Perivascular fluid cuffs decrease lung compliance by increasing tissue resistance

Hemopexin alleviates sterile inflammation in ischemia-reperfusion-induced lung injury

Introduction

Pulmonary ischemia-reperfusion (IR) injury (IRI) plays a significant role in various lung disorders and is a key factor in the development of primary graft dysfunction following lung transplantation. Hemopexin (Hx) is the major serum scavenger protein for heme, which is a prooxidant and pro-inflammatory compound. In the current study, we hypothesized that Hx could confer beneficial effects in sterile inflammation induced by IR-mediated lung injury.

Methods

To examine this hypothesis, we administered Hx in an experimental mouse model of unilateral lung IRI.

Results

Our results demonstrate that treatment with Hx alleviated histopathological signs of inflammation in ischemic lungs, as evidenced by a reduction in the number of infiltrating neutrophils and decreased levels of perivascular edema. In addition, thrombotic vaso-occlusion in pulmonary blood vessels of IRI lungs was reduced by Hx. Immunohistochemical analysis revealed that Hx inhibited the up-regulation of heme oxygenase-1, an enzyme highly induced by heme, in ischemic lungs. Finally, Hx administration caused a decrease in the levels of circulating B- and CD8+ T-lymphocytes in the peripheral blood of mice with pulmonary IRI.

Conclusion

These findings suggest that the serum heme scavenger protein Hx holds therapeutic promise in alleviating lung IRI-mediated sterile inflammation. Thus, Hx may represent a preemptive therapeutic approach in IR-related lung disorders such as primary graft dysfunction in lung transplantation.

Changes in the levels of free sialic acid during ex vivo lung perfusion do not correlate with pulmonary function. Experimental model

BACKGROUND

Ex vivo lung perfusion (EVLP) constitutes a tool with great research potential due to its advantages over in vivo and in vitro models. Despite its important contribution to lung reconditioning, this technique has the disadvantage of incurring high costs and can induce pulmonary endothelial injury through perfusion and ventilation. The pulmonary endothelium is made up of endothelial glycocalyx (EG), a coating of proteoglycans (PG) on the luminal surface. PGs are glycoproteins linked to terminal sialic acids (Sia) that can affect homeostasis with responses leading to edema formation. This study evaluated the effect of two ex vivo perfusion solutions on lung function and endothelial injury.

METHODS

We divided ten landrace swine into two groups and subjected them to EVLP for 120 min: Group I (n = 5) was perfused with Steen® solution, and Group II (n = 5) was perfused with low-potassium dextran-albumin solution. Ventilatory mechanics, histology, gravimetry, and sialic acid concentrations were evaluated.

RESULTS

Both groups showed changes in pulmonary vascular resistance and ventilatory mechanics (p < 0.05, Student's t-test). In addition, the lung injury severity score was better in Group I than in Group II (p < 0.05, Mann-Whitney U); and both groups exhibited a significant increase in Sia concentrations in the perfusate (p < 0.05 t-Student) and Sia immunohistochemical expression.

CONCLUSIONS

Sia, as a product of EG disruption during EVLP, was found in all samples obtained in the system; however, the changes in its concentration showed no apparent correlation with lung function.

An in silico approach to understanding the interaction between cardiovascular and pulmonary lymphatic dysfunction

The lung is extremely sensitive to interstitial fluid balance, yet the role of pulmonary lymphatics in lung fluid homeostasis and its interaction with cardiovascular pressures is poorly understood. In health, there is a fine balance between fluid extravasated from the pulmonary capillaries into the interstitium and the return of fluid to the circulation via the lymphatic vessels. This balance is maintained by an extremely interdependent system governed by pressures in the fluids (air and blood) and tissue (interstitium), lung motion during breathing, and the permeability of the tissues. Chronic elevation in left atrial pressure (LAP) due to left heart disease increases the capillary blood pressure. The consequent fluid accumulation in the delicate lung tissue increases its weight, decreases its compliance, and impairs gas exchange. This interdependent system is difficult, if not impossible, to study experimentally. Computational modeling provides a unique perspective to analyze fluid movement in the cardiopulmonary vasculature in health and disease. We have developed an initial in silico model of pulmonary lymphatic function using an anatomically structured model to represent ventilation and perfusion and underlying biophysical laws governing fluid transfer at the interstitium. This novel model was tested against increased LAP and noncardiogenic effects (increased permeability). The model returned physiologically reasonable values for all applications, predicting pulmonary edema when LAP reached 25 mmHg and with increased permeability.NEW & NOTEWORTHY This model presents a novel approach to understanding the interaction between cardiac dysfunction and pulmonary lymphatic function, using anatomically structured models and biophysical equations to estimate regional variation in fluid transport from blood to interstitial and lymphatic flux. This fluid transport model brings together advanced models of ventilation, perfusion, and lung mechanics to produce a detailed model of fluid transport in health and various altered pathological conditions.

Does Timing of Resection Influence the Presence of Inflammation within Congenital Lung Malformations?

INTRODUCTION

 Opinion remains divided on whether to resect an asymptomatic congenital lung malformation (CLM) and on optimal timing of resection. This study aimed to determine if age at resection of CLM correlates with the presence of histological inflammation and/or incidence of prior antibiotic administration for lower respiratory tract infection (LRTI).

MATERIALS AND METHODS

 A retrospective review of all CLMs resected between 2009 and 2021 was carried out. Data on antenatal detection, incidence of preoperative antibiotic use for LRTI, operative details, and histological reports were analyzed. Fisher's exact test and logistic regression were used to look for correlation between age at resection and (1) histological inflammation and/or (2) preoperative LRTI.

