Short-Chain Fatty Acids Activate Myenteric Neurons and Delay Colonic Motility via Free Fatty Acid Receptors 2 and 3 in the Mouse.

BACKGROUND

Short-chain fatty acids (SCFAs), metabolic products of the gut microbiota, are important regulators of intestinal homeostasis. SCFAs exert their effects through free fatty acid receptors (FFAR), which are located on enteroendocrine cells and enteric nerves. The actions of SCFAs include the regulation of motility. How SCFAs affect enteric neuronal activity and the regulation of colonic motility remains to be fully elucidated.

METHODS

Intact preparations of the proximal colon from mice expressing a genetically encoded fluorescent Ca2+ reporter specifically in intrinsic primary afferent neurons (IPANs; Calb1-GCaMP6 mice) or in all enteric neurons (Wnt1-GCaMP6 mice) were used. Preparations were luminally perfused with SCFAs, with or without the FFAR2 antagonist, β-hydroxybutyrate (BHB) or the FFAR3 antagonist, GLPG0976. SCFA-induced Ca2+ responses were visualized by confocal microscopy. Colonic transit was determined using a bead propulsion assay.

KEY

RESULTS

In Calb1-GCaMP6 mice, propionate exhibited the highest and most sustained Ca2+ fluorescence (∆F/F0 288.2 ± 81.2) with the fastest time to peak (7.3 ± 1.6 min) and longest decay time (10.1 ± 3.0 min), followed by acetate, butyrate, and a mixture of the three SCFAs at physiological concentrations. Similar patterns were observed in Wnt-1-GCaMP6 mice, where propionate induced the highest Ca2+ fluorescence (∆F/F0 240.5 ± 25.7) and the longest decay time (10.2 ± 0.9 min). BHB and GLPG0976 significantly attenuated SCFA-induced Ca2+ fluorescence in both IPANs and myenteric neurons. SCFAs delay colonic bead propulsion, an effect abolished by both FFAR antagonists.

CONCLUSIONS AND INFERENCES: Acutely, luminal administration of SCFAs activates myenteric neurons and slows colonic transit through FFAR2 and FFAR3 receptors.