Analysis of the transcription factor cascade that induces endocrine and exocrine cell lineages from pancreatic progenitor cells using a polyoma-based episomal vector system

Acinar-to-ductal metaplasia induced by adenovirus-mediated pancreatic expression of Isl1

Tubular complexes (TCs) are aggregates of duct-like monolayered cells in the developing and regenerating pancreas. Recent studies showed that TCs have regenerative potential, including islet neogenesis. We previously delivered adenovirus vector (AdV) into exocrine cells of the pancreas by intra-common bile ductal (ICBD) injection, and found that AdV expressing Pdx1, a pancreas-specific transcription factor, causes TC formation and islet neogenesis. We also established RTF-Pdx1-EGFP mice, which ubiquitously express Pdx1 when tetracycline is removed from the drinking water. However, exogenous Pdx1 expression in adult RTF-Pdx1-EGFP mice did not cause any pathological changes in the pancreas during three weeks of observation after tetracycline withdrawal. To examine whether the host immune response induced by AdV was involved in TC formation, we delivered AdVs expressing pancreas-related transcription factors or an irrelevant protein into the pancreas of RTF-Pdx1-EGFP mice. Histological analyses showed that both AdV injection and Pdx1 expression are required for TC formation. We also analyzed the effects of these ICBD-injected AdVs. AdV expressing Isl1, a proendocrine transcription factor, effectively induced TC formation through acinar-to-ductal metaplasia, and exogenous Pdx1 expression facilitated this process. Considering the regenerative potential of TCs, a strategy that efficiently induces TC formation may lead to novel therapies for diabetes.