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Highly efficient SARS-CoV-2 infection of human cardiomyocytes: spike protein-mediated cell fusion and its inhibition

By Chanakha K. Navaratnarajah, David R. Pease, Peter Halfmann, Biruhalem Taye, Alison Barkhymer, Kyle G. Howell, Jon E. Charlesworth, Trace A. Christensen, Yoshihiro Kawaoka, Roberto Cattaneo, Jay W. Schneider, Timothy J. Nelson (Director), Boyd Rasmussen and Frank J. Secreto

Posted 30 Jul 2021
bioRxiv DOI: 10.1101/2021.07.30.454437

Severe cardiovascular complications can occur in coronavirus disease of 2019 (COVID-19) patients. Cardiac damage is attributed mostly to a bystander effect: the aberrant host response to acute respiratory infection. However, direct infection of cardiac tissue by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) also occurs. We examined here the cardiac tropism of SARS-CoV-2 in human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CM) that beat spontaneously. These cardiomyocytes express the angiotensin I converting-enzyme 2 (ACE2) receptor and a subset of the proteases that mediate spike protein cleavage in the lungs, but not transmembrane protease serine 2 (TMPRSS2). Nevertheless, SARS-CoV-2 infection was productive: viral transcripts accounted for about 88% of total mRNA. In the cytoplasm of infected hiPSC-CM, smooth walled exocytic vesicles contained numerous 65-90 nm particles with typical ribonucleocapsid structures, and virus-like particles with knob-like spikes covered the cell surface. To better understand the mechanisms of SARS-CoV-2 spread in hiPSC-CM we engineered an expression vector coding for the spike protein with a monomeric emerald-green fluorescent protein fused to its cytoplasmic tail (S-mEm). Proteolytic processing of S-mEm and the parental spike were equivalent. Live cell imaging tracked spread of S-mEm signal from cell to cell and documented formation of syncytia. A cell-permeable, peptide-based molecule that blocks the catalytic site of furin abolished cell fusion. A spike mutant with the single amino acid change R682S that inactivates the furin cleavage site was fusion inactive. Thus, SARS-CoV-2 can replicate efficiently in hiPSC-CM and furin activation of its spike protein is required for fusion-based cytopathology. This hiPSC-CM platform provides an opportunity for target-based drug discovery in cardiac COVID-19.

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