Collectrin, a collecting duct-specific transmembrane glycoprotein, is a novel homolog of ACE2 and is developmentally regulated in embryonic kidneys

ACE2 Nascence, trafficking, and SARS-CoV-2 pathogenesis: the saga continues

With the emergence of the novel coronavirus SARS-CoV-2 since December 2019, more than 65 million cases have been reported worldwide. This virus has shown high infectivity and severe symptoms in some cases, leading to over 1.5 million deaths globally. Despite the collaborative and concerted research efforts that have been made, no effective medication for COVID-19 (coronavirus disease-2019) is currently available. SARS-CoV-2 uses the angiotensin-converting enzyme 2 (ACE2) as an initial mediator for viral attachment and host cell invasion. ACE2 is widely distributed in the human tissues including the cell surface of lung cells which represent the primary site of the infection. Inhibiting or reducing cell surface availability of ACE2 represents a promising therapy for tackling COVID-19. In this context, most ACE2-based therapeutic strategies have aimed to tackle the virus through the use of angiotensin-converting enzyme (ACE) inhibitors or neutralizing the virus by exogenous administration of ACE2, which does not directly aim to reduce its membrane availability. However, through this review, we present a different perspective focusing on the subcellular localization and trafficking of ACE2. Membrane targeting of ACE2, and shedding and cellular trafficking pathways including the internalization are not well elucidated in literature. Therefore, we hereby present an overview of the fate of newly synthesized ACE2, its post translational modifications, and what is known of its trafficking pathways. In addition, we highlight the possibility that some of the identified ACE2 missense variants might affect its trafficking efficiency and localization and hence may explain some of the observed variable severity of SARS-CoV-2 infections. Moreover, an extensive understanding of these processes is necessarily required to evaluate the potential use of ACE2 as a credible therapeutic target.

COVID-19 and gastrointestinal system: A brief review

COVID-19 is a recent pandemic that is still a major health problem of modern times and already more than 17.5 lakhs people succumbed to this deadly disease. This disease is caused by novel coronavirus which is named SARS-COV-2 by the International Committee on Taxonomy of Viruses. This virus originated from Wuhan city in Hubei province of China in December 2019 and within a short period spread across the many countries in the globe. There are a lot of basic as well as clinical research is going on to study the mode of transmission and the mechanism of action of SARS-COV-2 infection and its therapeutics. SARS-COV-2 is not only known to infect lungs, but it also infects other organs in the human body including the gastrointestinal (GI) tract, the liver, and the pancreas via the angiotensin-converting enzyme (ACE) 2, an important component of the renin-angiotensin system. In this short review, we are mainly discussing the mode of SARS-COV-2 transmission, physiological counterbalancing roles of ACE2 and ACE and the tissue patterns of ACE2 expression, and the overall effect of COVID19 on human gastrointestinal System. Therefore, this review sheds light on the possible mechanism of SARS-COV-2 infection in the GI system and its pathological symptoms raising a potential possibility of GI tract acting as a secondary site for SARS-CoV-2 tropism and infection. Finally, future studies to understand the fecal-oral transmission of the virus and the correlation of viral load and severity of GI symptoms are proposed to gain knowledge of the GI symptoms in COVID-19 to aid in early diagnosis and prognosis.

Identification of novel inhibitors of angiotensin-converting enzyme 2 (ACE-2) receptor from Urtica dioica to combat coronavirus disease 2019 (COVID-19)

Abstract

The pandemic outbreak of coronavirus (SARS-CoV-2) is rapidly spreading across the globe, so the development of anti-SARS-CoV-2 agents is urgently needed. Angiotensin-converting enzyme 2 (ACE-2), a human receptor that facilitates entry of SARS-CoV-2, serves as a prominent target for drug discovery. In the present study, we have applied the bioinformatics approach for screening of a series of bioactive chemical compounds from Himalayan stinging nettle (Urtica dioica) as potent inhibitors of ACE-2 receptor (PDB ID: 1R4L). The molecular docking was applied to dock a set of representative compounds within the active site region of target receptor protein using 0.8 version of the PyRx virtual screen tool and analyzed by using discovery studio visualizer. Based on the highest binding affinity, 23 compounds were shortlisted as a lead molecule using molecular docking analysis. Among them, β-sitosterol was found with the highest binding affinity − 12.2 kcal/mol and stable interactions with the amino acid residues present on the active site of the ACE-2 receptor. Similarly, luteoxanthin and violaxanthin followed by rutin also displayed stronger binding efficiency. We propose these compounds as potential lead candidates for the development of target-specific therapeutic drugs against COVID-19.

Graphic abstract

Electronic supplementary material

The online version of this article (10.1007/s11030-020-10159-2) contains supplementary material, which is available to authorized users.

Contributions of human ACE2 and TMPRSS2 in determining host-pathogen interaction of COVID-19

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection is at present an emerging global public health crisis. Angiotensin converting enzyme 2 (ACE2) and trans-membrane protease serine 2 (TMPRSS2) are the two major host factors that contribute to the virulence of SARS-CoV-2 and pathogenesis of coronavirus disease-19 (COVID-19). Transmission of SARS-CoV-2 from animal to human is considered a rare event that necessarily requires strong evolutionary adaptations. Till date no other human cellular receptors are identified beside ACE2 for SARS-CoV-2 entry inside the human cell. Proteolytic cleavage of viral spike (S)-protein and ACE2 by TMPRSS2 began the entire host-pathogen interaction initiated with the physical binding of ACE2 to S-protein. SARS-CoV-2 S-protein binds to ACE2 with much higher affinity and stability than that of SARS-CoVs. Molecular interactions between ACE2-S and TMPRSS2-S are crucial and preciously mediated by specific residues. Structural stability, binding affinity and level of expression of these three interacting proteins are key susceptibility factors for COVID-19. Specific protein-protein interactions (PPI) are being identified that explains uniqueness of SARS-CoV-2 infection. Amino acid substitutions due to naturally occurring genetic polymorphisms potentially alter these PPIs and poses further clinical heterogeneity of COVID-19. Repurposing of several phytochemicals and approved drugs against ACE2, TMPRSS2 and S-protein have been proposed that could inhibit PPI between them. We have also identified some novel lead phytochemicals present in Azadirachta indica and Aloe barbadensis which could be utilized for further in vitro and in vivo anti-COVID-19 drug discovery. Uncovering details of ACE2-S and TMPRSS2-S interactions would further contribute to future research on COVID-19.

Angiotensin-converting enzyme 2 (ACE2): SARS-CoV-2 receptor and RAS modulator

The coronavirus disease 2019 (COVID-19) outbreak is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Angiotensin-converting enzyme 2 (ACE2) was rapidly identified as the critical functional receptor for SARS-CoV-2. ACE2 is well-known as a counter-regulator of the renin-angiotensin system (RAS) and plays a key role in the cardiovascular system. Given that ACE2 functions as both a SARS-CoV-2 receptor and a RAS modulator, the treatment for COVID-19 presents a dilemma of how to limit virus entry but protect ACE2 physiological functions. Thus, an in-depth summary of the recent progress of ACE2 research and its relationship to the virus is urgently needed to provide possible solution to the dilemma. Here, we summarize the complexity and interplay between the coronavirus, ACE2 and RAS (including anti-RAS drugs). We propose five novel working modes for functional receptor for SARS-CoV-2 infection and the routes of ACE2-mediated virus entering host cells, as well as its regulatory mechanism. For the controversy of anti-RAS drugs application, we also give theoretical analysis and discussed for drug application. These will contribute to a deeper understanding of the complex mechanisms of underlying the relationship between the virus and ACE2, and provide guidance for virus intervention strategies.

