Local renin-angiotensin systems

The existence of a local cardiovascular renin-angiotensin system (RAS) is often invoked to explain the long-term beneficial effects of RAS inhibitors in heart failure and hypertension. The implicit assumption is that all components of the RAS are synthesized in situ, so that local angiotensin II formation may occur independently of the circulating RAS. Evidence for this assumption however is lacking. The angiotensin release from isolated perfused rat hearts or hindlimbs depends on the presence of renal renin. When calculating the in vivo angiotensin production at tissue sites in humans and pigs, taking into account the extensive regional angiotensin clearance by infusing radiolabeled angiotensin I or II, it was found that angiotensin production correlated closely with plasma renin activity. Moreover, in pigs the cardiac tissue levels of renin and angiotensin were directly correlated with their respective plasma levels, and both in tissue and plasma the levels were undetectably low after nephrectomy. Similarly, rat vascular renin and angiotensin decrease to low or undetectable levels within 48 h after nephrectomy. Aortic renin has a longer half life than plasma renin, suggesting that renin may be bound by the vessel wall. In support of this assumption, both renin receptors and renin-binding proteins have been described. Like ACE, renin was enriched in a purified membrane fraction prepared from cardiac tissue. Binding of renin to cardiac or vascular membranes may therefore be part of a mechanism by which renin is taken up from plasma. It appears that the concept of a local RAS needs to be reassessed. Local angiotensin formation in heart and vessel wall does occur, but depends, at least under normal circumstances, on the uptake of renal renin from the circulation. Tissues may regulate their local angiotensin concentrations by varying the number of renin receptors and/or renin-binding proteins, the ACE level, the amount of metabolizing enzymes and the angiotensin receptor density.Abbreviations RAS renin-angiotensin system - ANG angiotensin - ACE angiotensin-converting enzyme - PRA plasma renin activity     

Involvement of the Skeletal Renin-Angiotensin System in Age-Related Osteoporosis of Ageing Mice

The local tissue-specific renin-angiotensin system (RAS) was identified. The aim of this study was to investigate the role of local bone RAS in the osteoporosis of aging mice. Twelve-month-old and two-month-old male mice were respectively assigned to the ageing and young groups. The tibias and femurs were collected for an analysis of histomorphology, bone mass, and gene and protein expression. H&E staining and micro-CT measurement showed a loss of the trabecular bone network and decrease of bone mineral density in the proximal tibial metaphysis of the aged mice. The PCR results indicated the significant up-regulation of renin and angiotensinogen (AGT) mRNA expression in both the tibia and femur of the ageing mice. Western blotting data showed that the tibial angiotensin II protein expression was significantly increased in the ageing group. The enhancement of renin and AGT expression in the bone tissue resulted in the increased production of angiotensin II which plays an important role in the pathology of age-related osteoporosis.     

Involvement of the skeletal Renin-Angiotensin system in age-related osteoporosis of ageing mice

The local tissue-specific renin-angiotensin system (RAS) was identified. The aim of this study was to investigate the role of local bone RAS in the osteoporosis of aging mice. Twelve-month-old and two-month-old male mice were respectively assigned to the ageing and young groups. The tibias and femurs were collected for an analysis of histomorphology, bone mass, and gene and protein expression. H&E staining and micro-CT measurement showed a loss of the trabecular bone network and decrease of bone mineral density in the proximal tibial metaphysis of the aged mice. The PCR results indicated the significant up-regulation of renin and angiotensinogen (AGT) mRNA expression in both the tibia and femur of the ageing mice. Western blotting data showed that the tibial angiotensin II protein expression was significantly increased in the ageing group. The enhancement of renin and AGT expression in the bone tissue resulted in the increased production of angiotensin II which plays an important role in the pathology of age-related osteoporosis.     

