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

Bibliometric and visual analysis of ACE2/Ang 1-7/MasR axis in diabetes and its microvascular complications from 2000 to 2023

Background

The pathogenesis of diabetes and its microvascular complications are intimately associated with renin angiotensin system dysregulation. Evidence suggests the angiotensin converting enzyme 2 (ACE2)/angiotensin 1-7 (Ang 1-7)/Mas receptor (MasR) axis regulates metabolic imbalances, inflammatory responses, reduces oxidative stress, and sustains microvascular integrity, thereby strengthening defences against diabetic conditions. This study aims to conduct a comprehensive analysis of the ACE2/Ang 1-7/MasR axis in diabetes and its microvascular complications over the past two decades, focusing on key contributors, research hotspots, and thematic trends.

Methods

This cross-sectional bibliometric analysis of 349 English-language publications was performed using HistCite, VOSviewer, CiteSpace, and Bibliometrix R for visualization and metric analysis. Primary analytical metrics included publication count and keyword trend dynamics.

Results

The United States, contributing 105 articles, emerged as the most productive country, with the University of Florida leading institutions with 18 publications. Benter IF was the most prolific author with 14 publications, and Clinical Science was the leading journal with 13 articles. A total of 151 of the 527 author's keywords with two or more occurrences clustered into four major clusters: diabetic microvascular pathogenesis, metabolic systems, type 2 diabetes, and coronavirus infections. Keywords such as "SARS", "ACE2", "coronavirus", "receptor" and "infection" displayed the strongest citation bursts. The thematic evolution in this field expanded from focusing on the renin angiotensin system (2002-2009) to incorporating ACE2 and diabetes metabolism (2010-2016). The latter period (2017-2023) witnessed a significant surge in diabetes research, reflecting the impact of COVID-19 and associated conditions such as diabetic retinopathy and cardiomyopathy.

Conclusions

This scientometric study offers a detailed analysis of the ACE2/Ang 1-7/MasR axis in diabetes and its microvascular complications, providing valuable insights for future research directions.

The possible mechanism and research progress of ACE2 involved in cardiovascular injury caused by COVID-19: a review

ACE2 is the earliest receptor discovered to mediate the entry of SARS-CoV-2. In addition to the receptor, it also participates in complex pathological and physiological processes, including regulating the RAS system, apelin, KKS system, and immune system. In addition to affecting the respiratory system, viral infections also interact with cardiovascular diseases. SARS-CoV-2 can directly invade the cardiovascular system through ACE2; Similarly, cardiovascular diseases such as hypertension and coronary heart disease can affect ACE2 levels and exacerbate the disease, and ACE2 dysregulation may also be a potential mechanism for long-term acute sequelae of COVID-19. Since the SARS CoV-2 epidemic, many large population studies have tried to clarify the current focus of debate, that is, whether we should give COVID-19 patients ACEI and ARB drug treatment, but there is still no conclusive conclusion. We also discussed potential disease treatment options for ACE2 at present. Finally, we discussed the researchers' latest findings on ACE2 and their prospects for future research.

The gut-retina axis: a new perspective in the prevention and treatment of diabetic retinopathy

Diabetic retinopathy (DR) is a microvascular lesion that occurs as a complication of diabetes mellitus. Many studies reveal that retinal neurodegeneration occurs early in its pathogenesis, and abnormal retinal function can occur in patients without any signs of microvascular abnormalities. The gut microbiota is a large, diverse colony of microorganisms that colonize the human intestine. Studies indicated that the gut microbiota is involved in the pathophysiological processes of DR and plays an important role in its development. On the one hand, numerous studies demonstrated the involvement of gut microbiota in retinal neurodegeneration. On the other hand, alterations in gut bacteria in RD patients can cause or exacerbate DR. The present review aims to underline the critical relationship between gut microbiota and DR. After a brief overview of the composition, function, and essential role of the gut microbiota in ocular health, and the review explores the concept of the gut-retina axis and the conditions of the gut-retina axis crosstalk. Because gut dysbiosis has been associated with DR, the review intends to determine changes in the gut microbiome in DR, the hypothesized mechanisms linking to the gut-retina axis, and its predictive potential.

Pharmacologic Activation of Angiotensin-Converting Enzyme II Alleviates Diabetic Cardiomyopathy in db/db Mice by Reducing Reactive Oxidative Stress

BACKGRUOUND

Diabetes mellitus is one of the most common chronic diseases worldwide, and cardiovascular disease is the leading cause of morbidity and mortality in diabetic patients. Diabetic cardiomyopathy (DCM) is a phenomenon characterized by a deterioration in cardiac function and structure, independent of vascular complications. Among many possible causes, the renin-angiotensin-aldosterone system and angiotensin II have been proposed as major drivers of DCM development. In the current study, we aimed to investigate the effects of pharmacological activation of angiotensin-converting enzyme 2 (ACE2) on DCM.

METHODS

The ACE2 activator diminazene aceturate (DIZE) was administered intraperitoneally to male db/db mice (8 weeks old) for 8 weeks. Transthoracic echocardiography was used to assess cardiac mass and function in mice. Cardiac structure and fibrotic changes were examined using histology and immunohistochemistry. Gene and protein expression levels were examined using quantitative reverse transcription polymerase chain reaction and Western blotting, respectively. Additionally, RNA sequencing was performed to investigate the underlying mechanisms of the effects of DIZE and identify novel potential therapeutic targets for DCM.

RESULTS

Echocardiography revealed that in DCM, the administration of DIZE significantly improved cardiac function as well as reduced cardiac hypertrophy and fibrosis. Transcriptome analysis revealed that DIZE treatment suppresses oxidative stress and several pathways related to cardiac hypertrophy.

CONCLUSION

DIZE prevented the diabetes mellitus-mediated structural and functional deterioration of mouse hearts. Our findings suggest that the pharmacological activation of ACE2 could be a novel treatment strategy for DCM.

Cardiovascular complications of diabetes: role of non-coding RNAs in the crosstalk between immune and cardiovascular systems

Diabetes mellitus, a group of metabolic disorders characterized by high levels of blood glucose caused by insulin defect or impairment, is a major risk factor for cardiovascular diseases and related mortality. Patients with diabetes experience a state of chronic or intermittent hyperglycemia resulting in damage to the vasculature, leading to micro- and macro-vascular diseases. These conditions are associated with low-grade chronic inflammation and accelerated atherosclerosis. Several classes of leukocytes have been implicated in diabetic cardiovascular impairment. Although the molecular pathways through which diabetes elicits an inflammatory response have attracted significant attention, how they contribute to altering cardiovascular homeostasis is still incompletely understood. In this respect, non-coding RNAs (ncRNAs) are a still largely under-investigated class of transcripts that may play a fundamental role. This review article gathers the current knowledge on the function of ncRNAs in the crosstalk between immune and cardiovascular cells in the context of diabetic complications, highlighting the influence of biological sex in such mechanisms and exploring the potential role of ncRNAs as biomarkers and targets for treatments. The discussion closes by offering an overview of the ncRNAs involved in the increased cardiovascular risk suffered by patients with diabetes facing Sars-CoV-2 infection.

Association of COVID-19 with Comorbidities: An Update

Coronavirus disease (COVID-19) is caused by severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) which was identified in Wuhan, China in December 2019 and jeopardized human lives. It spreads at an unprecedented rate worldwide, with serious and still-unfolding health conditions and economic ramifications. Based on the clinical investigations, the severity of COVID-19 appears to be highly variable, ranging from mild to severe infections including the death of an infected individual. To add to this, patients with comorbid conditions such as age or concomitant illnesses are significant predictors of the disease's severity and progression. SARS-CoV-2 enters inside the host cells through ACE2 (angiotensin converting enzyme2) receptor expression; therefore, comorbidities associated with higher ACE2 expression may enhance the virus entry and the severity of COVID-19 infection. It has already been recognized that age-related comorbidities such as Parkinson's disease, cancer, diabetes, and cardiovascular diseases may lead to life-threatening illnesses in COVID-19-infected patients. COVID-19 infection results in the excessive release of cytokines, called "cytokine storm", which causes the worsening of comorbid disease conditions. Different mechanisms of COVID-19 infections leading to intensive care unit (ICU) admissions or deaths have been hypothesized. This review provides insights into the relationship between various comorbidities and COVID-19 infection. We further discuss the potential pathophysiological correlation between COVID-19 disease and comorbidities with the medical interventions for comorbid patients. Toward the end, different therapeutic options have been discussed for COVID-19-infected comorbid patients.

