Metalloproteinases and their inhibitors are associated with pulmonary arterial stiffness and ventricular function in pediatric pulmonary hypertension.

Disturbed balance between matrix metalloproteinases (MMPs) and their respective tissue inhibitors (TIMPs) is a well-recognized pathophysiological component of pulmonary arterial hypertension (PAH). Both classes of proteinases have been associated with clinical outcomes as well as with specific pathological features of ventricular dysfunction and pulmonary arterial remodeling. The purpose of this study was to evaluate the circulating levels of MMPs and TIMPs in children with PAH undergoing the same-day cardiac magnetic resonance imaging (MRI) and right heart catheterization. Children with PAH (n = 21) underwent a same-day catheterization, comprehensive cardiac MRI evaluation, and blood sample collection for proteomic analysis. Correlative analysis was performed between protein levels and 1) standard PAH indices from catheterization, 2) cardiac MRI hemodynamics, and 3) pulmonary arterial stiffness. MMP-8 was significantly associated with the right ventricular end-diastolic volume (R = 0.45, P = 0.04). MMP-9 levels were significantly associated with stroke volume (R = -0.49, P = 0.03) and pulmonary vascular resistance (R = 0.49, P = 0.03). MMP-9 was further associated with main pulmonary arterial stiffness evaluated by relative area change (R = -0.79, P < 0.01).TIMP-2 and TIMP-4 levels were further associated with the right pulmonary artery pulse wave velocity (R = 0.51, P = 0.03) and backward compression wave (R = 0.52, P = 0.02), respectively. MMPs and TIMPs warrant further clinically prognostic evaluation in conjunction with the conventional cardiac MRI hemodynamic indices.NEW & NOTEWORTHY Metalloproteinases have been associated with clinical outcomes in pulmonary hypertension and with specific pathological features of ventricular dysfunction and pulmonary arterial remodeling. In this study, we demonstrated that plasma circulating levels of metalloproteinases and their inhibitors are associated with standard cardiac MRI hemodynamic indices and with the markers of proximal pulmonary arterial stiffness. Particularly, MMP-9 and TIMP-2 were associated with several different markers of pulmonary arterial stiffness. These findings suggest the interplay between the extracellular matrix (ECM) remodeling and overall hemodynamic status in children with PAH might be assessed using the peripheral circulating MMP and TIMP levels.

The TRPM2 ion channel contributes to cytokine hyperproduction in a mouse model of Down Syndrome.

Trisomy 21 (Down Syndrome, DS) is the most common chromosomal anomaly. Although DS is mostly perceived as affecting cognitive abilities and cardiac health, individuals with DS also exhibit dysregulated immune functions. Levels of pro-inflammatory cytokines are increased, but intrinsic alterations of innate immunity are understudied in DS. Furthermore, elevated Reactive Oxygen Species (ROS) are well documented in individuals with DS, further exacerbating inflammatory processes. Chronic inflammation and oxidative stress are often precursors of subsequent tissue destruction and pathologies, which affect a majority of persons with DS. Together with ROS, the second messenger ion Ca2+ plays a central role in immune regulation. TRPM2 (Transient Receptor Potential Melastatin 2) is a Ca2+-permeable ion channel that is activated under conditions of oxidative stress. The Trpm2 gene is located on human Chromosome 21 (Hsa21). TRPM2 is strongly represented in innate immune cells, and numerous studies have documented its role in modulating inflammation. We have previously found that as a result of suboptimal cytokine production, TRPM2-/- mice are highly susceptible to the bacterial pathogen Listeria monocytogenes (Lm). We therefore used Lm infection to trigger and characterize immune responsiveness in the DS mouse model Dp10(yey), and to investigate the potential contribution of TRPM2. In comparison to wildtype (WT), Dp10(yey) mice show an increased resistance against Lm infection and higher IFNγ serum concentrations. Using a gene elimination approach, we show that these effects correlate with Trpm2 gene copy number, supporting the notion that Trpm2 might promote hyperinflammation in DS.

Biomarkers for pediatric pulmonary arterial hypertension: challenges and recommendations.

Pediatric pulmonary arterial hypertension (PAH) is an uncommon disease that can occur in neonates, infants, and children, and is associated with high morbidity and mortality. Despite advances in treatment strategies over the last two decades, the underlying structural and functional changes to the pulmonary arterial circulation are progressive and lead eventually to right heart failure. The management of PAH in children is complex due not only to the developmental aspects but also because most evidence-based practices derive from adult PAH studies. As such, the pediatric clinician would be greatly aided by specific characteristics (biomarkers) objectively measured in children with PAH to determine appropriate clinical management. This review highlights the current state of biomarkers in pediatric PAH and looks forward to potential biomarkers, and makes several recommendations for their use and interpretation.

