Airway epithelial epidermal growth factor receptor mediates hogbarn dust-induced cytokine release but not Ca2+ response

Amphiregulin modulates murine lung recovery and fibroblast function following exposure to agriculture organic dust

Exposure to agricultural bioaerosols can lead to chronic inflammatory lung diseases. Amphiregulin (AREG) can promote the lung repair process but can also lead to fibrotic remodeling. The objective of this study was to determine the role of AREG in altering recovery from environmental dust exposure in a murine in vivo model and in vitro using cultured human and murine lung fibroblasts. C57BL/6 mice were intranasally exposed to swine confinement facility dust extract (DE) or saline daily for 1 wk or allowed to recover for 3-7 days while being treated with an AREG-neutralizing antibody or recombinant AREG. Treatment with the anti-AREG antibody prevented resolution of DE exposure-induced airway influx of total cells, neutrophils, and macrophages and increased levels of TNF-α, IL-6, and CXCL1. Neutrophils and activated macrophages (CD11c+CD11bhi) persisted after recovery in lung tissues of anti-AREG-treated mice. In murine and human lung fibroblasts, DE induced the release of AREG and inflammatory cytokines. Fibroblast recellularization of primary human lung mesenchymal matrix scaffolds and wound closure was inhibited by DE and enhanced with recombinant AREG alone. AREG treatment rescued the DE-induced inhibitory fibroblast effects. AREG intranasal treatment for 3 days during recovery phase reduced repetitive DE-induced airway inflammatory cell influx and cytokine release. Collectively, these studies demonstrate that inhibition of AREG reduced, whereas AREG supplementation promoted, the airway inflammatory recovery response following environmental bioaerosol exposure, and AREG enhanced fibroblast function, suggesting that AREG could be targeted in agricultural workers repetitively exposed to organic dust environments to potentially prevent and/or reduce disease.

Organic dust induces inflammatory gene expression in lung epithelial cells via ROS-dependent STAT-3 activation

Exposure to dust in agricultural and animal environments, known as organic dust, is associated with the development of respiratory symptoms and respiratory diseases. Inflammation is a key feature of lung pathologies associated with organic dust exposure, and exposure to organic dust induces the expression of several immune and inflammatory mediators. However, information on transcription factors and cellular and molecular mechanisms controlling the production of immune and inflammatory mediators induced by organic dust is limited. In this study, we have identified STAT-3 as an important transcription factor controlling the induction of expression of immune and inflammatory mediators by poultry dust extracts in airway epithelial cells and in mouse lungs and delineated the cellular pathway for STAT-3 activation. Poultry dust extract activated STAT-3 phosphorylation in Beas2B and normal human bronchial epithelial cells and in mouse lungs. Chemical inhibition and siRNA knockdown of STAT-3 suppressed induction of immune and inflammatory mediator expression. Antioxidants suppressed the increase of STAT-3 phosphorylation induced by poultry dust extract indicating that oxidative stress [elevated reactive oxygen species (ROS) levels] is important for the activation. Chemical inhibition and siRNA knockdown experiments demonstrated that STAT-3 activation is dependent on the activation of nonreceptor tyrosine-protein kinase 2 (TYK2) and epidermal growth factor receptor (EGFR) tyrosine kinases. Our studies show that poultry dust extract controls the induction of immune and inflammatory mediator expression via a cellular pathway involving oxidative stress-mediated STAT-3 activation by TYK2 and EGFR tyrosine kinases.

Biphasic changes in airway epithelial cell EGF receptor binding and phosphorylation induced by components of hogbarn dust

PURPOSE OF THE STUDY

Workers in enclosed hogbarns experience an increased incidence of airway inflammation and obstructive lung disease, and an aqueous hogbarn dust extract (HDE) induces multiple inflammation-related responses in cultured airway epithelial cells. Epidermal growth factor receptor (EGFR) phosphorylation and activation has been identified as one important mediator of inflammatory cytokine release from these cells. The studies here investigated both early and late phase adaptive changes in EGFR binding properties and subcellular localization induced by exposure of cells to HDE.

MATERIALS AND METHODS

Cell surface EGFRs were quantified as binding to intact cells on ice. EGFR phosphorylation, expression, and localization were assessed with anti-EGFR antibodies and either blotting or confocal microscopy.

