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Rationale: Pulmonary endothelial permeability contributes to the high-permeability pulmonary edema that characterizes acute respiratory distress syndrome. Circulating BMP9 (bone morphogenetic protein 9) is emerging as an important regulator of pulmonary vascular homeostasis. Objectives:To determine whether endogenous BMP9 plays a role in preserving pulmonary endothelial integrity and whether loss of endogenous BMP9 occurs during LPS challenge. Methods: A BMP9-neutralizing antibody was administrated to healthy adult mice, and lung vasculature was examined. Potential mechanisms were delineated by transcript analysis in human lung endothelial cells. The impact of BMP9 administration was evaluated in a murine acute lung injury model induced by inhaled LPS. Levels of BMP9 were measured in plasma from patients with sepsis and from endotoxemic mice. Measurements and Main Results: Subacute neutralization of endogenous BMP9 in mice (N = 12) resulted in increased lung vascular permeability (P = 0.022), interstitial edema (P = 0.0047), and neutrophil extravasation (P = 0.029) compared with IgG control treatment (N = 6). In pulmonary endothelial cells, BMP9 regulated transcriptome pathways implicated in vascular permeability and cell-membrane integrity. Augmentation of BMP9 signaling in mice (N = 8) prevented inhaled LPS-induced lung injury (P = 0.0027) and edema (P < 0.0001). In endotoxemic mice (N = 12), endogenous circulating BMP9 concentrations were markedly reduced, the causes of which include a transient reduction in hepatic BMP9 mRNA expression and increased elastase activity in plasma. In human patients with sepsis (N = 10), circulating concentratons of BMP9 were also markedly reduced (P < 0.0001). Conclusions: Endogenous circulating BMP9 is a pulmonary endothelial-protective factor, downregulated during inflammation. Exogenous BMP9 offers a potential therapy to prevent increased pulmonary endothelial permeability in lung injury.

Schistosomiasis is a major cause of pulmonary arterial hypertension (PAH). Mutations in the bone morphogenetic protein type-II receptor (BMPR-II) are the commonest genetic cause of PAH.To determine whether Bmpr2(+/-) mice are more susceptible to schistosomiasis-induced pulmonary vascular remodeling.Wild-type (WT) and Bmpr2(+/-) mice were infected percutaneously with Schistosoma mansoni. At 17 weeks postinfection, right ventricular systolic pressure and liver and lung egg counts were measured. Serum, lung and liver cytokine, pulmonary vascular remodeling, and liver histology were assessed.By 17 weeks postinfection, there was a significant increase in pulmonary vascular remodeling in infected mice. This was greater in Bmpr2(+/-) mice and was associated with an increase in egg deposition and cytokine expression, which induced pulmonary arterial smooth muscle cell proliferation, in the lungs of these mice. Interestingly, Bmpr2(+/-) mice demonstrated dilatation of the hepatic central vein at baseline and postinfection, compared with WT. Bmpr2(+/-) mice also showed significant dilatation of the liver sinusoids and an increase in inflammatory cells surrounding the central hepatic vein, compared with WT. This is consistent with an increase in the transhepatic passage of eggs.This study has shown that levels of BMPR-II expression modify the pulmonary vascular response to chronic schistosomiasis. The likely mechanism involves the increased passage of eggs to the lungs, caused by altered diameter of the hepatic veins and sinusoids in Bmpr2(+/-) mice. Genetically determined differences in the remodeling of hepatic vessels may represent a new risk factor for PAH associated with schistosomiasis.

Schistosomiasis is considered to be the most common worldwide cause of pulmonary hypertension. At present there is no well-characterized animal model to study the pathobiology of this important condition.To develop a mouse model of schistosomiasis, characterize the extent of pulmonary vascular remodeling, and determine the potential role of inflammatory cytokines.Mice (C57/Bl6) were infected transcutaneously with a high dose (approximately 75-100 cercariae) or a low dose (approximately 30 cercariae) of Schistosoma mansoni, and the development of lung and liver pathology was studied in the subacute (high-dose) and chronic (low-dose) settings.In the subacute setting, mice showed few eggs in the lungs and no evidence of pulmonary vascular remodeling. In contrast, chronically infected animals had a much greater lung egg burden and developed marked pulmonary vascular remodeling accompanied by perivascular inflammation from 12 weeks onwards. In addition, we observed the presence of plexiform-like lesions in these mice. Lung egg burden correlated with both liver egg burden and right ventricular (RV) index in the chronic group, although significant RV hypertrophy was lacking. Plasma Th1 and Th2 cytokines increased with time in the chronic group and correlated with the degree of pulmonary vascular remodeling.This study provides evidence for extensive pulmonary vascular remodeling, despite the absence of RV hypertrophy, in a mouse model of schistosomiasis, including the formation of plexiform-like lesions. Inflammatory cytokines and lung egg burden may contribute to vascular lesion formation.

