Induction and origin of hepatocytes in rat pancreas

Acinar cells and the development of pancreatic fibrosis

Pancreatic fibrosis is caused by excessive deposition of extracellular matrixes of collagen and fibronectin in the pancreatic tissue as a result of repeated injury often seen in patients with chronic pancreatic diseases. The most common causative conditions include inborn errors of metabolism, chemical toxicity and autoimmune disorders. Its pathophysiology is highly complex, including acinar cell injury, acinar stress response, duct dysfunction, pancreatic stellate cell activation, and persistent inflammatory response. However, the specific mechanism remains to be fully clarified. Although the current therapeutic strategies targeting pancreatic stellate cells show good efficacy in cell culture and animal models, they are not satisfactory in the clinic. Without effective intervention, pancreatic fibrosis can promote the transformation from pancreatitis to pancreatic cancer, one of the most lethal malignancies. In the normal pancreas, the acinar component accounts for 82% of the exocrine tissue. Abnormal acinar cells may activate pancreatic stellate cells directly as cellular source of fibrosis or indirectly via releasing various substances and initiate pancreatic fibrosis. A comprehensive understanding of the role of acinar cells in pancreatic fibrosis is critical for designing effective intervention strategies. In this review, we focus on the role of and mechanisms underlying pancreatic acinar injury in pancreatic fibrosis and their potential clinical significance.

Conversion of Fibroblasts to Hepatocytes In Vitro

Primary hepatocytes are widely used in regenerative medicine, drug metabolism analysis, and in vitro drug screens. To overcome the shortage of liver donors, several strategies, such as differentiation of pluripotent stem cells and transdifferentiation from somatic cells, were developed to generate hepatocytes from alternative sources. Here, we describe in detail lenti-virus-based procedure for direct conversion of human fibroblasts to hepatocytes (hiHep cells) in vitro. A detailed protocol for preparation of human fibroblasts from scar tissues is also provided. Based on this protocol, FOXA3, HNF1A, and HNF4A are introduced into SV40-large-T-antigen-expressing human scar fibroblasts by lenti-virus. It usually takes about 5-7 days to get epithelial hiHep colonies. SV40-large-T-antigen-expressing hiHep (hiHep^LT) cells are proliferative and can be expanded to a large number for potential uses.

Expression of transcription factors and stem cell factor precedes hepatocyte differentiation in rat pancreas

Multiple foci of morphologically and functionally differentiated hepatocytes are induced in the pancreas of adult rats subjected to a copper depletion-repletion regimen. Differentiation of hepatocytes in pancreas is preceded by irreversible depletion of over 90% of pancreatic acinar cells. Progressive acinar cell loss during 4-6 weeks of copper deficiency results in the proliferation of oval cells, some of which may serve as the hepatocyte precursor or stem cells. Albumin mRNA is detected in oval cells at 5 and 6 weeks by in situ hybridization at which time no morphologically identifiable hepatocytes are evident in the pancreas. Immunocytochemical analysis demonstrated the presence of stem cell factor (SCF) in proliferating oval cells during 6 weeks of copper depletion, and Northern blot analysis revealed the expression of liver-enriched transcription factors in the rat pancreas during this 4-6-week period of copper deficiency. CCAAT/enhancer binding protein alpha (C/EBP alpha) mRNA was detected first at 4 weeks of copper deficiency. By 5 and 6 weeks of copper deficiency, the expression of mRNAs of C/EBP alpha, beta, and delta, and hepatocyte nuclear factor-3 factor (HNF-3 beta) was markedly enhanced. This enhanced expression of liver-enriched transcription factors and the SCF during oval cell proliferation in the pancreas preceding the expression of albumin mRNA and subsequent differentiation of hepatocyte phenotype further supports the identity of these oval cells as hepatocyte precursors or stem cells.

The Ever-Evolving Concept of the Cancer Stem Cell in Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC), the most common type of pancreatic cancer, is the 4th most frequent cause of cancer-related death worldwide, primarily due to the inherent chemoresistant nature and metastatic capacity of this tumor. The latter is believed to be mainly due to the existence of a subpopulation of highly plastic “stem”-like cells within the tumor, known as cancer stem cells (CSCs), which have been shown to have unique metabolic, autophagic, invasive, and chemoresistance properties that allow them to continuously self-renew and escape chemo-therapeutic elimination. As such, current treatments for the majority of PDAC patients are not effective and do not significantly impact overall patient survival (<7 months) as they do not affect the pancreatic CSC (PaCSC) population. In this context, it is important to highlight the need to better understand the characteristics of the PaCSC population in order to develop new therapies to target these cells. In this review, we will provide the latest updates and knowledge on the inherent characteristics of PaCSCs, particularly their unique biological properties including chemoresistance, epithelial to mesenchymal transition, plasticity, metabolism and autophagy.

Pancreatic B-13 Cell Trans-Differentiation to Hepatocytes Is Dependent on Epigenetic-Regulated Changes in Gene Expression

The proliferative B-13 pancreatic cell line is unique in its ability to generate functional hepatocyte-like (B-13/H) cells in response to exposure to glucocorticoid. In these studies, quantitatively comparable hepatic levels of liver-specific and liver-enriched transcription factor and hepatocyte defining mRNA transcripts were expressed after 10–14 days continuous treatment with glucocorticoid. This conversion in phenotype was associated with increased Gr-α mRNA expression and translation of a functional N-terminally truncated variant protein that localized to the nucleus in B-13/H cells. A short (6 hours) pulse exposure to glucocorticoid was also sufficient to transiently activate the Gr and irreversibly drive near identical conversion to B-13/H cells. Examination of epigenetic-related mechanisms demonstrated that B-13 DNA was rapidly methylated and de-methylated over the initial 2 days in response to both continuous or pulse exposure with glucocorticoid. DNA methylation and glucocorticoid-dependent conversion to an hepatic B-13/H phenotype was blocked by the methylation inhibitor, 5-azacytidine. Conversion to an hepatic B-13/H phenotype was also blocked by histone deacetylase inhibitors. Previous experiments have identified N-terminal Sgk1 variant proteins as pivotal to the mechanism(s) associated with pancreatic–hepatic differentiation. Both continuous and pulse exposure to DEX was sufficient to result in a near-similar robust transcriptional increase in Sgk1c mRNA expression from undetectable levels in B-13 cells. Notably, expression of Sgk1c mRNA remained constitutive 14 days later; including after pulse exposure to glucocorticoid and this induction was inhibited by 5-azacytidine or by histone deacetylase inhibitors. These data therefore suggest that exposing B-13 cells to glucocorticoid results in a Gr-dependent pulse in DNA methylation and likely other epigenetic changes such as histone modifications that leads to constitutive expression of Sgk1c and irreversible reprogramming of B-13 cells into B-13/H cells. Understanding and application of these mechanism(s) may enhance the functionality of stem cell-derived hepatocytes generated in vitro.

