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.

我们已经开始研究瑞典卡罗林斯卡研究所的合作者开发的转基因小鼠中发生的神经退行性疾病。 现在，我们已经在我们的研究所建立了这些小鼠的成功繁殖群，并将它们提供给我们当地的合作者。 这些小鼠的线粒体基因发生突变，称为线粒体转录因子 A (tFam)。 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 周的时间内缓慢退化，并且这些“MitoPark”小鼠表现出人类帕金森病的许多特征。 这包括对药物治疗（例如左旋多巴治疗）的敏感性，以及随着神经变性的进展而失去这种治疗效果。 我们的研究还表明，通过腺相关病毒（AAV）表达胶质细胞系源性神经营养因子（GDNF）可以保护这些多巴胺神经元，并防止小鼠受到神经毒素或遗传诱导的帕金森病。 此外，在用多巴胺神经毒素 MPTP 进行的初步研究中，我们发现多巴胺的丧失会导致纹状体生理特性发生深刻的变化，而 AAV 介导的 GDNF 基因表达也可以阻止这种变化。 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，并尝试逆转疾病进展过程中不同时间点的神经变性。 我们最近对 MitoPark 小鼠的研究揭示了在动物发育过程中无行为症状的时期，DA 神经元生理学发生了有趣的变化。 我们发现位于黑质的 DA 神经元中称为“Ih”的膜电流显着减少，该电流通常涉及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 的损失可能代表帕金森病中 DA 神经元退化的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，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 小鼠的 DA 神经元受损，并且这种受损导致可释放的可用 DA 池减少。 这些研究最令人惊讶的方面是，观察到的 DA 神经元功能损伤发生在这些小鼠不存在帕金森症状的年龄。 因此，我们相信该模型可能首次能够跟踪黑质纹状体 DA 系统随时间的变化，这应该会为治疗干预带来有希望的目标。