The interplay of inflammation, exosomes and Ca2+ dynamics in diabetic cardiomyopathy

Diabetes mellitus is one of the prime risk factors for cardiovascular complications and is linked with high morbidity and mortality. Diabetic cardiomyopathy (DCM) often manifests as reduced cardiac contractility, myocardial fibrosis, diastolic dysfunction, and chronic heart failure. Inflammation, changes in calcium (Ca²⁺) handling and cardiomyocyte loss are often implicated in the development and progression of DCM. Although the existence of DCM was established nearly four decades ago, the exact mechanisms underlying this disease pathophysiology is constantly evolving. Furthermore, the complex pathophysiology of DCM is linked with exosomes, which has recently shown to facilitate intercellular (cell-to-cell) communication through biomolecules such as micro RNA (miRNA), proteins, enzymes, cell surface receptors, growth factors, cytokines, and lipids. Inflammatory response and Ca²⁺ signaling are interrelated and DCM  has been known to adversely affect many of these signaling molecules either qualitatively and/or quantitatively. In this literature review, we have demonstrated that Ca²⁺ regulators are tightly controlled at different molecular and cellular levels during various biological processes in the heart. Inflammatory mediators, miRNA and exosomes are shown to interact with these regulators, however how these mediators are linked to Ca²⁺ handling during DCM pathogenesis remains elusive. Thus, further investigations are needed to understand the mechanisms to restore cardiac Ca²⁺ homeostasis and function, and to serve as potential therapeutic targets in the treatment of DCM.

Urinary angiotensin-converting enzyme 2 and metabolomics in COVID-19-mediated kidney injury

Background

Angiotensin-converting enzyme 2 (ACE2), the receptor for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is highly expressed in the kidneys. Beyond serving as a crucial endogenous regulator of the renin-angiotensin system, ACE2 also possess a unique function to facilitate amino acid absorption. Our observational study sought to explore the relationship between urine ACE2 (uACE2) and renal outcomes in coronavirus disease 2019 (COVID-19).

Methods

In a cohort of 104 patients with COVID-19 without acute kidney injury (AKI), 43 patients with COVID-19-mediated AKI and 36 non-COVID-19 controls, we measured uACE2, urine tumour necrosis factor receptors I and II (uTNF-RI and uTNF-RII) and neutrophil gelatinase-associated lipocalin (uNGAL). We also assessed ACE2 staining in autopsy kidney samples and generated a propensity score-matched subgroup of patients to perform a targeted urine metabolomic study to describe the characteristic signature of COVID-19.

Results

uACE2 is increased in patients with COVID-19 and further increased in those that developed AKI. After adjusting uACE2 levels for age, sex and previous comorbidities, increased uACE2 was independently associated with a >3-fold higher risk of developing AKI [odds ratio 3.05 (95% confidence interval 1.23‒7.58), P = .017]. Increased uACE2 corresponded to a tubular loss of ACE2 in kidney sections and strongly correlated with uTNF-RI and uTNF-RII. Urine quantitative metabolome analysis revealed an increased excretion of essential amino acids in patients with COVID-19, including leucine, isoleucine, tryptophan and phenylalanine. Additionally, a strong correlation was observed between urine amino acids and uACE2.

Conclusions

Elevated uACE2 is related to AKI in patients with COVID-19. The loss of tubular ACE2 during SARS-CoV-2 infection demonstrates a potential link between aminoaciduria and proximal tubular injury.

SARS-CoV-2 and the central nervous system: Emerging insights into hemorrhage-associated neurological consequences and therapeutic considerations

Coronavirus disease 2019 (COVID-19), caused by the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) continues to impact our lives by causing widespread illness and death and poses a threat due to the possibility of emerging strains. SARS-CoV-2 targets angiotensin-converting enzyme 2 (ACE2) before entering vital organs of the body, including the brain. Studies have shown systemic inflammation, cellular senescence, and viral toxicity-mediated multi-organ failure occur during infectious periods. However, prognostic investigations suggest that both acute and long-term neurological complications, including predisposition to irreversible neurodegenerative diseases, can be a serious concern for COVID-19 survivors, especially the elderly population. As emerging studies reveal sites of SARS-CoV-2 infection in different parts of the brain, potential causes of chronic lesions including cerebral and deep-brain microbleeds and the likelihood of developing stroke-like pathologies increases, with critical long-term consequences, particularly for individuals with neuropathological and/or age-associated comorbid conditions. Our recent studies linking the blood degradation products to genome instability, leading to cellular senescence and ferroptosis, raise the possibility of similar neurovascular events as a result of SARS-CoV-2 infection. In this review, we discuss the neuropathological consequences of SARS-CoV-2 infection in COVID survivors, focusing on possible hemorrhagic damage in brain cells, its association to aging, and the future directions in developing mechanism-guided therapeutic strategies.

Glycated ACE2 reduces anti-remodeling effects of renin-angiotensin system inhibition in human diabetic hearts

BACKGROUND

High glycated-hemoglobin (HbA1c) levels correlated with an elevated risk of adverse cardiovascular outcomes despite renin-angiotensin system (RAS) inhibition in type-2 diabetic (T2DM) patients with reduced ejection fraction. Using the routine biopsies of non-T2DM heart transplanted (HTX) in T2DM recipients, we evaluated whether the diabetic milieu modulates glycosylated ACE2 (GlycACE2) levels in cardiomyocytes, known to be affected by non-enzymatic glycosylation, and the relationship with glycemic control.

OBJECTIVES

We investigated the possible effects of GlycACE2 on the anti-remodeling pathways of the RAS inhibitors by evaluating the levels of Angiotensin (Ang) 1-9, Ang 1-7, and Mas receptor (MasR), Nuclear-factor of activated T-cells (NFAT), and fibrosis in human hearts.

METHODS

We evaluated 197 first HTX recipients (107 non-T2DM, 90 T2DM). All patients were treated with angiotensin-converting enzyme inhibitor (ACE-I) or angiotensin receptor blocker (ARB) at hospital discharge. Patients underwent clinical evaluation (metabolic status, echocardiography, coronary CT-angiography, and endomyocardial biopsies). Biopsies were used to evaluate ACE2, GlycACE2, Ang 1-9, Ang 1-7, MasR, NAFT, and fibrosis.

RESULTS

GlycACE2 was higher in T2DM compared tonon-T2DM cardiomyocytes. Moreover, reduced expressions of Ang 1-9, Ang 1-7, and MasR were observed, suggesting impaired effects of RAS-inhibition in diabetic hearts. Accordingly, biopsies from T2DM recipients showed higher fibrosis than those from non-T2DM recipients. Notably, the expression of GlycACE2 in heart biopsies was strongly dependent on glycemic control, as reflected by the correlation between mean plasma HbA1c, evaluated quarterly during the 12-month follow-up, and GlycACE2 expression.

CONCLUSION

Poor glycemic control, favoring GlycACE2, may attenuate the cardioprotective effects of RAS-inhibition. However, the achievement of tight glycemic control normalizes the anti-remodeling effects of RAS-inhibition.

TRIAL REGISTRATION

https://clinicaltrials.gov/ NCT03546062.

Cardiomyocyte-specific knockout of ADAM17 ameliorates left ventricular remodeling and function in diabetic cardiomyopathy of mice

Angiotensin-converting enzyme 2 (ACE2) has proven beneficial in attenuating diabetic cardiomyopathy (DCM) but has been found to be a substrate of a disintegrin and metalloprotease protein-17 (ADAM17). However, whether ADAM17 plays a role in the pathogenesis and intervention of DCM is obscure. In this study, we created cardiomyocyte-specific knockout of ADAM17 (A17^α-MHCKO) mice, and left ventricular dimension, function, pathology and molecular biology were assessed in ADAM17^fl/fl control, A17^α-MHCKO control, ADAM17^fl/fl diabetic and A17^α-MHCKO diabetic mice. Both differentiated H9c2 cells and neonatal rat cardiomyocytes (NRCMs) were used to explore the molecular mechanisms underlying the effect of ADAM17 on DCM. The results showed that protein expression and activity of ADAM17 were upregulated whereas the protein expression of ACE2 was downregulated in the myocardium of diabetic mice. Cardiomyocyte-specific knockout of ADAM17 mitigated cardiac fibrosis and cardiomyocyte apoptosis and ameliorated cardiac dysfunction in mice with DCM. Bioinformatic analyses detected a number of genes enriched in metabolic pathways, in particular the AMPK signaling pathway, expressed differentially between the hearts of A17^α-MHCKO and ADAM17^fl/fl diabetic mice. The mechanism may involve activated AMPK pathway, increased autophagosome formation and improved autophagic flux, which reduced the apoptotic response in cardiomyocytes. In addition, hypoxia-inducible factor-1α (HIF-1α) might act as an upstream mediator of upregulated ADAM17 and ADAM17 might affect AMPK signaling via α1 A-adrenergic receptor (ADRA1A). These results indicated that ADAM17 activity and ACE2 shedding were enhanced in DCM, which was reversed by cardiomyocyte-specific ADAM17 knockout. Thus, inhibition of ADAM17 may provide a promising approach to the treatment of DCM.

Proposed mechanisms underlying the salutary effects of ADAM17 deficiency on diabetic cardiomyopathy. ADAM17 deficiency increases autophagosome formation and improves autophagic flux via reducing ACE2 shedding, activating AMPK pathway, and promoting TFEB nuclear translocation, which reduces the apoptotic response in cardiomyocytes and attenuates left ventricular remodeling and dysfunction in DCM of mice.

