Hyperoxia synergizes with mutant bone morphogenic protein receptor 2 to cause metabolic stress, oxidant injury, and pulmonary hypertension

Hyperoxia Increases Kidney Injury During Renal Ischemia and Reperfusion in Mice

BACKGROUND

Renal ischemia and reperfusion (IR) contribute to perioperative acute kidney injury, and oxygen is a key regulator of this process. We hypothesized that oxygen administration during surgery and renal IR would impact postoperative kidney function and injury in mice.

METHODS

Mice were anesthetized, intubated, and mechanically ventilated with a fraction of inspired oxygen (F io2 ) 0.10 (hypoxia), 0.21 (normoxia), 0.60 (moderate hyperoxia), or 1.00 (severe hyperoxia) during 67 minutes of renal IR or sham IR surgery. Additional mice were treated before IR or sham IR surgery with 50 mg/kg tempol, a superoxide scavenger. At 24 hours, mice were sacrificed, and blood and kidney collected. We assessed and compared kidney function and injury across groups by measuring blood urea nitrogen (BUN, primary end point), renal histological injury, renal expression of neutrophil gelatinase-associated lipocalin (NGAL), and renal heme oxygenase 1 ( Ho-1 ), peroxisome proliferator-activated receptor gamma coactivator 1-α ( Pgc1-α ), and glutathione peroxidase 4 ( Gpx-4 ) transcripts, to explore potential mechanisms of any effect of oxygen.

RESULTS

Hyperoxia and hypoxia during renal IR surgery decreased renal function and increased kidney injury compared to normoxia. Baseline median (interquartile range) BUN was 22.2 mg/dL (18.4-26.0), and 24 hours after IR surgery, BUN was 17.5 mg/dL (95% confidence interval [CI], 1.3-38.4; P = .034) higher in moderate hyperoxia-treated animals, 51.8 mg/dL (95% CI, 24.9-74.8; P < .001) higher in severe hyperoxia-treated animals, and 64.9 mg/dL (95% CI, 41.2-80.3; P < .001) higher in hypoxia-treated animals compared to animals treated with normoxia ( P < .001, overall effect of hyperoxia). Hyperoxia-induced injury, but not hypoxia-induced injury, was attenuated by pretreatment with tempol. Histological injury scores, renal NGAL staining, and renal transcription of Ho-1 and suppression of Pgc1- α followed the same pattern as BUN, in relation to the effects of oxygen treatment.

CONCLUSIONS

In this controlled preclinical study of oxygen treatment during renal IR surgery, hyperoxia and hypoxia impaired renal function, increased renal injury, and impacted expression of genes that affect mitochondrial biogenesis and antioxidant response. These results might have implications for patients during surgery when high concentrations of oxygen are frequently administered, especially in cases involving renal IR.

Targeting Soluble Guanylyl Cyclase during Ischemia and Reperfusion

Ischemia and reperfusion (IR) damage organs and contribute to many disease states. Few effective treatments exist that attenuate IR injury. The augmentation of nitric oxide (NO) signaling remains a promising therapeutic target for IR injury. NO binds to soluble guanylyl cyclase (sGC) to regulate vasodilation, maintain endothelial barrier integrity, and modulate inflammation through the production of cyclic-GMP in vascular smooth muscle. Pharmacologic sGC stimulators and activators have recently been developed. In preclinical studies, sGC stimulators, which augment the reduced form of sGC, and activators, which activate the oxidized non-NO binding form of sGC, increase vasodilation and decrease cardiac, cerebral, renal, pulmonary, and hepatic injury following IR. These effects may be a result of the improved regulation of perfusion and decreased oxidative injury during IR. sGC stimulators are now used clinically to treat some chronic conditions such as heart failure and pulmonary hypertension. Clinical trials of sGC activators have been terminated secondary to adverse side effects including hypotension. Additional clinical studies to investigate the effects of sGC stimulation and activation during acute conditions, such as IR, are warranted.

BMPR2 Mutation and Metabolic Reprogramming in Pulmonary Arterial Hypertension

Pulmonary arterial hypertension forms the first and most severe of the 5 categories of pulmonary hypertension. Disease pathogenesis is driven by progressive remodeling of peripheral pulmonary arteries, caused by the excessive proliferation of vascular wall cells, including endothelial cells, smooth muscle cells and fibroblasts, and perivascular inflammation. Compelling evidence from animal models suggests endothelial cell dysfunction is a key initial trigger of pulmonary vascular remodeling, which is characterised by hyperproliferation and early apoptosis followed by enrichment of apoptosis-resistant populations. Dysfunctional pulmonary arterial endothelial cells lose their ability to produce vasodilatory mediators, together leading to augmented pulmonary arterial smooth muscle cell responses, increased pulmonary vascular pressures and right ventricular afterload, and progressive right ventricular hypertrophy and heart failure. It is recognized that a range of abnormal cellular molecular signatures underpin the pathophysiology of pulmonary arterial hypertension and are enhanced by loss-of-function mutations in the BMPR2 gene, the most common genetic cause of pulmonary arterial hypertension and associated with worse disease prognosis. Widespread metabolic abnormalities are observed in the heart, pulmonary vasculature, and systemic tissues, and may underpin heterogeneity in responsivity to treatment. Metabolic abnormalities include hyperglycolytic reprogramming, mitochondrial dysfunction, aberrant polyamine and sphingosine metabolism, reduced insulin sensitivity, and defective iron handling. This review critically discusses published mechanisms linking metabolic abnormalities with dysfunctional BMPR2 (bone morphogenetic protein receptor 2) signaling; hypothesized mechanistic links requiring further validation; and their relevance to pulmonary arterial hypertension pathogenesis and the development of potential therapeutic strategies.

