Inhibition of Apolipoprotein A-I Gene Expression by Obesity-Associated Endocannabinoids

• Published in: Obesity (Silver Spring, Md.) Md.), 2012-04, Vol.20 (4), p.721-729
• Main Authors: Haas, Michael J., Mazza, Angela D., Wong, Norman C.W., Mooradian, Arshag D.
• Format: Article
• Language: English
• Subjects: Apolipoprotein A-I - antagonists & inhibitors; Apolipoprotein A-I - genetics; Apolipoprotein A-I - metabolism; Arachidonic Acids - pharmacology; Blotting, Northern; Blotting, Western; Cannabinoid Receptor Modulators - metabolism; Cannabinoid Receptor Modulators - pharmacology; Endocannabinoids; Gene Expression Profiling; Gene Expression Regulation; Glycerides - pharmacology; Hep G2 Cells; Hepatocytes - drug effects; Hepatocytes - metabolism; Humans; Lipoproteins, HDL - drug effects; Lipoproteins, HDL - metabolism; Liver - drug effects; Liver - metabolism; Polyunsaturated Alkamides - pharmacology; RNA, Messenger - metabolism
• ISSN: 1930-7381; 1930-739X
• DOI: 10.1038/oby.2011.323

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.