Fatty Acid Metabolic Defects and Right Ventricular Lipotoxicity in Human Pulmonary Arterial Hypertension

Diagnosis and Treatment of Right Heart Failure in Pulmonary Vascular Diseases: A National Heart, Lung, and Blood Institute Workshop

Right ventricular dysfunction is a hallmark of advanced pulmonary vascular, lung parenchymal, and left heart disease, yet the underlying mechanisms that govern (mal)adaptation remain incompletely characterized. Owing to the knowledge gaps in our understanding of the right ventricle (RV) in health and disease, the National Heart, Lung, and Blood Institute (NHLBI) commissioned a working group to identify current challenges in the field. These included a need to define and standardize normal RV structure and function in populations; access to RV tissue for research purposes and the development of complex experimental platforms that recapitulate the in vivo environment; and the advancement of imaging and invasive methodologies to study the RV within basic, translational, and clinical research programs. Specific recommendations were provided, including a call to incorporate precision medicine and innovations in prognosis, diagnosis, and novel RV therapeutics for patients with pulmonary vascular disease.

Long-Chain Acylcarnitines and Monounsaturated Fatty Acids Discriminate Heart Failure Patients According to Pulmonary Hypertension Status

Defects in fatty acid (FA) utilization have been well described in group 1 pulmonary hypertension (PH) and in heart failure (HF), yet poorly studied in group 2 PH. This study was to assess whether the metabolomic profile of patients with pulmonary hypertension (PH) due HF, classified as group 2 PH, differs from those without PH. We conducted a proof-of-principle cross-sectional analysis of 60 patients with chronic HF with reduced ejection fraction and 72 healthy controls in which the circulating level of 71 energy-related metabolites was measured using various methods. Echocardiography was used to classify HF patients as noPH-HF (n = 27; mean pulmonary artery pressure [mPAP] 21 mmHg) and PH-HF (n = 33; mPAP 35 mmHg). The profile of circulating metabolites among groups was compared using principal component analysis (PCA), analysis of covariance (ANCOVA), and Pearson’s correlation tests. Patients with noPH-HF and PH-HF were aged 64 ± 11 and 68 ± 10 years, respectively, with baseline left ventricular ejection fractions of 27 ± 7% and 26 ± 7%. Principal component analysis segregated groups, more markedly for PH-HF, with long-chain acylcarnitines, acetylcarnitine, and monounsaturated FA carrying the highest loading scores. After adjustment for age, sex, kidney function, insulin resistance, and N-terminal pro-brain natriuretic peptide (NT-proBNP), 5/15 and 8/15 lipid-related metabolite levels were significantly different from controls in noPH-HF and PH-HF subjects, respectively. All metabolites for which circulating levels interacted between group and NT-proBNP significantly correlated with NT-proBNP in HF-PH, but none with HF-noPH. FA-related metabolites were differently affected in HF with or without PH, and may convey adverse outcomes given their distinct correlation with NT-proBNP in the setting of PH.

Interaction of maternal immune activation and genetic interneuronal inhibition

Genes and environment interact during intrauterine life, and potentially alter the developmental trajectory of the brain. This can result in life-long consequences on brain function. We have previously developed two transgenic mouse lines that suppress Gad1 expression in parvalbumin (PVALB) and neuropeptide Y (NPY) expressing interneuron populations using a bacterial artificial chromosome (BAC)-driven miRNA-based silencing technology. We were interested to assess if maternal immune activation (MIA), genetic interneuronal inhibition, and the combination of these two factors disrupt and result in long-term changes in neuroinflammatory gene expression, sterol biosynthesis, and acylcarnitine levels in the brain of maternally exposed offspring. Pregnant female WT mice were given a single intraperitoneal injection of saline or polyinosinic-polycytidilic acid [poly(I:C)] at E12.5. Brains of offspring were analyzed at postnatal day 90. We identified complex and persistent neuroinflammatory gene expression changes in the hippocampi of MIA-exposed offspring, as well in the hippocampi of Npy/Gad1 and Pvalb/Gad1 mice. In addition, both MIA and genetic inhibition altered the post-lanosterol sterol biosynthesis in the neocortex and disrupted the typical acylcarnitine profile. In conclusion, our findings suggest that both MIA and inhibition of interneuronal function have long-term consequences on critical homeostatic mechanisms of the brain, including immune function, sterol levels, and energy metabolism.

Metabolism in Pulmonary Hypertension

Pulmonary arterial hypertension (PAH) is characterized by impaired regulation of pulmonary hemodynamics and vascular growth. Alterations of metabolism and bioenergetics are increasingly recognized as universal hallmarks of PAH, as metabolic abnormalities are identified in lungs and hearts of patients, animal models of the disease, and cells derived from lungs of patients. Mitochondria are the primary organelle critically mediating the complex and integrative metabolic pathways in bioenergetics, biosynthetic pathways, and cell signaling. Here, we review the alterations in metabolic pathways that are linked to the pathologic vascular phenotype of PAH, including abnormalities in glycolysis and glucose oxidation, fatty acid oxidation, glutaminolysis, arginine metabolism, one-carbon metabolism, the reducing and oxidizing cell environment, and the tricarboxylic acid cycle, as well as the effects of PAH-associated nuclear and mitochondrial mutations on metabolism. Understanding of the metabolic mechanisms underlying PAH provides important knowledge for the design of new therapeutics for treatment of patients.

Single Mutation in the NFU1 Gene Metabolically Reprograms Pulmonary Artery Smooth Muscle Cells

OBJECTIVE

NFU1 is a mitochondrial iron-sulfur scaffold protein, involved in iron-sulfur assembly and transfer to complex II and LAS (lipoic acid synthase). Patients with the point mutation NFU1G208C and CRISPR/CAS9 (clustered regularly interspaced short palindromic repeats/clustered regularly interspaced short palindromic repeat-associated 9)-generated rats develop mitochondrial dysfunction leading to pulmonary arterial hypertension. However, the mechanistic understanding of pulmonary vascular proliferation due to a single mutation in NFU1 remains unresolved. Approach and Results: Quantitative proteomics of isolated mitochondria showed the entire phenotypic transformation of NFU1G206C rats with a disturbed mitochondrial proteomic landscape, involving significant changes in the expression of 208 mitochondrial proteins. The NFU1 mutation deranged the expression pattern of electron transport proteins, resulting in a significant decrease in mitochondrial respiration. Reduced reliance on mitochondrial respiration amplified glycolysis in pulmonary artery smooth muscle cell (PASMC) and activated GPD (glycerol-3-phosphate dehydrogenase), linking glycolysis to oxidative phosphorylation and lipid metabolism. Decreased PDH (pyruvate dehydrogenase) activity due to the lipoic acid shortage is compensated by increased fatty acid metabolism and oxidation. PASMC became dependent on extracellular fatty acid sources due to upregulated transporters such as CD36 (cluster of differentiation 36) and CPT (carnitine palmitoyltransferase)-1. Finally, the NFU1 mutation produced a dysregulated antioxidant system in the mitochondria, leading to increased reactive oxygen species levels. PASMC from NFU1 rats showed apoptosis resistance, increased anaplerosis, and attained a highly proliferative phenotype. Attenuation of mitochondrial reactive oxygen species by mitochondrial-targeted antioxidant significantly decreased PASMC proliferation.

CONCLUSIONS

The alteration in iron-sulfur metabolism completely transforms the proteomic landscape of the mitochondria, leading toward metabolic plasticity and redistribution of energy sources to the acquisition of a proliferative phenotype by the PASMC.