Bronchus-associated lymphoid tissue in pulmonary hypertension produces pathologic autoantibodies.

RATIONALE: Autoimmunity has long been associated with pulmonary hypertension. Bronchus-associated lymphoid tissue plays important roles in antigen sampling and self-tolerance during infection and inflammation. OBJECTIVES: We reasoned that activated bronchus-associated lymphoid tissue would be evident in rats with pulmonary hypertension, and that loss of self-tolerance would result in production of pathologic autoantibodies that drive vascular remodeling. METHODS: We used animal models, histology, and gene expression assays to evaluate the role of bronchus-associated lymphoid tissue in pulmonary hypertension. MEASUREMENTS AND MAIN RESULTS: Bronchus-associated lymphoid tissue was more numerous, larger, and more active in pulmonary hypertension compared with control animals. We found dendritic cells in and around lymphoid tissue, which were composed of CD3(+) T cells over a core of CD45RA(+) B cells. Antirat IgG and plasma from rats with pulmonary hypertension decorated B cells in lymphoid tissue, resistance vessels, and adventitia of large vessels. Lymphoid tissue in diseased rats was vascularized by aquaporin-1(+) high endothelial venules and vascular cell adhesion molecule-positive vessels. Autoantibodies are produced in bronchus-associated lymphoid tissue and, when bound to pulmonary adventitial fibroblasts, change their phenotype to one that may promote inflammation. Passive transfer of autoantibodies into rats caused pulmonary vascular remodeling and pulmonary hypertension. Diminution of lymphoid tissue reversed pulmonary hypertension, whereas immunologic blockade of CCR7 worsened pulmonary hypertension and hastened its onset. CONCLUSIONS: Bronchus-associated lymphoid tissue expands in pulmonary hypertension and is autoimmunologically active. Loss of self-tolerance contributes to pulmonary vascular remodeling and pulmonary hypertension. Lymphoid tissue-directed therapies may be beneficial in treating pulmonary hypertension.

Altered peripheral blood leukocyte subpopulations, function, and gene expression in children with Down syndrome: implications for respiratory tract infection.

OBJECTIVES: We tested the hypothesis that aberrant expression of Hsa21-encoded interferon genes in peripheral blood immune cells would correlate to immune cell dysfunction in children with Down syndrome (DS). STUDY DESIGN: We performed flow cytometry to quantify peripheral blood leukocyte subtypes and measured their ability to migrate and phagocytose. In matched samples, we measured gene expression levels for constituents of interferon signaling pathways. We screened 49 children, of which 29 were individuals with DS. RESULTS: We show that the percentages of two peripheral blood myeloid cell subtypes (alternatively-activated macrophages and low-density granulocytes) in children with DS differed significantly from typical children, children with DS circulate a very different pattern of cytokines vs. typical individuals, and higher expression levels of type III interferon receptor Interleukin-10Rb in individuals with DS correlated with reduced migratory and phagocytic capacity of macrophages. CONCLUSIONS: Increased susceptibility to severe and chronic infection in children with DS may result from inappropriate numbers and subtypes of immune cells that are phenotypically and functionally altered due to trisomy 21 associated interferonopathy.

Increased lethality of respiratory infection by Streptococcus pneumoniae in the Dp16 mouse model of Down syndrome.

Objectives: We sought to investigate whether the Dp16 mouse model of Down syndrome (DS) is more susceptible to severe and lethal respiratory tract infection by Streptococcus pneumoniae. Study Design: We infected controls and Dp16 mice with Streptococcus pneumoniae and measured survival rates. We compared cytokine production by primary lung cell cultures exposed to Streptococcus pneumoniae. We examined lung protein expression for interferon signaling related pathways. We characterized the histopathology and quantified the extent of bronchus-associated lymphoid tissue. Finally, we examined mouse tissues for the presence of oligomeric tau protein. Results: We found that the Dp16 mouse model of DS displayed significantly higher susceptibility to lethal respiratory infection with Streptococcus pneumoniae compared to control mice. Lung cells cultured from Dp16 mice displayed unique secreted cytokine profiles compared to control mice. The Dp16 mouse lungs were characterized by profound lobar pneumonia with massive diffuse consolidation involving nearly the entire lobe. Marked red hepatization was noted, and Dp16 mice lungs contained numerous bronchus-associated lymphoid tissues that were highly follicularized. Compared to uninfected mice, both control mice and Dp16 mice infected with Streptococcus pneumoniae showed evidence of oligomeric tau aggregates. Conclusions: Increased susceptibility to severe respiratory tract infection with Streptococcus pneumoniae in Dp16 mice closely phenocopies infection in individuals with DS. The increase does not appear to be linked to overexpression of mouse interferon genes syntenic to human chromosome 21.

