Differential expression in humans of the viral entry receptor ACE2 compared with the short deltaACE2 isoform lacking SARS-CoV-2 binding sites

Co-localization of the sodium-glucose co-transporter-2 channel (SGLT-2) with endothelin ETA and ETB receptors in human cardiorenal tissue

Endothelin (ET) receptor antagonists are being investigated in combination with sodium-glucose co-transporter-2 inhibitors (SGLT-2i). These drugs primarily inhibit the SGLT-2 transporter that, in humans, is thought to be mainly restricted to the renal proximal convoluted tubule, resulting in increased glucose excretion favouring improved glycaemic control and diuresis. This action reduces fluid retention with ET receptor antagonists. Studies have suggested SGLT-2 may also be expressed in cardiomyocytes of human heart. To understand the potential of combining the two classes of drugs, our aim was to compare the distribution of ET receptor sub-types in human kidney, with SGLT-2. Secondly, using the same experimental conditions, we determined if SGLT-2 expression could be detected in human heart and whether the transporter co-localised with ET receptors.

METHODS

Immunocytochemistry localised SGLT-2, ETA and ETB receptors in sections of histologically normal kidney, left ventricle from patients undergoing heart transplantation or controls. Primary antisera were visualised using fluorescent microscopy. Image analysis was used to measure intensity compared with background in adjacent control sections.

RESULTS

As expected, SGLT-2 localised to epithelial cells of the proximal convoluted tubules, and co-localised with both ET receptor sub-types. Similarly, ETA receptors predominated in cardiomyocytes; low (compared with kidney but above background) positive staining was also detected for SGLT-2.

DISCUSSION

Whether low levels of SGLT-2 have a (patho)physiological role in cardiomyocytes is not known but results suggest the effect of direct blockade of sodium (and glucose) influx via SGLT-2 inhibition in cardiomyocytes should be explored, with potential for additive effects with ETA antagonists.

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.

Mapping ACE2 and TMPRSS2 co-expression in human brain tissue: implications for SARS-CoV-2 neurological manifestations

The Coronavirus Disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) primarily targets respiratory cells, but emerging evidence shows neurological involvement, with the virus directly affecting neurons and glia. SARS-CoV-2 entry into a target cell requires co-expression of ACE2 (Angiotensin-converting enzyme-2) and TMPRSS2 (Trans membrane serine protease-2). Relevant literature on human neurological tissue is sparse and mostly focused on the olfactory areas. This prompted our study to map brain-wide expression of these entry proteins and assess age-related changes. The normal brain tissue samples were collected from cerebral cortex, hippocampus, basal ganglia, thalamus, hypothalamus, brain stem and cerebellum; and were divided into two groups - up to 40 years (n = 10) and above 40 years (n = 10). ACE2 and TMPRSS2 gene expression analysis was done using qRT-PCR and protein co-expression was seen by immunofluorescence. The ACE2 and TMPRSS2 gene expression was observed to be highest in hypothalamus and thalamus regions, respectively. Immunoreactivity for both ACE-2 and TMPRSS2 was observed in all examined brain regions, confirming the presence of these viral entry receptors. Co-localisation was maximum in hypothalamus. Our study did not find any trend related to different age groups. The expression of both these viral entry receptors suggests that normal human brain is susceptibility to SARS-CoV-2, perhaps which could be related to the cognitive and neurological impairment that occur in patients.

Sympathetic remodeling and altered angiotensin-converting enzyme 2 localization occur in patients with cardiac disease but are not exacerbated by severe COVID-19

PURPOSE

Remodeling of sympathetic nerves and ACE2 has been implicated in cardiac pathology, and ACE2 also serves as a receptor for SARS-CoV-2. However, there is limited histological knowledge about the transmural distribution of sympathetic nerves and the cellular localization and distribution of ACE2 in human left ventricles from normal or diseased hearts. Goals of this study were to establish the normal pattern for these parameters and determine changes that occurred in decedents with cardiovascular disease alone compared to those with cardiac pathology and severe COVID-19.

METHODS

We performed immunohistochemical analysis on sections of left ventricular wall from twenty autopsied human hearts consisting of a control group, a cardiovascular disease group, and COVID-19 ARDS, and COVID-19 non-ARDS groups.

RESULTS

Using tyrosine hydroxylase as a noradrenergic marker, we found substantial sympathetic nerve loss in cardiovascular disease samples compared to controls. Additionally, we found heterogeneous nerve loss in both COVID-19 groups. Using an ACE2 antibody, we observed robust transmural staining localized to pericytes in the control group. The cardiovascular disease hearts displayed regional loss of ACE2 in pericytes and regional increases in staining of cardiomyocytes for ACE2. Similar changes were observed in both COVID-19 groups.

