Downregulation of angiotensin converting enzyme II is associated with pacing-induced sustained atrial fibrillation

Exploring the association between atrial fibrillation and celiac disease: a comprehensive review

Objective

This paper aims to provide a comprehensive overview of the pathophysiology of atrial fibrillation (AF) and celiac disease (CD) individually while also exploring the emerging evidence of a potential association between the two conditions.

Methods

The pathophysiology of AF, the most prevalent arrhythmia globally, and CD, an autoimmune condition triggered by gluten consumption, is examined. Genetic, structural, electrophysiological, and inflammatory factors contributing to their development are explored.

Results

AF involves irregular atrial activity leading to electrical and structural remodeling of the atrium. CD is characterized by an immune response to gluten, primarily associated with HLA-DQ2 and HLA-DQ8 genetic mutations, resulting in damage to intestinal tissue. Emerging research suggests a link between AF and CD, possibly mediated through inflammation, fibrosis, and electromechanical delays in the atrium.

Conclusion

Understanding the association between AF and CD carries significant clinical implications. Recognition of this relationship can assist in identifying individuals at higher risk for AF and inform proactive management strategies. Additionally, it underscores the importance of comprehensive care for CD patients, considering potential cardiac implications. Further research is warranted to elucidate precise mechanisms and explore potential therapeutic interventions targeting common pathways, opening avenues for enhanced patient care and future investigations.

Mechanism and prevention of atrial remodeling and their related genes in cardiovascular disorders

Atrial fibrillation (AF) is associated with profound structural and functional changes in the atrium. Inflammation mediated atrial fibrosis is one of the key mechanisms in the pathogenesis of AF. The collagen deposition in extracellular matrix (ECM) is mainly mediated by transforming growth factor β1 (TGF-β1) which promotes AF via controlling smads mediated-collagen gene transcription and regulating the balance of metalloproteinases (MMPs)/ tissue inhibitor of metalloproteinases (TIMPs). Although many processes can alter atrial properties and promote AF, animal models and clinical studies have provided insights into two major forms of atrial remodeling: Atrial tachycardia remodeling (ATR), which occurs with rapid atrial tachyarrhythmia's such as AF and atrial flutter, and atrial structural remodeling (ASR), which is associated with CHF and other fibrosis-promoting conditions. The mechanism of atrial remodeling such as atrial enlargement, ultra structural changes of atrial muscle tissue and myocardial interstitial fibrosis in AF is still unclear. At present, many studies focus on calcium overload, renin angiotensin aldosterone system and transforming growth factor β1, that effect on atrial structural remodeling. Recent experimental studies and clinical investigations have provided structural remodeling is important contributor to the AF. This paper reviews the current understanding of the progresses about mechanism of atrial structural remodeling, and highlights the potential therapeutic approaches aimed at attenuating structural remodeling to prevent AF. Now some recent advancements of this area are reviewed in this paper.

Research Progress of Myocardial Fibrosis and Atrial Fibrillation

With the aging population and the increasing incidence of basic illnesses such as hypertension and diabetes (DM), the incidence of atrial fibrillation (AF) has increased significantly. AF is the most common arrhythmia in clinical practice, which can cause heart failure (HF) and ischemic stroke (IS), increasing disability and mortality. Current studies point out that myocardial fibrosis (MF) is one of the most critical substrates for the occurrence and maintenance of AF. Although myocardial biopsy is the gold standard for evaluating MF, it is rarely used in clinical practice because it is an invasive procedure. In addition, serological indicators and imaging methods have also been used to evaluate MF. Nevertheless, the accuracy of serological markers in evaluating MF is controversial. This review focuses on the pathogenesis of MF, serological evaluation, imaging evaluation, and anti-fibrosis treatment to discuss the existing problems and provide new ideas for MF and AF evaluation and treatment.

Altered heart cytokine profile and action potential modulation in cardiomyocytes from Mas-deficient mice

The renin-angiotensin system (RAS) is a key hormonal system. In recent years, the functional analysis of the novel axis of the RAS (ACE2/Ang-(1-7)/Mas receptor) revealed that its activation can become protective against several pathologies, including cardiovascular diseases. Mas knockout mice (Mas-KO) represent an important tool for new investigations. Indeed, extensive biological research has focused on investigating the functional implications of Mas receptor deletion. However, although the Mas receptor was identified in neonatal cardiomyocytes and also in adult ventricular myocytes, only few reports have explored the Ang-(1-7)/Mas signaling directly in cardiomyocytes to date. This study investigated the implication of Mas receptor knockout to the cytokine profile, energy metabolism, and electrical properties of mice-isolated cardiomyocytes. Here, we demonstrated that Mas-KO mice have modulation in some cytokines, such as G-CSF, IL-6, IL-10, and VEGF in the left ventricle. This model also presents increased mitochondrial number in cardiomyocytes and a reduction in the myocyte diameter. Finally, Mas-KO cardiomyocytes have altered action potential modulation after diazoxide challenge. Such electrical finding was different from the data showed for the TGR(A1-7)3292 (TGR) model, which overexpresses Ang-(1-7) in the plasma by 4.5, used by us as a control. Collectively, our findings exemplify the importance of understanding the ACE2/Ang-(1-7)/Mas pathway in cardiomyocytes and heart tissue. The Mas-KO mice model can be considered an important tool for new RAS investigations.