Overexpression of Msx1 in Mouse Lung Leads to Loss of Pulmonary Vessels Following Vascular Hypoxic Injury

Pulmonary arterial hypertension (PAH) is a progressive lung disease caused by thickening of the pulmonary arterial wall and luminal obliteration of the small peripheral arteries leading to increase in vascular resistance which elevates pulmonary artery pressure that eventually causes right heart failure and death. We have previously shown that transcription factor Msx1 (mainly expressed during embryogenesis) is strongly upregulated in transformed lymphocytes obtained from PAH patients, especially IPAH. Under pathological conditions, Msx1 overexpression can cause cell dedifferentiation or cell apoptosis. We hypothesized that Msx1 overexpression contributes to loss of small pulmonary vessels in PAH. In IPAH lung, MSX1 protein localization was strikingly increased in muscularized remodeled pulmonary vessels, whereas it was undetectable in control pulmonary arteries. We developed a transgenic mouse model overexpressing MSX1 (MSX1^OE) by about 4-fold and exposed these mice to normoxic, sugen hypoxic (3 weeks) or hyperoxic (100% 02 for 3 weeks) conditions. Under normoxic conditions, compared to controls, MSX1^OE mice demonstrated a 30-fold and 2-fold increase in lung Msx1 mRNA and protein expression, respectively. There was a significant retinal capillary dropout (p < 0.01) in MSX1^OE mice, which was increased further (p < 0.03) with sugen hypoxia. At baseline, the number of pulmonary vessels in MSX1^OE mice was similar to controls. In sugen-hypoxia-treated MSX1^OE mice, the number of small (0-25 uM) and medium (25-50 uM) size muscularized vessels increased approximately 2-fold (p < 0.01) compared to baseline controls; however, they were strikingly lower (p < 0.001) in number than in sugen-hypoxia-treated control mice. In MSX1^OE mouse lung, 104 genes were upregulated and 67 genes were downregulated compared to controls. Similarly, in PVECs, 156 genes were upregulated and 320 genes were downregulated from siRNA to MSX1^OE, and in PVSMCs, 65 genes were upregulated and 321 genes were downregulated from siRNA to MSX1^OE (with control in the middle). Many of the statistically significant GO groups associated with MSX1 expression in lung, PVECs, and PVSMCs were similar, and were involved in cell cycle, cytoskeletal and macromolecule organization, and programmed cell death. Overexpression of MSX1 suppresses many cell-cycle-related genes in PVSMCs but induces them in PVECs. In conclusion, overexpression of Msx1 leads to loss of pulmonary vessels, which is exacerbated by sugen hypoxia, and functional consequences of Msx1 overexpression are cell-dependent.

Pediatric Pulmonary Hypertension: Definitions, Mechanisms, Diagnosis, and Treatment

Pediatric pulmonary hypertension (PPH) is a multifactorial disease with diverse etiologies and presenting features. Pulmonary hypertension (PH), defined as elevated pulmonary artery pressure, is the presenting feature for several pulmonary vascular diseases. It is often a hidden component of other lung diseases, such as cystic fibrosis and bronchopulmonary dysplasia. Alterations in lung development and genetic conditions are an important contributor to pediatric pulmonary hypertensive disease, which is a distinct entity from adult PH. Many of the causes of pediatric PH have prenatal onset with altered lung development due to maternal and fetal conditions. Since lung growth is altered in several conditions that lead to PPH, therapy for PPH includes both pulmonary vasodilators and strategies to restore lung growth. These strategies include optimal alveolar recruitment, maintaining physiologic blood gas tension, nutritional support, and addressing contributing factors, such as airway disease and gastroesophageal reflux. The outcome for infants and children with PH is highly variable and largely dependent on the underlying cause. The best outcomes are for neonates with persistent pulmonary hypertension (PPHN) and reversible lung diseases, while some genetic conditions such as alveolar capillary dysplasia are lethal. © 2021 American Physiological Society. Compr Physiol 11:2135-2190, 2021.

Oxygen Toxicity in Critically Ill Adults

Oxygen supplementation is one of the most common interventions in critically ill patients. Despite over a century of data suggesting both beneficial and detrimental effects of supplemental oxygen, optimal arterial oxygenation targets in adult patients remain unclear. Experimental animal studies have consistently showed that exposure to a high fraction of inspired oxygen causes respiratory failure and early death. Human autopsy studies from the 1960s purported to provide histologic evidence of pulmonary oxygen toxicity in the form of diffuse alveolar damage. However, concomitant ventilator-induced lung injury and/or other causes of acute lung injury may explain these findings. While some observational studies in general populations of critically adults showed higher mortality in association with higher oxygen exposures, this finding has not been consistent. For some specific populations, such as those with cardiac arrest, studies have suggested harm from targeting supraphysiologic PaO2s. More recently, randomized clinical trials of arterial oxygenation targets in narrower physiologic ranges were conducted in critically ill adult patients. Though two smaller trials came to opposite conclusions, the two largest of these trials showed no differences in clinical outcomes in study groups that received conservative versus liberal oxygen targets, suggesting that either strategy is reasonable. It is possible that some strategies are of benefit in some sub-populations, and this remains an important ongoing area of research. Because of the ubiquity of oxygen supplementation in critically ill adults, even small treatment effects could have a large impact on a global scale.

