Abstract
BACKGROUND AND PURPOSEGlucagon-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.EXPERIMENTAL APPROACHExpression 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.KEY RESULTSQuantitative 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.CONCLUSIONS AND IMPLICATIONSOur 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.
Highlights
Glucagon-like peptide 1 (GLP-1) is an incretin hormone secreted from the intestinal L-cell after a meal
To investigate if activation of adenylate cyclase is sufficient to stimulate GLP-1 secretion we incubated GLUTag cells and Changes in cyclic adenosine monophosphate (cAMP) concentration in response to AC-activation. (A) GLUTag cells transfected with cytosolic Epac1-based Förster resonance energy transfer (FRET) probes were perfused with 1 mM or 3 mM forskolin, followed by 10 mM forskolin/100 mM isobutyl 1-methylxanthine (IBMX), as indicated while cyan fluorescent protein (CFP) and yellow fluorescent protein (YFP) emission was monitored in response to excitation with 435/10 nm
Each trace represents the CFP/YFP ratio of a single cell normalized to the starting value. (B) Changes in the CFP/YFP emission ratio in response to forskolin concentrations ranging from 100 nM to 30 mM for cells transfected with Epac1-camps or cAMP-regulated guanine nucleotide exchange factor II (Epac2)-camps
Summary
Glucagon-like peptide 1 (GLP-1) is an incretin hormone secreted from the intestinal L-cell after a meal. As the plasma GLP-1 levels and antidiabetic effects achieved by DPP-IV inhibition do not match those of injectable mimetics (Nauck et al, 2009) an obvious strategy would be to combine them with agents that boost secretion of endogenous GLP-1. That such a GLP-1 pool would be available and effective is suggested by the elevated GLP-1 concentrations seen after bariatric surgery (Morínigo et al, 2006; Dirksen et al, 2009; Vidal et al, 2009).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
