SARS-CoV-2 impairs interferon production via NSP2-induced repression of mRNA translation.

Viruses evade the innate immune response by suppressing the production or activity of cytokines such as type I interferons (IFNs). Here we report the discovery of a mechanism by which the SARS-CoV-2 virus coopts an intrinsic cellular machinery to suppress the production of the key immunostimulatory cytokine IFN-ß. We reveal that the SARS-CoV-2 encoded nonstructural protein 2 (NSP2) directly interacts with the cellular GIGYF2 protein. This interaction enhances the binding of GIGYF2 to the mRNA cap-binding protein 4EHP, thereby repressing the translation of the Ifnb1 mRNA. Depletion of GIGYF2 or 4EHP significantly enhances IFN-ß production, which inhibits SARS-CoV-2 replication. Our findings reveal a target for rescuing the antiviral innate immune response to SARS-CoV-2 and other RNA viruses.

α2,6-Sialylation Is Upregulated in Severe COVID-19, Implicating the Complement Cascade.

Better understanding of the molecular mechanisms underlying COVID-19 severity is desperately needed in current times. Although hyper-inflammation drives severe COVID-19, precise mechanisms triggering this cascade and what role glycosylation might play therein are unknown. Here we report the first high-throughput glycomic analysis of COVID-19 plasma samples and autopsy tissues. We find that α2,6-sialylation is upregulated in the plasma of patients with severe COVID-19 and in autopsied lung tissue. This glycan motif is enriched on members of the complement cascade (e.g., C5, C9), which show higher levels of sialylation in severe COVID-19. In the lung tissue, we observe increased complement deposition, associated with elevated α2,6-sialylation levels, corresponding to elevated markers of poor prognosis (IL-6) and fibrotic response. We also observe upregulation of the α2,6-sialylation enzyme ST6GAL1 in patients who succumbed to COVID-19. Our work identifies a heretofore undescribed relationship between sialylation and complement in severe COVID-19, potentially informing future therapeutic development.

Sialic acid-containing glycolipids mediate binding and viral entry of SARS-CoV-2.

Emerging evidence suggests that host glycans influence severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Here, we reveal that the receptor-binding domain (RBD) of the spike (S) protein on SARS-CoV-2 recognizes oligosaccharides containing sialic acid (Sia), with preference for monosialylated gangliosides. Gangliosides embedded within an artificial membrane also bind to the RBD. The monomeric affinities (Kd = 100-200 µM) of gangliosides for the RBD are similar to another negatively charged glycan ligand of the RBD proposed as a viral co-receptor, heparan sulfate (HS) dp2-dp6 oligosaccharides. RBD binding and infection of SARS-CoV-2 pseudotyped lentivirus to angiotensin-converting enzyme 2 (ACE2)-expressing cells is decreased following depletion of cell surface Sia levels using three approaches: sialyltransferase (ST) inhibition, genetic knockout of Sia biosynthesis, or neuraminidase treatment. These effects on RBD binding and both pseudotyped and authentic SARS-CoV-2 viral entry are recapitulated with pharmacological or genetic disruption of glycolipid biosynthesis. Together, these results suggest that sialylated glycans, specifically glycolipids, facilitate viral entry of SARS-CoV-2.

