Downregulation of protein phosphatase 2Aα in asthmatic airway smooth muscle

Airway smooth muscle cell (ASM) is renowned for its involvement in airway hyperresponsiveness through impaired ASM relaxation and bronchoconstriction in asthma, which poses a significant challenge in the field. Recent studies have explored different targets in ASM to alleviate airway hyperresponsiveness, however, a sizeable portion of patients with asthma still experience poor control. In our study, we explored protein phosphatase 2 A (PP2A) in ASM as it has been reported to regulate cellular contractility by controlling intracellular calcium ([Ca2+]i), ion channels, and respective regulatory proteins. We obtained human ASM cells and lung tissues from healthy and patients with asthma and evaluated PP2A expression using RNA-Seq data, immunofluorescence, and immunoblotting. We further investigated the functional importance of PP2A by determining its role in bronchoconstriction using mouse bronchus and human ASM cell [Ca2+]i regulation. We found robust expression of PP2A isoforms in human ASM cells with PP2Aα being highly expressed. Interestingly, PP2Aα was significantly downregulated in asthmatic tissue and human ASM cells exposed to proinflammatory cytokines. Functionally, FTY720 (PP2A agonist) inhibited acetylcholine- or methacholine-induced bronchial contraction in mouse bronchus and further potentiated isoproterenol-induced bronchial relaxation. Mechanistically, FTY720 inhibited histamine-evoked [Ca2+]i response and myosin light chain (MLC) phosphorylation in the presence of interleukin-13 (IL-13) in human ASM cells. To conclude, we for the first time established PP2A signaling in ASM, which can be further explored to develop novel therapeutics to alleviate airway hyperresponsiveness in asthma.NEW & NOTEWORTHY This novel study deciphered the expression and function of protein phosphatase 2Aα (PP2Aα) in airway smooth muscle (ASM) during asthma and/or inflammation. We showed robust expression of PP2Aα in human ASM while its downregulation in asthmatic ASM. Similarly, we demonstrated reduced PP2Aα expression in ASM exposed to proinflammatory cytokines. PP2Aα activation inhibited bronchoconstriction of isolated mouse bronchi. In addition, we unveiled that PP2Aα activation inhibits the intracellular calcium release and myosin light chain phosphorylation in human ASM.

Defining signals that promote human alveolar type I differentiation

Alveolar type I (ATI) cells cover >95% of the lung's distal surface and facilitate gas exchange through their exceptionally thin shape. ATI cells in vivo are replenished by alveolar type II cell division and differentiation, but a detailed understanding of ATI biology has been hampered by the challenges in direct isolation of these cells due to their fragility and incomplete understanding of the signaling interactions that promote differentiation of ATII to ATI cells. Here, we explored the signals that maintain ATII versus promote ATI fates in three-dimensional (3-D) organoid cultures and developed a human alveolar type I differentiation medium (hATIDM) suitable for generating ATI cells from either mixed distal human lung cells or purified ATII cells. This media adds bone morphogenetic protein 4 (BMP4) and removes epidermal growth factor (EGF), Wnt agonist CHIR99021, and transforming growth factor-beta (TGF-β) inhibitor SB431542 from previously developed alveolar organoid culture media. We demonstrate that BMP4 promotes expression of the ATI marker gene AGER and HOPX, whereas CHIR99021 and SB431542 maintain expression of the ATII marker gene SFTPC. The human ATI spheroids generated with hATIDM express multiple molecular and morphological features reminiscent of human ATI cells. Our results demonstrate that signaling interactions among BMP, TGF-β, and Wnt signaling pathways in alveolar spheroids and distal lung organoids including IPF-organoids coordinate human ATII to ATI differentiation.NEW & NOTEWORTHY Alveolar type I (ATI) epithelial cells perform essential roles in maintaining lung function but have been challenging to study. We explored the signals that promote ATI fate in 3-D organoid cultures generated from either mixed distal human lung cells or purified alveolar type II (ATII) cells. This work fills an important void in our experimental repertoire for studying alveolar epithelial cells and identifies signals that promote human ATII to ATI cell differentiation.

Kisspeptin/KISS1R Signaling Modulates Human Airway Smooth Muscle Cell Migration

Airway remodeling is a cardinal feature of asthma, associated with increased airway smooth muscle cell (ASM) mass and up-regulation of extracellular matrix deposition. Exaggerated ASM cell migration contributes to excessive ASM mass. Previously, we demonstrated the alleviating role of kisspeptin (Kp) receptor (KISS1R) activation by Kp-10 in mitogen (PDGF)-induced human ASM cell proliferation in vitro and airway remodeling in vivo in a mouse model of asthma. Here, we examined the mechanisms by which KISS1R activation regulates mitogen-induced ASM cell migration. KISS1R activation using Kp-10 significantly inhibited PDGF-induced ASM cell migration, further confirmed using KISS1R shRNA. Furthermore, KISS1R activation modulated F/G actin dynamics and the expression of pro-migration proteins like cell division control protein 42 (CDC42) and cofilin. Mechanistically, we observed reduced ASM RhoA-GTPAse with KISS1R activation. The anti-migratory effect of KISS1R was abolished by protein kinase A (PKA)-inhibitory peptide. Conversely, KISS1R activation significantly increased cAMP and phosphorylation of cAMP-response element binding protein (CREB) in PDGF-exposed ASM cells. Overall, these results highlight the alleviating properties of Kp-10 in the context of airway remodeling.

Nicotinic receptors in airway disease

With continued smoking of tobacco products and expanded use of nicotine delivery devices worldwide, understanding the impact of smoking and vaping on respiratory health remains a major global unmet need. Although multiple studies have shown a strong association between smoking and asthma, there is a relative paucity of mechanistic understanding of how elements in cigarette smoke impact the airway. Recognizing that nicotine is a major component in both smoking and vaping products, it is critical to understand the mechanisms by which nicotine impacts airways and promotes lung diseases such as asthma. There is now increasing evidence that α7 nicotinic acetylcholine receptors (α7nAChRs) are critical players in nicotine effects on airways, but the mechanisms by which α7nAChR influences different airway cell types have not been widely explored. In this review, we highlight and integrate the current state of knowledge regarding nicotine and α7nAChR in the context of asthma and identify potential approaches to alleviate the impact of smoking and vaping on the lungs.

Functional role of glial-derived neurotrophic factor in a mixed allergen murine model of asthma

Our previous study showed that glial-derived neurotrophic factor (GDNF) expression is upregulated in asthmatic human lungs, and GDNF regulates calcium responses through its receptor GDNF family receptor α1 (GFRα1) and RET receptor in human airway smooth muscle (ASM) cells. In this study, we tested the hypothesis that airway GDNF contributes to airway hyperreactivity (AHR) and remodeling using a mixed allergen mouse model. Adult C57BL/6J mice were intranasally exposed to mixed allergens (ovalbumin, Aspergillus, Alternaria, house dust mite) over 4 wk with concurrent exposure to recombinant GDNF, or extracellular GDNF chelator GFRα1-Fc. Airway resistance and compliance to methacholine were assessed using FlexiVent. Lung expression of GDNF, GFRα1, RET, collagen, and fibronectin was examined by RT-PCR and histology staining. Allergen exposure increased GDNF expression in bronchial airways including ASM and epithelium. Laser capture microdissection of the ASM layer showed increased mRNA for GDNF, GFRα1, and RET in allergen-treated mice. Allergen exposure increased protein expression of GDNF and RET, but not GFRα1, in ASM. Intranasal administration of GDNF enhanced baseline responses to methacholine but did not consistently potentiate allergen effects. GDNF also induced airway thickening, and collagen deposition in bronchial airways. Chelation of GDNF by GFRα1-Fc attenuated allergen-induced AHR and particularly remodeling. These data suggest that locally produced GDNF, potentially derived from epithelium and/or ASM, contributes to AHR and remodeling relevant to asthma.NEW & NOTEWORTHY Local production of growth factors within the airway with autocrine/paracrine effects can promote features of asthma. Here, we show that glial-derived neurotrophic factor (GDNF) is a procontractile and proremodeling factor that contributes to allergen-induced airway hyperreactivity and tissue remodeling in a mouse model of asthma. Blocking GDNF signaling attenuates allergen-induced airway hyperreactivity and remodeling, suggesting a novel approach to alleviating structural and functional changes in the asthmatic airway.

