Senescent Endothelial Cells Are Highly Susceptible to SARS-CoV-2 Infection, Which Might Account for the Aggravation of COVID-19 in the Elderly

Introduction: The pandemic of coronavirus disease 2019 (COVID-19), induced by the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, has posed a global health emergency. COVID-19 vaccines are certainly effective to prevent infection, severe disease, and hospitalization; however, its spreading remains to be uncontrolled worldwide. The striking feature of COVID-19 is the high mortality in the elderly; every 1,000 people infected with SARS-CoV-2, around 116 will die if they are mid-seventies or older, while little will die if they are under the age of 50. Though elderly is more fragile than younger people in general, this substantial difference in mortality strongly suggest a specific factor(s) that aggravate the disease in elder people. Systemic thrombosis has been highlighted in the pathogenesis of COVID-19, and lung microangiopathy in association with endothelial cells (ECs) injury has been reported by post-mortem analysis of the lungs. Hypothesis: Senescent endothelial cells are highly susceptible to SARS-CoV-2 infection. Methods: We experimentally investigated the SARS-CoV-2 infection in ECs, and performed a comparative analysis for post-infection molecular events using young and replicative senescent ECs. Results: We identify that; 1) SARS-CoV-2 infects ECs largely through endocytosis, 2) Senescent ECs are highly susceptible to SARS-CoV-2 infection, possibly through enhanced caveolae-mediated endocytosis, 3) SARS-CoV-2 infection alters various genes expression, which could cause EC dysfunctions, 4) More genes expression is affected in senescent ECs by SARS-CoV-2 infection than in young ECs, which might causes further exacerbated dysfunction in senescent ECs, 5) SARS-CoV-2 infection significantly affected coagulation cascade only in senescent ECs. Conclusions: These data strongly suggest that sustained EC dysfunctions due to SARS-CoV-2 infection may contribute to the microangiopathy in the lungs, leading to deteriorated inflammation and thrombosis in COVID-19. Our data also suggest a possible causative role of EC senescence in the aggravated disease in elder COVID-19 patients.