Obestatin Promotes Survival of Pancreatic -Cells and Human Islets and Induces Expression of Genes Involved in the Regulation of -Cell Mass and Function

RESULTS—Obestatin showed specific binding on HIT-T15 and INS-1E -cells, bound to glucagon-like peptide-1 receptor (GLP1R), and recognized ghrelin binding sites. Obestatin exerted proliferative, survival, and antiapoptotic effects under serumdeprived conditions and interferon/tumor necrosis factor/ interleukin-1 treatment, particularly at pharmacological concentrations. Ghrelin receptor antagonist [D-Lys]-growth hormone releasing peptide-6 and anti-ghrelin antibody prevented obestatin-induced survival in -cells and human islets. -Cells and islet cells released obestatin, and addition of anti-obestatin antibody reduced their viability. Obestatin increased -cell cAMP and activated extracellular signal–related kinase 1/2 (ERK1/2) and phosphatidylinositol 3-kinase (PI 3-kinase)/Akt; its antiapoptotic effect was blocked by inhibition of adenylyl cyclase/cAMP/ protein kinase A (PKA), PI 3-kinase/Akt, and ERK1/2 signaling. Moreover, obestatin upregulated GLP-1R mRNA and insulin receptor substrate-2 (IRS-2) expression and phosphorylation. The GLP-1R antagonist exendin-(9-39) reduced obestatin effect on -cell survival. In human islets, obestatin, whose immunoreactivity colocalized with that of ghrelin, promoted cell survival and blocked cytokine-induced apoptosis through cAMP increase and involvement of adenylyl cyclase/cAMP/PKA signaling. Moreover, obestatin 1) induced PI 3-kinase/Akt, ERK1/2, and also cAMP response element–binding protein phosphorylation; 2) stimulated insulin secretion and gene expression; and 3) upregulated GLP-1R, IRS-2, pancreatic and duodenal homeobox-1, and glucokinase mRNA.