Introduction

Aldosterone and the mineralocorticoid receptor (MR) are well-studied drivers of cardiac remodeling and MR antagonists are considered standard therapy of heart failure with reduced ejection fraction (HFrEF). However, their role in heart failure with preserved ejection fraction (HFpEF) is less clear, with clinical trials reporting divergent results. Therapeutic options for HFpEF are limited, which may be due to the lack of adequate preclinical models. In this study, we evaluated the impact of MR overactivation and inhibition on the development and treatment of HFpEF in mice.

Methods and Results

To induce MR overactivation, C57Bl/6 wildtype mice received aldosterone (ALDO) via osmotic minipumps (500 µg/kg BW/d) and a high salt diet (1% NaCl with drinking water) for two weeks or high salt diet alone (CTRL). Echocardiography revealed an increase in left ventricular (LV) ejection fraction, LV hypertrophy, and impaired diastolic function (E/E’ ALDO 36.2 ± 0.5 vs. CTRL 27.8 ± 0.7, P<0.0001), and left atrial dilation, resembling a typical HFpEF phenotype. This was associated with an increased occurrence for atrial arrhythmia (ALDO 55% vs CTRL 6%, chi2 P<0.01) in aldosterone treated mice and disturbed electrical conductance ex vivo. After aldosterone treatment, LV showed moderate fibrosis (Sirius red positive are ALDO 6.1% vs CTRL 3.6%, P<0.01) and increased passive mechanical tissue stiffness as determined by nanoindentation compared to CTRL.

To investigate whether the phenotype was reversible, aldosterone treatment was stopped after two weeks and the mice were followed for six months and received either the MR antagonist eplerenone (200 mg/kg/d with chow) or control diet. Remarkably, echocardiography indicated a spontaneous recovery of the phenotype treated with control diet or the MRA, already two months after aldosterone treatment was stopped. At the endpoint of the experiment, no signs of hypertrophy or fibrosis were detectable.

To investigate the molecular mechanisms underlying the HFpEF phenotype, single nucleus RNA-Seq was performed from LA and LV tissue after two weeks of aldosterone or CTRL treatment (n = 2 per group). In LV from aldosterone treated mice, the greatest difference compared to CTRL was observed in cardiomyocytes (345 differentially expressed genes in LV/182 in LA, FDR<0.05), endothelial cells (172/282 DEGs), fibroblasts (192/150 DEGs), and in pericytes (102/96 DEGs). Comparison of differential gene expression in LV and LA cells indicated a chamber-specific response to ALDO.

Conclusion

Aldosterone-salt treatment induces LV diastolic dysfunction, atrial dilation, and arrhythmia in mice, resembling a HFpEF phenotype, that spontaneously recovers after aldosterone treatment is stopped. This model could help to identify characteristics of HFpEF patients in whom the disease is still reversible and to develop appropriate biomarkers.