Enhanced susceptibility to biomechanical stress in ACE2 null mice is prevented by loss of the p47(phox) NADPH oxidase subunit

Redox signaling in cardiac physiology and pathology

Redox signaling refers to the specific and usually reversible oxidation/reduction modification of molecules involved in cellular signaling pathways. In the heart, redox signaling regulates several physiological processes (eg, excitation-contraction coupling) and is involved in a wide variety of pathophysiological and homoeostatic or stress response pathways. Reactive oxygen species involved in cardiac redox signaling may derive from many sources, but NADPH oxidases, as dedicated sources of signaling reactive oxygen species, seem to be especially important. An increasing number of specific posttranslational oxidative modifications involved in cardiac redox signaling are being defined, along with the reactive oxygen species sources that are involved. Here, we review current knowledge on the molecular targets of signaling reactive oxygen species in cardiac cells and their involvement in cardiac physiopathology. Advances in this field may allow the development of targeted therapeutic strategies for conditions such as heart failure as opposed to the general antioxidant approaches that have failed to date.

ACE/ACE2 ratio and MMP-9 activity as potential biomarkers in tuberculous pleural effusions

OBJECTIVE

Pleural effusion is common problem, but the rapid and reliable diagnosis for specific pathogenic effusions are lacking. This study aimed to identify the diagnosis based on clinical variables to differentiate pleural tuberculous exudates from other pleural effusions. We also investigated the role of renin-angiotensin system (RAS) and matrix metalloproteinase (MMPs) in the pathogenesis of pleural exudates.

EXPERIMENTAL DESIGN

The major components in RAS and extracellular matrix metabolism, including angiotensin converting enzyme (ACE), ACE2, MMP-2 and MMP-9 activities, were measured and compared in the patients with transudative (n = 45) and exudative (n = 80) effusions. The exudative effusions were come from the patients with tuberculosis (n = 20), pneumonia (n = 32), and adenocarcinoma (n = 28).

RESULTS

Increased ACE and equivalent ACE2 activities, resulting in a significantly increased ACE/ACE2 ratio in exudates, were detected compared to these values in transudates. MMP-9 activity in exudates was significantly higher than that in transudates. The significant correlation between ACE and ACE2 activity that was found in transudates was not found in exudates. Advanced analyses showed significantly increased ACE and MMP-9 activities, and decreased ACE2 activity in tuberculous pleural effusions compared with those in pneumonia and adenocarcinoma effusions. The results indicate that increased ACE and MMP-9 activities found in the exudates were mainly contributed from a higher level of both enzyme activities in the tuberculous pleural effusions.

CONCLUSION

Interplay between ACE and ACE2, essential functions in the RAS, and abnormal regulation of MMP-9 probably play a pivotal role in the development of exudative effusions. Moreover, the ACE/ACE2 ratio combined with MMP-9 activity in pleural fluid may be potential biomarkers for diagnosing tuberculous pleurisy.

The ACE2 gene: its potential as a functional candidate for cardiovascular disease

The RAS (renin–angiotensin system) plays an important role in the pathophysiology of CVD (cardiovascular disease), and RAS blockade is an important therapeutic strategy in the management of CVD. A new counterbalancing arm of the RAS is now known to exist in which ACE (angiotensin-converting enzyme) 2 degrades Ang (angiotensin) II, the main effector of the classic RAS, and generates Ang-(1–7). Altered ACE2 expression is associated with cardiac and vascular disease in experimental models of CVD, and ACE2 is increased in failing human hearts and atherosclerotic vessels. In man, circulating ACE2 activity increases with coronary heart disease, as well as heart failure, and a large proportion of the variation in plasma ACE2 levels has been attributed to hereditary factors. The ACE2 gene maps to chromosome Xp22 and this paper reviews the evidence associating ACE2 gene variation with CVD and considers clues to potential functional ACE2 variants that may alter gene expression or transcriptional activity. Studies to date have investigated ACE2 gene associations in hypertension, left ventricular hypertrophy and coronary artery disease, but the results have been inconsistent. The discrepancies may reflect the sample size of the studies, the gender or ethnicity of subjects, the cardiovascular phenotype or the ACE2 SNP investigated. The frequent observation of apparent sex-dependence might be of special importance, if confirmed. As yet, there are no studies to concurrently assess ACE2 gene polymorphisms and circulating ACE2 activity. Large-scale carefully conducted clinical studies are urgently needed to clarify more precisely the potential role of ACE2 in the CVD continuum.

