Neuronal mechanisms controlling number and function of presynaptic mitochondria

描述(申请人提供)：我们的总体目标是阐明控制线粒体以满足神经末梢能量需求的神经机制。线粒体聚集在神经末梢内，在那里它们产生神经递质释放和循环所需的大部分ATP。因此，神经功能依赖于线粒体产生足够的ATP来维持神经递质的释放。同样，线粒体为突触前钙离子稳态提供动力。神经元钙稳态的失败会带来灾难性的后果，是许多神经退行性疾病的标志。令人惊讶的是，我们对线粒体数量和功能与突触前能量需求协调的机制知之甚少，但了解这些机制对于了解神经退行性疾病的进展至关重要。我们的中心假设是，神经元机制控制线粒体的数量和功能，以适应突触前能量需求，并且这些机制是突触特有的。我们建议在果蝇幼虫的肌肉骨骼系统中阐明这些机制，在该系统中，每个运动神经元终端具有不同的工作速率，我们可以使用电生理和钙成像技术对其进行量化。突触前能量需求的多样性、遗传可控性和神经生理学技术的可获得性使这一系统成为研究控制线粒体适应突触前能量需求的神经机制的理想系统。在目标1中，我们将确定线粒体是否以与其工作率成比例的数量供应给运动神经末梢。将使用3D-EM重建来确定线粒体数量。我们还将探讨线粒体数量和功能之间的关系。在目标2中，我们将检验线粒体体积在同一轴突的不同终末水平上被控制的假设。线粒体功能参数将在各个终末确定，以测试同一轴突上不同终末的线粒体功能是否会有所不同。在目标3中，我们将检验这一假设，即在发育过程中，活动区间距和突触直径根据运动神经元的放电率进行调节，使突触前钙水平进入最有效地刺激突触前活动期间线粒体能量代谢的范围。鉴于钙调节是突触前ATP的重要消耗，这种突触前生物能量学的原位模型将为更好地理解神经退行性疾病中涉及线粒体功能障碍和钙调节失调的早期事件提供必要的背景。

DESCRIPTION (provided by applicant): Our overall goal is to elucidate the neuronal mechanisms that control mitochondria to satisfy the energy demands of nerve terminals. Mitochondria accumulate within nerve terminals where they generate most of the ATP required for the release and recycling of neurotransmitters. Neural function, therefore, relies on mitochondria generating sufficient ATP to sustain neurotransmitter release. Similarly, mitochondria power presynaptic Ca2+ homeostasis. A failure in neuronal Ca2+ homeostasis has catastrophic consequences and is a hallmark of many neurodegenerative diseases. Surprisingly, we know very little about the mechanisms that coordinate mitochondrial number and function with presynaptic energy requirements, yet understanding these mechanisms will be critical to understanding the progression of neurodegenerative disease. Our central hypothesis is that neuronal mechanisms control the number and function of mitochondria to accommodate presynaptic energy requirements, and that these mechanisms are synapse specific. We propose to elucidate these mechanisms in the musculoskeletal system of the fruit fly larva, where each motor neuron terminal has a different work rate which we can quantify using electrophysiological and Ca2+-imaging techniques. Diversity in presynaptic energy requirements, genetic tractability and accessibility to neurophysiological techniques, make this an ideal system in which to investigate neuronal mechanisms that control mitochondria to accommodate presynaptic energy requirements. In Aim 1, we will determine whether mitochondria are supplied to motor nerve terminals in numbers that are proportional to their work rate. 3D-EM reconstruction will be used to determine mitochondrial number. We will also probe the relationship between mitochondrial number and function. In Aim 2, we will test the hypothesis that mitochondrial volume is controlled at the level of different terminals on the same axon. Mitochondrial functional parameters will be determined at individual terminals to test whether mitochondrial function may be different between terminals on the same axon. In Aim 3, we will test the hypothesis that, over the course of development, active zone spacing and bouton diameter adjust to the firing rate of the motor neuron to bring presynaptic Ca2+ levels into a range most effective at stimulating mitochondrial energy metabolism during presynaptic activity. In so far as Ca2+ regulation is a heavy consumer of presynaptic ATP, this in situ model of presynaptic bioenergetics will provide an essential context for a better understanding of the early events involving mitochondrial dysfunction and Ca2+ dysregulation in neurodegenerative disease.