Acylated and unacylated ghrelin promote proliferation and inhibit apoptosis of pancreatic beta-cells and human islets: involvement of 3',5'-cyclic adenosine monophosphate/protein kinase A, extracellular signal-regulated kinase 1/2, and phosphatidyl inositol 3-Kinase/Akt signaling.
Among its pleiotropic actions, ghrelin modulates insulin secretion and glucose metabolism. Herein we investigated the role of ghrelin in pancreatic beta-cell proliferation and apoptosis induced by serum starvation or interferon (IFN)-gamma/TNF-alpha, whose synergism is a major cause for beta-cell destruction in type I diabetes. HIT-T15 beta-cells expressed ghrelin but not ghrelin receptor (GRLN-R), which binds acylated ghrelin (AG) only. However, both unacylated ghrelin (UAG) and AG recognized common high-affinity binding sites on these cells. Either AG or UAG stimulated cell proliferation through Galpha(s) protein and prevented serum starvation- and IFN-gamma/TNF-alpha-induced apoptosis. Antighrelin antibody enhanced apoptosis in either the presence or absence of serum but not cytokines. AG and UAG even up-regulated intracellular cAMP. Blockade of adenylyl cyclase/cAMP/protein kinase A signaling prevented the ghrelin cytoprotective effect. AG and UAG also activated phosphatidyl inositol 3-kinase (PI3K)/Akt and ERK1/2, whereas PI3K and MAPK inhibitors counteracted the ghrelin antiapoptotic effect. Furthermore, AG and UAG stimulated insulin secretion from HIT-T15 cells. In INS-1E beta-cells, which express GRLN-R, AG and UAG caused proliferation and protection against apoptosis through identical signaling pathways. Noteworthy, both peptides inhibited cytokine-induced NO increase in either HIT-T15 or INS-1E cells. Finally, they induced cell survival and protection against apoptosis in human islets of Langerhans. These expressed GRLN-R but showed also UAG and AG binding sites. Our data demonstrate that AG and UAG promote survival of both beta-cells and human islets. These effects are independent of GRLN-R, are likely mediated by AG/UAG binding sites, and involve cAMP/PKA, ERK1/2, and PI3K/Akt.
Granata
Riccarda
R
Laboratory of Molecular and Cellular Endocrinology, Division of Endocrinology and Metabolism, Department of Internal Medicine, University of Turin, Corso Dogliotti 14, 10126 Turin, Italy. riccarda.granata@unito.it
Settanni
Fabio
F
Biancone
Luigi
L
Trovato
Letizia
L
Nano
Rita
R
Bertuzzi
Federico
F
Destefanis
Silvia
S
Annunziata
Marta
M
Martinetti
Monica
M
Catapano
Filomena
F
Ghè
Corrado
C
Isgaard
Jorgen
J
Papotti
Mauro
M
Ghigo
Ezio
E
Muccioli
Giampiero
G
D000215:Acylation; D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D001665:Binding Sites; D002460:Cell Line; D049109:Cell Proliferation / Q000187:drug effects*; D006224:Cricetinae; D016895:Culture Media, Serum-Free / Q000494:pharmacology; D000242:Cyclic AMP / Q000502:physiology; D054746:Cyclic AMP-Dependent Protein Kinase Type II; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology; D004357:Drug Synergism; D048049:Extracellular Signal-Regulated MAP Kinases / Q000502:physiology; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000378:metabolism; D054439:Ghrelin; D006801:Humans; D066298:In Vitro Techniques; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000166:cytology* / Q000378:metabolism / Q000502:physiology*; D007371:Interferon-gamma / Q000494:pharmacology; D007515:Islets of Langerhans / Q000166:cytology* / Q000502:physiology*; D009569:Nitric Oxide / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D036361:Peptide Hormones / Q000737:chemistry / Q000494:pharmacology*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism; D054440:Receptors, Ghrelin; D015398:Signal Transduction / Q000502:physiology; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
D016895:Culture Media, Serum-Free; D054439:Ghrelin; D007328:Insulin; D036361:Peptide Hormones; D043562:Receptors, G-Protein-Coupled; D054440:Receptors, Ghrelin; D014409:Tumor Necrosis Factor-alpha; D009569:Nitric Oxide; D007371:Interferon-gamma; D000242:Cyclic AMP; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D054746:Cyclic AMP-Dependent Protein Kinase Type II; D017868:Cyclic AMP-Dependent Protein Kinases; D048049:Extracellular Signal-Regulated MAP Kinases; D019205:GTP-Binding Protein alpha Subunits, Gs