Accumulating evidence into the pathogenesis of COVID-19 highlight a hypercoagulability state with high risk of life-threatening thromboembolic complications. However, the mechanisms of hypercoagulability and their link to hyperinflammation remain poorly understood. Here we investigate functions and mechanisms of platelet activation and platelet-monocyte interactions in inflammatory amplification during SARS-CoV2 infection. We used a combination of immunophenotyping, single cell analysis, functional assays and pharmacological approaches to gain insights on mechanisms. Critically ill COVID-19 patients exhibited increased platelet-monocyte aggregates formation. We identified a subset of inflammatory monocytes presenting high CD16 and low HLA-DR expression as the subset mainly interacting with platelets during severe COVID-19. Single cell RNAseq analysis indicated enhanced fibrinogen receptor Mac-1 in monocytes from severe COVID-19 patients. Monocytes from severe COVID-19 patients displayed increased platelet binding and hyperresponsiveness to P-selectin and fibrinogen with respect to TFN-α and IL-1β secretion. Platelets were able to orchestrate monocyte responses driving TF expression, inflammatory activation and inflammatory cytokines secretion in SARS-CoV-2 infection. Platelet-monocyte interactions ex-vivo and in SARS-CoV-2 infection model in vitro reciprocally activated monocytes and platelets, inducing the heightened secretion of a wide panel of inflammatory mediators. We identified platelet adhesion as a primary signaling mechanism inducing mediator secretion and TF expression, while TF signaling played major roles in amplifying inflammation by inducing proinflammatory cytokines, especially TNF-α and IL-1β. Our data identify platelet-induced TF expression and activity at the crossroad of coagulation and inflammation in severe COVID-19.

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Background Critically ill 2019 coronavirus disease (COVID-19) patients under invasive mechanical ventilation (IMV) are 10 to 40 times more likely to die than the general population. Although progression from mild to severe COVID-19 has been associated with hypoxia, uncontrolled inflammation, and coagulopathy, the mechanisms involved in the progression to severity are poorly understood. Methods The virome of tracheal aspirates (TA) from 25 COVID-19 patients under IMV was assessed through unbiased RNA sequencing (RNA-seq), and correlation analyses were conducted using available clinical data. Unbiased sequences from nasopharyngeal swabs (NS) from mild cases and TA from non-COVID patients were included in our study for further comparisons. Results We found higher levels and differential expression of human endogenous retrovirus K (HERV-K) genes in TA from critically ill and deceased patients when comparing nasopharyngeal swabs from mild cases to TA from non-COVID patients. In critically ill patients, higher HERV-K levels were associated with early mortality (within 14 days of diagnosis) in the intensive care unit. Increased HERV-K expression in deceased patients was associated with IL-17-related inflammation, monocyte activation, and an increased consumption of clotting/fibrinolysis factors. Moreover, increased HERV-K expression was detected in human primary monocytes from healthy donors after experimental SARS-CoV-2 infection in vitro. Conclusion Our data implicate the levels of HERV-K transcripts in the physiopathology of COVID-19 in the respiratory tract of patients under invasive mechanical ventilation.

PurposeWe quantified lung glycolytic metabolic activity, clinical symptoms and inflammation, coagulation, and endothelial activation biomarkers in 2019 coronavirus disease (COVID-19) pneumonia survivors.MethodsAdults previously hospitalized with moderate to severe COVID-19 pneumonia were prospectively included. Subjects filled out a questionnaire on clinical consequences, underwent chest CT and 18F-FDG PET/CT, and provided blood samples on the same day. Forty-five volunteers served as control subjects. Analysis of CT images and quantitative voxel-based analysis of PET/CT images were performed for both groups. 18F-FDG uptake in the whole-lung volume and in high- and low-attenuation areas was calculated and normalized to liver values. Quantification of plasma markers of inflammation (interleukin 6), d-dimer, and endothelial cell activation (angiopoietins 1 and 2, vascular cell adhesion molecule 1, and intercellular adhesion molecule 1) was also performed.ResultsWe enrolled 53 COVID-19 survivors (62.3% were male; median age, 50 years). All survivors reported at least 1 persistent symptom, and 41.5% reported more than 6 symptoms. The mean lung density was greater in survivors than in control subjects, and more metabolic activity was observed in normal and dense lung areas, even months after symptom onset. Plasma proinflammatory, coagulation, and endothelial activation biomarker concentrations were also significantly higher in survivors.ConclusionWe observed more metabolic activity in areas of high and normal lung attenuation several months after moderate to severe COVID-19 pneumonia. In addition, plasma markers of thromboinflammation and endothelial activation persisted. These findings may have implications for our understanding of the in vivo pathogenesis and long-lasting effects of COVID-19 pneumonia.

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Critically ill 2019 coronavirus disease patients (COVID-19) under invasive mechanical ventilation (IMV) are 10- to 40-times more likely to die than the general population. Although progression from mild to severe COVID-19 has been associated with hypoxia, uncontrolled inflammation and coagulopathy, the mechanisms involved in progression to severity are poorly understood. By analyzing the virome from tracheal aspirates (TA) of 25 COVID-19 patients under IMV, we found higher levels and differential expression of human endogenous retrovirus K (HERV-K) genes compared to nasopharyngeal swabs from mild cases and TA from non-COVID patients. Proteomic analysis and RT-PCR confirmed the presence of HERV-K in these patients. Moreover, increased HERV-K expression was triggered in human primary monocytes from healthy donors after experimental SARS-CoV-2 infection in vitro. In critically ill patients, higher HERV-K levels were associated with early mortality (within 14 days) in the intensive care unit. Increased HERV-K expression in deceased patients associated with IL-17-related inflammation, monocyte activation and higher consumption of clotting/fibrinolysis factors. Our data implicate the levels of HERV-K transcripts in the outcome of critical COVID-19 patients under invasive mechanical ventilation.

BackgroundExtracellular vesicles (EVs) are a valuable source of biomarkers and display the pathophysiological status of various diseases. In COVID-19, EVs have been explored in several studies for their ability to reflect molecular changes caused by SARS-CoV-2. Here we provide insights into the roles of EVs in pathological processes associated with the progression and severity of COVID-19.MethodsIn this study, we used a label-free shotgun proteomic approach to identify and quantify alterations in EV protein abundance in severe COVID-19 patients. We isolated plasma extracellular vesicles from healthy donors and patients with severe COVID-19 by size exclusion chromatography (SEC). Then, flow cytometry was performed to assess the origin of EVs and to investigate the presence of circulating procoagulant EVs in COVID-19 patients. A total protein extraction was performed, and samples were analyzed by nLC-MS/MS in a Q-Exactive HF-X. Finally, computational analysis was applied to signify biological processes related to disease pathogenesis.ResultsWe report significant changes in the proteome of EVs from patients with severe COVID-19. Flow cytometry experiments indicated an increase in total circulating EVs and with tissue factor (TF) dependent procoagulant activity. Differentially expressed proteins in the disease groups were associated with complement and coagulation cascades, platelet degranulation, and acute inflammatory response.ConclusionsThe proteomic data reinforce the changes in the proteome of extracellular vesicles from patients infected with SARS-CoV-2 and suggest a role for EVs in severe COVID-19.

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