Background

Pulmonary hypertension (PH) is characterized by progressive remodeling of the pulmonary arteries, leading to increased right ventricular load and eventually right heart failure. PH and right heart failure are associated with a poor prognosis, however, this is not therapeutically targeted yet. Aldosterone and the mineralocorticoid receptor (MR) are key drivers of cardiovascular disease and there is a growing body of evidence suggesting a role in pulmonary hypertension. Thus, the aim of this study was to investigate the impact of cell type-specific deletion of MR on pulmonary vascular remodeling and right ventricular function.

Methods and results

Wildtype mice were exposed to chronic hypoxia for six weeks to induce pulmonary hypertension. Hypoxia increased plasma aldosterone levels about 2-fold (hypoxia 1069.05 ± 161.62 pg/ml vs. normoxia 538.39 ± 45.25 pg/ml, P<0.05). Treatment with the MR antagonist eplerenone (EPL) attenuated the development of pulmonary vascular remodelling (media area/total vessel area hypoxia EPL 42.31 ± 1.4 % vs. hypoxia CTRL 48.86 ± 2.01%, P<0.05) and hypertension (PAT/PET hypoxia EPL 0.32 ± 0.01 vs. hypoxia CTRL 0.27 ± 0.02, P<0.01) and improved RV function (TAPSE hypoxia EPL 0.84 ± 0.02 mm vs. hypoxia CTRL 0.60 ± 0.04 mm, P<0.001). In contrast, aldosterone infusion via osmotic minipumps induced pulmonary vascular remodeling similar to chronic hypoxia.

To examine the impact of MR on different cell types, we created four different mouse models with cell type-specific MR deletion in smooth muscle cells, endothelial cells, macrophages, or monocytes and exposed them to chronic hypoxia. MR deletion from endothelial cells fully recapitulated the beneficial effects of eplerenone on pulmonary vascular remodelling (media area/total vessel area hypoxia KO 34.19 ± 2.09% vs. hypoxia WT 39.34 ± 4.69%, P<0.01), hypertension (PAT/PET hypoxia KO 0.30 ± 0.05 vs. hypoxia WT 0.24 ± 0.04, P<0.001) and improved RV function (TAPSE hypoxia KO 0.90 ± 0.09 mm vs. hypoxia WT 0.69 ± 0.10 mm, P<0.001). In contrast, MR deletion from other cell types had no detectable effect on pulmonary vascular remodeling or right ventricular function.

To identify potential downstream mediators of MR related to pulmonary hypertension, we performed RNAseq from isolated MR-deficient and –wildtype pulmonary endothelial cells. Among the differentially expressed genes were apelin receptor (Aplnr, 2.0-fold up), tenascin XB (Tnxb, 2.0-fold down), early growth response protein 1 (Egr1, 2.7-fold down), and plasminogen activator inhibitor-1 (PAI-1, Serpine1, 1.6-fold down).

Conclusion

We show here that the beneficial effect of MR antagonists on PH and right ventricular failure is related to inhibition of MR in endothelial cells, independent from MR in smooth muscle cells, fibroblasts, or macrophages. Potential downstream mediators of MR in pulmonary endothelial cells were identified by RNAseq. Our results further support the clinical evaluation of MR antagonists in pulmonary hypertension.