ACE2: Entry Receptor for SARS-CoV-2

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ACE2: Entry Receptor for SARS-CoV-2 Mar 11, 2020 18:41:28 GMT

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Post by Admin on Mar 11, 2020 18:41:28 GMT

A viral entryway
To infect a human host, viruses must be able to gain entry into individual human cells. They use these cells' machinery to produce copies of themselves, which then spill out and spread to new cells.

On Feb. 19 in the journal Science, a research team led by scientists at the University of Texas at Austin described the tiny molecular key on SARS-CoV-2 that gives the virus entry into the cell. This key is called a spike protein, or S-protein. Last week, Zhou and his team described the rest of the puzzle: the structure of the ACE2 receptor protein (which is on the surfaces of respiratory cells) and how it and the spike protein interact. The researchers published their findings in the journal Science on March 4.

"If we think of the human body as a house and 2019-nCoV [another name for SARS-CoV-2] as a robber, then ACE2 would be the doorknob of the house's door. Once the S-protein grabs it, the virus can enter the house," Liang Tao, a researcher at Westlake University who was not involved in the new study, said in a statement.

Zhou and his team used a tool called cryo electron microscopy, which employs deeply frozen samples and electron beams to image the tiniest structures of biological molecules. The researchers found that the molecular bond between SARS-CoV-2's spike protein and ACE2 looks fairly similar to the binding pattern of the coronavirus that caused the outbreak of SARS in 2003. There are some differences, however, in the precise amino acids used to bind SARS-CoV-2 to that ACE2 receptor compared with the virus that causes SARS (severe acute respiratory syndrome), the researchers said.

"While some might consider the differences subtle," Gallagher said, "they might be meaningful with respect to the strength with which each of those viruses stick."

That "stickiness" could affect how easily a virus transmits from one person to another. If any given viral particle is more likely to enter a cell once it enters the human body, transmission of disease is more likely.

There are other coronaviruses that circulate regularly, causing upper respiratory infections that most people think of as the common cold. Those coronaviruses don't interact with the ACE2 receptor, Gallagher said, but rather, they get into the body using other receptors on human cells.

Coronavirus structure implications
The structure of SARS-CoV-2's "key" and the body's "lock" could theoretically provide a target for antiviral drugs that would stop the new coronavirus from getting into new cells. Most antiviral drugs already on the market focus on halting viral replication within the cell, so a drug that targeted viral entry would be new territory, Gallagher said.

"There is no effective clinical drug that will block that interaction that I know of" that's already in use, he said.

The viral spike protein is also a promising target for vaccines, because it's the part of the virus that interacts with its environment and so could be easily recognized by the immune system, Gallagher said.

Even so, developing either drugs or a vaccine will be a challenging task. Treatments and vaccines not only have to prove effective against the virus, but must also be safe for people, Gallagher said. U.S. Centers for Disease Control and Prevention officials have said that the earliest a coronavirus vaccine could be available is in a year to a year and a half.

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ACE2: Entry Receptor for SARS-CoV-2 Apr 1, 2020 21:16:25 GMT

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Post by Admin on Apr 1, 2020 21:16:25 GMT

Structural basis for the recognition of SARS-CoV-2 by full-length human ACE2
Renhong Yan1,2, Yuanyuan Zhang1,2,*, Yaning Li3,*, Lu Xia1,2, Yingying Guo1,2, Qiang Zhou1,2,†
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Science 27 Mar 2020:
Vol. 367, Issue 6485, pp. 1444-1448
DOI: 10.1126/science.abb2762

How SARS-CoV-2 binds to human cells
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

Abstract
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.

Severe acute respiratory syndrome–coronavirus 2 (SARS-CoV-2) is a positive-strand RNA virus that causes severe respiratory syndrome in humans. The resulting outbreak of coronavirus disease 2019 (COVID-19) has emerged as a severe epidemic, claiming more than 2000 lives worldwide between December 2019 and February 2020 (1, 2). The genome of SARS-CoV-2 shares about 80% identity with that of SARS-CoV and is about 96% identical to the bat coronavirus BatCoV RaTG13 (2).

