4090

SMAD5

DWFC|JV5-1|MADH5;SMAD family member 5;SMAD5;SMAD family member 5

MAD, mothers against decapentaplegic homolog 5|SMA- and MAD-related protein 5|SMAD, mothers against DPP homolog 5|mothers against decapentaplegic homolog 5|mothers against decapentaplegic, drosophila, homolog of, 5

5q31

protein-coding

Count: Smad5; 59328

Heterozygous mutations in the type II receptor for bone morphogenetic protein (BMPR-II) and dysfunction of BMPR-II have been implicated in patients with primary pulmonary hypertension (PH). To clarify the possible involvement of BMP and BMPR-II in the development of hypoxic PH, the expression of BMP-2, BMPR-II, and their downstream signals were investigated in rat lung under normal and hypoxic conditions by RT-PCR, immunoblot, and immunohistochemical methods. In rats under normal conditions, BMP-2 is localized in the endothelium of the pulmonary artery, whereas BMPR-II is abundantly expressed in the endothelium, smooth muscle cells, and adventitial fibroblasts. After 0.5 and 3 days of exposure to hypoxia, upregulation of BMP-2 was observed in the intrapulmonary arteries. The change was accompanied by activation of its downstream signaling, p38 MAPK, and Erk1/2 MAPK, and the apoptotic process, measured by caspase-3 activity and TdT-mediated dUTP nick end labeling-positive cells. In contrast, a significant decrease in the expression of BMPR-II and inactivation of p38 MAPK and caspase-3 were observed in the pulmonary vasculature after 7-21 days of hypoxia exposure. Because BMP-2 is known to inhibit proliferation of vascular smooth muscle cells and promote cellular apoptosis, disruption of BMP signaling pathway through downregulation of BMPR-II in chronic hypoxia may result in pulmonary vascular remodeling due to the failure of critical antiproliferative/differentiation programs in the pulmonary vasculature. These results suggest abrogation of BMP signaling may be a common molecular pathogenesis in the development of PH with various pathophysiological events, including primary and hypoxic PH.

RATIONALE: mutations in the bone morphogenetic protein type II receptor (BMPR-II) are responsible for the majority of cases of heritable pulmonary arterial hypertension (PAH). mutations lead to reduced Smad1/5-driven expression of inhibitor of DNA binding protein 1 (Id1) and loss of the growth suppressive effects of BMPs. The impact of existing PAH therapies on BMP signaling is lacking. OBJECTIVE: Because prostacyclin analogues are effective treatments for clinical PAH, we hypothesized that these agents enhance Smad1/Id1 signaling. METHODS AND RESULTS: Iloprost alone induced Id1 expression in human pulmonary artery smooth muscle cells (PASMCs), an effect that was independent of Smad1/5 activation but dependent on a cAMP-responsive element in the Id1 promoter. In addition, iloprost and treprostinil enhanced BMP-induced phosphorylation of Smad1/5 and Id1 expression in a cAMP-dependent manner. The mechanism involved suppression of inhibitory Smad, Smad6. Furthermore, iloprost rescued the deficit in Smad1/5 phosphorylation and Id gene expression in PASMCs harboring mutations in BMPR-II and restored growth suppression to BMP4 in mutant PASMCs. We confirmed a critical role for Id1 in PASMC proliferation. Reduced expression of Id1 was observed in concentric intimal lesions of heritable PAH cases. In the monocrotaline rat model of PAH, associated with reduced BMPR-II expression, we confirmed that treprostinil inhibited smooth muscle cell proliferation and prevented progression of PAH while enhancing Smad1/5 phosphorylation and Id1 gene expression. CONCLUSIONS: Prostacyclin analogues enhance Id1 expression in vitro and in vivo and restore deficient BMP signaling in BMPR-II mutant PASMCs.

RATIONALE: mutations in the bone morphogenetic protein type II receptor (BMPR-II) are responsible for the majority of cases of heritable pulmonary arterial hypertension (PAH). mutations lead to reduced Smad1/5-driven expression of inhibitor of DNA binding protein 1 (Id1) and loss of the growth suppressive effects of BMPs. The impact of existing PAH therapies on BMP signaling is lacking. OBJECTIVE: Because prostacyclin analogues are effective treatments for clinical PAH, we hypothesized that these agents enhance Smad1/Id1 signaling. METHODS AND RESULTS: Iloprost alone induced Id1 expression in human pulmonary artery smooth muscle cells (PASMCs), an effect that was independent of Smad1/5 activation but dependent on a cAMP-responsive element in the Id1 promoter. In addition, iloprost and treprostinil enhanced BMP-induced phosphorylation of Smad1/5 and Id1 expression in a cAMP-dependent manner. The mechanism involved suppression of inhibitory Smad, Smad6. Furthermore, iloprost rescued the deficit in Smad1/5 phosphorylation and Id gene expression in PASMCs harboring mutations in BMPR-II and restored growth suppression to BMP4 in mutant PASMCs. We confirmed a critical role for Id1 in PASMC proliferation. Reduced expression of Id1 was observed in concentric intimal lesions of heritable PAH cases. In the monocrotaline rat model of PAH, associated with reduced BMPR-II expression, we confirmed that treprostinil inhibited smooth muscle cell proliferation and prevented progression of PAH while enhancing Smad1/5 phosphorylation and Id1 gene expression. CONCLUSIONS: Prostacyclin analogues enhance Id1 expression in vitro and in vivo and restore deficient BMP signaling in BMPR-II mutant PASMCs.