Pathomechanism and Management of Stroke in COVID-19: Review of Immunopathogenesis, Coagulopathy, Endothelial Dysfunction, and Downregulation of ACE2

Coronavirus disease 2019 (COVID-19) can reportedly manifest as an acute stroke, with most cases presenting as large vessel ischemic stroke in patients with or without comorbidities. The exact pathomechanism of stroke in COVID-19 remains ambiguous. The findings of previous studies indicate that the most likely underlying mechanisms are cerebrovascular pathological conditions following viral infection, inflammation-induced endothelial dysfunction, and hypercoagulability. Acute endothelial damage due to inflammation triggers a coagulation cascade, thrombosis propagation, and destabilization of atherosclerosis plaques, leading to large-vessel occlusion and plaque ulceration with concomitant thromboemboli, and manifests as ischemic stroke. Another possible mechanism is the downregulation of angiotensin-converting enzyme 2 as the target action of severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2). Acute stroke management protocols need to be modified during the COVID-19 pandemic in order to adequately manage stroke patients with COVID-19.

Inhibition of UCHL1 by LDN-57444 attenuates Ang II-Induced atrial fibrillation in mice

Atrial fibrillation (AF) is the most common human arrhythmia in clinical practice and may be promoted by atrial inflammation and fibrosis. Ubiquitination is an important posttranslational modification process that is reversed by deubiquitinating enzymes (DUBs). DUBs play critical roles in modulating the degradation, activity, trafficking, and recycling of substrates. However, less research has focused on the role of DUBs in AF. Here, we investigated the effect of ubiquitin C-terminal hydrolase 1 (UCHL1), an important DUB, on the development of AF induced by angiotensin II (Ang II). Male wild-type mice were treated with the UCHL1 inhibitor LDN57444 (LDN) at a dose of 40 μg/kg and infused with Ang II (2000 ng/kg/min) for 3 weeks. Our results showed that Ang II-infused wild-type (WT) mice had higher systolic blood pressure and an increased incidence and duration of AF. Conversely, this effect was attenuated in LDN-treated mice. Moreover, the administration of LDN significantly reduced Ang II-induced left atrial dilation, fibrosis, inflammatory cell infiltration, and reactive oxygen species (ROS) production. Mechanistically, LDN treatment inhibited the activation of multiple signaling pathways (the AKT, ERK1/2, HIF-1α, and TGF-β/smad2/3 pathways) and the expression of CX43 protein in atrial tissues compared with that in vehicle-treated control mice. Overall, our study identified UCHL1 as a novel regulator that contributes to Ang II-induced AF and suggests that the administration of LDN may represent a potential therapeutic approach for treating hypertensive AF.

Angiotensin converting enzyme 2 activity and human atrial fibrillation: increased plasma angiotensin converting enzyme 2 activity is associated with atrial fibrillation and more advanced left atrial structural remodelling

Aim

Angiotensin converting enzyme 2 (ACE2) is an integral membrane protein whose main action is to degrade angiotensin II. Plasma ACE2 activity is increased in various cardiovascular diseases. We aimed to determine the relationship between plasma ACE2 activity and human atrial fibrillation (AF), and in particular its relationship to left atrial (LA) structural remodelling.

Methods and results

One hundred and three participants from a tertiary arrhythmia centre, including 58 with paroxysmal AF (PAF), 20 with persistent AF (PersAF), and 25 controls, underwent clinical evaluation, echocardiographic analysis, and measurement of plasma ACE2 activity. A subgroup of 20 participants underwent invasive LA electroanatomic mapping. Plasma ACE2 activity levels were increased in AF [control 13.3 (9.5-22.3) pmol/min/mL; PAF 16.9 (9.7-27.3) pmol/min/mL; PersAF 22.8 (13.7-33.4) pmol/min/mL, P = 0.006]. Elevated plasma ACE2 was associated with older age, male gender, hypertension and vascular disease, elevated left ventricular (LV) mass, impaired LV diastolic function and advanced atrial disease (P < 0.05 for all). Independent predictors of elevated plasma ACE2 activity were AF (P = 0.04) and vascular disease (P < 0.01). There was a significant relationship between elevated ACE2 activity and low mean LA bipolar voltage (adjusted R2 = 0.22, P = 0.03), a high proportion of complex fractionated electrograms (R2 = 0.32, P = 0.009) and a long LA activation time (R2 = 0.20, P = 0.04).

Conclusion

Plasma ACE2 activity is elevated in human AF. Both AF and vascular disease predict elevated plasma ACE2 activity, and elevated plasma ACE2 is significantly associated with more advanced LA structural remodelling.