Genetic evidence that lethality in angiotensinogen-deficient mice is due to loss of systemic but not renal angiotensinogen

Angiotensinogen (AGT)-deficient mice die shortly after birth presumably due to renal dysfunction caused by the presence of severe vascular and tubular lesions in the kidney. Because AGT is expressed in renal proximal tubule cells, we hypothesized that its loss may be the primary mediator of the lethal phenotype. We generated two models to test this hypothesis by breeding transgenic mice expressing human renin with mice expressing human AGT (hAGT) either systemically or kidney-specifically. We then bred double transgenic mice with AGT+/- mice, intercrossed the compound heterozygotes, and examined the offspring. We previously reported that the presence of the human renin and systemically expressed hAGT transgene complemented the lethality observed in AGT-/- mice. On the contrary, we show herein that the presence of the human renin and kidney-specific hAGT transgene cannot rescue lethality in AGT-/- mice. An analysis of newborns indicated that AGT-/- mice were born in normal numbers, and collection of dead 10-day old pups revealed an enrichment in AGT-/-. Importantly, we demonstrated that angiotensinogen protein and functional angiotensin II was generated in the kidney, and the kidney-specific transgene was temporally expressed during renal development similar to the endogenous AGT gene. These data strongly support the notion that the loss of systemic AGT, but not intrarenal AGT, is responsible for death in the AGT-/- mouse model. Taken together with our previous studies, we conclude that the intrarenal renin-angiotensin system located in the proximal tubule plays an important role in blood pressure regulation and may cause hypertension if overexpressed, but may not be required for continued development of the kidney after birth.     

血管紧张素转换酶2-血管紧张素1-7-Mas轴对血管作用的研究进展

血管紧张素转换酶2（ACE2）和Mas受体的发现使人们对肾素-血管紧张素（RAS）有了更全面的认识。ACE2可水解血管紧张素Ⅰ和血管紧张素Ⅱ直接或间接生成血管紧张素1-7（Ang 1-7）,并与高血压的形成密切相关。Ang 1-7主要通过Mas受体引起血管舒张、抑制细胞增殖。ACE2-Ang1-7-Mas轴的发现为RAS的研究、高血压等心血管疾病的防治和新药开发提供了新的思路和方向。     

The Influence of Angiotensin Converting Enzyme and Angiotensinogen Gene Polymorphisms on Hypertrophic Cardiomyopathy

Some studies have reported that angiotensin converting enzyme (ACE) and angiotensinogen (AGT) genes have been associated with hypertrophic cardiomyopathy (HCM). However, there have been inconsonant results among different studies. To clarify the influence of ACE and AGT on HCM, a systemic review and meta-analysis of case-control studies were performed. The following databases were searched to indentify related studies: PubMed database, the Embase database, the Cochrane Central Register of Controlled Trials database, China National Knowledge Information database, and Chinese Scientific and Technological Journal database. Search terms included “hypertrophic cardiomyopathy”, “angiotensin converting enzyme” (ACE) or “ACE” and “polymorphism or mutation”. For the association of AGT M235T polymorphism and HCM, “angiotensin converting enzyme” or “ACE” was replaced with “angiotensinogen”. A total of seventeen studies were included in our review. For the association of ACE I/D polymorphism and HCM, eleven literatures were included in the meta-analysis on association of penetrance and genotype. Similarly, six case-control studies were included in the meta-analysis for AGT M235T. For ACE I/D polymorphism, the comparison of DI/II genotype vs DD genotype was performed in the present meta-analysis. The OR was 0.73 (95% CI: 0.527, 0.998, P = 0.049, power = 94%, alpha = 0.05) after the study which deviated from Hardy-Weinberg Equilibrium was excluded, indicating that the ACE I/D gene polymorphism might be associated with HCM. The AGT M235T polymorphism did not significantly affect the risk of HCM. In addition, ACE I/D gene polymorphism did not significantly influence the interventricular septal thickness in HCM patients. In conclusion, the ACE I/D polymorphism might be associated with the risk of HCM.     

Renin-angiotensin system genes polymorphism in Egyptians with premature coronary artery disease

Genetics polymorphism of the renin-angiotensin system (RAS) affects the pathogenesis of atherosclerosis and associated with coronary artery disease (CAD). We aimed to investigate the association between the RAS genes and premature CAD (PCAD) in Egyptians. 116 patients with PCAD, 114 patients with late onset CAD and 119 controls were included in the study. Angiotensin converting enzyme (ACE), angiotensin II receptor type 1 (ATR1) and angiotensinogen (AGT) genes polymorphisms were analyzed by polymerase chain reaction (PCR). We found that ACE DD, AGT TT and ATR1 CC increased the risk of PCAD by 2.7, 2.8 and 2.86 respectively). Smoking, hypertension, diabetes, total cholesterol, triglycerides and LDL cholesterol were independent risk factors for the development of PCAD. We conclude that the ACE DD, AGT TT and ATR1 CC genotypes may increase the susceptibility of an individual to have PCAD. The coexistence of CAD risk factors with these risky RAS genotypes may lead to the development of PCAD in Egyptian patients.     