In the case of SARS-CoV, the spike glycoprotein (S protein) on the virion surface mediates receptor recognition and membrane fusion (3, 4). During viral infection, the trimeric S protein is cleaved into S1 and S2 subunits and S1 subunits are released in the transition to the postfusion conformation (4–7). S1 contains the receptor binding domain (RBD), which directly binds to the peptidase domain (PD) of angiotensin-converting enzyme 2 (ACE2) (8), whereas S2 is responsible for membrane fusion. When S1 binds to the host receptor ACE2, another cleavage site on S2 is exposed and is cleaved by host proteases, a process that is critical for viral infection (5, 9, 10). The S protein of SARS-CoV-2 may also exploit ACE2 for host infection (2, 11–13). A recent publication reported the structure of the S protein of SARS-CoV-2 and showed that the ectodomain of the SARS-CoV-2 S protein binds to the PD of ACE2 with a dissociation constant (Kd) of ~15 nM (14).

Although ACE2 is hijacked by some coronaviruses, its primary physiological role is in the maturation of angiotensin (Ang), a peptide hormone that controls vasoconstriction and blood pressure. ACE2 is a type I membrane protein expressed in lungs, heart, kidneys, and intestine (15–17). Decreased expression of ACE2 is associated with cardiovascular diseases (18–20). Full-length ACE2 consists of an N-terminal PD and a C-terminal collectrin-like domain (CLD) that ends with a single transmembrane helix and a ~40-residue intracellular segment (15, 21). The PD of ACE2 cleaves Ang I to produce Ang-(1-9), which is then processed by other enzymes to become Ang-(1-7). ACE2 can also directly process Ang II to give Ang-(1-7) (15, 22).

Structures of the claw-like ACE2-PD alone and in complex with the RBD or the S protein of SARS-CoV have revealed the molecular details of the interaction between the RBD of the S protein and PD of ACE2 (7, 8, 23, 24). Structural information on ACE2 is limited to the PD domain. The single transmembrane (TM) helix of ACE2 makes it challenging to determine the structure of the full-length protein.

ACE2 also functions as the chaperone for membrane trafficking of the amino acid transporter B0AT1, also known as SLC6A19 (25), which mediates uptake of neutral amino acids into intestinal cells in a sodium-dependent manner. Mutations in B0AT1 may cause Hartnup disorder, an inherited disease with symptoms such as pellagra, cerebellar ataxia, and psychosis (26–28). Structures have been determined for the SLC6 family members dDAT (Drosophila dopamine transporter) and human SERT (serotonin transporter, SLC6A4) (29, 30). It is unclear how ACE2 interacts with B0AT1. The membrane trafficking mechanism for ACE2 and B0AT1 is similar to that of the LAT1-4F2hc complex, a large neutral–amino acid transporter complex that requires 4F2hc for its plasma membrane localization (31). Our structure of LAT1-4F2hc shows that the cargo LAT1 and chaperone 4F2hc interact through both extracellular and transmembrane domains (32). We reasoned that the structure of full-length ACE2 may be revealed in the presence of B0AT1.

Here, we report cryo–electron microscopy (cryo-EM) structures of the full-length human ACE2-B0AT1 complex at an overall resolution of 2.9 Å and a complex between the RBD of SARS-CoV-2 and the ACE2-B0AT1 complex, also with an overall resolution of 2.9 Å and with 3.5-Å local resolution at the ACE2-RBD interface. The ACE2-B0AT1 complex exists as a dimer of heterodimers. Structural alignment of the RBD-ACE2-B0AT1 ternary complex with the S protein of SARS-CoV-2 suggests that two S protein trimers can simultaneously bind to an ACE2 homodimer.

