Comparison of the clinical characteristics and mortality of adults infected with human coronaviruses 229E and OC43

Structural proteins of human coronaviruses: what makes them different?

Following COVID-19 outbreak with its unprecedented effect on the entire world, the interest to the coronaviruses increased. The causative agent of the COVID-19, severe acute respiratory syndrome coronavirus - 2 (SARS-CoV-2) is one of seven coronaviruses that is pathogenic to humans. Others include SARS-CoV, MERS-CoV, HCoV-HKU1, HCoV-OC43, HCoV-NL63 and HCoV-229E. The viruses differ in their pathogenicity. SARS-CoV, MERS-CoV, and SARS-CoV-2 are capable to spread rapidly and cause epidemic, while HCoV-HKU1, HCoV-OC43, HCoV-NL63 and HCoV-229E cause mild respiratory disease. The difference in the viral behavior is due to structural and functional differences. All seven human coronaviruses possess four structural proteins: spike, envelope, membrane, and nucleocapsid. Spike protein with its receptor binding domain is crucial for the entry to the host cell, where different receptors on the host cell are recruited by different viruses. Envelope protein plays important role in viral assembly, and following cellular entry, contributes to immune response. Membrane protein is an abundant viral protein, contributing to the assembly and pathogenicity of the virus. Nucleocapsid protein encompasses the viral RNA into ribonucleocapsid, playing important role in viral replication. The present review provides detailed summary of structural and functional characteristics of structural proteins from seven human coronaviruses, and could serve as a practical reference when pathogenic human coronaviruses are compared, and novel treatments are proposed.

The unfolded protein response components IRE1α and XBP1 promote human coronavirus infection

The cellular processes that support human coronavirus replication and contribute to the pathogenesis of severe disease remain incompletely understood. Many viruses, including coronaviruses, cause endoplasmic reticulum (ER) stress during infection. IRE1α is a component of the cellular response to ER stress that initiates non-conventional splicing of XBP1 mRNA. Spliced XBP1 encodes a transcription factor that induces the expression of ER-related targets. Activation of the IRE1α-XBP1 pathway occurs in association with risk factors for severe human coronavirus infection. In this study, we found that the human coronaviruses HCoV-OC43 (human coronavirus OC43) and SARS-CoV-2 (severe acute respiratory syndrome coronavirus-2) both robustly activate the IRE1α-XBP1 branch of the unfolded protein response in cultured cells. Using IRE1α nuclease inhibitors and genetic knockdown of IRE1α and XBP1, we found that these host factors are required for optimal replication of both viruses. Our data suggest that IRE1α supports infection downstream of initial viral attachment and entry. In addition, we found that ER stress-inducing conditions are sufficient to enhance human coronavirus replication. Furthermore, we found markedly increased XBP1 in circulation in human patients with severe coronavirus disease 2019 (COVID-19). Together, these results demonstrate the importance of IRE1α and XBP1 for human coronavirus infection. IMPORTANCE There is a critical need to understand the cellular processes co-opted during human coronavirus replication, with an emphasis on identifying mechanisms underlying severe disease and potential therapeutic targets. Here, we demonstrate that the host proteins IRE1α and XBP1 are required for robust infection by the human coronaviruses, SARS-CoV-2 and HCoV-OC43. IRE1α and XBP1 participate in the cellular response to ER stress and are activated during conditions that predispose to severe COVID-19. We found enhanced viral replication with exogenous IRE1α activation, and evidence that this pathway is activated in humans during severe COVID-19. Together, these results demonstrate the importance of IRE1α and XBP1 for human coronavirus infection.

