Figure 1.

Proposed model for SARS-CoV-2-associated diarrhea. SARS-CoV uses ACE2 and the serine protease TMPRSS2 for entry in lung AT cells. ACE2 and TMPRSS2 are not only expressed in lung, but also the small intestinal epithelia. ACE2 is expressed in the upper esophagus, liver, and colon. ACE2 is also necessary for the surface expression of amino acid transporters of the small intestine. Amino acids, like tryptophan, regulate the secretion of antimicrobial peptides by Paneth cells via mTOR pathway activation. Antimicrobial peptides impact the composition and diversity of the microbiota. Disturbance of this pathway could drive inflammation (enteritis) and ultimately diarrhea. SARS-CoV-2 rendering courtesy of Centers for Disease Control and Prevention. The science cartoon was created with Servier Medical Art licensed under a Creative Commons Attribution 3.0 Unported License. AT, Alveolar Type; mTOR, mammalian target of rapamycin.