Effects of growth factors on the growth and differentiation of mouse fetal liver epithelial cells in primary cultures

Differential effects of epidermal growth factor (EGF) receptor ligands on receptor binding, downstream signalling pathways and DNA synthesis in hepatocytes

Hepatocytes are responsive to mitogenic effects of several ligands acting via EGFR. Studying primary cultures of rat hepatocytes, we found that, as compared to EGF, HB-EGF had a markedly higher affinity of the EGFR, while AR and TGFα had lower affinity. HB-EGF was also more potent compared to the other growth factors regarding phosphorylation of EGFR, Shc, ERK1/2 and Akt. All ligands induced phosphorylation of ErbB2, indicating receptor heterodimerization. TGFα, despite having much lower receptor affinity, was about equally potent and efficacious as HB-EGF as a stimulator of DNA synthesis. In contrast, EGF had relatively high affinity but markedly lower efficacy in stimulation of DNA synthesis. The results suggest that amplifying and/or inhibitory mechanisms may modulate the mitogenic responses downstream of the initial signalling steps, and that this may affect the effects of the EGFR ligands differentially.

A heparin-modified thermoresponsive surface with heparin-binding epidermal growth factor-like growth factor for maintaining hepatic functions in vitro and harvesting hepatocyte sheets

A heparin-modified thermoresponsive surface bound with heparin-binding epidermal growth factor-like growth factor (HB-EGF) was designed to allow creation of transferrable and functional hepatocyte sheets. A heparin-modified thermoresponsive surface was prepared by covalently tethering heparin onto poly(N-isopropylacrylamide-co-2-carboxyisopropylacrylamide)-grafted tissue culture polystyrene surfaces (Heparin-IC). HB-EGFs were able to stably bind to heparin-IC via affinity interaction. The survival of primary rat hepatocytes was maintained through HB-EGF-bound heparin-IC (HB-EGF/heparin-IC). Moreover, cultured rat primary hepatocytes on HB-EGF/heparin-IC exhibited higher albumin-secretion than hepatocytes cultured on PIPAAm-grafted and collagen-coated surfaces with soluble HB-EGF in the culture medium, regardless of whether soluble EGF was added. These results suggested that HB-EGF/heparin-IC is able to effectively maintain hepatic function via continuous signaling of HB-EGF. After a 4-day cultivation, the cultured hepatocytes on HB-EGF/heparin-IC detached as a cell sheet with fibronectin and HB-EGF only after the temperature was lowered to 20 °C. In addition, higher expression of hepatocyte-specific genes (albumin, hepatocyte nuclear factor 4 alpha, coagulation factor VII, and coagulation factor IX) in hepatocyte sheets was detected on HB-EGF/heparin-IC than on a PIPAAm surface with soluble HB-EGF, indicating that HB-EGF/heparin-IC suppressed the dedifferentiation of cultured hepatocytes. Hence, heparin-modified thermoresponsive surfaces bound with HB-EGF facilitate the fabrication of transferrable hepatocyte sheets with intact hepatic functions and have the potential to provide an in vitro culture system using functional hepatocyte sheet tissues, which may serve as an effective hepatocyte-based tissue engineering platform for liver disease treatments.

Establishment and characterization of hepatic stem-like cell lines from normal adult rat liver

The liver is a unique organ with the potential to regenerate from injury. Hepatic stem cells contribute to liver regeneration when surviving hepatocytes in injured liver are unable to proliferate. To investigate the mechanism of liver regeneration in vitro, we established hepatic stem cell lines named HY1, HY2 and HY3, derived from a healthy liver of adult rat. HY cells showed an expression pattern similar to oval cells, and efficiently induced hepatic differentiation following sequential treatment with type I collagen, transforming growth factor-beta1 (TGF-beta1), and hepatocyte growth factor (HGF) or oncostatin M (OSM). These results suggested that HY cells are liver stem cells representing an excellent tool for in vitro studies on liver regeneration.

A Diphtheria Toxin Receptor Deficient in Epidermal Growth Factor–Like Biological Activity

Targeted cell ablation in animals is a powerful method for analyzing the physiological function of cell populations and generating various animal models of organ dysfunction. To achieve more specific and conditional ablation of target cells, we have developed a method termed Toxin Receptor mediated Cell Knockout (TRECK). A potential shortcoming of this method, however, is that overexpression of human heparin-binding epidermal growth factor-like growth factor (hHB-EGF) as a diphtheria toxin (DT) receptor in target cells or tissues may cause abnormalities in transgenic mice, since hHB-EGF is a member of the EGF growth factor family. To create novel DT receptors that are defective in growth factor activity and resistant to metalloprotease-cleavage, we mutated five amino acids in the extracellular EGF-like domain of hHB-EGF, which contains both DT-binding and protease-cleavage sites. Two of the resultant hHB-EGF mutants, I117A/L148V and I117V/L148V, possessed little growth factor activity but retained DT receptor activity. Furthermore, these mutants were resistant to metalloprotease-cleavage by 12-O-tetradecanoylphorbol-13-acetate stimulation, which is expected to enhance DT receptor activity. These novel DT receptors should be useful for the generation of transgenic mice by TRECK.

In Vitro Differentiation of Human Placenta-Derived Multipotent Cells into Hepatocyte-Like Cells

Multipotent cells isolated from human term placenta (placenta-derived multipotent cells [PDMCs]) have been known to be able to differentiate into mesodermal lineage cells, including adipocytes and osteoclasts. The low infection rate and young age of placenta compared with other tissue origins of adult stem cells make theses cells attractive target for cell-based therapy. However, the differentiation potential of PDMCs toward hepatic cells has not been evaluated yet. In this study, we cultivated PDMCs with hepatic differentiation medium to evaluate the ability of these cells in differentiating toward hepatic cells. After treatment, the morphologies of differentiated PDMCs changed to polygonal epithelial cell-like. The differentiated cells not only show the hepatocyte-like morphologies but also express hepatocyte-specific markers, including albumin and cytokeratin 18. The bioactivity assays revealed that these hepatocyte-like cells could uptake lipoprotein and store glycogen. Furthermore, the addition of rifampicin increased the gene expression of CYP3A4, which is similar with the activities of human liver cells. According to our previous results, PDMCs were capable of differentiating into mesodermal and ectodermal lineage cells. Our results indicate that PDMCs can differentiate into three germ layer cells, which is similar to embryonic stem cells. In conclusion, placenta might be an easily accessible source for progenitor cells that are capable of differentiating toward hepatocyte-like cells in vitro.