SARS-CoV-2 infection of 3D <i>in vitro</i> cardiac spheroids models the activation of antiviral, inflammatory, fibrotic, and contractile responses in a dose-dependent manner

The emergence of SARS-CoV-2 led to a global pandemic with severe respiratory symptoms and substantial extrapulmonary manifestations. Increasing evidence suggests significant cardiovascular complications associated with SARS-CoV-2 infection, which are critical factors in morbidity and mortality. In this study, we assessed the viral infectivity and viral niche of SARS-CoV-2 using our clinically-amenable<i>in vitro</i>cardiac spheroids (CSs), which have previously been demonstrated to be an optimal tool to recapitulate the complex cardiac pathophysiology. We examined the expression profiles of cardiovascular-related disease genes and pathways involved in inflammation, interferon responses, and antiviral defence following infection. Genes associated with apoptosis, chemotaxis, fibrosis, and contractile function exhibited substantial increases, implicating these pathways in the cardiac response to SARS-CoV-2. Furthermore, our 3D rendering analyses using confocal imaging revealed cell-specific effects mediated by the virus by colocalising SARS-CoV-2 nucleocapsid protein with each cell type, supporting the ability of CSs to facilitate viral replication and contributing to the observed phenotypes. Additionally, SARS-CoV-2 could only infect intact CSs, whereas it did not infect individual cell types cultured individually. The unique ability of CSs to model SARS-CoV-2 in the heart may potentially mirror the pathophysiological changes observed in COVID-19-induced cardiac complications. Altogether, our results suggest that CSs offer a valuable tool for dissecting direct host-viral interactions and advancing our understanding of SARS-CoV-2-related cardiac injury. Our findings underscore the utility of CSs in revealing the mechanisms of SARS-CoV-2-induced cardiac damage and provide a basis for further studies into the long-term cardiovascular consequences of SARS-CoV-2.