Increased proliferation and resistance to apoptosis of pulmonary arterial vascular smooth muscle cells (PAVSMCs), coupled with metabolic reprogramming, are key components of pulmonary vascular remodeling, a major and currently irreversible pathophysiological feature of pulmonary arterial hypertension (PAH). We recently reported that activation of mammalian target of rapamycin (mTOR) plays a key role in increased energy generation and maintenance of the proliferative, apoptosis-resistant PAVSMC phenotype in human PAH, but the downstream effects of mTOR activation on PAH PAVSMC metabolism are not clear. Using liquid and gas chromatography-based mass spectrometry, we performed pilot metabolomic profiling of human microvascular PAVSMCs from idiopathic-PAH subjects before and after treatment with the selective adenosine triphosphate-competitive mTOR inhibitor PP242 and from nondiseased lungs. We have shown that PAH PAVSMCs have a distinct metabolomic signature of altered metabolites-components of fatty acid synthesis, deficiency of sugars, amino sugars, and nucleotide sugars-intermediates of protein and lipid glycosylation, and downregulation of key biochemicals involved in glutathione and nicotinamide adenine dinucleotide (NAD) metabolism. We also report that mTOR inhibition attenuated or reversed the majority of the PAH-specific abnormalities in lipogenesis, glycosylation, glutathione, and NAD metabolism without affecting altered polyunsaturated fatty acid metabolism. Collectively, our data demonstrate a critical role of mTOR in major PAH PAVSMC metabolic abnormalities and suggest the existence of de novo lipid synthesis in PAVSMCs in human PAH that may represent a new, important component of disease pathogenesis worthy of future investigation.

Objective

Obesity is associated with changes in both right (RV) and left (LV) ventricular morphology, but the biological basis of this finding is not well established. We examined whether adipokine levels were associated with RV morphology and function in a population-based multiethnic sample free of clinical cardiovascular disease.

Methods

We examined relationships of leptin, resistin, TNF-α, and adiponectin with RV morphology and function (from cardiac MRI) in participants (n = 1,267) free of clinical cardiovascular disease from the Multi-Ethnic Study of Atherosclerosis (MESA)-RV study. Multivariable regressions (linear, quantile [25th and 75th] and generalized additive models [GAM]) were used to examine the independent association of each adipokine with RV mass, RV end-diastolic volume (RVEDV), RV end-systolic volume (RVESV), RV stroke volume (RVSV) and RV ejection fraction (RVEF).

Results

Higher leptin levels were associated with significantly lower levels of RV mass, RVEDV, RVESV and stroke volume, but not RVEF, after adjustment for age, gender, race, height and weight. These associations were somewhat attenuated but still significant after adjustment for traditional risk factors and covariates, and were completely attenuated when correcting for the respective LV measures. There were no significant interactions of age, gender, or race/ethnicity on the relationship between the four adipokines and RV structure or function.

Conclusions

Leptin levels are associated with favorable RV morphology in a multi-ethnic population free of cardiovascular disease, however these associations may be explained by a yet to be understood bi-ventricular process as this association was no longer present after adjustment for LV values. These findings complement the associations previously shown between adipokines and LV structure and function in both healthy and diseased patients. The mechanisms linking adipokines to healthy cardiovascular function require further investigation.

Background

Enhanced proliferation, resistance to apoptosis, and metabolic shift to glycolysis of pulmonary arterial vascular smooth muscle cells (PAVSMCs) are key pathophysiological components of pulmonary vascular remodeling in idiopathic pulmonary arterial hypertension (PAH). The role of the distinct mammalian target of rapamycin (mTOR) complexes mTORC1 (mTOR-Raptor) and mTORC2 (mTOR-Rictor) in PAVSMC proliferation and survival in PAH and their therapeutic relevance are unknown.

