Niclou Simone P, Franssen Elske H P, Ehlert Erich M E, Taniguchi Masahiko, Verhaagen Joost
Graduate School of Neurosciences Amsterdam, Netherlands Institute for Brain Research, Meibergdreef 33, 1105 AZ Amsterdam, The Netherlands.
Mol Cell Neurosci. 2003 Dec;24(4):902-12. doi: 10.1016/s1044-7431(03)00243-4.
The neural scar that forms after injury to the mammalian central nervous system is a barrier to sprouting and regenerating axons. In addition to reactive astrocytes that are present throughout the lesion site, leptomeningeal fibroblasts invade the lesion core. When isolated in vitro, these cells form a very poor substrate for growing neurites, even more so than reactive astrocytes. Nevertheless the molecular mechanisms involved in this growth inhibition are not well understood. Semaphorins have been reported to be upregulated in meningeal cells (MCs) on mechanical injury to the brain and spinal cord. In the present study, we show that Sema3A mRNA and active protein are produced by cultured meningeal cells. A protein extract from these cells induces the collapse of embryonic dorsal root ganglion (DRG) growth cones. This collapsing activity is partially blocked by neuropilin-1 antibodies and is absent in meningeal cells derived from Sema3A-knockout mice. In addition to growth cone collapse, recombinant Sema3A but not Sema3C inhibits neurite outgrowth of embryonic DRGs. Consistent with this result we find that the inhibitory effect of meningeal cells on neurite outgrowth is partially overcome on Sema3A-deficient MCs. Furthermore we show that the inhibitory effect of MC-derived Sema3A on neurite outgrowth is modulated by nerve growth factor. Our results show that Sema3A, a chemorepellent during nervous system development, is a major neurite growth-inhibitory molecule in meningeal fibroblasts and is therefore likely to contribute to the inhibitory properties of the neural scar.
哺乳动物中枢神经系统损伤后形成的神经瘢痕是轴突发芽和再生的障碍。除了遍布损伤部位的反应性星形胶质细胞外，软脑膜成纤维细胞也侵入损伤核心。在体外分离培养时，这些细胞形成的神经突生长底物非常差，甚至比反应性星形胶质细胞还差。然而，这种生长抑制所涉及的分子机制尚不清楚。据报道，在脑和脊髓受到机械损伤时，信号素在脑膜细胞（MCs）中上调。在本研究中，我们发现培养的脑膜细胞能产生Sema3A mRNA和活性蛋白。这些细胞的蛋白质提取物可诱导胚胎背根神经节（DRG）生长锥的塌陷。这种塌陷活性被神经纤毛蛋白-1抗体部分阻断，并且在源自Sema3A基因敲除小鼠的脑膜细胞中不存在。除了生长锥塌陷外，重组Sema3A而非Sema3C可抑制胚胎DRG的神经突生长。与这一结果一致，我们发现脑膜细胞对神经突生长的抑制作用在Sema3A缺陷的MCs上部分被克服。此外，我们表明MC衍生的Sema3A对神经突生长的抑制作用受神经生长因子调节。我们的结果表明，Sema3A作为神经系统发育过程中的一种化学排斥剂，是脑膜成纤维细胞中主要的神经突生长抑制分子，因此可能对神经瘢痕的抑制特性有贡献。
