Bile Epithelial Cells Research Articles

C-Kit, a Double-Edged Sword in Liver Regeneration and Diseases.

Previous studies have reported an important role of c-kit in embryogenesis and adulthood. Activation of the SCF/KIT signal transduction pathway is customarily linked to cell proliferation, migration and survival thus influence hematopoiesis, pigmentation, and spermatogenesis. The role of c-kit in the liver is controversial, it is however argued that it is a double-edged sword in liver regeneration and diseases. First, liver c-kit+ cells, including oval cells, bile epithelial cells, and part of hepatocytes, participate in liver tissue repair by regenerating target cells according to the type of liver injury. At the same time, c-kit+ mast cells, act as immature progenitors in circulation, playing a critical role in liver fibrosis. Furthermore, c-kit is also a proto-oncogene. Notably, c-kit overexpression regulates gastrointestinal stromal tumors. Various studies have explored on c-kit and hepatocellular carcinoma, nevertheless, the intricate roles of c-kit in the liver are largely understudied. Herein, we extensively summarize previous studies geared toward providing hints for future clinical and basic research.

The Chronic Liver Diseases from Autoimmune cause, Autoimmune Hepatitis (AIH): Updating Review

The classic autoimmune liver diseases (AILDs) are one of the main causes of chronic liver disease; which include primary biliary cirrhosis (PBC), autoimmune hepatitis (AIH) constitute and primary sclerosing cholangitis (PSC).This pathological condition represents an immune attack on the bile epithelial liver cells, which leads to chronic inflammation in the liver, due to the proliferation of cells and the deposition of the matrix proteins between the hepatocytes and their types. Then the liver cells gradually lose their functions until the liver reaches the stage of myofibroblasts.The liver lost its functions inevitably and gradually gets until the liver loses its normal size leads to high blood pressure in the hepatic portal vein and from here begins the rapid deterioration of the liver condition so this requires follow-up and monitoring of liver cirrhosis and at this stage requires a liver biopsy examination In this case, liver transplantation is the effective and golden treatment option for liver disease at this stage. The abundance of MHC receptors class II in the surface liver cells, genetic predisposition or due to acute infection of the liver, leads to an immune response in the body, which leads to autoimmune hepatitis. This abnormal immune response leads to persistent hepatitis, which may lead to more symptoms and complications such as fatigue and cirrhosis. The disease may be related to race or age, diagnosis is often after the age of 40 years.

The Chronic Liver Diseases from Autoimmune cause, Autoimmune Hepatitis (AIH): Updating Review

The classic autoimmune liver diseases (AILDs) are one of the main causes of chronic liver disease; which include primary biliary cirrhosis (PBC), autoimmune hepatitis (AIH) constitute and primary sclerosing cholangitis (PSC).This pathological condition represents an immune attack on the bile epithelial liver cells, which leads to chronic inflammation in the liver, due to the proliferation of cells and the deposition of the matrix proteins between the hepatocytes and their types. Then the liver cells gradually lose their functions until the liver reaches the stage of myofibroblasts.The liver lost its functions inevitably and gradually gets until the liver loses its normal size leads to high blood pressure in the hepatic portal vein and from here begins the rapid deterioration of the liver condition so this requires follow-up and monitoring of liver cirrhosis and at this stage requires a liver biopsy examination In this case, liver transplantation is the effective and golden treatment option for liver disease at this stage. The abundance of MHC receptors class II in the surface liver cells, genetic predisposition or due to acute infection of the liver, leads to an immune response in the body, which leads to autoimmune hepatitis. This abnormal immune response leads to persistent hepatitis, which may lead to more symptoms and complications such as fatigue and cirrhosis. The disease may be related to race or age, diagnosis is often after the age of 40 years.

Abstract A13: Yap activity in bile ducts, but not in hepatocytes, is required for normal liver regeneration

