Emerging concepts in smooth muscle contributions to airway structure and function: implications for health and disease

Integrative Roles of Pro-Inflammatory Cytokines on Airway Smooth Muscle Structure and Function in Asthma

Asthma has become more appreciated for its heterogeneity with studies identifying type 2 and non-type 2 phenotypes/endotypes that ultimately lead to airflow obstruction, airway hyperresponsiveness, and remodeling. The pro-inflammatory environment in asthma influences airway smooth muscle (ASM) structure and function. ASM has a vast repertoire of inflammatory receptors that, upon activation, contribute to prominent features in asthma, notably immune cell recruitment and activation, hypercontractility, proliferation, migration, and extracellular matrix protein deposition. These pro-inflammatory responses in ASM can be mediated by both type 2 (e.g., IL-4, IL-13, and TSLP) and non-type 2 (e.g., TNFα, IFNγ, IL-17A, and TGFβ) cytokines, highlighting roles for ASM in type 2 and non-type 2 asthma phenotypes/endotypes. In recent years, there has been considerable advances in understanding how pro-inflammatory cytokines promote ASM dysfunction and impair responsiveness to asthma therapy, corticosteroids and long-acting β2-adrenergic receptor agonists (LABAs). Transcriptomic analyses on human ASM cells and tissues have expanded our knowledge in this area but have also raised new questions regarding ASM and its role in asthma. In this review, we discuss how pro-inflammatory cytokines, corticosteroids, and LABAs affect ASM structure and function, with particular focus on changes in gene expression and transcriptional programs in type 2 and non-type 2 asthma.

Nicotine-Induced Endoplasmic Reticulum Stress and Airway Smooth Muscle Cell Proliferation Is Mediated by α7nAChR and Chaperones-RIC-3 and TMEM35

Nicotine exposure in the context of smoking or vaping worsens airway function. Although nicotinic acetylcholine receptors (nAChRs) are commonly thought to exert effects through the peripheral nervous system, we previously showed that airway smooth muscle (ASM) expresses them, particularly α7 subtype nAChR (α7nAChR), with functional effects on contractility and metabolism. However, the mechanisms of nAChR regulation and downstream effects in ASM are not fully understood. Using ASM cells from people without asthma versus people with mild to moderate asthma, we tested the hypothesis that nAChR-specific endoplasmic reticulum (ER) chaperones, resistance to inhibitors of cholinesterase 3 (RIC-3) and transmembrane protein 35A (TMEM35A) promote cell surface localization of α7nAChR with downstream influence on its functionality: effects exacerbated by inflammation. We found that mild to moderate asthma and exposure to proinflammatory cytokines relevant to asthma promote chaperone and α7nAChR expression in ASM. Downstream, ER stress was linked to nicotine/α7nAChR signaling, where RIC-3 and TMEM35 regulate nicotine-induced ER stress, intracellular Ca2+ regulation, and ASM cell proliferation. Overall, our data highlight the importance α7nAChR chaperones in mediating and modulating nicotine effects in ASM toward airway contractility and remodeling.

Nanoparticles to target asthma

Asthma is a heterogeneous chronic lung disease that affects nearly 340 million people globally. Airway hyperresponsiveness, remodeling (thickening and fibrosis), and mucus hypersecretion are some hallmarks of asthma. With several current treatments having serious side effects from long-term use and a proportion of patients with uncontrolled asthma, there is an urgent need for new therapies. With an increasing understanding of asthma pathophysiology, there is a recognized need to target therapies to specific cell types of the airway, which necessitates the identification of delivery systems that can overcome increased mucus and thickened airways. Nanoparticles (NPs) that are highly customizable (material, size, charge, and surface modification) are a potential solution for delivery systems of a wide variety of cargoes (nucleic acids, proteins, and/or small molecules), as well as sole therapeutics for asthma. However, there is a need to consider the safety of the NPs in terms of potential for inflammation, toxicity, nonspecific targets, and accumulation in organs. Ongoing clinical trials using NPs, some FDA-approved for therapeutics in other diseases, provide confidence regarding the potential safety and efficacy of NPs in asthma treatment. This review highlights the current state of the use of NPs in asthma, identifying opportunities for further improvements in NP design and utilization for targeting this chronic lung disease.

Expression of Semaphorin3E/PlexinD1 in human airway smooth muscle cells of patients with COPD

Semaphorin3E (Sema3E) is a member of axon guidance proteins that have emerged recently as essential regulators of cell migration and proliferation. It binds to PlexinD1 with high affinity and is expressed in different cell types, including immune, cancer, and epithelial cells. Recent work in our lab has revealed a critical immunoregulatory role of Sema3E in experimental allergic asthma; however, its role in chronic obstructive pulmonary disease (COPD) remains unclear. This study aimed to investigate the expression of Sema3E and its receptor, PlexinD1, in the airways of patients with COPD and whether Sema3E regulates airway smooth muscle (ASM) cell proliferation, a key feature of airway remodeling in COPD. We first demonstrate that human ASM cells obtained from COPD express Sema3E and PlexinD1 at both mRNA and protein levels. Also, bronchial sections from patients with COPD displayed immunoreactivity of Sema3E and its receptor PlexinD1, suggestive of functional contribution of Sema3E in airway remodeling. In contrast to ASM cells from healthy donors, Sema3E did not inhibit the platelet-derived growth factor (PDGF) induced cell proliferation in ASM cells of patients with COPD that were consistent with the binding of endogenous Sema3E to its receptors on the cell surface and the expression and release of p61KDa-Sema3E isoform. Our results support the Sema3E-PlexinD1 axis involvement in COPD airway smooth muscle remodeling.NEW & NOTEWORTHY Semaphorin3E (Sema3E), a protein guiding cell movement, is found in various cell types like neural, immune, cancer, and epithelial cells. This study examines Sema3E in chronic obstructive pulmonary disease (COPD) airways. In patients with COPD, airway smooth muscle cells express Sema3E and its receptor PlxD1. Unlike healthy cells, Sema3E does not hinder cell proliferation in COPD, indicating involvement in airway remodeling. These findings highlight the Sema3E-PlxD1 axis in COPD airway changes.

Innate players in Th2 and non-Th2 asthma: emerging roles for the epithelial cell, mast cell, and monocyte/macrophage network

Asthma is one of the most common chronic respiratory diseases and is characterized by airway inflammation, increased mucus production, and structural changes in the airways. Recently, there is increasing evidence that the disease is much more heterogeneous than expected, with several distinct asthma endotypes. Based on the specificity of T cells as the best-known driving force in airway inflammation, bronchial asthma is categorized into T helper cell 2 (Th2) and non-Th2 asthma. The most studied effector cells in Th2 asthma include T cells and eosinophils. In contrast to Th2 asthma, much less is known about the pathophysiology of non-Th2 asthma, which is often associated with treatment resistance. Besides T cells, the interaction of myeloid cells such as monocytes/macrophages and mast cells with the airway epithelium significantly contributes to the pathogenesis of asthma. However, the underlying molecular regulation and particularly the specific relevance of this cellular network in certain asthma endotypes remain to be understood. In this review, we summarize recent findings on the regulation of and complex interplay between epithelial cells and the "nonclassical" innate effector cells mast cells and monocytes/macrophages in Th2 and non-Th2 asthma with the ultimate goal of providing the rationale for future research into targeted therapy regimens.

