Role of the Aryl Hydrocarbon Receptor in Sugen 5416-induced Experimental Pulmonary Hypertension

Redox regulation of lung endothelial PERK, unfolded protein response (UPR) and proliferation via NOX1: Targeted inhibition as a potential therapy for PAH

AIMS

Reactive oxygen species (ROS) play an important role in the pathogenesis of pulmonary arterial hypertension (PAH) and NADPH oxidases (NOXs) as sources of ROS are implicated in the development of the disease. We previously showed that NOX isozyme 1 (NOX1)-derived ROS contributes to pulmonary vascular endothelial cell (EC) proliferation in response to PAH triggers in vitro. However, whether and how NOX1 is involved in PAH in vivo have not been explored nor has NOX1 been examined as a viable and effective therapeutic disease target.

METHODS AND RESULTS

Herein, infusion of mice exposed to Sugen/hypoxia (10 % O2) with a specific NOX1 inhibitor, NOXA1ds, delivered via osmotic minipumps (i.p.), significantly suppressed pathological changes in hemodynamic parameters characteristic of PAH. Furthermore, lungs of human patients with idiopathic PAH (iPAH) and exploratory RNA-seq analysis of hypoxic human pulmonary ECs, in which NOX1 was suppressed, were probed. The findings showed a clear indication of NOX1 in the promotion of both protein disulfide isomerase (PDI) and the unfolded protein response (UPR; in particular, the PERK arm of the pathway including eIF2α and ATF4) leading to proliferation. In aggregate, these results are consistent with a causal role for NOX1 in the development of mouse and human PAH and reveal a novel and mechanistic pathway by which NOX1 activates the UPR response during EC proliferation.

CONCLUSION

NOX1 promotes phenotypic changes in ECs that are pivotal to proliferation and PAH through activation of the UPR. Taken together, our results are consistent with selective inhibition of NOX1 as a novel modality for attenuating PAH.

Traditional Mongolian medicine Wu-Lan thirteen-flavor decoction protects rat from hypertension-induced renal injury via aryl hydrocarbon receptor-mediated pathway

BACKGROUND

Wu-Lan Thirteen-Flavour decoction (WLTd), a traditional Mongolian medicine, has been used for treating hypertension in clinical practice, but the chemical basis and underlying mechanisms remain unknown.

METHODS

The main components of WLTd were identified and quantified using HPLC and UPLC-MS/MS techniques. A compound-target-disease network was constructed using network pharmacology analysis to forecast the potential anti-hypertension targets. In vivo animal and in vitro cellular experiments were performed to validate the efficacy and molecular mechanisms of renal protection of WLTd and its main active components in spontaneous hypertension.

RESULTS

A total of 136 active compounds in WLTd were collected through relevant databases, and network pharmacology analysis identified that the aryl hydrocarbon receptor (AhR) signaling pathway may serve as a potential anti-hypertension targets. Eight of the active components, including vitexin, kaempferol, toosendanin, ursolic acid, matrine, oxymatrine, gardenoside and quercetin, were identified and quantified by HPLC and UPLC-MS/MS. WLTd effectively lowered the mean blood pressure (159.16 ± 13.91 vs 135 ± 13.37 mmHg), reduced the BUN (391.55 ± 59.96 vs 240.88 ± 51.15 mmol/L) and creatinine (1.78 ± 0.41 vs 0.67 ± 0.34 nmol/L) levels, and reduced hypertension-induced renal damage in SHR. AhR and related key gene expression changes predicted by network pharmacology analysis were validated by immunohistochemistry, RT-qPCR, and Western blot analyses. In vitro, studies also showed that WLTd up-regulated AhR expression in angiotensin II-induced HEK293 cell injury.

CONCLUSIONS

Wu-Lan Thirteen-Flavour decoction effectively protects hypertension-induced renal injury by regulating the Aryl Hydrocarbon Receptor signaling pathway.

Current Overview of the Biology and Pharmacology in Sugen/Hypoxia-Induced Pulmonary Hypertension in Rats

The Sugen 5416/hypoxia (Su/Hx) rat model of pulmonary arterial hypertension (PAH) demonstrates most of the distinguishing features of PAH in humans, including increased wall thickness and obstruction of the small pulmonary arteries along with plexiform lesion formation. Recently, significant advancement has been made describing the epidemiology, genomics, biochemistry, physiology, and pharmacology in Su/Hx challenge in rats. For example, there are differences in the overall reactivity to Su/Hx challenge in different rat strains and only female rats respond to estrogen treatments. These conditions are also encountered in human subjects with PAH. Also, there is a good translation in both the biochemical and metabolic pathways in the pulmonary vasculature and right heart between Su/Hx rats and humans, particularly during the transition from the adaptive to the nonadaptive phase of right heart failure. Noninvasive techniques such as echocardiography and magnetic resonance imaging have recently been used to evaluate the progression of the pulmonary vascular and cardiac hemodynamics, which are important parameters to monitor the efficacy of drug treatment over time. From a pharmacological perspective, most of the compounds approved clinically for the treatment of PAH are efficacious in Su/Hx rats. Several compounds that show efficacy in Su/Hx rats have advanced into phase II/phase III studies in humans with positive results. Results from these drug trials, if successful, will provide additional treatment options for patients with PAH and will also further validate the excellent translation that currently exists between Su/Hx rats and the human PAH condition.

Pulmonary artery smooth muscle cell pyroptosis promotes the proliferation of PASMCs by paracrine IL‑1β and IL‑18 in monocrotaline‑induced pulmonary arterial hypertensive rats

Pulmonary arterial hypertension (PAH) is a common vascular disease, and pulmonary vascular remodeling is a pivotal pathophysiological mechanism of PAH. Major pathological changes of pulmonary arterial remodeling, including proliferation, hypertrophy and enhanced secretory activity, can occur in pulmonary artery smooth muscle cells (PASMCs). Multiple active factors and cytokines play important roles in PAH. However, the regulatory mechanisms of the active factors and cytokines in PAH remain unclear. The present study aimed to reveal the crucial role of PASMC pyroptosis in PAH and to elucidate the intrinsic mechanisms. To establish the PAH rat models, Sprague-Dawley rats were injected intraperitoneally with monocrotaline (MCT) at a dose of 60 mg/kg. The expression of proteins and interleukins were detected by western blotting and ELISA assay. The results indicated that the pyroptosis of PASMCs is significantly increased in MCT-induced PAH rats. Notably, pyroptotic PASMCs can secret IL-1β and IL-18 to promote the proliferation of PASMCs. On this basis, inhibiting the secretion of IL-1β and IL-18 can markedly inhibit PASMC proliferation. Collectively, the findings of the present study indicate a critical role for PASMC pyroptosis in MCT-induced PAH rats, prompting a new preventive and therapeutic strategy for PAH.

A comprehensive analysis of genes associated with hypoxia and cuproptosis in pulmonary arterial hypertension using machine learning methods and immune infiltration analysis: AHR is a key gene in the cuproptosis process

Background

Pulmonary arterial hypertension (PAH) is a serious condition characterized by elevated pulmonary artery pressure, leading to right heart failure and increased mortality. This study investigates the link between PAH and genes associated with hypoxia and cuproptosis.

