QTQTN motif upstream of the furin-cleavage site plays key role in SARS-CoV-2 infection and pathogenesis.

The furin cleavage site (FCS), an unusual feature in the SARS-CoV-2 spike protein, has been spotlighted as a factor key to facilitating infection and pathogenesis by increasing spike processing 1,2. Similarly, the QTQTN motif directly upstream of the FCS is also an unusual feature for group 2B coronaviruses (CoVs). The QTQTN deletion has consistently been observed in in vitro cultured virus stocks and some clinical isolates 3. To determine whether the QTQTN motif is critical to SARS-CoV-2 replication and pathogenesis, we generated a mutant deleting the QTQTN motif (ΔQTQTN). Here we report that the QTQTN deletion attenuates viral replication in respiratory cells in vitro and attenuates disease in vivo. The deletion results in a shortened, more rigid peptide loop that contains the FCS, and is less accessible to host proteases, such as TMPRSS2. Thus, the deletion reduced the efficiency of spike processing and attenuates SARS-CoV-2 infection. Importantly, the QTQTN motif also contains residues that are glycosylated4, and disruption its glycosylation also attenuates virus replication in a TMPRSS2-dependent manner. Together, our results reveal that three aspects of the S1/S2 cleavage site (the FCS, loop length, and glycosylation) are required for efficient SARS-CoV-2 replication and pathogenesis.

COVID-19: Gastrointestinal Manifestations and Complications

The virus responsible for the COVID-19 pandemic is the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which belongs to the genus Betacoronavirus. This genus also includes the severe acute respiratory syndrome coronavirus (SARS-CoV) and the Middle East respiratory syndrome coronavirus (MERS-CoV). The common symptoms of COVID-19 infection are fever and respiratory symptoms, but it can also involve the gastrointestinal tract (GIT), resulting in manifestations such as diarrhea, nausea and/or vomiting and abdominal pain. The emergence of COVID-19 led to public health emphasis on droplet transmission and precautions of contact with respiratory secretions. However, mounting evidence demonstrates detection of SARS-CoV-2 RNA in stool samples of COVID-19 patients. It has also been demonstrated that the host receptor angiotensin-converting-enzyme-2 (ACE-2) is highly expressed not just in respiratory cells but also in gastrointestinal sites involving the glandular cells of gastric, duodenal, and rectal epithelium. This suggests that SARS-CoV-2 can infect the digestive system, serving as another route of transmission. This review aims to study the prevalence of some of the gastrointestinal manifestations following COVID-19 infection and findings of positive SARS-CoV-2 RNA in stool specimens while making parallels to the severe acute respiratory syndrome (SARS) and the Middle East respiratory syndrome (MERS) infection. We will also discuss the possible pathophysiology of COVID-19 related gastrointestinal involvement.

Furin cleavage of the SARS-CoV-2 spike is modulated by O-glycosylation

The SARS-CoV-2 coronavirus responsible for the global pandemic contains a novel furin cleavage site in the spike protein (S) that increases viral infectivity and syncytia formation in cells. Here, we show that O-glycosylation near the furin cleavage site is mediated by members of the GALNT enzyme family, resulting in decreased furin cleavage and decreased syncytia formation. Moreover, we show that O-glycosylation is dependent on the novel proline at position 681 (P681). Mutations of P681 seen in the highly transmissible alpha and delta variants abrogate O-glycosylation, increase furin cleavage, and increase syncytia formation. Finally, we show that GALNT family members capable of glycosylating S are expressed in human respiratory cells that are targets for SARS-CoV-2 infection. Our results suggest that host O-glycosylation may influence viral infectivity/tropism by modulating furin cleavage of S and provide mechanistic insight into the role of the P681 mutations found in the highly transmissible alpha and delta variants.

The Extrapulmonary Manifestations of SARS-CoV-2

SARS-Coronavirus 2 (SARS-CoV-2) is the latest strain of coronavirus that causes the viral infection, Severe Acute Respiratory Syndrome (SARS). The initial studies on the Coronavirus Disease 2019 (COVID-19) focused on respiratory outcomes of this viral infection. More recent research on the mechanism of action of SARS-CoV-2 shows that the virus enters the cells through the Angiotensin-Converting Enzyme-2 (ACE-2) receptor. This receptor is present not just in the cell membranes of respiratory cells but also in the cell membranes of cells present in other organs of the body. This enables the virus to have severe outcomes in the body beyond the respiratory system. Providing a possible immunizing agent against coronavirus is a major challenge pertaining to the fact that ongoing pandemic has already taken millions of lives. This paper discusses the extrapulmonary effects of COVID-19, with an emphasis on clinical manifestations, mechanism of action, and special focus to management considerations in each of these cases. The essential therapeutics and treatments proposed for dealing with the COVID-19 infection have also been discussed. While the answer to whether these therapies work, successfully controlling the immunoinflammatory response is still unclear, ongoing trials of multiple drugs for this purpose are an excellent way to ultimately reach a product that works successfully.

