Rapid Estrogen Receptor-α Activation Improves Ischemic Tolerance in Aged Female Rats through a Novel Protein Kinase Cε-Dependent Mechanism

Abstract

The effects of estrogen deficiency on the loss of cardioprotection with advancing age are complex and poorly understood. A major focus of the current study was to uncover a cardioprotective role for rapid, nongenomic estrogen receptor (ER) signaling in the aged female myocardium. We hypothesized that selective ERalpha activation in aged females would reduce infarct size in part, through reversal of age-associated reductions in mitochondrial protein kinase Cepsilon (PKCepsilon). Hearts isolated from adult (6 month old) and aged (23-24 months old) female F344 rats with ovaries removed (n = 20 per group) were subjected to ischemia/reperfusion (47 min global ischemia). Rats were injected sc with the ERalpha agonist propylpyrazole triol (PPT) or vehicle 45 min before heart isolation (5 microg/kg). Infarct size was greatest in aged vs. adult ovariectomized rats, significantly reduced by PPT, and the protection reversed by prior administration of the ER inhibitor ICI 182,780 (3 mg/kg). Increased ERalpha particulate targeting occurred after PPT in conjunction with reversal of age-related reductions in nuclear PKCepsilon, mitochondrial PKCepsilon and pAkt (P < 0.05). PPT also increased mRNA levels for the PKCepsilon anchoring protein, receptor for activated C kinase2 (RACK2; P < 0.05). Our data suggest, for the first time, that selective ERalpha activation reduces ischemic injury in the aged, estrogen-deficient heart through a mechanism involving nongenomic redistribution of ERalpha and PKCepsilon activation. A novel feed-forward transcriptional mechanism to potentially enhance PKCepsilon-RACK2 interactions was also observed. Collectively, our findings may provide key insight into developing targeted therapeutic interventions in postmenopausal women to reduce ischemia/reperfusion injury, including selective ERalpha mimetics.