Nocturnal Hypoxemia Is Associated with Sarcopenia in COPD Patients.

OBJECTIVE: Chronic obstructive pulmonary disease (COPD) is the third leading cause of death worldwide. Our previous studies have identified that nocturnal hypoxemia causes skeletal muscle loss (i.e. sarcopenia) in in vitro models of COPD. RATIONALE: We aimed to extend our preclinical mechanistic findings by analyzing a large sleep registry to determine whether nocturnal hypoxemia is associated with sarcopenia in COPD patients. METHODS: Sleep studies from COPD patients (n=479) and control subjects without COPD (n=275) were analyzed. Patients with obstructive sleep apnea (OSA), as defined by apnea hypopnea index >5, were excluded. Pectoralis muscle cross sectional area (PMcsa) was quantified using CT scans performed within one year of the sleep study. We defined sarcopenia as less than the lowest 20% residuals for PMcsa of controls, which was adjusted for age, BMI, and stratified by sex. Youden's optimal cutpoint criteria was used to predict sarcopenia based on mean oxygen saturation (mean SaO2) during sleep. Additional measures of nocturnal hypoxemia were analyzed. Pectoralis muscle index (PMI) was defined as PMcsa normalized to BMI. RESULTS: On average, COPD males had 16.6% lower PMI than control males (1.41+0.44 vs 1.69+0.56 cm2/BMI, p<0.001), while COPD females had 9.4% lower PMI than control females (0.96+0.27 vs 1.06+0.33 cm2/BMI, p<0.001). COPD males with nocturnal hypoxemia had a 9.5% decrease in PMI versus COPD with normal O2 (1.33+0.39 vs 1.47+0.46 cm2/BMI, p<0.05), and 23.6% decrease compared to controls (1.33+0.39 vs 1.74+0.56 cm2/BMI, p<0.001). COPD females with nocturnal hypoxemia had a 11.2% decrease versus COPD with normal O2 (0.87+0.26 vs 0.98+0.28 cm2/BMI, p<0.05), and 17.9% decrease compared to controls (0.87+0.26 vs 1.06+0.33 cm2/BMI, p<0.001). These findings were largely replicated using multiple measures of nocturnal hypoxemia. CONCLUSIONS: We defined sarcopenia in the pectoralis muscle using residuals that take into account age, BMI, and sex. We found that COPD patients have lower PMI than non-COPD patients, and that nocturnal hypoxemia was associated with an additional decrease in the PMI of COPD patients. Additional prospective analyses are needed to determine a protective threshold of oxygen saturation to prevent or reverse sarcopenia due to nocturnal hypoxemia in COPD.

TRPV4 Regulates the Macrophage Metabolic Response to Limit Sepsis-induced Lung Injury.

Sepsis is a systemic inflammatory response that requires effective macrophage metabolic functions to resolve ongoing inflammation. Previous work showed that the mechanosensitive cation channel, transient receptor potential vanilloid 4 (TRPV4), mediates macrophage phagocytosis and cytokine production in response to lung infection. Here, we show that TRPV4 regulates glycolysis in a stiffness-dependent manner by augmenting macrophage glucose uptake by GLUT1. In addition, TRPV4 is required for LPS-induced phagolysosome maturation in a GLUT1-dependent manner. In a cecal slurry mouse model of sepsis, TRPV4 regulates sepsis-induced glycolysis as measured by BAL fluid (BALF) lactate and sepsis-induced lung injury as measured by BALF total protein and lung compliance. TRPV4 is necessary for bacterial clearance in the peritoneum to limit sepsis-induced lung injury. It is interesting that BALF lactate is increased in patients with sepsis compared with healthy control participants, supporting the relevance of lung cell glycolysis to human sepsis. These data show that macrophage TRPV4 is required for glucose uptake through GLUT1 for effective phagolysosome maturation to limit sepsis-induced lung injury. Our work presents TRPV4 as a potential target to protect the lung from injury in sepsis.

