Chang Diane T W, Honick Anthony S, Reynolds Ian J
Department of Pharmacology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA.
J Neurosci. 2006 Jun 28;26(26):7035-45. doi: 10.1523/JNEUROSCI.1012-06.2006.
Functional synapses require mitochondria to supply ATP and regulate local [Ca2+]i for neurotransmission. Mitochondria are thought to be transported to specific cellular regions of increased need such as synapses. However, little is known about how this occurs, including the spatiotemporal distribution of mitochondria relative to presynaptic and postsynaptic sites, whether mitochondria are dynamically recruited to synapses, and how synaptic activity affects these trafficking patterns. We used primary cortical neurons in culture that form synaptic connections and show spontaneous synaptic activity under normal conditions. Neurons were cotransfected with a mitochondrially targeted cyan fluorescent protein and an enhanced yellow fluorescent protein-tagged synaptophysin or postsynaptic density-95 plasmid to label presynaptic or postsynaptic structures, respectively. Fluorescence microscopy revealed longer dendritic mitochondria that occupied a greater fraction of neuronal process length than axonal mitochondria. Mitochondria were significantly more likely to be localized at synaptic sites. Although this localization was unchanged by inhibition of synaptic activity by tetrodotoxin, it increased in dendritic synapses and decreased in axonal synapses during overactivity by veratridine. Mitochondrial movement and recruitment to synapses also differed between axons and dendrites under basal conditions and when synaptic activity was altered. Additionally, we show that movement of dendritic mitochondria can be selectively impaired by glutamate and zinc. We conclude that mitochondrial trafficking to synapses is dynamic in neurons and is modulated by changes in synaptic activity. Furthermore, mitochondrial morphology and distribution may be optimized differentially to best serve the synaptic distributions in axons and dendrites. Last, selective cessation of mitochondrial movement in dendrites suggests early postsynaptic dysfunction in neuronal injury and degeneration.
功能性突触需要线粒体来提供三磷酸腺苷（ATP）并调节局部钙离子浓度（[Ca2+]i）以进行神经传递。线粒体被认为会被运输到需求增加的特定细胞区域，如突触。然而，对于这一过程如何发生，包括线粒体相对于突触前和突触后位点的时空分布、线粒体是否动态募集到突触以及突触活动如何影响这些运输模式，我们知之甚少。我们使用了培养的原代皮质神经元，这些神经元在正常条件下形成突触连接并表现出自发性突触活动。神经元被共转染了线粒体靶向的青色荧光蛋白和增强型黄色荧光蛋白标记的突触素或突触后致密蛋白95质粒，分别用于标记突触前或突触后结构。荧光显微镜观察发现，树突状线粒体比轴突状线粒体更长，占据神经元突起长度的比例更大。线粒体显著更有可能定位在突触部位。虽然河豚毒素抑制突触活动不会改变这种定位，但在藜芦碱引起的过度活动期间，树突状突触中的这种定位增加，轴突状突触中的这种定位减少。在基础条件下以及突触活动改变时，轴突和树突中线粒体向突触的移动和募集也有所不同。此外，我们发现谷氨酸和锌可以选择性地损害树突状线粒体的移动。我们得出结论，线粒体向突触的运输在神经元中是动态的，并受到突触活动变化的调节。此外，线粒体的形态和分布可能会有差异地进行优化，以最好地服务于轴突和树突中的突触分布。最后，树突中线粒体移动的选择性停止表明神经元损伤和退化时突触后早期功能障碍。
