Kayser Ernst-Bernhard, Sedensky Margaret M, Morgan Philip G
Center for Developmental Therapeutics, Seattle Children's Research Institute, Seattle, Washington, United States of America.
Department of Anesthesiology and Pain Medicine, University of Washington, Seattle, Washington, United States of America.
PLoS One. 2016 Jan 29;11(1):e0148219. doi: 10.1371/journal.pone.0148219. eCollection 2016.
Lack of NDUFS4, a subunit of mitochondrial complex I (NADH:ubiquinone oxidoreductase), causes Leigh syndrome (LS), a progressive encephalomyopathy. Knocking out Ndufs4, either systemically or in brain only, elicits LS in mice. In patients as well as in KO mice distinct regions of the brain degenerate while surrounding tissue survives despite systemic complex I dysfunction. For the understanding of disease etiology and ultimately for the development of rationale treatments for LS, it appears important to uncover the mechanisms that govern focal neurodegeneration.
Here we used the Ndufs4(KO) mouse to investigate whether regional and temporal differences in respiratory capacity of the brain could be correlated with neurodegeneration. In the KO the respiratory capacity of synaptosomes from the degeneration prone regions olfactory bulb, brainstem and cerebellum was significantly decreased. The difference was measurable even before the onset of neurological symptoms. Furthermore, neither compensating nor exacerbating changes in glycolytic capacity of the synaptosomes were found. By contrast, the KO retained near normal levels of synaptosomal respiration in the degeneration-resistant/resilient "rest" of the brain. We also investigated non-synaptic mitochondria. The KO expectedly had diminished capacity for oxidative phosphorylation (state 3 respiration) with complex I dependent substrate combinations pyruvate/malate and glutamate/malate but surprisingly had normal activity with α-ketoglutarate/malate. No correlation between oxidative phosphorylation (pyruvate/malate driven state 3 respiration) and neurodegeneration was found: Notably, state 3 remained constant in the KO while in controls it tended to increase with time leading to significant differences between the genotypes in older mice in both vulnerable and resilient brain regions. Neither regional ROS damage, measured as HNE-modified protein, nor regional complex I stability, assessed by blue native gels, could explain regional neurodegeneration.
Our data suggests that locally insufficient respiration capacity of the nerve terminals may drive focal neurodegeneration.
线粒体复合物I（NADH：泛醌氧化还原酶）的亚基NDUFS4的缺乏会导致 Leigh 综合征（LS），这是一种进行性脑肌病。在小鼠中，全身性或仅在大脑中敲除Ndufs4会引发LS。在患者和基因敲除小鼠中，尽管存在全身性复合物I功能障碍，但大脑的不同区域会退化，而周围组织却能存活。为了理解疾病病因并最终开发出合理的LS治疗方法，揭示控制局灶性神经变性的机制似乎很重要。
在这里，我们使用Ndufs4（KO）小鼠来研究大脑呼吸能力的区域和时间差异是否与神经变性相关。在基因敲除小鼠中，来自易发生变性的区域嗅球、脑干和小脑的突触体的呼吸能力显著降低。甚至在神经症状出现之前就可以检测到这种差异。此外，未发现突触体糖酵解能力的补偿性或加剧性变化。相比之下，基因敲除小鼠在大脑的抗变性/弹性“其余”部分保留了接近正常水平的突触体呼吸。我们还研究了非突触线粒体。基因敲除小鼠在使用复合物I依赖性底物组合丙酮酸/苹果酸和谷氨酸/苹果酸时，氧化磷酸化能力（状态3呼吸）预期会降低，但令人惊讶的是，在使用α-酮戊二酸/苹果酸时具有正常活性。未发现氧化磷酸化（丙酮酸/苹果酸驱动的状态3呼吸）与神经变性之间的相关性：值得注意的是，基因敲除小鼠中的状态3保持恒定，而在对照组中，它倾向于随时间增加，导致老年小鼠中易损和弹性脑区的基因型之间存在显著差异。无论是以HNE修饰蛋白衡量的区域ROS损伤，还是通过蓝色天然凝胶评估的区域复合物I稳定性，都无法解释区域神经变性。
我们的数据表明，神经末梢局部呼吸能力不足可能会驱动局灶性神经变性。
