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1.  Relevant Issues in the Pathology and Pathobiology of Pulmonary Hypertension 
Knowledge of the pathobiology of pulmonary hypertension continues to accelerate. However, fundamental gaps remain in our understanding of the underlying pathological changes in pulmonary arteries and veins in the different forms of this syndrome. Although pulmonary hypertension primarily affects the arteries, venous disease is increasingly recognized as an important entity. Moreover, prognosis in pulmonary hypertension is determined largely by the status of the right ventricle, rather than the levels of pulmonary artery pressures. It is increasingly clear that while vasospasm plays a role, pulmonary hypertension is an obstructive lung panvasculopathy. Disordered metabolism and mitochondrial structure, inflammation, and dysregulation of growth factors lead to a proliferative, apoptosis-resistant state. These abnormalities may be acquired, genetically mediated as a result of mutations in bone morphogenetic protein receptor (BMPR)2 or activin-like kinase (Alk)-1 or epigenetically-inherited (as a result of epigenetic silencing of genes such as superoxide dismutase 2). There is a pressing need to better understand how the pathobiology leads to severe disease in some patients versus mild pulmonary hypertension in others. Recent recognition of a potential role of acquired abnormalities of mitochondrial metabolism in the right ventricular myocytes and pulmonary vascular cells suggests new therapeutic approaches, diagnostic modalities, and biomarkers. Finally, dissection of role of pulmonary inflammation in the initiation and promotion of pulmonary hypertension has revealed a complex yet fascinating interplay with pulmonary vascular remodeling, promising to lead to novel therapeutics and diagnostics. Emerging concepts are also relevant to the pathobiology of pulmonary hypertension, including a role for bone marrow and circulating progenitor cells and microRNAs. Continued interest in the interface of the genetic basis of pulmonary hypertension and cellular and molecular pathogenetic links should expand further our understanding of the disease.
PMCID: PMC3970402  PMID: 24355640
inflammation; metabolism; pulmonary arteries; pulmonary veins
2.  Reduced BMPR2 expression induces GM-CSF translation and macrophage recruitment in humans and mice to exacerbate pulmonary hypertension 
Reduced expression of bone morphogenetic protein receptor 2 subverts a stress granule response, heightens GM-CSF mRNA translation, and increases inflammatory cell recruitment to exacerbate pulmonary arterial hypertension.
Idiopathic pulmonary arterial hypertension (PAH [IPAH]) is an insidious and potentially fatal disease linked to a mutation or reduced expression of bone morphogenetic protein receptor 2 (BMPR2). Because intravascular inflammatory cells are recruited in IPAH pathogenesis, we hypothesized that reduced BMPR2 enhances production of the potent chemokine granulocyte macrophage colony-stimulating factor (GM-CSF) in response to an inflammatory perturbation. When human pulmonary artery (PA) endothelial cells deficient in BMPR2 were stimulated with tumor necrosis factor (TNF), a twofold increase in GM-CSF was observed and related to enhanced messenger RNA (mRNA) translation. The mechanism was associated with disruption of stress granule formation. Specifically, loss of BMPR2 induced prolonged phospho-p38 mitogen-activated protein kinase (MAPK) in response to TNF, and this increased GADD34–PP1 phosphatase activity, dephosphorylating eukaryotic translation initiation factor (eIF2α), and derepressing GM-CSF mRNA translation. Lungs from IPAH patients versus unused donor controls revealed heightened PA expression of GM-CSF co-distributing with increased TNF and expanded populations of hematopoietic and endothelial GM-CSF receptor α (GM-CSFRα)–positive cells. Moreover, a 3-wk infusion of GM-CSF in mice increased hypoxia-induced PAH, in association with increased perivascular macrophages and muscularized distal arteries, whereas blockade of GM-CSF repressed these features. Thus, reduced BMPR2 can subvert a stress granule response, heighten GM-CSF mRNA translation, increase inflammatory cell recruitment, and exacerbate PAH.
PMCID: PMC3920564  PMID: 24446489
3.  Repair of congenital heart disease with associated pulmonary hypertension in children: what are the minimal investigative procedures? Consensus statement from the Congenital Heart Disease and Pediatric Task Forces, Pulmonary Vascular Research Institute (PVRI) 
Pulmonary Circulation  2014;4(2):330-341.
