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MyD88 mediates in vivo effector functions of alveolar macrophages in acute lung inflammatory responses to carbon nanotube exposure.

ABSTRACT: Carbon nanotubes (CNTs) are rapidly emerging as high-priority occupational toxicants. CNT powders contain fibrous particles that aerosolize readily in places of manufacture and handling, posing an inhalation risk for workers. Studies using animal models indicate that lung exposure to CNTs causes prolonged inflammatory responses and diffuse alveolar injury. The mechanisms governing CNT-induced lung inflammation are not fully understood but have been suggested to involve alveolar macrophages (AMs). In the current study, we sought to systematically assess the effector role of AMs in vivo in the induction of lung inflammatory responses to CNT exposures and investigate their cell type-specific mechanisms. Multi-wall CNTs characterized for various physicochemical attributes were used as the CNT type. Using an AM-specific depletion and repopulation approach in a mouse model, we unambiguously demonstrated that AMs are major effector cells necessary for the in vivo elaboration of CNT-induced lung inflammation. We further investigated in vitro AM responses and identified molecular targets which proved critical to pro-inflammatory responses in this model, namely MyD88 as well as MAPKs and Ca(2+)/CamKII. We further demonstrated that MyD88 inhibition in donor AMs abrogated their capacity to reconstitute CNT-induced inflammation when adoptively transferred into AM-depleted mice. Taken together, this is the first in vivo demonstration that AMs act as critical effector cell types in CNT-induced lung inflammation and that MyD88 is required for this in vivo effector function. AMs and their cell type-specific mechanisms may therefore represent potential targets for future therapeutic intervention of CNT-related lung injury.

SUBMITTER: Frank EA

PROVIDER: S-EPMC4623709 | biostudies-literature | 2015 Nov

REPOSITORIES: biostudies-literature

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MyD88 mediates in vivo effector functions of alveolar macrophages in acute lung inflammatory responses to carbon nanotube exposure.

Frank Evan A EA Birch M Eileen ME Yadav Jagjit S JS

Toxicology and applied pharmacology 20150810 3

Carbon nanotubes (CNTs) are rapidly emerging as high-priority occupational toxicants. CNT powders contain fibrous particles that aerosolize readily in places of manufacture and handling, posing an inhalation risk for workers. Studies using animal models indicate that lung exposure to CNTs causes prolonged inflammatory responses and diffuse alveolar injury. The mechanisms governing CNT-induced lung inflammation are not fully understood but have been suggested to involve alveolar macrophages (AMs) ...[more]

PMID: 26272622

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Project description:Human exposure to carbon nanotubes (CNT) has been associated with the development of pulmonary sarcoid-like granulomatous disease. Our previous studies demonstrated that multi-walled carbon nanotubes (MWCNT) induced chronic pulmonary granulomatous inflammation in mice. Granuloma formation was accompanied by decreased peroxisome proliferator-activated receptor gamma (PPARγ) and disrupted intracellular lipid homeostasis in alveolar macrophages. Others have shown that PPARγ activation increases mitochondrial fatty acid oxidation (FAO) to reduce free fatty acid accumulation. Hence, we hypothesized that the disrupted lipid metabolism suppresses mitochondrial FAO. To test our hypothesis, C57BL/6 J mice were instilled by an oropharyngeal route with 100 μg MWCNT freshly suspended in 35 % Infasurf. Control sham mice received vehicle alone. Sixty days following instillation, mitochondrial FAO was measured in permeabilized bronchoalveolar lavage (BAL) cells. MWCNT instillation reduced the mitochondrial oxygen consumption rate of BAL cells in the presence of palmitoyl-carnitine as mitochondrial fuel. MWCNT also reduced mRNA expression of mitochondrial genes regulating FAO, carnitine palmitoyl transferase-1 (CPT1), carnitine palmitoyl transferase-2 (CPT2), hydroxyacyl-CoA dehydrogenase subunit beta (HADHB), and PPARγ coactivator 1 alpha (PPARGC1A). Importantly, both oxidative stress and apoptosis in alveolar macrophages and lung tissues of MWCNT-instilled mice were increased. Because macrophage PPARγ expression has been reported to be controlled by miR-27b which is known to induce oxidative stress and apoptosis, we measured the expression of miR-27b. Results indicated elevated levels in alveolar macrophages from MWCNT-instilled mice compared to controls. Given that inhibition of FAO and apoptosis are linked to M1 and M2 macrophage activation, respectively, the expression of both M1 and M2 key indicator genes were measured. Interestingly, results showed that both M1 and M2 phenotypes of alveolar macrophages were activated in MWCNT-instilled mice. In conclusion, alveolar macrophages of MWCNT-instilled mice had increased miR-27b expression, which may reduce the expression of PPARγ resulting in attenuation of FAO. This reduction in FAO may lead to activation of M1 macrophages. The upregulation of miR-27b may also induce apoptosis, which in turn can cause M2 activation of alveolar macrophages. These observations indicate a possible role of miR-27b in impaired mitochondrial function in the chronic activation of alveolar macrophages by MWCNT and the development of chronic pulmonary granulomatous inflammation.

Project description:BackgroundWe and others have confirmed activation of macrophages plays a critical role in liver injury and fibrogenesis during HBV infection. And we have also proved HBeAg can obviously induce the production of macrophage inflammatory cytokines compared with HBsAg and HBcAg. However, the receptor and functional domain of HBeAg in macrophage activation and its effects and mechanisms on hepatic fibrosis remain elusive.MethodsThe potentially direct binding receptors of HBeAg were screened and verified by Co-IP assay. Meanwhile, the function domain and accessible peptides of HBeAg for macrophage activation were analyzed by prediction of surface accessible peptide, construction, and synthesis of truncated fragments. Furthermore, effects and mechanisms of the activation of hepatic stellate cells induced by HBeAg-treated macrophages were investigated by Transwell, CCK-8, Gel contraction assay, Phospho Explorer antibody microarray, and Luminex assay. Finally, the effect of HBeAg in hepatic inflammation and fibrosis was evaluated in both human and murine tissues by immunohistochemistry, immunofluorescence, ELISA, and detection of liver enzymes.ResultsHerein, we verified TLR-2 was the direct binding receptor of HBeAg. Meanwhile, C-terminal peptide (122-143 aa.) of core domain in HBeAg was critical for macrophage activation. But arginine-rich domain of HBcAg hided this function, although HBcAg and HBeAg shared the same core domain. Furthermore, HBeAg promoted the proliferation, motility, and contraction of hepatic stellate cells (HSCs) in a macrophage-dependent manner, but not alone. PI3K-AKT-mTOR and p38 MAPK signaling pathway were responsible for motility phenotype of HSCs, while the Smad-dependent TGF-β signaling pathway for proliferation and contraction of them. Additionally, multiple chemokines and cytokines, such as CCL2, CCL5, CXCL10, and TNF-α, might be key mediators of HSC activation. Consistently, HBeAg induced transient inflammation response and promoted early fibrogenesis via TLR-2 in mice. Finally, clinical investigations suggested that the level of HBeAg is associated with inflammation and fibrosis degrees in patients infected with HBV.ConclusionsHBeAg activated macrophages via the TLR-2/NF-κB signal pathway and further exacerbated hepatic fibrosis by facilitating motility, proliferation, and contraction of HSCs with the help of macrophages.

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MyD88 mediates in vivo effector functions of alveolar macrophages in acute lung inflammatory responses to carbon nanotube exposure.

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MyD88 mediates in vivo effector functions of alveolar macrophages in acute lung inflammatory responses to carbon nanotube exposure.

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