Changes in expression levels of genes involved in fatty acid metabolism: upregulation of all three members of the PPAR family (alpha, gamma, delta) and the newly described adiponectin receptor 2, but not adiponectin receptor 1 during neonatal cardiac development of the rat

During neonatal cardiac development, the heart changes its substrate preference from glucose to fatty acids. The aim of this study was to investigate the changes in mRNA expression levels of genes involved in the control of cardiac fatty acid metabolism in the transition from neonatal to adult life. mRNA expression levels for peroxisome proliferator activated receptor (PPAR) alpha, gamma and delta, PPARgamma co-factor 1 alpha and beta (PGC-1 alpha and beta), 9-cis retinoc-acid-activated receptor alpha, beta and gamma (RXR alpha, beta, gamma), 5'-AMP activated protein kinase (AMPK) alpha1 and alpha2, adiponectin receptor 1 and 2 (AR 1 and AR 2) were measured in heart tissue of neonatal 0-day, 7-day and 21- day old rats. mRNA expression of all three members of the PPAR family were upregulated significantly from day 0 to day 21 (alpha +117%, gamma +133%, delta +203%). In addition, m-RNA expression of all RXR isoforms increased from day 0 to day 7 (alpha +125%, beta +69%; gamma +41%). AR 2 exhibited a small but significant increase in mRNA expression (+ 46%). We were able to demonstrate for the first time that in addition to PPARalpha, also PPARgamma and delta, as well as all RXR isoforms and AR 2 are upregulated in the heart during neonatal development.