Introduction Short chain fatty acids are produced mainly by the gut microbiota. They mediate a variety of biological effects by acting on a two of G protein-coupled receptors. These receptors are expressed by various cell types, including in the gut. The exact contribution of free fatty acid 2 receptor (FFA2) in regulating gut physiology is unclear. Bolognini et al1, recently employed a novel FFA2-Designer Receptor Exclusively Activated by Designer Drugs (DREADD) to study the physiological role of FFA2. Now we describe and further explore the physiological roles of FFA2 with a novel agonist, 4-methoxy-3-methyl-benzoic acid (MOMBA) for the FFA2-DREADD variant following transgenic expression in mice.
Methods Following an extensive screening of more than 1200 small molecules, MOMBA was identified as a potential agonist for the hFFAR2-DREADD receptor. (1) The selectivity of MOMBA was assesses with β-arrestin-2 recruitment assay in HEK293 cells expressing hFFA2-DREADD and hFFA2-eYFP. The effect of FFA2 activation on the release of enteroendocrine hormones (GLP-1 and PYY) was assessed on (2) isolated crypts and (3) intact colonic segments. Isolated crypts and intact colon segments were challenged with different test compound. Supernatants were subsequently collected and GLP-1 and PYY concentration was measured by ELISA. (4) Furthermore, role of FFA2 in sensory signalling was investigated by measuring intracellular calcium [iCa2+] in isolated nodose ganglion (NG) and dorsal root ganglion (DRG).
Results (1) MOMBA is selective for hFFA2-DREAD (2) MOMBA (1mM-0.001mM) induces a FFA2 specific concentration dependent increase in GLP-1 secretion in colonic crypts. (3) Intraluminal infusion of MOMBA also resulted in a FFA2 mediated increase in GLP-1 and PYY secretion from intact colon. Furthermore, (4) MOMBA induced a Gq mediated increase in [iCa2+] in cells isolated from DREADD mice. Conversely, C3 induced a Gi mediated increase in these cells.
Conclusion MOMBA specifically activates hFFA2-DREADD, hence providing a novel tool ligand to further study the physiological and pathophysiological roles of FFA2 within the gut, as well as other cell types that express this receptor.
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