Isolation and characterization of hepatic stem cells, or "oval cells," from rat livers

Fk506 Inhibit liver regeneration in HOC model Rat

BACKGROUND

Studies have shown that lymphocytes support hepatic oval cell (HOC)-dependent liver regeneration and FK506（Tacrolimus） is known as an immunosuppressor. Therefore, we studied the role of FK506 in HOC activation and/or proliferation to guide the clinical use of FK506.

METHODS

Thirty male Lewis rats were randomly divided into 4 groups: (A) intervene in activation (n = 8), (B) intervene in proliferation (n = 8), (C) control HOC model (n = 8), and (D) pure partial hepatectomy (PH) (n = 6). The HOC model was established by 2AAF(2-acetylaminofluorene)/PH in groups A to C. FK506 (at a dose of 1 mg/kg/d) was given subcutaneously in group A except on operation day, and not until day 8 post-operation (PO) in group B. Half of the animals were euthanized on days 10 and 14 PO, respectively. The remnant liver was weighed and stained by hematoxylin and eosin and immunohistochemical staining of proliferating cell nuclear antigen and epithelial cell adhesion molecule enabled HOC proliferation analysis.

RESULTS

FK506 intervention exacerbated liver damage and hindered the recovery of the HOC model rat. Weight gain was severely retarded or even negative. Liver weight and the liver body weight ratio were lower than control group. HE and immunohistochemistry showed pooer proliferation of hepatocytes and fewer HOC numbers in group A.

CONCLUSION

FK506 inhibited HOC activation by affecting T and NK cells, ultimately blocking liver regeneration. Poor liver regeneration after auxiliary liver transplantation might be associated with the inhibition of HOC activation and proliferation caused by FK506 treatment.

p53 positively regulates the proliferation of hepatic progenitor cells promoted by laminin-521

Hepatic progenitor cells (HPCs) hold tremendous potential for liver regeneration, but their well-known limitation of proliferation hampers their broader use. There is evidence that laminin is required for the proliferation of HPCs, but the laminin isoform that plays the dominant role and the key intracellular downstream targets that mediate the regulation of HPC proliferation have yet to be determined. Here we showed that p53 expression increased gradually and reached maximal levels around 8 days when laminin α4, α5, β2, β1, and γ1 subunit levels also reached a maximum during HPC activation and expansion. Laminin-521 (LN-521) promoted greater proliferation of HPCs than do laminin, matrigel or other laminin isoforms. Inactivation of p53 by PFT-α or Ad-p53^V143A inhibited the promotion of proliferation by LN-521. Further complementary MRI and bioluminescence imaging analysis showed that p53 inactivation decreased the proliferation of transplanted HPCs in vivo. p53 was activated by LN-521 through the Integrin α6β1/FAK-Src-Paxillin/Akt axis. Activated p53 was involved in the nuclear translocation of CDK4 and inactivation of Rb by inducing p27^Kip1. Taken together, this study identifies LN-521 as an ideal candidate substrate for HPC culture and uncovers an unexpected positive role for p53 in regulating proliferation of HPCs, which makes it a potential target for HPC-based regenerative medicine.

Hepatogenic Potential and Liver Regeneration Effect of Human Liver-derived Mesenchymal-Like Stem Cells

Human liver-derived stem cells (hLD-SCs) have been proposed as a possible resource for stem cell therapy in patients with irreversible liver diseases. However, it is not known whether liver resident hLD-SCs can differentiate toward a hepatic fate better than mesenchymal stem cells (MSCs) obtained from other origins. In this study, we compared the differentiation ability and regeneration potency of hLD-SCs with those of human umbilical cord matrix-derived stem cells (hUC-MSCs) by inducing hepatic differentiation. Undifferentiated hLD-SCs expressed relatively high levels of endoderm-related markers (GATA4 and FOXA1). During directed hepatic differentiation supported by two small molecules (Fasudil and 5-azacytidine), hLD-SCs presented more advanced mitochondrial respiration compared to hUC-MSCs. Moreover, hLD-SCs featured higher numbers of hepatic progenitor cell markers on day 14 of differentiation (CPM and CD133) and matured into hepatocyte-like cells by day 7 through 21 with increased hepatocyte markers (ALB, HNF4A, and AFP). During in vivo cell transplantation, hLD-SCs migrated into the liver of ischemia-reperfusion injury-induced mice within 2 h and relieved liver injury. In the thioacetamide (TAA)-induced liver injury mouse model, transplanted hLD-SCs trafficked into the liver and spontaneously matured into hepatocyte-like cells within 14 days. These results collectively suggest that hLD-SCs hold greater hepatogenic potential, and hepatic differentiation-induced hLD-SCs may be a promising source of stem cells for liver regeneration.