RESULTS

 A total of 102 patients underwent resection at age 14 months (interquartile range: 6-23). Eighty percent of children were asymptomatic in the neonatal period and 22% of these went on to develop a respiratory symptom. In total, 59% of specimens had histological evidence of inflammation, with a significantly higher rate of inflammation after 10 months of age (71 vs. 35%; p = 0.0012). Logistic regression showed there was a positive correlation between age at resection and treatment for previous LRTI (p = 0.020).

CONCLUSION

 Detection rates of inflammation in specimens resected after 10 months of age are double the rates of those resected prior to 10 months. Delaying resection of CLMs showed a higher frequency of treatment of LRTI. Earlier resection may therefore be advantageous for centers pursuing a resection strategy for asymptomatic lesions.

Sex-specific responses to slow progressive pressure overload in a large animal model of HFpEF

Approximately 50% of all heart failure (HF) diagnoses can be classified as HF with preserved ejection fraction (HFpEF). HFpEF is more prevalent in females compared with males, but the underlying mechanisms are unknown. We previously showed that pressure overload (PO) in male felines induces a cardiopulmonary phenotype with essential features of human HFpEF. The goal of this study was to determine if slow progressive PO induces distinct cardiopulmonary phenotypes in females and males in the absence of other pathological stressors. Female and male felines underwent aortic constriction (banding) or sham surgery after baseline echocardiography, pulmonary function testing, and blood sampling. These assessments were repeated at 2 and 4 mo postsurgery to document the effects of slow progressive pressure overload. At 4 mo, invasive hemodynamic studies were also performed. Left ventricle (LV) tissue was collected for histology, myofibril mechanics, extracellular matrix (ECM) mass spectrometry, and single-nucleus RNA sequencing (snRNAseq). The induced pressure overload (PO) was not different between sexes. PO also induced comparable changes in LV wall thickness and myocyte cross-sectional area in both sexes. Both sexes had preserved ejection fraction, but males had a slightly more robust phenotype in hemodynamic and pulmonary parameters. There was no difference in LV fibrosis and ECM composition between banded male and female animals. LV snRNAseq revealed changes in gene programs of individual cell types unique to males and females after PO. Based on these results, both sexes develop cardiopulmonary dysfunction but the phenotype is somewhat less advanced in females.NEW & NOTEWORTHY We performed a comprehensive assessment to evaluate the effects of slow progressive pressure overload on cardiopulmonary function in a large animal model of heart failure with preserved ejection fraction (HFpEF) in males and females. Functional and structural assessments were performed at the organ, tissue, cellular, protein, and transcriptional levels. This is the first study to compare snRNAseq and ECM mass spectrometry of HFpEF myocardium from males and females. The results broaden our understanding of the pathophysiological response of both sexes to pressure overload. Both sexes developed a robust cardiopulmonary phenotype, but the phenotype was equal or a bit less robust in females.

Engineering Functional Vasculature in Decellularized Lungs Depends on Comprehensive Endothelial Cell Tropism

Tissue engineering using decellularized whole lungs as matrix scaffolds began as a promise for creating autologous transplantable lungs for patients with end-stage lung disease and can also be used to study strategies for lung regeneration. Vascularization remains a critical component for all solid organ bioengineering, yet there has been limited success in generating functional re-endothelialization of most pulmonary vascular segments. We evaluated recellularization of the blood vessel conduits of acellular mouse scaffolds with highly proliferating, rat pulmonary microvascular endothelial progenitor cells (RMEPCs), pulmonary arterial endothelial cells (PAECs) or microvascular endothelial cells (MVECs). After 8 days of pulsatile perfusion, histological analysis showed that PAECs and MVECs possessed selective tropism for larger vessels or microvasculature, respectively. In contrast, RMEPCs lacked site preference and repopulated all vascular segments. RMEPC-derived endothelium exhibited thrombomodulin activity, expression of junctional genes, ability to synthesize endothelial signaling molecules, and formation of a restrictive barrier. The RMEPC phenotype described here could be useful for identifying endothelial progenitors suitable for efficient vascular organ and tissue engineering, regeneration and repair.

Pulmonary Manifestations of Congenital Heart Disease in Children

This review addresses how anomalous cardiovascular anatomy imparts consequences to the airway, respiratory system mechanics, pulmonary vascular system, and lymphatic system. Abnormal formation or enlargement of great vessels can compress airways and cause large and small airway obstructions. Alterations in pulmonary blood flow associated with congenital heart disease (CHD) can cause abnormalities in pulmonary mechanics and limitation of exercise. CHD can lead to pulmonary arterial hypertension. Lymphatic abnormalities associated with CHD can cause pulmonary edema, chylothorax, or plastic bronchitis. Understanding how the cardiovascular system has an impact on pulmonary growth and function can help determine options and timing of intervention.

Bioengineering the Blood-gas Barrier

The pulmonary blood-gas barrier represents a remarkable feat of engineering. It achieves the exquisite thinness needed for gas exchange by diffusion, the strength to withstand the stresses and strains of repetitive and changing ventilation, and the ability to actively maintain itself under varied demands. Understanding the design principles of this barrier is essential to understanding a variety of lung diseases, and to successfully regenerating or artificially recapitulating the barrier ex vivo. Many classical studies helped to elucidate the unique structure and morphology of the mammalian blood-gas barrier, and ongoing investigations have helped to refine these descriptions and to understand the biological aspects of blood-gas barrier function and regulation. This article reviews the key features of the blood-gas barrier that enable achievement of the necessary design criteria and describes the mechanical environment to which the barrier is exposed. It then focuses on the biological and mechanical components of the barrier that preserve integrity during homeostasis, but which may be compromised in certain pathophysiological states, leading to disease. Finally, this article summarizes recent key advances in efforts to engineer the blood-gas barrier ex vivo, using the platforms of lung-on-a-chip and tissue-engineered whole lungs. © 2020 American Physiological Society. Compr Physiol 10:415-452, 2020.

