Alternative splicing of ACE2 possibly generates variants that may limit the entry of SARS-CoV-2: a potential therapeutic approach using SSOs

SARS-CoV-2 mechanisms of cell tropism in various organs considering host factors

A critical step in the drug design for SARS-CoV-2 is to discover its molecular targets. This study comprehensively reviewed the molecular mechanisms of SARS-CoV-2, exploring host cell tropism and interaction targets crucial for cell entry. The findings revealed that beyond ACE2 as the primary entry receptor, alternative receptors, co-receptors, and several proteases such as TMPRSS2, Furin, Cathepsin L, and ADAM play critical roles in virus entry and subsequent pathogenesis. Additionally, SARS-CoV-2 displays tropism in various human organs due to its diverse receptors. This review delves into the intricate details of receptors, host proteases, and the involvement of each organ. Polymorphisms in the ACE2 receptor and mutations in the spike or its RBD region contribute to the emergence of variants like Alpha, Beta, Gamma, Delta, and Omicron, impacting the pathogenicity of SARS-CoV-2. The challenge posed by mutations raises questions about the effectiveness of existing vaccines and drugs, necessitating consideration for updates in their formulations. In the urgency of these critical situations, repurposed drugs such as Camostat Mesylate and Nafamostat Mesylate emerge as viable pharmaceutical options. Numerous drugs are involved in inhibiting receptors and host factors crucial for SARS-CoV-2 entry, with most discussed in this review. In conclusion, this study may provide valuable insights to inform decisions in therapeutic approaches.

An intricate rewiring of cancer metabolism via alternative splicing

All human genes undergo alternative splicing leading to the diversity of the proteins. However, in some cases, abnormal regulation of alternative splicing can result in diseases that trigger defects in metabolism, reduced apoptosis, increased proliferation, and progression in almost all tumor types. Metabolic dysregulations and immune dysfunctions are crucial factors in cancer. In this respect, alternative splicing in tumors could be a potential target for therapeutic cancer strategies. Dysregulation of alternative splicing during mRNA maturation promotes carcinogenesis and drug resistance in many cancer types. Alternative splicing (changing the target mRNA 3'UTR binding site) can result in a protein with altered drug affinity, ultimately leading to drug resistance.. Here, we will highlight the function of various alternative splicing factors, how it regulates the reprogramming of cancer cell metabolism, and their contribution to tumor initiation and proliferation. Also, we will discuss emerging therapeutics for treating tumors via abnormal alternative splicing. Finally, we will discuss the challenges associated with these therapeutic strategies for clinical applications.

Molecular mechanisms of human coronavirus NL63 infection and replication

Human coronavirus NL63 (HCoV-NL63) is spread globally, causing upper and lower respiratory tract infections mainly in young children. HCoV-NL63 shares a host receptor (ACE2) with severe acute respiratory syndrome coronavirus (SARS-CoV) and SARS-CoV-2 but, unlike them, HCoV-NL63 primarily develops into self-limiting mild to moderate respiratory disease. Although with different efficiency, both HCoV-NL63 and SARS-like CoVs infect ciliated respiratory cells using ACE2 as receptor for binding and cell entry. Working with SARS-like CoVs require access to BSL-3 facilities, while HCoV-NL63 research can be performed at BSL-2 laboratories. Thus, HCoV-NL63 could be used as a safer surrogate for comparative studies on receptor dynamics, infectivity and virus replication, disease mechanism, and potential therapeutic interventions against SARS-like CoVs. This prompted us to review the current knowledge on the infection mechanism and replication of HCoV-NL63. Specifically, after a brief overview on the taxonomy, genomic organization and virus structure, this review compiles the current HCoV-NL63-related research in virus entry and replication mechanism, including virus attachment, endocytosis, genome translation, and replication and transcription. Furthermore, we reviewed cumulative knowledge on the susceptibility of different cells to HCoV-NL63 infection in vitro, which is essential for successful virus isolation and propagation, and contribute to address different scientific questions from basic science to the development and assessment of diagnostic tools, and antiviral therapies. Finally, we discussed different antiviral strategies that have been explored to suppress replication of HCoV-NL63, and other related human coronaviruses, by either targeting the virus or enhancing host antiviral mechanisms.

