ACE2: more of Ang-(1-7) or less Ang II? Curr Opin Nephrol Hypertens. 2011;20:1-6. [PMID: 21045683 DOI: 10.1097/mnh.0b013e3283406f57]

Combination renin-angiotensin system blockade and angiotensin-converting enzyme 2 in experimental myocardial infarction: implications for future therapeutic directions

The RAS (renin-angiotensin system) is activated after MI (myocardial infarction), and RAS blockade with ACEis [ACE (angiotensin-converting enzyme) inhibitors] or ARBs (angiotensin receptor blockers) slows but does not completely prevent progression to heart failure. Cardiac ACE is increased after MI and leads to the formation of the vasoconstrictor AngII (angiotensin II). The enzyme ACE2 is also activated after MI and degrades AngII to generate the vasodilator Ang-(1-7) [angiotensin-(1-7)]. Overexpression of ACE2 offers cardioprotective effects in experimental MI, but there is conflicting evidence as to whether the benefits of ACEis and ARBs are mediated through increasing ACE2 after MI. In the present study, we assessed the effect of an ACEi and ARB, alone and in combination, on cardiac ACE2 in a rat MI model. MI rats received vehicle, ACEi (ramipril; 1 mg/kg of body weight), ARB (valsartan; 10 mg/kg of body weight) or combination (ramipril at 1 mg/kg of body weight and valsartan at 10 mg/kg of body weight) orally for 28 days. Sham-operated rats were also studied and received vehicle alone. MI increased LV (left ventricular) mass (P<0.0001), impaired cardiac contractility (P<0.05) and activated cardiac ACE2 with increased gene (P<0.05) and protein expression (viable myocardium, P<0.05; border zone, P<0.001; infarct, P<0.05). Ramipril and valsartan improved remodelling (P<0.05), with no additional effect of dual therapy. Although ramipril inhibited ACE, and valsartan blocked the angiotensin receptor, neither treatment alone nor in combination augmented cardiac ACE2 expression. These results suggest that the cardioprotective effects of ramipril and valsartan are not mediated through up-regulation of cardiac ACE2. Strategies that do augment ACE2 after MI may be a useful addition to standard RAS blockade after MI.

AVE 0991, a non-peptide Mas-receptor agonist, facilitates penile erection

The renin-angiotensin system plays a crucial role in erectile function. It has been shown that elevated levels of angiotensin II contribute to the development of erectile dysfunction both in humans and in aminals. On the contrary, the heptapeptide angiotensin-(1-7) appears to mediate penile erection by activation of the Mas receptor. Recently, we have shown that the erectile function of Mas gene-deleted mice was substantially reduced, which was associated with a marked increase in fibrous tissue in the corpus cavernosum. We have hypothesized that the synthetic non-peptide Mas agonist, AVE 0991, would potentiate penile erectile function. We showed that intracavernosal injection of AVE 0991 potentiated the erectile response of anaesthetized Wistar rats, measured as the ratio between corpus cavernosum pressure and mean arterial pressure, upon electrical stimulation of the major pelvic ganglion. The facilitatory effect of AVE 0991 on erectile function was dose dependent and completely blunted by the nitric oxide synthesis inhibitor, l-NAME. Importantly, concomitant intracavernosal infusion of the specific Mas receptor blocker, A-779, abolished the effect of AVE 0991. We demonstrated that AVE 0991 potentiates the penile erectile response through Mas in an NO-dependent manner. Importantly, these results suggest that Mas agonists, such as AVE 0991, might have significant therapeutic benefits for the treatment of erectile dysfunction.

The renin-angiotensin-aldosterone system in 2011: role in hypertension and chronic kidney disease

Over the past two decades, considerable advances have been made in our understanding of the renin-angiotensin-aldosterone system (RAAS) and its roles in various disease states. In this review, we will discuss the current state of knowledge of the many components of the RAAS, including new data on prorenin and its receptors, and important angiotensin fragments. The roles of these components of the RAAS in the pathogenesis of primary hypertension and the progression of chronic kidney disease (CKD) will also be highlighted. Given the new understanding of the many components and roles of the RAAS, it may be possible to develop improved therapies for hypertension and CKD.