Lung and Heart Biology of the Dp16 Mouse Model of down Syndrome: Implications for Studying Cardiopulmonary Disease.

(1) Background: We sought to investigate the baseline lung and heart biology of the Dp16 mouse model of Down syndrome (DS) as a prelude to the investigation of recurrent respiratory tract infection. (2) Methods: In controls vs. Dp16 mice, we compared peripheral blood cell and plasma analytes. We examined baseline gene expression in lungs and hearts for key parameters related to susceptibility of lung infection. We investigated lung and heart protein expression and performed lung morphometry. Finally, and for the first time each in a model of DS, we performed pulmonary function testing and a hemodynamic assessment of cardiac function. (3) Results: Dp16 mice circulate unique blood plasma cytokines and chemokines. Dp16 mouse lungs over-express the mRNA of triplicated genes, but not necessarily corresponding proteins. We found a sex-specific decrease in the protein expression of interferon α receptors, yet an increased signal transducer and activator of transcription (STAT)-3 and phospho-STAT3. Platelet-activating factor receptor protein was not elevated in Dp16 mice. The lungs of Dp16 mice showed increased stiffness and mean linear intercept and contained bronchus-associated lymphoid tissue. The heart ventricles of Dp16 mice displayed hypotonicity. Finally, Dp16 mice required more ketamine to achieve an anesthetized state. (4) Conclusions: The Dp16 mouse model of DS displays key aspects of lung heart biology akin to people with DS. As such, it has the potential to be an extremely valuable model of recurrent severe respiratory tract infection in DS.

Endothelin-1, the unfolded protein response, and persistent inflammation: role of pulmonary artery smooth muscle cells.

Endothelin-1 is a potent vasoactive peptide that occurs in chronically high levels in humans with pulmonary hypertension and in animal models of the disease. Recently, the unfolded protein response was implicated in a variety of diseases, including pulmonary hypertension. In addition, evidence is increasing for pathological, persistent inflammation in the pathobiology of this disease. We investigated whether endothelin-1 might engage the unfolded protein response and thus link inflammation and the production of hyaluronic acid by pulmonary artery smooth muscle cells. Using immunoblot, real-time PCR, immunofluorescence, and luciferase assays, we found that endothelin-1 induces both a transcriptional and posttranslational activation of the three major arms of the unfolded protein response. The pharmacologic blockade of endothelin A receptors, but not endothelin B receptors, attenuated the observed release, as did a pharmacologic blockade of extracellular signal-regulated kinases 1 and 2 (ERK-1/2) signaling. Using short hairpin RNA and ELISA, we observed that the release by pulmonary artery smooth muscle cells of inflammatory modulators, including hyaluronic acid, is associated with endothelin-1-induced ERK-1/2 phosphorylation and the unfolded protein response. Furthermore, the synthesis of hyaluronic acid induced by endothelin-1 is permissive for persistent THP-1 monocyte binding. These results suggest that endothelin-1, in part because it induces the unfolded protein response in pulmonary artery smooth muscle cells, triggers proinflammatory processes that likely contribute to vascular remodeling in pulmonary hypertension.

Circulating cytokines and growth factors in pediatric pulmonary hypertension.

BACKGROUND: Management of pediatric pulmonary hypertension (PH) remains challenging. We have assessed a panel of circulating proteins in children with PH to investigate their value as predictive and/or prognostic biomarkers. From these determinations, we aim to develop a practical, noninvasive tool to aid in the management of pediatric PH. METHODS: Twelve cytokines and growth factors putatively associated with lung or vascular disease were examined in plasma specimens from 70 children with PH using multiplex protein array technology. Associations between hemodynamics, adverse events, and protein markers were evaluated. RESULTS: Epidermal growth factor (EGF) and IL-6 were associated with important hemodynamics. Of the twelve proteins, VEGF and IL-6 were significantly, univariately associated with the occurrence of an adverse event, with odds ratios (95% confidence intervals) of 0.56 (0.33-0.98) and 1.69 (1.03-2.77), respectively. When hemodynamic predictors were combined with protein markers, the ability to predict adverse outcomes within the following year significantly increased. CONCLUSIONS: Specific circulating proteins are associated with hemodynamic variables in pediatric PH. If confirmed in additional cohorts, measurement of these proteins could aid patient care and design of clinical trials by identifying patients at risk for adverse events. These findings also further support a role for inflammation in pediatric PH.

