Improved retention of zymogen granules in cultured murine pancreatic acinar cells and induction of acinar-ductal transdifferentiation in vitro

Objectives: To establish a primary culture model for murine pancreatic acinar cells and to investigate the effects of different culture conditions on the phenotype and plasticity of these cells in extended culture. Methods: Acinar cells, cultured in Chee (CME) or Waymouth/Ham F-12 (WHME) media, exhibited 2 markedly dissimilar phenotypes. We employed 5'-bromo-2'-deoxyuridine ( BrdU) incorporation, immunocytochemistry, and electron microscopy to investigate differences in cell cycle status and phenotype. Results: CME-cultured cells grew as discrete epithelial islands and retained zymogen granules and endoplasmic reticulum stacks, yet expressed cytokeratin 7, suggesting that they comprise an intermediate between the acinar and ductal cell types. Observed by timelapse videomicroscopy, cells transferred to WHME formed a confluent monolayer,flattened and dedifferentiated to a duct-like phenotype typified by loss of secretory apparatus, variable beta-catenin expression, an elongated teardrop shape, increased cell size, and nuclear pleomorphism. Transition between phenotypes did not involve apoptosis as assessed by morphologic criteria in Feulgen-stained cultures. The flattened cells exhibited increased BrdU incorporation and mitotic index, suggesting that dedifferentiation precedes the capacity for increased cell cycle entry, while the appearance of meganuclei is consistent with amplified DNA content. We also demonstrate greatly improved gene delivery to cultured acinar cells by adenovirus-mediated transduction compared with lipid-mediated transfection. Conclusions: This in vitro model confirms the plasticity of acinar cells and may serve to delineate the changes underlying acinar cell dedifferentiation and acquisition of a duct-like pluripotent phenotype.