An Allergic Lung Microenvironment Suppresses Carbon Nanotube-Induced Inflammasome Activation via STAT6-Dependent Inhibition of Caspase-1.

BACKGROUND: Multi-walled carbon nanotubes (MWCNTs) represent a human health risk as mice exposed by inhalation display pulmonary fibrosis. Production of IL-1ß via inflammasome activation is a mechanism of MWCNT-induced acute inflammation and has been implicated in chronic fibrogenesis. Mice sensitized to allergens have elevated T-helper 2 (Th2) cytokines, IL-4 and IL-13, and are susceptible to MWCNT-induced airway fibrosis. We postulated that Th2 cytokines would modulate MWCNT-induced inflammasome activation and IL-1ß release in vitro and in vivo during allergic inflammation. METHODS: THP-1 macrophages were primed with LPS, exposed to MWCNTs and/or IL-4 or IL-13 for 24 hours, and analyzed for indicators of inflammasome activation. C57BL6 mice were sensitized to house dust mite (HDM) allergen and MWCNTs were delivered to the lungs by oropharyngeal aspiration. Mice were euthanized 1 or 21 days post-MWCNT exposure and evaluated for lung inflammasome components and allergic inflammatory responses. RESULTS: Priming of THP-1 macrophages with LPS increased pro-IL-1ß and subsequent exposure to MWCNTs induced IL-1ß secretion. IL-4 or IL-13 decreased MWCNT-induced IL-1ß secretion by THP-1 cells and reduced pro-caspase-1 but not pro-IL-1ß. Treatment of THP-1 cells with STAT6 inhibitors, either Leflunomide or JAK I inhibitor, blocked suppression of caspase activity by IL-4 and IL-13. In vivo, MWCNTs alone caused neutrophilic infiltration into the lungs of mice 1 day post-exposure and increased IL-1ß in bronchoalveolar lavage fluid (BALF) and pro-caspase-1 immuno-staining in macrophages and airway epithelium. HDM sensitization alone caused eosinophilic inflammation with increased IL-13. MWCNT exposure after HDM sensitization increased total cell numbers in BALF, but decreased numbers of neutrophils and IL-1ß in BALF as well as reduced pro-caspase-1 in lung tissue. Despite reduced IL-1ß mice exposed to MWCNTs after HDM developed more severe airway fibrosis by 21 days and had increased pro-fibrogenic cytokine mRNAs. CONCLUSIONS: These data indicate that Th2 cytokines suppress MWCNT-induced inflammasome activation via STAT6-dependent down-regulation of pro-caspase-1 and suggest that suppression of inflammasome activation and IL-1ß by an allergic lung microenvironment is a mechanism through which MWCNTs exacerbate allergen-induced airway fibrosis.

Role of signal transducer and activator of transcription 1 in murine allergen-induced airway remodeling and exacerbation by carbon nanotubes.

Asthma is characterized by a T helper type 2 phenotype and by chronic allergen-induced airway inflammation (AAI). Environmental exposure to air pollution ultrafine particles (i.e., nanoparticles) exacerbates AAI, and a concern is possible exacerbation posed by engineered nanoparticles generated by emerging nanotechnologies. Signal transducer and activator of transcription (STAT) 1 is a transcription factor that maintains T helper type 1 cell development. However, the role of STAT1 in regulating AAI or exacerbation by nanoparticles has not been explored. In this study, mice with whole-body knockout of the Stat1 gene (Stat1(-/-)) or wild-type (WT) mice were sensitized to ovalbumin (OVA) allergen and then exposed to multiwalled carbon nanotubes (MWCNTs) by oropharygneal aspiration. In Stat1(-/-) and WT mice, OVA increased eosinophils in bronchoalveolar lavage fluid, whereas MWCNTs increased neutrophils. Interestingly, OVA sensitization prevented MWCNT-induced neutrophilia and caused only eosinophilic inflammation. Stat1(-/-) mice displayed increased IL-13 in bronchoalveolar lavage fluid at 1 day compared with WT mice after treatment with OVA or OVA and MWCNTs. At 21 days, the lungs of OVA-sensitized Stat1(-/-) mice displayed increased eosinophilia, goblet cell hyperplasia, airway fibrosis, and subepithelial apoptosis. MWCNTs further increased OVA-induced goblet cell hyperplasia, airway fibrosis, and apoptosis in Stat1(-/-) mice at 21 days. These changes corresponded to increased levels of profibrogenic mediators (transforming growth factor-ß1, TNF-α, osteopontin) but decreased IL-10 in Stat1(-/-) mice. Finally, fibroblasts isolated from the lungs of Stat1(-/-) mice produced significantly more collagen mRNA and protein in response to transforming growth factor-ß1 compared with WT lung fibroblasts. Our results support a protective role for STAT1 in chronic AAI and exacerbation of remodeling caused by MWCNTs.