Rhodiola crenulata extract decreases fatty acid oxidation and autophagy to ameliorate pulmonary arterial hypertension by targeting inhibiton of acylcarnitine in rats

Pulmonary arterial hypertension (PAH) is a devastating pulmonary circulation disease lacking high-efficiency therapeutics. The present study aims to decipher the therapeutic mechanism of Rhodiola crenulata, a well-known traditional chinese medicine with cardiopulmonary protection capacity, on PAH by exploiting functional lipidomics. The rat model with PAH was successfully established for first, following Rhodiola crenulata water extract (RCE) treatment, then analysis of chemical constituents of RCE was performed, additional morphologic, hemodynamic, echocardiographic measurements were examined, further targeted lipidomics assay was performed to identify differential lipidomes, at last accordingly mechanism assay was done by combining qRT-PCR, Western blot and ELISA. Differential lipidomes were identified and characterized to differentiate the rats with PAH from healthy controls, mostly assigned to acylcarnitines, phosphatidylcholines, sphingomyelin associated with the PAH development. Excitingly, RCE administration reversed high level of decadienyl-L-carnitine by the modulation of metabolic enzyme CPT1A in mRNA and protein level in serum and lung in the rats with PAH. Furthermore, RCE was observed to reduce autophagy, confirmed by significantly inhibited PPARγ, LC3B, ATG7 and upregulated p62, and inactivated LKB1-AMPK signal pathway. Notably, we accurately identified the constituents in RCE, and delineated the therapeutic mechansim that RCE ameliorated PAH through inhibition of fatty acid oxidation and autophagy. Altogether, RCE might be a potential therapeutic medicine with multi-targets characteristics to prevent the progression of PAH. This novel findings pave a critical foundation for the use of RCE in the treatment of PAH.

Pulmonary Vascular Disease as a Systemic and Multisystem Disease

Pulmonary arterial hypertension (PAH) is a disease of progressive pulmonary vascular remodeling due to abnormal proliferation of pulmonary vascular endothelial and smooth muscle cells and endothelial dysfunction. PAH is a multisystem disease with systemic manifestations and complications. This article covers the chronic heart failure syndrome, including the systemic consequences of right ventricle-pulmonary artery uncoupling and neurohormonal activation, skeletal and respiratory muscle effects, systemic endothelial dysfunction and coronary artery disease, systemic inflammation and infection, endocrine and metabolic changes, the liver and gut axis, sleep, neurologic complications, and skin and iron metabolic changes.

Cardiac 1H MR spectroscopy: development of the past five decades and future perspectives

Continued advances in laboratory medicine are required to realize the potential of individualized medicine to impact common cardiovascular diseases. Magnetic resonance imaging (MRI) and spectroscopy (MRS) techniques have advanced over recent years and offer unique, powerful insights into cardiac anatomic and metabolic changes, respectively, occurring in both nascent and advanced heart disease. Although numerous MRI-based in vivo diagnostics are already used in routine clinical practice and more are anticipated, MRS has been less incorporated into routine clinical practice. Given the ability of ¹H MRS to identify and quantify specific molecules with high sensitivity and specificity, its potential utility should be successfully transition from "bench-to-bedside" is tantalizing. The present review will highlight the development of ¹H MRS techniques for cardiac applications, observations in seminal studies with ¹H MRS, and the prospects and challenges for widespread application in patients with cardiovascular disease.

Treatment Targets for Right Ventricular Dysfunction in Pulmonary Arterial Hypertension

Right ventricle (RV) dysfunction is the strongest predictor of mortality in pulmonary arterial hypertension (PAH), but, at present, there are no therapies directly targeting the failing RV. Although there are shared molecular mechanisms in both RV and left ventricle (LV) dysfunction, there are important differences between the 2 ventricles that may allow for the development of RV-enhancing or RV-directed therapies. In this review, we discuss the current understandings of the dysregulated pathways that promote RV dysfunction, highlight RV-enriched or RV-specific pathways that may be of particular therapeutic value, and summarize recent and ongoing clinical trials that are investigating RV function in PAH. It is hoped that development of RV-targeted therapies will improve quality of life and enhance survival for this deadly disease.

Effects of macitentan and tadalafil monotherapy or their combination on the right ventricle and plasma metabolites in pulmonary hypertensive rats

Pulmonary arterial hypertension is a severe respiratory disease characterized by pulmonary artery remodeling. RV dysfunction and dysregulated circulating metabolomics are associated with adverse outcomes in pulmonary arterial hypertension. We investigated effects of tadalafil and macitentan alone or in combination on the RV and plasma metabolomics in SuHx and PAB models. For SuHx model, rats were injected with SU5416 and exposed to hypoxia for three weeks and then were returned to normoxia and treated with either tadalafil (10 mg/kg in chow) or macitentan (10 mg/kg in chow) or their combination (both 10 mg/kg in chow) for two weeks. For PAB model, rats were subjected to either sham or PAB surgery for three weeks and treated with above-mentioned drugs from week 1 to week 3. Following terminal echocardiographic and hemodynamic measurements, tissue samples were collected for metabolomic, histological and gene expression analysis. Both SuHx and PAB rats developed RV remodeling/dysfunction with severe and mild plasma metabolomic alterations, respectively. In SuHx rats, tadalafil and macitentan alone or in combination improved RV remodeling/function with the effects of macitentan and combination therapy being superior to tadalafil. All therapies similarly attenuated SuHx-induced changes in plasma metabolomics. In PAB rats, only macitentan improved RV remodeling/function, while only tadalafil attenuated PAB-induced changes in plasma metabolomics.

Metabolic Architecture of Acute Exercise Response in Middle-Aged Adults in the Community

BACKGROUND

Whereas regular exercise is associated with lower risk of cardiovascular disease and mortality, mechanisms of exercise-mediated health benefits remain less clear. We used metabolite profiling before and after acute exercise to delineate the metabolic architecture of exercise response patterns in humans.

METHODS

Cardiopulmonary exercise testing and metabolite profiling was performed on Framingham Heart Study participants (age 53±8 years, 63% women) with blood drawn at rest (n=471) and at peak exercise (n=411).

RESULTS

We observed changes in circulating levels for 502 of 588 measured metabolites from rest to peak exercise (exercise duration 11.9±2.1 minutes) at a 5% false discovery rate. Changes included reductions in metabolites implicated in insulin resistance (glutamate, -29%; P=1.5×10-55; dimethylguanidino valeric acid [DMGV], -18%; P=5.8×10-18) and increases in metabolites associated with lipolysis (1-methylnicotinamide, +33%; P=6.1×10-67), nitric oxide bioavailability (arginine/ornithine + citrulline, +29%; P=2.8×10-169), and adipose browning (12,13-dihydroxy-9Z-octadecenoic acid +26%; P=7.4×10-38), among other pathways relevant to cardiometabolic risk. We assayed 177 metabolites in a separate Framingham Heart Study replication sample (n=783, age 54±8 years, 51% women) and observed concordant changes in 164 metabolites (92.6%) at 5% false discovery rate. Exercise-induced metabolite changes were variably related to the amount of exercise performed (peak workload), sex, and body mass index. There was attenuation of favorable excursions in some metabolites in individuals with higher body mass index and greater excursions in select cardioprotective metabolites in women despite less exercise performed. Distinct preexercise metabolite levels were associated with different physiologic dimensions of fitness (eg, ventilatory efficiency, exercise blood pressure, peak Vo2). We identified 4 metabolite signatures of exercise response patterns that were then analyzed in a separate cohort (Framingham Offspring Study; n=2045, age 55±10 years, 51% women), 2 of which were associated with overall mortality over median follow-up of 23.1 years (P≤0.003 for both).

CONCLUSIONS

In a large sample of community-dwelling individuals, acute exercise elicits widespread changes in the circulating metabolome. Metabolic changes identify pathways central to cardiometabolic health, cardiovascular disease, and long-term outcome. These findings provide a detailed map of the metabolic response to acute exercise in humans and identify potential mechanisms responsible for the beneficial cardiometabolic effects of exercise for future study.

Mechanistic Phase II Clinical Trial of Metformin in Pulmonary Arterial Hypertension

Background Metabolic dysfunction is highly prevalent in pulmonary arterial hypertension (PAH) and likely contributes to both pulmonary vascular disease and right ventricular (RV) failure in part because of increased oxidant stress. Currently, there is no cure for PAH and human studies of metabolic interventions, generally well tolerated in other diseases, are limited in PAH. Metformin is a commonly used oral antidiabetic that decreases gluconeogenesis, increases fatty acid oxidation, and reduces oxidant stress and thus may be relevant to PAH. Methods and Results We performed a single-center, open-label 8-week phase II trial of up to 2 g/day of metformin in patients with idiopathic or heritable PAH with the co-primary end points of safety, including development of lactic acidosis and study withdrawal, and plasma oxidant stress markers. Exploratory end points included RV function via echocardiography, plasma metabolomic analysis performed before and after metformin therapy, and RV triglyceride content by magnetic resonance spectroscopy in a subset of 9 patients. We enrolled 20 patients; 19/20 reached the target dose and all completed the study protocol. There was no clinically significant lactic acidosis or change in oxidant stress markers. Metformin did not change 6-minute walk distance but did significantly improve RV fractional area change (23±8% to 26±6%, P=0.02), though other echocardiographic parameters were unchanged. RV triglyceride content decreased in 8/9 patients (3.2±1.8% to 1.6±1.4%, P=0.015). In an exploratory metabolomic analysis, plasma metabolomic correlates of ≥50% reduction in RV lipid included dihydroxybutyrate, acetylputrescine, hydroxystearate, and glucuronate (P<0.05 for all). In the entire cohort, lipid metabolites were among the most changed by metformin. Conclusions Metformin therapy was safe and well tolerated in patients with PAH in this single-arm, open-label phase II study. Exploratory analyses suggest that metformin may be associated with improved RV fractional area change and, in a subset of patients, reduced RV triglyceride content that correlated with altered lipid and glucose metabolism markers. Registration URL: http://www.clinicaltrials.gov; Unique identifier: NCT01884051.