Development of an efficient reproducible cell-cell transmission assay for rapid quantification of SARS-CoV-2 spike interaction with hACE2

Efficient quantitative assays for measurement of viral replication and infectivity are indispensable for future endeavors to develop prophylactic or therapeutic antiviral drugs or vaccines against SARS-CoV-2. We developed a SARS-CoV-2 cell-cell transmission assay that provides a rapid and quantitative readout to assess SARS-CoV-2 spike hACE2 interaction in the absence of pseudotyped particles or live virus. We established two well-behaved stable cell lines, which demonstrated a remarkable correlation with standard cell-free viral pseudotyping for inhibition by convalescent sera, small-molecule drugs, and murine anti-spike monoclonal antibodies. The assay is rapid, reliable, and highly reproducible, without a requirement for any specialized research reagents or laboratory equipment and should be easy to adapt for use in most investigative and clinical settings. It can be effectively used or modified for high-throughput screening for compounds and biologics that interfere with virus-cell binding and entry to complement other neutralization assays currently in use.

SARS-CoV-2: Receptor and Co-receptor Tropism Probability

The recent pandemic which arose from China, is caused by a pathogenic virus named "severe acute respiratory syndrome-related coronavirus-2 (SARS-CoV-2)". Its rapid global expansion has inflicted an extreme public health concern. The attachment of receptor-binding domains (RBD) of the spike proteins (S) to the host cell's membrane, with or without the help of other cellular components such as proteases and especially co-receptors, is required for the first stage of its pathogenesis. In addition to humans, angiotensin-converting enzyme 2 (ACE2) is found on a wide range of vertebrate host's cellular surface. SARS-CoV-2 has a broad spectrum of tropism; thus, it can infect a vast range of tissues, organs, and hosts; even though the surface amino acids of the spike protein conflict in the receptor-binding region. Due to the heterogeneous ACE2 distribution and the presence of different domains on the SARS-CoV-2 spike protein for binding, the virus entry into diverse host cell types may depend on the host cells' receptor presentation with or without co-receptors. This review investigates multiple current types of receptor and co-receptor tropisms, with other molecular factors alongside their respective mechanisms, which facilitate the binding and entry of SARS-CoV-2 into the cells, extending the severity of the coronavirus disease 2019 (COVID-19). Understanding the pathogenesis of COVID-19 from this perspective can effectively help prevent this disease and provide more potent treatment strategies, particularly in vulnerable people with various cellular-level susceptibilities.

Small Drugs, Huge Impact: The Extraordinary Impact of Antisense Oligonucleotides in Research and Drug Development

Antisense oligonucleotides (ASOs) are an increasingly represented class of drugs. These small sequences of nucleotides are designed to precisely target other oligonucleotides, usually RNA species, and are modified to protect them from degradation by nucleases. Their specificity is due to their sequence, so it is possible to target any RNA sequence that is already known. These molecules are very versatile and adaptable given that their sequence and chemistry can be custom manufactured. Based on the chemistry being used, their activity may significantly change and their effects on cell function and phenotypes can differ dramatically. While some will cause the target RNA to decay, others will only bind to the target and act as a steric blocker. Their incredible versatility is the key to manipulating several aspects of nucleic acid function as well as their process, and alter the transcriptome profile of a specific cell type or tissue. For example, they can be used to modify splicing or mask specific sites on a target. The entire design rather than just the sequence is essential to ensuring the specificity of the ASO to its target. Thus, it is vitally important to ensure that the complete process of drug design and testing is taken into account. ASOs' adaptability is a considerable advantage, and over the past decades has allowed multiple new drugs to be approved. This, in turn, has had a significant and positive impact on patient lives. Given current challenges presented by the COVID-19 pandemic, it is necessary to find new therapeutic strategies that would complement the vaccination efforts being used across the globe. ASOs may be a very powerful tool that can be used to target the virus RNA and provide a therapeutic paradigm. The proof of the efficacy of ASOs as an anti-viral agent is long-standing, yet no molecule currently has FDA approval. The emergence and widespread use of RNA vaccines during this health crisis might provide an ideal opportunity to develop the first anti-viral ASOs on the market. In this review, we describe the story of ASOs, the different characteristics of their chemistry, and how their characteristics translate into research and as a clinical tool.