Nonproliferative and Proliferative Lesions of the Gastrointestinal Tract, Pancreas and Salivary Glands of the Rat and Mouse

The INHAND (International Harmonization of Nomenclature and Diagnostic Criteria for Lesions in Rats and Mice) project is a joint initiative of the Societies of Toxicologic Pathology from Europe (ESTP), Great Britain (BSTP), Japan (JSTP), and North America (STP) to develop an internationally accepted nomenclature and diagnostic criteria for nonproliferative and proliferative lesions in laboratory animals. The purpose of this publication is to provide a standardized nomenclature and diagnostic criteria for classifying lesions in the digestive system including the salivary glands and the exocrine pancreas of laboratory rats and mice. Most lesions are illustrated by color photomicrographs. The standardized nomenclature, the diagnostic criteria, and the photomicrographs are also available electronically on the Internet (http://www.goreni.org/). Sources of material included histopathology databases from government, academia, and industrial laboratories throughout the world. Content includes spontaneous and age related lesions as well as lesions induced by exposure to test items. Relevant infectious and parasitic lesions are included as well. A widely accepted and utilized international harmonization of nomenclature and diagnostic criteria for the digestive system will decrease misunderstandings among regulatory and scientific research organizations in different countries and provide a common language to increase and enrich international exchanges of information among toxicologists and pathologists.

Liver Stem Cells: Experimental Findings and Implications for Human Liver Disease

Evidence from human histopathology and experimental studies with rodents and zebrafish has shown that hepatocytes and cholangiocytes may function as facultative stem cells for each other in conditions of impaired regeneration. The interpretation of the findings derived from these studies has generated considerable discussion and some controversies. This review examines the evidence obtained from the different experimental models and considers implications that these studies may have for human liver disease.

An expandable donor-free supply of functional hepatocytes for toxicology

The B-13 cell is a readily expandable rat pancreatic acinar-like cell that differentiates on simple plastic culture substrata into replicatively-senescent hepatocyte-like (B-13/H) cells in response to glucocorticoid exposure. B-13/H cells express a variety of liver-enriched and liver-specific genes, many at levels similar to hepatocytes in vivo. Furthermore, the B-13/H phenotype is maintained for at least several weeks in vitro, in contrast to normal hepatocytes which rapidly de-differentiate under the same simple – or even under more complex – culture conditions. The origin of the B-13 cell line and the current state of knowledge regarding differentiation to B-13/H cells are presented, followed by a review of recent advances in the use of B-13/H cells in a variety of toxicity endpoints. B-13 cells therefore offer Toxicologists a cost-effective and easy to use system to study a range of toxicologically-related questions. Dissecting the mechanism(s) regulating the formation of B-13/H cell may also increase the likelihood of engineering a human equivalent, providing Toxicologists with an expandable donor-free supply of functional rat and human hepatocytes, invaluable additions to the tool kit of in vitro toxicity tests.

Preferential gene expression and epigenetic memory of induced pluripotent stem cells derived from mouse pancreas

Induced pluripotent stem cells (iPSCs) have been established from various somatic cell types. Accumulating evidence suggests that iPSCs from different cell sources have distinct molecular and functional properties. Here, we establish iPSC derived from mouse pancreas (Panc-iPSC) and compared their properties with those of iPSC derived from tail-tip fibroblast (TTF-iPSC). The metabolic profile differs between Panc-iPSC and TTF-iPSC, indicating distinct cell properties in these iPSCs. Expression of Pdx1, a marker of pancreas differentiation, is increased through formation of embryoid body (EB) in Panc-iPSC, but the level is similar to that in TTF-iPSC. In contrast, EBs derived from Panc-iPSC express liver-specific albumin (Alb) and alpha-fetoprotein (Afp) genes much more strongly than those from TTF-iPSC. Epigenetic analysis shows a different histone modification pattern between Panc-iPSC and TTF-iPSC. Promoter regions of Alb and Afp genes in Panc-iPSC are suggested to have a more open chromatin structure than those in TTF-iPSC, which also is seen in primary cultured pancreatic cells. Our data suggest that Panc-iPSC possesses distinct differentiation capacity from that of TTF-PSC, which may be influenced by epigenetic memory.

Conversion of one cell type into another: implications for understanding organ development, pathogenesis of cancer and generating cells for therapy

Metaplasia is the irreversible conversion of one differentiated cell or tissue type into another. Metaplasia usually occurs in tissues that undergo regeneration, and may, in a pathological context, predispose to an increased risk of disease. Studying the conditions leading to the development of metaplasia is therefore of significant clinical interest. In contrast, transdifferentiation (or cellular reprogramming) is a subset of metaplasia that describes the permanent conversion of one differentiated cell type into another, and generally occurs between cells that arise from neighbouring regions of the same germ layer. Transdifferentiation, although rare, has been shown to occur in Nature. New insights into the signalling pathways involved in normal tissue development may be obtained by investigating the cellular and molecular mechanisms in metaplasia and transdifferentiation, and additional identification of key molecular regulators in transdifferentiation and metaplasia could provide new targets for therapeutic treatment of diseases such as cancer, as well as generating cells for transplantation into patients with degenerative disorders. In the present review, we focus on the transdifferentiation of pancreatic cells into hepatocyte-like cells, the development of Barrett's metaplasia in the oesophagus, and the cellular and molecular mechanisms underlying both processes.

Colony-forming progenitor cells in the postnatal mouse liver and pancreas give rise to morphologically distinct insulin-expressing colonies in 3D cultures

In our previous studies, colony-forming progenitor cells isolated from murine embryonic stem cell-derived cultures were differentiated into morphologically distinct insulin-expressing colonies. These colonies were small and not light-reflective when observed by phase-contrast microscopy (therefore termed "Dark" colonies). A single progenitor cell capable of giving rise to a Dark colony was termed a Dark colony-forming unit (CFU-Dark). The goal of the current study was to test whether endogenous pancreas, and its developmentally related liver, harbored CFU-Dark. Here we show that dissociated single cells from liver and pancreas of one-week-old mice give rise to Dark colonies in methylcellulose-based semisolid culture media containing either Matrigel or laminin hydrogel (an artificial extracellular matrix protein). CFU-Dark comprise approximately 0.1% and 0.03% of the postnatal hepatic and pancreatic cells, respectively. Adult liver also contains CFU-Dark, but at a much lower frequency (~0.003%). Microfluidic qRT-PCR, immunostaining, and electron microscopy analyses of individually handpicked colonies reveal the expression of insulin in many, but not all, Dark colonies. Most pancreatic insulin-positive Dark colonies also express glucagon, whereas liver colonies do not. Liver CFU-Dark require Matrigel, but not laminin hydrogel, to become insulin-positive. In contrast, laminin hydrogel is sufficient to support the development of pancreatic Dark colonies that express insulin. Postnatal liver CFU-Dark display a cell surface marker CD133⁺CD49f(low)CD107b(low) phenotype, while pancreatic CFU-Dark are CD133⁻. Together, these results demonstrate that specific progenitor cells in the postnatal liver and pancreas are capable of developing into insulin-expressing colonies, but they differ in frequency, marker expression, and matrix protein requirements for growth.

Artificial induction and disease-related conversion of the hepatic fate

Under normal physiological conditions, the fates of cells that compose various parts of organs are determined during development, and never change to those of other cell types. However, recent advances in induction of cellular reprogramming provide chances to generate a completely different cell type from an original cell source by artificially modulating the microenvironments or gene expressions pattern of cells. Although hepatocytes normally only reside in the liver, the hepatic program can be induced in skin-derived fibroblasts by expressing defined extrinsic transcription factors. These induced hepatocyte-like cells have hepatocyte-specific properties and functionally restore damaged hepatic tissues after transplantation. On the other hand, hepatocytes themselves can be converted into biliary lineage cells as a causative factor of hepatic diseases. Thus, blockade of such disease-related reprogramming of the hepatic fate will become a new therapeutic strategy for refractory diseases in the liver. Moreover, hepatocytes could partially accept the pancreatic program by expressing transcription factors required for pancreas development, suggesting that insulin-producing cells could be generated from hepatocytes and used to treat diabetes. The above-mentioned progress will stimulate studies on the molecular nature of cellular identity and plasticity in hepatocytes, and contribute to the development of potential therapies for liver diseases.