Plasma metabolomics exhibit response to therapy in chronic thromboembolic pulmonary hypertension

Pulmonary hypertension is a condition with limited effective treatment options. Chronic thromboembolic pulmonary hypertension (CTEPH) is a notable exception, with pulmonary endarterectomy (PEA) often proving curative. This study investigated the plasma metabolome of CTEPH patients, estimated reversibility to an effective treatment and explored the source of metabolic perturbations.We performed untargeted analysis of plasma metabolites in CTEPH patients compared to healthy controls and disease comparators. Changes in metabolic profile were evaluated in response to PEA. A subset of patients were sampled at three anatomical locations and plasma metabolite gradients calculated.We defined and validated altered plasma metabolite profiles in patients with CTEPH. 12 metabolites were confirmed by receiver operating characteristic analysis to distinguish CTEPH and both healthy (area under the curve (AUC) 0.64-0.94, all p<2×10^-5) and disease controls (AUC 0.58-0.77, all p<0.05). Many of the metabolic changes were notably similar to those observed in idiopathic pulmonary arterial hypertension (IPAH). Only five metabolites (5-methylthioadenosine, N1-methyladenosine, N1-methylinosine, 7-methylguanine, N-formylmethionine) distinguished CTEPH from chronic thromboembolic disease or IPAH. Significant corrections (15-100% of perturbation) in response to PEA were observed in some, but not all metabolites. Anatomical sampling identified 188 plasma metabolites, with significant gradients in tryptophan, sphingomyelin, methionine and Krebs cycle metabolites. In addition, metabolites associated with CTEPH and gradients showed significant associations with clinical measures of disease severity.We identified a specific metabolic profile that distinguishes CTEPH from controls and disease comparators, despite the observation that most metabolic changes were common to both CTEPH and IPAH patients. Plasma metabolite gradients implicate cardiopulmonary tissue metabolism of metabolites associated with pulmonary hypertension and metabolites that respond to PEA surgery could be a suitable noninvasive marker for evaluating future targeted therapeutic interventions.

Excess Protein O-GlcNAcylation Links Metabolic Derangements to Right Ventricular Dysfunction in Pulmonary Arterial Hypertension

The hexosamine biosynthetic pathway (HBP) converts glucose to uridine-diphosphate-N-acetylglucosamine, which, when added to serines or threonines, modulates protein function through protein O-GlcNAcylation. Glutamine-fructose-6-phosphate amidotransferase (GFAT) regulates HBP flux, and AMP-kinase phosphorylation of GFAT blunts GFAT activity and O-GlcNAcylation. While numerous studies demonstrate increased right ventricle (RV) glucose uptake in pulmonary arterial hypertension (PAH), the relationship between O-GlcNAcylation and RV function in PAH is unexplored. Therefore, we examined how colchicine-mediated AMP-kinase activation altered HBP intermediates, O-GlcNAcylation, mitochondrial function, and RV function in pulmonary artery-banded (PAB) and monocrotaline (MCT) rats. AMPK activation induced GFAT phosphorylation and reduced HBP intermediates and O-GlcNAcylation in MCT but not PAB rats. Reduced O-GlcNAcylation partially restored the RV metabolic signature and improved RV function in MCT rats. Proteomics revealed elevated expression of O-GlcNAcylated mitochondrial proteins in MCT RVs, which fractionation studies corroborated. Seahorse micropolarimetry analysis of H9c2 cardiomyocytes demonstrated colchicine improved mitochondrial function and reduced O-GlcNAcylation. Presence of diabetes in PAH, a condition of excess O-GlcNAcylation, reduced RV contractility when compared to nondiabetics. Furthermore, there was an inverse relationship between RV contractility and HgbA1C. Finally, RV biopsy specimens from PAH patients displayed increased O-GlcNAcylation. Thus, excess O-GlcNAcylation may contribute to metabolic derangements and RV dysfunction in PAH.

Molecular mechanisms of right ventricular dysfunction in pulmonary arterial hypertension: focus on the coronary vasculature, sex hormones, and glucose/lipid metabolism

Pulmonary arterial hypertension (PAH) is a rare, life-threatening condition characterized by dysregulated metabolism, pulmonary vascular remodeling, and loss of pulmonary vascular cross-sectional area due to a variety of etiologies. Right ventricular (RV) dysfunction in PAH is a critical mediator of both long-term morbidity and mortality. While combinatory oral pharmacotherapy and/or intravenous prostacyclin aimed at decreasing pulmonary vascular resistance (PVR) have improved clinical outcomes, there are currently no treatments that directly address RV failure in PAH. This is, in part, due to the incomplete understanding of the pathogenesis of RV dysfunction in PAH. The purpose of this review is to discuss the current understanding of key molecular mechanisms that cause, contribute and/or sustain RV dysfunction, with a special focus on pathways that either have led to or have the potential to lead to clinical therapeutic intervention. Specifically, this review discusses the mechanisms by which vessel loss and dysfunctional angiogenesis, sex hormones, and metabolic derangements in PAH directly contribute to RV dysfunction. Finally, this review discusses limitations and future areas of investigation that may lead to novel understanding and therapeutic interventions for RV dysfunction in PAH.

Mechanics of right ventricular dysfunction in pulmonary arterial hypertension and heart failure with preserved ejection fraction

Right ventricular (RV) dysfunction is the most important determinant of survival in patients with pulmonary hypertension (PH). The manifestations of RV dysfunction not only include changes in global RV systolic function but also abnormalities in the pattern of contraction and synchrony. The effects of PH on the right ventricle have been mainly studied in patients with pulmonary arterial hypertension (PAH). However, with the demographic shift towards an aging population, heart failure with preserved ejection fraction (HFpEF) has become an important etiology of PH in recent years. There are significant differences in RV mechanics, function and adaptation between patients with PAH and HFpEF (with or without PH), which are related to different patterns of remodeling and dysfunction. Due to the unique features of the RV chamber, its connection with the main pulmonary artery and the pulmonary circulation, an understanding of the mechanics of RV function and its clinical significance is mandatory for both entities. In this review, we describe the mechanics of the pressure overloaded right ventricle. We review the different mechanical components of RV dysfunction and ventricular dyssynchrony, followed by insights via analysis of pressure-volume loop, energetics and novel blood flow patterns, such as vortex imaging. We conduct an in-depth comparison of prevalence and characteristics of RV dysfunction in HFpEF and PAH, and summarize key outcome studies. Finally, we provide a perspective on needed and expected future work in the field of RV mechanics.

Role of 20-hydroxyeicosatetraenoic acid in pulmonary hypertension and proliferation of pulmonary arterial smooth muscle cells

OBJECTIVE

To investigate the level of 20-Hydroxyeicosatetraenoic acid (20-HETE) in model of pulmonary hypertension (PH) and its effect on the proliferation of pulmonary arterial smooth muscle cells (PASMCs).

METHODS

Twenty male Sprague-Dawley rats were randomly divided into two groups, including control group and PH group. PH was induced by intra-peritoneal injection of 20 mg/kg monocrotaline (MCT) twice in a week in 10 rats, and control rats were given equal amount of saline. Mean pulmonary arterial pressure (mPAP), right ventricular hypertrophy index (RVHI) and pulmonary vascular remodeling index (WA%, WT%) were assessed at the week 4. The levels of 20-HETE were analysed by liquid chromatography tandem-mass spectrometry (LC-MS/MS). EdU test was used to determine the proliferation of PASMCs. Intracellular levels of reactive oxygen species (ROS) were detected using DCFH-DA dye.