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ACE2: Entry Receptor for SARS-CoV-2 Apr 29, 2020 22:23:43 GMT

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Post by Admin on Apr 29, 2020 22:23:43 GMT

In December 2019, a distinctive coronavirus (CoV) was determined to be responsible for an outbreak of potentially fatal atypical pneumonia, ultimately defined as coronavirus disease 19 (COVID-19), in Wuhan, Hubei province, China. This novel CoV, termed severe acute respiratory syndrome (SARS)-CoV-2, was found to be similar to the CoV that was responsible for the SARS pandemic that occurred in 2002.

]It’s hard to predict what will pop out from these gene hunts, some researchers say. But there are obvious suspects, such as the gene coding for the cell surface protein angiotensin-converting enzyme 2 (ACE2), which the coronavirus uses to enter airway cells. Variations in the ACE2 gene that alter the receptor could make it easier or harder for the virus to get into cells, says immunologist Philip Murphy of the National Institute of Allergy and Infectious Diseases, whose lab identified a relatively common mutation in another human cell surface protein, CCR5, that makes some people highly resistant to HIV.

In addition to genetic variants of the ACE2 receptor, scientists want to see whether differences in the human leukocyte antigen genes, which influence the immune system’s response to viruses and bacteria, affect disease severity. And some investigators want to follow up a finding, which a Chinese team reported in a preprint: that people with type O blood may be protected from the virus. “We’re trying to figure out if those findings are robust,” says Stanford University human geneticist Manuel Rivas, who is contributing to Ganna’s initiative.

What Is Coronavirus?
CoVs are a large family of enveloped, positive-sense, single-stranded RNA viruses that infect a broad range of vertebrates. They are extensive in bats but can be found in many other birds and mammals including humans. CoVs can cause a variety of diseases such as enteritis in pigs and cows and upper respiratory disease in chickens.1 In humans, CoVs tend to cause mild to moderate upper respiratory tract infections such as the common cold.2,3 However, in the past couple of decades, there have been outbreaks of severe, and sometimes fatal, respiratory illnesses that were later found to be caused by novel, human pathogenic CoVs. These CoV strains, which were determined to be phylogenetically distinct from the common human CoVs, had originated in bats and were transmitted to humans, typically through an intermediate host.1,4,5 These strains exhibited stronger virulence and quickly passed from human to human. While infection with these CoVs typically produced mild symptoms, for certain individuals, responses were more severe. In extreme cases, death occurred due to gradual respiratory failure as the result of alveolar damage.3,4,6

Comparing the SARS and COVID-19 Pandemics
The SARS pandemic that occurred in 2002 originated in the Guangdong Province in southern China. According to the World Health Organization (WHO), the CoV responsible for this disease, SARS-CoV, spread rapidly through 29 countries in Southeast Asia where it resulted in 8096 confirmed cases of SARS, with 774 of these individuals dying.7,8 Today’s pandemic has surpassed these numbers. The WHO has estimated that to date, over 110,000 individuals in over 100 countries have been diagnosed with COVID-19, with over 4,000 of these individuals dying.9 The rapid spread of this respiratory illness has resulted in a coordinated international effort to quickly characterize the etiology agent in order to develop potential vaccines and/or therapeutic agents that specifically target the virus or host cell components necessary for viral replication.

Identification and Characterization of SARS-CoV-2
Identification and sequencing of the virus responsible for COVID-19 (view SARS-CoV-2 protein sequence) determined that it was a novel CoV that shared 88% sequence identity with two bat-derived SARS-like CoV, suggesting it had originated in bats.10 Additionally, it was shown that this CoV, which was termed 2019-nCoV or SARS-CoV-2, shared 79.5% sequence identity with SARS-CoV.5,10 The coronaviral genome encodes four major structural proteins: the spike (S) protein, nucleocapsid (N) protein, membrane (M) protein, and the envelope (E) protein.6 The S protein is responsible for facilitating entry of the CoV into the target cell. It is composed of a short intracellular tail, a transmembrane anchor, and a large ectodomain that consists of a receptor binding S1 subunit and a membrane-fusing S2 subunit.11 Sequence analysis of the SARS-CoV-2 S protein genome showed that it was only 75% identical with the SARS-CoV S protein.5,10 However, analysis of the receptor binding motif (RBM) in the S protein showed that most of the amino acid residues essential for receptor binding were conserved between SARS-CoV and SARS-CoV-2, suggesting that the 2 CoV strains use the same host receptor for cell entry.12 The entry receptor utilized by SARS-CoV is Angiotensin-Converting Enzyme 2 (ACE-2).13

