Feedlot dust stimulation of interleukin-6 and -8 requires protein kinase Cepsilon in human bronchial epithelial cells

NADPH and xanthine oxidases control induction of inflammatory mediator expression by organic dust in the lung

Exposure to organic dust in animal and agricultural farms and the ensuing lung inflammation are linked to the development of respiratory diseases. We found previously that elevated production of reactive oxygen species (ROS) by aqueous poultry organic dust extract (hereafter referred to as dust extract) mediates induction of proinflammatory mediators in airway epithelial cells. In the present study, we investigated whether ROS generated by NADPH oxidases (NOX) and xanthine oxidase (XO) controls induction of inflammatory mediators by dust extract and the underlying mechanisms in bronchial epithelial cells. Using chemical inhibitors and siRNA targeted knockdown, we found that NOX1, NOX2, NOX4, and XO-derived ROS regulates induction of proinflammatory mediator levels. Like airway epithelial cells in vitro, NOX inhibitor VAS2870 reduced keratinocyte chemoattractant (KC), IL-6, and TNF-α production and 4-hydroxynonenal (4-HNE) staining induced by dust extract in mouse lungs. VAS2870 inhibition of proinflammatory mediators was associated with reduced NFκB and Stat3 activation indicating that NOX generated ROS activates NFκB and Stat3 to induce proinflammatory gene expression. Dust extract increased the membrane association of p47^phox in airway epithelial cells indicating NOX2 activation but had no effect on NOX2 protein levels. In summary, our studies have shown that NOX and XO generated ROS control organic dust induction of proinflammatory mediators in airway epithelial cells via NFκB and Stat3 activation.

Bacterial extracellular vesicles isolated from organic dust induce neutrophilic inflammation in the lung

Inhalation of organic dust is an occupational hazard leading to the development of respiratory symptoms and respiratory diseases. Bioaerosols from concentrated animal feeding operations are rich in bacteria and could carry bacterial extracellular vesicles (EVs) that could induce lung inflammation. It is not known if organic dust contains bacterial EVs and whether they modulate lung inflammation. Herein, we show that poultry organic dust contains bacterial EVs (dust EVs) that induce lung inflammation. Treatment of airway epithelial cells, THP-1-monocytes and -macrophages with dust EVs rapidly induced IL-8, IL-6, ICAM-1, proIL-1β, and TNF-α levels. In airway epithelial cells, induction of inflammatory mediators was due to increased mRNA levels and NF-κB activation. Induction of inflammatory mediators by dust EVs was not inhibited by polymyxin B. Single and repeated treatments of mice with dust EVs increased lung KC, IL-6, and TNF-α levels without significantly altering IL-17A levels. Increases in cytokines were associated with enhanced neutrophil infiltration into the lung. Repeated treatments of mice with dust EVs increased lung mean linear intercept and increased collagen deposition around airways indicating lung remodeling. Peribronchial cell infiltrates and airway epithelial thickening were also observed in treated mice. Because bacterial EVs are nanometer-sized particles, they can reach and accumulate in the bronchiolar and alveolar regions causing lung injury leading to the development of respiratory diseases. Our studies have provided new evidence for the presence of bacterial EVs in organic dust and for their role as one of the causative agents of organic dust-induced lung inflammation and lung injury.

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.

Organic barn dust inhibits surfactant protein D production through protein kinase-c alpha dependent increase of GPR116

Prolonged exposure to organic barn dusts can lead to chronic inflammation and a broad range of lung problems over time, mediated by innate immune mechanisms. The immune surfactant or collectin surfactant protein D (SP-D) is a crucial multifunctional innate immune receptor. Little work to date has examined the effect of such collectins in response to organic dusts. We provide evidence here that agricultural organic dusts can inhibit mRNA and protein expression of SP-D in a human alveolar epithelial cell line, and an in vivo mouse model. This inhibition was not a result of lipopolysaccharide (LPS) or peptidoglycans, the two most commonly cited immune active components of these dusts. We further show that inhibition of the signaling molecule protein kinase C alpha (PKCα) can reverse this inhibition implicating it as a mechanism of SP-D inhibition. Examination of the SP-D regulatory receptor GPR116 showed that its mRNA expression was increased in response to dust and inhibited by blocking PKCα, implicating it as a means of inhibiting SP-D in the lungs in response to organic dusts. This reduction shows that organic barn dust can reduce lung SP-D, thus leaving workers potentially at risk for a host of pathogens.

Effect of low-level CO2 on innate inflammatory protein response to organic dust from swine confinement barns

BACKGROUND

Organic hog barn dust (HDE) exposure induces lung inflammation and long-term decreases in lung function in agricultural workers. While concentrations of common gasses in confined animal facilities are well characterized, few studies have been done addressing if exposure to elevated barn gasses impacts the lung immune response to organic dusts. Given the well documented effects of hypercapnia at much higher levels we hypothesized that CO2 at 8 h exposure limit levels (5000 ppm) could alter innate immune responses to HDE.

METHODS

Using a mouse model, C57BL/6 mice were nasally instilled with defined barn dust extracts and then housed in an exposure box maintained at one of several CO2 levels for six hours. Bronchiolar lavage (BAL) was tested for several cytokines while lung tissue was saved for mRNA purification and immunohistochemistry.

RESULTS

Exposure to elevated CO2 significantly increased the expression of pro-inflammatory markers, IL-6 and KC, in BAL fluid as compared to dust exposure alone. Expression of other pro-inflammatory markers, such as ICAM-1 and matrix metalloproteinase-9 (MMP-9), were also tested and showed similar increased expression upon HDE + CO2 exposure. A chemokine array analysis of BAL fluid revealed that MIP-1γ (CCL9) shows a similar increased response to HDE + CO2. Further testing showed CCL9 was significantly elevated by barn dust and further enhanced by CO2 co-exposure in a dose-dependent manner that was noticeable at the protein and mRNA levels. In all cases, except for ICAM-1, increases in tested markers in the presence of elevated CO2 were only significant in the presence of HDE as well.