Nickel nanoparticles cause exaggerated lung and airway remodeling in mice lacking the T-box transcription factor, TBX21 (T-bet).

BACKGROUND: Nickel nanoparticles (NiNPs) are increasingly used in a variety of industrial applications, including the manufacturing of multi-walled carbon nanotubes (MWCNTs). While occupational nickel exposure is a known cause of pulmonary alveolitis, fibrosis, and cancer, the health risks of NiNPs are not well understood, especially in susceptible individuals such as asthmatics. The T-box transcription factor Tbx21 (T-bet) maintains Th1 cell development and loss of T-bet is associated with a shift towards Th2 type allergic airway inflammation that characterizes asthma. The purpose of this study was to determine the role of T-bet in susceptibility to lung remodeling by NiNPs or MWCNTs. METHODS: Wild-type (WT) and T-bet-/- mice were exposed to NiNPs or MWCNTs (4 mg/kg) by oropharyngeal aspiration (OPA). Necropsy was performed at 1 and 21 days. Bronchoalveolar lavage fluid (BALF) was collected for differential counting of inflammatory cells and for measurement of cytokines by ELISA. The left lung was collected for histopathology. The right lung was analyzed for cytokine or mucin (MUC5AC and MUC5B) mRNAs. RESULTS: Morphometry of alcian-blue/periodic acid Schiff (AB/PAS)-stained lung tissue showed that NiNPs significantly increased mucous cell metaplasia in T-bet-/- mice at 21 days (p < 0.001) compared to WT mice, and increased MUC5AC and MUC5B mRNAs (p < 0.05). MWCNTs also increased mucous cell metaplasia in T-bet-/- mice, but to a lesser extent than NiNPs. Chronic alveolitis was also increased by NiNPs, but not MWCNTs, in T-bet-/- mice compared to WT mice at 21 days (P < 0.001). NiNPs also increased IL-13 and eosinophils (p < 0.001) in BALF from T-bet-/- mice after 1 day. Interestingly, the chemokine CCL2 in the BALF of T-bet-/- mice was increased at 1 and 21 days (p < 0.001 and p < 0.05, respectively) by NiNPs, and to a lesser extent by MWCNTs at 1 day. Treatment of T-bet-/- mice with a monoclonal anti-CCL2 antibody enhanced NiNP-induced mucous cell metaplasia and MUC5AC mRNA levels (p < 0.05), yet marginally reduced NiNP-induced alveolitis. CONCLUSION: These findings identify T-bet as a potentially important susceptibility factor for NiNP exposure and to a lesser extent for MWCNT exposure, and suggests that individuals with asthma are at greater risk.

Innate Immune Responses to Nanoparticle Exposure in the Lung.

The nanotechnology revolution offers enormous societal and economic benefits for innovation in the fields of engineering, electronics, and medicine. Nevertheless, evidence from rodent studies show that biopersistent engineered nanomaterials (ENMs) stimulate immune, inflammatory, and fibroproliferative responses in the lung, suggesting possible risks for lung diseases or systemic immune disorders as a consequence of occupational, environmental, or consumer exposure. Due to their nanoscale dimensions and increased surface area per unit mass, ENMs have a much greater potential to reach the distal regions of the lung and generate ROS. High aspect ratio ENMs (e.g., nanotubes, nanofibers) activate inflammasomes in macrophages, triggering IL-1ß release and neutrophilic infiltration into the lungs. Moreover, some ENMs alter allergen-induced eosinophilic inflammation by immunostimulation, immunosuppression, or modulating the balance between Th1, Th2, and Th17 cells, thereby influencing the nature of the inflammatory response. ENMs also migrate from the lungs across epithelial, endothelial, or mesothelial barriers to stimulate or suppress systemic immune responses.