Sex Dimorphism in Pulmonary Hypertension: The Role of the Sex Chromosomes

Pulmonary hypertension (PH) is a condition characterised by an abnormal elevation of pulmonary artery pressure caused by an increased pulmonary vascular resistance, frequently leading to right ventricular failure and reduced survival. Marked sexual dimorphism is observed in patients with pulmonary arterial hypertension, a form of pulmonary hypertension with a particularly severe clinical course. The incidence in females is 2-4 times greater than in males, although the disease is less severe in females. We review the contribution of the sex chromosomes to this sex dimorphism highlighting the impact of proteins, microRNAs and long non-coding RNAs encoded on the X and Y chromosomes. These genes are centrally involved in the cellular pathways that cause increased pulmonary vascular resistance including the production of reactive oxygen species, altered metabolism, apoptosis, inflammation, vasoconstriction and vascular remodelling. The interaction with genetic mutations on autosomal genes that cause heritable pulmonary arterial hypertension such as bone morphogenetic protein 2 (BMPR2) are examined. The mechanisms that can lead to differences in the expression of genes located on the X chromosomes between females and males are also reviewed. A better understanding of the mechanisms of sex dimorphism in this disease will contribute to the development of more effective therapies for both women and men.

The Third Man: DNA sensing as espionage in pulmonary vascular health and disease

For as long as nucleic acids have been utilized to vertically and horizontally transfer genetic material, living organisms have had to develop methods of recognizing cytosolic DNA as either pathogenic (microbial invasion) or physiologic (mitosis and cellular proliferation). Derangement in key signaling molecules involved in these pathways of DNA sensing result in a family of diseases labeled interferonopathies. An interferonopathy, characterized by constitutive expression of type I interferons, ultimately manifests as severe autoimmune disease at a young age. Afflicted patients present with a constellation of immune-mediated conditions, including primary lung manifestations such as pulmonary fibrosis and pulmonary hypertension. The latter condition is especially interesting in light of the known role that DNA damage plays in a variety of types of inherited and induced pulmonary hypertension, with free DNA detection elevated in the circulation of affected individuals. While little is known regarding the role of cytosolic DNA sensing in development of pulmonary vascular disease, exciting new research in the related fields of immunology and oncology potentially sheds light on future areas of fruitful exploration. As such, the goal of this review is to summarize the state of the field of nucleic acid sensing, extrapolating common shared pathways that parallel our knowledge of pulmonary hypertension, in a molecular and cell-specific manner. Principles of DNA sensing related to known pulmonary injury inducing stimuli are also evaluated, in addition to potential therapeutic targets. Finally, future directions in pulmonary hypertension research and treatments will be briefly discussed.

Prognostic Value of Gamma-Glutamyltransferase in Male Patients With Idiopathic Pulmonary Arterial Hypertension

Background: The elevated gamma-glutamyltransferase (GGT) activity is regarded as an indicator of cardiovascular disease, with males having higher values than females. The greater incidence of idiopathic pulmonary arterial hypertension (IPAH) is observed in women, whereas prognosis is poor in men. The present study aims to investigate the potential association of GGT on male patients.

Methods: Serum GGT levels were measured in 338 consecutive adult IPAH patients, who underwent bone morphogenetic protein receptor type 2 (BMPR2) genetic counseling, and matched with healthy subjects by sex and age. The followed interval was 48 ± 34 months.

Results: Increased serum GGT levels were more common in patients with IPAH than controls (p < 0.001). GGT values were significantly higher in male patients than those of females (p < 0.001). Compared with female patients with BMPR2 mutation, GGT level in male patients with BMPR2 mutation was further increased (p = 0.002). Higher GGT levels were associated with worse hemodynamics and Nterminal pro B-type natriuretic peptide in all patients. However, males with a GGT concentration ≥ 53 U/L had a worse survival than those of females. Contrarily, if GGT concentration <53 U/L, there was no survival difference between male and female patients. After adjustment for relevant variables of clinical features and hemodynamics, baseline higher GGT levels remained increased risks of all-cause mortality in males rather than females. During rehospitalization follow-up, male patients still had significantly higher values of GGT than females.

Conclusions: Increased GGT levels were correlated with BMPR2 mutation, hemodynamic dysfunction, and poor outcomes in male patients with IPAH. Further studies are needed to explain the origin of abnormal GGT and its potential pathogenesis in men.