RESULTS

(1) Prominent right ventricular hypertrophy and pulmonary vascular remodeling were verified in PH rats; (2) 20-HETE levels in lung tissue and serum were significantly lifted in PH rats; (3) Increased 20-HETE levels in cell culture supernatants were significantly noted in hypoxia condition; (4) Proliferation of PASMCs was induced by 20-HETE and hypoxia, and was inhibited by HET0016; (5) Production of ROS was elevated by 20-HETE and hypoxia, and was reduced by HET0016; CONCLUSION: Vascular remodeling was demonstrated in PH rats. 20-HETE levels were significantly increased in PH rats and under hypoxia condition. PASMCs proliferation and ROS production were elevated by 20-HETE and could be inhibited by HET0016, a specific inhibitor of 20-HETE. Taken together, changes in the level of 20-HETE may be related to the excessive proliferation of PASMCs in PH rats.

Exploring New Therapeutic Pathways in Pulmonary Hypertension. Metabolism, Proliferation, and Personalized Medicine

In this review, we explore the main themes from the 62nd Annual Aspen Lung Conference (hypoxia, cellular metabolism, inflammatory pathways, aberrant proliferation, and personalized medicine) and highlight challenges and opportunities in the coming decade of pulmonary vascular disease.

Cardiac magnetic resonance in heart failure with preserved ejection fraction: myocyte, interstitium, microvascular, and metabolic abnormalities

Heart failure (HF) with preserved ejection fraction (HFpEF) is a chronic cardiac condition whose prevalence continues to rise, with high social and economic burden, but with no specific approved treatment. Patients diagnosed with HFpEF have a high prevalence of comorbidities and exhibit a high misdiagnosis rate. True HFpEF is likely to have multiple pathophysiological causes - with these causes being clinically ill-defined due to limitations of current measurement techniques. Myocyte, interstitium, microvascular, and metabolic abnormalities have been regarded as key components of the pathophysiology and potential therapeutic targets. Cardiac magnetic resonance (CMR) has the capability to look deeper with a number of tissue characterization techniques which are closer to the underlying specific abnormalities and which could be linked to personalized medicine for HFpEF. This review aims to discuss the potential role of CMR to better define HFpEF phenotypes and to infer measurable therapeutic targets.

BMI Is Causally Associated With Pulmonary Artery Pressure But Not Hemodynamic Evidence of Pulmonary Vascular Remodeling

BACKGROUND

There is an unclear relationship of obesity to the pathogenesis and severity of pulmonary arterial hypertension (PAH) and pulmonary venous hypertension (PVH).

RESEARCH QUESTION

Is BMI casually associated with pulmonary artery pressure (PAP) and/or markers of pulmonary vascular remodeling?

STUDY DESIGN AND METHODS

The study design was a two-sample inverse-variance weighted Mendelian randomization. We constructed two BMI genetic risk scores from genome-wide association study summary data and deployed them in nonoverlapping cohorts of subjects referred for right heart catheterization (RHC) or echocardiography. A BMI highly polygenic risk score (hpGRS) optimally powered to detect shared genetic architecture of obesity with other traits was tested for association with RHC parameters including markers of pulmonary vascular remodeling. A BMI strict genetic risk score (sGRS) composed of high-confidence genetic variants was used for Mendelian randomization analyses to assess if higher BMI causes higher PAP.

RESULTS

Among all subjects, both directly measured BMI and hpGRS were positively associated with pulmonary arterial pressures but not markers of pulmonary vascular remodeling. Categorical analyses revealed BMI and hpGRS were associated with PVH but not PAH. Mendelian randomization of the sGRS supported that higher BMI is causal of higher systolic pulmonary artery pressure (sPAP). Sensitivity analyses showed sPAP-BMI sGRS relationship was preserved when either individuals with PAH or PVH were excluded. In the echocardiographic cohort, BMI and hpGRS were positively associated with estimated PAP and markers of left heart remodeling.

INTERPRETATION

BMI is a modifier of pulmonary hypertension severity in both PAH and PVH but is only involved in the pathogenesis of PVH.

Vascular Metabolic Mechanisms of Pulmonary Hypertension

Pulmonary hypertension (PH) is a severe and progressive disease characterized by increased pulmonary vascular resistance leading to right heart failure and death. In PH, the cellular metabolisms including those of the three major nutrients (carbohydrate, lipid and protein) are aberrant in pulmonary vascular cells. Glucose uptake, glycolysis, insulin resistance, sphingolipid S1P, PGE₂, TXA₂, leukotrienes and glutaminolysis are upregulated, and phospholipid-prostacyclin and L-arginine-nitric oxide pathway are compromised in lung vascular cells. Fatty acid metabolism is disordered in lung endothelial cells and smooth muscle cells. These molecular mechanisms are integrated to promote PH-specific abnormal vascular cell proliferation and vascular remodeling. This review summarizes the recent advances in the metabolic reprogramming of glucose, fatty acid, and amino acid metabolism in pulmonary vascular remodeling in PH and the mechanisms for how these alterations affect vascular cell fate and impact the course of PH.

Metabolic Pathways Fueling the Endothelial Cell Drive

Endothelial cell (EC) metabolism is important for health and disease. Metabolic pathways, such as glycolysis, fatty acid oxidation, and amino acid metabolism, determine vasculature formation. These metabolic pathways have different roles in securing the production of energy and biomass and the maintenance of redox homeostasis in vascular migratory tip cells, proliferating stalk cells, and quiescent phalanx cells, respectively. Emerging evidence demonstrates that perturbation of EC metabolism results in EC dysfunction and vascular pathologies. Here, we summarize recent insights into EC metabolic pathways and their deregulation in vascular diseases. We further discuss the therapeutic implications of targeting EC metabolism in various pathologies.

Beyond the Lungs: Systemic Manifestations of Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a disease characterized by progressive loss and remodeling of the pulmonary arteries, resulting in right heart failure and death. Until recently, PAH was seen as a disease restricted to the pulmonary circulation. However, there is growing evidence that patients with PAH also exhibit systemic vascular dysfunction, as evidenced by impaired brachial artery flow-mediated dilation, abnormal cerebral blood flow, skeletal myopathy, and intrinsic kidney disease. Although some of these anomalies are partially due to right ventricular insufficiency, recent data support a mechanistic link to the genetic and molecular events behind PAH pathogenesis. This review serves as an introduction to the major systemic findings in PAH and the evidence that supports a common mechanistic link with PAH pathophysiology. In addition, it discusses recent studies describing morphological changes in systemic vessels and the possible role of bronchopulmonary anastomoses in the development of plexogenic arteriopathy. On the basis of available evidence, we propose a paradigm in which metabolic abnormalities, genetic injury, and systemic vascular dysfunction contribute to systemic manifestations in PAH. This concept not only opens exciting research possibilities but also encourages clinicians to consider extrapulmonary manifestations in their management of patients with PAH.

The application of 'omics' to pulmonary arterial hypertension

Recent genome-wide analyses of rare and common sequence variations have brought greater clarity to the genetic architecture of pulmonary arterial hypertension and implicated novel genes in disease development. Transcriptional signatures have been reported in whole lung tissue, pulmonary vascular cells and peripheral circulating cells. High-throughput platforms for plasma proteomics and metabolomics have identified novel biomarkers associated with clinical outcomes and provided molecular instruments for risk assessment. There are methodological challenges to integrating these datasets, coupled to statistical power limitations inherent to the study of a rare disease, but the expectation is that this approach will reveal novel druggable targets and biomarkers that will open the way to personalized medicine. Here, we review the current state-of-the-art and future promise of 'omics' in the field of translational medicine in pulmonary arterial hypertension. LINKED ARTICLES: This article is part of a themed issue on Risk factors, comorbidities, and comedications in cardioprotection. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.1/issuetoc.

Trans-Right-Ventricle and Transpulmonary MicroRNA Gradients in Human Pulmonary Arterial Hypertension

OBJECTIVES

We investigated whether concentrations of circulating microRNAs differ across the hypertensive right ventricle and pulmonary circulation, and correlate with hemodynamic/echocardiographic variables in patients with pulmonary arterial hypertension versus nonpulmonary arterial hypertension controls.

