Molecular changes of AMPA receptors in ALS

肌萎缩侧索硬化症(ALS)是一种退行性神经系统疾病，AMPA/海人藻酸受体介导的迟发性神经毒性在ALS中起重要作用。已经证明，在培养的脊髓运动神经元中，细胞内钙离子浓度的升高先于AMPA受体介导的神经元死亡。AMPA受体由四个不同GluR亚基(GluR1-GluR4)的四个亚基组成，其钙通透性由亚基组装中Q/R位点编辑的Ghelt2亚基的存在来调节。应用逆转录聚合酶链式反应(RT-PCR)结合限制性内切酶酶切技术，研究了GluR2基因在ALS患者脊髓、其他神经系统疾病患者和正常人脊髓中的表达及编辑效率。我们发现ALS患者和疾病对照组腹侧灰质中GluR2基因的表达均低于正常对照组。此外，只有ALS患者的腹侧灰质的编辑效率显著低于疾病的任何脊髓区域和正常对照组。GluR2基因的上述分子变化可能通过AMPA受体增加钙内流，从而促进神经元的脆弱性。虽然GluR2 mRNA的降低是一种在各种病理条件下观察到的非选择性观察，但在阿尔茨海默病和Pick病的新皮质、亨廷顿病的纹状体、Machado-Joseph病的小脑、结节性苍白球松果体萎缩和肌肉系统萎缩等神经退行性疾病的任何实验或病理脑区都没有观察到GluR2 mRNA编辑的减少。这些结果表明，GluR2基因的改变，尤其是RNA编辑的减少，与ALS的发病密切相关。

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.