Hepatitis B and C virus infections as possible risk factor for pancreatic adenocarcinoma

Pancreatic adenocarcinoma (PAC) is a very aggressive and lethal cancer, with a very poor prognosis, because of absence of early symptoms, advanced stage at presentation, early metastatic dissemination and lack of both specific tests to detect its growth in the initial phases and effective systemic therapies. To date, the causes of PAC still remain largely unknown, but multiple lines of evidence from epidemiological and laboratory researches suggest that about 15-20% of all cancers are linked in some way to chronic infection, in particular it has been shown that several viruses have a role in human carcinogenesis. The purpose of this report is to discuss the hypothesis that two well-known oncogenic viruses, Human B hepatitis (HBV) and Human C hepatitis (HCV) are a possible risk factor for this cancer. Therefore, with the aim to examine the potential link between these viruses and PAC, we performed a selection of observational studies evaluating this association and we hypothesized that some pathogenetic mechanisms involved in liver carcinogenesis might be in common with pancreatic cancer development in patients with serum markers of present or past HBV and HCV infections. To date the available observational studies performed are few, heterogeneous in design as well as in end-points and with not univocal results, nevertheless they might represent the starting-point for future larger and better designed clinical trials to define this hypothesized relationship. Should these further studies confirm an association between HBV/HCV infection and PAC, screening programs might be justified in patients with active or previous hepatitis B and C viral infection.

MALDI imaging mass spectrometry for in situ proteomic analysis of preneoplastic lesions in pancreatic cancer

The identification of new biomarkers for preneoplastic pancreatic lesions (PanINs, IPMNs) and early pancreatic ductal adenocarcinoma (PDAC) is crucial due to the diseases high mortality rate upon late detection. To address this task we used the novel technique of matrix-assisted laser desorption/ionization (MALDI) imaging mass spectrometry (IMS) on genetically engineered mouse models (GEM) of pancreatic cancer. Various GEM were analyzed with MALDI IMS to investigate the peptide/protein-expression pattern of precursor lesions in comparison to normal pancreas and PDAC with cellular resolution. Statistical analysis revealed several discriminative m/z-species between normal and diseased tissue. Intraepithelial neoplasia (PanIN) and intraductal papillary mucinous neoplasm (IPMN) could be distinguished from normal pancreatic tissue and PDAC by 26 significant m/z-species. Among these m/z-species, we identified Albumin and Thymosin-beta 4 by liquid chromatography and tandem mass spectrometry (LC-MS/MS), which were further validated by immunohistochemistry, western blot, quantitative RT-PCR and ELISA in both murine and human tissue. Thymosin-beta 4 was found significantly increased in sera of mice with PanIN lesions. Upregulated PanIN expression of Albumin was accompanied by increased expression of liver-restricted genes suggesting a hepatic transdifferentiation program of preneoplastic cells. In conclusion we show that GEM of endogenous PDAC are a suitable model system for MALDI-IMS and subsequent LC-MS/MS analysis, allowing in situ analysis of small precursor lesions and identification of differentially expressed peptides and proteins.

Malignant intraductal oncocytic papillary neoplasm of the common bile duct

Recently, several cases of intraductal oncocytic papillary neoplasm (IOPN) of the liver and hepatic bile ducts have been reported. The author herein reports the first case of IOPN of the common bile duct (CBD). A 78-year-old man was admitted to our hospital because of jaundice. Imaging modalities including US, CT, MRI revealed an intraductal tumor of the middle CBD and biliary dilation distal to the tumor. A partial resection of the CBD was performed. Grossly, a papillary tumor measuring 20 × 15 mm was found within the CBD. Mucus is absent. Histologically, the papillary tumor was composed of atypical oncocytes. The atypia was enough to be diagnosed as adenocarcinoma. No invasive features were noted. Immunohistochemically, the tumor cells were positive for pancytokeratins (CK), CK 7, CK 18, CK19, EMA, CA19-9, CEA, mitochondria, p53 protein, C-erbB2, Ki-67 (labeling = 80%), MUC2, MUC5AC and MUC-6,. The tumor cells were negative for CK8, CK20, chromogranin, synaptophysin, neuron-specific enolase, S100 protein, CD56, MUC1, CD10 and CDX2. These immunohistochemical findings were compatible with IOPN. The patient died of other non-tumorous disease 7 year after the operation. In summary, the author presented the first case of IOPN of the CBD.

Huge pancreatic acinar cell carcinoma with high levels of AFP and fucosylated AFP (AFP-L3)

A 25-year-old Japanese woman with a large abdominal tumor (10 cm in diameter) and high level of serum alpha-fetoprotein (AFP, 1,222.4 ng/mL) was introduced and admitted to our hospital in January 2011. Pre-operative imaging modalities could not identify the tumor origin. There was no chronic hepatic viral disease, however, the elevated level of fucosylated AFP (87.8%) and connection with the left hepatic lobe led us to diagnose the tumor as a hepatocellular carcinoma. Surgical resection was performed in February. Histological findings revealed a pancreatic acinar cell carcinoma (ACC). Herein, we provide details of this difficulty to diagnose a case of ACC.

Direct conversion of mouse fibroblasts to hepatocyte-like cells by defined factors

The location and timing of cellular differentiation must be stringently controlled for proper organ formation. Normally, hepatocytes differentiate from hepatic progenitor cells to form the liver during development. However, previous studies have shown that the hepatic program can also be activated in non-hepatic lineage cells after exposure to particular stimuli or fusion with hepatocytes. These unexpected findings suggest that factors critical to hepatocyte differentiation exist and become activated to induce hepatocyte-specific properties in different cell types. Here, by screening the effects of twelve candidate factors, we identify three specific combinations of two transcription factors, comprising Hnf4α plus Foxa1, Foxa2 or Foxa3, that can convert mouse embryonic and adult fibroblasts into cells that closely resemble hepatocytes in vitro. The induced hepatocyte-like (iHep) cells have multiple hepatocyte-specific features and reconstitute damaged hepatic tissues after transplantation. The generation of iHep cells may provide insights into the molecular nature of hepatocyte differentiation and potential therapies for liver diseases.

Dexamethasone treatment induces the reprogramming of pancreatic acinar cells to hepatocytes and ductal cells

Background

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.

Methodology/Principal Findings

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.

Conclusions/Significance

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.

Differentiation of pancreatic acinar cells to hepatocytes requires an intermediate cell type

BACKGROUND & AIMS

The appearance of hepatic foci in pancreas has been well-documented in animal experiments and in patients with pancreatic cancer. We previously demonstrated that transdifferentiation of pancreatic exocrine cells to hepatocytes required members of the CCAAT enhancer binding protein family. Although the molecular basis of hepatic transdifferentiation is understood, the early cellular events remain to be defined.