DESIGN

Prospective blood collection during cardiac catheterization from the superior vena cava, pulmonary artery, and ascending aorta in 12 children with pulmonary arterial hypertension and nine matched nonpulmonary arterial hypertension controls, followed by an unbiased quantitative polymerase chain reaction array screen for 754 microRNAs in plasma.

SETTING

Children's hospital at a medical school.

PATIENTS

Twelve pulmonary arterial hypertension patients included as follows: idiopathic pulmonary arterial hypertension (5), pulmonary arterial hypertension (2), pulmonary arterial hypertension-repaired congenital heart disease (4), portopulmonary pulmonary hypertension (1). Nine nonpulmonary arterial hypertension controls included as follows: mild/moderate left ventricular outflow tract obstruction (7), mediastinal teratoma (1), portal vein stenosis (1).

INTERVENTIONS

Standard pulmonary arterial hypertension treatment.

MEASUREMENTS AND MAIN RESULTS

Analysis of differential concentrations (false discovery rate < 0.05) revealed two trans-right-ventricle microRNA gradients (pulmonary artery vs superior vena cava): miR-193a-5p (step-up in pulmonary arterial hypertension and step-down in control) and miR-423-5p (step-down in pulmonary arterial hypertension and step-up in control) and two transpulmonary microRNA gradients (ascending aorta vs pulmonary artery): miR-26b-5p (step-down only in control) and miR-331-3p (step-up only in pulmonary arterial hypertension). Between-group comparison revealed miR-29a-3p, miR-26a-5p, miR-590-5p, and miR-200c-3p as upregulated in pulmonary arterial hypertension-superior vena cava and miR-99a-5p as downregulated in pulmonary arterial hypertension-pulmonary artery. The differential microRNA-concentrations correlated with prognostic hemodynamic variables (pulmonary vascular resistance, tricuspid annular plane systolic excursion, etc.).

CONCLUSIONS

We identified for the first time in human disease (pulmonary arterial hypertension) trans-right-ventricle and transpulmonary microRNA gradients in blood plasma. Several of these microRNAs regulate transcripts that drive cardiac remodeling and pulmonary arterial hypertension and are now emerging as epigenetic pulmonary arterial hypertension biomarkers and targets for therapy.

Trans-right ventricle and transpulmonary metabolite gradients in human pulmonary arterial hypertension

OBJECTIVE

While metabolic dysfunction occurs in several pulmonary arterial hypertension (PAH) animal models, its role in the human hypertensive right ventricle (RV) and lung is not well characterised. We investigated whether circulating metabolite concentrations differ across the hypertensive RV and/or the pulmonary circulation, and correlate with invasive haemodynamic/echocardiographic variables in patients with PAH.

METHODS

Prospective EDTA blood collection during cardiac catheterisation from the superior vena cava (SVC), pulmonary artery (PA) and ascending aorta (AAO) in children with PAH (no shunt) and non-PAH controls (Con), followed by unbiased screens of 427 metabolites and 836 lipid species and fatty acids (FAs) in blood plasma (Metabolon and Lipidyzer platforms). Metabolite concentrations were correlated with echocardiographic and invasive haemodynamic variables.

RESULTS

Metabolomics/lipidomics analysis of differential concentrations (false discovery rate<0.15) revealed several metabolite gradients in the trans-RV (PA vs SVC) setting. Notably, dicarboxylic acids (eg, octadecanedioate: fold change (FC)_Control=0.77, FC_PAH=1.09, p value=0.044) and acylcarnitines (eg, stearoylcarnitine: FC_Control=0.74, FC_PAH=1.21, p value=0.058). Differentially regulated metabolites were also found in the transpulmonary (AAO vs PA) setting and between-group comparisons, that is, in the SVC (PAH-SVC vs Con-SVC), PA and AAO. Importantly, the differential PAH-metabolite concentrations correlated with numerous outcome-relevant variables (e.g., tricuspid annular plane systolic excursion, pulmonary vascular resistance).

CONCLUSIONS

In PAH, trans-RV and transpulmonary metabolite gradients exist and correlate with haemodynamic determinants of clinical outcome. The most pronounced differential trans-RV gradients are known to be involved in lipid metabolism/lipotoxicity, that is, accumulation of long chain FAs. The identified accumulation of dicarboxylic acids and acylcarnitines likely indicates impaired β-oxidation in the hypertensive RV and represents emerging biomarkers and therapeutic targets in PAH.

Metabolic syndrome, neurohumoral modulation, and pulmonary arterial hypertension

Pulmonary vascular disease, including pulmonary arterial hypertension (PAH), is increasingly recognized to be affected by systemic alterations including up-regulation of the renin-angiotensin-aldosterone system and perturbations to metabolic pathways, particularly glucose and fat metabolism. There is increasing preclinical and clinical data that each of these pathways can promote pulmonary vascular disease and right heart failure and are not simply disease markers. More recently, trials of therapeutics aimed at neurohormonal activation or metabolic dysfunction are beginning to shed light on how interventions in these pathways may affect patients with PAH. This review will focus on underlying mechanistic data that supports neurohormonal activation and metabolic dysfunction in the pathogenesis of PAH and right heart failure as well as discussing early translational data in patients with PAH.

A multifaceted investigation into molecular associations of chronic thromboembolic pulmonary hypertension pathogenesis

Purpose

Chronic thromboembolic pulmonary hypertension is characterized by incomplete thrombus resolution following acute pulmonary embolism, leading to pulmonary hypertension and right ventricular dysfunction. Conditions such as thrombophilias, dysfibrinogenemias, and inflammatory states have been associated with chronic thromboembolic pulmonary hypertension, but molecular mechanisms underlying this disease are poorly understood. We sought to characterize the molecular and functional features associated with chronic thromboembolic pulmonary hypertension using a multifaceted approach.

Methods

We utilized functional assays to compare clot lysis times between chronic thromboembolic pulmonary hypertension patients and multiple controls. We then performed immunohistochemical characterization of tissue from chronic thromboembolic pulmonary hypertension, pulmonary arterial hypertension, and healthy controls, and examined RNA expression patterns of cultured lymphocytes and pulmonary arterial specimens. We then confirmed RNA expression changes using immunohistochemistry, immunofluorescence, and Western blotting in pulmonary arterial tissue.

Results

Clot lysis times in chronic thromboembolic pulmonary hypertension patients are similar to multiple controls. Chronic thromboembolic pulmonary hypertension endarterectomized tissue has reduced expression of both smooth muscle and endothelial cell markers. RNA expression profiles in pulmonary arteries and peripheral blood lymphocytes identified differences in RNA transcript levels related to inflammation and growth factor signaling, which we confirmed using immunohistochemistry. Gene expression data also suggested significant alterations in metabolic pathways, and immunofluorescence and Western blot experiments confirmed that unglycosylated CD36 and adiponectin expression were increased in chronic thromboembolic pulmonary hypertension versus controls.

Conclusions

Our data do not support impaired clot lysis underlying chronic thromboembolic pulmonary hypertension, but did demonstrate distinct molecular patterns present both in peripheral blood and in pathologic specimens of chronic thromboembolic pulmonary hypertension patients suggesting that altered metabolism may play a role in chronic thromboembolic pulmonary hypertension pathogenesis.

Plasma metabolomic profile in chronic thromboembolic pulmonary hypertension

We aimed to characterize the plasma metabolome of chronic thromboembolic pulmonary hypertension patients using a high-throughput unbiased omics approach. We collected fasting plasma from a peripheral vein in 33 operable chronic thromboembolic pulmonary hypertension patients, 31 healthy controls, and 21 idiopathic pulmonary arterial hypertension patients matched for age, gender, and body mass index. Metabolomic analysis was performed using an untargeted approach (Metabolon Inc. Durham, NC). Of the total of 862 metabolites identified, 362 were different in chronic thromboembolic pulmonary hypertension compared to controls: 178 were higher and 184 were lower. Compared to idiopathic pulmonary arterial hypertension, 147 metabolites were different in chronic thromboembolic pulmonary hypertension: 45 were higher and 102 were lower. The plasma metabolome allowed us to distinguish subjects with chronic thromboembolic pulmonary hypertension and healthy controls with a predictive accuracy of 89%, and chronic thromboembolic pulmonary hypertension versus idiopathic pulmonary arterial hypertension with 80% accuracy. Compared to idiopathic pulmonary arterial hypertension and healthy controls, chronic thromboembolic pulmonary hypertension patients had higher fatty acids and glycerol; while acyl cholines and lysophospholipids were lower. Compared to healthy controls, both idiopathic pulmonary arterial hypertension and chronic thromboembolic pulmonary hypertension patients had increased acyl carnitines, beta-hydroxybutyrate, amino sugars and modified amino acids and nucleosides. The plasma global metabolomic profile of chronic thromboembolic pulmonary hypertension suggests aberrant lipid metabolism characterized by increased lipolysis, fatty acid oxidation, and ketogenesis, concomitant with reduced acyl choline and phospholipid moieties. Future research should investigate the pathogenetic and therapeutic potential of modulating lipid metabolism in chronic thromboembolic pulmonary hypertension.

