Department of Molecular Biophysics and Physiology, Rush University School of Medicine, Chicago, Illinois 60612, USA.
J Biol Chem. 2011 Sep 16;286(37):32436-43. doi: 10.1074/jbc.M110.217711. Epub 2011 Jul 27.
Defective coupling between sarcoplasmic reticulum and mitochondria during control of intracellular Ca(2+) signaling has been implicated in the progression of neuromuscular diseases. Our previous study showed that skeletal muscles derived from an amyotrophic lateral sclerosis (ALS) mouse model displayed segmental loss of mitochondrial function that was coupled with elevated and uncontrolled sarcoplasmic reticulum Ca(2+) release activity. The localized mitochondrial defect in the ALS muscle allows for examination of the mitochondrial contribution to Ca(2+) removal during excitation-contraction coupling by comparing Ca(2+) transients in regions with normal and defective mitochondria in the same muscle fiber. Here we show that Ca(2+) transients elicited by membrane depolarization in fiber segments with defective mitochondria display an ~10% increased amplitude. These regional differences in Ca(2+) transients were abolished by the application of 1,2-bis(O-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid, a fast Ca(2+) chelator that reduces mitochondrial Ca(2+) uptake. Using a mitochondria-targeted Ca(2+) biosensor (mt11-YC3.6) expressed in ALS muscle fibers, we monitored the dynamic change of mitochondrial Ca(2+) levels during voltage-induced Ca(2+) release and detected a reduced Ca(2+) uptake by mitochondria in the fiber segment with defective mitochondria, which mirrored the elevated Ca(2+) transients in the cytosol. Our study constitutes a direct demonstration of the importance of mitochondria in shaping the cytosolic Ca(2+) signaling in skeletal muscle during excitation-contraction coupling and establishes that malfunction of this mechanism may contribute to neuromuscular degeneration in ALS.
在细胞内 Ca(2+) 信号的控制过程中，肌浆网和线粒体之间的偶联缺陷与神经肌肉疾病的进展有关。我们之前的研究表明，来自肌萎缩侧索硬化症 (ALS) 小鼠模型的骨骼肌表现出线粒体功能的节段性丧失，同时伴有升高和不受控制的肌浆网 Ca(2+) 释放活性。ALS 肌肉中的局部线粒体缺陷允许通过比较同一肌纤维中正常和有缺陷的线粒体区域的 Ca(2+) 瞬变来检查线粒体对兴奋-收缩偶联期间 Ca(2+) 清除的贡献。在这里，我们显示在有缺陷的线粒体的纤维段中，膜去极化引起的 Ca(2+) 瞬变显示出约 10%的幅度增加。这些区域 Ca(2+) 瞬变的差异通过 1,2-双（O-氨基苯氧基）乙烷-N,N,N',N'-四乙酸的应用而消除，1,2-双（O-氨基苯氧基）乙烷-N,N,N',N'-四乙酸是一种快速的 Ca(2+) 螯合剂，可减少线粒体 Ca(2+) 摄取。使用在 ALS 肌纤维中表达的线粒体靶向 Ca(2+) 生物传感器 (mt11-YC3.6)，我们监测了电压诱导的 Ca(2+) 释放过程中线粒体 Ca(2+) 水平的动态变化，并在有缺陷的线粒体的纤维段中检测到线粒体摄取 Ca(2+) 的减少，这与细胞质中升高的 Ca(2+) 瞬变相吻合。我们的研究直接证明了线粒体在兴奋-收缩偶联过程中塑造骨骼肌细胞质 Ca(2+) 信号的重要性，并确立了该机制的故障可能导致 ALS 中的神经肌肉退化。