CONCLUSIONS

Heterogeneity of sympathetic innervation, which occurs in cardiac disease and is not increased by severe COVID-19, could contribute to arrhythmogenesis. The dominant localization of ACE2 to pericytes suggests that these cells would be the primary target for potential cardiac infection by SARS-CoV-2. Regional changes in ACE2 staining by myocytes and pericytes could have complex effects on cardiac pathophysiology.

Myocardial Angiotensin-Converting Enzyme 2 Protein Expression in Ischemic Heart Failure

The angiotensin-converting enzyme 2 (ACE2)-angiotensin-(1-7)-Mas receptor axis plays a significant role in regulating myocardial remodeling and the development of heart failure (HF), with ACE2 being the primary focus. However, contemporary understanding of the membrane-bound form of the human ACE2 protein remains insufficient. The purpose of this study was to determine the expression of ACE2 protein in different cells of the left ventricular myocardium in non-diseased hearts and at various stages of ischemic HF. A total of 103 myocardial tissue samples from the left ventricle underwent quantitative and semi-quantitative immunohistochemical analysis. Upon assessing ACE2 immunostaining in all myocardial cells through unselective digital image analysis, there was no change in the stage A HF group. Nevertheless, the expression of ACE2 membrane protein in cardiomyocytes showed a tendency to increase, while non-cardiomyocyte ACE2 expression decreased significantly (p < 0.001). In the stage B HF group, the intensity of ACE2 immunostaining continued to increase with rising cardiomyocyte ACE2 expression (p < 0.001). Non-cardiomyocyte expression, in contrast, remained similar to that observed in the stage A HF group. In the stages C/D HF group, ACE2 expression reached its highest level in cardiomyocytes (p < 0.001), while ACE2 expression in non-cardiomyocytes was the lowest (p < 0.001). These changes in ACE2 protein levels are associated with left ventricular remodeling in ischemic HF.

Renin-Angiotensin System and Sex Differences in COVID-19: A Critical Assessment

The current epidemic of corona virus disease (COVID-19) has resulted in an immense health burden that became the third leading cause of death and potentially contributed to a decline in life expectancy in the United States. The severe acute respiratory syndrome-related coronavirus-2 binds to the surface-bound peptidase angiotensin-converting enzyme 2 (ACE2, EC 3.4.17.23) leading to tissue infection and viral replication. ACE2 is an important enzymatic component of the renin-angiotensin system (RAS) expressed in the lung and other organs. The peptidase regulates the levels of the peptide hormones Ang II and Ang-(1-7), which have distinct and opposing actions to one another, as well as other cardiovascular peptides. A potential consequence of severe acute respiratory syndrome-related coronavirus-2 infection is reduced ACE2 activity by internalization of the viral-ACE2 complex and subsequent activation of the RAS (higher ratio of Ang II:Ang-[1-7]) that may exacerbate the acute inflammatory events in COVID-19 patients and possibly contribute to the effects of long COVID-19. Moreover, COVID-19 patients present with an array of autoantibodies to various components of the RAS including the peptide Ang II, the enzyme ACE2, and the AT1 AT2 and Mas receptors. Greater disease severity is also evident in male COVID-19 patients, which may reflect underlying sex differences in the regulation of the 2 distinct functional arms of the RAS. The current review provides a critical evaluation of the evidence for an activated RAS in COVID-19 subjects and whether this system contributes to the greater severity of severe acute respiratory syndrome-related coronavirus-2 infection in males as compared with females.

Smoking increases expression of the SARS-CoV-2 spike protein-binding long ACE2 isoform in bronchial epithelium

After more than two years the COVID-19 pandemic, that is caused by infection with the respiratory SARS-CoV-2 virus, is still ongoing. The risk to develop severe COVID-19 upon SARS-CoV-2 infection is increased in individuals with a high age, high body mass index, and who are smoking. The SARS-CoV-2 virus infects cells of the upper respiratory tract by entering these cells upon binding to the Angiotensin-converting enzyme 2 (ACE2) receptor. ACE2 is expressed in various cell types in the lung but the expression is especially high in goblet and ciliated cells. Recently, it was shown that next to its full-length isoform, ACE2 also has a short isoform. The short isoform is unable to bind SARS-CoV-2 and does not facilitate viral entry. In the current study we investigated whether active cigarette smoking increases the expression of the long or the short ACE2 isoform. We showed that in active smokers the expression of the long, active isoform, but not the short isoform of ACE2 is higher compared to never smokers. Additionally, it was shown that the expression of especially the long, active isoform of ACE2 was associated with secretory, club and goblet epithelial cells. This study increases our understanding of why current smokers are more susceptible to SARS-CoV-2 infection, in addition to the already established increased risk to develop severe COVID-19.