The Intersection between COVID-19, the Gene Family of ACE2 and Alzheimer's Disease

We reviewed factors that might influence COVID-19 outcomes (eg, neurological symptoms), including the link to Alzheimer's disease. Since the virus triggers COVID-19 infection through binding to ACE2, we focused on the ACE2 gene family, including ACE. Both ACE2 and ACE are involved in the renin-angiotensin system (RAS). In general, ACE causes inflammation and vasoconstriction, while ACE2 leads to anti-inflammation activity and vasodilation. The disturbed balance between these counter-regulatory pathways could influence susceptibility to COVID-19. Notably, dysregulation of the RAS-equilibrium contributes to Alzheimer's disease. Differences in the incidence and symptoms of COVID-19 in diverse populations could be attributed to variability in the human genome. For example, ACE and ACE2 variations could modify the outcome of COVID-19 in different populations. It would be important to conduct genome-wide studies to detect variants influencing COVID-19 presentation, with a special focus on variants affecting immune-related pathways and expression of RAS-related genes.

Computational Design of 25-mer Peptide Binders of SARS-CoV-2

SARS-CoV-2 is the novel coronavirus causing the COVID-19 pandemic. To enter human cells, the receptor-binding domain (RBD) of the S1 subunit of SARS-CoV-2 (SARS-CoV-2-RBD) initially binds to the peptidase domain of angiotensin-converting enzyme 2 receptor (ACE2-PD). Using peptides to inhibit SARS-CoV-2-RBD binding to ACE2 is a potential therapeutic solution for COVID-19. A previous study identified a 23-mer peptide (SBP1) that bound to SARS-CoV-2-RBD with comparable KD to ACE2. We employed computational protein design and molecular dynamics (MD) to design SARS-CoV-2-RBD 25-mer peptide binders (SPB25) with better predicted binding affinity than SBP1. Using residues 21-45 of the α1 helix of ACE2-PD as the template, our strategy is employing Rosetta to enhance SPB25 binding affinity to SARS-CoV-2-RBD and avoid disrupting existing favorable interactions by using residues that have not been reported to form favorable interactions with SARS-CoV-2-RBD as designed positions. Designed peptides with better predicted binding affinities, by Rosetta, than SPB25 were subjected to MD validation. The MD results show that five designed peptides (SPB25F8N, SPB25F8R, SPB25L25R, SPB25F8N/L25R, and SPB25F8R/L25R) have better predicted binding affinities, by the MM-GBSA method, than SPB25 and SBP1. This study developed an approach to design SARS-CoV-2-RBD peptide binders, and these peptides may be promising candidates as potential SARS-CoV-2 inhibitors.

Revisiting potential druggable targets against SARS-CoV-2 and repurposing therapeutics under preclinical study and clinical trials: A comprehensive review

Coronavirus disease-19 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is one of the most contagious diseases in human history that has already affected millions of lives worldwide. To date, no vaccines or effective therapeutics have been discovered yet that may successfully treat COVID-19 patients or contain the transmission of the virus. Scientific communities across the globe responded rapidly and have been working relentlessly to develop drugs and vaccines, which may require considerable time. In this uncertainty, repurposing the existing antiviral drugs could be the best strategy to speed up the discovery of effective therapeutics against SARS-CoV-2. Moreover, drug repurposing may leave some vital information on druggable targets that could be capitalized in target-based drug discovery. Information on possible drug targets and the progress on therapeutic and vaccine development also needs to be updated. In this review, we revisited the druggable targets that may hold promise in the development of the anti-SARS-CoV-2 agent. Progresses on the development of potential therapeutics and vaccines that are under the preclinical studies and clinical trials have been highlighted. We anticipate that this review will provide valuable information that would help to accelerate the development of therapeutics and vaccines against SARS-CoV-2 infection.

An innovative method for the selection of inhibitors of the viral spike-glycoprotein of the SARS-CoV

This paper has developed and described a detailed method for selecting inhibitors based on modified natural peptides for the SARS-CoV BJ01 spike-glycoprotein. The selection of inhibitors is carried out by increasing the affinity of the peptide to the active center of the protein. This paper also provides a step-by-step algorithm for analyzing the affinity of protein interactions and presents an analysis of energy interactions between the active center of a protein and the wild-type peptide interacting with it, taking into account modifications of the latter. A description of the software package that implements the presented algorithm is given on the website https://binomlabs.com/covid19.

Impact of SARS-CoV-2 on Male Reproductive Health: A Review of the Literature on Male Reproductive Involvement in COVID-19

Coronavirus Disease 2019 (COVID-19) has created a global pandemic. Global epidemiological results show that elderly men are susceptible to infection of COVID-19. The difference in the number of cases reported by gender increases progressively in favor of male subjects up to the age group ≥60-69 (66.6%) and ≥70-79 (66.1%). Through literature search and analysis, we also found that men are more susceptible to SARS-CoV-2 infection than women. In addition, men with COVID-19 have a higher mortality rate than women. Male represents 73% of deaths in China, 59% in South Korea, and 61.8% in the United States. Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) is the pathogen of COVID-19, which is transmitted through respiratory droplets, direct and indirect contact. Genomic analysis has shown that SARS-CoV-2 is 79% identical to SARS-CoV, and both use angiotensin-converting enzyme 2 (ACE2) as the receptor for invading cells. In addition, Transmembrane serine protease 2 (TMPRSS2) can enhance ACE2-mediated virus entry. However, SARS-CoV-2 has a high affinity with human ACE2, and its consequences are more serious than other coronaviruses. ACE2 acts as a "gate" for viruses to invade cells and is closely related to the clinical manifestations of COVID-19. Studies have found that ACE2 and TMPRSS2 are expressed in the testis and male reproductive tract and are regulated by testosterone. Mature spermatozoon even has all the machinery required to bind SARS-CoV-2, and these considerations raise the possibility that spermatozoa could act as potential vectors of this highly infectious disease. This review summarizes the gender differences in the pathogenesis and clinical manifestations of COVID-19 and proposes the possible mechanism of orchitis caused by SARS-CoV-2 and the potential transmission route of the virus. In the context of the pandemic, these data will improve the understanding of the poor clinical outcomes in male patients with COVID-19 and the design of new strategies to prevent and treat SARS-CoV-2 infection.

Progress in Studies on Structural and Remedial Aspects of Newly Born Coronavirus, SARS-CoV-2

The article highlights an up-to-date progress in studies on structural and the remedial aspects of novel coronavirus 2019-nCoV, renamed as SARS-CoV-2, leading to the disease COVID-19, a pandemic. In general, all CoVs including SARS-CoV-2 are spherical positive single-stranded RNA viruses containing spike (S) protein, envelope (E) protein, nucleocapsid (N) protein, and membrane (M) protein, where S protein has a Receptor-binding Domain (RBD) that mediates the binding to host cell receptor, Angiotensin Converting Enzyme 2 (ACE2). The article details the repurposing of some drugs to be tried for COVID-19 and presents the status of vaccine development so far. Besides drugs and vaccines, the role of Convalescent Plasma (CP) therapy to treat COVID-19 is also discussed.

ACE2 and ACE: structure-based insights into mechanism, regulation and receptor recognition by SARS-CoV

Angiotensin converting enzyme (ACE) is well-known for its role in blood pressure regulation via the renin–angiotensin aldosterone system (RAAS) but also functions in fertility, immunity, haematopoiesis and diseases such as obesity, fibrosis and Alzheimer’s dementia. Like ACE, the human homologue ACE2 is also involved in blood pressure regulation and cleaves a range of substrates involved in different physiological processes. Importantly, it is the functional receptor for severe acute respiratory syndrome (SARS)-coronavirus (CoV)-2 responsible for the 2020, coronavirus infectious disease 2019 (COVID-19) pandemic. Understanding the interaction between SARS-CoV-2 and ACE2 is crucial for the design of therapies to combat this disease. This review provides a comparative analysis of methodologies and findings to describe how structural biology techniques like X-ray crystallography and cryo-electron microscopy have enabled remarkable discoveries into the structure–function relationship of ACE and ACE2. This, in turn, has enabled the development of ACE inhibitors for the treatment of cardiovascular disease and candidate therapies for the treatment of COVID-19. However, despite these advances the function of ACE homologues in non-human organisms is not yet fully understood. ACE homologues have been discovered in the tissues, body fluids and venom of species from diverse lineages and are known to have important functions in fertility, envenoming and insect–host defence mechanisms. We, therefore, further highlight the need for structural insight into insect and venom ACE homologues for the potential development of novel anti-venoms and insecticides.

