The role of oval cells in rat hepatocyte transplantation

Human hepatic progenitor cells express hematopoietic cell markers CD45 and CD109

OBJECTIVE

To clarify the precise characteristics of human hepatic progenitor cells (HPCs) for future cytotherapy in liver diseases.

METHODS

Hepatic progenitor-like cells were isolated and cultured from the livers of patients who had undergone partial hepatectomy for various pathologies but displayed no sign of hepatic dysfunction. These cells were characterized by transcriptomic profiling, quantitative real-time PCR and immunocyto/histochemistry.

RESULTS

Cultured HPCs contained polygonal, high nucleus/cytoplasm ratio and exhibited a global gene expression profile similar (67.8%) to that of primary hepatocytes. Among the genes with more than 20-fold higher expression in HPCs were a progenitor marker (CD90), a pentraxin-related gene (PTX3), collagen proteins (COL5A2, COL1A1 and COL4A2), cytokines (EGF and PDGFD), metabolic enzymes (CYBRD1, BCAT1, TIMP2 and PAM), a secreted protein (SPARC) and an endothelial protein C receptor (PROCR). Moreover, eight markers (ALB, AFP, CK8, CK18, CK19, CD90, CD117 and Oval-6) previously described as HPC markers were validated by qRT-PCR and/or immunocyto/histochemistry. Interestingly, human HPCs were also positive for the hematopoietic cell markers CD45 and CD109. Finally, we characterized the localization of HPCs in the canals of Hering and periportal areas with six previously described markers (Oval-6, CK8, CK18, CK19, CD90 and CD117) and two potential markers (CD45 and CD109).

CONCLUSION

The human HPCs are highly similar to primary hepatocytes in their transcriptional profiles. The CD45 and CD109 markers could potentially be utilized to identify and isolate HPCs for further cytotherapy of liver diseases.

Mature hepatocytes exhibit unexpected plasticity by direct dedifferentiation into liver progenitor cells in culture

Although there have been numerous reports describing the isolation of liver progenitor cells from the adult liver, their exact origin has not been clearly defined; and the role played by mature hepatocytes as direct contributors to the hepatic progenitor cell pool has remained largely unknown. Here, we report strong evidence that mature hepatocytes in culture have the capacity to dedifferentiate into a population of adult liver progenitors without genetic or epigenetic manipulations. By using highly purified mature hepatocytes, which were obtained from untreated, healthy rat liver and labeled with fluorescent dye PKH2, we found that hepatocytes in culture gave rise to a population of PKH2-positive liver progenitor cells. These cells, liver-derived progenitor cells, which share phenotypic similarities with oval cells, were previously reported to be capable of forming mature hepatocytes, both in culture and in animals. Studies done at various time points during the course of dedifferentiation cultures revealed that hepatocytes rapidly transformed into liver progenitors within 1 week through a transient oval cell-like stage. This finding was supported by lineage-tracing studies involving double-transgenic AlbuminCreXRosa26 mice expressing β-galactosidase exclusively in hepatocytes. Cultures set up with hepatocytes obtained from these mice resulted in the generation of β-galactosidase-positive liver progenitor cells, demonstrating that they were a direct dedifferentiation product of mature hepatocytes. Additionally, these progenitors differentiated into hepatocytes in vivo when transplanted into rats that had undergone retrorsine pretreatment and partial hepatectomy.

CONCLUSION

Our studies provide strong evidence for the unexpected plasticity of mature hepatocytes to dedifferentiate into progenitor cells in culture, and this may potentially have a significant effect on the treatment of liver diseases requiring liver or hepatocyte transplantation.

Hepatic differentiation of liver-derived progenitor cells and their characterization by microRNA analysis

We recently reported the isolation and characterization of a novel population of progenitor cells called liver-derived progenitor cells (LDPCs), which could differentiate into functional hepatocytes in vitro. However, our original studies resulted in relatively low and variable hepatic differentiation efficiency without validation of in vivo potential of LDPCs. Here, we report an efficient and robust hepatic differentiation of LDPCs under well-defined culture conditions and in vivo differentiation of LDPCs to mature hepatocytes. In addition to morphological studies, we performed reverse-transcription polymerase chain reaction (RT-PCR) and microRNA analyses of the in vitro hepatic differentiation of LDPCs to substantiate the efficiency of the differentiation process. The histological studies on the differentiated LDPCs showed that more than 50% of the cells were positive for albumin, cytokeratin 18, and hepatocyte nuclear factor 1 alpha and contained glycogen particles, all consistent with differentiation to functional hepatocytes. We also demonstrated by RT-PCR that upon differentiation, they expressed several markers found in mature hepatocytes and the microRNA profile of LDPCs became similar to the profile of fresh hepatocytes, confirming our morphological findings. Finally, the transplantation of LDPCs in a dipeptidyl peptidase IV-deficient (DPPIV(-/-)) rat model showed that LDPCs were able to engraft and form mature hepatocytes in the livers of the DPPIV(-/-) rats. In summary, LDPCs are a unique population of liver progenitor cells capable of hepatic differentiation both in vitro and in vivo, which makes them a potentially valuable resource for important applications such as pharmacological studies and cell therapies for a variety of liver disorders.

