シンポジウム16　膜輸送タンパク質を標的とする神経変性疾患の新たな治療戦略

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シンポジウム16 膜輸送タンパク質を標的とする神経変性疾患の新たな治療戦略

S16-1 アルツハイマー病におけるNa⁺/Ca²⁺交換輸送体による機能調節森口茂樹¹，喜多紗斗美²，岩本隆宏²，福永浩司¹ 東北大学大学院薬学研究科薬理学分野¹，福岡大学医学部薬理学² 　The protein expression levels of Na⁺/Ca²⁺ exchangers（NCXs）are known to decrease in the brain of Alzheimer's disease patient. We here found that down-regulated mRNA levels of NCXs in APP23 mice. NCXs are mainly expressed in the plasma membrane and mediates electrogenical exchange of one Ca2+ for three Na+, depending on the electrochemical gradients across the plasma membrane. NCXs have three different isoforms（NCX1, NCX2, NCX3）encoded by distinct genes in mammals. We also found that mutant mice lacking neural NCX2（NCX2-KO）exhibit impaired memory. NCX2-KO mice showed significantly impairment of learning and memory-related behaviors measured by Y-maze, novel object recognition and passive avoidance tasks. Interestingly, NCX2-KO mice also impaired in long-term potentiation（LTP）expression in the hippocampal CA1 region. In immnoblot analyses, calcium/calmodulin-dependent protein kinase II（CaMKII）autophosphorylation significantly decreased in the hippocampal CA1 region of NCX2-KO mice compared to wild-type mice. Enhancement of CaMKII autophosphorylation following LTP was also impaired in NCX2-KO mice. Furthermore, decrease in CaMKII autophosphorylation was closely associated with reduced pGluR1（Ser-831）phosphorylation, without change in synapsin I（Ser-603）phosphorylation in the hippocampal CA1 region of NCX2-KO mice. Taken together, the decreased CaMKII activity with concomitant LTP impairment likely accounts for the learning disability observed in NCX2-KO mice.		S16-2 神経変性疾患におけるNa⁺/Ca²⁺交換系の病態意義田熊一敞^1,2，吾郷由希夫¹，松田敏夫^1,3 大阪大学大学院薬学研究科薬物治療学分野¹，大阪大学大学院歯学研究科薬理学教室²，大阪大学・金沢大学・浜松医科大学・千葉大学・福井大学連合小児発達学研究科³ There is growing evidence that dysfunction of Ca²⁺ homeostasis is closely related in the pathogenesis of neurodegenerative diseases, such as Alzheimer's disease and Parkinson's disease. The plasma membrane Na⁺/Ca²⁺ exchanger（NCX）plays a role in the regulation of intracellular Ca²⁺ levels by bi-directional membrane Ca²⁺ transport. In this sense NCX is considered as a key molecule mediating cytotoxicity in neurodegenerative diseases. On the other hand, we have previously found that nitric oxide（NO）stimulates the NCX activity in glial and neuronal preparations and NO is involved in nigrostriatal dopaminergic dysfunction in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine（MPTP）-treated mice, an animal model of Parkinson's disease. The previous findings suggest that NCX-mediated Ca²⁺ alteration is involved in NO-related neurodegeneration. To address this point, we examined the effects of the specific inhibitor of NCX 2-［4-［（2,5-difluorophenyl）methoxy]phenoxy]-5-ethoxyaniline（SEA0400）on NO-mediated dopaminergic neurotoxicity in MPTP-treated mice. We revealed that repeated MPTP caused nigral dopaminergic neurotoxicity including ERK activation and lipid peroxidation in the midbrain and dysfunction of motor coordination, and these effects were attenuated by SEA0400, as well as the neuronal NO synthase inhibitor 7-nitroindazole, in mice. Based on these findings, the present review discusses the role of NCX as a novel pharmacological target for the prevention of neurodegenerative diseases, especially Parkinson's disease.

