Elucidation of multiple actions of reactive nitrogen species in degeneration of midbrain dopaminergic neurons

特别提到的活性氮物种和相关化合物的行动，这项研究解决了氧化应激诱导选择性变性的中脑黑质多巴胺能神经元，帕金森病的病理学标志的作用。(1)激活microgia在中脑切片培养的脂多糖诱导的多巴胺能神经元的变性，这是介导的诱导型一氧化氮（NO）合酶的表达和生产的增加。歧化的超氧化物并不抑制诱导的神经元死亡，而JNK抑制剂和α-生育酚保护多巴胺神经元，而不影响NO的生产。另一方面，应用凝血酶中脑切片培养诱导多巴胺能神经元变性与多个MAP激酶家族成员的激活和随后的NO合酶表达增加有关。这些酶的抑制以及小胶质细胞的耗竭显着抑制多巴胺能神经变性。因此，凝血酶被认为是通过激活小胶质细胞和增加NO的产生来发挥选择性多巴胺能神经毒性。(2)3-硝基酪氨酸（3-NT）是由酪氨酸与NO相关分子反应生成的，可诱导培养的中脑多巴胺能神经元变性。细胞通过氨基酸转运体摄取3-NT是诱导细胞死亡所必需的，并且3-NT促进细胞中超氧化物的产生，这表明3-NT通过充当细胞内超氧化物发生器而促进多巴胺能神经元的变性。(3)DJ-1是家族性帕金森病基因编码的一种蛋白质，敲低DJ-1使SH-SY 5 Y细胞对包括6-OHDA、H_2O_2和NO供体在内的多种药物敏感。此外，H_2O_2处理SH-SY 5 Y细胞和C6细胞后，DJ-1的表达增加，表明DJ-1是抗氧化应激的内源性保护机制的一部分。

With special reference to the actions of reactive nitrogen species and related compounds, this study addressed the roles of oxidative stress in induction of selective degeneration of midbrain nigral dopaminergic neurons, a hallmark of Parkinson disease pathology. (1) Activation of microgia in midbrain slice cultures by lipopolysaccharide induced degeneration of dopaminergic neurons, which was mediated by increases in expression of inducible nitric oxide (NO) synthase and production of NO. Dismutation of superoxide did not inhibit induction of neuronal death, whereas a JNK inhibitor and α-tocopherol protected dopaminerguc neurons without affecting NO production. On the other hand, degeneration of dopaminergic neurons induced by application of thrombin to midbrain slice cultures was associated with activation of multiple MAP kinase family members and a subsequent increase in expression of NO synthase. Inhibition of these enzymes as well as depletion of microglia markedly suppressed dopaminergic neurodegeneration. Thus, thrombin was suggested to exert selective dopaminergic neurotoxicity via microglial activation and increased NO production. (2) 3-Nitrotyrosine (3-NT), which is formed by reaction of tyrosine with NO-related molecular species, induced degeneration of midbrain dopaminergic neurons in culture. Cellular uptake of 3-NT via amino acid transporters was essential for induction of cell death, and 3-NT promoted superoxide production in cells, suggesting that 3-NT promotes degeneration of dopaminergic neurons by acting as an intracellular superoxide generator. (3) Knockdown of DJ-1, a protein encoded by a gene responsible for familial Parkinson disease, rendered SH-SY5Y cells vulnerable to several agents including 6-OHDA, H_2O_2 and an NO donor. In addition, treatment of SH-SY5Y cells and C6 cells with H_2O_2 increased expression of DJ-1, suggesting that DJ-1 functions as a part of endogenous protective mechanisms against oxidative stress.