ACE-2
ACE-2 is a type I transmembrane metallocarboxypeptidase with homology to ACE, an enzyme long-known to be a key player in the Renin-Angiotensin system (RAS) and a target for the treatment of hypertension.14 It is mainly expressed in vascular endothelial cells, the renal tubular epithelium, and in Leydig cells in the testes.15,16 PCR analysis revealed that ACE-2 is also expressed in the lung, kidney, and gastrointestinal tract, tissues shown to harbor SARS-CoV.17-19 The major substrate for ACE-2 is Angiotensin II.20 ACE-2 degrades Angiotensin II to generate Angiotensin 1-7, thereby, negatively regulating RAS.15,20 ACE-2 has also been shown to exhibit a protective function in the cardiovascular system and other organs.15

ACE-2 is an Entry Receptor for SARS-CoV-2
Based on the sequence similarities of the RBM between SARS-CoV-2 and SARS-CoV, several independent research groups investigated if SARS-CoV-2 also utilizes ACE-2 as a cellular entry receptor. Zhou et al. showed that SARS-CoV-2 could use ACE-2 from humans, Chinese horseshoe bats, civet cats, and pigs to gain entry into ACE-2-expressing HeLa cells.5 Hoffmann et al. reported similar findings for human and bat ACE-2.21 Additionally, Hoffmann et al. showed that treating Vero-E6 cells, a monkey kidney cell line known to permit SARS-CoV replication, with an Anti-ACE-2 Antibody (R&D Systems, Catalog # AF933) blocked entry of VSV pseudotypes expressing the SARS-CoV-2 S protein.21

Inhibiting TMPRSS2 Activity Blocks SARS-CoV-2 Entry
For SARS-CoV entry into a host cell, its S protein needs to be cleaved by cellular proteases at 2 sites, termed S protein priming, so the viral and cellular membranes can fuse.22 Specifically, S protein priming by the serine protease TMPRSS2 is crucial for SARS-CoV infection of target cells and spread throughout the host.23,24 Hoffmann et al. investigated if SARS-CoV-2 entry is also dependent on S protein priming by TMPRSS2. Treatment of the Calu-3 human lung cell line with the serine protease inhibitor camostat mesylate partially blocked entry of VSV pseudotypes expressing the SARS-CoV-2 S protein.21 Similar effects of camostat mesylate treatment were seen with primary human lung cells and with Calu-3 cells incubated with authentic SARS-CoV-2.21

Avenues for COVID-19 Therapies
These new findings could greatly impact the development of effective therapies for COVID-19. For instance, anti-ACE-2 antibodies could be used to block SARS-CoV-2 binding to the receptor. Additionally, TMPRSS2 inhibitors could be used to prevent SARS-CoV-2 entry into host cells. Camostat has been used to treat chronic pancreatitis in Japan and is currently undergoing Phase 1/2 trial testing in the United States.26 If deemed safe, camostat could be a potential treatment option of CoV infections.27 It is also possible that antibodies developed during SARS-CoV infection could help prevent or treat COVID-19. Hoffmann et al. showed that sera from recovering SARS patients reduced SARS-CoV-2 S protein-driven entry into Vero-E6 cells.21 However, future studies are needed to determine whether any of these options are effective in disrupting the interaction between virus and receptor in vivo.

