Reduction of epithelial secretion in male rat distal colonic mucosa by bile acid receptor TGR5 agonist, INT-777: role of submucosal neurons.
BACKGROUND
Recent evidence from rat neuron-free mucosa study suggests that 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 immunohistochemistry 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.


RESULTS
TGR5 mRNA is expressed in full thickness dC and pC and immunoreactivity is located in colonocytes and pChAT-positive neurons. Addition of INT-777, and less potently UDCA, decreased 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's inhibitory effect while the 5-HT4antagonist, RS-39604, and lidocaine abolished it. INT-777 inhibited stimulated colonic secretion induced by nicotine, but not cisapride, carbachol or PGE2.


CONCLUSIONS
TGR5 activation inhibits 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.
CURE: Digestive Diseases Research Center and Center for Neurobiology of Stress, Department of Medicine, Division of Digestive Diseases, David Geffen School of Medicine at UCLA.|VA Greater Los Angeles Healthcare System, Los Angeles, CA 90073, USA.|DHU UNITY, Inserm UMR 1149, and Louis Mourier Hospital, Department of Gastroenterology and Hepatology, AP-HP, University Paris Diderot Sorbonne Paris Cité, Paris, France.
Henri
H
Duboc
CURE: Digestive Diseases Research Center and Center for Neurobiology of Stress, Department of Medicine, Division of Digestive Diseases, David Geffen School of Medicine at UCLA.|VA Greater Los Angeles Healthcare System, Los Angeles, CA 90073, USA.|Educational-Scientific Center "Institute of Biology" Taras Shevchenko National University of Kyiv, Kyiv, Ukraine.
Ganna
G
Tolstanova
CURE: Digestive Diseases Research Center and Center for Neurobiology of Stress, Department of Medicine, Division of Digestive Diseases, David Geffen School of Medicine at UCLA.|VA Greater Los Angeles Healthcare System, Los Angeles, CA 90073, USA.
Pu-Qing
PQ
Yuan
CURE: Digestive Diseases Research Center and Center for Neurobiology of Stress, Department of Medicine, Division of Digestive Diseases, David Geffen School of Medicine at UCLA.|VA Greater Los Angeles Healthcare System, Los Angeles, CA 90073, USA.
Vincent
V
Wu
Department of Medicine, School of Medicine, UCLA.|Brentwood Biomedical Research Institute, Los Angeles, California, USA.
Izumi
I
Kaji
CURE: Digestive Diseases Research Center and Center for Neurobiology of Stress, Department of Medicine, Division of Digestive Diseases, David Geffen School of Medicine at UCLA.|VA Greater Los Angeles Healthcare System, Los Angeles, CA 90073, USA.
Mandy
M
Biraud
VA Greater Los Angeles Healthcare System, Los Angeles, CA 90073, USA.|Department of Medicine, School of Medicine, UCLA.|Brentwood Biomedical Research Institute, Los Angeles, California, USA.
Yasutada
Y
Akiba
VA Greater Los Angeles Healthcare System, Los Angeles, CA 90073, USA.|Department of Medicine, School of Medicine, UCLA.|Department of Surgery, School of Medicine, UCLA.|Brentwood Biomedical Research Institute, Los Angeles, California, USA.
Jonathan
J
Kaunitz
CURE: Digestive Diseases Research Center and Center for Neurobiology of Stress, Department of Medicine, Division of Digestive Diseases, David Geffen School of Medicine at UCLA.|VA Greater Los Angeles Healthcare System, Los Angeles, CA 90073, USA.
Mulugeta
M
Million
CURE: Digestive Diseases Research Center and Center for Neurobiology of Stress, Department of Medicine, Division of Digestive Diseases, David Geffen School of Medicine at UCLA.|VA Greater Los Angeles Healthcare System, Los Angeles, CA 90073, USA.
Yvette
Y
Tache
CURE: Digestive Diseases Research Center and Center for Neurobiology of Stress, Department of Medicine, Division of Digestive Diseases, David Geffen School of Medicine at UCLA.|VA Greater Los Angeles Healthcare System, Los Angeles, CA 90073, USA.
Muriel
M
Larauche
D000818:Animals; D001647:Bile Acids and Salts / Q000378:metabolism; D002793:Cholic Acids / Q000494:pharmacology*; D003106:Colon / Q000187:drug effects* / Q000378:metabolism*; D007413:Intestinal Mucosa / Q000187:drug effects* / Q000378:metabolism*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D043562:Receptors, G-Protein-Coupled / Q000819:agonists* / Q000378:metabolism
C545501:6alpha-ethyl-23(S)-methylcholic acid; D001647:Bile Acids and Salts; D002793:Cholic Acids; C518268:Gpbar1 protein, rat; D043562:Receptors, G-Protein-Coupled
TGR5; Ussing chambers; bile acids; distal colon; secretion; submucosal neurons