Exogenous hydrogen sulfide attenuates hyperoxia effects on neonatal mouse airways

Supplemental O2 remains a necessary intervention for many premature infants (<34 wk gestation). Even moderate hyperoxia (<60% O2) poses a risk for subsequent airway disease, thereby predisposing premature infants to pediatric asthma involving chronic inflammation, airway hyperresponsiveness (AHR), airway remodeling, and airflow obstruction. Moderate hyperoxia promotes AHR via effects on airway smooth muscle (ASM), a cell type that also contributes to impaired bronchodilation and remodeling (proliferation, altered extracellular matrix). Understanding mechanisms by which O2 initiates long-term airway changes in prematurity is critical for therapeutic advancements for wheezing disorders and asthma in babies and children. Immature or dysfunctional antioxidant systems in the underdeveloped lungs of premature infants thereby heightens susceptibility to oxidative stress from O2. The novel gasotransmitter hydrogen sulfide (H2S) is involved in antioxidant defense and has vasodilatory effects with oxidative stress. We previously showed that exogenous H2S exhibits bronchodilatory effects in human developing airway in the context of hyperoxia exposure. Here, we proposed that exogenous H2S would attenuate effects of O2 on airway contractility, thickness, and remodeling in mice exposed to hyperoxia during the neonatal period. Using functional [flexiVent; precision-cut lung slices (PCLS)] and structural (histology; immunofluorescence) analyses, we show that H2S donors mitigate the effects of O2 on developing airway structure and function, with moderate O2 and H2S effects on developing mouse airways showing a sex difference. Our study demonstrates the potential applicability of low-dose H2S toward alleviating the detrimental effects of hyperoxia on the premature lung.NEW & NOTEWORTHY Chronic airway disease is a short- and long-term consequence of premature birth. Understanding effects of O2 exposure during the perinatal period is key to identify targetable mechanisms that initiate and sustain adverse airway changes. Our findings show a beneficial effect of exogenous H2S on developing mouse airway structure and function with notable sex differences. H2S donors alleviate effects of O2 on airway hyperreactivity, contractility, airway smooth muscle thickness, and extracellular matrix deposition.

Estrogen receptors differentially modifies lamellipodial and focal adhesion dynamics in airway smooth muscle cell migration

Sex-steroid signaling, especially estrogen, has a paradoxical impact on regulating airway remodeling. In our previous studies, we demonstrated differential effects of 17β-estradiol (E2) towards estrogen receptors (ERs: α and β) in regulating airway smooth muscle (ASM) cell proliferation and extracellular matrix (ECM) production. However, the role of ERs and their signaling on ASM migration is still unexplored. In this study, we examined how ERα versus ERβ affects the mitogen (Platelet-derived growth factor, PDGF)-induced human ASM cell migration as well as the underlying mechanisms involved. We used Lionheart-FX automated microscopy and transwell assays to measure cell migration and found that activating specific ERs had differential effects on PDGF-induced ASM cell migration. Pharmacological activation of ERβ or shRNA mediated knockdown of ERα and specific activation of ERβ blunted PDGF-induced cell migration. Furthermore, specific ERβ activation showed inhibition of actin polymerization by reducing the F/G-actin ratio. Using Zeiss confocal microscopy coupled with three-dimensional algorithmic ZEN-image analysis showed an ERβ-mediated reduction in PDGF-induced expressions of neural Wiskott-Aldrich syndrome protein (N-WASP) and actin-related proteins-2/3 (Arp2/3) complex, thereby inhibiting actin-branching and lamellipodia. In addition, ERβ activation also reduces the clustering of actin-binding proteins (vinculin and paxillin) at the leading edge of ASM cells. However, cells treated with E2 or ERα agonists do not show significant changes in actin/lamellipodial dynamics. Overall, these findings unveil the significance of ERβ activation in regulating lamellipodial and focal adhesion dynamics to regulate ASM cell migration and could be a novel target to blunt airway remodeling.

Nicotine affects mitochondrial structure and function in human airway smooth muscle cells

Exposure to cigarette smoke and e-cigarettes, with nicotine as the active constituent, contributes to increased health risks associated with asthma. Nicotine exerts its functional activity via nicotinic acetylcholine receptors (nAChRs), and the alpha7 subtype (α7nAChR) has recently been shown to adversely affect airway dynamics. The mechanisms of α7nAChR action in airways, particularly in the context of airway smooth muscle (ASM), a key cell type in asthma, are still under investigation. Mitochondria have garnered increasing interest for their role in regulating airway tone and adaptations to cellular stress. Here mitochondrial dynamics such as fusion versus fission, and mitochondrial Ca2+ ([Ca2+]m), play an important role in mitochondrial homeostasis. There is currently no information on effects and mechanisms by which nicotine regulates mitochondrial structure and function in ASM in the context of asthma. We hypothesized that nicotine disrupts mitochondrial morphology, fission-fusion balance, and [Ca2+]m regulation, with altered mitochondrial respiration and bioenergetics in the context of asthmatic ASM. Using human ASM (hASM) cells from nonasthmatics, asthmatics, and smokers, we examined the effects of nicotine on mitochondrial dynamics and [Ca2+]m. Fluorescence [Ca2+]m imaging of hASM cells with rhod-2 showed robust responses to 10 μM nicotine, particularly in asthmatics and smokers. In both asthmatics and smokers, nicotine increased the expression of fission proteins while decreasing fusion proteins. Seahorse analysis showed blunted oxidative phosphorylation parameters in response to nicotine in these groups. α7nAChR siRNA blunted nicotine effects, rescuing [Ca2+]m, changes in mitochondrial structural proteins, and mitochondrial dysfunction. These data highlight mitochondria as a target of nicotine effects on ASM, where mitochondrial disruption and impaired buffering could permit downstream effects of nicotine in the context of asthma.NEW & NOTEWORTHY Asthma is a major healthcare burden, which is further exacerbated by smoking. Recognizing the smoking risk of asthma, understanding the effects of nicotine on asthmatic airways becomes critical. Surprisingly, the mechanisms of nicotine action, even in normal and especially asthmatic airways, are understudied. Accordingly, the goal of this research is to investigate how nicotine influences asthmatic airways in terms of mitochondrial structure and function, via the a7nAChR.

MiR-326-mediated overexpression of NFIB offsets TGF-β induced epithelial to mesenchymal transition and reverses lung fibrosis

Idiopathic Pulmonary Fibrosis (IPF) is a progressively fatal and incurable disease characterized by the loss of alveolar structures, increased epithelial-mesenchymal transition (EMT), and aberrant tissue repair. In this study, we investigated the role of Nuclear Factor I-B (NFIB), a transcription factor critical for lung development and maturation, in IPF. Using both human lung tissue samples from patients with IPF, and a mouse model of lung fibrosis induced by bleomycin, we showed that there was a significant reduction of NFIB both in the lungs of patients and mice with IPF. Furthermore, our in vitro experiments using cultured human lung cells demonstrated that the loss of NFIB was associated with the induction of EMT by transforming growth factor beta (TGF-β). Knockdown of NFIB promoted EMT, while overexpression of NFIB suppressed EMT and attenuated the severity of bleomycin-induced lung fibrosis in mice. Mechanistically, we identified post-translational regulation of NFIB by miR-326, a miRNA with anti-fibrotic effects that is diminished in IPF. Specifically, we showed that miR-326 stabilized and increased the expression of NFIB through its 3'UTR target sites for Human antigen R (HuR). Moreover, treatment of mice with either NFIB plasmid or miR-326 reversed airway collagen deposition and fibrosis. In conclusion, our study emphasizes the critical role of NFIB in lung development and maturation, and its reduction in IPF leading to EMT and loss of alveolar structures. Our study highlights the potential of miR-326 as a therapeutic intervention for IPF. The schema shows the role of NFIB in maintaining the normal epithelial cell characteristics in the lungs and how its reduction leads to a shift towards mesenchymal cell-like features and pulmonary fibrosis. A In normal lungs, NFIB is expressed abundantly in the epithelial cells, which helps in maintaining their shape, cell polarity and adhesion molecules. However, when the lungs are exposed to factors that induce pulmonary fibrosis, such as bleomycin, or TGF-β, the epithelial cells undergo epithelial to mesenchymal transition (EMT), which leads to a decrease in NFIB. B The mesenchymal cells that arise from EMT appear as spindle-shaped with loss of cell junctions, increased cell migration, loss of polarity and expression of markers associated with mesenchymal cells/fibroblasts. C We designed a therapeutic approach that involves exogenous administration of NFIB in the form of overexpression plasmid or microRNA-326. This therapeutic approach decreases the mesenchymal cell phenotype and restores the epithelial cell phenotype, thus preventing the development or progression of pulmonary fibrosis.

Piezo channels in stretch effects on developing human airway smooth muscle

The use of respiratory support strategies such as continuous positive airway pressure in premature infants can substantially stretch highly compliant perinatal airways, leading to airway hyperreactivity and remodeling in the long term. The mechanisms by which stretch detrimentally affects the airway are unknown. Airway smooth muscle cells play a critical role in contractility and remodeling. Using 18-22-wk gestation human fetal airway smooth muscle (fASM) as an in vitro model, we tested the hypothesis that mechanosensitive Piezo (PZ) channels contribute to stretch effects. We found that PZ1 and PZ2 channels are expressed in the smooth muscle of developing airways and that their expression is influenced by stretch. PZ activation via agonist Yoda1 or stretch results in significant [Ca2+]i responses as well as increased extracellular matrix production. These data suggest that functional PZ channels may play a role in detrimental stretch-induced airway changes in the context of prematurity.NEW & NOTEWORTHY Piezo channels were first described just over a decade ago and their function in the lung is largely unknown. We found that piezo channels are present and functional in the developing airway and contribute to intracellular calcium responses and extracellular matrix remodeling in the setting of stretch. This may improve our understanding of the mechanisms behind development of chronic airway diseases, such as asthma, in former preterm infants exposed to respiratory support, such as continuous positive airway pressure (CPAP).