References
1.Fehr, A.R. and S. Perlman (2015) Methods Mol. Biol. 1282:1.
2.Centers for Disease Control and Prevention (n.d.) Common Human Coronaviruses. www.cdc.gov/coronavirus/general-information.html.
3.Yang, Y. et al. (2020) J. Autoimmun. [Epub ahead of print].
4.Gu, J. and C. Korteweg (2007) Am. J. Pathol. 170:1136.
5.Zhou, P. et al. (2020) Nature [Epub ahead of print].
6.Schoeman, D. and B.C. Fielding (2019) Virol. J. 16:69.
7.de Wit, E. et al. (2016) Nat. Rev. Microbiol. 14:523.
8.WHO (2003) Summary of Probable SARS Cases with Onset of Illness from 1 November 2002 to 31 July 2003.
9.WHO (2020) Coronavirus Disease 2019 (COVID-10) Situation Report – 50.
10.Lu, R. et al. (2020) Lancet. 395:565.
11.Li, F. (2016) Annu. Rev. Virol. 3:237.
12.Wan, Y. et al. (2020) J. Virol. [Epub ahead of print].
13.Li, W. et al. (2003) Nature 426:450.
14.Riordan, J.F. (2003) Genome Bio. 4:225.
15.Kuba, K. et al. (2010) Pharmacol. Ther. 128:119.
16.Jinag, F. et al. (2014) Nat. Rev. Cardiol. 11:413.
17.Ksiazek, T.G. et al. (2003) N. Engl. J. Med. 348:1953.
18.Harmer, D. et al. (2002) FEBS Lett. 532:107.
19.Leung, W.K. et al. (2003) Gastroenterology 125:1011.
20.Tikellis, C. and M.C. Thomas (2012) Int. J. Pept. 2012:256294.
21.Hoffmann, M. et al. (2020) Cell [Epub ahead of print].
22.Belouzard, S. et al. (2009) Proc. Natl. Acad. Sci. U.S.A. 106:5871.
23.Matsuyama, S. et al. (2010) J. Virol. 84:12658.
24.Iwata-Yoshikawa, N. et al. (2019) J. Virol. 93:e01815.
25.Huang, L. et al. (2003) J. Biol. Chem. 278:15532.
26.Ramsey, M.L. et al. (2019) Trials 20:501.
27.Zhou, Y. et al. (2015) Antiviral Res. 116:76.

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ACE2: Entry Receptor for SARS-CoV-2 Apr 30, 2020 5:54:09 GMT

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Post by Admin on Apr 30, 2020 5:54:09 GMT

Published: 24 February 2020
Comparative genetic analysis of the novel coronavirus (2019-nCoV/SARS-CoV-2) receptor ACE2 in different populations
Yanan Cao, Lin Li, Zhimin Feng, Shengqing Wan, Peide Huang, Xiaohui Sun, Fang Wen, Xuanlin Huang, Guang Ning & Weiqing Wang

The ACE2 gene encodes the angiotensin-converting enzyme-2, which has been proved to be the receptor for both the SARS-coronavirus (SARS-CoV) and the human respiratory coronavirus NL63. Recent studies and analyses indicate that ACE2 could be the host receptor for the novel coronavirus 2019-nCoV/SARS-CoV-21,2. Previous studies demonstrated the positive correlation of ACE2 expression and the infection of SARS-CoV in vitro3,4. A number of ACE2 variants could reduce the association between ACE2 and S-protein in SARS-CoV or NL635. Therefore, the expression level and expression pattern of human ACE2 in different tissues might be critical for the susceptibility, symptoms, and outcome of 2019-nCoV/SARS-CoV-2 infection. A recent single-cell RNA-sequencing (RNA-seq) analysis indicated that Asian males may have higher expression of ACE26. Currently, the clinical reports of 2019-nCoV/SARS-CoV-2 infection from non-Asian populations for comparison are very limited. A study from Munich reported four German cases, all of which showed mild clinical symptoms without severe illness7. However, the genetic basis of ACE2 expression and function in different populations is still largely unknown. Therefore, genetic analysis of expression quantitative trait loci (eQTLs)8 and potential functional coding variants in ACE2 among populations are required for further epidemiological investigations of 2019-nCoV/SARS-CoV-2 spreading in East Asian (EAS) and other populations.

