Tarabal Olga, Calderó Jordi, Casas Celia, Oppenheim Ronald W, Esquerda Josep E
Unitat de Neurobiologia Cel.lular, Departament de Ciències Mèdiques Bàsiques, Facultat de Medicina, Universitat de Lleida, C. Montserrat Roig 2, E25008 Lleida, Catalonia, Spain.
Mol Cell Neurosci. 2005 Jun;29(2):283-98. doi: 10.1016/j.mcn.2005.03.003.
We previously showed that, in contrast to the acute administration of NMDA, chronic treatment of chick embryos from embryonic day (E) 5 to E9 with this excitotoxin rescues motoneurons (MNs) from programmed cell death. Following this protocol, MNs are also protected against later acute excitotoxic cell death. Previously, we found that MNs treated from E5 to E9 develop long-lasting changes involving vesicular trafficking and other organelle pathology similar to the abnormalities observed in certain chronic neurological diseases including amyotrophic lateral sclerosis (ALS). Here we extend these previous results by showing that protein aggregation within the endoplasmic reticulum (ER) takes place selectively in MNs as an early event of chronic excitotoxicity. Although protein aggregates do not induce appreciable MN death, they foreshadow the activation of a conspicuous autophagic response leading to long-lasting degenerative changes that causes dysfunction but not immediate cell death. Chronic early treatment with NMDA results in a transient (between E6 and E10) lack of vulnerability to undergo cell death induced by different types of stimuli. It is suggested that blockade of protein translation in stressed ER may inhibit apoptosis in NMDA-treated MNs. However, in embryos older than E12, degenerating MNs are sensitized to die after limb ablation (axotomy) and accumulate hyperphosphorylated neurofilaments. Moreover, chronic NMDA treatment does not induce the upregulation of molecular chaperones in spinal cord. These results represent a new model of glutamate receptor-mediated neurotoxicity that selectively occurs in spinal cord MNs and also demonstrate an experimental system that may be valuable for understanding the mechanisms involved in chronic MN degeneration and in certain cytological hallmarks of ALS-diseased MNs such as inclusion bodies.
我们之前发现，与急性给予N-甲基-D-天冬氨酸（NMDA）不同，从胚胎期（E）第5天到第9天用这种兴奋性毒素对鸡胚进行慢性处理可挽救运动神经元（MNs）免于程序性细胞死亡。按照此方案，MNs也能免受随后急性兴奋性毒性细胞死亡的影响。之前，我们发现从E5到E9处理的MNs会出现持久变化，涉及囊泡运输和其他细胞器病理，类似于在某些慢性神经疾病（包括肌萎缩侧索硬化症，ALS）中观察到的异常。在此，我们扩展了这些先前的结果，表明内质网（ER）内的蛋白质聚集在MNs中选择性发生，是慢性兴奋性毒性的早期事件。虽然蛋白质聚集体不会诱导明显的MN死亡，但它们预示着明显的自噬反应被激活，导致长期的退行性变化，引起功能障碍但不会立即导致细胞死亡。用NMDA进行慢性早期处理会导致短暂（在E6和E10之间）缺乏对不同类型刺激诱导的细胞死亡的易感性。有人提出，在内质网应激时阻断蛋白质翻译可能会抑制NMDA处理的MNs中的细胞凋亡。然而，在E12以上的胚胎中，退化的MNs在肢体切除（轴突切断）后对死亡敏感，并积累过度磷酸化的神经丝。此外，慢性NMDA处理不会诱导脊髓中分子伴侣的上调。这些结果代表了一种谷氨酸受体介导的神经毒性新模型，该模型选择性地发生在脊髓MNs中，也证明了一个实验系统，对于理解慢性MN退化以及ALS患病MNs的某些细胞学特征（如包涵体）所涉及的机制可能具有重要价值。
