Abstract 284: Ovariectomy Exacerbates Mitochondrial Dysfunction, Oxidative Stress and Fibrosis to Cause Diastolic Dysfunction

Heart failure with preserved ejection fraction, characterized by diastolic dysfunction (DD) is most common in post-menopausal women, suggesting a link with estrogen (E2). However, the underlying mechanisms are not well understood. In this study we tested how ovariectomy (OVX)-induced E2-deficiency exacerbates DD. Female C57BL6/J mice (12 weeks old) underwent a sham or OVX surgery, and were administered either normal drinking water or L-N G -Nitroarginine methyl ester (L-NAME, 0.3 mg/ml in 1% NaCl solution) in the drinking water and Angiotensin II (AngII, 1.2 mg/kg/day) via subcutaneous osmotic pumps for 5 weeks to induce DD. Subsets of the OVX-DD mice were treated with E2, E2-receptor (ER) α agonist PPT, ERβ agonist DPN or G-protein ER-1 agonist G1. Echocardiography revealed reduced left ventricular (LV) internal diameter, LV volume, cardiac output but increased LV posterior wall thickness in OVX-DD mice compared with sham-DD mice. However, ejection fractions and fractional shortening were normal in all groups. Doppler studies showed E/A ratios dramatically suppressed and E/e’ ratios increased in mice treated with L-NAME+AngII, with larger changes in OVX mice. Extensive fibrosis was seen in OVX-DD hearts than sham-DD hearts. ADP-supported cardiac mitochondrial function with pyruvate-malate was moderately reduced in OVX-DD mice along with greater production of reactive oxygen species. Ionoptix studies revealed delayed relaxation but maintained contraction in cardiomyocytes isolated from OVX-DD mice, similar to effects of low-dose oligomycin in control mice. These data suggest that E2 deficiency is associated with impaired mitochondrial function to cause small decreases in ATP formation, which impair diastolic relaxation but not contraction. Treatment with E2, PPT, DPN and G1 reduced E/e’ ratios in OVX-DD mice, with the greatest effects of G1. Treatment of mice with L-NAME in this model excludes the previously described action of G1 through nitric oxide. In conclusion, OVX exacerbates mitochondrial dysfunction, oxidative stress and fibrosis in non-ischemic HF, leading to exacerbated DD. These may be some of the mechanisms by which E2 protects the myocardium in females. Activation of GPER1 offers a novel therapeutic target for DD after menopause.