ACE2 and gut amino acid transport

ACE2 is a type I membrane protein with extracellular carboxypeptidase activity displaying a broad tissue distribution with highest expression levels at the brush border membrane (BBM) of small intestine enterocytes and a lower expression in stomach and colon. In small intestinal mucosa, ACE2 mRNA expression appears to increase with age and to display higher levels in patients taking ACE-inhibitors (ACE-I). There, ACE2 protein heterodimerizes with the neutral amino acid transporter Broad neutral Amino acid Transporter 1 (B0AT1) (SLC6A19) or the imino acid transporter Sodium-dependent Imino Transporter 1 (SIT1) (SLC6A20), associations that are required for the surface expression of these transport proteins. These heterodimers can form quaternary structures able to function as binding sites for SARS-CoV-2 spike glycoproteins. The heterodimerization of the carboxypeptidase ACE2 with B0AT1 is suggested to favor the direct supply of substrate amino acids to the transporter, but whether this association impacts the ability of ACE2 to mediate viral infection is not known. B0AT1 mutations cause Hartnup disorder, a condition characterized by neutral aminoaciduria and, in some cases, pellagra-like symptoms, such as photosensitive rash, diarrhea, and cerebellar ataxia. Correspondingly, the lack of ACE2 and the concurrent absence of B0AT1 expression in small intestine causes a decrease in l-tryptophan absorption, niacin deficiency, decreased intestinal antimicrobial peptide production, and increased susceptibility to inflammatory bowel disease (IBD) in mice. Thus, the abundant expression of ACE2 in small intestine and its association with amino acid transporters appears to play a crucial role for the digestion of peptides and the absorption of amino acids and, thereby, for the maintenance of structural and functional gut integrity.

Origin and genomic characteristics of SARS-CoV-2 and its interaction with angiotensin converting enzyme type 2 receptors, focusing on the gastrointestinal tract

The emergence of coronavirus disease-2019 induced by a newly identified b-coronavirus, namely severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has constituted a public health emergency. Even though it was considered a zoonotic disease, the virus has also spread among humans via respiratory secretions. The expression and distribution of angiotensin converting enzyme type 2 (ACE2) in various human organs might also show other possible infection routes. High ACE2 ribonucleic acid expression has been identified in the gastrointestinal tract (GI) indicating its importance as a possible infection pathway of SARS-CoV-2. ACE2 induces viral entry into the host and most importantly has been found to be associated with the function of the gut. Its deficiency has been implicated in several pathologies such as colorectal inflammation. The renin-angiotensin system (RAS) is an essential regulatory cascade operating both at a local tissue level and at the systemic or circulatory level. The RAS may be important in the pathogenesis of chronic liver disease and is associated with the up-regulation of ACE2. Thus, the aim of this review is firstly, the analysis of some important general and genome characteristics of SARS-CoV-2 and secondly, and most importantly, to focus on the utility of ACE2 receptors in both SARS-CoV-2 replication and pathogenesis, especially in the GI tract.

Prioritizing potential ACE2 inhibitors in the COVID-19 pandemic: Insights from a molecular mechanics-assisted structure-based virtual screening experiment

Angiotensin-converting enzyme 2 (ACE2) is a membrane-bound zinc metallopeptidase that generates the vasodilatory peptide angiotensin 1-7 and thus performs a protective role in heart disease. It is considered an important therapeutic target in controlling the COVID-19 outbreak, since SARS-CoV-2 enters permissive cells via an ACE2-mediated mechanism. The present in silico study attempted to repurpose existing drugs for use as prospective viral-entry inhibitors targeting human ACE2. Initially, a clinically approved drug library of 7,173 ligands was screened against the receptor using molecular docking, followed by energy minimization and rescoring of docked ligands. Finally, potential binders were inspected to ensure molecules with different scaffolds were engaged in favorable contacts with both the metal cofactor and the critical residues lining the receptor's active site. The results of the calculations suggest that lividomycin, burixafor, quisinostat, fluprofylline, pemetrexed, spirofylline, edotecarin, and diniprofylline emerge as promising repositionable drug candidates for stabilizing the closed (substrate/inhibitor-bound) conformation of ACE2, thereby shifting the relative positions of the receptor's critical exterior residues recognized by SARS-CoV-2. This study is among the rare ones in the relevant scientific literature to search for potential ACE2 inhibitors. In practical terms, the drugs, unmodified as they are, may be introduced into the therapeutic armamentarium of the ongoing fight against COVID-19 now, or their scaffolds may serve as rich skeletons for designing novel ACE2 inhibitors in the near future.

Is highly expressed ACE 2 in pregnant women "a curse" in times of COVID-19 pandemic?

Angiotensin-converting enzyme 2 (ACE 2) is a membrane-bound enzyme that cleaves angiotensin II (Ang II) into angiotensin (1-7). It also serves as an important binding site for SARS-CoV-2, thereby, facilitating viral entry into target host cells. ACE 2 is abundantly present in the intestine, kidney, heart, lungs, and fetal tissues. Fetal ACE 2 is involved in myocardium growth, lungs and brain development. ACE 2 is highly expressed in pregnant women to compensate preeclampsia by modulating angiotensin (1-7) which binds to the Mas receptor, having vasodilator action and maintain fluid homeostasis. There are reports available on Zika, H1N1 and SARS-CoV where these viruses have shown to produce fetal defects but very little is known about SARS-CoV-2 involvement in pregnancy, but it might have the potential to interact with fetal ACE 2 and enhance COVID-19 transmission to the fetus, leading to fetal morbidity and mortality. This review sheds light on a path of SARS-CoV-2 transmission risk in pregnancy and its possible link with fetal ACE 2.

Discovery and characterization of ACE2 - a 20-year journey of surprises from vasopeptidase to COVID-19

Angiotensin-converting enzyme (ACE) is a zinc membrane metallopeptidase that plays a key role in regulating vasoactive peptide levels and hence cardiovascular activity through its conversion of angiotensin I (Ang I) to Ang II and its metabolism of bradykinin. The discovery of its homologue, ACE2, 20 years ago has led to intensive comparisons of these two enzymes revealing surprising structural, catalytic and functional distinctions between them. ACE2 plays multiple roles not only as a vasopeptidase but also as a regulator of amino acid transport and serendipitously as a viral receptor, mediating the cellular entry of the coronaviruses causing severe acute respiratory syndrome (SARS) and, very recently, COVID-19. Catalytically, ACE2 functions as a monocarboxypeptidase principally converting the vasoconstrictor angiotensin II to the vasodilatory peptide Ang-(1-7) thereby counterbalancing the action of ACE on the renin-angiotensin system (RAS) and providing a cardioprotective role. Unlike ACE, ACE2 does not metabolise bradykinin nor is it inhibited by classical ACE inhibitors. However, it does convert a number of other regulatory peptides in vitro and in vivo. Interest in ACE2 biology and its potential as a possible therapeutic target has surged in recent months as the COVID-19 pandemic rages worldwide. This review highlights the surprising discoveries of ACE2 biology during the last 20 years, its distinctions from classical ACE and the therapeutic opportunities arising from its multiple biological roles.