Angiotensin-converting enzyme-2 overexpression improves atrial electrical remodeling through TRPM7 signaling pathway

Atrial electrical remodeling is an important factor in the development and persistence of atrial fibrillation. The aim of this study was to examine the effects of atrial angiotensin-converting enzyme-2 overexpression on atrial electrical remodeling and to elucidate the molecular mechanisms underlying these effects. Twenty-eight male and female dogs were randomly divided into the following 4 groups: a sham-operation group, a control group, an adenovirus-enhanced green fluorescent protein (Ad-EGFP) gene group and an Ad-ACE2 gene group. All dogs in the Ad-EGFP and Ad-ACE2 groups were rhythmized at 450 bpm for 14 days. Two weeks later, all the dogs underwent thoracotomy and epicardial gene painting. On day 21 after gene transfer, all the animals were subjected to electrophysiological and molecular studies. AF induction rates and durations were significantly increased in the control and Ad-EGFP groups compared to the sham-operated and Ad-ACE2 groups. Transient receptor potential melastatin 7 (TRPM7) expression levels in the Ad-EGFP and control groups were significantly higher than those in the sham-operated and Ad-ACE2 groups.

Basal [Mg²⁺]_i was significantly decreased in siRNA transfected cells compared with control and non-silencing siRNA-transfected cells. Our results suggest that ACE2 overexpression suppresses atrial electrical remodeling and improves atrial function through the TRPM7 signaling pathway.

Altered physiological functions and ion currents in atrial fibroblasts from patients with chronic atrial fibrillation

The contribution of human atrial fibroblasts to cardiac physiology and pathophysiology is poorly understood. Fibroblasts may contribute to arrhythmogenesis through fibrosis, or by directly altering electrical activity in cardiomyocytes. The objective of our study was to uncover phenotypic differences between cells from patients in sinus rhythm (SR) and chronic atrial fibrillation (AF), with special emphasis on electrophysiological properties. We isolated fibroblasts from human right atrial tissue for patch-clamp experiments, proliferation, migration, and differentiation assays, and gene expression profiling. In culture, proliferation and migration of AF fibroblasts were strongly impaired but differentiation into myofibroblasts was increased. This was associated with a higher number of AF fibroblasts expressing functional Nav1.5 channels. Strikingly Na(+) currents were considerably larger in AF cells. Blocking Na(+) channels in culture with tetrodotoxin did not affect proliferation, migration, or differentiation in neither SR nor AF cells. While freshly isolated fibroblasts showed mostly weak rectifier currents, fibroblasts in culture developed outward rectifier K(+) currents of similar amplitude between the SR and AF groups. Adding the K(+) channel blockers tetraethylammonium and 4-aminopyridin in culture reduced current amplitude and inhibited proliferation in the SR group only. Analysis of gene expression revealed significant differences between SR and AF in genes encoding for ion channels, collagen, growth factors, connexins, and cadherins. In conclusion, this study shows that under AF conditions atrial fibroblasts undergo phenotypic changes that are revealed in culture. Future experiments should be performed in situ to understand the nature of those changes and whether they affect cardiac electrical activity.

Atrial overexpression of angiotensin-converting enzyme 2 improves the canine rapid atrial pacing-induced structural and electrical remodeling. Fan, ACE2 improves atrial substrate remodeling

The purpose of this study was to investigate whether atrial overexpression of angiotensin-converting enzyme 2 (ACE2) by homogeneous transmural atrial gene transfer can reverse atrial remodeling and its mechanisms in a canine atrial-pacing model. Twenty-eight mongrel dogs were randomly divided into four groups: Sham-operated, AF-control, gene therapy with adenovirus-enhanced green fluorescent protein (Ad-EGFP) and gene therapy with Ad-ACE2 (Ad-ACE2) (n = 7 per subgroup). AF was induced in all dogs except the Sham-operated group by rapid atrial pacing at 450 beats/min for 2 weeks. Ad-EGFP and Ad-ACE2 group then received epicardial gene painting. Three weeks after gene transfer, all animals except the Sham group underwent rapid atrial pacing for another 3 weeks and then invasive electrophysiological, histological and molecular studies. The Ad-ACE2 group showed an increased ACE2 and Angiotensin-(1–7) expression, and decreased Angiotensin II expression in comparison with Ad-EGFP and AF-control group. ACE2 overexpression attenuated rapid atrial pacing-induced increase in activated extracellular signal-regulated kinases and mitogen-activated protein kinases (MAPKs) levels, and decrease in MAPK phosphatase 1(MKP-1) level, resulting in attenuation of atrial fibrosis collagen protein markers and transforming growth factor-β1. Additionally, ACE2 overexpression also modulated the tachypacing-induced up-regulation of connexin 40, down-regulation of connexin 43 and Kv4.2, and significantly decreased the inducibility and duration of AF. ACE2 overexpression could shift the renin–angiotensin system balance towards the protective axis, attenuate cardiac fibrosis remodeling associated with up-regulation of MKP-1 and reduction of MAPKs activities, modulate tachypacing-induced ion channels and connexin remodeling, and subsequently reduce the inducibility and duration of AF.

