American journal of physiology. Lung cellular and molecular physiology最新文献

Acute lung injury (ALI) causes the highly lethal acute respiratory distress syndrome (ARDS) in children and adults, for which therapy is lacking. Children with pediatric ARDS have a mortality rate that is about half of adults with ARDS. Improved ALI measures can be reproduced in rodent models with juvenile animals, suggesting that physiologic differences may underlie these outcomes. Here, we show that pneumonia-induced ALI caused inflammatory signaling in the endothelium of adult mice, which depended on Yes-associated protein (YAP). This signaling was not present in 21-day-old weanling mice. Transcriptomic analysis of lung endothelial responses revealed nuclear factor-kappa B (NF-κB) as significantly increased with ALI in adult versus weanling mice. Blockade of YAP signaling protected against inflammatory response, hypoxemia, and NF-κB nuclear translocation in response to Pseudomonas aeruginosa pneumonia in adult mice. Our results demonstrate an important signaling cascade in the lung endothelium of adult mice that is not present in weanlings. We suggest other pathways may also exhibit age-dependent signaling, which would have important implications for ARDS therapeutics in the adult and pediatric age groups.NEW & NOTEWORTHY Like human patients, adult mice get worse lung injury than juveniles. In pneumonia-induced lung injury, Yes-associated protein is more highly expressed in the endothelium of adult mice than juveniles, causing more NF-κB nuclear translocation and inflammation. This could partly explain better outcomes in kids with pediatric acute respiratory distress syndrome as compared with adults with ARDS.

Prolonged absence of deep inspiration (DI) increases airway resistance. The underlying mechanism is not entirely clear. We hypothesize that DI prohibition allows basal airway smooth muscle (ASM) tone to narrow and close airways over time, resulting in elevation of airway and lung resistance, as well as air trapping. We further hypothesize that DI or pharmacological bronchodilators can prevent or alleviate the resistance increase and air trapping. Physiological respiration was simulated in ex vivo sheep lungs. Lung resistance, elastance, and volume were measured using small tidal volume (120 mL), ventilation frequencies of 0.25 and 2 Hz, and transpulmonary pressure of 7.5 cmH₂O in the presence and absence of DI and bronchodilators. A DI maneuver, involving rapid inflation to total lung capacity followed by deflation to zero transpulmonary pressure, was used to resolve air trapping. Lung resistance and elastance were recorded pre- and post-DI. The experiments were also conducted in the presence of the bronchodilator salbutamol to assess the role of ASM. Ventilation without DI increased lung resistance and elastance, as well as air trapping. DI effectively resolved air trapping, restoring resistance and elastance to their initial values. Salbutamol also alleviated the increase in lung resistance, elastance, and air trapping. DI prevented air trapping and reduced lung resistance and elastance in ex vivo sheep lungs during tidal ventilation, playing a similar role as a pharmacological bronchodilator.NEW & NOTEWORTHY We showed that air trapping is a consistent feature in ex vivo sheep lungs possessing spontaneous bronchoconstriction, when the lungs are ventilated with small tidal volume without intermittent deep inspirations. We further demonstrated that in the presence of salbutamol, air trapping does not occur. This explains the importance of deep inspirations in normal breathing and indicates that airway smooth muscle tone could result in air trapping in the absence of deep inspiration.