Alveolar Nitric Oxide as a Biomarker of COVID-19 Lung Sequelae: A Pivotal Study

Since SARS-CoV-2 emerged in 2019, strict monitoring of post-COVID-19 patients in order to ensure the early detection of sequelae and/or chronic organ damage that could been associated with the infection has been essential. Potential involvement of the NO pathway in the development of post-COVID-19 lung fibrotic alterations is feasible, since the majority of respiratory cells can produce NO, and fractional exhaled NO (FeNO) represents a biomarker of airway inflammation. The aim of this study was to investigate the potential utility of multiple-flow FeNO parameters in a post-COVID-19 population and to compare it with other indicators of lung damage proposed in the literature. We enrolled 20 patients hospitalized for COVID-19, who underwent clinical, respiratory functional (including PFTs and FeNO) and radiological follow-up after discharge. Compared with age- and sex-matched healthy controls, post-COVID-19 patients showed significantly higher FeNO 350 mL/s and CaNO levels. Moreover, among the parameters included in the follow-up, CaNO showed the best accuracy in indicating predominant fibrotic changes and GGO at CT scan. To our knowledge, this preliminary study has investigated for the first time multiple-flow FeNO parameters in a post-COVID-19 population. The evidence of increased CaNO values may imply the persistence of alveolar and bronchiolar inflammation and/or a mild impairment of the alveolar-capillary membrane in these patients.

The Effect of Azithromycin Plus Zinc Sulfate on ACE2 Expression through IκBα of Human Respiratory Cells in SARS-CoV-2: In Vitro Study

Large-scale efforts have been persistently undertaken for medical prophylaxis and treatment of COVID-19 disasters worldwide. A variety of novel viral spike protein-targeted vaccines have been extensively distributed for global inoculation based on accelerated approval. With concerns of emerging spike protein mutations, we revisited the early but inconclusive clinical interest in the repurposed combination of azithromycin (AZT) and zinc supplements with safety advantages. The aim of this study is to provide in vitro proof of concept for IκBα associated rapid and synergistic suppression of angiotensin-converting enzymes 2 (ACE2) following combination treatments with AZT plus zinc sulfate in two human airway cells with ACE2 expression, Calu-3 and H322M, representative cells of the human upper and lower airway origin respectively. Clinical timing of AZT combined with zinc is indicated based on suppression of the key cellular entry molecule, ACE2, of SARS-CoV-2.

Genome-wide bioinformatic analyses predict key host and viral factors in SARS-CoV-2 pathogenesis

The novel betacoronavirus severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) caused a worldwide pandemic (COVID-19) after emerging in Wuhan, China. Here we analyzed public host and viral RNA sequencing data to better understand how SARS-CoV-2 interacts with human respiratory cells. We identified genes, isoforms and transposable element families that are specifically altered in SARS-CoV-2-infected respiratory cells. Well-known immunoregulatory genes including CSF2, IL32, IL-6 and SERPINA3 were differentially expressed, while immunoregulatory transposable element families were upregulated. We predicted conserved interactions between the SARS-CoV-2 genome and human RNA-binding proteins such as the heterogeneous nuclear ribonucleoprotein A1 (hnRNPA1) and eukaryotic initiation factor 4 (eIF4b). We also identified a viral sequence variant with a statistically significant skew associated with age of infection, that may contribute to intracellular host–pathogen interactions. These findings can help identify host mechanisms that can be targeted by prophylactics and/or therapeutics to reduce the severity of COVID-19.

Perspectives on Epigenetics Alterations Associated with Smoking and Vaping

Epigenetic alterations, including DNA methylation, microRNA, and long non-coding RNA, play important roles in the pathogenesis of numerous respiratory health conditions and diseases. Exposure to tobacco smoking has been found to be associated with epigenetic changes in the respiratory tract. Marketed as a less harmful alternative to combustible cigarettes, electronic cigarette (e-cigarette) has rapidly gained popularity in recent years, especially among youth and young adults. Accumulative evidence from both animal and human studies has shown that e-cigarette use (vaping) is also linked to similar respiratory health conditions as observed with cigarette smoking, including wheezing, asthma, and COPD. This review aims to provide an overview of current studies on associations of vaping with epigenetic alterations in respiratory cells and provide future research directions in epigenetic studies related to vaping.