Bone morphogenetic protein 4 enhances canonical transient receptor potential expression, store-operated Ca2+ entry, and basal i in rat distal pulmonary arterial smooth muscle cells
Recent advances have identified an important role of bone morphogenetic protein 4 (BMP4) in pulmonary vascular remodeling, yet the underlying mechanisms remain largely unexplored. We have previously found that Ca2+ influx through store-operated calcium channels (SOCC), which are mainly thought to be composed of canonical transient receptor potential (TRPC) proteins, likely contribute to the pathogenic development of chronic hypoxic pulmonary hypertension. In this study, we investigated the effect of BMP4 on expression of TRPC and store-operated Ca2+ entry (SOCE) in pulmonary arterial smooth muscle cells (PASMCs). Real-time quantitative PCR and Western blotting revealed that treatment with BMP4 (50 ng/ml, 60 h) increased TRPC1, TRPC4, and TRPC6 mRNA and protein expression in growth-arrested rat distal PASMCs. Moreover, in comparison to vehicle control, cells treated with BMP4 also exhibited enhanced SOCE, and elevated basal intracellular calcium concentration ([Ca2+]i) as determined by fluorescent microscopy using the Ca2+ indicator Fura-2 AM. Perfusing cells with Ca2+-free Krebs-Ringer bicarbonate solution (KRBS) or KRBS containing SOCC antagonists SKF-96365 or NiCl2 attenuated the increases in basal [Ca2+]i caused by BMP4. Specific knockdown of BMP4 by small interference RNA significantly decreased the mRNA and protein expression of TRPC1, TRPC4, and TRPC6 and reduced SOCE and basal [Ca2+]i in serum-stimulated PASMCs. We conclude that BMP4 regulates calcium signaling in PASMCs likely via upregulation of TRPC expression, leading to enhanced SOCE and basal [Ca2+]i in PASMCs, and by this mechanism contributes to pulmonary vascular remodeling during pulmonary arterial hypertension.