Significance of hypoxia-inducible factor-1α expression with atrial fibrosis in rats induced with isoproterenol

Atrial interstitial fibrosis plays a dual role in inducing and maintaining atrial fibrillation (AF). Hypoxia-inducible factor-1α (HIF-1α) has been reported as closely associated with renal, liver and pulmonary fibrosis diseases. However, whether HIF-1α is involved in myocardial fibrosis, and the associations between HIF-1α, transforming growth factor-β₁ (TGF-β₁) and matrix metalloproteinase-9 (MMP-9) remain unknown. Therefore, this area warrants studying for the significance of AF diagnosis and treatment. The present study investigated the expression of HIF-1α in atrial fibrosis and its possible mechanism in isoproterenol (ISO)-induced rats. The three groups of rats; control, ISO and ISO plus sirolimus [also known as rapamycin (Rapa)], were treated for 15 days and sacrificed to remove the myocardial tissues. The expression levels of HIF-1α, TGF-β₁ and MMP-9 and their associations with atrial fibrosis were examined through histomorphology and protein and mRNA levels. The protein and mRNA levels of HIF-1α, TGF-β₁ and MMP-9 in the ISO group were increased markedly (P<0.01) compared with the control group, while those in the Rapa group were clearly decreased (P<0.01) compared with the ISO group. The protein and mRNA levels of HIF-1α, TGF-β₁ and MMP-9 were positively correlated (P<0.01) with atrial fibrosis (collagen volume fraction index), as were the HIF-1α, TGF-β₁ and MMP-9 mRNA levels (P<0.01) and the mRNA levels between MMP-9 and TGF-β₁ (P<0.01). During the process of atrial fibrosis in ISO-induced rats, HIF-1α promotes the expression of TGF-β₁ and MMP-9 protein, and thus is involved in in atrial fibrosis.

Activation of angiotensin-converting enzyme 2 improves cardiac electrical changes in ventricular repolarization in streptozotocin-induced hyperglycaemic rats

AIMS

Diabetic patients present a high level of cardiac arrhythmias and risk of cardiac sudden death. The renin-angiotensin system (RAS) plays a key role in diabetes and cardiac diseases. The present study aimed to evaluate whether an angiotensin-converting enzyme 2 (ACE2) activator, diminazene aceturate (DIZE), could improve the streptozotocin (STZ)-induced electrical changes in ventricular repolarization in hyperglycaemic rats.

METHODS AND RESULTS

Hyperglycaemia was induced in Wistar male rats with STZ (60 mg/kg/iv). After 4 weeks of STZ injection, rats were daily treated with saline (control) or DIZE (1 mg/kg/gavage) for four consecutive weeks. The cardiac electrical function was evaluated in vivo by electrocardiogram and in vitro by cardiac action potential records in different pacing frequencies. Treatment with DIZE was not able to reverse hyperglycaemia nor body weight loss. However, DIZE reversed hyperglycaemia-induced cardiac electrical changes in ventricular repolarization. Specifically, animals treated with DIZE showed shorter QT and QTc intervals. In addition, ACE2 activation was capable to shorten the cardiac action potential and also reverse the arrhythmic markers. Diminazene aceturate treatment did not induce arrhythmic events in normal, as well as in hyperglycaemic animals.

CONCLUSION

Our data indicate that activation of ACE2 has a beneficial effect in hyperglycaemic rats, improving the cardiac electrical function. Thus, DIZE represents a promising new therapeutic agent to treat hyperglycaemia-induced cardiac electrical changes in ventricular repolarization.

Association between serum angiotensin-converting enzyme 2 level with postoperative morbidity and mortality after major pulmonary resection in non-small cell lung cancer patients

BACKGROUND

To explore the association between serum angiotensin-converting enzyme 2 (ACE2) levels and postoperative morbidity and mortality after major pulmonary resection in non-small cell lung cancer (NSCLC) patients.

METHODS

Preoperative and postoperative serum ACE2 levels in 320 NSCLC patients who underwent major pulmonary resection were measured. The serum ACE2 levels on postoperative day 1 were divided into quartile categories.

RESULTS

After adjustment for age, sex, body mass index, current smoking status, forced expiratory volume in 1 second, coronary heart disease, hypertension, diabetes mellitus, chronic obstructive pulmonary disease, and tumour clinical stages, the risk of developing postoperative morbidities was significantly higher in the lowest serum ACE2 level quartile than in the highest quartile (hazard ratio, 2.12; 95% CI, 1.57-6.23; p=0.008). NSCLC patients with a serum ACE2 level ≤3.21 ng/mL had significantly higher rates of pneumonia, pleural effusion, atrial fibrillation as well as higher in-hospital mortality after major pulmonary resection, compared with those with a serum ACE2 level >3.21 ng/mL.

CONCLUSIONS

The serum ACE2 level one day post surgery is an independent risk factor for postoperative morbidities after major pulmonary resection in NSCLC patients. Thus, it could be used as a prognostic factor for postoperative morbidities after major pulmonary resection in NSCLC patients.

