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BACKGROUND: Activins are novel therapeutic targets in pulmonary arterial hypertension (PAH). We therefore studied whether key members of the activin pathway could be used as PAH biomarkers. METHODS: Serum levels of activin A, activin B, α-subunit of inhibin A and B proteins, and the antagonists follistatin and follistatin-like 3 (FSTL3) were measured in controls and in patients with newly diagnosed idiopathic, heritable, or anorexigen-associated PAH (n=80) at baseline and 3 to 4 months after treatment initiation. The primary outcome was death or lung transplantation. Expression patterns of the inhibin subunits, follistatin, FSTL3, Bambi, Cripto, and the activin receptors type I (ALK), type II (ACTRII), and betaglycan were analyzed in PAH and control lung tissues. RESULTS: Death or lung transplantation occurred in 26 of 80 patients (32.5%) over a median follow-up of 69 (interquartile range, 50–81) months. Both baseline (hazard ratio, 1.001 [95% CI, 1.000–1.001]; P =0.037 and 1.263 [95% CI, 1.049–1.520]; P =0.014, respectively) and follow-up (hazard ratio, 1.003 [95% CI, 1.001–1.005]; P =0.001 and 1.365 [95% CI, 1.185–1.573]; P P =0.009) and 0.17 (95% CI, 0.06–0.45; P P =0.019) and 0.27 (95% CI, 0.09–0.78, P =0.015), respectively. Prognostic values of activin A and FSTL3 were confirmed in an independent external validation cohort. Histological analyses showed a nuclear accumulation of the phosphorylated form of Smad2/3, higher immunoreactivities for ACTRIIB, ALK2, ALK4, ALK5, ALK7, Cripto, and FSTL3 in vascular endothelial and smooth muscle layers, and lower immunostaining for inhibin-α and follistatin. CONCLUSIONS: These findings offer new insights into the activin signaling system in PAH and show that activin A and FSTL3 are prognostic biomarkers for PAH.

Background Platelet‐derived growth factor is a major regulator of the vascular remodeling associated with pulmonary arterial hypertension. We previously showed that protein widely 1 (PW1 + ) vascular progenitor cells participate in early vessel neomuscularization during experimental pulmonary hypertension (PH) and we addressed the role of the platelet‐derived growth factor receptor type α (PDGFRα) pathway in progenitor cell‐dependent vascular remodeling and in PH development. Methods and Results Remodeled pulmonary arteries from patients with idiopathic pulmonary arterial hypertension showed an increased number of perivascular and vascular PW1 + cells expressing PDGFRα. PW1 nLacZ reporter mice were used to follow the fate of pulmonary PW1 + progenitor cells in a model of chronic hypoxia–induced PH development. Under chronic hypoxia, PDGFRα inhibition prevented the increase in PW1 + progenitor cell proliferation and differentiation into vascular smooth muscle cells and reduced pulmonary vessel neomuscularization, but did not prevent an increased right ventricular systolic pressure or the development of right ventricular hypertrophy. Conversely, constitutive PDGFRα activation led to neomuscularization via PW1 + progenitor cell differentiation into new smooth muscle cells and to PH development in male mice without fibrosis. In vitro, PW1 + progenitor cell proliferation, but not differentiation, was dependent on PDGFRα activity. Conclusions These results demonstrate a major role of PDGFRα signaling in progenitor cell–dependent lung vessel neomuscularization and vascular remodeling contributing to PH development, including in idiopathic pulmonary arterial hypertension patients. Our findings suggest that PDGFRα blockers may offer a therapeutic add‐on strategy to combine with current pulmonary arterial hypertension treatments to reduce vascular remodeling. Furthermore, our study highlights constitutive PDGFRα activation as a novel experimental PH model.