Effects of glial-derived neurotrophic factor on remodeling and mitochondrial function in human airway smooth muscle cells

Airway smooth muscle (ASM) cells play important roles in airway remodeling of asthma. Our previous studies show that in vivo administration of glial-derived neurotrophic factor (GDNF) in mice induces thickening and collagen deposition in bronchial airways, whereas chelation of GDNF by GFRα1-Fc attenuates airway remodeling in the context of allergen exposure. To determine whether GDNF has direct effects on ASM, in this study, we examined GDNF in ASM cells from normal versus asthmatic humans. We found that GDNF treatment of human ASM cells had only minor effects on cell proliferation and migration, intracellular expression or extracellular deposition of collagen I (COL1), collagen III (COL3), and fibronectin. Endoplasmic reticulum (ER) stress response and mitochondrial function have been implicated in asthma. We investigated whether GDNF regulates these aspects in human ASM. We found that GDNF treatment did not affect ER stress protein expression in normal or asthmatic cells. However, GDNF treatment impaired mitochondrial morphology in ASM but without significant effects on mitochondrial respiration. Thus, it is likely that in vivo effects of GDNF on airway remodeling per se involve cell types other than those on ASM, and thus ASM may serve more as a source of GDNF rather than a target.NEW & NOTEWORTHY Our previous study suggests that glial-derived neurotrophic factor (GDNF) is involved in allergen-induced airway hyperreactivity and remodeling in vivo. Here, we show that GDNF has no direct effects in remodeling of human airway smooth muscle (ASM) but GDNF dysregulates mitochondrial morphology in human ASM in the context of asthma.

Kiss1 receptor knockout exacerbates airway hyperresponsiveness and remodeling in a mouse model of allergic asthma

BACKGROUND

In asthma, sex-steroids signaling is recognized as a critical regulator of disease pathophysiology. However, the paradoxical role of sex-steroids, especially estrogen, suggests that an upstream mechanism or even independent of estrogen plays an important role in regulating asthma pathophysiology. In this context, in our previous studies, we explored kisspeptin (Kp) and its receptor Kiss1R's signaling in regulating human airway smooth muscle cell remodeling in vitro and airway hyperresponsiveness (AHR) in vivo in a mouse (wild-type, WT) model of asthma. In this study, we evaluated the effect of endogenous Kp in regulating AHR and remodeling using Kiss1R knockout (Kiss1R-/-) mice.

METHODS

C57BL/6J WT (Kiss1R+/+) and Kiss1R-/- mice, both male and female, were intranasally challenged with mixed-allergen (MA) and/or phosphate-buffered saline (PBS). We used flexiVent analysis to assess airway resistance (Rrs), elastance (Ers), and compliance (Crs). Following this, broncho-alveolar lavage (BAL) was performed for differential leukocyte count (DLC) and cytokine analysis. Histology staining was performed using hematoxylin and eosin (H&E) for morphological analysis and Masson's Trichrome (MT) for collagen deposition. Additionally, lung sections were processed for immunofluorescence (IF) of Ki-67, α-smooth muscle actin (α-SMA), and tenascin-c.

RESULTS

Interestingly, the loss of Kiss1R exacerbated lung function and airway contractility in mice challenged with MA, with more profound effects in Kiss1R-/- female mice. MA-challenged Kiss1R-/- mice showed a significant increase in immune cell infiltration and proinflammatory cytokine levels. Importantly, the loss of Kiss1R aggravated Th2/Th17 biased cytokines in MA-challenged mice. Furthermore, histology of lung sections from Kiss1R-/- mice showed increased collagen deposition on airway walls and mucin production in airway cells compared to Kiss1R+/+ mice. In addition, immunofluorescence analysis showed loss of Kiss1R significantly aggravated airway remodeling and subsequently AHR.

CONCLUSIONS

These findings demonstrate the importance of inherent Kiss1R signaling in regulating airway inflammation, AHR, and remodeling in the pathophysiology of asthma.

Toll-like receptor 4 mediated autophagy regulates airway smooth muscle cells behavior

OBJECTIVES

Airway remodeling, a prominent feature of asthma, involves aberrant proliferation, apoptosis, and migration of airway smooth muscle cells (ASMCs). Toll-like receptors (TLRs) are implicated in the regulation of the autophagy pathway. In this study, we aimed to investigate the influence of Toll-like receptor 4 (TLR4) on autophagy and its underlying mechanism in ASMC proliferation, apoptosis, and migration.

METHODS

Histopathological changes in the lungs of asthmatic mice assessed by Hematoxylin-Eosin (HE) and Masson staining. Cell proliferation, apoptosis and migration were evaluated utilizing CCK8, Edu, Flow cytometry and wound heading assays. The effectiveness of siRNA transfection and the expression of TLR4, autophagy, and proliferation-related proteins after siRNA treatment were examined through RT-PCR and Western blot (WB).

CONCLUSION

We observed an increase in TLR4 expression and autophagy in a mouse model of OVA-induced asthma. In vitro experiments showed that siRNA-mediated inhibition of TLR4 suppressed autophagy, proliferation, and migration of ASMCs, whereas TLR4 activation by lipopolysaccharide (LPS) had the opposite effect. Furthermore, the autophagy inhibitor 3-Methyladenine (3MA) inhibited ASMCs proliferation and migration while promoting apoptosis. Significantly, our study demonstrated that autophagy inhibition reversed the promotion effect of LPS on ASMC proliferation and migration. These findings suggest that TLR4 may modulate ASMC behavior through the regulation of autophagy.

The aging lung: microenvironment, mechanisms, and diseases

With the development of global social economy and the deepening of the aging population, diseases related to aging have received increasing attention. The pathogenesis of many respiratory diseases remains unclear, and lung aging is an independent risk factor for respiratory diseases. The aging mechanism of the lung may be involved in the occurrence and development of respiratory diseases. Aging-induced immune, oxidative stress, inflammation, and telomere changes can directly induce and promote the occurrence and development of lung aging. Meanwhile, the occurrence of lung aging also further aggravates the immune stress and inflammatory response of respiratory diseases; the two mutually affect each other and promote the development of respiratory diseases. Explaining the mechanism and treatment direction of these respiratory diseases from the perspective of lung aging will be a new idea and research field. This review summarizes the changes in pulmonary microenvironment, metabolic mechanisms, and the progression of respiratory diseases associated with aging.

Superoxide Anions Inhibit Intracellular Calcium Response in Porcine Airway Smooth Muscle Cells

Background  Superoxide anions (O 2 - ) have multiple effects on pulmonary parenchyma altering cell proliferation, cellular metabolism, and airway smooth muscle (ASM) contraction. Intracellular calcium ([Ca 2+ ] i ) concentration plays a significant role in the regulation of ASM contraction, relaxation, proliferation, and gene expression. Objective  We investigated the effects of O 2 - on agonist-stimulated changes in [Ca 2+ ] i in ASM cells. Design/Methods  Fura-2 AM-loaded, freshly isolated porcine ASM (PASM) cells were used to examine [Ca 2+ ] i release in response to acetylcholine (ACh), histamine, endothelin, caffeine, and thapsigargin (TPG) in the presence or absence of extracellular Ca 2+ . Results  Exposure of PASM cells to xanthine and xanthine oxidase (X + XO) resulted in a time-dependent generation of O 2 - , inhibited by superoxide dismutase (SOD). Preincubating PASM cells with X + XO for 15- or 45-minute inhibited net [Ca 2+ ] i responses to ACh, histamine, caffeine, and TPG compared with control cells. Pretreating PASM cells with SOD for 30 minutes mitigated the inhibitory effect of X + XO treatment on ACh-induced Ca 2+ elevation suggesting role of O 2 - . X + XO treatment also inhibited caffeine- and TPG-induced Ca 2+ elevation suggesting effect of O 2 - on [Ca 2+ ] i release and reuptake mechanisms. Conclusion  Superoxide attenuates [Ca 2+ ] i release, reuptake, and may interfere with physiological functions of ASM cells.