Obesity and malnutrition similarly alter the renin–angiotensin system and inflammation in mice and human adipose

The main goal of the present study was to evaluate the metabolic profile, inflammatory markers and the gene expression of the renin–angiotensin system (RAS) components in the visceral adipose tissue of eutrophic, obese and malnourished individuals and mice models of obesity and food restriction. Male Swiss mice were divided into eight groups and fed different levels of food restriction (20%, 40%, or 60%) using standard or high-fat diet. Metabolic profile and adipose tissues were assessed. The expression of AGT (Angiotensinogen), ACE (Angiotensin-converting enzyme), ACE2 (Angiotensin-converting enzyme 2), interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α) in the mice epididymal adipose tissue and the human visceral adipose tissue was assessed. The main findings showed reduced body weight, improved metabolism, decreased adipose tissues weight and reduced adipocyte area in mice submitted to food restriction. Diminished expression of IL-6, TNF-α, AGT, AT1 and ACE was detected in the 20% and 40% food restriction animal groups, although they were increased in the 60% malnourished group. Increased expression of IL-6, TNF-α, AGT and ACE in obese and malnourished individuals was observed. Adipocytes size was increased in obese individuals and reduced in malnutrition. In conclusion, we found that food restriction of 20% and 40% improved the metabolic profile, ameliorated the inflammatory status and down-regulated the RAS in mice. Severe 60% food restriction (malnutrition), however, stimulated a proinflammatory state and increased AGT and ACE expression in the adipose tissue of mice. A similar profile was observed in the adipose tissue of obese and malnourished humans, supporting the critical role of inflammation and RAS as mediators of metabolic disorders.     

New insights and perspectives on intrarenal renin-angiotensin system: focus on intracrine/intracellular angiotensin II

Although renin, the rate-limiting enzyme of the renin-angiotensin system (RAS), was first discovered by Robert Tigerstedt and Bergman more than a century ago, the research on the RAS still remains stronger than ever. The RAS, once considered to be an endocrine system, is now widely recognized as dual (circulating and local/tissue) or multiple hormonal systems (endocrine, paracrine and intracrine). In addition to the classical renin/angiotensin I-converting enzyme (ACE)/angiotensin II (Ang II)/Ang II receptor (AT₁/AT₂) axis, the prorenin/(Pro)renin receptor (PRR)/MAP kinase axis, the ACE2/Ang (1-7)/Mas receptor axis, and the Ang IV/AT₄/insulin-regulated aminopeptidase (IRAP) axis have recently been discovered. Furthermore, the roles of the evolving RAS have been extended far beyond blood pressure control, aldosterone synthesis, and body fluid and electrolyte homeostasis. Indeed, novel actions and underlying signaling mechanisms for each member of the RAS in physiology and diseases are continuously uncovered. However, many challenges still remain in the RAS research field despite of more than one century's research effort. It is expected that the research on the expanded RAS will continue to play a prominent role in cardiovascular, renal and hypertension research. The purpose of this article is to review the progress recently being made in the RAS research, with special emphasis on the local RAS in the kidney and the newly discovered prorenin/PRR/MAP kinase axis, the ACE2/Ang (1-7)/Mas receptor axis, the Ang IV/AT₄/IRAP axis, and intracrine/intracellular Ang II. The improved knowledge of the expanded RAS will help us better understand how the classical renin/ACE/Ang II/AT₁ receptor axis, extracellular and/or intracellular origin, interacts with other novel RAS axes to regulate blood pressure and cardiovascular and kidney function in both physiological and diseased states.     