Standardization of the diagnostic routine for children with congenital heart disease associated with pulmonary arterial hypertension (PAH-CHD) is crucial, in particular since inappropriate assignment to repair of the cardiac lesions (e.g., surgical repair in patients with elevated pulmonary vascular resistance) may be detrimental and associated with poor outcomes. Thus, members of the Congenital Heart Disease and Pediatric Task Forces of the Pulmonary Vascular Research Institute decided to conduct a survey aimed at collecting expert opinion from different institutions in several countries, covering many aspects of the management of PAH-CHD, from clinical recognition to noninvasive and invasive diagnostic procedures and immediate postoperative support. In privileged communities, the vast majority of children with congenital cardiac shunts are now treated early in life, on the basis of noninvasive diagnostic evaluation, and have an uneventful postoperative course, with no residual PAH. However, a small percentage of patients (older at presentation, with extracardiac syndromes or absence of clinical features of increased pulmonary blood flow, thus suggesting elevated pulmonary vascular resistance) remain at a higher risk of complications and unfavorable outcomes. These patients need a more sophisticated diagnostic approach, including invasive procedures. The authors emphasize that decision making regarding operability is based not only on cardiac catheterization data but also on the complete diagnostic picture, which includes the clinical history, physical examination, and all aspects of noninvasive evaluation.
PMCID: PMC4070778  PMID: 25006452
congenital heart disease; pulmonary hypertension; cardiac catheterization; pediatric cardiac surgery; postoperative care
4.  Blocking Macrophage Leukotriene B4 Prevents Endothelial Injury and Reverses Pulmonary Hypertension 
Science translational medicine  2013;5(200):200ra117.
Pulmonary hypertension (PH) is a serious condition that affects mainly young and middle-aged women, and its etiology is poorly understood. A prominent pathological feature of PH is accumulation of macrophages near the arterioles of the lung. In both clinical tissue and the SU5416 (SU)/athymic rat model of severe PH, we found that the accumulated macrophages expressed high levels of leukotriene A4 hydrolase (LTA4H), the biosynthetic enzyme for leukotriene B4 (LTB4). Moreover, macrophage-derived LTB4 directly induced apoptosis in pulmonary artery endothelial cells (PAECs). Further, LTB4 induced proliferation and hypertrophy of human pulmonary artery smooth muscle cells. We found that LTB4 acted through its receptor, BLT1, to induce PAEC apoptosis by inhibiting the protective endothelial sphingosine kinase 1 (Sphk1)–endothelial nitric oxide synthase (eNOS) pathway. Blocking LTA4H decreased in vivo LTB4 levels, prevented PAEC apoptosis, restored Sphk1-eNOS signaling, and reversed fulminant PH in the SU/athymic rat model of PH. Antagonizing BLT1 similarly reversed established PH. Inhibition of LTB4 biosynthesis or signal transduction in SU-treated athymic rats with established disease also improved cardiac function and reopened obstructed arterioles; this approach was also effective in the monocrotaline model of severe PH. Human plexiform lesions, one hallmark of PH, showed increased numbers of macrophages, which expressed LTA4H, and patients with connective tissue disease–associated pulmonary arterial hypertension exhibited significantly higher LTB4 concentrations in the systemic circulation than did healthy subjects. These results uncover a possible role for macrophage-derived LTB4 in PH pathogenesis and identify a pathway that may be amenable to therapeutic targeting.
PMCID: PMC4016764  PMID: 23986401
5.  Molecular Determinants of Lung Development 
Development of the pulmonary system is essential for terrestrial life. The molecular pathways that regulate this complex process are beginning to be defined, and such knowledge is critical to our understanding of congenital and acquired lung diseases. A recent workshop was convened by the National Heart, Lung, and Blood Institute to discuss the developmental principles that regulate the formation of the pulmonary system. Emerging evidence suggests that key developmental pathways not only regulate proper formation of the pulmonary system but are also reactivated upon postnatal injury and repair and in the pathogenesis of human lung diseases. Molecular understanding of early lung development has also led to new advances in areas such as generation of lung epithelium from pluripotent stem cells. The workshop was organized into four different topics, including early lung cell fate and morphogenesis, mechanisms of lung cell differentiation, tissue interactions in lung development, and environmental impact on early lung development. Critical points were raised, including the importance of epigenetic regulation of lung gene expression, the dearth of knowledge on important mesenchymal lineages within the lung, and the interaction between the developing pulmonary and cardiovascular system. This manuscript describes the summary of the discussion along with general recommendations to overcome the gaps in knowledge in lung developmental biology.
PMCID: PMC3955361  PMID: 23607856
lung development; lung cell fate; lung cell differentiation; tissue interaction; environmental impact
6.  Molecular Determinants of Lung Development 
Development of the pulmonary system is essential for terrestrial life. The molecular pathways that regulate this complex process are beginning to be defined, and such knowledge is critical to our understanding of congenital and acquired lung diseases. A recent workshop was convened by the National Heart, Lung, and Blood Institute to discuss the developmental principles that regulate the formation of the pulmonary system. Emerging evidence suggests that key developmental pathways not only regulate proper formation of the pulmonary system but are also reactivated upon postnatal injury and repair and in the pathogenesis of human lung diseases. Molecular understanding of early lung development has also led to new advances in areas such as generation of lung epithelium from pluripotent stem cells. The workshop was organized into four different topics, including early lung cell fate and morphogenesis, mechanisms of lung cell differentiation, tissue interactions in lung development, and environmental impact on early lung development. Critical points were raised, including the importance of epigenetic regulation of lung gene expression, the dearth of knowledge on important mesenchymal lineages within the lung, and the interaction between the developing pulmonary and cardiovascular system. This manuscript describes the summary of the discussion along with general recommendations to overcome the gaps in knowledge in lung developmental biology.