Regional variations in allergen-induced airway inflammation correspond to changes in soluble guanylyl cyclase heme and expression of heme oxygenase-1

Asthma is characterized by airway remodeling and hyperreactivity. Our earlier studies determined that the nitric oxide (NO)-soluble guanylyl cyclase (sGC)-cGMP pathway plays a significant role in human lung bronchodilation. However, this bronchodilation is dysfunctional in asthma due to high NO levels, which cause sGC to become heme-free and desensitized to its natural activator, NO. In order to determine how asthma impacts the various lung segments/lobes, we mapped the inflammatory regions of lungs to determine whether such regions coincided with molecular signatures of sGC dysfunction. We demonstrate using murine models of asthma (OVA and CFA/HDM) that the inflamed segments of these murine lungs can be tracked by upregulated expression of HO1 and these regions in turn overlap with regions of heme-free sGC as evidenced by a decreased sGC-α1β1 heterodimer and an increased response to heme-independent sGC activator, BAY 60-2770, relative to naïve uninflamed regions. We also find that NO generated from iNOS upregulation in the inflamed segments has a higher impact on developing heme-free sGC as increasing iNOS activity correlates linearly with elevated heme-independent sGC activation. This excess NO works by affecting the epithelial lung hemoglobin (Hb) to become heme-free in asthma, thereby causing the Hb to lose its NO scavenging function and exposing the underlying smooth muscle sGC to excess NO, which in turn becomes heme-free. Recognition of these specific lung segments enhances our understanding of the inflamed lungs in asthma with the ultimate aim to evaluate potential therapies and suggest that regional and not global inflammation impacts lung function in asthma.

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.

Therapeutic Targets and Precision Medicine in COPD: Inflammation, Ion Channels, Both, or Neither?

The development of a wider range of therapeutic options is a key objective in drug discovery for chronic obstructive pulmonary disease (COPD). Fundamental advances in lung biology have the potential to greatly expand the number of therapeutic targets in COPD. The recently reported successful Phase 3 clinical trial of the first biologic agent for COPD, the monoclonal antibody dupilumab, adds additional support to the importance of targeting inflammatory pathways in COPD. However, numerous other cellular mechanisms are important targets in COPD therapeutics, including airway remodeling, the CFTR ion channel, and mucociliary function. Some of these emerging targets can be exploited by the expanded use of existing COPD drugs, such as roflumilast, while targeting others will require the development of novel molecular entities. The identification of additional therapeutic targets and agents has the potential to greatly expand the value of using clinical and biomarker data to classify COPD into specific subsets, each of which can be predictive of an enhanced response to specific subset(s) of targeted therapies. The author reviews established and emerging drug targets in COPD and uses this as a framework to define a novel classification of COPD based on therapeutic targets. This novel classification has the potential to enhance precision medicine in COPD patient care and to accelerate clinical trials and pre-clinical drug discovery efforts.

Oxidized Phosphatidylcholines Trigger TRPA1 and Ryanodine Receptor-dependent Airway Smooth Muscle Contraction

Asthma pathobiology includes oxidative stress that modifies cell membranes and extracellular phospholipids. Oxidized phosphatidylcholines (OxPCs) in lung lavage from allergen-challenged human participants correlate with airway hyperresponsiveness and induce bronchial narrowing in murine thin-cut lung slices. OxPCs activate many signaling pathways, but mechanisms for these responses are unclear. We hypothesize that OxPCs stimulate intracellular free Ca2+ flux to trigger airway smooth muscle contraction. Intracellular Ca2+ flux was assessed in Fura-2-loaded, cultured human airway smooth muscle cells. Oxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine (OxPAPC) induced an approximately threefold increase in 20 kD myosin light chain phosphorylation. This correlated with a rapid peak in intracellular cytoplasmic Ca2+ concentration ([Ca2+]i) (143 nM) and a sustained plateau that included slow oscillations in [Ca2+]i. Sustained [Ca2+]i elevation was ablated in Ca2+-free buffer and by TRPA1 inhibition. Conversely, OxPAPC-induced peak [Ca2+]i was unaffected in Ca2+-free buffer, by TRPA1 inhibition, or by inositol 1,4,5-triphosphate receptor inhibition. Peak [Ca2+]i was ablated by pharmacologic inhibition of ryanodine receptor (RyR) Ca2+ release from the sarcoplasmic reticulum. Inhibiting the upstream RyR activator cyclic adenosine diphosphate ribose with 8-bromo-cyclic adenosine diphosphate ribose was sufficient to abolish OxPAPC-induced cytoplasmic Ca2+ flux. OxPAPC induced ∼15% bronchial narrowing in thin-cut lung slices that could be prevented by pharmacologic inhibition of either TRPA1 or RyR, which similarly inhibited OxPC-induced myosin light chain phosphorylation in cultured human airway smooth muscle cells. In summary, OxPC mediates airway narrowing by triggering TRPA1 and RyR-mediated mobilization of intracellular and extracellular Ca2+ in airway smooth muscle. These data suggest that OxPC in the airways of allergen-challenged subjects and subjects with asthma may contribute to airway hyperresponsiveness.

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.

Effects of TRPV4 channel blocker on airway inflammation and airway defense reflexes in experimentally induced model of allergic asthma

The transient receptor potential (TRP) channels regulate physiological and pathological processes. Changes in their activity and sensitivity may be involved in the pathophysiology of asthma. The present study investigates the effect of an inhaled TRPV4 channel blocker HC-067047 in an experimental guinea pig model of ovalbumin-induced allergic asthma. We monitored the effect of 50 nM, 100 nM, and 150 nM HC-067047 concentrations on airway defense reflexes in vivo and tracheal smooth muscle contractility in vitro. The anti-inflammatory action of HC-067047 was investigated by analysis of chronic inflammation markers from lung homogenates. The results suggest that HC-067047 can suppress airway defense reflexes in vivo and acetylcholine-induced contractility in vitro. Immunological analysis revealed that TRPV4 channel blockade leads to a decrease in the levels of inflammatory cytokines. An effect on airway defence reflexes and airway inflammation was observed using tested concentrations (50 mM, 100 mM, 150 mM) of HC-067047. The effects of HC-067047 on both airway defense reflexes and inflammation underline the role of TRPV4 channels in asthma and uncover therapeutic targets for developing innovative drugs in asthma therapy.

Epithelial-Mesenchymal Transition Mechanisms in Chronic Airway Diseases: A Common Process to Target?

Epithelial-to-mesenchymal transition (EMT) is a reversible process, in which epithelial cells lose their epithelial traits and acquire a mesenchymal phenotype. This transformation has been described in different lung diseases, such as lung cancer, interstitial lung diseases, asthma, chronic obstructive pulmonary disease and other muco-obstructive lung diseases, such as cystic fibrosis and non-cystic fibrosis bronchiectasis. The exaggerated chronic inflammation typical of these pulmonary diseases can induce molecular reprogramming with subsequent self-sustaining aberrant and excessive profibrotic tissue repair. Over time this process leads to structural changes with progressive organ dysfunction and lung function impairment. Although having common signalling pathways, specific triggers and regulation mechanisms might be present in each disease. This review aims to describe the various mechanisms associated with fibrotic changes and airway remodelling involved in chronic airway diseases. Having better knowledge of the mechanisms underlying the EMT process may help us to identify specific targets and thus lead to the development of novel therapeutic strategies to prevent or limit the onset of irreversible structural changes.