Background: The beneficial effects of parasympathetic stimulation have been reported in left heart failure, but whether it would be beneficial for pulmonary arterial hypertension (PAH) remains to be explored. Here, we investigated the relationship between parasympathetic activity and right ventricular (RV) function in patients with PAH, and the potential therapeutic effects of pyridostigmine (PYR), an oral drug stimulating the parasympathetic activity through acetylcholinesterase inhibition, in experimental pulmonary hypertension (PH). Methods: Heart rate recovery after a maximal cardiopulmonary exercise test was used as a surrogate for parasympathetic activity. RV ejection fraction was assessed in 112 patients with PAH. Expression of nicotinic (α-7 nicotinic acetylcholine receptor) and muscarinic (muscarinic acetylcholine type 2 receptor) receptors, and acetylcholinesterase activity were evaluated in RV (n=11) and lungs (n=7) from patients with PAH undergoing heart/lung transplantation and compared with tissue obtained from controls. In addition, we investigated the effects of PYR (40 mg/kg per day) in experimental PH. PH was induced in male rats by SU5416 (25 mg/kg subcutaneously) injection followed by 4 weeks of hypoxia. In a subgroup, sympathetic/parasympathetic modulation was assessed by power spectral analysis. At week 6, PH status was confirmed by echocardiography, and rats were randomly assigned to vehicle or treatment (both n=12). At the end of the study, echocardiography was repeated, with additional RV pressure-volume measurements, along with lung, RV histological, and protein analyses. Results: Patients with PAH with lower RV ejection fraction ( Conclusions: RV dysfunction is associated with reduced systemic parasympathetic activity in patients with PAH, with an inadequate adaptive response of the cholinergic system in the RV. Enhancing parasympathetic activity by PYR improved survival, RV function, and pulmonary vascular remodeling in experimental PH.

Purpose of review Pulmonary arterial hypertension (PAH) is a hemodynamic state defined by a resting mean pulmonary arterial pressure at or above 25 mmHg with a normal pulmonary capillary wedge pressure, ultimately leading to right heart failure and premature death. Although considerable progress has been made in the development of drug therapies for PAH targeting abnormalities found in the three main pathobiologic pathways (nitric oxide, prostacyclin, and endothelin-1), there is no drug available to specifically stop the progressive cellular accumulation into the pulmonary artery vessel wall. Indeed, this pulmonary vascular remodeling is a key pathological feature in PAH, contributing to the progressive narrowing of the lumen responsible to the functional decline and to the right ventricle hypertrophy and dysfunction. Recent findings Because numerous important discoveries in the PAH pathogenesis have been recently made, our improved understanding of additional pathways in this condition will presumably lead to the development of novel and more powerful therapeutic strategies in the near future. Summary In this review, we highlight some recent biological findings and discuss the opportunities that could lead to the identification of new promising targets in PAH paving the way for future therapeutic strategies.

Pulmonary arterial hypertension (PAH) corresponds to a heterogeneous group of severe clinical conditions characterized by precapillary pulmonary hypertension (PH) diagnosed when mean pulmonary artery pressure equals or exceeds 25 mm Hg at rest with normal pulmonary artery wedge pressure (≤15 mm Hg). According to the current clinical classification, PAH can be idiopathic (IPAH), heritable, drug or toxin induced, or associated with other diseases (eg, connective tissue diseases [CTDs], congenital heart diseases, HIV infection, and portal hypertension).1 PAH has a complex and multifactorial pathogenesis in which excessive migration and proliferation of pulmonary vascular cells (ie, endothelial cells [ECs] and smooth muscle cells [SMCs]) and dysregulated immune responses are critical contributors to the inappropriate pulmonary vascular remodeling. PAH is a fatal condition leading to right heart failure and death within 2 to 3 years after diagnosis if left untreated. During the last decade, therapeutic options for the treatment of this disease have improved exercise capacity, quality of life, and long-term outcomes. However, there is currently no cure available, and further insight into the disease pathophysiology is needed to advance drug development and to improve patient management. It is now widely accepted that altered immune mechanisms play a significant role in PAH by recruiting inflammatory cells, remodeling the pulmonary vasculature, and promoting autoimmune responses.2–4 Inflammation is a general term for the local accumulation of fluid, plasma proteins, and white blood cells that is initiated by physical injury, infection, or a local immune response. These phenomena represent the innate immune response. The innate immune response contributes to the activation of adaptive immunity, which is the response of antigen-specific lymphocytes to antigen, including the development of immunologic memory. The unique features of adaptive immunity, based on clonal selection of lymphocytes bearing antigen-specific receptors, provide the ability to recognize all pathogens specifically …

