Background The pathogenic mechanisms underlying pulmonary arterial hypertension (PAH) due to schistosomiasis, one of the most common causes of pulmonary hypertension (PH) worldwide, remains unknown. We hypothesized that TGF-β signaling as a consequence of Th2 inflammation is critical for the pathogenesis of this disease. Methods and Results Mice sensitized and subsequently challenged with S. mansoni eggs developed PH associated with an increase in right ventricular systolic pressure (RVSP), thickening of the pulmonary artery media, and right ventricular hypertrophy. Rho-kinase dependent vasoconstriction accounted for about 60% of the increase in RVSP. The pulmonary vascular remodeling and PH were dependent on increased TGF-β signaling, as pharmacological blockade of the TGF-β ligand and receptor, and mice lacking Smad3 were significantly protected from Schistosoma-induced PH. Blockade of TGF-β signaling also led to a decrease in IL4 and IL13 concentrations, which drive the Th2 responses characteristic of schistosomiasis lung pathology. Lungs of patients with schistosomiasis-associated PAH have evidence of TGF-β signaling in their remodeled pulmonary arteries. Conclusions Experimental S. mansoni-induced pulmonary vascular disease relies on canonical TGF-β signaling.

Pulmonary arterial hypertension (PAH) is an obstructive disease of the precapillary pulmonary arteries. Schistosomiasis-associated PAH shares altered vascular TGF-β signalling with idiopathic, heritable and autoimmune-associated etiologies; moreover, TGF-β blockade can prevent experimental pulmonary hypertension (PH) in pre-clinical models. TGF-β is regulated at the level of activation, but how TGF-β is activated in this disease is unknown. Here we show TGF-β activation by thrombospondin-1 (TSP-1) is both required and sufficient for the development of PH in Schistosoma-exposed mice. Following Schistosoma exposure, TSP-1 levels in the lung increase, via recruitment of circulating monocytes, while TSP-1 inhibition or knockout bone marrow prevents TGF-β activation and protects against PH development. TSP-1 blockade also prevents the PH in a second model, chronic hypoxia. Lastly, the plasma concentration of TSP-1 is significantly increased in subjects with scleroderma following PAH development. Targeting TSP-1-dependent activation of TGF-β could thus be a therapeutic approach in TGF-β-dependent vascular diseases.

Rationale: The etiology of schistosomiasis-associated pulmonary arterial hypertension (PAH), a major cause of PAH worldwide, is poorly understood. Schistosoma mansoni exposure results in prototypical type-2 inflammation. Furthermore, transforming growth factor (TGF)-b signaling is required for experimental pulmonary hypertension (PH) caused by Schistosoma exposure.Objectives: We hypothesized type-2 inflammation driven by IL-4 and IL-13 is necessary for Schistosoma-induced TGF-b-dependent vascular remodeling.Methods: Wild-type, IL-4 2/2

Schistosomiasis is one of the most common causes of pulmonary arterial hypertension worldwide, but the pathogenic mechanism by which the host inflammatory response contributes to vascular remodeling is unknown. We sought to identify signaling pathways that play protective or pathogenic roles in experimental Schistosomainduced pulmonary vascular disease via whole-lung transcriptome analysis. Wild-type mice were experimentally exposed to Schistosoma mansoni ova by intraperitoneal sensitization followed by tail-vein augmentation, and the phenotype was assessed by right ventricular catheterization and tissue histology, as well as RNA and protein analysis. Whole-lung transcriptome analysis by microarray and RNA sequencing was performed, and RNA sequencing was analyzed according to two bioinformatics methods. Functional testing of the candidate IL-6 pathway was determined using IL-6 knockout mice and the signal transducers and activators of transcription protein-3 (STAT3) inhibitor S3I-201. Wild-type mice exposed to S. mansoni demonstrated increased right ventricular systolic pressure and thickness of the pulmonary vascular media. Whole-lung transcriptome analysis determined that the IL-6-STAT3-nuclear factor of activated T cells c2(NFATc2) pathway was up-regulated, as confirmed by PCR and the immunostaining of lung tissue from S. mansoni-exposed mice and patients who died of the disease. Mice lacking IL-6 or treated with S3I-201 developed pulmonary hypertension, associated with significant intima remodeling after exposure to S. mansoni. Whole-lung transcriptome analysis identified the up-regulation of the IL-6-STAT3-NFATc2 pathway, and IL-6 signaling was found to be protective against Schistosomainduced intimal remodeling.Keywords: pulmonary hypertension; schistosomiasis; gene expression profiling; Schistosomiasis is one of the most common causes of World Health Organization (WHO) Group 1 pulmonary arterial hypertension (PAH) worldwide. More than 200 million people in 74 countries are infected with Schistosoma spp., and approximately 5-15 million people chronically and recurrently infected with Schistosoma mansoni manifest PAH, a progressive and fatal pulmonary vascular disease (1-4). Schistosomiasis-associated PAH shares common pulmonary vascular pathology with other forms of PAH, including remodeling of the vascular media and intima, resulting in vascular obstruction (5). Studies aimed at identifying the pathogenesis of schistosomiasis-associated PAH have revealed key roles of T helper (Th)2-mediated inflammation, which may also participate in other forms of PAH in which inflammation likely contributes to the disease, including idiopathic PAH (IPAH), connective tissue diseaseassociated PAH (6), and hypoxic pulmonary hypertension (PH) (7).Mice exposed to S. mansoni develop experimental pulmonary hypertension (PH), which recapitulates several key features of the human disease, including increased right ventricular (RV) pressure, pulmonary vascular remodeling, and RV hypertrophy. RV hypertrophy in particular is assoc...

