Results from omic approaches in rat or mouse models exposed to inhaled crystalline silica: a systematic review

BACKGROUND

Crystalline silica (cSiO2) is a mineral found in rocks; workers from the construction or denim industries are particularly exposed to cSiO2 through inhalation. cSiO2 inhalation increases the risk of silicosis and systemic autoimmune diseases. Inhaled cSiO2 microparticles can reach the alveoli where they induce inflammation, cell death, auto-immunity and fibrosis but the specific molecular pathways involved in these cSiO2 effects remain unclear. This systematic review aims to provide a comprehensive state of the art on omic approaches and exposure models used to study the effects of inhaled cSiO2 in mice and rats and to highlight key results from omic data in rodents also validated in human.

METHODS

The protocol of systematic review follows PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. Eligible articles were identified in PubMed, Embase and Web of Science. The search strategy included original articles published after 1990 and written in English which included mouse or rat models exposed to cSiO2 and utilized omic approaches to identify pathways modulated by cSiO2. Data were extracted and quality assessment was based on the SYRCLE's Risk of Bias tool for animal studies.

RESULTS

Rats and male rodents were the more used models while female rodents and autoimmune prone models were less studied. Exposure of animals were both acute and chronic and the timing of outcome measurement through omics approaches were homogeneously distributed. Transcriptomic techniques were more commonly performed while proteomic, metabolomic and single-cell omic methods were less utilized. Immunity and inflammation were the main domains modified by cSiO2 exposure in lungs of mice and rats. Less than 20% of the results obtained in rodents were finally verified in humans.

CONCLUSION

Omic technics offer new insights on the effects of cSiO2 exposure in mice and rats although the majority of data still need to be validated in humans. Autoimmune prone model should be better characterised and systemic effects of cSiO2 need to be further studied to better understand cSiO2-induced autoimmunity. Single-cell omics should be performed to inform on pathological processes induced by cSiO2 exposure.

Effects of different amosite preparations on macrophages, lung damages, and autoimmunity

The underlying mechanisms of asbestos-related autoimmunity are poorly understood. As the size, surface reactivity, and free radical activity of asbestos particles are considered crucial regarding the health effects, this study aims to compare the effects of exposure to pristine amosite (pAmo) or milled amosite (mAmo) particles on lung damage, autoimmunity, and macrophage phenotype. Four months after lung exposure to 0.1 mg of amosite, BAL levels of lactate dehydrogenase, protein, free DNA, CCL2, TGF-β1, TIMP-1, and immunoglobulin A of pAmo-exposed C57Bl/6 mice were increased when compared to fluids from control- and mAmo-exposed mice. Effects in pAmo-exposed mice were associated with lung fibrosis and autoimmunity including anti-double-strand DNA autoantibody production. mAmo or pAmo at 20 µg/cm2 induced a pro-inflammatory phenotype characterized by a significant increase in TNFα and IL-6 secretion on human monocyte-derived macrophages (MDMs). mAmo and pAmo exposure induced a decrease in the efferocytosis capacities of MDMs, whereas macrophage abilities to phagocyte fluorescent beads were unchanged when compared to control MDMs. mAmo induced IL-6 secretion and reduced the percentage of MDMs expressing MHCII and CD86 markers involved in antigen and T-lymphocyte stimulation. By contrast, pAmo but not mAmo activated the NLRP3 inflammasome, as evaluated through quantification of caspase-1 activity and IL-1β secretion. Our results demonstrated that long-term exposure to pAmo may induce significant lung damage and autoimmune effects, probably through an alteration of macrophage phenotype, supporting in vivo the higher toxicity of entire amosite (pAmo) with respect to grinded amosite. However, considering their impact on efferocytosis and co-stimulation markers, mAmo effects should not be neglected. KEY MESSAGES: Lung fibrosis and autoimmunity induced by amosite particles depend on their physicochemical characteristics (size and surface) Inhalation exposure of mice to pristine amosite fibers is associated with lung fibrosis and autoimmunity Anti-dsDNA antibody is a marker of autoimmunity in mice exposed to pristine amosite fibers Activation of lung mucosa-associated lymphoid tissue, characterized by IgA production, after exposure to pristine amosite fibers Pristine and milled amosite particle exposure reduced the efferocytosis capacity of human-derived macrophages.