S16-3 亜鉛恒常性異常と筋萎縮性側索硬化症金子雅幸^1,2，位田雅俊²，保住功² 広島大学大学院医歯薬保健学研究科分子細胞情報学¹，岐阜薬科大学薬物治療学² The loss of homeostasis of essential metals is associated with various diseases, including neurodegenerative diseases. Amyotrophic lateral sclerosis（ALS）is a progressive neurodegenerative disease that exhibits selective loss of cortical and spinal motor neurons. Zinc（Zn）plays important roles in the functions of various proteins because approximately 3－10% of human genes encode Zn-containing proteins. Zn transporters and metallothioneins（MTs）tightly control intracellular and extracellular Zn levels. Therefore, Zn deficiency causes many human disorders including neuronal dysfunctions. We found that the levels of Zn were significantly higher in the cerebrospinal fluid of patients with ALS. Furthermore, we have reported that immunopositivity for both MT-I/II and MT-III was diminished in the spinal cords of sporadic ALS patients. We here investigated the protein levels of ZnT, a Zn transporter family, in ALS patients and model mice. The mRNA expression of ZnT1, 3, 4, 5, 6, 7, and 10 was assessed in the spinal cords of human control subjects. ZnT3 and 6 protein levels were significantly diminished in the spinal cords of sporadic ALS patients. Furthermore, immunohistochemical staining demonstrated decreased ZnT3 and 6 immunoreactivity in the ventral horn of the spinal cords in ALS patients. Moreover, immunohistochemical analysis revealed that all ZnTs expressed in the spinal cords were localized in a distinct subset of motor neurons. In addition, ZnT3 and 6 protein levels were not altered in SOD1（G93A）mutant transgenic mice before and after the onset of ALS symptoms compared with controls. These results suggest that ZnT3 and 6 protein levels were decreased in the spinal cords of sporadic ALS patients；however, this did not occur merely via loss of motor neurons.		S16-4 膜輸送タンパク質OCTN1/SLC22A4を標的とする精神神経疾患治療中道範隆，増尾友佑，加藤将夫金沢大学医薬保健研究域薬学系　分子薬物治療学研究室モノアミンを始めとする種々の神経伝達物質の伝達異常が精神神経疾患の発症原因となる。したがって、神経伝達物質の受容体やその取り込みを担う膜輸送タンパク質は精神神経疾患の治療標的として着目されてきた。これら神経伝達物質の膜輸送タンパク質は、特定の神経伝達物質に高い特異性を示し、シナプスに高発現している。一方、種々の有機カチオンあるいは有機アニオンに対して幅広い基質認識性を有する膜輸送タンパク質は、生体内に幅広く存在しており、精神神経疾患との関連はほとんど解明されていない。そこで、有機カチオントランスポーターの中枢神経系における役割を解明し、精神神経疾患の新たな治療戦略を得ようと試みた。OCTN1/SLC22A4は有機カチオンや両性化合物に幅広い基質認識性を示す膜輸送タンパク質であるが、生体内での役割はほとんど不明である。近年、我々はoctn1遺伝子欠損（octn1^-/-）マウスを作製し、抗酸化物質エルゴチオネイン（ERGO）がOCTN1の生体内基質であることを見出した。さらにOCNT1が神経幹細胞に発現する主要な有機カチオントランスポーターであり、ERGOを細胞内へ取り込むことにより神経分化を促進することを明らかとした。したがって、OCTN1の機能異常が正常な脳の発達に影響を及ぼし、精神神経疾患の発症要因となる可能性が考えられる。そこで野生型とoctn1^-/-マウスで種々の神経関連マーカーの発現を比較し、OCTN1が関係する脳機能について検討した。さらに、両マウスで精神神経疾患モデルを作製し、OCTN1が精神神経疾患の発症に及ぼす影響についても検討を加えた。ERGOは水溶性の低分子化合物であるが、OCTN1の働きにより経口摂取によって容易に脳実質細胞へと送達され、抗酸化作用や神経分化促進作用を発揮し、精神神経疾患の症状を改善する可能性が考えられる。そこで精神神経疾患モデルマウスにERGOを経口摂取させ、症状の改善効果について検討を加えた。本発表では、以上の可能性を検討すべく行った我々の最近の研究成果を紹介し、膜輸送タンパク質OCTN1/SLC22A4が精神神経疾患の新たな治療標的となる可能性について論じる。