RESULTS

In BEAS-2B and primary human bronchial epithelial cells, HDE induced decreases in cell surface EGFR binding following both 15-min and 18-h exposures. In contrast, H292 cells exhibited only the 15-min decrease, with binding near the control level at 18 hr. Confocal microscopy showed that the 15-min decrease in binding is due to EGFR endocytosis. Although total EGFR immunoreactivity decreased markedly at 18 hr in confocal microscopy with BEAS-2B cells, immunoblots showed no loss of EGFR protein. HDE stimulated EGFR phosphorylation at both 15 min and 18 hr in BEAS-2B cells and primary cells, but only at 15 min in H292 cells, indicating that the different EGFR binding changes among these cell types is likely related to their different time-dependent changes in phosphorylation.

CONCLUSIONS

These studies extend the evidence for EGFRs as important cellular targets for components of HDE and they reveal novel patterns of EGFR phosphorylation and binding changes that vary among airway epithelial cell types. The results provide both impetus and convenient assays for identifying the EGFR-activating components and pathways that likely contribute to hogbarn dust-induced lung disease in agricultural workers.

MyD88 controls airway epithelial Muc5ac expression during TLR activation conditions from agricultural organic dust exposure

Inflammation from airborne microbes can overwhelm compensatory mucociliary clearance mechanisms, leading to mucous cell metaplasia. Toll-like receptor (TLR) activation via myeloid differentiation factor 88 (MyD88) signaling is central to pathogen responses. We have previously shown that agricultural organic dust extract (ODE), with abundant microbial component diversity, activates TLR-induced airway inflammation. With the use of an established model, C57BL/6J wild-type (WT) and global MyD88 knockout (KO) mice were treated with intranasal inhalation of ODE or saline, daily for 1 wk. ODE primarily increased mucin (Muc)5ac levels relative to Muc5b. Compared with ODE-challenged WT mice, ODE-challenged, MyD88-deficient mice demonstrated significantly increased Muc5ac immunostaining, protein levels by immunoblot, and expression by quantitative PCR. The enhanced Muc5ac levels in MyD88-deficient mice were not explained by differences in the differentiation program of airway secretory cells in naïve mice. Increased Muc5ac levels in MyD88-deficient mice were also not explained by augmented inflammation, IL-17A, or neutrophil elastase levels. Furthermore, the enhanced airway mucins in the MyD88-deficient mice were not due to defective secretion, as the mucin secretory capacity of MyD88-KO mice remained intact. Finally, ODE-induced Muc5ac levels were enhanced in MyD88-deficient airway epithelial cells in vitro. In conclusion, MyD88 deficiency enhances airway mucous cell metaplasia under environments with high TLR activation.

Docosahexaenoic acid enhances amphiregulin-mediated bronchial epithelial cell repair processes following organic dust exposure

Injurious dust exposures in the agricultural workplace involve the release of inflammatory mediators and activation of epidermal growth factor receptor (EGFR) in the respiratory epithelium. Amphiregulin (AREG), an EGFR ligand, mediates tissue repair and wound healing in the lung epithelium. Omega-3 fatty acids such as docosahexaenoic acid (DHA) are also known modulators of repair and resolution of inflammatory injury. This study investigated how AREG, DHA, and EGFR modulate lung repair processes following dust-induced injury. Primary human bronchial epithelial (BEC) and BEAS-2B cells were treated with an aqueous extract of swine confinement facility dust (DE) in the presence of DHA and AREG or EGFR inhibitors. Mice were exposed to DE intranasally with or without EGFR inhibition and DHA. Using a decellularized lung scaffolding tissue repair model, BEC recolonization of human lung scaffolds was analyzed in the context of DE, DHA, and AREG treatments. Through these investigations, we identified an important role for AREG in mediating BEC repair processes. DE-induced AREG release from BEC, and DHA treatment following DE exposure, enhanced this release. Both DHA and AREG also enhanced BEC repair capacities and rescued DE-induced recellularization deficits. In vivo, DHA treatment enhanced AREG production following DE exposure, whereas EGFR inhibitor-treated mice exhibited reduced AREG in their lung homogenates. These data indicate a role for AREG in the process of tissue repair after inflammatory lung injury caused by environmental dust exposure and implicate a role for DHA in regulating AREG-mediated repair signaling in BEC.

