Improvement of the survival rate by fetal liver cell transplantation in a mice lethal liver failure model. Transplantation. 2007;84:1233-1239. [PMID: 18049107 DOI: 10.1097/01.tp.0000287967.54222.4d]

Generation of a Humanized Mouse Liver Using Human Hepatic Stem Cells

A novel animal model involving chimeric mice with humanized livers established via human hepatocyte transplantation has been developed. These mice, in which the liver has been repopulated with functional human hepatocytes, could serve as a useful tool for investigating human hepatic cell biology, drug metabolism, and other preclinical applications. One of the key factors required for successful transplantation of human hepatocytes into mice is the elimination of the endogenous hepatocytes to prevent competition with the human cells and provide a suitable space and microenvironment for promoting human donor cell expansion and differentiation. To date, two major liver injury mouse models utilizing fumarylacetoacetate hydrolase (Fah) and uroplasminogen activator (uPA) mice have been established. However, Fah mice are used mainly with mature hepatocytes and the application of the uPA model is limited by decreased breeding. To overcome these limitations, Alb-toxin receptor mediated cell knockout (TRECK)/SCID mice were used for in vivo differentiation of immature human hepatocytes and humanized liver generation. Human hepatic stem cells (HpSCs) successfully repopulated the livers of Alb-TRECK/SCID mice that had developed lethal fulminant hepatic failure following diphtheria toxin (DT) treatment. This model of a humanized liver in Alb-TRECK/SCID mice will have functional applications in studies involving drug metabolism and drug-drug interactions and will promote other in vivo and in vitro studies.

Human hepatic stem cells transplanted into a fulminant hepatic failure Alb-TRECK/SCID mouse model exhibit liver reconstitution and drug metabolism capabilities

INTRODUCTION

Chimeric mice with humanized livers were recently established by transplanting human hepatocytes. This mouse model that is repopulated with functional human hepatocytes could be a useful tool for investigating human hepatic cell biology and drug metabolism and for other preclinical applications. Successfully transplanting human hepatocytes into mice requires that recipient mice with liver failure do not reject these human cells and provide a suitable microenvironment (supportive niche) to promote human donor cell expansion and differentiation. To overcome the limitations of current mouse models, we used Alb-TRECK/SCID mice for in vivo human immature hepatocyte differentiation and humanized liver generation.

METHODS

1.5 μg/kg diphtheria toxin was administrated into 8-week-old Alb-TRECK/SCID mice, and the degree of liver damage was assessed by serum aspartate aminotransferase activity levels. Forty-eight hours later, mice livers were sampled for histological analyses, and the human donor cells were then transplanted into mice livers on the same day. Chimeric rate and survival rate after cell transplantation was evaluated. Expressions of human hepatic-related genes were detected. A human albumin enzyme-linked immunosorbent assay was performed after 50 days of transplantation. On day 60 after transplantation, drug metabolism was examined in mice.

RESULTS

Both human primary fetal liver cells and hepatic stem cells were successfully repopulated in the livers of Alb-TRECK/SCID mice that developed lethal fulminant hepatic failure after administering diphtheria toxin; the repopulation rate in some mice was nearly 100%. Compared with human primary fetal liver cells, human hepatic stem cell transplantation rescued Alb-TRECK/SCID mice with lethal fulminant hepatic failure, and human hepatic stem cell-derived humanized livers secreted more human albumin into mouse sera and also functioned as a "human liver" that could metabolize the drugs ketoprofen and debrisoquine.

CONCLUSION

Our model of a humanized liver in Alb-TRECK/SCID mice may provide for functional applications such as drug metabolism, drug to drug interactions, and promote other in vivo and in vitro studies.

A model of liver carcinogenesis originating from hepatic progenitor cells with accumulation of genetic alterations

Activation-induced cytidine deaminase (AID) contributes to inflammation-associated carcinogenesis through its mutagenic activity. In our study, by taking advantage of the ability of AID to induce genetic aberrations, we investigated whether liver cancer originates from hepatic stem/progenitor cells that accumulate stepwise genetic alterations. For this purpose, hepatic progenitor cells enriched from the fetal liver of AID transgenic (Tg) mice were transplanted into recipient "toxin-receptor mediated conditional cell knockout" (TRECK) mice, which have enhanced liver regeneration activity under the condition of diphtheria toxin treatment. Whole exome sequencing was used to determine the landscape of the accumulated genetic alterations in the transplanted progenitor cells during tumorigenesis. Liver tumors developed in 7 of 11 (63.6%) recipient TRECK mice receiving enriched hepatic progenitor cells from AID Tg mice, while no tumorigenesis was observed in TRECK mice receiving hepatic progenitor cells of wild-type mice. Histologic examination revealed that the tumors showed characteristics of hepatocellular carcinoma and partial features of cholangiocarcinoma with expression of the AID transgene. Whole exome sequencing revealed that several dozen genes acquired single nucleotide variants in tumor tissues originating from the transplanted hepatic progenitor cells of AID Tg mice. Microarray analyses revealed that the majority of the mutations (>80%) were present in actively transcribed genes in the liver-lineage cells. These findings provided the evidence suggesting that accumulation of genetic alterations in fetal hepatic progenitor cells progressed to liver cancers, and the selection of mutagenesis depends on active transcription in the liver-lineage cells.