Prognostic Value of Oxidative Stress Markers in Patients with Pulmonary Arterial or Chronic Thromboembolic Pulmonary Hypertension

Oxidative stress is regarded to play a crucial role in the pathophysiology of pulmonary arterial hypertension (PAH) and inoperable chronic thromboembolic pulmonary hypertension (CTEPH). This study evaluated the prognostic value of serum oxidative stress markers (malondialdehyde (MDA), total antioxidant capacity (TAC), catalase activity (CAT), and superoxide activity (SOD)) in patients with PAH and CTEPH (n = 45). During 13 months of follow-up (median 9 months), clinical deterioration occurred in 14 patients (including 2 deaths). On the Cox regression analysis, MDA, TAC, and CAT were associated with clinical deterioration (p = 0.0068, HR = 1.42, 95% CI: 1.10-1.82; p = 0.0038, HR = 0.033, 95% CI: 0.0032-0.33; and p = 0.046, HR = 0.20, 95% CI: 0.04-0.98, respectively). There was no significant difference in SOD (p = 0.53, HR = 0.97, 95% CI: 0.87-1.08). The cut-off value derived from ROC curve analysis was 3.79 μM (p = 0.0048, AUC = 0.76, 95% CI: 0.62-0.91) for MDA, 0.49 mM (p = 0.027, AUC = 0.71, 95% CI: 0.18-0.47) for TAC, and 1.34 U/L (p = 0.029, AUC = 0.71, 95% CI: 0.55-0.86) for CAT. MDA in the group with deterioration was higher (p = 0.0041), while TAC as well as CAT were lower (p = 0.027 and p = 0.028, respectively) when compared to stable patients. Survival without clinical deterioration was significantly longer in patients with lower MDA (p = 0.037, HR = 0.37, 95% CI: 0.12-1.14, log-rank), higher TAC (p = 0.0018, HR = 0.19, 95% CI: 0.06-0.60, log-rank), and higher CAT (p = 0.044, HR = 0.31 95% CI: 0.11-0.88, log-rank). Markers of oxidative stress such as MDA, TAC, and CAT were associated with adverse clinical outcomes in patients with PAH and inoperable or residual CTEPH.

Neopterin as a Biomarker in Patients with Pulmonary Arterial Hypertension and Chronic Thromboembolic Pulmonary Hypertension

BACKGROUND

Upregulation of the immune system is regarded to play an important role in the etiopathobiology of pulmonary arterial hypertension (PAH) and inoperable chronic thromboembolic pulmonary hypertension (CTEPH). To the best of our knowledge, neopterin (NP) has never been investigated in patients with PAH and CTEPH.

OBJECTIVES

The aim of the study was to evaluate the concentration of NP in blood in order to examine its impact on outcome and relationship with disease severity in that population.

METHODS

Serum concentration of NP was analysed prospectively in 50 patients (36 with PAH and 14 with CTEPH vs. 31 healthy controls) and assessed in relation to clinical parameters and outcome.

RESULTS

NP concentration in the PAH and CTEPH groups combined was significantly higher than in the control group (8.68, 6.39-15.03 vs. 5.14, 4.16-5.98 nmol/L, p < 0.0000001). During 9 months of follow-up, clinical deterioration occurred in 18 patients (including 8 deaths), and NP concentration in this group was higher when compared to stable patients (15.6, 8.52-25.13 vs. 7.87, 6.18-9.89, p = 0.002). The cutoff value of NP derived from ROC curve analysis was 15.3 nmol/L (p = 0.002, AUC 0.77, p = 0.0004, HR = 4.35, 95% CI 1.43-13.18, log-rank test). On Cox regression analysis, NP predicted clinical deterioration (p = 0.009, 95% CI 1.01-1.06). NP correlated positively with NT-proBNP (p < 0.001), red blood cell distribution width (p < 0.001), and right atrium area (p = 0.002) and inversely with 6-min walking test (p = 0.002) and peak oxygen consumption (p = 0.001).

CONCLUSIONS

NP concentration is increased in patients with PAH and inoperable CTEPH. Elevated NP concentration is associated with adverse clinical outcomes and correlates with clinical parameters.

NEDD9 targets COL3A1 to promote endothelial fibrosis and pulmonary arterial hypertension

Germline mutations involving small mothers against decapentaplegic-transforming growth factor-β (SMAD-TGF-β) signaling are an important but rare cause of pulmonary arterial hypertension (PAH), which is a disease characterized, in part, by vascular fibrosis and hyperaldosteronism (ALDO). We developed and analyzed a fibrosis protein-protein network (fibrosome) in silico, which predicted that the SMAD3 target neural precursor cell expressed developmentally down-regulated 9 (NEDD9) is a critical ALDO-regulated node underpinning pathogenic vascular fibrosis. Bioinformatics and microscale thermophoresis demonstrated that oxidation of Cys18 in the SMAD3 docking region of NEDD9 impairs SMAD3-NEDD9 protein-protein interactions in vitro. This effect was reproduced by ALDO-induced oxidant stress in cultured human pulmonary artery endothelial cells (HPAECs), resulting in impaired NEDD9 proteolytic degradation, increased NEDD9 complex formation with Nk2 homeobox 5 (NKX2-5), and increased NKX2-5 binding to COL3A1 Up-regulation of NEDD9-dependent collagen III expression corresponded to changes in cell stiffness measured by atomic force microscopy. HPAEC-derived exosomal signaling targeted NEDD9 to increase collagen I/III expression in human pulmonary artery smooth muscle cells, identifying a second endothelial mechanism regulating vascular fibrosis. ALDO-NEDD9 signaling was not affected by treatment with a TGF-β ligand trap and, thus, was not contingent on TGF-β signaling. Colocalization of NEDD9 with collagen III in HPAECs was observed in fibrotic pulmonary arterioles from PAH patients. Furthermore, NEDD9 ablation or inhibition prevented fibrotic vascular remodeling and pulmonary hypertension in animal models of PAH in vivo. These data identify a critical TGF-β-independent posttranslational modification that impairs SMAD3-NEDD9 binding in HPAECs to modulate vascular fibrosis and promote PAH.

