Physiology of mitochondrial dysfunction in genetic models of Parkinson's disease

帕金森病遗传模型中线粒体功能障碍的生理学

• 批准号: 8148545
• 负责人: Carl R. Lupica
• 金额: $ 36.35万
• 依托单位: NATIONAL INSTITUTE ON DRUG ABUSE
• 依托单位国家: 美国
• 资助国家: 美国
• 起止时间: 至
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/8148545
• 关键词: Genetic Models; Parkinson Disease; Physiology; mitochondrial dysfunction

We have begun to examine the neurodegeneration that occurs in a genetically modified mouse that was developed by our collaborators at the Karolinska Institute in Sweden. We have now established a successful breeding colony of these mice at our institute, and we have made them available to our local collaborators. These mice possess a mutation in the mitochondrial gene known as mitochondrial transcription factor A (tFam). This gene regulates mitochondrial DNA transcription in all cells, and is necessary for continued oxidative phosphorylation. However, by targeting this mutation to dopamine neurons using the promoter that drives dopamine transporter expression, only these neurons are affected by the mutation. Our present work shows that the DA neurons degenerate slowly over a 30 week period, and that these "MitoPark" mice display many hallmarks of Parkinsons disease in humans. This includes sensitivity to pharmacological treatments, such as L-Dopa therapy, and the loss of this therapeutic benefit as the neurodegeneration progresses. Our studies have also shown that expression of glial cell line-derived neurotrophic factor (GDNF) through adeno-associated virus (AAV) can spare these dopamine neurons, and protect against either neurotoxin or genetically induced parkinsonism in mice. In addition, in pilot studies conducted with the dopamine neurotoxin MPTP, we have found that the loss of dopamine causes profound changes in the physiological properties of the striatum that were also prevented by AAV-mediated gene expression of GDNF. We will now begin to test this form of gene therapy in the tFam genetic model of Parkinsons disease, and attempt to reverse the neurodegeneration at various time points during the disease progression. Our most recent work with the MitoPark mice reveals an interesting change in DA neuron physiology at a time during development at which the animals are behaviorally asymptomatic. We find a dramatic reduction in the presence of a membrane current known as "Ih" in the DA neurons located in the substantia nigra, This current is normally involved in re-setting the neuronal membrane potential back near action potential threshold following a large inhibition. Therefore, Ih may be involved in maintaining normal pacemaking activity in DA neurons. We are currently assessing the relevance of this change in Ih density in MitoPark mice, and theorize that a loss of Ih may represent one of the early consequences of mitochondrial impairment in DA neurons degenerating in Parkinson's disease. Our current studies show that the mRNAs encoding Ih are not altered in MitoPark mice suggesting that the down-regulation of these ion channels is post-translational. In the most recent reporting period we have found that DA neurons in MitoPark mice are impaired compared to control mice, and that this impairment leads to a reduction in the available pool of DA that is releasable. The most surprising aspect of these studies is that the observed impairment in DA neuron function occurs at an age where parkinsonian symptoms are absent in these mice. Thus, we believe that this model may permit for the first time the ability to track changes in the nigrostriatal DA system over time, which should lead to promising targets for therapeutic intervention.

我们已经开始研究发生在转基因小鼠中的神经退行性变，这是由我们在瑞典卡罗林斯卡研究所的合作者开发的。 我们现在已经在我们的研究所建立了一个成功的这些小鼠的繁殖群，我们已经把它们提供给我们当地的合作者。 这些小鼠在线粒体基因中具有称为线粒体转录因子A（tFam）的突变。 该基因调节所有细胞中的线粒体DNA转录，并且是持续氧化磷酸化所必需的。 然而，通过使用驱动多巴胺转运蛋白表达的启动子将这种突变靶向多巴胺神经元，只有这些神经元受到突变的影响。 我们目前的工作表明，DA神经元在30周内缓慢退化，这些“MitoPark”小鼠显示出人类帕金森病的许多特征。 这包括对药物治疗（如左旋多巴治疗）的敏感性，以及随着神经退行性疾病的进展而丧失这种治疗益处。 我们的研究还表明，胶质细胞源性神经营养因子（GDNF）通过腺相关病毒（AAV）的表达可以节省这些多巴胺神经元，并防止神经毒素或遗传诱导的帕金森病小鼠。 此外，在用多巴胺神经毒素MPTP进行的试点研究中，我们发现多巴胺的损失引起纹状体生理特性的深刻变化，这也被AAV介导的GDNF基因表达所阻止。 我们现在将开始在帕金森病的tFam遗传模型中测试这种形式的基因治疗，并尝试在疾病进展期间的不同时间点逆转神经变性。 我们最近对MitoPark小鼠的研究揭示了DA神经元生理学在发育过程中的一个有趣变化，此时动物在行为上无症状。 我们发现位于黑质的DA神经元中存在称为“Ih”的膜电流，该电流通常参与在大的抑制后将神经元膜电位重新设置回接近动作电位阈值。 因此，Ih可能参与维持DA神经元的正常起搏活动。 我们目前正在评估MitoPark小鼠中Ih密度变化的相关性，并推测Ih的丢失可能代表帕金森病中DA神经元退化中线粒体损伤的早期后果之一。 我们目前的研究表明，编码Ih的mRNA在MitoPark小鼠中没有改变，这表明这些离子通道的下调是翻译后的。 在最近的报告期内，我们发现与对照小鼠相比，MitoPark小鼠中的DA神经元受损，并且这种损伤导致可释放的DA可用池减少。 这些研究中最令人惊讶的方面是，观察到的DA神经元功能障碍发生在这些小鼠中没有帕金森症状的年龄。 因此，我们认为，这种模型可能允许第一次的能力，跟踪黑质纹状体DA系统随时间的变化，这将导致有前途的治疗干预的目标。