Reduction of epithelial secretion in male rat distal colonic mucosa by bile acid receptor TGR5 agonist, INT‐777: role of submucosal neurons

Abstract

Background Recent evidence in rat neuron-free mucosa suggests the membrane bile acid receptor TGR5 decreases colonic secretion under basal and stimulated conditions. As submucosal neurons are key players in secretory processes and highly express TGR5, we investigated their role in TGR5 agonist-induced inhibition of secretion and the pathways recruited. Methods TGR5 expression and localization were assessed in rat proximal (pC) and distal (dC) colon by qPCR and IHC with double labeling for cholinergic neurons in whole-mount preparations. The influence of a selective (INT-777) or weak (ursodeoxycholic acid, UDCA) TGR5 agonist on colonic secretion was assessed in Ussing chambers, in dC preparation removing seromuscular ± submucosal tissues, in the presence of different inhibitors of secretion pathways. Key Results TGR5 mRNA is expressed in whole thickness dC and pC and immunoreactivity is located in colonocytes and pChAT positive neurons. Addition of INT-777, and less potently UDCA, decreases colonic secretion in seromuscular stripped dC by −58.17 ± 2.6%. INT-777 effect on basal secretion was reduced in neuron-free and TTX-treated mucosal-submucosal preparations. Atropine, hexamethonium, indomethacin, and L-NAME all reduced significantly INT-777 inhibitory effect while the 5-HT4 antagonist RS-39604 and lidocaine abolished it. INT-777 inhibited stimulated colonic secretion induced by nicotine, but not cisapride, carbachol or PGE2. Conclusions and Inferences TGR5 activation inhibits the basal and stimulated distal colonic secretion in rats by acting directly on epithelial cells and also inhibiting submucosal neurons. This could represent a counter-regulatory mechanism, at the submucosal level, of the known prosecretory effect of bile acids in the colon.

Synthetic G protein‐coupled bile acid receptor agonists and bile acids act via basolateral receptors in ileal and colonic mucosa

“…While the L cell GPBA signaling was consistent in WT mouse and human mucosae, basolateral TDCA activity involved coincident mechanisms that included epithelial 5‐HT 4 , 41 and enteric cholinergic responses 45,48,49 . Both 5‐HT and cholinergic secretory effects were more evident in PYY−/− colon (where the peptide's antisecretory effects were absent).…”

A Novel Antiserum Against a Predicted Human Peripheral Choline Acetyltransferase (hpChAT) for Labeling Neuronal Structures in Human Colon

“…For visualizing human enteric cholinergic cells, IHC using cChAT antibodies have been applied to studies in normal and diseased tissues (Porter et al, 1996, 2002; Ratcliffe et al, 1998; Neunlist et al, 2003; Beck et al, 2009). In addition, rpChAT antiserum has been utilized in human and animal model studies to clarify the cholinergic roles in the PNS (Tangsucharit et al, 2012; Wang et al, 2012; Duboc et al, 2016; Giancola et al, 2017; Rice et al, 2017; Uranga et al, 2017). For future disease-oriented studies, the hpChAT antiserum may become a novel tool to analyze morphological changes in peripheral cholinergic structures underlying pathological conditions in humans.…”

“…This antiserum against rat pChAT (rpChAT) has been successfully used to study presumed cholinergic cells and fibers in the PNS not only in the rat but also in various species, including vertebrates (mouse, guinea-pig, sheep, pig and monkey) and invertebrates (molluscan octopus; Chiocchetti et al, 2003, 2004; Brehmer et al, 2004; Yuan et al, 2005; Wang et al, 2007; Koga et al, 2013; Sakaue et al, 2014; Bellier et al, 2017). The rpChAT antiserum has been further used for studying animal models of diseases by IHC (Tangsucharit et al, 2012; Wang et al, 2012; Duboc et al, 2016; Rice et al, 2017; Uranga et al, 2017).…”

Microbiota-gut-brain axis: enteroendocrine cells and the enteric nervous system form an interface between the microbiota and the central nervous system

“…Bile acids activate farnesoid X receptor (FXR), and Takeda G protein-coupled receptor 5 (TGR5) (also known as the G protein-coupled bile acid receptor 1) (Schaap et al 2014; Florucci and Distrutti 2015; Copple and Li 2016). TGR5 immunoreactivity is widely distributed throughout the GI tract of mice, with prominent expression in the ENS (Poole et al 2010;Duboc et al 2016). In the colon, bile acids are modified by the gut microbiota, which coverts primary bile acids into secondary more-hydrophobic bile acids via α-dehydroxylation (Li and Chiang 2014; Copple and Li 2016).…”

“…Taken together, these data suggest that luminal secondary bile acids are directly detected by the TGR5 located on EECs to trigger the release of GLP-1 and PYY from L-cells. Then the released gut peptides affect the enteric neuronal circuit to send the information to the CNS (Poole et al 2010;Duboc et al 2016). Alternatively, absorbed secondary bile acids directly active TGR5 on enteric neurons to modulate neuronal activity and send the luminal information to the CNS.…”