Abstract 17230: BMP9 Regulates Endothelin-1 Gene Transcription in Cooperation With TGF-β Signaling

Abstract

Pulmonary arterial hypertension (PAH) is characterized by abnormal pulmonary vasoreactivity and pulmonary angiopathy, leading to progressively increased pulmonary resistance, right heart failure and high mortality. The mechanisms of PAH have not been fully elucidated, although dysregulated bone morphogenetic protein (BMP) signaling due to loss-of-function mutations in the gene encoding the BMP type II receptor (BMPRII) are implicated in heritable PAH. It has been recently reported that BMP9, a BMPRII ligand, regulates transcription of the potent vasoconstrictor and smooth muscle mitogen endothelin-1 (ET-1), an important mediator of PAH. BMP9 functions as a circulating vascular quiescence factor that promotes endothelial survival while inhibiting angiogenesis. We hypothesized that altered BMP signaling in pulmonary vascular endothelium may affect the regulation of ET-1 and thereby contribute to the pathophysiology of PAH. We found that stimulation of cultured human and murine lung microvascular endothelial cells with BMP9 activates both canonical BMP and TGF-β pathways via their respective effector molecules, SMAD1/5/8 and SMAD2/3. BMP9-induced transcription of ET-1 appeared to require coordinated activation of both BMP and TGF-β signaling pathways, based on the finding that ET-1 gene transcription was inhibited by selective small molecule inhibitors of BMP or TGF-β receptor kinases, by recombinant BMP receptor ectodomains, or by siRNA-mediated suppression of BMP or TGF-β type I receptor expression. In addition, functional analysis of the human ET-1 gene promoter revealed the presence of distinct cis -regulatory elements involved in BMP9- versus TGF-β-mediated activation of ET-1 gene transcription. Mutational inactivation of a novel BMP-responsive regulatory element, as well as known TGF-β-responsive elements, abolished ET-1 gene promoter activity in response to BMP9, underscoring further the cooperative nature of BMP and TGF-β signaling in ET-1 regulation. These results suggest that perturbation of BMP signaling may alter the regulation of ET-1 in the endothelium, impact endothelial and vascular homeostasis, and thus contribute to the pathogenesis of PAH.