Activation of the Metabolic Master Regulator PPARγ: A Potential PIOneering Therapy for Pulmonary Arterial Hypertension

Translational research is essential to the development of reverse-remodeling strategies for the treatment of pulmonary vascular disease, pulmonary hypertension, and heart failure via mechanistic in vivo studies using animal models resembling human pulmonary arterial hypertension (PAH), cardiovascular remodeling, and progressive right heart failure. Since 2007, peroxisome proliferator-activated receptor γ (PPARγ) agonists have emerged as promising novel, antiproliferative, antiinflammatory, insulin-sensitizing, efficient medications for the treatment of PAH. However, early diabetes study results, their subsequent misinterpretations, errors in published review articles, and rumors regarding potential adverse effects in the literature have dampened enthusiasm for considering pharmacological PPARγ activation for the treatment of cardiovascular diseases, including PAH. Most recently, the thiazolidinedione class PPARγ agonist pioglitazone underwent a clinical revival, especially based on the IRIS (Insulin Resistance Intervention After Stroke) study, a randomized controlled trial in 3,876 patients without diabetes status post-transient ischemic attack/ischemic stroke who were clinically followed for 4.8 years. We discuss preclinical basic translational findings and randomized controlled trials related to the beneficial and adverse effects of PPARγ agonists of the thiazolidinedione class, with a particular focus on the last 5 years. The objective is a data-driven approach to set the preclinical and clinical study record straight. The convincing recent clinical trial data on the lack of significant toxicity in high-risk populations justify the timely conduct of clinical studies to achieve "repurposing" or "repositioning" of pioglitazone for the treatment of clinical PAH.

BMPR2 dysfunction impairs insulin signaling and glucose homeostasis in cardiomyocytes

Insulin resistance and right ventricular (RV) dysfunction are associated with lipotoxicity in heritable forms of pulmonary arterial hypertension (PAH), commonly due to mutations in bone morphogenetic protein receptor type 2 (BMPR2). How BMPR2 dysfunction in cardiomyocytes alters glucose metabolism and the response of these cells to insulin are unknown. We hypothesized that BMPR2 mutation in cardiomyocytes alters glucose-supported mitochondrial respiration and impairs cellular responses to insulin, including glucose and lipid uptake. We performed metabolic assays, immunofluorescence and Western analysis, RNA profiling, and radioactive isotope uptake studies in H9c2 cardiomyocyte cell lines with and without patient-derived BMPR2 mutations (mutant cells), with and without insulin. Unlike control cells, BMPR2 mutant cardiomyocytes have reduced metabolic plasticity as indicated by reduced mitochondrial respiration with increased mitochondrial superoxide production. These mutant cells show enhanced baseline phosphorylation of insulin-signaling protein as indicated by increased Akt, AMPK, and acetyl-CoA carboxylase phosphorylation that may negatively influence fatty acid oxidation and enhance lipid uptake, and are insulin insensitive. Furthermore, mutant cells demonstrate an increase in milk fat globule-EGF factor-8 protein (MFGE8), which influences the insulin-signaling pathway by phosphorylating AktSer473 via phosphatidylinositol 3-kinase and mammalian target of rapamycin. In conclusion, BMPR2 mutant cardiomyocytes have reduced metabolic plasticity and fail to respond to glucose. These cells have enhanced baseline insulin-signaling pattern favoring insulin resistance with failure to augment this pattern in response to insulin. BMPR2 mutation possibly blunts glucose uptake and enhances lipid uptake in these cardiomyocytes. The MFGE8-driven signaling pathway may suggest a new mechanism underlying RV lipotoxicity in PAH.

Metabolomics reveals metabolite changes of patients with pulmonary arterial hypertension in China

The specific mechanism of pulmonary arterial hypertension (PAH) remains elusive. The present study aimed to explore the underlying mechanism of PAH through the identity of novel biomarkers for PAH using metabolomics approach. Serum samples from 40 patients with idiopathic PAH (IPAH), 20 patients with congenital heart disease-associated PAH (CHD-PAH) and 20 healthy controls were collected and analysed by ultra-high-performance liquid chromatography coupled with high-resolution mass spectrometry (UPLC-HRMS). Orthogonal partial least square-discriminate analysis (OPLS-DA) was applied to screen potential biomarkers. These results were validated in monocrotaline (MCT)-induced PAH rat model. The OPLS-DA model was successful in screening distinct metabolite signatures which distinguished IPAH and CHD-PAH patients from healthy controls, respectively (26 and 15 metabolites). Unbiased analysis from OPLS-DA identified 31 metabolites from PAH patients which were differentially regulated compared to the healthy controls. Our analysis showed dysregulation of the different metabolic pathways, including lipid metabolism, glucose metabolism, amino acid metabolism and phospholipid metabolism pathways in PAH patients compared to their healthy counterpart. Among these metabolites from dysregulated metabolic pathways, a panel of metabolites from lipid metabolism and fatty acid oxidation (lysophosphatidylcholine, phosphatidylcholine, perillic acid, palmitoleic acid, N-acetylcholine-d-sphingomyelin, oleic acid, palmitic acid and 2-Octenoylcarnitine metabolites) were found to have a close association with PAH. The results from the analysis of both real-time quantitative PCR and Western blot showed that expression of LDHA, CD36, FASN, PDK1 GLUT1 and CPT-1 in right heart/lung were significantly up-regulated in MCT group than the control group.

Involvement of Low-Density Lipoprotein Receptor in the Pathogenesis of Pulmonary Hypertension

Background

Recently, we and others have reported a causal role for oxidized lipids in the pathogenesis of pulmonary hypertension (PH). However, the role of low‐density lipoprotein receptor (LDL‐R) in PH is not known.

Methods and Results

We examined the role of LDL‐R in the development of PH and determined the efficacy of high‐density lipoprotein mimetic peptide 4F in mitigating PH. Explanted human lungs and plasma from patients with PH and control subjects were analyzed for gene expression, histological characteristics, and lipoprotein oxidation. Male LDL‐R null (LDL‐R knockout) mice (12–15 months old) were fed chow, Western diet (WD), WD with 4F, and WD with scramble peptide for 12 weeks. Serial echocardiography, cardiac catheterization, oxidized LDL assay, real‐time quantitative reverse transcription–polymerase chain reaction, and histological analysis were performed. The effect of LDL‐R knockdown and oxidized LDL on human pulmonary artery smooth muscle cell proliferation was assessed in vitro. LDL‐R and CD36 expression levels were significantly downregulated in the lungs of patients with PH. Patients with PH also had increased lung lipid deposits, oxidized LDL, E06 immunoreactivity, and plasma oxidized LDL/LDL ratio. LDL‐R knockout mice on WD developed PH, right ventricular hypertrophy, right ventricular dysfunction, pulmonary vascular remodeling, fibrosis, and lipid deposition in lungs, aortic atherosclerosis, and left ventricular dysfunction, which were prevented by 4F. Interestingly, PH in WD group preceded left ventricular dysfunction. Oxidized LDL or LDL‐R knockdown significantly increased proliferation of human pulmonary artery smooth muscle cells in vitro.

Conclusions

Human PH is associated with decreased LDL‐R in lungs and increased oxidized LDL in lungs and plasma. WD‐fed LDL‐R knockout mice develop PH and right ventricular dysfunction, implicating a role for LDL‐R and oxidized lipids in PH.