Methods

We utilized expression profiles and single-cell RNA-seq data of PAH from the GEO database and genecad. Genes related to cuproptosis and hypoxia were identified. After normalizing the data, differential gene expression was analyzed between PAH and control groups. We performed clustering analyses on cuproptosis-related genes and constructed a weighted gene co-expression network (WGCNA) to identify key genes linked to cuproptosis subtype scores. KEGG, GO, and DO enrichment analyses were conducted for hypoxia-related genes, and a protein-protein interaction (PPI) network was created using STRING. Immune cell composition differences were examined between groups. SingleR and Seurat were used for scRNA-seq data analysis, with PCA and t-SNE for dimensionality reduction. We analyzed hub gene expression across single-cell clusters and built a diagnostic model using LASSO and random forest, optimizing parameters with 10-fold cross-validation. A total of 113 combinations of 12 machine learning algorithms were employed to evaluate model accuracy. GSEA was utilized for pathway enrichment analysis of AHR and FAS, and a Nomogram was created to assess risk impact. We also analyzed the correlation between key genes and immune cell types using Spearman correlation.

Results

We identified several diagnostic genes for PAH linked to hypoxia and cuproptosis. PPI networks illustrated relationships among these hub genes, with immune infiltration analysis highlighting associations with monocytes, macrophages, and CD8 T cells. The genes AHR, FAS, and FGF2 emerged as key markers, forming a robust diagnostic model (NaiveBayes) with an AUC of 0.9.

Conclusion

AHR, FAS, and FGF2 were identified as potential biomarkers for PAH, influencing cell proliferation and inflammatory responses, thereby offering new insights for PAH prevention and treatment.

Salidroside protects pulmonary artery endothelial cells against hypoxia-induced apoptosis via the AhR/NF-κB and Nrf2/HO-1 pathways

BACKGROUND

The apoptosis of pulmonary artery endothelial cells (PAECs) is an important factor contributing to the development of pulmonary hypertension (PH), a serious cardio-pulmonary vascular disorder. Salidroside (SAL) is a bioactive compound derived from an herb Rhodiola, but the potential protective effects of SAL on PAECs and the underlying mechanisms remain elusive.

PURPOSE

The objective of this study was to determine the role of SAL in the hypoxia-induced apoptosis of PAECs and to dissect the underlying mechanisms.

STUDY DESIGN

Male Sprague-Dawley (SD) rats were subjected to hypoxia (10% O2) for 4 weeks to establish a model of PH. Rats were intraperitoneally injected daily with SAL (2, 8, and 32 mg/kg/d) or vehicle. To define the molecular mechanisms of SAL in PAECs, an in vitro model of hypoxic cell injury was also generated by exposed PAECs to 1% O2 for 48 h.

METHODS

Various techniques including hematoxylin and eosin (HE) staining, immunofluorescence, flow cytometry, CCK-8, Western blot, qPCR, molecular docking, and surface plasmon resonance (SPR) were used to determine the role of SAL in rats and in PAECs in vitro.

RESULTS

Hypoxia stimulation increases AhR nuclear translocation and activates the NF-κB signaling pathway, as evidenced by upregulated expression of CYP1A1, CYP1B1, IL-1β, and IL-6, resulting in oxidative stress and inflammatory response and ultimately apoptosis of PAECs. SAL inhibited the activation of AhR and NF-κB, while promoted the nuclear translocation of Nrf2 and increased the expression of its downstream antioxidant proteins HO-1 and NQO1 in PAECs, ameliorating the hypoxia-induced oxidative stress in PAECs. Furthermore, SAL lowered right ventricular systolic pressure, and decreased pulmonary vascular remodeling and right ventricular hypertrophy in hypoxia-exposed rats.

CONCLUSIONS

SAL may attenuate the apoptosis of PAECs by suppressing NF-κB and activating Nrf2/HO-1 pathways, thereby delaying the progressive pathology of PH.

Pulmonary arterial hypertension: Sex matters

Pulmonary arterial hypertension (PAH) is a complex disease of multifactorial origin. While registries have demonstrated that women are more susceptible to the disease, females with PAH have superior right ventricle (RV) function and a better prognosis than their male counterparts, a phenomenon referred to as the 'estrogen paradox'. Numerous pre-clinical studies have investigated the involvement of sex hormones in PAH pathobiology, often with conflicting results. However, recent advances suggest that abnormal estrogen synthesis, metabolism and signalling underpin the sexual dimorphism of this disease. Other sex hormones, such as progesterone, testosterone and dehydroepiandrosterone may also play a role. Several non-hormonal factor including sex chromosomes and epigenetics have also been implicated. Though the underlying pathophysiological mechanisms are complex, several compounds that modulate sex hormones levels and signalling are under investigation in PAH patients. Further elucidation of the estrogen paradox will set the stage for the identification of additional therapeutic targets for this disease.

Kynurenine pathway metabolism evolves with development of preclinical and scleroderma-associated pulmonary arterial hypertension

Understanding metabolic evolution underlying pulmonary arterial hypertension (PAH) development may clarify pathobiology and reveal disease-specific biomarkers. Patients with systemic sclerosis (SSc) are regularly surveilled for PAH, presenting an opportunity to examine metabolic change as disease develops in an at-risk cohort. We performed mass spectrometry-based metabolomics on longitudinal serum samples collected before and near SSc-PAH diagnosis, compared with time-matched SSc subjects without PAH, in a SSc surveillance cohort. We validated metabolic differences in a second cohort and determined metabolite-phenotype relationships. In parallel, we performed serial metabolomic and hemodynamic assessments as the disease developed in a preclinical model. For differentially expressed metabolites, we investigated corresponding gene expression in human and rodent PAH lungs. Kynurenine and its ratio to tryptophan (kyn/trp) increased over the surveillance period in patients with SSc who developed PAH. Higher kyn/trp measured two years before diagnostic right heart catheterization increased the odds of SSc-PAH diagnosis (OR 1.57, 95% CI 1.05-2.36, P = 0.028). The slope of kyn/trp rise during SSc surveillance predicted PAH development and mortality. In both clinical and experimental PAH, higher kynurenine pathway metabolites correlated with adverse pulmonary vascular and RV measurements. In human and rodent PAH lungs, expression of TDO2, which encodes tryptophan 2,3 dioxygenase (TDO), a protein that catalyzes tryptophan conversion to kynurenine, was significantly upregulated and tightly correlated with pulmonary hypertensive features. Upregulated kynurenine pathway metabolism occurs early in PAH, localizes to the lung, and may be modulated by TDO2. Kynurenine pathway metabolites may be candidate PAH biomarkers and TDO warrants exploration as a potential novel therapeutic target.NEW & NOTEWORTHY Our study shows an early increase in kynurenine pathway metabolism in at-risk subjects with systemic sclerosis who develop pulmonary arterial hypertension (PAH). We show that kynurenine pathway upregulation precedes clinical diagnosis and that this metabolic shift is associated with increased disease severity and shorter survival times. We also show that gene expression of TDO2, an enzyme that generates kynurenine from tryptophan, rises with PAH development.