Testis and blood-testis barrier in Covid-19 infestation: role of angiotensin-converting enzyme 2 in male infertility

Severe acute respiratory syndrome coronavirus 2 (SARS- CoV-2) that causes COVID-19 infections penetrates body cells by binding to angiotensin-converting enzyme-2 (ACE2) receptors. Evidence shows that SARS-CoV-2 can also affect the urogenital tract. Hence, it should be given serious attention when treating COVID-19-infected male patients of reproductive age group. Other viruses like HIV, mumps, papilloma and Epstein-Barr can induce viral orchitis, germ cell apoptosis, inflammation and germ cell destruction with attending infertility and tumors. The blood-testis barrier (BTB) and blood-epididymis barrier (BEB) are essential physical barricades in the male reproductive tract located between the blood vessel and seminiferous tubules in the testes. Despite the significant role of these barriers in male reproductive function, studies have shown that a wide range of viruses can still penetrate the barriers and induce testicular dysfunctions. Therefore, this mini-review highlights the role of ACE2 receptors in promoting SARS-CoV-2-induced blood-testis/epididymal barrier infiltration and testicular dysfunction.

Clinical management of lung cancer patients during the outbreak of COVID-19 epidemic

The rapid growth of 2019 novel coronavirus (COVID-19) outbreak in Wuhan, China, at the early December 2019. COVID-19 spread all over the word just a few months. The outbreak of COVID-19 infection poses major threat to international health and economy. World Health Organization (WHO) announced that the new coronavirus was an international public health emergency on January 30, 2020. However, with the spread of COVID-19, the routine medical care of lung cancer patients was affected. Because lung cancer patients have low immunity after anti-tumor treatment, they should become the main targets for epidemic prevention. Lung cancer patients are increasingly concerned about the prevention of COVID-19. It is necessary to provide individualized medical treatment and management for lung cancer patients based on patients' conditions and regional epidemic patterns.

ACE2 imbalance as a key player for the poor outcomes in COVID-19 patients with age-related comorbidities - Role of gut microbiota dysbiosis

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COVID-19 patients with pre-existing age-related comorbidities have poor outcomes.

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Gut microbiota dysbiosis is associated with ageing and age-related diseases.

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Viral-mediated ACE2 shedding favors poor outcomes by RAS-dependent mechanisms.

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Viral-mediated ACE2 shedding favors poor outcomes by RAS-independent gut dysbiosis.

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Potential of ACE2 and gut microbiota-based therapeutic opportunities for COVID-19.

Coronavirus disease 19 (COVID-19) is a pandemic condition caused by the new coronavirus SARS-CoV-2. The typical symptoms are fever, cough, shortness of breath, evolving to a clinical picture of pneumonia and, ultimately, death. Nausea and diarrhea are equally frequent, suggesting viral infection or transmission via the gastrointestinal-enteric system. SARS-CoV-2 infects human cells by using angiotensin converting enzyme 2 (ACE2) as a receptor, which is cleaved by transmembrane proteases during host cells infection, thus reducing its activities. ACE2 is a relevant player in the renin-angiotensin system (RAS), counterbalancing the deleterious effects of angiotensin II. Furthermore, intestinal ACE2 functions as a chaperone for the aminoacid transporter B⁰AT1. It has been suggested that B⁰AT1/ACE2 complex in the intestinal epithelium regulates gut microbiota (GM) composition and function, with important repercussions on local and systemic immune responses against pathogenic agents, namely virus. Notably, productive infection of SARS-CoV-2 in ACE2⁺ mature human enterocytes and patients’ GM dysbiosis was recently demonstrated. This review outlines the evidence linking abnormal ACE2 functions with the poor outcomes (higher disease severity and mortality rate) in COVID-19 patients with pre-existing age-related comorbidities and addresses a possible role for GM dysbiosis. The article culminates with the therapeutics opportunities based on these pathways.

Drug Weaponry to Fight Against SARS-CoV-2

The current outbreak of SARS-CoV-2 virus has caused a large increase in mortality and morbidity associated with respiratory diseases. Huge efforts are currently ongoing to develop a vaccine against this virus. However, alternative approaches could be considered in the fight against this disease. Among other strategies, structural-based drug design could be an effective approach to generate specific molecules against SARS-CoV-2, thus reducing viral burden in infected patients. Here, in addition to this structural approach, we also revise several therapeutic strategies to fight against this viral threat. Furthermore, we report ACE-2 genetic polymorphic variants affecting residues involved in close contacts with SARS-CoV-2 that might be associated to different infection risks. These analyses could provide valuable information to predict the course of the disease.

ACE2 Protein Landscape in the Head and Neck Region: The Conundrum of SARS-CoV-2 Infection

The coronavirus pandemic raging worldwide since December 2019 is caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which invades human cells via the angiotensin-converting enzyme 2 (ACE2) receptor. Although it has already been identified in many organs, ACE2 expression remains largely unknown in the head and neck (HN) sphere. Thus, this study aims to investigate its protein expression in several sites of the upper aerodigestive tract in order to highlight potential routes of infection. We compared ACE2 immunohistochemical expression between 70 paraffin-embedded specimens with two different antibodies and reported the quantified expression in each histological location. Surprisingly, we obtained different results depending on the antibody, an absence of labeling having been observed with a monoclonal antibody raised against the extracellular domain, whereas the polyclonal, against the cytoplasmic part of the protein, revealed enriched ACE2 expression, particularly in sinuses, vocal cords, salivary glands and oral cavity epithelial cells. The interpretation of these discordant results has brought several exciting lines of reflection. In conclusion, this study provides possible routes of entry for the SARS-CoV-2 in HN region and, above all, has led us to encourage caution when studying the ACE2 expression which is currently at the center of all attention.

Identification of a Potential Peptide Inhibitor of SARS-CoV-2 Targeting its Entry into the Host Cells

BACKGROUND AND OBJECTIVE

Coronavirus disease (COVID-19) is an ongoing pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Due to the incessant spread of the disease with substantial morbidity and mortality rates, there is an urgent demand for effective therapeutics and vaccines to control and diminish this pandemic. A critical step in the crosstalk between the virus and the host cell is the binding of SARS-CoV-2 spike protein to the angiotensin-converting enzyme 2 (ACE2) receptor present on the surface of the host cells. Hence, inhibition of this interaction could be a promising strategy to combat the SARS-CoV-2 infection.

METHODS

Docking and Molecular Dynamics (MD) simulation studies revealed that designed peptide maintains their secondary structure and provide a highly specific and stable binding (blocking) to SARS-CoV-2.

RESULTS

We have designed a novel peptide that could inhibit SARS-CoV-2 spike protein interaction with ACE2, thereby blocking the cellular entry of the virus.

CONCLUSION

Our findings suggest that computationally developed inhibitory peptide may be developed as an anti-SARS-CoV-2 agent for the treatment of SARS-CoV-2 infection. We further plan to pursue the peptide in cell-based assays and eventually for clinical trials.

Angiotensin-converting Enzyme 2 roles in the Pathogenesis of COVID-19

The new pandemic Coronavirus Disease 2019 (COVID-19) causes a wide range of clinical consequences, from asymptomatic infection to acute respiratory failure and it is very heterogeneous. The renin-angiotensin system (RAS) is well recognized as a key regulating system in circulatory homeostasis that play prominent roles in pathophysiological processes in abnormal activation for instance renal and cardiovascular diseases, obesity, and stroke. Angiotensin converting enzyme 2(ACE2) as a component of the RAS system. However, unlike the ACE, its activity is not inhibited by the ACE inhibitors. The major product of ACE2 is Ang1-7, known as a vasodilator peptide and part of the depressant arm of the RAS. There are two form of ACE2. Coronavirus cover with some proteins in order to help viral attachment to the cell membrane ACE2 as a receptor and then fuse and enter the cells. ACE2 was expressed in oral Cavity, salivary glands of the mouth, esophagus, myocardial cells, kidney, and enterocytes, along all the respiratory tract, intestine, and blood vessels. In this article, we explain the renin-angiotensin system and its components. Also, we shortly explain the organs involved in COVID-19 disease and we will talk about the possible causes of damage to these organs. We also reviewed the probable mechanism of using ACE2 in viral attachment and the probable treatment processes will also be discussed based on the surface proteins of the virus and ACE2. In addition, we briefly discuss the anti-angiotensin drugs and why patients with chronic disease are more susceptible to COVID-19 infection and show worse progression.

