Comparison of Contemporary Risk Scores in All Groups of Pulmonary Hypertension: A Pulmonary Vascular Research Institute GoDeep Meta-Registry Analysis

BACKGROUND

Pulmonary hypertension (PH) is a heterogeneous disease with a poor prognosis. Accurate risk stratification is essential for guiding treatment decisions in pulmonary arterial hypertension (PAH). Although various risk models have been developed for PAH, their comparative prognostic potential requires further exploration. Additionally, the applicability of risk scores in PH groups beyond group 1 remains to be investigated.

RESEARCH QUESTION

Are risk scores originally developed for PAH predictive in PH groups 1 through 4?

STUDY DESIGN AND METHODS

We conducted a comprehensive analysis of outcomes among patients with incident PH enrolled in the multicenter worldwide Pulmonary Vascular Research Institute GoDeep meta-registry. Analyses were performed across PH groups 1 through 4 and further subgroups to evaluate the predictive value of PAH risk scores, including REVEAL Lite 2, REVEAL 2.0, ESC/ERS 2022, COMPERA 3-strata, and COMPERA 4-strata.

RESULTS

Eight thousand five hundred sixty-five patients were included in the study, of whom 3,537 patients were assigned to group 1 PH, whereas 1,807 patients, 1,635 patients, and 1,586 patients were assigned to group 2 PH, group 3 PH, and group 4 PH, respectively. Pulmonary hemodynamics were impaired with median mean pulmonary arterial pressure of 42 mm Hg (33-52 mm Hg) and pulmonary vascular resistance of 7 WU (4-11 WU). All risk scores were prognostic in the entire PH population and in each of the PH groups 1 through 4. The REVEAL scores, when used as continuous prediction models, demonstrated the highest statistical prognostic power and granularity; the COMPERA 4-strata risk score provided subdifferentiation of the intermediate-risk group. Similar results were obtained when separately analyzing various subgroups (PH subgroups 1.1, 1.4.1, and 1.4.4; PH subgroups 3.1 and 3.2; group 2 with isolated postcapillary PH vs combined precapillary and postcapillary PH; patients of all groups with concomitant cardiac comorbidities; and severe [> 5 WU] vs nonsevere PH).

INTERPRETATION

This comprehensive study with real-world data from 15 PH centers showed that PAH-designed risk scores possess predictive power in a large PH cohort, whether considered as common to the group or calculated separately for each PH group (1-4) and various subgroups.

Persistence of pulmonary hypertension in patients undergoing ventricular assist devices and orthotopic heart transplantation

Pulmonary hypertension (PH) is common in advanced heart failure and often improves quickly after left ventricular assist device (VAD) implantation or orthotopic heart transplantation (OHT), but long-term effects and outcomes are not well-described. This study evaluated PH persistence after VAD as destination therapy (VAD-DT), bridge to transplant (VAD-OHT), or OHT-alone. The study constituted a retrospective review of patients who underwent VAD-DT (n = 164), VAD-OHT (n = 111), or OHT-alone (n = 138) at a single tertiary-care center. Right heart catheterization (RHC) data was collected pre-, post-intervention (VAD and/or OHT), and 1-year from final intervention (latest-RHC) to evaluate the longitudinal hemodynamic course of right ventricular function and pulmonary vasculature. PH (Group II and Group I) definitions were adapted from expert guidelines. All groups showed significant improvements in mean pulmonary artery pressure (mPAP), pulmonary artery wedge pressure (PAWP), cardiac output, and pulmonary vascular resistance (PVR) at each RHC with greatest improvement at post-intervention RHC (post-VAD or post-OHT). PH was reduced from 98% to 26% in VAD-OHT, 92%-49% in VAD-DT, and 76%-28% in OHT-alone from preintervention to latest-RHC. At latest-RHC mPAP remained elevated in all groups despite normalization of PAWP and PVR. VAD-supported patients exhibited suppressed pulmonary artery pulsatility index (PaPi < 3.7) with improvement only posttransplant at latest-RHC. Posttransplant patients with PH at latest-RHC (n = 60) exhibited lower survival (HR: 2.1 [95% CI: 1.3-3.4], p < 0.001). Despite an overall significant improvement in pulmonary pressures and PH proportion, a notable subset of patients exhibited PH post-intervention. Post-intervention PH was associated with lower posttransplant survival.

Specificity Protein 1-Mediated Promotion of CXCL12 Advances Endothelial Cell Metabolism and Proliferation in Pulmonary Hypertension

Pulmonary arterial hypertension (PAH) is a rare yet devastating and incurable disease with few treatment options. The underlying mechanisms of PAH appear to involve substantial cellular proliferation and vascular remodeling, causing right ventricular overload and eventual heart failure. Recent evidence suggests a significant seminal role of the pulmonary endothelium in the initiation and promotion of PAH. Our previous work identified elevated reactive oxygen species (ROS)-producing enzyme NADPH oxidase 1 (NOX1) in human pulmonary artery endothelial cells (HPAECs) of PAH patients promoting endothelial cell proliferation in vitro. In this study, we interrogated chemokine CXCL12's (aka SDF-1) role in EC proliferation under the control of NOX1 and specificity protein 1 (Sp1). We report here that NOX1 can drive hypoxia-induced endothelial CXCL12 expression via the transcription factor Sp1 leading to HPAEC proliferation and migration. Indeed, NOX1 drove hypoxia-induced Sp1 activation, along with an increased capacity of Sp1 to bind cognate promoter regions in the CXCL12 promoter. Sp1 activation induced elevated expression of CXCL12 in hypoxic HPAECs, supporting downstream induction of expression at the CXCL12 promoter via NOX1 activity. Pathological levels of CXCL12 mimicking those reported in human PAH patient serum restored EC proliferation impeded by specific NOX1 inhibitor. The translational relevance of our findings is highlighted by elevated NOX1 activity, Sp1 activation, and CXCL12 expression in explanted lung samples from PAH patients compared to non-PAH controls. Analysis of phosphofructokinase, glucose-6-phosphate dehydrogenase, and glutaminase activity revealed that CXCL12 induces glutamine and glucose metabolism, which are foundational to EC cell proliferation. Indeed, in explanted human PAH lungs, demonstrably higher glutaminase activity was detected compared to healthy controls. Finally, infusion of recombinant CXCL12 into healthy mice amplified pulmonary arterial pressure, right ventricle remodeling, and elevated glucose and glutamine metabolism. Together these data suggest a central role for a novel NOX1-Sp1-CXCL12 pathway in mediating PAH phenotype in the lung endothelium.