PMCID: PMC3955361  PMID: 23607856
lung development; lung cell fate; lung cell differentiation; tissue interaction; environmental impact
7.  Loss of Adenomatous Poliposis Coli-α3 Integrin Interaction Promotes Endothelial Apoptosis in Mice and Humans 
Circulation research  2012;111(12):10.1161/CIRCRESAHA.112.267849.
Pulmonary hypertension (PH) is characterized by progressive elevation in pulmonary pressure and loss of small pulmonary arteries. As bone morphogenetic proteins (BMPs) promote pulmonary angiogenesis by recruiting the Wnt/βcatenin pathway, we proposed that βcatenin activation could reduce loss and/or induce regeneration of small PAs and attenuate PH.
This study aims to establish the role of β–catenin in protecting the pulmonary endothelium and stimulating compensatory angiogenesis following injury.
Methods and Results
To assess the impact of β-catenin activation on chronic hypoxia-induced PH, we used the adenomatous polyposis coli (ApcMin/+) mouse, where reduced APC causes constitutive β–catenin elevation. Surprisingly, hypoxic ApcMin/+ mice displayed greater PH and small PA loss compared to control C57Bl6J (C57) littermates. Pulmonary artery endothelial cells (PAECs) isolated from ApcMin/+ demonstrated reduced survival and angiogenic responses along with a profound reduction in adhesion to laminin. The mechanism involved failure of APC to interact with the cytoplasmic domain of the α3 integrin, to stabilize focal adhesions and activate integrin-linked kinase (ILK-1) and pAkt. We found that PAECs from lungs of patients with idiopathic PH have reduced APC expression, decreased adhesion to laminin and impaired vascular tube formation. These defects were corrected in the cultured cells by transfection of APC.
We show that APC is integral to PAEC adhesion and survival and is reduced in PAECs from PH patient lungs. The data suggest that decreased APC may be a cause of increased risk or severity of PH in genetically susceptible individuals.
PMCID: PMC3821702  PMID: 23011394
Adenomatous poliposis coli; Wnt signaling; integrin signaling; angiogenesis; pulmonary hypertension
8.  Estrogen Paradox in Pulmonary Hypertension 
Although the incidence of pulmonary hypertension is higher in female patients, numerous experimental studies have demonstrated better outcome in female animals, exacerbation of the disease after ovariectomy, and a strong protective effect of estrogen: a phenomenon known as the “estrogen paradox” of pulmonary hypertension. On the other hand, some clinical studies have indirectly linked estrogen to increased risk of portopulmonary hypertension, whereas others implicate increased estrogen metabolism and high levels of certain estrogen metabolites in promoting pulmonary vascular remodeling in familial pulmonary arterial hypertension. In this review we investigate the estrogen paradox through highlighting the differential receptor-mediated effects of estrogen. Although estrogen and estrogen receptor–based therapies have shown promise in rescuing preexisting pulmonary hypertension in animals, their role is yet to be defined in humans.
PMCID: PMC3406082  PMID: 22561960
estrogen paradox; pulmonary hypertension; estrogen receptors; estrogen metabolites
9.  FK506 activates BMPR2, rescues endothelial dysfunction, and reverses pulmonary hypertension 
The Journal of Clinical Investigation  2013;123(8):3600-3613.
Dysfunctional bone morphogenetic protein receptor-2 (BMPR2) signaling is implicated in the pathogenesis of pulmonary arterial hypertension (PAH). We used a transcriptional high-throughput luciferase reporter assay to screen 3,756 FDA-approved drugs and bioactive compounds for induction of BMPR2 signaling. The best response was achieved with FK506 (tacrolimus), via a dual mechanism of action as a calcineurin inhibitor that also binds FK-binding protein-12 (FKBP12), a repressor of BMP signaling. FK506 released FKBP12 from type I receptors activin receptor-like kinase 1 (ALK1), ALK2, and ALK3 and activated downstream SMAD1/5 and MAPK signaling and ID1 gene regulation in a manner superior to the calcineurin inhibitor cyclosporine and the FKBP12 ligand rapamycin. In pulmonary artery endothelial cells (ECs) from patients with idiopathic PAH, low-dose FK506 reversed dysfunctional BMPR2 signaling. In mice with conditional Bmpr2 deletion in ECs, low-dose FK506 prevented exaggerated chronic hypoxic PAH associated with induction of EC targets of BMP signaling, such as apelin. Low-dose FK506 also reversed severe PAH in rats with medial hypertrophy following monocrotaline and in rats with neointima formation following VEGF receptor blockade and chronic hypoxia. Our studies indicate that low-dose FK506 could be useful in the treatment of PAH.
