FIGURE 2.

Interactions between the various receptors of enteroendocrine cells and the intestinal microbiota and/or microbial metabolites. G protein-coupled receptors, including GPR40, GPR41, GPR43, GPR119, and GPR120, have been recognized as sensing receptors for gut microbiota–derived SCFAs or LCFAs. Olfactory receptor 558, a microbial metabolite detector on EECs, can sense isovalerate, which is an SCFA. Toll-like receptors, such as TLR1, TLR2, and TLR4, can detect multiple intestinal bacterial TLR ligands (eg, bacterial LPS, flagellin, peptidoglycan). Taste receptors can respond to intestinal nutrients and bacterial quorum sensing molecules from Gram-negative bacteria.