of the treatment and the cell type. These data confirm the existence of a different dynamic progression of RAS cascade in each tumoral cell line as a consequence of the treatment with doxazosin and time of action, which also implies a very dynamic metabolism of the peptides which participate in each step of RAS cascade. Our results indicate that doxazosin modifies the proteolytic regulatory enzymes of RAS cascade, modulating the bioactive efficacy of the different angiotensin peptides, and therefore, of their functional roles as initiators/promoters of cell proliferation as autocrine/paracrine mediators.

Sex dimorphism in ANGII-mediated crosstalk between ACE2 and ACE in diabetic nephropathy

Angiotensin-converting enzyme (ACE) and ACE2 play a critical role in the renin–angiotensin system (RAS) by altering angiotensin II (ANGII) levels, thus governing its deleterious effects. Both enzymes are altered by sex and diabetes, and play an important role in the development of diabetic nephropathy (DN). Importantly, previous evidence in diabetic and ACE2-deficient (ACE2KO) males suggest a sex-dependent crosstalk between renal ACE and ACE2. In the present work, we aimed to study the sex-specific susceptibility to diabetes and direct infusion of ANGII in kidney disease progression, with a special focus on its link to ACE2 and ACE. In our mouse model, ANGII promoted hypertension, albuminuria, reduced glomerular filtration, and glomerular histological alterations. ANGII adverse effects were accentuated by diabetes and ACE2 deficiency, in a sex-dependent fashion: ACE2 deficiency accentuated ANGII-induced hypertension, albuminuria, and glomerular hypertrophy in diabetic females, whereas in diabetic males exacerbated ANGII-mediated glomerular hypertrophy, mesangial expansion, and podocyte loss. At the molecular level, ANGII downregulated renal ACE gene and enzymatic activity levels, as well as renin gene expression in ACE2KO mice. Interestingly, male sex and diabetes accentuated this effect. Here we show sex dimorphism in the severity of diabetes- and ANGII-related renal lesions, and demonstrate that ACE2- and ACE-related compensatory mechanisms are sex-specific. Supporting our previous findings, the modulation and ANGII-mediated crosstalk between ACE2 and ACE in DN progression was more evident in males. This work increases the understanding of the sex-specific role of ACE2 and ACE in DN, reinforcing the necessity of more personalized treatments targeting RAS.Sex and diabetes affect angiotensin-converting enzyme (ACE) and ACE2 expression and are key determinants of kidney disease progression. Here the authors demonstrate that there are sex differences in the severity of angiotensin II (ANGII)-hypertension and diabetic nephropathy, the activation of the renin-angiotensin system cascade, and the crosstalk between ACE and ACE2 in vivo. This work increases our understanding of the sex-specific role of ACE2 and ACE in diabetic nephropathy, reinforcing the necessity of individualized treatments.

TAK-272 (imarikiren), a novel renin inhibitor, improves cardiac remodeling and mortality in a murine heart failure model.

The renin-angiotensin system (RAS), which plays an important role in the progression of heart failure, is efficiently blocked by the inhibition of renin, the rate-limiting enzyme in the RAS cascade. In the present study, we investigated the cardioprotective effects of TAK-272 (SCO-272, imarikiren), a novel, orally effective direct renin inhibitor (DRI), and compared its efficacy with that of aliskiren, a DRI that is already available in the market. TAK-272 was administered to calsequestrin transgenic (CSQ-tg) heart failure mouse model that show severe symptoms and high mortality. The CSQ-tg mice treated with 300 mg/kg, the highest dose tested, of TAK-272 showed significantly reduced plasma renin activity (PRA), cardiac hypertrophy, and lung congestion. Further, TAK-272 reduced cardiomyocyte injury accompanied by an attenuation of the increase in NADPH oxidase 4 and nitric oxide synthase 3 expressions. TAK-272 also prolonged the survival of CSQ-tg mice in a dose-dependent manner (30 mg/kg: P = 0.42, 100 mg/kg: P = 0.12, 300 mg/kg: P < 0.01). Additionally, when compared at the same dose level (300 mg/kg), TAK-272 showed strong and sustained PRA inhibition and reduced the heart weight and plasma N-terminal pro-brain natriuretic peptide (NT-proBNP) concentration, a heart failure biomarker, while aliskiren showed a significant weaker PRA inhibition and failed to demonstrate any cardioprotective effects. Our results showed that TAK-272 is an orally active and persistent renin inhibitor, which reduced the mortality of CSQ-tg mice and conferred protection against cardiac hypertrophy and injury. Thus, TAK-272 treatment could provide a new therapeutic approach for heart failure.

