1 German Centre for Neurodegenerative Diseases (DZNE), Ludwig-Erhard-Allee 2, 53175 Bonn, Germany.
2 Department of Biochemistry, College of Medicine and Health Sciences, United Arab Emirates University, Tawam Medical Campus, Khalifa Ibn Zayed street, Al-Ain, United Arab Emirates.
Brain. 2016 Mar;139(Pt 3):856-70. doi: 10.1093/brain/awv376. Epub 2015 Dec 30.
Aggregation and neuron-to-neuron transmission are attributes of α-synuclein relevant to its pathogenetic role in human synucleinopathies such as Parkinson's disease. Intraparenchymal injections of fibrillar α-synuclein trigger widespread propagation of amyloidogenic protein species via mechanisms that require expression of endogenous α-synuclein and, possibly, its structural corruption by misfolded conformers acting as pathological seeds. Here we describe another paradigm of long-distance brain diffusion of α-synuclein that involves inter-neuronal transfer of monomeric and/or oligomeric species and is independent of recruitment of the endogenous protein. Targeted expression of human α-synuclein was induced in the mouse medulla oblongata through an injection of viral vectors into the vagus nerve. Enhanced levels of intra-neuronal α-synuclein were sufficient to initiate its caudo-rostral diffusion that likely involved at least one synaptic transfer and progressively reached specific brain regions such as the locus coeruleus, dorsal raphae and amygdala in the pons, midbrain and forebrain. Transfer of human α-synuclein was compared in two separate lines of α-synuclein-deficient mice versus their respective wild-type controls and, interestingly, lack of endogenous α-synuclein expression did not counteract diffusion but actually resulted in a more pronounced and advanced propagation of exogenous α-synuclein. Self-interaction of adjacent molecules of human α-synuclein was detected in both wild-type and mutant mice. In the former, interaction of human α-synuclein with mouse α-synuclein was also observed and might have contributed to differences in protein transmission. In wild-type and α-synuclein-deficient mice, accumulation of human α-synuclein within recipient axons in the pons, midbrain and forebrain caused morphological evidence of neuritic pathology. Tissue sections from the medulla oblongata and pons were stained with different antibodies recognizing oligomeric, fibrillar and/or total (monomeric and aggregated) α-synuclein. Following viral vector transduction, monomeric, oligomeric and fibrillar protein was detected within donor neurons in the medulla oblongata. In contrast, recipient axons in the pons were devoid of immunoreactivity for fibrillar α-synuclein, indicating that non-fibrillar forms of α-synuclein were primarily transferred from one neuron to the other, diffused within the brain and led to initial neuronal injury. This study elucidates a paradigm of α-synuclein propagation that may play a particularly important role under pathophysiological conditions associated with enhanced α-synuclein expression. Rapid long-distance diffusion and accumulation of monomeric and oligomeric α-synuclein does not necessarily involve pathological seeding but could still result in a significant neuronal burden during the pathogenesis of neurodegenerative diseases.
聚集和神经元到神经元的传递是 α-突触核蛋白的属性，与人类突触核蛋白病（如帕金森病）的发病机制有关。纤维状 α-突触核蛋白的脑内注射通过需要表达内源性 α-突触核蛋白的机制触发淀粉样蛋白物种的广泛传播，并且可能需要其结构通过错误折叠的构象体（充当病理性种子）发生腐败。在这里，我们描述了 α-突触核蛋白在大脑中的远距离扩散的另一种范例，涉及单体和/或低聚物的神经元间转移，并且不依赖于内源性蛋白质的募集。通过将病毒载体注射到迷走神经中，在小鼠延髓中诱导人 α-突触核蛋白的靶向表达。增强的神经元内 α-突触核蛋白水平足以引发其从头至尾的扩散，这可能至少涉及一次突触转移，并逐渐到达特定的脑区，如桥脑的蓝斑、中脑和前脑的中缝核、中脑和前脑。在两个不同的 α-突触核蛋白缺陷型小鼠与各自的野生型对照中比较了人 α-突触核蛋白的转移，有趣的是，缺乏内源性 α-突触核蛋白表达并没有阻止扩散，而是实际上导致了外源性 α-突触核蛋白的更明显和更高级的传播。在野生型和突变型小鼠中均检测到相邻人 α-突触核蛋白分子的自我相互作用。在前者中，还观察到人 α-突触核蛋白与鼠 α-突触核蛋白的相互作用，这可能导致了蛋白质传递的差异。在野生型和 α-突触核蛋白缺陷型小鼠中，人 α-突触核蛋白在桥脑、中脑和前脑的受体内轴中的积累导致了神经突病理学的形态学证据。使用不同的抗体对延髓和桥脑组织切片进行染色，这些抗体识别寡聚体、纤维状和/或总（单体和聚集）α-突触核蛋白。在延髓的供体神经元中检测到病毒载体转导后的单体、寡聚体和纤维状蛋白。相比之下，桥脑的受体内轴缺乏纤维状 α-突触核蛋白的免疫反应性，这表明 α-突触核蛋白的非纤维形式主要从一个神经元转移到另一个神经元，在大脑内扩散，并导致初始神经元损伤。本研究阐明了一种 α-突触核蛋白传播的范例，这种传播可能在与 α-突触核蛋白表达增强相关的病理生理条件下发挥特别重要的作用。单体和寡聚体 α-突触核蛋白的快速远距离扩散和积累不一定涉及病理性播种，但仍可能导致神经退行性疾病发病过程中的显著神经元负担。
