Adhihetty Peter J, Ljubicic Vladimir, Menzies Keir J, Hood David A
School of Kinesiology and Health Science, York University, Farquharson Building, 302, Toronto, Ontario, Canada M3J 1P3.
Am J Physiol Cell Physiol. 2005 Oct;289(4):C994-C1001. doi: 10.1152/ajpcell.00031.2005. Epub 2005 May 18.
Apoptosis can be evoked by reactive oxygen species (ROS)-induced mitochondrial release of the proapoptotic factors cytochrome c and apoptosis-inducing factor (AIF). Because skeletal muscle is composed of two mitochondrial subfractions that reside in distinct subcellular regions, we investigated the apoptotic susceptibility of subsarcolemmal (SS) and intermyofibrillar (IMF) mitochondria. SS and IMF mitochondria exhibited a dose-dependent release of protein in response to H2O2 (0, 25, 50, and 100 microM). However, IMF mitochondria were more sensitive to H2O2 and released a 2.5-fold and 10-fold greater amount of cytochrome c and AIF, respectively, compared with SS mitochondria. This finding coincided with a 44% (P < 0.05) greater rate of opening (maximum rate of absorbance decrease, V(max)) of the protein release channel, the mitochondrial permeability transition pore (mtPTP), in IMF mitochondria. IMF mitochondria also exhibited a 47% (P < 0.05) and 60% (0.05 < P < 0.1) greater expression of the key mtPTP component voltage-dependent anion channel and cyclophilin D, respectively, along with a threefold greater cytochrome c content, but similar levels of AIF compared with SS mitochondria. Despite a lower susceptibility to H2O2-induced release, SS mitochondria possessed a 10-fold greater Bax-to-Bcl-2 ratio (P < 0.05), a 2.7-fold greater rate of ROS production, and an approximately twofold greater membrane potential compared with IMF mitochondria. The expression of the antioxidant enzyme Mn2+-superoxide dismutase was similar between subfractions. Thus the divergent protein composition and function of the mtPTP between SS and IMF mitochondria contributes to a differential release of cytochrome c and AIF in response to ROS. Given the relatively high proportion of IMF mitochondria within a muscle fiber, this subfraction is likely most important in inducing apoptosis when presented with apoptotic stimuli, ultimately leading to myonuclear decay and muscle fiber atrophy.
活性氧（ROS）诱导促凋亡因子细胞色素c和凋亡诱导因子（AIF）从线粒体释放，可引发细胞凋亡。由于骨骼肌由位于不同亚细胞区域的两个线粒体亚组分组成，我们研究了肌膜下（SS）和肌原纤维间（IMF）线粒体的凋亡易感性。SS和IMF线粒体对H2O2（0、25、50和100微摩尔）呈剂量依赖性蛋白质释放。然而，与SS线粒体相比，IMF线粒体对H2O2更敏感，分别释放出多2.5倍和10倍的细胞色素c和AIF。这一发现与IMF线粒体中蛋白质释放通道——线粒体通透性转换孔（mtPTP）的开放速率（吸光度最大下降速率，V(max)）高44%（P<0.05）相吻合。IMF线粒体中关键的mtPTP组分电压依赖性阴离子通道和亲环蛋白D的表达也分别高47%（P<0.05）和60%（0.05<P<0.1），同时细胞色素c含量高三倍，但与SS线粒体相比，AIF水平相似。尽管对H2O2诱导的释放敏感性较低，但与IMF线粒体相比，SS线粒体的Bax与Bcl-2比值高10倍（P<0.05），ROS产生速率高2.7倍，膜电位高约两倍。亚组分之间抗氧化酶锰超氧化物歧化酶的表达相似。因此，SS和IMF线粒体之间mtPTP的不同蛋白质组成和功能导致了细胞色素c和AIF对ROS的差异性释放。鉴于IMF线粒体在肌纤维中所占比例相对较高，当受到凋亡刺激时，该亚组分可能在诱导细胞凋亡中最为重要，最终导致肌核衰变和肌纤维萎缩。