Mechanosensitive Channels in Lung Health and Disease

The lung is an inherently mechanosensitive organ, where cells of the airway and parenchyma experience a range of mechanical forces throughout life including shear, stretch, and compression, in both health and disease. In this regard, pediatric and adult lung diseases such as wheezing and asthma, bronchopulmonary dysplasia (BPD), chronic obstructive pulmonary disease (COPD), and pulmonary fibrosis (PF) all involve macroscopic and cellular changes to the mechanical properties of the bronchial airways and/or parenchyma to varying extents. Accordingly, understanding how mechanical forces are sensed in the lung, and the responses of cells and tissues in the context of normal development and health versus disease conditions becomes highly relevant. There is increasing recognition that transduction of mechanical forces into cellular responses involves a number of channels, some of which are inherently mechanosensitive. Such channels trigger mechanotransduction pathways that may further mediate cellular remodeling, inflammation, and other pathophysiologic mechanisms in response to stretch, stiffness, and inflammatory cascades. Two particularly important channel families have emerged in pulmonary pathophysiology: the transient receptor potential vanilloid family with focus on member TRPV4 and the recently identified Piezo (PZ) channels. Here, we explore current understanding of the contributions of TRPV4 and PZ channels in lung health and disease states, focusing on the interactions between these mechanosensitive channels and their local environment including immune cells, the extracellular matrix, and cellular cytoskeletal elements. We further discuss potential areas for future research to better understand the impact of mechanical channels on pulmonary health and disease. © 2023 American Physiological Society. Compr Physiol 13:5157-5178, 2023.

Building Career Paths for Ph.D., Basic and Translational Scientists in Clinical Departments in the United States: An Official American Thoracic Society Workshop Report

Rationale: To identify barriers and opportunities for Ph.D., basic and translational scientists to be fully integrated into clinical units. Objectives: In 2022, an ad hoc committee of the American Thoracic Society developed a project proposal and workshop to identify opportunities and barriers for scientists who do not practice medicine to develop successful careers and achieve tenure-track faculty positions in clinical departments and divisions within academic medical centers (AMCs) in the United States. Methods: This document focuses on results from a survey of adult and pediatric pulmonary, critical care, and sleep medicine division chiefs as well as a survey of workshop participants, including faculty in departmental and school leadership roles in both basic science and clinical units within U.S. AMCs. Results: We conclude that full integration of non-clinically practicing basic and translational scientists into the clinical units, in addition to their traditional placements in basic science units, best serves the tripartite mission of AMCs to provide care, perform research, and educate the next generation. Evidence suggests clinical units do employ Ph.D. scientists in large numbers, but these faculty are often hired into non-tenure track positions, which do not provide the salary support, start-up funds, research independence, or space often associated with hiring in basic science units within the same institution. These barriers to success of Ph.D. faculty in clinical units are largely financial. Conclusions: Our recommendation is for AMCs to consider and explore some of our proposed strategies to accomplish the goal of integrating basic and translational scientists into clinical units in a meaningful way.

Interactions between calcium regulatory pathways and mechanosensitive channels in airways

INTRODUCTION

Asthma is a chronic lung disease influenced by environmental and inflammatory triggers and involving complex signaling pathways across resident airway cells such as epithelium, airway smooth muscle, fibroblasts, and immune cells. While our understanding of asthma pathophysiology is continually progressing, there is a growing realization that cellular microdomains play critical roles in mediating signaling relevant to asthma in the context of contractility and remodeling. Mechanosensitive pathways are increasingly recognized as important to microdomain signaling, with Piezo and transient receptor protein (TRP) channels at the plasma membrane considered important for converting mechanical stimuli into cellular behavior. Given their ion channel properties, particularly Ca2+ conduction, a question becomes whether and how mechanosensitive channels contribute to Ca2+ microdomains in airway cells relevant to asthma.

AREAS COVERED

Mechanosensitive TRP and Piezo channels regulate key Ca2+ regulatory proteins such as store operated calcium entry (SOCE) involving STIM and Orai channels, and sarcoendoplasmic (SR) mechanisms such as IP3 receptor channels (IP3Rs), and SR Ca2+ ATPase (SERCA) that are important in asthma pathophysiology including airway hyperreactivity and remodeling.

EXPERT OPINION

Physical and/or functional interactions between Ca2+ regulatory proteins and mechanosensitive channels such as TRP and Piezo can toward understanding asthma pathophysiology and identifying novel therapeutic approaches.

Functional α7 nicotinic receptors in human airway smooth muscle increase intracellular calcium concentration and contractility in asthmatics

Although nicotinic acetylcholine receptors (nAChRs) are commonly associated with neurons in the brain and periphery, recent data indicate they are also expressed in non-neuronal tissues. We recently found the alpha7 (α7nAChR) subunit is highly expressed in human airway smooth muscle (hASM) with substantial increase in asthmatics, but their functionality remains unknown. We investigated the location and functional role of α7nAChRs in hASM cells from normal vs. mild-moderate asthmatic patients. Immunostaining and protein analyses showed α7nAChR in the plasma membrane including in asthmatics. Patch clamp recordings showed functional homomeric α7nAChR channels at are significantly higher in asthmatic hASM. Real-time fluorescence imaging showed nicotine, via α7nAChR, increases intracellular Ca²⁺ ([Ca²⁺]_i) independent of ACh effects, particularly in asthmatic hASM, while cellular traction force microscopy showed nicotine-induced contractility including in asthmatics. These results indicate functional homomeric and heteromeric nAChRs that are increased in asthmatic hASM, with pharmacology that likely differ owing to different subunit interfaces that form the orthosteric sites. nAChRs may represent a novel target in alleviating airway hyperresponsiveness in asthma. New and Noteworthy Cigarette smoking and vaping exacerbate asthma. Understanding mechanisms of nicotine effects in asthmatic airways is important. This study demonstrates functional alpha7 nicotinic acetylcholine receptors (α7nAChRs) are expressed in human airway smooth muscle, including from asthmatics, and enhance intracellular calcium and contractility. Although a7nAChRs are associated with neuronal pathways, α7nAChR in smooth muscle suggests inhaled nicotine (e.g. vaping) can directly influence airway contractility. Targeting α7nAChR may represent a novel approach to alleviating airway hyperresponsiveness in asthma.

Age-associated Differences in the Human Lung Extracellular Matrix

Extracellular matrix (ECM) remodeling has been associated with chronic lung diseases. However, information about specific age‑associated differences in lung ECM is currently limited. In this study we aimed to identify and localize age‑associated ECM differences in human lung using comprehensive transcriptomic, proteomic and immunohistochemical analyses. Our previously identified age-associated gene expression signature of the lung was re‑analyzed limiting it to an aging signature based on 270 control patients (37-80 years) and focused on the Matrisome core geneset using geneset enrichment analysis. To validate the age‑associated transcriptomic differences on protein level, we compared the age-associated ECM genes (FDR <0.05) with a profile of age‑associated proteins identified from a lung tissue proteomics dataset from 9 control patients (49-76 years) (FDR<0.05). Extensive immunohistochemical analysis was used to localize and semi-quantify the age-associated ECM differences in lung tissues from 62 control patients (18-82 years). Comparative analysis of transcriptomic and proteomic data identified 7 ECM proteins with higher expression with age at both gene and protein level: COL1A1, COL6A1, COL6A2, COL14A1, FBLN2, LTBP4 and LUM. With immunohistochemistry we demonstrated higher protein level with age for COL6A2 in whole tissue, parenchyma, airway wall and blood vessel, for COL14A1 and LUM in bronchial epithelium, and COL1A1 in lung parenchyma. Our study revealed that higher age is associated with lung ECM remodeling, with specific differences occurring in defined regions within the lung. These differences may affect lung structure and physiology with aging and as such may increase susceptibility for developing chronic lung diseases.

CPAP-induced airway hyper-reactivity in mice is modulated by hyaluronan synthase-3

BACKGROUND

Continuous positive airway pressure (CPAP) is a primary mode of respiratory support for preterm infants. Animal studies have shown long-term detrimental effects on lung/airway development, particularly airway (AW) hyper-reactivity, as an unfortunate consequence of neonatal CPAP. Since the hyaluronan (HA) synthesizing enzyme hyaluronan synthase-3 (HAS3) is involved in various adult pulmonary disorders, the present study used a neonatal mouse model to investigate the role of HAS3 in CPAP-induced AW hyper-reactivity.