Unconventional avenues to decelerated diabetic retinopathy

Diabetic retinopathy (DR) is an important microvascular complication of diabetes mellitus (DM), causing significant visual impairment worldwide. Current gold standards for retarding the progress of DR include blood sugar control and regular fundus screening. Despite these measures, the incidence and prevalence of DR and vision-threatening DR remain high. Given its slowly progressive course and long latent period, opportunities to contain or slow DR before it threatens vision must be explored. This narrative review assesses the recently described unconventional strategies to retard DR progression. These include gut-ocular flow, gene therapy, mitochondrial dysfunction-oxidative stress, stem cell therapeutics, neurodegeneration, anti-inflammatory treatments, lifestyle modification, and usage of phytochemicals. These therapies impact DR directly, while some of them also influence DM control. Most of these strategies are currently in the preclinical stage, and clinical evidence remains low. Nevertheless, our review suggests that these approaches have the potential for human use to prevent the progression of DR.

Mechanisms of COVID-19 Pathogenesis in Diabetes

Coronavirus disease 2019 (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus, is a global pandemic impacting 254 million people in 190 countries. Comorbidities, particularly cardiovascular disease, diabetes, and hypertension, increase the risk of infection and poor outcomes. SARS-CoV-2 enters host cells through the angiotensin-converting enzyme-2 receptor, generating inflammation and cytokine storm, often resulting in multiorgan failure. The mechanisms and effects of COVID-19 on patients with high-risk diabetes are not yet completely understood. In this review, we discuss the variety of coronaviruses, structure of SARS-CoV-2, mutations in SARS-CoV-2 spike proteins, receptors associated with viral host entry, and disease progression. Furthermore, we focus on possible mechanisms of SARS-CoV-2 in diabetes, leading to inflammation and heart failure. Finally, we discuss existing therapeutic approaches, unanswered questions, and future directions.

Myocardial Iron Deficiency and Mitochondrial Dysfunction in Advanced Heart Failure in Humans

Background

Myocardial iron deficiency (MID) in heart failure (HF) remains largely unexplored. We aim to establish defining criterion for MID, evaluate its pathophysiological role, and evaluate the applicability of monitoring it non‐invasively in human explanted hearts.

Methods and Results

Biventricular tissue iron levels were measured in both failing (n=138) and non‐failing control (NFC, n=46) explanted human hearts. Clinical phenotyping was complemented with comprehensive assessment of myocardial remodeling and mitochondrial functional profiles, including metabolic and oxidative stress. Myocardial iron status was further investigated by cardiac magnetic resonance imaging. Myocardial iron content in the left ventricle was lower in HF versus NFC (121.4 [88.1–150.3] versus 137.4 [109.2–165.9] μg/g dry weight), which was absent in the right ventricle. With a priori cutoff of 86.1 μg/g d.w. in left ventricle, we identified 23% of HF patients with MID (HF‐MID) associated with higher NYHA class and worsened left ventricle function. Respiratory chain and Krebs cycle enzymatic activities were suppressed and strongly correlated with depleted iron stores in HF‐MID hearts. Defenses against oxidative stress were severely impaired in association with worsened adverse remodeling in iron‐deficient hearts. Mechanistically, iron uptake pathways were impeded in HF‐MID including decreased translocation to the sarcolemma, while transmembrane fraction of ferroportin positively correlated with MID. Cardiac magnetic resonance with T2* effectively captured myocardial iron levels in failing hearts.

Conclusions

MID is highly prevalent in advanced human HF and exacerbates pathological remodeling in HF driven primarily by dysfunctional mitochondria and increased oxidative stress in the left ventricle. Cardiac magnetic resonance demonstrates clinical potential to non‐invasively monitor MID.

Lipids and diastolic dysfunction: Recent evidence and findings

AIM

Diastolic dysfunction is the decreased flexibility of the left ventricle due to the impaired ability of the myocardium to relax and plays an important role in the pathogenesis of heart failure. Lipid metabolism is a well-known contributor to cardiac conditions, including ventricular function. In this article, we aimed to review the literature addressing the connections between lipids, their storage, and metabolism with left ventricular diastolic dysfunction.

DATA SYNTHESIS

We searched Google scholar, Pubmed, Embase and Researchgate for our keywords: "Diastolic function", "Fat" and "Lipid profile". Initially, 250 articles were selected by title and 84 of them were chosen as most relevant and directly reviewed.

CONCLUSIONS

Alterations of lipid metabolism in cardiac muscle and cardiac lipid content can occur in many conditions, including consumption of a high-fat diet, obesity, metabolic syndrome, and non-alcoholic fatty liver disease (NAFLD). These conditions induce alterations in myocardial lipid metabolism, increase myocardial fat content and epicardial fat thickness and increase inflammation and oxidative stress which ultimately lead to cardiac lipotoxicity and diastolic dysfunction. The effects of lipids on diastolic function can differ based on gender. Lipid profile and metabolism are as important in the pathogenesis of diastolic dysfunction as they are in other cardiovascular disorders. A more careful look at cardiac lipid metabolism in molecular, histological and gross levels results in more precise understanding of its role in myocardial function and leads to development of potential treatments for diastolic dysfunction.

Gut microbiota production of trimethyl-5-aminovaleric acid reduces fatty acid oxidation and accelerates cardiac hypertrophy

Numerous studies found intestinal microbiota alterations which are thought to affect the development of various diseases through the production of gut-derived metabolites. However, the specific metabolites and their pathophysiological contribution to cardiac hypertrophy or heart failure progression still remain unclear. N,N,N-trimethyl-5-aminovaleric acid (TMAVA), derived from trimethyllysine through the gut microbiota, was elevated with gradually increased risk of cardiac mortality and transplantation in a prospective heart failure cohort (n = 1647). TMAVA treatment aggravated cardiac hypertrophy and dysfunction in high-fat diet-fed mice. Decreased fatty acid oxidation (FAO) is a hallmark of metabolic reprogramming in the diseased heart and contributes to impaired myocardial energetics and contractile dysfunction. Proteomics uncovered that TMAVA disturbed cardiac energy metabolism, leading to inhibition of FAO and myocardial lipid accumulation. TMAVA treatment altered mitochondrial ultrastructure, respiration and FAO and inhibited carnitine metabolism. Mice with γ-butyrobetaine hydroxylase (BBOX) deficiency displayed a similar cardiac hypertrophy phenotype, indicating that TMAVA functions through BBOX. Finally, exogenous carnitine supplementation reversed TMAVA induced cardiac hypertrophy. These data suggest that the gut microbiota-derived TMAVA is a key determinant for the development of cardiac hypertrophy through inhibition of carnitine synthesis and subsequent FAO.

Intestinal microbiota alterations may affect heart function through the production of gut-derived metabolites. Here the authors found that gut microbiota-derived TMAVA is a key determinant for the development of cardiac hypertrophy through inhibition of carnitine synthesis and subsequent fatty acid oxidation.

The Molecular Mechanism of Aerobic Exercise Improving Vascular Remodeling in Hypertension

The treatment and prevention of hypertension has been a worldwide medical challenge. The key pathological hallmark of hypertension is altered arterial vascular structure and function, i.e., increased peripheral vascular resistance due to vascular remodeling. The aim of this review is to elucidate the molecular mechanisms of vascular remodeling in hypertension and the protective mechanisms of aerobic exercise against vascular remodeling during the pathological process of hypertension. The main focus is on the mechanisms of oxidative stress and inflammation in the pathological condition of hypertension and vascular phenotypic transformation induced by the trilaminar structure of vascular endothelial cells, smooth muscle cells and extracellular matrix, and the peripheral adipose layer of the vasculature. To further explore the possible mechanisms by which aerobic exercise ameliorates vascular remodeling in the pathological process of hypertension through anti-proliferative, anti-inflammatory, antioxidant and thus inhibiting vascular phenotypic transformation. It provides a new perspective to reveal the intervention targets of vascular remodeling for the prevention and treatment of hypertension and its complications.

Dysregulation of ACE (Angiotensin-Converting Enzyme)-2 and Renin-Angiotensin Peptides in SARS-CoV-2 Mediated Mortality and End-Organ Injuries

ACE (angiotensin-converting enzyme)-2 as the target for SARS-CoV-2 also negatively regulates the renin-angiotensin system. Pathological activation of ADAM17 (A disintegrin and metalloproteinase-17) may potentiate inflammation and diminish ACE2-mediated tissue protection through proteolytic shedding, contributing to SARS-CoV-2 pathogenesis. We aim to examine plasma soluble ACE2 and angiotensin profiles in relation to outcomes by enrolling consecutive patients admitted for COVID-19 with baseline blood collection at admission and repeated sampling at 7 days. The primary outcome was 90-day mortality, and secondary outcomes were the incidence of end-organ injuries. Overall, 242 patients were included, the median age was 63 (52-74) years, 155 (64.0%) were men, and 57 (23.6%) patients reached the primary end point. Baseline soluble ACE2 was elevated in COVID-19 but was not associated with disease severity or mortality. In contrast, an upward trajectory of soluble ACE2 at repeat sampling was independently associated with an elevated risk of mortality and incidence of acute myocardial injury and circulatory shock. Similarly, an increase in soluble tumor necrosis factor receptor levels was also associated with adverse outcomes. Plasma Ang I, Ang 1-7 (angiotensin 1-7) levels, and the Ang 1-7/Ang II (angiotensin II) ratio were elevated during SARS-CoV-2 infection related to downregulation of ACE activity at baseline. Moreover, patients having an upward trajectory of soluble ACE2 were characterized by an imbalance in the Ang 1-7/Ang II ratio. The observed dysregulation of ACE2 and angiotensin peptides with disease progression suggest a potential role of ADAM17 inhibition and enhancing the beneficial Ang 1-7/Mas axis to improve outcomes against SARS-CoV-2 infection.