BMPR2 mutations and endothelial dysfunction in pulmonary arterial hypertension (2017 Grover Conference Series)

Despite the discovery more than 15 years ago that patients with hereditary pulmonary arterial hypertension (HPAH) inherit BMP type 2 receptor ( BMPR2) mutations, it is still unclear how these mutations cause disease. In part, this is attributable to the rarity of HPAH and difficulty obtaining tissue samples from patients with early disease. However, in addition, limitations to the approaches used to study the effects of BMPR2 mutations on the pulmonary vasculature have restricted our ability to determine how individual mutations give rise to progressive pulmonary vascular pathology in HPAH. The importance of understanding the mechanisms by which BMPR2 mutations cause disease in patients with HPAH is underscored by evidence that there is reduced BMPR2 expression in patients with other, more common, non-hereditary form of PAH, and that restoration of BMPR2 expression reverses established disease in experimental models of pulmonary hypertension. In this paper, we focus on the effects on endothelial function. We discuss some of the controversies and challenges that have faced investigators exploring the role of BMPR2 mutations in HPAH, focusing specifically on the effects different BMPR2 mutation have on endothelial function, and whether there are qualitative differences between different BMPR2 mutations. We discuss evidence that BMPR2 signaling regulates a number of responses that may account for endothelial abnormalities in HPAH and summarize limitations of the models that are used to study these effects. Finally, we discuss evidence that BMPR2-dependent effects on endothelial metabolism provides a unifying explanation for the many of the BMPR2 mutation-dependent effects that have been described in patients with HPAH.

Mitochondrial dysfunction and pulmonary hypertension: cause, effect, or both

Pulmonary hypertension describes a heterogeneous disease defined by increased pulmonary artery pressures, and progressive increase in pulmonary vascular resistance due to pathologic remodeling of the pulmonary vasculature involving pulmonary endothelial cells, pericytes, and smooth muscle cells. This process occurs under various conditions, and although these populations vary, the clinical manifestations are the same: progressive dyspnea, increases in right ventricular (RV) afterload and dysfunction, RV-pulmonary artery uncoupling, and right-sided heart failure with systemic circulatory collapse. The overall estimated 5-yr survival rate is 72% in highly functioning patients, and as low as 28% for those presenting with advanced symptoms. Metabolic theories have been suggested as underlying the pathogenesis of pulmonary hypertension with growing evidence of the role of mitochondrial dysfunction involving the major proteins of the electron transport chain, redox-related enzymes, regulators of the proton gradient and calcium homeostasis, regulators of apoptosis, and mitophagy. There remain more studies needed to characterize mitochondrial dysfunction leading to impaired vascular relaxation, increase proliferation, and failure of regulatory mechanisms. The effects on endothelial cells and resulting interactions with their microenvironment remain uncharted territory for future discovery. Additionally, on the basis of observations that the "plexigenic lesions" of pulmonary hypertension resemble the unregulated proliferation of tumor cells, similarities between cancer pathobiology and pulmonary hypertension have been drawn, suggesting interactions between mitochondria and angiogenesis. Recently, mitochondria targeting has become feasible, which may yield new therapeutic strategies. We present a state-of-the-art review of the role of mitochondria in both the pathobiology of pulmonary hypertension and potential therapeutic targets in pulmonary vascular processes.

Mitochondrial dysfunction in the APP/PSEN1 mouse model of Alzheimer's disease and a novel protective role for ascorbate

Mitochondrial dysfunction is elevated in very early stages of Alzheimer's disease and exacerbates oxidative stress, which contributes to disease pathology. Mitochondria were isolated from 4-month-old wild-type mice, transgenic mice carrying the APP_SWE and PSEN1_dE9 mutations, mice with decreased brain and mitochondrial ascorbate (vitamin C) via heterozygous knockout of the sodium dependent vitamin C transporter (SVCT2^+/-) and transgenic APP/PSEN1 mice with heterozygous SVCT2 expression. Mitochondrial isolates from SVCT2^+/- mice were observed to consume less oxygen using high-resolution respirometry, and also exhibited decreased mitochondrial membrane potential compared to wild type isolates. Conversely, isolates from young (4 months) APP/PSEN1 mice consumed more oxygen, and exhibited an increase in mitochondrial membrane potential, but had a significantly lower ATP/ADP ratio compared to wild type isolates. Greater levels of reactive oxygen species were also produced in mitochondria isolated from both APP/PSEN1 and SVCT2^+/- mice compared to wild type isolates. Acute administration of ascorbate to mitochondria isolated from wild-type mice increased oxygen consumption compared with untreated mitochondria suggesting ascorbate may support energy production. This study suggests that both presence of amyloid and ascorbate deficiency can contribute to mitochondrial dysfunction, even at an early, prodromal stage of Alzheimer's disease, although occurring via different pathways. Ascorbate may, therefore, provide a useful preventative strategy against neurodegenerative disease, particularly in populations most at risk for Alzheimer's disease in which stores are often depleted through mitochondrial dysfunction and elevated oxidative stress.