To systematically investigate the candidate functional coding variants in ACE2 and the allele frequency (AF) differences between populations, we analyzed all the 1700 variants (Supplementary Table S1) in ACE2 gene region from the ChinaMAP (China Metabolic Analytics Project, under reviewing) and 1KGP (1000 Genomes Project)9 databases. The AFs of 62 variants located in the coding regions of ACE2 in ChinaMAP, 1KGP, and other large-scale genome databases were summarized (Supplementary Table S2). All of the 32 variants potentially affecting the amino acid sequence of ACE2 in databases were shown (Fig. 1a). Previous study showed that the residues near lysine 31, and tyrosine 41, 82–84, and 353–357 in human ACE2 were important for the binding of S-protein in coronavirus5. The mutations in these residues were not found in different populations in our study. Only a singleton truncating variant of ACE2 (Gln300X) was identified in the ChinaMAP (Fig. 1a). These data suggested that there was a lack of natural resistant mutations for coronavirus S-protein binding in populations. The effects of low-frequency missense variants in populations for S-protein binding could be further investigated. The distributions of seven hotspot variants (Lys26Arg, Ile468Val, Ala627Val, Asn638Ser, Ser692Pro, Asn720Asp, and Leu731Ile/Leu731Phe) in different populations were shown (Fig. 1b). Six low-frequency loci (rs200180615, rs140473595, rs199951323, rs147311723, rs149039346, and rs73635825) were found to be specific in 1KGP database, the AFs of which were also low in the gnomAD and TopMed10 database. Only two of these six variants (rs200180615 and rs140473595) could be found in CHB (Han Chinese in Beijing) population with the AF < 0.01. Interestingly, the SNP rs2285666 with the highest AF in the 62 variants exhibited much higher AF in the ChinaMAP (0.556) and CHS (Han Chinese South, 0.557) populations compared to others (AMR, Ad Mixed American, 0.336; AFR, African, 0.2114; EUR, European, 0.235). In addition, the homozygous mutation rate in males (0.550) was much higher than females (0.310) in the Chinese population (Supplementary Table S2). Taken together, the differences in AFs of ACE2 coding variants among different populations suggested that the diverse genetic basis might affect ACE2 functions among populations.

Fig. 1: The coding-region variants and eQTL variants for ACE2 in East Asian and other populations.

To analyze the distribution of eQTLs for ACE2, we used the Genotype Tissue Expression (GTEx) database (https://www.gtexportal.org/home/datasets). We found 15 unique eQTL variants (14 SNPs and 1 INDELs) for ACE2 with q value ≤ 0.05 in 20 tissues from the GTEx database (rs112171234, rs12010448, rs143695310, rs1996225, rs200781818, rs2158082, rs4060, rs4646127, rs4830974, rs4830983, rs5936011, rs5936029, rs6629110, rs6632704, and rs75979613). The AFs of the 15 eQTL variants were compared among different populations. Notably, our results showed most of the 15 eQTL variants had much higher AFs in the ChinaMAP dataset and EAS populations compared to European populations (Fig. 1c and Supplementary Table S3). The AFs of the top 6 common variants (rs4646127, rs2158082, rs5936011, rs6629110, rs4830983, and rs5936029) were higher than 95% in EAS populations, whereas the AFs of these variants in European populations were much lower (52%–65%). All of the 11 common variants (AF > 0.05) and 1 rare variant (rs143695310) in the 15 eQTLs are associated with high expression of ACE2 in tissues (Supplementary Table S3). For instance, the eQTL variant rs4646127 (log allelic fold change = 0.314), which locates in the intron of ACE2 gene, has the highest AFs in both of the ChinaMAP (0.997) and EAS (0.994) populations. Comparatively, the AFs of rs4646127 in EUR (0.651) and AMR (0.754) populations are much lower. These findings suggested the genotypes of ACE2 gene polymorphism may be associated higher expression levels of ACE2 in EAS population.

