Bone morphogenetic proteins induce apoptosis in human pulmonary vascular smooth muscle cells

1 Division of Pulmonary and Critical Care Medicine, Department of Medicine, 2 Department of Pathology, and 3 Division of Cardiothoracic Surgery, Department of Surgery, University of California, San Diego, California 92103-8382 Submitted 16 August 2002 ; accepted in final form 28 April 2003 Pulmonary vascular medial hypertrophy in primary pulmonary hypertension (PPH) is mainly caused by increased proliferation and decreased apoptosis in pulmonary artery smooth muscle cells (PASMCs). Mutations of the bone morphogenetic protein (BMP) receptor type II (BMP-RII) gene have been implicated in patients with familial and sporadic PPH. The objective of this study was to elucidate the apoptotic effects of BMPs on normal human PASMCs and to examine whether BMP-induced effects are altered in PASMCs from PPH patients. Using RT-PCR, we detected six isoforms of BMPs (BMP-1 through -6) and three subunits of BMP receptors (BMP-RIa, -RIb, and -RII) in PASMCs. Treatment of normal PASMCs with BMP-2 or -7 (100-200 nM, 24-48 h) markedly increased the percentage of cells undergoing apoptosis. The BMP-2-mediated apoptosis in normal PASMCs was associated with a transient activation or phosphorylation of Smad1 and a marked downregulation of the antiapoptotic protein Bcl-2. In PASMCs from PPH patients, the BMP-2- or BMP-7-induced apoptosis was significantly inhibited compared with PASMCs from patients with secondary pulmonary hypertension. These results suggest that the antiproliferative effect of BMPs is partially due to induction of PASMC apoptosis, which serves as a critical mechanism to maintain normal cell number in the pulmonary vasculature. Inhibition of BMP-induced PASMC apoptosis in PPH patients may play an important role in the development of pulmonary vascular medial hypertrophy in these patients. hypertension; arteries; Smad; Bcl; transforming growth factor- Address for reprint requests and other correspondence: J. X.-J. Yuan, Dept. of Medicine, UCSD Medical Center, 200 West Arbor Dr., San Diego, CA 92103-8382 (E-mail: xiyuan{at}ucsd.edu ).