Introduction: Although estrogen-mediated cardiac protection has been appreciated for many years, most these studies utilize an approach of pre-ischemic treatment in animal experiments and the preventive usage in clinical studies. Given clinical therapeutic potential in the treatment of acute myocardial ischemia, a strategy of post-ischemic administration of estrogen will be more practical compared to pretreatment. Therefore, in this study, we aimed to evaluate the therapeutic efficacy of this new approach on myocardial protection following ischemia, and to determine its influence on distribution of cardiac mitochondrial (mito-) connexin-43 (Cx43), mito-caveolin-3 (Cav3), and mito-estrogen receptor (ER)α, considering that the interaction of ERα/Cx43/Cav3 has been shown to improve mitochondrial function in other disease models.
Methods: Langendorff perfused mouse hearts (age-matched normal females, ovariectomized females [OVX F] and OVX F with acute post-ischemic treatment of 17β-estradiol [E2, 2nM], n=4-6/group) were subjected to 25-min warm ischemia and 40-min reperfusion (I/R). The left ventricular developed pressure (LVDP) was recorded. Mitochondrial performance was analyzed by mito-H2O2 production in isolated mitochondria. The expression levels of mito-Cx43, mito-Cav3, and mito-ERα were measured by Western blotting. Co-immunoprecipitation assay was employed to identify the interaction of Cx43 or Cav3 with ERα. p<0.05=statistically significant.
Results: Female (vs. OVX F) had significantly better myocardial function and less mito-H2O2 after I/R. Post-ischemic infusion of E2 markedly improved LVDP recovery and reduced mito-H2O2 production in OVX F hearts. E2 treatment also augmented distribution of Cx43, Cav3, and ERα in myocardial mitochondria compared to untreated counterparts. Furthermore, binding of Cx43 to ERα and Cav3 to ERα was observed, indicating that Cx43 and Cav3 are interacting partners of ERα in the heart following I/R.
Conclusions: Our results represent the initial evidence that post-injury treatment with estrogen provided effective protection in I/R-induced mitochondrial dysfunction and an increased protective interaction among Cx43, Cav3 and ERα in myocardial mitochondria.