Liu J, Zhang Y L, Spence M J, Vestal R E, Wallace P M, Grass D S
Department of Veterans Affairs Medical Center, Boise, Idaho, USA.
Arterioscler Thromb Vasc Biol. 1997 Nov;17(11):2948-54. doi: 10.1161/01.atv.17.11.2948.
We have investigated liver LDL receptor mRNA expression in nontransgenic, human cholesteryl ester transfer protein (CETP) transgenic, and human apolipoprotein (Apo) B/CETP double transgenic mice fed a normal chow diet and a high fat, high cholesterol diet (HFHC). Three weeks of HFHC feeding increased total serum cholesterol 1.5-fold in the nontransgenic, 3.1-fold in the CETP transgenic, and 3.4-fold in the ApoB/CETP double transgenic mice. To examine the liver LDL receptor mRNA expression among the different groups of mice fed the normal diet or fed the HFHC diet, we developed a quantitative reverse-transcribed polymerase chain reaction assay in which the LDL receptor mRNA level was normalized with the beta-actin mRNA. The results show that on the normal chow diet, the LDL receptor mRNA expression levels were lower in the ApoB/CETP mice than in the nontransgenic mice and the human CETP transgenic mice. Liver LDL receptor gene expression was lower in all groups of mice fed the HFHC diet, with the lowest level of expression in the ApoB/CETP mice. Similar results were obtained by Northern blot analysis. In addition, we have previously shown that the cytokine oncostatin M (OM) increases LDL receptor gene expression in HepG2 cells. In this study, we used the ApoB/CETP mice as the model system to examine the in vivo activity of OM on liver LDL receptor gene expression. Our data show that OM increased the level of liver LDL receptor mRNA up to 80% to 90% when the animals were fed the HFHC diet. The results from these studies demonstrate that the expression of the liver LDL receptor in the ApoB/CETP mice is suppressed compared with nontransgenic mice and that the expression of the hepatic LDL receptor gene in these mice is subjected to the normal cholesterol feedback regulation. In addition, LDL receptor gene expression in these mice is also inducible by a positive regulator.
我们研究了喂食正常饲料和高脂高胆固醇饮食（HFHC）的非转基因小鼠、人胆固醇酯转运蛋白（CETP）转基因小鼠以及人载脂蛋白（Apo）B/CETP双转基因小鼠肝脏低密度脂蛋白受体（LDL受体）mRNA的表达情况。喂食HFHC三周后，非转基因小鼠的血清总胆固醇增加了1.5倍，CETP转基因小鼠增加了3.1倍，ApoB/CETP双转基因小鼠增加了3.4倍。为了检测喂食正常饮食或HFHC饮食的不同组小鼠肝脏LDL受体mRNA的表达情况，我们开发了一种定量逆转录聚合酶链反应检测方法，其中LDL受体mRNA水平用β-肌动蛋白mRNA进行标准化。结果显示，在正常饲料喂养下，ApoB/CETP小鼠的LDL受体mRNA表达水平低于非转基因小鼠和人CETP转基因小鼠。喂食HFHC饮食的所有组小鼠肝脏LDL受体基因表达均降低，其中ApoB/CETP小鼠的表达水平最低。Northern印迹分析也得到了类似结果。此外，我们之前已表明细胞因子抑瘤素M（OM）可增加HepG2细胞中LDL受体基因的表达。在本研究中，我们以ApoB/CETP小鼠作为模型系统，检测OM对肝脏LDL受体基因表达的体内活性。我们的数据表明，当给动物喂食HFHC饮食时，OM可使肝脏LDL受体mRNA水平提高80%至90%。这些研究结果表明，与非转基因小鼠相比，ApoB/CETP小鼠肝脏LDL受体的表达受到抑制，并且这些小鼠肝脏LDL受体基因的表达受到正常胆固醇反馈调节。此外，这些小鼠的LDL受体基因表达也可被一种正调节因子诱导。