Distinct Pro-Inflammatory Mechanisms Elicited by Short and Long Amosite Asbestos Fibers in Macrophages

While exposure to long amphibolic asbestos fibers (L > 10 µm) results in the development of severe diseases including inflammation, fibrosis, and mesothelioma, the pathogenic activity associated with short fibers (L < 5 µm) is less clear. By exposing murine macrophages to short (SFA) or long (LFA) fibers of amosite asbestos different in size and surface chemistry, we observed that SFA internalization resulted in pyroptotic-related immunogenic cell death (ICD) characterized by the release of the pro-inflammatory damage signal (DAMP) IL-1α after inflammasome activation and gasdermin D (GSDMD)-pore formation. In contrast, macrophage responses to non-internalizable LFA were associated with tumor necrosis factor alpha (TNF-α) release, caspase-3 and -7 activation, and apoptosis. SFA effects exclusively resulted from Toll-like receptor 4 (TLR4), a pattern-recognition receptor (PRR) recognized for its ability to sense particles, while the response to LFA was elicited by a multifactorial ignition system involving the macrophage receptor with collagenous structure (SR-A6 or MARCO), reactive oxygen species (ROS) cascade, and TLR4. Our findings indicate that asbestos fiber size and surface features play major roles in modulating ICD and inflammatory pathways. They also suggest that SFA are biologically reactive in vitro and, therefore, their inflammatory and toxic effects in vivo should not be underestimated.

Interactions of janus kinase inhibitors with drug transporters and consequences for pharmacokinetics and toxicity

Introduction: Janus kinase inhibitors (JAKinibs) constitute an emerging and promising pharmacological class of anti-inflammatory or anti-cancer drugs, used notably for the treatment of rheumatoid arthritis and some myeloproliferative neoplasms.Areas covered: This review provides an overview of the interactions between marketed JAKinibs and major uptake and efflux drug transporters. Consequences regarding pharmacokinetics, drug-drug interactions and toxicity are summarized.Expert opinion: JAKinibs interact in vitro with transporters in various ways, as inhibitors or as substrates of transporters or as regulators of transporter expression. This may theoretically result in drug-drug interactions (DDIs), with JAKinibs acting as perpetrators or as victims, or in toxicity, via impairment of thiamine transport. Clinical significance in terms of DDIs for JAKinib-transporter interactions remains however poorly documented. In this context, the in vivo unbound concentration of JAKinibs is likely a key parameter to consider for evaluating the clinical relevance of JAKinibs-mediated transporter inhibition. Additionally, the interplay with drug metabolism as well as possible interactions with transporters of emerging importance and time-dependent inhibition have to be taken into account. The role drug transporters may play in controlling cellular JAKinib concentrations and efficacy in target cells is also an issue of interest.

Comparative study on gene expression profile in rat lung after repeated exposure to diesel and biodiesel exhausts upstream and downstream of a particle filter

