Abstract 292: Isoform-Specific Expression of Estrogen-Related Receptors Regulates Cardiomyocyte Metabolic Adaptation to Oxidative Stress
In the ischemic heart, metabolic adaptation of cardiomyocytes exposed to prolonged hypoxia is critical to sustain myocardial energy production. Metabolic gene expression is regulated by Estrogen-Related Receptor (ERR) transcription factors and Peroxisome Proliferator-Activated Receptor γ Coactivator-1 (PGC-1) co-activators. ERRs do not require ligand to achieve an active conformation and regulate an array of target genes involved in myocardial energy metabolism. These studies aim to determine the regulatory mechanisms governing expression of ERR isoforms (ERRα and ERRβ) in cardiomyocytes undergoing oxidative stress. We hypothesize that metabolic energy production in myocardium initially adapts to hypoxia by inducing transient ERRβ expression, and maintains this compensatory expression through induction of sustained ERRα expression.
Adult feline cardiomyocytes in primary culture were electrically stimulated to contract continuously at 1 Hz under normoxia (21% [O2]), hypoxia (0.5% [O2]), or hypoxia followed by reoxygenation. Expression of ERR, PGC-1 and target genes was measured by QRT-PCR (n≥5). QRT-PCR arrays were used to screen for prospective target genes.
In response to 24 hours of hypoxia, mRNA levels increased for ERRα (3-fold by 24 hours), ERRβ (11-fold by 12 hours), PGC-1α (16-fold by 24 hours) and PGC-1β (8-fold by 24 hours). Subsequent reoxygenation for 24 hours decreased ERRβ, PGC-1α and PGC-1β mRNA levels to that of normoxia controls. However, reoxygenation did not markedly decrease (∼25%; 0.7 of 3.0-fold) ERRα mRNA levels. Cytochrome C Oxidase Subunit VIc (Cox6c) and Fatty Acid Binding Protein 3 (Fabp3) were identified as potential ERRα target genes in adult cardiomyocytes based on correlation of expression. Moreover, hypoxia-induced increases in Cox6c and Fabp3 mRNA levels were partially blocked by treatment with XCT-790, an inhibitor of ERRα activity.
We conclude that hypoxia and subsequent reoxygenation elicit isoform-specific changes in ERR and PGC-1 mRNA expression in adult cardiomyocytes. This observed regulation of expression for ERR isoforms and their target genes may play a critical role in metabolic adaptation to oxidative stress.
- © 2012 by American Heart Association, Inc.