Study of Angiotensin Converting Enzyme Gene Polymorphism in Egyptian Type 2 Diabetes Mellitus with Diabetic Kidney Disease

Objective: Diabetic kidney disease DKD (Diabetic nephropathy DN) is considered one of the chronic micro vascular complications of diabetes mellitus and considered the commonest cause leading to chronic renal failure and chronic renal dialysis. Genetic susceptibility has been implicated in DKD. The angiotensin converting enzyme (ACE) is one of the key roles in the renin angiotensin system cascade by converting angiotensin I to angiotensin II which plays a key role in regulation of blood pressure as well as electrolytes and fluid balance. This study addressed the association of (ACE) gene polymorphisms with DN in Egyptian (T2DM) patients. Methods: Our research comprised of 75 cases of T2DM with diabetic kidney disease, 100 cases of T2DM without DKD and 94 healthy volunteers. Different genotypes of ACE gene were determined by SSP-PCR analysis. Results: Gene polymorphism of ACE (DD, ID, II) in diabetic patient with DKD is 44%, 52%, 4% respectively and for T2DM individuals without DKD is 23%, 72%, 5% respectively. (DD) had significant higher frequencies in T2DM patients with DKD compared to those without DKD (p < 0.005) and (ID) had significant higher frequencies in T2DM without DKD (p < 0.0001). These results indicated that there is an association between ACE gene polymorphisms and susceptibility of diabetic patients to be affected by diabetic kidney disease. Conclusion: From our results, we can conclude that genotype of ACE in Egypt DD is the genotype of cases diabetic kidney disease. So the presence of D allele has a significant relation with diabetic kidney disease. Our data confirm the role of ACE in its relationship with diabetic kidney disease in Egyptian type 2 diabetic patients.

Hesperidin Suppresses Renin-Angiotensin System Mediated NOX2 Over-Expression and Sympathoexcitation in 2K-1C Hypertensive Rats.

Hesperidin, a flavonoid derived from citrus fruits, possesses several beneficial effects including anti-oxidation and anti-inflammation. The aim of this study was to investigate the effects of hesperidin on the renin-angiotensin system (RAS) cascade that mediated oxidative stress and sympathoexcitation in two-kidney, one-clipped (2K-1C) hypertensive rats. 2K-1C hypertension was induced in male Sprague-Dawley rats. Hypertensive rats were treated with hesperidin at 20[Formula: see text]mg/kg or 40[Formula: see text]mg/kg or losartan at 10[Formula: see text]mg/kg beginning at three weeks after surgery and then continued for four weeks ([Formula: see text]/group). Hesperidin reduced blood pressure in a dose-dependent manner in hypertensive rats compared to untreated rats ([Formula: see text]). Increased plasma angiotensin converting enzyme (ACE) activity and angiotensin II levels, as well as, upregulated AT1 receptor protein expression in aortic tissues were attenuated in hypertensive rats treated with hesperidin. Hesperidin suppressed oxidative stress markers and NADPH oxidase over-expression, and restored plasma nitric oxide metabolites in 2K-1C rats. This was associated with improvement of the vascular response to acetylcholine in isolated mesenteric vascular beds and aortic rings from 2K-1C rats treated with hesperidin ([Formula: see text]). Enhancement of nerve-mediated vasoconstriction related to high plasma noradrenaline in the 2K-1C group was alleviated by hesperidin treatment ([Formula: see text]). Furthermore, losartan exhibited antihypertensive effects by suppressing the RAS cascade and oxidative stress and improved vascular dysfunction observed in 2K-1C rats ([Formula: see text]). Based on these results, it can be presumed that hesperidin is an antihypertensive agent. Its antihypertensive action might be associated with reducing RAS cascade-induced NOX2 over-expression and sympathoexcitation in 2K-1C hypertensive rats.

