Regulation of Cpt1b Gene Transcription in liver and muscle cell lines

Abstract

Regulation of mitochondrial fatty acid oxidation resides at the outer membrane enzyme carnitine palmitoyltransferase‐1 (Cpt1). The Cpt1b isoform is expressed in skeletal muscle cells while liver cells express Cpt1a. Fatty acids stimulate expression of Cpt1 genes through PPARa response elements (PPRE). We found a similar expression spectrum of Cpt1b‐luciferase activities in C2C12, L6 and H4IIE cell lines. WY‐14,643 (WY) stimulated expression in H4IIE cells, but not in C2C12 or L6 cells. Measurement of PPARa mRNA by real‐time PCR indicated the muscle cell lines had low levels of PPARa as well as PGC1a. After cotransfection of L6 cells with PPARa and PGC1a expression vectors, luciferase activity was increased by PPARa and additionally enhanced by PGC1a. WY further stimulated expression in cells with PPARa overexpression. Mutation of the PPRE in the ‐391/+80 Cpt1b construct eliminated WY stimulation of transcription, but co‐transfection with the PGC1a still increased luciferase activity in the mutant construct. Results show that activation through PPRE is highly dependent on PPARa binding, but PGC1a can stimulate through PPARa and independently of PPARa.