Fatty acids activate transcription of the muscle carnitine palmitoyltransferase I gene in cardiac myocytes via the peroxisome proliferator-activated receptor α

Abstract

To explore the gene regulatory mechanisms involved in the metabolic control of cardiac fatty acid oxidative flux, the expression of muscle-type carnitine palmitoyl-transferase I (M-CPT I) was characterized in primary cardiac myocytes in culture following exposure to the long-chain mono- unsaturated fatty acid, oleate. Oleate induced steady-state levels of M-CPT I mRNA 4.5-fold. The transcription of a plasmid construct containing the human M-CPT I gene promoter region fused to a luciferase gene reporter transfected into cardiac myocytes, was induced over 20-fold by long-chain fatty acid in a concentration-dependent and fatty acyl-chain length-specific manner. The M- CPT I gene promoter fatty acid response element (FARE-1) was localized to a hexameric repeat sequence located between 775 and 763 base pairs upstream of the initiator codon. Cotransfection experiments with expression vectors for the peroxisome proliferator-activated receptor α (PPARα) demonstrated that FARE-1 is a PPARα response element capable of conferring oleate-mediated transcriptional activation to homologous or heterologous promoters. Electrophoretic mobility shift assays demonstrated that PPARα bound FARE-1 with the retinoid X receptor α. The expression of M-CPT I in hearts of mice null for PPARα was approximately 50% lower than levels in wild-type controls. Moreover, a PPARα activator did not induce cardiac expression of the M-CPT I gene in the PPARα null mice. These results demonstrate that long-chain fatty acids regulate the transcription of a gene encoding a pivotal enzyme in the mitochondrial fatty acid uptake pathway in cardiac myocytes and define a role for PPARα in the control of myocardial lipid metabolism.