Role of caveolin-1 in atrial fibrillation as an anti-fibrotic signaling molecule in human atrial fibroblasts

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia in the general population; yet, the precise mechanisms resulting in AF are not fully understood. Caveolin-1 (Cav-1), the principal structural component of caveolae organelles in cardiac fibroblasts, is involved in several cardiovascular conditions; however, the study on its function in atrium, in particular, in AF, is still lacking. This report examines the hypothesis that Cav-1 confers an anti-AF effect by mediating atrial structural remodeling through its anti-fibrotic action. We evaluated the expression of Cav-1, transforming growth factor-β1 (TGF-β1), and fibrosis in atrial specimens of 13 patients with AF and 10 subjects with sinus rhythm, and found that the expression of Cav-1 was significantly downregulated, whereas TGF-β1 level, collagens I/III contents and atrial fibrosis were markedly increased, in AF. Western blot analysis demonstrated that treatment of human atrial fibroblasts (HAFs) with TGF-β1 resulted in a concentration- and time-dependent repression of Cav-1. Downregulation of Cav-1 with siRNA increased the TGF-β1-induced activation of Smad signal pathway and collagens production in HAFs. Furthermore, incubation of HAFs with the peptides derived from Cav-1 to achieve Cav-1 gain-of-function abolished the TGF-β1-induced production of collagens I/III and decreases of MMP-2/-9 expression. Therefore it was concluded that Cav-1 is an important anti-AF signaling mediator by conferring its anti-fibrotic effects in atrium.

Role of Magnetic Resonance Imaging of Atrial Fibrosis in Atrial Fibrillation Ablation

Atrial fibrillation (AF) likely involves a complex interplay between triggering activity, usually from pulmonary vein foci, and maintenance of the arrhythmia by an arrhythmogenic substrate. Both components of AF, triggers and substrate have been linked to atrial fibrosis and attendant changes in atrial electrophysiology. Recently, there has been a growing use of imaging modalities, particularly cardiac magnetic resonance (CMR), to quantify the burden of atrial fibrosis and scar in patients either undergoing AF ablation, or who have recently had the procedure. How to use the CMR derived data is still an open area of investigation. The aim of this article is to summarise what is known as atrial fibrosis, as assessed by traditional catheter-based techniques and newer imaging approaches, and to report on novel efforts from our group to advance the use of CMR in AF ablation patients.

Atrial fibrosis: a risk stratifier for atrial fibrillation

Atrial fibrillation (AF), especially persistent and long-standing persistent AF, may result in electro-anatomical changes in the left atrium, resulting in remodeling and deposition of fibrous tissue. There are emerging data that atrial substrate modification may increase the risk of thromboembolic complications, including stroke. Several studies have reported that atrial fibrosis is due to complex interactions among several cellular and neurohumoral mediators. Late gadolinium enhancement MRI has been reported to allow quantitative assessment of myocardial fibrosis in patients at risk of developing a stroke. Current stroke risk stratification criteria for AF do not utilize atrial fibrosis as an independent risk factor despite its association with AF and stroke. Further research is required in developing adequate risk stratification tools for predicting the stroke risk and catheter ablation outcomes in AF.

Atrial fibrillation and heart failure in the elderly

Atrial fibrillation (AF) is a common clinical problem in elderly patients and especially in those with heart failure (HF). It is a major risk factor for serious cardiovascular events, such as stroke, HF and premature death. Both the prevalence and incidence of AF increase with age and its prevalence in the United States are estimated at more than 2.2 million, with nearly 75% of patients aged >65 years. Aging-related atrial remodeling with fibrosis, dilation and mitochondrial DNA mutations predispose elderly patients to AF. Current management options for AF, including rate control and anticoagulation therapy, can be successfully applied to the elderly population. New antiarrhythmic and anticoagulation medications such as dronedarone and dabigatran, respectively, can impact the approach to therapy in the elderly. Non-pharmacological options such as catheter-based ablation have also gained prominence and have been incorporated into the guidelines for management of AF. However, more trials in the elderly and very elderly segments are needed to clarify the safety and long-term efficacy of the new treatment options.

Left Atrial Fibrosis: Role in Atrial Fibrillation Pathophysiology and Treatment Outcomes

The mechanisms of atrial fibrillation are complex, and have been the subject of intensive study for over fifty years. There is likely a complex interplay between triggers and substrate that mediates the initiation and maintenance of AF. Increasingly, atrial fibrosis has been recognized as a key component of that substrate, playing a critical role in conduction abnormalities in the left atrium that appear necessary to maintaining AF. In the last several years, our abilities to quantify left atrial fibrosis - both through catheter- and MRI-based techniques - has shed important light on the underlying mechanisms of AF, and on therapeutic strategies to treat AF. Whether our increased appreciation of the role of atrial fibrosis in AF translates into improved efficacy of catheter ablation or anti-arrhythmic therapy, though, remains to be seen. The aim of this review is to summarize clinical investigations of atrial fibrosis as a factor in the development and treatment of atrial fibrillation.

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.

