Endothelin-1 alters BMP signaling to promote proliferation of pulmonary artery smooth muscle cells.

Pulmonary arterial hypertension (PAH) is characterized by abnormal outgrowth of pulmonary artery smooth muscle cells (PASMCs) of the media. Abundant expression of endothelin-1 (ET-1) and activated p38 mitogen-activated protein kinase (p38MAPK) has been observed in PAH patients. p38MAPK has been implicated in cell proliferation. An unspecified disturbance in bone morphogenetic protein (BMP) signaling may be involved in the development of PAH. Type I receptors (BMPR1A and BMPR1B) and type II receptor (BMPR2) transduce signals via two distinct pathways, i.e., canonical and non-canonical pathways, activating Smad1/5/8 and p38MAPK, respectively. BMPR1B expression was previously reported to be enhanced in the PASMCs of patients with idiopathic PAH. BMP15 binds specifically to BMPR1B. We assessed the effects of ET-1 on BMP receptor expression and cell proliferation. BMP2 increased BMPR1B expression in human PASMCs after pretreatment with ET-1 in vitro. Although BMP2 alone did not affect PASMC proliferation, BMP2 treatment after ET-1 pretreatment significantly accelerated PASMC proliferation. PH-797804, a selective p38MAPK inhibitor, abrogated this proliferation. Similarly, after ET-1 pretreatment, BMP15 significantly accelerated the proliferation of PASMCs, whereas stimulation with BMP15 alone did not. In conclusion, in PASMCs, ET-1 exposure under pathological conditions alters BMP signaling to activate p38MAPK, resulting in cell proliferation.