Cardiovascular complications after COVID-19 in chronic kidney disease, dialysis and kidney transplant patients

The coronavirus disease 2019 (COVID-19) is associated with increased mortality in patients with chronic kidney disease (CKD), dialysis patients and kidney transplant recipients (KTR). Cardiovascular complications, such as sudden arrhythmias, thromboembolic events, coronary events, cardiomyopathies and heart failure, may present in about 10–20% of patients with COVID-19. Patients with CKD, dialysis patients and KTR are all at increased cardiovascular risk and present with more cardiovascular complications after COVID-19 compared to the general population. During the pandemic, health care giving has rapidly changed by reducing elective outpatient reviews, which may refrain these high-risk patients from the appropriate management of their medical conditions, further increasing cardiovascular risk. Importantly, acute kidney injury (AKI) is another common complication of severe COVID-19 and associates with increased mortality. A large proportion of the AKI patients need renal replacement treatment, while 30% of them may not present renal function recovery and remain dialysis-dependent after discharge, thereby having potentially increased future cardiovascular risk. This review summarizes current knowledge regarding the cardiovascular events and mortality in patients with CKD or undergoing hemodialysis and in KTR.

Coronary Large Conductance Ca2+-Activated K+ Channel Dysfunction in Diabetes Mellitus

Diabetes mellitus (DM) is an independent risk of macrovascular and microvascular complications, while cardiovascular diseases remain a leading cause of death in both men and women with diabetes. Large conductance Ca2+-activated K+ (BK) channels are abundantly expressed in arteries and are the key ionic determinant of vascular tone and organ perfusion. It is well established that the downregulation of vascular BK channel function with reduced BK channel protein expression and altered intrinsic BK channel biophysical properties is associated with diabetic vasculopathy. Recent efforts also showed that diabetes-associated changes in signaling pathways and transcriptional factors contribute to the downregulation of BK channel expression. This manuscript will review our current understandings on the molecular, physiological, and biophysical mechanisms that underlie coronary BK channelopathy in diabetes mellitus.

Potential role of epicardial adipose tissue in coronary artery endothelial cell dysfunction in type 2 diabetes

Cardiovascular disease is the most prevalent cause of morbidity and mortality in diabetes. Epicardial adipose tissue (EAT) lies in direct contact with the myocardium and coronary arteries and can influence cardiac (patho) physiology through paracrine signaling pathways. This study hypothesized that the proteins released from EAT represent a critical molecular link between the diabetic state and coronary artery endothelial cell dysfunction. To simulate type 2 diabetes-associated metabolic and inflammatory status in an ex vivo tissue culture model, human EAT samples were treated with a cocktail composed of high glucose, high palmitate, and lipopolysaccharide (gplEAT) and were compared with control EAT (conEAT). Compared to conEAT, gplEAT showed a markedly increased gene expression profile of proinflammatory cytokines, corroborating EAT inflammation, a hallmark feature observed in patients with type 2 diabetes. Luminex assay of EAT-secretome identified increased release of various proinflammatory cytokines, including tumor necrosis factor-alpha (TNF-alpha), interferon-alpha 2 (IFNA2), interleukin 1 beta (IL1B), interleukin 5 (IL5), interleukin 13 (IL13), and CCL5, among others, in response to high glucose, high palmitate, and lipopolysaccharide. Conditioned culture media was used to collect the concentrated proteins (CPs). In response to gplEAT-CPs, human coronary artery endothelial cells (HCAECs) exhibited an inflammatory endothelial cell phenotype, featuring a significantly increased gene expression of proinflammatory cytokines and cell surface expression of VCAM-1. Moreover, gplEAT-CPs severely decreased Akt-eNOS signaling, nitric oxide production, and angiogenic potential of HCAECs, when compared with conEAT-CPs. These findings indicate that EAT inflammation may play a key role in coronary artery endothelial cell dysfunction in type 2 diabetes.

Expression of the SARS-CoV-2 Receptor ACE2 in Human Retina and Diabetes-Implications for Retinopathy

Purpose

To investigate the expression of angiotensin-converting enzyme 2 (ACE2), the receptor for SARS-CoV-2 in human retina.

Methods

Human post-mortem eyes from 13 non-diabetic control cases and 11 diabetic retinopathy cases were analyzed for the expression of ACE2. To compare the vascular ACE2 expression between different organs that involve in diabetes, the expression of ACE2 was investigated in renal specimens from nondiabetic and diabetic nephropathy patients. Expression of TMPRSS2, a cell-surface protease that facilitates SARS-CoV-2 entry, was also investigated in human nondiabetic retinas. Primary human retinal endothelial cells (HRECs) and primary human retinal pericytes (HRPCs) were further used to confirm the vascular ACE2 expression in human retina.

Results

We found that ACE2 was expressed in multiple nonvascular neuroretinal cells, including the retinal ganglion cell layer, inner plexiform layer, inner nuclear layer, and photoreceptor outer segments in both nondiabetic and diabetic retinopathy specimens. Strikingly, we observed significantly more ACE2 positive vessels in the diabetic retinopathy specimens. By contrast, in another end-stage organ affected by diabetes, the kidney, ACE2 in nondiabetic and diabetic nephropathy showed apical expression of ACE2 tubular epithelial cells, but no endothelial expression in glomerular or peritubular capillaries. Western blot analysis of protein lysates from HRECs and HRPCs confirmed expression of ACE2. TMPRSS2 expression was present in multiple retinal neuronal cells, vascular and perivascular cells, and Müller glia.

Conclusions

Together, these results indicate that retina expresses ACE2 and TMPRSS2. Moreover, there are increased vascular ACE2 expression in diabetic retinopathy retinas.

Effect of ramipril on kidney, lung and heart ACE2 in a diabetic mice model

BACKGROUND

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is responsible for the current coronavirus disease 2019 (COVID-19). The main organ affected in this infection is the lung and the virus uses the angiotensin-converting enzyme 2 (ACE2) as a receptor to enter the target cells. In this context, a controversy raised regarding the use of renin-angiotensin system (RAAS) blockers, as these drugs might increase ACE2 expression in some tissues and potentially increase the risk for SARS-CoV-2 infection. This is specially concerning in diabetic patients as diabetes is a risk factor for COVID-19.

METHODS

12-week old diabetic mice (db/db) were treated with ramipril, or vehicle control for 8 weeks. Non-diabetic db/m mice were included as controls. ACE2 expression and activity were studied in lung, kidney and heart of these animals.

RESULTS

Kidney ACE2 activity was increased in the db/db mice as compared to the db/m (143.2% ± 23% vs 100% ± 22.3%, p = 0.004), whereas ramipril had no significant effect. In the lung, no differences were found in ACE2 when comparing db/db mice to db/m and ramipril also had no significant effect. In the heart, diabetes decreased ACE2 activity (83% ± 16.8%, vs 100% ± 23.1% p = 0.02), and ramipril increased ACE2 significantly (83% ± 16.8% vs 98.2% ± 15%, p = 0.04).

CONCLUSIONS

In a mouse model of type 2 diabetes, ramipril had no significant effect on ACE2 activity in either kidneys or in the lungs. Therefore, it is unlikely that RAAS blockers or at least angiotensin-converting enzyme inhibitors increase the risk of SARS-CoV-2 infection through increasing ACE2.

Barth syndrome-related cardiomyopathy is associated with a reduction in myocardial glucose oxidation

Heart failure presents as the leading cause of infant mortality in individuals with Barth syndrome (BTHS), a rare genetic disorder due to mutations in the tafazzin (TAZ) gene affecting mitochondrial structure and function. Investigations into the perturbed bioenergetics in the BTHS heart remain limited. Hence, our objective was to identify the potential alterations in myocardial energy metabolism and molecular underpinnings that may contribute to the early cardiomyopathy and heart failure development in BTHS. Cardiac function and myocardial energy metabolism were assessed via ultrasound echocardiography and isolated working heart perfusions, respectively, in a mouse model of BTHS [doxycycline-inducible Taz knockdown (TazKD) mice]. In addition, we also performed mRNA/protein expression profiling for key regulators of energy metabolism in hearts from TazKD mice and their wild-type (WT) littermates. TazKD mice developed hypertrophic cardiomyopathy as evidenced by increased left ventricular anterior and posterior wall thickness, as well as increased cardiac myocyte cross-sectional area, though no functional impairments were observed. Glucose oxidation rates were markedly reduced in isolated working hearts from TazKD mice compared with their WT littermates in the presence of insulin, which was associated with decreased pyruvate dehydrogenase activity. Conversely, myocardial fatty acid oxidation rates were elevated in TazKD mice, whereas no differences in glycolytic flux or ketone body oxidation rates were observed. Our findings demonstrate that myocardial glucose oxidation is impaired before the development of overt cardiac dysfunction in TazKD mice, and may thus represent a pharmacological target for mitigating the development of cardiomyopathy in BTHS.NEW & NOTEWORTHY Barth syndrome (BTHS) is a rare genetic disorder due to mutations in tafazzin that is frequently associated with infantile-onset cardiomyopathy and subsequent heart failure. Although previous studies have provided evidence of perturbed myocardial energy metabolism in BTHS, actual measurements of flux are lacking. We now report a complete energy metabolism profile that quantifies flux in isolated working hearts from a murine model of BTHS, demonstrating that BTHS is associated with a reduction in glucose oxidation.