The adipose tissue renin-angiotensin system and metabolic disorders: a review of molecular mechanisms

The renin-angiotensin system (RAS) is classically known for its role in regulation of blood pressure, fluid and electrolyte balance. In this system, angiotensinogen (Agt), the obligate precursor of all bioactive angiotensin peptides, undergoes two enzymatic cleavages by renin and angiotensin converting enzyme (ACE) to produce angiotensin I (Ang I) and angiotensin II (Ang II), respectively. The contemporary view of RAS has become more complex with the discovery of additional angiotensin degradation pathways such as ACE2. All components of the RAS are expressed in and have independent regulation of adipose tissue. This local adipose RAS exerts important auto/paracrine functions in modulating lipogenesis, lipolysis, adipogenesis as well as systemic and adipose tissue inflammation. Mice with adipose-specific Agt overproduction have a 30% increase in plasma Agt levels and develop hypertension and insulin resistance, while mice with adipose-specific Agt knockout have a 25% reduction in Agt plasma levels, demonstrating endocrine actions of adipose RAS. Emerging evidence also points towards a role of RAS in regulation of energy balance. Because adipose RAS is overactivated in many obesity conditions, it is considered a potential candidate linking obesity to hypertension, insulin resistance and other metabolic derangements.     

The adipose tissue renin-angiotensin system and metabolic disorders: a review of molecular mechanisms

The renin-angiotensin system (RAS) is classically known for its role in regulation of blood pressure, fluid and electrolyte balance. In this system, angiotensinogen (Agt), the obligate precursor of all bioactive angiotensin peptides, undergoes two enzymatic cleavages by renin and angiotensin converting enzyme (ACE) to produce angiotensin I (Ang I) and angiotensin II (Ang II), respectively. The contemporary view of RAS has become more complex with the discovery of additional angiotensin degradation pathways such as ACE2. All components of the RAS are expressed in and have independent regulation of adipose tissue. This local adipose RAS exerts important auto/paracrine functions in modulating lipogenesis, lipolysis, adipogenesis as well as systemic and adipose tissue inflammation. Mice with adipose-specific Agt overproduction have a 30% increase in plasma Agt levels and develop hypertension and insulin resistance, while mice with adipose-specific Agt knockout have a 25% reduction in Agt plasma levels, demonstrating endocrine actions of adipose RAS. Emerging evidence also points towards a role of RAS in regulation of energy balance. Because adipose RAS is overactivated in many obesity conditions, it is considered a potential candidate linking obesity to hypertension, insulin resistance and other metabolic derangements.     

AT1A angiotensin receptors in the renal proximal tubule regulate blood pressure

Hypertension affects more than 1.5 billion people worldwide but the precise cause of elevated blood pressure (BP) cannot be determined in most affected individuals. Nonetheless, blockade of the renin-angiotensin system (RAS) lowers BP in the majority of patients with hypertension. Despite its apparent role in hypertension pathogenesis, the key cellular targets of the RAS that control BP have not been clearly identified. Here we demonstrate that RAS actions in the epithelium of the proximal tubule have a critical and nonredundant role in determining the level of BP. Abrogation of AT(1) angiotensin receptor signaling in the proximal tubule alone is sufficient to lower BP, despite intact vascular responses. Elimination of this pathway reduces proximal fluid reabsorption and alters expression of key sodium transporters, modifying pressure-natriuresis and providing substantial protection against hypertension. Thus, effectively targeting epithelial functions of the proximal tubule of the kidney should be a useful therapeutic strategy in hypertension.     

Working outside the system: an update on the unconventional behavior of the renin-angiotensin system components

The renin-angiotensin system (RAS) plays an important role in regulating arterial pressure, blood volume, thirst, cardiac function, and cellular growth. Both a circulating and multiple tissue-localized systems have been identified, and are generally portrayed as a series of reactions that occur sequentially with a single outcome: angiotensinogen is cleaved by renin to form angiotensin I, which in turn is processed by angiotensin-converting enzyme (ACE) to angiotensin II, which then activates either the AT1 or the AT2 plasma membrane receptor. Evidence has emerged, however, showing that some RAS components play important roles outside of this canonical scheme. This article provides an overview of some recently identified extra-system functions. In addition to forming angiotensin II, ACE is a multifunctional enzyme equally important in the metabolism of vasodilator and antifibrotic peptides. As the membrane-bound form, ACE functions as a "receptor" that initiates intracellular signaling leading to gene expression. Both angiotensin I and II may lead to actions that are independent of, or even oppose, those of the RAS via their metabolism by the novel ACE-homologue ACE2. The two angiotensin II receptor types have ligand-independent roles that influence cellular signaling and growth, some of which may result from the ability to form hetero-dimers with other 7-transmembrane receptors. Finally, intracellular angiotensin II has been demonstrated to have actions on cell-communication, gene expression, and cellular growth, through both receptor-dependent and independent means. A greater understanding of these extra-system functions of the RAS components may aid in the development of novel treatments for hypertension, myocardial ischemia, and heart failure.     

