Background: Previous studies have shown that a combination of both the extracellular matrix and secretagogues plays critical roles in the maintenance of well-differentiated pancreatic acinar cells in culture. In the present study, we have shown that, upon proper stimulation, acinar cells change their growth pattern and morphologic appearance to a duct like phenotype.
Experimental design: Both rat and guinea pig acinar cells were cultured on or embedded into the Matrigel basement membrane, in the presence of differentiating agents such as dimethylsulfoxide (DMSO), hexamethyl-bis-acetamide, dimethylformamide, triiodothyronine, and butyric acid. The growth patterns, cell proliferation, ultrastructural appearance, intracellular contents, secretion and immunolocalization of amylase, as well as the expression of the ductal marker carbonic anhydrase II and lectin-binding specific sites were analyzed. Moreover, the effects of metabolic inhibitors such as cycloheximide and actinomycin D on the DMSO induced action were also examined.
Results: Isolated acinar cells from both rat and guinea pig pancreas showed an important modification of their growth pattern and morphologic appearance when culture embedded into Matrigel in the presence of 2% DMSO. They reaggregate and form isolated branched tubular structures lined by a single cell layer. These tubules can be maintained in culture for over a period of 21 days. The cells lining the tubules were originally acinar cells that became elongated and progressively lost their secretory granules. They displayed a lower number of apical microvilli and established long junctional complexes with elaborated interdigitations. The immunocytochemical localization and biochemical determination of intracellular and secreted amylase revealed a progressive decrease reaching minimal values by the 12th day of culture. The cells further expressed the duct cell marker carbonic anhydrase II and lost the Helix pomatia lectin-binding affinity characteristic of acinar cells. Cell proliferation by modified cells as measured by thymidine incorporation and the autoradiographic labeling index, was significantly lower than in control cultured acinar cells. The DMSO differentiating action was mimicked, but to a lesser extent, by the other agents except butyric acid. Since cycloheximide and actinomycin D inhibited the DMSO-induced changes, protein synthesis and DNA transcription seem to be required.
Conclusions: Our results demonstrate that normal pancreatic acinar cells retain a morphogenetic plasticity and, upon particular stimulation, can change their differentiation commitment pattern toward that of the duct cell phenotype.