Primary pulmonary hypertension (PPH), characterized by obstruction of pre-capillary pulmonary arteries, leads to sustained elevation of pulmonary arterial pressure (mean >25 mm Hg at rest or >30 mm Hg during exercise). The aetiology is unknown, but the histological features reveal proliferation of endothelial and smooth muscle cells with vascular remodelling (Fig. 1). More than one affected relative has been identified in at least 6% of cases (familial PPH, MIM 178600). Familial PPH (FPPH) segregates as an autosomal dominant disorder with reduced penetrance and has been mapped to a locus designated PPH1 on 2q33, with no evidence of heterogeneity. We now show that FPPH is caused by mutations in BMPR2, encoding a TGF-beta type II receptor (BMPR-II). Members of the TGF-beta superfamily transduce signals by binding to heteromeric complexes of type I and II receptors, which activates serine/threonine kinases, leading to transcriptional regulation by phosphorylated Smads. By comparison with in vitro studies, identified defects of BMPR-II in FPPH are predicted to disrupt ligand binding, kinase activity and heteromeric dimer formation. Our data demonstrate the molecular basis of FPPH and underscore the importance in vivo of the TGF-beta signalling pathway in the maintenance of blood vessel integrity.

Background-Inflammation is a feature of pulmonary arterial hypertension (PAH), and increased circulating levels of cytokines are reported in patients with PAH. However, to date, no information exists on the significance of elevated cytokines or their potential as biomarkers. We sought to determine the levels of a range of cytokines in PAH and to examine their impact on survival and relationship to hemodynamic indexes. Methods and Results-We measured levels of serum cytokines (tumor necrosis factor-␣, interferon-␥ and interleukin-1␤, -2, -4, -5, -6, -8, -10, -12p70, and -13) using ELISAs in idiopathic and heritable PAH patients (nϭ60). Concurrent clinical data included hemodynamics, 6-minute walk distance, and survival time from sampling to death or transplantation. Healthy volunteers served as control subjects (nϭ21). PAH patients had significantly higher levels of interleukin-1␤, -2, -4, -6, -8, -10, and -12p70 and tumor necrosis factor-␣ compared with healthy control subjects. Kaplan-Meier analysis showed that levels of interleukin-6, 8, 10, and 12p70 predicted survival in patients. For example, 5-year survival with interleukin-6 levels of Ͼ9 pg/mL was 30% compared with 63% for patients with levels Յ9 pg/mL (Pϭ0.008). In this PAH cohort, cytokine levels were superior to traditional markers of prognosis such as 6-minute walk distance and hemodynamics. Conclusions-This study illustrates dysregulation of a broad range of inflammatory mediators in idiopathic and familial PAH and demonstrates that cytokine levels have a previously unrecognized impact on patient survival. They may prove to be useful biomarkers and provide insight into the contribution of inflammation in PAH. (Circulation. 2010;122:920-927.)

Genetic evidence implicates the loss of bone morphogenetic protein type II receptor (BMPR-II) signaling in the endothelium as an initiating factor in pulmonary arterial hypertension (PAH). However, selective targeting of this signaling pathway using BMP ligands has not yet been explored as a therapeutic strategy. We identified BMP9 as the preferred ligand for preventing apoptosis and enhancing monolayer integrity in both pulmonary arterial endothelial cells and blood outgrowth endothelial cells from subjects with PAH bearing mutations in BMPR-II. In vivo, we report the spontaneous generation of PAH in a mouse model bearing a heterozygous knock-in of a human BMPR-II mutation, R899X. Administration of BMP9 reversed established PAH in Bmpr2+/R899X mice, as well as in models of disease developed in response to either monocrotaline or VEGF receptor inhibition combined with chronic hypoxia. These results demonstrate the promise of direct enhancement of endothelial BMP signaling as a novel therapeutic strategy for PAH.

Background-Mutations in the type II receptor for bone morphogenetic protein (BMPR-II), a receptor member of the transforming growth factor-␤ (TGF-␤) superfamily, underlie many familial and sporadic cases of primary pulmonary hypertension (PPH). Methods and Results-Because the sites of expression of BMPR-II in the normal and hypertensive lung are unknown, we studied the cellular localization of BMPR-II and the related type I and II receptors for TGF-␤ by immunohistochemistry in lung sections from patients undergoing heart-lung transplantation for PPH (nϭ11, including 3 familial cases) or secondary pulmonary hypertension (nϭ6) and from unused donor lungs (nϭ4). In situ hybridization was performed for BMPR-II mRNA. Patients were screened for the presence of mutations in BMPR2. In normal lungs, BMPR-II expression was prominent on vascular endothelium, with minimal expression in airway and arterial smooth muscle. In pulmonary hypertension cases, the intensity of BMPR-II immunostaining varied between lesions but involved endothelial and myofibroblast components. Image analysis confirmed that expression of BMPR-II was markedly reduced in the peripheral lung of PPH patients, especially in those harboring heterozygous BMPR2 mutations. A less marked reduction was also observed in patients with secondary pulmonary hypertension. In contrast, there was no difference in level of staining for TGF-␤RII or the endothelial marker CD31. Conclusions-The cellular localization of BMPR-II is consistent with a role in the formation of pulmonary vascular lesions in PPH, and reduced BMPR-II expression may contribute to the process of vascular obliteration in severe pulmonary hypertension.