Structural analysis of ACE2 variant N720D demonstrates a higher binding affinity to TMPRSS2

Aims

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a novel member of the betacoronaviruses family affecting the lower respiratory tract mainly through binding to angiotensin converting enzyme 2 (ACE2) via its S-protein. Genetic analysis of (ACE2) gene revealed several variants that have been suggested to regulate the interaction with S protein. This study investigates the N720D variant, positioned in the collectrin-like domain (CLD) at proximity to type II transmembrane serine protease (TMPRSS2) cleavage site.

Main methods

The effect of N720D variant on ACE2 structure and thermodynamic stability was studied by DynaMut. HDOCK was utilised to model TMPRSS2 protease binding to ACE2 WT and D720 variant cleavage site. PRODIGY was used to calculate binding affinities and MD simulation tools calculated the at 100 ns for ACE2 apo structure and the ACE2-TMPRSS2 complex.

Key findings

The N720D variant is a more dynamic structure with a free energy change (ΔΔG): −0.470 kcal/mol. As such, introducing a tighter binding affinity of K_d = 3.2 × 10⁻¹⁰ M between TMPRSS2 and N720D variant. RMSD, RMSF calculations showed the N720D variant is less stable, however, RMSF values of the D720-TMPRSS2 complex reflected a slower dynamic motion.

Significance

The hotspot N720D variant in the CLD of ACE2 affected the stability and flexibility of ACE2 by increasing the level of motion in the loop region, resulting in a more favourable site for TMPRSS2 binding and cleavage. Consequently, this would facilitate S-protein binding and can potentially increase viral entry highlighting the importance of variants affecting the ACE2-TMPRSS2 complex.

COVID-19, Renin-Angiotensin System and Endothelial Dysfunction

The newly emergent novel coronavirus disease 2019 (COVID-19) outbreak, which is caused by SARS-CoV-2 virus, has posed a serious threat to global public health and caused worldwide social and economic breakdown. Angiotensin-converting enzyme 2 (ACE2) is expressed in human vascular endothelium, respiratory epithelium, and other cell types, and is thought to be a primary mechanism of SARS-CoV-2 entry and infection. In physiological condition, ACE2 via its carboxypeptidase activity generates angiotensin fragments (Ang 1-9 and Ang 1-7), and plays an essential role in the renin-angiotensin system (RAS), which is a critical regulator of cardiovascular homeostasis. SARS-CoV-2 via its surface spike glycoprotein interacts with ACE2 and invades the host cells. Once inside the host cells, SARS-CoV-2 induces acute respiratory distress syndrome (ARDS), stimulates immune response (i.e., cytokine storm) and vascular damage. SARS-CoV-2 induced endothelial cell injury could exacerbate endothelial dysfunction, which is a hallmark of aging, hypertension, and obesity, leading to further complications. The pathophysiology of endothelial dysfunction and injury offers insights into COVID-19 associated mortality. Here we reviewed the molecular basis of SARS-CoV-2 infection, the roles of ACE2, RAS signaling, and a possible link between the pre-existing endothelial dysfunction and SARS-CoV-2 induced endothelial injury in COVID-19 associated mortality. We also surveyed the roles of cell adhesion molecules (CAMs), including CD209L/L-SIGN and CD209/DC-SIGN in SARS-CoV-2 infection and other related viruses. Understanding the molecular mechanisms of infection, the vascular damage caused by SARS-CoV-2 and pathways involved in the regulation of endothelial dysfunction could lead to new therapeutic strategies against COVID-19.

SARS-CoV-2 pandemic and research gaps: Understanding SARS-CoV-2 interaction with the ACE2 receptor and implications for therapy

The COVID-19 pandemic is an emerging threat to global public health. While our current understanding of COVID-19 pathogenesis is limited, a better understanding will help us develop efficacious treatment and prevention strategies for COVID-19. One potential therapeutic target is angiotensin converting enzyme 2 (ACE2). ACE2 primarily catalyzes the conversion of angiotensin I (Ang I) to a nonapeptide angiotensin or the conversion of angiotensin II (Ang II) to angiotensin 1-7 (Ang 1-7) and has direct effects on cardiac function and multiple organs via counter-regulation of the renin-angiotensin system (RAS). Significant to COVID-19, ACE2 is postulated to serve as a major entry receptor for SARS-CoV-2 in human cells, as it does for SARS-CoV. Many infected individuals develop COVID-19 with fever, cough, and shortness of breath that can progress to pneumonia. Disease progression promotes the activation of immune cells, platelets, and coagulation pathways that can lead to multiple organ failure and death. ACE2 is expressed by epithelial cells of the lungs at high level, a major target of the disease, as seen in post-mortem lung tissue of patients who died with COVID-19, which reveals diffuse alveolar damage with cellular fibromyxoid exudates bilaterally. Comparatively, ACE2 is expressed at low level by vascular endothelial cells of the heart and kidney but may also be targeted by the virus in severe COVID-19 cases. Interestingly, SARS-CoV-2 infection downregulates ACE2 expression, which may also play a critical pathogenic role in COVID-19. Importantly, targeting ACE2/Ang 1-7 axis and blocking ACE2 interaction with the S protein of SARS-CoV-2 to curtail SARS-CoV-2 infection are becoming very attractive therapeutics potential for treatment and prevention of COVID-19. Here, we will discuss the following subtopics: 1) ACE2 as a receptor of SARS-CoV-2; 2) clinical and pathological features of COVID-19; 3) role of ACE2 in the infection and pathogenesis of SARS; 4) potential pathogenic role of ACE2 in COVID-19; 5) animal models for pathological studies and therapeutics; and 6) therapeutics development for COVID-19.

ACE2 receptor polymorphism: Susceptibility to SARS-CoV-2, hypertension, multi-organ failure, and COVID-19 disease outcome

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has emerged in Chinese people in December 2019 and has currently spread worldwide causing the COVID-19 pandemic with more than 150,000 deaths. In order for a SARS-CoV like virus circulating in wild life for a very long time to infect the index case-patient, a number of conditions must be met, foremost among which is the encounter with humans and the presence in homo sapiens of a cellular receptor allowing the virus to bind. Recently it was shown that the SARS-CoV-2 spike protein, binds to the human angiotensin I converting enzyme 2 (ACE2). This molecule is a peptidase expressed at the surface of lung epithelial cells and other tissues, that regulates the renin-angiotensin-aldosterone system. Humans are not equal with respect to the expression levels of the cellular ACE2. Moreover, ACE2 polymorphisms were recently described in human populations. Here we review the most recent evidence that ACE2 expression and/or polymorphism could influence both the susceptibility of people to SARS-CoV-2 infection and the outcome of the COVID-19 disease. Further exploration of the relationship between the virus, the peptidase function of ACE2 and the levels of angiotensin II in SARS-CoV-2 infected patients should help to better understand the pathophysiology of the disease and the multi-organ failures observed in severe COVID-19 cases, particularly heart failure.

Clinical Implications of SARS-CoV-2 Interaction With Renin Angiotensin System: JACC Review Topic of the Week

Severe acute respiratory-syndrome coronavirus-2 (SARS-CoV-2) host cell infection is mediated by binding to angiotensin-converting enzyme 2 (ACE2). Systemic dysregulation observed in SARS-CoV was previously postulated to be due to ACE2/angiotensin 1-7 (Ang1-7)/Mas axis downregulation; increased ACE2 activity was shown to mediate disease protection. Because angiotensin II receptor blockers, ACE inhibitors, and mineralocorticoid receptor antagonists increase ACE2 receptor expression, it has been tacitly believed that the use of these agents may facilitate viral disease; thus, they should not be used in high-risk patients with cardiovascular disease. Based on the anti-inflammatory benefits of the upregulation of the ACE2/Ang1-7/Mas axis and previously demonstrated benefits of lung function improvement in SARS-CoV infections, it has been hypothesized that the benefits of treatment with renin-angiotensin system inhibitors in SARS-CoV-2 may outweigh the risks and at the very least should not be withheld.

