The purinergic receptor P2X7 and the NLRP3 inflammasome are druggable host factors required for SARS-CoV-2 infection (preprint)

Purinergic receptors and NOD-like receptor protein 3 (NLRP3) inflammasome regulate inflammation and viral infection, but their effects on severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection remain poorly understood. Here, we report that the purinergic receptor P2X7 and NLRP3 inflammasome are cellular host factors required for SARS-CoV-2 infection. Lung autopsies from patients with severe coronavirus disease 2019 (COVID-19) reveal that NLRP3 expression is increased in host cellular targets of SARS-CoV-2 including alveolar macrophages, type II pneumocytes and syncytia arising from the fusion of infected macrophages, thus suggesting a potential role of NLRP3 and associated signaling pathways to both inflammation and viral replication. In vitro studies demonstrate that NLRP3-dependent inflammasome activation is detected upon macrophage abortive infection. More importantly, a weak activation of NLRP3 inflammasome is also detected during the early steps of SARS-CoV-2 infection of epithelial cells and promotes the viral replication in these cells. Interestingly, the purinergic receptor P2X7, which is known to control NLRP3 inflammasome activation, also favors the replication of D614G and alpha SARS-CoV-2 variants. Altogether, our results reveal an unexpected relationship between the purinergic receptor P2X7, the NLRP3 inflammasome and the permissiveness to SARS-CoV-2 infection that offers novel opportunities for COVID-19 treatment.

SARS-CoV-2 spike protein dictates syncytium-mediated lymphocyte elimination.

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus is highly contagious and causes lymphocytopenia, but the underlying mechanisms are poorly understood. We demonstrate here that heterotypic cell-in-cell structures with lymphocytes inside multinucleate syncytia are prevalent in the lung tissues of coronavirus disease 2019 (COVID-19) patients. These unique cellular structures are a direct result of SARS-CoV-2 infection, as the expression of the SARS-CoV-2 spike glycoprotein is sufficient to induce a rapid (~45.1 nm/s) membrane fusion to produce syncytium, which could readily internalize multiple lines of lymphocytes to form typical cell-in-cell structures, remarkably leading to the death of internalized cells. This membrane fusion is dictated by a bi-arginine motif within the polybasic S1/S2 cleavage site, which is frequently present in the surface glycoprotein of most highly contagious viruses. Moreover, candidate anti-viral drugs could efficiently inhibit spike glycoprotein processing, membrane fusion, and cell-in-cell formation. Together, we delineate a molecular and cellular rationale for SARS-CoV-2 pathogenesis and identify novel targets for COVID-19 therapy.

SARS-CoV-2 Spike Protein Dictates Syncytium-mediated Lymphocyte Elimination (preprint)

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus is highly contagious and causes lymphocytopenia, but the underlying mechanisms are poorly understood. We demonstrate here that heterotypic cell-in-cell structures with lymphocytes inside multinucleate syncytia are prevalent in the lung tissues of coronavirus disease 2019 (COVID-19) patients. These unique cellular structures are a direct result of SARS-CoV-2 infection, as the expression of the SARS-CoV-2 spike glycoprotein is sufficient to induce a rapid (approximately 45.1 nm/sec) membrane fusion to produce syncytium, which could readily internalize multiple lines of lymphocytes to form typical cell-in-cell structures, remarkably leading to the death of internalized cells. This membrane fusion is dictated by a bi-arginine motif within the polybasic S1/S2 cleavage site, which is frequently present in the surface glycoprotein of most highly contagious viruses. Moreover, candidate anti-viral drugs could efficiently inhibit spike glycoprotein processing, membrane fusion, and cell-in-cell formation. Together, we delineate a molecular and cellular rationale for SARS-CoV-2 pathogenesis and identify novel targets for COVID-19 therapy.

Asymptomatic COVID-19 Patient, Occurrence of Fatal Pulmonary Arterial Thrombosis. (preprint)

The induction of hypercoagulability is one of the pathophysiological mechanism in patients with a severe presentation of the SARS-CoV-2 infection that can contribute to death. A considerable number of SARS-Cov-2 infected individuals could be asymptomatic and they don’t need medical treatment. We reported autoptic evidences of COVID-19 trombotic fatal lesions in a asymptomatic COVID-19 patient after negative conversion.This study provides evidences that an appropriate diagnostic screening for thrombotic complications and the early treatment recommendations of antithrombotic drugs could represent an important topic even in asymptomatic individuals. 

SARS-CoV-2 cytopathogenesis in cultured cells and in COVID-19 autoptic lung, evidences of lipid involvement. (preprint)

Background: The pathogenesis of SARS-CoV-2 remains to be defined. Elucidating SARS-CoV-2 cellular localization within cells and its cytopathic effects requires definition. We performed a comparative ultrastructural study of SARS-CoV-2 infection of Vero-6 cells and lung from COVID-19 patients. Main findings: SARS-CoV-2 induces rapid ultrastructural changes and death in Vero cells. Ultrastructural changes in SARS-CoV-2 infection differ from those in SARS-CoV-1.  Type II pneumocytes in lung tissue showed prominent altered morphological features with numerous vacuoles and swollen mitochondria with presence of abundant lipid droplets. The accumulation of lipid droplets was the most striking finding we observed in cultured cells and in infected pneumocytes. Virus particles were also found associated with lipo-lysosomes suggesting that they can play an important step in virus assembly.Interpretation: The cytopathology of SARS-CoV-2 appears to be different to that caused by SARS-CoV-1. Our findings highlight important open topics which may represent future targets to contrast the pathogenicity of SARS-CoV-2.