Interaction between the apelinergic system and ACE2 in the cardiovascular system: therapeutic implications

The apelinergic system is widely expressed and acts through autocrine and paracrine signaling to exert protective effects, including vasodilatory, metabolic, and inotropic effects on the cardiovascular (CV) system. The apelin pathway's dominant physiological role has delineated therapeutic implications for coronary artery disease, heart failure (HF), aortic aneurysm, pulmonary arterial hypertension (PAH), and transplant vasculopathy. Apelin peptides interact with the renin-angiotensin system (RAS) by promoting angiotensin converting enzyme 2 (ACE2) transcription leading to increased ACE2 protein and activity while also antagonizing the effects of angiotensin II (Ang II). Apelin modulation of the RAS by increasing ACE2 action is limited due to its rapid degradation by proteases, including ACE2, neprilysin (NEP), and kallikrein. Apelin peptides are hence tightly regulated in a negative feedback manner by ACE2. Plasma apelin levels are suppressed in pathological conditions, but its diagnostic and prognostic utility requires further clinical exploration. Enhancing the beneficial actions of apelin peptides and ACE2 axes while complementing existing pharmacological blockade of detrimental pathways is an exciting pathway for developing new therapies. In this review, we highlight the interaction between the apelin and ACE2 systems, discuss their pathophysiological roles and potential for treating a wide array of CV diseases (CVDs).

Downregulation of Membrane-bound Angiotensin Converting Enzyme 2 (ACE2) Receptor has a Pivotal Role in COVID-19 Immunopathology

BACKGROUND

The Coronavirus Disease 2019 (COVID-19) is becoming the major health issue in recent human history with thousands of deaths and millions of cases worldwide. Newer research and old experience with other coronaviruses highlighted a probable underlying mechanism of disturbance of the renin-angiotensin system (RAS) that is associated with the intrinsic effects of SARS-CoV-2 infection.

OBJECTIVE

In this review, we aimed to describe the intimate connections between the RAS components, the immune system and COVID-19 pathophysiology.

METHODS

This non-systematic review article summarizes recent evidence on the relationship between COVID-19 and the RAS.

RESULTS

Several studies have indicated that the downregulation of membrane-bound ACE2 may exert a key role for the impairment of immune functions and for COVID-19 patients' outcomes. The downregulation may occur by distinct mechanisms, particularly: (1) the shedding process induced by the SARS-CoV-2 fusion pathway, which reduces the amount of membrane-bound ACE2, stimulating more shedding by the high levels of Angiotensin II; (2) the endocytosis of ACE2 receptor with the virus itself and (3) by the interferon inhibition caused by SARS-CoV-2 effects on the immune system, which leads to a reduction of ACE2 receptor expression.

CONCLUSION

Recent research provides evidence of a reduction of the components of the alternative RAS axis, including ACE2 and Angiotensin-(1-7). In contrast, increased levels of Angiotensin II can activate the AT1 receptor in several organs. Consequently, increased inflammation, thrombosis and angiogenesis occur in patients infected with SARS-COV-2. Attention should be paid to the interactions of the RAS and COVID-19, mainly in the context of novel vaccines and proposed medications.

Association of ACE2 variant rs4646188 with the risks of atrial fibrillation and cardioembolic stroke in Uygur patients with type 2 diabetes

Background

Atrial fibrillation (AF) is the most common cardiac arrhythmia. Type 2 diabetes (T2D) is an independent risk factor for AF. The cardioembolic stroke (CS) risk is increased when both conditions coexist. Whether angiotensin-converting enzyme 2 (ACE2) genetic variants predict increased risks AF and CS in Uygur patients with T2D remain elusive.

Methods

A total of 547 Uygur subjects (272 controls and 275 T2D patients) were recruited to the study from south Xinjiang. Eight ACE2 variants were identified by MassARRAY system.

Results

ACE2 rs2074192 (CC, adjusted RR = 2.55, 95% CI 1.35–4.80, P = 0.004), rs4240157 (CC + CT, adjusted RR = 2.26, 95% CI 1.27–4.04, P = 0.006) and rs4646188 (TT, adjusted RR = 2.37, 95% CI 1.16–4.86, P = 0.018) were associated with higher AF risk. ACE2 rs4240157 (CC + CT, adjusted RR = 2.68, 95% CI 1.36–5.27, P = 0.004) and rs4646188 (TT, adjusted RR = 2.56, 95% CI 1.06–6.20, P = 0.037) were further associated with higher CS risk. The 3 ACE2 variants were related to larger left atrial end-systolic diameter (LAD) (all P < 0.05), but not all of the 3 ACE2 variants were related to increased levels of serum sodium (rs4240157 and rs4646188, all P < 0.05), HsCRP (rs4240157 and rs4646188, all P < 0.05) as well as decreased serum potassium levels (rs2074192 and rs4646188, all P < 0.05). The 3 ACE2 variants exhibited heterogeneity on circulating RAAS activation. In particular, ACE2 rs4646188 was associated with higher levels of ACE (P = 0.017 and 0.037), Ang I (P = 0.002 and 0.001), Ang II (both P < 0.001) and ALD (P = 0.005 and 0.011).

Conclusion

These results indicated ACE2 rs4646188 was associated with increased risk of AF and CS among diabetic patients in Uygurs, which could be a promising genetic predisposition marker for early and personalized prevention strategies for the aforementioned clinical pathologies.

Association of ACE inhibitors and angiotensin type II blockers with ACE2 overexpression in COVID-19 comorbidities: A pathway-based analytical study

Severe Acute Respiratory Syndrome Corona Virus 2 (SARS-CoV-2) outbreak is a major public health concern, which has accounted for >1.7 million deaths across the world. A surge in the case fatality ratio as compared with the infection ratio has been observed in most of the countries. The novel Coronavirus SARS-CoV-2 shares the most common sequence with SARS-CoV, but it has a higher rate of transmission. The SARS-CoV-2 pathogenesis is initiated by the binding of viral spike protein with the target receptor Angiotensin-Converting Enzyme 2 (ACE2) facilitating virus internalization within host cells. SARS-CoV-2 mainly causes alveolar damage ranging from mild to severe clinical respiratory manifestations. Most of the cases have revealed the association of Coronavirus disease with patients having earlier comorbidities like Hypertension, Diabetes mellitus, and Cerebrovascular diseases. Pharmacological investigation of the SARS-Cov-2 patients has revealed the frequent use of drugs belongs to Angiotensin-converting enzyme inhibitors (ACEi) and/or Angiotensin II type I receptor blockers (ARBs). Interestingly, a significant increase in ACE2 expression was noticed in patients routinely treated with the above group of drugs were also reported. To date, the association of ACEi and/or ARBs with the up-regulation of ACE2 expression has not been defined distinctively. The proposed review will focus on the pathways which are responsible for the upregulation of ACE2 and its impact on gravity of SARS-CoV-2 disease.

Angiotensin-converting enzyme 2 and COVID-19 in cardiorenal diseases

The rapid spread of the novel coronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has brought into focus the key role of angiotensin-converting enzyme 2 (ACE2), which serves as a cell surface receptor required for the virus to enter cells. SARS-CoV-2 can decrease cell surface ACE2 directly by internalization of ACE2 bound to the virus and indirectly by increased ADAM17 (a disintegrin and metalloproteinase 17)-mediated shedding of ACE2. ACE2 is widely expressed in the heart, lungs, vasculature, kidney and the gastrointestinal (GI) tract, where it counteracts the deleterious effects of angiotensin II (AngII) by catalyzing the conversion of AngII into the vasodilator peptide angiotensin-(1-7) (Ang-(1-7)). The down-regulation of ACE2 by SARS-CoV-2 can be detrimental to the cardiovascular system and kidneys. Further, decreased ACE2 can cause gut dysbiosis, inflammation and potentially worsen the systemic inflammatory response and coagulopathy associated with SARS-CoV-2. This review aims to elucidate the crucial role of ACE2 both as a regulator of the renin–angiotensin system and a receptor for SARS-CoV-2 as well as the implications for Coronavirus disease 19 and its associated cardiovascular and renal complications.

