Morphologic characteristics of human hepatic cells and expressions of growth factors and their receptors / 中国组织工程研究

ABSTRACT

BACKGROUND: There is an intimate temporal and spatial relationship between growth of primitive cardiac cells, septum transversum mesenchyme and liver development. The signal from primitive cardiac cells and septum transversum mesenchyme induces the ventral foregut endoderm cells specialize toward hepatocytes. While the septum transversum mesenchyme provides a suitable environment for forming the liver bud and promoting the growth and differentiation. However, the molecular mechanism of this induction is not yet delineated.OBJECTIVE: Using alpha-fetal protein (AFP), c-Met and cytokeratin (CK) 19 as markers of hepatic stem cells, the growth of early human embryo of 3-5 weeks and morphologic characteristic of hepatic stem cells were observed to demonstrate the characteristic and factors that affected the proliferation and differentiation of hepatic stem cell, which provided experimental evidence for basic research and clinical application of hepatic stem cells.DESIGN: An opening experiment was designed.SETTING: Department of Anatomy, Weifang Medical College.MATERIALS The experiment was carried out at the Scientific Research Center of Chengdu Medical College between September 2004 and January 2005. Twenty cases fresh human embryos aged less than 2 months were collected with signed agreements of the pregnant women suffering from pregnancy termination with mifepristone. The samples were fixed with 40 g/L polymerisatum in 20 minutes and embedded routinely in paraffin, and then 5 μm thick series sections were continuously made. After hematoxylin-eosin staining, the embryonicage was determined under the microscope according to the length of embryos, the number of somites and the development of organs, which was referring to the Jirasek's staging standard of human embryo.METHODS: The immunohistochemical staining was conducted with SABC method on one of every ten sections, which were incubated overnight at 4 ℃ with polyclonal antibodies against hepatocyte growth factor (HGF),c-Met, insulin-like growth factor (IGF-Ⅰ), IGF-Ⅰ receptor (IGF-IR), transforming growth factor (TGFβ1), TGFβR1, TGFβR2 or monoclonal antibodies against proliferating cell nuclear antigen (PCNA), AFP and CK19.The following day, the sections were incubated for 2 hours at room temperature with biotinylated anti-mouse or anti-rabbit IgG and SABC liquid respectively, and then diaminobenzidine (DAB) was used to color them. The negative control was conducted with the phosphate buffer, then the sections were observed and photographed under light microscope.MAIN OUTCOME MEASUERS ①the morphologic characteristic of human hepatic stem cells and immunohistochemical staining of markers②the expression of HGF, IGF-Ⅰ, TGFβ1 and their receptors on human embryonic livers of 3-5 weeks, primitive cardiac cells and septum transversum mesenchyme.RESULTS: ①The morphologic characteristic of human hepatic stem cells and immunohistochemical staining of markers The hepatic bud formed at the end of 3rd week and migrated into the septum transversum mesenchyme to form the hepatic cords at the 4th week. The cells structuring the hepatic cords displayed the typical characteristic of immature cells. At the 5th week, the number of cells within the hepatic cords, the size of cell body,the cytoplasmic acidophilia all increased, whereas the basophilia of nuclei decreased. However the cellular forms were still homogeneous and displayed the typical characteristic of immature cells. The cells of hepatic cords were negative for PCNA response during 3rd-4th week but began to express positive at the 5th week, mainly in the nucleus and minority cellular cytoplasm showed weak positive. Most hepatic cells during 3rd-5th weeks were positive for AFP, c-Met and negative for CK19. The immunologic reaction depositors of AFP positive cells were located in the nuclei, cytoplasm and membrane of the hepatocytes, and c-Met presented mainly in the nuclei and the positive signal was weak in the cytoplasm. ②Expressions of HGF, IGF-Ⅰ, TGFβ1 and their receptors in the embryonic human liver, primitive heart and septum transversum mesenchyme At the 4th week,the c-Met expressed only in all hepatocytes, whereas the other growth factors and their receptors were undetectable. At the 5th week, all the growth factors, except HGF, were expressed in the hepatocytes. The immunologic reaction depositors of TGFβ1, TGFβ1R1 and TGFβ1R2 were located in the cytoplasm and cell membrane. The positive response of IGF-Ⅰ and IGF-IR were present at nuclei, cytoplasm and cell membrane. At the 3rd-5th week, myocardial cells surrounding liver bud or hepatic cord and the septum transversum mesenchyme were positive for HGF, TGFβ1 and IGF-Ⅰ,with the signals were aggregated mainly in cytoplasm and minority nucei.CONCLUSION: ①It was at the end of 3rd week that part of endoderm cells in foregut ventral were specialized to hepatic stem cells. ②The undifferentiated hepatic stem cells could be drawn to develop to the liver stem cells with bi-directional differentiation potentials by using specific markers for studying human embryonic liver stem cells. According to the corresponding relation of embryonic age between human and rats, the time studying the rat hepatic stem cells could be calculated. ③HGF, IGF-Ⅰ,TGFβ1 and their receptors promoted the early development of human embryonic liver.