HDAC inhibition improves cardiopulmonary function in a feline model of diastolic dysfunction

Heart failure with preserved ejection fraction (HFpEF) is a major health problem without effective therapies. This study assessed the effects of histone deacetylase (HDAC) inhibition on cardiopulmonary structure, function, and metabolism in a large mammalian model of pressure overload recapitulating features of diastolic dysfunction common to human HFpEF. Male domestic short-hair felines (n = 31, aged 2 months) underwent a sham procedure (n = 10) or loose aortic banding (n = 21), resulting in slow-progressive pressure overload. Two months after banding, animals were treated daily with suberoylanilide hydroxamic acid (b + SAHA, 10 mg/kg, n = 8), a Food and Drug Administration-approved pan-HDAC inhibitor, or vehicle (b + veh, n = 8) for 2 months. Echocardiography at 4 months after banding revealed that b + SAHA animals had significantly reduced left ventricular hypertrophy (LVH) (P < 0.0001) and left atrium size (P < 0.0001) versus b + veh animals. Left ventricular (LV) end-diastolic pressure and mean pulmonary arterial pressure were significantly reduced in b + SAHA (P < 0.01) versus b + veh. SAHA increased myofibril relaxation ex vivo, which correlated with in vivo improvements of LV relaxation. Furthermore, SAHA treatment preserved lung structure, compliance, blood oxygenation, and reduced perivascular fluid cuffs around extra-alveolar vessels, suggesting attenuated alveolar capillary stress failure. Acetylation proteomics revealed that SAHA altered lysine acetylation of mitochondrial metabolic enzymes. These results suggest that acetylation defects in hypertrophic stress can be reversed by HDAC inhibitors, with implications for improving cardiac structure and function in patients.

Analysis of pulmonary vascular injury and repair during Pseudomonas aeruginosa infection-induced pneumonia and acute respiratory distress syndrome

Herein we describe lung vascular injury and repair using a rodent model of Pseudomonas aeruginosa pneumonia-induced acute respiratory distress syndrome (ARDS) during: 1) the exudative phase (48-hour survivors) and 2) the reparative/fibro-proliferative phase (1-week survivors). Pneumonia was induced by intratracheal instillation of P. aeruginosa strain PA103, and lung morphology and pulmonary vascular function were determined subsequently. Pulmonary vascular function was assessed in mechanically ventilated animals in vivo (air dead space, P_aO₂, and lung mechanics) and lung permeability was determined in isolated perfused lungs ex vivo (vascular filtration coefficient and extravascular lung water). At 48 hours post infection, histological analyses demonstrated capillary endothelial disruption, diffuse alveolar damage, perivascular cuffs, and neutrophil influx into lung parenchyma. Infected animals displayed clinical hallmarks of ARDS, including increased vascular permeability, increased dead space, impaired gas exchange, and decreased lung compliance. Overall, the animal infection model recapitulated the morphological and functional changes typically observed in lungs from patients during the exudative phase of ARDS. At 1 week post infection, there was lung histological and pulmonary vascular functional evidence of repair when compared with 48 hours post infection; however, some parameters were still impaired when compared with uninfected controls. Importantly, lungs displayed increased fibrosis and cellular hyperplasia reminiscent of lungs from patients during the fibro-proliferative phase of ARDS. Control, sham inoculated animals showed normal lung histology and function. These data represent the first comprehensive assessment of lung pathophysiology during the exudative and reparative/fibro-proliferative phases of P. aeruginosa pneumonia-induced ARDS, and position this pre-clinical model for use in interventional studies aimed at advancing clinical care.

Impact of Non-cardiac Comorbidities in Adults with Congenital Heart Disease: Management of Multisystem Complications

The prevalence and impact of non-cardiac comorbidities in adult patients with congenital heart disease increase over time, and these complications are often specifically a consequence of the long-term altered cardiovascular physiology or sequelae of previous therapies. For the ACHD patient admitted to the intensive care unit (ICU) for either surgical or medical treatment, an assessment of the burden of multisystem disease, as well as an understanding of the underlying cardiovascular pathophysiology, is essential for optimal management of these complex patients. This chapter takes an organ-system-based approach to reviewing common comorbidities in the ACHD patient, focusing on conditions that are directly related to ACHD status and may significantly impact ICU care.

The role of endothelial leak in pulmonary hypertension (2017 Grover Conference Series)

The canonical transient receptor potential 4 (TRPC4) protein contributes to the molecular make-up of endothelial store-operated calcium entry channels. Store-operated calcium entry is a prominent mode of calcium influx in endothelium. Store-operated calcium entry channels are activated by inflammatory mediators and growth factors, and in endothelium, this process induces inter-endothelial cell gaps that increase permeability. Pulmonary endothelium within extra-alveolar segments, including pulmonary arteries, is especially sensitive to the activation of store-operated calcium entry. Pulmonary arterial hypertension (PAH) is characterized by endothelial cell dysfunction in arteries. As one of the topics for the 2017 Grover Conference Series, we examined whether an endothelial cell permeability defect accompanies PAH and, if so, whether TRPC4 contributes to this defect. Through a series of studies conducted over the past five years, we find endothelial cell barrier dysfunction occurs early in the progression of experimental PAH. Endothelium within the arterial segment, and perhaps in other vascular segments, is highly susceptible to disruption secondary to both activation of store-operated calcium entry channels and high flow. This phenomenon partly depends upon TRPC4 channels. We discuss whether endothelial cell hyperpermeability is relevant to human disease, and more specifically, whether it is relevant to all groups of pulmonary hypertension.