Effects of SGLT2 Inhibitors and GLP-1 Receptor Agonists on Renin-Angiotensin-Aldosterone System

Sodium-glucose cotransporters inhibitors (SGLT2-i) and GLP-1 receptor agonists (GLP1-RA) are glucose-lowering drugs that are proved to reduce the cardiovascular (CV) risk in type 2 diabetes mellitus (T2DM). In this process, the renin-angiotensin-aldosterone system (RAAS) is assumed to play a role. The inhibition of SGLT2 improves hyperglycemia hampering urinary reabsorption of glucose and inducing glycosuria. This "hybrid" diuretic effect, which couples natriuresis with osmotic diuresis, potentially leads to systemic RAAS activation. However, the association between SGLT2-i and systemic RAAS activation is not straightforward. Available data indicate that SGLT2-i cause plasma renin activity (PRA) increase in the early phase of treatment, while PRA and aldosterone levels remain unchanged in chronic treated patients. Furthermore, emerging studies provide evidence that SGLT2-i might have an interfering effect on aldosterone/renin ratio (ARR) in patients with T2DM, due to their diuretic and sympathoinhibition effects. The cardio- and reno-protective effects of GLP-1-RA are at least in part related to the interaction with RAAS. In particular, GLP1-RA counteract the action of angiotensin II (ANG II) inhibiting its synthesis, increasing the inactivation of its circulating form and contrasting its action on target tissue like glomerular endothelial cells and cardiomyocytes. Furthermore, GLP1-RA stimulate natriuresis inhibiting Na+/H+ exchanger NHE-3, which is conversely activated by ANG II. Moreover, GLP1 infusion acutely reduces circulating aldosterone, but this effect does not seem to be chronically maintained in patients treated with GLP1-RA. In conclusion, both SGLT2-i and GLP1-RA seem to have several effects on RAAS, though additional studies are needed to clarify this relationship.

ACE2 in the renin-angiotensin system

In 2020 we are celebrating the 20th anniversary of the angiotensin-converting enzyme 2 (ACE2) discovery. This event was a landmark that shaped the way that we see the renin-angiotensin system (RAS) today. ACE2 is an important molecular hub that connects the RAS classical arm, formed mainly by the octapeptide angiotensin II (Ang II) and its receptor AT1, with the RAS alternative or protective arm, formed mainly by the heptapeptides Ang-(1-7) and alamandine, and their receptors, Mas and MrgD, respectively. In this work we reviewed classical and modern literature to describe how ACE2 is a critical component of the protective arm, particularly in the context of the cardiac function, coagulation homeostasis and immune system. We also review recent literature to present a critical view of the role of ACE2 and RAS in the SARS-CoV-2 pandemic.

The Potential Role of Osteopontin and Furin in Worsening Disease Outcomes in COVID-19 Patients with Pre-Existing Diabetes

The novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused the ongoing coronavirus disease 2019 (COVID-19) pandemic, with more than 50 million cases reported globally. Findings have consistently identified an increased severity of SARS-CoV-2 infection in individuals with diabetes. Osteopontin, a cytokine-like matrix-associated phosphoglycoprotein, is elevated in diabetes and drives the expression of furin, a proprotein convertase implicated in the proteolytic processing and activation of several precursors, including chemokines, growth factors, hormones, adhesion molecules, and receptors. Elevated serum furin is a signature of diabetes mellitus progression and is associated with a dysmetabolic phenotype and increased risk of diabetes-linked premature mortality. Additionally, furin plays an important role in enhancing the infectivity of SARS-CoV-2 by promoting its entry and replication in the host cell. Here, we hypothesize that diabetes-induced osteopontin and furin protein upregulation results in worse outcomes in diabetic patients with SARS-CoV-2 infection owing to the roles of these protein in promoting viral infection and increasing metabolic dysfunction. Thus, targeting the osteopontin-furin axis may be a plausible strategy for reducing mortality in SARS-CoV-2 patients with diabetes.

Dual deficiency of angiotensin-converting enzyme-2 and Mas receptor enhances angiotensin II-induced hypertension and hypertensive nephropathy

Angiotensin-converting enzyme-2 (ACE2) and Mas receptor are the major components of the ACE2/Ang 1-7/Mas axis and have been shown to play a protective role in hypertension and hypertensive nephropathy individually. However, the effects of dual deficiency of ACE2 and Mas (ACE2/Mas) on Ang II-induced hypertensive nephropathy remain unexplored, which was investigated in this study in a mouse model of hypertension induced in either ACE2 knockout (KO) or Mas KO mice and in double ACE2/Mas KO mice by subcutaneously chronic infusion of Ang II. Compared with wild-type (WT) animals, mice lacking either ACE2 or Mas significantly increased blood pressure over 7-28 days following a chronic Ang II infusion (P < .001), which was further exacerbated in double ACE2/Mas KO mice (P < .001). Furthermore, compared to a single ACE2 or Mas KO mice, mice lacking ACE2/Mas developed more severe renal injury including higher levels of serum creatinine and a further reduction in creatinine clearance, and progressive renal inflammation and fibrosis. Mechanistically, worsen hypertensive nephropathy in double ACE2/Mas KO mice was associated with markedly enhanced AT1-ERK1/2-Smad3 and NF-κB signalling, thereby promoting renal fibrosis and renal inflammation in the hypertensive kidney. In conclusion, ACE2 and Mas play an additive protective role in Ang II-induced hypertension and hypertensive nephropathy. Thus, restoring the ACE2/Ang1-7/Mas axis may represent a novel therapy for hypertension and hypertensive nephropathy.

ACE2 mouse models: a toolbox for cardiovascular and pulmonary research

Angiotensin-converting enzyme 2 (ACE2) has been identified as the host entry receptor for the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) responsible for the COVID-19 pandemic. ACE2 is a regulatory enzyme of the renin-angiotensin system and has protective functions in many cardiovascular, pulmonary and metabolic diseases. This review summarizes available murine models with systemic or organ-specific deletion of ACE2, or with overexpression of murine or human ACE2. The purpose of this review is to provide researchers with the genetic tools available for further understanding of ACE2 biology and for the investigation of ACE2 in the pathogenesis and treatment of COVID-19.

Pathophysiology of Cardiovascular Complications in COVID-19

Numerous recent studies have shown that patients with underlying cardiovascular disease (CVD) are at increased risk of more severe clinical course as well as mortality of COVID-19. Also, the available data suggests that COVID-19 is related to numerous de novo cardiovascular complications especially in the older population and those with pre-existing chronic cardiometabolic conditions. SARS-CoV-2 virus can cause acute cardiovascular injury, as well as increase the risk of chronic cardiovascular damage. As CVD seem to be the major comorbidity in critically unwell patients with COVID-19 and patients often die of cardiovascular complications, we review the literature and discuss the possible pathophysiology and molecular pathways driving these disease processes: cytokine release syndrome, RAAS system dysregulation, plaque destabilization and coagulation disorders with the aim to identify novel treatment targets. In addition, we review the pediatric population, the major cause of the cardiovascular complications is pediatric inflammatory multisystem syndrome that is believed to be associated with COVID-19 infection. Due to the increasingly recognized CVD damage in COVID-19, there is a need to establish clear clinical and follow-up protocols and to identify and treat possible comorbidities that may be risk factors for the development of cardiovascular complications.

The role of mesenchymal stromal cells in immune modulation of COVID-19: focus on cytokine storm

The outbreak of coronavirus disease 2019 (COVID-19) pandemic is quickly spreading all over the world. This virus, which is called SARS-CoV-2, has infected tens of thousands of people. Based on symptoms, the pathogenesis of acute respiratory illness is responsible for highly homogenous coronaviruses as well as other pathogens. Evidence suggests that high inflammation rates, oxidation, and overwhelming immune response probably contribute to pathology of COVID-19. COVID-19 causes cytokine storm, which subsequently leads to acute respiratory distress syndrome (ARDS), often ending up in the death of patients. Mesenchymal stem cells (MSCs) are multipotential stem cells that are recognized via self-renewal capacity, generation of clonal populations, and multilineage differentiation. MSCs are present in nearly all tissues of the body, playing an essential role in repair and generation of tissues. Furthermore, MSCs have broad immunoregulatory properties through the interaction of immune cells in both innate and adaptive immune systems, leading to immunosuppression of many effector activities. MSCs can reduce the cytokine storm produced by coronavirus infection. In a number of studies, the administration of these cells has been beneficial for COVID-19 patients. Also, MSCs may be able to improve pulmonary fibrosis and lung function. In this review, we will review the newest research findings regarding MSC-based immunomodulation in patients with COVID-19.