Abstract The Hippo-pathway effectors Yap/Taz are assumed to be master regulators of organ regeneration. In the mouse liver, loss of Yap indeed affects the regeneration potential of hepatocytes. However, we found that this is not due to a requirement for Yap in hepatocytes to drive proliferation and regeneration, but is rather due to non-cell autonomous effects of the bile duct defects that develop in the absence of Yap. Developmental deletion of Yap and Taz in liver progenitors, which develop into hepatocytes and bile epithelial cells (BECs), impaired liver regeneration after toxin-induced injury. However, hepatocyte-specific deletion of Yap/Taz in adult mice revealed that Yap/Taz are dispensable in hepatocytes for liver regeneration. In contrast, deletion of Yap/Taz in mature BECs recapitulated the liver regeneration defects that were observed after knockout in liver progenitor cells. Notably, loss of Yap/Taz in BECs impaired bile duct integrity over time, induced a cholestatic liver phenotype, and increased apoptosis in wild-type hepatocytes after toxic liver injury. Our data show that Yap and Taz are required to maintain bile duct integrity, which is essential to maintain the regenerative capacity of adult hepatocytes. Citation Format: Elisabeth Verboven, Ivan M. Moya, Georg Halder. Yap activity in bile ducts, but not in hepatocytes, is required for normal liver regeneration [abstract]. In: Proceedings of the AACR Special Conference on the Hippo Pathway: Signaling, Cancer, and Beyond; 2019 May 8-11; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2020;18(8_Suppl):Abstract nr A13.

In vitro and in vivo assessment of biocompatibility of AZ31 alloy as biliary stents: a preclinical approach.

IntroductionBiomaterial technology due to its lack of or minimal side effects in tissues has great potential. Traditionally biomaterials used were cobalt-chromium, stainless steel and nitinol alloys. Biomaterials such as magnesium (Mg) and zinc (Zn) have good biocompatibility and consequently can be a potential material for medical implants. To date, the effects of AZ31 alloy stent on cell apoptosis are still unclear. The current investigation was designed to determine the effect of AZ31 alloy stent on necrosis and apoptosis of common bile duct (CBD) epithelial cells.Material and methodsWe experimented with application of different concentrations of AZ31 alloy stent to primary mouse extrahepatic bile epithelial cells (MEBECs) and estimated the effect on apoptosis and necrotic cells. Apoptosis and pro-apoptosis expression were estimated through real-time PCR. For in vivo protocol, we used rabbits, implanted the AZ31 bile stent, and estimated its effect on the CBD. AZ31 (40%) concentration showed an effect on the apoptotic and necrotic cells.ResultsReal-time PCR revealed that AZ31 (40%) concentration increased the apoptotic genes such as NF-κB, caspase-3, Bax and Bax/Bcl-2 ratio as compared to the control group. In the in vivo experiment, AZ31 alloy stents were implanted into the CBD and showed an effect on the alteration the hematological, hepatic and non-hepatic parameters.ConclusionsTo conclude, it can be stated that AZ31 induces apoptosis via alteration in genes including nuclear factor kappa-B (NF-κB), caspase-3, Bax and Bax/Bcl-2 ratio and improved the hematological, hepatic and non-hepatic parameters.

Transient Elastography in Acute Cellular Rejection Following Liver Transplantation: Systematic Review

BackgroundTransient elastography (TE) is a noninvasive technique that measures liver stiffness. When an inflammatory process is present, this is shown by elevated levels of stiffness. Acute cellular rejection (ACR) is a consequence of an inflammatory response directed at endothelial and bile epithelial cells, and it is diagnosed through liver biopsy. This is a systematic review of the viability of TE in ACR following liver transplantation. MethodsThe Cochrane Library, Embase, and Medline PubMed databases were searched and updated to November 2016. The MESH terms used were “Liver Transplantation,” “Graft Rejection,” “Elasticity Imaging Techniques” (PubMed), and “Elastography” (Cochrane and Embase). ResultsSeventy studies were retrieved and selected using the PICO (patient, intervention, comparison or control, outcome) criteria. Three prospective studies were selected to meta-analysis and evaluation. A total of 33 patients with ACR were assessed with TE. One study showed a cutoff point of >7.9 kPa to define graft damage and <5.3 kPa to exclude graft damage (receiver operating characteristic 0.93; P < .001). Another study showed elevated levels of liver stiffness in ACR patients. However, in this study, no cutoff point for ACR was suggested. The final prospective study included 27 patients with ACR at liver biopsy. Cutoff points were defined as TE > 8.5 kPa, moderate to severe ACR, with a specificity of 100% and receiver operating characteristic curve of 0.924. The measurement of TE < 4.2 kPa excludes the possibility of any ACR (P = .02). ConclusionsTE may be an important tool for the severity of ACR in patients following liver transplantation. Further studies should be performed to better define the cutoff points and applicability of the exam.

In vivo and in vitro evaluation of effects of Mg-6Zn alloy on apoptosis of common bile duct epithelial cell.