Mass Cytometry Reveals Global Immune Remodeling with Multi-lineage Hypersensitivity to Type I Interferon in Down Syndrome.

People with Down syndrome (DS; trisomy 21) display a different disease spectrum relative to the general population, including lower rates of solid malignancies and higher incidence of neurological and autoimmune conditions. However, the mechanisms driving this unique clinical profile await elucidation. We completed a deep mapping of the immune system in adults with DS using mass cytometry to evaluate 100 immune cell types, which revealed global immune dysregulation consistent with chronic inflammation, including key changes in the myeloid and lymphoid cell compartments. Furthermore, measurement of interferon-inducible phosphorylation events revealed widespread hypersensitivity to interferon-α in DS, with cell-type-specific variations in downstream intracellular signaling. Mechanistically, this could be explained by overexpression of the interferon receptors encoded on chromosome 21, as demonstrated by increased IFNAR1 surface expression in all immune lineages tested. These results point to interferon-driven immune dysregulation as a likely contributor to the developmental and clinical hallmarks of DS.

What people with Down Syndrome can teach us about cardiopulmonary disease.

Down syndrome is the most common chromosomal abnormality among live-born infants. Through full or partial trisomy of chromosome 21, Down syndrome is associated with cognitive impairment, congenital malformations (particularly cardiovascular) and dysmorphic features. Immune disturbances in Down syndrome account for an enormous disease burden ranging from quality-of-life issues (autoimmune alopecia) to more serious health issues (autoimmune thyroiditis) and life-threatening issues (leukaemia, respiratory tract infections and pulmonary hypertension). Cardiovascular and pulmonary diseases account for ∼75% of the mortality seen in persons with Down syndrome. This review summarises the cardiovascular, respiratory and immune challenges faced by individuals with Down syndrome, and the genetic underpinnings of their pathobiology. We strongly advocate increased comparative studies of cardiopulmonary disease in persons with and without Down syndrome, as we believe these will lead to new strategies to prevent and treat diseases affecting millions of people worldwide.

Development of occlusive neointimal lesions in distal pulmonary arteries of endothelin B receptor-deficient rats: a new model of severe pulmonary arterial hypertension.

BACKGROUND: Human pulmonary arterial hypertension (PAH) is characterized by proliferation of vascular smooth muscle and, in its more severe form, by the development of occlusive neointimal lesions. However, few animal models of pulmonary neointimal proliferation exist, thereby limiting a complete understanding of the pathobiology of PAH. Recent studies of the endothelin (ET) system demonstrate that deficiency of the ET(B) receptor predisposes adult rats to acute and chronic hypoxic PAH, yet these animals fail to develop neointimal lesions. Herein, we determined and thereafter showed that exposure of ET(B) receptor-deficient rats to the endothelial toxin monocrotaline (MCT) leads to the development of neointimal lesions that share hallmarks of human PAH. METHODS AND RESULTS: The pulmonary hemodynamic and morphometric effects of 60 mg/kg MCT in control (MCT(+/+)) and ET(B) receptor-deficient (MCT(sl/sl)) rats at 6 weeks of age were assessed. MCT(sl/sl) rats developed more severe PAH, characterized by elevated pulmonary artery pressure, diminished cardiac output, and right ventricular hypertrophy. In MCT(sl/sl) rats, morphometric evaluation revealed the presence of neointimal lesions within small distal pulmonary arteries, increased medial wall thickness, and decreased arterial-to-alveolar ratio. In keeping with this, barium angiography revealed diminished distal pulmonary vasculature of MCT(sl/sl) rat lungs. Cells within neointimal lesions expressed smooth muscle and endothelial cell markers. Moreover, cells within neointimal lesions exhibited increased levels of proliferation and were located in a tissue microenvironment enriched with vascular endothelial growth factor, tenascin-C, and activated matrix metalloproteinase-9, factors already implicated in human PAH. Finally, assessment of steady state mRNA showed that whereas expression of ET(B) receptors was decreased in MCT(sl/sl) rat lungs, ET(A) receptor expression increased. CONCLUSIONS: Deficiency of the ET(B) receptor markedly accelerates the progression of PAH in rats treated with MCT and enhances the appearance of cellular and molecular markers associated with the pathobiology of PAH. Collectively, these results suggest an overall antiproliferative effect of the ET(B) receptor in pulmonary vascular homeostasis.