METHODS

Dexamethasone and oncostatin M were used to induce transdifferentiation of primary cultures of mouse acinar cells and exocrine cell lines into hepatocytes. Fluorescent-activated cell sorting was used to identify intermediate cell types and side-population characteristics. Cre-loxP-based lineage tracing was used to investigate whether acinar cells contribute directly to hepatocytes via intermediates that express adenosine triphosphate-binding cassette subfamily G member 2 (ABCG2).

RESULTS

Lineage tracing studies showed that hepatocytes were derived directly from pancreatic cells via ABCG2-expressing intermediates. Exposure of cells to insulin increased Akt phosphorylation, ABCG2 expression, and hepatic transdifferentiation. Inhibition of the phosphoinositide 3-kinase pathway, through addition of LY294002 or overexpression of a dominant-negative form of Akt, was sufficient to prevent transdifferentiation. When ABCG2-expressing cells were incubated with glucagon-like-peptide 1 or epidermal growth factor, the intermediate cells could differentiate into insulin-producing beta-like cells.

CONCLUSIONS

The phosphoinositide 3-kinase pathway is important in the transdifferentiation of acinar cells to hepatocytes and those hepatocytes arise from acinar cells via ABCG2-expressing intermediates. Furthermore, ABCG2-expressing cells are multipotent and able to differentiate into hepatocytes and insulin-producing beta cells.

In vitro reprogramming of pancreatic cells to hepatocytes

Transdifferentiation is defined as the conversion of one cell type to another. One well-documented example of transdifferentiation is the conversion of pancreatic cells to hepatocytes. Here we describe a robust in vitro model to study pancreas to liver transdifferentiation. It is based on the addition of the synthetic glucocorticoid dexamethasone to the rat pancreatic exocrine cell line AR42J. Following glucocorticoid treatment, cells resembling hepatocytes are induced. Transdifferentiated hepatocytes express many of the properties of bona fide hepatocytes, e.g. production of albumin and ability to respond to xenobiotics. These hepatocytes can be used for studying liver function in vitro as well as studying the molecular basis of transdifferentiation.

Role of cadherin-mediated cell-cell adhesion in pancreatic exocrine-to-endocrine transdifferentiation

Although pancreatic exocrine acinar cells have the potential to transdifferentiate into pancreatic endocrine cells, the mechanisms are poorly understood. Here we report that intracellular signaling pathways, including those involving MAPK and phosphatidylinositol 3 (PI3)-kinase, are activated by enzymatic dissociation of pancreatic acinar cells and that spherical cell clusters are formed by cadherin-mediated cell-cell adhesion during transdifferentiation. Inhibition of PI3-kinase by LY294002 prevents spheroid formation by degrading E-cadherin and beta-catenin, blocking transdifferentiation into insulin-secreting cells. In addition, neutralizing antibody against E-cadherin suppresses the induction of genes characteristic of pancreatic beta-cells. We also show that loss of cadherin-mediated cell-cell adhesion induces and maintains a dedifferentiated state in isolated pancreatic acinar cells. Thus, disruption and remodeling of cadherin-mediated cell-cell adhesion is critical in pancreatic exocrine-to-endocrine transdifferentiation, in which the PI3-kinase pathway plays an essential role.

Copper deprivation in rats induces islet hyperplasia and hepatic metaplasia in the pancreas

BACKGROUND INFORMATION

Prolonged copper deprivation in rats followed by refeeding with a normal diet has previously been used to induce the appearance of hepatocyte-like cells in the pancreas, but the effects on islet size and morphology have not been determined.

RESULTS

In the present study we investigated the distribution of pancreatic alpha- and beta-cells and of hepatocytes in adult rats fed a copper-deficient diet followed by refeeding with a normal diet. Immunohistochemical staining for insulin and glucagon showed that the islets of the copper-deficient group were up to 2.4 times larger in mass compared with controls. The islets were disorganized, with alpha-cells found in multiple layers at the periphery of the islet and sometimes deep in the core. Isolated alpha- and beta-cells were also found in increased numbers in the ductular system. Copper deprivation caused almost complete ablation of the acinar cells, and refeeding induced adipogenesis, acinar regeneration and hepatocyte-like cells. Ductular proliferation and nerve hyperplasia were also present. The hepatocytes tended to be associated with islets or with ducts, rather than with residual pancreatic exocrine tissue.

CONCLUSIONS

These data show that copper deficiency in rats, as well as inducing the appearance of hepatocytes, is capable of causing islet hyperplasia.

Pancreatitis associated with hyperlipoproteinaemia type I in mink (Mustela vison): earliest detectable changes occur in mitochondria of exocrine cells

Pancreatic tissue from young mink homozygous for a mutation in the lipoprotein lipase gene was studied by light and electron microscopy, with the aim of describing the earliest detectable changes in a process which rapidly progresses into overt pancreatitis. The mutation leads to hyperlipoproteinaemia, corresponding to hyperlipoproteinaemia type I in man. Assessment of relevant hepatic and pancreatic enzymes were included in the investigation. The earliest detectable changes consisted of widespread swelling and vacuolation of exocrine cells, arising mainly from swollen mitochondria. To a lesser extent, vesiculation of endoplasmic reticulum occurred. Mitochondria exhibited various changes, including cavitation and dilution of the matrix, with shortened and disorganized cristae displaced towards the periphery. Lamellar figures that developed within mitochondria were numerous. Acinar lumina were somewhat dilated, while plasma membranes were relatively well preserved and secretory granules seemed unchanged. Exfoliative processes progressively occurred, resulting in total necrosis of groups of parenchymal cells, while intercalated ducts were spared. The necrosis was rapidly followed by inflammatory reactions. The activity of the mitochondrial enzyme carnitine O-palmitoyltransferase, essential for the transport of fatty acids into the mitochondria, was lower in the pancreas than in the liver. The activity of the peroxisomal fatty acid beta-oxidation was high in the liver and low in the pancreas of both lipoprotein lipase-deficient and control mink. It is concluded that pancreatic lesions associated with hyperlipoproteinaemia start in exocrine cells, and are most probably the result of a metabolic disturbance, possibly a toxic effect of an excess of free fatty acids.

Hepatocyte-like cells transdifferentiated from a pancreatic origin can support replication of hepatitis B virus

Recently, a rat pancreatic cell line (AR42J-B13) was shown to transdifferentiate to hepatocyte-like cells upon induction with dexamethasone (Dex). The aim of this study is to determine whether transdifferentiated hepatocytes can indeed function like bona fide liver cells and support replication of hepatotropic hepatitis B virus (HBV). We stably transfected AR42J-B13 cells with HBV DNA and examined the expression of hepatocyte markers and viral activities in control and transdifferentiated cells. A full spectrum of HBV replicative intermediates, including covalently closed circular DNA (cccDNA) and Dane particles, were detected only after induction with Dex and oncostatin M. Strikingly, the small envelope protein and RNA of HBV were increased by 40- to 100-fold upon induction. When HBV RNAs were examined by primer extension analysis, novel core- and precore-specific transcripts were induced by Dex which initiated at nucleotide (nt) 1820 and nt 1789, respectively. Most surprisingly, another species of core-specific RNA, which initiates at nt 1825, is always present at almost equal intensity before and after Dex treatment, a result consistent with Northern blot analysis. The fact that HBV core protein is dramatically produced only after transdifferentiation suggests the possibility of both transcriptional and translational regulation of HBV core antigen in HBV-transfected AR42J-B13 cells. Upon withdrawal of Dex, HBV replication and gene expression decreased rapidly-less than 50% of the cccDNA remained detectable in 1.5 days. Our studies demonstrate that the transdifferentiated AR42J-B13 cells can function like bona fide hepatocytes. This system offers a new opportunity for basic research of virus-host interactions and pancreatic transdifferentiation.