Endogenous beta-galactosidase activity marks a TREM2-expressing Kupffer cell population in injured livers of Lgr5-LacZ and wild-type mice

Lgr5-LacZ mice harbor the Escherichia coli LacZ gene encoding β-galactosidase (β-gal) under the control of the Lgr5 promoter, a stem/progenitor cell marker. In injured livers of Lgr5-LacZ mice, cells expressing β-galactosidase (β-gal) are considered as potential bipotent liver progenitors; however, their origin and identity remain unknown. Unexpectedly, using lineage tracing, we demonstrate that the β-gal⁺ cells do not originate from liver parenchymal cells. Instead, β-gal⁺ cells, isolated from injured livers of both Lgr5-LacZ and wild-type mice, are positive for markers of Kupffer cells, liver-resident macrophages. The β-gal expression in these cells is a result of elevated expression of the endogenous beta-galactosidase Glb1. In injured livers of Lgr5-LacZ mice, bacterial β-gal expression is very low, suggesting transgene silencing. The gene expression profile of the β-gal⁺ Kupffer cells from injured livers suggests a role in liver regeneration.

Advances in Hepatic Tissue Bioengineering with Decellularized Liver Bioscaffold

The burden of liver diseases continues to grow worldwide, and liver transplantation is the only option for patients with end-stage liver disease. This procedure is limited by critical issues, including the low availability of donor organs; thus, novel therapeutic strategies are greatly needed. Recently, bioengineering approaches using decellularized liver scaffolds have been proposed as a novel strategy to overcome these challenges. The aim of this systematic literature review was to identify the major advances in the field of bioengineering using decellularized liver scaffolds and to identify obstacles and challenges for clinical application. The main findings of the articles and each contribution for technique optimization were highlighted, including the protocols of perfusion and decellularization, duration, demonstration of quality control—scaffold acellularity, matrix composition, and preservation of growth factors—and tissue functionality after recellularization. In previous years, many advances have been made as this technique has evolved from studies in animal models to human livers. As the field develops and this promising technique has become much more feasible, many challenges remain, including the selection of appropriate cell types for recellularization, route of cell administration, cell-seeding protocol, and scalability that must be standardized prior to clinical application.

Expression of receptor interacting protein 1 and receptor interacting protein 3 oval cells in a rat model of hepatocarcinogenesis

When apoptosis is suppressed in a neoplastic state, necroptosis may enable an anticancer response. In the present study, the association between apoptosis and necroptosis was assessed in a partial hepatectomy (PH)/diethylnitrosamine (DEN) rat model of hepatocarcinogenesis. Isolated oval cells (OCs) were analysed at 24, 48 and 72 h and at the first and second week of incubation. Phenotypic studies, apoptosis and necroptosis detection and proliferative activity assays were also performed on the OCs. The OCs were isolated from non-neoplastic (PH) and neoplastic (PH/DEN) livers, which expressed receptor interacting protein (RIP) 1 and RIP3. Western blot analysis revealed that the RIP1 and RIP3 expression in the PH/DEN OCs started to increase at 72 h and continually increased to the end of cell culture. Compared with the PH OCs, the cells isolated from PH/DEN rats exhibited significantly less potential for apoptosis (P<0.05). There were a minimal number of apoptotic PH/DEN OCs (2.82±1.1%) at 72 h. In addition, the PH/DEN OCs demonstrated progressive proliferative activity during incubation, which was significantly increased compared with the PH OCs at ≥72 h. The present study revealed that PH/DEN OCs, which trigger hepatic cancer, have a high proliferative activity and suppress apoptosis. It was also observed that, based on the expression of RIP3 and RIP1, necroptosis may be maintained and may serve as an alternative pathway for programmed PH/DEN OC death.