Loss of TIMP3 selectively exacerbates diabetic nephropathy

Diabetic nephropathy is the most common cause of end-stage renal disease. Polymorphism in the tissue inhibitor of metalloproteinase-3 (TIMP3) gene, and the ECM-bound inhibitor of matrix metalloproteinases (MMPs), has been linked to diabetic nephropathy in humans. To elucidate the mechanism, we generated double mutant mice in which the TIMP3 gene was deleted in the genetic diabetic Akita mouse background. The aggravation of diabetic injury occurred in the absence of worsening of hypertension or hyperglycemia. In fact, myocardial TIMP3 levels were not affected in Akita hearts, and cardiac diastolic and systolic function remained unchanged in the double mutant mice. However, TIMP3 levels increased in Akita kidneys and deletion of TIMP3 exacerbated the diabetic renal injury in the Akita mouse, characterized by increased albuminuria, mesangial matrix expansion, and kidney hypertrophy. The progression of diabetic renal injury was accompanied by the upregulation of fibrotic and inflammatory markers, increased production of reactive oxygen species and NADPH oxidase activity, and elevated activity of TNF-α-converting enzyme (TACE) in the TIMP3(-/-)/Akita kidneys. Moreover, while the elevated phospho-Akt (S473 and T308) and phospho-ERK1/2 in the Akita mice was not detected in the TIMP3(-/-)/Akita kidneys, PKCβ1 (but not PKCα) was markedly elevated in the double mutant kidneys. Our data provide definitive evidence for a critical and selective role of TIMP3 in diabetic renal injury consistent with gene expression findings from human diabetic kidneys.

Angiotensin-converting enzyme 2 antagonizes angiotensin II-induced pressor response and NADPH oxidase activation in Wistar-Kyoto rats and spontaneously hypertensive rats

Angiotensin-converting enzyme 2 (ACE2), a monocarboxypeptidase capable of metabolizing angiotensin II (Ang II) into angiotensin-(1-7) [Ang-(1-7)], has emerged as a potential therapeutic target. We hypothesized that ACE2 is a negative regulator of Ang II-mediated pathological effects in vivo. In Wistar-Kyoto (WKY) rats, Ang II infusion (0.1 μg min(-1) kg(-1)) induced a pressor response, activation of NADPH oxidase and generation of superoxide in the heart, kidney and blood vessels; these effects were significantly blunted by recombinant human ACE2 (rhACE2; 2 mg kg(-1)), in association with a lowering of plasma Ang II and elevation of Ang-(1-7) levels. In the spontaneously hypertensive rat (SHR) model, rhACE2 (2 mg kg(-1) day(-1)) delivered over a 14 day period partly corrected the hypertension, the NADPH oxidase activation and the increased superoxide generation in the heart, kidney and blood vessels. Treatment with rhACE2 inhibited Ang II-mediated phosphorylation of the myocardial extracellular signal-regulated kinase 1/2 pathway in WKY rats, with congruent results seen in SHR hearts. Hence, rhACE2 is an important negative regulator of the Ang II-induced pressor response and NADPH oxidase activation and suppresses pathological myocardial signalling, thereby providing a novel therapeutic agent with which to antagonize an activated renin-angiotesin system.