COVID-19 in pregnancy: What we know from the first year of the pandemic

The COVID-19 pandemic has infected nearly 178 million people and claimed the lives of over 3.8 million in less than 15 months. This has prompted a flurry of research studies into the mechanisms and effects of SARS-CoV-2 viral infection in humans. However, studies examining the effects of COVID-19 in pregnant women, their placentae and their babies remain limited. Furthermore, reports of safety and efficacy of vaccines for SARS-CoV-2 in pregnancy are limited. This review concisely summarises the case studies and research on COVID-19 in pregnancy, to date. It also reviews the mechanism of infection with SARS-CoV-2, and its reliance and effects upon the renin-angiotensin-aldosterone system. Overall, the data suggest that infection during pregnancy can be dangerous at any time, but this risk to both the mother and fetus, as well as placental damage, increases during the third trimester. The possibility of vertical transmission, which is explored in this review, remains contentious. However, maternal infection with SARS-CoV-2 can increase risk of miscarriage, preterm birth and stillbirth, which is likely due to damage to the placenta.

Which ones, when and why should renin-angiotensin system inhibitors work against COVID-19?

The article describes the possible pathophysiological origin of COVID-19 and the crucial role of renin-angiotensin system (RAS), providing several “converging” evidence in support of this hypothesis. SARS-CoV-2 has been shown to initially upregulate ACE2 systemic activity (early phase), which can subsequently induce compensatory responses leading to upregulation of both arms of the RAS (late phase) and consequently to critical, advanced and untreatable stages of COVID-19 disease. The main and initial actors of the process are ACE2 and ADAM17 zinc-metalloproteases, which, initially triggered by SARS-CoV-2 spike proteins, work together in increasing circulating Ang 1–7 and Ang 1–9 peptides and downstream (Mas and Angiotensin type 2 receptors) pathways with anti-inflammatory, hypotensive and antithrombotic activities. During the late phase of severe COVID-19, compensatory secretion of renin and ACE enzymes are subsequently upregulated, leading to inflammation, hypertension and thrombosis, which further sustain ACE2 and ADAM17 upregulation. Based on this hypothesis, COVID-19-phase-specific inhibition of different RAS enzymes is proposed as a pharmacological strategy against COVID-19 and vaccine-induced adverse effects. The aim is to prevent the establishment of positive feedback-loops, which can sustain hyperactivity of both arms of the RAS independently of viral trigger and, in some cases, may lead to Long-COVID syndrome.

Identification of cell lines CL-14, CL-40 and CAL-51 as suitable models for SARS-CoV-2 infection studies

The SARS-CoV-2 pandemic is a major global threat that sparked global research efforts. Pre-clinical and biochemical SARS-CoV-2 studies firstly rely on cell culture experiments where the importance of choosing an appropriate cell culture model is often underestimated. We here present a bottom-up approach to identify suitable permissive cancer cell lines for drug screening and virus research. Human cancer cell lines were screened for the SARS-CoV-2 cellular entry factors ACE2 and TMPRSS2 based on RNA-seq data of the Cancer Cell Line Encyclopedia (CCLE). However, experimentally testing permissiveness towards SARS-CoV-2 infection, we found limited correlation between receptor expression and permissiveness. This underlines that permissiveness of cells towards viral infection is determined not only by the presence of entry receptors but is defined by the availability of cellular resources, intrinsic immunity, and apoptosis. Aside from established cell culture infection models CACO-2 and CALU-3, three highly permissive human cell lines, colon cancer cell lines CL-14 and CL-40 and the breast cancer cell line CAL-51 and several low permissive cell lines were identified. Cell lines were characterised in more detail offering a broader choice of non-overexpression in vitro infection models to the scientific community. For some cell lines a truncated ACE2 mRNA and missense variants in TMPRSS2 might hint at disturbed host susceptibility towards viral entry.

