Research Article: Dexamethasone Treatment Induces the Reprogramming of Pancreatic Acinar Cells to Hepatocytes and Ductal Cells

Date Published: October 27, 2010

Publisher: Public Library of Science

Author(s): Amani Al-Adsani, Zoë D. Burke, Daniel Eberhard, Katherine L. Lawrence, Chia-Ning Shen, Anil K. Rustgi, Hiroshi Sakaue, J. Mark Farrant, David Tosh, Irene Oi Lin Ng.

Abstract: The pancreatic exocrine cell line AR42J-B13 can be reprogrammed to hepatocytes following treatment with dexamethasone. The question arises whether dexamethasone also has the capacity to induce ductal cells as well as hepatocytes.

AR42J-B13 cells were treated with and without dexamethasone and analyzed for the expression of pancreatic exocrine, hepatocyte and ductal markers. Addition of dexamethasone inhibited pancreatic amylase expression, induced expression of the hepatocyte marker transferrin as well as markers typical of ductal cells: cytokeratin 7 and 19 and the lectin peanut agglutinin. However, the number of ductal cells was low compared to hepatocytes. The proportion of ductal cells was enhanced by culture with dexamethasone and epidermal growth factor (EGF). We established several features of the mechanism underlying the transdifferentiation of pancreatic exocrine cells to ductal cells. Using a CK19 promoter reporter, we show that a proportion of the ductal cells arise from differentiated pancreatic exocrine-like cells. We also examined whether C/EBPβ (a transcription factor important in the conversion of pancreatic cells to hepatocytes) could alter the conversion from acinar cells to a ductal phenotype. Overexpression of an activated form of C/EBPβ in dexamethasone/EGF-treated cells provoked the expression of hepatocyte markers and inhibited the expression of ductal markers. Conversely, ectopic expression of a dominant-negative form of C/EBPβ, liver inhibitory protein, inhibited hepatocyte formation in dexamethasone-treated cultures and enhanced the ductal phenotype.

These results indicate that hepatocytes and ductal cells may be induced from pancreatic exocrine AR42J-B13 cells following treatment with dexamethasone. The conversion from pancreatic to hepatocyte or ductal cells is dependent upon the expression of C/EBPβ.

Partial Text: Transdifferentiation belongs to the wider class of cell type conversions known as reprogramming [1]. One example of reprogramming is the conversion of pancreatic cells to hepatocytes. The appearance of hepatic foci in adult pancreas has been observed in rodent models and cancer patients [2], [3], [4], [5].

Acinar-ductal transdifferentiation is clinically significant as it is present in pancreatitis. The switch from acinar to ductal cell can be induced in vivo by pancreatic ductal ligation [21], overexpression of Pdx1 [31], or in vitro by the addition of external factors (DMSO) [32] or EGF [19], [24]. In the present study, we demonstrate that cells resembling a ductal phenotype are also induced following treatment of pancreatic B13 cells with Dex. The efficiency of conversion to a ductal phenotype is very low but can be enhanced by a combined treatment of Dex followed by EGF. Dex treatment has been shown previously to induce the conversion of pancreatic cells towards a hepatocyte phenotype [6], [7], [30], [33]. Remarkably, the conversion to ductal cells is stable as ductal cells maintained their phenotype for at least for 7 days after withdrawal of EGF. These observations suggest a bistable switch operates in which pancreatic B13 cells can generate either hepatocytes or ductal cells following Dex treatment. Due to the acinar nature (amylase-expression) of the B13 cells it is possible that the cells can undergo acinar-ductal metaplasia similar to that described in a number of other systems [20], [32], [34]. The evidence for a genuine acinar-ductal conversion in the B13 cell model is threefold. First, the typical duct cytokeratin CK7 is induced after treatment and are not present in control cells. Moreover, other duct and progenitor markers such as CK20, OV-6 and PNA are increased in Dex treated compared to untreated cultures. Second, morphological and ultrastructural features reminiscent of ductal cells (such as well-formed microvilli) are present. Third, we were able to identify a population of cells co-expressing amylase and CK19 (as shown by a GFP reporter construct) which indicates an intermediate population of amylase expressing cells may generate at least some of the ductal cells. At the same time there were no cells co-staining for hepatocyte markers and CK19. Therefore, we propose that ductal cells can arise from amylase-positive acinar cells following treatment with Dex and that ductal cells form a separate population of cells independent of the reprogrammed hepatocytes (Figure 8).