Methods and results

Immunohistochemical and immunoblot analyses revealed that mTORC1 and mTORC2 pathways are markedly upregulated in small remodeled pulmonary arteries and isolated distal PAVSMCs from subjects with idiopathic PAH that have increased ATP levels, proliferation, and survival that depend on glycolytic metabolism. Small interfering RNA- and pharmacology-based analysis showed that although both mTORC1 and mTORC2 contribute to proliferation, only mTORC2 is required for ATP generation and survival of idiopathic PAH PAVSMCs. mTORC2 downregulated the energy sensor AMP-activated protein kinase, which led to activation of mTORC1-S6 and increased proliferation, as well as a deficiency of the proapoptotic protein Bim and idiopathic PAH PAVSMC survival. NADPH oxidase 4 (Nox4) protein levels were increased in idiopathic PAH PAVSMCs, which was necessary for mTORC2 activation, proliferation, and survival. Nox4 levels and mTORC2 signaling were significantly upregulated in small pulmonary arteries from hypoxia-exposed rats at days 2 to 28 of hypoxia. Treatment with the mTOR kinase inhibitor PP242 at days 15 to 28 suppressed mTORC2 but not Nox4, induced smooth muscle-specific apoptosis in small pulmonary arteries, and reversed hypoxia-induced pulmonary vascular remodeling in rats.

Conclusions

These data provide a novel mechanistic link of Nox4-dependent activation of mTORC2 via the energy sensor AMP-activated protein kinase to increased proliferation and survival of PAVSMCs in PAH, which suggests a new potential pathway for therapeutic interventions.

Rationale

Primary graft dysfunction (PGD) is a significant cause of early morbidity and mortality after lung transplant and is characterized by severe hypoxemia and infiltrates in the allograft. The pathogenesis of PGD involves ischemia-reperfusion injury. However, subclinical increases in pulmonary venous pressure due to left ventricular diastolic dysfunction may contribute by exacerbating capillary leak.

Objectives

To determine whether a higher ratio of early mitral inflow velocity (E) to early diastolic mitral annular velocity (é), indicative of worse left ventricular diastolic function, is associated with a higher risk of PGD.

Methods

We performed a retrospective cohort study of patients in the Lung Transplant Outcomes Group who underwent bilateral lung transplant at our institution between 2004 and 2014 for interstitial lung disease, chronic obstructive pulmonary disease, or pulmonary arterial hypertension. Transthoracic echocardiograms obtained during evaluation for transplant listing were analyzed for E/é and other measures of diastolic function. PGD was defined as PaO2/FiO2 less than or equal to 200 with allograft infiltrates at 48 or 72 hours after reperfusion. The association between E/é and PGD was assessed with multivariable logistic regression.

Measurements and main results

After adjustment for recipient age, body mass index, mean pulmonary arterial pressure, and pretransplant diagnosis, higher E/é and E/é greater than 8 were associated with an increased risk of PGD (E/é odds ratio, 1.93; 95% confidence interval, 1.02-3.64; P = 0.04; E/é >8 odds ratio, 5.29; 95% confidence interval, 1.40-20.01; P = 0.01).

Conclusions

Differences in left ventricular diastolic function may contribute to the development of PGD. Future trials are needed to determine whether optimization of left ventricular diastolic function reduces the risk of PGD.

Background

Pericardial fat has been associated with adverse cardiovascular outcomes through adiposity-associated inflammation and insulin resistance, which in turn are linked to cardiac dysfunction. We sought to evaluate the association between pericardial fat volume and cardiac structure and function in adults without baseline cardiovascular disease.

Methods

We analyzed data from the Multi-Ethnic Study of Atherosclerosis. Linear regression was used to examine the association between pericardial fat volume (by cardiac computed tomography during exam 1, 2000-2002) and cardiac function by echocardiography, six-minute walk distance (6MWD), and symptom severity as assessed using the Kansas City Cardiomyopathy Questionnaire-12 (exam 6, 2016-18).

Results

Among 3,032 participants, each 1 SD (39.3 cm³) increase in pericardial fat volume was associated with lower (worse) absolute left atrial reservoir strain (β = -0.98%; 95% CI, -1.29, -0.68; P < .001), right ventricular free wall strain (β = -0.75%; 95% CI, -1.00, -0.51; P < .001), and right atrial reservoir strain (β = -0.59%; 95% CI, -1.00, -0.19; P < .01) after adjustment for potential confounders. Greater pericardial fat volume was associated with lower 6MWDs (β = -5.70 m; 95% CI, -10.34, -1.06; P = .02) but not with Kansas City Cardiomyopathy Questionnaire-12 scores or N-terminal pro b-type natriuretic peptide after multivariable adjustment.

