Angiotensin-Converting Enzyme 2 (ACE2) is Rate-limiting for Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Viral Infection in Beating Stem Cell-Derived Cardiomyocytes

Introduction: Cardiovascular comorbidities are a major risk factor in patients infected with SARS-CoV-2. SARS-CoV-2 Spike protein binds to host cell surface ACE2 to gain entry. ACE2 is subsequently downregulated by internalisation. We hypothesise that an ACE2 knockdown system in beating human embryonic stem cell-derived cardiomyocytes (hESC-CMs) will recapitulate the downregulation of ACE2, and reduce the ability of a SARS-CoV-2 Spike protein pseudotyped virus to infect these clinically relevant cells. Method: ACE2 was knocked down (KD) with CRISPR/Cas9 in hESCs, before differentiating to hESC-CMs and sub-culturing in 96 well plates. Sanger sequencing confirmed amino acid changes. Catalytic ACE2 activity was measured by mass spectrometry in wild-type versus KD by conversion of apelin-13 to apelin-12 in hESC-CMs supernatant. ACE2 activity was also measured by fluorescent substrate assay. Pseudotyped virus infection was visualised by high content screening in ACE2 KD versus wild-type (n=4). All data are mean±SEM. Results: Sequencing revealed two substitutions at ACE2 222-223 , and three deletions at ACE2 224-226 . This reduced ACE2 catalytic activity by ~60-70% by apelin-12 accumulation using mass spectrometry (Fig 1a), and fluorescent assay. Furthermore, KD reduced infection of hESC-CMs by pseudotyped virus to 27.3±9.6% of the cell population versus 74.8±4.7% for wild-type (Fig 1b,c). This is consistent with our previous data, showing DX600 (peptidic inhibitor of ACE2 catalytic site) significantly reduced infection of wild-type hESC-CMs to 20.5±6.5%. Conclusions: In conclusion, we generated a functional ACE2 knockdown in a beating cardiomyocyte cell model. Both the catalytic activity and the ability to bind SARS-CoV-2 Spike protein of ACE2 reduced, importantly indicating ACE2 is rate limiting for infection. We aim to use this system to further explore the cardiovascular consequences of SARS-CoV-2 infection and subsequent downregulation of ACE2.