Spatial and temporal resolution of metabolic dysregulation in the Sugen hypoxia model of pulmonary hypertension

Although PAH is partially attributed to disordered metabolism, previous human studies have mostly examined circulating metabolites at a single time point, potentially overlooking crucial disease biology. Current knowledge gaps include an understanding of temporal changes that occur within and across relevant tissues, and whether observed metabolic changes might contribute to disease pathobiology. We utilized targeted tissue metabolomics in the Sugen hypoxia (SuHx) rodent model to investigate tissue-specific metabolic relationships with pulmonary hypertensive features over time using regression modeling and time-series analysis. Our hypotheses were that some metabolic changes would precede phenotypic changes, and that examining metabolic interactions across heart, lung, and liver tissues would yield insight into interconnected metabolic mechanisms. To support the relevance of our findings, we sought to establish links between SuHx tissue metabolomics and human PAH -omics data using bioinformatic predictions. Metabolic differences between and within tissue types were evident by Day 7 postinduction, demonstrating distinct tissue-specific metabolism in experimental pulmonary hypertension. Various metabolites demonstrated significant tissue-specific associations with hemodynamics and RV remodeling. Individual metabolite profiles were dynamic, and some metabolic shifts temporally preceded the emergence of overt pulmonary hypertension and RV remodeling. Metabolic interactions were observed such that abundance of several liver metabolites modulated lung and RV metabolite-phenotype relationships. Taken all together, regression analyses, pathway analyses and time-series analyses implicated aspartate and glutamate signaling and transport, glycine homeostasis, lung nucleotide abundance, and oxidative stress as relevant to early PAH pathobiology. These findings offer valuable insights into potential targets for early intervention in PAH.

Aryl Hydrocarbon Receptor Agonism Antagonizes the Hypoxia-driven Inflammation in Cystic Fibrosis

Hypoxia contributes to the exaggerated yet ineffective airway inflammation that fails to oppose infections in cystic fibrosis (CF). However, the potential for impairment of essential immune functions by HIF-1α (hypoxia-inducible factor 1α) inhibition demands a better comprehension of downstream hypoxia-dependent pathways that are amenable for manipulation. We assessed here whether hypoxia may interfere with the activity of AhR (aryl hydrocarbon receptor), a versatile environmental sensor highly expressed in the lungs, where it plays a homeostatic role. We used murine models of Aspergillus fumigatus infection in vivo and human cells in vitro to define the functional role of AhR in CF, evaluate the impact of hypoxia on AhR expression and activity, and assess whether AhR agonism may antagonize hypoxia-driven inflammation. We demonstrated that there is an important interferential cross-talk between the AhR and HIF-1α signaling pathways in murine and human CF, in that HIF-1α induction squelched the normal AhR response through an impaired formation of the AhR:ARNT (aryl hydrocarbon receptor nuclear translocator)/HIF-1β heterodimer. However, functional studies and analysis of the AhR genetic variability in patients with CF proved that AhR agonism could prevent hypoxia-driven inflammation, restore immune homeostasis, and improve lung function. This study emphasizes the contribution of environmental factors, such as infections, in CF disease progression and suggests the exploitation of hypoxia:xenobiotic receptor cross-talk for antiinflammatory therapy in CF.

Skeletal Muscle Dysfunction in Experimental Pulmonary Hypertension

Pulmonary arterial hypertension (PAH) is a serious, progressive, and often fatal disease that is in urgent need of improved therapies that treat it. One of the remaining therapeutic challenges is the increasingly recognized skeletal muscle dysfunction that interferes with exercise tolerance. Here we report that in the adult rat Sugen/hypoxia (SU/Hx) model of severe pulmonary hypertension (PH), there is highly significant, almost 50%, decrease in exercise endurance, and this is associated with a 25% increase in the abundance of type II muscle fiber markers, thick sarcomeric aggregates and an increase in the levels of FoxO1 in the soleus (a predominantly type I fiber muscle), with additional alterations in the transcriptomic profiles of the diaphragm (a mixed fiber muscle) and the extensor digitorum longus (a predominantly Type II fiber muscle). In addition, soleus atrophy may contribute to impaired exercise endurance. Studies in L6 rat myoblasts have showed that myotube differentiation is associated with increased FoxO1 levels and type II fiber markers, while the inhibition of FoxO1 leads to increased type I fiber markers. We conclude that the formation of aggregates and a FoxO1-mediated shift in the skeletal muscle fiber-type specification may underlie skeletal muscle dysfunction in an experimental study of PH.

Serotonin and Pulmonary Hypertension; Sex and Drugs and ROCK and Rho

Serotonin is often referred to as a "happy hormone" as it maintains good mood, well-being, and happiness. It is involved in communication between nerve cells and plays a role in sleeping and digestion. However, too much serotonin can have pathogenic effects and serotonin synthesis is elevated in pulmonary artery endothelial cells from patients with pulmonary arterial hypertension (PAH). PAH is characterized by elevated pulmonary pressures, right ventricular failure, inflammation, and pulmonary vascular remodeling; serotonin has been shown to be associated with these pathologies. The rate-limiting enzyme in the synthesis of serotonin in the periphery of the body is tryptophan hydroxylase 1 (TPH1). TPH1 expression and serotonin synthesis are elevated in pulmonary artery endothelial cells in patients with PAH. The serotonin synthesized in the pulmonary arterial endothelium can act on the adjacent pulmonary arterial smooth muscle cells (PASMCs), adventitial macrophages, and fibroblasts, in a paracrine fashion. In humans, serotonin enters PASMCs cells via the serotonin transporter (SERT) and it can cooperate with the 5-HT1B receptor on the plasma membrane; this activates both contractile and proliferative signaling pathways. The "serotonin hypothesis of pulmonary hypertension" arose when serotonin was associated with PAH induced by diet pills such as fenfluramine, aminorex, and chlorphentermine; these act as indirect serotonergic agonists causing the release of serotonin from platelets and cells through the SERT. Here the role of serotonin in PAH is reviewed. Targeting serotonin synthesis or signaling is a promising novel alternative approach which may lead to novel therapies for PAH. © 2022 American Physiological Society. Compr Physiol 12: 1-16, 2022.

Single-cell RNA sequencing profiling of mouse endothelial cells in response to pulmonary arterial hypertension

AIMS

Endothelial cell (EC) dysfunction drives the initiation and pathogenesis of pulmonary arterial hypertension (PAH). We aimed to characterize EC dynamics in PAH at single-cell resolution.

METHODS AND RESULTS

We carried out single-cell RNA sequencing (scRNA-seq) of lung ECs isolated from an EC lineage-tracing mouse model in Control and SU5416/hypoxia-induced PAH conditions. EC populations corresponding to distinct lung vessel types, including two discrete capillary populations, were identified in both Control and PAH mice. Differential gene expression analysis revealed global PAH-induced EC changes that were confirmed by bulk RNA-seq. This included upregulation of the major histocompatibility complex class II pathway, supporting a role for ECs in the inflammatory response in PAH. We also identified a PAH response specific to the second capillary EC population including upregulation of genes involved in cell death, cell motility, and angiogenesis. Interestingly, four genes with genetic variants associated with PAH were dysregulated in mouse ECs in PAH. To compare relevance across PAH models and species, we performed a detailed analysis of EC heterogeneity and response to PAH in rats and humans through whole-lung PAH scRNA-seq datasets, revealing that 51% of up-regulated mouse genes were also up-regulated in rat or human PAH. We identified promising new candidates to target endothelial dysfunction including CD74, the knockdown of which regulates EC proliferation and barrier integrity in vitro. Finally, with an in silico cell ordering approach, we identified zonation-dependent changes across the arteriovenous axis in mouse PAH and showed upregulation of the Serine/threonine-protein kinase Sgk1 at the junction between the macro- and microvasculature.

