Role of tumor necrosis factor-α and its receptors in diesel exhaust particle-induced pulmonary inflammation

Inhalation of diesel exhaust particles (DEP) induces an inflammatory reaction in the lung. However, the underlying mechanisms remain to be elucidated. Tumor necrosis factor alpha (TNF-alpha) is a proinflammatory cytokine that operates by binding to tumor necrosis factor receptor 1 (TNFR1) and tumor necrosis factor receptor 2 (TNFR2). The role of TNF-alpha signaling and the importance of either TNFR1 or TNFR2 in the DEP-induced inflammatory response has not yet been elucidated. TNF-alpha knockout (KO), TNFR1 KO, TNFR2 KO, TNFR1/TNFR2 double KO (TNFR-DKO) and wild type (WT) mice were intratracheally exposed to saline or DEP. Pro-inflammatory cells and cytokines were assessed in the bronchoalveolar lavage fluid (BALF). Exposure to DEP induced a dose-dependent inflammation in the BALF in WT mice. In addition, levels of TNF-alpha and its soluble receptors were increased upon exposure to DEP. The DEP-induced inflammation in the BALF was decreased in TNF-alpha KO, TNFR-DKO and TNFR2 KO mice. In contrast, the inflammatory response in the BALF of DEP-exposed TNFR1 KO mice was largely comparable with WT controls. In conclusion, these data provide evidence for a regulatory role of TNF-alpha in DEP-induced pulmonary inflammation and identify TNFR2 as the most important receptor in mediating these inflammatory effects

miR449 Protects Airway Regeneration by Controlling AURKA/HDAC6-Mediated Ciliary Disassembly

Airway mucociliary regeneration and function are key players for airway defense and are impaired in chronic obstructive pulmonary disease (COPD). Using transcriptome analysis in COPD-derived bronchial biopsies, we observed a positive correlation between cilia-related genes and microRNA-449 (miR449). In vitro, miR449 was strongly increased during airway epithelial mucociliary differentiation. In vivo, miR449 was upregulated during recovery from chemical or infective insults. miR0449-/- mice (both alleles are deleted) showed impaired ciliated epithelial regeneration after naphthalene and Haemophilus influenzae exposure, accompanied by more intense inflammation and emphysematous manifestations of COPD. The latter occurred spontaneously in aged miR449-/- mice. We identified Aurora kinase A and its effector target HDAC6 as key mediators in miR449-regulated ciliary homeostasis and epithelial regeneration. Aurora kinase A is downregulated upon miR449 overexpression in vitro and upregulated in miR449-/- mouse lungs. Accordingly, imaging studies showed profoundly altered cilia length and morphology accompanied by reduced mucociliary clearance. Pharmacological inhibition of HDAC6 rescued cilia length and coverage in miR449-/- cells, consistent with its tubulin-deacetylating function. Altogether, our study establishes a link between miR449, ciliary dysfunction, and COPD pathogenesis

miR449 Protects Airway Regeneration by Controlling AURKA/HDAC6-Mediated Ciliary Disassembly

Airway mucociliary regeneration and function are key players for airway defense and are impaired in chronic obstructive pulmonary disease (COPD). Using transcriptome analysis in COPD-derived bronchial biopsies, we observed a positive correlation between cilia-related genes and microRNA-449 (miR449). In vitro, miR449 was strongly increased during airway epithelial mucociliary differentiation. In vivo, miR449 was upregulated during recovery from chemical or infective insults. miR0449−/− mice (both alleles are deleted) showed impaired ciliated epithelial regeneration after naphthalene and Haemophilus influenzae exposure, accompanied by more intense inflammation and emphysematous manifestations of COPD. The latter occurred spontaneously in aged miR449−/− mice. We identified Aurora kinase A and its effector target HDAC6 as key mediators in miR449-regulated ciliary homeostasis and epithelial regeneration. Aurora kinase A is downregulated upon miR449 overexpression in vitro and upregulated in miR449−/− mouse lungs. Accordingly, imaging studies showed profoundly altered cilia length and morphology accompanied by reduced mucociliary clearance. Pharmacological inhibition of HDAC6 rescued cilia length and coverage in miR449−/− cells, consistent with its tubulin-deacetylating function. Altogether, our study establishes a link between miR449, ciliary dysfunction, and COPD pathogenesis