Background— Pulmonary arterial hypertension (PAH) is characterized by dysregulated proliferation of pulmonary artery smooth muscle cells leading to (mal)adaptive vascular remodeling. In the systemic circulation, vascular injury is associated with downregulation of sarcoplasmic reticulum Ca 2+ -ATPase 2a (SERCA2a) and alterations in Ca 2+ homeostasis in vascular smooth muscle cells that stimulate proliferation. We, therefore, hypothesized that downregulation of SERCA2a is permissive for pulmonary vascular remodeling and the development of PAH. Methods and Results— SERCA2a expression was decreased significantly in remodeled pulmonary arteries from patients with PAH and the rat monocrotaline model of PAH in comparison with controls. In human pulmonary artery smooth muscle cells in vitro, SERCA2a overexpression by gene transfer decreased proliferation and migration significantly by inhibiting NFAT/STAT3. Overexpresion of SERCA2a in human pulmonary artery endothelial cells in vitro increased endothelial nitric oxide synthase expression and activation. In monocrotaline rats with established PAH, gene transfer of SERCA2a via intratracheal delivery of aerosolized adeno-associated virus serotype 1 (AAV1) carrying the human SERCA2a gene (AAV1.SERCA2a) decreased pulmonary artery pressure, vascular remodeling, right ventricular hypertrophy, and fibrosis in comparison with monocrotaline-PAH rats treated with a control AAV1 carrying β-galactosidase or saline. In a prevention protocol, aerosolized AAV1.SERCA2a delivered at the time of monocrotaline administration limited adverse hemodynamic profiles and indices of pulmonary and cardiac remodeling in comparison with rats administered AAV1 carrying β-galactosidase or saline. Conclusions— Downregulation of SERCA2a plays a critical role in modulating the vascular and right ventricular pathophenotype associated with PAH. Selective pulmonary SERCA2a gene transfer may offer benefit as a therapeutic intervention in PAH.

Rationale: S100A4/Mts1 is implicated in motility of human pulmonary artery smooth muscle cells (hPASMCs), through an interaction with the RAGE (receptor for advanced glycation end products). Objective: We hypothesized that S100A4/Mts1-mediated hPASMC motility might be enhanced by loss of function of bone morphogenetic protein (BMP) receptor (BMPR)II, observed in pulmonary arterial hypertension. Methods and Results: Both S100A4/Mts1 (500 ng/mL) and BMP-2 (10 ng/mL) induce migration of hPASMCs in a novel codependent manner, in that the response to either ligand is lost with anti-RAGE or BMPRII short interference (si)RNA. Phosphorylation of extracellular signal-regulated kinase is induced by both ligands and is required for motility by inducing matrix metalloproteinase 2 activity, but phospho–extracellular signal-regulated kinase 1/2 is blocked by anti-RAGE and not by BMPRII short interference RNA. In contrast, BMPRII short interference RNA, but not anti-RAGE, reduces expression of intracellular chloride channel (CLIC)4, a scaffolding molecule necessary for motility in response to S100A4/Mts1 or BMP-2. Reduced CLIC4 expression does not interfere with S100A4/Mts1 internalization or its interaction with myosin heavy chain IIA, but does alter alignment of myosin heavy chain IIA and actin filaments creating the appearance of vacuoles. This abnormality is associated with reduced peripheral distribution and/or delayed activation of RhoA and Rac1, small GTPases required for retraction and extension of lamellipodia in motile cells. Conclusions: Our studies demonstrate how a single ligand (BMP-2 or S100A4/Mts1) can recruit multiple cell surface receptors to relay signals that coordinate events culminating in a functional response, ie, cell motility. We speculate that this carefully controlled process limits signals from multiple ligands, but could be subverted in disease.

