Zhou Z D, Yap B P, Gung A Y T, Leong S M, Ang S T, Lim T M
Department of Biological Science, National University of Singapore, 14 Science Drive 4, 117543, Singapore.
Exp Cell Res. 2006 Jan 15;312(2):156-70. doi: 10.1016/j.yexcr.2005.10.012. Epub 2005 Nov 17.
Human wild type (WT) and mutant alpha-synuclein (alpha-syn) genes were overexpressed using a Tet-on expression system in stably transfected dopaminergic MN9D cells. Their overexpression induced caspase-independent and dopamine-related apoptosis not rescued by general caspase inhibitor Z-VAD-FMK. While apoptosis due to overexpression of WT alpha-syn was completely abrogated by a specific tyrosine hydroxylase (TH) inhibitor, alpha-methyl-p-tyrosine (alpha-MT), the inhibitor only partially rescued apoptosis caused by overexpression of alpha-syn mutants. In addition, overexpression of mutants enhanced the toxicity of 1-methyl-4-phenylpyridinium (MPP+) and 6-hydroxyldopamine (6-OHDA) to MN9D cells, whereas overexpression of WT protected MN9D cells against MPP+ toxicity, but not against 6-OHDA. We conclude that WT alpha-syn is beneficial to dopaminergic neurons but its overexpression in the presence of endogenous dopamine makes it a potential threat to the cells. In contrast, mutant alpha-syn not only caused the loss of WT protective function but also the gain-of-toxicity which becomes more serious in the presence of dopamine and neurotoxins.
使用Tet-on表达系统在稳定转染的多巴胺能MN9D细胞中过表达人野生型（WT）和突变型α-突触核蛋白（α-syn）基因。它们的过表达诱导了不依赖于半胱天冬酶且与多巴胺相关的细胞凋亡，一般的半胱天冬酶抑制剂Z-VAD-FMK无法挽救这种凋亡。虽然WT α-syn过表达引起的细胞凋亡可被特异性酪氨酸羟化酶（TH）抑制剂α-甲基对酪氨酸（α-MT）完全消除，但该抑制剂只能部分挽救α-syn突变体过表达引起的细胞凋亡。此外，突变体的过表达增强了1-甲基-4-苯基吡啶鎓（MPP +）和6-羟基多巴胺（6-OHDA）对MN9D细胞的毒性，而WT的过表达可保护MN9D细胞免受MPP +毒性的影响，但不能抵御6-OHDA。我们得出结论，WT α-syn对多巴胺能神经元有益，但在内源性多巴胺存在的情况下其过表达会对细胞构成潜在威胁。相比之下，突变型α-syn不仅导致WT保护功能丧失，还会产生毒性增强的现象，在多巴胺和神经毒素存在的情况下这种现象会更加严重。
