Molecular changes of AMPA receptors in ALS

肌萎缩侧索硬化症（amyotrophiclateralsclerosis，ALS）是一种退行性神经系统疾病，AMPA/红藻氨酸受体介导的迟发性神经毒性在其中发挥着重要作用。在体外培养的脊髓运动神经元中，AMPA受体介导的神经元死亡之前，细胞内钙离子浓度升高。AMPA受体由四种不同GluR亚基（GluR 1-GluR 4）的四种亚基的组合组成，并且它们的钙渗透性由Ghilt 2亚基的存在调节，Ghilt 2亚基在亚基组装中的Q/R位点处被编辑。采用逆转录-聚合酶链反应（RT-PCR）结合限制性内切酶酶切技术，检测ALS患者脊髓、其他神经系统疾病患者脊髓和正常人脊髓中GluR 2 mRNA的表达和编辑效率。结果发现ALS患者和正常对照组腹侧灰质GluR 2 mRNA表达均低于正常对照组。此外，编辑效率仅在ALS病例的腹侧灰质中显著低于疾病和正常对照的任何脊髓区域。GluR 2 mRNA的上述分子变化可能增加通过AMPA受体的钙内流，从而促进神经元的脆弱性。虽然GluR 2 mRNA的减少是在各种病理条件下观察到的非选择性观察，但GluR 2 mRNA编辑的减少尚未在神经变性疾病的任何实验或病理脑区域中得到证实，所述神经变性疾病例如阿尔茨海默病和皮克病的新皮质、亨廷顿病的纹状体、马查多-约瑟夫病的小脑、齿状核红核苍白球路易体萎缩和肌肉系统萎缩。这些结果表明，GluR 2 mRNA的改变，特别是RNA编辑的减少，与ALS的病因学密切相关。

Amyotrophic lateral sclerosis (ALS) is a degenerative neurological disease in which AMPA/kainate receptor-mediated delayed neurotoxicity most plausibly plays a central role. It has been demonstrated that a rise in intracellular calcium concentration preceded AMPA receptor-mediated neuronal death in the cultured spinal motoneurons. AMPA receptors are composed of a combination of four subunits of four different GluR subunits (GluR1 - GluR4) and their calcium permeability is regulated by the presence of the Ghilt2 subunit that is edited at the Q/R site in the subunit assembly. We investigated the expression and editing efficiency of GluR2 mRNA in the spinal cord of ALS cases and the spinal cord of cases with other neurological diseases and that of normal cases using reverse transcription-polymerase chan reaction (RT-PCR) combined with restriction enzyme cleavage. We found that expression of GluR2 mRNA is lower in the ventral gray of the ALS cases and disease controls than that in the normal controls. In addition, the editing efficiency was significantly lower only in the ventral gray of ALS cases than in any spinal region of the disease and normal controls. The above molecular changes of GluR2 mRNA may increase calcium influx through AMPA receptors, thereby promoting neuronal vulnerability. While reduction of GluR2 mRNA is a non-selective observation that is observed in various pathological conditions, the decrement of GluR2 mRNA editing has not been demonstrated in any experimental or pathological brain areas of neurodegenerative diseases, such as neocortices of Alzheimer's and Pick's diseases, striatum of Huntington's disease, cerebellum of Machado-Joseph disease, dendatoruburopallidoluysian atrophy and mustiple system atrophy. These results suggest that the alteration of GluR2 mRNA, particularly the reduction of RNA editing, is closely linked to the etiology of ALS.