Endothelin B receptor deficiency predisposes to pulmonary edema formation via increased lung vascular endothelial cell growth factor expression.

Endothelin (ET) may contribute to pulmonary edema formation, particularly under hypoxic conditions, and decreases in ET-B receptor expression can lead to reduced ET clearance. ET increases vascular endothelial cell growth factor (VEGF) production in vitro, and VEGF overexpression in the lung causes pulmonary edema in vivo. We hypothesized that pulmonary vascular ET-B receptor deficiency leads to increased lung ET, that excess ET increases lung VEGF levels, promoting pulmonary edema formation, and that hypoxia exaggerates these effects. We studied these hypotheses in ET-B receptor-deficient rats. In normoxia, homozygous ET-B-deficient animals had significantly more lung vascular leak than heterozygous or control animals. Hypoxia increased vascular leak regardless of genotype, and hypoxic ET-B-deficient animals leaked more than hypoxic control animals. ET-B-deficient animals had higher lung ET levels in both normoxia and hypoxia. Lung HIF-1alpha and VEGF content was greater in the ET-B-deficient animals in both normoxia and hypoxia, and both HIF-1alpha and VEGF levels were reduced by ET-A receptor antagonism. Both ET-A receptor blockade and VEGF antagonism reduced vascular leak in hypoxic ET-B-deficient animals. We conclude that ET-B receptor-deficient animals display an exaggerated lung vascular protein leak in normoxia, that hypoxia exacerbates that leak, and that this effect is in part attributable to an ET-mediated increase in lung VEGF content.

Proteomics of pulmonary hypertension: could personalized profiles lead to personalized medicine?

Pulmonary hypertension (PH) is a fatal syndrome that arises from a multifactorial and complex background, is characterized by increased pulmonary vascular resistance and right heart afterload, and often leads to cor pulmonale. Over the past decades, remarkable progress has been made in reducing patient symptoms and delaying the progression of the disease. Unfortunately, PH remains a disease with no cure. The substantial heterogeneity of PH continues to be a major limitation to the development of newer and more efficacious therapies. New advances in our understanding of the biological pathways leading to such a complex pathogenesis will require the identification of the important proteins and protein networks that differ between a healthy lung (or right ventricle) and a remodeled lung in an individual with PH. In this article, we present the case for the increased use of proteomics--the study of proteins and protein networks--as a discovery tool for key proteins and protein networks operational in the PH lung. We review recent applications of proteomics in PH, and summarize the biological pathways identified. Finally, we attempt to presage what the future will bring with regard to proteomics in PH and offer our perspectives on the prospects of developing personalized proteomics and custom-tailored therapies.

Applying Biotechnology and Bioengineering to Pediatric Lung Disease: Emerging Paradigms and Platforms.

Pediatric lung diseases remain a costly worldwide health burden. For many children with end-stage lung disease, lung transplantation remains the only therapeutic option. Due to the limited number of lungs available for transplantation, alternatives to lung transplant are desperately needed. Recently, major improvements in tissue engineering have resulted in newer technology and methodology to develop viable bioengineered lungs. These include critical advances in lung cell biology, stem cell biology, lung extracellular matrix, microfabrication techniques, and orthotopic transplantation of bioartificial lungs. The goal of this short review is to engage the reader's interest with regard to these emerging concepts and to stimulate their interest to learn more. We review the existing state of the art of lung tissue engineering, and point to emerging paradigms and platforms in the field. Finally, we summarize the challenges and unmet needs that remain to be overcome.

Animal Models of Pulmonary Hypertension: Matching Disease Mechanisms to Etiology of the Human Disease.