CONCLUSION

This study uncovers PAH-induced EC transcriptomic changes at a high resolution, revealing novel targets for potential therapeutic candidate development.

Evolving Concepts in Endothelial Pathobiology of Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a deadly disease, characterized by increased vascular resistance, pulmonary arteriolar loss, and occlusive arterial remodeling, leading to eventual right heart failure. Evidence increasingly points to the pulmonary endothelium as a central actor in PAH. Endothelial cell apoptosis can result directly in distal lung arteriolar pruning and indirectly in the formation of complex and occlusive arterial lesions, reflecting an imbalance between endothelial injury and repair in the development and progression of PAH. Many of the mutations implicated in PAH are in genes, which are predominantly, or solely, expressed in endothelial cells, and the endothelium is a major target for therapeutic interventions to restore BMP signaling. We explore how arterial pruning can promote the emergence of occlusive arterial remodeling mediated by ongoing endothelial injury secondary to hemodynamic perturbation and pathological increases in luminal shear stress. The emerging role of endothelial cell senescence is discussed in the transition from reversible to irreversible arterial remodeling in advanced PAH, and we review the sometimes conflicting evidence that female sex hormones can both protect or promote vascular changes in disease. Finally, we explore the contribution of the endothelium to metabolic changes and the altered inflammatory and immune state in the PAH lung, focusing on the role of excessive TGFβ signaling. Given the complexity of the endothelial pathobiology of PAH, we anticipate that emerging technologies that allow the study of molecular events at a single cell level will provide answers to many of the questions raised in this review.

Exploring the failing right ventricle in pulmonary hypertension by cardiac magnetic resonance: An in vivo study utilizing Macitentan

Cardiac magnetic resonance (CMR) imaging is used to assess the right ventricle (RV) of pulmonary hypertensive (PH) patients and more recently to track changes in response to therapy. We wished to investigate if repeat CMRs could be used to assess ventricular changes in the Sugen 5416 hypoxic (Su/Hx) rat model of PH treated with the dual endothelin receptor antagonist Macitentan. Male Sprague Dawley Su/Hx rats were dosed for 3 weeks with either vehicle or Macitentan (30 mg/kg) daily, control rats received only vehicle. All rats underwent three CMR scans; before treatment, 2 weeks into treatment, and end of the study. A separate group of Su/Hx and control rats, treated as above, underwent terminal hemodynamic measurements. Using terminal and CMR measurements, Macitentan was found to lower RV systolic pressure pulmonary artery remodeling and increase RV ejection fraction but not change RV hypertrophy (RVH). Repeat CMRs determined that Su/Hx rats treated with Macitentan had significantly reversed RVH via reducing RV mass as well as reducing elevated left ventricular eccentricity index; reductions in RV mass were also observed in Su/Hx vehicle rats exposed to normoxic conditions. We have demonstrated that repeat CMRs can be used to assess the volume and structural changes in the ventricles of the Su/Hx rat model. Using repeat CMRs has allowed us to build a more complete picture of the response of the RV and the left ventricle to treatment. It is unknown if these effects are a consequence of direct action on the RV or secondary to improvements in the lung vasculature.

Aryl Hydrocarbon Receptor in Oxidative Stress as a Double Agent and Its Biological and Therapeutic Significance

The aryl hydrocarbon receptor (AhR) has long been implicated in the induction of a battery of genes involved in the metabolism of xenobiotics and endogenous compounds. AhR is a ligand-activated transcription factor necessary for the launch of transcriptional responses important in health and disease. In past decades, evidence has accumulated that AhR is associated with the cellular response to oxidative stress, and this property of AhR must be taken into account during investigations into a mechanism of action of xenobiotics that is able to activate AhR or that is susceptible to metabolic activation by enzymes encoded by the genes that are under the control of AhR. In this review, we examine various mechanisms by which AhR takes part in the oxidative-stress response, including antioxidant and prooxidant enzymes and cytochrome P450. We also show that AhR, as a participant in the redox balance and as a modulator of redox signals, is being increasingly studied as a target for a new class of therapeutic compounds and as an explanation for the pathogenesis of some disorders.

The Aryl Hydrocarbon Receptor (AHR): A Novel Therapeutic Target for Pulmonary Diseases?

The aryl hydrocarbon receptor (AHR) is a cytoplasmic transcription factor that is well-known for regulating xenobiotic metabolism. Studies in knockout and transgenic mice indicate that the AHR plays a vital role in the development of liver and regulation of reproductive, cardiovascular, hematopoietic, and immune homeostasis. In this focused review on lung diseases associated with acute injury and alveolar development, we reviewed and summarized the current literature on the mechanistic role(s) and therapeutic potential of the AHR in acute lung injury, chronic obstructive pulmonary disease, and bronchopulmonary dysplasia (BPD). Pre-clinical studies indicate that endogenous AHR activation is necessary to protect neonatal and adult lungs against hyperoxia- and cigarette smoke-induced injury. Our goal is to provide insight into the high translational potential of the AHR in the meaningful management of infants and adults with these lung disorders that lack curative therapies.

Treatment-refractory ulcerative colitis responsive to indigo naturalis

Background

Indigo naturalis (IN) is an herbal medicine that has been used for ulcerative colitis with an unclear mechanism of action. Indigo and indirubin, its main constituents, are ligands of the aryl hydrocarbon receptor (AhR). We assessed the safety, efficacy, and colon AhR activity of IN given orally to patients with treatment-refractory ulcerative colitis. The role of AhR in IN benefit was further evaluated with an AhR antagonist in a murine colitis model.

Methods

This open-label, dose-escalation study sequentially treated 11 patients with ulcerative colitis with either IN 500 mg/day or 1.5 g/day for 8 weeks, followed by a 4-week non-treatment period. The primary efficacy endpoint was clinical response at week 8, assessed by total Mayo score. Secondary endpoints included clinical remission, Ulcerative Colitis Endoscopic Index of Severity, quality of life, and colon AhR activity measured by cytochrome P450 1A1 (CYP1A1) RNA expression.

Results

Ten of 11 (91%) patients, including 8/9 (89%) with moderate-to-severe disease, achieved a clinical response. Among these 10 patients, all had failed treatment with 5-aminosalicylic acid, 8 patients with a tumour necrosis factor (TNF)-alpha inhibitor, and 6 patients with TNF-alpha inhibitor and vedolizumab. Five patients were corticosteroid dependent. Clinical response was observed in all five patients who had been recommended for colectomy. Three patients achieved clinical remission. All patients experienced improved endoscopic severity and quality of life. Four weeks after treatment completion, six patients had worsened partial Mayo scores. Four patients progressed to colectomy after study completion. Colon CYP1A1 RNA expression increased 12 557-fold at week 8 among six patients evaluated. No patient discontinued IN due to an adverse event. Concomitant administration of 3-methoxy-4-nitroflavone, an AhR antagonist, in a murine colitis model abrogated the benefit of IN.

Conclusion

IN is a potentially effective therapy for patients with treatment-refractory ulcerative colitis. This benefit is likely through AhR activation.

Trial registration number

NCT02442960.