House Dust Mite-Induced Allergic Airway Disease Is Independent of IgE and FcεRIα

IgE contributes to disease exacerbations but not to baseline airway hyperresponsiveness (AHR) in human asthma. In rodent allergic airway disease (AAD), mast cell and IgE dependence for the induction of AHR has only been observed when mice are immunized with a relatively weak allergen without adjuvant. To evaluate the role of IgE in murine AAD that is induced by a potent allergen, we inoculated BALB/c and FVB/N background wild-type and IgE- or FcεRIα-deficient mice intratracheally with large or limiting doses of house dust mite extract (HDM) and evaluated AHR, pulmonary eosinophilia, goblet cell metaplasia, serum IgE, and lung mastocytosis. We found that neither IgE nor FcεRIα contributed to AAD, even in mice inoculated with the lowest dose of HDM, which readily induced detectable disease, but did not increase serum IgE or pulmonary mast cell levels. In contrast, high doses of HDM strikingly increased serum IgE and pulmonary mast cells, although both AHR and airway mast cell degranulation were equally elevated in wild-type and IgE-deficient mice. Surprisingly, allergen challenge of mice with severe AAD and pulmonary mastocytosis failed to acutely increase airway resistance, lung Newtonian resistance, or hysteresis. Overall, this study shows that, although mice may not reliably model acute asthma exacerbations, mechanisms that are IgE and FcεRIα independent are responsible for AHR and airway inflammation when low doses of a potent allergen are inhaled repetitively.

A Feline HFpEF Model with Pulmonary Hypertension and Compromised Pulmonary Function

Heart Failure with preserved Ejection Fraction (HFpEF) represents a major public health problem. The causative mechanisms are multifactorial and there are no effective treatments for HFpEF, partially attributable to the lack of well-established HFpEF animal models. We established a feline HFpEF model induced by slow-progressive pressure overload. Male domestic short hair cats (n = 20), underwent either sham procedures (n = 8) or aortic constriction (n = 12) with a customized pre-shaped band. Pulmonary function, gas exchange, and invasive hemodynamics were measured at 4-months post-banding. In banded cats, echocardiography at 4-months revealed concentric left ventricular (LV) hypertrophy, left atrial (LA) enlargement and dysfunction, and LV diastolic dysfunction with preserved systolic function, which subsequently led to elevated LV end-diastolic pressures and pulmonary hypertension. Furthermore, LV diastolic dysfunction was associated with increased LV fibrosis, cardiomyocyte hypertrophy, elevated NT-proBNP plasma levels, fluid and protein loss in pulmonary interstitium, impaired lung expansion, and alveolar-capillary membrane thickening. We report for the first time in HFpEF perivascular fluid cuff formation around extra-alveolar vessels with decreased respiratory compliance. Ultimately, these cardiopulmonary abnormalities resulted in impaired oxygenation. Our findings support the idea that this model can be used for testing novel therapeutic strategies to treat the ever growing HFpEF population.

Permeability and calcium signaling in lung endothelium: unpack the box…

This brief review assesses the role of Ca²⁺ signaling in lung endothelium in regulation of endothelial permeability. The disconnect between experimental and clinical outcomes to date may be due, in part, to the use of tools which yield information about aggregate permeability or Ca²⁺ responses in lung or in endothelial monolayers. The teaching point of this review is to “unpack the box,” i.e. consider the many potential issues which could impact interpretation of outcomes. These include phenotypic heterogeneity and resultant segment-specific permeability responses, methodologic issues related to permeability measures, contributions from Ca²⁺ channels in cells other than endothelium—such as alveolar macrophages or blood leukocytes), Ca²⁺ dynamic patterns, rather than averaged Ca²⁺ responses to channel activation, and the background context, such as changes in endothelial bioenergetics with sepsis. Any or all of these issues might color interpretation of permeability and Ca²⁺ signaling in lung.

Re-endothelialization of rat lung scaffolds through passive, gravity-driven seeding of segment-specific pulmonary endothelial cells

Effective re-endothelialization is critical for the use of decellularized scaffolds for ex vivo lung engineering. Current approaches yield insufficiently re-endothelialized scaffolds that haemorrhage and become thrombogenic upon implantation. Herein, gravity-driven seeding coupled with bioreactor culture facilitated widespread distribution and engraftment of endothelial cells throughout rat lung scaffolds. Initially, human umbilical vein endothelial cells were seeded into the pulmonary artery by either gravity-driven, variable flow perfusion seeding or pump-driven, pulsatile flow perfusion seeding. Gravity seeding evenly distributed cells and supported cell survival and re-lining of the vascular walls while perfusion pump-driven seeding led to increased cell fragmentation and death. Using gravity seeding, rat pulmonary artery endothelial cells and rat pulmonary vein endothelial cells attached in intermediate and large vessels, while rat pulmonary microvascular endothelial cells deposited mostly in microvessels. Combination seeding of these cells led to positive vascular endothelial cadherin staining. In addition, combination seeding improved barrier function as assessed by serum albumin extravasation; however, leakage was observed in the distal portions of the re-endothelialized tissue suggesting that recellularization of the alveoli is necessary to complete barrier function of the capillary-alveolar network. Overall, these data indicate that vascular recellularization of rat lung scaffolds is achieved through gravity seeding. Copyright © 2016 John Wiley & Sons, Ltd.