Transforming growth factor β1 (TGFβ1) is a pleiotropic cytokine implicated in the pathophysiology of chronic lung diseases such as asthma and chronic obstructive pulmonary disease. Epithelial TGFβ1 is released in response to injury, inflammatory stimuli, and during bronchoconstriction to induce fibrosis. We hypothesized that elevated expression of endogenous TGFβ1, localized to the lung, would elicit autocrine effects to alter airway responsiveness. We utilized a transgenic mouse model of doxycycline (Dox)-induced, lung-specific overexpression of active TGFβ1 by giving Dox (0.25 mg/mL in drinking water, 8 wk), or normal water as a control. Comparing Dox with control groups, levels of TGFβ1 were ∼30-fold higher in bronchoalveolar lavage fluid (BALF), but not in serum, as measured by ELISA. BALF cells, predominantly macrophages, were ∼3.5-fold higher, with no evidence of tissue inflammation in hematoxylin and eosin (H&E)-stained sections from Dox mice. Higher collagen deposition was evident around the airways in Masson's trichrome-stained sections [subepithelial thickness (µm): control 10.4 ± 10.9, n = 9; Dox 25.8 ± 1.5, n = 13, P < 0.0001]. TGFβ1 overexpression increased baseline airway resistance and induced airway hyperresponsiveness (AHR) to methacholine (MCh) in vivo, as measured using in vivo plethysmography. Comparing precision-cut lung slices (PCLS) from separate Dox-treated and control mice, maximum contraction of intrapulmonary airways to MCh was increased ex vivo. Overall, elevated lung TGFβ1 levels resulted in localized airway fibrosis associated with increased airway contraction to MCh. These autocrine effects of endogenous TGFβ1 implicate its potential contribution to AHR, suggesting that targeting TGFβ1 may provide a novel approach to oppose excessive airway contraction in chronic lung diseases.NEW & NOTEWORTHY TGFβ upregulation is common in respiratory diseases. Here, the authors have utilized for the first time a mouse model of lung-specific overexpression of active TGFβ to demonstrate the dual role of TGFβ1 in structural remodeling and dysregulation of airway contractility. Given these pathologies are common to asthma and COPD, this model provides a unique opportunity to identify essential novel therapeutics for the treatment of chronic lung diseases.

Karl von Neegaard's classic publication, in 1929, first identified the physiological function of pulmonary surfactant on alveolar mechanics. Dr. John Allen Clements brought this work to the clinic in the 1960s, culminating in the development of surfactant replacement therapy for infant respiratory distress syndrome (RDS). In this mini-review, we discuss pulmonary surfactants' role in maintaining lung fluid balance, which is essential in preventing pulmonary edema. Alveolar surface tension (γ) is transmitted into the perialveolar space surrounding pulmonary capillaries and corner vessels. Increasing surface tension at end expiration would increase alveolar recoil pressure and decrease alveolar radius, thus causing more subatmospheric pressure in the perialveolar space, generating an increased gradient for microvascular filtration. Studies have demonstrated a positive correlation between increased pulmonary extravascular water volume (PEWV) and high γ (γ = 8.3 ± 1.7 dyn/cm; PEWV = 3.4 ± 0.2 mL/g vs. γ = 23.2 ± 0.4 dyn/cm; PEWV = 6.1 ± 1.0 mL/g dry lung). A subsequent study demonstrated that the high γ did not increase capillary permeability, supporting the mechanism of high γ-induced pulmonary edema as a decrease in interstitial hydrostatic pressure. Computational modeling, as presented in our previous publications based on the Starling equation of fluid flux, identifies the impact of elevated alveolar surface tension on lung fluid balance. Loss of surfactant function favors fluid moving from the capillary across the endothelium into the perialveolar space and across the epithelium into the alveoli. We conclude that elevated alveolar surface tension plays a pivotal role in lung fluid balance and, if sufficiently elevated, can cause pulmonary edema even with normal capillary permeability.

Intrauterine inflammation is associated with lung injury in offspring and long-term adverse pulmonary outcomes, but the underlying mechanism remains elusive. This study aimed to investigate the underlying molecular mechanism from the perspective of metabolites. Pregnant C57BL/6 mice received an intraperitoneal injection of LPS on gestational day 12.5 to establish an intrauterine inflammation model. The results showed that prenatal LPS exposure induced bronchopulmonary dysplasia (BPD)-like alveolar simplification. Then, by LC/MS untargeted metabolomics analysis, succinic acid was found to be elevated in murine placentas and preterm human umbilical cord blood with intrauterine inflammation. Besides, the expression of succinate dehydrogenase B subunit (Sdhb), a key catalytic enzyme of succinic acid, was downregulated in the murine placentas with intrauterine inflammation. Tail intravenous administration of Sdhb siRNA led to the accumulation of succinic acid in the placenta and aggravated LPS-induced lung injury in the offspring. In offspring mice, intrauterine inflammation decreased E-cadherin levels in lung tissue, which were further reduced by Sdhb siRNA injection. Conversely, overexpression of E-cadherin alleviated inflammation-induced lung injury. In vitro experiments revealed that succinic acid downregulated E-cadherin expression in alveolar epithelial cells through the PI3K/Akt/Hif-1α pathway. Succinic acid also indirectly downregulated the E-cadherin expression in alveolar epithelial cells by inducing macrophage M2 polarization and the production of Tgf-β1. In conclusion, this study demonstrates that succinic acid is a critical mediator of intrauterine inflammation-induced lung injury in offspring.NEW & NOTEWORTHY Intrauterine inflammation induces the accumulation of succinic acid in the placenta, which subsequently downregulated E-cadherin expression in the alveolar epithelial cells, thereby contributing to lung injury.