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.

Kisspeptin regulates airway hyperresponsiveness and remodeling in a mouse model of asthma

Asthma is a multifactorial disease of origin characterized by airway hyperresponsiveness (AHR) and airway remodeling. Several pieces of evidence from other pathologies suggest that Kisspeptins (Kp) regulate cell proliferation, migration, and invasion, mechanisms that are highly relevant to asthma. Our recent in vitro studies show Kp-10 (active peptide of Kp), via its receptor, KISS1R, inhibits human airway smooth muscle cell proliferation. Here, we hypothesize a crucial role for Kp-10 in regulating AHR and airway remodeling in vivo. Utilizing C57BL/6J mice, we assessed the effect of chronic intranasal Kp-10 exposure on mixed allergen (MA)-induced mouse model of asthma. MA-challenged mice showed significant deterioration of lung function compared to those exposed to vehicle (DPBS); Kp-10 treatment significantly improved the MA-altered lung functions. Mice treated with Kp-10 alone did not show any notable changes in lung functions. MA-exposed mice showed a significant reduction in KISS1R expression as compared to vehicle alone. MA-challenged mice showed significant alterations in immune cell infiltration in the airways and remodeling changes. Proinflammatory cytokines were significantly increased upon MA exposure, an effect abrogated by Kp-10 treatment. Furthermore, biochemical and histological studies showed Kp-10 exposure significantly reduced MA-induced smooth muscle mass and soluble collagen in the lung. Overall, our findings highlight the effect of chronic Kp-10 exposure in regulating MA-induced AHR and remodeling. © 2023 The Pathological Society of Great Britain and Ireland.

Human Airway Basal Cells Undergo Reversible Squamous Differentiation and Reshape Innate Immunity

Histological and lineage immunofluorescence examination revealed that healthy conducting airways of humans and animals harbor sporadic poorly differentiated epithelial patches mostly in the dorsal noncartilage regions that remarkably manifest squamous differentiation. In vitro analysis demonstrated that this squamous phenotype is not due to intrinsic functional change in underlying airway basal cells. Rather, it is a reversible physiological response to persistent Wnt signaling stimulation during de novo differentiation. Squamous epithelial cells have elevated gene signatures of glucose uptake and cellular glycolysis. Inhibition of glycolysis or a decrease in glucose availability suppresses Wnt-induced squamous epithelial differentiation. Compared with pseudostratified airway epithelial cells, a cascade of mucosal protective functions is impaired in squamous epithelial cells, featuring increased epithelial permeability, spontaneous epithelial unjamming, and enhanced inflammatory responses. Our study raises the possibility that the squamous differentiation naturally occurring in healthy airways identified herein may represent "vulnerable spots" within the airway mucosa that are sensitive to damage and inflammation when confronted by infection or injury. Squamous metaplasia and hyperplasia are hallmarks of many airway diseases, thereby expanding these areas of vulnerability with potential pathological consequences. Thus, investigation of physiological and reversible squamous differentiation from healthy airway basal cells may provide critical knowledge to understand pathogenic squamous remodeling, which is often nonreversible, progressive, and hyperinflammatory.

Aging-Related Mechanisms Contribute to Corticosteroid Insensitivity in Elderly Asthma

Asthma in elderly populations is an increasing health problem that is accompanied by diminished lung function and frequent exacerbations. As potent anti-inflammatory drugs, corticosteroids are commonly used to reduce lung inflammation, improve lung function, and manage disease symptoms in asthma. Although effective for most individuals, older patients are more insensitive to corticosteroids, making it difficult to manage asthma in this population. With the number of individuals older than 65 continuing to increase, it is important to understand the distinct mechanisms that promote corticosteroid insensitivity in the aging lung. In this review, we discuss corticosteroid insensitivity in asthma with an emphasis on mechanisms that contribute to persistent inflammation and diminished lung function in older individuals.

Airway smooth muscle in contractility and remodeling of asthma: potential drug target mechanisms

INTRODUCTION

Asthma is characterized by enhanced airway contractility and remodeling where airway smooth muscle (ASM) plays a key role, modulated by inflammation. Understanding the mechanisms by which ASM contributes to these features of asthma is essential for the development of novel asthma therapies.

AREAS COVERED

Inflammation in asthma contributes to a multitude of changes within ASM including enhanced airway contractility, proliferation, and fibrosis. Altered intracellular calcium ([Ca²⁺]_i) regulation or Ca²⁺ sensitization contributes to airway hyperreactivity. Increased airway wall thickness from ASM proliferation and fibrosis contributes to structural changes seen with asthma.

EXPERT OPINION

ASM plays a significant role in multiple features of asthma. Increased ASM contractility contributes to hyperresponsiveness, while altered ASM proliferation and extracellular matrix production promote airway remodeling both influenced by inflammation of asthma and conversely even influencing the local inflammatory milieu. While standard therapies such as corticosteroids or biologics target inflammation, cytokines, or their receptors to alleviate asthma symptoms, these approaches do not address the underlying contribution of ASM to hyperresponsiveness and particularly remodeling. Therefore, novel therapies for asthma need to target abnormal contractility mechanisms in ASM and/or the contribution of ASM to remodeling, particularly in asthmatics resistant to current therapies.

Basic Science Perspective on Engineering and Modeling the Large Airways

The airway epithelium provides a physical and biochemical barrier playing a key role in protecting the lung from infiltration of pathogens and irritants and is, therefore, crucial in maintaining tissue homeostasis and regulating innate immunity. Due to continual inspiration and expiration of air during breathing, the epithelium is exposed to a plethora of environmental insults. When severe or persistent, these insults lead to inflammation and infection. The effectiveness of the epithelium as a barrier is reliant upon its capacity for mucociliary clearance, immune surveillance, and regeneration upon injury. These functions are accomplished by the cells that comprise the airway epithelium and the niche in which they reside. Engineering of new physiological and pathological models of the proximal airways requires the generation of complex structures comprising the surface airway epithelium, submucosal gland epithelium, extracellular matrix, and niche cells, including smooth muscle cells, fibroblasts, and immune cells. This chapter focuses on the structure-function relationships in the airways and the challenges of developing complex engineered models of the human airway.

MicroRNA-101-3p Suppresses mTOR and Causes Mitochondrial Fragmentation and Cell Degeneration in COPD

BACKGROUND

Cigarette smoke is assumed to cause the loss of airway wall structure in chronic obstructive pulmonary disease (COPD) by reducing airway smooth muscle cell (ASMC) function. It also modifies mTOR activity, microRNA (miR)-101-3p expression, and mitochondria function. Here, the link between miR-101-3p and mTOR-regulated mitochondria integrity and ASMC deterioration was assessed.

METHODS

Disease-specific miR-101-3p expression was determined by RT-PCR in primary ASMC (non-COPD smokers: n = 6; COPD: n = 8; healthy: n = 6). The regulatory effect of miR-101-3p modification on mTOR expression, mitochondrial fragmentation, and remodeling properties (α-SMA, fibronectin, MTCO2, and p70S6 kinase) was assessed in ASMC (healthy nonsmokers: n = 3; COPD: n = 3) by Western blotting and immunofluorescence microscopy. MiR-101-3p was modified by specific mimics or inhibitors, in ASMC stimulated with TNF-α (10 ng/ml) or cigarette smoke extract (CSE).