Extracellular matrix alterations in the atria: insights into the mechanisms and perpetuation of atrial fibrillation

Atrial fibrillation is the most common arrhythmia in clinical practice and is associated with increased cardiovascular morbidity and mortality. Atrial fibrosis, a detrimental process that causes imbalance in extracellular matrix deposition and degradation, has been implicated as a substrate for atrial fibrillation, but the precise mechanisms of structural remodelling and the relationship between atrial fibrosis and atrial fibrillation are not completely understood. A large number of experimental and clinical studies have shed light on the mechanisms of atrial fibrosis at the molecular and cellular level, including interactions between matrix metalloproteinases and their endogenous tissue inhibitors, and profibrotic signals through specific molecules and mediators such as angiotensin II, transforming growth factor-β1, connective tissue growth factor, and platelet-derived growth factor. This review focuses on the mechanisms of atrial fibrosis and highlights the relationship between atrial fibrosis and atrial fibrillation.

Identifying the regulatory element for human angiotensin-converting enzyme 2 (ACE2) expression in human cardiofibroblasts

Angiotensin-converting enzyme 2 (ACE2) has been proposed as a potential target for cardioprotection in regulating cardiovascular functions, owing to its key role in the formation of the vasoprotective peptides angiotensin-(1-7) from angiotensin II (Ang II). The regulatory mechanism of ace2 expression, however, remains to be explored. In this study, we investigated the regulatory element within the upstream of ace2. The human ace2 promoter region, from position -2069 to +20, was cloned and a series of upstream deletion mutants were constructed and cloned into a luciferase reporter vector. The reporter luciferase activity was analyzed by transient transfection of the constructs into human cardiofibroblasts (HCFs) and an activating domain was identified in the -516/-481 region. Deletion or reversal of this domain within ace2 resulted in a significant decrease in promoter activity. The nuclear proteins isolated from the HCFs formed a DNA-protein complex with double stranded oligonucleotides of the -516/-481 domain, as detected by electrophoretic mobility shift assay. Site-directed mutagenesis of this region identified a putative protein binding domain and a potential binding site, ATTTGGA, homologous to that of an Ikaros binding domain. This regulatory element was responsible for Ang II stimulation via the Ang II-Ang II type-1 receptor (AT1R) signaling pathway, but was not responsible for pro-inflammatory cytokines TGF-β1 and TNF-α. Our results suggest that the nucleotide sequences -516/-481 of human ace2 may be a binding domain for an as yet unidentified regulatory factor(s) that regulates ace2 expression and is associated with Ang II stimulation.

Regulation of angiotensin converting enzyme II by angiotensin peptides in human cardiofibroblasts

Numerous studies have suggested that angiotensin peptides modulate the expression of angiotensin converting enzyme II (ACE2) in the cardiovascular system, but the molecular mechanisms remain poorly understood. In the present study, human cardiac fibroblasts (HCF) were used to test the regulatory effects of angiotensin II (Ang II) and angiotensin-(1-7) [Ang-(1-7)] on ACE2 expression. The results show that Ang II upregulates ACE2 expression. This action is modulated through activation of Ang II type 1 receptor (AT1R). Ang II-mediated ACE2 upregulation was blocked by antagonists of AT1R and ERK-MAPK signaling pathways. Additionally, Ang-(1-7) increased ACE2 expression, and this upregulation was inhibited by Ang-(1-7) Mas receptor blockade. Our results further reveal that the activation of p-ERK1/2 proteins plays a critical role in upregulating ACE2 in Ang-(1-7)-stimulated HCF cells. This effect occurs independently of the Ang II-AT1R signaling pathway. In conclusion, we propose that Ang II-upregulated ACE2 may increase Ang-(1-7) formation from Ang II, and that ACE2 expression is further enhanced by Ang-(1-7) in a positive feedback loop.

Advances in the renin angiotensin system focus on angiotensin-converting enzyme 2 and angiotensin-(1-7)

The contribution of the renin angiotensin system to physiology and pathology is undergoing a rapid reconsideration of its mechanisms from emerging new concepts implicating angiotensin-converting enzyme 2 and angiotensin-(1-7) as new elements negatively influencing the vasoconstrictor, trophic, and pro-inflammatory actions of angiotensin II. This component of the system acts to oppose the vasoconstrictor and proliferative effects on angiotensin II through signaling mechanisms mediated by the mas receptor. In addition, a reduced expression of the vasodepressor axis composed by angiotensin-converting enzyme 2 and angiotensin-(1-7) may contribute to the expression of essential hypertension, the remodeling of heart and renal function associated with this disease, and even the physiology of pregnancy and the development of eclampsia.

Redox regulation, NF-kappaB, and atrial fibrillation

Atrial fibrillation (AF) is the most common clinically encountered abnormal heart beat. It is associated with an increased risk of stroke and symptoms of heart failure. Current therapies are directed toward controlling the rate of ventricular activation and preventing strokes through anticoagulation. Attempts at suppressing the arrhythmia are often ineffective, in part because the underlying pathogenesis is poorly understood. Recently, structural and electrical remodeling has been shown to occur during AF. These changes involve alterations in gene regulation and help perpetuate the arrhythmia. Some signals for remodeling are have been identified. Moreover, AF is associated with oxidative stress, and this redox imbalance may contribute to the altered gene regulation. One likely mediator of this change in transcriptional regulation is the redox sensitive transcription factor, nuclear factor-kappaB (NF-kappaB). Recently, NF-kappaB has been shown to downregulate transcription of the cardiac sodium channel in response to oxidative stress. NF-kappaB may contribute to the regulation of other ion channels, transcription factors, or splicing factors altered in AF and may represent a therapeutic target in AF management.

