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

The primary cause of death from opioid overdose is opioid-induced respiratory depression (OIRD), characterized by severe suppression of respiratory rate, destabilized breathing patterns, hypercapnia, and heightened risk of apnea. The retrotrapezoid nucleus (RTN), a critical chemosensitive brainstem region in the rostral ventrolateral medullary reticular formation, contains Phox2b⁺/neuromedin-B (Nmb) propriobulbar neurons. These neurons, stimulated by CO₂/H⁺, regulate breathing to prevent respiratory acidosis. Since the RTN shows limited expression of opioid receptors, we expected that opioid-induced hypoventilation should activate these neurons to restore ventilation and stabilize arterial blood gases. However, the ability of the RTN to stimulate ventilation during OIRD has never been tested. We used optogenetic and pharmacogenetic approaches, to activate and inhibit RTN Phox2b⁺/Nmb⁺ neurons before and after fentanyl administration. As expected, fentanyl (500 µg/kg ip) suppressed respiratory rate and destabilized breathing. Before fentanyl, optogenetic stimulation of Phox2b⁺/Nmb⁺ or chemogenetic inhibition of Nmb⁺ cells increased and decreased breathing activity, respectively. Surprisingly, optogenetic stimulation after fentanyl administration caused a significantly greater increase in breathing activity compared with prefentanyl levels. In contrast, chemogenetic inhibition of RTN Nmb neurons caused profound hypoventilation and breathing instability after fentanyl. The results suggest that fentanyl does not inhibit the ability of Phox2b⁺/Nmb⁺ cells within the RTN region to stimulate breathing. Thus, this study highlights the potential of stimulating RTN neurons as a possible therapeutic approach to restore respiratory function in cases of opioid-induced respiratory depression (OIRD).NEW & NOTEWORTHY Opioid-induced respiratory depression (OIRD) suppresses breathing and destabilizes ventilation. Using optogenetic and chemogenetic tools, we demonstrated that stimulating retrotrapezoid nucleus (RTN) Phox2b⁺/Nmb⁺ neurons enhances breathing, even after fentanyl administration, whereas their inhibition exacerbates hypoventilation. These findings reveal that RTN neurons retain their ability to drive ventilation during OIRD, highlighting their potential as a therapeutic target to restore respiratory function in opioid overdose cases.

Most people with severe asthma have obesity. Metabolic dysfunction, often associated with obesity, is particularly associated with severe asthma. Mechanisms linking metabolic dysfunction with asthma, and whether improving metabolic function can affect asthma, are not known. The endocannabinoid system plays a significant role in metabolism; inhibition of cannabinoid receptor 1 (CB₁R) induces weight loss and improves serum lipid profiles. We used a CB₁R inverse agonist, INV-202, in a mouse model of obese asthma and investigated changes in weight, inflammation, airway reactivity, and surfactant lipids. Mice were fed low or high-fat diets (LFD, HFD), and house dust mite (HDM) extract was delivered intranasally to induce allergic airway inflammation. Mice received INV-202 by oral gavage. Airway hyperresponsiveness was measured by FlexiVent, and lung tissue cytokines were measured by ELISA. Leukocytes and lipids in the bronchoalveolar lavage fluid (BALF) were analyzed by flow cytometry and mass spectroscopy, respectively. LFD and HFD mice lost an average of 11% and 27% of their body weight, respectively. LFD mice had a 33% decrease in CCL20 in lung tissue and a 55% decrease in neutrophils in BALF. LFD and HFD mice had improvements in airway hyperresponsiveness, particularly as measured by reduced elastance. Phosphatidylglycerol in BALF increased with INV-202, which significantly correlated with compliance in LFD mice. This study supports a significant contribution of metabolic factors related to the endocannabinoid system in lung compliance and airway reactivity, in part through effects on surfactant lipid composition, and demonstrates the potential of CB₁R inverse agonists to treat obese asthma.NEW & NOTEWORTHY Inhibition of the cannabinoid receptor 1, through a pharmacological inverse agonist, not only induces weight loss in a mouse model of obese asthma but also reduces airway hyperresponsiveness, particularly through decreasing elastance/increasing compliance.

A molecular understanding of lung organogenesis requires delineation of the timing and regulation of the cellular transitions that ultimately form and support a surface capable of gas exchange. Although the advent of single-cell transcriptomics has allowed for the discovery and identification of transcriptionally distinct cell populations present during lung development, the spatiotemporal dynamics of these transcriptional shifts remain undefined. With imaging-based spatial transcriptomics, we analyzed the gene expression patterns in 17 human infant lungs at varying stages of development and injury, creating a spatial transcriptomic atlas of approximately 1.2 million cells. We applied computational clustering approaches to identify shared molecular patterns among this cohort, informing how tissue architecture and molecular spatial relationships are coordinated during development and disrupted in disease. Recognizing that all preterm birth represents an injury to the developing lung, we created a simplified classification scheme that relies upon the routinely collected objective measures of gestational age and lifespan. Within this framework, we have identified cell type patterns across gestational age and life span variables that would likely be overlooked when using the conventional "disease versus control" binary comparison. Together, these data represent an open resource for the lung research community, supporting discovery-based inquiry and identification of targetable molecular mechanisms in both normal and arrested human lung development.NEW & NOTEWORTHY Mapping the spatial and temporal transcriptional relationships during lung development is fundamental to understanding regeneration and chronic lung disease; however, the classification of samples as control or disease is especially challenging in the setting of preterm birth (itself a lung injury). Here, we report the largest neonatal lung transcriptomic atlas to date and an analysis framework based only on gestational age and lifespan, providing a new resource for hypothesis generation to the lung community.

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.