Guangdong Provincial Key Laboratory of Food, Nutrition, and Health, School of Public Health, Sun Yat-sen University (Northern Campus), Guangzhou, Guangdong Province, China.
J Biol Chem. 2011 Apr 1;286(13):11119-31. doi: 10.1074/jbc.M110.203323. Epub 2011 Feb 4.
Hepatocytes show endoplasmic reticulum (ER) stress when exposed to lipotoxic stimuli such as hyperlipidemia. Recent work has revealed that AMP- activated protein kinase (AMPK) can mitigate ER stress. In this study we investigated the impact of AMPK on lipid-induced ER stress in hepatocytes and its underlying molecular mechanism. Treatment with 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR), an AMPK agonist, or overexpression of a constitutively active AMPK significantly suppressed lipid-mediated ER stress, leading to marked protection against lipotoxic death. Incubation with AICAR and constitutively active AMPK overexpression induced the expression of an ER-associated chaperone, 150-kDa oxygen-regulated protein (ORP150), at both the mRNA and protein levels in hepatocytes. Forkhead box O1 (FOXO1) was identified as the critical transcription factor regulating ORP150 expression because silencing FOXO1 expression prevented the induction of ORP150 expression by AMPK. In contrast, overexpression of FOXO1-ADA promoted ORP150 expression in hepatocytes. FOXO1 bound directly to the ORP150 promoter, which was enhanced in the presence of AICAR. AMPK acts to activate FOXO1 by increasing its deacetylation and transcriptional activity via silent mating type information regulation 2 homolog 1 (SIRT1). Furthermore, AICAR infusion enhanced ORP150 expression, resulting in the marked amelioration of hepatic ER stress and apoptosis in C57BL/6J mice fed a high fat diet. Our results reveal a novel mechanism by which AMPK regulates ER homeostasis in hepatocytes and suggest that AMPK has a protective role against hypercholesterolemia-related liver damage.
肝细胞在暴露于脂毒性刺激物（如高血脂）时会显示内质网（ER）应激。最近的研究表明，AMP 激活的蛋白激酶（AMPK）可以减轻 ER 应激。在这项研究中，我们研究了 AMPK 对肝细胞中脂质诱导的 ER 应激的影响及其潜在的分子机制。用 5-氨基咪唑-4-甲酰胺核糖核苷酸（AICAR），一种 AMPK 激动剂，或过表达组成型激活的 AMPK 处理，可显著抑制脂质介导的 ER 应激，从而显著防止脂毒性死亡。用 AICAR 和组成型激活的 AMPK 过表达孵育，可在肝细胞中诱导 ER 相关伴侣 150-kDa 氧调节蛋白（ORP150）的表达，在 mRNA 和蛋白质水平上均有显著提高。叉头框 O1（FOXO1）被鉴定为调节 ORP150 表达的关键转录因子，因为沉默 FOXO1 表达可阻止 AMPK 诱导 ORP150 表达。相反，FOXO1-ADA 的过表达可促进肝细胞中 ORP150 的表达。FOXO1 直接与 ORP150 启动子结合，在存在 AICAR 的情况下，该启动子增强。AMPK 通过增加沉默交配型信息调节 2 同源物 1（SIRT1）的去乙酰化和转录活性来激活 FOXO1。此外，AICAR 输注可增强 ORP150 的表达，从而显著改善高脂肪饮食喂养的 C57BL/6J 小鼠的肝 ER 应激和凋亡。我们的研究结果揭示了 AMPK 调节肝细胞 ER 动态平衡的新机制，并表明 AMPK 在对抗高胆固醇血症相关的肝损伤中具有保护作用。
