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Physiological roles of rat fetuin on bone metabolism

大鼠胎球蛋白对骨代谢的生理作用

基本信息

批准号：
08457492
负责人：
DAIKUHARA Yasushi
金额：
$ 4.93万
依托单位：
Kagoshima University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1996
资助国家：
日本
起止时间：
1996 至 1997
项目状态：
已结题

项目摘要

Previously, we reported that a 59 kDa bone sialoprotein purified from rat mandible, is the rat counterpart of human alpha_2-HS glycoprotein and bovine fetuin. Immunohistochemically, this protein is only detectable in calcified tissues such as bone matrices and dentin. In order to study the physiological role of rat fetuin in bone metabolism, the effect of this protein on bone resorption was examined using ^<45>Ca-prelabeled radius of mice. We found that 200 mug/ml of rat fetuin enhanced the activity of bone resorption in the presence of low concentrations (0.1-0.5 nM) of parathyroid hormone (PTH), but it had no activity on bone resorption without PTH.The increase in bone resorption by PTH and PTH plus rat fetuin was inhibited by addition of chymostatin, an inhibitor for cathepsin L.Moreover, we demonstrated that when type I collagen from rat was preincubated with rat fetuin, the digestion of rat type I collagen by cathepsin L was enhanced. These findings suggest that rat fetuin brings about a favorable conformation of type I collagen for the digestion by cathepsin L.During doing above study, we also found that phosphorylated rat fetuin synthesized and secreted by the liver dose-dependently inhibited the mitogenic activity of hepatocyte growth factor (HGF) in vitro. The maximum inhibition was about 50% at the concentration of 1 mug/ml. We showed that this inhibition of HGF activity was due to binding of fetuin to HGF and thus the binding of HGF to its receptor (c-Met) was suppressed. In addition, we have demonstrated that the fetuin concentrations in normal rat serum determined by Western blotting were 2.5-4.5 mg/ml. These concentrations were three orders of magnitude higher than previously published concentrations. Fetuin mRNA level in the liver changes almost in parallel with its serum concentration. Tibia also express fetuin, but much less than the liver.

以前，我们报道了从大鼠下颌骨中纯化的一种59 kDa的骨唾液酸蛋白，是人α_2-HS糖蛋白和牛胎球蛋白的大鼠对应物。免疫组织化学上，这种蛋白质仅在钙化组织如骨基质和牙本质中可检测到。为了研究大鼠胎球蛋白在骨代谢中的生理作用，用~（13）Ca-预标记的小鼠桡骨检测了胎球蛋白对骨吸收的影响<45>。我们发现，200 μ g/ml的大鼠胎球蛋白在低浓度的情况下增强了骨吸收的活性（0.1-0.5 nM）的甲状旁腺激素（PTH），但它没有活性的骨吸收没有PTH。骨吸收的PTH和PTH加大鼠胎球蛋白的增加被抑制，通过添加凝乳酶抑制剂，组织蛋白酶L的抑制剂。此外，我们证明，当大鼠I型胶原与大鼠胎球蛋白预孵育时，组织蛋白酶L对大鼠I型胶原的消化增强。这些结果表明，大鼠胎球蛋白带来了一个良好的构象的I型胶原的组织蛋白酶L的消化。在做上述研究中，我们还发现，磷酸化大鼠胎球蛋白合成和分泌的肝细胞生长因子（HGF）在体外的促有丝分裂活性的抑制剂量依赖性。在1 μ g/ml的浓度下，最大抑制约为50%。我们发现，这种抑制肝细胞生长因子的活性是由于结合胎球蛋白的肝细胞生长因子，从而抑制肝细胞生长因子结合其受体（c-Met）。此外，我们已经证明，正常大鼠血清中的胎球蛋白浓度为2.5-4.5毫克/毫升。这些浓度比先前公布的浓度高出三个数量级。肝脏中胎球蛋白mRNA水平的变化几乎与其血清浓度平行。胫骨也表达胎球蛋白，但比肝脏少得多。