PMCID: PMC3726153  PMID: 23867624
10.  Patchy deletion of Bmpr1a potentiates proximal pulmonary artery remodeling in mice exposed to chronic hypoxia 
Reduced vascular expression of bone morphogenetic type IA receptor (Bmpr1a) has been found in patients with pulmonary arterial hypertension (PAH). Our previous studies in mice with patchy deletion of Bmpr1a in vascular smooth muscle cells and cardiac myocytes showed decreased distal vascular remodeling despite a similar severity of hypoxic pulmonary hypertension (HPH). We speculate increased stiffness from ectopic deposition of collagen in proximal pulmonary arteries (PAs) might account for HPH. Pulsatile pressure-flow relationships were measured in isolated, ventilated, perfused lungs of SM22α;TRE-Cre;R26R;Bmpr1aflox/flox (KO) mice and wild-type (WT) littermates following 21 days (hypoxia) and 0 days (control) of chronic hypoxia. Pulmonary vascular impedance, which yields insight into proximal and distal arterial remodeling, was calculated. Reduced Bmpr1a expression had no effect on input impedance Z0 (P=0.52) or characteristic impedance ZC (P=0.18) under control conditions; it also had no effect on the decrease in Z0 via acute rho kinase inhibition. However, following chronic hypoxia, reduced Bmpr1a expression increased ZC (P<0.001) without affecting Z0 (P=0.72). These results demonstrate that Bmpr1a deficiency does not significantly alter the hemodynamic function of the distal vasculature or its response to chronic hypoxia but larger, more proximal arteries are affected. In particular, reduced Bmpr1a expression likely decreased dilatation and increased stiffening in response to hypoxia, probably by collagen accumulation. Increased PA stiffness can have a significant impact on right ventricular function. This study illustrates for the first time how proximal pulmonary artery changes in the absence of distal pulmonary artery changes contribute to pulmonary hypertension.
PMCID: PMC3505237  PMID: 22314711
Characteristic impedance; pulsatile pressure-flow relationships; arterial stiffness; pulmonary hypertension; knockout mouse; pulmonary hemodynamics
11.  Molecular pathogenesis of pulmonary arterial hypertension 
The Journal of Clinical Investigation  2012;122(12):4306-4313.
Recent clinical and experimental studies are redefining the cellular and molecular bases of pulmonary arterial hypertension (PAH). The genetic abnormalities first identified in association with the idiopathic form of PAH — together with a vast increase in our understanding of cell signaling, cell transformation, and cell-cell interactions; gene expression; microRNA processing; and mitochondrial and ion channel function — have helped explain the abnormal response of vascular cells to injury. Experimental and clinical studies now converge on the intersection and interactions between a genetic predisposition involving the BMPR2 signaling pathway and an impaired metabolic and chronic inflammatory state in the vessel wall. These deranged processes culminate in an exuberant proliferative response that occludes the pulmonary arterial (PA) lumen and obliterates the most distal intraacinar vessels. Here, we describe emerging therapies based on preclinical studies that address these converging pathways.
PMCID: PMC3533531  PMID: 23202738
13.  Anticipated classes of new medications and molecular targets for pulmonary arterial hypertension 
Pulmonary Circulation  2013;3(1):226-244.
Pulmonary arterial hypertension (PAH) remains a life-limiting condition with a major impact on the ability to lead a normal life. Although existing therapies may improve the outlook in some patients there remains a major unmet need to develop more effective therapies in this condition. There have been significant advances in our understanding of the genetic, cell and molecular basis of PAH over the last few years. This research has identified important new targets that could be explored as potential therapies for PAH. In this review we discuss whether further exploitation of vasoactive agents could bring additional benefits over existing approaches. Approaches to enhance smooth muscle cell apotosis and the potential of receptor tyrosine kinase inhibition are summarised. We evaluate the role of inflammation, epigenetic changes and altered glycolytic metabolism as potential targets for therapy, and whether inherited genetic mutations in PAH have revealed druggable targets. The potential of cell based therapies and gene therapy are also discussed. Potential candidate pathways that could be explored in the context of experimental medicine are identified.
PMCID: PMC3641734  PMID: 23662201
pulmonary arterial hypertension; cellular mechanisms; inflammation; metabolism; tyrosine kinase inhibition; genetics; epigenetics; apoptosis
14.  Regulatory T cells limit vascular endothelial injury and prevent pulmonary hypertension. 
Circulation research  2011;109(8):867-879.
Pulmonary arterial hypertension (PAH) is an incurable disease associated with viral infections and connective tissue diseases. The relationship between inflammation and disease pathogenesis in these disorders remains poorly understood.
To determine whether immune dysregulation due to absent T cell populations directly contributes to the development of PAH.