Biodegradable magnesium alloy implants have attracted much attention because of their excellent biocompatibility and good mechanical properties. However, effects of Mg alloy on cell apoptosis remain unclear. The aim of this study was to investigate the effects of the Mg-6Zn alloy on the apoptosis and necrosis of common bile duct (CBD) epithelial cells. In the in vitro experiments, primary mouse extrahepatic bile epithelial cells (MEBECs) were exposed to Mg-6Zn alloy extracts with different concentrations (0, 40, 80, and 100%). Flow cytometry analysis indicated that low concentration Mg-6Zn extract can induce apoptosis of MEBECs, and high concentration Mg-6Zn extracts may relate to necrosis and/or 'apoptotic necrosis'. Real-time PCR results showed that when MEBECs were treated with 40% extracts for 3days, the relative apoptotic genes including Bax, Bax/Bcl-2 ratio, NF-κB and caspase-3 were higher than those in the control group. In the in vivo experiments, Mg-6Zn alloy stents were implanted into rabbits' CBD for 1, 2, 3weeks, respectively. Based on the hematoxylin and eosin (H&E) staining of peri-implant CBD tissue, no apoptotic bodies and necrotic cells were observed. Results of immunohistochemical staining also showed Mg-6Zn stents did not increase expression levels of apoptosis related gene such as Bax, Bcl-2, Bax/Bcl-2 ratio, TNF-α, NF-κB and caspase-3 in CBD, which indicating Mg-6Zn did not induce significant apoptosis in the in vivo experiments. The different results of in vitro and in vivo experiment may result from the low corrosion rate of Mg-6Zn alloy stents in vivo and local Mg(2+) ion concentration in CBD.

Expression and significance of Cyclin D1 in cholangioncarcinoma

Objective To detect the expression of Cyclin D1 protein and gene in cholangioncarcinoma and to elucidate its role. Methods The expression of Cyclin D1 protein was detected by flow cytometry ( FCM ) in 42 cases of cholangioncarcinoma and 20 cases of normal bile duct, and the expression of Cyclin D1 gene was assayed in 42 cases of cholangioncarcinoma, 17 cases of tissues adjacent to cholangioncarcinoma and 20 cases of normal bile duct by reverse transcription-polymerase chain reaction ( RT-PCR) .The correlation was analyzed statistically between the expression of Cyclin D1 protein and mRNA and clinicopathological parameters in cholangioncarcinoma. Results The expression of Cyclin D1 mRNA in normal bile duct, tissues adjacent to cholangioncarcinoma, and cholangioncarcinoma was 0.5845 ± 0.0310,0. 5608 ± 0. 0577, 0. 6288 ± 0. 0942 respectively. The expression of Cyclin D1 mRNA was higher in cholangioncarcinoma than in others (P ＜0. 05). The protein expression of Cyclin D1 was higher in cholangioncarcinoma than in normal bile duct tissue (P＜0. 05). Conclusion Cyclin D1 gene transcription and protein expression is mostly likely involved in the proliferation and malignant transformation of bile epithelial cells and then malignant progression of bile duct carcinomas. The detection of Cyclin D1 expression may elucidate the carcinogenesis of bile duct. Key words: Cholangioncarcinoma; Cyclin D1

The expression and significance of vascular endothelial growth factor-C in cholangioncarcinoma

Objective To detect the expression of vascular endothelial growth factor (VEGF)-C protein and gene in cholangioncarcinoma and to elucidate its role. Methods The expression of VEGF-C protein was detected by immunohistochemical technique (SP) in 42 cases of cholangioncarcinomas and 20cases of normal bile duct, and that of VEGF-C gene was detected in 42 cases of cholangioncarcinomas, tissues adjacent to cholangioncarcinoma and normal bile duct by using reverse transcription-polymerase chain reaction (RT-PCR). The correlation was analysed statistically between the expression of VEGF-C protein and mRNA and clinicopathological parameters in cholangioncarcinoma. Results The expression of VEGFC mRNA in normal bile duct, tissues adjacent to cholangioncarcinoma, cholangioncarcinoma was 0. 6105 ±0. 0577, 0. 6270 ± 0. 0664, 0. 6930 ± 0. 1078 respectively, and that of VEGF-C mRNA was higher in cholangioncarcinomas than the others (P ＜ 0. 05 ). The protein expression of VEGF-C was higher in cholangioncarcinoma than normal bile duct tissue (P ＜ 0. 05 ). Conclusion VEGF-C gene transcription and protein expression are mostly like involved in the proliferation and malignant transformation of bile epithelial cells and then malignant progression of bile duct carcinomas. The detection of VEGF-C expression may elucidate the carcinogenesis of bile duct. Key words: Cholangion carcinoma; VEGF