Caspase-1 Activation Protects Lung Endothelial Barrier Function during Infection-Induced Stress

Dysregulated activation of the inflammasome-caspase-1-IL-1β axis elicits damaging hyperinflammation during critical illnesses, such as pneumonia and sepsis. However, in critical illness models of Salmonella infection, burn, or shock, caspase-1 inhibition worsens outcomes. These paradoxical effects suggest that caspase-1 drives novel protective responses. Whether the protective effects of caspase-1 activation involve canonical immune cell and/or nonimmune cell responses is unknown. The objective of this study was to test the hypothesis that, in addition to its recognized proinflammatory function, caspase-1 initiates protective stress responses in nonimmune cells. In vivo, lung epithelial and endothelial barrier function and inflammation were assessed in mice infected with Pseudomonas aeruginosa in the presence or absence of a caspase-1 inhibitor. Lung endothelial barrier function was assessed ex vivo in isolated, perfused rat lungs infected with P. aeruginosa in the presence or absence of a caspase-1 inhibitor. Endothelial barrier function during P. aeruginosa infection was assessed in vitro in cultured rat wild-type pulmonary microvascular endothelial cells (PMVECs) or recombinant PMVECs engineered to decrease caspase-1 expression. We demonstrated in vivo that caspase-1 inhibition in P. aeruginosa-infected mice ameliorated hyperinflammation, but, counterintuitively, increased pulmonary edema. Ex vivo, caspase-1 inhibition increased pulmonary permeability in P. aeruginosa-infected isolated rat lungs. To uncouple caspase-1 from its canonical inflammatory role, we used cultured rat PMVECs in vitro and discovered that genetic knockdown of caspase-1 accelerated P. aeruginosa-induced barrier disruption. In conclusion, caspase-1 is a sentinel stress-response regulator that initiates proinflammatory responses and also initiates novel response(s) to protect PMVEC barrier function during pneumonia.

Endothelial hyperpermeability in severe pulmonary arterial hypertension: role of store-operated calcium entry

Here, we tested the hypothesis that animals with severe pulmonary arterial hypertension (PAH) display increased sensitivity to vascular permeability induced by activation of store-operated calcium entry. To test this hypothesis, wild-type and transient receptor potential channel 4 (TRPC4) knockout Fischer 344 rats were given a single injection of Semaxanib (SU5416; 20 mg/kg) followed by 3 wk of exposure to hypoxia (10% oxygen) and a return to normoxia (21% oxygen) for an additional 2-3 wk. This Semaxanib/hypoxia/normoxia (i.e., SU5416/hypoxia/normoxia) treatment caused PAH, as evidenced by development of right ventricular hypertrophy, pulmonary artery medial hypertrophy, and occlusive lesions within precapillary arterioles. Pulmonary artery pressure was increased fivefold in Semaxanib/hypoxia/normoxia-treated animals compared with untreated, Semaxanib-treated, and hypoxia-treated controls, determined by isolated perfused lung studies. Thapsigargin induced a dose-dependent increase in permeability that was dependent on TRPC4 in the normotensive perfused lung. This increase in permeability was accentuated in PAH lungs but not in Semaxanib- or hypoxia-treated lungs. Fluid accumulated in large perivascular cuffs, and although alveolar fluid accumulation was not seen in histological sections, Evans blue dye conjugated to albumin was present in bronchoalveolar lavage fluid of hypertensive but not normotensive lungs. Thus PAH is accompanied by a TRPC4-dependent increase in the sensitivity to edemagenic agents that activate store-operated calcium entry.

The Transient Receptor Potential Vanilloid 1 Antagonist Capsazepine Improves the Impaired Lung Mechanics during Endotoxemia

Acute lung injury (ALI) caused by systemic inflammatory response remains a leading cause of morbidity and mortality in critically ill patients. Management of patients with sepsis is largely limited to supportive therapies, reflecting an incomplete understanding of the underlying pathophysiology. Furthermore, there have been limited advances in the treatments for ALI. In this study, lung function and a histological analysis were performed to evaluate the impact of transient receptor potential vanilloid-1 receptor (TRPV1) antagonist (capsazepine; CPZ) on the lipopolysaccharide (LPS)-induced lung injury in mice. For this, adult mice pre-treated with CPZ or vehicle received intraperitoneal injections of LPS or saline and 24 hr after, the mice were anaesthetized, and lung mechanics was evaluated. The LPS-challenged mice exhibited substantial mechanical impairment, characterized by increases in respiratory system resistance, respiratory system elastance, tissue damping and tissue elastance. The pre-treatment with CPZ prevented the increase in respiratory system resistance and decreased the increase in tissue damping during endotoxemia. In addition, mice pre-treated with CPZ had an attenuated lung injury evidenced by reduction on collapsed area of the lung parenchyma induced by LPS. This suggests that the TRPV1 antagonist capsazepine has a protective effect on lung mechanics in ALI during endotoxemia and that it may be a target for enhanced therapeutic efficacy in ALI.

Genome Wide Identification of SARS-CoV Susceptibility Loci Using the Collaborative Cross

New systems genetics approaches are needed to rapidly identify host genes and genetic networks that regulate complex disease outcomes. Using genetically diverse animals from incipient lines of the Collaborative Cross mouse panel, we demonstrate a greatly expanded range of phenotypes relative to classical mouse models of SARS-CoV infection including lung pathology, weight loss and viral titer. Genetic mapping revealed several loci contributing to differential disease responses, including an 8.5Mb locus associated with vascular cuffing on chromosome 3 that contained 23 genes and 13 noncoding RNAs. Integrating phenotypic and genetic data narrowed this region to a single gene, Trim55, an E3 ubiquitin ligase with a role in muscle fiber maintenance. Lung pathology and transcriptomic data from mice genetically deficient in Trim55 were used to validate its role in SARS-CoV-induced vascular cuffing and inflammation. These data establish the Collaborative Cross platform as a powerful genetic resource for uncovering genetic contributions of complex traits in microbial disease severity, inflammation and virus replication in models of outbred populations.