Methods and Results
Vascular endothelial growth factor receptor 2 (VEGFR2) blockade induced significant pulmonary endothelial apoptosis in T-cell deficient rats but not in immune-reconstituted (IR) rats. T cell-lymphopenia in association with VEGFR2 blockade resulted in periarteriolar inflammation with macrophages, and B cells even prior to vascular remodeling and elevated pulmonary pressures. IR prevented early inflammation and attenuated PAH development. IR with either CD8 T cells alone or with CD4-depleted spleen cells was ineffective in preventing PAH whereas CD4-depleting immunocompetent euthymic animals increased PAH susceptibility. IR with either CD4+CD25hi or CD4+CD25- T cell subsets prior to vascular injury attenuated the development of PAH. Immune reconstitution limited perivascular inflammation and endothelial apoptosis in rat lungs in association with increased FoxP3+-, IL-10- and TGF-β– expressing CD4 cells, and upregulation of pulmonary bone morphogenetic protein receptor type 2 (BMPR2)-expressing cells, a receptor that activates endothelial cell survival pathways.
PAH may arise when regulatory T cell (Treg) activity fails to control endothelial injury. These studies suggest that regulatory T cells normally function to limit vascular injury and may protect against the development of PAH.
PMCID: PMC3204361  PMID: 21868697
pulmonary arterial hypertension; inflammation; regulatory T cell; bone morphogenetic protein receptor type 2
15.  Inhibiting Lung Elastase Activity Enables Lung Growth in Mechanically Ventilated Newborn Mice 
Rationale: Mechanical ventilation with O2-rich gas (MV-O2) offers life-saving treatment for respiratory failure, but also promotes lung injury. We previously reported that MV-O2 of newborn mice increased lung elastase activity, causing elastin degradation and redistribution of elastic fibers from septal tips to alveolar walls. These changes were associated with transforming growth factor (TGF)-β activation and increased apoptosis leading to defective alveolarization and lung growth arrest, as seen in neonatal chronic lung disease.
Objectives: To determine if intratracheal treatment of newborn mice with the serine elastase inhibitor elafin would prevent MV-O2–induced lung elastin degradation and the ensuing cascade of events causing lung growth arrest.
Methods: Five-day-old mice were treated via tracheotomy with recombinant human elafin or vehicle (lactated-Ringer solution), followed by MV with 40% O2 for 8–24 hours; control animals breathed 40% O2 without MV. At study's end, lungs were harvested to assess key variables noted below.
Measurements and Main Results: MV-O2 of vehicle-treated pups increased lung elastase and matrix metalloproteinase-9 activity when compared with unventilated control animals, causing elastin degradation (urine desmosine doubled), TGF-β activation (pSmad-2 tripled), and apoptosis (cleaved-caspase-3 increased 10-fold). Quantitative lung histology showed larger and fewer alveoli, greater inflammation, and scattered elastic fibers. Elafin blocked these MV-O2–induced changes.
Conclusions: Intratracheal elafin, by blocking lung protease activity, prevented MV-O2–induced elastin degradation, TGF-β activation, apoptosis, and dispersion of matrix elastin, and attenuated lung structural abnormalities noted in vehicle-treated mice after 24 hours of MV-O2. These findings suggest that elastin breakdown contributes to defective lung growth in response to MV-O2 and might be targeted therapeutically to prevent MV-O2–induced lung injury.
PMCID: PMC3175547  PMID: 21562133
elafin; elastin degradation; neonatal chronic lung disease; ventilator-induced lung injury; bronchopulmonary dysplasia
16.  Autophagic Protein LC3B Confers Resistance against Hypoxia-induced Pulmonary Hypertension 
Rationale: Pulmonary hypertension (PH) is a progressive disease with unclear etiology. The significance of autophagy in PH remains unknown.
Objectives: To determine the mechanisms by which autophagic proteins regulate tissue responses during PH.
Methods: Lungs from patients with PH, lungs from mice exposed to chronic hypoxia, and human pulmonary vascular cells were examined for autophagy using electron microscopy and Western analysis. Mice deficient in microtubule-associated protein-1 light chain-3B (LC3B−/−), or early growth response-1 (Egr-1−/−), were evaluated for vascular morphology and hemodynamics.
Measurements and Main Results: Human PH lungs displayed elevated lipid-conjugated LC3B, and autophagosomes relative to normal lungs. These autophagic markers increased in hypoxic mice, and in human pulmonary vascular cells exposed to hypoxia. Egr-1, which regulates LC3B expression, was elevated in PH, and increased by hypoxia in vivo and in vitro. LC3B−/− or Egr-1−/−, but not Beclin 1+/−, mice displayed exaggerated PH during hypoxia. In vitro, LC3B knockdown increased reactive oxygen species production, hypoxia-inducible factor-1α stabilization, and hypoxic cell proliferation. LC3B and Egr-1 localized to caveolae, associated with caveolin-1, and trafficked to the cytosol during hypoxia.
