Sexually dimorphic role of estrogen receptor α in preserving right ventricular endothelial integrity

Right ventricular (RV) function and adaptation to afterload increase determine survival in pulmonary hypertension (PH). RV adaptation in PH is sexually dimorphic and more preserved in females, mediated by protective estrogen receptor α (ERα) signaling in cardiomyocytes. However, the effects of ERα on RV endothelial cells (RVECs), a critical mediator of RV homeostasis and adaptation, are unknown. We hypothesized that ERα exerts sexually dimorphic pro-angiogenic effects on RVECs in vitro and promotes RV vascularization in vivo. Compared to cells isolated from wild-type animals, RVECs from male and female rats with an ERα loss-of-function mutation (ERα^Mut) showed reduced ability to form pseudo-vascular networks and migrate. RVECs from female ERα^Mut rats demonstrated increased apoptosis. In a PH model induced by monocrotaline (MCT), female ERα^Mut rats exhibited increased RV hypertrophy and reduced RV capillary density before (10 days) and at the time of established PH (28 days). Capillary rarefaction was associated with increased RVEC apoptosis, and, as identified by single-nucleus RNA-sequencing, by a net loss of the endocardial RVEC sub-population. Differentially expressed gene analysis and pathway analysis identified that capillary and endocardial RVECs from female MCT-PH ERα^Mut rats demonstrated decreased expression of migration pathways and increased expression of apoptosis pathways. These findings reveal a sex-specific endothelial-intrinsic role of ERα that is essential for angiogenesis in the RV under both homeostatic and pathological conditions. This effect appears to stem from the enhanced survival and migration capacity of capillary and endocardial RVEC. Collectively, our results identify ERα as a potential target for developing sex-specific RV-directed therapies in PH.