Pulmonary Vascular Research Institute GoDeep: A meta-registry merging deep phenotyping datafrom international PH reference centers

The Pulmonary Vascular Research Institute GoDeep meta-registry is a collaboration of pulmonary hypertension (PH) reference centers across the globe. Merging worldwide PH data in a central meta-registry to allow advanced analysis of the heterogeneity of PH and its groups/subgroups on a worldwide geographical, ethnical, and etiological landscape (ClinTrial. gov NCT05329714). Retrospective and prospective PH patient data (diagnosis based on catheterization; individuals with exclusion of PH are included as a comparator group) are mapped to a common clinical parameter set of more than 350 items, anonymized and electronically exported to a central server. Use and access is decided by the GoDeep steering board, where each center has one vote. As of April 2022, GoDeep comprised 15,742 individuals with 1.9 million data points from eight PH centers. Geographic distribution comprises 3990 enrollees (25%) from America and 11,752 (75%) from Europe. Eighty-nine perecent were diagnosed with PH and 11% were classified as not PH and provided a comparator group. The retrospective observation period is an average of 3.5 years (standard error of the mean 0.04), with 1159 PH patients followed for over 10 years. Pulmonary arterial hypertension represents the largest PH group (42.6%), followed by Group 2 (21.7%), Group 3 (17.3%), Group 4 (15.2%), and Group 5 (3.3%). The age distribution spans several decades, with patients 60 years or older comprising 60%. The majority of patients met an intermediate risk profile upon diagnosis. Data entry from a further six centers is ongoing, and negotiations with >10 centers worldwide have commenced. Using electronic interface-based automated retrospective and prospective data transfer, GoDeep aims to provide in-depth epidemiological and etiological understanding of PH and its various groups/subgroups on a global scale, offering insights for improved management.

Computational repurposing of therapeutic small molecules from cancer to pulmonary hypertension

Cancer therapies are being considered for treating rare noncancerous diseases like pulmonary hypertension (PH), but effective computational screening is lacking. Via transcriptomic differential dependency analyses leveraging parallels between cancer and PH, we mapped a landscape of cancer drug functions dependent upon rewiring of PH gene clusters. Bromodomain and extra-terminal motif (BET) protein inhibitors were predicted to rely upon several gene clusters inclusive of galectin-8 (LGALS8). Correspondingly, LGALS8 was found to mediate the BET inhibitor–dependent control of endothelial apoptosis, an essential role for PH in vivo. Separately, a piperlongumine analog’s actions were predicted to depend upon the iron-sulfur biogenesis gene ISCU. Correspondingly, the analog was found to inhibit ISCU glutathionylation, rescuing oxidative metabolism, decreasing endothelial apoptosis, and improving PH. Thus, we identified crucial drug-gene axes central to endothelial dysfunction and therapeutic priorities for PH. These results establish a wide-ranging, network dependency platform to redefine cancer drugs for use in noncancerous conditions.

Recent advancements in pulmonary arterial hypertension and right heart failure research: overview of selected abstracts from ATS2020 and emerging COVID-19 research

Each year the American Thoracic Society (ATS) Conference brings together scientists who conduct basic, translational and clinical research to present on the recent advances in the field of respirology. Due to the Coronavirus Disease of 2019 (COVID-19) pandemic, the ATS2020 Conference was held online in a series of virtual meetings. In this review, we focus on the breakthroughs in pulmonary hypertension research. We have selected 11 of the best basic science abstracts which were presented at the ATS2020 Assembly on Pulmonary Circulation mini-symposium "What's New in Pulmonary Arterial Hypertension (PAH) and Right Ventricular (RV) Signaling: Lessons from the Best Abstracts," reflecting the current state of the art and associated challenges in PH. Particular emphasis is placed on understanding the mechanisms underlying RV failure, the regulation of inflammation, and the novel therapeutic targets that emerged from preclinical research. The pathologic interactions between pulmonary hypertension, right ventricular function and COVID-19 are also discussed.

Endothelial-to-Mesenchymal Transition in Pulmonary Arterial Hypertension

Endothelial-to-mesenchymal transition (EndMT) is a process that encompasses extensive transcriptional reprogramming of activated endothelial cells leading to a shift toward mesenchymal cellular phenotypes and functional responses. Initially observed in the context of embryonic development, in the last few decades EndMT is increasingly recognized as a process that contributes to a variety of pathologies in the adult organism. Within the settings of cardiovascular biology, EndMT plays a role in various diseases, including atherosclerosis, heart valvular disease, cardiac fibrosis, and myocardial infarction. EndMT is also being progressively implicated in development and progression of pulmonary hypertension (PH) and pulmonary arterial hypertension (PAH). This review covers the current knowledge about EndMT in PH and PAH, and provides comprehensive overview of seminal discoveries. Topics covered include evidence linking EndMT to factors associated with PAH development, including hypoxia responses, inflammation, dysregulation of bone-morphogenetic protein receptor 2 (BMPR2), and redox signaling. This review amalgamates these discoveries into potential insights for the identification of underlying mechanisms driving EndMT in PH and PAH, and discusses future directions for EndMT-based therapeutic strategies in disease management.

