The Human and Mouse Islet Peptidome: Effects of Obesity and Type 2 Diabetes, and Assessment of Intraislet Production of Glucagon-like Peptide-1.

Sam G Galvin,Peter Ravn,Pierre Larraufie,Lutz Jermutus,Claire L Meek,Rachel Foreman,Frank Reimann,Emma Biggs,Fiona M Gribble,Richard G Kay

doi:10.1021/acs.jproteome.1c00463

Sam G Galvin, Peter Ravn + Show 8 more

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https://doi.org/10.1021/acs.jproteome.1c00463

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Abstract

To characterize the impact of metabolic disease on the peptidome of human and mouse pancreatic islets, LC-MS was used to analyze extracts of human and mouse islets, purified mouse alpha, beta, and delta cells, supernatants from mouse islet incubations, and plasma from patients with type 2 diabetes. Islets were obtained from healthy and type 2 diabetic human donors, and mice on chow or high fat diet. All major islet hormones were detected in lysed islets as well as numerous peptides from vesicular proteins including granins and processing enzymes. Glucose-dependent insulinotropic peptide (GIP) was not detectable. High fat diet modestly increased islet content of proinsulin-derived peptides in mice. Human diabetic islets contained increased content of proglucagon-derived peptides at the expense of insulin, but no evident prohormone processing defects. Diabetic plasma, however, contained increased ratios of proinsulin and des-31,32-proinsulin to insulin. Active GLP-1 was detectable in human and mouse islets but 100–1000-fold less abundant than glucagon. LC-MS offers advantages over antibody-based approaches for identifying exact peptide sequences, and revealed a shift toward islet insulin production in high fat fed mice, and toward proglucagon production in type 2 diabetes, with no evidence of systematic defective prohormone processing.

Highlights

Pancreatic islets secrete multiple biologically active peptide hormones, most notably insulin, glucagon, and somatostatin (SST), but a number of recent studies have highlighted the possibility that they might secrete the incretin hormones, glucagon-like peptide 1 (GLP-1)[1−6] and glucose-dependent insulinotropic peptide (GIP).[7,8] Intraislet release of GLP-1 has been postulated to modulate insulin secretion under conditions such as metabolic stress, it remains unclear whether it is produced locally at levels sufficient to exert physiologically significant effects on beta cells
The major islet hormones insulin, glucagon, SST, pancreatic polypeptide (PPY), and islet amyloid polypeptide (IAPP) were detected by liquid chromatography coupled to mass spectrometry (LC-MS)/MS in extracts of lysed human and mouse islets (Figure 1a,b)
Using data dependent acquisition (DDA), we detected a range of other peptides, including proinsulin, C-peptide, and partially processed insulins, as well as GRPP and inactive forms of GLP-1 (1−36amide and 1−37)

Summary

Introduction

Pancreatic islets secrete multiple biologically active peptide hormones, most notably insulin, glucagon, and somatostatin (SST), but a number of recent studies have highlighted the possibility that they might secrete the incretin hormones, glucagon-like peptide 1 (GLP-1)[1−6] and glucose-dependent insulinotropic peptide (GIP).[7,8] Intraislet release of GLP-1 has been postulated to modulate insulin secretion under conditions such as metabolic stress, it remains unclear whether it is produced locally at levels sufficient to exert physiologically significant effects on beta cells. Five islet cell populations have been described, including the 3 major cell types: beta cells producing insulin and islet amyloid polypeptide (IAPP), alpha cells producing glucagon and delta cells producing SST-14, together with rarer PP-cells producing pancreatic polypeptide (PPY), and epsilon cells producing ghrelin.[9] Pancreatic islet development shares common endodermal origins and transcription factor requirements with intestinal enteroendocrine cells, so it is not surprising to find overlap of hormone expression between islets and the gut. The intestinal hormone peptide YY (PYY) has been detected in alpha, delta, and gamma cells in mouse but not humans.[10,11] GIP has been detected as a shortened version in human and mouse islets (GIP(1−30), compared with (1−42) in the gut), some antibodies against GIP have been questioned due to their propensity to bind to proglucagon derived peptides,[12−14] and transcriptomic studies failed to find expression of Gip in mouse[11] or human islets.[10]

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