The brain renin-angiotensin system and cardiovascular responses to stress: insights from transgenic rats with low brain angiotensinogen

The renin-angiotensin system (RAS) has been identified as an attractive target for the treatment of stress-induced cardiovascular disorders. The effects of angiotensin (ANG) peptides during stress responses likely result from an integration of actions by circulating peptides and brain peptides derived from neuronal and glial sources. The present review focuses on the contribution of endogenous brain ANG peptides to pathways involved in cardiovascular responses to stressors. During a variety of forms of stress, neuronal pathways in forebrain areas containing ANG II or ANG-(1-7) are activated to stimulate descending angiotensinergic pathways that increase sympathetic outflow to increase blood pressure. We provide evidence that glia-derived ANG peptides influence brain AT(1) receptors. This appears to result in modulation of the responsiveness of the neuronal pathways activated during stressors that elevate circulating ANG peptides to activate brain pathways involving descending hypothalamic projections. It is well established that increased cardiovascular reactivity to stress is a significant predictor of hypertension and other cardiovascular diseases. This review highlights the importance of understanding the impact of RAS components from the circulation, neurons, and glia on the integration of cardiovascular responses to stressors.

Angiotensin-(1-7) in kidney disease: a review of the controversies

Ang-(1-7) [angiotensin-(1-7)] is a biologically active heptapeptide component of the RAS (renin-angiotensin system), and is generated in the kidney at relatively high levels, via enzymatic pathways that include ACE2 (angiotensin-converting enzyme 2). The biological effects of Ang-(1-7) in the kidney are primarily mediated by interaction with the G-protein-coupled receptor Mas. However, other complex effects have been described that may involve receptor-receptor interactions with AT(1) (angiotensin II type 1) or AT(2) (angiotensin II type 2) receptors, as well as nuclear receptor binding. In the renal vasculature, Ang-(1-7) has vasodilatory properties and it opposes growth-stimulatory signalling in tubular epithelial cells. In several kidney diseases, including hypertensive and diabetic nephropathy, glomerulonephritis, tubulointerstitial fibrosis, pre-eclampsia and acute kidney injury, a growing body of evidence supports a role for endogenous or exogenous Ang-(1-7) as an antagonist of signalling mediated by AT(1) receptors and thereby as a protector against nephron injury. In certain experimental conditions, Ang-(1-7) appears to paradoxically exacerbate renal injury, suggesting that dose or route of administration, state of activation of the local RAS, cell-specific signalling or non-Mas receptor-mediated pathways may contribute to the deleterious responses. Although Ang-(1-7) has promise as a potential therapeutic agent in humans with kidney disease, further studies are required to delineate its signalling mechanisms in the kidney under physiological and pathophysiological conditions.

Loss of angiotensin-converting enzyme 2 enhances TGF-β/Smad-mediated renal fibrosis and NF-κB-driven renal inflammation in a mouse model of obstructive nephropathy

It is known that angiotensin (Ang)-converting enzyme (ACE) 2 catalyzes Ang II to Ang 1-7 to prevent the detrimental effect of Ang II on blood pressure, renal fibrosis, and inflammation. However, mechanisms of renoprotective role of Ace2 remain largely unclear. The present study tested the hypothesis that deficiency of Ace2 may accelerate intrarenal Ang II-mediated fibrosis and inflammation independent of blood pressure in a model of unilateral ureteral obstructive (UUO) nephropathy induced in Ace2(+/y) and Ace2(-/y) mice. Results showed that both Ace2(+/y) and Ace2(-/y) mice had normal levels of blood pressure and plasma Ang II/Ang 1-7. In contrast, deletion of ACE2 resulted in a fourfold increase in the ratio of intrarenal Ang II/Ang 1-7 in the UUO nephropathy. These changes were associated with the development of more intensive tubulointerstitial fibrosis (α-SMA, collagen I) and inflammation (TNF-α, IL-1β, MCP-1, F4/80(+) cells, and CD3(+)T cells) in Ace2(-/y) mice at day 3 (all P<0.05) after UUO, becoming more profound at day 7 (all P<0.01). Enhanced renal fibrosis and inflammation in the UUO kidney of Ace2(-/y) mice were largely attributed to a marked increase in the intrarenal Ang II signaling (AT1-ERK1/2 mitogen-activated protein kinase), TGF-β/Smad2/3, and NF-κB signaling pathways. Further studies revealed that enhanced TGF-β/Smad and NF-κB signaling in the UUO kidney of Ace2(-/y) mice was associated with upregulation of an E3 ligase Smurf2 and a loss of renal Smad7. In conclusion, enhanced Ang II-mediated TGF-β/Smad and NF-κB signaling may be the mechanisms by which loss of Ace2 enhances renal fibrosis and inflammation. Smad7 ubiquitin degradation mediated by Smurf2 may be a central mechanism by which Ace2(-/y) mice promote TGF-β/Smad2/3-mediated renal fibrosis and NF-κB-driven renal inflammation in a mouse model of UUO nephropathy.

