Estrogen action has been shown in animal models and to an extent in humans to mitigate various forms of cardiovascular disease, including hypertension, atherosclerosis, and ischemia/reperfusion injury. Estrogen acts at its receptors, ERalpha and ERbeta. There is also strong data that estrogen prevents the development of cardiac hypertrophy, fibrosis, and progression to heart failure, particularly in human-relevant animal models when started early in the course of disease. These effects of estrogen are mainly through actions at the ERbeta isoform, especially from the membrane-localized pool that stimulates signal transduction. One potential target of ERbeta is the important transcription factor, KLF15 that is proposed to have anti- hypertrophic properties. Using a relevant model for human disease, involving low dose Angiotensin II (Ang II) infusion over 4 weeks in ovariectomized, wild type and ERbeta KO female mice will occur. The impact of AngII and estradiol (E2) or an ERbeta-specific agonist, ?-LGND2, is used to determine effects on the expression of this transcription factor in the left cardiac ventricle, postulating that membrane E2/ERbeta signaling restores the expression of KLF15 that is reduced by AngII alone infusion. Male mice will also be investigated. Also, in- vitro studies using cultured, freshly isolated neonatal rat cardiomyocytes will determine whether AngII reduces, while E2 or BLGND restores nuclear localization of KLF15, and interaction with important hypertrophy- controlling nuclear proteins such as myocardin, SRF, GATA-2 and MEF, and recruit epigenetic regulators including HDACs 2 and 5, and p300. We propose this regulates important myocyte effector genes/protein expression and myocyte function that will be determined. Whether nuclear ER??contributes will be determined in 2 cell models of cell-selective ER? pool loss. An important cardiovascular protein and its myocyte cell membrane receptor, apelin and APJ respectively, are known to mitigate the development of cardiac hypertrophy, fibrosis, and disease progression. It may be that membrane ERbeta signaling and actions require this complex and activation of this system at the abundance and functional levels. This will be determined in-vitro and in-vivo, the latter using ovariectomized, wild type, ERbeta KO, and cardiomyocyte-specific APJ KO mice (Cre-Flox). This model will definitively implicate the role of APJ in these cells for the action of E2/ERbeta to mitigate in-vivo AngII effects on blood pressure and cardiac hypertrophy, fibrosis, and cardiac functional compromise. Male mice will also be used. Two compelling issues in considering whether a proprietary ERbeta agonist could eventually be used in humans are whether ERbeta activation 1) reverses established disease, and 2) whether this might be relevant to male mammals. The 4 week model of AngII infusion +/- E2 or BLGND will be done in ovariectomized female WT and ERbeta KO mice, where AngII is started 2 weeks earlier than estrogenic compound administration, sufficient to induce cardiac changes. This tests whether this early disease state can be reversed by E2 or BLGND. Also, treatment and prevention studies of cardiac disease from AngII infusion will be carried out in male mice treated with E2 or BLGND including normalization of AngII-induced hypertension. Whether ER? contributes to the anti-hypertensive effects of E2 will also be determined using ER? KO mice.
From the Women?s Health Initiative clinical trial in 25,000 post-menopausal women results show that in women starting hormones within 10 years of the menopause, estrogen replacement menopause clearly reduces the occurrence of heart attacks. Others and we showed that estrogen reduces heart enlargement in rodents that results from poorly controlled high blood pressure in humans. We propose that estrogen prevents high blood pressure and blocks heart enlargement that compromises the function of the heart leading to heart failure. Estrogen acting through one of the estrogen receptors may prevent this in women disposed to developing heart enlargement. By giving a very selective drug that stimulates the estrogen receptor in the heart, but does not stimulate breast or uterine cancer, post-menopausal women and perhaps men (including veterans) may benefit.