Localisation of swine hepatitis E virus in experimentally infected pigs

The distribution of intravenously inoculated swine hepatitis E virus (HEV) was assessed by in situ hybridisation for a period of 50 days. Evidence of apparent clinical disease was found in only one pig in the HEV infected group. The only gross lesion observed was mildly enlarged mesenteric lymph nodes at 50 days post infection (dpi). Histopathologically, mild lymphoplasmacytic infiltration and focal hepatocellular necrotic lesions were found in HEV-infected pigs. Swine HEV nucleic acids were detected by RT-PCR in the faeces at 3 dpi in 100% of the 18 pigs infected with the virus. Thereafter, the number of positives declined. The most consistent and intense signal was found in the liver of infected animals using in situ hybridisation. The positive cells were hepatocytes, Kupffer cells, bile epithelial cells and interstitial lymphocytes. Swine HEV RNA was localised in the cytoplasm of the hepatocytes, with a slightly granular pattern of staining, but hybridisation signals were not observed in degenerative or vacuolated hepatocytes. HEV was much less frequently detected in extrahepatic tissues such as lymph nodes, tonsil, spleen and small and large intestine. It was concluded that swine HEV had replicated primarily in the hepatocytes and infection resulted in subclinical infection with minimal histopathological changes in the liver.

Basolateral Budding of Marburg Virus: VP40 Retargets Viral Glycoprotein GP to the Basolateral Surface

Virus budding from the basolateral domain of infected polarized cells could be one of the mechanisms underlying the quick systemic infection induced by Marburg virus (MARV). We found that MARV buds from the basolateral pole of hepatocytes and bile epithelial cells in infected guinea pigs, which leads to the release of infectious virus into the vascular system. Basolateral budding might be orchestrated by the basolaterally located MARV matrix protein VP40, which induces a partial relocalization of MARV glycoprotein from the apical to the basolateral plasma membrane. This redistribution is a prerequisite for budding of infectious virions from the basolateral domain.

Cholangiocyte Endothelin 1 and Transforming Growth Factor β1 Production in Rat Experimental Hepatopulmonary Syndrome

Cholangiocyte Endothelin 1 and Transforming Growth Factor β1 Production in Rat Experimental Hepatopulmonary Syndrome

Differentiation of putative hepatic stem cells derived from adult rats into mature hepatocytes in the presence of epidermal growth factor and hepatocyte growth factor

Oval cells, putative hepatic stem cells, can differentiate into a wide range of cell types including hepatocytes, bile epithelial cells, pancreatic cells and intestinal epithelial cells. In this study, we used different growth factor combinations to induce oval cells to differentiate into mature hepatocytes. We isolated and purified oval cells utilizing selective enzymatic digestion and density gradient centrifugation. Oval cells were identified by their morphological characteristics and the strong expressions of OV-6, albumin, cytokeratin (CK)-19 and CK-7. Using a 2-step induction protocol, we demonstrated that oval cells first changed into small hepatocytes, then differentiated into mature hepatocytes. Small hepatocytes were distinguished from oval cells by their morphological features (e.g. round shape and nuclei) and the lack of CK-19 mRNA expression. Mature hepatocytes were identified by their ultrastructural traits and their expressions of albumin, CK-18, tyrosine aminotransferase (TAT), and alpha-1-antitrypsin (α-1-AT). Differentiated cells acquired the functional attributes of hepatocytes in that they secreted albumin and synthesized urea at a high level throughout differentiation. Oval cells can thus differentiate into cells with the morphological, phenotypic and functional characteristics of hepatocytes. This 2-step induction procedure could provide an abundant source of hepatocytes for cell transplantation and tissue engineering.

