Plasma Metabolomics Implicate Modified Transfer RNAs and Altered Bioenergetics in the Outcome of Pulmonary Arterial Hypertension.

BACKGROUND: -Pulmonary arterial hypertension (PAH) is a heterogeneous disorder with high mortality. METHODS: -We conducted a comprehensive study of plasma metabolites using ultra-performance liquid chromatography mass-spectrometry to (1) identify patients at high risk of early death, (2) identify patients who respond well to treatment and (3) provide novel molecular insights into disease pathogenesis. RESULTS: -53 circulating metabolites distinguished well-phenotyped patients with idiopathic or heritable PAH (n=365) from healthy controls (n=121) following correction for multiple testing (p<7.3e-5) and confounding factors, including drug therapy, renal and hepatic impairment. A subset of 20/53 metabolites also discriminated PAH patients from disease controls (symptomatic patients without pulmonary hypertension, n=139). 62 metabolites were prognostic in PAH, with 36/62 independent of established prognostic markers. Increased levels of tRNA-specific modified nucleosides (N2,N2-dimethylguanosine, N1-methylinosine), TCA cycle intermediates (malate, fumarate), glutamate, fatty acid acylcarnitines, tryptophan and polyamine metabolites and decreased levels of steroids, sphingomyelins and phosphatidylcholines distinguished patients from controls. The largest differences correlated with increased risk of death and correction of several metabolites over time was associated with a better outcome. Patients who responded to calcium channel blocker therapy had metabolic profiles similar to healthy controls. CONCLUSIONS: -Metabolic profiles in PAH are strongly related to survival and should be considered part of the deep phenotypic characterisation of this disease. Our results support the investigation of targeted therapeutic strategies that seek to address the alterations in translational regulation and energy metabolism that characterize these patients

Blood DNA methylation profiling identifies cathepsin Z dysregulation in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is characterised by pulmonary vascular remodelling causing premature death from right heart failure. Established DNA variants influence PAH risk, but susceptibility from epigenetic changes is unknown. We addressed this through epigenome-wide association study (EWAS), testing 865,848 CpG sites for association with PAH in 429 individuals with PAH and 1226 controls. Three loci, at Cathepsin Z (CTSZ, cg04917472), Conserved oligomeric Golgi complex 6 (COG6, cg27396197), and Zinc Finger Protein 678 (ZNF678, cg03144189), reached epigenome-wide significance (p < 10−7) and are hypermethylated in PAH, including in individuals with PAH at 1-year follow-up. Of 16 established PAH genes, only cg10976975 in BMP10 shows hypermethylation in PAH. Hypermethylation at CTSZ is associated with decreased blood cathepsin Z mRNA levels. Knockdown of CTSZ expression in human pulmonary artery endothelial cells increases caspase-3/7 activity (p < 10−4). DNA methylation profiles are altered in PAH, exemplified by the pulmonary endothelial function modifier CTSZ, encoding protease cathepsin Z

Traffic exposures, air pollution and outcomes in pulmonary arterial hypertension: A United Kingdom cohort study analysis

While traffic and air pollution exposure is associated with increased mortality in numerous diseases, its association with disease severity and outcomes in pulmonary arterial hypertension (PAH) remains unknown.Exposure to particulate matter ≤2.5 μm3 (PM2.5), nitrogen dioxide (NO2) and indirect measures of traffic-related air pollution (distance to main road and length of roads within buffer zones surrounding residential addresses) were estimated for 301 patients with idiopathic/heritable PAH recruited in the UK PAH national Cohort study. Associations with transplant-free survival and pulmonary hemodynamic severity at baseline were assessed, adjusting for confounding variables defined a priori.Higher estimated exposure to PM2.5 was associated with higher risk of death or lung transplant (Unadjusted hazard ratio (HR) 2.68; 95% CI 1.11-6.47 per 3 μg·m-3, p=0.028). This association remained similar when adjusted for potential confounding variables (HR 4.38; 95% CI 1.44-13.36 per 3 μg·m-3, p=0.009). No associations were found between NO2 exposure or other traffic pollution indicators and transplant-free survival Conversely, indirect measures of exposure to traffic-related air pollution within the 500-1000 m buffer zones correlated with the ERS/ESC risk categories as well as pulmonary hemodynamics at baseline. This association was strongest for pulmonary vascular resistance.In idiopathic/heritable PAH, indirect measures of exposure to traffic-related air pollution were associated with disease severity at baseline, whereas higher PM2.5 exposure may independently predict shorter transplant-free survival

EmPHasis-10 health-related quality of life score predicts outcomes in patients with idiopathic and connective tissue disease-associated pulmonary arterial hypertension: results from a UK multi-centre study

