Cortese J D
Department of Cell Biology and Anatomy, University of North Carolina at Chapel Hill 25799-7099, USA.
Exp Cell Res. 1998 Apr 10;240(1):122-33. doi: 10.1006/excr.1998.4004.
In normal livers, hepatocytes contain a large number of spheroidal mitochondria. Mitochondrial morphology changes drastically in liver disease, but the underlying fusion-fission mechanisms are not known. We detected GTP- and aluminum fluoride-dependent membrane fusion events between rat liver mitochondria. Separation of outer mitochondrial membrane-derived proteins led to a subfraction containing a 60-kDa protein band that is detected by specific antibodies directed to common amino acid sequences of the GTP-binding site or carboxyl-terminus of eukaryotic heterotrimeric G-protein alpha subunits. Addition of this subfraction and aluminum fluoride to permeabilized rat hepatocytes triggered a substantial morphological change in hepatic mitochondria, giving them the three-dimensional appearance of a tubulovesicular network. Comparative stereology using electron and confocal microscopy showed that these morphological changes represent true mitochondrial fusion. Addition of aluminum fluoride alone induces a more limited change in mitochondrial morphology, from spheroidal organelles to short rods. Mitochondria maintained their normal membrane potential and overall membrane ultrastructure after all these morphological changes. Our results reveal that mammalian liver mitochondria contain proteins that stimulate mitochondrial fusion and suggest that members of the GTPase superfamily control the normalcy of mitochondrial morphology, which is closely linked to physiological cellular energetics.
在正常肝脏中，肝细胞含有大量球形线粒体。线粒体形态在肝脏疾病中会发生剧烈变化，但其潜在的融合-裂变机制尚不清楚。我们检测到大鼠肝脏线粒体之间存在依赖于鸟苷三磷酸（GTP）和氟化铝的膜融合事件。线粒体外膜衍生蛋白的分离产生了一个含有60 kDa蛋白条带的亚组分，该条带可被针对真核异源三聚体G蛋白α亚基GTP结合位点或羧基末端共同氨基酸序列的特异性抗体检测到。将该亚组分和氟化铝添加到透化的大鼠肝细胞中，引发了肝线粒体的显著形态变化，使其呈现出三维的管状囊泡网络外观。使用电子显微镜和共聚焦显微镜进行的比较体视学研究表明，这些形态变化代表了真正的线粒体融合。单独添加氟化铝会使线粒体形态发生更有限的变化，从球形细胞器变为短杆状。在所有这些形态变化后，线粒体保持其正常的膜电位和整体膜超微结构。我们的结果表明，哺乳动物肝脏线粒体含有刺激线粒体融合的蛋白质，并提示GTP酶超家族成员控制着与细胞生理能量密切相关的线粒体形态的正常状态。