Are there any stem cells in the pancreas?

A vast number of studies indicate the presence of stem/progenitor cells virtually in all tissues in adult organs, particularly in bone marrow. Recent studies, however, cast doubt about the existence of true stem cells in adult tissue. The complex integrity of several cells with distinct morphologic and functional properties in the mature pancreas confers an appropriate status for stem cell research. Several different types of cells residing in the islets or in the ductal epithelium have been proposed as adult pancreatic stem cells or progenitor cells. However, these reports do not provide conceivable proof for the presence of true pancreatic stem cells. On the other hand, there is considerable evidence indicating transdifferentiation of all adult pancreatic cells into each other, and under proper conditions, to nonpancreatic cells including oncocytes and hepatocytes. Observations pertaining to the putative pancreatic stem cells, transdifferentiation ability of the differentiated mature pancreatic cells in the normal and diseased pancreas will be discussed, and our own findings supporting the transdifferentiation pathway are presented in this article.

Metaplasia in the pancreas

There is currently much interest in the possibility to treat chronic diseases by cell replacement or regenerative therapies. Most of these studies focus on the manipulation of undifferentiated stem cells. However, tissue repair and regeneration can also be achieved by differentiated cells, which, in certain conditions, can even transdifferentiate to other cell types. Such transdifferentiations can lead to tissue metaplasia. The pancreas is an organ wherein metaplasia has been well investigated and for which experimental models have been recently developed allowing to unravel the molecular basis of transdifferentiation. Pancreatic metaplasias studied so far include the conversion of exocrine acinar cells to duct cells, exocrine cells to endocrine islet cells, endocrine cells to duct cells, and acinar cells to hepatocytes. Epitheliomesenchymal transitions have also been described. The available evidence indicates that mature cells can be reprogrammed by specific environmental cues inducing the expression of cell type-specific transcription factors. For example, the glucocorticoid hormone dexamethasone induces pancreatic transdifferentiation to hepatocytes, whereas the combination of epidermal growth factor and leukemia-inhibitory factor induces exocrine-endocrine transdifferentiation in vitro. Further unravelling of the involved signal transduction pathways, transcription factor networks, and chromatin modifications is required to manipulate metaplasia at will and to apply it in tissue repair or regeneration.

Pancreatic hepatocellular tumor

BACKGROUND

Hepatocellular differentiation of pancreatic cells has been observed under certain conditions in several species, including humans. Their cell of origin and biology has remained controversial. Generally, these lesions have been considered a degenerative process. The present study describes a neoplastic hepatocellular lesion in Syrian hamsters.

METHODS AND RESULTS

Syrian hamsters were treated with a high dose of pancreatic carcinogen, N-nitrosobis(2-oxopropyl)amine. The lesion was confined within a single islet and expressed albumin and HSA (hepatocyte-specific antigen). The pleomorphic tumor cells exhibited numerous mitotic figures and were intermingled with insulin and glucagon cells. The hamster had multicentric premalignant and malignant ductal-type lesions, most of which appeared to arise from within the islets. This is the first demonstration of pancreatic hepatoma.

CONCLUSION

Pancreatic islet cells appear to have the potential to transdifferentiate into neoplastic hepatocytes.

Redox-mediated enrichment of self-renewing adult human pancreatic cells that possess endocrine differentiation potential

OBJECTIVES

The limited availability of transplantable human islets has stimulated the development of methods needed to isolate adult pancreatic stem/progenitor cells capable of self-renewal and endocrine differentiation. The objective of this study was to determine whether modulation of intracellular redox state with N-acetyl-L-cysteine (NAC) would allow for the propagation of pancreatic stem/progenitor cells from adult human pancreatic tissue.

METHODS

Cells were propagated from human pancreatic tissue using a serum-free, low-calcium medium supplemented with NAC and tested for their ability to differentiate when cultured under different growth conditions.

RESULTS

Human pancreatic cell (HPC) cultures coexpressed alpha-amylase, albumin, vimentin, and nestin. The HPC cultures, however, did not express other genes associated with differentiated pancreatic exocrine, duct, or endocrine cells. A number of transcription factors involved in endocrine cell development including Beta 2, Islet-1, Nkx6.1, Pax4, and Pax6 were expressed at variable levels in HPC cultures. In contrast, pancreatic duodenal homeobox factor 1 (Pdx-1) expression was extremely low and at times undetectable. Overexpression of Pdx-1 in HPC cultures stimulated somatostatin, glucagon, and carbonic anhydrase expression but had no effect on insulin gene expression. HPC cultures could form 3-dimensional islet-like cell aggregates, and this was associated with expression of somatostatin and glucagon but not insulin. Cultivation of HPCs in a differentiation medium supplemented with nicotinamide, exendin-4, and/or LY294002, an inhibitor of phosphatidylinositol-3 kinase, stimulated expression of insulin mRNA and protein.

CONCLUSION

These data support the use of intracellular redox modulation for the enrichment of pancreatic stem/progenitor cells capable of self-renewal and endocrine differentiation.

Plasticity in the adult rat pancreas: transdifferentiation of exocrine to hepatocyte-like cells in primary culture

Under certain experimental conditions, hepatocytes can arise in the pancreas. It has been suggested that the pancreas retains a source of hepatocyte progenitor cells. However, such cells have not been yet identified in the adult pancreas. We describe here the transdifferentiation of primary rat pancreatic exocrine cells into hepatocyte-like cells during 5 days of tissue culture in the presence of dexamethasone (DX). Using reverse-transcription polymerase chain reaction and immunocytochemistry, it was observed that DX treatment induced albumin RNA and protein expression in the cells. Coexpression of albumin and amylase, and the absence of cell proliferation, demonstrated a direct transdifferentiation of acinar cells to hepatocytic cells. CCAAT enhancer-binding protein-ss protein, a liver-enriched transcription factor that is considered to be the master switch in pancreatohepatic transdifferentiation, and alpha-fetoprotein were markedly upregulated in the cells after treatment with DX. We compared transcriptional profiles of freshly isolated exocrine cells and DX-treated cells using oligonucleotide microarrays and found that multiple liver-specific genes are induced along with albumin, and that certain pancreatic genes are downregulated in the DX-treated cells. In conclusion, these observations support the notion of plasticity in the adult pancreas and that exocrine cells can be reprogrammed to transdifferentiate into other cell types such as hepatocytes.