Targeting PI3K-p110α Suppresses Influenza Virus Infection in Chronic Obstructive Pulmonary Disease

RATIONALE

Chronic obstructive pulmonary disease (COPD) and influenza virus infections are major global health issues. Patients with COPD are more susceptible to infection, which exacerbates their condition and increases morbidity and mortality. The mechanisms of increased susceptibility remain poorly understood, and current preventions and treatments have substantial limitations.

OBJECTIVES

To characterize the mechanisms of increased susceptibility to influenza virus infection in COPD and the potential for therapeutic targeting.

METHODS

We used a combination of primary bronchial epithelial cells (pBECs) from COPD and healthy control subjects, a mouse model of cigarette smoke-induced experimental COPD, and influenza infection. The role of the phosphoinositide-3-kinase (PI3K) pathway was characterized using molecular methods, and its potential for targeting assessed using inhibitors.

MEASUREMENTS AND MAIN RESULTS

COPD pBECs were susceptible to increased viral entry and replication. Infected mice with experimental COPD also had more severe infection (increased viral titer and pulmonary inflammation, and compromised lung function). These processes were associated with impaired antiviral immunity, reduced retinoic acid-inducible gene-I, and IFN/cytokine and chemokine responses. Increased PI3K-p110α levels and activity in COPD pBECs and/or mice were responsible for increased infection and reduced antiviral responses. Global PI3K, specific therapeutic p110α inhibitors, or exogenous IFN-β restored protective antiviral responses, suppressed infection, and improved lung function.

CONCLUSIONS

The increased susceptibility of individuals with COPD to influenza likely results from impaired antiviral responses, which are mediated by increased PI3K-p110α activity. This pathway may be targeted therapeutically in COPD, or in healthy individuals, during seasonal or pandemic outbreaks to prevent and/or treat influenza.

The cardiac protein αT-catenin contributes to chemical-induced asthma

Ten to 25% of adult asthma is occupational induced, a subtype caused by exposure to workplace chemicals. A recent genomewide association study identified single-nucleotide polymorphisms in the cardiac protein αT-catenin (αT-cat) that correlated with the incidence and severity of toluene diisocyanate (TDI) occupational asthma. αT-cat is a critical mediator of cell-cell adhesion and is predominantly expressed in cardiomyocytes, but its connection to asthma remains unknown. Therefore, we sought to determine the primary αT-cat-expressing cell type in the lung and its contribution to lung physiology in a murine model of TDI asthma. We show that αT-cat is expressed in lung within the cardiac sheath of pulmonary veins. Mechanically ventilated αT-cat knockout (KO) mice exhibit a significantly increased pressure-volume curve area compared with wild-type (WT) mice, suggesting that αT-cat loss affects lung hysteresis. Using a murine model of TDI asthma, we find that αT-cat KO mice show increased airway hyperresponsiveness to methacholine compared with WT mice. Bronchoalveolar lavage reveals only a mild macrophage-dominant inflammation that is not significantly different between WT and KO mice. These data suggest that αT-cat may contribute to asthma through a mechanism independent of inflammation and related to heart and pulmonary vein dysfunction.

Intrapulmonary instillation of perflurooctylbromide improves lung growth, alveolarization, and lung mechanics in a fetal rabbit model of diaphragmatic hernia

OBJECTIVES

Fetal tracheal occlusion of hypoplastic rabbit lungs results in lung growth and alveolarization although the surfactant protein messenger RNA expression is decreased and the transforming growth factor-β pathway induced. The prenatal filling of healthy rabbit lungs with perfluorooctylbromide augments lung growth without suppression of surfactant protein synthesis. We hypothesizes that Intratracheal perfluorooctylbromide instillation improves lung growth, mechanics, and extracellular matrix synthesis in a fetal rabbit model of lung hypoplasia induced by diaphragmatic hernia.

SETTING AND INTERVENTIONS

On day 23 of gestation, DH was induced by fetal surgery in healthy rabbit fetuses. Five days later, 0.8ml of perfluorooctylbromide (diaphragmatic hernia-perfluorooctylbromide) or saline (diaphragmatic hernia-saline) was randomly administered into the lungs of previously operated fetuses. After term delivery (day 31), lung mechanics, lung to body weight ratio, messenger RNA levels of target genes, assessment of lung histology, and morphological distribution of elastin and collagen were determined. Nonoperated fetuses served as controls.

MEASUREMENTS AND MAIN RESULTS

Fetal instillation of perfluorooctylbromide in hypoplastic lungs resulted in an improvement of lung-to-body weight ratio (0.016 vs 0.013 g/g; p = 0.05), total lung capacity (23.4 vs 15.4 μL/g; p = 0.03), and compliance (2.4 vs 1.2 mL/cm H2O; p = 0.007) as compared to diaphragmatic hernia-saline. In accordance with the results from lung function analysis, elastin staining of pulmonary tissue revealed a physiological distribution of elastic fiber to the tips of the secondary crests in the diaphragmatic hernia-perfluorooctylbromide group. Likewise, messenger RNA expression was induced in genes associated with extracellular matrix remodeling (matrix metalloproteinase-2, tissue inhibitor of metalloproteinase-1, and tissue inhibitor of metalloproteinase-2). Surfactant protein expression was similar in the diaphragmatic hernia-perfluorooctylbromide and diaphragmatic hernia-saline groups. Distal airway size, mean linear intercept, as well as airspace and tissue fractions were similar in diaphragmatic hernia-perfluorooctylbromide, diaphragmatic hernia-saline, and control groups.

