Department of Biochemistry and Molecular Biology, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, People's Republic of China.
J Physiol Biochem. 2011 Jun;67(2):153-63. doi: 10.1007/s13105-010-0058-y. Epub 2010 Dec 22.
The reported data indicate that oleic acid (OA) decreases cholesterol absorption. To explore the underlying mechanisms, the effects of OA on the expression of cholesterol transport-related proteins (NPC1L1, ABCG5/8, ACAT2, MTP) and the unfolded protein response (UPR) pathway were studied in CaCo-2 enterocytes by incubating CaCo-2 cells with taurocholate micelles or taurocholate micelles containing different concentrations of OA (0.25-1.0 mM). We show that OA effectively induces XBP1 mRNA splicing, a key component of the UPR signaling, and the expression of BiP and mature ATF6 proteins in a concentration-dependent manner, leading to the induction of endoplasmic reticulum (ER) stress and activation of the UPR. Interestingly, OA decreases NPC1L1 expression in a dose-dependent manner while it has no effects on ABCG5 and MTP mRNA level or SREBP-2, ABCG8, and ACAT2 protein level. In CaCo-2 cells treated with 1.0 mM OA, both the NPC1L1 mRNA level and the NPC1L1 protein expression in brush-border membrane fractions were decreased by 39% and 37%, respectively (P < 0.01). A dose of 1 mM dithiothreitol (DTT), a positive control for ER stress induction, also decreases NPC1L1 mRNA and protein expression by 27% and 23%, respectively (P < 0.05). Furthermore, 4-phenyl-butyric acid, an UPR inhibitor, blocks OA- and DTT-induced reduction on NPC1L1 mRNA and protein levels. The results suggest that OA down-regulates NPC1L1 mRNA and protein expression via the induction of the UPR, which may play an important role in reducing intestinal cholesterol absorption.
报告的数据表明，油酸（OA）可降低胆固醇吸收。为了探索其潜在机制，我们用牛磺胆酸钠微胶束或含不同浓度 OA（0.25-1.0 mM）的牛磺胆酸钠微胶束孵育 CaCo-2 细胞，研究了 OA 对胆固醇转运相关蛋白（NPC1L1、ABCG5/8、ACAT2、MTP）表达和未折叠蛋白反应（UPR）途径的影响。结果表明，OA 能有效诱导 UPR 信号关键组分 XBP1 mRNA 剪接，以及 BiP 和成熟 ATF6 蛋白的表达，呈浓度依赖性，导致内质网（ER）应激和 UPR 的激活。有趣的是，OA 呈剂量依赖性降低 NPC1L1 表达，而对 ABCG5 和 MTP mRNA 水平或 SREBP-2、ABCG8 和 ACAT2 蛋白水平无影响。在经 1.0 mM OA 处理的 CaCo-2 细胞中，NPC1L1 mRNA 水平和刷状缘膜部分 NPC1L1 蛋白表达分别降低了 39%和 37%（P<0.01）。作为 ER 应激诱导的阳性对照，1.0 mM 二硫苏糖醇（DTT）也使 NPC1L1 mRNA 和蛋白表达分别降低了 27%和 23%（P<0.05）。此外，UPR 抑制剂 4-苯基丁酸阻断了 OA 和 DTT 诱导的 NPC1L1 mRNA 和蛋白水平降低。结果表明，OA 通过诱导 UPR 下调 NPC1L1 mRNA 和蛋白表达，这可能在降低肠道胆固醇吸收中起重要作用。
