The ghrelin gene products and exendin-4 promote survival of human pancreatic islet endothelial cells in hyperglycaemic conditions, through phosphoinositide 3-kinase/Akt, extracellular signal-related kinase (ERK)1/2 and cAMP/protein kinase A (PKA) signalling pathways.
OBJECTIVE
Pancreatic islet microendothelium exhibits unique features in interdependent relationship with beta cells. Gastrointestinal products of the ghrelin gene, acylated ghrelin (AG), unacylated ghrelin (UAG) and obestatin (Ob), and the incretin, glucagon-like peptide-1 (GLP-1), prevent apoptosis of pancreatic beta cells. We investigated whether the ghrelin gene products and the GLP-1 receptor agonist exendin-4 (Ex-4) display survival effects in human pancreatic islet microendothelial cells (MECs) exposed to chronic hyperglycaemia.


METHODS
Islet MECs were cultured in high glucose concentration and treated with AG, UAG, Ob or Ex-4. Apoptosis was assessed by DNA fragmentation, Hoechst staining of the nuclei and caspase-3 activity. Western blot analyses and pharmacological inhibition of protein kinase B (Akt) and extracellular signal-related kinase (ERK)1/2 pathways, detection of intracellular cAMP levels and blockade of adenylyl cyclase (AC)/cAMP/protein kinase A (PKA) signalling were performed. Levels of NO, IL-1β and vascular endothelial growth factor (VEGF)-A in cell culture supernatant fractions were measured.


RESULTS
Islet MECs express the ghrelin receptor GHS-R1A as well as GLP-1R. Treatment with AG, UAG, Ob and Ex-4 promoted cell survival and significantly inhibited glucose-induced apoptosis, through activation of PI3K/Akt, ERK1/2 phosphorylation and intracellular cAMP increase. Moreover, peptides upregulated B cell lymphoma 2 (BCL-2) and downregulated BCL-2-associated X protein (BAX) and CD40 ligand (CD40L) production, and significantly reduced the secretion of NO, IL-1β and VEGF-A.


CONCLUSIONS
The ghrelin gene-derived peptides and Ex-4 exert cytoprotective effects in islet MECs. The anti-apoptotic effects involve phosphoinositide 3-kinase (PI3K)/Akt, ERK1/2 and cAMP/PKA pathways. These peptides could therefore represent a potential tool to improve islet vascularisation and, indirectly, islet cell function.
Department of Internal Medicine, University of Turin, Turin, Italy.
E
E
Favaro
R
R
Granata
I
I
Miceli
A
A
Baragli
F
F
Settanni
P
P
Cavallo Perin
E
E
Ghigo
G
G
Camussi
M M
MM
Zanone
D017209:Apoptosis / Q000187:drug effects / Q000502:physiology; D053148:Caspase 3 / Q000378:metabolism; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D042783:Endothelial Cells / Q000187:drug effects* / Q000201:enzymology; D000077270:Exenatide; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D054439:Ghrelin / Q000494:pharmacology*; D005947:Glucose / Q000378:metabolism / Q000494:pharmacology*; D006801:Humans; D007515:Islets of Langerhans / Q000187:drug effects* / Q000201:enzymology; D010455:Peptides / Q000494:pharmacology*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects / Q000502:physiology; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D054440:Receptors, Ghrelin / Q000037:antagonists & inhibitors / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism; D014688:Venoms / Q000494:pharmacology*; D051028:bcl-2-Associated X Protein / Q000378:metabolism
D054439:Ghrelin; D010455:Peptides; D054440:Receptors, Ghrelin; D042461:Vascular Endothelial Growth Factor A; D014688:Venoms; D051028:bcl-2-Associated X Protein; D000077270:Exenatide; D000242:Cyclic AMP; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D017868:Cyclic AMP-Dependent Protein Kinases; D048049:Extracellular Signal-Regulated MAP Kinases; D053148:Caspase 3; D005947:Glucose