Regulation of angiotensin II receptors beyond the classical pathway

The RAS (renin–angiotensin system) plays a role not only in the cardiovascular system, including blood pressure regulation, but also in the central nervous system. AngII (angiotensin II) binds two major receptors: the AT1 receptor (AngII type 1 receptor) and AT2 receptor (AngII type 2 receptor). It has been recognized that AT2 receptor activation not only opposes AT1 receptor actions, but also has unique effects beyond inhibitory cross-talk with AT1 receptor signalling. Novel pathways beyond the classical actions of RAS, the ACE (angiotensin-converting enzyme)/AngII/AT1 receptor axis, have been highlighted: the ACE2/Ang-(1–7) [angiotensin-(1–7)]/Mas receptor axis as a new opposing axis against the ACE/AngII/AT1 receptor axis, novel AngII-receptor-interacting proteins and various AngII-receptor-activation mechanisms including dimer formation. ATRAP (AT1-receptor-associated protein) and ATIP (AT2-receptor-interacting protein) are well-characterized AngII-receptor-associated proteins. These proteins could regulate the functions of AngII receptors and thereby influence various pathophysiological states. Moreover, the possible cross-talk between PPAR (peroxisome-proliferator-activated receptor)-γ and AngII receptor subtypes is an intriguing issue to be addressed in order to understand the roles of RAS in the metabolic syndrome, and interestingly some ARBs (AT1-receptor blockers) have been reported to have an AT1-receptor-blocking action with a partial PPAR-γ agonistic effect. These emerging concepts concerning the regulation of AngII receptors are discussed in the present review.

Angiotensin-(1-7)-mediated signaling in cardiomyocytes

The Renin-Angiotensin System (RAS) acts at multiple targets and has its synthesis machinery present in different tissues, including the heart. Actually, it is well known that besides Ang II, the RAS has other active peptides. Of particular interest is the heptapeptide Ang-(1-7) that has been shown to exert cardioprotective effects. In this way, great compilations about Ang-(1-7) actions in the heart have been presented in the literature. However, much less information is available concerning the Ang-(1-7) actions directly in cardiomyocytes. In this paper, we show the actual knowledge about Ang-(1-7)-mediated signaling in cardiac cells more specifically we provide a brief overview of ACE2/Ang-(1-7)/Mas axis; and highlight the discoveries made in cardiomyocyte physiology through the use of genetic approaches. Finally, we discuss the protective signaling induced by Ang-(1-7) in cardiomyocytes and point molecular determinants of these effects.

Angiotensin converting enzyme 2, Angiotensin-(1-7), and receptor MAS axis in the kidney

In the past few years the understanding of the renin-angiotensin system (RAS) has improved, helping to better define the role of this system in physiological conditions and in human diseases. Besides Angiotensin (Ang) II, the biological importance of other Ang fragments was progressively evidenced. In this regard, Angiotensin- (Ang-) (1-7) was recognized as a biologically active product of the RAS cascade with a specific receptor, the G-protein-coupled receptor Mas, and that is mainly formed by the action of the angiotensin-converting enzyme (ACE) homolog enzyme, ACE2, which converts Ang II into Ang-(1-7). Taking into account the biological effects of these two mediators, Ang II and Ang-(1-7), the RAS can be envisioned as a dual function system in which the vasoconstrictor/proliferative or vasodilator/antiproliferative actions are primarily driven by the balance between Ang II and Ang-(1-7), respectively. In this paper, we will discuss our current understanding of the ACE2/Ang-(1-7)/Mas axis of the RAS in renal physiology and in the pathogenesis of primary hypertension and chronic kidney disease.

Renoprotective Effects of AVE0991, a Nonpeptide Mas Receptor Agonist, in Experimental Acute Renal Injury

Renal ischemia and reperfusion (I/R) is the major cause of acute kidney injury in hospitalized patients. Mechanisms underlying reperfusion-associated injury include recruitment and activation of leukocytes and release of inflammatory mediators. In this study, we investigated the renal effects of acute administration of AVE0991, an agonist of Mas, the angiotensin-(1–7) receptor, the angiotensin-(1–7) receptor, in a murine model of renal I/R. Male C57BL/6 wild-type or Mas^−/− mice were subjected to 30 min of bilateral ischemia and 24 h of reperfusion. Administration of AVE0991 promoted renoprotective effects, as seen by improvement of function, decreased tissue injury, prevention of local and remote leucocyte infiltration, and release of the chemokine, CXCL1. I/R injury was similar in WT and Mas^−/− mice, suggesting that endogenous activation of this receptor does not control renal damage under baseline conditions. In conclusion, pharmacological interventions using Mas receptor agonists may represent a therapeutic opportunity for the treatment of renal I/R injury.