Therapeutic targets in liver transplantation: angiotensin II in nonsteatotic grafts and angiotensin-(1-7) in steatotic grafts

Numerous steatotic livers are discarded as unsuitable for transplantation because of their poor tolerance of ischemia-reperfusion(I/R). The injurious effects of angiotensin (Ang)-II and the benefits of Ang-(1-7) in various pathologies are well documented. We examined the generation of Ang II and Ang-(1-7) in steatotic and nonsteatotic liver grafts from Zucker rats following transplantation. We also studied in both liver grafts the effects of Ang-II receptors antagonists and Ang-(1-7) receptor antagonists on hepatic I/R damage associated with transplantation. Nonsteatotic grafts showed higher Ang II levels than steatotic grafts, whereas steatotic grafts showed higher Ang-(1-7) levels than nonsteatotic grafts. Ang II receptor antagonists protected only nonsteatotic grafts against damage, whereas Ang-(1-7) receptor antagonists were effective only in steatotic grafts. The protection conferred by Ang II receptor antagonists in nonsteatotic grafts was associated with ERK 1/2 overexpression, whereas the beneficial effects of Ang-(1-7) receptor antagonists in steatotic grafts may be mediated by NO inhibition. Our results show that Ang II receptor antagonists are effective only in nonsteatotic liver transplantation and point to a novel therapeutic target in liver transplantation based on Ang-(1-7), which is specific for steatotic liver grafts.

Genomic and proteomic approaches for targeting of angiotensin-converting enzyme2 for cardiovascular diseases

PURPOSE OF REVIEW

Our objective in this review is to summarize current understanding of the role of angiotensin-converting enzyme2 in cardiovascular pathophysiology. In addition, we will present recent advances and future directions in the use of genomic and proteomic approaches for the development of new therapeutic strategies that target angiotensin-converting enzyme2 for cardiovascular diseases.

RECENT FINDINGS

The angiotensin-converting enzyme homologue, angiotensin-converting enzyme2, plays a central role in counterbalancing the vasoconstrictive, proliferative, and hypertensive peptide, angiotensin II, by generating angiotensin-(1-7), which induces vasodilatory and antiproliferative actions in the cardiovascular system. Gene therapy is a strategy in which a vector is used to deliver beneficial genes systemically or directly into a specific organ. Recent observations suggest that angiotensin-converting enzyme2 overexpression by lentiviral vector-mediated gene delivery leads to an increased local angiotensin-converting enzyme2 expression and evokes protective mechanisms against hypertension and cardiovascular diseases. In addition, endogenous angiotensin-converting enzyme2 activation leads to cardiovascular protection.

SUMMARY

Prevalence of cardiovascular diseases continues to rise in spite of recent success in both the use of combination therapy and introduction of new pharmacotherapeutic agents. Thus, new and innovative approaches must be discovered in order to bring these diseases under control. Angiotensin-converting enzyme2 offers a new target in this regard and the use of state-of-the-art genomic and proteomic-based strategies to target this important member of the renin-angiotensin system holds potential for the development of improved therapeutics for cardiovascular diseases.

Angiotensin converting enzyme-2 is protective but downregulated in human and experimental lung fibrosis

Earlier work from this laboratory showed that local generation of angiotensin (ANG) II is required for the pathogenesis of experimental pulmonary fibrosis and that ANG peptides are expressed robustly in the lungs of patients with idiopathic pulmonary fibrosis (IPF). Angiotensin converting enzyme-2 (ACE-2) degrades the octapeptide ANG II to form the heptapeptide ANG1-7 and thereby limits ANG II accumulation. On this basis, we hypothesized that ACE-2 would be protective against experimental lung fibrogenesis and might be downregulated in human and experimental lung fibrosis. In lung biopsy specimens from patients with IPF, ACE-2 mRNA and enzyme activity were decreased by 92% (P<0.01) and 74% (P<0.05), respectively. ACE-2 mRNA and activity were also decreased similarly in the lungs of bleomycin-treated rats and C57-BL6 mice. In mice exposed to low doses of bleomycin, lung collagen accumulation was enhanced by intratracheal administration of either ACE-2-specific small interfering RNAs (siRNAs) or the peptide DX(600), a competitive inhibitor of ACE-2 (P<0.05). Administration of either ACE-2 siRNA or DX(600) significantly increased the ANG II content of mouse lung tissue above the level induced by bleomycin alone. Coadministration of the ANG II receptor antagonist saralasin blocked the DX(600)-induced increase in lung collagen. Moreover, purified recombinant human ACE-2, delivered to mice systemically by osmotic minipump, attenuated bleomycin-induced lung collagen accumulation. Together, these data show that ACE-2 mRNA and activity are severely downregulated in both human and experimental lung fibrosis and suggest that ACE-2 protects against lung fibrogenesis by limiting the local accumulation of the profibrotic peptide ANG II.