Structural basis for the recognition of SARS-CoV-2 by full-length human ACE2

Angiotensin-converting enzyme 2 (ACE2) is the cellular receptor for severe acute respiratory syndrome-coronavirus (SARS-CoV) and the new coronavirus (SARS-CoV-2) that is causing the serious coronavirus disease 2019 (COVID-19) epidemic. Here, we present cryo-electron microscopy structures of full-length human ACE2 in the presence of the neutral amino acid transporter B⁰AT1 with or without the receptor binding domain (RBD) of the surface spike glycoprotein (S protein) of SARS-CoV-2, both at an overall resolution of 2.9 angstroms, with a local resolution of 3.5 angstroms at the ACE2-RBD interface. The ACE2-B⁰AT1 complex is assembled as a dimer of heterodimers, with the collectrin-like domain of ACE2 mediating homodimerization. The RBD is recognized by the extracellular peptidase domain of ACE2 mainly through polar residues. These findings provide important insights into the molecular basis for coronavirus recognition and infection.

Structural basis for the recognition of SARS-CoV-2 by full-length human ACE2

Scientists are racing to learn the secrets of severe acute respiratory syndrome–coronavirus 2 (SARS-CoV-2), which is the cause of the pandemic disease COVID-19. The first step in viral entry is the binding of the viral trimeric spike protein to the human receptor angiotensin-converting enzyme 2 (ACE2). Yan et al. present the structure of human ACE2 in complex with a membrane protein that it chaperones, B⁰AT1. In the context of this complex, ACE2 is a dimer. A further structure shows how the receptor binding domain of SARS-CoV-2 interacts with ACE2 and suggests that it is possible that two trimeric spike proteins bind to an ACE2 dimer. The structures provide a basis for the development of therapeutics targeting this crucial interaction.

Science, this issue p. 1444

Angiotensin-converting enzyme 2 (ACE2) is the cellular receptor for severe acute respiratory syndrome–coronavirus (SARS-CoV) and the new coronavirus (SARS-CoV-2) that is causing the serious coronavirus disease 2019 (COVID-19) epidemic. Here, we present cryo–electron microscopy structures of full-length human ACE2 in the presence of the neutral amino acid transporter B⁰AT1 with or without the receptor binding domain (RBD) of the surface spike glycoprotein (S protein) of SARS-CoV-2, both at an overall resolution of 2.9 angstroms, with a local resolution of 3.5 angstroms at the ACE2-RBD interface. The ACE2-B⁰AT1 complex is assembled as a dimer of heterodimers, with the collectrin-like domain of ACE2 mediating homodimerization. The RBD is recognized by the extracellular peptidase domain of ACE2 mainly through polar residues. These findings provide important insights into the molecular basis for coronavirus recognition and infection.

ACE2 in Brain Physiology and Pathophysiology: Evidence from Transgenic Animal Models

Angiotensin-converting enzyme 2 (ACE2) is a protein consisting of two domains, the N-terminus is a carboxypeptidase homologous to ACE and the C-terminus is homologous to collectrin and responsible for the trafficking of the neutral amino acid transporter B(0)AT1 to the plasma membrane of gut epithelial cells. The carboxypeptidase domain not only metabolizes angiotensin II to angiotensin-(1–7), but also other peptide substrates, such as apelin, kinins and morphins. In addition, the collectrin domain regulates the levels of some amino acids in the blood, in particular of tryptophan. Therefore it is of no surprise that animals with genetic alterations in the expression of ACE2 develop a diverse pattern of phenotypes ranging from hypertension, metabolic and behavioural dysfunctions, to impairments in serotonin synthesis and neurogenesis. This review summarizes the phenotypes of such animals with a particular focus on the central nervous system.

The expressional disorder of the renal RAS mediates nephrotic syndrome of male rat offspring induced by prenatal ethanol exposure

This study aimed to prove that prenatal ethanol exposure (PEE) can induce nephrotic syndrome in male rat offspring and to explore the underlying intrauterine programming mechanisms. Pregnant Wistar rats were intragastrically administered ethanol (4 g/kg d) from gestational day (GD) 9 to GD 20, and the male fetuses were delivered by cesarean section at GD20 and the male adult offspring were euthanized at postnatal week (PW) 24. In vitro, the primary metanephric mesenchyme cells were treated with ethanol at concentrations of 15-60 mM. The results indicated that the kidneys of adult offspring in the PEE group exhibited glomerulosclerosis as well as interstitial fibrosis. The levels of serum creatinine and urine protein were elevated; the serum total cholesterol level was increased and the serum albumin concentration was reduced. In the fetal kidney, developmental retardation was presented in the PEE group via pathological examinations, accompanied by the expressional inhibition of the glial-cell-line-derived neurotrophic factor/c-ret tyrosine kinase receptor (GDNF/c-ret) signaling pathway. Although serum angiotensin II (Ang II) level and the gene expression of renal angiotensin-converting enzyme (ACE) were increased in the PEE group, the expression of renal angiotensin II type 2 receptor (AT₂R) was significantly inhibited, accompanied by a reduction in the H3K27ac level on the AT₂R gene promoter. In the non-classical renin-angiotensin system (RAS), the expression of renal angiotensin converting enzyme 2 (ACE2) and Mas receptor (MasR) were inhibited in the PEE group. The above changes of the classical and non-classical RAS all sustained from utero to adulthood. In vitro, ethanol elevated the gene expression of ACE and angiotensin II type 1a receptor (AT_1aR) whereas it reduced the expression of AT₂R, ACE2, and MasR, accompanied by a reduction in the H3K27ac level on AT₂R gene promoter. Taken together, these results suggested that PEE can induce fetal kidney developmental retardation and adult nephrotic syndrome, and direct regulation of ethanol to the renal RAS was involved in the mechanism of nephrotic syndrome induced by PEE.

Relationship between genetic variants of ACE2 gene and circulating levels of ACE2 and its metabolites

WHAT IS KNOWN

Angiotensin-converting enzyme 2 (ACE2) plays an important role in the development of essential hypertension (EH). Genetic factors remarkably influence circulating ACE2 level.

OBJECTIVE

Because heritability had remarkable effects on circulating ACE2, we designed this study to shed light on whether circulating levels of ACE2, angiotensin-(1-7) and angiotensin-(1-9) were linked to single nucleotide polymorphisms (SNPs) and haplotypes in ACE2 gene.

METHODS

A total of 213 patients with newly diagnosed mild to moderate EH were enrolled in the present study. Four ACE2 tag SNPs (rs2074192, rs4646171, rs4646155 and rs2106809) were genotyped, and major haplotypes consisting of these 4 SNPs were reconstructed for all subjects. Circulating levels of ACE2, angiotensin-(1-7) and angiotensin-(1-9) were measured using enzyme-linked immunosorbent assay.

RESULTS

In female subjects, linear regression analysis suggested that rare alleles of ACE2 rs2074192 and rs2106809 were associated with reduced circulating angiotensin-(1-7) levels (P=.007 and P=.006, respectively). ACE2 haplotype CAGC was associated with elevated circulating angiotensin-(1-7) levels (P=.03) whereas TAGT was associated with reduced circulating angiotensin-(1-7) levels in females (P<.001). Univariate linear regression analysis revealed that circulating ACE2 levels were positively associated with systolic blood pressure (P=.02), mean arterial pressure (P=.02) and serum creatinine (P<.001) in females whereas circulating ACE2 levels were positively associated with age (P<.001) and serum creatinine (P<.001) in males.

WHAT IS NEW AND CONCLUSION

ACE2 SNPs and haplotypes are associated with circulating angiotensin-(1-7) levels. ACE2 genetic variants may be the determinants of circulating angiotensin-(1-7) levels in hypertensive females.