CONCLUSIONS

We show that even at mandated safe exposure limits, CO2 is capable of enhancing multiple markers of inflammation in response to HDE.

Pulmonary innate inflammatory responses to agricultural occupational contaminants

Agricultural workers are exposed to many contaminants and suffer from respiratory and other symptoms. Dusts, gases, microbial products and pesticide residues from farms have been linked to effects on the health of agricultural workers. Growing sets of data from in vitro and in vivo models demonstrate the role of the innate immune system, especially Toll-like receptor 4 (TLR4) and TLR9, in lung inflammation induced following exposure to contaminants in agricultural environments. Interestingly, inflammation and lung function changes appear to be discordant indicating the complexity of inflammatory responses to exposures. Whereas the recent development of rodent models and exposure systems have yielded valuable data, we need new systems to examine the combined effects of multiple contaminants in order to increase our understanding of farm-exposure-induced negative health effects.

Proteases and oxidant stress control organic dust induction of inflammatory gene expression in lung epithelial cells

Background

Persistant inflammatory responses to infectious agents and other components in organic dust underlie lung injury and development of respiratory diseases. Organic dust components responsible for eliciting inflammation and the mechanisms by which they cause lung inflammation are not fully understood. We studied the mechanisms by which protease activities in poultry dust extracts and intracellular oxidant stress induce inflammatory gene expression in A549 and Beas2B lung epithelial cells.

Methods

The effects of dust extracts on inflammatory gene expression were analyzed by quantitative polymerase chain reaction (qPCR), enzyme linked immunosorbent (ELISA) and western blot assays. Oxidant stress was probed by dihydroethidium (DHE) labeling, and immunostaining for 4-hydroxynonenal (4-HNE). Effects on interleukin-8 (IL-8) promoter regulation were determined by transient transfection assay.

Results

Dust extracts contained trypsin and elastase activities, and activated protease activated receptor (PAR)-1 and -2. Serine protease inhibitors and PAR-1 or PAR-2 knockdown suppressed inflammatory gene induction. Dust extract induction of IL-8 gene expression was associated with increased DHE-fluorescence and 4-HNE staining, and antioxidants suppressed inflammatory gene induction. Protease inhibitors and antioxidants suppressed protein kinase C and NF-κB activation and induction of IL-8 promoter activity in cells exposed to dust extract.

Conclusions

Our studies demonstrate that proteases and intracellular oxidants control organic dust induction of inflammatory gene expression in lung epithelial cells. Targeting proteases and oxidant stress may serve as novel approaches for the treatment of organic dust induced lung diseases. This is the first report on the involvement of oxidant stress in the induction of inflammatory gene expression by organic dust.

Electronic supplementary material

The online version of this article (doi:10.1186/s12931-016-0455-z) contains supplementary material, which is available to authorized users.

CXCR1/CXCR2 antagonist CXCL8(3-74)K11R/G31P blocks lung inflammation in swine barn dust-instilled mice

Inhalation of agricultural occupational dusts from swine confinement facilities can result in lung inflammation. The innate immune response to organic barn dusts results in production of a number of pro-inflammatory factors in the lungs of barn workers such as cytokines, chemokines, and an influx of neutrophils. Many of these inflammatory factors are influenced by the chemokine CXCL8/IL-8 (KC or MIP-2 in mice). Previously, we have demonstrated that an endotoxin-independent component of swine barn dust extract (SBE) elevates lung chemokines in a protein kinase C (PKC)-dependent manner resulting in the significant formation of lung inflammatory cell infiltrates in a mouse model of SBE injury. In this study we test the ability of a CXCR1/CXCR2 antagonist, CXCL8(3-74)K11R/G31P (G31P) to block many of the features of lung-inflammation in response to challenge with SBE in an established mouse exposure system. Injection of G31P concurrent with SBE nasal instillation over a course of 3 weeks significantly reduced neutrophil accumulation in the lungs of barn dust exposed animals compared to those given SBE alone. There was a similar reduction in pro-inflammatory cytokines and chemokines IL-6, KC, and MIP-2 in SBE plus G31P-treated mice. In addition to excreted products, the receptors ICAM-1, CXCR1, and CXCR2, which all were elevated with SBE exposure, were also decreased with G31P treatment. SBE activation of PKCα and PKCε was reduced as well with G31P treatment. Thus, G31P was found to be highly effective at reducing several features of lung inflammation in mice exposed to barn dust extracts.

Transcriptional mechanisms and protein kinase signaling mediate organic dust induction of IL-8 expression in lung epithelial and THP-1 cells

Exposure to the agricultural work environment is a risk factor for the development of respiratory symptoms and chronic lung diseases. Inflammation is an important contributor to the pathogenesis of tissue injury and disease. Cellular and molecular mechanisms mediating lung inflammatory responses to agricultural dust are not yet fully understood. We studied the effects of poultry dust extract on molecular regulation of interleukin-8 (IL-8), a proinflammatory cytokine, in A549 and Beas2B lung epithelial and THP-1 monocytic cells. Our findings indicate that poultry dust extract potently induces IL-8 levels by increasing IL-8 gene transcription without altering IL-8 mRNA stability. Increase in IL-8 promoter activity was due to enhanced binding of activator protein 1 and NF-κB. IL-8 induction was associated with protein kinase C (PKC) and mitogen-activated protein kinase (MAPK) activation and inhibited by PKC and MAPK inhibitors. IL-8 increase was not inhibited by polymyxin B or l-nitroarginine methyl ester, indicating lack of involvement of lipopolysaccharide and nitric oxide in the induction. Lung epithelial and THP-1 cells share common mechanisms for induction of IL-8 levels. Our findings identify key roles for transcriptional mechanisms and protein kinase signaling pathways for IL-8 induction and provide insights into the mechanisms regulating lung inflammatory responses to organic dust exposure.