A novel mechanoeffector role of fibroblast S100A4 in myofibroblast transdifferentiation and fibrosis.

Fibroblast to myofibroblast transdifferentiation mediates numerous fibrotic disorders, such as idiopathic pulmonary fibrosis (IPF). We have previously demonstrated that non-muscle myosin II (NMII) is activated in response to fibrotic lung extracellular matrix, thereby mediating myofibroblast transdifferentiation. NMII-A is known to interact with the calcium-binding protein S100A4, but the mechanism by which S100A4 regulates fibrotic disorders is unclear. In this study, we show that fibroblast S100A4 is a calcium-dependent, mechanoeffector protein that is uniquely sensitive to pathophysiologic-range lung stiffness (8-25 kPa) and thereby mediates myofibroblast transdifferentiation. Re-expression of endogenous fibroblast S100A4 rescues the myofibroblastic phenotype in S100A4 KO fibroblasts. Analysis of NMII-A/actin dynamics reveals that S100A4 mediates the unraveling and redistribution of peripheral actomyosin to a central location, resulting in a contractile myofibroblast. Furthermore, S100A4 loss protects against murine in vivo pulmonary fibrosis, and S100A4 expression is dysregulated in IPF. Our data reveal a novel mechanosensor/effector role for endogenous fibroblast S100A4 in inducing cytoskeletal redistribution in fibrotic disorders such as IPF.

Clinical Characteristics and Transplant-Free Survival Across the Spectrum of Pulmonary Vascular Disease.

BACKGROUND: PVDOMICS (Pulmonary Vascular Disease Phenomics) is a precision medicine initiative to characterize pulmonary vascular disease (PVD) using deep phenotyping. PVDOMICS tests the hypothesis that integration of clinical metrics with omic measures will enhance understanding of PVD and facilitate an updated PVD classification. OBJECTIVES: The purpose of this study was to describe clinical characteristics and transplant-free survival in the PVDOMICS cohort. METHODS: Subjects with World Symposium Pulmonary Hypertension (WSPH) group 1-5 PH, disease comparators with similar underlying diseases and mild or no PH and healthy control subjects enrolled in a cross-sectional study. PH groups, comparators were compared using standard statistical tests including log-rank tests for comparing time to transplant or death. RESULTS: A total of 1,193 subjects were included. Multiple WSPH groups were identified in 38.9% of PH subjects. Nocturnal desaturation was more frequently observed in groups 1, 3, and 4 PH vs comparators. A total of 50.2% of group 1 PH subjects had ground glass opacities on chest computed tomography. Diffusing capacity for carbon monoxide was significantly lower in groups 1-3 PH than their respective comparators. Right atrial volume index was higher in WSPH groups 1-4 than comparators. A total of 110 participants had a mean pulmonary artery pressure of 21-24 mm Hg. Transplant-free survival was poorest in group 3 PH. CONCLUSIONS: PVDOMICS enrolled subjects across the spectrum of PVD, including mild and mixed etiology PH. Novel findings include low diffusing capacity for carbon monoxide and enlarged right atrial volume index as shared features of groups 1-3 and 1-4 PH, respectively; unexpected, frequent presence of ground glass opacities on computed tomography; and sleep alterations in group 1 PH, and poorest survival in group 3 PH. PVDOMICS will facilitate a new understanding of PVD and refine the current PVD classification. (Pulmonary Vascular Disease Phenomics Program PVDOMICS [PVDOMICS]; NCT02980887).

Stretching the Function of Innate Immune Cells.