RESULTS

MiR-101-3p expression was significantly higher in ASMC of COPD patients, compared to ASMC of healthy or active smokers. MiR-101-3p expression was increased by TNF-α or CSE. TNF-α or miR-101-3p deteriorated ASMC and mitochondria, while decreasing mTOR signaling, α-SMA, fibronectin, and MTCO2. MiR-101-3p inhibition reduced ASMC deterioration and mitochondrial fragmentation.

CONCLUSION

Constitutive high miR-101-3p expression characterizes COPD-ASMC, causing increased mitochondrial fragmentation and ASMC deterioration. Thus, reactivation mTOR or blocking miR-101-3p presents a potential new strategy for COPD therapy.

Biologics and airway remodeling in severe asthma

Asthma is a chronic inflammatory airway disease resulting in airflow obstruction, which in part can become irreversible to conventional therapies, defining the concept of airway remodeling. The introduction of biologics in severe asthma has led in some patients to the complete normalization of previously considered irreversible airflow obstruction. This highlights the need to distinguish a "fixed" airflow obstruction due to structural changes unresponsive to current therapies, from a "reversible" one as demonstrated by lung function normalization during biological therapies not previously obtained even with high-dose systemic glucocorticoids. The mechanisms by which exposure to environmental factors initiates the inflammatory responses that trigger airway remodeling are still incompletely understood. Alarmins represent epithelial-derived cytokines that initiate immunologic events leading to inflammatory airway remodeling. Biological therapies can improve airflow obstruction by addressing these airway inflammatory changes. In addition, biologics might prevent and possibly even revert "fixed" remodeling due to structural changes. Hence, it appears clinically important to separate the therapeutic effects (early and late) of biologics as a new paradigm to evaluate the effects of these drugs and future treatments on airway remodeling in severe asthma.

Sex Steroids Effects on Asthma: A Network Perspective of Immune and Airway Cells

A multitude of evidence has suggested the differential incidence, prevalence and severity of asthma between males and females. A compilation of recent literature recognized sex differences as a significant non-modifiable risk factor in asthma pathogenesis. Understanding the cellular and mechanistic basis of sex differences remains complex and the pivotal point of this ever elusive quest, which remains to be clarified in the current scenario. Sex steroids are an integral part of human development and evolution while also playing a critical role in the conditioning of the immune system and thereby influencing the function of peripheral organs. Classical perspectives suggest a pre-defined effect of sex steroids, generalizing estrogens popularly under the “estrogen paradox” due to conflicting reports associating estrogen with a pro- and anti-inflammatory role. On the other hand, androgens are classified as “anti-inflammatory,” serving a protective role in mitigating inflammation. Although considered mainstream and simplistic, this observation remains valid for numerous reasons, as elaborated in the current review. Women appear immune-favored with stronger and more responsive immune elements than men. However, the remarkable female predominance of diverse autoimmune and allergic diseases contradicts this observation suggesting that hormonal differences between the sexes might modulate the normal and dysfunctional regulation of the immune system. This review illustrates the potential relationship between key elements of the immune cell system and their interplay with sex steroids, relevant to structural cells in the pathophysiology of asthma and many other lung diseases. Here, we discuss established and emerging paradigms in the clarification of observed sex differences in asthma in the context of the immune system, which will deepen our understanding of asthma etiopathology.

Th1 cytokines synergize to change gene expression and promote corticosteroid insensitivity in pediatric airway smooth muscle

Background

Corticosteroids remain a key therapy for treating children with asthma. Patients with severe asthma are insensitive, resistant, or refractory to corticosteroids and have poorly controlled symptoms that involve airway inflammation, airflow obstruction, and frequent exacerbations. While the pathways that mediate corticosteroid insensitivity in asthma remain poorly defined, recent studies suggest that enhanced Th1 pathways, mediated by TNFα and IFNγ, may play a role. We previously reported that the combined effects of TNFα and IFNγ promote corticosteroid insensitivity in developing human airway smooth muscle (ASM).

Methods

To further understand the effects of TNFα and IFNγ on corticosteroid sensitivity in the context of neonatal and pediatric asthma, we performed RNA sequencing (RNA-seq) on human pediatric ASM treated with fluticasone propionate (FP), TNFα, and/or IFNγ.

Results

We found that TNFα had a greater effect on gene expression (~ 1000 differentially expressed genes) than IFNγ (~ 500 differentially expressed genes). Pathway and transcription factor analyses revealed enrichment of several pro-inflammatory responses and signaling pathways. Interestingly, treatment with TNFα and IFNγ augmented gene expression with more than 4000 differentially expressed genes. Effects of TNFα and IFNγ enhanced several pro-inflammatory genes and pathways related to ASM and its contributions to asthma pathogenesis, which persisted in the presence of corticosteroids. Co-expression analysis revealed several gene networks related to TNFα- and IFNγ-mediated signaling, pro-inflammatory mediator production, and smooth muscle contractility. Many of the co-expression network hubs were associated with genes that are insensitive to corticosteroids.

Conclusions

Together, these novel studies show the combined effects of TNFα and IFNγ on pediatric ASM and implicate Th1-associated cytokines in promoting ASM inflammation and hypercontractility in severe asthma.

Human epididymis protein 4 aggravates airway inflammation and remodeling in chronic obstructive pulmonary disease

Background

Chronic obstructive pulmonary disease (COPD) is a progressive disease characterized by chronic inflammation and airway remodeling. Human epididymis protein 4 (HE4) plays a critical role in various inflammatory or fibrotic diseases. However, the role of HE4 in COPD remains unidentified.

Methods

HE4 expression was determined in the lung tissues from COPD patients and cigarette smoke (CS)-exposed mice using immunohistochemical staining, qPCR, or western blot. The plasma level of HE4 was detected by ELISA. The regulations of HE4 in the expressions of CS extract (CSE)-induced inflammatory cytokines in human bronchial epithelial cells (HBE) were investigated through knockdown or overexpression of HE4. The role of secretory HE4 (sHE4) in the differentiation and proliferation in human pulmonary fibroblast cells (HPF) was explored via qPCR, western blot, CCK8 assay or 5-ethynyl-2′-deoxyuridine (EdU) staining. The probe of related mechanism in CSE-induced HE4 increase in HBE was conducted by administrating N-acetylcysteine (NAC).

Results

HE4 was up-regulated in both the lung tissue and plasma of COPD patients relative to controls, and the plasma HE4 was negatively associated with lung function in COPD patients. The same enhanced HE4 expression was verified in CS-exposed mice and CSE-induced HBE, but CSE failed to increase HE4 expression in HPF. In vitro experiments showed that reducing HE4 expression in HBE alleviated CSE-induced IL-6 release while overexpressing HE4 facilitated IL-6 expression, mechanistically through affecting phosphorylation of NFκB-p65, whereas intervening HE4 expression had no distinctive influence on IL-8 secretion. Furthermore, we confirmed that sHE4 promoted fibroblast-myofibroblast transition, as indicated by promoting the expression of fibronectin, collagen I and α-SMA via phosphorylation of Smad2. EdU staining and CCK-8 assay demonstrated the pro-proliferative role of sHE4 in HPF, which was further confirmed by enhanced expression of survivin and PCNA. Pretreatment of NAC in CSE or H₂O₂-induced HBE mitigated HE4 expression.

Conclusions

Our study indicates that HE4 may participate in airway inflammation and remodeling of COPD. Cigarette smoke enhances HE4 expression and secretion in bronchial epithelium mediated by oxidative stress. Increased HE4 promotes IL-6 release in HBE via phosphorylation of NFκB-p65, and sHE4 promotes fibroblastic differentiation and proliferation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12931-022-02040-7.