Protective Role of the ACE2/Ang-(1-9) Axis in Cardiovascular Remodeling

Despite reduction in cardiovascular (CV) events and end-organ damage with the current pharmacologic strategies, CV disease remains the primary cause of death in the world. Pharmacological therapies based on the renin angiotensin system (RAS) blockade are used extensively for the treatment of hypertension, heart failure, and CV remodeling but in spite of their success the prevalence of end-organ damage and residual risk remain still high. Novel approaches must be discovered for a more effective treatment of residual CV remodeling and risk. The ACE2/Ang-(1–9) axis is a new and important target to counterbalance the vasoconstrictive/proliferative RAS axis. Ang-(1–9) is hydrolyzed slower than Ang-(1–7) and is able to bind the Ang II type 2 receptor. We review here the current experimental evidence suggesting that activation of the ACE2/Ang-(1–9) axis protects the heart and vessels (and possibly the kidney) from adverse cardiovascular remodeling in hypertension as well as in heart failure.

Ontogeny of angiotensin-converting enzyme 2

INTRODUCTION

This study examined the temporal expression of angiotensin (Ang)-converting enzyme 2 (ACE2) during renal, heart, lung, and brain organogenesis in the mouse.

RESULTS

We demonstrate that kidney ACE2 mRNA levels are low on embryonic day (E) 12.5, increase fourfold during development, and decline in adulthood. In extrarenal tissues, ACE2 mRNA levels are also low during early gestation, increase in perinatal period, and peak in adulthood. The lung shows the highest age-related increase in ACE2 mRNA levels followed by the brain, kidney, and heart. ACE2 protein levels and enzymatic activity are high in all organs studied during gestation and decline postnatally. Ang II decreases ACE2 mRNA levels and enzymatic activity in kidneys grown ex vivo. These effects of Ang II are blocked by the specific Ang II AT(1) receptor (AT(1)R) antagonist candesartan, but not by the AT(2) receptor (AT(2)R) antagonist PD123319.

DISCUSSION

We conclude that ACE2 gene and protein expression and enzymatic activity are developmentally regulated in a tissue-specific manner. Ang II, acting through AT(1)R, exerts a negative feedback on ACE2 during kidney development. We postulate that relatively high ACE2 protein levels and enzymatic activity observed during gestation may play a role in kidney, lung, brain, and heart organogenesis.

Chronic kidney disease: cardiac and renal angiotensin-converting enzyme (ACE) 2 expression in rats after subtotal nephrectomy and the effect of ACE inhibition

Renin-angiotensin system blockade slows but does not prevent the cardiovascular complications of chronic kidney disease (CKD). Angiotensin-converting enzyme (ACE) 2 is differentially regulated in acute kidney injury, with increased cardiac ACE2 but decreased kidney ACE2 levels. This study investigated the effect of long-term ACE inhibition on cardiac and renal ACE2 in rats with CKD induced by subtotal nephrectomy (STNx). Sprague-Dawley rats had sham (control) or STNx surgery. Control rats received vehicle (n = 9) and STNx rats ramipril (1 mg kg(-1) day(-1); n = 10) or vehicle (n = 10) for 28 days. Subtotal nephrectomy resulted in impaired creatinine clearance (P < 0.05), proteinuria (P < 0.05), renal fibrosis (P < 0.05) and reduced renal cortical ACE2 mRNA (P < 0.05) and activity (P < 0.05). In rats with CKD, ramipril improved creatinine clearance (P < 0.05) and was associated with an increase in cortical but not medullary ACE2 activity (P < 0.05). Compared with control rats, STNx rats were hypertensive (P < 0.01), with increased left ventricular end-diastolic pressure (LVEDP; P < 0.01), left ventricular hypertrophy (LVH; P < 0.05) and interstitial (P < 0.05) and perivascular fibrosis (P < 0.01). In rats with CKD, ramipril decreased blood pressure (P < 0.001) and reduced LVEDP (P < 0.01), LVH (P < 0.01) and perivascular fibrosis (P < 0.05) but did not significantly reduce interstitial fibrosis. There was no change in cardiac ACE2 in rats with CKD compared with control rats. In rats with CKD, ACE inhibition had major benefits to reduce blood pressure and cardiac hypertrophy and to improve creatinine clearance, but did not significantly impact on cardiac ACE2, cardiac interstitial fibrosis, renal fibrosis or proteinuria. Thus, in rats with CKD, renal ACE2 deficiency and lack of activation of cardiac ACE2 may contribute to the progression of cardiac and renal tissue injury. As long-term ACE inhibition only partly ameliorated the adverse cardio-renal effects of CKD, adjunctive therapies that lead to further increases in ACE2 activity may be needed to combat the cardio-renal complications of CKD.