Differential response of human nasal and bronchial epithelial cells upon exposure to size-fractionated dairy dust

Exposure to organic dusts is associated with increased respiratory morbidity and mortality in agricultural workers. Organic dusts in dairy farm environments are complex, polydisperse mixtures of toxic and immunogenic compounds. Previous toxicological studies focused primarily on exposures to the respirable size fraction; however, organic dusts in dairy farm environments are known to contain larger particles. Given the size distribution of dusts from dairy farm environments, the nasal and bronchial epithelia represent targets of agricultural dust exposures. In this study, well-differentiated normal human bronchial epithelial cells and human nasal epithelial cells were exposed to two different size fractions (PM10 and PM>10) of dairy parlor dust using a novel aerosol-to-cell exposure system. Levels of proinflammatory transcripts (interleukin [IL]-8, IL-6, and tumor necrosis factor [TNF]-α) were measured 2 h after exposure. Lactate dehydrogenase (LDH) release was also measured as an indicator of cytotoxicity. Cell exposure to dust was measured in each size fraction as a function of mass, endotoxin, and muramic acid levels. To our knowledge, this is the first study to evaluate the effects of distinct size fractions of agricultural dust on human airway epithelial cells. Our results suggest that both PM10 and PM>10 size fractions elicit a proinflammatory response in airway epithelial cells and that the entire inhalable size fraction needs to be considered when assessing potential risks from exposure to agricultural dusts. Further, data suggest that human bronchial cells respond differently to these dusts than human nasal cells, and therefore that the two cell types need to be considered separately in airway cell models of agricultural dust toxicity.

Oxidative stress and aromatic hydrocarbon response of human bronchial epithelial cells exposed to petro- or biodiesel exhaust treated with a diesel particulate filter

The composition of diesel exhaust has changed over the past decade due to the increased use of alternative fuels, like biodiesel, and to new regulations on diesel engine emissions. Given the changing nature of diesel fuels and diesel exhaust emissions, a need exists to understand the human health implications of switching to "cleaner" diesel engines run with particulate filters and engines run on alternative fuels like biodiesel. We exposed well-differentiated normal human bronchial epithelial cells to fresh, complete exhaust from a diesel engine run (1) with and without a diesel particulate filter and (2) using either traditional petro- or alternative biodiesel. Despite the lowered emissions in filter-treated exhaust (a 91-96% reduction in mass), significant increases in transcripts associated with oxidative stress and polycyclic aromatic hydrocarbon response were observed in all exposure groups and were not significantly different between exposure groups. Our results suggest that biodiesel and filter-treated diesel exhaust elicits as great, or greater a cellular response as unfiltered, traditional petrodiesel exhaust in a representative model of the bronchial epithelium.

Dimethylarginine dimethylaminohydrolase (DDAH) overexpression attenuates agricultural organic dust extract-induced inflammation

Modern, industrialized farming practices have lead to working conditions that include high levels of airborne dust. Agricultural workers inhale these complex organic dusts on a daily basis, leading to airway inflammation and higher risk for developing chronic obstructive pulmonary disease. The mechanisms regulating the organic dust-induced airway inflammatory response are not well-defined. We investigated whether overexpression of dimethylarginine dimethylaminohydrolase (DDAH) would lead to diminished pulmonary inflammation in an animal model of organic dust extract exposure. We instilled wild-type (WT) and DDAH overexpressing mice with an aqueous organic dust extract (ODE) collected from a swine confinement building. We found that inflammatory indices such as neutrophil influx and inflammatory cytokine production was lower in the DDAH overexpressing mice compared to WT after organic dust extract (ODE) instillation. We went on to determine how DDAH was mediating the decrease in inflammation induced by ODE. PKCα and PKCε play an essential role in the ODE inflammatory response. In a model of lung slices from WT and DDAH overexpressing mice, we demonstrated an increase in PKCα and PKCε in the WT mice exposed to ODE. This increase was diminished in the DDAH overexpressing mice exposed to ODE. We also tested an important component of the ODE, peptidoglycan (PGN). We noted a similar decrease in neutrophils and inflammatory cytokines in the DDAH overexpressing animals instilled with PGN compared to WT. In conclusion, our studies found a role for DDAH in regulating the ODE-triggered activation of epithelial PKCα and PKCε, a previously unrecognized mechanism of action. This ultimately results in diminished pulmonary inflammation.

Aging causes a slowing in ciliary beat frequency, mediated by PKCε

The elderly are at much higher risk for developing pneumonia than younger individuals. Pneumonia is a leading cause of death and is the third most common reason for hospitalization in the elderly. One reason that elderly people may be more susceptible to pneumonia is a breakdown in the lung's first line of defense, mucociliary clearance. Cilia beat in a coordinated manner to propel out invading microorganisms and particles. Ciliary beat frequency (CBF) is known to slow with aging, however, little is known about the mechanism(s) involved. We compared the CBF in BALB/c and C57BL/6 mice aged 2, 12, and 24 mo and found that CBF diminishes with age. Cilia in the mice at age 12 and 24 mo retained their ability to be stimulated by the β2 agonist procaterol. To help determine the mechanism of ciliary slowing, we measured protein kinase C alpha and epsilon (PKCα and PKCε) activity. There were no activity differences in PKCα between the mice aged 2, 12, or 24 mo. However, we demonstrated a significantly higher PKCε activity in the mice at 12 and 24 mo than the in the mice 2 mo of age. The increase in activity is likely due to a nearly threefold increase in PKCε protein in the lung during aging. To strengthen the connection between activation of PKCε and ciliary slowing, we treated tracheas of mice at 2 mo with the PKCε agonist 8-[2-(2-pentylcyclopropylmethyl)-cyclopropyl]-octanoic acid (DCP-LA). We noted a similar decrease in baseline CBF, and the cilia remained sensitive to stimulation with β2 agonists. The mechanisms for the slowing of baseline CBF have not been previously determined. In this mouse model of aging we were able to show that decreases in CBF are related to an increase in PKCε activity.

