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. 2019 Apr 16;10:428. doi: 10.3389/fphys.2019.00428

FIGURE 2.

FIGURE 2

Microbial signaling to enteroendocrine cells. Resident microbiota within the intestinal lumen signal to enteroendocrine (EE) cells via multiple pathways. Firstly, microbiota convert indigestible carbohydrates to short chain fatty acids (SCFA), which in turn signal to EE cells via free fatty acid receptors 2 or 3 (FFAR2/3) or by activation of nuclear histone deacetylases (HDAC). Secondly, microbiota convert primary (1°) bile acids to secondary (2°) bile acids, such as deoxycholate, which then signal to EE cells via the membrane G protein-coupled bile acid receptor, TGR5, or nuclear FXR. Finally, structural components of microbiota, such as flagella, and the endotoxin lipopolysaccharide (LPS), signal to toll-like receptors (TLRs).