A map of the SARS-CoV-2 RNA structurome

SARS-CoV-2 has exploded throughout the human population. To facilitate efforts to gain insights into SARS-CoV-2 biology and to target the virus therapeutically, it is essential to have a roadmap of likely functional regions embedded in its RNA genome. In this report, we used a bioinformatics approach, ScanFold, to deduce the local RNA structural landscape of the SARS-CoV-2 genome with the highest likelihood of being functional. We recapitulate previously-known elements of RNA structure and provide a model for the folding of an essential frameshift signal. Our results find that SARS-CoV-2 is greatly enriched in unusually stable and likely evolutionarily ordered RNA structure, which provides a large reservoir of potential drug targets for RNA-binding small molecules. Results are enhanced via the re-analyses of publicly-available genome-wide biochemical structure probing datasets that are broadly in agreement with our models. Additionally, ScanFold was updated to incorporate experimental data as constraints in the analysis to facilitate comparisons between ScanFold and other RNA modelling approaches. Ultimately, ScanFold was able to identify eight highly structured/conserved motifs in SARS-CoV-2 that agree with experimental data, without explicitly using these data. All results are made available via a public database (the RNAStructuromeDB: https://structurome.bb.iastate.edu/sars-cov-2) and model comparisons are readily viewable at https://structurome.bb.iastate.edu/sars-cov-2-global-model-comparisons.

Rapid, reliable, and reproducible cell fusion assay to quantify SARS-Cov-2 spike interaction with hACE2

COVID-19 is a global crisis of unimagined dimensions. Currently, Remedesivir is only fully licensed FDA therapeutic. A major target of the vaccine effort is the SARS-CoV-2 spike-hACE2 interaction, and assessment of efficacy relies on time consuming neutralization assay. Here, we developed a cell fusion assay based upon spike-hACE2 interaction. The system was tested by transient co-transfection of 293T cells, which demonstrated good correlation with standard spike pseudotyping for inhibition by sera and biologics. Then established stable cell lines were very well behaved and gave even better correlation with pseudotyping results, after a short, overnight co-incubation. Results with the stable cell fusion assay also correlated well with those of a live virus assay. In summary we have established a rapid, reliable, and reproducible cell fusion assay that will serve to complement the other neutralization assays currently in use, is easy to implement in most laboratories, and may serve as the basis for high throughput screens to identify inhibitors of SARS-CoV-2 virus-cell binding and entry.

Alternative Splicing of Pre-mRNA in the Control of Immune Activity

The human immune response is a complex process that responds to numerous exogenous antigens in preventing infection by microorganisms, as well as to endogenous components in the surveillance of tumors and autoimmune diseases, and a great number of molecules are necessary to carry the functional complexity of immune activity. Alternative splicing of pre-mRNA plays an important role in immune cell development and regulation of immune activity through yielding diverse transcriptional isoforms to supplement the function of limited genes associated with the immune reaction. In addition, multiple factors have been identified as being involved in the control of alternative splicing at the cis, trans, or co-transcriptional level, and the aberrant splicing of RNA leads to the abnormal modulation of immune activity in infections, immune diseases, and tumors. In this review, we summarize the recent discoveries on the generation of immune-associated alternative splice variants, clinical disorders, and possible regulatory mechanisms. We also discuss the immune responses to the neoantigens produced by alternative splicing, and finally, we issue some alternative splicing and immunity correlated questions based on our knowledge.

The contrasting role of nasopharyngeal angiotensin converting enzyme 2 (ACE2) transcription in SARS-CoV-2 infection: A cross-sectional study of people tested for COVID-19 in British Columbia, Canada

Background

Angiotensin converting enzyme 2 (ACE2) protein serves as the host receptor for SARS-CoV-2, with a critical role in viral infection. We aim to understand population level variation of nasopharyngeal ACE2 transcription in people tested for COVID-19 and the relationship between ACE2 transcription and SARS-CoV-2 viral load, while adjusting for expression of: (i) the complementary protease, Transmembrane serine protease 2 (TMPRSS2), (ii) soluble ACE2, (iii) age, and (iv) biological sex. The ACE2 gene was targeted to measure expression of transmembrane and soluble transcripts.

Methods

A cross-sectional study of n = 424 “participants” aged 1–104 years referred for COVID-19 testing was performed in British Columbia, Canada. Patients who tested positive for COVID-19 were matched by age and biological sex to patients who tested negative. Viral load and host gene expression were assessed by quantitative reverse-transcriptase polymerase chain reaction. Bivariate analysis and multiple linear regression were performed to understand the role of nasopharyngeal ACE2 expression in SARS-CoV-2 infection.

