Estrogen receptors in the female heart and in a rat model of heart failure with preserved ejection fraction

Background: Heart failure with preserved ejection fraction (HFpEF) is more prevalent in women and declining estrogen levels after menopause may be involved in the genesis of the disease. Estrogen signaling has been found to be cardio-protective by positively affecting blood pressure and vasodilatation. HFpEF on the other hand may be underpinned by endothelial dysfunction. Despite this potential link between HFpEF and the expression of estrogen receptors alpha (ERα), beta (ERβ) and the G protein-coupled estrogen receptor (GPER), little data is currently available.

Purpose: We characterized the cardiac expression of three estrogen receptors in female body donors and subsequently analyzed them in rats with HFpEF, considering potential differences between left and right ventricle and the septum.

Methods: Hearts from six female body donors (age 78±9 years, BMI 25±6, heart weight 389±87g, post-mortem time 27±4 hours) and from obese ZSF1 rats with HFpEF (O-ZSF1, n=12) and lean healthy ZSF1 rats (L-ZSF1, n=12) at 20 weeks of age were analyzed. The manifestation of HFpEF in the rats was confirmed by echocardiography and determination of NT-proBNP by ELISA. Expression of the estrogen receptors was determined by Western Blot analysis in the left ventricle (LV), septum and right ventricle (RV). The body donors suffered from age-related congestive heart disease, while the specific presence of HFpEF was not documented.

Results: ERβ and the canonical ERα-66kDa isoform were weakly expressed in all analyzed tissues. GPER was present but unchanged. The ERα-46kDa isoform was prominent in human and rat hearts. In O-ZSF1 rats with HFpEF the ERα-46kDa expression in the LV was lower (-46%, p=0.008) compared to healthy L-ZSF1 rats. In addition, ERα-46kDa expression in LV was 2-fold higher than in septum and 5-fold higher than in RV (p<0.001). In RV and septum, no differences in ERα-46kDa expression were observed. This compartment specific expression was not observed in the human heart compartments.

Discussion and conclusion: The ERα-46kDa isoform is the most prominent estrogen receptor isoform in human and rat heart compartments. In ZSF1 rats, HFpEF manifestation is associated with an LV-specific decrease in ERα-46kDa expression, whereas the RV is unaffected. The ERα-46kDa isoform was found to repress the transcriptional activity of the classical ERα-66kDa isoform and to be an acute regulator of endothelial NO synthase in response to estrogen. Thus, altered ERα-46kDa expression in the LV may have detrimental consequences for left ventricular NO production and gene regulation and may represent a novel, targetable HFpEF pathomechanism.