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.

Proinflammatory effects of cookstove emissions on human bronchial epithelial cells

Approximately half of the world's population uses biomass fuel for indoor cooking and heating. This form of combustion typically occurs in open fires or primitive stoves. Human exposure to emissions from indoor biomass combustion is a global health concern, causing an estimated 1.5 million premature deaths each year. Many 'improved' stoves have been developed to address this concern; however, studies that examine exposure-response with cleaner-burning, more efficient stoves are few. The objective of this research was to evaluate the effects of traditional and cleaner-burning stove emissions on an established model of the bronchial epithelium. We exposed well-differentiated, normal human bronchial epithelial cells to emissions from a single biomass combustion event using either a traditional three-stone fire or one of two energy-efficient stoves. Air-liquid interface cultures were exposed using a novel, aerosol-to-cell deposition system. Cellular expression of a panel of three pro-inflammatory markers was evaluated at 1 and 24 h following exposure. Cells exposed to emissions from the cleaner-burning stoves generated significantly fewer amounts of pro-inflammatory markers than cells exposed to emissions from a traditional three-stone fire. Particulate matter emissions from each cookstove were substantially different, with the three-stone fire producing the largest concentrations of particles (by both number and mass). This study supports emerging evidence that more efficient cookstoves have the potential to reduce respiratory inflammation in settings where solid fuel combustion is used to meet basic domestic needs.

PRACTICAL IMPLICATIONS

Emissions from more efficient, cleaner-burning cookstoves produced less inflammation in well-differentiated bronchial lung cells. The results support evidence that more efficient cookstoves can reduce the health burden associated with exposure to indoor pollution from the combustion of biomass.

Regulation of interleukin-6 secretion by the two-pore-domain potassium channel Trek-1 in alveolar epithelial cells

We recently proposed a role for the two-pore-domain K(+) (K2P) channel Trek-1 in the regulation of cytokine release from mouse alveolar epithelial cells (AECs) by demonstrating decreased interleukin-6 (IL-6) secretion from Trek-1-deficient cells, but the underlying mechanisms remained unknown. This study was designed to investigate the mechanisms by which Trek-1 decreases IL-6 secretion. We hypothesized that Trek-1 regulates tumor necrosis factor-α (TNF-α)-induced IL-6 release via NF-κB-, p38-, and PKC-dependent pathways. We found that Trek-1 deficiency decreased IL-6 secretion from mouse and human AECs at both transcriptional and translational levels. While NF-κB/p65 phosphorylation was unchanged, p38 phosphorylation was decreased in Trek-1-deficient cells, and pharmacological inhibition of p38 decreased IL-6 secretion in control but not Trek-1-deficient cells. Similarly, pharmacological inhibition of PKC also decreased IL-6 release, and we found decreased phosphorylation of the isoforms PKC/PKDμ (Ser(744/748)), PKCθ, PKCδ, PKCα/βII, and PKCζ/λ, but not PKC/PKDμ (Ser(916)) in Trek-1-deficient AECs. Phosphorylation of PKCθ, a Ca(2+)-independent isoform, was intact in control cells but impaired in Trek-1-deficient cells. Furthermore, TNF-α did not elevate the intracellular Ca(2+) concentration in control or Trek-1-deficient cells, and removal of extracellular Ca(2+) did not impair IL-6 release. In summary, we report the expression of Trek-1 in human AECs and propose that Trek-1 deficiency may alter both IL-6 translation and transcription in AECs without affecting Ca(2+) signaling. The results of this study identify Trek-1 as a new potential target for the development of novel treatment strategies against acute lung injury.

Knowledge translation: airway epithelial cell migration and respiratory diseases

Airway epithelial cell migration is essential for lung development and growth, as well as the maintenance of respiratory tissue integrity. This vital cellular process is also important for the repair and regeneration of damaged airway epithelium. More importantly, several lung diseases characterized by aberrant tissue remodeling result from the improper repair of damaged respiratory tissue. Epithelial cell migration relies upon extracellular matrix molecules and is further regulated by numerous local, neuronal, and hormonal factors. Under inflammatory conditions, cell migration can also be stimulated by certain cytokines and chemokines. Many well-known environmental factors involved in the pathogenesis of chronic lung diseases (e.g., cigarette smoking, air pollution, alcohol intake, inflammation, viral and bacterial infections) can inhibit airway epithelial cell migration. Further investigation of cellular and molecular mechanisms of cell migration with advanced techniques may provide knowledge that is relevant to physiological and pathological conditions. These studies may eventually lead to the development of therapeutic interventions to improve lung repair and regeneration and to prevent aberrant remodeling in the lung.