Findings

Analysis showed no association between age and nasopharyngeal ACE2 transcription in those who tested negative for COVID-19 (P = 0•092). Mean relative transcription of transmembrane (P = 0•00012) and soluble (P<0•0001) ACE2 isoforms, as well as TMPRSS2 (P<0•0001) was higher in COVID-19-negative participants than COVID--19 positive ones, yielding a negative correlation between targeted host gene expression and positive COVID-19 diagnosis. In bivariate analysis of COVID-19-positive participants, transcription of transmembrane ACE2 positively correlated with SARS-CoV-2 viral RNA load (B = 0•49, R²=0•14, P<0•0001), transcription of soluble ACE2 negatively correlated (B= -0•85, R²= 0•26, P<0•0001), and no correlation was found with TMPRSS2 transcription (B= -0•042, R²=<0•10, P = 0•69). Multivariable analysis showed that the greatest viral RNA loads were observed in participants with high transmembrane ACE2 transcription (Β= 0•89, 95%CI: [0•59 to 1•18]), while transcription of the soluble isoform appears to protect against high viral RNA load in the upper respiratory tract (Β= -0•099, 95%CI: [-0•18 to -0•022]).

Interpretation

Nasopharyngeal ACE2 transcription plays a dual, contrasting role in SARS-CoV-2 infection of the upper respiratory tract. Transcription of the transmembrane ACE2 isoform positively correlates, while transcription of the soluble isoform negatively correlates with viral RNA load after adjusting for age, biological sex, and transcription of TMPRSS2.

Funding

This project (COV-55) was funded by Genome British Columbia as part of their COVID-19 rapid response initiative.

Potential drug targets of SARS-CoV-2: From genomics to therapeutics

The emergence of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) from China has become a global threat due to the continuous rise in cases of Coronavirus disease 2019 (COVID-19). The problem with COVID-19 therapeutics is due to complexity of the mechanism of the pathogenesis of this virus. In this review, an extensive analysis of genome architecture and mode of pathogenesis of SARS-CoV-2 with an emphasis on therapeutic approaches is performed. SARS-CoV-2 genome consists of a single, ~29.9 kb long RNA having significant sequence similarity to BAT-CoV, SARS-CoV and MERS-CoV genome. Two-third part of SARS-Cov-2 genome comprises of ORF (ORF1ab) resulting in the formation of 2 polyproteins, pp1a and pp1ab, later processed into 16 smaller non-structural proteins (NSPs). The four major structural proteins of SARS-CoV-2 are the spike surface glycoprotein (S), a small envelope (E), membrane (M), and nucleocapsid (N) proteins. S protein helps in receptor binding and membrane fusion and hence plays the most important role in the transmission of CoVs. Priming of S protein is done by serine 2 transmembrane protease and thus plays a key role in virus and host cell fusion. This review highlights the possible mechanism of action of SARS-CoV-2 to search for possible therapeutic options.

Human eggs, zygotes, and embryos express the receptor angiotensin 1-converting enzyme 2 and transmembrane serine protease 2 protein necessary for severe acute respiratory syndrome coronavirus 2 infection

OBJECTIVE

To study messenger ribonucleic acid (mRNA) and protein expressions of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) entry receptors (angiotensin 1-converting enzyme 2 [ACE2] and CD147) and proteases (transmembrane serine protease 2 [TMPRSS2] and cathepsin L [CTSL]) in human oocytes, embryos, and cumulus (CCs) and granulosa cells (GCs).

DESIGN

Research study.

SETTING

Clinical in vitro fertilization (IVF) treatment center.

PATIENTS

Patients undergoing IVF were treated at the Colorado Center for Reproductive Medicine.

INTERVENTIONS

Oocytes (germinal vesicle and metaphase II [MII]) and embryos (1-cell [1C] and blastocyst [BL]) were donated for research at the disposition by the patients undergoing IVF. Follicular cells (CC and GC) were collected from women undergoing egg retrieval after ovarian stimulation without an ovulatory trigger for in vitro maturation/IVF treatment cycles.