Loss-of-function of EBP50 is a new cause of hereditary peripheral neuropathy: EBP50 functions in peripheral nerve system

Finding causative genetic mutations is important in the diagnosis and treatment of hereditary peripheral neuropathies. This study was conducted to find new genes involved in the pathophysiology of hereditary peripheral neuropathy. We identified a new mutation in the EBP50 gene, which is co-segregated with neuropathic phenotypes, including motor and sensory deficit in a family with Charcot-Marie-Tooth disease. EBP50 is known to be important for the formation of microvilli in epithelial cells, and the discovery of this gene mutation allowed us to study the function of EBP50 in the nervous system. EBP50 was strongly expressed in the nodal and paranodal regions of sciatic nerve fibers, where Schwann cell microvilli contact the axolemma, and at the growth tips of primary Schwann cells. In addition, EBP50 expression was decreased in mouse models of peripheral neuropathy. Knockout mice were used to study EBP50 function in the peripheral nervous system. Interestingly motor function deficit and abnormal histology of nerve fibers were observed in EBP50^+/- heterozygous mice at 12 months of age, but not 3 months. in vitro studies using Schwann cells showed that NRG1-induced AKT activation and migration were significantly reduced in cells overexpressing the I325V mutant of EBP50 or cells with knocked-down EBP50 expression. In conclusion, we show for the first time that loss of function due to EBP50 gene deficiency or mutation can cause peripheral neuropathy.

Focus on Early Events: Pathogenesis of Pulmonary Arterial Hypertension Development

Significance: Pulmonary arterial hypertension (PAH) is a progressive disease of the lung vasculature characterized by the proliferation of all vascular wall cell types, including endothelial, smooth muscle, and fibroblasts. The disease rapidly advances into a form with extensive pulmonary vascular remodeling, leading to a rapid increase in pulmonary vascular resistance, which results in right heart failure. Recent Advances: Most current research in the PAH field has been focused on the late stage of the disease, largely due to an urgent need for patient treatment options in clinics. Further, the pathobiology of PAH is multifaceted in the advanced disease, and there has been promising recent progress in identifying various pathological pathways related to the late clinical picture. Critical Issues: Early stage PAH still requires additional attention from the scientific community, and although the survival of patients with early diagnosis is comparatively higher, the disease develops in patients asymptomatically, making it difficult to identify and treat early. Future Directions: There are several reasons to focus on the early stage of PAH. First, the complexity of late stage disease, owing to multiple pathways being activated in a complex system with intra- and intercellular signaling, leads to an unclear picture of the key contributors to the pathobiology. Second, an understanding of early pathophysiological events can increase the ability to identify PAH patients earlier than what is currently possible. Third, the prompt diagnosis of PAH would allow for the therapy to start earlier, which has proved to be a more successful strategy, and it ensures better survival in PAH patients.

The matricellular protein TSP1 promotes human and mouse endothelial cell senescence through CD47 and Nox1

Senescent cells withdraw from the cell cycle and do not proliferate. The prevalence of senescent compared to normally functioning parenchymal cells increases with age, impairing tissue and organ homeostasis. A contentious principle governing this process has been the redox theory of aging. We linked matricellular protein thrombospondin 1 (TSP1) and its receptor CD47 to the activation of NADPH oxidase 1 (Nox1), but not of the other closely related Nox isoforms, and associated oxidative stress, and to senescence in human cells and aged tissue. In human endothelial cells, TSP1 promoted senescence and attenuated cell cycle progression and proliferation. At the molecular level, TSP1 increased Nox1-dependent generation of reactive oxygen species (ROS), leading to the increased abundance of the transcription factor p53. p53 mediated a DNA damage response that led to senescence through Rb and p21^cip, both of which inhibit cell cycle progression. Nox1 inhibition blocked the ability of TSP1 to increase p53 nuclear localization and p21^cip abundance and its ability to promote senescence. Mice lacking TSP1 showed decreases in ROS production, p21^cip expression, p53 activity, and aging-induced senescence. Conversely, lung tissue from aging humans displayed increases in the abundance of vascular TSP1, Nox1, p53, and p21^cip Finally, genetic ablation or pharmacological blockade of Nox1 in human endothelial cells attenuated TSP1-mediated ROS generation, restored cell cycle progression, and protected against senescence. Together, our results provide insights into the functional interplay between TSP1 and Nox1 in the regulation of endothelial senescence and suggest potential targets for controlling the aging process at the molecular level.

CD47 and Nox1 Mediate Dynamic Fluid-Phase Macropinocytosis of Native LDL

AIMS

Macropinocytosis has been implicated in cardiovascular and other disorders, yet physiological factors that initiate fluid-phase internalization and the signaling mechanisms involved remain poorly identified. The present study was designed to examine whether matrix protein thrombospondin-1 (TSP1) stimulates macrophage macropinocytosis and, if so, to investigate the potential signaling mechanism involved.

