Single-cell expression profiles of <i>ACE2</i> and <i>TMPRSS2</i> reveals potential vertical transmission and fetus infection of SARS-CoV-2

Abstract

Morbidity and mortality of coronavirus disease 2019 (COVID-19) is age-dependent. It remains unclear whether vertical severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) occurs during pregnancy and how such infection will affect fetal development. Here, we performed single-cell transcriptomic analysis of placenta and other tissues from fetuses in comparison with those from adults using public-available datasets. Our analysis revealed that a very small proportion of trophoblast cells expressed the <i>Angiotensin I Converting Enzyme 2</i> (<i>ACE2</i>) gene, suggesting a low possibility of vertical transmission of SARS-CoV-2 from mother to fetus during pregnancy. We found that the fetal adrenal gland, heart, kidney and stomach were susceptible to SARS-CoV-2 infection, because these organs contained cell clusters that expressed high levels of the <i>ACE2</i> gene. In particular, a higher proportion of <i>ACE2</i>-expressing cell clusters in the adrenal gland and kidney also expressed the <i>Transmembrane Serine Protease 2</i> (<i>TMPRSS2</i>) gene compared with other organs. Surprisingly, <i>ACE2</i>-expressing type II alveolar (AT2) equivalent cells were absent in fetal lungs. This is in sharp contrast to adult lungs. As <i>ACE2</i> expression is regulated by various conditions, including oxygen concentration, inflammation and smoking, caution is warranted to avoid triggering potential <i>ACE2</i> expression in fetal and placental tissue.