CONCLUSIONS

Fetal perfluorooctylbromide treatment improves lung growth, lung mechanics, and extracellular matrix remodeling in hypoplastic lungs, most probably due to transient pulmonary stretch, preserved fetal breathing movements, and its physical characteristics. Perfluorooctylbromide instillation is a promising approach for prenatal therapy of lung hypoplasia.

Mechanical ventilation causes airway distension with proinflammatory sequelae in mice

The pathogenesis of ventilator-induced lung injury has predominantly been attributed to overdistension or mechanical opening and collapse of alveoli, whereas mechanical strain on the airways is rarely taken into consideration. Here, we hypothesized that mechanical ventilation may cause significant airway distension, which may contribute to the pathological features of ventilator-induced lung injury. C57BL/6J mice were anesthetized and mechanically ventilated at tidal volumes of 6, 10, or 15 ml/kg body wt. Mice were imaged by flat-panel volume computer tomography, and central airways were segmented and rendered in 3D for quantitative assessment of airway distension. Alveolar distension was imaged by intravital microscopy. Functional dead space was analyzed in vivo, and proinflammatory cytokine release was analyzed in isolated, ventilated tracheae. CT scans revealed a reversible, up to 2.5-fold increase in upper airway volume during mechanical ventilation compared with spontaneous breathing. Airway distension was most pronounced in main bronchi, which showed the largest volumes at tidal volumes of 10 ml/kg body wt. Conversely, airway distension in segmental bronchi and functional dead space increased almost linearly, and alveolar distension increased even disproportionately with higher tidal volumes. In isolated tracheae, mechanical ventilation stimulated the release of the early-response cytokines TNF-α and IL-1β. Mechanical ventilation causes a rapid, pronounced, and reversible distension of upper airways in mice that is associated with an increase in functional dead space. Upper airway distension is most pronounced at moderate tidal volumes, whereas higher tidal volumes redistribute preferentially to the alveolar compartment. Airway distension triggers proinflammatory responses and may thus contribute relevantly to ventilator-induced pathologies.

The heterogeneity of regional specific ventilation is unchanged following heavy exercise in athletes

Heavy exercise increases ventilation-perfusion mismatch and decreases pulmonary gas exchange efficiency. Previous work using magnetic resonance imaging (MRI) arterial spin labeling in athletes has shown that, after 45 min of heavy exercise, the spatial heterogeneity of pulmonary blood flow was increased in recovery. We hypothesized that the heterogeneity of regional specific ventilation (SV, the local tidal volume over functional residual capacity ratio) would also be increased following sustained exercise, consistent with the previously documented changes in blood flow heterogeneity. Trained subjects (n = 6, maximal O2 consumption = 61 ± 7 ml·kg(-1)·min(-1)) cycled 45 min at their individually determined ventilatory threshold. Oxygen-enhanced MRI was used to quantify SV in a sagittal slice of the right lung in supine posture pre- (preexercise) and 15- and 60-min postexercise. Arterial spin labeling was used to measure pulmonary blood flow in the same slice bracketing the SV measures. Heterogeneity of SV and blood flow were quantified by relative dispersion (RD = SD/mean). The alveolar-arterial oxygen difference was increased during exercise, 23.3 ± 5.3 Torr, compared with rest, 6.3 ± 3.7 Torr, indicating a gas exchange impairment during exercise. No significant change in RD of SV was seen after exercise: preexercise 0.78 ± 0.15, 15 min postexercise 0.81 ± 0.13, 60 min postexercise 0.78 ± 0.08 (P = 0.5). The RD of blood flow increased significantly postexercise: preexercise 1.00 ± 0.12, 15 min postexercise 1.15 ± 0.10, 45 min postexercise 1.10 ± 0.10, 60 min postexercise 1.19 ± 0.11, 90 min postexercise 1.11 ± 0.12 (P < 0.005). The lack of a significant change in RD of SV postexercise, despite an increase in the RD of blood flow, suggests that airways may be less susceptible to the effects of exercise than blood vessels.

Ex vivo lung evaluation of prearrest heparinization in donation after cardiac death

OBJECTIVE

To evaluate the effects of prearrest heparin administration on lung quality in a model of donation after cardiac death (DCD), and to assess the potential application of ex vivo lung perfusion (EVLP) in the identification of better grafts from the DCD donor pool.

METHODS

Cardiac death was induced by electric shock in 10 pigs. One group received a prearrest heparin dose of 300 units/kg (H group, n = 5) and the other did not (NH group, n = 5). Animals remained at room temperature for 1 hour without ventilation, defining the warm ischemic time. After harvest, the lungs underwent 6 hours of cold ischemia before being evaluated with EVLP for 4 hours.

RESULTS

Static compliance 28 ± 3 versus 29 ± 2 (Cstat-cm H2O), pulmonary vascular resistance (PVR) 593 ± 127 versus 495 ± 70 (PVR-dyn·s/cm), and oxygenation 327 ± 32 versus 330 ± 28 (ΔPO2-mm Hg) remained stable from the beginning until the end of EVLP in the H group. In the NH group, Cstat started to decline after the first hour (25 ± 2 vs 21 ± 2), ΔPO2 after hour 2 (265 ± 44 vs 207 ± 44), and PVR started to increase after hour 3 (765 ± 132 vs 916 ± 168). Significant differences between the groups were observed at the end of EVLP (P < 0.001). Parameters of lung quality after EVLP also showed significant differences between the groups: wet weight-to-dry weight ratio (P < 0.001), protein in the bronchial lavage (P < 0.01), Na + K-ATPase activity (P < 0.001), and E-selectin (P < 0.001) in the perfusate.

