17β-estradiol prevents cardiac diastolic dysfunction by stimulating mitochondrial function: A preclinical study in a mouse model of a human hypertrophic cardiomyopathy mutation

Objective: We investigated the effect of ovariectomy (OVX) and 17 beta-estradiol (E2) replacement on both mitochondrial and myocardial function in cTnT-Q92 transgenic mice generated by cardiac-restricted expression of a human hypertrophic cardiomyopathy (HCM) mutation. Methods: The cTnT-Q92 mice were ovariectomized at twenty weeks of age and were treated with either placebo (OVX group) or E2 (OVX+E2 group) for twelve weeks before being sacrificed. Wild-type and cTnT-Q92 female mice receiving sham operation were used as controls. Indices of diastolic function such as mitral early (E) and late (A) inflow as well as isovolumic relaxation time (IVRT) were measured by echocardiography. A Clark-type electrode was used to detect respiratory control, and ATP levels were determined at the mitochondrial level using HPLC. Key components related to mitochondrial energy metabolism, such as peroxisome proliferator-activated receptor alpha (PPAR alpha), PPAR gamma coactivator 1 alpha (PGC-1 alpha) and nuclear respiratory factor-1 (NRF-1), were also analyzed using Western blot and RT-PCR. The levels of oxidative stress markers were determined by measuring malondialdehyde (MDA) using the thiobarbituric acid assay. Results: The cTnT-Q92 mice had impaired diastolic function compared with wild-type mice (E/A ratio, 1.39 +/- 0.04 vs. 1.21 +/- 0.01, p < 0.001; IVRT, 19.17 +/- 0.85 vs. 22.15 +/- 1.43 ms, p = 0.028). In response to ovariectomy, cardiac function further decreased compared with that observed in cTnT-Q92 mice that received the sham operation (E/A ratio, 1.15 +/- 0.04 vs. 1.21 +/- 0.01, p < 0.001; IVRT, 28.31 +/- 0.39 vs. 22.15 +/- 1.43 ms, p = 0.002). Myocardial energy metabolism, as determined by ATP levels (3.49 +/- 0.31 vs. 5.07 +/- 0.47 mu mol/g, p < 0.001), and the mitochondrial respiratory ratio (2.04 +/- 0.10 vs. 2.63 +/- 0.11, p = 0.01) also decreased significantly. By contrast, myocardial concentrations of MDA increased significantly in the OVX group, and PGC-1 alpha, PPAR alpha and NRF-1decreased significantly. E2 supplementation significantly elevated myocardial ATP levels (4.55 +/- 0.21 vs. 3.49 +/- 0.31 mu mol/g, p = 0.003) and mitochondrial respiratory function (3.93 +/- 0.05 vs. 2.63 +/- 0.11, p = 0.001); however, it reduced the MDA level (0.21 +/- 0.02 vs. 0.36 +/- 0.03 nmol/g, p < 0.001), which subsequently improved diastolic function (E/A ratio, 1.35 +/- 0.06 vs. 1.15 +/- 0.04, p < 0.001; IVRT, 18.22 +/- 1.16 vs. 28.31 +/- 0.39 ms, p = 0.007). Conclusions: Our study has shown that 17 beta-estradiol improved myocardial diastolic function, prevented myocardial energy dysregulation, and reduced myocardial oxidative stress in cTnT-Q92 mice. (C) 2014 Elsevier Ltd. All rights reserved.