The importance of innate immune cells to sense and respond to their physical environment is becoming increasingly recognized. Innate immune cells (e.g. macrophages and neutrophils) are able to receive mechanical signals through several mechanisms. In this review, we discuss the role of mechanosensitive ion channels, such as Piezo1 and transient receptor potential vanilloid 4 (TRPV4), and cell adhesion molecules, such as integrins, selectins, and cadherins in biology and human disease. Furthermore, we explain that these mechanical stimuli activate intracellular signaling pathways, such as MAPK (p38, JNK), YAP/TAZ, EDN1, NF-kB, and HIF-1α, to induce protein conformation changes and modulate gene expression to drive cellular function. Understanding the mechanisms by which immune cells interpret mechanosensitive information presents potential targets to treat human disease. Important areas of future study in this area include autoimmune, allergic, infectious, and malignant conditions.

RSV infection potentiates TRPV1-mediated calcium transport in bronchial epithelium of asthmatic children.

The transient receptor potential vanilloid 1 (TRPV1) channel is expressed in human bronchial epithelium (HBE), where it transduces Ca2+ in response to airborne irritants. TRPV1 activation results in bronchoconstriction, cough, and mucus production, and may therefore contribute to the pathophysiology of obstructive airway disease. Since children with asthma face the greatest risk of developing virus-induced airway obstruction, we hypothesized that changes in TRPV1 expression, localization, and function in the airway epithelium may play a role in bronchiolitis and asthma in childhood. We sought to measure TRPV1 protein expression, localization, and function in HBE cells from children with versus without asthma, both at baseline and after RSV infection. We determined changes in TRPV1 protein expression, subcellular localization, and function both at baseline and after RSV infection in primary HBE cells from normal children and children with asthma. Basal TRPV1 protein expression was higher in HBE from children with versus without asthma and primarily localized to plasma membranes (PMs). During RSV infection, TRPV1 protein increased more in the PM of asthmatic HBE as compared with nonasthmatic cells. TRPV1-mediated increase in intracellular Ca2+ was greater in RSV-infected asthmatic cells, but this increase was attenuated when extracellular Ca2+ was removed. Nerve growth factor (NGF) recapitulated the effect of RSV on TRPV1 activation in HBE cells. Our data suggest that children with asthma have intrinsically hyperreactive airways due in part to higher TRPV1-mediated Ca2+ influx across epithelial membranes, and this abnormality is further exacerbated by NGF overexpression during RSV infection driving additional Ca2+ from intracellular stores.

The Role of TRPV4 in Regulating Innate Immune Cell Function in Lung Inflammation.

Ion channels/pumps are essential regulators of innate immune cell function. Macrophages have been increasingly recognized to have phenotypic plasticity and location-specific functions in the lung. Transient receptor potential vanilloid 4 (TRPV4) function in lung injury has been shown to be stimulus- and cell-type specific. In the current review, we discuss the importance of TRPV4 in macrophages and its role in phagocytosis and cytokine secretion in acute lung injury/acute respiratory distress syndrome (ARDS). Furthermore, TRPV4 controls a MAPK molecular switch from predominately c-Jun N-terminal kinase, JNK activation, to that of p38 activation, that mediates phagocytosis and cytokine secretion in a matrix stiffness-dependent manner. Expanding knowledge regarding the downstream mechanisms by which TRPV4 acts to tailor macrophage function in pulmonary inflammatory diseases will allow for formulation of novel therapeutics.

Circulating matrix metalloproteinases and tissue metalloproteinase inhibitors in patients with idiopathic pulmonary fibrosis in the multicenter IPF-PRO Registry cohort.

