Down-Regulation of Acyl-CoA Oxidase Gene Expression in Heart of Troglitazone-Treated Mice through a Mechanism Involving Chicken Ovalbumin Upstream Promoter Transcription Factor II

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Abstract
Cardiac expression of genes involved in fatty acid metabolism may suffer alterations depending on the substrate availability. We studied how troglitazone, an antidiabetic drug that selectively activates peroxisome proliferator-activated receptor γ (PPARγ), affected the expression of several of these genes. A single-day troglitazone administration (100 mg/kg/day) did not significantly alter plasma free fatty acids or triglyceride levels. In contrast, a 10-day period of troglitazone treatment significantly reduced plasma free fatty acids and triglyceride levels by 74% (P < 0.001) and 56% (P < 0.01), respectively. Cardiac mRNA expression of acyl-CoA oxidase (ACO) increased (8.3-fold induction) after 1-day troglitazone treatment, whereas after 10 days of treatment ACO mRNA levels were dramatically reduced (98% reduction, P < 0.02), as well as those of uncoupling protein 3 (41% reduction, P = 0.05). The mRNA expression of PPARα and several PPAR target genes, such as medium chain acyl-CoA dehydrogenase or fatty acid translocase were not altered after 10 days of troglitazone treatment, whereas muscle-type carnitine palmitoyltransferase I increased 1.7-fold (P < 0.05). The reduction in ACO expression in the hearts of 10-day troglitazone-treated mice was accompanied by an increase in the protein levels of the transcriptional repressor chicken ovalbumin upstream promoter transcription factor II (COUP-TF II). Electrophoretic mobility shift assays performed with COUP-TF II antibody to examine its interaction with a labeled peroxisome proliferator response element probe showed enhanced binding of COUP-TFII in cardiac nuclear extracts from troglitazone-treated mice for 10 days but not in the control nuclear extracts. Overall, the findings presented here show that 10 days of troglitazone treatment decreased expression of the ACO gene through a mechanism involving the transcriptional repressor COUP-TF II.