Expansion of divergent SEA domains in cell surface proteins and nucleoporin 54

SEA (sea urchin sperm protein, enterokinase, agrin) domains, many of which possess autoproteolysis activity, have been found in a number of cell surface and secreted proteins. Despite high sequence divergence, SEA domains were also proposed to be present in dystroglycan based on a conserved autoproteolysis motif and receptor-type protein phosphatase IA-2 based on structural similarity. The presence of a SEA domain adjacent to the transmembrane segment appears to be a recurring theme in quite a number of type I transmembrane proteins on the cell surface, such as MUC1, dystroglycan, IA-2, and Notch receptors. By comparative sequence and structural analyses, we identified dystroglycan-like proteins with SEA domains in Capsaspora owczarzaki of the Filasterea group, one of the closest single-cell relatives of metazoans. We also detected novel and divergent SEA domains in a variety of cell surface proteins such as EpCAM, α/ε-sarcoglycan, PTPRR, collectrin/Tmem27, amnionless, CD34, KIAA0319, fibrocystin-like protein, and a number of cadherins. While these proteins are mostly from metazoans or their single cell relatives such as choanoflagellates and Filasterea, fibrocystin-like proteins with SEA domains were found in several other eukaryotic lineages including green algae, Alveolata, Euglenozoa, and Haptophyta, suggesting an ancient evolutionary origin. In addition, the intracellular protein Nucleoporin 54 (Nup54) acquired a divergent SEA domain in choanoflagellates and metazoans.

Cross-Presentation of Soluble and Cell-Associated Antigen by Murine Hepatocytes Is Enhanced by Collectrin Expression

Cross-presentation is a modular series of intracellular events dictating the internalization and subsequent MHC class I (MHC I) display of extracellular Ags. This process has been defined in dendritic cells and plays a fundamental role in the induction of CD8⁺ T cell immunity during viral, intracellular bacterial, and antitumor responses. Herein, acute viral infection of murine liver with adenovirus, a model for intrahepatic cross-presentation, confirms hepatocytes directly contribute to cross-presentation of Ags and priming the pool of naive CD8⁺ T cells within the liver microenvironment. Processing of soluble and cell-associated Ags into peptide displayed by MHC I is however defective in hepatocytes lacking collectrin, an intracellular chaperone protein that localizes within the endoplasmic reticulum-Golgi intermediate compartment. Loss of hepatic collectrin expression leads to the diminished cross-priming and expansion of cytolytic antiviral CD8⁺ T cells. This study demonstrates that collectrin positively regulates processing of engulfed Ags into MHC I:peptide complexes within hepatocytes. Collectrin-mediated cross-presentation supports intrahepatic adaptive antiviral immune responses and may lead to insights into the nature of how the liver acts as a primary site of CD8⁺ T cell activation.

Renal Collectrin Protects against Salt-Sensitive Hypertension and Is Downregulated by Angiotensin II

Collectrin, encoded by the Tmem27 gene, is a transmembrane glycoprotein with approximately 50% homology with angiotensin converting enzyme 2, but without a catalytic domain. Collectrin is most abundantly expressed in the kidney proximal tubule and collecting duct epithelia, where it has an important role in amino acid transport. Collectrin is also expressed in endothelial cells throughout the vasculature, where it regulates L-arginine uptake. We previously reported that global deletion of collectrin leads to endothelial dysfunction, augmented salt sensitivity, and hypertension. Here, we performed kidney crosstransplants between wild-type (WT) and collectrin knockout (Tmem27^Y/- ) mice to delineate the specific contribution of renal versus extrarenal collectrin on BP regulation and salt sensitivity. On a high-salt diet, WT mice with Tmem27^Y/- kidneys had the highest systolic BP and were the only group to exhibit glomerular mesangial hypercellularity. Additional studies showed that, on a high-salt diet, Tmem27^Y/- mice had lower renal blood flow, higher abundance of renal sodium-hydrogen antiporter 3, and lower lithium clearance than WT mice. In WT mice, administration of angiotensin II for 2 weeks downregulated collectrin expression in a type 1 angiotensin II receptor-dependent manner. This downregulation coincided with the onset of hypertension, such that WT and Tmem27^Y/- mice had similar levels of hypertension after 2 weeks of angiotensin II administration. Altogether, these data suggest that salt sensitivity is determined by intrarenal collectrin, and increasing the abundance or activity of collectrin may have therapeutic benefits in the treatment of hypertension and salt sensitivity.

ACE2 and Microbiota: Emerging Targets for Cardiopulmonary Disease Therapy

The health of the cardiovascular and pulmonary systems is inextricably linked to the renin-angiotensin system (RAS). Physiologically speaking, a balance between the vasodeleterious (Angiotensin-converting enzyme [ACE]/Angiotensin II [Ang II]/Ang II type 1 receptor [AT1R]) and vasoprotective (Angiotensin-converting enzyme 2 [ACE2]/Angiotensin-(1-7) [Ang-(1-7)]/Mas receptor [MasR]) components of the RAS is critical for cardiopulmonary homeostasis. Upregulation of the ACE/Ang II/AT1R axis shifts the system toward vasoconstriction, proliferation, hypertrophy, inflammation, and fibrosis, all factors that contribute to the development and progression of cardiopulmonary diseases. Conversely, stimulation of the vasoprotective ACE2/Ang-(1-7)/MasR axis produces a counter-regulatory response that promotes cardiovascular health. Current research is investigating novel strategies to augment actions of the vasoprotective RAS components, particularly ACE2, in order to treat various pathologies. Although multiple approaches to increase the activity of ACE2 have displayed beneficial effects against experimental disease models, the mechanisms behind its protective actions remain incompletely understood. Recent work demonstrating a non-catalytic role for ACE2 in amino acid transport in the gut has led us to speculate that the therapeutic effects of ACE2 can be mediated, in part, by its actions on the gastrointestinal tract and/or gut microbiome. This is consistent with emerging data which suggest that dysbiosis of the gut and lung microbiomes is associated with cardiopulmonary disease. This review highlights new developments in the protective actions of ACE2 against cardiopulmonary disorders, discusses innovative approaches to targeting ACE2 for therapy, and explores an evolving role for gut and lung microbiota in cardiopulmonary health.

Myosin 1b Regulates Amino Acid Transport by Associating Transporters with the Apical Plasma Membrane of Kidney Cells

Amino acid transporters (AATers) in the brush border of the apical plasma membrane (APM) of renal proximal tubule (PT) cells mediate amino acid transport (AAT). We found that the membrane-associated class I myosin myosin 1b (Myo1b) localized at the apical brush border membrane of PTs. In opossum kidney (OK) 3B/2 epithelial cells, which are derived from PTs, expressed rat Myo1b-GFP colocalized in patched microvilli with expressed mouse V5-tagged SIT1 (SIT1-V5), which mediates neutral amino acid transport in OK cells. Lentivirus-mediated delivery of opossum Myo1b-specific shRNA resulted in knockdown (kd) of Myo1b expression, less SIT1-V5 at the APM as determined by localization studies, and a decrease in neutral AAT as determined by radioactive uptake assays. Myo1b kd had no effect on Pi transport or noticeable change in microvilli structure as determined by rhodamine phalloidin staining. The studies are the first to define a physiological role for Myo1b, that of regulating renal AAT by modulating the association of AATers with the APM.

