Local small airway epithelial injury induces global smooth muscle contraction and airway constriction

The epithelium takes the stage in asthma and inflammatory bowel diseases

The epithelium is a dynamic barrier and the damage to this epithelial layer governs a variety of complex mechanisms involving not only epithelial cells but all resident tissue constituents, including immune and stroma cells. Traditionally, diseases characterized by a damaged epithelium have been considered "immunological diseases," and research efforts aimed at preventing and treating these diseases have primarily focused on immuno-centric therapeutic strategies, that often fail to halt or reverse the natural progression of the disease. In this review, we intend to focus on specific mechanisms driven by the epithelium that ensure barrier function. We will bring asthma and Inflammatory Bowel Diseases into the spotlight, as we believe that these two diseases serve as pertinent examples of epithelium derived pathologies. Finally, we will argue how targeting the epithelium is emerging as a novel therapeutic strategy that holds promise for addressing these chronic diseases.

Bronchial epithelial and airway smooth muscle cell interactions in health and disease

Chronic pulmonary diseases such as asthma, COPD, and Idiopathic pulmonary fibrosis are significant causes of mortality and morbidity worldwide. Currently, there is no radical treatment for many chronic pulmonary diseases, and the treatment options focus on relieving the symptoms and improving lung function. Therefore, efficient therapeutic agents are highly needed. Bronchial epithelial cells and airway smooth muscle cells and their crosstalk play a significant role in the pathogenesis of these diseases. Thus, targeting the interactions of these two cell types could open the door to a new generation of effective therapeutic options. However, the studies on how these two cell types interact and how their crosstalk adds up to respiratory diseases are not well established. With the rise of modern research tools and technology, such as lab-on-a-chip, organoids, co-culture techniques, and advanced immunofluorescence imaging, a substantial degree of evidence about these cell interactions emerged. Hence, this contribution aims to summarize the growing evidence of bronchial epithelial cells and airway smooth muscle cells crosstalk under normal and pathophysiological conditions. The review first discusses the impact of airway smooth muscle cells on the epithelium in inflammatory settings. Later, it examines the role of airway smooth muscle cells in the early development of bronchial epithelial cells and their recovery after injury. Then, it deliberates the effects of both healthy and stressed epithelial cells on airway smooth muscle cells, taking into account three themes; contraction, migration, and proliferation.

A Combination of α-Lipoic Acid (ALA) and Palmitoylethanolamide (PEA) Blocks Endotoxin-Induced Oxidative Stress and Cytokine Storm: A Possible Intervention for COVID-19

The global scientific community is striving to understand the pathophysiological mechanisms and develop effective therapeutic strategies for COVID-19. Despite overwhelming data, there is limited knowledge about the molecular mechanisms involved in the prominent cytokine storm syndrome and multiple organ failure and fatality in COVID-19 cases. The aim of this work is to investigate the possible role of of α-lipoic acid (ALA) and palmitoylethanolamide (PEA), in countering the mechanisms in overproduction of reactive oxygen species (ROS), and inflammatory cytokines. An in vitro model of lipopolysaccharide (LPS)-stimulated human epithelial lung cells that mimics the pathogen-associated molecular pattern and reproduces the cell signaling pathways in cytokine storm syndrome has been used. In this model of acute lung injury, the combination effects of ALAPEA, administered before and after LPS injury, were investigated. Our data demonstrated that a combination of 50 µM ALA + 5 µM PEA can reduce ROS and nitric oxide (NO) levels modulating the major cytokines involved on COVID-19 infection when administered either before or after LPS-induced damage. The best outcome was observed when administered after LPS, thus reinforcing the hypothesis that ALA combined with PEA to modulate the key point of cytokine storm syndrome. This work supports for the first time that the combination of ALA with PEA may represent a novel intervention strategy to counteract inflammatory damage related to COVID-19 by restoring the cascade activation of the immune response and acting as a powerful antioxidant.

Naringin as a plant-derived bitter tastant promotes proliferation of cultured human airway epithelial cells via activation of TAS2R signaling

BACKGROUND

Bitter tastants can activate bitter taste receptors (TAS2Rs) and thus initiate relaxation of airway smooth muscle cells (ASMCs), which have great potential in the development of novel bronchodilator drugs for asthma therapy. However, the canonical bitter substance, denatonium is known to induce apoptosis of airway epithelial cells (AECs), indicating that other bitter tastants may also impair the epithelial integrity to prevent hazardous particulate matters such as coronaviruses. Therefore, any bitter tastants intended for treating airway disease should be carefully evaluated for potential toxicity to AECs.

