Objectives: Glucagon-like peptide-1 (GLP-1) is known to stimulate glucose-dependent insulin production and secretion by pancreatic beta-cells. Preliminary evidence suggests that GLP-1 may also influence endocrine differentiation from pancreatic progenitor cells. Additionally, TGF-beta signaling can also control endocrine differentiation by both inhibiting proliferation and enhancing differentiation of endocrine progenitor cells to become mature beta-cells. Here we document synergy of these two signaling pathways in the differentiation of endocrine cells in the developing pancreas.
Methods: Embryonic pancreas was harvested from mice at day 11.5 and cultured for six days with GLP-1 agonist, exendin-4, and/or TGF-beta1 ligand. Also, a pan-neutralizing TGF-beta isoform antibody was used alone or with exendin-4 to study TGF-beta inhibition in this system. Pancreatic cultures were processed for immunohistochemistry.
Results: Exogenous TGF-beta1 and exendin-4 each individually enhanced both insulin and glucagon differentiation dose-dependently. However, when combined there was an additive effect to a 4.5-fold increase in insulin-positive differentiation. We also saw suppression of amylase-positive differentiation. Surprisingly, TGF-beta pan-neutralizing antibody also gave an augmentation of endocrine differentiation by 1.5 to 2-fold, but no synergistic effect was seen with exendin-4.
Conclusion: We conclude that TGF-beta isoforms have a specific synergistic role with GLP-1 pathway signaling in early pancreatic development, toward endocrine differentiation and away from acinar differentiation.