Many Faces of Renin-angiotensin System - Focus on Eye.

The renin-angiotensin system (RAS), that is known for its role in the regulation of blood pressure as well as in fluid and electrolyte homeostasis, comprises dozens of angiotensin peptides and peptidases and at least six receptors. Six central components constitute the two main axes of the RAS cascade. Angiotensin (1-7), an angiotensin converting enzyme 2 and Mas receptor axis (ACE2-Ang(1-7)-MasR) counterbalances the harmful effects of the angiotensin II, angiotensin converting enzyme 1 and angiotensin II type 1 receptor axis (ACE1-AngII-AT1R) Whereas systemic RAS is an important factor in blood pressure regulation, tissue-specific regulatory system, responsible for long term regional changes, that has been found in various organs. In other words, RAS is not only endocrine but also complicated autocrine system. The human eye has its own intraocular RAS that is present e.g. in the structures involved in aqueous humor dynamics. Local RAS may thus be a target in the development of new anti-glaucomatous drugs. In this review, we first describe the systemic RAS cascade and then the local ocular RAS especially in the anterior part of the eye.

Renin-angiotensin system in vertebrates: phylogenetic view of structure and function.

Renin substrate, biological renin activity, and/or renin-secreting cells in kidneys evolved at an early stage of vertebrate phylogeny. Angiotensin (Ang) I and II molecules have been identified biochemically in representative species of all vertebrate classes, although variation occurs in amino acids at positions 1, 5, and 9 of Ang I. Variations have also evolved in amino acid positions 3 and 4 in some cartilaginous fish. Angiotensin receptors, AT1 and AT2 homologues, have been identified molecularly or characterized pharmacologically in nonmammalian vertebrates. Also, various forms of angiotensins that bypass the traditional renin-angiotensin system (RAS) cascades or those from large peptide substrates, particularly in tissues, are present. Nonetheless, the phylogenetically important functions of RAS are to maintain blood pressure/blood volume homeostasis and ion-fluid balance via the kidney and central mechanisms. Stimulation of cell growth and vascularization, possibly via paracrine action of angiotensins, and the molecular biology of RAS and its receptors have been intensive research foci. This review provides an overview of: (1) the phylogenetic appearance, structure, and biochemistry of the RAS cascade; (2) the properties of angiotensin receptors from comparative viewpoints; and (3) the functions and regulation of the RAS in nonmammalian vertebrates. Discussions focus on the most fundamental functions of the RAS that have been conserved throughout phylogenetic advancement, as well as on their physiological implications and significance. Examining the biological history of RAS will help us analyze the complex RAS systems of mammals. Furthermore, suitable models for answering specific questions are often found in more primitive animals.

Prorenin stimulates a pro-angiogenic and pro-inflammatory response in retinal endothelial cells and an M1 phenotype in retinal microglia.

