Impaired Interleukin-15 Signaling via BMPR2 Loss Drives Natural Killer Cell Deficiency and Pulmonary Hypertension.

BACKGROUND: Natural killer (NK) cell impairment is a feature of pulmonary arterial hypertension (PAH) and contributes to vascular remodeling in animal models of disease. Although mutations in BMPR2, the gene encoding the BMP (bone morphogenetic protein) type-II receptor, are strongly associated with PAH, the contribution of BMPR2 loss to NK cell impairment remains unknown. We explored the impairment of IL (interleukin)-15 signaling, a central mediator of NK cell homeostasis, as both a downstream target of BMPR2 loss and a contributor to the pathogenesis of PAH. METHODS: The expression, trafficking, and secretion of IL-15 and IL-15Rα (interleukin 15 α-type receptor) were assessed in human pulmonary artery endothelial cells, with or without BMPR2 silencing. NK cell development and IL-15/IL-15Rα levels were quantified in mice bearing a heterozygous knock-in of the R899X-BMPR2 mutation (bmpr2+/R899X). NK-deficient Il15-/- rats were exposed to the Sugen/hypoxia and monocrotaline models of PAH to assess the impact of impaired IL-15 signaling on disease severity. RESULTS: BMPR2 loss reduced IL-15Rα surface presentation and secretion in human pulmonary artery endothelial cells via impaired trafficking through the trans-Golgi network. bmpr2+/R899X mice exhibited a decrease in NK cells, which was not attributable to impaired hematopoietic development but was instead associated with reduced IL-15/IL-15Rα levels in these animals. Il15-/- rats of both sexes exhibited enhanced disease severity in the Sugen/hypoxia model, with only male Il15-/- rats developing more severe PAH in response to monocrotaline. CONCLUSIONS: This work identifies the loss of IL-15 signaling as a novel BMPR2-dependent contributor to NK cell impairment and pulmonary vascular disease.

Endothelial BMPR2 Loss Drives a Proliferative Response to BMP (Bone Morphogenetic Protein) 9 via Prolonged Canonical Signaling.

OBJECTIVE: Pulmonary arterial hypertension is a disease of proliferative vascular occlusion that is strongly linked to mutations in BMPR2-the gene encoding the BMPR-II (BMP [bone morphogenetic protein] type II receptor). The endothelial-selective BMPR-II ligand, BMP9, reverses disease in animal models of pulmonary arterial hypertension and suppresses the proliferation of healthy endothelial cells. However, the impact of BMPR2 loss on the antiproliferative actions of BMP9 has yet to be assessed. Approach and Results: BMP9 suppressed proliferation in blood outgrowth endothelial cells from healthy control subjects but increased proliferation in blood outgrowth endothelial cells from pulmonary arterial hypertension patients with BMPR2 mutations. This shift from growth suppression to enhanced proliferation was recapitulated in control human pulmonary artery endothelial cells following siRNA-mediated BMPR2 silencing, as well as in mouse pulmonary endothelial cells isolated from endothelial-conditional Bmpr2 knockout mice (Bmpr2EC-/-). BMP9-induced proliferation was not attributable to altered metabolic activity or elevated TGFß (transforming growth factor beta) signaling but was linked to the prolonged induction of the canonical BMP target ID1 in the context of BMPR2 loss. In vivo, daily BMP9 administration to neonatal mice impaired both retinal and lung vascular patterning in control mice (Bmpr2EC+/+) but had no measurable effect on mice bearing a heterozygous endothelial Bmpr2 deletion (Bmpr2EC+/-) and caused excessive angiogenesis in both vascular beds for Bmpr2EC-/- mice. CONCLUSIONS: BMPR2 loss reverses the endothelial response to BMP9, causing enhanced proliferation. This finding has potential implications for the proposed translation of BMP9 as a treatment for pulmonary arterial hypertension and suggests the need for focused patient selection in clinical trials.