Conclusions: The results demonstrate elevated LC3B in the lungs of humans with PH, and of mice with hypoxic PH. The increased susceptibility of LC3B−/− and Egr-1−/− mice to hypoxia-induced PH and increased hypoxic proliferation of LC3B knockdown cells suggest adaptive functions of these proteins during hypoxic vascular remodeling. The results suggest that autophagic protein LC3B exerts a protective function during the pathogenesis of PH, through the regulation of hypoxic cell proliferation.
PMCID: PMC3081281  PMID: 20889906
autophagy; hypoxia; hypertension, pulmonary
17.  Development of pulmonary arterial hypertension in mice over-expressing S100A4/Mts1 is specific to females 
Respiratory Research  2011;12(1):159.
Idiopathic and familial forms of pulmonary arterial hypertension (PAH) occur more frequently in women than men. However, the reason for this remains unknown. Both the calcium binding protein S100A4/Mts1 (Mts1) and its endogenous receptor (receptor for advanced glycosylation end products; RAGE) have been implicated in the development of PAH. We wished to investigate if the Mts1/RAGE pathway may play a role in the gender bias associated with PAH.
We investigated the effects of gender on development of PAH in mice over-expressing Mts1 (Mts1+ mice) via measurement of pulmonary arterial remodeling, systolic right ventricular pressure (sRVP) and right ventricular hypertrophy (RVH). Gender differences in pulmonary arterial Mts1 and RAGE expression were assessed by qRT-PCR and immunohistochemistry. Western blotting and cell counts were used to investigate interactions between 17β-estradiol, Mts1 and RAGE on proliferation of human pulmonary artery smooth muscle cells (hPASMCs). Statistical analysis was by one-way analysis of variance with Dunnetts post test or two-way analysis of variance with Bonferronis post test, as appropriate.
Female Mts1+ mice developed increased sRVP and pulmonary vascular remodeling, whereas male Mts1+ mice remained unaffected. The development of plexiform-like lesions in Mts1+ mice was specific to females. These lesions stained positive for both Mts1 and RAGE in the endothelial and adventitial layers. Expression of pulmonary arterial Mts1 was greater in female than male Mts1+ mice, and was localised to the medial and adventitial layers in non plexiform-like pulmonary arteries. RAGE gene expression and immunoreactivity were similar between male and female Mts1+ mice and RAGE staining was localised to the endothelial layer in non plexiform-like pulmonary arteries adjacent to airways. In non-plexiform like pulmonary arteries not associated with airways RAGE staining was present in the medial and adventitial layers. Physiological concentrations of 17β-estradiol increased Mts1 expression in hPASMCs. 17β-estradiol-induced hPASMC proliferation was inhibited by soluble RAGE, which antagonises the membrane bound form of RAGE.
Mts1 over-expression combined with female gender is permissive to the development of experimental PAH in mice. Up-regulation of Mts1 and subsequent activation of RAGE may contribute to 17β-estradiol-induced proliferation of hPASMCs.
PMCID: PMC3276452  PMID: 22185646
18.  Strategic Plan for Lung Vascular Research 
The Division of Lung Diseases of the National Heart, Lung, and Blood Institute, with the Office of Rare Diseases Research, held a workshop to identify priority areas and strategic goals to enhance and accelerate research that will result in improved understanding of the lung vasculature, translational research needs, and ultimately the care of patients with pulmonary vascular diseases. Multidisciplinary experts with diverse experience in laboratory, translational, and clinical studies identified seven priority areas and discussed limitations in our current knowledge, technologies, and approaches. The focus for future research efforts include the following: (1) better characterizing vascular genotype–phenotype relationships and incorporating systems biology approaches when appropriate; (2) advancing our understanding of pulmonary vascular metabolic regulatory signaling in health and disease; (3) expanding our knowledge of the biologic relationships between the lung circulation and circulating elements, systemic vascular function, and right heart function and disease; (4) improving translational research for identifying disease-modifying therapies for the pulmonary hypertensive diseases; (5) establishing an appropriate and effective platform for advancing translational findings into clinical studies testing; and (6) developing the specific technologies and tools that will be enabling for these goals, such as question-guided imaging techniques and lung vascular investigator training programs. Recommendations from this workshop will be used within the Lung Vascular Biology and Disease Extramural Research Program for planning and strategic implementation purposes.
PMCID: PMC3029941  PMID: 20833821
right ventricle; pulmonary hypertension; metabolism; genomics; phenotyping
19.  Autophagy proteins regulate innate immune response by inhibiting NALP3 inflammasome-mediated mitochondrial DNA release 
Nature immunology  2010;12(3):222-230.