Pulmonary Arterial Hypertension: Emerging Principles of Precision Medicine across Basic Science to Clinical Practice

Pulmonary arterial hypertension (PAH) is an enigmatic and deadly vascular disease with no known cure. Recent years have seen rapid advances in our understanding of the molecular underpinnings of PAH, with an expanding knowledge of the molecular, cellular, and systems-level drivers of disease that are being translated into novel therapeutic modalities. Simultaneous advances in clinical technology have led to a growing list of tools with potential application to diagnosis and phenotyping. Guided by fundamental biology, these developments hold the potential to usher in a new era of personalized medicine in PAH with broad implications for patient management and great promise for improved outcomes.

Sex and gender in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a rare disease characterised by pulmonary vascular remodelling and elevated pulmonary pressure, which eventually leads to right heart failure and death. Registries worldwide have noted a female predominance of the disease, spurring particular interest in hormonal involvement in the disease pathobiology. Several experimental models have shown both protective and deleterious effects of oestrogens, suggesting that complex mechanisms participate in PAH pathogenesis. In fact, oestrogen metabolites as well as receptors and enzymes implicated in oestrogen signalling pathways and associated conditions such as BMPR2 mutation contribute to PAH penetrance more specifically in women. Conversely, females have better right ventricular function, translating to a better prognosis. Along with right ventricular adaptation, women tend to respond to PAH treatment differently from men. As some young women suffer from PAH, contraception is of particular importance, considering that pregnancy in patients with PAH is strongly discouraged due to high risk of death. When contraception measures fail, pregnant women need a multidisciplinary team-based approach. This article aims to review epidemiology, mechanisms underlying the higher female predominance, but better prognosis and the intricacies in management of women affected by PAH.

Pharmacological blockage of the AHR-CYP1A1 axis: a call for in vivo evidence

The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that can be activated by structurally diverse compounds arising from the environment and the microbiota and host metabolism. Expanding evidence has been shown that the modulation of the canonical pathway of AHR occurs during several chronic diseases and that its abrogation might be of clinical interest for metabolic and inflammatory pathological processes. However, most of the evidence on the pharmacological abrogation of the AHR-CYP1A1 axis has been reported in vitro, and therefore, guidance for in vivo studies is needed. In this review, we cover the state-of-the-art of the pharmacodynamic and pharmacokinetic properties of AHR antagonists and CYP1A1 inhibitors in different in vivo rodent (mouse or rat) models of disease. This review will serve as a road map for those researchers embracing this emerging therapeutic area targeting the AHR. Moreover, it is a timely opportunity as the first AHR antagonists have recently entered the clinical stage of drug development.

3'-Oxo-tabernaelegantine A (OTNA) selectively relaxes pulmonary arteries by inhibiting AhR

BACKGROUND

Pulmonary arterial hypertension (PAH), characterized by pulmonary artery constriction and vascular remodeling, has a high mortality rate. New drugs for the treatment of PAH urgently need to be developed.

PURPOSE

This study was designed to investigate the vasorelaxant activity of OTNA in isolated pulmonary arteries, and explore its molecular mechanism.

METHODS

Pulmonary arteries and thoracic aortas were isolated from mice, and vascular tone was tested with a Wire Myograph System. Nitric oxide levels were determined with DAF-FM DA and DAX-J2™ Red. Cellular thermal shift assays, microscale thermophoresis, and molecular docking were used to identify the interaction between OTNA and aryl hydrocarbon receptor (AhR). The levels of PI3K, p-PI3K, Akt, p-Akt, eNOS, p-eNOS, and AhR were analyzed by Western blotting.

RESULTS

OTNA selectively relaxed the isolated pulmonary artery rings in an endothelium-dependent manner. Mechanistic study showed that OTNA induced NO production through activation of the PI3K/Akt/eNOS pathway in endothelial cells. Furthermore, we also found that OTNA directly bound to AhR and activated the PI3K/Akt/eNOS pathway to dilate pulmonary arteries by inhibiting AhR.

CONCLUSIONS

OTNA relaxes pulmonary arteries by antagonizing AhR. This study provides a new natural antagonist of AhR as a promising lead compound for PAH treatment.

Penetrance of Severe Pulmonary Arterial Hypertension in Response to Vascular Endothelial Growth Factor Receptor 2 Blockade in a Genetically Prone Rat Model Is Reduced by Female Sex

Background We have previously reported important strain differences in response to SU5416 (SU, a vascular endothelial growth factor receptor 2 inhibitor) in rats and have identified a specific colony of Sprague-Dawley rats that are hyperresponsive (SDHR) to SU alone and develop severe pulmonary arterial hypertension (PAH) with a single injection of SU, even in the absence of hypoxia. Interestingly, SDHR rats exhibit incomplete penetrance of the severe PAH phenotype with an "all-or-none" response to SU alone, which provides a unique opportunity to assess the influence of female sex and sex hormones on susceptibility to PAH after endothelial injury in a genetically prone model. Methods and Results SDHR rats were injected with SU (20 mg/kg SC) and, in the absence of hypoxia, 72% of male but only 27% of female rats developed severe PAH at 7 weeks, which was associated with persistent endothelial cell apoptosis. This sex difference in susceptibility for severe PAH was abolished by ovariectomy. Estradiol replacement, beginning 2 days before SU (prevention), inhibited lung endothelial cell apoptosis and completely abrogated severe PAH phenotype in both male and ovariectomized female rats, while progesterone was only protective in ovariectomized female rats. In contrast, delayed treatment of SDHR rats with established PAH with estradiol or progesterone (initiated at 4 weeks post-SU) failed to reduce lung endothelial cell apoptosis or improve PAH phenotype. Conclusions Female sex hormones markedly reduced susceptibility for the severe PAH phenotype in response to SU alone in a hyperresponsive rat strain by abolishing SU-induced endothelial cell apoptosis, but did not reverse severe PAH in established disease.

Sex-dependent right ventricular hypertrophic gene changes after methamphetamine treatment in mice

Methamphetamine (MA) abuse is associated with the development of pulmonary arterial hypertension (PAH) and subsequent right ventricular failure. A recent clinical study demonstrated that female sex is a major risk factor for MA-induced PAH. The mechanisms associated with increased prevalence and severity of MA-induced PAH in females are still unclear. We hypothesized that MA may promote changes in gene expression in the right ventricle contributing to the development and/or worsening of PAH in females. Male and female C57BL/6 mice were treated with either MA or vehicle. Right and left ventricular systolic pressures (RVSP and LVSP, respectively) were assessed and tissue samples were collected for gene expression and histology. LVSP and RVSP were not affected by MA in either males or females. Right ventricular hypertrophy was significantly increased by MA in females but it was not affected by MA in males. In the female mice, MA-induced right ventricular hypertrophy was associated with increased expression of brain natriuretic peptide gene and members of the TGF-β receptor signaling pathway such as TGF-β receptor-1, smad3 and smad7. In male mice, there were no changes in right ventricular gene expression. Our results suggest that MA caused right ventricular hypertrophy in female mice, but not in males and that this was associated with an increase in hypertrophic genes. The right ventricular hypertrophy was not dependent on increased RVSP suggesting a direct effect of MA on the right ventricle. If this translates to PAH patients, it might explain the poor outcome observed in MA-associated female PAH patients.

