Xie Ping, Zhu Hongling, Jia Lin, Ma Yinyan, Tang Weiqing, Wang Youlin, Xue Bingzhong, Shi Hang, Yu Liqing
Department of Pathology Section on Lipid Sciences, Wake Forest University School of Medicine, Medical Center Boulevard, Winston-Salem, NC 27157, USA; Department of Biochemistry, Wake Forest University School of Medicine, Medical Center Boulevard, Winston-Salem, NC 27157, USA; Institute of Medicinal Plant Development, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing 100193, China.
Department of Animal and Avian Sciences, University of Maryland, College Park, MD 20742, USA.
Atherosclerosis. 2014 Dec;237(2):609-17. doi: 10.1016/j.atherosclerosis.2014.09.036. Epub 2014 Oct 17.
The correlation between intestinal cholesterol absorption values and plasma low-density lipoprotein-cholesterol (LDL-C) levels remains controversial. Niemann-Pick-C1-Like 1 (NPC1L1) is essential for intestinal cholesterol absorption, and is the target of ezetimibe, a cholesterol absorption inhibitor. However, studies with NPC1L1 knockout mice or ezetimibe cannot definitively clarify this correlation because NPC1L1 expression is not restricted to intestine in humans and mice. In this study we sought to genetically address this issue.
We developed a mouse model that lacks endogenous (NPC1L1) and LDL receptor (LDLR) (DKO), but transgenically expresses human NPC1L1 in gastrointestinal tract only (DKO/L1(IntOnly) mice). Our novel model eliminated potential effects of non-intestinal NPC1L1 on cholesterol homeostasis. We found that human NPC1L1 was localized at the intestinal brush border membrane of DKO/L1(IntOnly) mice. Cholesterol feeding induced formation of NPC1L1-positive vesicles beneath this membrane in an ezetimibe-sensitive manner. Compared to DKO mice, DKO/L1(IntOnly) mice showed significant increases in cholesterol absorption and blood/hepatic/biliary cholesterol. Increased blood cholesterol was restricted to very low-density lipoprotein (VLDL) and LDL fractions, which was associated with increased secretion and plasma levels of apolipoproteins B100 and B48. Additionally, DKO/L1(IntOnly) mice displayed decreased fecal cholesterol excretion and hepatic/intestinal expression of cholesterologenic genes. Ezetimibe treatment virtually reversed all of the transgene-related phenotypes in DKO/L1(IntOnly) mice.
Our findings from DKO/L1(IntOnly) mice clearly demonstrate that NPC1L1-mediated cholesterol absorption is a major determinant of blood levels of apolipoprotein B-containing atherogenic lipoproteins, at least in mice.
肠道胆固醇吸收值与血浆低密度脂蛋白胆固醇（LDL-C）水平之间的相关性仍存在争议。尼曼-匹克C1样1蛋白（NPC1L1）对肠道胆固醇吸收至关重要，且是胆固醇吸收抑制剂依泽替米贝的作用靶点。然而，使用NPC1L1基因敲除小鼠或依泽替米贝进行的研究无法明确阐明这种相关性，因为NPC1L1在人类和小鼠中的表达并不局限于肠道。在本研究中，我们试图通过基因手段解决这一问题。
我们构建了一种小鼠模型，该模型缺乏内源性（NPC1L1）和低密度脂蛋白受体（LDLR）（双敲除，DKO），但仅在胃肠道中转基因表达人NPC1L1（DKO/L1（IntOnly）小鼠）。我们的新模型消除了非肠道NPC1L1对胆固醇稳态的潜在影响。我们发现人NPC1L1定位于DKO/L1（IntOnly）小鼠的肠道刷状缘膜。胆固醇喂养以依泽替米贝敏感的方式诱导该膜下NPC1L1阳性小泡的形成。与DKO小鼠相比，DKO/L1（IntOnly）小鼠的胆固醇吸收以及血液/肝脏/胆汁胆固醇水平显著升高。血液胆固醇升高仅限于极低密度脂蛋白（VLDL）和LDL部分，这与载脂蛋白B100和B48的分泌增加及血浆水平升高有关。此外，DKO/L1（IntOnly）小鼠的粪便胆固醇排泄以及胆固醇生成基因的肝脏/肠道表达降低。依泽替米贝治疗几乎逆转了DKO/L1（IntOnly）小鼠所有与转基因相关的表型。
我们从DKO/L1（IntOnly）小鼠获得的研究结果清楚地表明，至少在小鼠中，NPC1L1介导的胆固醇吸收是含载脂蛋白B的致动脉粥样硬化脂蛋白血液水平的主要决定因素。
