Abstract 446: Estrogen and Estrogen Receptor Protect the Female Heart From Ischemia/reperfusion Injury by Increasing the Activity of Mitochondrial p38β and MnSOD

Abstract

Background: We have previously demonstrated a novel in-vitro mechanism of how 17β-estradiol (E2) protects cultured neonatal cardiomyocytes from H/R by identifying a functionally active mitochondrial pool of p38β and E2-driven upregulation of manganese superoxide (MnSOD) activity via p38β. This protective mechanism leads to E2-mediated suppression of reactive oxygen species and attenuates apoptosis. However, little is known about these cytoprotective actions of E2 in the heart after myocardial I/R in vivo . The aim of this study is to determine whether the cardioprotective effects of E2 involve the interaction of mitochondrial p38β and MnSOD in the heart in vivo . Methods and Results: Left coronary ligation for 45 min and reperfusion for 24 hr was used to produce myocardial I/R injury in ovariectomized female mice with or without E2 pellet (0.1 mg/pellet). TTC staining showed that the infarct size was approximately 30% of the left ventricle at risk in untreated mice after I/R. The infarct size was reduced by more than half in the E2-treated group. Western blotting showed that the phosphorylation of p38β (p-p38β) in the heart homogenate was upregulated by E2, compared to the untreated mice, while the total p38β protein level was not altered. Mitochondrial p-p38β isolated from the hearts decreased after I/R, while E2 administration attenuated this effect. The total protein level of MnSOD decreased after I/R, regardless of E2 treatment. However, the MnSOD activity was normalized by E2 treatment, suggesting that E2 specifically increased the enzymatically active subset of MnSOD. Physical interaction between mitochondrial p38β and MnSOD was found by using co-immunoprecipitation from the hearts of the studied animals. Estrogen receptor (ER) α, β and double knockout female mice exhibited larger infarct size after I/R injury than that of WT mice while no significant difference was observed between the knockout mice. Loss of both ERs led to reduced activity of mitochondrial p38β and MnSOD at the baseline and after myocardial I/R. Conclusion: This work offers in-vivo evidence to our previously detailed mechanistic data that the protective effects of estrogen and ER against cardiac I/R injury involve the regulation of MnSOD activity via mitochondrial p38β.