The hypoxia-mimetic agent cobalt chloride induces the expression of intrinsic BMP antagonist noggin independent /INS;of the /INS;endothelin pathway

Abstract

Background: Mutations in the bone morphogenetic protein type 2 receptor (BMPR2) are responsible for themajority of cases of heritable pulmonary arterial hypertension (PAH). Low penetrance of BMPR2 mutation in heritable PAH, however, suggests the involvement of second-hit elements in the pathogenesis of PAH. We have previously reported that treatment with endothelin-1 induced in vitro increased expression of noggin, an intrinsic bone morphogenetic protein antagonist, in human pulmonary artery smooth muscle cells (PA-SMCs). Moreover, chronic exposure to hypoxia is a well-known inducer of remodeling in pulmonary arteries. However, the potential link between chronic hypoxia exposure and noggin expression has not been elucidated. Aims: We hypothesized that hypoxia could induce, in PA-SMCs, the expression of endothelin-1 which could secondarily result in the upregulation of noggin. Methods and results: Cultured human PA-SMCs were treated for 3, 6, 24, and 48 h with the hypoxiamimetic agent, cobalt chloride (CoCl2; 100 μM) and gene expressions of preproendothelin-1 (ppET1), endothelin converting enzyme-1 (ECE1) and noggin were then evaluated by QRT-PCR. CoCl2 treatment progressively increased the expressions of ppET1 and noggin, with maximal response after 24 h and 48 h of stimulation respectively. Gene expression of ECE1 was not changed. After pretreatment or not with a non-selective endothelin receptor antagonist (bosentan), we stimulated PA-SMCs with CoCl2 for 5 h. Gene expression of noggin significantly increased after CoCl2 treatment and this reaction was not changed by pretreatment with bosentan. Conclusions: Noggin, an intrinsic bone morphogenetic protein antagonist, was upregulated by CoCl2, independent of hypoxia-induced endothelin-1 pathway at earlier timing (5 h).