Obesity and diabetes as comorbidities for COVID-19: Underlying mechanisms and the role of viral-bacterial interactions

Obesity and diabetes are established comorbidities for COVID-19. Adipose tissue demonstrates high expression of ACE2 which SARS- CoV-2 exploits to enter host cells. This makes adipose tissue a reservoir for SARS-CoV-2 viruses and thus increases the integral viral load. Acute viral infection results in ACE2 downregulation. This relative deficiency can lead to disturbances in other systems controlled by ACE2, including the renin-angiotensin system. This will be further increased in the case of pre-conditions with already compromised functioning of these systems, such as in patients with obesity and diabetes. Here, we propose that interactions of virally-induced ACE2 deficiency with obesity and/or diabetes leads to a synergistic further impairment of endothelial and gut barrier function. The appearance of bacteria and/or their products in the lungs of obese and diabetic patients promotes interactions between viral and bacterial pathogens, resulting in a more severe lung injury in COVID-19.

ACE2 (Angiotensin-Converting Enzyme 2) in Cardiopulmonary Diseases: Ramifications for the Control of SARS-CoV-2

Discovery of ACE2 (angiotensin-converting enzyme 2) revealed that the renin-angiotensin system has 2 counterbalancing arms. ACE2 is a major player in the protective arm, highly expressed in lungs and gut with the ability to mitigate cardiopulmonary diseases such as inflammatory lung disease. ACE2 also exhibits activities involving gut microbiome, nutrition, and as a chaperone stabilizing the neutral amino acid transporter, B⁰AT1, in gut. But the current interest in ACE2 arises because it is the cell surface receptor for the novel coronavirus, severe acute respiratory syndrome coronavirus-2, to infect host cells, similar to severe acute respiratory syndrome coronavirus-2. This suggests that ACE2 be considered harmful, however, because of its important other roles, it is paradoxically a potential therapeutic target for cardiopulmonary diseases, including coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus-2. This review describes the discovery of ACE2, its physiological functions, and its place in the renin-angiotensin system. It illustrates new analyses of the structure of ACE2 that provides better understanding of its actions particularly in lung and gut, shedding of ACE2 by ADAM17 (a disintegrin and metallopeptidase domain 17 protein), and role of TMPRSS2 (transmembrane serine proteases 2) in severe acute respiratory syndrome coronavirus-2 entry into host cells. Cardiopulmonary diseases are associated with decreased ACE2 activity and the mitigation by increasing ACE2 activity along with its therapeutic relevance are addressed. Finally, the potential use of ACE2 as a treatment target in COVID-19, despite its role to allow viral entry into host cells, is suggested.

Role of angiotensin-converting enzyme 2 (ACE2) in COVID-19

Abstract

An outbreak of pneumonia caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that started in Wuhan, China, at the end of 2019 has become a global pandemic. Both SARS-CoV-2 and SARS-CoV enter host cells via the angiotensin-converting enzyme 2 (ACE2) receptor, which is expressed in various human organs. We have reviewed previously published studies on SARS and recent studies on SARS-CoV-2 infection, named coronavirus disease 2019 (COVID-19) by the World Health Organization (WHO), confirming that many other organs besides the lungs are vulnerable to the virus. ACE2 catalyzes angiotensin II conversion to angiotensin-(1–7), and the ACE2/angiotensin-(1–7)/MAS axis counteracts the negative effects of the renin-angiotensin system (RAS), which plays important roles in maintaining the physiological and pathophysiological balance of the body. In addition to the direct viral effects and inflammatory and immune factors associated with COVID-19 pathogenesis, ACE2 downregulation and the imbalance between the RAS and ACE2/angiotensin-(1–7)/MAS after infection may also contribute to multiple organ injury in COVID-19. The SARS-CoV-2 spike glycoprotein, which binds to ACE2, is a potential target for developing specific drugs, antibodies, and vaccines. Restoring the balance between the RAS and ACE2/angiotensin-(1–7)/MAS may help attenuate organ injuries.

Graphical abstract

SARS-CoV-2 enters lung cells via the ACE2 receptor. The cell-free and macrophage-phagocytosed virus can spread to other organs and infect ACE2-expressing cells at local sites, causing multi-organ injury.

Interactions between antihyperglycemic drugs and the renin-angiotensin system: Putative roles in COVID-19. A mini-review

BACKGROUND

Diabetes mellitus is associated with a more severe course of coronavirus disease 2019 (COVID-19). The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) utilizes angiotensin-converting enzyme II (ACE2) receptor for host cell entry. We aimed to assess the interactions between antihyperglycemic drugs and the renin-angiotensin system (RAS) and their putative roles in COVID-19.

METHODS

A literature search was performed using Pubmed to review the interrelationships between hyperglycemia, RAS and COVID-19, and the effects of antihyperglycemic medications.

RESULTS

The RAS has an essential role in glucose homeostasis and may have a role in COVID-19-induced lung injury. Some antihyperglycemic medications modulate RAS and might hypothetically alleviate the deleterious effect of angiotensin II on lung injury. Furthermore, most antihyperglycemic medications showed anti-inflammatory effects in animal models of lung injury.

CONCLUSIONS

Some antihyperglycemic medications might have protective effects against COVID-19-induced lung injury. Early insulin therapy seems very promising in alleviating lung injury.

Genetic gateways to COVID-19 infection: Implications for risk, severity, and outcomes

The dynamics, such as transmission, spatial epidemiology, and clinical course of Coronavirus Disease-2019 (COVID-19) have emerged as the most intriguing features and remain incompletely understood. The genetic landscape of an individual in particular, and a population in general seems to play a pivotal role in shaping the above COVID-19 dynamics. Considering the implications of host genes in the entry and replication of SARS-CoV-2 and in mounting the host immune response, it appears that multiple genes might be crucially involved in the above processes. Herein, we propose three potentially important genetic gateways to COVID-19 infection; these could explain at least in part the discrepancies of its spread, severity, and mortality. The variations within Angiotensin-converting enzyme 2 (ACE2) gene might constitute the first genetic gateway, influencing the spatial transmission dynamics of COVID-19. The Human Leukocyte Antigen locus, a master regulator of immunity against infection seems to be crucial in influencing susceptibility and severity of COVID-19 and can be the second genetic gateway. The genes regulating Toll-like receptor and complement pathways and subsequently cytokine storm induced exaggerated inflammatory pathways seem to underlie the severity of COVID-19, and such genes might represent the third genetic gateway. Host-pathogen interaction is a complex event and some additional genes might also contribute to the dynamics of COVID-19. Overall, these three genetic gateways proposed here might be the critical host determinants governing the risk, severity, and outcome of COVID-19. Genetic variations within these gateways could be key in influencing geographical discrepancies of COVID-19.

Angiotensin-Converting Enzyme 2: SARS-CoV-2 Receptor and Regulator of the Renin-Angiotensin System: Celebrating the 20th Anniversary of the Discovery of ACE2

ACE2 (angiotensin-converting enzyme 2) has a multiplicity of physiological roles that revolve around its trivalent function: a negative regulator of the renin-angiotensin system, facilitator of amino acid transport, and the severe acute respiratory syndrome-coronavirus (SARS-CoV) and SARS-CoV-2 receptor. ACE2 is widely expressed, including, in the lungs, cardiovascular system, gut, kidneys, central nervous system, and adipose tissue. ACE2 has recently been identified as the SARS-CoV-2 receptor, the infective agent responsible for coronavirus disease 2019, providing a critical link between immunity, inflammation, ACE2, and cardiovascular disease. Although sharing a close evolutionary relationship with SARS-CoV, the receptor-binding domain of SARS-CoV-2 differs in several key amino acid residues, allowing for stronger binding affinity with the human ACE2 receptor, which may account for the greater pathogenicity of SARS-CoV-2. The loss of ACE2 function following binding by SARS-CoV-2 is driven by endocytosis and activation of proteolytic cleavage and processing. The ACE2 system is a critical protective pathway against heart failure with reduced and preserved ejection fraction including, myocardial infarction and hypertension, and against lung disease and diabetes mellitus. The control of gut dysbiosis and vascular permeability by ACE2 has emerged as an essential mechanism of pulmonary hypertension and diabetic cardiovascular complications. Recombinant ACE2, gene-delivery of Ace2, Ang 1-7 analogs, and Mas receptor agonists enhance ACE2 action and serve as potential therapies for disease conditions associated with an activated renin-angiotensin system. rhACE2 (recombinant human ACE2) has completed clinical trials and efficiently lowered or increased plasma angiotensin II and angiotensin 1-7 levels, respectively. Our review summarizes the progress over the past 20 years, highlighting the critical role of ACE2 as the novel SARS-CoV-2 receptor and as the negative regulator of the renin-angiotensin system, together with implications for the coronavirus disease 2019 pandemic and associated cardiovascular diseases.