O-GlcNAc Transferase Regulates Angiogenesis in Idiopathic Pulmonary Arterial Hypertension

Idiopathic pulmonary arterial hypertension (IPAH) is considered a vasculopathy characterized by elevated pulmonary vascular resistance due to vasoconstriction and/or lung remodeling such as plexiform lesions, the hallmark of the PAH, as well as cell proliferation and vascular and angiogenic dysfunction. The serine/threonine hydroxyl-linked N-Acetylglucosamine (O-GlcNAc) transferase (OGT) has been shown to drive pulmonary arterial smooth muscle cell (PASMC) proliferation in IPAH. OGT is a cellular nutrient sensor that is essential in maintaining proper cell function through the regulation of cell signaling, proliferation, and metabolism. The aim of this study was to determine the role of OGT and O-GlcNAc in vascular and angiogenic dysfunction in IPAH. Primary isolated human control and IPAH patient PASMCs and pulmonary arterial endothelial cells (PAECs) were grown in the presence or absence of OGT inhibitors and subjected to biochemical assessments in monolayer cultures and tube formation assays, in vitro vascular sprouting 3D spheroid co-culture models, and de novo vascularization models in NODSCID mice. We showed that knockdown of OGT resulted in reduced vascular endothelial growth factor (VEGF) expression in IPAH primary isolated vascular cells. In addition, specificity protein 1 (SP1), a known stimulator of VEGF expression, was shown to have higher O-GlcNAc levels in IPAH compared to control at physiological (5 mM) and high (25 mM) glucose concentrations, and knockdown resulted in decreased VEGF protein levels. Furthermore, human IPAH PAECs demonstrated a significantly higher degree of capillary tube-like structures and increased length compared to control PAECs. Addition of an OGT inhibitor, OSMI-1, significantly reduced the number of tube-like structures and tube length similar to control levels. Assessment of vascular sprouting from an in vitro 3D spheroid co-culture model using IPAH and control PAEC/PASMCs and an in vivo vascularization model using control and PAEC-embedded collagen implants demonstrated higher vascularization in IPAH compared to control. Blocking OGT activity in these experiments, however, altered the vascular sprouting and de novo vascularization in IPAH similar to control levels when compared to controls. Our findings in this report are the first to describe a role for the OGT/O-GlcNAc axis in modulating VEGF expression and vascularization in IPAH. These findings provide greater insight into the potential role that altered glucose uptake and metabolism may have on the angiogenic process and the development of plexiform lesions. Therefore, we believe that the OGT/O-GlcNAc axis may be a potential therapeutic target for treating the angiogenic dysregulation that is present in IPAH.

Cor Pulmonale Revisited. From Ferrer and Harvey to the Present

The term cor pulmonale has traditionally been used as a synonym for right heart failure due to chronic respiratory diseases, although this condition is less frequently seen in the modern era because of the use of long-term oxygen therapy along with aggressive measures directed at optimizing ventilation and gas exchange. The mechanisms by which adaptation or maladaptation of right heart structure and function in the broader setting of pulmonary vascular disease, either intrinsic to the pulmonary circulation or due to respiratory diseases, have garnered considerable interest along with the development of medical and surgical treatments for pulmonary hypertension. Thus, the right heart is no longer considered an "innocent bystander" in pulmonary hypertension, but rather a key component in its pathophysiology. Furthermore, the status of right heart function is a major determinant of outcome. Accordingly, the right heart has become a potential, appealing target for novel therapies to treat hypertensive pulmonary vascular disease.

Metabolic Remodeling in the Pressure-Loaded Right Ventricle: Shifts in Glucose and Fatty Acid Metabolism-A Systematic Review and Meta-Analysis

Background

Right ventricular (RV) failure because of chronic pressure load is an important determinant of outcome in pulmonary hypertension. Progression towards RV failure is characterized by diastolic dysfunction, fibrosis and metabolic dysregulation. Metabolic modulation has been suggested as therapeutic option, yet, metabolic dysregulation may have various faces in different experimental models and disease severity. In this systematic review and meta‐analysis, we aimed to identify metabolic changes in the pressure loaded RV and formulate recommendations required to optimize translation between animal models and human disease.

Methods and Results

Medline and EMBASE were searched to identify original studies describing cardiac metabolic variables in the pressure loaded RV. We identified mostly rat‐models, inducing pressure load by hypoxia, Sugen‐hypoxia, monocrotaline (MCT), pulmonary artery banding (PAB) or strain (fawn hooded rats, FHR), and human studies. Meta‐analysis revealed increased Hedges’ g (effect size) of the gene expression of GLUT1 and HK1 and glycolytic flux. The expression of MCAD was uniformly decreased. Mitochondrial respiratory capacity and fatty acid uptake varied considerably between studies, yet there was a model effect in carbohydrate respiratory capacity in MCT‐rats.

Conclusions

This systematic review and meta‐analysis on metabolic remodeling in the pressure‐loaded RV showed a consistent increase in glucose uptake and glycolysis, strongly suggest a downregulation of beta‐oxidation, and showed divergent and model‐specific changes regarding fatty acid uptake and oxidative metabolism. To translate metabolic results from animal models to human disease, more extensive characterization, including function, and uniformity in methodology and studied variables, will be required.

High-Fat Diet from Weaning until Early Adulthood Impairs T Cell Development in the Thymus

The growing prevalence of childhood obesity has become a serious health problem over the past few decades. Although the immune system is greatly affected by childhood obesity, whether obesity influences the T cell development in the thymus is poorly understood. In this study, we used a high-fat diet (HFD)-induced obesity mice model to study the influence of HFD from weaning on the thymus. C57BL/6 mice (male, 3 weeks old) were fed a HFD or standard diet (lean controls) for 6 weeks. The bodyweight of mice fed with an HFD was 28% higher than that in the control group, while the thymus weight of HFD mice decreased by 15% compared with controls. As expected, thymic triacylglycerol content of the HFD mice increased by 37% compared to the control mice. Importantly, the frequencies of CD4⁺ and CD8⁺ single-positive (SP) thymocytes decreased by 38% and 44%, respectively. The apoptotic analysis revealed that thymic tissue of HFD mice had a higher level of Annexin-V positive thymocytes than control animals. Furthermore, the immunoblotting analysis showed that survival signal pathways in the thymus were impaired in the HFD mice, including the AKT/mTOR and ERK pathways. With the analysis of T-cell receptor excision circles (TREC), we found that HFD-induced obesity decreased recent thymic emigrants in spleen tissue. Our findings indicate that HFD from the weaning period impairs T cell development in the thymus, possibly by induction of apoptosis of thymocytes, involving disruption of survival signal pathways.

Metabolism and Redox in Pulmonary Vascular Physiology and Pathophysiology

Significance: This review considers how some systems controlling pulmonary vascular function are potentially regulated by redox processes to examine how and why conditions such as prolonged hypoxia, pathological mediators, and other factors promoting vascular remodeling contribute to the development of pulmonary hypertension (PH). Recent Advances and Critical Issues: Aspects of vascular remodeling induction mechanisms described are associated with shifts in glucose metabolism through the pentose phosphate pathway and increased cytosolic NADPH generation by glucose-6-phosphate dehydrogenase, increased glycolysis generation of cytosolic NADH and lactate, mitochondrial dysfunction associated with superoxide dismutase-2 depletion, changes in reactive oxygen species and iron metabolism, and redox signaling. Future Directions: The regulation and impact of hypoxia-inducible factor and the function of cGMP-dependent and redox regulation of protein kinase G are considered for their potential roles as key sensors and coordinators of redox and metabolic processes controlling the progression of vascular pathophysiology in PH, and how modulating aspects of metabolic and redox regulatory systems potentially function in beneficial therapeutic approaches.