Vascular expression of bone morphogenetic type IA receptor ( Bmpr1a ) is reduced in lungs of patients with pulmonary arterial hypertension, but the significance of this observation is poorly understood. To elucidate the role of Bmpr1a in the vascular pathology of pulmonary arterial hypertension and associated right ventricular (RV) dysfunction, we deleted Bmpr1a in vascular smooth muscle cells and in cardiac myocytes in mice using the SM22α;TRE-Cre/LoxP;R26R system. The LacZ distribution reflected patchy deletion of Bmpr1a in the lung vessels, aorta, and heart of SM22α;TRE-Cre;R26R;Bmpr1a flox /+ and flox/flox mutants. This reduction in BMPR-IA expression was confirmed by Western immunoblot and immunohistochemistry in the flox/flox group. This did not affect pulmonary vasoreactivity to acute hypoxia (10% O 2 ) or the increase in RV systolic pressure and RV hypertrophy following 3 weeks in chronic hypoxia. However, both SM22α;TRE-Cre;R26R;Bmpr1a flox /+ and flox/flox mutant mice had fewer muscularized distal pulmonary arteries and attenuated loss of peripheral pulmonary arteries compared with age-matched control littermates in hypoxia. When Bmpr1a expression was reduced by short interference RNA in cultured pulmonary arterial smooth muscle cells, serum-induced proliferation was attenuated explaining decreased hypoxia-mediated muscularization of distal vessels. When Bmpr1a was reduced in cultured microvascular pericytes by short interference RNA, resistance to apoptosis was observed and this could account for protection against hypoxia-mediated vessel loss. The similar elevation in RV systolic pressure and RV hypertrophy, despite the attenuated remodeling with chronic hypoxia in the flox/flox mutants versus controls, was not a function of elevated left ventricular end diastolic pressure but was associated with increased periadventitial deposition of elastin and collagen, potentially influencing vascular stiffness.

Background: Interleukin (IL)-6 has been linked to the prognosis of pulmonary arterial hypertension (PAH). However, precise contributions of IL-6 and its signaling system to PAH progression is still obscure. Objectives: To study pathogenic roles of IL-6 cis- and trans-signaling in experimental and human PAH and to evaluate the translational potential of IL-6 signaling inhibition. Methods: We examined the global expression pattern of key actors of the IL-6 signaling in human lung tissues, blood samples and cultured pulmonary artery-smooth muscle cells (PA-SMCs) of 10 controls and 10 idiopathic PAH (IPAH) patients. In addition, two complementary animal models of pulmonary hypertension (PH) have been studied: the monocrotaline and SU5416 plus chronic hypoxia rat models. Results: In IPAH, serum levels of IL-6 and soluble IL-6 receptors (sIL-6R) proteins were higher than in control subjects. We also found stronger immunoreactivity for IL-6R, p-STAT3 and myeloid leukemia-cell protein 1 (Mcl-1, a downstream target of IL-6) in the media of remodeled pulmonary arteries and cultured PA-SMCs of IPAH patients compared with controls. These abnormalities in the IL-6/IL-6R signaling were also histologically found in the two rat models. Consistent with these findings, we also found that IL-6 with or without sIL-6R could substantially increase p-STAT3 and the anti-apoptotic Mcl-1 protein in cultured IPAH PA-SMCs compared with control cells. These effects were totally abolished in the presence of IL-6R neutralizing antibodies and an IL-6R antagonist. Finally, we found that daily treatment with IL-6R antagonist started 1 week after a subcutaneous monocrotaline injection substantially attenuates the abnormal increase in p-STAT3 and Mcl-1 and regresses established PH. Conclusions: We demonstrate here that anti-IL-6R strategies may represent promising novels anti-proliferative and anti-inflammatory approaches for treatment of PAH.

