Malhi Harmeet, Bronk Steven F, Werneburg Nathan W, Gores Gregory J
Mayo Clinic College of Medicine, Rochester, Minnesota 55905, USA.
J Biol Chem. 2006 Apr 28;281(17):12093-101. doi: 10.1074/jbc.M510660200. Epub 2006 Feb 27.
Elevated serum free fatty acids (FFAs) and hepatocyte lipoapoptosis are features of non-alcoholic fatty liver disease. However, the mechanism by which FFAs mediate lipoapoptosis is unclear. Because JNK activation is pivotal in both the metabolic syndrome accompanying non-alcoholic fatty liver disease and cellular apoptosis, we examined the role of JNK activation in FFA-induced lipoapoptosis. Multiple hepatocyte cell lines and primary mouse hepatocytes were treated in culture with monounsaturated fatty acids and saturated fatty acids. Despite equal cellular steatosis, apoptosis and JNK activation were greater during exposure to saturated versus monounsaturated FFAs. Inhibition of JNK, pharmacologically as well as genetically, reduced saturated FFA-mediated hepatocyte lipoapoptosis. Cell death was caspase-dependent and associated with mitochondrial membrane depolarization and cytochrome c release indicating activation of the mitochondrial pathway of apoptosis. JNK-dependent lipoapoptosis was associated with activation of Bax, a known mediator of mitochondrial dysfunction. As JNK can activate Bim, a BH3 domain-only protein capable of binding to and activating Bax, its role in lipoapoptosis was also examined. Small interfering RNA-targeted knock-down of Bim attenuated both Bax activation and cell death. Collectively the data indicate that saturated FFAs induce JNK-dependent hepatocyte lipoapoptosis by activating the proapoptotic Bcl-2 proteins Bim and Bax, which trigger the mitochondrial apoptotic pathway.
血清游离脂肪酸（FFA）升高和肝细胞脂肪凋亡是非酒精性脂肪性肝病的特征。然而，FFA介导脂肪凋亡的机制尚不清楚。由于JNK激活在伴随非酒精性脂肪性肝病的代谢综合征和细胞凋亡中都起着关键作用，我们研究了JNK激活在FFA诱导的脂肪凋亡中的作用。用单不饱和脂肪酸和饱和脂肪酸在培养物中处理多种肝细胞系和原代小鼠肝细胞。尽管细胞脂肪变性程度相同，但与单不饱和FFA相比，暴露于饱和FFA期间细胞凋亡和JNK激活更为明显。通过药理学和遗传学方法抑制JNK可减少饱和FFA介导的肝细胞脂肪凋亡。细胞死亡依赖于半胱天冬酶，并与线粒体膜去极化和细胞色素c释放有关，表明凋亡的线粒体途径被激活。JNK依赖性脂肪凋亡与Bax的激活有关，Bax是线粒体功能障碍的已知介质。由于JNK可以激活Bim，一种仅含BH3结构域的蛋白，能够结合并激活Bax，因此也研究了其在脂肪凋亡中的作用。靶向Bim的小干扰RNA敲低减弱了Bax激活和细胞死亡。总体而言，数据表明饱和FFA通过激活促凋亡Bcl-2蛋白Bim和Bax诱导JNK依赖性肝细胞脂肪凋亡，这两种蛋白触发线粒体凋亡途径。
