Abstract 3952: Transcriptional Regulation of the Peroxisome Proliferator-Activated Receptor γ Coactivator-1α
Healthy adult cardiomyocytes derive >60% of their energy from fatty acid oxidation. The nuclear receptor subfamily of peroxisome proliferator-activated receptors (PPAR) regulate cardiac metabolic gene expression by transcriptional activation. Reduced expression of PPARα and its co-activator, PPARγ coactivator-1α (PGC-1α), has been shown in human and animal studies of heart failure and ischemia, concomitant with reduced fatty acid use. PGC-1α regulates mitochondrial biogenesis and energy metabolic gene expression, thus elucidating the transcriptional regulation of PGC-1α gene expression is important for understanding metabolic gene expression in cardiac health and disease. We hypothesized that estrogen related receptor ERRα, which also plays a role in cardiac energy metabolism, regulates expression of PGC-1α by direct interaction with its gene promoter. To examine this possibility we employed a PGC-1α promoter-luciferase reporter in transient transfection assays of COS-7 cells. ERRα significantly transactivated the PGC-1α promoter. By in silico analysis we identified a putative ERRα binding site, mutation of which attenuated transactivation of the promoter by ERRα. Binding of ERRα to the identified sequence was confirmed by electrophoretic mobility shift assay using biotin labeled oligonucleotides incubated with nuclear extract from ERRα-transfected COS-7 cells. To confirm binding of ERRα to the PGC-1α promoter in vivo, we performed a chromatin immunoprecipitation (ChIP) assay in neonatal rat cardiomyocytes using an anti-ERRα antibody. We successfully obtained a PCR amplicon from co-immunoprecipitated genomic DNA using primers encompassing the region of the putative ERRα binding site. Quantitative real-time PCR revealed reduced expression of PGC-1α mRNA in hypoxic neonatal rat cardiomyocytes compared to normoxia. ChIP demonstrated that ERRα binding to the PGC-1α promoter was unaltered, but histone acetylation of this region decreased. Our data identify ERRα as a novel regulator of PGC-1α gene expression, and suggest that promoter deacetylation in hypoxia plays a role in reduced PGC-1α expression. These results reveal a new mechanism that may contribute to energetic derangement in the heart during ischemia and/or failure.