ACE2 deficiency enhances angiotensin II-mediated aortic profilin-1 expression, inflammation and peroxynitrite production

Inflammation and oxidative stress play a crucial role in angiotensin (Ang) II-mediated vascular injury. Angiotensin-converting enzyme 2 (ACE2) has recently been identified as a specific Ang II-degrading enzyme but its role in vascular biology remains elusive. We hypothesized that loss of ACE2 would facilitate Ang II-mediated vascular inflammation and peroxynitrite production. 10-week wildtype (WT, Ace2^+/y) and ACE2 knockout (ACE2KO, Ace2^−/y) mice received with mini-osmotic pumps with Ang II (1.5 mg.kg⁻¹.d⁻¹) or saline for 2 weeks. Aortic ACE2 protein was obviously reduced in WT mice in response to Ang II related to increases in profilin-1 protein and plasma levels of Ang II and Ang-(1–7). Loss of ACE2 resulted in greater increases in Ang II-induced mRNA expressions of inflammatory cytokines monocyte chemoattractant protein-1 (MCP-1), interleukin (IL)-1β, and IL-6 without affecting tumor necrosis factor-α in aortas of ACE2KO mice. Furthermore, ACE2 deficiency led to greater increases in Ang II-mediated profilin-1 expression, NADPH oxidase activity, and superoxide and peroxynitrite production in the aortas of ACE2KO mice associated with enhanced phosphorylated levels of Akt, p70S6 kinase, extracellular signal-regulated kinases (ERK1/2) and endothelial nitric oxide synthase (eNOS). Interestingly, daily treatment with AT1 receptor blocker irbesartan (50 mg/kg) significantly prevented Ang II-mediated aortic profilin-1 expression, inflammation, and peroxynitrite production in WT mice with enhanced ACE2 levels and the suppression of the Akt-ERK-eNOS signaling pathways. Our findings reveal that ACE2 deficiency worsens Ang II-mediated aortic inflammation and peroxynitrite production associated with the augmentation of profilin-1 expression and the activation of the Akt-ERK-eNOS signaling, suggesting potential therapeutic approaches by enhancing ACE2 action for patients with vascular diseases.

Olmesartan medoxomil treatment potently improves cardiac myosin-induced dilated cardiomyopathy via the modulation of ACE-2 and ANG 1-7 mas receptor

Angiotensin converting enzyme-2 (ACE-2) is a monocarboxypeptidase that metabolises angiotensin (ANG)-II into angiotensin 1-7 (ANG 1-7), thereby functioning as a negative regulator of the renin-angiotensin system. We investigated whether treatment with ANG-II type 1 receptor blocker, olmesartan medoxomil is associated with the attenuation of cardiac myosin-induced dilated cardiomyopathy (DCM) through recently established new axis of ACE-2/ANG 1-7 mas receptor. DCM was elicited in Lewis rats by immunisation with cardiac myosin, and 28 days after immunisation, the surviving Lewis rats were divided into two groups and treated with either olmesartan medoxomil (10 mg/kg/day) or vehicle. Myocardial protein and mRNA levels of ACE-2, ANG 1-7 mas receptor were upregulated in the olmesartan-treated group compared with those of vehicle-treated DCM rats. In contrast, Olmesartan treatment effectively suppressed the myocardial protein and mRNA expressions of inflammatory markers in comparison to the vehicle-treated DCM rats. Olmesartan treatment significantly reduced fibrosis, hypertrophy and their marker molecules (OPN, CTGF, ANP and GATA-4, respectively), as well as matrix metalloproteinases compared with those of vehicle-treated DCM rats. Enhanced myocardial protein levels of phospho-p38 MAPK, phospho-JNK and phospho MAPKAPK-2 in the vehicle-treated DCM rats were prevented by olmesartan treatment. In addition, olmesartan treatment significantly lowered the protein expressions (Nitrotyrosine, p47phox and p67phox) and superoxide radical production compared with those of vehicle-treated DCM rats. Our present study might serve as a new therapeutic target of DCM in cardiovascular diseases and cardiac myosin-induced DCM via the modulation of ACE-2/ANG 1-7 mas receptor axis in rats with DCM after myosin-immunisation.