Auraptene Has Antiviral Activity against Human Coronavirus OC43 in MRC-5 Cells

Auraptene (7-geranyloxycoumarin) is the abundant prenyloxycoumarin found in the fruits of Citrus spp. Auraptene has a variety of pharmacological and therapeutic functions, such as anticancer, antioxidant, immunomodulatory, and anti-inflammation activities, with excellent safety profiles. In this study, we evaluated the anticoronaviral activity of auraptene in HCoV-OC43-infected human lung fibroblast MRC-5 cells. We found that auraptene effectively inhibited HCoV-OC43-induced cytopathic effects with 4.3 μM IC₅₀ and 6.1 μM IC₉₀, resulting in a selectivity index (CC₅₀/IC₅₀) of >3.5. Auraptene treatment also decreased viral RNA levels in HCoV-OC43-infected cells, as detected through quantitative real-time PCR, and decreased the expression level of spike proteins and nucleocapsid proteins in virus-infected cells, as detected through the Western blot analysis and immunofluorescence staining. Time-of-addition analysis showed auraptene's inhibitory effects at the post-entry stage of the virus life cycle; however, auraptene did not induce the antiviral interferon families, IFN-α1, IFN-β1, and IFN-λ1. Additionally, auraptene-treated MRC-5 cells during HCoV-OC43 infection decreased the MMP-9 mRNA levels which are usually increased due to the infection, as auraptene is a previously reported MMP-9 inhibitor. Therefore, auraptene showed antiviral activity against HCoV-OC43 infection, and we suggest that auraptene has the potential to serve as a therapeutic agent against human coronavirus.

Unravelling Antigenic Cross-Reactions toward the World of Coronaviruses: Extent of the Stability of Shared Epitopes and SARS-CoV-2 Anti-Spike Cross-Neutralizing Antibodies

The human immune repertoire retains the molecular memory of a very great diversity of target antigens (epitopes) and can recall this upon a second encounter with epitopes against which it has previously been primed. Although genetically diverse, proteins of coronaviruses exhibit sufficient conservation to lead to antigenic cross-reactions. In this review, our goal is to question whether pre-existing immunity against seasonal human coronaviruses (HCoVs) or exposure to animal CoVs has influenced the susceptibility of human populations to SARS-CoV-2 and/or had an impact upon the physiopathological outcome of COVID-19. With the hindsight that we now have regarding COVID-19, we conclude that although antigenic cross-reactions between different coronaviruses exist, cross-reactive antibody levels (titers) do not necessarily reflect on memory B cell frequencies and are not always directed against epitopes which confer cross-protection against SARS-CoV-2. Moreover, the immunological memory of these infections is short-term and occurs in only a small percentage of the population. Thus, in contrast to what might be observed in terms of cross-protection at the level of a single individual recently exposed to circulating coronaviruses, a pre-existing immunity against HCoVs or other CoVs can only have a very minor impact on SARS-CoV-2 circulation at the level of human populations.

Prevalence of Common Human Coronaviruses (NL63, 229E, and OC43) in Adults before the COVID-19 Pandemic: a Single-Center Study from Turkey, 2015-2020

Common Human Coronaviruses (HCoVs), such as NL63, HKU1, 229E, and OC43, induce respiratory tract infections worldwide. Epidemiological studies of HCoVs are of paramount importance because the disease burden and trajectory (in years) have not been well addressed in adults. Here, we aimed to describe the burden of HCoVs in a hospital setting over five years before the coronavirus disease 2019 pandemic. This was a retrospective study of patients (>18 years) between January 1, 2015, and January 1, 2020, whose respiratory specimens were tested by multiplex real-time polymerase chain reaction. In total, 7,861 respiratory samples (4,540 patients) were included, 38% of which tested positive for any respiratory virus. Of these, 212 (12.2%) samples were positive for HCoVs, and their co-infection with other respiratory viruses was 30.6%. Rhinovirus (27.6%) was the most common co-infection among all three HCoVs. The overall prevalence of HCoVs tended to be the highest in the winter (40.9%). Patients aged ≥60 years had the highest prevalence of overall HCoVs (39.7%). Given the duration and large sample size, this study from Turkey is one of the largest to date among adults in the literature. These epidemiological data and molecular surveillance of HCoVs have important implications for the control and prevention of respiratory infections.

Comparison of the Antiviral Activity of Remdesivir, Chloroquine, and Interferon-β as Single or Dual Agents Against the Human Beta-Coronavirus OC43

The human beta-coronavirus strain, OC43, provides a useful model for testing the antiviral activity of various agents. We compared the activity of several antiviral drugs against OC43, including remdesivir, chloroquine, interferon (IFN)-β, IFN-λ1, and IFN-λ4, in two distinct cell types: human colorectal carcinoma cell line (HCT-8 cells) and normal human bronchial epithelial (NHBE) cells. We also tested whether these agents mediate additive, synergistic, or antagonistic activity against OC43 infection when used in combination. When used as single agents, remdesivir exhibited stronger antiviral activity than chloroquine, and IFN-β exhibited stronger activity than IFN-λ1 or IFN-λ4 against OC43 in both HCT-8 and NHBE cells. Anakinra (IL-1 inhibitor) and tocilizumab (IL-6 inhibitor) did not mediate any antiviral activity. The combination of IFN-β plus chloroquine or remdesivir resulted in higher synergy scores and higher expression of IFN-stimulated genes than did IFN-β alone. In contrast, the combination of remdesivir plus chloroquine resulted in an antagonistic interaction in NHBE cells. Our findings indicate that the combined use of IFN-β plus remdesivir or chloroquine induces maximal antiviral activity against human coronavirus strain OC43 in primary human respiratory epithelial cells. Furthermore, our experimental OC43 virus infection model provides an excellent method for evaluating the biological activity of antiviral drugs.