One intrinsic abnormality of pulmonary artery smooth muscle cells (PA-SMCs) in human idiopathic pulmonary hypertension (iPH) is an exaggerated proliferative response to internalized serotonin (5-HT) caused by increased expression of the 5-HT transporter (5-HTT). To investigate whether 5-HTT overexpression in PA-SMCs is sufficient to produce PH, we generated transgenic mice overexpressing 5-HTT under the control of the SM22 promoter. Studies in SM22-LacZ + mice showed that the transgene was expressed predominantly in SMCs of pulmonary and systemic vessels. Compared with wild-type mice, SM22–5-HTT + mice exhibited a 3- to 4-fold increase in lung 5-HTT mRNA and protein, together with increased lung 5-HT uptake activity, but no changes in platelet 5-HTT activity or blood 5-HT levels. At 8 weeks of age, SM22–5-HTT + mice exhibited PH, with marked increases in right ventricular systolic pressure (RVSP), right ventricle/left ventricle+septum ratio, and muscularization of distal pulmonary vessels, but no changes in systemic arterial pressure. PH worsened with age. Except a marked decrease in Kv channels, no changes in the lung expression of mediators of pulmonary vascular remodeling were observed in SM22–5-HTT + mice. Compared with wild-type mice, SM22–5-HTT + mice showed depressed hypoxic pulmonary vasoconstriction contrasting with greater severity of hypoxia- or monocrotaline-induced PH. These results show that increased 5-HTT expression in PA-SMCs, to a level close to that found in human iPH, lead to PH in mice. They further support a central role for 5-HTT in the pathogenesis of PH, making 5-HTT a potential therapeutic target.

We previously observed that mice with deletion of peroxisome proliferator-activated receptor γ (PPARγ) in endothelial cells (EC) (EC-Pparγ-/-) do not reverse pulmonary hypertension (PH) during recovery in room air after three weeks of chronic hypoxia. Impaired PPARγ interaction with ß-catenin was linked to pulmonary arterial (PA) EC dysfunction in the pathogenesis of PH. To gain further insight into PPARγ function, important in reversing PH, we applied affinity purification-mass spectrometry in HEK293T cells to analyse the PPARγ interactome. Analyses revealed a network highly enriched in DNA damage response (DDR) proteins, including the MRE11, RAD50 and NBN (MRN) heterotrimeric complex. MRN senses damaged DNA and activates the ATM/ATR pathway essential for DNA repair. Using co-immmunoprecipitation in PAECs, we confirmed the PPARγ:MRN interaction via the PPARγ ligand binding domain. To determine the function of this novel interaction, we depleted PPARγ with siRNA and induced DNA damage with doxorubicin (DOX) or hydroxyurea (HU). PPARγ depletion impaired DDR activation after DOX/HU, with reduced levels of pATM and its substrates, pCHK1, pCHK2 and γH2AX. To test whether these abnormalities were related to reduced DNA repair, we assessed damaged DNA 24h after removal of DOX/HU using the COMET assay. PPARγ depleted PAECs showed longer comet tails reflective of unrepaired DNA. To investigate if persistent PH in EC-Pparγ-/- mice after chronic hypoxia correlated with impaired DDR, we evaluated both γH2AX (sensor) and Brca1 (repair) foci formation in the mouse lung tissues using confocal microscopy. Consistent with impaired DNA repair, Brca1 foci formation was significantly increased in ECs of EC-Pparγ-/- mice compared to the wildtype littermates. Moreover, reduced PPARγ previously described in PAECs from PH patients relative to controls was also associated with unrepaired DNA, judged by longer comet tails and by persistent γH2AX foci as assessed by confocal microscopy in tissue sections. In summary we report a novel interaction between PPARγ and the MRN that is necessary in DNA damage sensing and repair. We suggest that persistent DNA damage associated with PPARγ deficiency in PAECs could cause dysfunction or transformation related to the pathology of PH.