RESULTS

TSP1 treatment of human and murine macrophages stimulated membrane ruffle formation and pericellular solute internalization by macropinocytosis. Blockade of TSP1 cognate receptor CD47 and NADPH oxidase 1 (Nox1) signaling, inhibition of phosphoinositide 3-kinase, and transcriptional knockdown of myotubularin-related protein 6 abolished TSP1-induced macropinocytosis. Our results demonstrate that Nox1 signaling leads to dephosphorylation of actin-binding protein cofilin at Ser-3, actin remodeling, and macropinocytotic uptake of unmodified native low-density lipoprotein (nLDL), leading to foam cell formation. Finally, peritoneal chimera studies suggest the role of CD47 in macrophage lipid macropinocytosis in hypercholesterolemic ApoE^-/- mice in vivo.

INNOVATION

Activation of a previously unidentified TSP1-CD47 signaling pathway in macrophages stimulates direct receptor-independent internalization of nLDL, leading to significant lipid accumulation and foam cell formation. These findings reveal a new paradigm in which delimited Nox1-mediated redox signaling, independent of classical lipid oxidation, contributes to early propagation of vascular inflammatory disease.

CONCLUSIONS

The findings of the present study demonstrate a new mechanism of solute uptake with implications for a wide array of cell types, including macrophages, dendritic cells, and cancer cells, and multiple pathological conditions in which matrix proteins are upregulated. Antioxid. Redox Signal. 26, 886-901.

MEF2C-MYOCD and Leiomodin1 Suppression by miRNA-214 Promotes Smooth Muscle Cell Phenotype Switching in Pulmonary Arterial Hypertension

BACKGROUND

Vascular hyperproliferative disorders are characterized by excessive smooth muscle cell (SMC) proliferation leading to vessel remodeling and occlusion. In pulmonary arterial hypertension (PAH), SMC phenotype switching from a terminally differentiated contractile to synthetic state is gaining traction as our understanding of the disease progression improves. While maintenance of SMC contractile phenotype is reportedly orchestrated by a MEF2C-myocardin (MYOCD) interplay, little is known regarding molecular control at this nexus. Moreover, the burgeoning interest in microRNAs (miRs) provides the basis for exploring their modulation of MEF2C-MYOCD signaling, and in turn, a pro-proliferative, synthetic SMC phenotype. We hypothesized that suppression of SMC contractile phenotype in pulmonary hypertension is mediated by miR-214 via repression of the MEF2C-MYOCD-leiomodin1 (LMOD1) signaling axis.

METHODS AND RESULTS

In SMCs isolated from a PAH patient cohort and commercially obtained hPASMCs exposed to hypoxia, miR-214 expression was monitored by qRT-PCR. miR-214 was upregulated in PAH- vs. control subject hPASMCs as well as in commercially obtained hPASMCs exposed to hypoxia. These increases in miR-214 were paralleled by MEF2C, MYOCD and SMC contractile protein downregulation. Of these, LMOD1 and MEF2C were directly targeted by the miR. Mir-214 overexpression mimicked the PAH profile, downregulating MEF2C and LMOD1. AntagomiR-214 abrogated hypoxia-induced suppression of the contractile phenotype and its attendant proliferation. Anti-miR-214 also restored PAH-PASMCs to a contractile phenotype seen during vascular homeostasis.

CONCLUSIONS

Our findings illustrate a key role for miR-214 in modulation of MEF2C-MYOCD-LMOD1 signaling and suggest that an antagonist of miR-214 could mitigate SMC phenotype changes and proliferation in vascular hyperproliferative disorders including PAH.

Abstract 096: Sequential Activation of Nox1 and Gremlin1 Leads to Endothelial Proliferation in Human Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a rapidly degenerating and devastating disease of increased pulmonary vessel resistance leading to eventual right heart failure. Until now, palliative modalities have targeted the reduction of vascular tone with little success. Recent studies have delved into the mechanisms regulating increased pulmonary vascular resistance: aberrant vascular remodeling and occlusion. However, little is known of the molecular mechanisms responsible for endothelial proliferation, a root cause of PAH-associated vascular remodeling. We provide the first evidence to our knowledge of an upregulation of NADPH oxidase 1 (Nox1) at the transcript and protein (2.1±0.62 -fold, P < 0.05) level in resistance vessels from PAH vs. non-PAH subjects. This coincided with an increase in bone morphogenetic protein (BMP) antagonist Gremlin1 protein expression (2.3±0.47 [[Unable to Display Character: &#8211;]]fold vs. non-PAH, P < 0.05) and reactive oxygen species (ROS) production (iodonium-inhibitable hydrogen peroxide production: 0.69±0.06 vs. 0.43±0.032 nmol/min/mg protein for PAH vs. non-PAH, respectively, P < 0.05). In vitro studies in human pulmonary artery endothelial cells (HPAEC) demonstrate that hypoxia (24 hr, 1 % O 2 ) drives Nox1 subunit expression (Nox1 protein: 1.4±0.075-fold vs. normoxia, P < 0.05), assembly and oxidase activity (superoxide production, nmol/min/mg protein: 14.0±1.9 vs. 6.00±0.94 for normoxia, P < 0.01) leading to elevation in sonic hedgehog (SHH; 1.5±0.011 fold, P < 0.05) and Gremlin1 (1.90±0.32-fold, P < 0.01) expression. Nox1 gene-silencing in hypoxia-exposed HPAEC abrogated this cascade. Moreover, hypoxia-induced endothelial cell proliferation (1.18±0.038-fold vs. normoxia, P < 0.05) was attenuated with loss of either Nox1 or Gremlin1. Finally, incubation of normoxic HPAEC with conditioned media from hypoxia-exposed HPAEC resulted in increased proliferation, which was abrogated by Nox1 suppression of donor cells. Together these data support a Nox1-Gremlin1 signaling axis in pulmonary vascular endothelium that is likely to contribute to pathophysiological endothelial proliferation and the progression of pulmonary hypertension. The findings also support targeting of Nox1 as a viable therapeutic option to combat PAH.

