* Redox Biology Center.
Toxicol Sci. 2013 Nov;136(1):166-82. doi: 10.1093/toxsci/kft188. Epub 2013 Aug 31.
Controversial reports on the role of autophagy as a survival or cell death mechanism in dopaminergic cell death induced by parkinsonian toxins exist. We investigated the alterations in autophagic flux and the role of autophagy protein 5 (Atg5)-dependent autophagy in dopaminergic cell death induced by parkinsonian toxins. Dopaminergic cell death induced by the mitochondrial complex I inhibitors 1-methyl-4-phenylpyridinium (MPP⁺) and rotenone, the pesticide paraquat, and the dopamine analog 6-hydroxydopamine (6-OHDA) was paralleled by increased autophagosome accumulation. However, when compared with basal autophagy levels using chloroquine, autophagosome accumulation was a result of impaired autophagic flux. Only 6-OHDA induced an increase in autophagosome formation. Overexpression of a dominant negative form of Atg5 increased paraquat- and MPP⁺-induced cell death. Stimulation of mammalian target of rapamycin (mTOR)-dependent signaling protected against cell death induced by paraquat, whereas MPP⁺-induced toxicity was enhanced by wortmannin, a phosphoinositide 3-kinase class III inhibitor, rapamycin, and trehalose, an mTOR-independent autophagy activator. Modulation of autophagy by either pharmacological or genetic approaches had no effect on rotenone or 6-OHDA toxicity. Cell death induced by parkinsonian neurotoxins was inhibited by the pan caspase inhibitor (Z-VAD), but only caspase-3 inhibition was able to decrease MPP⁺-induced cell death. Finally, inhibition of the lysosomal hydrolases, cathepsins, increased the toxicity by paraquat and MPP⁺, supporting a protective role of Atg5-dependent autophagy and lysosomes degradation pathways on dopaminegic cell death. These results demonstrate that in dopaminergic cells, Atg5-dependent autophagy acts as a protective mechanism during apoptotic cell death induced by paraquat and MPP⁺ but not during rotenone or 6-OHDA toxicity.
存在关于自噬作为帕金森病毒素诱导的多巴胺能细胞死亡的存活或细胞死亡机制的争议性报告。我们研究了帕金森病毒素诱导的多巴胺能细胞死亡中自噬流的改变和自噬蛋白 5(Atg5)依赖性自噬的作用。线粒体复合物 I 抑制剂 1-甲基-4-苯基吡啶(MPP+)和鱼藤酮、杀虫剂百草枯和多巴胺类似物 6-羟多巴胺(6-OHDA)诱导的多巴胺能细胞死亡伴随着自噬体积累的增加。然而,与使用氯喹的基础自噬水平相比,自噬体积累是自噬流受损的结果。只有 6-OHDA 诱导自噬体形成增加。过表达显性失活形式的 Atg5 增加了百草枯和 MPP+诱导的细胞死亡。刺激雷帕霉素靶蛋白(mTOR)依赖性信号转导可防止百草枯诱导的细胞死亡,而鱼藤酮诱导的毒性则被磷脂酰肌醇 3-激酶类 III 抑制剂渥曼青霉素、雷帕霉素和 trehalose(一种 mTOR 非依赖性自噬激活剂)增强。通过药理学或遗传学方法调节自噬对鱼藤酮或 6-OHDA 毒性没有影响。帕金森病神经毒素诱导的细胞死亡被泛半胱天冬酶抑制剂(Z-VAD)抑制,但只有 caspase-3 抑制才能降低 MPP+诱导的细胞死亡。最后,抑制溶酶体水解酶组织蛋白酶增加了百草枯和 MPP+的毒性,支持 Atg5 依赖性自噬和溶酶体降解途径在多巴胺能细胞死亡中的保护作用。这些结果表明,在多巴胺能细胞中,Atg5 依赖性自噬在百草枯和 MPP+诱导的细胞凋亡性死亡中作为一种保护机制起作用,但在鱼藤酮或 6-OHDA 毒性中不起作用。
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