Directed Differentiation of Adult Liver Derived Mesenchymal Like Stem Cells into Functional Hepatocytes

Shortage of functional hepatocytes hampers drug safety testing and therapeutic applications because mature hepatocytes cannot be expanded and maintain functions in vitro. Recent studies have reported that liver progenitor cells can originate from mature hepatocytes in vivo. Derivation of proliferating progenitor cells from mature hepatocytes, and re-differentiation into functional hepatocytes in vitro has not been successful. Here we report the derivation of novel mesenchymal-like stem cells (arHMSCs) from adult rat hepatocytes. Immunofluorescence and flow cytometry characterization of arHMSCs found expression of mesenchymal markers CD29, CD44, CD90, vimentin and alpha smooth muscle actin. These arHMSCs proliferated in vitro for 4 passages yielding 10⁴ fold increase in cell number in 28 days, and differentiated into hepatocyte-like cells (arHMSC-H). The arHMSC-H expressed significantly higher level of hepatocyte-specific markers (200 fold for albumin and 6 fold for Cyp450 enzymes) than arHMSCs. The arHMSC-H also demonstrated dose response curves similar to primary hepatocytes for 3 of the 6 paradigm hepatotoxicants tested, demonstrating utility in drug safety testing applications.

A label-retaining but unipotent cell population resides in biliary compartment of mammalian liver

Cells with slow proliferation kinetics that retain the nuclear label over long time periods-the label-retaining cells (LRCs)-represent multipotent stem cells in a number of adult tissues. Since the identity of liver LRCs (LLRCs) had remained elusive we utilized a genetic approach to reveal LLRCs in normal non-injured livers and characterized their regenerative properties in vivo and in culture. We found that LLRCs were located in biliary vessels and participated in the regeneration of biliary but not hepatocyte injury. In culture experiments the sorted LLRCs displayed an enhanced self-renewal capacity but a unipotent biliary differentiation potential. Transcriptome analysis revealed a unique set of tumorigenesis- and nervous system-related genes upregulated in LLRCs when compared to non-LRC cholangiocytes. We conclude that the LLRCs established during the normal morphogenesis of the liver do not represent a multipotent primitive somatic stem cell population but act as unipotent biliary progenitor cells.

Prospects for Adult Stem Cells in the Treatment of Liver Diseases

Hepatocytes constitute the main bulk of the liver and perform several essential functions. After injury, the hepatocytes have a remarkable capacity to regenerate and restore functionality. However, in some cases, the endogenous hepatocytes cannot replicate or restore the function, and liver transplantation, which is not exempt of complications, is required. Stem cells offer in theory the possibility of generating unlimited supply of hepatocytes in vitro due to their capacity to self-renew and differentiate when given the right cues. Stem cells isolated from an array of tissues have been investigated for their capacity to differentiate into hepatocyte-like cells in vitro and are employed in rescue experiments in vivo. Adult stem cells have gained in attractiveness over embryonic stem cells for liver cell therapy due to their origin, multipotentiality, and the possibility of autologous transplantation. This review deals with the promise and limitations of adult stem cells in clinically restoring liver functionality.

Multi-organ Mapping of Cancer Risk

Cancers are distributed unevenly across the body, but the importance of cell intrinsic factors such as stem cell function in determining organ cancer risk is unknown. Therefore, we used Cre-recombination of conditional lineage tracing, oncogene, and tumor suppressor alleles to define populations of stem and non-stem cells in mouse organs and test their life-long susceptibility to tumorigenesis. We show that tumor incidence is determined by the life-long generative capacity of mutated cells. This relationship held true in the presence of multiple genotypes and regardless of developmental stage, strongly supporting the notion that stem cells dictate organ cancer risk. Using the liver as a model system, we further show that damage-induced activation of stem cell function markedly increases cancer risk. Therefore, we propose that a combination of stem cell mutagenesis and extrinsic factors that enhance the proliferation of these cell populations, creates a "perfect storm" that ultimately determines organ cancer risk. VIDEO ABSTRACT.

