Ravera Silvia, Panfoli Isabella, Calzia Daniela, Aluigi Maria Grazia, Bianchini Paolo, Diaspro Alberto, Mancardi Gianluigi, Morelli Alessandro
Biology Department, University of Genova, Faculty of Sciences MFN, Viale Benedetto XV, Genoa, Italy.
Int J Biochem Cell Biol. 2009 Jul;41(7):1581-91. doi: 10.1016/j.biocel.2009.01.009. Epub 2009 Jan 22.
Even though brain represents only 2-3% of the body weight, it consumes 20% of total body oxygen, and 25% of total body glucose. This sounds surprising, in that mitochondrial density in brain is low, while mitochondria are thought to be the sole site of aerobic energy supply. These data would suggest that structures other than mitochondria are involved in aerobic ATP production. Considering that a sustained aerobic metabolism needs a great surface extension and that the oxygen solubility is higher in neutral lipids, we have focused our attention on myelin sheath, the multilayered membrane produced by oligodendrocytes, hypothesizing it to be an ATP production site. Myelin has long been supposed to augment the speed of conduction, however, there is growing evidence that it exerts an as yet unexplained neuro-trophic role. In this work, by biochemical assays, Western Blot analysis, confocal laser microscopy, we present evidence that isolated myelin vesicles (IMV) are able to consume O(2) and produce ATP through the operation of a proton gradient across their membranes. Living optic nerve sections were exposed to MitoTracker, a classical mitochondrial dye, by a technique that we have developed and it was found that structures closely resembling nerve axons were stained. By immunohistochemistry we show that ATP synthase and myelin basic protein colocalize on both IMV and optic nerves. The complex of data suggests that myelin sheath may be the site of oxygen absorption and aerobic metabolism for the axons.
尽管大脑仅占体重的2%-3%，但它却消耗了全身20%的氧气和25%的葡萄糖。这听起来令人惊讶，因为大脑中的线粒体密度较低，而线粒体被认为是有氧能量供应的唯一部位。这些数据表明，除线粒体之外的其他结构也参与了有氧ATP的产生。鉴于持续的有氧代谢需要很大的表面积，且氧气在中性脂质中的溶解度更高，我们将注意力集中在了髓鞘上，髓鞘是由少突胶质细胞产生的多层膜，我们推测它是一个ATP产生部位。长期以来，髓鞘一直被认为可提高传导速度，然而，越来越多的证据表明，它发挥着一种尚未得到解释的神经营养作用。在这项研究中，我们通过生化分析、蛋白质免疫印迹分析和共聚焦激光显微镜技术，证明了分离出的髓鞘小泡（IMV）能够消耗氧气，并通过跨膜质子梯度的作用产生ATP。我们开发了一种技术，将活的视神经切片用经典的线粒体染料MitoTracker进行处理，结果发现与神经轴突非常相似的结构被染色。通过免疫组织化学我们发现，ATP合酶和髓鞘碱性蛋白在IMV和视神经上均共定位。这些综合数据表明，髓鞘可能是轴突吸收氧气和进行有氧代谢的部位。