Utilizing the Precision-Cut Lung Slice to Study the Contractile Regulation of Airway and Intrapulmonary Arterial Smooth Muscle

Smooth muscle cells (SMC) mediate the contraction of the airway and the intrapulmonary artery to modify airflow resistance and pulmonary circulation, respectively, hence playing a critical role in the homeostasis of the pulmonary system. Deregulation of SMC contractility contributes to several pulmonary diseases, including asthma and pulmonary hypertension. However, due to limited tissue access and a lack of culture systems to maintain in vivo SMC phenotypes, molecular mechanisms underlying the deregulated SMC contractility in these diseases remain fully identified. The precision-cut lung slice (PCLS) offers an ex vivo model that circumvents these technical difficulties. As a live, thin lung tissue section, the PCLS retains SMC in natural surroundings and allows in situ tracking of SMC contraction and intracellular Ca2+ signaling that regulates SMC contractility. Here, a detailed mouse PCLS preparation protocol is provided, which preserves intact airways and intrapulmonary arteries. This protocol involves two essential steps before subjecting the lung lobe to slicing: inflating the airway with low-melting-point agarose through the trachea and infilling pulmonary vessels with gelatin through the right ventricle. The PCLS prepared using this protocol can be used for bioassays to evaluate Ca2+-mediated contractile regulation of SMC in both the airway and the intrapulmonary arterial compartments. When applied to mouse models of respiratory diseases, this protocol enables the functional investigation of SMC, thereby providing insight into the underlying mechanism of SMC contractility deregulation in diseases.

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.

A narrative review of research advances in the study of molecular markers of airway smooth muscle cells

Background and Objective

Airway smooth muscle cells (ASMCs) are an important component of the airway. Their thickening and proliferation are important in pathological situations, such as airway remodeling in asthma, but their origin remains unclear. Therefore, characterizing molecular markers of ASMCs were sought to identify the source of increased ASMCs in asthmatic airway remodeling.

Methods

Articles for this review were derived from a review of the literature related to surface markers and biological properties of ASMCs and smooth muscle cells (SMCs) using PubMed, Google Scholar, and Web of Science.

Key Content and Findings

This review discusses several SMC molecular markers, describes the different developmental stages of SMCs that express different molecular markers, and summarizes several classical SMC molecular markers. However, the establishment of a specific molecular marker detection system for ASMCs still faces great challenges.

Conclusions

Although there is no recognized molecular marker detection system for ASMCs, and the study of the properties and sources of increased ASMCs in asthma airway remodeling is still in a state of exploration, the future is promising. Among the SMC markers described in this review, Myosin heavy chain 11 (MYH11) is a molecular marker for mature SMCs and Transgelin (TAGLN) is an early marker for SMC differentiation, and different molecular markers or combinations of molecular markers can be selected for the identification of the properties and sources of increased ASMCs in asthma airway remodeling according to the differentiation period and research needs.

Abi1 mediates airway smooth muscle cell proliferation and airway remodeling via Jak2/STAT3 signaling

Asthma is a complex pulmonary disorder with multiple pathological mechanisms. A key pathological feature of chronic asthma is airway remodeling, which is largely attributed to airway smooth muscle (ASM) hyperplasia that contributes to thickening of the airway wall and further drives asthma pathology. The cellular processes that mediate ASM cell proliferation are not completely elucidated. Using multiple approaches, we demonstrate that the adapter protein Abi1 (Abelson interactor 1) is upregulated in ∼50% of ASM cell cultures derived from patients with asthma. Loss-of-function studies demonstrate that Abi1 regulates the activation of Jak2 (Janus kinase 2) and STAT3 (signal transducers and activators of transcription 3) as well as the proliferation of both nonasthmatic and asthmatic human ASM cell cultures. These findings identify Abi1 as a molecular switch that activates Jak2 kinase and STAT3 in ASM cells and demonstrate that a dysfunctional Abi1-associated pathway contributes to the progression of asthma.

Novel Hyperspectral imaging approaches allow 3D measurement of cAMP signals in localized subcellular domains of human airway smooth muscle cells

Studies of the cAMP signaling pathway have led to the hypothesis that localized cAMP signals regulate distinct cellular responses. Much of this work focused on measurement of localized cAMP signals using cAMP sensors based upon Fӧrster resonance energy transfer (FRET). FRET-based probes are comprised of a cAMP binding domain sandwiched between donor and acceptor fluorophores. Binding of cAMP triggers a conformational change which alters FRET efficiency. In order to study localized cAMP signals, investigators have targeted FRET probes to distinct subcellular domains. This approach allows detection of cAMP signals at distinct subcellular locations. However, these approaches do not measure localized cAMP signals per se, rather they measure cAMP signals at specific locations and typically averaged throughout the cell. To address these concerns, our group implemented hyperspectral imaging approaches for measuring highly multiplexed signals in cells and tissues. We have combined these approaches with custom analysis software implemented in MATLAB and Python. Images were filtered both spatially and temporally, prior to adaptive thresholding (OTSU) to detect cAMP signals. These approaches were used to interrogate the distributions of isoproterenol and prostaglandin-triggered cAMP signals in human airway smooth muscle cells (HASMCs). Results demonstrate that cAMP signals are spatially and temporally complex. We observed that isoproterenol- and prostaglandin-induced cAMP signals are triggered at the plasma membrane and in the cytosolic space. We are currently implementing analysis approaches to better quantify and visualize the complex distributions of cAMP signals. This work was supported by NIH P01HL066299, R01HL058506, and S10RR027535.

Bitter Taste Receptors in the Airway Cells Functions

G protein-coupled receptors (GPCRs) play a central role in regulating the functions of a diverse range of cell types in the airway. Taste 2 receptor (T2R) family of GPCRs is responsible for the transduction of bitter taste; however, recent studies have demonstrated that different subtypes of T2Rs and key components of T2R signaling are expressed in several extra-oral tissues including airways with many physiological roles. In the lung, expression of T2Rs has been confirmed in multiple airway cell types including airway smooth muscle (ASM) cells, various epithelial cell subtypes, and on both resident and migratory immune cells. Most importantly, activation of T2Rs with a variety of putative agonists elicits unique signaling in ASM and specialized airway epithelial cells resulting in the inhibition of ASM contraction and proliferation, promotion of ciliary motility, and innate immune response in chemosensory airway epithelial cells. Here we discuss the expression of T2Rs and the mechanistic basis of their function in the structural cells of the airways with some useful insights on immune cells in the context of allergic asthma and other upper airway inflammatory disorders. Emphasis on T2R biology and pharmacology in airway cells has an ulterior goal of exploiting T2Rs for therapeutic benefit in obstructive airway diseases.

Diacylglycerol Kinase Inhibition Reduces Airway Contraction by Negative Feedback Regulation of Gq-Signaling

Exaggerated airway smooth muscle (ASM) contraction regulated by the Gq family of G protein-coupled receptors causes airway hyperresponsiveness in asthma. Activation of Gq-coupled G protein-coupled receptors leads to phospholipase C (PLC)-mediated generation of inositol triphosphate (IP3) and diacylglycerol (DAG). DAG signaling is terminated by the action of DAG kinase (DGK) that converts DAG into phosphatidic acid (PA). Our previous study demonstrated that DGKζ and α isoform knockout mice are protected from the development of allergen-induced airway hyperresponsiveness. Here we aimed to determine the mechanism by which DGK regulates ASM contraction. Activity of DGK isoforms was inhibited in human ASM cells by siRNA-mediated knockdown of DGKα and ζ, whereas pharmacological inhibition was achieved by pan DGK inhibitor I (R59022). Effects of DGK inhibition on contractile agonist-induced activation of PLC and myosin light chain (MLC) kinase, elevation of IP3, and calcium levels were assessed. Furthermore, we used precision-cut human lung slices and assessed the role of DGK in agonist-induced bronchoconstriction. DGK inhibitor I attenuated histamine- and methacholine-induced bronchoconstriction. DGKα and ζ knockdown or pretreatment with DGK inhibitor I resulted in attenuated agonist-induced phosphorylation of MLC and MLC phosphatase in ASM cells. Furthermore, DGK inhibition decreased Gq agonist-induced calcium elevation and generation of IP3 and increased histamine-induced production of PA. Finally, DGK inhibition or treatment with DAG analog resulted in attenuation of activation of PLC in human ASM cells. Our findings suggest that DGK inhibition perturbed the DAG:PA ratio, resulting in inhibition of Gq-PLC activation in a negative feedback manner, resulting in protection against ASM contraction.

