Role of phosphodiesterase and adenylate cyclase isozymes in murine colonic glucagon-like peptide 1 secreting cells.
Glucagon-like peptide-1 (GLP-1) is secreted from enteroendocrine L-cells after food intake. Increasing GLP-1 signalling either through inhibition of the GLP-1 degrading enzyme dipeptidyl-peptidase IV or injection of GLP-1-mimetics has recently been successfully introduced for the treatment of type 2 diabetes. Boosting secretion from the L-cell has so far not been exploited, due to our incomplete understanding of L-cell physiology. Elevation of cyclic adenosine monophosphate (cAMP) has been shown to be a strong stimulus for GLP-1 secretion and here we investigate the activities of adenylate cyclase (AC) and phosphodiesterase (PDE) isozymes likely to shape cAMP responses in L-cells.



Expression of AC and PDE isoforms was quantified by RT-PCR. Single cell responses to stimulation or inhibition of AC and PDE isoforms were monitored with real-time cAMP probes. GLP-1 secretion was assessed by elisa.



Quantitative PCR identified expression of protein kinase C- and Ca²+-activated ACs, corresponding with phorbolester and cytosolic Ca²+-stimulated cAMP elevation. Inhibition of PDE2, 3 and 4 were found to stimulate GLP-1 secretion from murine L-cells in primary culture. This corresponded with cAMP elevations monitored with a plasma membrane targeted cAMP probe. Inhibition of PDE3 but not PDE2 was further shown to prevent GLP-1 secretion in response to guanylin, a peptide secreted into the gut lumen, which had not previously been implicated in L-cell secretion.



Our results reveal several mechanisms shaping cAMP responses in GLP-1 secreting cells, with some of the molecular components specifically expressed in L-cells when compared with their epithelial neighbours, thus opening new strategies for targeting these cells therapeutically.
Cambridge Institute for Medical Research, University of Cambridge, Addenbrooke's Hospital, Cambridge, UK.
Ronn S
RS
Friedlander
Daryl
D
Hodge
Jessica
J
Mace
Helen E
HE
Parker
Gwen
G
Tolhurst
Abdella M
AM
Habib
Sebastian
S
Wachten
Dermot M
DM
Cooper
Fiona M
FM
Gribble
Frank
F
Reimann
D000262:Adenylyl Cyclases / Q000502:physiology*; D000818:Animals; D002478:Cells, Cultured; D003106:Colon / Q000166:cytology / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism; D019858:Enteroendocrine Cells / Q000378:metabolism*; D052216:Glucagon-Like Peptide 1 / Q000378:metabolism*; D007413:Intestinal Mucosa / Q000166:cytology / Q000378:metabolism*; D007527:Isoenzymes / Q000502:physiology; D051379:Mice; D008822:Mice, Transgenic; D010727:Phosphoric Diester Hydrolases / Q000502:physiology*
D007527:Isoenzymes; D052216:Glucagon-Like Peptide 1; D000242:Cyclic AMP; D010727:Phosphoric Diester Hydrolases; D000262:Adenylyl Cyclases