Abstract 21338: Molecular Interactions of Plasma Membrane Estrogen Receptor Beta and Sulfonylurea Receptor 2
Estrogen receptors (ER) have been previously detected in many tissues and organs including the heart, to mediate the genomic and non-genomic actions of estrogen to its targets. ERβ is known to be important in cardioprotection as ERβ knockout mice suffer worse cardiac injuries in ischemia. Our prior findings on a KATP channel knockout model, in which the regulatory subunit SUR2 was disrupted (SUR2KO), showed that the mutant females displayed larger infarcts and lost the capability to be preconditioned. SUR2 expression was further found to be up-regulated by estrogen in WT ovariectomized female mice implanted with estrogen pellets. We hypothesized that estrogen modulation on cardiac KATP channel activities is through the binding of plasma membrane ERβ to SUR2. In this study, we found that ERβ expression levels were markedly up-regulated in the left ventricular tissues isolated from ∼15-wk-old WT ovariectomized females implanted with estrogen pellets (0.1 μg/g/day, 21-day release). The increase in ERβ expression was not observed in mice implanted with placebo pellets. However, ERβ levels were not significantly up-regulated in ischemic SUR2KO females implanted with estrogen pellets. A quantitative Bioluminescence Resonance Energy Transfer (BRET) Assay was used to confirm the positive interaction between ERβ and SUR2 detected by Co-IP. The ERβ gene was fused to a Renilla Luciferase luminescent reporter while the full-length SUR2A cDNA was fused to a Yellow Fluorescent Protein reporter. We detected a direct binding between ERβ and SUR2A in the presence of 100 nM 17β-estradiol (0.24±0.03, n=6) but not DMSO (vehicle, 0.03±0.01, n=6, p<0.05). In a high throughput screening of ∼4300 natural substances to search for ERβ-specific estrogenic compounds, two flavones, Cosmosiin and Liquiritigenin, were identified with 10–100 fold higher selectivity to ERβ over ERα. These results suggest that ERβ binds to SUR2A, and our future study will address whether the identified phytoestrogens can surpass synthetic estrogens to better protect a female heart.
- © 2010 by American Heart Association, Inc.