Control of CDH1/E-Cadherin Gene Expression and Release of a Soluble Form of E-Cadherin in SARS-CoV-2 Infected Caco-2 Intestinal Cells: Physiopathological Consequences for the Intestinal Forms of COVID-19

COVID-19 is the biggest pandemic the world has seen this century. Alongside the respiratory damage observed in patients with severe forms of the disease, gastrointestinal symptoms have been frequently reported. These symptoms (e.g., diarrhoea), sometimes precede the development of respiratory tract illnesses, as if the digestive tract was a major target during early SARS-CoV-2 dissemination. We hypothesize that in patients carrying intestinal SARS-CoV-2, the virus may trigger epithelial barrier damage through the disruption of E-cadherin (E-cad) adherens junctions, thereby contributing to the overall gastrointestinal symptoms of COVID-19. Here, we use an intestinal Caco-2 cell line of human origin which expresses the viral receptor/co-receptor as well as the membrane anchored cell surface adhesion protein E-cad to investigate the expression of E-cad after exposure to SARS-CoV-2. We found that the expression of CDH1/E-cad mRNA was significantly lower in cells infected with SARS-CoV-2 at 24 hours post-infection, compared to virus-free Caco-2 cells. The viral receptor ACE2 mRNA expression was specifically down-regulated in SARS-CoV-2-infected Caco-2 cells, while it remained stable in HCoV-OC43-infected Caco-2 cells, a virus which uses HLA class I instead of ACE2 to enter cells. It is worth noting that SARS-CoV-2 induces lower transcription of TMPRSS2 (involved in viral entry) and higher expression of B0AT1 mRNA (that encodes a protein known to co-express with ACE2 on intestinal cells). At 48 hours post-exposure to the virus, we also detected a small but significant increase of soluble E-cad protein (sE-cad) in the culture supernatant of SARS-CoV-2-infected Caco-2 cells. The increase of sE-cad release was also found in the intestinal HT29 cell line when infected by SARS-CoV-2. Beside the dysregulation of E-cad, SARS-CoV-2 infection of Caco-2 cells also leads to the dysregulation of other cell adhesion proteins (occludin, JAMA-A, zonulin, connexin-43 and PECAM-1). Taken together, these results shed light on the fact that infection of Caco-2 cells with SARS-CoV-2 affects tight-, adherens-, and gap-junctions. Moreover, intestinal tissues damage was associated to the intranasal SARS-CoV-2 infection in human ACE2 transgenic mice.

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.

Non-SARS Non-MERS Human Coronaviruses: Clinical Characteristics and Outcome

Human coronaviruses (HCoVs) have become evident sources of human respiratory infections with new emerging HCoVs as a significant cause of morbidity and mortality. The common four coronaviruses (229E, HKU1, NL63, and OC43) are known to cause respiratory illness in humans, but their clinical impact is poorly described in the literature. We analyzed the data of all patients who tested positive for at least one of the four HCoVs from October 2015 to January 2020 in a tertiary care center. HCoVs were detected in 1062 specimens, with an incidence rate of 1.01%, out of all documented respiratory illnesses. Detection of these viruses was reported sporadically throughout the years, with a peak of occurrence during winter seasons. OC43 had the highest incidence (53.7%), followed by NL63 (21.9%), HKU1 (12.6%), and 229E (11.8%). Most of these infections were community-acquired, with symptoms of both upper and lower respiratory tract. Co-detection with other viruses were observed, mostly with rhinovirus. 229E was the most frequent (26.4%) HCoV in patients requiring intensive care, while NL63 and 229E were the most common in patients requiring invasive ventilation. The highest 30-day mortality rate was observed in patients infected with 229E (6.4%). HCoVs are common circulating pathogens that have been present for decades, with 229E being the most virulent in this study cohort.