Aggravation of allergic airway inflammation by cigarette smoke in mice is CD44-dependent

Background : Although epidemiological studies reveal that cigarette smoke (CS) facilitates the development and exacerbation of allergic asthma, these studies offer limited information on the mechanisms involved. The transmembrane glycoprotein CD44 is involved in cell adhesion and acts as a receptor for hyaluronic acid and osteopontin. We aimed to investigate the role of CD44 in a murine model of CS-facilitated allergic airway inflammation. Methods : Wild type (WT) and CD44 knock-out (KO) mice were exposed simultaneously to house dust mite (HDM) extract and CS. Inflammatory cells, hyaluronic acid (HA) and osteopontin (OPN) levels were measured in bronchoalveolar lavage fluid (BALF). Proinflammatory mediators, goblet cell metaplasia and peribronchial eosinophilia were assessed in lung tissue. T-helper (Th) 1, Th2 and Th17 cytokine production was evaluated in mediastinal lymph node cultures. Results : In WT mice, combined HDM/CS exposure increased the number of inflammatory cells and the levels of HA and OPN in BALF and Th2 cytokine production in mediastinal lymph nodes compared to control groups exposed to phosphate buffered saline (PBS)/CS, HDM/Air or PBS/Air. Furthermore, HDM/CS exposure significantly increased goblet cell metaplasia, peribronchial eosinophilia and inflammatory mediators in the lung. CD44 KO mice exposed to HDM/CS had significantly fewer inflammatory cells in BALF, an attenuated Th2 cytokine production, as well as decreased goblet cells and peribronchial eosinophils compared to WT mice. In contrast, the levels of inflammatory mediators were similar or higher than in WT mice. Conclusion : We demonstrate for the first time that the aggravation of pulmonary inflammation upon combined exposure to allergen and an environmental pollutant is CD44-dependent. Data from this murine model of concomitant exposure to CS and HDM might be of importance for smoking allergic asthmatics

Characterization of the pulmonary immune response after exposure to diesel particles

Epidemiological studies have shown that air pollution – of which diesel exhaust particles (DEP) are an important component – has several adverse health effects. Inhalation of DEP is associated with acute inflammatory reactions in the lung, via modulation of the innate immune system. Moreover, murine studies showed that exposure to DEP also can facilitate allergic sensitization and the development of asthma, via modulation of the adaptive immune system. Until now, the immunological mechanisms involved in the adverse health effects of DEP are largely unknown. The aim of this dissertation was to further investigate these mechanisms. In the first part of this dissertation, the impact of DEP on the innate immune system was examined. In particular, the interleukin-1 (IL-1) signaling pathway was studied, since it is crucial in the defence against toxic agents. Using wild type and knock out mice, and with neutralization experiments the importance of IL-1 signaling in DEP-induced innate immune responses was demonstrated for the first time. Moreover, it was shown that pro-IL-1β activation upon DEP was not dependent on the classical NLRP3/caspase-1 pathway; suggesting alternative mechanisms were involved. In the second part of the dissertation, the impact of DEP inhalation on the adaptive immune system and the induction of T helper 2 immune responses was studied. More specifically, the effects of DEP on the dendritic cell were studied, since these are crucial for the induction of allergic sensitization and asthma. Exposure to DEP induced dendritic cell maturation and increased migration of dendritic cells towards the mediastinal lymph nodes. DEP themselves were also demonstrated to be transported towards the mediastinal lymph nodes in a CC chemokine receptor (CCR) 7-dependent manner. This resulted in a T helper 2 response in the lymph node. These findings suggest a mechanism how DEP inhalation can induce allergic sensitization. In addition, we investigated how dendritic cells are recruited towards the pulmonary tissue upon exposure to diesel. In response to DEP, dendritic cells migrated towards the lung in a CCR2- and CCR6-, but not CCR5-, dependent manner

