NRIP自體抗體在肌萎縮性脊髓側索硬化症所扮演的角色

Abstract

接受體交互作用蛋白 (Nuclear receptor interaction protein, NRIP) 由860個胺基酸所組成，包含7個WD40 domain與1個IQ motif。NRIP為乙醯膽鹼受體 (acetylcholine receptor, AChR) 複合物的一個單元蛋白，參與神經肌肉接合處 (neuromuscular junction, NMJ) 的形成。肌肉的NRIP會透過成肌蛋白 (myogenin) 調控運動神經元 (motoneuron) 的存活。在本篇研究中，我們藉由在運動神經剔除NRIP基因，分析小鼠運動神經元中NRIP的功能，發現到在運動神經元剃除NRIP會造成脊髓中腰椎部位的大體積運動神經元數量下降。 肌萎縮性脊髓側索硬化症 (Amyotrophic lateral sclerosis, ALS) 是一種致命性的神經退化疾病。運動神經元會逐漸失去進而造成肌肉萎縮與骨骼肌無力。自體免疫缺陷經常與神經病變有關。重症肌無力 (Myasthenia gravis, MG) 屬於一種發生在NMJ的自體免疫疾病，在我們之前的研究中顯示，NRIP的自體抗體存在於MG病患並且與疾病進展有關。在本篇研究的87位ALS病患中，我們發現NRIP的自體抗體存在26位ALS病患體內(29.9%)。我們檢測NRIP抗體在ALS病例中的影響，發現到四肢發病的ALS (Limb-onset ALS) 受試者在有NRIP自體抗體的情況下，相較於無NRIP自體抗體的受試者表現出較快速的疾病進程。接著我們將NRIP抗體力價 (titer) 與疾病進程進行相關性分析，發現到NRIP抗體力價與病程發展速度呈現正相關，尤其是在四肢發病的ALS。此外，我們發現NRIP抗體力價與ALS存活率具有高度相關。接著，為了釐清NRIP抗體所引起的免疫反應，我們鑑定出NRIP抗體的抗原結合位 (epitope) 位於NRIP的IQ motif。並且發現到NRIP抗體屬於IgG亞族群中的IgG1與IgG3分支。 綜上所述，NRIP會表現在運動神經元並且影響大體積運動神經元的表現。NRIP自體抗體為一種新發現的ALS疾病相關性自體抗體，與ALS疾病的進展具有高度正相關。

Nuclear receptor interaction protein (NRIP) composes of 860 amino acids, includes 7 WD40 domains and 1 IQ motif. NRIP is a member of acetylcholine receptor (AChR) complex which plays an important role in the formation of neuromuscular junction (NMJ). Muscular NRIP regulates the survival of motoneuron through myogenin at the NMJ. In this study, we analyzed the function of NRIP in motoneuron by Hb9-cKO mice. Motoneuron-restricted NRIP knockout caused the number of large size motoneurons decreased in the spinal cord lumbar region. Amyotrophic lateral sclerosis (ALS) is a fetal neurodegenerative disease. Progressive motoneuron loss leads to muscle atrophy and weakness of skeletal muscle. Autoimmune deficiency is often associated with neuropathy. Myasthenia gravis (MG) is an autoimmune disease of the NMJ. In our previous study, we found anti-NRIP autoantibody existed in MG and correlated with disease progression. In this study, we identified the existence of anti-NRIP autoantibody in 26 out of 87 ALS patients (29.9%). We investigated the effect of anti-NRIP autoantibody in ALS cases. In limb-onset ALS patients, subjects having anti-NRIP autoantibody showed significantly more rapid disease progression than those without anti-NRIP autoantibody. We then correlated the titers of anti-NRIP autoantibody to speed of disease progression, finding the titers of anti-NRIP autoantibody positively correlated with the speed of disease progression, especially in the limb-onset ALS. Besides, we found that the survival conditions were significantly associated with titers of anti-NRIP autoantibody. Next, to clarify the underlying immune response of anti-NRIP autoantibody, we identified the epitope of anti-NRIP autoantibody was on the IQ motif of NRIP. Plus, we discovered the IgG subclass of anti-NRIP autoantibody belonged to IgG1 and IgG3 subclasses. In conclusion, NRIP in motoneuron regulates the number of large size motoneuron. Anti-NRIP autoantibody is a newly identified ALS-related autoantibody, which positively correlates with the ALS disease progression.