Cross-roads in the lung: immune cells and tissue interactions as determinants of allergic asthma

Paeoniflorin ameliorates airway inflammation and immune response in ovalbumin induced asthmatic mice: From oxidative stress to autophagy

BACKGROUND

Asthma characterized by airway remodeling is a multiple pulmonary disease, which is associated with various physiological processes including inflammation reaction, immune response, oxidative stress and autophagy.

PURPOSE

This study aimed to investigate whether these processes are modulated by the total glucosides of Paeonia lactiflora Pall (TGP), and its active compound paeoniflorin (PF) with anti-inflammatory and immune-regulatory effects could alleviate ovalbumin (OVA)-induced mouse asthma.

METHODS

In vivo, models of mouse asthma were established by intraperitoneally with a mixture of OVA and aluminum hydroxide, plus a single nasal injected with OVA to female C57BL/6 mice. The results were observed with PET imaging, TEM, RT-PCR, western blotting. In vitro, CD4⁺ T cells were isolated and detected with flow cytometry.

RESULTS

TGP, either in its crude or processed form, and PF effectively ameliorated lung injury in mice induced by OVA, regulated immune/inflammatory response by inhibiting the release of pro-inflammatory cytokines, thereby decreasing Th2 cell proportion, inhibited oxidative stress by recovering mitochondrial membrane potential and regulating metabolic activity in dose-dependent manner. Moreover, PF could inhibit autophagy by regulating mitochondrial function. In addition, the therapeutic effects of TGP and PF on pulmonary injury in asthmatic mice were not affected by processing.

CONCLUSION

PF may be a valuable agent in ameliorating inflammation and immune response in asthmatic mice, and the possible mechanism involved in this response rang may from oxidative stress to autophagy.

Perinatal Nutritional and Metabolic Pathways: Early Origins of Chronic Lung Diseases

Lung development is not completed at birth, but expands beyond infancy, rendering the lung highly susceptible to injury. Exposure to various influences during a critical window of organ growth can interfere with the finely-tuned process of development and induce pathological processes with aberrant alveolarization and long-term structural and functional sequelae. This concept of developmental origins of chronic disease has been coined as perinatal programming. Some adverse perinatal factors, including prematurity along with respiratory support, are well-recognized to induce bronchopulmonary dysplasia (BPD), a neonatal chronic lung disease that is characterized by arrest of alveolar and microvascular formation as well as lung matrix remodeling. While the pathogenesis of various experimental models focus on oxygen toxicity, mechanical ventilation and inflammation, the role of nutrition before and after birth remain poorly investigated. There is accumulating clinical and experimental evidence that intrauterine growth restriction (IUGR) as a consequence of limited nutritive supply due to placental insufficiency or maternal malnutrition is a major risk factor for BPD and impaired lung function later in life. In contrast, a surplus of nutrition with perinatal maternal obesity, accelerated postnatal weight gain and early childhood obesity is associated with wheezing and adverse clinical course of chronic lung diseases, such as asthma. While the link between perinatal nutrition and lung health has been described, the underlying mechanisms remain poorly understood. There are initial data showing that inflammatory and nutrient sensing processes are involved in programming of alveolarization, pulmonary angiogenesis, and composition of extracellular matrix. Here, we provide a comprehensive overview of the current knowledge regarding the impact of perinatal metabolism and nutrition on the lung and beyond the cardiopulmonary system as well as possible mechanisms determining the individual susceptibility to CLD early in life. We aim to emphasize the importance of unraveling the mechanisms of perinatal metabolic programming to develop novel preventive and therapeutic avenues.