Isolation and characterization of a novel population of progenitor cells from unmanipulated rat liver

Widespread use of liver transplantation in the treatment of hepatic diseases is restricted by the limited availability of donated organs. One potential solution to this problem would be isolation and propagation of liver progenitor cells or stem cells. Here, we report on the isolation of a novel progenitor cell population from unmanipulated (that is, no prior exposure to chemicals and no injury) adult rat liver. Rat liver cells were cultured following a protocol developed in our laboratory to generate a unique progenitor cell population called liver-derived progenitor cells (LDPCs). LDPCs were analyzed by fluorescence-activated cell sorting, real-time polymerase chain reaction (RT-PCR), immunostaining and microarray gene expression. LDPCs were also differentiated into hepatocytes and biliary epithelium in vitro and examined for mature hepatic markers and urea and albumin production. These analyses showed that, LDPCs expressed stem cell markers such as cluster domain (CD)45, CD34, c-kit, and Thy 1, similar to hematopoietic stem cells, as well as endodermal/hepatic markers such as hepatocyte nuclear factor (HNF)3beta, hematopoietically-expressed homeobox gene-1, c-met, and transthyretin. LDPCs were negative for OV-6, cytokeratins (CKs), albumin, and HNF1alpha. The microarray gene expression profile demonstrated that they showed some similarities to known liver progenitor/stem cells such as oval cells. In addition, LDPCs differentiated into functional hepatocytes in vitro as shown by albumin expression and urea production. In conclusion, LDPCs are a population of unique liver progenitors that can be generated from unmanipulated adult liver, which makes them potentially useful for clinical applications, especially for cell transplantation in the treatment of liver diseases.

Ultrastructure of oval cells in children with chronic hepatitis B, with special emphasis on the stage of liver fibrosis: The first pediatric study

AIM: To investigate the ultrastructure of oval cells in children with chronic hepatitis B, with special emphasis on their location in areas of collagen fibroplasia.

METHODS: Morphological investigations were conducted on biopsy material obtained from 40 children, aged 3-16 years with chronic hepatitis B. The stage of fibrosis was assessed histologically using the arbitrary semiquantitative numerical scoring system proposed by Ishak et al. The material for ultrastructural investigation was fixed in glutaraldehyde and paraformaldehyde and processed for transmission–electron microscopic analysis.

RESULTS: Ultrastructural examination of biopsy specimens obtained from children with chronic hepatitis B showed the presence of two types of oval cells, the hepatic progenitor cells and intermediate hepatic-like cells. These cells were present in the parenchyma and were seen most commonly in areas of intense periportal fibrosis (at least stage 2 according to Ishak et al) and in the vicinity of the limiting plate of the lobule. The activated nonparenchymal hepatic cells, i.e. transformed hepatic stellate cells and Kupffer cells were seen in close proximity to the intermediate hepatic-like cells.

CONCLUSION: We found a distinct relationship between the prevalence of oval cells (hepatic progenitor cells and intermediate hepatocyte-like cells) and fibrosis stage in pediatric patients with chronic hepatitis B.

The role of p28GANK in rat oval cells activation and proliferation

BACKGROUND

Human gankyrin gene product (p28GANK) is a novel oncogenic protein ubiquitously overexpressed in hepatocellular carcinoma and also plays a role in cell cycle progression in normal hepatocytes and liver regeneration. However, little is known about the physiological role of p28GANK in the liver oval cell activation and proliferation. We investigated the possible involvement of p28GANK in oval cell-mediated liver regeneration and cell cycle progression.