BACKGROUND: Matrix metalloproteinases (MMPs) and tissue inhibitors of MMPs (TIMPs) play important roles in the turnover of extracellular matrix and in the pathogenesis of idiopathic pulmonary fibrosis (IPF). This study aimed to determine the utility of circulating MMPs and TIMPs in distinguishing patients with IPF from controls and to explore associations between MMPs/TIMPs and measures of disease severity in patients with IPF. METHODS: The IPF cohort (n = 300) came from the IPF-PRO Registry, an observational multicenter registry of patients with IPF that was diagnosed or confirmed at the enrolling center in the past 6 months. Controls (n = 100) without known lung disease came from a population-based registry. Generalized linear models were used to compare circulating concentrations of MMPs 1, 2, 3, 7, 8, 9, 12, and 13 and TIMPs 1, 2, and 4 between patients with IPF and controls, and to investigate associations between circulating levels of these proteins and measures of IPF severity. Multivariable models were fit to identify the MMP/TIMPs that best distinguished patients with IPF from controls. RESULTS: All the MMP/TIMPs analyzed were present at significantly higher levels in patients with IPF compared with controls except for TIMP2. Multivariable analyses selected MMP8, MMP9 and TIMP1 as top candidates for distinguishing patients with IPF from controls. Higher concentrations of MMP7, MMP12, MMP13 and TIMP4 were significantly associated with lower diffusion capacity of the lung for carbon monoxide (DLCO) % predicted and higher composite physiologic index (worse disease). MMP9 was associated with the composite physiologic index. No MMP/TIMPs were associated with forced vital capacity % predicted. CONCLUSIONS: Circulating MMPs and TIMPs were broadly elevated among patients with IPF. Select MMP/TIMPs strongly associated with measures of disease severity. Our results identify potential MMP/TIMP targets for further development as disease-related biomarkers.

TRPV4 Protects the Lung from Bacterial Pneumonia via MAPK Molecular Pathway Switching.

Mechanical cell-matrix interactions can drive the innate immune responses to infection; however, the molecular underpinnings of these responses remain elusive. This study was undertaken to understand the molecular mechanism by which the mechanosensitive cation channel, transient receptor potential vanilloid 4 (TRPV4), alters the in vivo response to lung infection. For the first time, to our knowledge, we show that TRPV4 protects the lung from injury upon intratracheal Pseudomonas aeruginosa in mice. TRPV4 functions to enhance macrophage bacterial clearance and downregulate proinflammatory cytokine secretion. TRPV4 mediates these effects through a novel mechanism of molecular switching of LPS signaling from predominant activation of the MAPK, JNK, to that of p38. This is accomplished through the activation of the master regulator of inflammation, dual-specificity phosphatase 1. Further, TRPV4's modulation of the LPS signal is mechanosensitive in that both upstream activation of p38 and its downstream biological consequences depend on pathophysiological range extracellular matrix stiffness. We further show the importance of TRPV4 on LPS-induced activation of macrophages from healthy human controls. These data are the first, to our knowledge, to demonstrate new roles for macrophage TRPV4 in regulating innate immunity in a mechanosensitive manner through the modulation of dual-specificity phosphatase 1 expression to mediate MAPK activation switching.

Vasopressin Plasma Concentrations Are Not Associated with Hemodynamic Response to Exogenous Vasopressin for Septic Shock.

INTRODUCTION: Positive hemodynamic response to vasopressin after 6 hours of infusion was independently associated with lower mortality in a previous retrospective study of patients with septic shock. However, factors previously associated with higher plasma vasopressin concentration were not associated with response, and the relationship between plasma vasopressin concentration and hemodynamic response has not been evaluated. OBJECTIVES: This cross-sectional study compared plasma vasopressin concentrations in hemodynamic responders and nonresponders to vasopressin in patients with septic shock to evaluate plasma vasopressin concentration as a therapeutic target for hemodynamic response to vasopressin. METHODS: Adult patients with septic shock were included if they were treated with fixed-dose vasopressin as an adjunct to catecholamines for at least 3 hours. Patients were assigned to groups based on vasopressin response. RESULTS: Ten hemodynamic responders to vasopressin and eight nonresponders were included. Blood samples for plasma vasopressin concentration were collected 3-6 hours after vasopressin initiation. Baseline characteristics were similar between groups. No difference was detected in plasma vasopressin concentrations between hemodynamic responders and nonresponders (median 88.6 pg/ml [interquartile range (IQR) 84.4-107.5 pg/ml] vs 89.9 pg/ml [IQR 67.5-157.4 pg/ml], p=0.79, respectively). We also did not detect a difference between groups after correcting for vasopressin dose; median vasopressin plasma concentration per 0.01 units/minute of vasopressin infusion for responders was 25.9 pg/ml (IQR 21.8-31.8 pg/ml) versus 29.5 pg/ml (IQR 23.0-57.5 pg/ml, p=0.48) for nonresponders. No difference in clinical outcomes was detected between groups. The findings were robust to multiple sensitivity analyses. CONCLUSIONS: This study does not support the use of plasma vasopressin concentrations as a therapeutic target to predict hemodynamic response to exogenous vasopressin in septic shock.