Role of Proteases in Lung Disease: A Brief Overview

Proteases play an important role in health and disease of the lung. In the normal lungs, proteases maintain their homeostatic functions that regulate processes like its regeneration and repair. Dysregulation of proteases–antiproteases balance is crucial in the manifestation of different types of lung diseases. Chronic inflammatory lung pathologies are associated with a marked increase in protease activities. Thus, in addition to protease activities, inhibition of anti-proteolytic control mechanisms are also important for effective microbial infection and inflammation in the lung. Herein, we briefly summarize the role of different proteases and to some extent antiproteases in regulating a variety of lung diseases.

Proteases in agricultural dust induce lung inflammation through PAR-1 and PAR-2 activation

Workers exposed to aerosolized dust present in concentrated animal feeding operations (CAFOs) are susceptible to inflammatory lung diseases, such as chronic obstructive pulmonary disease. Extracts of dust collected from hog CAFOs [hog dust extract (HDE)] are potent stimulators of lung inflammatory responses in several model systems. The observation that HDE contains active proteases prompted the present study, which evaluated the role of CAFO dust proteases in lung inflammatory processes and tested whether protease-activated receptors (PARs) are involved in the signaling pathway for these events. We hypothesized that the damaging proinflammatory effect of HDE is due, in part, to the proteolytic activation of PARs, and inhibiting the proteases in HDE or disrupting PAR activation would attenuate HDE-mediated inflammatory indexes in bronchial epithelial cells (BECs), in mouse lung slices in vitro, and in a murine in vivo exposure model. Human BECs and mouse lung slice cultures stimulated with 5% HDE released significantly more of each of the cytokines measured (IL-6, IL-8, TNF-α, keratinocyte-derived chemokine/CXC chemokine ligand 1, and macrophage inflammatory protein-2/CXC chemokine ligand 2) than controls, and these effects were markedly diminished by protease inhibition. Inhibition of PARs also blunted the HDE-induced cytokine release from BECs. In addition, protease depletion inhibited HDE-induced BEC intracellular PKCα and PKCε activation. C57BL/6J mice administered 12.5% HDE intranasally, either once or daily for 3 wk, exhibited increased total cellular and neutrophil influx, bronchial alveolar fluid inflammatory cytokines, lung histopathology, and inflammatory scores compared with mice receiving protease-depleted HDE. These data suggest that proteases in dust from CAFOs are important mediators of lung inflammation, and these proteases and their receptors may provide novel targets for therapeutic intervention in CAFO dust-induced airways disease.

Motile cilia harbor serum response factor as a mechanism of environment sensing and injury response in the airway

Nonmotile primary cilia are recognized as important sensory organelles during development and normal biological functioning. For example, recent work demonstrates that transcriptional regulators of the sonic hedgehog signaling pathway localize to primary cilia and participate in sensing and transducing signals regarding the cellular environment. In contrast, motile cilia are traditionally viewed as mechanical machinery, vital for the movement of solutes and clearance of bacteria and debris, but not participants in cellular sensing and signaling mechanisms. Recently, motile cilia were found to harbor receptors responsible for sensing and responding to environmental stimuli. However, no transcription factors are known to be regulated by cilia localization as a sensing mechanism in vertebrates. Using a mouse model of organic dust-induced airway inflammation, we found that the transcription factor serum response factor (SRF) localizes to motile cilia of airway epithelial cells and alters its localization in response to inflammatory stimuli. Furthermore, inhibition of SRF signaling using the small molecule CCG-1423 reduces organic dust-induced IL-8 release from bronchial epithelial cells and stimulates cilia beat frequency in ciliated mouse tracheal epithelial cells. Immunohistochemical analyses reveal that SRF localizes to the cilia of mouse brain ependymal and ovarian epithelial cells as well. These data reveal a novel mechanism by which a transcription factor localizes to motile cilia and modulates cell activities including cilia motility and inflammation response. These data challenge current dogma regarding motile cilia functioning and may lead to significant contributions in understanding motile ciliary signaling dynamics, as well as mechanisms involving SRF-mediated responses to inflammation and injury.

