Central Presynaptic Terminals Are Enriched in ATP but the Majority Lack Mitochondria
Central Presynaptic Terminals Are Enriched in ATP but the Majority Lack Mitochondria
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DOI：
10.1371/journal.pone.0125185
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发表时间：
2015-04-30
期刊：
影响因子：
3.7
通讯作者：
Mukherjee, Konark
中科院分区：
文献类型：
--
作者：
Chavan, Vrushali;Willis, Jeffery;Mukherjee, Konark
已知突触神经传递是一个需要能量的过程。在突触前，需要ATP将神经递质装载到突触囊泡中，在释放前启动突触囊泡，并作为各种激酶和ATP酶的底物。虽然人们认为突触前位点通常含有局部线粒体，其可以作为产生ATP的能量发电站以及突触前钙库，但突触前线粒体在突触前的生化功能中的明确作用尚未明确。除了一些突触亚型，如苔藓纤维和赫尔德萼，大多数中央突触前部位要么是过路的，要么是微小的轴突终末，几乎没有空间容纳一个大的轴突。在这里，我们已经使用成像研究证明，线粒体抗原与突触囊泡簇和活性区标记物在大脑皮层，海马和小脑中的共定位差。神经元培养物的共聚焦成像分析显示，大多数神经元线粒体要么是体细胞的，要么分布在主要树突的近端。培养物中的大量突触缺乏任何线粒体。神经元培养的电子显微照片进一步证实了我们的发现，即大多数突触前细胞可能没有线粒体。我们证实了我们的超微结构的研究结果，使用连续块面扫描电子显微镜（SBFSEM），发现超过60%的突触前末梢缺乏可辨别的线粒体在野生型小鼠海马。粗突触体的生化分馏成线粒体和纯突触体也揭示了一个稀疏存在的线粒体抗原在突触前扣。尽管线粒体丰度较低，但发现突触体膜高度富集ATP，这表明突触前体可能具有浓缩ATP以实现其功能的替代机制。讨论了可能的机制，包括局部糖酵解和ATP结合的突触蛋白，如突触蛋白的可能作用。
Synaptic neurotransmission is known to be an energy demanding process. At the presynapse, ATP is required for loading neurotransmitters into synaptic vesicles, for priming synaptic vesicles before release, and as a substrate for various kinases and ATPases. Although it is assumed that presynaptic sites usually harbor local mitochondria, which may serve as energy powerhouse to generate ATP as well as a presynaptic calcium depot, a clear role of presynaptic mitochondria in biochemical functioning of the presynapse is not well-defined. Besides a few synaptic subtypes like the mossy fibers and the Calyx of Held, most central presynaptic sites are either en passant or tiny axonal terminals that have little space to accommodate a large mitochondrion. Here, we have used imaging studies to demonstrate that mitochondrial antigens poorly co-localize with the synaptic vesicle clusters and active zone marker in the cerebral cortex, hippocampus and the cerebellum. Confocal imaging analysis on neuronal cultures revealed that most neuronal mitochondria are either somatic or distributed in the proximal part of major dendrites. A large number of synapses in culture are devoid of any mitochondria. Electron micrographs from neuronal cultures further confirm our finding that the majority of presynapses may not harbor resident mitochondria. We corroborated our ultrastructural findings using serial block face scanning electron microscopy (SBFSEM) and found that more than 60% of the presynaptic terminals lacked discernible mitochondria in the wild-type mice hippocampus. Biochemical fractionation of crude synaptosomes into mitochondria and pure synaptosomes also revealed a sparse presence of mitochondrial antigen at the presynaptic boutons. Despite a low abundance of mitochondria, the synaptosomal membranes were found to be highly enriched in ATP suggesting that the presynapse may possess alternative mechanism/s for concentrating ATP for its function. The potential mechanisms including local glycolysis and the possible roles of ATP-binding synaptic proteins such as synapsins, are discussed.