Role of c- kit receptor tyrosine kinase-mediated signal transduction in proliferation of bile epithelial cells in young rats after ligation of bile duct: a study using Ws/Ws c- kit mutant rats

Background/Aims: Recently, it has been shown that the c- kit receptor tyrosine kinase (KIT) is expressed in the liver of young rats, and its expression is up-regulated in bile epithelial cells (BEC) after ligation of the common bile duct (BDL). To clarify a role of KIT in BEC, we examined whether BEC of Ws/Ws rats, whose KIT kinase activity was severely impaired, could proliferate in response to bile stasis after BDL. Methods/Results: When 2-week-old control normal (+/+) and Ws/Ws mutant rats underwent BDL, only a few BEC were found in the portal field of livers of Ws/Ws rats, whereas many BEC were found in that of +/+ rats. Furthermore, Ki-67 immunostaining showed that the proliferative activity of BEC in 2-week-old Ws/Ws rats was much lower than that in +/+ rats of the same age. In contrast, when 6-week-old +/+ and Ws/Ws rats underwent BDL, BEC similarly proliferated in the livers of +/+ and Ws/Ws rats, and the proliferative activity of BEC was comparable. Conclusions: The mechanism whereby BEC proliferate in response to bile stasis after BDL may be different between 2- and 6-week-old rats, and KIT mediated-signal transduction plays a crucial role in the proliferation of immature BEC in young rats.

Stem cell properties and repopulation of the rat liver by fetal liver epithelial progenitor cells.

The potential of embryonal day (ED) 14 fetal liver epithelial progenitor (FLEP) cells from Fischer (F)344 rats to repopulate the normal and retrorsine-treated liver was studied throughout a 6-month period in syngeneic dipeptidyl peptidase IV (DPPIV-) mutant F344 rats. In normal liver, FLEP cells formed: 1) hepatocytic clusters ranging in size up to approximately 800 to 1000 cells; 2) bile duct structures connected to pre-existing host bile ducts; and 3) mixed clusters containing both hepatocytes and bile duct epithelial cells. Liver repopulation after 6 months was moderate (5 to 10%). In retrorsine-treated liver, transplanted cells formed large multilobular structures containing both parenchymal and bile duct cells and liver repopulation was extensive (60 to 80%). When the repopulating capacity of ED 14 FLEP cells transplanted into normal liver was compared to adult hepatocytes, three important differences were noted: 1) FLEP cells continued to proliferate at 6 months after transplantation, whereas adult hepatocytes ceased proliferation within the first month; 2) both the number and size of clusters derived from FLEP cells gradually increased throughout time but decreased throughout time with transplanted mature hepatocytes; and 3) FLEP cells differentiated into hepatocytes when engrafted into the liver parenchyma and into bile epithelial cells when engrafted in the vicinity of the host bile ducts, whereas adult hepatocytes did not form bile duct structures. Finally, after transplantation of ED 14 FLEP cells, new clusters of DPPIV+ cells appeared after 4 to 6 months, suggesting reseeding of the liver by transplanted cells. This study represents the first report with an isolated fetal liver epithelial cell fraction in which the cells exhibit properties of tissue-determined stem cells after their transplantation into normal adult liver; namely, bipotency and continued proliferation long after their transplantation.

Origin and Structural Evolution of the Early Proliferating Oval Cells in Rat Liver

We have analyzed the histological changes in rat liver after 2-acetylaminofluorene (AAF) administration. The data demonstrate that AAF-induced oval cells were preferentially generated by proliferation of the terminal biliary ductules that we suggest constitute the primary hepatic stem cell niche. The oval cells formed ductular structures, representing an extension of the canals of Hering. This histological organization provides continuous bile drainage of the hepatocytes and uninterrupted blood flow in the sinusoids. The oval cell ductules are surrounded by a continuous basement membrane that is intermittently disrupted by processes of stellate cells that form direct cell-cell contact with the oval cells. Although both AAF treatment and bile duct ligation results in proliferation of biliary epithelial cells, the mechanism(s) responsible for the proliferation of the biliary epithelium seems to differ in the two models. In contrast to the biliary proliferation stimulated by bile ligation, AAF-induced oval cell proliferation as well as the capacity of these cells to differentiate into hepatocytes, bile epithelial cells and possibly other cell lineages can be blocked by administration of dexamethasone.

Restitutive response of Mini rat liver to injury induced by a single oral administration of thioacetamide.