Recent reports of the ACE2 expression analysis in lung tissues from Asian and Caucasian populations are still controversial. The single-cell RNA-seq analysis reported that the Asian donor had much higher ACE2 expression cell ratio than white and African-American donors6. In contrast, the ACE2 expression analysis using the RNA-seq and microarray datasets from control lung tissues indicated there were no significant differences between Asian and Caucasian, or male and female11. The ACE2-expressing cells are a very small part of cells in lung tissues6. The sample size and the purity of ACE2-positive cells in the selected samples would influence the conclusions. Our analysis showed the differences in distribution and AFs of eQTLs for ACE2 in different populations, indicating the diversity of ACE2 expression pattern in populations (Supplementary Table S3). Large-scale and multiple tissue-level analysis of single-cell RNA-seq would be more accurate for the expression analysis of ACE2 in different populations. In addition, our data showed the moderate difference in AFs of eQTLs between South Asian and EAS, which suggests the potential difference of ACE2 expression in different populations and ethnics in Asia (Fig. 1c).

In summary, we systematically analyzed coding-region variants in ACE2 and the eQTL variants, which may affect the expression of ACE2 using the GTEx database to compare the genomic characteristics of ACE2 among different populations. Our findings indicated that no direct evidence was identified genetically supporting the existence of coronavirus S-protein binding-resistant ACE2 mutants in different populations (Fig. 1a). The data of variant distribution and AFs may contribute to the further investigations of ACE2, including its roles in acute lung injury and lung function12. The East Asian populations have much higher AFs in the eQTL variants associated with higher ACE2 expression in tissues (Fig. 1c), which may suggest different susceptibility or response to 2019-nCoV/SARS-CoV-2 from different populations under the similar conditions.

Cao, Y., Li, L., Feng, Z. et al. Comparative genetic analysis of the novel coronavirus (2019-nCoV/SARS-CoV-2) receptor ACE2 in different populations. Cell Discov 6, 11 (2020). doi.org/10.1038/s41421-020-0147-1

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ACE2: Entry Receptor for SARS-CoV-2 May 1, 2020 2:49:57 GMT

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Interactions of coronaviruses with ACE2, angiotensin II, and RAS inhibitors—lessons from available evidence and insights into COVID-19

Hisashi Kai & Mamiko Kai

Abstract
The rapid spread of a novel coronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has led to an ongoing pandemic of coronavirus disease 2019 (COVID-19). Recently, angiotensin-converting enzyme 2 (ACE2) has been shown to be a functional receptor for SARS-CoV-2 to enter host target cells. Given that angiotensin receptor blockers (ARBs) and an ACE inhibitor (ACEI) upregulated ACE2 expression in animal studies, the concern might arise regarding whether ARBs and ACEIs would increase the morbidity and mortality of COVID-19. On the other hand, animal data suggested a potential protective effect of ARBs against COVID-19 pneumonia because an ARB prevented the aggravation of acute lung injury in mice infected with SARS-CoV, which is closely related to SARS-CoV-2. Importantly, however, there is no clinical or experimental evidence supporting that ARBs and ACEIs either augment the susceptibility to SARS-CoV-2 or aggravate the severity and outcomes of COVID-19 at present. Until further data are available, it is recommended that ARB and ACEI medications be continued for the treatment of patients with cardiovascular disease and hypertension, especially those at high risk, according to guideline-directed medical therapy based on the currently available evidence.