Induction and regulation of acute phase proteins in transdifferentiated hepatocytes

Acute phase proteins (APPs) are predominantly synthesized in the liver and play an important role in restoring homeostasis. In the present study, we set out to answer two questions using transdifferentiated hepatocytes induced from pancreatic cells as a model for studying the acute phase response. Firstly, do transdifferentiated hepatocytes express acute phase proteins following culture with glucocorticoid and cytokines? Secondly, what is the molecular basis of the induction of acute phase proteins in transdifferentiated hepatocytes? Hepatic transdifferentiation was induced in 11.5-day mouse embryonic pancreas or the pancreatic cell line AR42J-B13 (B13) by culture with dexamethasone. We found that acute phase proteins [alpha2-macroglobulin (MG), haptoglobin (Hp)] were induced in both systems following culture with dexamethasone. The combined treatment of dexamethasone and oncostatin M (OSM) enhanced the expression of the acute phase proteins in B13 cells and the mechanism of the up-regulation by the cytokine is probably mediated by phosphorylation of STAT3 and STAT1. In addition, ectopic expression of either C/EBPbeta or C/EBPalpha in B13 cells induced haptoglobin expression and culture with oncostatin M was sufficient to enhance the expression of haptoglobin in C/EBPbeta transfected cells from 18% to 43%. The results of the present study indicate transdifferentiated hepatocytes have the potential to be a useful model to study liver function in vitro.

[Current concepts in stem cell research]

In the last few years, advances in stem cell research have opened up new horizons in the treatment of human diseases and in regenerative medicine. It is not unusual to find news on stem cell research in newspapers and other media. This review describes some basic concepts in research needed to understand the medical literature on stem cells and to provide the information and bibliography necessary to be up to date in one of the subjects that has generated the greatest number of publications in the last few years.

Functional, persistent, and extended liver to pancreas transdifferentiation

Pancreatic and duodenal homeobox gene-1 (PDX-1) regulates pancreas development during embryogenesis, whereas in the adult it controls beta-cell function. Here we analyze whether PDX-1 functions as a pancreatic differentiation factor and a bona fide master regulator when ectopically expressed in mature fully differentiated liver in vivo. By ectopic and transient PDX-1 expression in liver in vivo, using the first generation recombinant adenoviruses, we demonstrate that PDX-1 induces in liver a wide repertoire of both exocrine and endocrine pancreatic gene expression. Moreover, PDX-1 induces its own expression (auto-induction), which in turn may explain the long lasting nature of the "liver to pancreas" transdifferentiation. Insulin as well glucagon-producing cells are mainly located in the proximity of hepatic central veins, possibly allowing direct hormone release into the bloodstream, without affecting normal hepatic function. Importantly, we demonstrate that hepatic insulin production triggered by Ad-CMV-PDX-1 recombinant adenovirus administration is functional and prevents streptozotocin-induced hyperglycemia in Balb/c mice even 8 months after the initial treatment. We conclude that PDX-1 plays an important instructive role in pancreas differentiation, not only from primitive gut endoderm but also from mature liver. Transconversion of liver to pancreas may serve as a novel approach for generating endocrine-pancreatic tissue that can replace malfunctioning beta-cells in diabetics.

Transdifferentiation of pancreas to liver

Transdifferentiation is the name used to describe the direct conversion of one differentiated cell type into another. Cells which have the potential to interconvert by transdifferentiation generally arise from adjacent regions in the developing embryo. For example, the liver and pancreas arise from the same region of the endoderm. The transdifferentiation of pancreas to liver (and vice versa) has been observed in animal experiments and in certain human pathologies. Understanding transdifferentiation is important to developmental biologists because it will help elucidate the cellular and molecular differences that distinguish neighbouring regions of the embryo. While the in vivo models for the transdifferentiation of liver to pancreas have been valuable, it is more difficult to extrapolate from these studies to individual changes at the cellular or molecular levels. The recent development of two in vitro systems (AR42J cells and embryonic pancreatic cultures) for the transdifferentiation of pancreas to liver has shown that an environmental change in the form of an exogenous glucocorticoid can cause the conversion of pancreatic exocrine cells into hepatocytes. The AR42J cell system has been used to elucidate the cell lineage and the molecular basis of transdifferentiation of pancreas to liver.

Differentiated properties of hepatocytes induced from pancreatic cells

Transdifferentiation of pancreas to liver is a well-recognized phenomenon and has been described in animal experiments and human pathology. We recently produced an in vitro model for the transdifferentiation (or conversion) of the pancreatic cell line AR42J-B13 to hepatocytes based on culture with dexamethasone (Dex). To determine whether the hepatocytes express markers of hepatic intermediary metabolism and detoxification, we investigated the patterns of expression of glucokinase, cytochrome P450s CYP3A1 and CYP2B1/2, testosterone/4-nitrophenol uridine diphosphate glucuronosyltransferase (UDPGT), and aryl sulfotransferase. All were expressed. We also determined the expression of 2 enzymes involved in ammonia detoxification: carbamoylphosphate synthetase I (CPS I) and glutamine synthetase (GS). These enzymes are normally strictly compartmentalized in liver in a wide periportal pattern and the last downstream perivenous hepatocytes, respectively. Following culture with Dex, CPS I and GS are expressed in 2 different cell populations, suggesting that both periportal and perivenous hepatocytes are induced. We also produced a reporter assay based on the activation of green fluorescent protein (GFP) by the transthyretin (TTR) promoter or glucose-6-phosphatase (G6Pase) promoter. After culture with Dex, transfected cells begin to express GFP, showing that hepatic promoters are activated in concert with the induction of the hepatocyte phenotype. Lastly, we examined the stability of the hepatic phenotype and found that some cells still express liver markers (transferrin or albumin) up to 14 days after removal of Dex. In conclusion, these results suggest that pancreatic hepatocytes produced by this method may offer an alternative model to primary cultures of hepatocytes for the study of liver function.

Pancreatic stem cells

beta-cell replacement therapy via islet transplantation has had renewed interest, due to the recent improved success. In order to make such a therapy available to more than a few of the thousands of patients with diabetes, new sources of insulin-producing cells must be readily available. The recent conceptual revolution of the presence of adult pluripotent stem cells in bone marrow and in most, if not all, organs suggests that adult stem cells may be a potential source of insulin-producing cells. Pancreatic stem/progenitor cells or markers for these cells have been sought in both islets and ducts. There is considerable evidence that such cells exist and several candidate cells have been reported. However, no clearly identifiable adult pancreatic stem cell has been found as yet. The putative pancreatic stem cells will be the focus of this review.

How cells change their phenotype

Recent attention has focused on the remarkable ability of adult stem cells to produce differentiated cells from embryologically unrelated tissues. This phenomenon is an example of metaplasia and shows that embryological commitments can be reversed or erased under certain circumstances. In some cases, even fully differentiated cells can change their phenotype (transdifferentiation). This review examines recently discovered cases of metaplasia, and speculates on the potential molecular and cellular mechanisms that underlie the switches, and their significance to developmental biology and medicine.

The facultative stem cell: A new star in liver pathology

Although the unlimited capacity of hepatocytes to divide has been recently proven, more and more evidences support the existence of a primitive stem cell compartment in the liver. These cells probably do not participate in the usual maintenance of the liver mass, but they are activated in case of extensive hepatocyte injury. In vivo the oval cells show deep similarly to the primitive cells of the embryonic liver and seem to be the amplification compartment of the hepatic stem cells. A primitive epithelial cell population can be isolated from the normal liver and maintained in vitro. Studies of these two experimental systems provide most of the data about liver stem cells, which may become important for the clinical practice if we understand how their growth is regulated.

alpha-Fetoprotein-producing adenocarcinoma of the pancreas presenting focal hepatoid differentiation

We report a rare case of pancreatic carcinoma producing alpha-fetoprotein (AFP), showing focal hepatoid differentiation in metastatic lymph nodes. A 65-yr-old female was admitted because of abdominal pain. The serum AFP was measured at 16,170 ng/mL. Radiological examinations revealed a mass measuring 6 cm in diameter in the body and tail of the pancreas. A right supraclavicular lymphadenopathy was found and biopsied. Light microscopy showed a tumor consisting of a portion of a hepatoid area and well-differentiated adenocarcinoma, which was suggestive of a hepatoid adenocarcinoma. Immunohistochemical analysis showed that the tumor cells expressed AFP, alpha 1-antitrypsin (AT) and albumin. Although the pathological diagnosis of the primary pancreatic tumor was not obtained, this appears to be the first case of hepatoid adenocarcinoma of the pancreas.