Mini rats are a transgenic rat strain carrying antisense gene for rat growth hormone (GH), resulting in retarded growth and a lower blood GH level (136 +/- 42.0 ng/mL) compared with that of age-matched parental strain Wistar rats (329 +/- 337 ng/mL). Mini rats have been used by several investigators as a GH deficiency model. In this work, we gave a single oral administration of thioacetamide (TAA), a hepatotoxicant, to both Mini rats and Wistar rats to ascertain the influence of GH deficiency on liver response to chemically induced injury and subsequent regeneration. TAA administration caused liver injury in both strains, with a greater extent of injury in Mini rats. Proliferation of bile epithelial cells and so-called oval cells was prominent at Day 3 in Mini rats only, and this change correlated well with serum total bilirubin concentrations. Antibody against Ki-67 antigen revealed that cellular proliferation after TAA-induced liver injury was suppressed but prolonged in the Mini rat liver. Although hepatic stellate cells and Kupffer cells/macrophages were more abundant in the livers of TAA-treated Mini rats, the hepatic expression patterns of hepatocyte growth factor and transforming growth factor beta 1 were comparable to those of Wistar rats. Insulin-like growth factor-I gene expression was significantly reduced in the Mini rat liver. Our results imply that a lower GH level may exacerbate chemically induced liver injury, enhance infiltration/proliferation of non-parenchymal cells, suppress regeneration of hepatocytes, and induce proliferation of bile epithelial cells and oval cells when the liver is injured by TAA.

Shift of hepatitis E virus RNA from hepatocytes to biliary epithelial cells during acute infection of rhesus monkey.

Hepatitis E virus (HEV) has been considered to be the major cause of enterically transmitted non-A, non-B hepatitis in developing countries. However, little is known about viral replication and localization in the liver. The aim of this study was to examine the distribution of HEV-infected cells in experimentally infected animals. Seven captured wild rhesus monkeys were inoculated intravenously with faecal extract derived from a Myanmar strain of HEV. Animals were killed at different time-points of clinical illness: during early infection, during prehepatitis with viral-like particles in bile, during acute hepatitis and during convalescence. Intrahepatic localization of HEV was analysed using non-isotopic thymine dimer in situ hybridization (NITDISH). Both plus and minus strands of HEV RNA were found in hepatocytes during the early infection period. Staining in the submembranous cytoplasmic region of hepatocytes was observed. In the prehepatitis period, both plus and minus strand HEV RNAs appeared in the canalicular side of isolated bile epithelial cells. Subsequently, HEV RNA became universally distributed in the cytoplasm of medium-size bile epithelial cells. After recovery, HEV RNA disappeared.

Dexamethasone inhibits the proliferation of hepatocytes and oval cells but not bile duct cells in rat liver.

Recent advances have implicated the importance of tumor necrosis factor (TNF) and interleukin 6 (IL-6) in the regulation of liver growth. Therefore, we studied how dexamethasone, a well-known inhibitor of these cytokines, influences the proliferation of different hepatic cell populations. As we expected, dexamethasone pretreatment suppressed the expression of both TNF and IL-6 after partial hepatectomy and significantly reduced the proliferative response of the hepatocytes. Furthermore, the proliferative response of hepatocytes could be rescued by IL-6 administration. Dexamethasone also severely diminished the induction and expansion of oval cells induced by the 2-acetylaminofluorene/partial hepatectomy (AAF/PH) protocol but did not have any effect on the proliferation of the bile duct cells stimulated by bile duct ligation. The differential inhibition of these two morphologically very similar cell types may be used to characterize divergent regulatory mechanisms responsible for the proliferative response of oval cells and adult bile epithelial cells.

Expression of α-fetoprotein and stem cell factor/c-kit system in bile duct ligated young rats

The existence of a facultative hepatic stem cell compartment in bile ductules that participates in the renewal process of epithelial cell populations in the liver is well documented. The present study was undertaken to determine whether the immature bile epithelium responds differently to growth stimulus induced by bile stasis to that seen in the adult animal. In addition, the possible involvement of the growth factor/receptor systems associated with early activation of hepatic stem cells in bile duct proliferation was also examined. Bile duct ligation was used to induce the proliferation of bile epithelial cells. The expression of full-length alpha-fetoprotein (AFP) was used as an indicator for activation of the stem cell compartment. AFP was highly and selectively expressed in small bile ducts 7 days after bile duct ligation in immature rats up to 5 weeks of age. Although no significant increase in the expression of stem cell factor (SCF) c-kit, hepatocyte growth factor (HGF), and transforming growth factor-alpha (TGF-alpha) was observed 7 days after bile duct ligation in adult rats, the expression of all these growth factors was increased in bile duct ligated rats up to 5 weeks of age. These results suggest that the bile ductular epithelium in the young rats responds to bile stasis in a fashion that is phenotypically similar to that seen during early activation of hepatic stem cells in adult liver.