Conclusions

In a population-based cohort of adults, pericardial fat volume was independently associated with subclinical atrial and right ventricular dysfunction and reduced 6MWD. These distinct changes in cardiac structure and function suggest a potential mechanistic role for pericardial fat in early heart failure.

Monocyte chemotactic protein-1 (MCP-1), also known as "chemokine ligand 2" (CCL2), is a monocyte-attracting chemokine produced in lung epithelial cells. We previously reported an association of increased levels of plasma MCP-1 with primary graft dysfunction (PGD) after lung transplantation in a nested case-control study of extreme phenotypes using a multiplex platform. In this study, we sought to evaluate the role of plasma MCP-1 level as a biomarker across the full spectrum of PGD. We performed a prospective cohort study of 108 lung transplant recipients within the Lung Transplant Outcomes Group cohort. Plasma MCP-1 levels were measured pretransplantation and 6 and 24 hours after transplantation. The primary outcome was development of grade 3 PGD within 72 hours of transplant, with secondary analyses at the 72-hour time point. Multivariable logistic regression was used to evaluate confounding. Thirty subjects (28%) developed PGD. Median MCP-1 measured at 24 hours post-transplant was elevated in subjects with PGD (167.95 vs 103.5 pg/mL, P = .04). MCP-1 levels at 24 hours were associated with increased odds of grade 3 PGD after lung transplantation (odds ratio for each 100 pg/mL, 1.24; 95% confidence interval, 1.00-1.53) and with grade 3 PGD present at the 72-hour time point (odds ratio for each 100 pg/mL, 1.57; 95% confidence interval, 1.18-2.08), independent of confounding variables in multivariable analyses. MCP-1 levels measured preoperatively and 6 hours after transplant were not significantly associated with PGD. Persistent elevations in MCP-1 levels at 24 hours are a biomarker of grade 3 PGD post-transplantation. Monocyte chemotaxis may play a role in the pathogenesis of PGD.

Background

Air pollution alters small pulmonary vessels in animal models. We hypothesised that long-term ambient air pollution exposure would be associated with differences in pulmonary vascular volumes in a population-based study.

Methods

The Multi-Ethnic Study of Atherosclerosis recruited adults in six US cities. Personalised long-term exposures to ambient black carbon, nitrogen dioxide (NO₂), oxides of nitrogen (NO _x ), particulate matter with a 50% cut-off aerodynamic diameter of <2.5 μm (PM_2.5) and ozone were estimated using spatiotemporal models. In 2010-2012, total pulmonary vascular volume was measured as the volume of detectable pulmonary arteries and veins, including vessel walls and luminal blood volume, on noncontrast chest computed tomography (TPVV_CT). Peripheral TPVV_CT was limited to the peripheral 2 cm to isolate smaller vessels. Linear regression adjusted for demographics, anthropometrics, smoking, second-hand smoke, renal function and scanner manufacturer.

Results

The mean±sd age of the 3023 participants was 69.3±9.3 years; 46% were never-smokers. Mean exposures were 0.80 μg·m^-3 black carbon, 14.6 ppb NO₂ and 11.0 μg·m^-3 ambient PM_2.5. Mean±sd peripheral TPVV_CT was 79.2±18.2 cm³ and TPVV_CT was 129.3±35.1 cm³. Greater black carbon exposure was associated with a larger peripheral TPVV_CT, including after adjustment for city (mean difference 0.41 (95% CI 0.03-0.79) cm³ per interquartile range; p=0.036). Associations for peripheral TPVV_CT with NO₂ were similar but nonsignificant after city adjustment, while those for PM_2.5 were of similar magnitude but nonsignificant after full adjustment. There were no associations for NO _x or ozone, or between any pollutant and TPVV_CT.

Conclusions

Long-term black carbon exposure was associated with a larger peripheral TPVV_CT, suggesting diesel exhaust may contribute to remodelling of small pulmonary vessels in the general population.

Background

Adipokines have inflammatory and fibrotic properties that may be critical in interstitial lung disease (ILD). We examined associations of serum adipokine levels with CT imaging-based measures of subclinical ILD and lung function among community-dwelling adults.