An efficient protocol for deriving liver stem cells from neonatal mice: validating its differentiation potential

The success of liver regeneration depends on the availability of suitable cell types and their potential to differentiate into functional hepatocytes. To identify the stem cells which have the ability to differentiate into hepatocytes, we used neonatal liver as source. However, the current protocol for isolating stem cells from liver involves enzymes like collagenase, hyaluronidase exposed for longer duration which limits the success. This results in the keen interest to develop an easy single step enzyme digestion protocol for isolating stem cells from liver for tissue engineering approaches. Thus, the unlimited availability of cell type favors setting up the functional recovery of the damaged liver, ensuring ahead success towards treating liver diseases. We attempted to isolate liver stem derived cells (LDSCs) from mouse neonatal liver using single step minimal exposure to enzyme followed by in vitro culturing. The cells isolated were characterized for stem cell markers and subjected to lineage differentiation. Further, LDSCs were induced to hepatocyte differentiation and validated with hepatocyte markers. Finally, we developed a reproducible, efficient protocol for isolation of LDSCs with functional hepatocytes differentiation potential, which further can be used as in vitro model system for assessing drug toxicity assays in various preclinical trials.

Stiffness of hyaluronic acid gels containing liver extracellular matrix supports human hepatocyte function and alters cell morphology

Tissue engineering and cell based liver therapies have utilized primary hepatocytes with limited success due to the failure of hepatocytes to maintain their phenotype in vitro. In order to overcome this challenge, hyaluronic acid (HA) cell culture substrates were formulated to closely mimic the composition and stiffness of the normal liver cellular microenvironment. The stiffness of the substrate was modulated by adjusting HA hydrogel crosslinking. Additionally, the repertoire of bioactive molecules within the HA substrate was bolstered by supplementation with normal liver extracellular matrix (ECM). Primary human hepatocyte viability and phenotype were determined over a narrow physiologically relevant range of substrate stiffnesses from 600 to 4600Pa in both the presence and absence of liver ECM. Cell attachment, viability, and organization of the actin cytoskeleton improved with increased stiffness up to 4600Pa. These differences were not evident in earlier time points or substrates containing only HA. However, gene expression for the hepatocyte markers hepatocyte nuclear factor 4 alpha (HNF4α) and albumin significantly decreased on the 4600Pa stiffness at day 7 indicating that cells may not have maintained their phenotype long-term at this stiffness. Function, as measured by albumin secretion, varied with both stiffness and time in culture and peaked at day 7 at the 1200Pa stiffness, slightly below the stiffness of normal liver ECM at 3000Pa. Overall, gel stiffness affected primary human hepatocyte cell adhesion, functional marker expression, and morphological characteristics dependent on both the presence of liver ECM in gel substrates and time in culture.

New Tools in Experimental Cellular Therapy for the Treatment of Liver Diseases

The current standard of care for end stage liver disease is orthotopic liver transplantation (OLT). Through improvement in surgical techniques, immunosuppression, and general medical care, liver transplantation has become an effective treatment over the course of the last half-century. Unfortunately, due to the limited availability of donor organs, there is a finite limit to the number of patients who will benefit from this therapy. This review will discuss current research in experimental cellular therapies for acute, chronic, and metabolic liver failure that may be appropriate when liver transplantation is not an immediate option.

Unbalanced distribution of materials: the art of giving rise to hepatocytes from liver stem/progenitor cells

Liver stem/progenitor cells (LSPCs) are able to duplicate themselves and differentiate into each type of cells in the liver, including mature hepatocytes and cholangiocytes. Understanding how to accurately control the hepatic differentiation of LSPCs is a challenge in many fields from preclinical to clinical treatments. This review summarizes the recent advances made to control the hepatic differentiation of LSPCs over the last few decades. The hepatic differentiation of LSPCs is a gradual process consisting of three main steps: initiation, progression and accomplishment. The unbalanced distribution of the affecting materials in each step results in the hepatic maturation of LSPCs. As the innovative and creative works for generating hepatocytes with full functions from LSPCs are gradually accumulated, LSPC therapies will soon be a new choice for treating liver diseases.