Urinary angiotensin-converting enzyme 2 in patients with CKD

AIM

Angiotensin-converting enzyme 2 (ACE2) is a type I membrane protein that antagonizes the action of angiotensin II. Because of the need for invasive kidney biopsy, little is known about the role of renal ACE2 in human kidney diseases. The authors studied if urinary ACE2 could provide a novel clue to renal ACE2 in chronic kidney disease (CKD).

METHODS

Subjects were 190 patients with CKD including 38 patients with diabetic nephropathy and 36 healthy subjects. Parameters were urinary ACE2 by enzyme-linked immunosorbent assay, blood pressure, casual plasma glucose, proteinuria, microalbuminuria, serum creatinine and estimated glomerular filtration rate. Urine and serum samples were also subjected to western blotting of ACE2.

RESULTS

Western blotting confirmed increased urinary ACE2 levels in patients with CKD. Urinary ACE2 was significantly higher in patients with CKD than healthy subjects (median 9.64 (interquartile range, 4.41-16.89) vs 1.50 (0.40-2.33) mg/g·creatinine, P < 0.001) and in patients with diabetic nephropathy than patients without diabetic nephropathy (median 13.16 (interquartile range 6.81-18.70) vs 8.90 (4.19-16.67) mg/g·creatinine, P < 0.05). No significant difference in urinary ACE2 was observed by the use of angiotensin-converting enzyme inhibitor and angiotensin receptor blocker.

CONCLUSION

Urinary ACE2 could be used as a non-invasive marker to understand the role of renal ACE2 in CKD.

A new look at the renin-angiotensin system--focusing on the vascular system

The renin-angiotensin system (RAS), critically involved in the control of blood pressure and volume homeostasis, is a dual system comprising a circulating component and a local tissue component. The rate limiting enzyme is renin, which in the circulating RAS derives from the kidney to generate Ang II, which in turn regulates cardiovascular function by binding to AT(1) and AT(2) receptors on cardiac, renal and vascular cells. The tissue RAS can operate independently of the circulating RAS and may be activated even when the circulating RAS is suppressed or normal. A functional tissue RAS has been identified in brain, kidney, heart, adipose tissue, hematopoietic tissue, gastrointestinal tract, liver, endocrine system and blood vessels. Whereas angiotensinsinogen, angiotensin converting enzyme (ACE), Ang I and Ang II are synthesized within these tissues, there is still controversy as to whether renin is produced locally or whether it is taken up from the circulation, possibly by the (pro)renin receptor. This is particularly true in the vascular wall, where expression of renin is very low. The exact function of the vascular RAS remains elusive, but may contribute to fine-tuning of vascular tone and arterial structure and may amplify vascular effects of the circulating RAS, particularly in pathological conditions, such as in hypertension, atherosclerosis and diabetes. New concepts relating to the vascular RAS have recently been elucidated including: (1) the presence of functionally active Ang-(1-7)-Mas axis in the vascular system, (2) the importance of the RAS in perivascular adipose tissue and cross talk with vessels, and (3) the contribution to vascular RAS of Ang II derived from immune and inflammatory cells within the vascular wall. The present review highlights recent progress in the RAS field, focusing on the tissue system and particularly on the vascular RAS.

Local ocular renin-angiotensin system - a target for glaucoma therapy?

An active local intraocular renin-angiotensin system (RAS) has recently been shown to exist in the human eye, and evidence is now accumulating that antihypertensive drugs acting on RAS can also lower intraocular pressure. They seem also to work as neuroprotective agents against retinal ganglion cell loss in vivo; though no compounds are in ophthalmological use at present. Classically, the highly vasoconstrictive angiotensin II (Ang II) is the key peptide in the circulatory RAS. However, the final effect of RAS activation at tissue level is more complex, being based not only on the biological activity of Ang II but also on the activities of other products of angiotensinogen metabolism, often exerting opposite effects to Ang II action.