Corticosteroid insensitivity persists in the absence of STAT1 signaling in severe allergic airway inflammation

Corticosteroid insensitivity in asthma limits the ability to effectively manage severe asthma, which is characterized by persistent airway inflammation, airway hyperresponsiveness (AHR), and airflow obstruction despite corticosteroid treatment. Recent reports indicate that corticosteroid insensitivity is associated with increased interferon-γ (IFN-γ) levels and T-helper (Th) 1 lymphocyte infiltration in severe asthma. Signal transducer and activator of transcription 1 (STAT1) activation by IFN-γ is a key signaling pathway in Th1 inflammation; however, its role in the context of severe allergic airway inflammation and corticosteroid sensitivity remains unclear. In this study, we challenged wild-type (WT) and Stat1^-/- mice with mixed allergens (MA) augmented with c-di-GMP [bis-(3'-5')-cyclic dimeric guanosine monophosphate], an inducer of Th1 cell infiltration with increased eosinophils, neutrophils, Th1, Th2, and Th17 cells. Compared with WT mice, Stat1^-/- had reduced neutrophils, Th1, and Th17 cell infiltration. To evaluate corticosteroid sensitivity, mice were treated with either vehicle, 1 or 3 mg/kg fluticasone propionate (FP). Corticosteroids significantly reduced eosinophil infiltration and cytokine levels in both c-di-GMP + MA-challenged WT and Stat1^-/- mice. However, histological and functional analyses show that corticosteroids did not reduce airway inflammation, epithelial mucous cell abundance, airway smooth muscle mass, and AHR in c-di-GMP + MA-challenged WT or Stat1^-/- mice. Collectively, our data suggest that increased Th1 inflammation is associated with a decrease in corticosteroid sensitivity. However, increased airway pathology and AHR persist in the absence of STAT1 indicate corticosteroid insensitivity in structural airway cells is a STAT1 independent process.

Oxidative Stress Promotes Corticosteroid Insensitivity in Asthma and COPD

Corticosteroid insensitivity is a key characteristic of patients with severe asthma and COPD. These individuals experience greater pulmonary oxidative stress and inflammation, which contribute to diminished lung function and frequent exacerbations despite the often and prolonged use of systemic, high dose corticosteroids. Reactive oxygen and nitrogen species (RONS) promote corticosteroid insensitivity by disrupting glucocorticoid receptor (GR) signaling, leading to the sustained activation of pro-inflammatory pathways in immune and airway structural cells. Studies in asthma and COPD models suggest that corticosteroids need a balanced redox environment to be effective and to reduce airway inflammation. In this review, we discuss how oxidative stress contributes to corticosteroid insensitivity and the importance of optimizing endogenous antioxidant responses to enhance corticosteroid sensitivity. Future studies should aim to identify how antioxidant-based therapies can complement corticosteroids to reduce the need for prolonged high dose regimens in patients with severe asthma and COPD.

Aging increases senescence, calcium signaling, and extracellular matrix deposition in human airway smooth muscle

Lung function declines as people age and their lungs become stiffer. With an increasing elderly population, understanding mechanisms that contribute to these structural and functional changes in the aging lung is important. Part of the aging process is characterized by thicker, more fibrotic airways, and senile emphysema caused by changes in lung parenchyma. There is also senescence, which occurs throughout the body with aging. Here, using human airway smooth muscle (ASM) cells from patients in different age groups, we explored senescence pathways and changes in intracellular calcium signaling and extracellular matrix (ECM) deposition to elucidate potential mechanisms by which aging leads to thicker and stiffer lungs. Senescent markers p21, γH2AX, and β-gal, and some senescence-associated secretory proteins (SASP) increased with aging, as shown by staining and biochemical analyses. Agonist-induced intracellular Ca2+ responses, measured using fura-2 loaded cells and fluorescence imaging, increased with age. However, biochemical analysis showed that expression of the following markers decreased with age: M3 muscarinic receptor, TRPC3, Orai1, STIM1, SERCA2, MMP2 and MMP9. In contrast, collagen III, and fibronectin deposition increased with age. These data show that senescence increases in the aging airways that is associated with a stiffer but surprisingly greater intracellular calcium signaling as a marker for contractility. ASM senescence may enhance fibrosis in a feed forward loop promoting remodeling and altered calcium storage and buffering.

Network and co-expression analysis of airway smooth muscle cell transcriptome delineates potential gene signatures in asthma

Airway smooth muscle (ASM) is known for its role in asthma exacerbations characterized by acute bronchoconstriction and remodeling. The molecular mechanisms underlying multiple gene interactions regulating gene expression in asthma remain elusive. Herein, we explored the regulatory relationship between ASM genes to uncover the putative mechanism underlying asthma in humans. To this end, the gene expression from human ASM was measured with RNA-Seq in non-asthmatic and asthmatic groups. The gene network for the asthmatic and non-asthmatic group was constructed by prioritizing differentially expressed genes (DEGs) (121) and transcription factors (TFs) (116). Furthermore, we identified differentially connected or co-expressed genes in each group. The asthmatic group showed a loss of gene connectivity due to the rewiring of major regulators. Notably, TFs such as ZNF792, SMAD1, and SMAD7 were differentially correlated in the asthmatic ASM. Additionally, the DEGs, TFs, and differentially connected genes over-represented in the pathways involved with herpes simplex virus infection, Hippo and TGF-β signaling, adherens junctions, gap junctions, and ferroptosis. The rewiring of major regulators unveiled in this study likely modulates the expression of gene-targets as an adaptive response to asthma. These multiple gene interactions pointed out novel targets and pathways for asthma exacerbations.

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.

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.

LIMK2 is required for membrane cytoskeleton reorganization of contracting airway smooth muscle

Airway smooth muscle (ASM) has developed a mechanical adaption mechanism by which it transduces force and responds to environmental forces, which is essential for periodic breathing. Cytoskeletal reorganization has been implicated in this process, but the regulatory mechanism remains to be determined. We here observe that ASM abundantly expresses cytoskeleton regulators Limk1 and Limk2, and their expression levels are further upregulated in chronic obstructive pulmonary disease (COPD) animals. By establishing mouse lines with deletions of Limk1 or Limk2, we analyse the length-sensitive contraction, F/G-actin dynamics, and F-actin pool of mutant ASM cells. As LIMK1 phosphorylation does not respond to the contractile stimulation, LIMK1-deficient ASM develops normal maximal force, while LIMK2 or LIMK1/LIMK2 deficient ASMs show approximately 30% inhibition. LIMK2 deletion causes a significant decrease in cofilin phosphorylation along with a reduced F/G-actin ratio. As LIMK2 functions independently of cross-bridge movement, this observation indicates that LIMK2 is necessary for F-actin dynamics and hence force transduction. Moreover, LIMK2-deficient ASMs display abolishes stretching-induced suppression of 5-hydroxytryptamine (5-HT) but not acetylcholine-evoks force, which is due to the differential contraction mechanisms adopted by the agonists. We propose that LIMK2-mediated cofilin phosphorylation is required for membrane cytoskeleton reorganization that is necessary for ASM mechanical adaption including the 5-HT-evoked length-sensitive effect.