Translocation of TRPV4-PI3Kγ complexes to the plasma membrane drives myofibroblast transdifferentiation.

Myofibroblasts are key contributors to pathological fibrotic conditions of several major organs. The transdifferentiation of fibroblasts into myofibroblasts requires both a mechanical signal and transforming growth factor-ß (TGF-ß) signaling. The cation channel transient receptor potential vanilloid 4 (TRPV4) is a critical mediator of myofibroblast transdifferentiation and in vivo fibrosis through its mechanosensitivity to extracellular matrix stiffness. Here, we showed that TRPV4 promoted the transdifferentiation of human and mouse lung fibroblasts through its interaction with phosphoinositide 3-kinase γ (PI3Kγ), forming nanomolar-affinity, intracellular TRPV4-PI3Kγ complexes. TGF-ß induced the recruitment of TRPV4-PI3Kγ complexes to the plasma membrane and increased the activities of both TRPV4 and PI3Kγ. Using gain- and loss-of-function approaches, we showed that both TRPV4 and PI3Kγ were required for myofibroblast transdifferentiation as assessed by the increased production of α-smooth muscle actin and its incorporation into stress fibers, cytoskeletal changes, collagen-1 production, and contractile force. Expression of various mutant forms of the PI3Kγ catalytic subunit (p110γ) in cells lacking PI3Kγ revealed that only the noncatalytic, amino-terminal domain of p110γ was necessary and sufficient for TGF-ß-induced TRPV4 plasma membrane recruitment and myofibroblast transdifferentiation. These data suggest that TGF-ß stimulates a noncanonical scaffolding action of PI3Kγ, which recruits TRPV4-PI3Kγ complexes to the plasma membrane, thereby increasing myofibroblast transdifferentiation. Given that both TRPV4 and PI3Kγ have pleiotropic actions, targeting the interaction between them could provide a specific therapeutic approach for inhibiting myofibroblast transdifferentiation.

Choice of antifibrotic medication and disease severity predict weight loss in idiopathic pulmonary fibrosis.

PURPOSE: Although safety and tolerability of approved antifibrotics has been reported extensively, little is known about their effects on weight. We analyzed predictors of weight change after one year of uninterrupted antifibrotic therapy in patients followed at our institution's interstitial lung disease clinic. METHODS/RESULTS: We identified 80 patients on antifibrotic therapy (44 pirfenidone/36 nintedanib) with at least one year of follow-up and no therapy interruptions. Thirty-five patients (44%) lost more than 5% of their baseline body weight, and 11 (19%) lost more than 10%. A higher proportion of patients on nintedanib experienced a clinically significant weight loss (>5%) versus pirfenidone (61% vs 30%, p = 0.005). Univariate and multivariate analyses identified nintedanib therapy and a higher composite physiologic index (CPI) as predictors of weight loss. CONCLUSIONS: Weight loss is common among IPF patients on antifibrotic therapy. Nintedanib therapy and more advanced disease were identified as predictors of weight loss in this population.

Venous Thromboembolism After Adult Lung Transplantation: A Frequent Event Associated With Lower Survival.

