INCREASING GLP-1-INDUCED β-CELL PROLIFERATION BY SILENCING THE NEGATIVE REGULATORS OF SIGNALING CREMα AND DUSP14

Abstract

Objective: Glucagon-like peptide-1 (GLP-1) is a growth and differentiation factor for mature β-cells and their precursors. However, the overall effect of GLP-1 on increasing β-cell mass both in in vivo and in vitro conditions is relatively small and augmenting this effect would be beneficial for the treatment or prevention of both type 1 and type 2 diabetes. Here, we searched for cellular mechanisms that may limit the proliferative effect of GLP-1 and tested whether blocking them could increase β-cell proliferation.

Research Design and Methods: We examined GLP-1-regulated genes in βTC-Tet cells by cDNA microarrays. To assess the effect of some of these gene on cell proliferation, we reduced their expression using shRNA in β-cell lines and primary mouse islets and measured [³H]thymidine or 5′-bromo-2′-deoxyuridine incorporation.

Results: We identified four negative regulators of intracellular signaling that were rapidly and strongly activated by GLP-1: the regulator of G protein signaling RGS2; the CREB antagonists CREMα and ICERI; and the dual specificity phosphatase DUSP14, a negative regulator of the MAPK/ERK1/2 pathway. We show that knockdown of CREMα or DUSP14, or expression of a dominant-negative form of DUSP14, increased β-cell line proliferation, and enhanced the GLP-1-induced proliferation of primary β-cells.

Conclusions: Together, our data show that: i) the cAMP/PKA/CREB and MAPK/ERK1/2 pathways can additively control β-cell proliferation, ii) β-cells have evolved several mechanisms limiting GLP-1-induced cellular proliferation, iii) blocking these mechanisms increases the positive effect of GLP-1 on β-cell mass.