Autophagy, a cellular process for organelle and protein turnover, regulates innate immune responses. We demonstrate that depletion of autophagic proteins microtubule associated protein-1 light chain 3B (LC3B) and Beclin 1 enhances caspase-1 activation and secretion of interleukin-1β and interleukin-18. Autophagic protein depletion promoted accumulation of dysfunctional mitochondria and cytosolic translocation of mitochondrial DNA (mtDNA) in response to lipopolysaccharide (LPS) and ATP in macrophages. Release of mtDNA into the cytosol depended on the NALP3 inflammasome and mitochondrial ROS. Cytosolic mtDNA contributed to IL-1β and IL-18 secretion in response to LPS and ATP. LC3B-deficient mice produced more caspase-1-dependent cytokines in two sepsis models and were susceptible to LPS-induced mortality. Our study suggests that autophagic proteins regulate NALP3-dependent inflammation by preserving mitochondrial integrity.
PMCID: PMC3079381  PMID: 21151103
20.  Disruption of PPARγ/β-catenin–mediated regulation of apelin impairs BMP-induced mouse and human pulmonary arterial EC survival 
The Journal of Clinical Investigation  2011;121(9):3735-3746.
Reduced bone morphogenetic protein receptor 2 (BMPR2) expression in patients with pulmonary arterial hypertension (PAH) can impair pulmonary arterial EC (PAEC) function. This can adversely affect EC survival and promote SMC proliferation. We hypothesized that interventions to normalize expression of genes that are targets of BMPR2 signaling could restore PAEC function and prevent or reverse PAH. Here we have characterized, in human PAECs, a BMPR2-mediated transcriptional complex between PPARγ and β-catenin and shown that disruption of this complex impaired BMP-mediated PAEC survival. Using whole genome-wide ChIP-Chip promoter analysis and gene expression microarrays, we delineated PPARγ/β-catenin–dependent transcription of target genes including APLN, which encodes apelin. We documented reduced PAEC expression of apelin in PAH patients versus controls. In cell culture experiments, we showed that apelin-deficient PAECs were prone to apoptosis and promoted pulmonary arterial SMC (PASMC) proliferation. Conversely, we established that apelin, like BMPR2 ligands, suppressed proliferation and induced apoptosis of PASMCs. Consistent with these functions, administration of apelin reversed PAH in mice with reduced production of apelin resulting from deletion of PPARγ in ECs. Taken together, our findings suggest that apelin could be effective in treating PAH by rescuing BMPR2 and PAEC dysfunction.
PMCID: PMC3163943  PMID: 21821917
21.  Cholinergic modulation of angiogenesis: Role of the endothelial α7 nicotine acetylcholine receptor 
Journal of cellular biochemistry  2009;108(2):433-446.
Pathological angiogenesis contributes to tobacco-related diseases such as malignancy, atherosclerosis and age-related macular degeneration. Nicotine acts on endothelial nicotinic acetylcholine receptors (nAChRs) to activate endothelial cells and to augment pathological angiogenesis. In the current study, we studied nAChR subunits involved in these actions. We detected mRNA for all mammalian nAChR subunits except α2, α4, γ and δ in four different types of ECs. Using siRNA methodology, we found that the α7 nAChR plays a dominant role in nicotine-induced cell signaling (assessed by intracellular calcium and NO imaging, and studies of protein expression and phosphorylation), as well as nicotine-activated EC functions (proliferation, survival, migration and tube formation). The α9 and α7 nAChRs have opposing effects on nicotine-induced cell proliferation and survival. Our studies reveal a critical role for the α7 nAChR in mediating the effects of nicotine on the endothelium. Other subunits play a modulatory role. These findings may have therapeutic implications for diseases characterized by pathological angiogenesis.
PMCID: PMC3140170  PMID: 19623583
22.  BMP promotes motility and represses growth of smooth muscle cells by activation of tandem Wnt pathways 
The Journal of Cell Biology  2011;192(1):171-188.
Vascular smooth muscle cell motility relies on interdependent activation of canonical and noncanonical Wnt signal transduction pathways; fibronectin, produced in response to BMP-2–mediated activation of β-catenin, promotes motility by activating an integrin-linked kinase via α4-integrin.
We present a novel cell-signaling paradigm in which bone morphogenetic protein 2 (BMP-2) consecutively and interdependently activates the wingless (Wnt)–β-catenin (βC) and Wnt–planar cell polarity (PCP) signaling pathways to facilitate vascular smooth muscle motility while simultaneously suppressing growth. We show that BMP-2, in a phospho-Akt–dependent manner, induces βC transcriptional activity to produce fibronectin, which then activates integrin-linked kinase 1 (ILK-1) via α4-integrins. ILK-1 then induces the Wnt–PCP pathway by binding a proline-rich motif in disheveled (Dvl) and consequently activating RhoA-Rac1–mediated motility. Transfection of a Dvl mutant that binds βC without activating RhoA-Rac1 not only prevents BMP-2–mediated vascular smooth muscle cell motility but promotes proliferation in association with persistent βC activity. Interfering with the Dvl-dependent Wnt–PCP activation in a murine stented aortic graft injury model promotes extensive neointima formation, as shown by optical coherence tomography and histopathology. We speculate that, in response to injury, factors that subvert BMP-2–mediated tandem activation of Wnt–βC and Wnt–PCP pathways contribute to obliterative vascular disease in both the systemic and pulmonary circulations.