Comparative study of transplantation of hepatocytes at various differentiation stages into mice with lethal liver damage

Hepatocyte transplantation utilizing induced pluripotent stem cells (iPSCs) or embryonic stem cells (ESCs) has been expected to provide an alternative to liver transplantation. However, it remains uncertain precisely which cell type is the best suited for cell transplantation. In particular, it is unclear whether mature hepatocytes, which have sufficient liver function, or immature hepatic progenitor cells, which have a higher proliferative capacity, will provide a better outcome. The main objective of this study was to investigate the therapeutic efficacy of the transplantation of hepatocytes at various differentiation stages. We utilized transgenic mice that expressed diphtheria toxin (DT) receptors under the control of an albumin enhancer/promoter. ESC-derived endodermal cells, fetal hepatocytes, and adult hepatocytes were transplanted into these mice with experimentally induced lethal acute liver injury caused by DT administration. The transplanted cells were marked by enhanced green fluorescent protein. We evaluated their effects on survival. At 35 days after transplantation, the survival rate of the adult hepatocyte-transplanted group (8/20, 40%) was significantly improved in comparison to that of the sham-operated group (2/25, 8%), the fetal hepatocyte-transplanted group (1/20, 5%), and the ESC-derived endodermal cell-transplanted group (0/21, 0%). The adult hepatocytes proliferated in the recipient livers and replaced a large part of their parenchyma. The transplantation of adult hepatocytes for acute liver failure significantly improved the survival rate in comparison to that of transplantation of immature cells, thus suggesting that ESCs and iPSCs should be differentiated into mature hepatocytes before cell transplantation for acute liver failure.

Liver progenitor cell interactions with the extracellular matrix

Liver progenitor cells (LPCs) are a promising source of cells to treat liver disease by cell therapy, due to their capability for self-replication and bipotentiality. In order to establish useful culture systems of LPCs and apply them to future clinical therapies, it is necessary to understand their interactions with their microenvironment and especially with the extracellular matrix (ECM). There is considerable evidence from in vivo studies that matrix proteins affect the activation, expansion, migration and differentiation of LPCs, but the information on the role that specific ECMs play in regulating LPCs in vitro is more limited. Nevertheless, current studies suggest that laminin, collagen type III, collagen type IV and hyaluronic acid help to maintain the undifferentiated phenotype of LPCs and promote their proliferation when cultured in media supplemented with growth factors chosen for LPC expansion, whereas collagen type I and fibronectin are generally associated with a differentiated phenotype under the same conditions. Experimental evidence suggests that α6β1 and α5β1 integrins as well as CD44 on the surface of LPCs, and their related downstream signals, are important mediators of interactions between LPCs and the ECM. The interactions of LPCs with the ECM form the focus of this review and the contribution of ECM molecules to strategies for optimizing in vitro LPC cultures for therapeutic applications is discussed.

Embryonic hepatocyte transplantation for hepatic cirrhosis: Efficacy and mechanism of action

AIM: To investigate the efficacy and mechanism of action of allogeneic embryonic hepatocyte transplantation for the treatment of hepatic cirrhosis.

METHODS: Rat embryonic hepatocytes were characterized by examining cell markers. Wistar rats with CCl₄-induced cirrhosis were randomly divided into two groups: a model group receiving continuous CCl₄, and a cell transplantation group receiving continuous CCl₄ and transplanted with embryonic fluorescent-labeled hepatocytes. In addition, a normal control group was composed of healthy rats. All rats were sacrificed after 2 wk following the initiation of the cell transplant. Ultrasound, pathological analyses and serum biochemical tests were used to evaluate the efficacy of embryonic hepatocyte transplantation. To analyze the recovery status of cirrhotic hepatocytes and the signaling pathways influenced by embryonic hepatocyte transplantation, real-time polymerase chain reaction was performed to examine the mRNA expression of stellate activation-associated protein (STAP), c-myb, α smooth muscle actin (α-SMA) and endothelin-1 (ET-1). Western blotting and immunohistochemistry were employed to detect α-SMA and ET-1 protein expression in hepatic tissues.