SARS-CoV-2 Nonstructural Protein 1 Inhibits the Interferon Response by Causing Depletion of Key Host Signaling Factors.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the causative agent of the ongoing coronavirus disease 2019 (COVID-19) pandemic. While previous studies have shown that several SARS-CoV-2 proteins can antagonize the interferon (IFN) response, some of the mechanisms by which they do so are not well understood. In this study, we describe two novel mechanisms by which SARS-CoV-2 blocks the IFN pathway. Type I IFNs and IFN-stimulated genes (ISGs) were poorly induced during SARS-CoV-2 infection, and once infection was established, cells were highly resistant to ectopic induction of IFNs and ISGs. Levels of two key IFN signaling pathway components, Tyk2 and STAT2, were significantly lower in SARS-CoV-2-infected cells. Expression of nonstructural protein 1 (NSP1) or nucleocapsid in the absence of other viral proteins was sufficient to block IFN induction, but only NSP1 was able to inhibit IFN signaling. Mapping studies suggest that NSP1 prevents IFN induction in part by blocking IRF3 phosphorylation. In addition, NSP1-induced depletion of Tyk2 and STAT2 dampened ISG induction. Together, our data provide new insights into how SARS-CoV-2 successfully evades the IFN system to establish infection. IMPORTANCE SARS-CoV-2 is the causative agent of COVID-19, a serious disease that can have a myriad of symptoms from loss of taste and smell to pneumonia and hypercoagulation. The rapid spread of SARS-CoV-2 can be attributed in part to asymptomatic transmission, where infected individuals shed large amounts of virus before the onset of disease. This is likely due to the ability of SARS-CoV-2 to effectively suppress the innate immune system, including the IFN response. Indeed, we show that the IFN response is efficiently blocked during SARS-CoV-2 infection, a process that is mediated in large part by nonstructural protein 1 and nucleocapsid. Our study provides new insights on how SARS-CoV-2 evades the IFN response to successfully establish infection. These findings should be considered for the development and administration of therapeutics against SARS-CoV-2.

Endothelium Infection and Dysregulation by SARS-CoV-2: Evidence and Caveats in COVID-19.

The ongoing pandemic of coronavirus disease 2019 (COVID-19) caused by the acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) poses a persistent threat to global public health. Although primarily a respiratory illness, extrapulmonary manifestations of COVID-19 include gastrointestinal, cardiovascular, renal and neurological diseases. Recent studies suggest that dysfunction of the endothelium during COVID-19 may exacerbate these deleterious events by inciting inflammatory and microvascular thrombotic processes. Although controversial, there is evidence that SARS-CoV-2 may infect endothelial cells by binding to the angiotensin-converting enzyme 2 (ACE2) cellular receptor using the viral Spike protein. In this review, we explore current insights into the relationship between SARS-CoV-2 infection, endothelial dysfunction due to ACE2 downregulation, and deleterious pulmonary and extra-pulmonary immunothrombotic complications in severe COVID-19. We also discuss preclinical and clinical development of therapeutic agents targeting SARS-CoV-2-mediated endothelial dysfunction. Finally, we present evidence of SARS-CoV-2 replication in primary human lung and cardiac microvascular endothelial cells. Accordingly, in striving to understand the parameters that lead to severe disease in COVID-19 patients, it is important to consider how direct infection of endothelial cells by SARS-CoV-2 may contribute to this process.

Endothelium Infection and Dysregulation by SARS-CoV-2: Evidence and Caveats in COVID-19

The ongoing pandemic of coronavirus disease 2019 (COVID-19) caused by the acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) poses a persistent threat to global public health. Although primarily a respiratory illness, extrapulmonary manifestations of COVID-19 include gastrointestinal, cardiovascular, renal and neurological diseases. Recent studies suggest that dysfunction of the endothelium during COVID-19 may exacerbate these deleterious events by inciting inflammatory and microvascular thrombotic processes. Although controversial, there is evidence that SARS-CoV-2 may infect endothelial cells by binding to the angiotensin-converting enzyme 2 (ACE2) cellular receptor using the viral Spike protein. In this review, we explore current insights into the relationship between SARS-CoV-2 infection, endothelial dysfunction due to ACE2 downregulation, and deleterious pulmonary and extra-pulmonary immunothrombotic complications in severe COVID-19. We also discuss preclinical and clinical development of therapeutic agents targeting SARS-CoV-2-mediated endothelial dysfunction. Finally, we present evidence of SARS-CoV-2 replication in primary human lung and cardiac microvascular endothelial cells. Accordingly, in striving to understand the parameters that lead to severe disease in COVID-19 patients, it is important to consider how direct infection of endothelial cells by SARS-CoV-2 may contribute to this process.