Monocyte-derived dendritic cell recruitment and allergic TH2 responses after exposure to diesel particles are CCR2 dependent

Background: The inhalation of diesel exhaust particles (DEPs) is associated with increased sensitization toward inhaled allergens. Dendritic cells (DCs) are important mediators in immune regulation. We previously showed that the inhalation of DEPs increased the accumulation of DCs in the lung and enhanced the T(H)2 response in the mediastinal lymph node. Objective: We hypothesized that CC chemokine receptors CCR2, CCR5, and CCR6 critically mediate the DC recruitment upon exposure to DEPs and that these CC chemokine receptors are important in the DEP-induced TH2 response. Methods: We exposed CCR2 knockout, CCR5 knockout, CCR6 knockout, and wild-type mice to DEPs and examined the pulmonary monocyte and DC accumulation. By an adoptive transfer experiment, we assessed the direct involvement of CCR2 and CCR6 in the recruitment of blood monocytes toward the lung upon exposure to DEPs. We also examined the TH2 cytokine production in the mediastinal lymph nodes of DEP-exposed CCR2 knockout and CCR6 knockout mice. Results: We observed that the DEP-induced monocyte and monocyte-derived DC recruitment was completely abolished in CCR2 knockout mice. CCR6 knockout mice also showed impaired monocyte recruitment upon exposure to DEPs. In contrast, monocyte and DC recruitment was comparable between DEP-exposed wild-type and CCR5 knockout mice. The impaired monocyte-derived DC recruitment in DEP-exposed CCR2 knockout, not CCR6 knockout, mice resulted in an abolished TH2 response in the mediastinal lymph node. Conclusion: These data suggest that monocyte-derived DCs, recruited in a CCR2-dependent manner, are critical in inducing TH2 responses upon inhalation of DEPs

Inflammasomes in respiratory disease: from bench to bedside

The respiratory tract of human subjects is constantly exposed to harmful microbes and air pollutants. The immune system responds to these offenders to protect the host, but an unbalanced inflammatory response itself may promote tissue damage and ultimately lead to acute and chronic respiratory diseases. Deregulated inflammasome activation is emerging as a key modulator of respiratory infections and pathologic airway inflammation in patients with asthma, COPD, and pulmonary fibrosis. Assembly of these intracellular danger sensors in cells of the respiratory mucosa and alveolar compartment triggers a proinflammatory cell death mode termed pyroptosis and leads to secretion of bioactive IL-1 beta and IL-18. Here, we summarize and review the inflammasome and its downstream effectors as therapeutic targets for the treatment of respiratory diseases

Insights in particulate matter-induced allergic airway inflammation : focus on the epithelium

Outdoor air pollution is a major environmental health problem throughout the world. In particular, exposure to particulate matter (PM) has been associated with the development and exacerbation of several respiratory diseases, including asthma. Although the adverse health effects of PM have been demonstrated for many years, the underlying mechanisms have not been fully identified. In this review, we focus on the role of the lung epithelium and specifically highlight multiple cytokines in PM-induced respiratory responses. We describe the available literature on the topic including invitro studies, findings in humans (ie observations in human cohorts, human controlled exposure and exvivo studies) and invivo animal studies. In brief, it has been shown that exposure to PM modulates the airway epithelium and promotes the production of several cytokines, including IL-1, IL-6, IL-8, IL-25, IL-33, TNF-, TSLP and GM-CSF. Further, we propose that PM-induced type 2-promoting cytokines are important mediators in the acute and aggravating effects of PM on airway inflammation. Targeting these cytokines could therefore be a new approach in the treatment of asthma