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-15R alpha (interleukin 15 alpha-type receptor) were assessed in human pulmonary artery endothelial cells, with or without BMPR2 silencing. NK cell development and IL-15/IL-15R alpha 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-15R alpha 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-15R alpha 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.