Chronic obstructive pulmonary disease (COPD) is a progressive lung disease caused mainly by cigarette smoke-mediated induction of oxidative stress. Sirtuin 3 (SIRT3) regulates reactive oxygen species levels, but there are no definitive reports on its role in COPD pathogenesis. We hypothesized that SIRT3 plays a protective role in COPD. First, we observed significantly reduced SIRT3 expression in COPD lungs and identified smoking as a suppressive factor for SIRT3 expression in the airway epithelium. Next, we analyzed the lung phenotypes of SIRT3 knockout (KO) mice and SIRT3-overexpressing transgenic (OE) mice, and induced a COPD model in these mice using elastase and lipopolysaccharide. We subsequently investigated the effects of SIRT3 on cytokine production, oxidative stress, and apoptosis in airway epithelial cells in vitro. SIRT3 knockout mice exhibited increased expression of apoptosis markers, and aged SIRT3 KO mice and SIRT3 KO COPD model mice exhibited a worsened emphysematous phenotype. By contrast, this effect was mitigated in SIRT3 OE COPD model mice. In vitro studies revealed that SIRT3 deficiency exacerbated inflammation, oxidative stress, and apoptosis in airway epithelial cells. We concluded that SIRT3 plays a vital role in COPD pathogenesis and could be a novel therapeutic target.NEW & NOTEWORTHY Our study is the first to elucidate the protective role of SIRT3 in the pathogenesis of COPD by modulating inflammatory responses and apoptosis. We have demonstrated that SIRT3 knockout mice spontaneously develop emphysema, and SIRT3 overexpression reduced elastase and LPS-induced emphysematous changes. In vitro studies have shown that SIRT3 deficiency leads to increased inflammation, oxidative stress, and apoptosis in airway and alveolar epithelium, contributing to the formation and exacerbation of emphysema.

Carbonic anhydrase IX (CA IX) is a unique transmembrane CA isoform that is associated with chronic pulmonary vascular diseases and is upregulated in the lungs during infection. Whether CA IX contributes to alveolar-capillary dysfunction in the acute respiratory distress syndrome (ARDS) is unknown. Here, we tested the hypothesis that CA IX promotes acute lung injury during metabolic acidosis and pneumonia. Wild-type (WT) and CA IX knockout (KO) mice were fed 0.5% sucrose water (control) or 0.28 M NH₄Cl + 0.5% sucrose water for 7 days to induce metabolic acidosis, followed by intratracheal instillation of bacteria. Metabolic acidosis by itself did not cause pulmonary edema but modestly increased the lung wet-to-dry ratio in WT mice during pneumonia. A major sex difference in outcome was seen, where WT females had a higher filtration coefficient (K_f) in the isolated perfused lung and increased mortality compared with KO females. The K_f of WT and KO males did not differ; however, WT males had a 20% lower survival rate than KO males. In vitro expression of CA IX in pulmonary microvascular endothelial cells increased gap formation in the cell monolayer compared with KO cells during infection. No difference in lung bacterial clearance and plasma cytokines were seen between WT and KO mice regardless of sex. Thus, we report that CA IX promotes lung permeability and mortality but does not affect lung bacterial clearance, suggesting that CA IX may facilitate lung injury by directly affecting alveolar-capillary permeability and may serve as a therapeutic target in ARDS.NEW & NOTEWORTHY Acidosis is prevalent in patients with ARDS, yet the mechanisms involved in alveolar-capillary dysfunction during metabolic acidosis and lung injury remain poorly defined. Here, we report that carbonic anhydrase IX, a unique pH regulatory protein, promotes pulmonary edema and mortality but does not affect lung bacterial clearance during metabolic acidosis and pneumonia. Our findings suggest that carbonic anhydrase IX may serve as a therapeutic target to alleviate lung injury in patients with acidosis and ARDS.