Atrial fibrosis: mechanisms and clinical relevance in atrial fibrillation

Atrial fibrillation (AF) is the most common arrhythmia in the clinical setting, and traditional pharmacological approaches have proved to have important weaknesses. Structural remodeling has been observed in both clinical and experimental AF paradigms, and is an important feature of the AF substrate, producing fibrosis that alters atrial tissue composition and function. The precise mechanisms underlying atrial fibrosis are not fully elucidated, but recent experimental studies and clinical investigations have provided valuable insights. A variety of signaling systems, particularly involving angiotensin II and related mediators, seem to be centrally involved in the promotion of fibrosis. This paper reviews the current understanding of how atrial fibrosis creates a substrate for AF, summarizes what is known about the mechanisms underlying fibrosis and its progression, and highlights emerging therapeutic approaches aimed at attenuating structural remodeling to prevent AF.

Interplay of angiotensin II and angiotensin(1-7) in the regulation of matrix metalloproteinases of human cardiocytes

Angiotensin II (Ang II) is a critical effector in the renin-angiotensin system (RAS), which modulates cardiovascular homeostasis, and the matrix metalloproteinases (MMPs) and tissue inhibitors of matrix metalloproteinases (TIMPs) related metabolism of extracellular matrix (ECM). Angiotensin(1-7) [Ang(1-7)] is another bioactive peptide in the RAS and is considered to have opposite effects to Ang II. However, the modulation of MMPs and TIMPs by Ang(1-7) is largely unclear in cardiocytes, and the antagonistic effects of Ang(1-7) on Ang II-mediated expression of MMPs and TIMPs have yet to be identified. In the present study, we examined the transcript expression of MMPs and TIMPs in human cardiac fibroblasts (HCF) and myocytes (HCM) after Ang II or Ang(1-7) stimulation, and analysed the antagonistic effects of Ang(1-7) to Ang II. The results show that Ang II decreased transcript expression of MMP-1, MMP-2, TIMP-1, TIMP-2 and TIMP-3, but upregulated MMP-9 expression in the HCF cells. Transcript expression of MMP-9 and TIMP-2 was downregulated by Ang(1-7) in the same cells. In the HCM cells, Ang II induced MMP-1 and MMP-9 overexpression but MMP-2 was downregulated. All of the examined MMPs and TIMPs, except MMP-9, were markedly decreased by Ang(1-7). In the studies of antagonistic effects of Ang(1-7) to Ang II, Ang(1-7) counteracted the effects of Ang II-mediated regulation on MMP-9 and TIMP-1 in the HCF cells compared with the control group. The regulations of all examined MMPs by Ang II were reversed to basal expression by Ang(1-7) in the HCM cells. Our results suggest that Ang(1-7) and Ang II have opposite and antagonistic effects on regulation of transcription of MMPs and TIMPs in primary cultures of human cardiocytes. These effects lead to increased ratios of MMPs to TIMPs after Ang II stimulation and decreased ratios of MMPs to TIMPs after Ang(1-7) stimulation; effects which may partly depend of the type of cardiac cells. These results suggest a potential role for Ang(1-7) in attenuatating cardiac damage in Ang II-induced ECM remodelling.

Increased expression of extracellular matrix proteins in rapid atrial pacing-induced atrial fibrillation

BACKGROUND

Atrial fibrillation (AF) is characterized by structural remodeling of the extracellular matrix (ECM) in cardiac atrium.

OBJECTIVE

The purpose of this study was to gain further insight into atrial ECM remodeling at the molecular level and to test whether altered expression of ECM proteins was associated with the disease.

METHODS

Sustained AF was induced in nine adult pigs after 3-4 weeks of continuous rapid atrial pacing at a rate of 600 bpm. Histologic studies and immunohistochemical stain were performed to identify the potential pathologic substrate underlying abnormalities in atrial tissues with sustained AF.

RESULTS

In the pathologic findings, the fraction of myocardial ECM (ECM%) was measured, with a significantly greater ECM% found in the AF group compared with the sham operated group (n = 6; i.e., pigs with normal sinus rhythm [SR]). A set of 9,182 genes was screened with cDNA microarray analysis. In AF animals, expression of 121 genes increased and 24 genes decreased by > or =1.75-fold compared with SR animals. Significant up-regulation of fibronectin-1 (4.9-fold), fibrillin-1 (3.1-fold), and fibromodulin (1.9-fold) in the fibrillating atria was confirmed by quantitative real-time reverse transcriptase-polymerase chain reaction. Western blot analysis revealed significantly increased atrial fibronectin-1, fibrillin-1, and fibromodulin in the AF group compared with the SR group (1.5-, 2.7-, and 2.1-fold, respectively). Immunohistochemical staining of AF tissue displayed increased accumulation of fibronectin-1 and fibrillin-1 in the atrial interstitial space.

CONCLUSION

Increased expression of ECM proteins in fibrillating atria supports the hypothesis that ECM metabolism contributes to the development of AF.