Protein kinase C epsilon is important in modulating organic-dust-induced airway inflammation

Organic dust samples from swine confinement facilities elicit pro-inflammatory cytokine/chemokine release from bronchial epithelial cells and monocytes, dependent, in part, upon dust-induced activation of the protein kinase C (PKC) isoform, PKCε. PKCε is also rapidly activated in murine tracheal epithelial cells following in vivo organic dust challenges, yet the functional role of PKCε in modulating dust-induced airway inflammatory outcomes is not defined. Utilizing an established intranasal inhalation animal model, experiments investigated the biologic and physiologic responses following organic dust extract (ODE) treatments in wild-type (WT) and PKCε knock-out (KO) mice. We found that neutrophil influx increased more than twofold in PKCε KO mice following both a one-time challenge and 3 weeks of daily challenges with ODE as compared with WT mice. Lung pathology revealed increased bronchiolar and alveolar inflammation, lymphoid aggregates, and T cell influx in ODE-treated PKCε KO mice. Airway hyperresponsiveness to methacholine increased in PKCε KO + ODE to a greater magnitude than WT + ODE animals. There were no significant differences in cytokine/chemokine release elicited by ODE treatment between groups. However, ODE-induced nitric oxide (NO) production differed in that ODE exposure increased nitrate levels in WT mice but not in PKCε KO mice. Moreover, ODE failed to upregulate NO from ex vivo stimulated PKCε KO lung macrophages. Collectively, these studies demonstrate that PKCε-deficient mice were hypersensitive to organic dust exposure and suggest that PKCε is important in the normative lung inflammatory response to ODE. Dampening of ODE-induced NO may contribute to these enhanced inflammatory findings.

CD11c(+)/CD11b(+) cells are critical for organic dust-elicited murine lung inflammation

Organic dust exposure in the agricultural industry results in significant lung disease. Macrophage infiltrates are increased in the lungs after organic dust exposures, yet the phenotype and functional importance of these cells remain unclear. Using an established intranasal inhalation murine model of dust-induced lung inflammation, animals were treated once or daily for 3 weeks with swine confinement organic dust extract (DE). Repetitive DE treatment for 3 weeks resulted in significant increases in CD11c(+)/CD11b(+) macrophages in whole lung-associated tissue. These cells displayed increased costimulatory molecule (CD80 and CD86) expression, enhanced phagocytic ability, and an increased production of IL-6, CXCL1, and CXCL2. Similar findings were observed with the CD11c(+)/CD11b(+) macrophage infiltrate after repetitive exposure to peptidoglycan, a major DE component. To determine the functional importance of macrophages in mediating DE-induced airway inflammation, lung macrophages were selectively depleted using a well-established intranasal clodronate liposome depletion/suicide strategy. First, macrophage depletion by clodronate liposomes resulted in significant reductions in airway neutrophil influx and TNF-α and IL-6 production after a single exposure to DE. In contrast, after repetitive 3-week exposure to DE, airway lavage fluid and lung tissue neutrophils were significantly increased in clodronate liposome-treated mice compared with control mice. A histological examination of lung tissue demonstrated striking increases in alveolar and bronchiolar inflammation, as well as in the size and distribution of cellular aggregates in clodronate-liposome versus saline-liposome groups repetitively exposed to DE. These studies demonstrate that DE elicits activated CD11c(+)/CD11b(+) macrophages in the lung, which play a critical role in regulating the outcome of DE-induced airway inflammation.

Non-typeable Haemophilus influenzae decreases cilia beating via protein kinase Cε

BACKGROUND

Haemophilus influenzae infection of the nasal epithelium has long been associated with observations of decreased nasal ciliary beat frequency (CBF) and injury to the ciliated epithelium. Previously, we have reported that several agents that slow CBF also have the effect of activating protein kinase C epsilon (PKCε) activity in bronchial epithelial cells. The subsequent auto-downregulation of PKCε or the direct inhibition of PKCε leads to the specific detachment of the ciliated cells.

METHODS

Primary cultures of ciliated bovine bronchial epithelial cells were exposed to filtered conditioned media supernatants from non-typeable H. influenzae (NTHi) cultures. CBF and motile points were measured and PKCε activity assayed.

RESULTS

NTHi supernatant exposure significantly and rapidly decreased CBF in a dose-dependent manner within 10 minutes of exposure. After 3 hours of exposure, the number of motile ciliated cells significantly decreased. Direct measurement of PKCε activity revealed a dose-dependent activation of PKCε in response to NTHi supernatant exposure. Both CBF and PKCε activity changes were only observed in fresh NTHi culture supernatant and not observed in exposures to heat-inactivated or frozen supernatants.

CONCLUSIONS

Our results suggest that CBF slowing observed in response to NTHi is consistent with the stimulated activation of PKCε. Ciliated cell detachment is associated with PKCε autodownregulation.

Histopathological analogies in chronic pulmonary lesions between cattle and humans: basis for an alternative animal model

Most of the natural cases of pneumonia in feedlot cattle are characterized by a longer clinical course due to chronic lung lesions. Microscopically, these lesions include interstitial fibroplasia, bronchitis, bronchiectasis, bronchiolitis obliterans, and epithelial metaplasia of the airways. Herein, the aim was to review, under a medical perspective, the pathologic mechanisms operating in these chronic pneumonic lesions in calves. Based on the similarities of these changes to those reported in bronchiolitis obliterans/organising pneumonia (BO/OP) and chronic obstructive pulmonary disease (COPD) in human beings, calves are proposed as an alternative animal model.

Respiratory health effects of large animal farming environments

With increases in large animal-feeding operations to meet consumer demand, adverse upper and lower respiratory health effects in exposed agriculture workers are a concern. The aim of this study was to review large animal confinement feeding operational exposures associated with respiratory disease with a focus on recent advances in the knowledge of causative factors and cellular and immunological mechanisms. A PubMed search was conducted with the keywords airway, farm, swine, dairy, horse, cattle inflammation, organic dust, endotoxin, and peptidoglycan, among items were published between 1980 and now. Articles were selected based on their relevance to environmental exposure and reference to airway diseases. Airway diseases included rhinitis, sinusitis, mucus membrane inflammation syndrome, asthma, chronic bronchitis, chronic obstructive pulmonary disease, hypersensitivity pneumonitis, and organic dust toxic syndrome. There is lower prevalence of immunoglobulin (Ig) E-mediated asthma and atopy in farmers and their children, but organic dust worsens existing asthma. Multiple etiologic factors are linked to disease, including allergens, organic dusts, endotoxins, peptidoglycans, and gases. Large animal confinement feeding operations contain a wide diversity of microbes with increasing focus on gram-positive bacteria and archaebacteria as opposed to gram-negative bacteria in mediating disease. Toll-like receptors (TLR) and nucleotide oligomerization domain (NOD)-like innate immune pathways respond to these exposures. Finally, a chronic inflammatory adaptation, tolerance-like response in chronically exposed workers occurs. Large animal confinement farming exposures produce a wide spectrum of upper and lower respiratory tract diseases due to the complex diversity of organic dust, particulates, microbial cell wall components, and gases and resultant activation of various innate immune receptor signaling pathways.