Preterm infants frequently require respiratory support, including continuous positive airway pressure (CPAP), that imposes mechanical stretch on highly compliant perinatal airways. How this excess stress impacts airway development and function is not completely understood. Using human fetal airway smooth muscle (fASM), a key cell type in airway contractility and remodeling, as a model, we investigated the effects of stretch, focusing on the role of mechanosensitive ion channels Piezo1 and Piezo2. We found that CPAP-like static stretch did not alter Piezo1 and Piezo2 protein expression per se and had a minimal effect on fASM cell proliferation or IL-6 production during the stretch period. However, CPAP-like stretch produces long-term effects in fASM, leading to increased cell proliferation and IL-6 production during the poststretch period, though interestingly, it does not enhance extracellular matrix deposition. The role of Piezo channels appears context-dependent in that the Piezo1 antagonist GsMTx4 reduced baseline proliferation in nonstretched cells but slightly increased proliferation in stretched cells. Piezo1 and Piezo2 inhibition did not alter IL-6 production. These results suggest that stretch induces a sustained increase in cell proliferation and inflammatory responses, which may contribute to long-term remodeling in former preterm infants initially exposed to CPAP.NEW & NOTEWORTHY Mechanical stretch associated with respiratory support can impair airway development and function in neonates, but the mechanisms are not fully understood. Using developing human airway smooth muscle cells exposed to cyclic forces with static stretch to mimic continuous positive airway pressure, we found that stretch dysregulates long-term cell proliferation and inflammatory cytokine production, and mechanosensitive Piezo ion channels may play a role in the proliferation response.

Recent evidence suggests that oxidized phospholipids (oxPLs) play a critical role in the pathogenesis of pulmonary fibrosis. The precise mechanism by which oxPL contributes to fibrosis remains unknown and likely involves complex interactions between epithelial cell injury, phospholipid accumulation, and macrophage activation. We have previously identified lysosomal phospholipase A2 (LPLA2, PLAG15) as a critical enzyme involved in the catabolism of oxPL, especially within alveolar macrophages. We hypothesized that LPLA2 activity would mitigate the accumulation of oxPL within macrophages and thereby influence the development of pulmonary fibrosis. Using wild-type (WT) and LPLA2-null mice, we induced lung injury with bleomycin and assessed lung fibrosis severity, bronchoalveolar lavage (BAL) cell lipid accumulation, and monocyte/macrophage profibrotic activation. Our results show that LPLA2-null mice accumulated significantly more intracellular lipid within their alveolar cells, exhibited higher transforming growth factor-β (TGFβ) levels in their BAL fluid, and developed more severe fibrosis after bleomycin injury compared with WT mice. In vitro studies confirmed that LPLA2 expression in WT bone marrow-derived macrophages limits oxPL accumulation and thereby mitigates their profibrotic activation. Overexpression of LPLA2 in WT mice reduced alveolar cell lipid accumulation, decreased BAL fluid (BALF) TGFβ levels, and attenuated fibrosis. These findings underscore the critical role that LPLA2 plays in regulating lipid accumulation and suggest that enhancing LPLA2 activity within alveolar cells (or the alveolar compartment) could attenuate the fibrotic response following lung injury. By identifying LPLA2 as a key regulator in this pathway, we propose that targeting LPLA2 and related lipid metabolic processes offers a promising therapeutic strategy.NEW & NOTEWORTHY During lung injury and fibrosis, there is accumulation of oxidized phospholipid within macrophages in the alveolar space. This promotes profibrotic macrophage activation, resulting in pulmonary fibrosis. We find that degradation of oxidized phospholipid by lysosomal phospholipase A2 is important in preventing fibrosis. This offers a potential therapeutic target.