METHODS

We examined the different p28GANK expression in 2-acetylaminofuorene/partial heptectomy (2-AAF/PH) rats, as a model of oval cell activation, and PH rats by Western blot and immunohistochemistry. Oval cells isolated from 2-AAF/PH rat model were cultured in our study. p28GANK expression was examined in the oval cells after mitogenic stimulation.

RESULTS

In 2-AAF/PH rats, p28GANK was expressed in the activated oval cells and located in the nucleus. p28GANK protein expression was increased in 2-AFF/PH rats after hepatectomy lasting for 96 h when retinoblastoma maintained hyperphosphorylation status at Ser-795. The isolated oval cells express AFP, OV6, CK19, CD34, CD45, c-kit and albumin. After epidermal growth factor stimulation, p28GANK protein was up-regulated in oval cells from 24 to 72 h, which coincided with increased expression of CyclinD1, CDK4 and decreased of Rb protein.

CONCLUSIONS

p28GANK expression was increased in oval cell-mediated liver regeneration and oval cells after mitogenic stimulation. Thus, p28GANK may play a role in oval cell-mediated liver regeneration and liver oval cell cycle progression.

Characteristics of rat bone marrow cells differentiated into a liver cell lineage and dynamics of the transplanted cells in the injured liver

BACKGROUND

Bone marrow cells (BMCs) have been shown to differentiate into a liver cell lineage, but little is known about their dynamics following transplantation. BMCs were cultured to investigate the expression of liver-specific genes in vitro and transplanted into in vivo liver-injury models to elucidate their dynamics in the liver.

METHODS

The mRNA expression of various liver-specific genes in BMCs cocultured with hepatocytes was analyzed using reverse transcription-polymerase chain reaction. BMCs from transgenic rats expressing green fiuorescent protein were transplanted into the spleen of rat liver-injury models induced with 2-acetylaminofiuorene (2-AAF) or carbon tetrachloride (CCl4). BMCs were also transplanted directly into livers treated with CCl4 to determine which route is better for transplantation.

RESULTS

BMCs differentiated into a liver cell lineage in vitro and expressed mRNAs consistent with mature hepatocytes, including albumin. The transplanted BMCs were found in the liver in the CCl4-induced injury model, but not in the 2-AAF-induced model. The hepatocyte growth factor and fibroblast growth factor mRNA levels in the liver were significantly higher in the CCl4-induced model than in the 2-AAF-induced model. Migration of BMCs to the liver was more effective following injection into the liver, rather than into the spleen.

CONCLUSIONS

Cultured BMCs differentiated into a liver cell lineage are a potential source for cell transplantation. Transplantation is successful in the severely injured liver with a high level of expression of mRNAs for growth factors. Injection of BMCs directly into the liver is the preferred route of administration.

Repopulation of athymic mouse liver by cryopreserved early human fetal hepatoblasts

Transplantation of hepatocytes is a promising alternative to liver transplantation for the treatment of severe liver diseases. However, this approach is hampered by the shortage of donor organs and intrinsic limitations of adult hepatocytes. To investigate whether most of the hurdles faced with adult hepatocytes could be surmounted by the use of human fetal hepatoblasts, we have developed a method to isolate, transduce, and cryopreserve hepatoblasts from human livers at an early stage of development (11-13 weeks of gestation). Cells were characterized in vitro for expression of specific markers, and in vivo for their proliferation and differentiation potential after transplantation into athymic mice. Most of the cells (80-90%) harbored a bipotent phenotype, expressing cytokeratins 8/18, albumin, and CK19. They proliferated spontaneously in culture and were efficiently transduced by a beta-galactosidase-expressing retrovirus (90%). After transplantation, cryopreserved cells engrafted into the liver of athymic mice and proliferated, resulting in up to 10% repopulation. Engrafted cells expressed markers of differentiated adult hepatocytes including albumin, alpha1-antitrypsin, cytochrome P450 3A4, and alpha-glutathione-S-transferase. When retrovirally transduced before transplantation they expressed the transgene in vivo. In summary, early human fetal hepatoblasts engraft, proliferate, and mature in athymic mouse liver, without conditioning the donor.