Background Right ventricular ( RV ) diastolic function is impaired in patients with pulmonary arterial hypertension ( PAH ). Our previous study showed that elevated cardiomyocyte stiffness and myofilament Ca 2+ sensitivity underlie diastolic dysfunction in PAH . This study investigates protein modifications contributing to cellular diastolic dysfunction in PAH . Methods and Results RV samples from PAH patients undergoing heart‐lung transplantation were compared to non‐failing donors (Don). Titin stiffness contribution to RV diastolic dysfunction was determined by Western‐blot analyses using antibodies to protein‐kinase‐A (PKA), Cα (PKCα) and Ca 2+ /calmoduling‐dependent‐kinase (CamKIIδ) titin and phospholamban (PLN) phosphorylation sites: N2B (Ser469), PEVK (Ser170 and Ser26), and PLN (Thr17), respectively. PKA and PKCα sites were significantly less phosphorylated in PAH compared with donors ( P IIδ ‐mediated titin phosphorylation, we measured the stiffness of single RV cardiomyocytes before and after kinase incubation. PKA significantly decreased PAH RV cardiomyocyte diastolic stiffness, PKCα further increased stiffness while CamK IIδ had no major effect. CamKIIδ activation was determined indirectly by measuring PLN Thr17phosphorylation level. No significant changes were found between the groups. Myofilament Ca 2+ sensitivity is mediated by sarcomeric troponin I ( cTnI ) phosphorylation. We observed increased unphosphorylated cTnI in PAH compared with donors ( P cTnI phosphorylation (Ser22/23) ( P Ca 2+ ‐handling proteins contribute to RV diastolic dysfunction due to insufficient diastolic Ca 2+ clearance. PAH SERCA2a levels and PLN phosphorylation were significantly reduced compared with donors ( P Conclusions Increased titin stiffness, reduced cTnI phosphorylation, and altered levels of phosphorylation of Ca 2+ handling proteins contribute to RV diastolic dysfunction in PAH.

Background: Kawasaki disease (KD) is a leading cause of acquired heart disease in children. However, the molecular mechanisms leading to coronary aneurysms, and the host factors determining high-risk patients are unknown. We have previously shown that mice haploinsufficient for tropoelastin (EL ±), develop more severe destruction of the coronary elastin compared to wild type (WT) mice after injection with Lactobacillus casei wall extract (LCWE), an inducer of coronary arteritis. In contrast to the beneficial effect of TGFβ blockade on the aneurysms that form in Marfan syndrome (MS), we hypothesized that TGFβ protects against aneurysm formation in this inflammatory model by: enhancing tropoelastin; and suppressing proteolytic activity. Methods: WT and EL ± mice were given either TGFβ neutralizing antibody (TGFβ-Nab) or control IgG in addition to LCWE. At 14d, tropoelastin and plasminogen activator inhibitor-1 (PAI-1) protein was determined, and matrix metalloproteinase (MMP)-2 and -9 and serine elastase activity was measured. Elastin degradation and total medial elastin content was assessed by morphometric analysis at 42d. Results: TGFβ blockade worsened the LCWE-mediated fragmentation of the coronary elastin, with areas of complete dissolution of the external lamina in WT mice, and even more severe features in EL ± mice. Tropoelastin protein was 40% lower in the EL ± vs. WT mice after LCWE (P < 0.05), and TGFβ blockade further exaggerated this discrepancy. TGFβ-Nab markedly reduced PAI-1 in the WT mice after LCWE (P < 0.05), and produced a similar pattern in the EL ± mice, and induced a four-fold induction of MMP-9 activity in both genotypes. This effect was associated with increased elastin fragmentation (P < 0.05), and decreased total medial elastin content (P < 0.05), despite inhibition of the LCWE-mediated induction of serine elastase activity. Conclusions: We conclude that: diminished tropoelastin expression worsens elastin destruction in the setting of acute coronary arteritis; and TGFβ protects the vasculature in this model by maintaining PAI-1 levels and suppressing activation of MMP-9. Thus strategies to block TGFβ, currently in use to prevent aneurysms in MS, are unlikely to be beneficial in KD, and may be detrimental. This research has received full or partial funding support from the American Heart Association, AHA National Center.

