Abstract
Imbalanced transforming growth factor beta (TGFβ) and bone morphogenetic protein (BMP) signaling are postulated to favor a pathological pulmonary endothelial cell (EC) phenotype in pulmonary arterial hypertension (PAH). BMP9 is shown to reinstate BMP receptor type-II (BMPR2) levels and thereby mitigate hemodynamic and vascular abnormalities in several animal models of pulmonary hypertension (PH). Yet, responses of the pulmonary endothelium of PAH patients to BMP9 are unknown. Therefore, we treated primary PAH patient-derived and healthy pulmonary ECs with BMP9 and observed that stimulation induces transient transcriptional signaling associated with the process of endothelial-to-mesenchymal transition (EndMT). However, solely PAH pulmonary ECs showed signs of a mesenchymal trans-differentiation characterized by a loss of VE-cadherin, induction of transgelin (SM22α), and reorganization of the cytoskeleton. In the PAH cells, a prolonged EndMT signaling was found accompanied by sustained elevation of pro-inflammatory, pro-hypoxic, and pro-apoptotic signaling. Herein we identified interleukin-6 (IL6)-dependent signaling to be the central mediator required for the BMP9-induced phenotypic change in PAH pulmonary ECs. Furthermore, we were able to target the BMP9-induced EndMT process by an IL6 capturing antibody that normalized autocrine IL6 levels, prevented mesenchymal transformation, and maintained a functional EC phenotype in PAH pulmonary ECs. In conclusion, our results show that the BMP9-induced aberrant EndMT in PAH pulmonary ECs is dependent on exacerbated pro-inflammatory signaling mediated through IL6.
Highlights
Progressive occlusive remodeling of the distal pulmonary vasculature is the hallmark of pulmonary arterial hypertension (PAH), a heterogenous group of deadly lung disorders clinically defined by a highly increased mean pulmonary artery pressure at rest in the absence of other causes of precapillary pulmonary hypertension (PH) [1, 2]
endothelial colony-forming cells (ECFCs) reacted to 24-h BMP9 stimulation with a median two-fold increase in BMPR2 and approximately four-fold increase in ID1 gene expression that was similar between the two donor groups (PAH vs. controls)
In PAH pulmonary artery endothelial cells (PAECs), ID1 was significantly different from controls (p = 0.007), with controls even trending towards decreased expression upon BMP9
Summary
Progressive occlusive remodeling of the distal pulmonary vasculature is the hallmark of pulmonary arterial hypertension (PAH), a heterogenous group of deadly lung disorders clinically defined by a highly increased mean pulmonary artery pressure at rest in the absence of other causes of precapillary pulmonary hypertension (PH) [1, 2]. Imbalanced TGFβ signaling is a characteristic feature in all PAH subtypes that includes loss-of-function genetic mutations in components of the bone morphogenetic protein (BMP) signaling pathway (i.e., ACVRL1, BMPR1B, BMPR2) and reduced expression of the BMP type-II receptor (BMPR2) in mutation-positive and -negative cases of PAH [9]. This shift is associated with decreased BMPdependent signaling and increased TGFβ-responsiveness in pulmonary ECs of PAH patients [10]. Novel experimental treatment efforts aim to restore BMPR2 levels and consecutive downstream signaling to reinstate the balance in TGFβ/BMP activity [11], for example, by administration of BMP ligands or agonists [12,13,14]
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