Chronic Exposure to GLP-1 Increases GLP-1 Synthesis and Release in a Pancreatic Alpha Cell Line (α-TC1): Evidence of a Direct Effect of GLP-1 on Pancreatic Alpha Cells

Abstract

Aims/HypothesisIncretin therapies, which are used to treat diabetic patients, cause a chronic supra-physiological increase in GLP-1 circulating levels. It is still unclear how the resulting high hormone concentrations may affect pancreatic alpha cells. The present study was designed to investigate the effects of chronic exposure to high GLP-1 levels on a cultured pancreatic alpha cell line.Methodsα-TC1-6 cell line was cultured in the presence or absence of GLP-1 (100 nmol/l) for up to 72 h. In our model GLP-1 receptor (GLP-1R) was measured. After the cells were exposed to GLP-1 the levels of glucagon secretion were measured. Because GLP-1 acts on intracellular cAMP production, the function of GLP-1R was studied. We also investigated the effects of chronic GLP-1 exposure on the cAMP/MAPK pathway, Pax6 levels, the expression of prohormone convertases (PCs), glucagon gene (Gcg) and protein expression, glucagon and GLP-1 production.ResultsIn our model, we were able to detect GLP-1R. After GLP-1 exposure we found a reduction in glucagon secretion. During further investigation of the function of GLP-1R, we found an activation of the cAMP/MAPK/Pax6 pathway and an increase of Gcg gene and protein expression. Furthermore we observed a significant increase in PC1/3 protein expression, GLP-1 intracellular content and GLP-1 secretion.Conclusions/InterpretationOur data indicate that the chronic exposure of pancreatic alpha cells to GLP-1 increases the ability of these cells to produce and release GLP-1. This phenomenon occurs through the stimulation of the transcription factor Pax6 and the increased expression of the protein convertase PC1/3.

Glucagon-Like Peptide 1 Increases β-Cell Regeneration by Promoting α- to β-Cell Transdifferentiation

“…In our study, we found increased proliferation of a-cells in the pancreas of rAd-GLP-1-treated mice compared with rAd-bgal-treated mice after ablation of b-cells by STZ. Similarly, we found that treatment of aTC1-9 cells, which produce glucagon but not preproinsulin mRNA (20,30), with exendin-4, a GLP-1 receptor agonist, increased the proliferation of a-cells.…”

Atorvastatin but Not Pravastatin Impairs Mitochondrial Function in Human Pancreatic Islets and Rat β-Cells. Direct Effect of Oxidative Stress

“…Proteins were extracted from INS-1 cells with RIPA lysis buffer, and Western blotting was performed as previously described 59 . Membranes were incubated with primary antibodies (used at a final dilution 1:1000 in 5% BSA, over night at 4 °C with gentle agitation) for representative subunit of the Complexes I, IV (Thermo Fisher Scientific, Cambridge, UK), III, V (Santa Cruz Biotechnology, Santa Cruz, CA, USA) and for coenzyme Q10 (Abcam, Cambridge, UK) and then exposed to anti-rabbit, anti-mouse (GE Healthcare Life Sciences, Little Chalfont, UK) or anti-goat (Santa Cruz Biotechnology) secondary antibodies (used at a final dilution 1:2000 in 5% milk, 1 hour at room temperature with gentle agitation), conjugated to horseradish peroxidase.…”

GLP-1 Receptor in Pancreatic α-Cells Regulates Glucagon Secretion in a Glucose-Dependent Bidirectional Manner

“…In particular, there is little consensus regarding whether GLP-1R is expressed in glucagon-producing a-cells located in pancreatic islets. Some studies show no GLP-1R protein or mRNA expression in a-cells of normal mice (7), some show GLP-1R is expressed in a small portion of a-cells in adult mice (8,9), and others show clear GLP-1R expression in a-cells, especially during early development and throughout life in mice with a-cell hyperplasia (10,11). To make the topic even more complicated, studies have reported that the commonly used anti-GLP-1R antibodies are neither specific nor sensitive enough to reliably detect GLP-1R expression in tissues (1,12).…”