Loss of insulin signaling may contribute to atrial fibrillation and atrial electrical remodeling in type 1 diabetes

Atrial fibrillation (AF) is prevalent in diabetes mellitus (DM); however, the basis for this is unknown. This study investigated AF susceptibility and atrial electrophysiology in type 1 diabetic Akita mice using in vivo intracardiac electrophysiology, high-resolution optical mapping in atrial preparations, and patch clamping in isolated atrial myocytes. qPCR and western blotting were used to assess ion channel expression. Akita mice were highly susceptible to AF in association with increased P-wave duration and slowed atrial conduction velocity. In a second model of type 1 DM, mice treated with streptozotocin (STZ) showed a similar increase in susceptibility to AF. Chronic insulin treatment reduced susceptibility and duration of AF and shortened P-wave duration in Akita mice. Atrial action potential (AP) morphology was altered in Akita mice due to a reduction in upstroke velocity and increases in AP duration. In Akita mice, atrial Na⁺ current (I_Na) and repolarizing K⁺ current (I_K) carried by voltage gated K⁺ (K_v1.5) channels were reduced. The reduction in I_Na occurred in association with reduced expression of SCN5a and voltage gated Na⁺ (Na_V1.5) channels as well as a shift in I_Na activation kinetics. Insulin potently and selectively increased I_Na in Akita mice without affecting I_K Chronic insulin treatment increased I_Na in association with increased expression of Na_V1.5. Acute insulin also increased I_Na, although to a smaller extent, due to enhanced insulin signaling via phosphatidylinositol 3,4,5-triphosphate (PIP₃). Our study reveals a critical, selective role for insulin in regulating atrial I_Na, which impacts susceptibility to AF in type 1 DM.

The contribution of chymase-dependent formation of ANG II to cardiac dysfunction in metabolic syndrome of young rats: roles of fructose and EETs

The roles of ACE-independent ANG II production via chymase and therapeutic potential of epoxyeicosatrienoic acids (EETs) in fructose-induced metabolic syndrome (MetS) in the adolescent population remain elusive. Thus we tested the hypothesis that a high-fructose diet (HFD) in young rats elicits chymase-dependent increases in ANG II production and oxidative stress, responses that are reversible by 1-trifluoromethoxyphenyl-3-(1-propionylpiperidin-4-yl) urea (TPPU), an inhibitor of soluble epoxide hydrolase (sEH) that metabolizes EETs. Three groups of weanling rats (21-day-old) were fed a normal diet, 60% HFD, and HFD with TPPU, respectively, for 30 days. HFD rats developed MetS, characterized by hyperglycemia, hyperinsulinemia, and hypertension and associated with decreases in cardiac output and stroke volume and loss of nitric oxide (NO) modulation of myocardial oxygen consumption; all impairments were normalized by TPPU that significantly elevated circulating 11,12-EET, a major cardiac EET isoform. In the presence of comparable cardiac angiotensin-converting enzyme (ACE) expression/activity among the three groups, HFD rats exhibited significantly greater chymase-dependent ANG II formation in hearts, as indicated by an augmented cardiac chymase content as a function of enhanced mast cell degranulation. The enhanced chymase-dependent ANG II production was paralleled with increases in ANG II type 1 receptor (AT₁R) expression and NADPH oxidase (Nox)-induced superoxide, alterations that were significantly reversed by TPPU. Conversely, HFD-induced downregulation of cardiac ACE2, followed by a lower Ang-(1-7) level displayed in an TPPU-irreversible manner. In conclusion, HFD-driven adverse chymase/ANG II/Nox/superoxide signaling in young rats was prevented by inhibition of sEH via, at least in part, an EET-mediated stabilization of mast cells, highlighting chymase and sEH as therapeutic targets during treatment of MetS.NEW & NOTEWORTHY As the highest fructose consumers, the adolescent population is highly susceptible to the metabolic syndrome, where increases in mast cell chymase-dependent formation of ANG II, ensued by cardiometabolic dysfunction, are reversible in response to inhibition of soluble epoxide hydrolase (sEH). This study highlights chymase and sEH as therapeutic targets and unravels novel avenues for the development of optimal strategies for young patients with fructose-induced metabolic syndrome.

Different effects of the deletion of angiotensin converting enzyme 2 and chronic activation of the renin-angiotensin system on muscle weakness in middle-aged mice

Inhibition of the renin-angiotensin system (RAS) has been shown to alleviate muscle atrophy both under pathological conditions and during physiological aging. We recently reported that the deletion of angiotensin converting enzyme 2 (ACE2), which converts Angiotensin II to Angiotensin-(1-7) in mice, leads to the early manifestation of aging-associated muscle weakness along with the increased expression of p16^INK4a, a senescence-associated gene, and increased central nuclei in the tibialis anterior (TA) muscle in middle age. As ACE2 is multifunctional and functions beyond its role in the RAS, we investigated whether activation of the RAS primarily contributes to muscle weakness in ACE2 knockout (KO) mice by comparing these mice to Tsukuba hypertensive (TH) mice that overproduce human angiotensin II. The grip strength of young (6 months) and middle-aged (15 months) TH mice was consistently lower than that of wild-type mice at the same ages. Middle-aged TH mice were continuously lean with extremely reduced adiposity. Central nuclei in the gastrocnemius (GM) muscle were increased in ACE2KO mice, while no apparent morphological change was observed in the GM muscles of TH mice. Increased expression of p16^INK4a along with alterations in the expression of several sarcopenia-associated genes were observed in the GM muscles of ACE2KO mice but not TH mice. These findings suggest that chronic overactivation of the RAS does not primarily contribute to the early aging phenotypes of skeletal muscle in ACE2KO mice.

Bone Marrow-Derived Cells Restore Functional Integrity of the Gut Epithelial and Vascular Barriers in a Model of Diabetes and ACE2 Deficiency

RATIONALE

There is incomplete knowledge of the impact of bone marrow cells on the gut microbiome and gut barrier function.

OBJECTIVE

We postulated that diabetes mellitus and systemic ACE2 (angiotensin-converting enzyme 2) deficiency would synergize to adversely impact both the microbiome and gut barrier function.

METHODS AND RESULTS

Bacterial 16S rRNA sequencing and metatranscriptomic analysis were performed on fecal samples from wild-type, ACE2^-/y, Akita (type 1 diabetes mellitus), and ACE2^-/y-Akita mice. Gut barrier integrity was assessed by immunofluorescence, and bone marrow cell extravasation into the small intestine was evaluated by flow cytometry. In the ACE2^-/y-Akita or Akita mice, the disrupted barrier was associated with reduced levels of myeloid angiogenic cells, but no increase in inflammatory monocytes was observed within the gut parenchyma. Genomic and metatranscriptomic analysis of the microbiome of ACE2^-/y-Akita mice demonstrated a marked increase in peptidoglycan-producing bacteria. When compared with control cohorts treated with saline, intraperitoneal administration of myeloid angiogenic cells significantly decreased the microbiome gene expression associated with peptidoglycan biosynthesis and restored epithelial and endothelial gut barrier integrity. Also indicative of diabetic gut barrier dysfunction, increased levels of peptidoglycan and FABP-2 (intestinal fatty acid-binding protein 2) were observed in plasma of human subjects with type 1 diabetes mellitus (n=21) and type 2 diabetes mellitus (n=23) compared with nondiabetic controls (n=23). Using human retinal endothelial cells, we determined that peptidoglycan activates a noncanonical TLR-2 (Toll-like receptor 2) associated MyD88 (myeloid differentiation primary response protein 88)-ARNO (ADP-ribosylation factor nucleotide-binding site opener)-ARF6 (ADP-ribosylation factor 6) signaling cascade, resulting in destabilization of p120-catenin and internalization of VE-cadherin as a mechanism of deleterious impact of peptidoglycan on the endothelium.

CONCLUSIONS

We demonstrate for the first time that the defect in gut barrier function and dysbiosis in ACE2^-/y-Akita mice can be favorably impacted by exogenous administration of myeloid angiogenic cells.

Angiotensin 1-7 alleviates aging-associated muscle weakness and bone loss, but is not associated with accelerated aging in ACE2-knockout mice

The angiotensin-converting enzyme 2 (ACE2)-angiotensin 1-7 (A1-7)-A1-7 receptor (Mas) axis plays a protective role in the renin-angiotensin system (RAS). We recently found that ACE2 knockout (ACE2KO) mice exhibit earlier aging-associated muscle weakness, and that A1-7 alleviates muscle weakness in aging mice. In the present study, we investigated the role of the A1-7-Mas pathway in the effect of ACE2 on physiological aging. Male wild-type, ACE2KO, and Mas knockout (MasKO) mice were subjected to periodical grip strength measurement, followed by administration of A1-7 or vehicle for 4 weeks at 24 months of age. ACE2KO mice exhibited decreased grip strength after 6 months of age, while grip strength of MasKO mice was similar to that of wild-type mice. A1-7 improved grip strength in ACE2KO and wild-type mice, but not in MasKO mice. Muscle fibre size was smaller in ACE2KO mice than that in wild-type and MasKO mice, and increased with A1-7 in ACE2KO and WT mice, but not in MasKO mice. Centrally nucleated fibres (CNFs) and expression of the senescence-associated gene p16INK4a in skeletal muscles were enhanced only in ACE2KO mice and were not altered by A1-7. ACE2KO mice, but not MasKO mice, exhibited thinning of peripheral fat along with increased adipose expression of p16INK4a A1-7 significantly increased bone volume in wild-type and ACE2KO mice, but not in MasKO mice. Our findings suggest that the impact of ACE2 on physiological aging does not depend on the endogenous production of A1-7 by ACE2, while overactivation of the A1-7-Mas pathway could alleviate sarcopenia and osteoporosis in aged mice.