Abstract P132: MEF2C-MYOCD and Leiomodin1 Suppression by miRNA-214 Promotes Smooth Muscle Cell Phenotype Switching in Pulmonary Arterial Hypertension

Vascular hyperproliferative disorders are characterized by excessive smooth muscle cell (SMC) proliferation leading to vessel remodeling and occlusion. In pulmonary arterial hypertension (PAH), SMC phenotype switching from a differentiated contractile to a synthetic state contributes to disease progression. While SMC contractile phenotype is reportedly maintained by a MEF2C-Myocardin (MYOCD) transcription factor interplay, its molecular control is poorly understood. MicroRNAs (miRs) have emerged as modulators of many cellular processes and some evidence associates them to MEF2C-MYOCD signaling. It is, therefore, plausible that miRs can regulate the synthetic SMC phenotype. We hypothesized that suppression of SMC contractile phenotype in PAH is mediated by miR-214 via repression of signaling by MEF2C-MYOCD and downstream contractile proteins leiomodin1 and smoothelin. Using qRT-PCR, the levels of miR-214 expression were shown to be upregulated in pulmonary artery SMC (PASMCs) from PAH- vs. control human subjects as well as in commercially obtained human PASMC (hPASMCs) exposed to hypoxia (~1.5 fold, p<0.05). These increases in miR-214 were paralleled by downregulation of MEF2C, MYOCD, and SMC-specific contractile proteins, leiomodin1 and smoothelin. MicroRNA-214 overexpression mimicked the PAH profile, downregulating MEF2C (1.00±0.054 vs. 0.696±0.026, p<0.05) and leiomodin1 (1.00± 0.051 vs. 0.281±0.095, p<0.05) protein levels for control vs miR-214 mimic, respectively. Hypoxia significantly reduced expression of SMC-specific contractile proteins leiomodin1, calponin1 (~50%) and smoothelin (~30%), and miR-214 antagomiR abrogated this response. We also investigated whether miR-214 participates in the induction of hPASMC proliferation, and found that hypoxia-induced hPASMC proliferation was significantly attenuated by the anti-miR (~2-fold). Further, anti-miR-214 restored PAH-PASMCs to a contractile (~50% reversal of MEF2C and leiomodin1 expression) and less proliferative phenotype. Our data illustrate a key role for miR-214 in modulation of MEF2C-MYOCD-leiomodin1 signaling and suggest that an antagonist of miR-214 could mitigate SMC phenotype changes in vascular hyperproliferative disorders including PAH.

Abstract 123: Age-Related Endothelial Senescence is Driven by Thrombospondin-1-Activated NADPH Oxidase Nox1

Organismal aging represents an independent risk factor underlying many vascular diseases, including systemic and pulmonary hypertension, and atherosclerosis. While the mechanisms driving aging are largely elusive, a steady persistent increase in tissue oxidative stress has been associated with senescence. Previously we showed TSP1 elicits NADPH oxidase (Nox)-dependent vascular smooth muscle cell oxidative stress. However mechanisms by which TSP1 affects endothelial redox biology are unknown. Here, we tested the hypothesis that TSP1 induces endothelial oxidative stress-linked senescence in aging. Using rapid autopsy disease-free human pulmonary (PA) artery, we identified a significant positive correlation between age, protein levels of TSP1, Nox1 and the cell-cycle repressor p21cip (p<0.05). Age also positively associated with increased Amplex Red-detected PA hydrogen peroxide levels (p<0.05). Moreover, treatment of human PA endothelial cells (HPAEC) with TSP1 (2.2nM; 24h) increased expression (~1.9 fold; p<0.05) and activation of Nox1 (~1.7 fold; p<0.05) compared to control, as assessed by Western blot and SOD-inhibitable cytochrome c reduction. Western blotting and immunofluorescence showed a TSP1-mediated increase in p53 activation, indicative of the DNA damage response. Moreover, TSP1 significantly increased HPAEC senescence in a p53/p21cip/Rb-dependent manner, as assessed by immunofluorescent detection of subcellular localization and senescence-associated β-galactosidase staining. To explore this pathway in vivo, middle-aged (8-10 month) wild-type and TSP1-null mice were utilized. In the TSP1-null, reduced lung senescence, oxidative stress, Nox1 levels and p21cip expression were observed compared to wild-type supporting findings in human samples and cell experiments. Finally, prophylactic treatment with specific Nox1 inhibitor NoxA1ds (10μM) attenuated TSP1-induced HPAEC ROS, p53 activation, p21cip expression and senescence. Taken together, our results provide molecular insight into the functional interplay between TSP1 and Nox1 in the regulation of endothelial senescence, with implications for molecular control of the aging process.

Abstract P131: Mef2C-MYOCD and Leiomodin1 Suppression by miRNA-214 Promotes Smooth Muscle Cell Phenotype Switching in Pulmonary Arterial Hypertension

Background: In pulmonary arterial hypertension (PAH), smooth muscle cell (SMC) phenotype switching from a terminally differentiated contractile to synthetic state is gaining traction as our understanding of disease progression improves. While maintenance of SMC contractile phenotype is reportedly orchestrated by a MEF2C- Myocardin (MYOCD) interplay, little is known regarding molecular control at this nexus. Moreover, the burgeoning interest in microRNAs (miRs) provides a basis for exploring their modulation of MEF2C-MYOCD signaling, and, in turn, a pro-proliferative, synthetic SMC phenotype. We hypothesized that suppression of SMC contractile phenotype in pulmonary hypertension is mediated by miR-214 via repression of the MEF2C-MYOCD-leiomodin1 signaling axis.