Pancreatic expression of keratinocyte growth factor leads to differentiation of islet hepatocytes and proliferation of duct cells

Keratinocyte growth factor, (KGF), a member of the fibroblast growth factor (FGF) family, is involved in wound healing. It also promotes the differentiation of many epithelial tissues and proliferation of epithelial cells as well as pancreatic duct cells. Additionally, many members of the highly homologous FGF family (including KGF), influence both growth and cellular morphology in the developing embryo. We have previously observed elevated levels of KGF in our interferon-gamma transgenic mouse model of pancreatic regeneration. To understand the role of KGF in pancreatic differentiation, we generated insulin promoter-regulated KGF transgenic mice. Remarkably, we have found that ectopic KGF expression resulted in the emergence of hepatocytes within the islets of Langerhans in the pancreas. Additionally, significant intra-islet duct cell proliferation in the pancreata of transgenic KGF mice was observed. The unexpected appearance of hepatocytes and proliferation of intra-islet duct cells in the pancreata of these mice evidently stemmed directly from local exposure to KGF.

Comparison of liver progenitor cells in human atypical ductular reactions with those seen in experimental models of liver injury

The ultrastructural characteristics of liver progenitor cell types of human atypical ductular reactions seen in chronic cholestasis, in regenerating human liver after submassive necrosis, in alcoholic liver disease, and in focal nodular hyperplasia are compared with liver progenitor cell types seen during experimental cholangiocarcinogenesis in hamsters; during hepatocarcinogenesis in rats; and in response to periportal liver injury induced by allyl alcohol in rats. Three types of progenitor cells have been identified in human atypical ductular reactions: type I: primitive, has an oval shape, marginal chromatin, few cellular organelles, rare tonofilaments, and forms desmosomal junctions with adjacent liver cells; type II: bile duct-like, is located within ducts, has few organelles, and forms lateral membrane interdigitations with other duct-like cells; and type III: hepatocyte-like, is located in hepatic cords, forms a bile canaliculus, has tight junctions with other hepatocyte-like cells, prominent mitochondria and rough endoplasmic reticulum, and some have lysosomes and a poorly developed Golgi apparatus. Each type is seen during cholangiocarcinogenesis in hamsters, but the most prominent cell type is type II, duct-like. A more primitive cell type ("type 0 cell"), as well as type I cells, are seen in the intraportal zone of the liver within 1 to 2 days after carcinogen exposure or periportal injury in the rat, but both type II and type III are seen later as the progenitor cells expand into the liver lobule. After allyl alcohol injury, type 0 cells precede the appearance of type I and type III cells, but most of the cells that span the periportal necrotic zone are type III hepatocyte-like cells showing different degrees of hepatocytic differentiation. Some type II cells are also seen, but these are essentially limited to ducts. It is concluded that there is a primitive stem cell type in the liver (type 0) that may differentiate directly into type I and then into type II, duct-like or or type III hepatocyte-like cells. The terms oval cell, transitional hepatocyte, biliary hepatocyte, hepatocyte-like cell, atypical ductular cell, neocholangiole, etc., are used to describe these cells. Although these terms are useful as general descriptive terms for liver precursor cells at the light microscopic level, the cells included in these descriptive categories may be very different from one another biologically and ultrastructurally.

Redifferentiation and apoptosis of pancreatic cells during acute pancreatitis

The pancreatic cells reorganize their genetic program in a rapid and precise manner during the course of pancreatitis. These phenotypic changes probably confer increased resistance to acute pancreatitis. Then, understanding the mechanism and the finality of these changes can allow us to act earlier and more efficiently against acute pancreatitis with the development of rational therapeutic strategies. Two major phenotypic changes that occur during acute pancreatitis are the appearance of stem cells and activation of the apoptotic program of the acinar cells. In this article I discuss a recent observation about origin and pluripotency of the tubular complex-forming cells during the postacute period of pancreatitis. In addition, I summarize our knowledge on apoptosis in the pancreatic cells, particularly during acute pancreatitis.

Hepatocytic differentiation of cultured rat pancreatic ductal epithelial cells after in vivo implantation

We have investigated the differentiation potential of propagable cultured rat pancreatic duct epithelial cells after in vivo implantation in isogeneic Fischer-344 rats. Cells genetically labeled with Escherichia coli beta-galactosidase (lacZ) reporter gene were embedded in a mixture of collagen and Matrigel (basement membrane matrix) and implanted either subcutaneously or intraperitoneally. Tissues from the two locations were harvested 4 to 8 weeks later. The great majority of the lacZ-labeled epithelial cells colonizing both sites phenotypically resembled hepatocytes, although they demonstrated different degrees of hepatocytic differentiation. Less than 5% of lacZ-labeled cells formed ductular structures. The hepatocyte-like cells from the subcutaneous implantation site expressed mixed phenotypes of both hepatocyte and ductal cell, including the expression of alpha-fetoprotein, tyrosine amino-transferase, gamma-glutamyl transpeptidase, carbonic anhydrase II, and cytokeratin 19. In contrast, the hepatocyte-like cells colonizing the mesentery showed the phenotype of mature hepatocytes, including an abundant glycogen storage and a lack of alpha-fetoprotein and carbonic anhydrase II expressions. Neither acinar cell nor endocrine differentiation was seen. These findings demonstrate that pancreatic ductal cells can be the progenitor cell for transdifferentiated hepatocytes.

Tissue distribution of liver regulating protein. Evidence for a cell recognition signal common to liver, pancreas, gonads, and hemopoietic tissues

Liver regulating protein (LRP) is an integral plasma membrane protein that plays a critical role in maintaining the differentiated phenotype of adult rat hepatocytes by mediating cell-cell interactions with rat liver epithelial cells. Using a specific monoclonal antibody (MAb L8) capable of inhibiting the interactions between these two cell types, the cellular distribution of LRP was analyzed in the liver. Various cell types, including hepatocytes and several sinusoidal cells, were found to be positive, whereas vascular endothelial cells and bile duct cells were consistently negative. This observation led us to question whether cells of nonhepatic origin would also express LRP. We show that MAb L8 immunoreactive material was detected in only three groups of tissues and corresponded to molecules similar to LRP but with different molecular weights. LRP-like molecules were demonstrated on acinar cells of the exocrine pancreas and on all hemopoietic cells regardless of their localization in the organism. LRP-like molecules were also expressed by germ cells and surrounding feeder cells in the testis and ovary in a stage-dependent manner. These results demonstrate the existence of a family of LRP proteins and strongly suggest a critical role for these molecules in regulating cell-cell communication in specific tissues.