Maresin-1 reduces the pro-inflammatory response of bronchial epithelial cells to organic dust

Background

Exposure to organic dust causes detrimental airway inflammation. Current preventative and therapeutic measures do not adequately treat resulting disease, necessitating novel therapeutic interventions. Recently identified mediators derived from polyunsaturated fatty acids exhibit anti-inflammatory and pro-resolving actions. We tested the potential of one of these mediators, maresin-1 (MaR1), in reducing organic dust-associated airway inflammation.

Methods

As bronchial epithelial cells (BECs) are pivotal in initiating organic dust-induced inflammation, we investigated the in vitro effects of MaR1 on a human BEC cell line (BEAS-2B). Cells were pretreated for 1 hour with 0–200 nM MaR1, followed by 1–24 hour treatment with 5% hog confinement facility-derived organic dust extract (HDE). Alternatively, a mouse lung slice model was utilized in supportive cytokine studies. Supernatants were harvested and cytokine levels determined via enzyme-linked immunosorbent assays. Epithelial cell protein kinase C (PKC) isoforms α and ϵ, and PKA activities were assessed via radioactivity assays, and NFκB and MAPK-related signaling mechanisms were investigated using luciferase vector reporters.

Results

MaR1 dose-dependently reduced IL-6 and IL-8 production following HDE treatment of BECs. MaR1 also reduced HDE-stimulated cytokine release including TNF-α in a mouse lung slice model when given before or following HDE treatment. Previous studies have established that HDE sequentially activates epithelial PKCα and PKCϵ at 1 and 6 hours, respectively that regulated TNF-α, IL-6, and IL-8 release. MaR1 pretreatment abrogated these HDE-induced PKC activities. Furthermore, HDE treatment over a 24-hour period revealed temporal increases in NFκB, AP-1, SP-1, and SRE DNA binding activities, using luciferase reporter assays. MaR1 pretreatment did not alter the activation of NFκB, AP-1, or SP-1, but did reduce the activation of DNA binding at SRE.

Conclusions

These observations indicate a role for MaR1 in attenuating the pro-inflammatory responses of BECs to organic dust extract, through a mechanism that does not appear to rely on reduced NFκB, AP-1, or SP-1-related signaling, but may be mediated partly through SRE-related signaling. These data offer insights for a novel mechanistic action of MaR1 in bronchial epithelial cells, and support future in vivo studies to test MaR1’s utility in reducing the deleterious inflammatory effects of environmental dust exposures.

Dust from hog confinement facilities impairs Ca2+ mobilization from sarco(endo)plasmic reticulum by inhibiting ryanodine receptors

Individuals working in commercial hog confinement facilities have elevated incidences of headaches, depression, nausea, skeletal muscle weakness, fatigue, gastrointestinal disorders, and cardiovascular diseases, and the molecular mechanisms for these nonrespiratory ailments remain incompletely undefined. A common element underlying these diverse pathophysiologies is perturbation of intracellular Ca(2+) homeostasis. This study assessed whether the dust generated inside hog confinement facilities contains compounds that alter Ca(2+) mobilization via ryanodine receptors (RyRs), key intracellular channels responsible for mobilizing Ca(2+) from internal stores to elicit an array of physiologic functions. Hog barn dust (HBD) was extracted with phosphate-buffered saline, sterile-filtered (0.22 μm), and size-separated using Sephadex G-100 resin. Fractions (F) 1 through 9 (Mw >10,000 Da) had no measurable effects on RyR isoforms. However, F10 through F17, which contained compounds of Mw ≤2,000 Da, modulated the [(3)H]ryanodine binding to RyR1, RyR2, and RyR3 in a biphasic (Gaussian) manner. The Ki values for F13, the most potent fraction, were 3.8 ± 0.2 μg/ml for RyR1, 0.2 ± 0.01 μg/ml and 19.1 ± 2.8 μg/ml for RyR2 (two binding sites), and 44.9 ± 2.8 μg/ml and 501.6 ± 9.2 μg/ml for RyR3 (two binding sites). In lipid bilayer assays, F13 dose-dependently decreased the open probabilities of RyR1, RyR2, and RyR3. Pretreating differentiated mouse skeletal myotubes (C2C12 cells) with F13 blunted the amplitudes of ryanodine- and K(+)-induced Ca(2+) transients. Because RyRs are present in many cell types, impairment in Ca(2+) mobilization from internal stores via these channels is a possible mechanism by which HBD may trigger these seemingly unrelated pathophysiologies.