HYPOTHESIS/PURPOSE

Considering the vast diversity of bitter tastants in nature and different types of TAS2Rs expressed in airway cells, we hypothesized that there must be some natural bitter tastants to be not only potent in inducing relaxation of ASMCs but also unharmful to AECs.

STUDY DESIGN AND METHODS

Here we evaluated a group of bitter flavonoids that are derived from fruits and commonly used in traditional herbal medicine, including apigenin, hesperetin, kaempferol, naringenin, quercetin, and naringin, for their effects on the proliferation of human airway epithelial-like (16HBE14o-, BEAS-2B, and A549) cells cultured in vitro. Cell proliferation and associated signaling pathways were assessed by cell counting, ATP assay, cell cycling assay, quantitative RT-PCR, Fluo-4 labeling, and fluorescence resonance energy transfer, respectively.

RESULTS

The results show that five of the six tested bitter tastants inhibited, but only naringin promoted the proliferation of the 16HBE14o-, BEAS-2B, and A549 cells at the dose of a few hundred micromoles. Furthermore, the naringin-promoted proliferation of the 16HBE14o- cells was associated with enhanced cell cycle progression, mRNA expression of cyclin E, and evoked calcium signaling/ERK signaling, which were all attenuated by inhibition of the TAS2R signaling pathways with specific blockers.

CONCLUSION

These findings indicate that although the majority of the bitter flavonoids may inhibit the proliferation of AECs, naringin emerged as one to promote the proliferation of AECs via cell cycle progression and TAS2R-activated intracellular signaling. It suggests that naringin and not a few other bitter tastants can be proven with nontoxicity to the airway epithelial structure and function, which provides further confidence in the development of safe and effective TAS2R-based bronchodilators for asthma therapy.

Structure and function of small airways in asthma patients revisited

Small airways (<2 mm in diameter) are probably involved across almost all asthma severities and they show proportionally more structural and functional abnormalities with increasing asthma severity. The structural and functional alterations of the epithelium, extracellular matrix and airway smooth muscle in small airways of people with asthma have been described over many years using in vitro studies, animal models or imaging and modelling methods. The purpose of this review was to provide an overview of these observations and to outline several potential pathophysiological mechanisms regarding the role of small airways in asthma.

Asthma and Lung Mechanics

This article will discuss in detail the pathophysiology of asthma from the point of view of lung mechanics. In particular, we will explain how asthma is more than just airflow limitation resulting from airway narrowing but in fact involves multiple consequences of airway narrowing, including ventilation heterogeneity, airway closure, and airway hyperresponsiveness. In addition, the relationship between the airway and surrounding lung parenchyma is thought to be critically important in asthma, especially as related to the response to deep inspiration. Furthermore, dynamic changes in lung mechanics over time may yield important information about asthma stability, as well as potentially provide a window into future disease control. All of these features of mechanical properties of the lung in asthma will be explained by providing evidence from multiple investigative methods, including not only traditional pulmonary function testing but also more sophisticated techniques such as forced oscillation, multiple breath nitrogen washout, and different imaging modalities. Throughout the article, we will link the lung mechanical features of asthma to clinical manifestations of asthma symptoms, severity, and control. © 2020 American Physiological Society. Compr Physiol 10:975-1007, 2020.

A microphysiological model of the bronchial airways reveals the interplay of mechanical and biochemical signals in bronchospasm

In asthma, airway smooth muscle (ASM) contraction and the subsequent decrease in airflow involve a poorly understood set of mechanical and biochemical events. Organ-level and molecular-scale models of the airway are frequently based on purely mechanical or biochemical considerations and do not account for physiological mechanochemical couplings. Here, we present a microphysiological model of the airway that allows for the quantitative analysis of the interactions between mechanical and biochemical signals triggered by compressive stress on epithelial cells. We show that a mechanical stimulus mimicking a bronchospastic challenge triggers the marked contraction and delayed relaxation of ASM, and that this is mediated by the discordant expression of cyclooxygenase genes in epithelial cells and regulated by the mechanosensor and transcriptional co-activator YAP (Yes-associated protein). A mathematical model of the intercellular feedback interactions recapitulates aspects of obstructive disease of the airways, including pathognomonic features of severe, difficult-to-treat asthma. The microphysiological model could be used to investigate the mechanisms of asthma pathogenesis and to develop therapeutic strategies that disrupt the positive feedback loop that leads to persistent airway constriction.