Dissimilar frequency of hepatoblastomas and hepatic cystadenomas and adenocarcinomas arising in hepatocellular neoplasms of D2B6F1 mice initiated with N-nitrosodiethylamine and subsequently given Aroclor-1254, dichlorodiphenyltrichloroethane, or phenobarbital

Aroclor-1254 (Ar-1254) and dichlorodiphenyltrichloroethane (DDT) were compared to phenobarbital (PB) for their ability to promote hepatocellular proliferative lesions to hepatocellular adenomas and carcinomas and to hepatoblastomas in D2B6F1 male mice initiated with N-nitrosodiethylamine (NDEA). Hepatocellular neoplasms developed in all mice given NDEA and were more numerous in mice fed promoters. Multiplicities decreased in the order Ar-1254 > PB > DDT, indicating that Ar-1254 was more potent than either PB or DDT at the dosage levels used. PB was the most effective of the 3 agents in stimulating the evolution of hepatocellular neoplasms to hepatoblastoma. The incidence of hepatoblastomas in the NDEA.PB group was 72% but was only 27% in NDEA-initiated, DDT-promoted mice and 33% in low-dose and only 9% in high-dose Ar-1254-promoted mice. In contrast, lesions resembling benign and malignant cholangiocellular neoplasms were frequently found within hepatocellular tumors in Ar-1254-promoted mice but not in mice fed PB or DDT, either alone or after NDEA. Some cystic glandular structures in Ar-1254-promoted mice contained mucous cells, argentaffin cells, and Paneth cells and thus constituted intestinal metaplasia. Hepatoblastoma and intestinal metaplasia/cholangiocellular tumor morphology appear to constitute different patterns of genetic programming induced by certain promoters in expanding clones of initiated hepatocytes, on favorable genetic backgrounds such as that of D2B6F1 male mice.

Cellular origin of cancer: dedifferentiation or stem cell maturation arrest?

Given the fundamental principle that cancer must arise from a cell that has the potential to divide, two major nonexclusive hypotheses of the cellular origin of cancer are that malignancy arises a) from stem cells due to maturation arrest or b) from dedifferentiation of mature cells that retain the ability to proliferate. The role of stem cells in carcinogenesis is clearly demonstrated in teratocarcinomas. The malignant stem cells of teratocarcinomas are derived from normal multipotent stem cells and have the potential to differentiate into normal benign mature tissue. A widely studied model supporting dedifferentiation has been the putative origin of hepatocarcinomas from "premalignant" foci and nodules induced in the rat liver by chemicals. However, the dedifferentiation concept for hepatocarcinogenesis is challenged by more recent interpretations indicating that hepatocellular carcinoma arises from maturation arrest caused by aberrant differentiation of determined stem cells. Either hypothesis is supported by the cellular changes that occur in the rodent liver after different hepatocarcinogenic regimens. The formation of foci and nodules from altered hepatocytes supports dedifferentiation; the proliferation of small oval cells with the potential to differentiate into either biliary ducts or hepatocytes supports arrested maturation of determined stem cells. It is now postulated that foci and nodular change reflect adaptive changes to the toxic effects of carcinogens and not "preneoplastic" stages to cancer. The stem cell model predicts that genotoxic chemicals induce mutations in the determined stem cell which may be expressed in its progeny. Proliferation of initiated cells is induced by promoting events which also allow additional mutations to occur.

Alpha-fetoprotein-producing acinar cell carcinoma of the pancreas

A pancreatic carcinoma and liver metastases associated with marked elevation of the serum alpha-fetoprotein (AFP) level were resected from a 57-year-old man. On microscopic examination, the tumor cells showed a predominantly acinar arrangement, with tubular and trabecular structures; in some foci it had features of a medullary pattern. Alpha-fetoprotein, lipase, trypsin, chymotrypsin, and alpha 1-antitrypsin were strongly demonstrated in tumor tissue by immunohistochemical techniques. A biochemical analysis of AFP on affinity sepharose columns revealed that the AFP derived from the tumor tissues was similar to that of hepatocellular carcinoma. Ultrastructural study showed that most of the tumor cells had abundant rough endoplastic reticulum and numerous zymogen granules. No squamoid corpuscles, neuroendocrine granules, bile production, or bile canaliculi were recognized. These findings suggest that this unique tumor originated from acinar cells.

Immunohistochemical evidence of high concentrations of metallothionein in pancreatic hepatocytes induced by cadmium in rats

A recent study from our laboratory has shown that cadmium, a toxic heavy metal, is one of the most effective agents known for inducing hepatocytic transdifferentiation of the rat pancreas. With repeated injections of cadmium, the incidence of rats with pancreatic hepatocytic foci can be as high as 93%. Cadmium is also well known as a very potent inducer of metallothionein, a metal-binding protein that appears to be important in the biologic response to several toxic heavy metals in most tissues, including the pancreas. Therefore, the present study sought to determine if metallothionein was associated with cadmium-induced transdifferentiation of pancreatic cells. Expression of metallothionein was studied immunohistochemically by the peroxidase-antiperoxidase method in tissue sections of the pancreas of rats with pancreatic hepatocytes. High levels of metallothionein were localized primarily within the pancreatic hepatocytes. Surrounding normal pancreatic islet and acinar cells were not immunoreactive. Thus, metallothionein is expressed actively in cells transdifferentiated to hepatocytes by cadmium within the pancreas.

Drug-induced lysosomal disorders in laboratory animals: new substances acting on lysosomes

Several substances with lysosomotropic activity were investigated in toxicological studies. AR-L 115 BS (sulmazol, a cardiotonic agent) was tested on beagle dogs; HX-CH 44 BS (a beta-blocker) and SX-AB 1316 SE (an antithrombotic agent) were tested on rats, and AF-CX 1325 XX (an antiepileptic agent) was tested on both rats and beagle dogs. All organ systems were examined morphologically by light and/or electron microscopy. When an increase in the number of lysosomes occurred this was confirmed by the pigment scheme according to Krutsay (1971) as well as by the detection of acid phosphatase and compared with earlier histochemical results. At higher dosages, all substances caused very marked proliferation of lysosomes in the liver and/or kidneys. HX-CH 44 BS also caused such proliferation in striated muscles and in the lungs. A brown discolouration of the kidneys was found with sulmazol and AF-CX 1325 XX. This finding corresponded to the microscopically detectable occurrence of numerous lipofuscin granules. The reticulum cells in the lymph nodes of dogs were also affected by AF-CX 1325 XX. It is concluded that the proliferation of lysosomes in various organs after administration of the above-mentioned substances is due to an excess of substance. The increased substance in the body is then stored in the lysosomes. With HX-CH 44 BS, lysosomal autodigestion of mitochondria in the skeletal musculature and in the alveolar macrophages of the lungs was found. The selective lysosomal incorporation of mitochondria has not been described up to now and in our opinion, this constitutes a special feature. The results otherwise largely correspond to those already described in the literature. Systemic phospholipidosis such as occurs with some other substances was not detectable. The incorporation of the substance causes several types of lysosomal inclusion. Uptake of the substance in lysosomes either leads to overt autodigestion of organelles such as mitochondria (HX-CH 44 BS) or peroxisomes or to residual lysosomes of dense structure which histochemically resemble lipofuscin. SX-AB 1316 SE serves as an example of a substance which is stored directly by lysosomes in crystalline form. Above all, in the liver the substance is taken up not only by the sinusoidal stellate cells but also by hepatocytes.