Oestrogen inhibition reverses pulmonary arterial hypertension and associated metabolic defects

Increased oestrogen is a strong epidemiological risk factor for development of pulmonary arterial hypertension (PAH) in patients, associated with metabolic defects. In addition, oestrogens drive penetrance in mice carrying mutations in bone morphogenetic protein receptor type II (BMPR2), the cause of most heritable PAH. The goal of the present study was to determine whether inhibition of oestrogens was effective in the treatment of PAH in these mice.The oestrogen inhibitors fulvestrant and anastrozole were used in a prevention and treatment paradigm in BMPR2 mutant mice, and tamoxifen was used for treatment. In addition, BMPR2 mutant mice were crossed onto oestrogen receptor (ESR)1 and ESR2 knockout backgrounds to assess receptor specificity. Haemodynamic and metabolic outcomes were measured.Oestrogen inhibition both prevented and treated PAH in BMPR2 mutant mice. This was associated with reduction in metabolic defects including oxidised lipid formation, insulin resistance and rescue of peroxisome proliferator-activated receptor-γ and CD36. The effect was mediated primarily through ESR2, but partially through ESR1.Our data suggest that trials of oestrogen inhibition in human PAH are warranted, and may improve pulmonary vascular disease through amelioration of metabolic defects. Although fulvestrant and anastrozole were more effective than tamoxifen, tamoxifen may be useful in premenopausal females, because of a reduced risk of induction of menopause.

The Risk of Oxygen during Cardiac Surgery (ROCS) trial: study protocol for a randomized clinical trial

Background

Anesthesiologists administer excess supplemental oxygen (hyper-oxygenation) to patients during surgery to avoid hypoxia. Hyper-oxygenation, however, may increase the generation of reactive oxygen species and cause oxidative damage. In cardiac surgery, increased oxidative damage has been associated with postoperative kidney and brain injury. We hypothesize that maintenance of normoxia during cardiac surgery (physiologic oxygenation) decreases kidney injury and oxidative damage compared to hyper-oxygenation.

Methods/design

The Risk of Oxygen during Cardiac Surgery (ROCS) trial will randomly assign 200 cardiac surgery patients to receive physiologic oxygenation, defined as the lowest fraction of inspired oxygen (FIO₂) necessary to maintain an arterial hemoglobin saturation of 95 to 97%, or hyper-oxygenation (FIO₂ = 1.0) during surgery. The primary clinical endpoint is serum creatinine change from baseline to postoperative day 2, and the primary mechanism endpoint is change in plasma concentrations of F₂-isoprostanes and isofurans. Secondary endpoints include superoxide production, clinical delirium, myocardial injury, and length of stay. An endothelial function substudy will examine the effects of oxygen treatment and oxidative stress on endothelial function, measured using flow mediated dilation, peripheral arterial tonometry, and wire tension myography of epicardial fat arterioles.

Discussion

The ROCS trial will test the hypothesis that intraoperative physiologic oxygenation decreases oxidative damage and organ injury compared to hyper-oxygenation in patients undergoing cardiac surgery.

Trial registration

ClinicalTrials.gov, ID: NCT02361944. Registered on the 30th of January 2015.

Electronic supplementary material

The online version of this article (doi:10.1186/s13063-017-2021-5) contains supplementary material, which is available to authorized users.

Dysfunctional BMPR2 signaling drives an abnormal endothelial requirement for glutamine in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is increasingly recognized as a systemic disease driven by alteration in the normal functioning of multiple metabolic pathways affecting all of the major carbon substrates, including amino acids. We found that human pulmonary hypertension patients (WHO Group I, PAH) exhibit systemic and pulmonary-specific alterations in glutamine metabolism, with the diseased pulmonary vasculature taking up significantly more glutamine than that of controls. Using cell culture models and transgenic mice expressing PAH-causing BMPR2 mutations, we found that the pulmonary endothelium in PAH shunts significantly more glutamine carbon into the tricarboxylic acid (TCA) cycle than wild-type endothelium. Increased glutamine metabolism through the TCA cycle is required by the endothelium in PAH to survive, to sustain normal energetics, and to manifest the hyperproliferative phenotype characteristic of disease. The strict requirement for glutamine is driven by loss of sirtuin-3 (SIRT3) activity through covalent modification by reactive products of lipid peroxidation. Using 2-hydroxybenzylamine, a scavenger of reactive lipid peroxidation products, we were able to preserve SIRT3 function, to normalize glutamine metabolism, and to prevent the development of PAH in BMPR2 mutant mice. In PAH, targeting glutamine metabolism and the mechanisms that underlie glutamine-driven metabolic reprogramming represent a viable novel avenue for the development of potentially disease-modifying therapeutics that could be rapidly translated to human studies.

DNA Damage and Pulmonary Hypertension

Pulmonary hypertension (PH) is defined by a mean pulmonary arterial pressure over 25 mmHg at rest and is diagnosed by right heart catheterization. Among the different groups of PH, pulmonary arterial hypertension (PAH) is characterized by a progressive obstruction of distal pulmonary arteries, related to endothelial cell dysfunction and vascular cell proliferation, which leads to an increased pulmonary vascular resistance, right ventricular hypertrophy, and right heart failure. Although the primary trigger of PAH remains unknown, oxidative stress and inflammation have been shown to play a key role in the development and progression of vascular remodeling. These factors are known to increase DNA damage that might favor the emergence of the proliferative and apoptosis-resistant phenotype observed in PAH vascular cells. High levels of DNA damage were reported to occur in PAH lungs and remodeled arteries as well as in animal models of PH. Moreover, recent studies have demonstrated that impaired DNA-response mechanisms may lead to an increased mutagen sensitivity in PAH patients. Finally, PAH was linked with decreased breast cancer 1 protein (BRCA1) and DNA topoisomerase 2-binding protein 1 (TopBP1) expression, both involved in maintaining genome integrity. This review aims to provide an overview of recent evidence of DNA damage and DNA repair deficiency and their implication in PAH pathogenesis.