Alcohol increases the permeability of airway epithelial tight junctions in Beas-2B and NHBE cells

BACKGROUND

Tight junctions form a continuous belt-like structure between cells and act to regulate paracellular signaling. Protein kinase C (PKC) has been shown to regulate tight junction assembly and disassembly and is activated by alcohol. Previous research has shown that alcohol increases the permeability of tight junctions in lung alveolar cells. However, little is known about alcohol's effect on tight junctions in epithelium of the conducting airways. We hypothesized that long-term alcohol exposure reduces zonula occluden-1 (ZO-1) and claudin-1 localization at the cell membrane and increases permeability through a PKC-dependent mechanism.

METHODS

To test this hypothesis, we exposed normal human bronchial epithelial (NHBE) cells, cells from a human bronchial epithelial transformed cell line (Beas-2B), and Beas-2B expressing a PKCα dominant negative (DN) to alcohol (20, 50, and 100 mM) for up to 48 hours. Immunofluorescence was used to assess changes in ZO-1, claudin-1, claudin-5, and claudin-7 localization. Electric cell-substrate impedance sensing was used to measure the permeability of tight junctions between monolayers of NHBE, Beas-2B, and DN cells.

RESULTS

Alcohol increased tight junction permeability in a concentration-dependent manner and decreased ZO-1, claudin-1, claudin-5, and claudin-7 localization at the cell membrane. To determine a possible signaling mechanism, we measured the activity of PKC isoforms (alpha, delta, epsilon, and zeta). PKCα activity significantly increased in Beas-2B cells from 1 to 6 hours of 100 mM alcohol exposure, while PKCζ activity significantly decreased at 1 hour and increased at 3 hours. Inhibiting PKCα with Gö-6976 prevented the alcohol-induced protein changes in both ZO-1 and claudin-1 at the cell membrane. PKCα DN Beas-2B cells were resistant to alcohol-induced protein alterations.

CONCLUSIONS

These results suggest that alcohol disrupts ZO-1, claudin-1, claudin-5, and claudin-7 through the activation of PKCα, leading to an alcohol-induced "leakiness" in bronchial epithelial cells. Such alcohol-induced airway-leak state likely contributes to the impaired airway host defenses associated with acute and chronic alcohol ingestion.

Chloroform extract of hog barn dust modulates skeletal muscle ryanodine receptor calcium-release channel (RyR1)

Skeletal muscle weakness is a reported ailment in individuals working in commercial hog confinement facilities. To date, specific mechanisms responsible for this symptom remain undefined. The purpose of this study was to assess whether hog barn dust (HBD) contains components that are capable of binding to and modulating the activity of type 1 ryanodine receptor Ca2+-release channel (RyR1), a key regulator of skeletal muscle function. HBD collected from confinement facilities in Nebraska were extracted with chloroform, filtered, and rotary evaporated to dryness. Residues were resuspended in hexane-chloroform (20:1) and precipitates, referred to as HBDorg, were air-dried and studied further. In competition assays, HBDorg dose-dependently displaced [3H]ryanodine from binding sites on RyR1 with an IC50 of 1.5±0.1 microg/ml (Ki=0.4±0.0 microg/ml). In single-channel assays using RyR1 reconstituted into a lipid bilayer, HBDorg exhibited three distinct dose-dependent effects: first it increased the open probability of RyR1 by increasing its gating frequency and dwell time in the open state, then it induced a state of reduced conductance (55% of maximum) that was more likely to occur and persist at positive holding potentials, and finally it irreversibly closed RyR1. In differentiated C2C12 myotubes, addition of HBD triggered a rise in intracellular Ca2+ that was blocked by pretreatment with ryanodine. Since persistent activation and/or closure of RyR1 results in skeletal muscle weakness, these new data suggest that HBD is responsible, at least in part, for the muscle ailment reported by hog confinement workers.

Prostaglandin F2alpha represses IGF-I-stimulated IRS1/phosphatidylinositol-3-kinase/AKT signaling in the corpus luteum: role of ERK and P70 ribosomal S6 kinase

Little is known about the early intracellular events that contribute to corpus luteum regression. Experiments were designed to determine the effects of prostaglandin F2alpha (PGF2alpha) on phosphatidylinositol-3-kinase (PI3K)/Akt signaling in the corpus luteum in vivo and in vitro. Treatment of midluteal-phase cows with a luteolytic dose of PGF2alpha resulted in a rapid increase in ERK and mammalian target of rapamycin (mTOR)/p70 ribosomal protein S6 kinase (p70S6K1) signaling and a rapid suppression of Akt phosphorylation in luteal tissue. In vitro treatment of primary cultures of luteal cells with PGF2alpha also resulted in an increase in ERK and mTOR/p70S6K1 signaling and a diminished capacity of IGF-I to stimulate PI3K, Akt, and protein kinase C zeta activation. Accounting for the reductions in PI3K and Akt activation observed in response to PGF2alpha treatment, we found that PGF2alpha promoted the phosphorylation of serine residues (307, 612, 636) in the insulin receptor substrate 1 (IRS1) peptide sequence in vivo and in vitro. Serine phosphorylation of IRS1 was associated with reduced formation of IGF-I-stimulated IRS1/PI3Kp85 complexes. Furthermore, treatment with inhibitors of the MAPK kinase 1/ERK or mTOR/p70S6K1 signaling pathways prevented PGF2alpha-induced serine phosphorylation of IRS1 and abrogated the inhibitory actions of PGF2alpha on Akt activation. Taken together, these experiments provide compelling evidence that PGF2alpha treatment stimulates IRS1 serine phosphorylation, which may contribute to a diminished capacity to respond to IGF-I. It seems likely that the rapid changes in phosphorylation events are among the early events that mediate PGF2alpha-induced corpus luteum regression.

