Department of Biological Sciences, The State University of New York at Buffalo, Buffalo, NY, 14260, USA.
Instituto de Biología Celular y Neurociencias IBCN (CONICET-UBA), Universidad De Buenos Aires, Buenos Aires, Argentina.
Cell Death Dis. 2021 Aug 17;12(9):796. doi: 10.1038/s41419-021-04046-3.
Mitochondria are highly dynamic organelles with strict quality control processes that maintain cellular homeostasis. Within axons, coordinated cycles of fission-fusion mediated by dynamin related GTPase protein (DRP1) and mitofusins (MFN), together with regulated motility of healthy mitochondria anterogradely and damaged/oxidized mitochondria retrogradely, control mitochondrial shape, distribution and size. Disruption of this tight regulation has been linked to aberrant oxidative stress and mitochondrial dysfunction causing mitochondrial disease and neurodegeneration. Although pharmacological induction of Parkinson's disease (PD) in humans/animals with toxins or in mice overexpressing α-synuclein (α-syn) exhibited mitochondrial dysfunction and oxidative stress, mice lacking α-syn showed resistance to mitochondrial toxins; yet, how α-syn influences mitochondrial dynamics and turnover is unclear. Here, we isolate the mechanistic role of α-syn in mitochondrial homeostasis in vivo in a humanized Drosophila model of Parkinson's disease (PD). We show that excess α-syn causes fragmented mitochondria, which persists with either truncation of the C-terminus (α-syn) or deletion of the NAC region (α-syn). Using in vivo oxidation reporters Mito-roGFP2-ORP1/GRX1 and MitoTimer, we found that α-syn-mediated fragments were oxidized/damaged, but α-syn-induced fragments were healthy, suggesting that the C-terminus is required for oxidation. α-syn-mediated oxidized fragments showed biased retrograde motility, but α-syn-mediated healthy fragments did not, demonstrating that the C-terminus likely mediates the retrograde motility of oxidized mitochondria. Depletion/inhibition or excess DRP1-rescued α-syn-mediated fragmentation, oxidation, and the biased retrograde motility, indicating that DRP1-mediated fragmentation is likely upstream of oxidation and motility changes. Further, excess PINK/Parkin, two PD-associated proteins that function to coordinate mitochondrial turnover via induction of selective mitophagy, rescued α-syn-mediated membrane depolarization, oxidation and cell death in a C-terminus-dependent manner, suggesting a functional interaction between α-syn and PINK/Parkin. Taken together, our findings identify distinct roles for α-syn in mitochondrial homeostasis, highlighting a previously unknown pathogenic pathway for the initiation of PD.
线粒体是具有严格质量控制过程的高度动态细胞器，可维持细胞内稳态。在轴突中，由与 GTP 酶蛋白（DRP1）和线粒体融合蛋白（MFN）相关的分裂融合协调循环，以及健康线粒体向顺行和受损/氧化线粒体逆行的调节运动，控制线粒体的形状、分布和大小。这种紧密调节的破坏与异常氧化应激和线粒体功能障碍有关，导致线粒体疾病和神经退行性变。尽管用毒素在人类/动物中诱导帕金森病（PD）或在过度表达α-突触核蛋白（α-syn）的小鼠中诱导帕金森病（PD），会表现出线粒体功能障碍和氧化应激，但缺乏α-syn 的小鼠对线粒体毒素表现出抗性；然而，α-syn 如何影响线粒体动力学和周转率尚不清楚。在这里，我们在帕金森病（PD）的人类化果蝇模型中体内分离α-syn 对线粒体动态平衡的机制作用。我们表明，过量的α-syn 导致线粒体碎片化，这种碎片化在截断 C 端（α-syn）或删除 NAC 区（α-syn）后仍然存在。使用体内氧化报告物 Mito-roGFP2-ORP1/GRX1 和 MitoTimer，我们发现α-syn 介导的片段被氧化/损伤，但α-syn 诱导的片段是健康的，这表明 C 端是氧化所必需的。α-syn 介导的氧化片段表现出偏向逆行的运动，但α-syn 介导的健康片段没有，这表明 C 端可能介导氧化线粒体的逆行运动。DRP1 耗竭/抑制或过量恢复了α-syn 介导的片段化、氧化和偏向逆行的运动，表明 DRP1 介导的片段化可能是氧化和运动变化的上游。此外，过量的 PINK/Parkin，两种与 PD 相关的蛋白质，通过诱导选择性线粒体自噬来协调线粒体周转，以 C 端依赖的方式挽救了α-syn 介导的膜去极化、氧化和细胞死亡，这表明α-syn 和 PINK/Parkin 之间存在功能相互作用。总之，我们的发现确定了α-syn 在线粒体动态平衡中的不同作用，突出了 PD 起始的一个以前未知的致病途径。
