TGR5 Activation Promotes Stimulus-Secretion Coupling of Pancreatic ß-Cells via a PKA-Dependent Pathway.
Diabetes
; 68(2): 324-336, 2019 02.
Article
in En
| MEDLINE
| ID: mdl-30409782
ABSTRACT
The Takeda-G-protein-receptor-5 (TGR5) mediates physiological actions of bile acids. Since it was shown that TGR5 is expressed in pancreatic tissue, a direct TGR5 activation in ß-cells is currently postulated and discussed. The current study reveals that oleanolic acid (OLA) affects murine ß-cell function by TGR5 activation. Both a Gαs inhibitor and an inhibitor of adenylyl cyclase (AC) prevented stimulating effects of OLA. Accordingly, OLA augmented the intracellular cAMP concentration. OLA and two well-established TGR5 agonists, RG239 and tauroursodeoxycholic acid (TUDCA), acutely promoted stimulus-secretion coupling (SSC). OLA reduced KATP current and elevated current through Ca2+ channels. Accordingly, in mouse and human ß-cells, TGR5 ligands increased the cytosolic Ca2+ concentration by stimulating Ca2+ influx. Higher OLA concentrations evoked a dual reaction, probably due to activation of a counterregulating pathway. Protein kinase A (PKA) was identified as a downstream target of TGR5 activation. In contrast, inhibition of phospholipase C and phosphoinositide 3-kinase did not prevent stimulating effects of OLA. Involvement of exchange protein directly activated by cAMP 2 (Epac2) or farnesoid X receptor (FXR2) was ruled out by experiments with knockout mice. The proposed pathway was not influenced by local glucagon-like peptide 1 (GLP-1) secretion from α-cells, shown by experiments with MIN6 cells, and a GLP-1 receptor antagonist. In summary, these data clearly demonstrate that activation of TGR5 in ß-cells stimulates insulin secretion via an AC/cAMP/PKA-dependent pathway, which is supposed to interfere with SSC by affecting KATP and Ca2+ currents and thus membrane potential.
Full text:
1
Collection:
01-internacional
Database:
MEDLINE
Main subject:
Cyclic AMP-Dependent Protein Kinases
/
Receptors, G-Protein-Coupled
/
Insulin-Secreting Cells
Type of study:
Prognostic_studies
Limits:
Animals
/
Female
/
Humans
/
Male
Language:
En
Journal:
Diabetes
Year:
2019
Document type:
Article
Affiliation country:
Germany