Sequential activation of protein kinase C isoforms by organic dust is mediated by tumor necrosis factor

Dust samples collected from Nebraska swine confinement facilities (hog dust extract [HDE]) are known to elicit proinflammatory cytokine release from human bronchial epithelial (HBE) cells in vitro. This response involves the activation of two protein kinase C (PKC) isoforms: PKCalpha and PKCepsilon. Experiments were designed to investigate the relationship between the two isoenzymes and the degree to which each is responsible for cytokine release in HBE. Experiments also examined the contribution of TNF-alpha to IL-6 and IL-8 release. PKCalpha and PKCepsilon activities were inhibited using isoform-specific pharmacologic inhibitors and genetically modified dominant-negative (DN) expressing cell lines. Release of the proinflammatory cytokines IL-6, IL-8, and TNF-alpha was measured and PKC isoform activities assessed. We found that HDE stimulates PKCalpha activity by 1 hour, and within 6 hours the activity returns to baseline. PKCalpha-specific inhibitor or PKCalphaDN cells abolish this HDE-mediated effect. Both IL-6 and IL-8 release are likewise diminished under these conditions compared with normal HBE, and treatment with TNF-alpha-neutralizing antibody does not further inhibit cytokine release. In contrast, PKCepsilon activity was enhanced by 6 hours after HDE treatment. TNF-alpha blockade abrogated this effect. HDE-stimulated IL-6, but not IL-8 release in PKCepsilonDN cells. The concentration of TNF-alpha released by HDE-stimulated HBE is sufficient to have a potent cytokine-eliciting effect. A time course of TNF-alpha release suggests that TNF-alpha is produced after PKCalpha activation, but before PKCepsilon. These results suggest a temporal ordering of events responsible for the release of cytokines, which initiate and exacerbate inflammatory events in the airways of people exposed to agricultural dust.

Intranasal organic dust exposure-induced airway adaptation response marked by persistent lung inflammation and pathology in mice

Organic dust exposure in agricultural environments results in an inflammatory response that attenuates over time, but repetitive exposures can result in chronic respiratory disease. Animal models to study these mechanisms are limited. This study investigated the effects of single vs. repetitive dust-induced airway inflammation in mice by intranasal exposure method. Mice were exposed to swine facility dust extract (DE) or saline once and once daily for 1 and 2 wk. Dust exposure resulted in increased bronchoalveolar lavage fluid neutrophils and macrophages after single and repetitive exposures. Lavage fluid TNFalpha, IL-6, keratinocyte chemoattractant, and macrophage inflammatory protein-2 were significantly increased after single and repetitive dust exposures, but were dampened in 2-wk dust-exposed mice compared with single exposure. Dust exposure induced PKCalpha and -epsilon activation in isolated tracheal epithelial cells but were dampened with repetitive exposures. Ex vivo stimulation of alveolar macrophages from 2-wk animals demonstrated reduced cytokine responsiveness and phagocytic ability. Significant lung pathology occurred with development of mixed mononuclear cellular aggregates (T and B lymphocytes, phagocytes) after repetitive dust exposure, a novel observation. Airway hyperresponsiveness to methacholine occurred after single dust exposure but resolved after 2 wk. Collectively, intranasal exposure to DE results in significant lung inflammatory and pathological responses marked by a modulated innate immune response to single and repetitive dust exposures that is associated with PKC activity.

Alcohol functionally upregulates Toll-like receptor 2 in airway epithelial cells

BACKGROUND

Alcoholics are known to have more severe airway diseases of the lung, such as bronchitis. Little is known about why this phenomenon is observed. We hypothesized that alcohol may modulate Toll-like receptor 2 (TLR2), which regulates inflammation caused by gram-positive bacteria.

METHODS

Airway epithelial cells [primary bronchial epithelial cells (NHBE) and 16HBE 14o-] were exposed to 0 to 100 mM alcohol for 0 to 24 hours. Real time PCR was used to quantify TLR2 mRNA. Protein levels of TLR2 were determined using Western blots and fluorescence activated cell sorting (FACS) on cells exposed to 0, 50, and 100 mM alcohol. Finally, cells were "primed" with alcohol, stimulated with a TLR2 agonist (peptidoglycan), and interleukin 8 (IL-8) release was measured.

RESULTS

Alcohol, at biologically relevant concentrations (25 to 100 mM), caused a 2 to 3-fold time- and concentration-dependent increase in TLR2 mRNA in normal human bronchial epithelial cells and 16HBE 14o- cells. Western blots for TLR2 revealed a qualitative increase in TLR2 protein in cells exposed to 100 mM alcohol. FACS showed that TLR2 was quantitatively increased on the surface of airway epithelial cells that were exposed to alcohol. Airway cells that were primed with alcohol produced nearly twice as much IL-8 in response to 40 ng of peptidoglycan than naive cells.

CONCLUSIONS

Alcohol upregulates TLR2 message and protein in the airway epithelium. This leads to exaggerated inflammation in response to environmental stimuli that would normally be well tolerated in airway epithelial cells. This may be a partial explanation of why alcoholics have more severe airway disease than nonalcoholics.