METHODS

Male and female neonatal mice were fitted with a custom-made mask for delivery of daily CPAP 3 h/day for 7 days. At postnatal day 21 (2 weeks after CPAP ended), airway (AW) hyper-reactivity and HAS3 expression were assessed with and without in vitro HAS3 siRNA treatment.

RESULTS

MRIs of 3-day-old mice confirmed that CPAP increased lung volume with incrementing inflation pressures. CPAP increased AW reactivity in both male and female mice, which was associated with increased airway smooth muscle and epithelial HAS3 immunoreactivity. CPAP did not affect HA accumulation, but HAS3 siRNA reversed CPAP-induced AW hyper-reactivity and reduced HAS3 expression.

CONCLUSIONS

These data in mice implicate a role for HAS3 in long-term effects of CPAP in the developing airway in the context of preterm birth and CPAP therapy.

IMPACT

Neonatal CPAP increases airway smooth muscle and epithelial HAS3 expression in mice. CPAP-induced airway hyper-reactivity is modulated by HAS3. These data enhance our understanding of the role mechanical forces play on lung development. These data are a significance step toward understanding CPAP effects on developing airway. These data may impact clinical recognition of the ways that CPAP may contribute to wheezing disorders of former preterm infants.

Hormonal Effects on Asthma, Rhinitis, and Eczema

Hormones significantly influence the pathogenesis of asthma, rhinitis, and eczema. This review aims to summarize relevant clinical considerations for practicing allergists and immunologists. The first section reviews the effects of sex hormones: estrogen, progesterone, and testosterone. The second concerns insulin production in the context of type 1 and type 2 diabetes. The third concludes with a discussion of thyroid and adrenal pathology in relationship to asthma, rhinitis, and eczema.

Calcium-sensing receptor and CPAP-induced neonatal airway hyperreactivity in mice

BACKGROUND

Continuous positive airway pressure (CPAP) in preterm infants is initially beneficial, but animal models suggest longer term detrimental airway effects towards asthma. We used a neonatal CPAP mouse model and human fetal airway smooth muscle (ASM) to investigate the role of extracellular calcium-sensing receptor (CaSR) in these effects.

METHODS

Newborn wild type and smooth muscle-specific CaSR^-/- mice were given CPAP for 7 days via a custom device (mimicking CPAP in premature infants), and recovered in normoxia for another 14 days (representing infants at 3-4 years). Airway reactivity was tested using lung slices, and airway CaSR quantified. Role of CaSR was tested using NPS2143 (inhibitor) or siRNA in WT mice. Fetal ASM cells stretched cyclically with/without static stretch mimicking breathing and CPAP were analyzed for intracellular Ca²⁺ ([Ca²⁺]_i) responses, role of CaSR, and signaling cascades.

RESULTS

CPAP increased airway reactivity in WT but not CaSR^-/- mice, increasing ASM CaSR. NPS2143 or CaSR siRNA reversed CPAP effects in WT mice. CPAP increased fetal ASM [Ca²⁺]_I, blocked by NPS2143, and increased ERK1/2 and RhoA suggesting two mechanisms by which stretch increases CaSR.

CONCLUSIONS

These data implicate CaSR in CPAP effects on airway function with implications for wheezing in former preterm infants.

IMPACT

Neonatal CPAP increases airway reactivity to bronchoconstrictor agonist. CPAP increases smooth muscle expression of the extracellular calcium-sensing receptor (CaSR). Inhibition or absence of CaSR blunts CPAP effects on contractility. These data suggest a causal/contributory role for CaSR in stretch effects on the developing airway. These data may impact clinical recognition of the ways that CPAP may contribute to wheezing disorders of former preterm infants.

Kisspeptins inhibit human airway smooth muscle proliferation

Sex/gender disparity in asthma is recognized, and suggests a modulatory role for sex-steroids, particularly estrogen. However, studies including our own show a dichotomous role for estrogen in airway remodeling, making it unclear whether sex hormones are protective or detrimental in asthma, and suggesting a need to explore mechanisms upstream or independent of estrogen. We hypothesize that Kisspeptin (Kp)/KISS1R signaling serves this role. Airway smooth muscle (ASM) is a key structural cell type that contributes to remodeling in asthma. We explored the role of Kp/KISS1R in regulating ASM proliferation. We report novel data that Kp and KISS1R are expressed in human airways, especially ASM, with lower expression in ASM from females compared to males, and asthmatics showing lowest expression compared to non-asthmatics. Proliferation studies showed that cleaved forms of Kp, particularly Kp-10 mitigates PDGF-induced ASM proliferation. Pharmacological inhibition and shRNA knockdown of KISS1R increased basal ASM proliferation, further amplified by PDGF. The anti-proliferative effect of Kp-10 in ASM was found to be mediated by inhibition of MAPK-ERK-Akt pathways, with altered expression of PCNA, C/EBP-alpha, Ki-67, Cyclin-D1, and Cyclin-E leading to cell-cycle arrest at G0/G1 phase. Overall, we demonstrate the importance of Kp/KISS1R signaling in regulating ASM proliferation and a potentially novel therapeutic avenue to blunt remodeling in asthma.

Electrogenic sodium bicarbonate cotransporter NBCe1 regulates pancreatic β cell function in type 2 diabetes

Pancreatic β cell failure in type 2 diabetes mellitus (T2DM) is attributed to perturbations of the β cell's transcriptional landscape resulting in impaired glucose-stimulated insulin secretion. Recent studies identified SLC4A4 (a gene encoding an electrogenic Na+-coupled HCO3- cotransporter and intracellular pH regulator, NBCe1) as one of the misexpressed genes in β cells of patients with T2DM. Thus, in the current study, we set out to test the hypothesis that misexpression of SLC4A4/NBCe1 in T2DM β cells contributes to β cell dysfunction and impaired glucose homeostasis. To address this hypothesis, we first confirmed induction of SLC4A4/NBCe1 expression in β cells of patients with T2DM and demonstrated that its expression was associated with loss of β cell transcriptional identity, intracellular alkalinization, and β cell dysfunction. In addition, we generated a β cell-selective Slc4a4/NBCe1-KO mouse model and found that these mice were protected from diet-induced metabolic stress and β cell dysfunction. Importantly, improved glucose tolerance and enhanced β cell function in Slc4a4/NBCe1-deficient mice were due to augmented mitochondrial function and increased expression of genes regulating β cell identity and function. These results suggest that increased β cell expression of SLC4A4/NBCe1 in T2DM plays a contributory role in promotion of β cell failure and should be considered as a potential therapeutic target.

Sex, Cells, and Asthma

There are marked sex differences in asthma prevalence and severity. Sex hormones play a central role in these sex biases and directly interact with multiple key cells involved in the pathogenesis of asthma. Here we review the known effects of estrogen, progesterone, and testosterone on airway epithelial cells, airway smooth muscle cells, the mononuclear phagocyte system, innate lymphoid cells, eosinophils, mast cells, T cells, and B cells, all in the context of asthma. Furthermore, we explore unresolved clinical questions, such as the role of sex hormones in the link between asthma and obesity.

CPAP protects against hyperoxia-induced increase in airway reactivity in neonatal mice

BACKGROUND

Oxygen and continuous positive airway pressure (CPAP) are primary modes of respiratory support for preterm infants. Animal models, however, have demonstrated adverse unintended effects of hyperoxia and CPAP on lung development. We investigate the effects of combined neonatal hyperoxia and CPAP exposure on airway function and morphology in mice.

METHODS

Newborn mice were exposed to hyperoxia (40% O₂) 24 h/day for 7 consecutive days with or without daily (3 h/day) concomitant CPAP. Two weeks after CPAP and/or hyperoxia treatment ended, lungs were assessed for airway (AW) hyperreactivity and morphology.

RESULTS

CPAP and hyperoxia exposure alone increased airway reactivity compared to untreated control mice. CPAP-induced airway hyperreactivity was associated with epithelial and smooth muscle proliferation. In contrast, combined CPAP and hyperoxia treatment no longer resulted in increased airway reactivity, which was associated with normalization of smooth muscle and epithelial proliferation to values similar to untreated mice.

CONCLUSIONS

Our data suggest that the combination of CPAP and hyperoxia decreases the adverse consequences on airway remodeling of either intervention alone. The complex interaction between mechanical stretch (via CPAP) and hyperoxia exposure on development of immature airways has implications for the pathophysiology of airway disease in former preterm infants receiving non-invasive respiratory support.

IMPACT

CPAP and mild hyperoxia exposure alone increase airway reactivity in the neonatal mouse model. In contrast, combined CPAP and hyperoxia no longer induce airway hyperreactivity. Combined CPAP and hyperoxia normalize smooth muscle and epithelial proliferation to control values. Interaction between CPAP-induced stretch and mild hyperoxia exposure on immature airways has important implications for airway pathophysiology in former preterm infants.