RGS4 Overexpression in Lung Attenuates Airway Hyperresponsiveness in Mice

A cardinal feature of asthma is airway hyperresponsiveness (AHR) to spasmogens, many of which activate G protein-coupled receptors (GPCRs) on airway smooth muscle (ASM) cells. Asthma subtypes associated with allergy are characterized by eosinophilic inflammation in the lung due to the type 2 immune response to allergens and proinflammatory mediators that promote AHR. The degree to which intrinsic abnormalities of ASM contribute to this phenotype remains unknown. The regulators of G protein signaling (RGS) proteins are a large group of intracellular proteins that inhibit GPCR signaling pathways. RGS2- and RGS5-deficient mice develop AHR spontaneously. Although RGS4 is upregulated in ASM from patients with severe asthma, the effects of increased RGS4 expression on AHR in vivo are unknown. Here, we examined the impact of forced RGS4 overexpression in lung on AHR using transgenic (Tg) mice. Tg RGS4 was expressed in bronchial epithelium and ASM in vivo, and protein expression in lung was increased at least 4-fold in Tg mice compared with wild-type (WT) mice. Lung slices from Tg mice contracted less in response to the m3 muscarinic receptor agonist methacholine compared with the WT, although airway resistance in live, unchallenged mice of both strains was similar. Tg mice were partially protected against AHR induced by fungal allergen challenge due to weakened contraction signaling in ASM and reduced type 2 cytokine (IL-5 and IL-13) levels in Tg mice compared with the WT. These results provide support for the hypothesis that increasing RGS4 expression and/or function could be a viable therapeutic strategy for asthma.

Role of Polyamines in Asthma Pathophysiology

Asthma is a complex disease of airways, where the interactions of immune and structural cells result in disease outcomes with airway remodeling and airway hyper-responsiveness. Polyamines, which are small-sized, natural super-cations, interact with negatively charged intracellular macromolecules, and altered levels of polyamines and their interactions have been associated with different pathological conditions including asthma. Elevated levels of polyamines have been reported in the circulation of asthmatic patients as well as in the lungs of a murine model of asthma. In various studies, polyamines were found to potentiate the pathogenic potential of inflammatory cells, such as mast cells and granulocytes (eosinophils and neutrophils), by either inducing the release of their pro-inflammatory mediators or prolonging their life span. Additionally, polyamines were crucial in the differentiation and alternative activation of macrophages, which play an important role in asthma pathology. Importantly, polyamines cause airway smooth muscle contraction and thus airway hyper-responsiveness, which is the key feature in asthma pathophysiology. High levels of polyamines in asthma and their active cellular and macromolecular interactions indicate the importance of the polyamine pathway in asthma pathogenesis; therefore, modulation of polyamine levels could be a suitable approach in acute and severe asthma management. This review summarizes the possible roles of polyamines in different pathophysiological features of asthma.

Caffeic acid phenethyl ester alleviates asthma by regulating the airway microenvironment via the ROS-responsive MAPK/Akt pathway

In the pathophysiology of asthma, structural cell dysfunction and concomitant microenvironment changes in airways are crucial to pathological progression, which involves oxidative stress. Caffeic acid phenethyl ester (CAPE) is an active anti-oxidative component obtained from propolis, and has been shown to have beneficial effects on several respiratory disorders, such as chronic obstructive pulmonary disease and lung cancer. However, the impact of CAPE on asthma is not well understood. Therefore, this study investigated the advantages of using CAPE to treat asthma and demonstrated the roles of CAPE in the regulation of airway microenvironments. In ovalbumin (OVA)-sensitized mice, CAPE treatments notably reduced airway hyperresponsiveness, attenuated extensive inflammatory cell infiltration and inhibited goblet cell hyperplasia and collagen deposition and fibrosis. In addition, CAPE improved the airway microenvironment in a dose-dependent manner by inhibiting OVA-induced increases in immunoglobulin E, tumor necrosis factor alpha (TNF-α), transforming growth factor-β1 (TGF-β1), interleukin (IL)-4 and IL-13 and suppressing matrix metalloproteinase-9 and alpha-smooth muscle actin expression as well as malondialdehyde production. To determine the underlying mechanisms responsible for these effects, we used TNF-α-stimulated BECs and TGF-β1-challenged human ASMCs to explore the impacts of CAPE on pro-inflammatory proteins and ASMC proliferation. The results indicated that CAPE significantly limited the secretion of eotaxin-1, monocyte chemoattractant protein-1, IL-8 and intercellular adhesion molecule-1 and dramatically inhibited the proliferation of ASMCs. These effects were shown to be associated with decreased reactive oxidant species (ROS) levels. The phosphorylation of Akt and Mitogen-Activated Protein Kinase (MAPK) caused by increased ROS was significantly decreased by CAPE, which implied a contribution of ROS-MAPK/Akt signaling to the attenuation of asthma. Our findings indicated for the first time that CAPE alleviates airway inflammation and remodeling in chronic asthma by balancing the airway microenvironment, which highlights a novel profile of CAPE as a potent agent for asthma management.