Inhibition of Glucose-6-Phosphate Dehydrogenase Activity Attenuates Right Ventricle Pressure and Hypertrophy Elicited by VEGFR Inhibitor + Hypoxia

Pulmonary hypertension (PH) is a disease of hyperplasia of pulmonary vascular cells. The pentose phosphate pathway (PPP)-a fundamental glucose metabolism pathway-is vital for cell growth. Because treatment of PH is inadequate, our goal was to determine whether inhibition of glucose-6-phosphate dehydrogenase (G6PD), the rate-limiting enzyme of the PPP, prevents maladaptive gene expression that promotes smooth muscle cell (SMC) growth, reduces pulmonary artery remodeling, and normalizes hemodynamics in experimental models of PH. PH was induced in mice by exposure to 10% oxygen (Hx) or weekly injection of vascular endothelial growth factor receptor blocker [Sugen5416 (SU); 20 mg kg-1] during exposure to hypoxia (Hx + SU). A novel G6PD inhibitor (N-[(3β,5α)-17-oxoandrostan-3-yl]sulfamide; 1.5 mg kg-1) was injected daily during exposure to Hx. We measured right ventricle (RV) pressure and left ventricle pressure-volume relationships and gene expression in lungs of normoxic, Hx, and Hx + SU and G6PD inhibitor-treated mice. RV systolic and end-diastolic pressures were higher in Hx and Hx + SU than normoxic control mice. Hx and Hx + SU decreased expression of epigenetic modifiers (writers and erasers), increased hypomethylation of the DNA, and induced aberrant gene expression in lungs. G6PD inhibition decreased maladaptive expression of genes and SMC growth, reduced pulmonary vascular remodeling, and decreased right ventricle pressures compared with untreated PH groups. Pharmacologic inhibition of G6PD activity, by normalizing activity of epigenetic modifiers and DNA methylation, efficaciously reduces RV pressure overload in Hx and Hx + SU mice and preclinical models of PH and appears to be a safe pharmacotherapeutic strategy. SIGNIFICANCE STATEMENT: The results of this study demonstrated that inhibition of a metabolic enzyme efficaciously reduces pulmonary hypertension. For the first time, this study shows that a novel inhibitor of glucose-6-phosphate dehydrogenase, the rate-limiting enzyme in the fundamental pentose phosphate pathway, modulates DNA methylation and alleviates pulmonary artery remodeling and dilates pulmonary artery to reduce pulmonary hypertension.

Aryl hydrocarbon receptor is essential for the pathogenesis of pulmonary arterial hypertension

Inflammatory signals are thought to be crucial for the pathogenesis of PAH; however, the underlying mechanism is still largely unknown. In this study, we demonstrate that AHR makes a causal contribution to the pathogenesis of PAH, activating a focal inflammatory response in the lungs and promoting infiltration of immune cells from the bone marrow. Furthermore, we found that PAH patients with higher AHR agonistic activity in sera are more susceptible to severe clinical events than those with lower activity. Because conventional therapy for pulmonary hypertension targeting pulmonary artery vasodilation has limited efficacy against severe PAH, the AHR-signaling pathway represents a promising therapeutic target for PAH. In addition, AHR agonistic activity in serum represents a biomarker for PAH.

Pulmonary arterial hypertension (PAH) is a devastating disease characterized by arteriopathy in the small to medium-sized distal pulmonary arteries, often accompanied by infiltration of inflammatory cells. Aryl hydrocarbon receptor (AHR), a nuclear receptor/transcription factor, detoxifies xenobiotics and regulates the differentiation and function of various immune cells. However, the role of AHR in the pathogenesis of PAH is largely unknown. Here, we explore the role of AHR in the pathogenesis of PAH. AHR agonistic activity in serum was significantly higher in PAH patients than in healthy volunteers and was associated with poor prognosis of PAH. Sprague–Dawley rats treated with the potent endogenous AHR agonist, 6-formylindolo[3,2-b]carbazole, in combination with hypoxia develop severe pulmonary hypertension (PH) with plexiform-like lesions, whereas Sprague–Dawley rats treated with the potent vascular endothelial growth factor receptor 2 inhibitors did not. Ahr-knockout (Ahr^−/−) rats generated using the CRISPR/Cas9 system did not develop PH in the SU5416/hypoxia model. A diet containing Qing-Dai, a Chinese herbal drug, in combination with hypoxia led to development of PH in Ahr^+/+ rats, but not in Ahr^−/− rats. RNA-seq analysis, chromatin immunoprecipitation (ChIP)-seq analysis, immunohistochemical analysis, and bone marrow transplantation experiments show that activation of several inflammatory signaling pathways was up-regulated in endothelial cells and peripheral blood mononuclear cells, which led to infiltration of CD4⁺ IL-21⁺ T cells and MRC1⁺ macrophages into vascular lesions in an AHR-dependent manner. Taken together, AHR plays crucial roles in the development and progression of PAH, and the AHR-signaling pathway represents a promising therapeutic target for PAH.

Sex Differences in Pulmonary Hypertension

Pulmonary arterial hypertension (PAH) occurs in women more than men whereas survival in men is worse than in women. In recent years, much research has been carried out to understand these sex differences in PAH. This article discusses clinical and preclinical studies that have investigated the influences of sex, serotonin, obesity, estrogen, estrogen synthesis, and estrogen metabolism on bone morphogenetic protein receptor type II signaling, the pulmonary circulation and right ventricle in both heritable and idiopathic pulmonary hypertension.

Induction of aryl hydrocarbon receptor in granulosa cells by endoplasmic reticulum stress contributes to pathology of polycystic ovary syndrome

Recent studies have uncovered the critical role of aryl hydrocarbon receptor (AHR) in various diseases, including obesity and cancer progression, independent of its previously identified role as a receptor for endocrine-disrupting chemicals (EDCs). We previously showed that endoplasmic reticulum (ER) stress, a newly recognized local factor in the follicular microenvironment, is activated in granulosa cells from patients with polycystic ovary syndrome (PCOS) and a mouse model of the disease. By affecting diverse functions of granulosa cells, ER stress contributes to PCOS pathology. We hypothesized that expression of AHR and activation of its downstream signaling were upregulated by ER stress in granulosa cells, irrespective of the presence of EDCs, thereby promoting PCOS pathogenesis. In this study, we found that AHR, AHR nuclear translocator (ARNT), and AHR target gene cytochrome P450 1B1 (CYP1B1) were upregulated in the granulosa cells of PCOS patients and model mice. We examined CYP1B1 as a representative AHR target gene. AHR and ARNT were upregulated by ER stress in human granulosa-lutein cells (GLCs), resulting in an increase in the expression and activity of CYP1B1. Administration of the AHR antagonist CH223191 to PCOS mice restored estrous cycling and decreased the number of atretic antral follicles, concomitant with downregulation of AHR and CYP1B1 in granulosa cells. Taken together, our findings indicate that AHR activated by ER stress in the follicular microenvironment contributes to PCOS pathology, and that AHR represents a novel therapeutic target for PCOS.