Methods

A subset of the original Multi-Ethnic Study of Atherosclerosis cohort (n = 1,968) had adiponectin, leptin, and resistin measured during follow-up visits (2002-2005). We used regression models to examine associations of adiponectin, leptin, and resistin levels with (1) high-attenuation areas (HAAs) from CT scans (2004-2005, n = 1,144), (2) interstitial lung abnormalities (ILAs) from CT scans (2010-2012, n = 872), and (3) FVC from spirometry (2004-2006, n = 1,446). We used -(1/HAA²), which we denoted with H, to model HAA as our outcome to meet model assumptions.

Results

Higher adiponectin was associated with lower HAA on CT imaging among adults with a BMI ≥ 25 kg/m² (P for BMI interaction = .07). Leptin was more strongly associated with ILA among never smokers compared with ever smokers (P for smoking interaction = .004). For every 1-SD increment of log-transformed leptin, the percent predicted FVC was 3.8% lower (95% CI, -5.0 to -2.5). Higher serum resistin levels were associated with greater HAA on CT in a fully adjusted model. For every 1-SD increment of log-transformed resistin there was an increase in H of 14.8 (95% CI, 3.4-26.3).

Conclusions

Higher adiponectin levels were associated with lower HAA on CT imaging among adults with a higher BMI. Higher leptin and resistin levels were associated with lower FVC and greater HAA, respectively.

Background

COPD is associated with reduced physical capacity. However, it is unclear whether pulmonary emphysema, which can occur without COPD, is associated with reduced physical activity in daily life, particularly among people without COPD and never smokers. We hypothesized that greater percentage of emphysema-like lung on CT scan is associated with reduced physical activity assessed by actigraphy and self-report.

Methods

The Multi-Ethnic Study of Atherosclerosis (MESA) enrolled participants free of clinical cardiovascular disease from the general population. Percent emphysema was defined as percentage of voxels < -950 Hounsfield units on full-lung CT scans. Physical activity was measured by wrist actigraphy over 7 days and a questionnaire. Multivariable linear regression was used to adjust for age, sex, race/ethnicity, height, weight, education, smoking, pack-years, and lung function.

Results

Among 1,435 participants with actigraphy and lung measures, 47% had never smoked, and 8% had COPD. Percent emphysema was associated with lower activity levels on actigraphy (P = .001), corresponding to 1.5 hour less per week of moderately paced walking for the average participant in quintile 2 vs 4 of percent emphysema. This association was significant among participants without COPD (P = .004) and among ever (P = .01) and never smokers (P = .03). It was also independent of coronary artery calcium and left ventricular ejection fraction. There was no evidence that percent emphysema was associated with self-reported activity levels.

Conclusions

Percent emphysema was associated with decreased physical activity in daily life objectively assessed by actigraphy in the general population, among participants without COPD, and nonsmokers.

Background

Right ventricular (RV) adaptation to acute and chronic pulmonary hypertensive syndromes is a significant determinant of short- and long-term outcomes. Although remarkable progress has been made in the understanding of RV function and failure since the meeting of the NIH Working Group on Cellular and Molecular Mechanisms of Right Heart Failure in 2005, significant gaps remain at many levels in the understanding of cellular and molecular mechanisms of RV responses to pressure and volume overload, in the validation of diagnostic modalities, and in the development of evidence-based therapies.

Methods

A multidisciplinary working group of 20 international experts from the American Thoracic Society Assemblies on Pulmonary Circulation and Critical Care, as well as external content experts, reviewed the literature, identified important knowledge gaps, and provided recommendations.

Results

This document reviews the knowledge in the field of RV failure, identifies and prioritizes the most pertinent research gaps, and provides a prioritized pathway for addressing these preclinical and clinical questions. The group identified knowledge gaps and research opportunities in three major topic areas: 1) optimizing the methodology to assess RV function in acute and chronic conditions in preclinical models, human studies, and clinical trials; 2) analyzing advanced RV hemodynamic parameters at rest and in response to exercise; and 3) deciphering the underlying molecular and pathogenic mechanisms of RV function and failure in diverse pulmonary hypertension syndromes.

Conclusions

This statement provides a roadmap to further advance the state of knowledge, with the ultimate goal of developing RV-targeted therapies for patients with RV failure of any etiology.