Health-related quality of life (HRQoL) scores assess symptom burden in pulmonary arterial hypertension (PAH) but data regarding their role in prognostication and risk stratification are limited. We assessed these relationships using the emPHasis-10 HRQoL measure. 1745 patients with idiopathic or connective tissue disease-associated PAH who had completed emPHasis-10 questionnaires between 2014–17 at 6 UK referral centres were identified. Correlations with exercise capacity and WHO functional class (FC) were assessed, and exploratory risk stratification thresholds were tested. Moderate correlations were seen between emPHasis-10 scores and 6-minute walk distance (r=−0.546), incremental shuttle walking distance (r=−0.504) and WHO FC (r=0.497; p all <0.0001). Distribution of emPHasis-10 differed significantly between each WHO FC (p all <0.0001). At multivariate analysis, emPHasis-10, but not WHO FC, was an independent predictor of mortality. In a risk stratification approach, scores of 0–16, 17–33 and 34–50 identified incident patients with one-year mortality of 5%, 10% and 23%, respectively. Survival of patients in WHO FC III could be further stratified using an emPHasis-10 score ≥34 (p<0.01). At follow-up, patients with improved emPHasis-10 had improved exercise capacity (p<0.0001), and patients who transitioned risk groups demonstrated similar survival to patients originally in those risk groups. The emPHasis-10 score is an independent prognostic marker in patients with idiopathic or connective tissue disease-associated PAH. It has utility in risk stratification in addition to currently used parameters. Improvement in emPHasis-10 score is associated with improved exercise capacity

First genotype-phenotype study in TBX4 syndrome : gain-of-function mutations causative for lung disease

Rationale: Despite the increased recognition of TBX4-associated pulmonary arterial hypertension (PAH), genotype-phenotype associations are lacking and may provide important insights. Methods: We assembled a multi-center cohort of 137 patients harboring monoallelic TBX4 variants and assessed the pathogenicity of missense variation (n = 42) using a novel luciferase reporter assay containing T-BOX binding motifs. We sought genotype-phenotype correlations and undertook a comparative analysis with PAH patients with BMPR2 causal variants (n = 162) or no identified variants in PAH-associated genes (n = 741) genotyped via the NIHR BioResource - Rare Diseases (NBR). Results: Functional assessment of TBX4 missense variants led to the novel finding of gain-of-function effects associated with older age at diagnosis of lung disease compared to loss-of-function (p = 0.038). Variants located in the T-BOX and nuclear localization domains were associated with earlier presentation (p = 0.005) and increased incidence of interstitial lung disease (p = 0.003). Event-free survival (death or transplantation) was shorter in the T-BOX group (p = 0.022) although age had a significant effect in the hazard model (p = 0.0461). Carriers of TBX4 variants were diagnosed at a younger age (p < 0.001) and had worse baseline lung function (FEV1, FVC) (p = 0.009) compared to the BMPR2 and no identified causal variant groups. Conclusions: We demonstrated that TBX4 syndrome is not strictly the result of haploinsufficiency but can also be caused by gain-of-function. The pleiotropic effects of TBX4 in lung disease may be in part explained by the differential effect of pathogenic mutations located in critical protein domains

Loss-of-function ABCC8 mutations in pulmonary arterial hypertension

Background: In pulmonary arterial hypertension (PAH), pathological changes in pulmonary arterioles progressively raise pulmonary artery pressure and increase pulmonary vascular resistance, leading to right heart failure and high mortality rates. Recently, the first potassium channelopathy in PAH, because of mutations in KCNK3, was identified as a genetic cause and pharmacological target. Methods: Exome sequencing was performed to identify novel genes in a cohort of 99 pediatric and 134 adult-onset group I PAH patients. Novel rare variants in the gene identified were independently identified in a cohort of 680 adult-onset patients. Variants were expressed in COS cells and function assessed by patch-clamp and rubidium flux analysis. Results: We identified a de novo novel heterozygous predicted deleterious missense variant c.G2873A (p.R958H) in ABCC8 in a child with idiopathic PAH. We then evaluated all individuals in the original and a second cohort for rare or novel variants in ABCC8 and identified 11 additional heterozygous predicted damaging ABCC8 variants. ABCC8 encodes SUR1 (sulfonylurea receptor 1)—a regulatory subunit of the ATP-sensitive potassium channel. We observed loss of ATP-sensitive potassium channel function for all ABCC8 variants evaluated and pharmacological rescue of all channel currents in vitro by the SUR1 activator, diazoxide. Conclusions: Novel and rare missense variants in ABCC8 are associated with PAH. Identified ABCC8 mutations decreased ATP-sensitive potassium channel function, which was pharmacologically recovered

Use of intravenous iron in cyanotic patients with congenital heart disease and/or pulmonary hypertension.