In severe pulmonary hypertension (SPH), prior studies have shown an increase in right ventricle (RV) uptake of glucose, but it is unclear whether there is a change in the relative utilization of fatty acids. We hypothesized that in the RV in SPH, as in left ventricular (LV) failure, there is altered substrate utilization, with increased glucose uptake and decreased fatty acid uptake. SPH was induced in rats by treatment with the VEGF receptor inhibitor SU5416 and 3 wk of hypoxia (10% FiO2 ), followed by an additional 4 wk of normoxia (SU-Hx group). Control rats were treated with carboxymethylcellulose vehicle and 7 wk of normoxia (CMC-Nx group). The rodents then underwent positron emission tomography with sequential administration of two radiotracers, 2-deoxy-2-[(18)F]fluoroglucose ((18)F-FDG) and 14-(R,S)-[(18)F]fluoro-6-thia-heptadecanoic acid ((18)F-FTHA), analogs of glucose and fatty acid, respectively. Five CMC-Nx and 3 SU-Hx rats completed the entire experimental protocol. In the RV, there was a mild increase in (18)F-FDG uptake (1.35-fold, P = 0.085) and a significant decrease in (18)F-FTHA uptake (-2.1-fold, P< 0.05) in the SU-Hx rats relative to the CMC-Nx rats. In the LV, SU-Hx rats had less uptake of both radiotracers compared with CMC-Nx rats. Less RV fatty acid uptake in SPH was corroborated by decreased fatty acid transporters and enzymes in the RV tissue, and specifically a decrease in lipoprotein lipase. In the RV in rats with SPH, there is a major shift in metabolic substrate preference, largely due to decreased fatty acid uptake.

There is significant evidence that Th2 (T helper 2)-mediated inflammation supports the pathogenesis of both human and experimental animal models of pulmonary hypertension (PH). A key immune regulator is vascular endothelial growth factor (VEGF), which is produced by Th2 inflammation and can itself contribute to Th2 pulmonary responses. In this study, we interrogated the role of VEGF signaling in a murine model of schistosomiasis-induced PH with a phenotype of significant intrapulmonary Th2 inflammation, vascular remodeling, and elevated right ventricular pressures. We found that VEGF receptor blockade partially suppressed the levels of the Th2 inflammatory cytokines interleukin (IL)-4 and IL-13 in both the lung and the liver after Schistosoma mansoni exposure and suppressed pulmonary vascular remodeling. These findings suggest that VEGF positively contributes to schistosomiasis-induced vascular inflammation and remodeling, and they also provide evidence for a VEGF-dependent signaling pathway necessary for pulmonary vascular remodeling and inflammation in this model.

• Caveolin-1 deficiency in hematopoietic stem cells induces right heart disease.• Healthy BM protects the right heart from maladaptation.Accumulating evidence shows a causative role for the bone marrow (BM) in the genesis and progression of pulmonary hypertension (PH). Engraftment of BM hematopoietic stem cells from PH patients to mice reproduces the cardiopulmonary pathology of PH. However, it is unknown whether healthy BM can prevent the development of right heart disease.Caveolin

Background: Schistosomiasis‐associated pulmonary arterial hypertension (PAH) occurs in the context of Th2 inflammation, which is induced by IL‐4 and IL‐13. We had previously observed that TGF‐β signaling is necessary for Schistosoma‐induced pulmonary hypertension (PH) in the mouse. We hypothesized that IL‐4 and IL‐13 were necessary for the TGF‐β‐induced pulmonary vascular disease induced by Schistosoma. Methods: Wild type, IL‐13YFP, IL‐4GFP, IL‐4‐/‐, IL‐13‐/‐ and IL‐4‐/‐IL‐13‐/‐ mice (N=5‐17 per group) were intraperitoneally (IP) sensitized with 175 S. mansoni eggs/gram body weight, two weeks later intravenously (IV) challenged via tail vein with the same dose of eggs, and one week thereafter underwent right ventricular catheterization followed by quantitative histologic and protein analysis, or lung digestion and flow cytometry. Lung tissue from patients who died of schistosomiasis‐associated PAH was studied by immunostaining. Results: The lungs of patients with schistosomiasis‐associated PAH and mice with experimental disease had an increase in IL‐13, IL‐4Rα, phospho‐STAT6 and periostin, a target of IL‐13 signaling. Flow cytometry with IL‐13YFP and IL‐4GFP mice identified both of these cytokines were produced by CD4+ T‐cells. IL‐4‐/‐IL‐13‐/‐ mice, but not IL‐4‐/‐IL13+/+ or IL4+/+IL‐13‐/‐ mice, were protected from Schistosoma‐induced vascular remodeling, although the elevated right ventricular pressure persisted. Immunostaining of Schistosoma‐exposed mice demonstrated decreased phospho‐STAT6, perivascular TGF‐β ligand, and intravascular nuclear phospho‐Smad2/3 in IL4/IL13 double‐deficient mice only. Conclusions: Combined IL‐4 and IL‐13 deficiency are required for protection against Schistosoma‐induced pulmonary vascular remodeling.