Expression and function of the bile acid receptor GpBAR1 (TGR5) in the murine enteric nervous system.
BACKGROUND
Bile acids (BAs) regulate cells by activating nuclear and membrane-bound receptors. G protein coupled bile acid receptor 1 (GpBAR1) is a membrane-bound G-protein-coupled receptor that can mediate the rapid, transcription-independent actions of BAs. Although BAs have well-known actions on motility and secretion, nothing is known about the localization and function of GpBAR1 in the gastrointestinal tract.


METHODS
We generated an antibody to the C-terminus of human GpBAR1, and characterized the antibody by immunofluorescence and Western blotting of HEK293-GpBAR1-GFP cells. We localized GpBAR1 immunoreactivity (IR) and mRNA in the mouse intestine, and determined the mechanism by which BAs activate GpBAR1 to regulate intestinal motility.


RESULTS
The GpBAR1 antibody specifically detected GpBAR1-GFP at the plasma membrane of HEK293 cells, and interacted with proteins corresponding in mass to the GpBAR1-GFP fusion protein. GpBAR1-IR and mRNA were detected in enteric ganglia of the mouse stomach and small and large intestine, and in the muscularis externa and mucosa of the small intestine. Within the myenteric plexus of the intestine, GpBAR1-IR was localized to approximately 50% of all neurons and to >80% of inhibitory motor neurons and descending interneurons expressing nitric oxide synthase. Deoxycholic acid, a GpBAR1 agonist, caused a rapid and sustained inhibition of spontaneous phasic activity of isolated segments of ileum and colon by a neurogenic, cholinergic and nitrergic mechanism, and delayed gastrointestinal transit.


CONCLUSIONS
G protein coupled bile acid receptor 1 is unexpectedly expressed in enteric neurons. Bile acids activate GpBAR1 on inhibitory motor neurons to release nitric oxide and suppress motility, revealing a novel mechanism for the actions of BAs on intestinal motility.
Department of Surgery, University of California, San Francisco, CA, USA.
D P
DP
Poole
C
C
Godfrey
F
F
Cattaruzza
G S
GS
Cottrell
J G
JG
Kirkland
J C
JC
Pelayo
N W
NW
Bunnett
C U
CU
Corvera
D000818:Animals; D015153:Blotting, Western; D002460:Cell Line; D000242:Cyclic AMP / Q000096:biosynthesis; D017615:Enteric Nervous System / Q000378:metabolism*; D005455:Fluorescent Antibody Technique; D005746:Gastric Emptying; D005769:Gastrointestinal Motility; D041981:Gastrointestinal Tract / Q000033:anatomy & histology / Q000378:metabolism; D007150:Immunohistochemistry; D007422:Intestines / Q000294:innervation; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018613:Microscopy, Confocal; D009046:Motor Neurons / Q000502:physiology; D009197:Myenteric Plexus / Q000378:metabolism; D009569:Nitric Oxide / Q000502:physiology; D012313:RNA / Q000096:biosynthesis / Q000235:genetics; D043562:Receptors, G-Protein-Coupled / Q000096:biosynthesis* / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction
C513561:Gpbar1 protein, mouse; D043562:Receptors, G-Protein-Coupled; D009569:Nitric Oxide; D012313:RNA; D000242:Cyclic AMP