Cigarette smoke preferentially induces full length ACE2 expression in differentiated primary human airway cultures but does not alter the efficiency of cellular SARS-CoV-2 infection

Cigarette smoking has many serious negative health consequences. The relationship between smoking and SARS-CoV-2 infection is controversial, specifically whether smokers are at increased risk of infection. We investigated the impact of cigarette smoke on ACE2 isoform expression and SARS-CoV-2 infection in differentiated primary human bronchial epithelial cells at the air-liquid-interface (ALI). We assessed the expression of ACE2 in response to CSE and therapeutics reported to modulate ACE2. We exposed ALI cultures to cigarette smoke extract (CSE) and then infected them with SARS-CoV-2. We measured cellular infection using flow cytometry and whole-transwell immunofluorescence. We found that CSE increased expression of full-length ACE2 (flACE2) but did not alter the expression of a Type I-interferon sensitive truncated isoform (dACE2) that lacks the capacity to bind SARS-CoV-2. CSE did not have a significant impact on key mediators of the innate immune response. Importantly, we show that, despite the increase in flACE2, CSE did not alter airway cell infection after CSE exposure. We found that nicotine does not significantly alter flACE2 expression but that NRF2 agonists do lead to an increase in flACE2 expression. This increase was not associated with an increase in SARS-CoV-2 infection. Our results are consistent with the epidemiological data suggesting that current smokers do not have an excess of SARS-CoV-2 infection. but that those with chronic respiratory or cardiovascular disease are more vulnerable to severe COVID-19. They suggest that, in differentiated conducting airway cells, flACE2 expression levels may not limit airway SARS-CoV-2 infection.

Regulation of angiotensin-converting enzyme 2 isoforms by type 2 inflammation and viral infection in human airway epithelium

SARS-CoV-2 enters human cells through its main receptor, angiotensin-converting enzyme 2 (ACE2), which constitutes a limiting factor of infection. Recent findings demonstrating novel ACE2 isoforms implicate that this receptor is regulated in a more complex way than previously anticipated. However, it remains unknown how various inflammatory conditions influence the abundance of these ACE2 variants. Hence, we studied expression of ACE2 messenger RNA (mRNA) and protein isoforms, together with its glycosylation and spatial localization in primary human airway epithelium upon allergic inflammation and viral infection. We found that interleukin-13, the main type 2 cytokine, decreased expression of long ACE2 mRNA and reduced glycosylation of full-length ACE2 protein via alteration of N-linked glycosylation process, limiting its availability on the apical side of ciliated cells. House dust mite allergen did not affect the expression of ACE2. Rhinovirus infection increased short ACE2 mRNA, but it did not influence its protein expression. In addition, by screening other SARS-CoV-2 related host molecules, we found that interleukin-13 and rhinovirus significantly regulated mRNA, but not protein of transmembrane serine protease 2 and neuropilin 1. Regulation of ACE2 and other host proteins was comparable in healthy and asthmatic epithelium, underlining the lack of intrinsic differences but dependence on the inflammatory milieu in the airways.

Expanding the apelin receptor pharmacological toolbox using novel fluorescent ligands

INTRODUCTION

The apelin receptor binds two distinct endogenous peptides, apelin and ELA, which act in an autocrine/paracrine manner to regulate the human cardiovascular system. As a class A GPCR, targeting the apelin receptor is an attractive therapeutic strategy. With improvements in imaging techniques, and the stability and brightness of dyes, fluorescent ligands are becoming increasingly useful in studying protein targets. Here, we describe the design and validation of four novel fluorescent ligands; two based on [Pyr1]apelin-13 (apelin488 and apelin647), and two based on ELA-14 (ELA488 and ELA647).

METHODS

Fluorescent ligands were pharmacologically assessed using radioligand and functional in vitro assays. Apelin647 was validated in high content imaging and internalisation studies, and in a clinically relevant human embryonic stem cell-derived cardiomyocyte model. Apelin488 and ELA488 were used to visualise apelin receptor binding in human renal tissue.

RESULTS

All four fluorescent ligands retained the ability to bind and activate the apelin receptor and, crucially, triggered receptor internalisation. In high content imaging studies, apelin647 bound specifically to CHO-K1 cells stably expressing apelin receptor, providing proof-of-principle for a platform that could screen novel hits targeting this GPCR. The ligand also bound specifically to endogenous apelin receptor in stem cell-derived cardiomyocytes. Apelin488 and ELA488 bound specifically to apelin receptor, localising to blood vessels and tubules of the renal cortex.