The origin of biliary ductular cells that appear in the spleen after transplantation of hepatocytes

Transplantation of rat hepatocytes into the syngeneic rat spleen results in the appearance of cytokeration (CK)-19-positive biliary cells that form ductules. The exact origin of CK-19-positive cells is not known and the possibility that they are derived from biliary cells or precursors of oval cells in transplanted hepatocyte preparations has been raised. In the present study, we found that the number of CK-19-positive biliary cells increased rapidly after transplantation of hepatocytes, reached the maximum at 4 weeks, and then gradually decreased. However, a Ki-67 labeling index of CK-19-positive biliary cells was low and showed no significant changes throughout the experimental period. In addition, no or few CK-19-positive cells appeared in the spleen after transplantation of nonparenchymal liver cells enriched with biliary cells. These results showed that biliary cells were not the source of CK-19-positive cells in the spleen. Impairment of precursors of oval cells in the liver by administration of 4,4'-diaminodiphenylmethane 24 h before transplantation of hepatocytes did not prevent the appearance of CK-19-positive biliary cells in the spleen. Moreover, transplantation of nonparenchymal cells carrying an increased number of oval cells by means of treatment with 2-acetylaminofluorene and partial hepatectomy resulted in no appearance of CK-19-positive biliary cells in the spleen. These results ruled out oval cells as the origin of CK-19-positive biliary cells in the spleen. Because CK-19-positive biliary cells appeared in the spleen only when hepatocyte fractions were transplanted, we suggest transdifferentiation of heptocytes may be the mechanism by which CK-19-positive biliary cells are generated.

Enhanced proliferation of hepatic progenitor cells in rats after portal branch occlusion

It is known that hepatic progenitor cells increase in number after liver injury caused by carcinogens, but this injury cannot be reproduced in humans. In order to create a practical source of hepatic progenitor cells, changes in the number of liver epithelial cells (LECs), a type of hepatic progenitor cell, were examined following partial interruption of the portal flow. Efficiency in this isolation procedure was investigated, and isolated LECs were transplanted into livers to demonstrate their differentiation into hepatocytes in vivo.A volume of 70% of Sprague-Dawley rat's livers was exposed to portal vein ligation. LECs, identified as alpha-fetoprotein (AFP)-positive and albumin-negative cells, were counted and LECs isolated from the portal vein ligated-lobe were characterized by immunostaining and Western blotting. Isolated cells were subjected to a 1-week-culture, and the number of colonies formed on dishes was counted. The cells were then transplanted to the livers of genetic analbuminemic rats and identified by immunohistochemistry. The number of LECs in the portal ligated-lobes on day 7 was 14.7 +/- 6.5 cells/1,000 hepatocytes: 18 times higher than numbers in a normal liver. A significant increase was noted from day 3 until day 28. Isolated LECs were AFP-positive, albumin-negative, and cytokeratin-19-positive cells. The number of colonies on the 7th day following portal vein ligation was 42 times higher than in a normal liver. After transplantation of the LECs to the analbuminemic rat, a cluster of albumin-producing cells was present until day 56, suggesting that they differentiate into hepatocytes. We conclude that after portal vein occlusion, the liver can be a good source of hepatic progenitor cell. These results open up the possibility of cellular transplantation for liver functional support in clinical settings.

Liver regeneration in a retrorsine/CCl4-induced acute liver failure model: do bone marrow-derived cells contribute?

BACKGROUND/AIMS

Adult bone marrow contains progenitors capable of generating hepatocytes. Here a new liver failure model is introduced to assess whether bone marrow-derived progeny contribute to liver regeneration after acute hepatotoxic liver failure.

METHODS

Retrorsine was used to inhibit endogenous hepatocyte proliferation, before inducing acute liver failure by carbon tetrachloride. Bone marrow chimeras were generated before inducing liver failure to trace bone marrow-derived cells. Therefore, CD45 and major histocompatibility complex (MHC) class I dimorphic rat models were applied.

RESULTS

Early after acute liver failure a multilineage inflammatory infiltrate was observed, mainly consisting of granulocytes. In long-term experiments small numbers of CD90+/CD45- cells of donor origin occurred in clusters associated with portal triads. Bone marrow cell infusion was not able to enhance liver regeneration. Cellular hypertrophy was the predominant way of liver mass regeneration in models applying retrorsine.

CONCLUSIONS

Retrorsine pretreatment did not affect sensitivity for carbon tetrachloride. A multilineage inflammatory infiltrate was observed in rats whether pretreated with retrorsine or not. Few donor cells co-expressing CD90 (THY 1) were present in recipient livers, which may resemble donor-derived hematopoietic progenitors or oval cells. No other donor cells within liver parenchyma were detected. This is in contrast to other cell infusion models of acute cell death.