PKCdelta mediates thrombin-augmented fibroblast-mediated collagen gel contraction

Fibroblast-mediated collagen gel contraction has been used as an in vitro model of tissue remodeling. Thrombin is one of the mediators present in the milieu of airway inflammation and may be involved in airway tissue remodeling. We have previously reported that thrombin stimulates fibroblast-mediated collagen gel contraction partially through the PAR1/PKCepsilon signaling pathway [Q. Fang, X. Liu, S. Abe, T. Kobayashi, X.Q. Wang, T. Kohyama, M. Hashimoto, T. Wyatt, S.I. Rennard, Thrombin induces collagen gel contraction partially through PAR1 activation and PKC-epsilon, Eur. Respir. J. 24 (2004) 918-924]. Here, we further report that the delta-isoform of PKC (PKCdelta) is also activated by thrombin and involved in the thrombin-mediated augmentation of collagen gel contraction. Thrombin (10nM) significantly increased PKCdelta activity (over 5-fold increase after 15-30min stimulation) and stimulated phosphorylation of PKCdelta. Rottlerin, a PKCdelta inhibitor, completely inhibited activation of PKCdelta and partially blocked collagen gel contraction stimulated by thrombin. Similarly, PKCdelta-specific siRNA significantly inhibited PKCdelta activation without affecting PKCepsilon expression and activation. Furthermore, suppression of PKCdelta by siRNA resulted in partial blockade of thrombin-augmented collagen gel contraction. These results suggest that thrombin contributes to the tissue remodeling in inflammatory airways and lung diseases at least partially through both PKCdelta and PKCepsilon signaling.

Lysophosphatidic acid induces rapid and sustained decreases in epidermal growth factor receptor binding via different signaling pathways in BEAS-2B airway epithelial cells

Lysophosphatidic acid (LPA) and epidermal growth factor (EGF) are important mediators of lung cell function and lung diseases. We showed previously that LPA decreases epidermal growth factor receptor (EGFR) binding rapidly in BEAS-2B airway epithelial cells, and this decrease is sustained to at least 18 h. The current studies investigate which LPA signaling pathways mediate the rapid versus sustained decreases in EGFR binding in BEAS-2B cells. The G(i/o) inhibitor pertussis toxin and the Rho kinase inhibitor Y-27632 [(R)-(+)-trans-N-(4-pyridyl)-4-(1-aminoethyl)-cyclohexanecarboxamide] had no effect on the rapid or sustained decreases. However, the mitogen-activated protein kinase kinase (MEK) inhibitor U0126 [1,4-diamino-2,3-dicyano-1,4-bis(o-aminophenylmercapto)-butadiene ethanolate] decreased extracellular signal-regulated kinase (ERK) 1/2 phosphorylation, completely inhibited the rapid decrease in binding, and partially inhibited the sustained decrease. The direct Ca2+- and phospholipid-dependent protein kinase (PKC) activator phorbol-12-myristate-13-acetate stimulated ERK1/2 phosphorylation and decreased EGFR binding at both 15 min and 18 h. Furthermore, inhibitors of PKC partially inhibited ERK1/2 phosphorylation and the 15-min decrease but completely inhibited the 18-h decrease. Inhibitor time course studies showed that PKC induction of the 18-h decrease occurred during the first 3 h of treatment. We showed previously that LPA-stimulated EGFR transactivation contributes to the rapid decrease. Two transactivation inhibitors partially inhibited ERK1/2 phosphorylation, and U0126 partially inhibited EGFR transactivation, indicating that MEK may be involved both upstream and downstream of EGFR activation. Together, the data presented here indicate that LPA mediates the rapid decrease in EGFR binding via EGFR transactivation, MEK/ERK, and PKC, whereas the sustained decrease is regulated primarily by PKC.

Hog barn dust slows airway epithelial cell migration in vitro through a PKCalpha-dependent mechanism

Agricultural work and other occupational exposures are responsible for approximately 15% of chronic obstructive pulmonary disease (COPD). COPD involves airway remodeling in response to chronic lung inflammatory events and altered airway repair mechanisms. However, the effect of agricultural dust exposure on signaling pathways that regulate airway injury and repair has not been well characterized. A key step in this process is migration of airway cells to restore epithelial integrity. We have previously shown that agents that activate the critical regulatory enzyme protein kinase C (PKC) slow cell migration during wound repair. Based on this observation and direct kinase measurements that demonstrate that dust extract from hog confinement barns (HDE) specifically activates the PKC isoforms PKCalpha and PKCepsilon, we hypothesized that HDE would slow wound closure time in airway epithelial cells. We utilized the human bronchial epithelial cell line BEAS-2B and transfected BEAS-2B cell lines that express dominant negative (DN) forms of PKC isoforms to demonstrate that HDE slows wound closure in BEAS-2B and PKCepsilon DN cell lines. However, in PKCalpha DN cells, wound closure following HDE treatment is not significantly different than media-treated cells. These results suggest that the PKCalpha isoform is an important regulator of cell migration in response to agricultural dust exposure.

RACK1, a PKC targeting protein, is exclusively localized to basal airway epithelial cells

The novel isoform of protein kinase C (PKC), PKCepsilon, is an important regulator of ciliated cell function in airway epithelial cells, including cilia motility and detachment of ciliated cells after environmental insult. However, the mechanism of PKCepsilon signaling in the airways and the potential role of the PKCepsilon-interacting protein, receptor for activated C kinase 1 (RACK1), has not been widely explored. We used immunohistochemistry and Western blot analysis to show that RACK1 is localized exclusively to basal, non-ciliated (and non-goblet) bovine and human bronchial epithelial cells. Our immunohistochemistry experiments used the basal body marker pericentrin, a marker for cilia, beta-tubulin, and an airway goblet cell marker, MUC5AC, to confirm that RACK1 was excluded from differentiated airway cell subtypes and is only expressed in the basal cells. These results suggest that PKCepsilon signaling in the basal airway cell may involve RACK1; however, PKCepsilon regulation in ciliated cells uses RACK1-independent pathways.