Methods and Results: In SMCs isolated from a PAH patient cohort and commercially obtained hPASMCs exposed to hypoxia, miR-214 expression was upregulated approx. ~1.5 fold compared to controls (p<0.05). These increases in miR-214 were paralleled by downregulation of MEF2C, MYOCD and SMC-specific contractile proteins, leiomodin1 and smoothelin. Of these, leiomodin1 was directly targeted by the miR. MicroRNA-214 overexpression mimicked the PAH profile, downregulating MEF2C (1±0.054 vs 0.696±0.026, p<0.05) and leiomodin1 (1± 0.051 vs 0.281±0.095, for scrambled control vs miR-214 mimic, p<0.05). Hypoxia significantly reduced expression of SMC-specific contractile proteins, leiomodin1 and calponin1 (5 of 10 percent), and smoothelin (approx. 3 of 10 percent), and miR-214 antagomiR abrogated hypoxia-induced suppression of the contractile phenotype. We also found that hypoxia-induced hPASMC proliferation was significantly attenuated by the anti-miR (approx. 2-fold less compared to hypoxia control). Further, anti-miR-214 also restored PAH-PASMCs to a contractile (approx.5 of 10 percent reversal of MEF2C and leiomodin1 expression), and less proliferative phenotype seen during vascular homeostasis.

Conclusions: Our findings illustrate a key role for miR-214 in modulation of MEF2C-MYOCD-leiomodin1 signaling and suggest that an antagonist of miR-214 could mitigate SMC phenotype changes and proliferation in vascular hyperproliferative disorders including PAH.

Nox-derived ROS are acutely activated in pressure overload pulmonary hypertension: indications for a seminal role for mitochondrial Nox4

Pulmonary arterial hypertension is a severe progressive disease with marked morbidity and high mortality in which right ventricular (RV) failure is the major cause of death. Thus knowledge of the mechanisms underlying RV failure is an area of active interest. Previous studies suggest a role of NADPH oxidase in cardiomyocyte dysfunction in the left heart. Here we postulate that acute pressure overload induced by pulmonary artery banding (PAB) leads to a Nox4-initiated increase in reactive oxygen species (ROS) in mouse RV that may lead to feed-forward induction of Nox2. To test our hypothesis, ROS production was measured in RV and left ventricle homogenates. The data show that hydrogen peroxide (H2O2), but not superoxide anion (O2(·-)), was increased in the early phases (within 6 h) of PAB in RV and that this increase was diminished by catalase and diphenyleneiodonium chloride but not by SOD, N(ω)-nitro-l-arginin methyl ester, febuxostat, or indomethacin. H2O2 production in RV was not attenuated in Nox2 null mice subjected to 6 h PAB. Moreover, we observed an upregulation of Nox4 mRNA after 1 h of PAB and an increase in mitochondrial Nox4 protein 6 h post-PAB. In contrast, we observed an increase in Nox2 mRNA 1 day post-PAB. Expression of antioxidant enzymes SOD, catalase, and glutathione peroxidase did not change, but catalase activity increased 6 h post-PAB. Taken together, these findings show a role of mitochondria-localized Nox4 in the early phase of PAB and suggest an involvement of this isozyme in early ROS generation possibly contributing to progression of RV dysfunction and failure.

Bridged tetrahydroisoquinolines as selective NADPH oxidase 2 (Nox2) inhibitors

(1SR,4RS)-3,3-Dimethyl-1,2,3,4-tetrahydro-1,4-(epiminomethano)naphthalenes were synthesized in 2-3 steps from commercially available materials and assessed for specificity and effectiveness across a range of Nox isoforms. The N-pentyl and N-methylenethiophene substituted analogs 11g and 11h emerged as selective Nox2 inhibitors with cellular IC50 values of 20 and 32 μM, respectively.

Thrombospondin-1 regulates blood flow via CD47 receptor-mediated activation of NADPH oxidase 1

OBJECTIVE

Although the matricellular protein thrombospondin-1 (TSP1) is highly expressed in the vessel wall in response to injury, its pathophysiological role in the development of vascular disease is poorly understood. This study was designed to test the hypothesis that TSP1 stimulates reactive oxygen species production in vascular smooth muscle cells and induces vascular dysfunction by promoting oxidative stress.

METHODS AND RESULTS

Nanomolar concentrations of TSP1 found in human vascular disease robustly stimulated superoxide (O(2)(•-)) levels in vascular smooth muscle cells at both cellular and tissue level as measured by cytochrome c and electron paramagnetic resonance. A peptide mimicking the C terminus of TSP1 known to specifically bind CD47 recapitulated this response. Transcriptional knockdown of CD47 and a monoclonal inhibitory CD47 antibody abrogated TSP1-triggered O(2)(•-) in vitro and ex vivo. TSP1 treatment of vascular smooth muscle cells activated phospholipase C and protein kinase C, resulting in phosphorylation of the NADPH oxidase organizer subunit p47(phox) and subsequent Nox1 activation, leading to impairment of arterial vasodilatation ex vivo. Further, we observed that blockade of CD47 and NADPH oxidase 1 gene silencing in vivo in rats improves TSP1-induced impairment of tissue blood flow after ischemia reperfusion.

CONCLUSIONS

Our data suggest a highly regulated process of reactive oxygen species stimulation and blood flow regulation promoted through a direct TSP1/CD47-mediated activation of Nox1. This is the first report, to our knowledge, of a matricellular protein acting as a ligand for NADPH oxidase activation and through specific engagement of integrin-associated protein CD47.

