Identification of N-syndecan in the developing rat bran and its binding to heparin-binding growth factor.

为了研究细胞表面硫酸肝素蛋白聚糖（HSPGs）在脑发育过程中参与的生长因子信号传导，利用从10日龄大鼠脑中制备的膜结合蛋白聚糖单克隆抗体（mab）对HSPGs进行了鉴定。4个单抗识别一个150 kDa硫酸软骨素蛋白多糖和一个120 kDa核心糖蛋白。核心蛋白的分子克隆表明，该蛋白多糖被命名为神经聚糖C (NGC)，是一种新型的跨膜蛋白多糖。其他三种单克隆抗体识别N-syndecan，一种具有140 kDa核心糖蛋白的跨膜硫酸肝素蛋白多糖。N-syndecan在中枢神经系统的表达受时空调控。western blot分析显示，在出生后0 ~ 20天的大鼠脑中，该蛋白的表达水平达到峰值，此时神经和突触的发生最为频繁。免疫组织化学研究表明，N-syndecan主要与发育中的大脑中活跃生长的神经纤维有关。在成年大鼠中，当轴突和突触的更新不断发生时，嗅觉神经和肾小球上的高水平表达被特别识别。在PVDF膜上发现的N-syndecan结合了一些肝素结合生长因子，如碱性成纤维细胞生长因子（bFGF）、多营养因子（HB-GAM）和肝细胞生长因子（HGF），可以促进原代培养神经元的神经突生长。用肝素酶I消化N-syndecan导致与这些生长因子结合失败。这些发现，结合免疫组化结果，提示N-syndecan可以通过促进生长的神经纤维的神经突活性捕获肝素结合生长因子，并参与这些生长因子的信号转导，从而刺激轴突生长。

To examine the involvement of cell surface heparan sulfate proteoglycans (HSPGs) in the growth factor signaling in the brain development, identification of HSPGs were perrormed with monoclonal antibodies (MAbs) against membrane-bound proteoglycans prepared from 10-day-old rat brains. Four MAbs recognized a 150 kDa chondroitin sulfate proteoglycan with a 120 kDa core glycoprotein. Molecular cloning of the core protein revealed that the proteoglycan, designated neuroglycan C (NGC), is a novel transmembrane proteoglycan. Other three MAbs recognized N-syndecan, a transmembrane heparan sulfate proteoglycan with a 140 kDa core glycoprotein.The expression of N-syndecan was spatially and temporally regulated in the central nervous system. Westem blot analysis revealed that the peak level of expression was oserved in the rat brain during the period from postnatal days 0 to 20 when neuritogenesis and synaptogenesis occur most extensively. Immunohistochemical studies showed that N-syndecan was associated mainly with the actively growing nerve fibers in the developing brain. In the adult rat, high-level expression was exceptionally recognized on the olfactory nerves and glomeruli, when the renewal of both axons and synapses is occurring constantly.N-syndecan spotted on a PVDF membrane bound some heparin-binding growth factors such as basic fibroblast growth factors (bFGF), pleiotrophin (HB-GAM) and hepatocyte growth factor (HGF), which can promote neurite outgrowth from primary-cultured neurons. Digestion of N-syndecan with heparitinase I resulted in the failure of the binding to these growth factors. These findings, together with the results of immunohistochemistry, suggest that N-syndecan would catch the heparin-binding growth factors with the neurite-promoting activity of the growing nerve fibers, and that it would be involved in the signal transduction of these growth factors to stimulate the axonal growth.