Department of Medicine, University of Florida College of Medicine, Jacksonville, Florida, USA.
Obesity (Silver Spring). 2012 Apr;20(4):721-9. doi: 10.1038/oby.2011.323. Epub 2011 Oct 20.
Obesity is associated with increased serum endocannabinoid (EC) levels and decreased high-density lipoprotein cholesterol (HDLc). Apolipoprotein A-I (apo A-I), the primary protein component of HDL is expressed primarily in the liver and small intestine. To determine whether ECs regulate apo A-I gene expression directly, the effect of the obesity-associated ECs anandamide and 2-arachidonylglycerol on apo A-I gene expression was examined in the hepatocyte cell line HepG2 and the intestinal cell line Caco-2. Apo A-I protein secretion was suppressed nearly 50% by anandamide and 2-arachidonoylglycerol in a dose-dependent manner in both cell lines. Anandamide treatment suppressed both apo A-I mRNA and apo A-I gene promoter activity in both cell lines. Studies using apo A-I promoter deletion constructs indicated that repression of apo A-I promoter activity by anandamide requires a previously identified nuclear receptor binding site designated as site A. Furthermore, anandamide-treatment inhibited protein-DNA complex formation with the site A probe. Exogenous over expression of cannabinoid receptor 1 (CBR1) in HepG2 cells suppressed apo A-I promoter activity, while in Caco-2 cells, exogenous expression of both CBR1 and CBR2 could repress apo A-I promoter activity. The suppressive effect of anandamide on apo A-I promoter activity in Hep G2 cells could be inhibited by CBR1 antagonist AM251 but not by AM630, a selective and potent CBR2 inhibitor. These results indicate that ECs directly suppress apo A-I gene expression in both hepatocytes and intestinal cells, contributing to the decrease in serum HDLc in obese individuals.
肥胖与血清内源性大麻素（EC）水平升高和高密度脂蛋白胆固醇（HDLc）降低有关。载脂蛋白 A-I（apo A-I）是 HDL 的主要蛋白成分，主要在肝脏和小肠中表达。为了确定 EC 是否直接调节 apo A-I 基因表达，研究了肥胖相关的 EC 大麻素和 2-花生四烯酰甘油对 HepG2 肝细胞系和 Caco-2 肠细胞系中 apo A-I 基因表达的影响。在两种细胞系中，大麻素和 2-花生四烯酰甘油以剂量依赖的方式几乎抑制了 apo A-I 蛋白分泌近 50%。大麻素处理抑制了两种细胞系中 apo A-I mRNA 和 apo A-I 基因启动子活性。使用 apo A-I 启动子缺失构建体的研究表明，大麻素对 apo A-I 启动子活性的抑制需要先前鉴定的核受体结合位点，称为位点 A。此外，大麻素处理抑制了与位点 A 探针的蛋白质-DNA 复合物形成。在 HepG2 细胞中过表达大麻素受体 1（CBR1）抑制了 apo A-I 启动子活性，而在 Caco-2 细胞中，CBR1 和 CBR2 的外源表达均可抑制 apo A-I 启动子活性。大麻素对 Hep G2 细胞中 apo A-I 启动子活性的抑制作用可被 CBR1 拮抗剂 AM251 抑制，但不能被选择性和有效的 CBR2 抑制剂 AM630 抑制。这些结果表明，ECs 直接抑制肝和肠细胞中 apo A-I 基因表达，导致肥胖个体血清 HDLc 降低。
