Apolipoprotein D Transgenic Mice Develop Hepatic Steatosis through Activation of PPAR? and Fatty Acid Uptake

Labrie, Marilyne; Lalonde, Simon; Najyb, Ouafa; Thiery, Maxime; Daneault, Caroline; Des Rosiers, Chrisitne; Rassart, Eric; Mounier, Catherine

To understand the link between apoD and PPARγ over-expression and activation, we evaluated the potential role of apoD as an AA transporter, one of the main ligands of PPARγ. We used the human hepatocarcinoma HepG2 cell line as a well-characterized model for the study of hepatic lipid metabolism. Cells were transfected with a construct containing the cDNA of human apoD. No apoD was detected in cells either untransfected or transfected with an empty vector. Transfection with the H-apoD cDNA showed a strong expression of the protein ( Fig 6A) . We next co-transfected the H-apoD cDNA construct with a construct containing five peroxisomes proliferator-activator receptor elements (PPRE) linked to a luciferase reporter gene. Thereafter, cells were incubated with 7 μM of AA in presence or absence of apoD. At this concentration, AA does not induce any cellular toxicity [53] but a slight decrease in apoD expression (Fig 6A) . Over-expression of apoD increased PPARγ transcriptional activity (3.7 fold, Fig 6B) . Addition of AA alone increased PPARγ transcriptional activity to a similar extent (3.9-fold). Very interestingly, a combination of AA and apoD over-expression showed a very strong synergistic transactivation effect on PPARγ transcriptional activity (approximately 9-fold) (Fig 6B) .