Angiogenesis and inflammation are causative factors in the development of neovascular retinopathies. These processes involve the retinal endothelium and the retinal immune cells, microglia. The renin-angiotensin system contributes to retinal injury via the actions of the type 1 angiotensin receptor (AT1R). However, it has been suggested that prorenin, the initiator of the renin-angiotensin system cascade, influences retinal injury independently from the AT1R. We evaluated whether prorenin induced a pro-angiogenic and pro-inflammatory response in retinal endothelial cells and a pro-inflammatory phenotype in retinal microglia. Primary cultures of retinal endothelial cells and microglia were studied. Rat recombinant prorenin (2 nmol/L) stimulated the proliferation and tubulogenesis of retinal endothelial cells; it increased the levels of pro-angiogenic factors, vascular endothelial growth factor, angiopoietin-1, and tyrosine kinase with immunoglobulin and epidermal growth factor homology domains, and pro-inflammatory factors, intercellular adhesion molecule-1 and monocyte chemoattractant protein-1, relative to the controls. The messenger RNA levels of the (pro)renin receptor were also increased. These effects occurred in the presence of the AT1R blocker candesartan (10 μmol/L) and the renin inhibitor aliskiren (10 μmol/L). Microglia, which express the (pro)renin receptor, elicited an activated phenotype when exposed to prorenin, which was characterized by increased levels of intercellular adhesion molecule-1, monocyte chemoattractant protein-1, tumour necrosis factor-α, interleukin-6, and interleukin-1β and by decreased levels of interleukin-10 and arginase-1 relative to controls. Candesartan did not influence the effects of prorenin on retinal microglia. In conclusion, prorenin has distinct pro-angiogenic and pro-inflammatory effects on retinal cells that are independent of the AT1R, indicating the potential importance of prorenin in retinopathy.

The renin-angiotensin system mediates EGF receptor-vitamin d receptor cross-talk in colitis-associated colon cancer.

We previously showed that EGF receptor (EGFR) promotes tumorigenesis in the azoxymethane/dextran sulfate sodium (AOM/DSS) model, whereas vitamin D suppresses tumorigenesis. EGFR-vitamin D receptor (VDR) interactions, however, are incompletely understood. Vitamin D inhibits the renin-angiotensin system (RAS), whereas RAS can activate EGFR. We aimed to elucidate EGFR-VDR cross-talk in colorectal carcinogenesis. To examine VDR-RAS interactions, we treated Vdr(+/+) and Vdr(-/-) mice with AOM/DSS. Effects of VDR on RAS and EGFR were examined by Western blotting, immunostaining, and real-time PCR. We also examined the effect of vitamin D3 on colonic RAS in Vdr(+/+) mice. EGFR regulation of VDR was examined in hypomorphic Egfr(Waved2) (Wa2) and Egfr(wild-type) mice. Angiotensin II (Ang II)-induced EGFR activation was studied in cell culture. Vdr deletion significantly increased tumorigenesis, activated EGFR and β-catenin signaling, and increased colonic RAS components, including renin and angiotensin II. Dietary VD3 supplementation suppressed colonic renin. Renin was increased in human colon cancers. In studies in vitro, Ang II activated EGFR and stimulated colon cancer cell proliferation by an EGFR-mediated mechanism. Ang II also activated macrophages and colonic fibroblasts. Compared with tumors from Egfr(Waved2) mice, tumors from Egfr(wild-type) mice showed upregulated Snail1, a suppressor of VDR, and downregulated VDR. VDR suppresses the colonic RAS cascade, limits EGFR signals, and inhibits colitis-associated tumorigenesis, whereas EGFR increases Snail1 and downregulates VDR in colonic tumors. Taken together, these results uncover a RAS-dependent mechanism mediating EGFR and VDR cross-talk in colon cancer.

Structural determinants for binding, activation, and functional selectivity of the angiotensin AT1 receptor.

