SARS-CoV-2 enhances complement-mediated endothelial injury via the suppression of membrane complement regulatory proteins.

Complement hyperactivation and thrombotic microangiopathy are closely associated with severe COVID-19. Endothelial dysfunction is a key mechanism underlying thrombotic microangiopathy. To address the relationship between endothelial injury, complement activation and thrombotic microangiopathy of severe COVID-19, we wonder whether, and if so, what and how SARS-CoV-2 factors make endothelial cells (ECs) sensitive to complement-mediated cytotoxicity. We revealed that multiple SARS-CoV-2 proteins enhanced complement-mediated cytotoxicity to ECs by inhibiting membrane complement regulatory proteins (CRPs) and enhancing the deposition of complement-recognizing component FCN1. By screening with CRISPR/Cas9-gRNA libraries, we identified that ADAMTS9, SYAP1, and HIGD1A as intrinsic regulators of CD59 on ECs, which were inhibited by the SARS-CoV-2 M, NSP16, and ORF9b proteins. IFN-γ, GM-CSF, and IFN-α upregulated CD55 and CD59, while IFN-γ antagonized the inhibition of CD59 by the three SARS-CoV-2 proteins. So, the deficiency of IFN-γ weakened the protection of ECs by CRPs against complement-mediated injury which may be enhanced during infection. Our findings illustrated the regulation of protection against complement-mediated attack on self-cells by SARS-CoV-2 infection and immune responses, providing insights into endothelial injury, thrombotic microangiopathy, and potential targets for treating severe COVID-19.