Aquaporin 1, Nox1, and Ask1 mediate oxidant-induced smooth muscle cell hypertrophy

AIMS

Reactive oxygen species (ROS)-mediated intracellular signalling is well described in the vasculature, yet the precise roles of ROS in paracrine signalling are not known. Studies implicate interstitial ROS hydrogen peroxide (H(2)O(2)) in vascular disease, and plasma H(2)O(2) levels in the micromolar range are detectable in animal models and humans with hypertension. Recently, H(2)O(2) was shown to cross biological membranes of non-vascular cells via aquaporin (Aqp) water channels. Previous findings suggest that H(2)O(2) activates NADPH oxidase (Nox) enzymes in vascular cells and apoptosis signal-regulating kinase 1 (Ask1) in non-vascular cells. We hypothesized that extracellular H(2)O(2) induces smooth muscle cell (SMC) hypertrophy by a mechanism involving Aqp1, Nox1, and Ask1.

METHODS AND RESULTS

Treatment of rat aortic SMCs (rASMC) with exogenous H(2)O(2) resulted in a concentration-dependent increase in Nox-derived superoxide (O(2)(•-)), determined by L-012 chemiluminescence, cytochrome c and electron paramagnetic resonance. Nox1 was verified as the source of O(2)(·-) by siRNA. Aqp1 siRNA attenuated H(2)O(2) cellular entry and H(2)O(2)-induced O(2)(•-) production. H(2)O(2) treatment increased Ask1 activation and induced rASMC hypertrophy in a Nox1-dependent mechanism. Adenoviral-dominant-negative Ask1 attenuated H(2)O(2)-induced rASMC hypertrophy and adenoviral overexpression of Ask1 augmented it.

CONCLUSION

Our results demonstrate for the first time that extracellular H(2)O(2), at pathophysiological concentrations, stimulates rASMC Nox1-derived O(2)(•-), subsequent Ask1 activation and SMC hypertrophy. The data demonstrate a novel pathway by which H(2)O(2) enters vascular cells via aquaporins and activates Nox, leading to hypertrophy, and provide multiple novel targets for combinatorial therapeutics development targeting hypertrophy and vascular disease.

Abstract 195: Nitro-Oleic Acid is a Dual Inhibitor of Nox1 and Nox2

Nitrated fatty acids (NFAs) are α,β-unsaturated keto derivatives of ω-3 fatty acids formed from redox reactions of nitric oxide and nitrite and have recently emerged as anti-inflammatory agents that act as electrophiles. NFAs activate Nrf2 and PPARγ signaling and inhibit NF-κB. Recent data suggest a role in inhibition of reactive oxygen species (ROS) production. This function however, remains largely unexplored. The Nox family of oxidases is a major source of ROS implicated in hypertension and other cardiovascular diseases (CVDs). Here we postulate that the NFA nitro-oleic acid (OA-NO 2 ) specifically inhibits ROS production by the Nox1 and Nox2 oxidases. Treatment of canonical Nox1-expressing COS-7 cells with OA-NO 2 vs its oleic acid (OA) control resulted in a concentration-dependent inhibition of ROS production (101.5, 98.9, 91.7, 94.8, 54.2, and 45.5 % of vehicle treated groups for 0.1, 1, 2, 4, 8, and 10 μM OA-NO 2 , respectively), with an IC 50 of 6.5 μM. Treatment of phorbol ester (PMA)-stimulated Nox2-expressing COS-7 cells yielded similar results (103.6, 106.6, 112.2, 102.1, 51.8 and 35.1 % vehicle treated groups for the same OA-NO 2 concentration range) with an IC 50 of 7.0 μM. Treatment with the same OA-NO 2 concentrations of Nox4- or Nox5-expressing COS-7 cells did not result in any inhibition. The effects of OA-NO 2 on Nox1 and Nox2 were unique to its electrophilic unsaturated keto structure, as OA (lacking NO 2 group), palmitic acid (lacking both double bond and NO 2 group) and linoleic acid (containing two cis double bonds) did not result in any inhibition, demonstrating that fatty acids other than NFAs are incapable of this inhibition. Moreover, experiments using potassium superoxide (O 2 •- ) ruled out any scavenging effects of OA-NO 2 on O 2 •- . Finally, 10 μM OA-NO 2 inhibited both angiotensin II (AngII)- and PMA-stimulated O 2 •- in rat aortic smooth muscle cells (4.4 ± 0.9, 10.8 ± 1.7 and 9.0 ± 2.5 in OA-treated vehicle, AngII and PMA groups vs. 5.8 ± 0.6, 5.7 ± 0.3 and 3.3 ± 1.0 pmol O 2 •- /min/mg protein in OA-NO 2 -treated vehicle, AngII and PMA groups, respectively). Taken together, these results identify NFAs as potent inhibitors of Nox1- and Nox2-derived ROS raising the possibility for their use as therapeutic agents to treat hypertension and other CVDs.

