Legros Frédéric, Lombès Anne, Frachon Paule, Rojo Manuel
Institut National de la Santé et de la Recharche Médicale U523, Institut de Myologie, Groupe Hospitalier Pitié-Salpêtrière, 75651 Paris, France.
Mol Biol Cell. 2002 Dec;13(12):4343-54. doi: 10.1091/mbc.e02-06-0330.
Mitochondrial fusion remains a largely unknown process despite its observation by live microscopy and the identification of few implicated proteins. Using green and red fluorescent proteins targeted to the mitochondrial matrix, we show that mitochondrial fusion in human cells is efficient and achieves complete mixing of matrix contents within 12 h. This process is maintained in the absence of a functional respiratory chain, despite disruption of microtubules or after significant reduction of cellular ATP levels. In contrast, mitochondrial fusion is completely inhibited by protonophores that dissipate the inner membrane potential. This inhibition, which results in rapid fragmentation of mitochondrial filaments, is reversible: small and punctate mitochondria fuse to reform elongated and interconnected ones upon withdrawal of protonophores. Expression of wild-type or dominant-negative dynamin-related protein 1 showed that fragmentation is due to dynamin-related protein 1-mediated mitochondrial division. On the other hand, expression of mitofusin 1 (Mfn1), one of the human Fzo homologues, increased mitochondrial length and interconnectivity. This process, but not Mfn1 targeting, was dependent on the inner membrane potential, indicating that overexpressed Mfn1 stimulates fusion. These results show that human mitochondria represent a single cellular compartment whose exchanges and interconnectivity are dynamically regulated by the balance between continuous fusion and fission reactions.
尽管通过活细胞显微镜观察以及对少数相关蛋白的鉴定，线粒体融合在很大程度上仍是一个未知的过程。利用靶向线粒体基质的绿色和红色荧光蛋白，我们发现人类细胞中的线粒体融合效率很高，能在12小时内实现基质内容物的完全混合。即使在没有功能性呼吸链的情况下，或者在微管被破坏或细胞ATP水平显著降低之后，这个过程仍能维持。相反，能消除内膜电位的质子载体可完全抑制线粒体融合。这种抑制作用会导致线粒体细丝迅速断裂，而且是可逆的：在撤去质子载体后，小的点状线粒体融合，重新形成细长且相互连接的线粒体。野生型或显性负性动力蛋白相关蛋白1的表达表明，线粒体断裂是由动力蛋白相关蛋白1介导的线粒体分裂所致。另一方面，人类Fzo同源物之一的线粒体融合蛋白1（Mfn1）的表达增加了线粒体的长度和相互连接性。这一过程，而非Mfn1的靶向作用，依赖于内膜电位，表明过表达的Mfn1刺激了融合。这些结果表明，人类线粒体代表了一个单一的细胞区室，其交换和相互连接性由持续的融合与裂变反应之间的平衡动态调节。