Targeting the ACE2 and Apelin Pathways Are Novel Therapies for Heart Failure: Opportunities and Challenges

Angiotensin-converting enzyme 2 (ACE2)/Ang II/Ang 1-7 and the apelin/APJ are two important peptide systems which exert diverse effects on the cardiovascular system. ACE2 is a key negative regulator of the renin-angiotensin system (RAS) where it metabolizes angiotensin (Ang) II into Ang 1-7, an endogenous antagonist of Ang II. Both the prolonged activation of RAS and the loss of ACE2 can be detrimental as they lead to functional deterioration of the heart and progression of cardiac, renal, and vascular diseases. Recombinant human ACE2 in an animal model of ACE2 knockout mice lowers Ang II. These interactions neutralize the pressor and subpressor pathologic effects of Ang II by producing Ang 1-7 levels in vivo, that might be cardiovascular protective. ACE2 hydrolyzes apelin to Ang II and, therefore, is responsible for the degradation of both peptides. Apelin has emerged as a promising peptide biomarker of heart failure. The serum level of apelin in cardiovascular diseases tends to be decreased. Apelin is recognized as an imperative controller of systemic blood pressure and myocardium contractility. Dysregulation of the apelin/APJ system may be involved in the predisposition to cardiovascular diseases, and enhancing apelin action may have important therapeutic effects.

The renin–angiotensin system, bone marrow and progenitor cells

Modulation of the RAS (renin–angiotensin system), in particular of the function of the hormones AngII (angiotensin II) and Ang-(1–7) [angiotensin-(1–7)], is an important target for pharmacotherapy in the cardiovascular system. In the classical view, such modulation affects cardiovascular cells to decrease hypertrophy, fibrosis and endothelial dysfunction, and improves diuresis. In this view, excessive stimulation of AT1 receptors (AngII type 1 receptors) fulfils a detrimental role, as it promotes cardiovascular pathogenesis, and this is opposed by stimulation of the AT2 receptor (angiotensin II type 2 receptor) and the Ang-(1–7) receptor encoded by the Mas proto-oncogene. In recent years, this view has been broadened with the observation that the RAS regulates bone marrow stromal cells and stem cells, thus involving haematopoiesis and tissue regeneration by progenitor cells. This change of paradigm has enlarged the field of perspectives for therapeutic application of existing as well as newly developed medicines that alter angiotensin signalling, which now stretches beyond cardiovascular therapy. In the present article, we review the role of AngII and Ang-(1–7) and their respective receptors in haematopoietic and mesenchymal stem cells, and discuss possible pharmacotherapeutical implications.

Loss of angiotensin-converting enzyme-2 exacerbates diabetic cardiovascular complications and leads to systolic and vascular dysfunction: a critical role of the angiotensin II/AT1 receptor axis

RATIONALE

Diabetic cardiovascular complications are reaching epidemic proportions. Angiotensin-converting enzyme-2 (ACE2) is a negative regulator of the renin-angiotensin system. We hypothesize that loss of ACE2 exacerbates cardiovascular complications induced by diabetes.

OBJECTIVE

To define the role of ACE2 in diabetic cardiovascular complications.

METHODS AND RESULTS

We used the well-validated Akita mice, a model of human diabetes, and generated double-mutant mice using the ACE2 knockout (KO) mice (Akita/ACE2(-/y)). Diabetic state was associated with increased ACE2 in Akita mice, whereas additional loss of ACE2 in these mice leads to increased plasma and tissue angiotensin II levels, resulting in systolic dysfunction on a background of impaired diastolic function. Downregulation of SERCA2 and lipotoxicity were equivalent in Akita and Akita/ACE2KO hearts and are likely mediators of the diastolic dysfunction. However, greater activation of protein kinase C and loss of Akt and endothelial nitric oxide synthase phosphorylation occurred in the Akita/ACE2KO hearts. Systolic dysfunction in Akita/ACE2KO mice was linked to enhanced activation of NADPH oxidase and metalloproteinases, resulting in greater oxidative stress and degradation of the extracellular matrix. Impaired flow-mediated dilation in vivo correlated with increased vascular oxidative stress in Akita/ACE2KO mice. Treatment with the AT1 receptor blocker, irbesartan rescued the systolic dysfunction, normalized altered signaling pathways, flow-mediated dilation, and the increased oxidative stress in the cardiovascular system.

