OBESTATIN PROMOTES SURVIVAL OF PANCREATIC β-CELLS AND HUMAN ISLETS AND INDUCES EXPRESSION OF GENES INVOLVED IN THE REGULATION OF β-CELL MASS AND FUNCTION

Abstract

Objective: Obestatin is a newly discovered peptide encoded by the ghrelin gene whose biological functions are poorly understood. We investigated obestatin effect on survival of β-cells and human pancreatic islets and the underlying signaling pathways.

Research Design and Methods: β-cells and human islets were used to assess obestatin effect on cell proliferation, survival, apoptosis, intracellular signaling and gene expression.

Results: Obestatin showed specific binding on HIT-T15 and INS-1E β-cells, bound to GLP-1R and recognized ghrelin binding sites. Obestatin, exerted proliferative, survival and antiapoptotic effects, under serum deprived conditions and IFN-γ/TNF-α/IL-1β treatment, particularly at pharmacological concentrations. Ghrelin receptor antagonist [D-Lys³]-GHRP-6 and anti-ghrelin antibody prevented obestatin-induced survival in β-cells and human islets. β-cells and islet cells released obestatin and addition of anti-obestatin antibody reduced their viability. Obestatin increased β-cell cAMP and activated ERK1/2 and PI3K/Akt; its antiapoptotic effect was blocked by inhibition of AC/cAMP/PKA, PI3K/Akt and ERK1/2 signaling. Moreover, obestatin up-regulated GLP-1R mRNA and IRS-2 expression and phosphorylation. The GLP-1R antagonist exendin-(9-39) reduced obestatin effect on β-cell survival. In human islets, obestatin, whose immunoreactivity co-localized with that of ghrelin, promoted cell survival and blocked cytokine-induced apoptosis through cAMP increase and involvement of AC/cAMP/PKA signaling. Moreover, obestatin: i) induced PI3K/Akt, ERK1/2 and also CREB phosphorylation; ii) stimulated insulin secretion and gene expression; iii) up-regulated GLP-1R, IRS-2, PDX-1 and glucokinase mRNA.

Conclusions: These results indicate that obestatin promotes β-cell and human islet cell survival and stimulates the expression of main regulatory β-cell genes, identifying a new role for this peptide within the endocrine pancreas.