Expression of mutant bone morphogenetic protein receptor II worsens pulmonary hypertension secondary to pulmonary fibrosis

Pulmonary fibrosis is often complicated by pulmonary hypertension (PH), and previous studies have shown a potential link between bone morphogenetic protein receptor II (BMPR2) and PH secondary to pulmonary fibrosis. We exposed transgenic mice expressing mutant BMPR2 and control mice to repetitive intraperitoneal injections of bleomycin for 4 weeks. The duration of transgene activation was too short for mutant BMPR2 mice to develop spontaneous PH. Mutant BMPR2 mice had increased right ventricular systolic pressure compared to control mice, without differences in pulmonary fibrosis. We found increased hypoxia-inducible factor (HIF)1-α stabilization in lungs of mutant-BMPR2-expressing mice compared to controls following bleomycin treatment. In addition, expression of the hypoxia response element protein connective tissue growth factor was increased in transgenic mice as well as in a human pulmonary microvascular endothelial cell line expressing mutant BMPR2. In mouse pulmonary vascular endothelial cells, mutant BMPR2 expression resulted in increased HIF1-α and reactive oxygen species production following exposure to hypoxia, both of which were attenuated with the antioxidant TEMPOL. These data suggest that expression of mutant BMPR2 worsens secondary PH through increased HIF activity in vascular endothelium. This pathway could be therapeutically targeted in patients with PH secondary to pulmonary fibrosis.

Redox biology in pulmonary arterial hypertension (2013 Grover Conference Series)

Through detailed interrogation of the molecular pathways that contribute to the development of pulmonary arterial hypertension (PAH), the separate but related processes of oxidative stress and cellular metabolic dysfunction have emerged as being critical pathogenic mechanisms that are as yet relatively untargeted therapeutically. In this review, we have attempted to summarize some of the important existing studies, to point out areas of overlap between oxidative stress and metabolic dysfunction, and to do so under the unifying heading of redox biology. We discuss the importance of precision in assessing oxidant signaling versus oxidant injury and why this distinction matters. We endeavor to advance the discussion of carbon-substrate metabolism beyond a focus on glucose and its fate in the cell to encompass other carbon substrates and some of the murkiness surrounding our understanding of how they are handled in different cell types. Finally, we try to bring these ideas together at the level of the mitochondrion and to point out some additional points of possible cognitive dissonance that warrant further experimental probing. The body of beautiful science regarding the molecular and cellular details of redox biology in PAH points to a future that includes clinically useful therapies that target these pathways. To fully realize the potential of these future interventions, we hope that some of the issues raised in this review can be addressed proactively.

Estrogen Metabolite 16α-Hydroxyestrone Exacerbates Bone Morphogenetic Protein Receptor Type II-Associated Pulmonary Arterial Hypertension Through MicroRNA-29-Mediated Modulation of Cellular Metabolism

BACKGROUND

Pulmonary arterial hypertension (PAH) is a proliferative disease of the pulmonary vasculature that preferentially affects women. Estrogens such as the metabolite 16α-hydroxyestrone (16αOHE) may contribute to PAH pathogenesis, and alterations in cellular energy metabolism associate with PAH. We hypothesized that 16αOHE promotes heritable PAH (HPAH) via microRNA-29 (miR-29) family upregulation and that antagonism of miR-29 would attenuate pulmonary hypertension in transgenic mouse models of Bmpr2 mutation.

METHODS AND RESULTS

MicroRNA array profiling of human lung tissue found elevation of microRNAs associated with energy metabolism, including the miR-29 family, among HPAH patients. miR-29 expression was 2-fold higher in Bmpr2 mutant mice lungs at baseline compared with controls and 4 to 8-fold higher in Bmpr2 mice exposed to 16αOHE 1.25 μg/h for 4 weeks. Blot analyses of Bmpr2 mouse lung protein showed significant reductions in peroxisome proliferator-activated receptor-γ and CD36 in those mice exposed to 16αOHE and protein derived from HPAH lungs compared with controls. Bmpr2 mice treated with anti-miR-29 (20-mg/kg injections for 6 weeks) had improvements in hemodynamic profile, histology, and markers of dysregulated energy metabolism compared with controls. Pulmonary artery smooth muscle cells derived from Bmpr2 murine lungs demonstrated mitochondrial abnormalities, which improved with anti-miR-29 transfection in vitro; endothelial-like cells derived from HPAH patient induced pluripotent stem cell lines were similar and improved with anti-miR-29 treatment.

CONCLUSIONS

16αOHE promotes the development of HPAH via upregulation of miR-29, which alters molecular and functional indexes of energy metabolism. Antagonism of miR-29 improves in vivo and in vitro features of HPAH and reveals a possible novel therapeutic target.