MAIN OUTCOME MEASURES

Presence or absence of ACE2, CD147, TMPRSS2, and CTSL mRNAs detected using quantitative reverse transcription polymerase chain reaction and proteins detected using capillary Western blotting in human oocytes, embryos, and ovarian follicular cells.

RESULTS

The quantitative reverse transcription polymerase chain reaction analysis revealed high abundance of ACE2 gene transcripts in germinal vesicle and MII oocytes than in CC, GC, and BL. ACE2 protein was present only in the MII oocytes, and 1C and BL embryos, but other ACE2 protein variants were observed in all the samples. TMPRSS2 protein was present in all the samples, whereas mRNA was observed only in the BL stage. All the samples were positive for CD147 and CTSL mRNA expressions. However, CCs and GCs were the only samples that showed coexpression of both CD147 and CTSL proteins in low abundance.

CONCLUSIONS

CCs and GCs are the least susceptible to SARS-CoV-2 infection because of lack of the required combination of receptors and proteases (ACE2/TMPRSS2 or CD147/CTSL) in high abundance. The coexpression of ACE2 and TMPRSS2 proteins in the MII oocytes, zygotes, and BLs demonstrated that these gametes and embryos have the cellular machinery required and, thus, are potentially susceptible to SARS-CoV-2 infection if exposed to the virus. However, we do not know whether the infection occurs in vivo or in vitro in an assisted reproductive technology setting yet.

Markers Associated with COVID-19 Susceptibility, Resistance, and Severity

In December 2019, the latest member of the coronavirus family, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), emerged in Wuhan, China, leading to the outbreak of an unusual viral pneumonia known as coronavirus disease 2019 (COVID-19). COVID-19 was then declared as a pandemic in March 2020 by the World Health Organization (WHO). The initial mortality rate of COVID-19 declared by WHO was 2%; however, this rate has increased to 3.4% as of 3 March 2020. People of all ages can be infected with SARS-CoV-2, but those aged 60 or above and those with underlying medical conditions are more prone to develop severe symptoms that may lead to death. Patients with severe infection usually experience a hyper pro-inflammatory immune reaction (i.e., cytokine storm) causing acute respiratory distress syndrome (ARDS), which has been shown to be the leading cause of death in COVID-19 patients. However, the factors associated with COVID-19 susceptibility, resistance and severity remain poorly understood. In this review, we thoroughly explore the correlation between various host, viral and environmental markers, and SARS-CoV-2 in terms of susceptibility and severity.

Ferritin as a Platform for Creating Antiviral Mosaic Nanocages: Prospects for Treating COVID-19

Infectious diseases are a continues threat to human health and the economy worldwide. The latest example is the global pandemic of COVID-19 caused by SARS-CoV-2. Antibody therapy and vaccines are promising approaches to treat the disease; however, they have bottlenecks: they might have low efficacy or narrow breadth due to the continuous emergence of new strains of the virus or antibodies could cause antibody-dependent enhancement (ADE) of infection. To address these bottlenecks, I propose the use of 24-meric ferritin for the synthesis of mosaic nanocages to deliver a cocktail of antibodies or nanobodies alone or in combination with another therapeutic, like a nucleotide analogue, to mimic the viral entry process and deceive the virus, or to develop mosaic vaccines. I argue that available data showing the effectiveness of ferritin-antibody conjugates in targeting specific cells and ferritin-haemagglutinin nanocages in developing influenza vaccines strongly support my proposals.

ACE2: The Major Cell Entry Receptor for SARS-CoV-2

Despite the unprecedented effort of the scientific community, the novel SARS-CoV-2 virus has infected more than 46 million people worldwide, killing over one million two hundred thousand. Understanding the mechanisms by which some individuals are more susceptible to SARS-CoV-2 infection and why a subgroup of them are prone to experience severe pneumonia, and death should lead to a better approach and more effective treatments for COVID-19. Here, we focus our attention on ACE2, a primary receptor of SARS-CoV-2. We will discuss its biology, tissue expression, and post-translational regulation that determine its potential to be employed by SARS-CoV-2 for cell entry. Particular attention will be given to how the ACE2 soluble form can have a great impact on disease progression and thus be used in a potential therapeutic strategy. Furthermore, we will discuss repercussions that SARS-CoV-2/ACE2 binding has on the renin–angiotensin system and beyond. Indeed, although mostly neglected, ACE2 can also act on [des-Arg 937]-bradykinin of the kinin–kallikrein system regulating coagulation and inflammation. Thorough comprehension of the role that ACE2 plays in different pathways will be the key to assess the impact that SARS-CoV-2/ACE2 binding has on organismal physiology and will help us to find better therapies and diagnostic tools.