Introduction: Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) is a nuclear receptor expressed in endothelial cells (EC) and known to regulate enzymes important in vascular dilatation and angiogenesis such as endothelial nitric oxide synthase (eNOS) and heme oxygenase-1 (HO-1). Expression of PPAR-gamma is reduced in the pulmonary arteries (PA) of patients with severe PA hypertension (PAH). Objective: We therefore investigated whether loss of PPAR-gamma in EC might cause PAH under normoxic conditions or might worsen the severity of PAH induced by chronic hypoxia. Materials and Methods: We generated transgenic mice with targeted deletion of PPAR-gamma in ECs by breeding a mouse expressing Cre under the regulation of the Tie2 promoter with a mouse in which critical exons of PPAR-gamma were flanked by LoxP sites. We compared right ventricular systolic pressure (RVSP), RV hypertrophy (RV/LV+S), in Tie2CrePPAR-gamma flox/flox and wild type littermate controls (WT) in normoxia and following 3 weeks of chronic hypoxia (CH) (10 mice per group, 5 per gender) and also assessed muscularization of distal pulmonary vessels and number of peripheral arteries in CH. Results: Tie2CrePPAR-gamma flox/flox vs. WT mice had mildly elevated RVSP (24.6 vs 21.56mmHg) and RVH during normoxia (P flox/flox and WT mice (28.1mmHg vs 28.5mmHg) as was RVH and muscularizaton of distal vessels, and number of arteries relative to alveoli. Conclusions: Thus loss of PPAR-gamma in ECs appears to result in mild pulmonary vasoconstricton, and while not exacerbated during chronic hypoxia, this feature may have an impact on recovery during return to normoxia, if EC production of eNOS and HO-1 are necessary for regression of vascular disease.

Lung tissues of patients with PAH have reduced levels of the peroxisome proliferator activated receptor gamma (PPARγ) and we previously reported that transgenic male mice with deletion of PPARγ in arterial smooth muscle (SM22CrePPARγ flox/flox ) develop spontaneous PAH. Moreover, PPARγ is necessary in mediating bone morphogenetic protein (BMP-2) inhibition of PDGF-BB induced SMC proliferation. We therefore hypothesized that PAH would be exacerbated in SM22CrePPARγ flox/flox mice under conditions like chronic hypoxia (3 weeks, FiO 2 =0.10) that induce PDGF-BB mediated SMC proliferation. Results: Consistent with this hypothesis, we report a more severe PAH phenotype only in the male SM22CrePPARγ flox/flox mice, as measured by greater right ventricular systolic pressure (RVSP: 38.6 vs. 30.9 mmHg), right ventricular hypertrophy (RVH=right ventricle/left ventricle+septum: 0.58 vs 0.35), and arterial muscularization (90.6 vs 60.3 %), when compared to littermate controls (pflox/flox mice were resistant to spontaneous or chronic hypoxia-induced PAH (RVSP: 18.5mmHg). We investigated the acute hypoxic vasoconstrictive response and found it exaggerated in the male but suppressed in the female (RVSP: 43.12 vs 20.42mmHg) SM22CrePPARγ flox/flox mice. We found no reduction in endothelin-1 (Pflox/flox mice but serum levels of adiponectin were twofold higher (14.5 vs 6.9 μg/ml; pflox/flox mice, BMP2 fails to suppress PA SMC proliferation in response to PDGF-BB (p Conclusion : These findings strengthen the potential efficacy of PPAR-α/ γ agonists in the treatment of PAH patients with low endogenous levels of PPAR-γ and/or adiponectin, such as those with BMP-RII dysfunction or insulin resistance.