Mutations in the gene encoding for bone morphogenetic protein receptor-2 (BMPR2) have been identified to be the inherited molecular mechanism in idiopathic pulmonary arterial hypertension (IPAH). Endothelin-1 (ET-1) is a potent vasoconstrictor and comitogen for vascular smooth muscle, which has been implicated in IPAH. The aim of this study was to investigate the effect of bone morphogenetic protein-7 (BMP7), a ligand for BMPR2 on the release of endothelin-1 by human pulmonary smooth muscle cells.

Specimens of human pulmonary artery were obtained from lung specimens from patients with normotensive lungs undergoing lung resection, from which pulmonary artery smooth muscle cells (PASMC) were cultured. Cultured smooth muscle cells from three different patients were incubated with TNF- (10ng/ml) and IFN- (10ng/ml) to induce ET-1 release as previously described (Wort et al..2002),in the absence and presence of a concentration range of BMP7 (1-100ng/ml) for 24hr. The amount of ET-1 released by the cells was measured in cell supernatant using a commercially available endothelin-1 enzyme linked immunoassay. The localization of BMP7 and BMPR2 was examined in ring sections of pulmonary artery by immunohistochemical studies.

PASMCs released detectable levels of ET-1 into the supernatant under control conditions (0.29 ± 0.02 fmol/ml). This was significantly increased in the presence of TNF- and IFN- (1.25 ±0.18 fmol/ml, p< 0.001). Co-incubation with BMP7 at 1, 10 and 100ng/ml reduced the amount of ET-1 released from these cells, reaching statistical significance at 100ng/ml (0.67±0.05 fmol/ml, p< 0.05). None of the treatments affected cell viability as determined by MTT assay. By immunohistochemical staining, BMP7 was detected strongly in endothelium and the media. BMPR2 was mainly found on endothelium but was also present in the media. Neither BMP7 nor BMPR2 were found in the adventitia.

This data provides evidence that BMP7 can inhibit the release of ET-1 from the pulmonary vessel wall, suggesting a protective role for bone morphogenetic proteins against the action of ET-1 in the pulmonary circulation. This establishes a functional link between BMP7 and the endothelin-1 system, helping in our understanding of the function of the BMPR2 and therefore how mutations in this receptor may impact upon the mechanisms that regulate pulmonary vascular tone.

Wort SJ et al., Mol Pharmacol. 2002 Nov, 62 (5): 1147-53