ACE2: Evidence of role as entry receptor for SARS-CoV-2 and implications in comorbidities

Pandemic severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes coronavirus 19 disease (COVID-19) which presents a large spectrum of manifestations with fatal outcomes in vulnerable people over 70-years-old and with hypertension, diabetes, obesity, cardiovascular disease, COPD, and smoking status. Knowledge of the entry receptor is key to understand SARS-CoV-2 tropism, transmission and pathogenesis. Early evidence pointed to angiotensin-converting enzyme 2 (ACE2) as SARS-CoV-2 entry receptor. Here, we provide a critical summary of the current knowledge highlighting the limitations and remaining gaps that need to be addressed to fully characterize ACE2 function in SARS-CoV-2 infection and associated pathogenesis. We also discuss ACE2 expression and potential role in the context of comorbidities associated with poor COVID-19 outcomes. Finally, we discuss the potential co-receptors/attachment factors such as neuropilins, heparan sulfate and sialic acids and the putative alternative receptors, such as CD147 and GRP78.

The Role of Host Genetic Factors in Coronavirus Susceptibility: Review of Animal and Systematic Review of Human Literature

The SARS-CoV-2 pandemic raises many scientific and clinical questions. These include how host genetic factors affect disease susceptibility and pathogenesis. New work is emerging related to SARS-CoV-2; previous work has been conducted on other coronaviruses that affect different species. We reviewed the literature on host genetic factors related to coronaviruses, systematically focusing on human studies. We identified 1,832 articles of potential relevance. Seventy-five involved human host genetic factors, 36 of which involved analysis of specific genes or loci; aside from one meta-analysis, all were candidate-driven studies, typically investigating small numbers of research subjects and loci. Three additional case reports were described. Multiple significant loci were identified, including 16 related to susceptibility (seven of which identified protective alleles) and 16 related to outcomes (three of which identified protective alleles). The types of cases and controls used varied considerably; four studies used traditional replication/validation cohorts. Among other studies, 30 involved both human and non-human host genetic factors related to coronavirus, 178 involved study of non-human (animal) host genetic factors related to coronavirus, and 984 involved study of non-genetic host factors related to coronavirus, including involving immunopathogenesis. Previous human studies have been limited by issues that may be less impactful now, including low numbers of eligible participants and limited availability of advanced genomic methods; however, these may raise additional considerations. We outline key genes and loci from animal and human host genetic studies that may bear investigation in the study of COVID-19. We also discuss how previous studies may direct current lines of inquiry.

Do genetic polymorphisms in angiotensin converting enzyme 2 (ACE2) gene play a role in coronavirus disease 2019 (COVID-19)?

Although some demographic, clinical and environmental factors have been associated with a higher risk of developing coronavirus disease 2019 (COVID-19) and progressing towards severe disease, altogether these variables do not completely account for the different clinical presentations observed in patients with comparable baseline risk, whereby some subjects may remain totally asymptomatic, whilst others develop a very aggressive illness. Some predisposing genetic backgrounds can hence potentially explain the broad inter-individual variation of disease susceptibility and/or severity. It has been now clearly established that severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus causing COVID-19, infects the host cell through biding and being internalized with angiotensin converting enzyme 2 (ACE2), a surface protein expressed in a noticeable number of human cells, especially in those of upper and lower respiratory tracts, heart, kidney, testis, adipose tissue, gastrointestinal system and in lymphocytes. Accumulating evidence now suggests that genetic polymorphisms in the ACE2 gene may modulate intermolecular interactions with the spike protein of SARS-CoV-2 and/or contribute to pulmonary and systemic injury by fostering vasoconstriction, inflammation, oxidation and fibrosis. We hence argue that the development of genetic tests aimed at specifically identifying specific COVID-19-susceptible or -protective ACE2 variants in the general population may be a reasonable strategy for stratifying the risk of infection and/or unfavorable disease progression.