Sex-Dependent Changes in Right Ventricular Gene Expression in Response to Pressure Overload in a Rat Model of Pulmonary Trunk Banding

Right ventricular hypertrophy (RVH) and subsequent failure are consequences of pulmonary arterial hypertension (PAH). While females are four times more likely to develop PAH, male patients have poorer survival even with treatment, suggesting a sex-dependent dimorphism in right ventricular (RV) hypertrophy/compensation. This may result from differential gene expression in the RV in male vs. female. To date, the sex dependent effect of pressure overload on RV function and changes in gene expression is still unclear. We hypothesize that pressure overload promotes gene expression changes in the RV that may contribute to a poorer outcome in males vs. females. To test this hypothesis, male and female Wistar rats underwent either a sham procedure (sham controls) or moderate pulmonary trunk banding (PTB) (a model of pressure overload induced compensated RV hypertrophy) surgery. Seven weeks post-surgery, RV function was assessed in vivo, and tissue samples were collected for gene expression using qPCR. Compared to sham controls, PTB induced significant increases in the right ventricular systolic pressure, the filling pressure and contractility, which were similar between male and female rats. PTB resulted in an increase in RVH indexes (RV weight, RV weight/tibia length and Fulton index) in both male and female groups. However, RVH indexes were significantly higher in male-PTB when compared to female-PTB rats. Whilst end of procedure body weight was greater in male rats, end of procedure pulmonary artery (PA) diameters were the same in both males and females. RV gene expression analysis revealed that the following genes were increased in PTB-male rats compared with the sham-operated controls: natriuretic peptide A (ANP) and B (BNP), as well as the markers of fibrosis; collagen type I and III. In females, only BNP was significantly increased in the RV when compared to the sham-operated female rats. Furthermore, ANP, BNP and collagen III were significantly higher in the RV from PTB-males when compared to RV from PTB-female rats. Our data suggest that pressure overload-mediated changes in gene expression in the RV from male rats may worsen RVH and increase the susceptibility of males to a poorer outcome when compared to females.

Direct Delivery of MicroRNA96 to the Lungs Reduces Progression of Sugen/Hypoxia-Induced Pulmonary Hypertension in the Rat

The 5HT1B receptor (5HT1BR) contributes to the pathogenic effects of serotonin in pulmonary arterial hypertension. Here, we determine the effect of a microRNA96 (miR96) mimic delivered directly to the lungs on development of severe pulmonary hypertension in rats. Female rats were dosed with sugen (30 mg/kg) and subjected to 3 weeks of hypobaric hypoxia. In normoxia, rats were dosed with either a 5HT1BR antagonist SB216641 (7.5 mg/kg/day for 3 weeks), miR96, or scramble sequence (50 μg per rat), delivered by intratracheal (i.t) administration, once a week for 3 weeks. Cardiac hemodynamics were determined, pulmonary vascular remodeling was assessed, and gene expression was assessed by qRT-PCR, and in situ hybridization and protein expression were assessed by western blot and ELISA. miR96 expression was increased in pulmonary arteries and associated with a downregulation of the 5HT1BR protein in the lung. miR96 reduced progression of right ventricular systolic pressure, pulmonary arterial remodeling, right ventricular hypertrophy, and the occurrence of occlusive pulmonary lesions. Importantly, miR96 had no off-target effects and did not affect fibrotic markers of liver and kidney function. In conclusion, direct delivery of miR96 to the lungs was effective, reducing progression of sugen/hypoxia-induced pulmonary hypertension with no measured off-target effects. miR96 may be a novel therapy for pulmonary arterial hypertension, acting through downregulation of 5HT1BR.

Heart‑lung crosstalk in pulmonary arterial hypertension following myocardial infarction (Review)

Left heart disease is the main cause of clinical pulmonary arterial hypertension (PAH). Common types of left heart disease that result in PAH include heart failure, left ventricular systolic dysfunction, left ventricular diastolic dysfunction and valvular disease. It is currently believed that mechanical pressure caused by high pulmonary venous pressure is the main cause of myocardial infarction (MI) in individuals with ischemic cardiomyopathy and left ventricular systolic dysfunction. In the presence of decreased cardiac function, vascular remodeling of pulmonary vessels in response to long-term stimulation by high pressure in turn leads to exacerbation of PAH. However, the underlying pathological mechanisms remain unclear. Elucidating the association between the development of MI and PAH may lead to a better understanding of potential risk factors and better disease treatment. In this article, the pathophysiological effects of multiple systems in individuals with MI and PAH were reviewed in order to provide a general perspective on various potential interactions between cardiomyocytes and pulmonary vascular cells.

Sex, Gender, and Sex Hormones in Pulmonary Hypertension and Right Ventricular Failure

Pulmonary hypertension (PH) encompasses a syndrome of diseases that are characterized by elevated pulmonary artery pressure and pulmonary vascular remodeling and that frequently lead to right ventricular (RV) failure and death. Several types of PH exhibit sexually dimorphic features in disease penetrance, presentation, and progression. Most sexually dimorphic features in PH have been described in pulmonary arterial hypertension (PAH), a devastating and progressive pulmonary vasculopathy with a 3-year survival rate <60%. While patient registries show that women are more susceptible to development of PAH, female PAH patients display better RV function and increased survival compared to their male counterparts, a phenomenon referred to as the "estrogen paradox" or "estrogen puzzle" of PAH. Recent advances in the field have demonstrated that multiple sex hormones, receptors, and metabolites play a role in the estrogen puzzle and that the effects of hormone signaling may be time and compartment specific. While the underlying physiological mechanisms are complex, unraveling the estrogen puzzle may reveal novel therapeutic strategies to treat and reverse the effects of PAH/PH. In this article, we (i) review PH classification and pathophysiology; (ii) discuss sex/gender differences observed in patients and animal models; (iii) review sex hormone synthesis and metabolism; (iv) review in detail the scientific literature of sex hormone signaling in PAH/PH, particularly estrogen-, testosterone-, progesterone-, and dehydroepiandrosterone (DHEA)-mediated effects in the pulmonary vasculature and RV; (v) discuss hormone-independent variables contributing to sexually dimorphic disease presentation; and (vi) identify knowledge gaps and pathways forward. © 2020 American Physiological Society. Compr Physiol 10:125-170, 2020.

Aryl hydrocarbon receptor modulates stroke-induced astrogliosis and neurogenesis in the adult mouse brain

BACKGROUND

The aryl hydrocarbon receptor (AHR) is a ligand-dependent transcription factor activated by environmental agonists and dietary tryptophan metabolites for the immune response and cell cycle regulation. Emerging evidence suggests that AHR activation after acute stroke may play a role in brain ischemic injury. However, whether AHR activation alters poststroke astrogliosis and neurogenesis remains unknown.

METHODS

We adopted conditional knockout of AHR from nestin-expressing neural stem/progenitor cells (AHRcKO) and wild-type (WT) mice in the permanent middle cerebral artery occlusion (MCAO) model. WT mice were treated with either vehicle or the AHR antagonist 6,2',4'-trimethoxyflavone (TMF, 5 mg/kg/day) intraperitoneally. The animals were examined at 2 and 7 days after MCAO.

RESULTS

The AHR signaling pathway was significantly upregulated after stroke. Both TMF-treated WT and AHRcKO mice showed significantly decreased infarct volume, improved sensorimotor, and nonspatial working memory functions compared with their respective controls. AHR immunoreactivities were increased predominantly in activated microglia and astrocytes after MCAO compared with the normal WT controls. The TMF-treated WT and AHRcKO mice demonstrated significant amelioration of astrogliosis and microgliosis. Interestingly, these mice also showed augmentation of neural progenitor cell proliferation at the ipsilesional neurogenic subventricular zone (SVZ) and the hippocampal subgranular zone. At the peri-infarct cortex, the ipsilesional SVZ/striatum, and the hippocampus, both the TMF-treated and AHRcKO mice demonstrated downregulated IL-1β, IL-6, IFN-γ, CXCL1, and S100β, and concomitantly upregulated Neurogenin 2 and Neurogenin 1.

