Hypoxia‐induced Pulmonary Hypertension Upregulates Enos and TGF‐β Contributing to Sex‐linked Differences in BMPR2+/R899X Mutant Mice

Dysfunctional bone morphogenetic protein receptor 2 (BMPR2) and endothelial nitric oxide synthase (eNOS) have been largely implicated in the pathogenesis of pulmonary arterial hypertension (PAH); a life-threatening cardiopulmonary disease. Although the incident of PAH is about three times higher in females, males with PAH usually have a worse prognosis, which seems to be dependent on estrogen-associated cardiac and vascular protection. Here, we evaluated whether hypoxia-induced pulmonary hypertension (PH) in humanized BMPR2(+/R899X) loss-of-function mutant mice contributes to sex-associated differences observed in PAH by altering eNOS expression and inducing expansion of hyperactivated TGF-beta-producing pulmonary myofibroblasts. To test this hypothesis, male and female wild-type (WT) and BMPR2(+/R899X) mutant mice were kept under hypoxic or normoxic conditions for 4 weeks, and then right ventricular systolic pressure (RVSP) and right ventricular hypertrophy (RVH) were measured. Chronic hypoxia exposure elevated RVSP, inducing RVH in both groups, with a greater effect in BMPR2(+/R899X) female mice. Lung histology revealed no differences in vessel thickness/area between sexes, suggesting RVSP differences in this model are unlikely to be in response to sex-dependent vascular narrowing. On the other hand, hypoxia exposure increased vascular collagen deposition, the number of TGF-beta-associated alpha-SMA-positive microvessels, and eNOS expression, whereas it also reduced caveolin-1 expression in the lungs of BMPR2(+/R899X) females compared to males. Taken together, this brief report reveals elevated myofibroblast-derived TGF-beta and eNOS-derived oxidants contribute to pulmonary microvascular muscularization and sex-linked differences in incidence, severity, and outcome of PAH.