Airway smooth muscle pathophysiology in asthma

The airway smooth muscle (ASM) cell plays a central role in the pathogenesis of asthma and constitutes an important target for treatment. These cells control muscle tone and thus regulate the opening of the airway lumen and air passage. Evidence indicates that ASM cells participate in the airway hyperresponsiveness as well as the inflammatory and remodeling processes observed in asthmatic subjects. Therapeutic approaches require a comprehensive understanding of the structure and function of the ASM in both the normal and disease states. This review updates current knowledge about ASM and its effects on airway narrowing, remodeling, and inflammation in asthma.

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.

Acute cigarette smoke or extract exposure rapidly activates TRPA1-mediated calcium influx in primary human airway smooth muscle cells

Tobacco smoking is the largest risk factor for developing chronic obstructive pulmonary disease (COPD), and is associated with hyperresponsiveness of airway smooth muscle (ASM). Chronic exposure to cigarette smoke (CS) leads to airway inflammation and remodelling. However, the direct effect of gaseous CS or CS extract (CSE) on human airway smooth muscle cell (hASMC) function remains poorly understood. This study investigated the acute effect of CS/CSE on calcium homeostasis, a key regulator of ASM physiology and pathophysiology. Primary hASMC were isolated from non-smoking donor lungs, and subjected to Ca2+ imaging studies. We found that both CS, and CSE, rapidly elevated cytosolic Ca2+ in hASMC through stimulation of plasmalemmal Ca2+ influx, but excluded store-operated and L-type Ca2+ channels as mediators of this effect. Using a specific pharmacological inhibitor, or shRNA-driven knockdown, we established that both CS and CSE stimulated Ca2+ influx in hASMC through the neurogenic pain receptor channel, transient receptor potential ankyrin 1 (TRPA1). CS/CSE-dependent, TRPA1-mediated Ca2+ influx led to myosin light-chain phosphorylation, a key process regulating ASM contractility. We conclude that TRPA1 is likely an important link between CS/CSE exposure and airway hyperresponsiveness, and speculate that acute CS/CSE-induced Ca2+ influx could lead to exacerbated ASM contraction and potentially initiate further chronic pathological effects of tobacco smoke.

ORMDL3 expression in ASM regulates hypertrophy, hyperplasia via TPM1 and TPM4, and contractility

ORM1-like 3 (ORMDL3) has strong genetic linkage to childhood onset asthma. To determine whether ORMDL3 selective expression in airway smooth muscle (ASM) influences ASM function, we used Cre-loxP techniques to generate transgenic mice (hORMDL3Myh11eGFP-cre), which express human ORMDL3 selectively in smooth muscle cells. In vitro studies of ASM cells isolated from the bronchi of hORMDL3Myh11eGFP-cre mice demonstrated that they developed hypertrophy (quantitated by FACS and image analysis), developed hyperplasia (assessed by BrdU incorporation), and expressed increased levels of tropomysin proteins TPM1 and TPM4. siRNA knockdown of TPM1 or TPM4 demonstrated their importance to ORMDL3-mediated ASM proliferation but not hypertrophy. In addition, ASM derived from hORMDL3Myh11eGFP-cre mice had increased contractility to histamine in vitro, which was associated with increased levels of intracellular Ca2+; increased cell surface membrane Orai1 Ca2+ channels, which mediate influx of Ca2+ into the cytoplasm; and increased expression of ASM contractile genes sarco/endoplasmic reticulum Ca2+ ATPase 2b and smooth muscle 22. In vivo studies of hORMDL3Myh11eGFP-cre mice demonstrated that they had a spontaneous increase in ASM and airway hyperreactivity (AHR). ORMDL3 expression in ASM thus induces changes in ASM (hypertrophy, hyperplasia, increased contractility), which may explain the contribution of ORMDL3 to the development of AHR in childhood onset asthma, which is highly linked to ORMDL3 on chromosome 17q12-21.

Sex-Steroid Signaling in Lung Diseases and Inflammation

Sex/gender difference exists in the physiology of multiple organs. Recent epidemiological reports suggest the influence of sex-steroids in modulating a wide variety of disease conditions. Sex-based discrepancies have been reported in pulmonary physiology and various chronic inflammatory responses associated with lung diseases like asthma, chronic obstructive pulmonary disease (COPD), pulmonary fibrosis, and rare lung diseases. Notably, emerging clinical evidence suggests that several respiratory diseases affect women to a greater degree, with increased severity and prevalence than men. Although sex-specific differences in various lung diseases are evident, such differences are inherent to sex-steroids, which are major biological variables in men and women who play a central role to control these differences. The focus of this chapter is to comprehend the sex-steroid biology in inflammatory lung diseases and to understand the mechanistic role of sex-steroids signaling in regulating these diseases. Exploring the roles of sex-steroid signaling in the regulation of lung diseases and inflammation is crucial for the development of novel and effective therapy. Overall, we will illustrate the importance of differential sex-steroid signaling in lung diseases and their possible clinical implications for the development of complementary and alternative medicine to treat lung diseases.

NOX4-Derived ROS Promotes Collagen I Deposition in Bronchial Smooth Muscle Cells by Activating Noncanonical p38MAPK/Akt-Mediated TGF-β Signaling

Background

Airway smooth muscle (ASM) remodeling is a hallmark in chronic obstructive pulmonary disease (COPD). NADPH oxidase 4- (NOX4-) mediated reactive oxygen species (ROS) production plays a crucial role in cell differentiation and extracellular matrix (ECM) synthesis in ASM remodeling. However, the precise mechanisms underpinning its pathogenic roles remain elusive.

Methods

The expression of NOX4 and TGF-β₁ in the airway of the lung was measured in COPD patients and the control group. Cigarette smoke- (CS-) induced emphysema mice were generated, and the alteration of α-SMA, NOX4, TGF-β₁, and collagen I was accessed. The changes of the expression of ECM markers, NOX4, components of TGF-β/Smad, and MAPK/Akt signaling in human bronchial smooth muscle cells (HBSMCs) were ascertained for delineating mechanisms of NOX4-mediated ROS production on cell differentiation and remodeling in human ASM cells.

Results

An increased abundance of NOX4 and TGF-β₁ proteins in the epithelial cells and ASM of lung was observed in COPD patients compared with the control group. Additionally, an increased abundance expression of NOX4 and α-SMA was observed in the lungs of the CS-induced emphysema mouse model. TGF-β₁ displayed abilities to increase the oxidative burden and collagen I production, along with enhanced phosphorylation of ERK, p38MAPK, and p-Akt473 in HBSMCs. These effects of TGF-β₁ could be inhibited by the ROS scavenger N-acetylcysteine (NAC), siRNA-mediated knockdown of Smad3 and NOX4, and pharmacological inhibitors SB203580 (p38MAPK inhibitor) and LY294002 (Akt inhibitor).

Conclusions

NOX4-mediated ROS production alters TGF-β₁-induced cell differentiation and collagen I protein synthesis in HBSMCs in part through the p38MAPK/Akt signaling pathway in a Smad-dependent manner.

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.