RESULTS: Gross morphological, ultrasound and histopathological examinations, serum biochemical tests and radioimmunoassays demonstrated that hepatic cirrhosis was successfully established in the Wistar rats. Stem cell factor receptor (c-kit), hepatocyte growth factor receptor (c-Met), Nestin, α fetal protein, albumin and cytokeratin19 markers were observed in the rat embryonic hepatocytes. Following embryonic hepatocyte transplantation, there was a significant reversal in the gross appearance, ultrasound findings, histopathological properties, and serum biochemical parameters of the rat liver. In addition, after the activation of hepatic stellate cells and STAP signaling, α-SMA, c-myb and ET-1 mRNA levels became significantly lower than in the untreated cirrhotic group (P < 0.05). These levels, however, were not statistically different from those of the normal healthy group. Immunohistochemical staining and Western blot analyses revealed that α-SMA and ET-1 protein expression levels in the transplantation group were significantly lower than in the untreated cirrhotic group, but being not statistically different from the normal group.

CONCLUSION: Transplantation of embryonic hepatocytes in rats has therapeutic effects on cirrhosis. The described treatment may significantly reduce the expression of STAP and ET-1.

Transplantation of human umbilical cord blood mesenchymal stem cells improves survival rates in a rat model of acute hepatic necrosis

INTRODUCTION

Stem cell-based therapies are emerging as important and promising methods in the treatment of end-stage liver disease. This study is aimed to evaluate the effects of human umbilical cord blood mesenchymal stem cell (HUCBMSC) transplantation in acute hepatic necrosis (AHN).

METHODS

Green fluorescent protein (GFP)-labeled HUCBMSCs were injected into the liver of rats in which AHN was induced by carbon tetrachloride, and the migration of these cells in liver slices was evaluated from 48 hours to 4 weeks post-transplantation. The transdifferentiation status of the HUCBMSCs was evaluated using immunohistochemistry and real-time reverse transcription-polymerase chain reaction, and survival rates were statistically analyzed.

RESULTS

Dispersed GFP fluorescence was observed along the portal area 48 hours after transplantation. One week post-transplantation, GFP-positive cells were found in necrotic liver areas, and GFP-positive cells persisted after 4 weeks. Immunohistochemistry and real-time polymerase chain reaction analysis showed that transplanted HUCBMSCs expressed several human liver tissue-specific markers in rats with AHN. Statistical analysis revealed that rats with AHN that were transplanted with HUCBMSCs had significantly lower death rates after 48 hours than those receiving no HUCBMSCs.

CONCLUSION

HUCBMSC transplantation can significantly improve the survival of rats with AHN. The underlying mechanisms involved may include the transdifferentiation of HUCBMSCs into hepatocyte-like cells and targeted migration of these cells to liver lesion sites.

Inducible and conditional promoter systems to generate transgenic animals

Transgenic animals are very useful models that can be utilized for the analysis of temporal and spatial gene expression in vivo. However, generation of a transgenic animal may become problematic if the presence of the transgene leads to conditions which are toxic or lethal to cell growth. In an effort to delineate the mechanism by which a specific gene contributes to cell growth and viability, an inducible and/or conditional system was established to generate transgenic animals. The systems comprise the following: (1) Selecting a specific promoter, (2) replacing a normal gene with other gene sequences (knock out), (3) promoting destruction of the mRNA (RNAi), (4) inducing and/or conditioning by drugs (Tet on/off), and (5) conditional cell knock out with cell death. The choice of system employed is dependent on the particular aim of the investigation, and may influence the final result. The inducible and conditional promoter system represents a useful experimental approach for the development of transgenic animals and the precise examination of gene function.

Cellular Transplantation for Liver Diseases

Presently, the orthotropic liver transplantation (OLT) is still the most effective therapeutic for patients with acute or chronic hepatic failure. However, due to the shortage of donor livers, the number of patients benefited from this approach is limited. Therefore, some alternative modalities have been paid attention for restoring the liver function. The cell transplantation is one of the promising modalities to realize this purpose. The types of cells used in the cell transplantation include syngeneic hepatocytes, allogeneic hepatocytes, immortalized hepatocytes, and stem cells derived heptocytes. The stem cells, especially the adult stem cells from bone marrow, are shown as a promising cell source for liver repopulation. The mesenchymal bone marrow stem cells and embryonic stem cells can be induced to differentiate into the hepatic lineage and might be used in the cell transplantation for liver diseases. Compared to OLT, the advantages of cell-based therapy for liver disease are, but not limited to, less invasive, less expensive, easy manipulated, easy expansion of cells in vitro. Cells can be stored in a cell bank for future use. Though most of the current studies are experimental and animal based, the cellular therapy for liver disease is expected to be an effective alternative in clinical settings in near future.