Tolö Johan, Taschenberger Grit, Leite Kristian, Stahlberg Markus A, Spehlbrink Gesche, Kues Janina, Munari Francesca, Capaldi Stefano, Becker Stefan, Zweckstetter Markus, Dean Camin, Bähr Mathias, Kügler Sebastian
Department of Physiology, The Sahlgrenska Academy at Gothenburg University, Gothenburg, Sweden.
Department of Neurology, University Medical Center Goettingen, Göttingen, Germany.
Front Mol Neurosci. 2018 Mar 7;11:49. doi: 10.3389/fnmol.2018.00049. eCollection 2018.
α-Synuclein (α-Syn) is intimately linked to the etiology of Parkinson's Disease, as mutations and even subtle increases in gene dosage result in early onset of the disease. However, how this protein causes neuronal dysfunction and neurodegeneration is incompletely understood. We thus examined a comprehensive range of physiological parameters in cultured rat primary neurons overexpressing α-Syn at levels causing a slowly progressive neurodegeneration. In contradiction to earlier reports from non-neuronal assay systems we demonstrate that α-Syn does not interfere with essential ion handling capacities, mitochondrial capability of ATP production or basic electro-physiological properties like resting membrane potential or the general ability to generate action potentials. α-Syn also does not activate canonical stress kinase Signaling converging on SAPK/Jun, p38 MAPK or Erk kinases. Causative for α-Syn-induced neurodegeneration are mitochondrial thiol oxidation and activation of caspases downstream of mitochondrial outer membrane permeabilization, leading to apoptosis-like cell death execution with some unusual aspects. We also aimed to elucidate neuroprotective strategies counteracting the pathophysiological processes caused by α-Syn. Neurotrophic factors, calpain inhibition and increased lysosomal protease capacity showed no protective effects against α-Syn overexpression. In contrast, the major watchdog of outer mitochondrial membrane integrity, Bcl-Xl, was capable of almost completely preventing neuron death, but did not prevent mitochondrial thiol oxidation. Importantly, independent from the quite mono-causal induction of neurotoxicity, α-Syn causes diminished excitability of neurons by external stimuli and robust impairments in endogenous neuronal network activity by decreasing the frequency of action potentials generated without external stimulation. This latter finding suggests that α-Syn can induce neuronal dysfunction independent from its induction of neurotoxicity and might serve as an explanation for functional deficits that precede neuronal cell loss in synucleopathies like Parkinson's disease or dementia with Lewy bodies.
α-突触核蛋白（α-Syn）与帕金森病的病因密切相关，因为基因突变甚至基因剂量的微小增加都会导致该疾病的早发。然而，这种蛋白质如何导致神经元功能障碍和神经退行性变尚不完全清楚。因此，我们在培养的大鼠原代神经元中检测了一系列生理参数，这些神经元过表达α-Syn，其水平会导致缓慢进展的神经退行性变。与非神经元检测系统早期的报道相反，我们证明α-Syn不会干扰基本的离子处理能力、线粒体产生ATP的能力或基本的电生理特性，如静息膜电位或产生动作电位的一般能力。α-Syn也不会激活汇聚于SAPK/Jun、p38丝裂原活化蛋白激酶（MAPK）或细胞外信号调节激酶（Erk）激酶的经典应激激酶信号通路。α-Syn诱导神经退行性变的原因是线粒体硫醇氧化以及线粒体外膜通透性改变下游的半胱天冬酶激活，导致具有一些不寻常特征的凋亡样细胞死亡。我们还旨在阐明对抗由α-Syn引起的病理生理过程的神经保护策略。神经营养因子、钙蛋白酶抑制和溶酶体蛋白酶能力增加对α-Syn过表达没有保护作用。相反，线粒体外膜完整性的主要监测者Bcl-Xl几乎能够完全防止神经元死亡，但不能防止线粒体硫醇氧化。重要的是，独立于相当单一原因的神经毒性诱导，α-Syn通过外部刺激导致神经元兴奋性降低，并通过降低无外部刺激时产生的动作电位频率对内源性神经元网络活动造成严重损害。后一发现表明，α-Syn可以独立于其神经毒性诱导而导致神经元功能障碍，这可能解释了帕金森病或路易体痴呆等突触核蛋白病中神经元细胞丢失之前的功能缺陷。