Glial-derived neurotrophic factor in human airway smooth muscle

Airway smooth muscle (ASM) cells modulate the local airway milieu via production of inflammatory mediators and growth factors including classical neurotrophins, such as brain-derived neurotrophic factor (BDNF). The glial cell-derived neurotrophic factor (GDNF) family of ligands (GFLs) are nonclassical neurotrophins and their role in the airway is barely understood. The major GFLs, GDNF and Neurturin (NRTN) bind to GDNF family receptor (GFR) α1 and α2 respectively that pair with Ret receptor to accomplish signaling. In this study, we found GDNF is expressed in human lung and increased in adult asthma, while human ASM expresses GDNF and its receptors. Accordingly, we used human ASM cells to test the hypothesis that ASM expression and autocrine signaling by GFLs regulate [Ca²⁺ ]_i . Serum-deprived ASM cells from non-asthmatics were exposed to 10 ng/ml GDNF or NRTN for 15 min (acute) or 24 h (chronic). In fura-2 loaded cells, acute GDNF or NRTN alone induced [Ca²⁺ ]_i responses, and further enhanced responses to 1 µM ACh or 10 µM histamine. Ret inhibitor (SPP86; 10 µM) or specific GDNF chelator GFRα1-Fc (1 µg/ml) showed roles of these receptors in GDNF effects. In contrast, NRTN did not enhance [Ca²⁺ ]_i response to histamine. Furthermore, conditioned media of nonasthmatic and asthmatic ASM cells showed GDNF secretion. SPP86, Ret inhibitor and GFRα1-Fc chelator markedly decreased [Ca²⁺ ]_i response compared with vehicle, highlighting autocrine effects of secreted GDNF. Chronic GDNF treatment increased histamine-induced myosin light chain phosphorylation. These novel data demonstrate GFLs particularly GDNF/GFRα1 influence ASM [Ca²⁺ ]_i and raise the possibility that GFLs are potential targets of airway hyperresponsiveness.

Senolytics reduce coronavirus-related mortality in old mice

Cellular senescence is a state elicited in response to stress signals and is associated with a damaging secretory phenotype. The number of senescent cells increases with advanced age and this in turn drives age-related diseases. Camell et al. show that senescent cells have an amplified inflammatory response to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) (see the Perspective by Cox and Lord). This response is communicated to nonsenescent cells, suppressing viral defense mechanisms and increasing the expression of viral entry proteins. In old mice infected with a SARS-CoV-2–related virus, treatment with senolytics to reduce the senolytic cell burden reduced mortality and increased antiviral antibodies.

Science, abe4832, this issue p. eabe4832; see also abi4474, p. 281

INTRODUCTION

The COVID-19 pandemic revealed enhanced vulnerability of the elderly and chronically ill to adverse outcomes upon severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Senescence is a cell fate elicited by cellular stress that results in changes in gene expression, morphology, metabolism, and resistance to apoptosis. Senescent cells (SnCs) secrete pro-inflammatory factors, called the senescence-associated secretory phenotype (SASP). SnCs accumulate with age and drive chronic inflammation. In human cells and tissues and using a new infection paradigm, we asked whether SnCs are a cause of adverse outcomes of infection with aging. This is relevant because SnCs can be selectively eliminated in vivo with a new class of therapeutics called senolytics, potentially affording a new approach to treat COVID-19.

RATIONALE

We hypothesized that SnCs, because of their pro-inflammatory SASP, might have a heightened response to pathogen-associated molecular pattern (PAMP) factors, resulting in increased risk of cytokine storm and multi-organ failure. To test this, we treated senescent and nonsenescent human cells with the PAMPs lipopolysaccharide (LPS) and SARS-CoV-2 spike protein (S1) and measured the SASP and its effect on non-SnCs. Similarly, old and progeroid mice were challenged with LPS, and we measured the SASP. Previously, we created a “normal microbial experience” (NME) for mice by transmitting environmental pathogens to specified-pathogen–free (SPF) mice through exposure to pet store mice or their bedding. The first pathogen transferred was mouse hepatitis virus (MHV), a β-coronavirus closely related to SARS-CoV-2. NME rapidly killed aged SPF mice known to have an increased burden of SnCs compared with young SPF mice, which survive NME. This afforded an experimental paradigm to test whether senolytics blunt adverse outcomes in β-coronavirus infection.

RESULTS

Human endothelial SnCs became hyperinflammatory in response to challenge with LPS and S1, relative to non-SnCs. The PAMP-elicited secretome of SnCs caused increased expression of viral entry proteins and reduced expression of antiviral genes in nonsenescent human endothelial and lung epithelial cells, and the proximity of these events was established in human lung biopsies. Treatment of old mice with LPS significantly increased SASP expression in several organs relative to young mice, confirming our hypothesis in vivo. Similarly, old mice exposed to NME displayed a significant multi-organ increase in SnCs and the SASP, impaired immune response to MHV, and 100% mortality, whereas inoculation with antibodies against MHV before NME afforded complete rescue of mortality. Treating old mice with the senolytic fisetin, which selectively eliminates SnCs after NME reduced mortality by 50%, reduced expression of inflammatory proteins in serum and tissue and improved the immune response. This was confirmed with a second senolytic regimen, Dasatinib plus Quercetin, as well as genetic ablation of SnCs in aged mice, establishing SnCs as a cause of adverse outcomes in aged organisms exposed to a new viral pathogen.

CONCLUSION

SnCs amplify susceptibility to COVID-19 and pathogen-induced hyperinflammation. Reducing SnC burden in aged mice reduces mortality after pathogen exposure, including a β-coronavirus. Our findings strongly support the Geroscience hypothesis that therapeutically targeting fundamental aging mechanisms improves resilience in the elderly, with alleviation of morbidity and mortality due to pathogenic stress. This suggests that senolytics might protect others vulnerable to adverse COVID-19 outcomes in whom increased SnCs occur (such as in obesity or numerous chronic diseases).

The COVID-19 pandemic has revealed the pronounced vulnerability of the elderly and chronically ill to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)–induced morbidity and mortality. Cellular senescence contributes to inflammation, multiple chronic diseases, and age-related dysfunction, but effects on responses to viral infection are unclear. Here, we demonstrate that senescent cells (SnCs) become hyper-inflammatory in response to pathogen-associated molecular patterns (PAMPs), including SARS-CoV-2 spike protein-1, increasing expression of viral entry proteins and reducing antiviral gene expression in non-SnCs through a paracrine mechanism. Old mice acutely infected with pathogens that included a SARS-CoV-2–related mouse β-coronavirus experienced increased senescence and inflammation, with nearly 100% mortality. Targeting SnCs by using senolytic drugs before or after pathogen exposure significantly reduced mortality, cellular senescence, and inflammatory markers and increased antiviral antibodies. Thus, reducing the SnC burden in diseased or aged individuals should enhance resilience and reduce mortality after viral infection, including that of SARS-CoV-2.

Passive siRNA transfection method for gene knockdown in air-liquid interface airway epithelial cell cultures

Differentiation of human bronchial epithelial cells (HBEs) in air-liquid interface (ALI) cultures recapitulates organotypic modeling of the in vivo environment. Although ALI cultures are invaluable for studying the respiratory epithelial barrier, loss-of-function studies are limited by potentially cytotoxic reagents in classical transfection methods, the length of the differentiation protocol, and the number of primary epithelial cell passages. Here, we present the efficacy and use of a simple method for small interfering RNA (siRNA) transfection of normal HBEs (NHBEs) in ALI cultures that does not require potentially cytotoxic transfection reagents and does not detrimentally alter the physiology or morphology of NHBEs during the differentiation process. This transfection protocol introduces a reproducible and efficient method for loss-of-function studies in HBE ALI cultures that can be leveraged for modeling the respiratory system and airway diseases.

Nicotinic α7 acetylcholine receptor (α7nAChR) in human airway smooth muscle

Diseases such as asthma are exacerbated by inflammation, cigarette smoke and even nicotine delivery devices such as e-cigarettes. However, there is currently little information on how nicotine affects airways, particularly in humans, and changes in the context of inflammation or asthma. Here, a longstanding assumption is that airway smooth muscle (ASM) that is key to bronchoconstriction has muscarinic receptors while nicotinic receptors (nAChRs) are only on airway neurons. In this study, we tested the hypothesis that human ASM expresses α7nAChR and explored its profile in inflammation and asthma using ASM of non-asthmatics vs. mild-moderate asthmatics. mRNA and western analysis showed the α7 subunit is most expressed in ASM cells and further increased in asthmatics and smokers, or by exposure to nicotine, cigarette smoke or pro-inflammatory cytokines TNFα and IL-13. In these effects, signaling pathways relevant to asthma such as NFκB, AP-1 and CREB are involved. These novel data demonstrate the expression of α7nAChR in human ASM and suggest their potential role in asthma pathophysiology in the context of nicotine exposure.

The Stress of Lung Aging: Endoplasmic Reticulum and Senescence Tête-à-Tête

Beyond the structural changes, features including the dysregulation of endoplasmic reticulum (ER) stress response and increased senescence characterize the lung aging. ER stress response and senescence have been reported to be induced by factors like cigarette smoke. Therefore, deciphering the mechanisms underlying ER and senescent pathways interaction has become a challenge. In this review we highlight the known and unknown regarding ER stress response and senescence and their cross talk in aged lung.

