Roles of Hepatoma-derived growth factor(HDGF) on the proliferation and differentiation of hepatic stem cells and liver development

肝癌源性生长因子（HDGF）是一种肝素结合蛋白，已在hh -7肝癌细胞条件培养基中纯化。最近的研究表明，HDGF显著参与肝脏、心血管系统、肠道和肾脏的发育。在本研究中，我们研究了HDGF在肝祖细胞（包括卵圆细胞）的细胞增殖和分化以及肝个体发生中的作用。肝卵圆细胞是双电位肝祖细胞之一，可分化为肝实质细胞和胆管细胞。采用Western blot、Northern blot、免疫组织化学和原位杂交等方法分析乙酰氨基芴/部分肝切除术后大鼠肝脏中HDGF的表达。Northern blot和Western blot结果显示HDGF的表达水平与肝脏中出现的卵形细胞数量平行。原位杂交法检测到HDGF在卵形细胞中表达，免疫组化法检测到HDGF在细胞核中的表达强于在细胞质中的表达。在大鼠卵圆细胞系Oct15-5中，HDGF在细胞核和细胞质中均有显著表达，但主要在细胞核中表达。重组HDGF轻度刺激Oct15-5细胞的增殖。PPAR-γ配体15d-前列腺素（PG） J2抑制Oct15-5细胞的增殖，显著抑制HDGF的表达。因此，这些数据表明HDGF在卵圆细胞的增殖中起重要作用。我们使用白蛋白启动子生成了HDGF转基因小鼠。在正常肝脏中，出生后通过肝细胞成熟显著诱导葡萄糖-6-磷酸酶（G-6-Pase）表达降低和色氨酸加氧酶（TO）表达，而在HDGF转基因小鼠的肝脏中，出生后12周G-6-Pase表达未被抑制，TO未被诱导。提示HDGF的持续过表达可能抑制肝细胞的分化。提示HDGF在肝发生过程中对肝祖细胞的增殖和分化起重要作用。少

Hepatoma-derived growth factor(HDGF) is a heparin-binding protein, which has been purified the conditioned media of HuH-7 hepatoma cells. Recent studies suggest that HDGF is significantly involved in the development of the liver, cardiovascular system, gut and kidney. In the present study, we investigated the roles of HDGF in the cellular proliferation and differentiation of hepatic progenitor cells, including oval cells, and in the hepatic ontogeny. Hepatic oval cells are one of bipotential hepatic progenitor cells, which can differentiate to both parenchymal hepatocytes and bile duct cells. We analyzed the expression of HDGF in rat liver after acetoaminofluorene/partial hepatectomy treatment by Western blot, Northern blot, immunohistochemisry and in situ hybridization. The expression levels of HDGF by Northern blot and Western blot are parallel to the number of oval cells appeared in the liver. HDGF was expressed in oval cells by in situ hybridization, and more strongly in the nucleu … More s than the cytoplasm by immunohistochemistry. In rat oval cell line, Oct15-5,HDGF was also prominently expressed both in the nucleus and cytoplasm, but in dominantly in the nucleus. Recombinant HDGF mildly stimulated the proliferation of Oct15-5 cells. PPAR-γ ligand, 15d-prostaglandins(PG) J2 inhibited the proliferation of Oct15-5 cells, and significantly suppressed the expression of HDGF. Thus, these data suggest that HDGF plas an important roles on the proliferation of oval cells.We generated HDGF transgenic mouse using albumin promoter. In normal liver, the expression of glucose-6-phoshatase(G-6-Pase) decreases and tryptophan oxygenase(TO) is significantly induced through hepatocyte maturation after birth, however in the liver of HDGF transgenic mouse, the expression of G-6-Pase was not suppressed and TO was not induced at 12 weeks after birth. These findings suggest that the continuous over-expression of HDGF may suppress the differentiation of hepatocytes.Present findings suggest that HDGF should play important roles on the proliferation and differentiation of hepatic progenitor cells in liver ontogeny. Less