PPARγ agonist pioglitazone reverses pulmonary hypertension and prevents right heart failure via fatty acid oxidation

Right ventricular (RV) heart failure is the leading cause of death in pulmonary arterial hypertension (PAH). Peroxisome proliferator-activated receptor γ (PPARγ) acts as a vasoprotective metabolic regulator in smooth muscle and endothelial cells; however, its role in the heart is unclear. We report that deletion of PPARγ in cardiomyocytes leads to biventricular systolic dysfunction and intramyocellular lipid accumulation in mice. In the SU5416/hypoxia (SuHx) rat model, oral treatment with the PPARγ agonist pioglitazone completely reverses severe PAH and vascular remodeling and prevents RV failure. Failing RV cardiomyocytes exhibited mitochondrial disarray and increased intramyocellular lipids (lipotoxicity) in the SuHx heart, which was prevented by pioglitazone. Unbiased ventricular microRNA (miRNA) arrays, mRNA sequencing, and lipid metabolism studies revealed dysregulation of cardiac hypertrophy, fibrosis, myocardial contractility, fatty acid transport/oxidation (FAO), and transforming growth factor-β signaling in the failing RV. These epigenetic, transcriptional, and metabolic alterations were modulated by pioglitazone through miRNA/mRNA networks previously not associated with PAH/RV dysfunction. Consistently, pre-miR-197 and pre-miR-146b repressed genes that drive FAO (Cpt1b and Fabp4) in primary cardiomyocytes. We recapitulated our major pathogenic findings in human end-stage PAH: (i) in the pressure-overloaded failing RV (miR-197 and miR-146b up-regulated), (ii) in peripheral pulmonary arteries (miR-146b up-regulated, miR-133b down-regulated), and (iii) in plexiform vasculopathy (miR-133b up-regulated, miR-146b down-regulated). Together, PPARγ activation can normalize epigenetic and transcriptional regulation primarily related to disturbed lipid metabolism and mitochondrial morphology/function in the failing RV and the hypertensive pulmonary vasculature, representing a therapeutic approach for PAH and other cardiovascular/pulmonary diseases.

Low-grade albuminuria in pulmonary arterial hypertension

Low-grade albuminuria, determined by the urinary albumin to creatinine ratio, has been linked to systemic vascular dysfunction and is associated with cardiovascular mortality. Pulmonary arterial hypertension is related to mutations in the bone morphogenetic protein receptor type 2, pulmonary vascular dysfunction and is increasingly recognized as a systemic disease. In a total of 283 patients (two independent cohorts) diagnosed with pulmonary arterial hypertension, 18 unaffected BMPR2 mutation carriers and 68 healthy controls, spot urinary albumin to creatinine ratio and its relationship to demographic, functional, hemodynamic and outcome data were analyzed. Pulmonary arterial hypertension patients and unaffected BMPR2 mutation carriers had significantly elevated urinary albumin to creatinine ratios compared with healthy controls ( P < 0.01; P = 0.04). In pulmonary arterial hypertension patients, the urinary albumin to creatinine ratio was associated with older age, lower six-minute walking distance, elevated levels of C-reactive protein and hemoglobin A1c, but there was no correlation between the urinary albumin to creatinine ratio and hemodynamic variables. Pulmonary arterial hypertension patients with a urinary albumin to creatinine ratio above 10 µg/mg had significantly higher rates of poor outcome ( P < 0.001). This study shows that low-grade albuminuria is prevalent in pulmonary arterial hypertension patients and is associated with poor outcome. This study shows that albuminuria in pulmonary arterial hypertension is associated with systemic inflammation and insulin resistance.

NSD2 silencing alleviates pulmonary arterial hypertension by inhibiting trehalose metabolism and autophagy

Nuclear receptor binding SET domain 2 (NSD2)-mediated metabolic reprogramming has been demonstrated to regulate oncogenesis via catalyzing the methylation of histones. The present study aimed to investigate the role of NSD2-mediated metabolic abnormality in pulmonary arterial hypertension (PAH). Monocrotaline (MCT)-induced PAH rat model was established and infected with adeno-associated virus carrying short hairpin RNA (shRNA) targeting NSD2. Hemodynamic parameters, ventricular function, and pathology were evaluated by microcatheter, echocardiography, and histological analysis. Metabolomics changes in lung tissue were analyzed by LC-MS. The results showed that silencing of NSD2 effectively ameliorated MCT-induced PAH and right ventricle dysfunction, and partially reversed pathological remodeling of pulmonary artery and right ventricular hypertrophy. In addition, the silencing of NSD2 markedly reduced the di-methylation level of H3K36 (H3K36me2 level) and inhibited autophagy in pulmonary artery. Non-targeted LC-MS based metabolomics analysis indicated that trehalose showed the most significant change in lung tissue. NSD2-regulated trehalose mainly affected ABC transporters, mineral absorption, protein digestion and absorption, metabolic pathways, and aminoacyl-tRNA biosynthesis. In conclusion, we reveal a new role of NSD2 in the pathogenesis of PAH related to the regulation of trehalose metabolism and autophagy via increasing the H3K36me2 level. NSD2 is a promising target for PAH therapy.

EXPRESS: Right Heart in Pulmonary Hypertension: From Adaptation to Failure

Right ventricular (RV) failure (RVF) has garnered significant attention in recent years because of its negative impact on clinical outcomes in patients with pulmonary hypertension (PH). PH triggers a series of events, including activation of several signaling pathways that regulate cell growth, metabolism, extracellular matrix remodeling, and energy production. These processes render the RV adaptive to PH. However, RVF develops when PH persists, accompanied by RV ischemia, alterations in substrate and mitochondrial energy metabolism, increased free oxygen radicals, increased cell loss, downregulation of adrenergic receptors, increased inflammation and fibrosis, and pathologic microRNAs. Diastolic dysfunction is also an integral part of RVF. Emerging non-invasive technologies such as molecular or metallic imaging, cardiac MRI, and ultrafast Doppler coronary flow mapping will be valuable tools to monitor RVF, especially the transition to RVF. Most PH therapies cannot treat RVF once it has occurred. A variety of therapies are available to treat acute and chronic RVF, but they are mainly supportive, and no effective therapy directly targets the failing RV. Therapies that target cell growth, cellular metabolism, oxidative stress, and myocyte regeneration are being tested preclinically. Future research should include establishing novel RVF models based on existing models, increasing use of human samples, creating human stem cell-based in vitro models, and characterizing alterations in cardiac excitation–contraction coupling during transition from adaptive RV to RVF. More successful strategies to manage RVF will likely be developed as we learn more about the transition from adaptive remodeling to maladaptive RVF in the future.

3-Bromopyruvate Attenuates Experimental Pulmonary Hypertension via Inhibition of Glycolysis

BACKGROUND

The shift of metabolism from mitochondrial oxidative phosphorylation to glycolysis and mitochondria binding partner of hexokinase are features common to cancer. These have been seen in pulmonary hypertension (PH) as well. An inhibitor of hexokinase 2 (HK 2), the small molecule 3-bromopyruvate (3-BrPA) is an incredibly powerful and swift-acting anticancer agent. However, whether it could be of potential benefit to PH has still been unknown.

METHODS

Sprague-Dawley rats with monocrotaline (MCT)-induced PH were administered 2 oral doses of 3-BrPA (15 and 30 mg/kg/day, respectively) for 14 days. Hemodynamic parameters were obtained by right heart catheterization. Histopathology, immunohistochemistry, transmission electron microscopy, flow cytometry, and assessments of relative protein expressions were conducted.

RESULTS

Compared with MCT treatment, 3-BrPA decreased mean pulmonary arterial pressure and pulmonary vascular resistance, and increased cardiac output. 3-BrPA significantly suppressed proliferation in addition to enhancing apoptosis of pulmonary artery smooth muscle cells, attenuating small pulmonary artery remodeling and right ventricular hypertrophy. Treatment with 3-BrPA markedly reduced the mitochondrial membrane potential and restored mitochondrial structure. Furthermore, 3-BrPA significantly inhibited HK 2 expression but not HK 1. The expression of both pyruvate dehydrogenase kinase and lactate dehydrogenase was decreased whereas that of pyruvate dehydrogenase and cytosolic cytochrome c was upregulated with 3-BrPA administration.

CONCLUSION

This study demonstrates the reversal of PH by 3-BrPA is related to alteration in glycolysis and improved mitochondria function, indicating the "metabolic targeting" as a rational therapeutic strategy for PH.

Echocardiographic evaluation of diastolic function in the setting of pulmonary hypertension

Heart failure due to diastolic dysfunction and pulmonary hypertension are frequent comorbid conditions with significant morbidity and mortality. Identifying the presence and etiology of diastolic dysfunction in the setting of pulmonary hypertension remains challenging despite profound therapeutic and prognostic implications. Additionally, there is little guidance in identifying and parsing etiology of diastolic dysfunction in patients found to have pulmonary hypertension. This review discusses the complex interplay between left ventricular diastolic dysfunction and pulmonary hypertension. With an explicit focus on the use of echocardiography for determination of diastolic dysfunction and etiology of pulmonary hypertension, this review also provides a comprehensive review of the literature and provides a framework by which to assess diastolic dysfunction echocardiographically in the setting of pulmonary hypertension.