DISCUSSION

Our data indicate that the described novel fluorescent ligands expand the pharmacological toolbox for studying the apelin receptor across multiple platforms to facilitate drug discovery.

Significance of Catecholamine Biosynthetic/Metabolic Pathway in SARS-CoV-2 Infection and COVID-19 Severity

The SARS-CoV-2 infection was previously associated with the expression of the dopamine biosynthetic enzyme L-Dopa decarboxylase (DDC). Specifically, a negative correlation was detected between DDC mRNA and SARS-CoV-2 RNA levels in in vitro infected epithelial cells and the nasopharyngeal tissue of COVID-19 patients with mild/no symptoms. However, DDC, among other genes related to both DDC expression and SARS-CoV-2-infection (ACE2, dACE2, EPO), was upregulated in these patients, possibly attributed to an orchestrated host antiviral response. Herein, by comparing DDC expression in the nasopharyngeal swab samples of severe/critical to mild COVID-19 cases, we showed a 20 mean-fold reduction, highlighting the importance of the expression of this gene as a potential marker of COVID-19 severity. Moreover, we identified an association of SARS-CoV-2 infection with the expression of key catecholamine biosynthesis/metabolism-related genes, in whole blood samples from hospitalized patients and in cultured cells. Specifically, viral infection downregulated the biosynthetic part of the dopamine pathway (reduction in DDC expression up to 7.5 mean-fold), while enhanced the catabolizing part (increase in monoamine oxidases A and B expression up to 15 and 10 mean-fold, respectively) in vivo, irrespectively of the presence of comorbidities. In accordance, dopamine levels in the sera of severe cases were reduced (up to 3.8 mean-fold). Additionally, a moderate positive correlation between DDC and MAOA mRNA levels (r = 0.527, p < 00001) in the blood was identified upon SARS-CoV-2-infection. These observations were consistent to the gene expression data from SARS-CoV-2-infected Vero E6 and A549 epithelial cells. Furthermore, L-Dopa or dopamine treatment of infected cells attenuated the virus-derived cytopathic effect by 55% and 59%, respectively. The SARS-CoV-2 mediated suppression of dopamine biosynthesis in cell culture was, at least in part, attributed to hypoxia-like conditions triggered by viral infection. These findings suggest that L-Dopa/dopamine intake may have a preventive or therapeutic value for COVID-19 patients.

Liver, NAFLD and COVID-19

Coronavirus disease 2019 (COVID-19) is characterized by a wide clinical spectrum that includes abnormalities in liver function indicative of liver damage. Conversely, people with liver diseases are at higher risk of severe COVID-19. In the current review, we summarize first the epidemiologic evidence describing the bidirectional relationship between COVID-19 and liver function/liver diseases. Additionally, we present the most frequent histologic findings as well as the most important direct and indirect mechanisms supporting a COVID-19 mediated liver injury. Furthermore, we focus on the most frequent liver disease in the general population, non-alcoholic or metabolic-associated fatty liver disease (NAFLD/MAFLD), and describe how COVID-19 may affect NAFLD/MAFLD development and progression and conversely how NAFLD/MAFLD may further aggravate a COVID-19 infection. Finally, we present the long-term consequences of the pandemic on the development and management of NAFLD.

Angiotensin-converting enzyme 2 (ACE2): Two decades of revelations and re-evaluation

Angiotensin-converting enzyme-2, or ACE2, is primarily a zinc-dependent peptidase and ectoenzyme expressed in numerous cell types and functioning as a counterbalance to ACE in the renin-angiotensin system. It was discovered 21 years ago more than 40 years after the discovery of ACE itself. Its primary physiological activity is believed to be in the conversion of angiotensin II to the vasodilatory angiotensin-(1-7) acting through the Mas receptor. As such it has been implicated in numerous pathological conditions, largely in a protective mode which has led to the search for ACE2 activatory mechanisms. ACE2 has a diverse substrate specificity allowing its participation in multiple peptide pathways. It also regulates aspects of amino acid transport through its homology with a membrane protein, collectrin. It also serves as a viral receptor for the SARS virus, and subsequently SARS-CoV2, driving the current COVID-19 pandemic. ACE2 therefore provides a therapeutic target for the treatment of COVID and understanding the biological events following viral binding can provide insight into the multiple pathologies caused by the virus, particularly inflammatory and vascular. In part this may relate to the ability of ACE2, like ACE, to be shed from the cell membrane. The shed form of ACE2 (sACE2) may be a factor in determining susceptibility to certain COVID pathologies. Hence, for just over 20 years, ACE2 has provided numerous surprises in the field of vasoactive peptides with, no doubt, more to come but it is its central role in COVID pathology that is producing the current intense interest in its biology.