Cell-contact dependent inhibition of monocytes by airway epithelial cells and reversion by infection with Respiratory Syncytial Virus

Airway epithelial cells (AEC) are the first line of defense against airborne infectious microbes and play an important role in regulating the local immune response. However, the interplay of epithelial cells and professional immune cells during both homeostasis and infection has only been partially studied. The present study was performed to determine how bronchial epithelial cells affect the activation of monocytes. Under healthy conditions, AECs were shown to inhibit reactivity of monocytes. We hypothesized that upon infection, monocytes might be released from inhibition by AECs. We report that direct contact of monocytes with unstimulated BEAS2B epithelial cells results in inhibition of TNF secretion by activated monocytes. In addition to the known soluble modulators, we show that cell contacts between epithelial cells and monocytes or macrophages also contribute to homeostatic inhibitory actions. We find AECs to express the inhibitory molecule PD-L1 and blockade of PD-L1 results in increased secretion of pro-inflammatory cytokines from monocytes. Contrary to the inhibitory activities during homeostasis, epithelial cells infected with Respiratory Syncitial Virus (RSV) induce a significant release of inhibition. However, release of inhibition was not due to modulation of PD-L1 expression in AECs. We conclude that airway epithelial cells control the reactivity of monocytes through direct and indirect interactions; however tonic inhibition can be reverted upon stimulation of AECs with RSV and thereof derived molecular patterns. The study confirms the important role of airway epithelial cells for local immune reactions.

Dual oxidase regulates neutrophil recruitment in allergic airways

Enhanced reactive oxygen species production in allergic airways is well described and correlates with increased airway contractions, inflammatory cell infiltration, goblet cell metaplasia, and mucus hypersecretion. There is also an abundance of interleukin-4/interleukin-13 (IL-4/IL-13)- or interleukin-5-secreting cells that are thought to be central to the pathogenesis of allergic asthma. We postulated that the dual oxidases (DUOX1 and DUOX2), members of the nicotinamide adenine dinucleotide phosphate oxidase family that release hydrogen peroxide (H2O2) in the respiratory tract, are critical proteins in the pathogenesis of allergic airways. DUOX activity is regulated by cytokines, including IL-4 and IL-13, and DUOX-mediated H2O2 influences several important features of allergic asthma: mucin production, IL-8 secretion, and wound healing. The objective of this study was to establish the contribution of DUOXs to the development of allergic asthma in a murine model. To accomplish this goal, we utilized a DUOXA-deficient mouse model (Duoxa(-/-)) that lacked maturation factors for both DUOX1 and DUOX2. Our results are the first to demonstrate evidence of DUOX protein and DUOX functional activity in murine airway epithelium. We also demonstrate that DUOXA maturation factors are required for airway-specific H2O2 production and localization of DUOX to cilia of fully differentiated airway epithelial cells. We compared wild-type and Duoxa(-/-) mice in an ovalbumin exposure model to determine the role of DUOX in allergic asthma. In comparison to DUOX-intact mice, Duoxa(-/-) mice had reduced mucous cell metaplasia and lower levels of TH2 cytokine levels in bronchoalveolar fluid. In addition, increased airway resistance in response to methacholine was observed in Duoxa(+/+) mice, as expected, but was absent in Duoxa(-/-) mice. Surprisingly, Duoxa(-/-) mice had decreased influx of neutrophils in bronchoalveolar fluid and lung tissue sections associated with a lower level of the chemotactic cytokine IL-6. These findings suggest that DUOX-derived H2O2 has an important role in signaling neutrophils into allergic airways.