Li ZhengZheng, Berk Michael, McIntyre Thomas M, Gores Gregory J, Feldstein Ariel E
Department of Cell Biology, Cleveland Clinic, Cleveland, OH 44195, USA.
Hepatology. 2008 May;47(5):1495-503. doi: 10.1002/hep.22183.
Impaired mitochondrial function is largely thought to be a core abnormality responsible for disease progression in nonalcoholic fatty liver disease (NAFLD). However, the molecular mechanisms resulting in mitochondrial dysfunction in NAFLD remain poorly understood. This study examined the effects of excessive accumulation of free fatty acids (FFAs) in liver cells on mitochondrial function and the role of the lysosomal-mitochondrial axis on lipotoxicity. Primary mouse hepatocytes, HepG2 and McNtcp.24 cells, were treated with varied concentrations of FFAs with different degrees of saturation for up to 24 hours. Mitochondrial function was monitored by real-time imaging, cytochrome c redistribution, and reactive oxygen species (ROS) production. The temporal relationship of lysosomal and mitochondrial permeabilization was established. Activity of the lysosomal protease cathepsin B was suppressed by genetic and pharmacological approaches. Cathepsin B-knockout mice and wild-type animals were place on a high-carbohydrate diet for 16 weeks, and mitochondrial function and liver damage were assessed. Exposure of liver cells to saturated FFAs resulted in mitochondrial depolarization, cytochrome c release, and increased ROS production. Lysosomal permeabilization and cathepsin B redistribution into the cytoplasm occurred several hours prior to mitochondrial dysfunction. Either pharmacological or genetic inhibition of cathepsin B preserved mitochondrial function. Finally, cathepsin B inactivation protected mitochondria, decreased oxidative stress, and attenuated hepatic injury in vivo.
These data strongly suggest excessive accumulation of saturated FFAs in liver cells directly induce mitochondrial dysfunction and oxidative stress. Our data further suggest this process is dependent on lysosomal disruption and activation of cathepsin B.
线粒体功能受损在很大程度上被认为是导致非酒精性脂肪性肝病（NAFLD）疾病进展的核心异常。然而，NAFLD中线粒体功能障碍的分子机制仍知之甚少。本研究探讨了肝细胞中游离脂肪酸（FFA）过度积累对线粒体功能的影响以及溶酶体-线粒体轴在脂毒性中的作用。将原代小鼠肝细胞、HepG2和McNtcp.24细胞用不同浓度、不同饱和度的FFA处理长达24小时。通过实时成像、细胞色素c重新分布和活性氧（ROS）生成监测线粒体功能。确定了溶酶体和线粒体通透性改变的时间关系。通过基因和药理学方法抑制溶酶体蛋白酶组织蛋白酶B的活性。将组织蛋白酶B基因敲除小鼠和野生型动物置于高碳水化合物饮食16周，评估线粒体功能和肝损伤情况。肝细胞暴露于饱和FFA会导致线粒体去极化、细胞色素c释放和ROS生成增加。溶酶体通透性改变和组织蛋白酶B重新分布到细胞质中发生在线粒体功能障碍前数小时。对组织蛋白酶B的药理学或基因抑制均可保留线粒体功能。最后，组织蛋白酶B失活可保护线粒体、降低氧化应激并减轻体内肝损伤。
这些数据有力地表明，肝细胞中饱和FFA的过度积累直接诱导线粒体功能障碍和氧化应激。我们的数据进一步表明，这一过程依赖于溶酶体破坏和组织蛋白酶B的激活。