Calcium-Sensing Receptor Contributes to Hyperoxia Effects on Human Fetal Airway Smooth Muscle

Supplemental O₂ (hyperoxia), necessary for maintenance of oxygenation in premature infants, contributes to neonatal and pediatric airway diseases including asthma. Airway smooth muscle (ASM) is a key resident cell type, responding to hyperoxia with increased contractility and remodeling [proliferation, extracellular matrix (ECM) production], making the mechanisms underlying hyperoxia effects on ASM significant. Recognizing that fetal lungs experience a higher extracellular Ca²⁺ ([Ca²⁺]_o) environment, we previously reported that the calcium sensing receptor (CaSR) is expressed and functional in human fetal ASM (fASM). In this study, using fASM cells from 18 to 22 week human fetal lungs, we tested the hypothesis that CaSR contributes to hyperoxia effects on developing ASM. Moderate hyperoxia (50% O₂) increased fASM CaSR expression. Fluorescence [Ca²⁺]_i imaging showed hyperoxia increased [Ca²⁺]_i responses to histamine that was more sensitive to altered [Ca²⁺]_o, and promoted IP₃ induced intracellular Ca²⁺ release and store-operated Ca²⁺ entry: effects blunted by the calcilytic NPS2143. Hyperoxia did not significantly increase mitochondrial calcium which was regulated by CaSR irrespective of oxygen levels. Separately, fASM cell proliferation and ECM deposition (collagens but not fibronectin) showed sensitivity to [Ca²⁺]_o that was enhanced by hyperoxia, but blunted by NPS2143. Effects of hyperoxia involved p42/44 ERK via CaSR and HIF1α. These results demonstrate functional CaSR in developing ASM that contributes to hyperoxia-induced contractility and remodeling that may be relevant to perinatal airway disease.

Cellular clocks in hyperoxia effects on [Ca2+]i regulation in developing human airway smooth muscle

Supplemental O2 (hyperoxia) is necessary for preterm infant survival but is associated with development of bronchial airway hyperreactivity and childhood asthma. Understanding early mechanisms that link hyperoxia to altered airway structure and function are key to developing advanced therapies. We previously showed that even moderate hyperoxia (50% O2) enhances intracellular calcium ([Ca2+]i) and proliferation of human fetal airway smooth muscle (fASM), thereby facilitating bronchoconstriction and remodeling. Here, we introduce cellular clock biology as a novel mechanism linking early oxygen exposure to airway biology. Peripheral, intracellular clocks are a network of transcription-translation feedback loops that produce circadian oscillations with downstream targets highly relevant to airway function and asthma. Premature infants suffer circadian disruption whereas entrainment strategies improve outcomes, highlighting the need to understand relationships between clocks and developing airways. We hypothesized that hyperoxia impacts clock function in fASM and that the clock can be leveraged to attenuate deleterious effects of O2 on the developing airway. We report that human fASM express core clock machinery (PER1, PER2, CRY1, ARNTL/BMAL1, CLOCK) that is responsive to dexamethasone (Dex) and altered by O2. Disruption of the clock via siRNA-mediated PER1 or ARNTL knockdown alters store-operated calcium entry (SOCE) and [Ca2+]i response to histamine in hyperoxia. Effects of O2 on [Ca2+]i are rescued by driving expression of clock proteins, via effects on the Ca2+ channels IP3R and Orai1. These data reveal a functional fASM clock that modulates [Ca2+]i regulation, particularly in hyperoxia. Harnessing clock biology may be a novel therapeutic consideration for neonatal airway diseases following prematurity.

Neurotrophin Regulation and Signaling in Airway Smooth Muscle

Structural and functional aspects of bronchial airways are key throughout life and play critical roles in diseases such as asthma. Asthma involves functional changes such as airway irritability and hyperreactivity, as well as structural changes such as enhanced cellular proliferation of airway smooth muscle (ASM), epithelium, and fibroblasts, and altered extracellular matrix (ECM) and fibrosis, all modulated by factors such as inflammation. There is now increasing recognition that disease maintenance following initial triggers involves a prominent role for resident nonimmune airway cells that secrete growth factors with pleiotropic autocrine and paracrine effects. The family of neurotrophins may be particularly relevant in this regard. Long recognized in the nervous system, classical neurotrophins such as brain-derived neurotrophic factor (BDNF) and nonclassical ligands such as glial-derived neurotrophic factor (GDNF) are now known to be expressed and functional in non-neuronal systems including lung. However, the sources, targets, regulation, and downstream effects are still under investigation. In this chapter, we discuss current state of knowledge and future directions regarding BDNF and GDNF in airway physiology and on pathophysiological contributions in asthma.

Sex steroids skew ACE2 expression in human airway: a contributing factor to sex differences in COVID-19?

The incidence, severity, and mortality of ongoing coronavirus infectious disease 19 (COVID-19) is greater in men compared with women, but the underlying factors contributing to this sex difference are still being explored. In the current study, using primary isolated human airway smooth muscle (ASM) cells from normal males versus females as a model, we explored the effect of estrogen versus testosterone in modulating the expression of angiotensin converting enzyme 2 (ACE2), a cell entry point for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Using confocal imaging, we found that ACE2 is expressed in human ASM. Furthermore, Western analysis of ASM cell lysates showed significantly lower ACE2 expression in females compared with males at baseline. In addition, ASM cells exposed to estrogen and testosterone for 24 h showed that testosterone significantly upregulates ACE2 expression in both males and females, whereas estrogen downregulates ACE2, albeit not significant compared with vehicle. These intrinsic and sex steroids induced differences may help explain sex differences in COVID-19.

Selective YAP/TAZ inhibition in fibroblasts via dopamine receptor D1 agonism reverses fibrosis

Tissue fibrosis is characterized by uncontrolled deposition and diminished clearance of fibrous connective tissue proteins, ultimately leading to organ scarring. Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) have recently emerged as pivotal drivers of mesenchymal cell activation in human fibrosis. Therapeutic strategies inhibiting YAP and TAZ have been hindered by the critical role that these proteins play in regeneration and homeostasis in different cell types. Here, we find that the Gα_s-coupled dopamine receptor D1 (DRD1) is preferentially expressed in lung and liver mesenchymal cells relative to other resident cells of these organs. Agonism of DRD1 selectively inhibits YAP/TAZ function in mesenchymal cells and shifts their phenotype from profibrotic to fibrosis resolving, reversing in vitro extracellular matrix stiffening and in vivo tissue fibrosis in mouse models. Aromatic l-amino acid decarboxylase [DOPA decarboxylase (DDC)], the enzyme responsible for the final step in biosynthesis of dopamine, is decreased in the lungs of subjects with idiopathic pulmonary fibrosis, and its expression inversely correlates with disease severity, consistent with an endogenous protective role for dopamine signaling that is lost in pulmonary fibrosis. Together, these findings establish a pharmacologically tractable and cell-selective approach to targeting YAP/TAZ via DRD1 that reverses fibrosis in mice.

Noncanonical role for Ku70/80 in the prevention of allergic airway inflammation via maintenance of airway epithelial cell organelle homeostasis

Airway epithelial homeostasis is under constant threat due to continuous exposure to the external environment, and abnormally robust sensitivity to external stimuli is critical to the development of airway diseases, including asthma. Ku is a key nonhomologous end-joining DNA repair protein with diverse cellular functions such as VDJ recombination and telomere length maintenance. Here, we show a novel function of Ku in alleviating features of allergic airway inflammation via the regulation of mitochondrial and endoplasmic reticulum (ER) stress. We first determined that airway epithelial cells derived from both asthmatic lungs and murine asthma models demonstrate increased expression of 8-hydroxy-deoxyguanosine (8-OHdG), a marker of oxidative DNA damage. Ku protein expression was dramatically reduced in the bronchial epithelium of patients with asthma as well as in human bronchial epithelial cells exposed to oxidative stress. Knockdown of Ku70 or Ku80 in naïve mice elicited mitochondrial collapse or ER stress, leading to bronchial epithelial cell apoptosis and spontaneous development of asthma-like features, including airway hyperresponsiveness, airway inflammation, and subepithelial fibrosis. These findings demonstrate an essential noncanonical role for Ku proteins in asthma pathogenesis, likely via maintenance of organelle homeostasis. This novel function of Ku proteins may also be important in other disease processes associated with organelle stress.

