Linking malnutrition and intestinal inflammation

ACE2 (angiotensin-converting enzyme 2) is a key enzyme of the renin–angiotensin system, and studies in Ace2^−/− mice now reveal a link between malnutrition and intestinal inflammation. Hashimoto et al. observed that Ace2^−/− mice display more severe dextran sodium sulphate (DSS)-induced colitis than wild-type mice. ACE2 promotes the function of the amino acid transporter B⁰AT1 (also known as SLC6A19), and Ace2^−/− mice had low tryptophan levels in the serum. Similarly, wild-type mice on a protein-free or tryptophan-free diet developed severe DSS-induced colitis. This correlated with reduced expression of antimicrobial peptides in the small intestine, which affected the composition of the intestinal microbiota. The authors suggest that tryptophan reabsorption regulates the intestinal microbiome and gut homeostasis through the tryptophan derivative nicotinamide (also known as vitamin B3) and the activation of mTOR signalling.