The renin-angiotensin system (RAS) plays an important role in the pathophysiology of cardiovascular disorders. Pharmacologic interventions targeting the RAS cascade have led to the discovery of renin inhibitors, angiotensin-converting enzyme inhibitors, and AT(1) receptor blockers (ARBs) to treat hypertension and some cardiovascular and renal disorders. Mutagenesis and modeling studies have revealed that differential functional outcomes are the results of multiple active states conformed by the AT(1) receptor upon interaction with angiotensin II (Ang II). The binding of agonist is dependent on both extracellular and intramembrane regions of the receptor molecule, and as a consequence occupies more extensive area of the receptor than a non-peptide antagonist. Both agonist and antagonist bind to the same intramembrane regions to interfere with each other's binding to exhibit competitive, surmountable interaction. The nature of interactions with the amino acids in the receptor is different for each of the ARBs given the small differences in the molecular structure between drugs. AT(1) receptors attain different conformation states after binding various Ang II analogues, resulting in variable responses through activation of multiple signaling pathways. These include both classical and non-classical pathways mediated through growth factor receptor transactivations, and provide cross-communication between downstream signaling molecules. The structural requirements for AT(1) receptors to activate extracellular signal-regulated kinases 1 and 2 through G proteins, or G protein-independently through β-arrestin, are different. We review the structural and functional characteristics of Ang II and its analogs and antagonists, and their interaction with amino acid residues in the AT(1) receptor.

Renin inhibition improves ovariectomy-induced osteoporosis of lumbar vertebra in mice.

The skeletal renin–angiotensin system (RAS) is involved in the progression of osteoporosis and the active peptide within the RAS, angiotensin II (ANG II), has deleterious effects on bones. This study was performed to investigate whether suppression of the rate-limiting step of the RAS cascade by the renin inhibitor aliskiren has a benefit on trabecular bone in osteoporotic mice. A postmenopausal osteoporosis model was induced by bilateral ovariectomy. The ovariectomized (OVX) mice were treated with a low (5 mg/kg) or high (25 mg/kg) dose of aliskiren for 6 weeks. Micro-computed tomography was performed to detect trabecular bone parameters of lumbar vertebra and to obtain 3-dimensional (3D) images. Treatment with aliskiren markedly increased bone volume over total volume (p<0.05), trabecular bone number (p<0.05), connectivity density (p<0.05), and bone mineral density (p<0.05) and reduced trabecular bone separation (p<0.05) compared to vehicle-treated OVX mice. Similarly, the 3D images were consistent with the quantitative data that showed aliskiren could markedly reverse the ovariectomy-induced pathological changes of trabecular bone. Thus, this study indicated that the treatment of estrogen-deficient mice with aliskiren could markedly increase bone mass and improve trabecular bone structure, suggesting its potential application in treating postmenopausal osteoporosis.

ACE2, angiotensin‐(1‐7) and Mas receptor axis in inflammation and fibrosis

Recent advances have improved our understanding of the renin-angiotensin system (RAS). These have included the recognition that angiotensin (Ang)-(1-7) is a biologically active product of the RAS cascade. The identification of the ACE homologue ACE2, which forms Ang-(1-7) from Ang II, and the GPCR Mas as an Ang-(1-7) receptor have provided the necessary biochemical and molecular background and tools to study the biological significance of Ang-(1-7). Most available evidence supports a counter-regulatory role for Ang-(1-7) by opposing many actions of Ang II on AT₁ receptors, especially vasoconstriction and proliferation. Many studies have now shown that Ang-(1-7) by acting via Mas receptor exerts inhibitory effects on inflammation and on vascular and cellular growth mechanisms. Ang-(1-7) has also been shown to reduce key signalling pathways and molecules thought to be relevant for fibrogenesis. Here, we review recent findings related to the function of the ACE2/Ang-(1-7)/Mas axis and focus on the role of this axis in modifying processes associated with acute and chronic inflammation, including leukocyte influx, fibrogenesis and proliferation of certain cell types. More attention will be given to the involvement of the ACE2/Ang-(1-7)/Mas axis in the context of renal disease because of the known relevance of the RAS for the function of this organ and for the regulation of kidney inflammation and fibrosis. Taken together, this knowledge may help in paving the way for the development of novel treatments for chronic inflammatory and renal diseases.