Expansion and Maintenance of CD133-Expressing Pancreatic Ductal Epithelial Cells by Inhibition of TGF-β Signaling.

Restoring β-cell mass by the transplantation of pancreatic islets is an effective diabetes treatment, but it is limited by the shortage of donor organs. CD133-expressing pancreatic ductal epithelial cells (PDECs) have the ability to generate insulin-producing cells. The expansion of these cells is dependent on extrinsic niche factors, but few of those signals have been identified. In this study, CD133-expressing PDECs were purified by sorting from adult wild-type C57BL/6 mice and TGFβRIInull/null mice. Furthermore, using immunofluorescence and transplantation assays, we found that the inhibition of the transforming growth factor-β (TGF-β) pathway promoted the expansion of CD133-expressing PDECs for many generations and maintained the ability of CD133-expressing PDECs to generate insulin-producing cells. Moreover, western blot, qRT-PCR, and dual luciferase assays using TGF-β inhibitors were performed to identify the mechanisms by which TGF-β signaling regulates proliferation and differentiation. The results showed that the inhibition of TGF-β signaling enhanced Id2 binding to the promoter region of the cell proliferation repressor p16 and promoted the expansion of CD133-expressing PDECs, and the increased Id2 binding to NeuroD1 decreased the transcription of Pax6 to maintain CD133-expressing PDECs in the Pdx1-expression stage. Taken together, the effect of TGF-β antagonists on CD133-expressing PDECs reveals a novel paradigm of signaling that explains the balance between the expansion and differentiation of pancreatic duct epithelial progenitors.