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乙酰肝素蛋白聚糖（HSPGs）在脑发育中生长因子信号传导中的作用，用10日龄大鼠脑制备的抗膜结合蛋白聚糖的单克隆抗体（MAbs）鉴定HSPGs。四个单克隆抗体识别150 kDa的硫酸软骨素蛋白聚糖与120 kDa的核心糖蛋白。核心蛋白的分子克隆表明，蛋白聚糖，命名为神经聚糖C（NGC），是一种新的跨膜蛋白聚糖。另外3株单抗识别N-syndecan，N-syndecan是一种跨膜硫酸乙酰肝素蛋白聚糖，其核心糖蛋白分子量为140 kDa，在中枢神经系统的表达受时间和空间的调控。Westem blot分析表明，在出生后0 ~ 20天的大鼠脑中，当神经突发生和突触发生最广泛时，观察到表达的峰值水平。免疫组织化学研究表明，N-多配体蛋白聚糖主要与发育中大脑中活跃生长的神经纤维有关。N-syndecan在成年大鼠嗅神经和肾小球中的高水平表达，此时轴突和突触都在不断更新。N-syndecan在PVDF膜上与一些肝素结合生长因子如碱性成纤维细胞生长因子（bFGF）、多效生长因子（HB-GAM）和肝细胞生长因子（HGF）结合，可以促进原代培养的神经元突起生长。用肝素酶I消化N-多配体聚糖导致与这些生长因子的结合失败。结合免疫组化结果，提示N-syndecan能捕获具有促轴突生长活性的肝素结合生长因子，并参与这些生长因子的信号转导，从而促进轴突的生长。

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.