Hormonal and nutritional regulation of the M‐CPTI gene expression in a transgenic mice model in vivo

Abstract

To study the molecular basis of tissue –specific and hormonally regulated expression of the muscle carnitine palmitoyltransferase I (M-CPTI) gene in vivo, we generated lines of transgenic mice carrying 1.1-kb of the 5′-flanking region (-1194 to +54) of the human heart M-CPTI gene fused to a chloramphenicol acetyltransferase (CAT) reporter gene. The reporter gene was strongly expressed in tissues that normally express high levels of M-CPTI mRNA, which include heart and skeletal muscle, but not in liver and kidney. We also examined the hormonal and nutritional regulation of the M-CPTI (1.1)-CAT reporter gene in the transgenic mice. When the mice were fasted for 48 h, CAT activity and mRNA levels increased by more than 2-fold in heart and skeletal muscle, but not liver or kidney. To examine the effect of insulin deficiency on the M-CPTI (1.1) promoter-CAT reporter gene, we made the mice diabetic by streptozotocin (SZ)-treatment. In the SZ-diabetic transgenic mice, there was a 2 to 3-fold increase in CAT activity and CAT mRNA levels driven by the M-CPTI promoter in heart and skeletal muscle. Insulin treatment of the SZ-diabetic transgenic mice decreased CAT activity and mRNA levels in heart and muscle to that observed with the control insulin sufficient transgenic mice. Feeding a high fat diet for several weeks increased CAT activity and mRNA levels by 2 to 4-fold in heart and skeletal muscle but not liver or kidney of the transgenic mice compared to the control transgenic mice that were fed a low fat diet. Overall, the 1.1-kb 5′-flanking region of the human heart M-CPTI gene that contains the fatty acid response element was shown to be necessary for the tissue-specific hormonal and dietary regulation of the M-CPTI gene expression characteristics similar to those of the endogenous M-CPTI gene. (supported by NIH & AHA).