Secondary erythrocytosis is common in patients with cyanosis secondary to congenital heart disease (CHD) and/or pulmonary hypertension (PH). This compensatory mechanism aims at increasing oxygen delivery to the tissues, but it requires adequate iron stores. Optimal methods of iron supplementation in this setting remain controversial, with fears of excessive erythropoiesis and hyperviscosity symptoms. We describe our experience using intravenous ferrous carboxymaltose. 142 consecutive cyanotic patients were treated over 5.7 years (201 administrations). Mean age was 51.3 ± 17.6 years and 55 (38.7%) were male. Eisenmenger syndrome (ES) was present in 41 (28.8%), other pulmonary arterial hypertension (PAH) related to CHD (PAH-CHD) in 27 (19.0%), cyanotic CHD without PAH in 16 (11.3%) and PH without CHD in 58(40.8%). Baseline haemoglobin (Hb) concentration was 14.6 ± 3.0 g/dL and haematocrit 0.45 ± 0.09. A 500 mg dose of intravenous (IV) iron carboxymaltose was given in 163 (81.1%) of administrations and a 1000 mg dose in 37 (18.4%). A significant improvement in average Hb, haematocrit, ferritin and transferrin saturation was observed after a median follow-up of 100.0 [70.0-161.0] days (p ≤ 0.0001 for all). There were no cases of excessive erythropoiesis resulting in new hyperviscosity symptoms and/or requiring venesection. A minor transient rash was observed in 2 patients and one patient experienced an air embolus causing a transient ischemic attack. Intravenous ferrous carboxymaltose appears to be safe in iron deficient patients with cyanosis due to CHD and/or PH, as long as care is taken to avoid air emboli. Further randomised studies are needed to confirm the safety and efficacy of intravenous iron in this setting

Arrhythmias in adult patients with congenital heart disease and pulmonary arterial hypertension

Objectives: Approximately 5%-10% of adults with congenital heart disease (CHD) develop pulmonary arterial hypertension (PAH), which affects life expectancy and quality of life. Arrhythmias are common among these patients, but their incidence and impact on outcome remains uncertain. Methods: All adult patients with PAH associated with CHD (PAH-CHD) seen in a tertiary centre between 2007 and 2015 were followed for new-onset atrial or ventricular arrhythmia. Clinical variables associated with arrhythmia and their relation to mortality were assessed using Cox analysis. Results: A total of 310 patients (mean age 34.9±12.3 years, 36.8% male) were enrolled. The majority had Eisenmenger syndrome (58.4%), 15.2% had a prior defect repair and a third had Down syndrome. At baseline, 14.2% had a prior history of arrhythmia, mostly supraventricular arrhythmia (86.4%). During a median follow-up of 6.1 years, 64 patients developed at least one new arrhythmic episode (incidence 3.47% per year), mostly supraventricular tachycardia or atrial fibrillation (78.1% of patients). Arrhythmia was associated with symptoms in 75.0% of cases. The type of PAH-CHD, markers of disease severity and prior arrhythmia were associated with arrhythmia during follow-up. Arrhythmia was a strong predictor of death, even after adjusting for demographic and clinical variables (HR 3.41, 95% CI 2.10 to 5.53, p&lt;0.0001). Conclusions: Arrhythmia is common in PAH-CHD and is associated with an adverse long-term outcome, even when managed in a specialist centre. © Article author(s) 2018. All rights reserved

miR-424-5p reduces ribosomal RNA and protein synthesis in muscle wasting

Background: a loss of muscle mass occurs as a consequence of a range of chronic and acute diseases as well as in older age. This wasting results from an imbalance of protein synthesis and degradation with a reduction in synthesis and resistance to anabolic stimulation often reported features. Ribosomes are required for protein synthesis, so changes in the control of ribosome synthesis are potential contributors to muscle wasting. MicroRNAs (miRNAs) are known regulators of muscle phenotype and have been shown to modulate components of the protein synthetic pathway. One miRNA that is predicted to target a number of components of protein synthetic pathway is miR-424-5p, which is elevated in the quadriceps of patients with chronic obstructive pulmonary disease (COPD).Methods: targets of miR-424-5p were identified by Argonaute2 pull down, and the effects of the miRNA on RNA and protein expression were determined by quantitative polymerase chain reaction and western blotting in muscle cells in vitro. Protein synthesis was determined by puromycin incorporation in vitro. The miRNA was over-expressed in the tibialis anterior muscle of mice by electroporation and the effects quantified. Finally, quadriceps expression of the miRNA was determined by quantitative polymerase chain reaction in patients with COPD and intensive care unit (ICU)-acquired weakness and in patients undergoing aortic surgery as well as in individuals from the Hertfordshire Sarcopenia Study.Results: pull-down assays showed that miR-424-5p bound to messenger RNAs encoding proteins associated with muscle protein synthesis. The most highly enriched messenger RNAs encoded proteins required for the Pol I RNA pre-initiation complex required for ribosomal RNA (rRNA) transcription, (PolR1A and upstream binding transcription factor). In vitro, miR-424-5p reduced the expression of these RNAs, reduced rRNA levels, and inhibited protein synthesis. In mice, over-expression of miR-322 (rodent miR-424 orthologue) caused fibre atrophy and reduced upstream binding transcription factor expression and rRNA levels. In humans, elevated miR-424-5p associated with markers of disease severity in COPD (FEV1%), in patients undergoing aortic surgery (LVEF%), and in patients with ICU-acquired weakness (days in ICU). In patients undergoing aortic surgery, preoperative miR-424-5p expression in skeletal muscle was associated with muscle loss over the following 7 days.Conclusions: these data suggest that miR-424-5p regulates rRNA synthesis by inhibiting Pol I pre-initiation complex formation. Increased miR-424-5p expression in patients with conditions associated with muscle wasting is likely to contribute to the inhibition of protein synthesis and loss of muscle mass