The S protein of SARS-CoV-2 injures cardiomyocytes indirectly through the release of cytokines instead of direct action

Background: Emerging evidence has shown that severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection is associated with cardiac injury, but it remains unclear whether cardiac injury is mainly caused by direct viral infection or is secondary to SARS-CoV-2-induced cytokine storm. Methods: Through directly treating cardiomyocytes with S protein, a crucial surface protein of SARS-CoV-2, and indirectly treating cardiomyocytes with S protein-derived human T lymphocyte conditioned medium, we compared the intensities of cardiomyocyte injuries caused by either S protein of the virus or S protein of virus-triggered cytokines. Results: The directly treated cardiomyocytes did not show increasing cell apoptosis. In contrast, cardiomyocytes treated with the supernatant medium of S protein pre-conditioned peripheral blood mononuclear cells showed significantly suppressed viability. In addition, using a cardiovascular disease-specific PCR array, genes associated with hypertrophy, apoptosis, inflammation and angiogenesis were observed to be affected by cytokine stress. Conclusions: Collectively, we found that SARS-CoV-2-induced heart injury may be mainly through the S protein of the virus enhancing host immune responses instead of the S protein of the virus per se. With regards to clinical application, the strategy for treating COVID-19 should not only focus on anti-viral therapy but also on suppressing over-activated immunity.