Role of cyclooxygenase-2 in exacerbation of allergen-induced airway remodeling by multiwalled carbon nanotubes.

The emergence of nanotechnology has produced a multitude of engineered nanomaterials such as carbon nanotubes (CNTs), and concerns have been raised about their effects on human health, especially for susceptible populations such as individuals with asthma. Multiwalled CNTs (MWCNTs) have been shown to exacerbate ovalbumin (OVA)-induced airway remodeling in mice. Moreover, cyclooxygenase-2 (COX-2) has been described as a protective factor in asthma. We postulated that COX-2-deficient (COX-2(-/-)) mice would be susceptible to MWCNT-induced exacerbations of allergen-induced airway remodeling, including airway inflammation, fibrosis, and mucus-cell metaplasia (i.e., the formation of goblet cells). Wild-type (WT) or COX-2(-/-) mice were sensitized to OVA to induce allergic airway inflammation before a single dose of MWCNTs (4 mg/kg) delivered to the lungs by oropharyngeal aspiration. MWCNTs significantly increased OVA-induced lung inflammation and mucus-cell metaplasia in COX-2(-/-) mice compared with WT mice. However, airway fibrosis after exposure to allergen and MWCNTs was no different between WT and COX-2(-/-) mice. Concentrations of certain prostanoids (prostaglandin D2 and thromboxane B2) were enhanced by OVA or MWCNTs in COX-2(-/-) mice. No differences in COX-1 mRNA concentrations were evident between WT and COX-2(-/-) mice treated with OVA and MWCNTs. Interestingly, MWCNTs significantly enhanced allergen-induced cytokines involved in Th2 (IL-13 and IL-5), Th1 (CXCL10), and Th17 (IL-17A) inflammatory responses in COX-2(-/-) mice, but not in WT mice. We conclude that exacerbations of allergen-induced airway inflammation and mucus-cell metaplasia by MWCNTs are enhanced by deficiencies in COX-2, and are associated with the activation of a mixed Th1/Th2/Th17 immune response.

Nickel nanoparticles enhance platelet-derived growth factor-induced chemokine expression by mesothelial cells via prolonged mitogen-activated protein kinase activation.

Pleural diseases (fibrosis and mesothelioma) are a major concern for individuals exposed by inhalation to certain types of particles, metals, and fibers. Increasing attention has focused on the possibility that certain types of engineered nanoparticles (NPs), especially those containing nickel, might also pose a risk for pleural diseases. Platelet-derived growth factor (PDGF) is an important mediator of fibrosis and cancer that has been implicated in the pathogenesis of pleural diseases. In this study, we discovered that PDGF synergistically enhanced nickel NP (NiNP)-induced increases in mRNA and protein levels of the profibrogenic chemokine monocyte chemoattractant protein-1 (MCP-1 or CCL2), and the antifibrogenic IFN-inducible CXC chemokine (CXCL10) in normal rat pleural mesothelial 2 (NRM2) cells in vitro. Carbon black NPs (CBNPs), used as a negative control NP, did not cause a significant increase in CCL2 or CXCL10 in the absence or presence of PDGF. NiNPs prolonged PDGF-induced phosphorylation of the mitogen-activated protein kinase family termed extracellular signal-regulated kinases (ERK)-1 and -2 for up to 24 hours, and NiNPs also synergistically increased PDGF-induced hypoxia-inducible factor (HIF)-1α protein levels in NRM2 cells. Inhibition of ERK-1,2 phosphorylation with the mitogen-activated protein kinase kinase (MEK) inhibitor, PD98059, blocked the synergistic increase in CCL2, CXCL10, and HIF-1α levels induced by PDGF and NiNPs. Moreover, the antioxidant, N-acetyl-L-cysteine (NAC), significantly reduced HIF-1α, ERK-1,2 phosphorylation, and CCL2 protein levels that were synergistically increased by the combination of PDGF and NiNPs. These data indicate that NiNPs enhance the activity of PDGF in regulating chemokine production in NRM2 cells through a mechanism involving reactive oxygen species generation and prolonged activation of ERK-1,2.