Contributions of IL-33 in Non-hematopoietic Lung Cells to Obstructive Lung Disease

Interleukin (IL)-33 plays important roles in pulmonary immune responses and lung diseases including asthma and chronic obstructive pulmonary disease (COPD). There is substantial interest in identifying and characterizing cellular sources vs. targets of IL-33, and downstream signaling pathways involved in disease pathophysiology. While epithelial and immune cells have largely been the focus, in this review, we summarize current knowledge of expression, induction, and function of IL-33 and its receptor ST2 in non-hematopoietic lung cells in the context of health and disease. Under basal conditions, epithelial cells and endothelial cells are thought to be the primary resident cell types that express high levels of IL-33 and serve as ligand sources compared to mesenchymal cells (smooth muscle cells and fibroblasts). Under inflammatory conditions, IL-33 expression is increased in most non-hematopoietic lung cells, including epithelial, endothelial, and mesenchymal cells. In comparison to its ligand, the receptor ST2 shows low expression levels at baseline but similar to IL-33, ST2 expression is upregulated by inflammation in these non-hematopoietic lung cells which may then participate in chronic inflammation both as sources and autocrine/paracrine targets of IL-33. Downstream effects of IL-33 may occur via direct receptor activation or indirect interactions with the immune system, overall contributing to lung inflammation, airway hyper-responsiveness and remodeling (proliferation and fibrosis). Accordingly from a therapeutic perspective, targeting IL-33 and/or its receptor in non-hematopoietic lung cells becomes relevant.

It's about time: clocks in the developing lung

The discovery of peripheral intracellular clocks revealed circadian oscillations of clock genes and their targets in all cell types, including those in the lung, sparking exploration of clocks in lung disease pathophysiology. While the focus has been on the role of these clocks in adult airway diseases, clock biology is also likely to be important in perinatal lung development, where it has received far less attention. Historically, fetal circadian rhythms have been considered irrelevant owing to lack of external light exposure, but more recent insights into peripheral clock biology raise questions of clock emergence, its concordance with tissue-specific structure/function, the interdependence of clock synchrony and functionality in perinatal lung development, and the possibility of lung clocks in priming the fetus for postnatal life. Understanding the perinatal molecular clock may unravel mechanistic targets for chronic airway disease across the lifespan. With current research providing more questions than answers, it is about time to investigate clocks in the developing lung.

Estrogen regulates the expression of SARS-CoV-2 receptor ACE2 in differentiated airway epithelial cells

There is marked sexual dimorphism in the current coronavirus disease 2019 (COVID-19) pandemic. Here we report that estrogen can regulate the expression of angiotensin-converting enzyme 2 (ACE2), a key component for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) cell entry, in differentiated airway epithelial cells. Further studies are required to elucidate the mechanisms by which sex steroids regulate SARS-CoV-2 infectivity.

Class C GPCRs in the airway

Understanding and targeting of GPCRs remain a critical aspect of airway pharmacology and therapeutics for diseases such as asthma or COPD. Most attention has been on the large Class A GPCRs towards improved bronchodilation and blunting of remodeling. Better known in the central or peripheral nervous system, there is increasing evidence that Class C GPCRs which include metabotropic glutamate and GABA receptors, the calcium sensing receptor, sweet/umami taste receptors and a number of orphan receptors, can contribute to airway structure and function. In this review, we will summarize current state of knowledge regarding the pharmacology of Class C GPCRs, their expression and potential functions in the airways, and the application of pharmacological agents targeting this group in the context of airway diseases.

Cholinergic neuroplasticity in asthma driven by TrkB signaling

Parasympathetic neurons in the airways control bronchomotor tone. Increased activity of cholinergic neurons are mediators of airway hyperresponsiveness (AHR) in asthma, however, mechanisms are not elucidated. We describe remodeling of the cholinergic neuronal network in asthmatic airways driven by brain‐derived neurotrophic factor (BDNF) and Tropomyosin receptor kinase B (TrkB). Human bronchial biopsies were stained for cholinergic marker vesicular acetylcholine transporter (VAChT). Human lung gene expression and single nucleotide polymorphisms (SNP) in neuroplasticity‐related genes were compared between asthma and healthy patients. Wild‐type (WT) and mutated TrkB knock‐in mice (Ntrk2tm1Ddg/J) with impaired BDNF signaling were chronically exposed to ovalbumin (OVA). Neuronal VAChT staining and airway narrowing in response to electrical field stimulation in precision cut lung slices (PCLS) were assessed. Increased cholinergic fibers in asthmatic airway biopsies was found, paralleled by increased TrkB gene expression in human lung tissue, and SNPs in the NTRK2 [TrkB] and BDNF genes linked to asthma. Chronic allergen exposure in mice resulted in increased density of cholinergic nerves, which was prevented by inhibiting TrkB. Increased nerve density resulted in AHR in vivo and in increased nerve‐dependent airway reactivity in lung slices mediated via TrkB. These findings show cholinergic neuroplasticity in asthma driven by TrkB signaling and suggest that the BDNF‐TrkB pathway may be a potential target.

YAP/TAZ are Activated by Mechanical and Hormonal Stimuli in Myometrium and Exhibit Increased Baseline Activation in Uterine Fibroids

Uterine fibroids (UFs) are benign myometrial neoplasms. The mechanical environment activates signaling through the Hippo pathway effectors Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding domain (TAZ) in other fibrotic disorders. Here, we assess the differences in YAP/TAZ responsiveness to signals in UF compared with myometrium (Myo). Matched samples of UF and Myo were collected. Atomic force microscopy (AFM) was used to determine in situ stiffness. Cells were plated sparsely on hydrogels or at confluence. Ten nanomolars of estradiol (E2) and 100 nM progesterone (P4) were used. Immunostaining for YAP/TAZ and extracellular matrix (ECM) proteins was performed. Cells were incubated with control or YAP1 (YAP)/WWTR1 (TAZ) small interfering RNA (siRNA). Real time qPCR was completed for connective tissue growth factor (CTGF). Cells were treated with verteporfin (a YAP inhibitor) or Y27632 (a ROCK inhibitor), and ECM gene expression was analyzed. Paired t test and Wilcoxon sign-rank test were used. AFM-measured tissue stiffness and YAP/TAZ nuclear localization in situ and in confluent cells were higher in UF compared with Myo (p < 0.05). Decreasing substrate stiffness reduced YAP/TAZ nuclear localization for both Myo and UF (p = 0.05). Stimulating cells with E2 or P4 increased YAP/TAZ nuclear localization, but only in Myo (p = 0.01). UFs had increased FN, COLI, and COLIII deposition. Following siRNA targeting, CTGF was found to be statistically decreased. Verteporfin treatment reduced cell survival and reduced FN deposition. Treatment with Y27632 demonstrated better cell tolerance and a reduction in ECM deposition. The mechanosensitive pathway may be linked to YAP/TAZ function and involved in transducing fibroid growth.

Upregulation of airway smooth muscle calcium-sensing receptor by low-molecular-weight hyaluronan

We investigated the mechanisms involved in the development of airway hyperresponsiveness (AHR) following exposure of mice to halogens. Male mice (C57BL/6; 20-25 g) exposed to either bromine (Br2) or Cl2 (600 or 400 ppm, respectively, for 30 min) developed AHR 24 h after exposure. Nifedipine (5 mg/kg body wt; an L-type calcium channel blocker), administered subcutaneously after Br2 or Cl2 exposure, produced higher AHR compared with Br2 or Cl2 alone. In contrast, diltiazem (5 mg/kg body wt; a nondihydropyridine L-type calcium channel blocker) decreased AHR to control (air) values. Exposure of immortalized human airway smooth muscle cells (hASMC) to Br2 resulted in membrane potential depolarization (Vm Air: 62 ± 3 mV; 3 h post Br2:-45 ± 5 mV; means ± 1 SE; P < 0.001), increased intracellular [Ca2+]i, and increased expression of the calcium-sensing receptor (Ca-SR) protein. Treatment of hASMC with a siRNA against Ca-SR significantly inhibited the Br2 and nifedipine-induced Vm depolarization and [Ca2+]i increase. Intranasal administration of an antagonist to Ca-SR in mice postexposure to Br2 reversed the effects of Br2 and nifedipine on AHR. Incubation of hASMC with low-molecular-weight hyaluronan (LMW-HA), generated by exposing high-molecular-weight hyaluronan (HMW-HA) to Br2, caused Vm depolarization, [Ca2+]i increase, and Ca-SR expression to a similar extent as exposure to Br2 and Cl2. The addition of HMW-HA to cells or mice exposed to Br2, Cl2, or LMW-HA reversed these effects in vitro and improved AHR in vivo. We conclude that detrimental effects of halogen exposure on AHR are mediated via activation of the Ca-SR by LMW-HA.

