Craig E E, Hood D A
Department of Biology, York University, North York, Ontario, Canada.
Am J Physiol. 1997 Jun;272(6 Pt 2):H2983-8. doi: 10.1152/ajpheart.1997.272.6.H2983.
This study was undertaken to determine whether age-related changes in the content and composition of cardiac mitochondria could be due, in part, to alterations in mitochondrial protein import. Precursor proteins malate dehydrogenase and ornithine carbamoyltransferase were synthesized by in vitro transcription and translation and were incubated with mitochondria isolated from the hearts of young (4-mo), old (22-mo), and senescent (28-mo) rats. Mitochondria from senescent animals exhibited a twofold higher import rate of both precursors into the matrix compartment compared with mitochondria from young and old animals. The expression of glucose regulated protein 75 and heat shock protein 60, two matrix chaperonins that are essential for import, was elevated in the mitochondria of both old and senescent animals before the observed changes in import. Import was equally affected in senescent and young heart mitochondria by inhibition of cardiolipin, a mitochondrial phospholipid involved in protein translocation. The results indicate that the altered mitochondrial phenotype evident in the aging myocardium cannot be accounted for by reduced rates of protein import. Furthermore, levels of cardiolipin and matrix chaperonins do not appear to be rate-limiting steps in the import process. These data suggest that the protein import step of mitochondrial assembly is subject to adaptations under pathophysiological conditions.
本研究旨在确定心脏线粒体含量和组成的年龄相关变化是否部分归因于线粒体蛋白导入的改变。通过体外转录和翻译合成前体蛋白苹果酸脱氢酶和鸟氨酸氨甲酰基转移酶，并将其与从年轻（4个月）、老年（22个月）和衰老（28个月）大鼠心脏分离的线粒体一起孵育。与年轻和老年动物的线粒体相比，衰老动物的线粒体对两种前体蛋白导入基质区室的速率高出两倍。在观察到导入变化之前，老年和衰老动物的线粒体中，两种对导入至关重要的基质伴侣蛋白——葡萄糖调节蛋白75和热休克蛋白60的表达均升高。衰老和年轻心脏线粒体中的导入受到心磷脂抑制的同等影响，心磷脂是一种参与蛋白转运的线粒体磷脂。结果表明，衰老心肌中明显改变的线粒体表型不能用降低的蛋白导入速率来解释。此外，心磷脂和基质伴侣蛋白的水平似乎不是导入过程中的限速步骤。这些数据表明，线粒体组装的蛋白导入步骤在病理生理条件下会发生适应性变化。