Severe pulmonary arterial hypertension (PAH) is characterized by the formation of plexiform lesions and concentric intimal fibrosis in small pulmonary arteries. The origin of cells contributing to these vascular lesions is uncertain. Endogenous endothelial progenitor cells are potential contributors to this process.To determine whether progenitors are involved in the pathobiology of PAH.We performed immunohistochemistry to determine the expression of progenitor cell markers (CD133 and c-Kit) and the major homing signal pathway stromal cell-derived factor-1 and its chemokine receptor (CXCR4) in lung tissue from patients with idiopathic PAH, familial PAH, and PAH associated with congenital heart disease. Two separate flow cytometric methods were employed to determine peripheral blood circulating numbers of angiogenic progenitors. Late-outgrowth progenitor cells were expanded ex vivo from the peripheral blood of patients with mutations in the gene encoding bone morphogenetic protein receptor type II (BMPRII), and functional assays of migration, proliferation, and angiogenesis were undertaken. measurements and main results: There was a striking up-regulation of progenitor cell markers in remodeled arteries from all patients with PAH, specifically in plexiform lesions. These lesions also displayed increased stromal cell-derived factor-1 expression. Circulating angiogenic progenitor numbers in patients with PAH were increased compared with control subjects and functional studies of late-outgrowth progenitor cells from patients with PAH with BMPRII mutations revealed a hyperproliferative phenotype with impaired ability to form vascular networks.These findings provide evidence of the involvement of progenitor cells in the vascular remodeling associated with PAH. Dysfunction of circulating progenitors in PAH may contribute to this process.

Mutations in bone morphogenetic protein receptor type II (BMPR-II) underlie most cases of heritable pulmonary arterial hypertension (PAH). However, disease penetrance is only 20-30%, suggesting a requirement for additional triggers. Inflammation is emerging as a key disease-related factor in PAH, but to date there is no clear mechanism linking BMPR-II deficiency and inflammation.To establish a direct link between BMPR-II deficiency, a consequentially heightened inflammatory response, and development of PAH.We used pulmonary artery smooth muscle cells from Bmpr2(+/-) mice and patients with BMPR2 mutations and compared them with wild-type controls. For the in vivo model, we used mice heterozygous for a null allele in Bmpr2 (Bmpr2(+/-)) and wild-type littermates.Acute exposure to LPS increased lung and circulating IL-6 and KC (IL-8 analog) levels in Bmpr2(+/-) mice to a greater extent than in wild-type controls. Similarly, pulmonary artery smooth muscle cells from Bmpr2(+/-) mice and patients with BMPR2 mutations produced higher levels of IL-6 and KC/IL-8 after lipopolysaccharide stimulation compared with controls. BMPR-II deficiency in mouse and human pulmonary artery smooth muscle cells was associated with increased phospho-STAT3 and loss of extracellular superoxide dismutase. Chronic lipopolysaccharide administration caused pulmonary hypertension in Bmpr2(+/-) mice but not in wild-type littermates. Coadministration of tempol, a superoxide dismutase mimetic, ameliorated the exaggerated inflammatory response and prevented development of PAH.This study demonstrates that BMPR-II deficiency promotes an exaggerated inflammatory response in vitro and in vivo, which can instigate development of pulmonary hypertension.

Schistosomiasis is the most common worldwide cause of pulmonary arterial hypertension. The anti-schistosome drug praziquantel has been shown to reverse the liver fibrosis associated with Schistosoma mansoni in mice.We sought to determine whether praziquantel reverses established pulmonary vascular remodeling and pulmonary hypertension in a mouse model of S. mansoni.Mice were infected percutaneously with S. mansoni. At 17 weeks after infection mice were either killed or received two doses of praziquantel or vehicle by oral gavage. Treated mice were studied at 25 weeks after infection.Vehicle-treated mice demonstrated significant increases in right ventricular systolic pressures (RVSP) and right ventricular hypertrophy (RVH) at 25 weeks, accompanied by pulmonary vascular remodeling. The degree of vascular remodeling correlated with proximity to granulomas. The elevation of RVSP and RVH at 25 weeks was dependent on the presence of eggs in the lung. Praziquantel eliminated the production of eggs in feces and led to clearance of eggs from the lung and to a lesser extent from liver. Praziquantel prevented the rise in RVSP and RVH seen in vehicle-treated mice and reversed established pulmonary vascular remodeling. Praziquantel significantly reduced lung mRNA expression of IL-13, IL-8, and IL-4, but did not reduce serum cytokine levels.The development of pulmonary hypertension associated with S. mansoni infection can be prevented by praziquantel, and established vascular remodeling can be reversed. The mechanism involves clearance of lung eggs and reduced local expression of lung cytokines.