Upregulation of alpha cell glucagon-like peptide 1 (GLP-1) in Psammomys obesus—an adaptive response to hyperglycaemia?

Abstract

Aims/hypothesis The hormone glucagon-like peptide 1 (GLP-1) is released in response to a meal from the intestinal L-cells, where it is processed from proglucagon by the proconvertase (PC)1/3. In contrast, in the adult islets proglucagon is processed to glucagon by the PC2 enzyme.

A local glucagon-like peptide 1 (GLP-1) system in human pancreatic islets

“…GLP-1-like immunoreactivity was detected by a polyclonal and a monoclonal anti-GLP-1 antibody reacting, respectively, with the mid to C terminal region of GLP-1 [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] and the amidated C-terminus of the peptide (see the Methods). These antibodies generated similar staining patterns with NCI-H716 cells and human islets (ESM Figs 2 and 3).…”

“…The corresponding spectra of the GLP-1(7-37) and GLP-1 (7-36) tryptic sequences were matched with the putative digested sequences of the peptides using the sequence editor implemented on BIOTOOLS. GLP-1(7-37) and GLP-1(7-36) peptides were identified by the species at m/z 1105 (aa [21][22][23][24][25][26][27][28] and at m/z 2098 (aa [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20].…”

“…Primary antibodies were: guinea pig polyclonal anti-swine insulin (A0564; DAKO, Carpinteria, CA, USA); mouse monoclonal anti-human/ mouse glucagon (MAB1249, clone 181402; R&D Systems, Abingdon, UK); rat monoclonal anti-somatostatin (ab30788; Abcam, Cambridge, UK); rabbit polyclonal anti-GLP-1 (ab22625; Abcam), which reacts with the mid to C terminal region of GLP-1 [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19], enabling immunoreactivity with N terminal truncated and C terminally extended forms of GLP-1; mouse monoclonal anti-GLP-1 (HYB 147-06; BioPorto Diagnostic, Gentofte, Denmark), which is specific for the amidated C-terminus of the peptide [20]; and rabbit polyclonal antibody to PC1/3 and PC2 (Chemicon, Rosemont, IL, USA). Secondary antibodies were: Alexa Fluor 488: goat anti-guinea pig IgG, goat anti-rabbit IgG, and goat anti-mouse IgG; and Alexa Fluor 594: goat anti-mouse IgG and goat antirabbit IgG (all from Invitrogen, Molecular Probes, Leiden, the Netherlands).…”

“…Purified cell preparations were tested with 5.5 mmol/l glucose and 5.5 mmol/l glucose plus 20 mmol/l arginine. In addition, GLP-1 and glucagon release were measured from batches of 50 islets of similar size from non-diabetic and type 2 diabetic preparations, kept in M199 culture medium for 4 h. Finally, to test the bioactivity of islet-released GLP-1, experiments were performed similarly to methods previously reported [17,18], by assessing insulin release from islets exposed to cell culture medium from untreated non-diabetic human islets; this was done at 11 mmol/l glucose, and in the absence or presence of the GLP-1 receptor antagonist, exendin(9-39) (0.5 μmol/l).…”

“…Furthermore, when partial beta cell loss was induced in neonatal rats by streptozotocin, islet cell regeneration was accompanied by alpha cell hyperplasia, with an altered phenotype of increased GLP-1 synthesis [15]. More recently, a study mainly focused on the alpha cell line, αTC1-6, showed the processing of proglucagon to GLP-1, with the incretin also found in rat and human islets [16], while investigators working on the Psammomys obesus gerbil incidentally observed that human islets could release GLP-1 [17]. Finally, an extensive study in rats showed that interleukin-6 could increase GLP-1 release from L cells and alpha cells, with some of the results reproduced with human islets [18].…”