Bioinformatic characterization of angiotensin-converting enzyme 2, the entry receptor for SARS-CoV-2

Harlan Barker; Seppo Parkkila

Data on the localization of virus receptors can provide insight into mechanisms of virus entry, tissue tropism, and pathogenesis of the disease. Therefore, it is of particular interest to correlate COVID-19 symptoms with the distribution pattern of ACE2. The first studies performed by northern blotting indicated that ACE2 is located in the human heart, kidney, and testis (2) . By immunohistochemistry, the expression of the ACE2 protein was identified in the human lung alveolar epithelial cells (type I and II pneumocytes), enterocytes of the small intestine, the brush border of the renal proximal tubules, and the endothelial cells of arteries and veins and arterial smooth muscle cells in several organs (25). It was proposed that this distribution pattern of ACE2 could explain the tissue tropism of SARS-CoV-1 for the lung, small intestine, and kidney (26). On the other hand, the symptoms of COVID-19, in contrast to SARS-CoV-1 infection, are not associated to the same extent with the gastrointestinal tract in spite of the high expression of ACE2 in the intestinal enterocytes (27). In COVID-19, diarrhea has been reported in just 3.8% of patients, in contrast to 40-70% in SARS-CoV-1 infection (21, 28) . A recent preprint report indicated diarrhea in 18.1% of 254 COVID-19 patients (29).