Induction of hepatocyte growth factor by physiological agents : its effects on hepatocyte proliferation and protein production

肝细胞生长因子（HGF）被认为是一种多效性因子，据报道可调节基因表达并刺激许多细胞类型（包括肝细胞）的增殖和功能。已经假设HGF对几种类型的疾病的潜在应用。氨基酸可以作为调节分子调节许多细胞功能。支链氨基酸（BCAAs）对细胞代谢、氨基酸转运和基因表达有重要影响。BCAA补充治疗是目前肝硬化患者的治疗方法，因此，应检查特定的BCAA活性。在这个研究项目中，我们发现了BCAA刺激肝脏HGF合成的潜力。将肝星状细胞克隆在补充有各种浓度的缬氨酸、亮氨酸或异亮氨酸的培养基中培养。在这些支链氨基酸中，亮氨酸以剂量依赖性方式显著诱导培养基中HGF水平的增加。 关于我们 添加缬氨酸或异亮氨酸对HGF水平没有显著影响。当大鼠接受缬氨酸，亮氨酸或异亮氨酸腹腔注射，只有亮氨酸治疗增加肝和循环水平的肝细胞生长因子在剂量依赖性的方式，比对照组。在患者研究中，肝硬化患者口服BCAA混合颗粒后血清HGF水平显著高于对照组。接下来，为了阐明亮氨酸对HGF产生的刺激作用的机制，我们研究了细胞内信号通路。亮氨酸处理肝星状细胞克隆后，p70 S6激酶活性和真核起始因子4 E结合蛋白1（4 E-BP 1）的磷酸化迅速上调。用缬氨酸或异亮氨酸处理后未观察到这种激活。雷帕霉素是雷帕霉素靶蛋白（mTOR）的抑制剂，能抑制亮氨酸诱导的p70 S6激酶和4 E-BP 1的激活，并以剂量依赖的方式完全消除亮氨酸对HGF产生的刺激作用。亮氨酸通过mTOR依赖性信号通路刺激肝星状细胞产生HGF少

Hepatocyte growth factor (HGF) is considered to be a pleiotropic factor, and is reported to modulate gene expression and to stimulate the proliferation and functions of many cell types, including hepatocytes. A potential application of HGF for several types of diseases has been postulated. Amino acids can serve as regulatory molecules that modulate numerous cellular functions. Branched chain amino acids (BCAAs) are known to exert influences on cellular metabolism, amino acid transport and gene expression. BCAA supplementation therapy is a current treatment for patients with liver cirrhosis, therefore, specific BCAA activities should be examined. In this research project, we found the potential of BCAAs for stimulating HGF synthesis in the liver. A hepatic stellate cell clone was cultured in medium supplemented with various concentrations of valine, leucine or isoleucine. Of these BCAAs, leucine markedly induced an increase in the levels of HGF in the medium in a dose-dependent manner. … More The addition of valine or isoleucine had no significant effect on the HGF levels. When rats received intraperitoneal injections of valine, leucine or isoleucine, only leucine treatment increased both hepatic and circulating levels of HGF in a dose-dependent manner, than in controls. In patient study, serum HGF levels were significantly higher in patients with liver cirrhosis who received BCAA-mixture granules orally than in control patients. Next, to clarify the mechanisms of stimulatory effect of leucine on HGF production, we studied intracellular signaling pathway. p70 S6 kinase activity and phosphorylation of the eukaryotic initiation factor 4E binding protein 1 (4E-BP1) were up-regulated rapidly after leucine treatment in a hepatic stellate cell clone. No such activation was observed following treatment with valine or isoleucine. Rapamycin, an inhibitor of mammalian target of rapamycin (mTOR), suppressed leucine-induced activation of p70 S6 kinase and 4E-BP1, and negated completely the stimulatory effect of leucine on HGF production in a dose-dependent manner. Leucine stimulates HGF production by hepatic stellate cells through an mTOR-dependent signaling pathway. Less