Hyperoxia-induced Cellular Senescence in Fetal Airway Smooth Muscle Cells

Supplemental O₂ (hyperoxia; 30-90% O₂) is a necessary intervention for premature infants, but it contributes to development of neonatal and pediatric asthma, necessitating better understanding of contributory mechanisms in hyperoxia-induced changes to airway structure and function. In adults, environmental stressors promote formation of senescent cells that secrete factors (senescence-associated secretory phenotype), which can be inflammatory and have paracrine effects that enhance chronic lung diseases. Hyperoxia-induced changes in airway structure and function are mediated in part by effects on airway smooth muscle (ASM). In the present study, using human fetal ASM cells as a model of prematurity, we ascertained the effects of clinically relevant moderate hyperoxia (40% O₂) on cellular senescence. Fetal ASM exposed to 40% O₂ for 7 days exhibited elevated concentrations of senescence-associated markers, including β-galactosidase; cell cycle checkpoint proteins p16, p21, and p-p53; and the DNA damage marker p-γH2A.X (phosphorylated γ-histone family member X). The combination of dasatinib and quercetin, compounds known to eliminate senescent cells (senolytics), reduced the number of hyperoxia-exposed β-galactosidase-, p21-, p16-, and p-γH2A.X-positive ASM cells. The senescence-associated secretory phenotype profile of hyperoxia-exposed cells included both profibrotic and proinflammatory mediators. Naive ASM exposed to media from hyperoxia-exposed senescent cells exhibited increased collagen and fibronectin and higher contractility. Our data show that induction of cellular senescence by hyperoxia leads to secretion of inflammatory factors and has a functional effect on naive ASM. Cellular senescence in the airway may thus contribute to pediatric airway disease in the context of sequelae of preterm birth.

Airway Innervation and Plasticity in Asthma

Airway nerves represent a mechanistically and therapeutically important aspect that requires better highlighting in the context of diseases such as asthma. Altered structure and function (plasticity) of afferent and efferent airway innervation can contribute to airway diseases. We describe established anatomy, current understanding of how plasticity occurs, and contributions of plasticity to asthma, focusing on target-derived growth factors (neurotrophins). Perspectives toward novel treatment strategies and future research are provided.

Differential estrogen-receptor activation regulates extracellular matrix deposition in human airway smooth muscle remodeling via NF-κB pathway

Altered airway smooth muscle (ASM) mass and extracellular matrix (ECM) deposition in airways are characteristic features of remodeling in asthma. Increased ECM production modulates ASM cell proliferation and leads to airway remodeling. Our previous studies showed that ASM from patients with asthma exhibited increased expression of estrogen receptor (ER)-β, which upon activation down-regulated ASM proliferation, implicating an important role for estrogen signaling in airway physiology. There is no current information on the effect of differential ER activation on ECM production. In this study, we evaluated the effect of ER-α vs. ER-β activation on ECM production, deposition, and underlying pathways. Primary human ASM cells isolated from asthmatics and nonasthmatics were treated with E₂, an ER-α agonist [propylpyrazoletriol (PPT)], and an ER-β agonist [WAY-200070 (WAY)] with TNF-α or platelet-derived growth factor (PDGF) followed by evaluation of ECM production and deposition. Expression of proteins and genes corresponding to ECM were measured using Western blotting and quantitative RT-PCR with subsequent matrix metalloproteinase (MMP) activity. Molecular mechanisms of ER activation in regulating ECM were evaluated by luciferase reporter assays for activator protein 1 (AP-1) and NF-κB. TNF-α or PDGF significantly (P < 0.001) increased ECM deposition and MMP activity in human ASM cells, which was significantly reduced with WAY treatment but not with PPT. Furthermore, TNF-α- or PDGF-induced ECM gene expression in ASM cells was significantly reduced with WAY (P < 0.001). Moreover, WAY significantly down-regulated the activation of NF-κB (P < 0.001) and AP-1 (P < 0.01, P < 0.05) in ASM cells from asthmatics and nonasthmatics. Overall, we demonstrate differential ER signaling in controlling ECM production and deposition. Activation of ER-β diminishes ECM deposition via suppressing the NF-κB pathway activity and might serve as a novel target to blunt airway remodeling.-Ambhore, N. S., Kalidhindi, R. S. R., Pabelick, C. M., Hawse, J. R., Prakash, Y. S., Sathish, V. Differential estrogen-receptor activation regulates extracellular matrix deposition in human airway smooth muscle remodeling via NF-κB pathway.

Estrogen receptors differentially regulate intracellular calcium handling in human nonasthmatic and asthmatic airway smooth muscle cells

Asthma is defined as chronic inflammation of the airways and is characterized by airway remodeling, hyperresponsiveness, and acute bronchoconstriction of airway smooth muscle (ASM) cells. Clinical findings suggest a higher incidence and severity of asthma in adult women, indicating a concrete role of sex steroids in modulating the airway tone. Estrogen, a major female sex steroid mediates its role through estrogen receptors (ER) ERα and ERβ, which are shown to be expressed in human ASM, and their expression is upregulated in lung inflammation and asthma. Previous studies suggested rapid, nongenomic signaling of estrogen via ERs reduces intracellular calcium ([Ca²⁺]_i), thereby promoting relaxation of ASM. However, long-term ER activation on [Ca²⁺]_i regulation in human ASM during inflammation or in asthma is still not known. In Fura-2-loaded nonasthmatic and asthmatic human ASM cells, we found that prolonged (24 h) exposure to ERα agonist (PPT) increased [Ca²⁺]_i response to histamine, whereas ERβ activation (WAY) led to decreased [Ca²⁺] compared with vehicle. This was further confirmed by ER overexpression and knockdown studies using various bronchoconstrictor agents. Interestingly, ERβ activation was more effective than 17β-estradiol in reducing [Ca²⁺]_i responses in the presence of TNF-α or IL-13, while no observable changes were noticed with PPT in the presence of either cytokine. The [Ca²⁺]_i-reducing effects of ERβ were mediated partially via L-type calcium channel inhibition and increased Ca²⁺ sequestration by sarcoplasmic reticulum_. Overall, these data highlight the differential signaling of ERα and ERβ in ASM during inflammation. Specific ERβ activation reduces [Ca²⁺]_i in the inflamed ASM cells and is likely to play a crucial role in regulating ASM contractility, thereby relaxing airways.

Female Sex and Gender in Lung/Sleep Health and Disease. Increased Understanding of Basic Biological, Pathophysiological, and Behavioral Mechanisms Leading to Better Health for Female Patients with Lung Disease

Female sex/gender is an undercharacterized variable in studies related to lung development and disease. Notwithstanding, many aspects of lung and sleep biology and pathobiology are impacted by female sex and female reproductive transitions. These may manifest as differential gene expression or peculiar organ development. Some conditions are more prevalent in women, such as asthma and insomnia, or, in the case of lymphangioleiomyomatosis, are seen almost exclusively in women. In other diseases, presentation differs, such as the higher frequency of exacerbations experienced by women with chronic obstructive pulmonary disease or greater cardiac morbidity among women with sleep-disordered breathing. Recent advances in -omics and behavioral science provide an opportunity to specifically address sex-based differences and explore research needs and opportunities that will elucidate biochemical pathways, thus enabling more targeted/personalized therapies. To explore the status of and opportunities for research in this area, the NHLBI, in partnership with the NIH Office of Research on Women's Health and the Office of Rare Diseases Research, convened a workshop of investigators in Bethesda, Maryland on September 18 and 19, 2017. At the workshop, the participants reviewed the current understanding of the biological, behavioral, and clinical implications of female sex and gender on lung and sleep health and disease, and formulated recommendations that address research gaps, with a view to achieving better health outcomes through more precise management of female patients with nonneoplastic lung disease. This report summarizes those discussions.

Moderate hyperoxia induces senescence in developing human lung fibroblasts

Hyperoxia exposure in premature infants increases the risk of subsequent lung diseases, such as asthma and bronchopulmonary dysplasia. Fibroblasts help maintain bronchial and alveolar integrity. Thus, understanding mechanisms by which hyperoxia influences fibroblasts is critical. Cellular senescence is increasingly recognized as important to the pathophysiology of multiple diseases. We hypothesized that clinically relevant moderate hyperoxia (<50% O₂) induces senescence in developing fibroblasts. Using primary human fetal lung fibroblasts, we investigated effects of 40% O₂ on senescence, endoplasmic reticulum (ER) stress, and autophagy pathways. Fibroblasts were exposed to 21% or 40% O₂ for 7 days with etoposide as a positive control to induce senescence, evaluated by morphological changes, β-galactosidase activity, and DNA damage markers. Senescence-associated secretory phenotype (SASP) profile of inflammatory and profibrotic markers was further assessed. Hyperoxia decreased proliferation but increased cell size. SA-β-gal activity and DNA damage response, cell cycle arrest in G₂/M phase, and marked upregulation of phosphorylated p53 and p21 were noted. Reduced autophagy was noted with hyperoxia. mRNA expression of proinflammatory and profibrotic factors (TNF-α, IL-1, IL-8, MMP3) was elevated by hyperoxia or etoposide. Hyperoxia increased several SASP factors (PAI-1, IL1-α, IL1-β, IL-6, LAP, TNF-α). The secretome of senescent fibroblasts promoted extracellular matrix formation by naïve fibroblasts. Overall, we demonstrate that moderate hyperoxia enhances senescence in primary human fetal lung fibroblasts with reduced autophagy but not enhanced ER stress. The resulting SASP is profibrotic and may contribute to abnormal repair in the lung following hyperoxia.