Differential hepatic stem cell proliferation and differentiation after partial hepatectomy in rats

Stem cell‑derived hepatocyte precursor cells represent a promising model for clinical transplantation to diseased livers, as well as for establishment of in vitro systems for drug metabolism and toxicology studies. The present study aimed to establish a new method of induction of hepatocyte differentiation using various factors and evaluate the effect of different partial hepatectomies and the duration of collagenase perfusion on hepatic stem cell proliferation and differentiation. A rat model of hepatic oval cell proliferation was established by partial hepatectomy (PH). Following 73.1 and 83.4% PH, rats underwent perfusion with IV collagenase for 10, 20 and 30 min. Density gradient centrifugation was performed and cells in the supernatant were cultured in various combinations of factors to induce oval cells to differentiate into mature hepatocytes. Cells were characterized for hepatocyte marker expression by morphology, flow cytometry, immunofluorescence and western blot analysis. Hepatic oval cells isolated from rats at 7 and 14 days post‑PH exhibited properties of hepatic stem/progenitor cells. Following culturing in RPMI‑1640 medium with hepatocyte growth factor and fibroblast growth factor‑4, the cells resembled primary human hepatocytes with regard to morphology and expression of the hepatocyte markers, cytokeratin 18 (CK‑18) and α‑1‑fetoprotein (AFP). Optimal differentiation of hepatic stem cells to CK‑18‑ and AFP‑positive cells was observed when stem cells isolated from 83.4% PH rats (7 days following surgery) were perfused with IV collagenase for 20 min. The results of this study provide novel insights into characteristics of rat hepatic stem cells.

Up-regulation of thy-1 promotes invasion and metastasis of hepatocarcinomas

Increasing evidence has revealed that thy-1 was a potential stem cell marker of liver cancer, but no data have been shown on how thy-1 regulates the pathophysiology of liver cancer, such as proliferation, apoptosis, invasion and migration. We previously demonstrated that thy-1 was expressed in about 1% of hepg2 cells, thy-1+ hepg2 cells, but not thy-1-, demonstrating high tumorigenesis on inoculation 0.5x10⁵ cells per BACA/LA mouse after 2 months. In the present study, our results showed that higher expression of thy-1 occurs in 72% (36/50 cases) of neoplastic hepatic tissues as compared to 40% (20/50 cases) of control tissues, and the expression of thy-1 is higher in poorly differentiated liver tumors than in the well-differentiated ones. In addition, thy-1 expression was detected in 85% of blood samples from liver cancer patients, but none in normal subjects or patients with cirrhosis or hepatitis. There was a significant negative correlation between thy-1 expression and E-cadherin expression (a marker of invasion and migraton), but not between thy-1 expression and AFP expression in all the liver cancer and blood samples. We further investigated the relationship between thy-1 and E- cadherin in liver cancer hepg2 cell line which was transfected with pReceiver-M29/thy-1 eukaryotic expression vector followed by aspirin treatment. Lower expression of E- cadherin but higher expressions of thy-1 were detected in hepg2 cells transfected with pReceiver-M29/thy-1. Taken together, our study suggested that thy-1 probably regulates liver cancer invasion and migration.

Method for the decellularization of intact rat liver

We have developed a method for the decellularization of whole rat livers by perfusion with increasing concentrations of detergents. This procedure resulted in an intact, decellularized organ with an intact liver capsule. These decellularized organs were analyzed by immunohistochemistry, and retained an appropriate distribution of extracellular matrix components. The laminin basement membranes of the liver vasculature also remain intact. These acellular vessel remnants were strong enough to be cannulated, providing a convenient means for the delivery of cells to areas deep within the decellularized organ. Cannulation of the extrahepatic vessel remnants allow for media to be circulated through the decellularized organ. These decellularized livers provide a natural matrix for research in the fields of bio-artificial livers and liver engineering.