CONCLUSIONS

Prearrest heparin administration improved organ function by preserving endothelial homeostasis. EVLP proved to be a useful platform for assessing DCD lungs, providing reliable means of discriminating injured grafts.

Pseudomonas aeruginosa exotoxin Y is a promiscuous cyclase that increases endothelial tau phosphorylation and permeability

Exotoxin Y (ExoY) is a type III secretion system effector found in ~ 90% of the Pseudomonas aeruginosa isolates. Although it is known that ExoY causes inter-endothelial gaps and vascular leak, the mechanisms by which this occurs are poorly understood. Using both a bacteria-delivered and a codon-optimized conditionally expressed ExoY, we report that this toxin is a dual soluble adenylyl and guanylyl cyclase that results in intracellular cAMP and cGMP accumulation. The enzymatic activity of ExoY caused phosphorylation of endothelial Tau serine 214, accumulation of insoluble Tau, inter-endothelial cell gap formation, and increased macromolecular permeability. To discern whether the cAMP or cGMP signal was responsible for Tau phosphorylation and barrier disruption, pulmonary microvascular endothelial cells were engineered for the conditional expression of either wild-type guanylyl cyclase, which synthesizes cGMP, or a mutated guanylyl cyclase, which synthesizes cAMP. Sodium nitroprusside stimulation of the cGMP-generating cyclase resulted in transient Tau serine 214 phosphorylation and gap formation, whereas stimulation of the cAMP-generating cyclase induced a robust increase in Tau serine 214 phosphorylation, gap formation, and macromolecular permeability. These results indicate that the cAMP signal is the dominant stimulus for Tau phosphorylation. Hence, ExoY is a promiscuous cyclase and edema factor that uses cAMP and, to some extent, cGMP to induce the hyperphosphorylation and insolubility of endothelial Tau. Because hyperphosphorylated and insoluble Tau are hallmarks in neurodegenerative tauopathies such as Alzheimer disease, acute Pseudomonas infections cause a pathophysiological sequela in endothelium previously recognized only in chronic neurodegenerative diseases.

Pulmonary complications of congenital heart disease

Cardiac and pulmonary pathophysiologies are closely interdependent, which makes the management of patients with congenital heart disease (CHD) all the more complex. Pulmonary complications of CHD can be structural due to compression causing airway malacia or atelectasis of the lung. Surgical repair of CHD can also result in structural trauma to the respiratory system, e.g., chylothorax, subglottic stenosis, or diaphragmatic paralysis. Disruption of the Starling forces in the pulmonary vascular system in certain types of CHD lead to alveolar-capillary membrane damage and pulmonary oedema. This in turn results in poorly compliant lungs with a restrictive lung function pattern that can deteriorate to cause hypoxemia. The circulation post single ventricle palliative surgery (the so called "Fontan circulation") poses a unique spectrum of pulmonary pathophysiology with restrictive lung function and a low pulmonary blood flow state that predisposes to thromboembolic complications and plastic bronchitis. As the population of patients surviving post CHD repair increases, the incidence of pulmonary complications has also increased and presents a unique cohort in both the paediatric and adult clinics.

Studies on the cell biology of interendothelial cell gaps

Pain, redness, heat, and swelling are hallmarks of inflammation that were recognized as early as the first century AD. Despite these early observations, the mechanisms responsible for swelling, in particular, remained an enigma for nearly two millennia. Only in the past century have scientists and physicians gained an appreciation for the role that vascular endothelium plays in controlling the exudation that is responsible for swelling. One of these mechanisms is the formation of transient gaps between adjacent endothelial cell borders. Inflammatory mediators act on endothelium to reorganize the cytoskeleton, decrease the strength of proteins that connect cells together, and induce transient gaps between endothelial cells. These gaps form a paracellular route responsible for exudation. The discovery that interendothelial cell gaps are causally linked to exudation began in the 1960s and was accompanied by significant controversy. Today, the role of gap formation in tissue edema is accepted by many, and significant scientific effort is dedicated toward developing therapeutic strategies that will prevent or reverse the endothelial cell gaps that are present during the course of inflammatory illness. Given the importance of this field in endothelial cell biology and inflammatory disease, this focused review catalogs key historical advances that contributed to our modern-day understanding of the cell biology of interendothelial gap formation.

Cardiogenic oscillations in spontaneous breathing airway signal reflect respiratory system mechanics

BACKGROUND

Heartbeat-related pressure oscillations appear at the airway opening. We investigated whether these cardiogenic oscillations (COS) - extracted from spontaneous breathing signals - reflect the compliance of the respiratory system.

METHODS

Fifteen volunteers breathed spontaneously at normal or reduced chest wall compliance, i.e. with and without thorax strapping, and at normal or reduced lung compliance, induced by positive end-expiratory pressure (PEEP). COS-related signals were extracted by averaging the flow and pressure curve sections, temporally aligned to the electrocardiogram signal.

RESULTS

COS-related airway pressure and flow curves correlated closely for each subject (r(2) =0.97 ± 0.02, P<0.0001). At the unstrapped thorax, the oscillation's amplitudes were 0.07 ± 0.03 cm H(2) O (pressure) and 22 ± 10 ml/s (flow). COS-related pressure amplitudes correlated closely with the ratio of tidal volume divided by pressure amplitude (r(2) =0.88, P<0.001) and furthermore increased with either thorax strapping (P<0.001) or with increasing PEEP (P=0.049).

CONCLUSION

We conclude that COS extracted from the pressure and flow signal reflect the compliance of the respiratory system and could potentially allow estimating respiratory system mechanics during spontaneous breathing.