CONCLUSIONS

Loss of ACE2 disrupts the balance of the renin-angiotensin system in a diabetic state and leads to an angiotensin II/AT1 receptor-dependent systolic dysfunction and impaired vascular function. Our study demonstrates that ACE2 serves as a protective mechanism against diabetes-induced cardiovascular complications.

Angiotensin-Converting Enzyme 2 (ACE2) Is a Key Modulator of the Renin Angiotensin System in Health and Disease

Angiotensin-converting enzyme 2 (ACE2) shares some homology with angiotensin-converting enzyme (ACE) but is not inhibited by ACE inhibitors. The main role of ACE2 is the degradation of Ang II resulting in the formation of angiotensin 1–7 (Ang 1–7) which opposes the actions of Ang II. Increased Ang II levels are thought to upregulate ACE2 activity, and in ACE2 deficient mice Ang II levels are approximately double that of wild-type mice, whilst Ang 1–7 levels are almost undetectable. Thus, ACE2 plays a crucial role in the RAS because it opposes the actions of Ang II. Consequently, it has a beneficial role in many diseases such as hypertension, diabetes, and cardiovascular disease where its expression is decreased. Not surprisingly, current therapeutic strategies for ACE2 involve augmenting its expression using ACE2 adenoviruses, recombinant ACE2 or compounds in these diseases thereby affording some organ protection.

Angiotensin-(1-7)-induced activation of ERK1/2 is cAMP/protein kinase A-dependent in glomerular mesangial cells

The renin-angiotensin system (RAS) plays an important role in renal physiology and kidney injury. Although the cellular effects of the RAS activation are generally attributed to angiotensin II (ANG II), the recent identification of angiotensin-converting enzyme 2 has shifted the focus to other peptides including Ang-(1-7). The G protein-coupled receptor for Ang-(1-7), mas, is expressed by mesangial cells (MC) but the signal transduction pathways activated by Ang-(1-7) in MC have not been fully elucidated. Accordingly, we studied the effect of Ang-(1-7) on extracellular signal-related kinase (ERK)1/2 activation in rat MC. Ang-(1-7)-induced ERK1/2 phosphorylation in MC is time- and concentration-dependent. Pretreatment of MC with the mas receptor antagonist A-779 but not the AT(1) antagonist losartan or the AT(2) antagonist PD123319 abrogated ERK1/2 activation. Neither pretreatment with the NADPH oxidase inhibitors diphenyleneiodonium and apocynin nor pretreatment with the epidermal growth factor (EGF) receptor antagonists AG1478 and PD158780 attenuated Ang-(1-7)-induced activation of ERK1/2. Even though each of these compounds abolished ANG II-induced activation of ERK1/2. Ang-(1-7) increased intracellular cAMP levels and activated protein kinase A (PKA) and inhibition of either adenylyl cyclase or PKA activity attenuated Ang-(1-7)-induced ERK1/2 activation. In conclusion, Ang-(1-7)-induced activation of ERK1/2 is cAMP/PKA-dependent in MC, but independent of NADPH oxidase and the EGF receptor.

Angiotensin-converting enzyme 2: the first decade

The renin-angiotensin system (RAS) is a critical regulator of hypertension, primarily through the actions of the vasoactive peptide Ang II, which is generated by the action of angiotensin-converting enzyme (ACE) mediating an increase in blood pressure. The discovery of ACE2, which primarily metabolises Ang II into the vasodilatory Ang-(1-7), has added a new dimension to the traditional RAS. As a result there has been huge interest in ACE2 over the past decade as a potential therapeutic for lowering blood pressure, especially elevation resulting from excess Ang II. Studies focusing on ACE2 have helped to reveal other actions of Ang-(1-7), outside vasodilation, such as antifibrotic and antiproliferative effects. Moreover, investigations focusing on ACE2 have revealed a variety of roles not just catalytic but also as a viral receptor and amino acid transporter. This paper focuses on what is known about ACE2 and its biological roles, paying particular attention to the regulation of ACE2 expression. In light of the entrance of human recombinant ACE2 into clinical trials, we discuss the potential use of ACE2 as a therapeutic and highlight some pertinent questions that still remain unanswered about ACE2.