CONCLUSION

Neural cell-specific AHR activation following acute ischemic stroke increased astrogliosis and suppressed neurogenesis in adult mice. AHR inhibition in acute stroke may potentially benefit functional outcomes likely through reducing proinflammatory gliosis and preserving neurogenesis.

Hot topics in the mechanisms of pulmonary arterial hypertension disease: cancer-like pathobiology, the role of the adventitia, systemic involvement, and right ventricular failure

In order to intervene appropriately and develop disease-modifying therapeutics for pulmonary arterial hypertension, it is crucial to understand the mechanisms of disease pathogenesis and progression. We herein discuss four topics of disease mechanisms that are currently highly debated, yet still unsolved, in the field of pulmonary arterial hypertension. Is pulmonary arterial hypertension a cancer-like disease? Does the adventitia play an important role in the initiation of pulmonary vascular remodeling? Is pulmonary arterial hypertension a systemic disease? Does capillary loss drive right ventricular failure? While pulmonary arterial hypertension does not replicate all features of cancer, anti-proliferative cancer therapeutics might still be beneficial in pulmonary arterial hypertension if monitored for safety and tolerability. It was recognized that the adventitia as a cell-rich compartment is important in the disease pathogenesis of pulmonary arterial hypertension and should be a therapeutic target, albeit the data are inconclusive as to whether the adventitia is involved in the initiation of neointima formation. There was agreement that systemic diseases can lead to pulmonary arterial hypertension and that pulmonary arterial hypertension can have systemic effects related to the advanced lung pathology, yet there was less agreement on whether idiopathic pulmonary arterial hypertension is a systemic disease per se. Despite acknowledging the limitations of exactly assessing vascular density in the right ventricle, it was recognized that the failing right ventricle may show inadequate vascular adaptation resulting in inadequate delivery of oxygen and other metabolites. Although the debate was not meant to result in a definite resolution of the specific arguments, it sparked ideas about how we might resolve the discrepancies by improving our disease modeling (rodent models, large-animal studies, studies of human cells, tissues, and organs) as well as standardization of the models. Novel experimental approaches, such as lineage tracing and better three-dimensional imaging of experimental as well as human lung and heart tissues, might unravel how different cells contribute to the disease pathology.

Role of the Aryl Hydrocarbon Receptor/ARNT/Cytochrome P450 System in Pulmonary Vascular Diseases

RATIONALE

CYPs (cytochrome p450) are critically involved in the metabolism of xenobiotics and toxins. Given that pulmonary hypertension is strongly associated with environmental exposure, we hypothesize that CYPs play a role in the development and maintenance of pathological vascular remodeling.

OBJECTIVE

We sought to identify key CYPs that could link drug or hormone metabolism to the development of pulmonary hypertension.

METHODS AND RESULTS

We searched in Medline (PubMed) database, as well as http://www.clinicaltrials.gov, for CYPs associated with many key aspects of pulmonary arterial hypertension including, but not limited to, severe pulmonary hypertension, estrogen metabolism, inflammation mechanisms, quasi-malignant cell growth, drug susceptibility, and metabolism of the pulmonary arterial hypertension-specific drugs.

CONCLUSIONS

We postulate a hypothesis where the AhR (aryl hydrocarbon receptor) mediates aberrant cell growth via expression of different CYPs associated with estrogen metabolism and inflammation.

Influence of 2-Methoxyestradiol and Sex on Hypoxia-Induced Pulmonary Hypertension and Hypoxia-Inducible Factor-1-α

Background Women are at greater risk of developing pulmonary arterial hypertension, with estrogen and its downstream metabolites playing a potential role in the pathogenesis of the disease. Hypoxia-inducible factor-1-α (HIF 1α) is a pro-proliferative mediator and may be involved in the development of human pulmonary arterial hypertension . The estrogen metabolite 2-methoxyestradiol (2 ME 2) has antiproliferative properties and is also an inhibitor of HIF 1α. Here, we examine sex differences in  HIF 1α signaling in the rat and human pulmonary circulation and determine if 2 ME 2 can inhibit HIF 1α in vivo and in vitro. Methods and Results HIF 1α signaling was assessed in male and female distal human pulmonary artery smooth muscle cells ( hPASMC s), and the effects of 2 ME 2 were also studied in female hPASMC s. The in vivo effects of 2 ME 2 in the chronic hypoxic rat (male and female) model of pulmonary hypertension were also determined. Basal HIF 1α protein expression was higher in female hPASMC s compared with male. Both factor-inhibiting HIF and prolyl hydroxylase-2 (hydroxylates HIF leading to proteosomal degradation) protein levels were significantly lower in female hPASMC s when compared with males. In vivo, 2 ME 2 ablated hypoxia-induced pulmonary hypertension in male and female rats while decreasing protein expression of HIF 1α. 2 ME 2 reduced proliferation in hPASMC s and reduced basal protein expression of HIF 1α. Furthermore, 2 ME 2 caused apoptosis and significant disruption to the microtubule network. Conclusions Higher basal HIF 1α in female hPASMC s may increase susceptibility to developing pulmonary arterial hypertension . These data also demonstrate that the antiproliferative and therapeutic effects of 2 ME 2 in pulmonary hypertension may involve inhibition of HIF 1α and/or microtubular disruption in PASMC s.

miR-1 is increased in pulmonary hypertension and downregulates Kv1.5 channels in rat pulmonary arteries

KEY POINTS

The expression of miR-1 is increased in lungs from the Hyp/Su5416 PAH rat model. Pulmonary artery smooth muscle cells from this animal model are more depolarized and show decreased expression and activity of voltage-dependent potassium channel (Kv)1.5. miR-1 directly targets Kv1.5 channels, reduces Kv1.5 activity and induces membrane depolarization. Antagomir-1 prevents Kv1.5 channel downregulation and the depolarization induced by hypoxia/Su5416 exposition.

ABSTRACT

Impairment of the voltage-dependent potassium channel (Kv) plays a central role in the development of cardiovascular diseases, including pulmonary arterial hypertension (PAH). MicroRNAs are non-coding RNAs that regulate gene expression by binding to the 3'-untranslated region region of specific mRNAs. The present study aimed to analyse the effects of miR-1 on Kv channel function in pulmonary arteries (PA). Kv channel activity was studied in PA from healthy animals transfected with miR-1 or scrambled-miR. Kv currents were studied using the whole-cell configuration of the patch clamp technique. The characterization of the Kv1.5 currents was performed with the selective inhibitor DPO-1. miR-1 expression was increased and Kv1.5 channels were decreased in lungs from a rat model of PAH induced by hypoxia and Su5416. miR-1 transfection increased cell capacitance, reduced Kv1.5 currents and induced membrane depolarization in isolated pulmonary artery smooth muscle cells. A luciferase reporter assay indicated that KCNA5, which encodes Kv1.5 channels, is a direct target gene of miR-1. Incubation of PA with Su5416 and hypoxia (3% O2 ) increased miR-1 and induced a decline in Kv1.5 currents, which was prevented by antagomiR-1. In conclusion, these data indicate that miR-1 induces pulmonary artery smooth muscle cell hypertrophy and reduces the activity and expression of Kv channels, suggesting a pathophysiological role in PAH.