Placental insufficiency results in temporal alterations in the renin angiotensin system in male hypertensive growth restricted offspring

Reduced uterine perfusion initiated in late gestation in the rat results in intrauterine growth restriction (IUGR) and development of hypertension by 4 wk of age. We hypothesize that the renin angiotensin system (RAS), a regulatory system important in the long-term control of blood pressure, may be programmed by placental insufficiency and may contribute to the etiology of IUGR hypertension. We previously reported that RAS blockade abolished hypertension in adult IUGR offspring; however, the mechanisms responsible for the early phase of hypertension are unresolved. Therefore, the purpose of this study was to examine RAS involvement in early programmed hypertension and to determine whether temporal changes in RAS expression are observed in IUGR offspring. Renal renin and angiotensinogen mRNA expression were significantly decreased at birth (80 and 60%, respectively); plasma and renal RAS did not differ in conjunction with hypertension (mean increase of 14 mmHg) in young IUGR offspring; however, hypertension (mean increase of 22 mmHg) in adult IUGR offspring was associated with marked increases in renal angiotensin-converting enzyme (ACE) activity (122%) and renal renin and angiotensinogen mRNA (7-fold and 7.4-fold, respectively), but no change in renal ANG II or angiotensin type 1 receptor. ACE inhibition (enalapril, 10 mg x kg(-1) x day(-1), administered from 2 to 4 wk of age) abolished hypertension in IUGR at 4 wk of age (decrease of 15 mmHg, respectively) with no significant depressor effect in control offspring. Therefore, temporal alterations in renal RAS are observed in IUGR offspring and may play a key role in the etiology of IUGR hypertension.     

Evolving concepts of the intrarenal renin-angiotensin system in health and disease: contributions of molecular biology.

Previous physiological and biochemical studies suggest the existence of an endogenous renin-angiotensin system (RAS) in the kidney. However, these data cannot exclude the contribution of the circulating RAS. Proof of the local synthesis of RAS components in the kidney has been obtained recently through the use of molecular biological techniques. Using Northern blot analysis, we have demonstrated the intrarenal expression of renin, angiotensinogen, and angiotensin-converting enzyme messenger RNAs. Employing in situ hybridization histochemistry, we have localized the intrarenal tissue sites of renin and angiotensinogen messenger RNA synthesis. Renin gene expression was found in cells of the juxtaglomerular apparatus. Angiotensinogen mRNA was primarily produced in the proximal convoluted tubule with lesser amounts in glomerular tufts and vasculature. These findings led us to hypothesize that the proximal tubule is a major site of renal Ang II synthesis and that locally synthesized Ang II might directly modulate tubular function. Both genes are subject to feedback regulation. Our studies showed that Ang II exerted a stimulatory effect on angiotensinogen but a negative feedback effect on renin gene expression. Dietary NaCl restriction stimulated the expression of both genes, although the onset of renin gene activation required more prolonged sodium chloride restriction. Furthermore, our data indicated that the sodium cation, irrespective of the anion, was primarily important in regulating renal angiotensinogen mRNA levels. Our studies also showed altered intrarenal renin or angiotensinogen expressions in pathophysiological states, e.g. in experimental heart failure and the spontaneously hypertensive rat. Taken together, these data support the existence of a intrarenal RAS and suggest its potential roles in the regulation of renal function in health and disease.     