Hepatobiliary inflammation, neoplasia, and argyrophilic bacteria in a ferret colony

Hepatobiliary disease was diagnosed in eight of 34 genetically unrelated cohabitating pet ferrets (Mustela putorios furo) during a 7-year period. The eight ferrets ranged in age from 5 to 8 years and exhibited chronic cholangiohepatitis coupled with cellular proliferation ranging from hyperplasia to frank neoplasia. Spiral-shaped argyrophilic bacteria were demonstrated in livers of three ferrets, including two with carcinoma. Sequence analysis of a 400-base pair polymerase chain reaction product amplified from DNA derived from fecal bacteria from one ferret demonstrated 98% and 97% similarity to Helicobacter cholecystus and Helicobacter sp. strain 266-1 , respectively. The clustering of severe hepatic disease in these cohabitating ferroes suggests a possible infectious etiology. The role of Helicobacter species and other bacteria in hepatitis and/or neoplasia in ferrets requires further study.

Recent developments on human cell lines for the bioartificial liver

Most bioartificial liver (BAL) devices contain porcine primary hepatocytes as their biological component. However, alternatives are needed due to xenotransplantation associated risks. Human liver cell lines have excellent growth characteristics and are therefore candidates for application in BAL devices. Tumour-derived cell lines HepG2 and C3A express a variety of liver functions, but some specific liver functions, like ammonia detoxification and ureagenesis are insufficient. Immortalised human hepatocytes might offer better prospects. The balance between immortalisation and transformation with dedifferentiation of cells seems controllable by conditional immortalisation and/or the use of telomerase as immortalising agent. Another promising approach will be the use of embryonic or adult human stem cells. Rodent stem cells have been directed to hepatic differentiation in vitro, which might be applicable to human stem cells. However, both functionality and safety of immortalised human liver cell lines and differentiated stem cells should be improved before successful use in BAL devices becomes reality.

Intrasplenic transplantation of IL-18 gene-modified hepatocytes: an effective approach to reverse hepatic fibrosis in schistosomiasis through induction of dominant Th1 response

Hepatic fibrosis is a common outcome of chronic liver diseases. In schistosomiasis, chronic parasite egg-induced granuloma formation can lead to fibrosis, which is immunologically characterized by the dominant Th2 response. Recently, it has been shown that gene therapy is an attractive approach for the treatment of hepatic fibrosis. To investigate the antifibrotic effects of IL-18 gene transfer, a normal murine liver cell line BNL.CL2 was transfected with recombinant adenovirus encoding mouse IL-18, and then intrasplenically transplanted into mice infected with Schistosoma japonicum (S. japonicum). Our data show that IL-18 gene-modified hepatocytes intrasplenically transplanted into mice can effectively express IL-18 in the liver and in peripheral blood. Intrasplenic transplantation of IL-18 gene-modified hepatocytes into S. japonicum-infected mice could result in a significantly increased IFN-gamma and IL-2 but decreased IL-4 and IL-10 concentration both in the liver and in the serum, suggesting that the dominant Th2 response in mice with schistosomiasis could be reversed by this intervention. Consistent with the changes in Th1 and Th2 cytokine production, mice intrasplenically transplanted with IL-18 gene-modified hepatocytes developed much less hepatic fibrosis at 20 weeks after infection, which was evaluated by liver content of hydroxyproline, collagens, and hepatic mRNA expression of procollagens. These data indicate that intrasplenic transplantation of IL-18 gene-modified hepatocytes can be a candidate for therapeutic intervention in hepatic fibrosis through induction of a dominant Th1 response.

Immunohistochemical study of hepatic oval cells in human chronic viral hepatitis

AIM: To detect immunohistochemically the presence of oval cells in chronic viral hepatitis with antibody against c-kit.

METHODS: We detected oval cells in paraffin embedded liver sections of 3 normal controls and 26 liver samples from patients with chronic viral hepatitis, using immunohistochemistry with antibodies against c-kit, π class glutathione S-transferase (π-GST) and cytokeratins 19 (CK19).

RESULTS: Oval cells were not observed in normal livers. In chronic viral hepatitis, hepatic oval cells were located predominantly in the periportal region and fibrosis septa, characterized by an ovoid nucleus, small size, and scant cytoplasm. Antibody against stem cell factor receptor, c-kit, had higher sensitivity and specificity than π-GST and CK19. About 50%-70% of c-kit positive oval cells were stained positively for either π-GST or CK19.

CONCLUSION: Oval cells are frequently detected in human livers with chronic viral hepatitis, suggesting that oval cell proliferation is asso ciated with the liver regeneration in this condition.