BACKGROUND: The incidence of venous thromboembolism (VTE) after lung transplantation (LTX) varies significantly across studies. Two studies have suggested that these thrombotic events are associated with a lower posttransplant survival. Herein, we sought to determine the incidence, predictors, and impact of VTE on survival after LTX at a quaternary referral center. METHODS: This was a large cohort study of LTX recipients. Key outcome parameters were time to VTE after transplant and survival. Deep vein thrombosis (DVT) diagnosis required a positive ultrasound. Pulmonary embolism diagnosis required either a positive chest computed tomography angiogram or a high-probability ventilation/perfusion scan. RESULTS: The overall incidence of VTE among 701 LTX recipients was 43.8%, of which 97.7% were DVT episodes, of which 71.3% were in the upper extremities. Predictors of VTE were prior history of DVT (hazard ratio [HR], 2.82; 95% confidence interval [CI], 1.49-5.37), days in intensive care (HR, 1.01; 95% CI, 1.01-1.02), and the use of extracorporeal membrane oxygenation (HR, 2.22; 95% CI, 1.43-3.45). Importantly, VTE predicted a lower posttransplant survival (HR, 1.70; 95% CI, 1.28-2.26), when occurring within or after the first 30 days. The location of the DVT, either upper extremity or below the knee, also predicted a poor survival. CONCLUSIONS: VTE was frequent in LTX recipients and predicted a poor survival even when located in the upper extremities or below the knee. These data suggest that aggressive VTE screening/treatment protocols be implemented in post-LTX population.

An Official American Thoracic Society Workshop Report: Use of Animal Models for the Preclinical Assessment of Potential Therapies for Pulmonary Fibrosis.

Numerous compounds have shown efficacy in limiting development of pulmonary fibrosis using animal models, yet few of these compounds have replicated these beneficial effects in clinical trials. Given the challenges associated with performing clinical trials in patients with idiopathic pulmonary fibrosis (IPF), it is imperative that preclinical data packages be robust in their analyses and interpretations to have the best chance of selecting promising drug candidates to advance to clinical trials. The American Thoracic Society has convened a group of experts in lung fibrosis to discuss and formalize recommendations for preclinical assessment of antifibrotic compounds. The panel considered three major themes (choice of animal, practical considerations of fibrosis modeling, and fibrotic endpoints for evaluation). Recognizing the need for practical considerations, we have taken a pragmatic approach. The consensus view is that use of the murine intratracheal bleomycin model in animals of both genders, using hydroxyproline measurements for collagen accumulation along with histologic assessments, is the best-characterized animal model available for preclinical testing. Testing of antifibrotic compounds in this model is recommended to occur after the acute inflammatory phase has subsided (generally after Day 7). Robust analyses may also include confirmatory studies in human IPF specimens and validation of results in a second system using in vivo or in vitro approaches. The panel also strongly encourages the publication of negative results to inform the lung fibrosis community. These recommendations are for preclinical therapeutic evaluation only and are not intended to dissuade development of emerging technologies to better understand IPF pathogenesis.

The Role of Transient Receptor Potential Vanilloid 4 in Pulmonary Inflammatory Diseases.

Ion channels/pumps are essential regulators of organ homeostasis and disease. In the present review, we discuss the role of the mechanosensitive cation channel, transient receptor potential vanilloid 4 (TRPV4), in cytokine secretion and pulmonary inflammatory diseases such as asthma, cystic fibrosis (CF), and acute lung injury/acute respiratory distress syndrome (ARDS). TRPV4 has been shown to play a role in lung diseases associated with lung parenchymal stretch or stiffness. TRPV4 indirectly mediates hypotonicity-induced smooth muscle contraction and airway remodeling in asthma. Further, the literature suggests that in CF TRPV4 may improve ciliary beat frequency enhancing mucociliary clearance, while at the same time increasing pro-inflammatory cytokine secretion/lung tissue injury. Currently it is understood that the role of TRPV4 in immune cell function and associated lung tissue injury/ARDS may depend on the injury stimulus. Uncovering the downstream mechanisms of TRPV4 action in pulmonary inflammatory diseases is likely important to understanding disease pathogenesis and may lead to novel therapeutics.