Contributions of new hepatocyte lineages to liver growth, maintenance, and regeneration in mice

The contributions that de novo differentiation of new hepatocyte lineages makes to normal liver physiology are unknown. In this study, a system that uniquely marks cells during a finite period following primary activation of a serum albumin gene promoter/enhancer-driven Cre recombinase (albCre) transgene was used to investigate birthrates of new hepatocyte lineages from albumin (Alb)-naive precursors in mice. Elapsed time was measured with a two-color fluorescent marker gene that converts from expressing tandem dimer Tomato (tdT; a red fluorescent protein) to expressing green fluorescent protein (GFP) following primary exposure to Cre. The accumulation of GFP and the decay of tdT each contributed to a regular fluorescence transition, which was calibrated in vivo. In normal adults, this system revealed that a steady-state level of 0.076% of all hepatocytes had differentiated within the previous 4 days from albCre-naive cell lineages. In comparison with resting adult livers, the relative abundance of these newborn hepatocytes was elevated 3.7-fold in the growing livers of juveniles and 8.6-fold during liver regeneration after partial hepatectomy in adults.

CONCLUSION

Newborn hepatocyte lineages arising from Alb-naive cells contribute to liver maintenance under normal conditions. Hepatocyte lineage birthrates can vary in response to the liver's physiological status.

MRI of magnetically labeled mesenchymal stem cells in hepatic failure model

AIM: To track intravascularly transplanted mesenchymal stem cells (MSCs) labeled with superparamagnetic iron oxide (SPIO) by using magnetic resonance imaging (MRI) in an experimental rabbit model of hepatic failure.

METHODS: Human MSCs labeled with FDA-approved SPIO particles (Feridex) were transplanted via the mesenteric vein into rabbits (n = 16) with carbon tetrachloride-induced hepatic failure. Magnetic resonance (MR) examinations were performed with a 3.0 T clinical scanner immediately before and 2 h and 1, 3, and 7 d after transplantation. Signal intensity (SI) changes on T2*-weighted MRI were measured, and correlation between MR findings and histomorphologic findings was also investigated.

RESULTS: SI on T2*-weighted MRI decreased significantly in the liver 2 h after injection of human MSCs and returned gradually to the levels found before injection in 7 d. Changes in SI in the liver at 2 h, 1, 3, and 7 d were 41.87% ± 9.63%, 10.42% ± 4.3%, 5.12% ± 1.9%, 3.75% ± 1.2%, respectively (P < 0.001). Histologic analyses confirmed the presence of MSCs in the liver, localized mainly in the sinusoids in early period (2 h and 1 d) and concentrated to the border zone in late period (3 and 7 d). The number of iron-positive cells in the liver at 2 h and on 1, 3 and 7 d after transplantation was 29.2 ± 4.8, 10.1 ± 3.7, 6.7 ± 2.2, and 5.8 ± 2.1, respectively (P = 0.013).

CONCLUSION: Intravascularly injected SPIO-labeled MSCs in an experimental rabbit model of hepatic failure can be detected and followed with MRI.

Stem cell origins and animal models of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a common malignant tumor that almost always occurs within a preexisting background of chronic liver disease and cirrhosis. Currently, medical therapy is not effective in treating most HCC, and the only hope of cure is either resection or liver transplantation. A small minority of patients is eligible for these therapies, which entail major morbidity at the very least. In spite of immense scientific advances during the past 3 decades, patient survival has improved very little. In order to reduce morbidity and mortality from HCC, improvements in early diagnosis and development of novel local and systemic therapies for advanced disease are essential, in addition to efforts geared towards primary prevention. Studies with experimental animal models that closely mimic human disease are very valuable in understanding physiological, cellular and molecular mechanisms underlying the disease. Furthermore, appropriate animal models have the potential to increase our understanding of the effects of image-guided minimally invasive therapies and thereby help to improve such therapies. In this review, we examine the evidence for stem cell origins of such tumors, critically evaluate existing models and reflect on how to develop new models for minimally invasive, image-guided treatment of HCC.

The quest for liver progenitor cells: a practical point of view

Many chronic liver diseases can lead to hepatic dysfunction with organ failure. At present, orthotopic liver transplantation represents the benchmark therapy of terminal liver disease. However this practice is limited by shortage of donor grafts, the need for lifelong immunosuppression and very demanding state-of-the-art surgery. For this reason, new therapies have been developed to restore liver function, primarily in the form of hepatocyte transplantation and artificial liver support devices. While already offered in very specialized centers, both of these modalities still remain experimental. Recently, liver progenitor cells have shown great promise for cell therapy, and consequently they have attracted a lot of attention as an alternative or supportive tool for liver transplantation. These liver progenitor cells are quiescent in the healthy liver and become activated in certain liver diseases in which the regenerative capacity of mature hepatocytes and/or cholangiocytes is impaired. Although reports describing liver progenitor cells are numerous, they have not led to a consensus on the identity of the liver progenitor cell. In this review, we will discuss some of the characteristics of these cells and the different ways that have been used to obtain these from rodents. We will also highlight the challenges that researchers are facing in their quest to identify and use liver progenitor cells.