Abstract 94: Scaffolding Protein EBP50 Regulates Vascular Smooth Muscle Nox1 Activity by Binding p47 phox

The NADPH oxidase (Nox) enzyme family is implicated in the pathogenesis of cardiovascular diseases (CVDs) including hypertension. In large vessel smooth muscle cells (SMCs), a unique hybrid Nox1 oxidase exists which propagates SMC dysfunction and hypertrophy. We recently demonstrated that these actions involve activation of Nox1 by hydrogen peroxide (H 2 O 2 ) leading to feed-forward production of reactive oxygen species and activation of apoptosis signal regulating kinase 1 (Ask1). Here we postulate that Ezrin-radixin-moesin-binding phosphoprotein 50 (EBP50), a PDZ-domain scaffolding protein, is required for H 2 O 2 -mediated activation of SMC Nox1. In SMCs, knockdown of EBP50 by shRNA abolished superoxide (O 2 •- ) production in 50 μM H 2 O 2 -treated cells (37.7 ± 4.5, 79.9 ± 2.3 and 29.0 ± 3.5 x10 4 O 2 •- -mediated RLU for GFP plasmid vehicle-treated, GFP plasmid H 2 O 2 -treated and EBP50 shRNA plasmid H 2 O 2 -treated groups, respectively). Furthermore, H 2 O 2 -induced O 2 •- production was absent in SMCs isolated from EBP50 knockout (KO) mice (29.0 ± 2.7 vs 79.1 ± 2.4 x10 4 RLU for EBP50 KO vs wildtype after H 2 O 2 treatment). Intriguingly, p47 phox , an essential cytosolic subunit of the hybrid SMC Nox1 system, upon phosphorylation co-immunoprecipitated with EBP50 in COS-7 cells transfected with both proteins (Fig 1). Taken together, our data suggest that EBP50 promotes Nox activity by binding active p47 phox . These studies identify a novel partner in Nox1 activation and potentially provide new insights into the broader regulation of this enzyme family. Moreover, this added level of complexity could yield new therapeutic strategies to disrupt Nox in the treatment of hypertension and other CVDs.

Oxidases and peroxidases in cardiovascular and lung disease: new concepts in reactive oxygen species signaling

Reactive oxygen species (ROS) are involved in numerous physiological and pathophysiological responses. Increasing evidence implicates ROS as signaling molecules involved in the propagation of cellular pathways. The NADPH oxidase (Nox) family of enzymes is a major source of ROS in the cell and has been related to the progression of many diseases and even environmental toxicity. The complexity of this family's effects on cellular processes stems from the fact that there are seven members, each with unique tissue distribution, cellular localization, and expression. Nox proteins also differ in activation mechanisms and the major ROS detected as their product. To add to this complexity, mounting evidence suggests that other cellular oxidases or their products may be involved in Nox regulation. The overall redox and metabolic status of the cell, specifically the mitochondria, also has implications on ROS signaling. Signaling of such molecules as electrophilic fatty acids has an impact on many redox-sensitive pathologies and thus, as anti-inflammatory molecules, contributes to the complexity of ROS regulation. This review is based on the proceedings of a recent international Oxidase Signaling Symposium at the University of Pittsburgh's Vascular Medicine Institute and Department of Pharmacology and Chemical Biology and encompasses further interaction and discussion among the presenters.

Adventitia-derived hydrogen peroxide impairs relaxation of the rat carotid artery via smooth muscle cell p38 mitogen-activated protein kinase

The role of adventitia-derived reactive oxygen species (ROS) in vascular disease and impaired vascular relaxation is not clear. Based on robust adventitial ROS generation and effects on MAPK involvement in vascular dysfunction, we hypothesized that adventitia-derived ROS hydrogen peroxide (H(2)O(2)) impairs vascular relaxation through activation of medial smooth muscle p38 MAPK. By using a novel in vivo model, the adventitial surface of rat carotid arteries was bathed in situ for 90 min with vehicle, angiotensin II (AngII; 500 nM), AngII+H(2)O(2)-scavenger catalase (3,000 U/ml), AngII+p38 MAPK inhibitor SB203580 (10 μM), or AngII+superoxide dismutase (SOD; 150 U/ml). After these in vivo treatments, ex vivo tone measurements on isolated vessels revealed that periadventitial application of AngII impaired both acetylcholine-induced (endothelium-dependent) and sodium nitroprusside-induced (endothelium-independent) relaxations. In vivo coincubation with catalase or SB203580 significantly improved, but SOD exacerbated AngII-induced impairment of in vitro endothelium-dependent and -independent vascular relaxations. Western blots of vascular media, separated from the adventitia, demonstrated increased medial p38 MAPK activation and decreased medial phosphatase SHP-2 activity in AngII-treated vessels. These effects were reversed by in vivo periadventitial addition of catalase. These findings provide the first evidence that adventitia-derived H(2)O(2) participates in vascular dysfunction through p38 MAPK activation and SHP-2 inhibition.

Nox2 B-loop peptide, Nox2ds, specifically inhibits the NADPH oxidase Nox2

In recent years, reactive oxygen species (ROS) derived from the vascular isoforms of NADPH oxidase, Nox1, Nox2, and Nox4, have been implicated in many cardiovascular pathologies. As a result, the selective inhibition of these isoforms is an area of intense current investigation. In this study, we postulated that Nox2ds, a peptidic inhibitor that mimics a sequence in the cytosolic B-loop of Nox2, would inhibit ROS production by the Nox2-, but not the Nox1- and Nox4-oxidase systems. To test our hypothesis, the inhibitory activity of Nox2ds was assessed in cell-free assays using reconstituted systems expressing the Nox2-, canonical or hybrid Nox1-, or Nox4-oxidase. Our findings demonstrate that Nox2ds, but not its scrambled control, potently inhibited superoxide (O(2)(•-)) production in the Nox2 cell-free system, as assessed by the cytochrome c assay. Electron paramagnetic resonance confirmed that Nox2ds inhibits O(2)(•-) production by Nox2 oxidase. In contrast, Nox2ds did not inhibit ROS production by either Nox1- or Nox4-oxidase. These findings demonstrate that Nox2ds is a selective inhibitor of Nox2-oxidase and support its utility to elucidate the role of Nox2 in organ pathophysiology and its potential as a therapeutic agent.