Recently a great deal of progress has been made in our understanding of pulmonary hypertension (PH). Research from the past 30 years has resulted in newer treatments that provide symptomatic improvements and delayed disease progression. Unfortunately, the cure for patients with this lethal syndrome remains stubbornly elusive. With the relative explosion of scientific literature regarding PH, confusion has arisen regarding animal models of the disease and their correlation to the human condition. This short review uniquely focuses on the clear and present need to better correlate mechanistic insights from existing and emerging animal models of PH to specific etiologies and histopathologies of human PH. A better understanding of the pathologic processes in various animal models and how they relate to the human disease should accelerate the development of newer and more efficacious therapies.

Biomarkers for pediatric pulmonary arterial hypertension - a call to collaborate.

Therapeutic approaches in pediatric pulmonary arterial hypertension (PAH) are based primarily on clinician experience, in contrast to the evidence-based approach in adults with pulmonary hypertension. There is a clear and present need for non-invasive and objective biomarkers to guide the accurate diagnosis, treatment, and prognosis of this disease in children. The multifaceted spectrum of disease, clinical presentation, and association with other diseases makes this a formidable challenge. However, as more progress is being made in the understanding and management of adult PAH, the potential to apply this knowledge to children has never been greater. This review explores the state of the art with regard to non-invasive biomarkers in PAH, with an eye toward those adult PAH biomarkers potentially suitable for application in pediatric PAH.

Circulating myeloid-derived suppressor cells are increased and activated in pulmonary hypertension.

BACKGROUND: Myeloid-derived suppressor cells (MDSCs) are increased in inflammatory and autoimmune disorders and orchestrate immune cell responses therein. Pulmonary hypertension (PH) is associated with inflammation, autoimmunity, and lung vascular remodeling. Immature myeloid cells are found in the lungs of humans and animals with PH, and we hypothesized that they would be increased in the blood of patients with PH compared with control subjects. METHODS: Twenty-six children with PH and 10 undergoing cardiac catheterization for arrhythmia ablation were studied. Five milliliters of fresh blood were analyzed using flow cytometry. Results were confirmed using magnetic bead sorting and immunofluorescence, while quantitative polymerase chain reaction and intracellular urea concentration assays were used as measures of MDSC arginase-1 activation. RESULTS: Flow cytometry demonstrated enrichment of circulating MDSCs among patients with PH (n = 26; mean, 0.271 × 10(6) cells/mL ± 0.17; 1.86% of CD45(+) population ± 1.51) compared with control subjects (n = 10; mean, 0.176 × 10(6) cells/mL ± 0.05; 0.57% of CD45(+) population ± 0.29; P < .05). Higher numbers of circulating MDSCs correlated to increasing mean pulmonary artery pressure (r = 0.510, P < .05). Among patients with PH, female patients had a twofold increase in MDSCs compared with male patients. Immunofluorescence analysis confirmed the results of flow cytometry. Quantitative reverse transcription polymerase chain reaction assay results for arginase-1 and measurement of intracellular urea concentration revealed increased activity of MDSCs from patients with PH compared with control subjects. CONCLUSIONS: Circulating activated MDSCs are significantly increased in children with PH compared with control subjects. Further investigation of these cells is warranted, and we speculate that they might play significant immunomodulatory roles in the disease pathogenesis of PH.

Activation of the unfolded protein response is associated with pulmonary hypertension.

Pulmonary hypertension remains an important cause of morbidity and mortality. Although there is currently no cure, descriptions of defective intracellular trafficking and protein misfolding in vascular cell models of pulmonary hypertension have been recently reported. We tested the hypothesis that activation of the unfolded protein response (UPR) would be associated with the development of severe PH. We investigated activation of the UPR in archival tissues from patients with severe PH, and in the monocrotaline-induced rat model of severe PH. We tested the ability of a pharmacologic agent capable of modulating the UPR to prevent and reverse pulmonary hypertension. We found evidence of an active UPR in archival tissue from humans with PH, but not in control lungs. Similarly, monocrotaline-treated rats demonstrated a significant difference in expression of each of the major arms of the UPR compared to controls. Interestingly, the UPR preceded the appearance of macrophages and the development of lung vascular remodeling in the rats. Treatment of monocrotaline rats with salubrinal, a modulator of the PERK arm of the UPR, attenuated PH and was associated with a decrease in lung macrophages. In culture, pulmonary artery smooth muscle cells with UPR induction produced IL-6 and CCL-2/MCP-1, and stimulated macrophage migration. These effects were abolished by pretreatment of cells with salubrinal. These data support the hypothesis that the UPR may play a role in the pathogenesis of inflammatory vascular remodeling and PH. As such, understanding the functional contributions of the UPR in the setting of PH may have important therapeutic implications.