Role of collectrin, an ACE2 homologue, in blood pressure homeostasis

Collectrin (Tmem27) is a transmembrane glycoprotein that is highly expressed in the kidney and vascular endothelium. It is a homologue of the angiotensin-converting enzyme 2 (ACE2) but harbors no catalytic domain. In the extravascular tissues of the kidney, collectrin is localized to the proximal tubule and collecting duct. Collectrin-deficient mice are featured with hypertension and exaggerated salt sensitivity. These phenotypes are associated with impaired uptake of the nitric oxide precursor L-arginine and the expression of its amino acid transporters, CAT-1 and y(+)LAT1, in endothelial cells. In addition, collectrin-deficient mice display decreased dimerization of nitric oxide synthase and decreased nitric oxide synthesis, but enhanced superoxide generation, suggesting that deletion of collectrin leads to a state of nitric oxide synthase uncoupling. These findings suggest that collectrin plays a protective role against hypertension. The collectrin knockout mouse represents a unique model for hypertension research. Furthermore, collectrin may serve as a novel therapeutic target in the treatment of hypertension.

The ACE2/Ang-(1-7)/Mas Axis Regulates the Development of Pancreatic Endocrine Cells in Mouse Embryos

Angiotensin-converting enzyme 2 (ACE2), its product Angiotensin-(1-7) [Ang-(1-7)], and Ang-(1-7) receptor Mas, have been shown to regulate organogenesis during embryonic development in various species. However, it is not known whether a local ACE2/Ang-(1-7)/Mas axis is present in the fetal pancreas. It is hypothesized that there is a local ACE2/Ang-(1-7)/Mas axis in the embryonic pancreas in mice that is involved in regulating islet cell development. To address this issue, the endogenous expression profile of axis constituents in embryonic mouse pancreata was examined. Involvement of the ACE2 axis in the regulation of pancreatic development was also examined. The present experiments showed in an in vivo animal model that endogenous expression levels of ACE2 and the Mas receptor were upregulated in mouse pancreata in late embryogenesis, peaking on embryonic day E16.5, when it reached 3 folds compared to that seen at E12.5. Consistently, endogenous expression of Ang-(1-7) also peaked at E16.5. Treatment with the ACE2 inhibitor DX600 did not alter islet development. However, prenatal treatment with A779, a Mas receptor antagonist, reduced the β-cell to α-cell ratio in neonatal islets, impaired islet insulin secretory function, and impaired the pups' glucose tolerance. In ex vivo pancreas explant cultures, A779 again decreased the β-cell to α-cell ratio, apparently through its effects on β-cell proliferation (reduced proliferation shown with Ki67 staining), and also decreased Insulin and Ngn3 mRNA expression. Furthermore, treatment of explant cultures with Ang-(1-7) increased mRNA levels of Insulin and pancreatic progenitor marker Ngn3, as well as Nox4, the ROS generation enzyme; these stimulatory effects were attenuated by co-treatment with A779, suggesting that Ang-(1-7), via Mas receptor signaling, may promote differentiation of pancreatic progenitors into insulin-producing cells via modulation of reactive oxygen species. These data together suggest that a Mas receptor-mediated mechanism may stimulate pancreatic cell development.

Classical Renin-Angiotensin system in kidney physiology

The renin-angiotensin system has powerful effects in control of the blood pressure and sodium homeostasis. These actions are coordinated through integrated actions in the kidney, cardiovascular system and the central nervous system. Along with its impact on blood pressure, the renin-angiotensin system also influences a range of processes from inflammation and immune responses to longevity. Here, we review the actions of the "classical" renin-angiotensin system, whereby the substrate protein angiotensinogen is processed in a two-step reaction by renin and angiotensin converting enzyme, resulting in the sequential generation of angiotensin I and angiotensin II, the major biologically active renin-angiotensin system peptide, which exerts its actions via type 1 and type 2 angiotensin receptors. In recent years, several new enzymes, peptides, and receptors related to the renin-angiotensin system have been identified, manifesting a complexity that was previously unappreciated. While the functions of these alternative pathways will be reviewed elsewhere in this journal, our focus here is on the physiological role of components of the "classical" renin-angiotensin system, with an emphasis on new developments and modern concepts.

Roles of HNF1α and HNF4α in pancreatic β-cells: lessons from a monogenic form of diabetes (MODY)

Mutations in the genes encoding hepatocyte nuclear factor (HNF)1α and HNF4α cause a monogenic form of diabetes mellitus known as maturity-onset diabetes of the young (MODY). The primary cause of MODY is an impairment of glucose-stimulated insulin secretion by pancreatic β-cells, indicating the important roles of HNF1α and HNF4α in β-cells. Large-scale genetic studies have clarified that the common variants of HNF1α and HNF4α genes are also associated with type 2 diabetes, suggesting that they are involved in the pathogenesis of both diseases. Recent experimental studies revealed that HNF1α controls both β-cell function and growth by regulating target genes such as glucose transporter 2, pyruvate kinase, collectrin, hepatocyte growth factor activator, and HNF4α. In contrast, HNF4α mainly regulates the function of β-cells. Although direct target genes of HNF4α in β-cells are largely unknown, we recently identified Anks4b as a novel target of HNF4α that regulates β-cell susceptibility to endoplasmic reticulum stress. Studies of MODY have led to a better understanding of the molecular mechanism of glucose-stimulated insulin secretion by pancreatic β-cells.

Generation of outbred Ace2 knockout mice by RNA transfection of TALENs displaying colitis reminiscent pathophysiology and inflammation

The angiotensin I converting enzyme 2 (ACE2) is a key factor in the maintenance of intestinal homeostasis. Dysregulation of homeostasis can lead to inflammation of the colon (colitis), which can cause life-threatening enfeeblement or even cancer. Animal models are valuable surrogates in deciphering the pathology behind such human conditions and for screening of putative therapeutic targets or treatment paradigms. However, development of disease models can be time-consuming and technical demanding, which might hamper their application-value. In this study, we genetically disrupted the mouse Ace2 gene by direct injection of in vitro transcribed mRNA coding for transcription activator-like effector nucleases (TALENs) into the cytoplasm of outbred Kunming mouse zygotes. Consequently, somatic mutations were induced with an efficiency of 57 %, of which 39 % were frameshift mutations. Moreover, all modifications were stably transferred during germline transmission. In Ace2-knockout male mice (Ace2^−/y), we observed severe chemical induced colitis, characterized by considerable weight loss, diarrhea and a shortened colon length. Histologically, Ace2 mutations resulted in the infiltration of leukocytes and the overt damage of the intestinal mucosal barrier. In addition, we detected an increased expression of inflammatory cytokines in the colon tissue of Ace2^−/y mice. Collectively, the data indicate that high targeting efficiency and heritability can be achieved in an outbred mouse model by zygote injection of TALEN mRNA. Furthermore, the generated Ace2^−/y mice display phenotypic traits reminiscent of colitis and we anticipate that such mice can be of value in studies of the intestinal microbiome or fecal transplantation.

Function, therapeutic potential and cell biology of BACE proteases: current status and future prospects

The β-site APP cleaving enzymes 1 and 2 (BACE1 and BACE2) were initially identified as transmembrane aspartyl proteases cleaving the amyloid precursor protein (APP). BACE1 is a major drug target for Alzheimer's disease because BACE1-mediated cleavage of APP is the first step in the generation of the pathogenic amyloid-β peptides. BACE1, which is highly expressed in the nervous system, is also required for myelination by cleaving neuregulin 1. Several recent proteomic and in vivo studies using BACE1- and BACE2-deficient mice demonstrate a much wider range of physiological substrates and functions for both proteases within and outside of the nervous system. For BACE1 this includes axon guidance, neurogenesis, muscle spindle formation, and neuronal network functions, whereas BACE2 was shown to be involved in pigmentation and pancreatic β-cell function. This review highlights the recent progress in understanding cell biology, substrates, and functions of BACE proteases and discusses the therapeutic options and potential mechanism-based liabilities, in particular for BACE inhibitors in Alzheimer's disease. The protease BACE1 is a major drug target in Alzheimer disease. Together with its homolog BACE2, both proteases have an increasing number of functions within and outside of the nervous system. This review highlights recent progress in understanding cell biology, substrates, and functions of BACE proteases and discusses the therapeutic options and potential mechanism-based liabilities, in particular for BACE inhibitors in Alzheimer disease.