Mechanisms of airway hyper-responsiveness in asthma: the past, present and yet to come

Airway hyper-responsiveness (AHR) has long been considered a cardinal feature of asthma. The development of the measurement of AHR 40 years ago initiated many important contributions to our understanding of asthma and other airway diseases. However, our understanding of AHR in asthma remains complicated by the multitude of potential underlying mechanisms which in reality are likely to have different contributions amongst individual patients. Therefore, the present review will discuss the current state of understanding of the major mechanisms proposed to contribute to AHR and highlight the way in which AHR testing is beginning to highlight distinct abnormalities associated with clinically relevant patient populations. In doing so we aim to provide a foundation by which future research can begin to ascribe certain mechanisms to specific patterns of bronchoconstriction and subsequently match phenotypes of bronchoconstriction with clinical phenotypes. We believe that this approach is not only within our grasp but will lead to improved mechanistic understanding of asthma phenotypes and we hoped to better inform the development of phenotype-targeted therapy.

Immune circuits in asthma

Asthma is an inflammatory disorder of the conducting airways that has traditionally been classified according to severity. While this has been helpful in guiding treatment with drugs that are currently available such as β2-adrenoceptor agonists and corticosteroids, it takes little account of disease heterogeneity and causal pathways. This review draws attention to subphenotypes of asthma involving different mechanisms and moves the focus away from the adaptive immune response more towards innate immune mechanisms. This mandates a new view of the disease in which causal pathways linked to biomarkers are found and treatments targeted to these pathways as described in a more personalised approach to medicine.

Adenosine A(1) and prostaglandin E receptor 3 receptors mediate global airway contraction after local epithelial injury

Epithelial injury and airway hyperresponsiveness are prominent features of asthma. We have previously demonstrated that laser ablation of single epithelial cells immediately induces global airway constriction through Ca(2+)-dependent smooth muscle shortening. The response is mediated by soluble mediators released from wounded single epithelial cells; however, the soluble mediators and signaling mechanisms have not been identified. In this study, we investigated the nature of the epithelial-derived soluble mediators and the associated signaling pathways that lead to the L-type voltage-dependent Ca(2+) channel (VGCC)-mediated Ca(2+) influx. We found that inhibition of adenosine A1 receptors (or removal of adenosine with adenosine deaminase), cyclooxygenase (COX)-2 or prostaglandin E receptor 3 (EP3) receptors, epidermal growth factor receptor (EGFR), or platelet-derived growth factor receptor (PDGFR) all significantly blocked Ca(2+) oscillations in smooth muscle cells and airway contraction induced by local epithelial injury. Using selective agonists to activate the receptors in the presence and absence of selective receptor antagonists, we found that adenosine activated the signaling pathway A1R→EGFR/PDGFR→COX-2→EP3→VGCCs→calcium-induced calcium release, leading to intracellular Ca(2+) oscillations in airway smooth muscle cells and airway constriction.

Models to study airway smooth muscle contraction in vivo, ex vivo and in vitro: implications in understanding asthma

Asthma is a chronic obstructive airway disease characterised by airway hyperresponsiveness (AHR) and airway wall remodelling. The effector of airway narrowing is the contraction of airway smooth muscle (ASM), yet the question of whether an inherent or acquired dysfunction in ASM contractile function plays a significant role in the disease pathophysiology remains contentious. The difficulty in determining the role of ASM lies in limitations with the models used to assess contraction. In vivo models provide a fully integrated physiological response but ASM contraction cannot be directly measured. Ex vivo and in vitro models can provide more direct assessment of ASM contraction but the loss of factors that may modulate ASM responsiveness and AHR, including interaction between multiple cell types and disruption of the mechanical environment, precludes a complete understanding of the disease process. In this review we detail key advantages of common in vivo, ex vivo and in vitro models of ASM contraction, as well as emerging tissue engineered models of ASM and whole airways. We also highlight important findings from each model with respect to the pathophysiology of asthma.