Thymus cell antigen-1-expressing cells in the oval cell compartment

Thymus cell antigen-1 (Thy-1)-expressing cells proliferate in the liver during oval cell (OC)-mediated liver regeneration. We characterized these cells in normal liver, in carbon tetrachloride-injured liver, and in several models of OC activation. The gene expression analyses were performed using reverse-transcriptase polymerase chain reaction (RT-PCR), quantitative RT-PCR (Q-RT-PCR) of cells isolated by fluorescence-activated cell sorting (FACS), and by immunofluorescent microscopy of tissue sections and isolated cells. In normal liver, Thy-1(+) cells are a heterogeneous population: those located in the periportal region do not coexpress desmin or alpha smooth muscle actin (alpha-SMA). The majority of Thy-1(+) cells located at the lobular interface and in the parenchyma coexpress desmin but not alpha-SMA, i.e., they are not resident myofibroblasts. Although Thy-1(+) cells proliferate moderately after carbon tetrachloride injury, in all models of OC-mediated liver regeneration they proliferate quickly and expand significantly and disappear from the liver when the OC response subsides. Activated Thy-1(+) cells do not express OC genes but they express genes known to be expressed in mesenchymal stem cells (CD105, CD73, CD29), genes considered specific for activated stellate cells (desmin, collagen I-a2, Mmp2, Mmp14) and myofibroblasts (alpha-SMA, fibulin-2), as well as growth factors and cytokines (Hgf, Tweak, IL-1b, IL-6, IL-15) that can affect OC growth. Activated in vitro stellate cells do not express Thy-1. Subcloning of Thy-1(+) cells from OC-activated livers yield Thy-1(+) fibroblastic cells and a population of E-cadherin(+) mesenchymal cells that gradually discontinue expression of Thy-1 and begin to express cytokeratins. However, upon transplantation these cells do not differentiate into hepatocytes or cholangiocytes. Activated Thy-1(+) cells produce predominantly latent transforming growth factor beta.

CONCLUSION

Thy-1(+) cells in the OC niche are activated mesenchymal-epithelial cells that are distinct from resident stellate cells, myofibroblasts, and oval cells.

Establishment of cancer cell lines from rat hepatocholangiocarcinoma and assessment of the role of granulocyte-colony stimulating factor and hepatocyte growth factor in their growth, motility and survival

BACKGROUND/AIMS

Oval cells (OCs), putative hepatic stem cells, may give rise to liver cancers. We developed a carcinogenesis regimen, based upon induction of OC proliferation prior to carcinogen exposure. In our model, rats subjected to 2-acetylaminofluorene/ partial-hepatectomy followed by aflatoxin injection (APA regimen) developed well-differentiated hepatocholangiocarcinomas. The aim of this study was to establish and characterize cancer cell lines from this animal model.

METHODS

Cancer cells were cultured from animals sacrificed eight months after treatment, and single clones were selected. The established cell lines, named LCSCs, were characterized, and their tumorigenicity was assessed in vivo. The roles of granulocyte-colony stimulating factor (G-CSF) and hepatocyte growth factor (HGF) in LCSC growth, survival and motility were also investigated.

RESULTS

From primary tumors, six cell lines were developed. LCSCs shared with the primary tumors the expression of various OC-associated markers, including cMet and G-CSF receptor. In vitro, HGF conferred protection from death by serum withdrawal. Stimulation with G-CSF increased LCSC growth and motility, while the blockage of its receptor inhibited LCSC proliferation and migration.

CONCLUSIONS

Six cancer cell lines were established from our model of hepatocholangiocarcinoma. HGF modulated LCSC resistance to apoptosis, while G-CSF acted on LCSCs as a proliferative and chemotactic agent.