BMPR2 preserves mitochondrial function and DNA during reoxygenation to promote endothelial cell survival and reverse pulmonary hypertension

Mitochondrial dysfunction, inflammation, and mutant bone morphogenetic protein receptor 2 (BMPR2) are associated with pulmonary arterial hypertension (PAH), an incurable disease characterized by pulmonary arterial (PA) endothelial cell (EC) apoptosis, decreased microvessels, and occlusive vascular remodeling. We hypothesized that reduced BMPR2 induces PAEC mitochondrial dysfunction, promoting a pro-inflammatory or pro-apoptotic state. Mice with EC deletion of BMPR2 develop hypoxia-induced pulmonary hypertension that, in contrast to non-transgenic littermates, does not reverse upon reoxygenation and is associated with reduced PA microvessels and lung EC p53, PGC1α and TFAM, regulators of mitochondrial biogenesis, and mitochondrial DNA. Decreasing PAEC BMPR2 by siRNA during reoxygenation represses p53, PGC1α, NRF2, TFAM, mitochondrial membrane potential, and ATP and induces mitochondrial DNA deletion and apoptosis. Reducing PAEC BMPR2 in normoxia increases p53, PGC1α, TFAM, mitochondrial membrane potential, ATP production, and glycolysis, and induces mitochondrial fission and a pro-inflammatory state. These features are recapitulated in PAECs from PAH patients with mutant BMPR2.

Endothelial uncoupling protein 2 regulates mitophagy and pulmonary hypertension during intermittent hypoxia

OBJECTIVES

Pulmonary hypertension (PH) is a process of lung vascular remodeling, which can lead to right heart dysfunction and significant morbidity. The underlying mechanisms leading to PH are not well understood, and therapies are limited. Using intermittent hypoxia (IH) as a model of oxidant-induced PH, we identified an important role for endothelial cell mitophagy via mitochondrial uncoupling protein 2 (Ucp2) in the development of IH-induced PH.

APPROACH AND RESULTS

Ucp2 endothelial knockout (VE-KO) and Ucp2 Flox (Flox) mice were subjected to 5 weeks of IH. Ucp2 VE-KO mice exhibited higher right ventricular systolic pressure and worse right heart hypertrophy, as measured by increased right ventricle weight/left ventricle plus septal weight (RV/LV+S) ratio, at baseline and after IH. These changes were accompanied by increased mitophagy. Primary mouse lung endothelial cells transfected with Ucp2 siRNA and subjected to cyclic exposures to CoCl2 (chemical hypoxia) showed increased mitophagy, as measured by PTEN-induced putative kinase 1 and LC3BII/I ratios, decreased mitochondrial biogenesis, and increased apoptosis. Similar results were obtained in primary lung endothelial cells isolated from VE-KO mice. Moreover, silencing PTEN-induced putative kinase 1 in the endothelium of Ucp2 knockout mice, using endothelial-targeted lentiviral silencing RNA in vivo, prevented IH-induced PH. Human pulmonary artery endothelial cells from people with PH demonstrated changes similar to Ucp2-silenced mouse lung endothelial cells.

CONCLUSIONS

The loss of endothelial Ucp2 leads to excessive PTEN-induced putative kinase 1-induced mitophagy, inadequate mitochondrial biosynthesis, and increased apoptosis in endothelium. An endothelial Ucp2-PTEN-induced putative kinase 1 axis may be effective therapeutic targets in PH.

Parabiotic model for differentiating local and systemic effects of continuous and intermittent hypoxia

Hypoxia can be damaging either because cells are directly sensitive to low oxygen pressure in their local microenvironment and/or because they are exposed to circulating factors systemically secreted in response to hypoxia. The conventional hypoxia model, breathing hypoxic air, does not allow one to distinguish between these local and systemic effects. Here we propose and validate a model for differentially applying local and systemic hypoxic challenges in an animal. We used parabiosis, two mice sharing circulation by surgical union through the skin, and tested the hypothesis that when one of the parabionts breathes room air and the other one is subjected to hypoxic air, both mice share systemic circulation but remain normoxic and hypoxic, respectively. We tested two common hypoxic paradigms in 10 parabiotic pairs: continuous hypoxia (10% O2) mimicking chronic lung diseases, and intermittent hypoxia (40 s, 21% O2; 20 s, 5% O2) simulating sleep apnea. Arterial oxygen saturation and oxygen partial pressure at muscle tissue were measured in both parabionts. Effective cross-circulation was assessed by intraperitoneally injecting a dye in one of the parabionts and measuring blood dye concentration in both animals after 2 h. The results confirmed the hypothesis that tissues of the parabiont under room air were perfused with normally oxygenated blood and, at the same time, were exposed to all of the systemic mediators secreted by the other parabiont actually subjected to hypoxia. In conclusion, combination of parabiosis and hypoxic/normoxic air breathing is a novel approach to investigate the effects of local and systemic hypoxia in respiratory diseases.

Endothelial progenitor cells and pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a progressive disease characterised by lung endothelial cell dysfunction and vascular remodelling. A number of studies now suggest that endothelial progenitor cells (EPCs) may induce neovascularisation and could be a promising approach for cell based therapy for PAH. On the contrary EPCs may contribute to pulmonary vascular remodelling, particularly in end-stage pulmonary disease. This review article will provide a brief summary of the relationship between PAH and EPCs, the application of the EPCs to PAH and highlight the potential clinical application of the EPCs cell therapy to PAH.