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

• DOI: 10.1007/s00125-012-2716-9
• Publication Date: 2012-09-10T19:51:58Z
• Authors: P. Marchetti; R. Lupi; M. Bugliani; C. L. Kirkpatrick; G. Sebastiani; F. A. Grieco; S. Del Guerra; V. D’Aleo; S. Piro; L. Marselli; U. Boggi; F. Filipponi; L. Tinti; L. Salvini; C. B. Wollheim; F. Purrello; F. Dotta
• Keywords: Male; 0301 basic medicine; Insulin/metabolism; Insulin -- metabolism; Pancreas -- metabolism; Pancreatic islets; Glucagon-Like Peptide 1 -- metabolism; Alpha cell; Mass Spectrometry; 03 medical and health sciences; Glucagon-Like Peptide 1/metabolism; Glucagon-Like Peptide 1; Diabetes Mellitus; Humans; Insulin; info:eu-repo/classification/ddc/612; Glucagon/metabolism; ddc:612; Alpha cells; GLP-1; Glucagon; Pancreatic islets; Pancreas; Glucagon-Secreting Cells/metabolism; Pancreas/metabolism; Diabetes Mellitus, Type 2 -- metabolism; Sciences bio-médicales et agricoles; Middle Aged; Glucagon; Glucagon-Secreting Cells -- metabolism; Diabetes Mellitus, Type 2/metabolism; Immunohistochemistry; Type 2 -- metabolism; 3. Good health; Glucagon -- metabolism; Diabetes Mellitus, Type 2; Glucagon-Secreting Cells; Female; GLP-1

Glucagon-like peptide 1 (GLP-1) is a major incretin, mainly produced by the intestinal L cells, with beneficial actions on pancreatic beta cells. However, while in vivo only very small amounts of GLP-1 reach the pancreas in bioactive form, some observations indicate that GLP-1 may also be produced in the islets. We performed comprehensive morphological, functional and molecular studies to evaluate the presence and various features of a local GLP-1 system in human pancreatic islet cells, including those from type 2 diabetic patients.The presence of insulin, glucagon, GLP-1, proconvertase (PC) 1/3 and PC2 was determined in human pancreas by immunohistochemistry with confocal microscopy. Islets were isolated from non-diabetic and type 2 diabetic donors. GLP-1 protein abundance was evaluated by immunoblotting and matrix-assisted laser desorption-ionisation-time of flight (MALDI-TOF) mass spectrometry. Single alpha and beta cell suspensions were obtained by enzymatic dissociation and FACS sorting. Glucagon and GLP-1 release were measured in response to nutrients.Confocal microscopy showed the presence of GLP-1-like and PC1/3 immunoreactivity in subsets of alpha cells, whereas GLP-1 was not observed in beta cells. The presence of GLP-1 in isolated islets was confirmed by immunoblotting, followed by mass spectrometry. Isolated islets and alpha (but not beta) cell fractions released GLP-1, which was regulated by glucose and arginine. PC1/3 (also known as PCSK1) gene expression was shown in alpha cells. GLP-1 release was significantly higher from type 2 diabetic than from non-diabetic isolated islets.We have shown the presence of a functionally competent GLP-1 system in human pancreatic islets, which resides in alpha cells and might be modulated by type 2 diabetes.