Introduction
A novel coronavirus, named severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), was discovered in December 2019 in Wuhan, China, and an ongoing pandemic of coronavirus disease 2019 (COVID-19) has been spreading around the world as of early April 2020. The clinical spectrum of COVID-19 ranges from asymptomatic upper respiratory infection to critically ill pneumonia associated with acute respiratory distress syndrome (ARDS) [1,2,3]. In initial reports from China, the prevalence of older age, hypertension, diabetes mellitus, and cardiovascular disease (CVD) was high in COVID-19 patients, and individuals with these comorbidities tended to have greater case fatality rates [3, 4]. In addition, it has been shown that angiotensin-converting enzyme 2 (ACE2) is a functional receptor for SARS-CoV-2 infection [5,6,7]. Given that experimental studies suggested that angiotensin receptor blockers (ARBs) and an ACE inhibitor (ACEI) could increase ACE2 expression in cardiovascular and renal systems [8,9,10,11,12,13,14,15,16,17,18,19,20], concerns may have been raised regarding whether ARBs and ACEIs would augment the infection of SARS-CoV-2 and the severity of COVID-19 in hypertension and CVD patients receiving these drugs [21]. In contrast, ARBs have potential benefits in the prevention and treatment of lung injury caused by COVID-19 [22]. These conflicting views appear to arise based on the results of experimental studies, especially those of severe acute respiratory syndrome coronavirus (SARS-CoV), because direct clinical data on COVID-19 are lacking at present. SARS-CoV caused the SARS epidemic in China in 2002–2003, and its virological characteristics are closely related to those of SARS-CoV-2 [23, 24]. Here, available investigations on the association of the renin–angiotensin system (RAS), particularly ACE2 and angiotensin II, with SARS-CoV-induced lung injury and the latest information on COVID-19 were reviewed as of early April 2020, which would provide insight into COVID-19 and the direction of future research on COVID-19.

ACE2 as a receptor for SARS-CoV and SARS-CoV-2
ACE2 belongs to the membrane-bound carboxydipeptidase family and is widely distributed in the human body, including the heart, kidney, small intestine, and, to a lesser extent, the lung. Lung ACE2 expression is concentrated mainly in type II alveolar cells and macrophages and modestly in bronchial and tracheal epithelial cells [25]. ACE2 degrades angiotensin II to generate angiotensin 1-7, which activates the mas oncogene receptor that negatively regulates a variety of angiotensin II actions mediated by angiotensin II type 1 receptor (AT1R) [26]. Therefore, it is thought that the ACE2/angiotensin 1-7/mas receptor axis has counteracting effects against the excessively activated ACE/angiotensin II/AT1R axis, as seen in hypertension, cardiac hypertrophy, heart failure, and other CVDs [26].

On the other hand, human ACE2 is an established functional receptor by which SARS-CoV enters host target cells (Fig. 1) [23, 24]. The transmembrane spike glycoprotein (S protein) of SARS-CoV binds to the cellular membrane ACE2; SARS-CoV then attaches to the target cells, followed by SARS-CoV-S protein priming by cellular surface proteases, such as transmembrane protease serine 2 (TMPRSS2), allowing the fusion of viral and cellular membranes and resulting in SARS-CoV entry and replication in the target cells [6]. Moreover, ACE2 knockout greatly reduces viral infection and replication in mice after experimental SARS-CoV infection [27]. Thus, it is suggested that the binding of the SARS-CoV-S protein to ACE2 is crucial for SARS-CoV infection.

Fig. 1
Possible scheme of the association of ACE2, angiotensin II, and AT1R and acute lung injury of SARS and COVID-19. Ang II, angiotensin II; ACE, angiotensin-converting enzyme; ACE2, angiotensin-converting enzyme 2; ACEI, angiotensin-converting enzyme inhibitor; AT1R, angiotensin II type-1 receptor; ARB, angiotensin II type-1 receptor blocker; SARS-CoV, severe acute respiratory syndrome coronavirus; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2; S-protein, spike-glycoprotein

Recently, it has been shown that the SARS-CoV-2-S protein shares nearly 80% amino acid identity with the SARS-CoV-S protein, and the binding affinity of the SARS-CoV-2-S protein to human ACE2 is similar to that of the SARS-CoV-S protein [5,6,7]. Anti-human ACE2 antibodies or antisera can inhibit SARS-CoV-2-S protein-mediated entry into cultured cells in vitro [5,6,7]. Accordingly, SARS-CoV-2 utilizes ACE2 for target cell entry as well. However, it is still not clear whether ACE2 is the sole receptor for SARS-CoV-2 infection because CD209L (a glycoprotein of C-type lectin also called L-SIGN) is identified as a possible secondary receptor for SARS-CoV in cultured Chinese hamster ovary cells [28].

Last Edit: May 1, 2020 2:50:28 GMT by Admin