The peptide network regulated by angiotensin converting enzyme (ACE) in hematopoiesis

The concept of a local bone marrow renin-angiotensin system (RAS) has been introduced and accumulating evidence suggests that the local RAS is actively involved in hematopoiesis. Angiotensin converting enzyme (ACE) is a key player in the RAS and makes the final effector angiotensin II. Besides angiotensin II, ACE also regulates a panel of bioactive peptides, such as substance P, Ac-SDKP and angiotensin 1–7. These peptides have also been individually reported in the regulation of pathways of hematopoiesis. In this setting, an ACE-regulated peptide network orchestrating hematopoiesis has emerged. Here, we focus on this peptide network and discuss the roles of ACE and its peptides in aspects of hematopoiesis. Special attention is given to the recent revelation that ACE is a bona fide marker of hematopoietic stem cells.Key words: hematopoiesis, myelopoiesis, angiotensin converting enzyme (ACE), angiotensin II, AT1 receptor, renin-angiotensin system (RAS), substance P, Ac-SDKP, angiotensin 1–7     

Renin released from mast cells activated by circulating MCP-1 initiates the microvascular phase of the systemic inflammation of alveolar hypoxia

Reduced alveolar Po(2) in rats produces a rapid systemic inflammation characterized by reactive O(2) species generation, mast cell (MC) degranulation, leukocyte-endothelial interactions, and increased vascular permeability. The inflammation is not initiated by the low systemic Po(2) but rather by the release of monocyte chemoattractant protein-1 (MCP-1) from alveolar macrophages (AMO) activated by alveolar hypoxia. Circulating AMO-borne MCP-1 induces MC degranulation, which activates the local renin-angiotensin system (RAS) and mediates the microvascular inflammation. This study was directed to determine the mechanism of RAS activation by MCP-1-induced MC degranulation. Experiments in isolated rat peritoneal MCs showed the following: 1) Western blots and immunocytochemistry demonstrated the presence of renin and angiotensin-converting enzyme (ACE) in MCs and their release upon degranulation; 2) MCP-1-induced degranulation of MCs incubated in plasma produced an increase in angiotensin II (ANG II) concentration; and 3) this increase was inhibited completely by the following agents: the MCP-1 receptor antagonist RS-102895, the specific rat renin inhibitor WFML, or the ACE inhibitor captopril administered separately. Captopril also inhibited ANG II generation by MCs incubated in culture medium plus ANG I. The results show that peritoneal MCs contain active renin, which activates the RAS upon degranulation, and that peritoneal MCs are a source of ACE and suggest that conversion of ANG I to ANG II is mediated predominantly by ACE. This study provides novel evidence of the presence of active renin in rat peritoneal MCs and helps explain the mechanism of activation of the RAS during alveolar hypoxia.     

The renin-angiotensin system: a target of and contributor to dyslipidemias, altered glucose homeostasis, and hypertension of the metabolic syndrome

The renin-angiotensin system (RAS) is an important therapeutic target in the treatment of hypertension. Obesity has emerged as a primary contributor to essential hypertension in the United States and clusters with other metabolic disorders (hyperglycemia, hypertension, high triglycerides, low HDL cholesterol) defined within the metabolic syndrome. In addition to hypertension, RAS blockade may also serve as an effective treatment strategy to control impaired glucose and insulin tolerance and dyslipidemias in patients with the metabolic syndrome. Hyperglycemia, insulin resistance, and/or specific cholesterol metabolites have been demonstrated to activate components required for the synthesis [angiotensinogen, renin, angiotensin-converting enzyme (ACE)], degradation (ACE2), or responsiveness (angiotensin II type 1 receptors, Mas receptors) to angiotensin peptides in cell types (e.g., pancreatic islet cells, adipocytes, macrophages) that mediate specific disorders of the metabolic syndrome. An activated local RAS in these cell types may contribute to dysregulated function by promoting oxidative stress, apoptosis, and inflammation. This review will discuss data demonstrating the regulation of components of the RAS by cholesterol and its metabolites, glucose, and/or insulin in cell types implicated in disorders of the metabolic syndrome. In addition, we discuss data supporting a role for an activated local RAS in dyslipidemias and glucose intolerance/insulin resistance and the development of hypertension in the metabolic syndrome. Identification of an activated RAS as a common thread contributing to several disorders of the metabolic syndrome makes the use of angiotensin receptor blockers and ACE inhibitors an intriguing and novel option for multisymptom treatment.