PMCID: PMC3019546  PMID: 21220513
23.  LC3 Mediated Fibronectin mRNA Translation Induces Fibrosarcoma Growth by Increasing Connective Tissue Growth Factor 
Journal of cell science  2009;122(Pt 9):1441-1451.
Previously we related fibronectin (FN) mRNA translation to an interaction between an AU-rich element (ARE) in the FN-3′ UTR and Light Chain 3 (LC3) of microtubule associated proteins 1A and 1B. Since human fibrosarcoma (HT1080) cells produce both little FN and LC3, we used these cells to investigate how LC3-mediated FN mRNA translation might alter tumor growth. Transfection of HT1080 cells with LC3 enhanced FN mRNA translation that depended on an interaction between a triple arginine motif in LC3 and the ARE in FN mRNA, as determined by relating FN synthesis to mRNA levels, by polysome analysis of the FN mRNA transcript, and by RNA binding assays. Wild type, (WT) but not mutant LC3, accelerated HT1080 cell growth in culture and when implanted in SCID mice. Comparison of LC3-WT with vector-transfected HT1080 cells revealed increased FN-dependent proliferation, adhesion and invasion. Microarray analysis of genes differentially expressed in LC3-WT vs. vector-transfected control cells indicated enhanced expression of connective tissue growth factor (CTGF). Using siRNA, we show by qRT-PCR that enhanced expression of CTGF is FN- dependent and that LC3 mediated adhesion, invasion and proliferation are CTGF-dependent. Expression profiling of soft tissue tumors revealed increased expression of both LC3 and CTGF in some locally invasive tumor types.
PMCID: PMC2672968  PMID: 19366727
mRNA translation; microtubule associated protein; tumor invasiveness; LC3; fibronectin; connective tissue growth factor
24.  S100A4 and BMP-2 Co-Dependently Induce Vascular Smooth Muscle Cell Migration via pERK and Chloride Intracellular Channel 4 (CLIC4) 
Circulation research  2009;105(7):639.
S100A4/Mts1 is implicated in motility of human pulmonary artery smooth muscle cells (hPASMC), through an interaction with the receptor for advanced glycation end products (RAGE).
We hypothesized that S100A4/Mts1-mediated hPASMC motility might be enhanced by loss of function of bone morphogenetic protein (BMP) receptor (R) II, observed in pulmonary arterial hypertension (PAH).
Methods and Results
Both S100A4/Mts1 (500ng/ml) and BMP-2 (10ng/ml) induce migration of hPASMCS in a novel co-dependent manner, in that the response to either ligand is lost with anti-RAGE or BMPRII siRNA. Phosphorylation of ERK is induced by both ligands and is required for motility by inducing MMP2 activity, but phosphoERK1/2 is blocked by anti-RAGE and not by BMPRII siRNA. In contrast, BMPRII siRNA, but not anti-RAGE, reduces expression of intracellular chloride channel 4 (CLIC4), 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 (MHCIIA), but does alter alignment of MHCIIA 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 lamellipodiae in motile cells.
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, i.e., cell motility. We speculate that this carefully controlled process limits signals from multiple ligands, but could be subverted in disease.
PMCID: PMC2818124  PMID: 19713532
Bone morphogenetic protein; S100 protein; Vascular smooth muscle cells; Intracellular chloride channel; migration
25.  Insulin Resistance in Pulmonary Arterial Hypertension 
Although obesity, dyslipidemia, and insulin resistance (IR) are well known risk factors for systemic cardiovascular disease, their impact on pulmonary arterial hypertension (PAH) is unknown. Our previous studies indicate that IR may be a risk factor for PAH. We now investigate the prevalence of IR in PAH and explore its relationship to disease severity.
Clinical data and fasting blood samples were evaluated in 81 non-diabetic PAH females. National Health and Nutrition Examination Surveys (NHANES) females (n=967) served as controls. Fasting triglyceride to high-density lipoprotein cholesterol ratio (TG/HDL-C) was used as a surrogate of insulin sensitivity.
While BMI was similar in NHANES vs PAH females (28.6 vs. 28.7 kg/m2), PAH females were more likely to be IR (45.7% vs. 21.5%) and less likely to be IS (43.2% vs. 57.8%, p<0.0001). PAH females mostly had NYHA class II and III symptoms (82.7%). Etiology, NYHA class, 6-minute-walk-distance, and hemodynamics did not differ between IR and IS PAH groups. However, the presence of IR and a higher NYHA class were associated with poorer 6-months event-free survival (58% vs. 79%, p<0.05).
Insulin Resistance appears to be more common in PAH females than in the general population, and may be a novel risk factor or disease modifier which might impact survival.
PMCID: PMC2785883  PMID: 19047320
Insulin Resistance; Obesity; Pulmonary Arterial Hypertension

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