Biodiesel is considered as a valuable and less toxic alternative to diesel. However, cellular and molecular effects of repeated exposure to biodiesel emissions from a recent engine equipped with a diesel particle filter (DPF) remain to be characterized. To gain insights about this point, the lung transcriptional signatures were analyzed for rats (n = 6 per group) exposed to filtered air, 30% rapeseed biodiesel (B30) blend or reference diesel (RF0), upstream and downstream a DPF, for 3 weeks (3 h/day, 5 days/week). Genomic analysis revealed a modest regulation of gene expression level (lower than a 2-fold) by both fuels and a higher number of genes regulated downstream the DPF than upstream, in response to either RF0 or to B30 exhaust emissions. The presence of DPF was found to notably impact the lung gene signature of rats exposed to B30. The number of genes regulated in common by both fuels was low, which is likely due to differences in concentrations of regulated pollutants in exhausts, notably for compound organic volatiles, polycyclic aromatic hydrocarbons, NO or NOx. Nevertheless, we have identified some pathways that were activated for both exhaust emissions, such as integrin-, IGF-1- and Rac-signaling pathways, likely reflecting the effects of gas phase products. By contrast, some canonical pathways relative to "oxidative phosphorylation" and "mitochondrial dysfunction" appear as specific to B30 exhaust emission; the repression of transcripts of mitochondrial respiratory chain in lung of rats exposed to B30 downstream of DPF supports the perturbation of mitochondria function. This study done with a recent diesel engine (compliant with the European IV emission standard) and commercially-available fuels reveals that the diesel blend composition and the presence of an after treatment system may modify lung gene signature of rats repeatedly exposed to exhaust emissions, however in a rather modest manner.

AB0158 IMPACT OF JAK INHIBITORS ON MACROPHAGE POLARISATION: PERSPECTIVES FOR SYSTEMIC SCLEROSIS

Background:

Macrophage can adopt various phenotypes and activation states according to their surrounding microenvironment. M1 or inflammatory macrophages are generated under IFNɣ/LPS signaling and express the membrane marker CD86. Different subtypes of M2 macrophages are also described: M2a macrophages (generated under IL4/IL13 signaling) and characterized by a high expression of CD206 and pro-fibrotic properties and, M2c macrophages (generated under IL10 and/or glucorticoid signaling), considered as anti-inflammatory resolving macrophages. There is growing interest in the role of macrophages in the pathogenesis of Systemic Sclerosis (SSc). Recent studies highlight that macrophages from fibrotic tissues such as lung or skin from SSc patients have a M2 phenotype whereas, in blood-monocytes derived macrophages (MDM), SSc MDM have a mixed signature associating M1 and M2 characteristics. Jak inhibitors are treatments used in rheumatoid arthritis and that can variously target signals that could be involved both in M1 and in M2 polarisation.

Objectives:

This study evaluates the impact of three Jak inhibitors on the polarisation state of human MDM in vitro.

Methods:

Blood monocytes form healthy donors (HD) were differentiated with M-CSF (for 7 days) in MDM and pre-treated by ruxolitinib (Jak2-Jak1 inhibitor), tofacitinib (Jak3 inhibitor) or itacitinib (Jak1 inhibitor) (1µM for all). They were then polarised into M1i (IFNɣ, 20µg/mL), M1Li (IFNɣ+LPS, 20µg/mL), M2a (IL4+IL13; 20µg/ML), M2c (IL10, 20µg/mL) and M2c(dex) (IL10+dexamethasone, 10 nM). The impact of each Jak inhibitor on phenotype (flow cytometry), gene expression (qPCR) and cytokine secretion (ELISA) was evaluated in each polarisation state.

Results:

Concerning phenotypes, all Jak inhibitors reduced the expression of the M1i and M1Li marker CD86, but ruxolitinib had a higher effect. Only ruxolitinib reduced the expression of the M1i marker MHCII. All Jak inhibitors reduced the expression of CD206 in M2a. They had no impact on the expression of CD163, CD204 in any M2 conditions. Key M1 genes were repressed by all Jak inhibitors, such as CXCL10, IL6 or TNFα with a more significant effect of ruxolitinib. All Jak inhibitors reduced the gene expression of CXCL13 and SOCS3 in M2c. Secretion levels of IL6 and CCL18 were also repressed, with a more significant effect of ruxolitinib.

Conclusion:

Jak inhibitors can limit M1 and M2 polarisation state in vitro, with a more significant effect of the Jak2-Jak1 inhibitor ruxolitinib. The relevance of these results in MDM from SSc patients and in vivo models of SSc is still to be determined.

Disclosure of Interests:

Alain LESCOAT: None declared, Alice Ballerie: None declared, Marie Lelong: None declared, Claudie Morzadec: None declared, Stéphane Jouneau Grant/research support from: AIRB, Boehringer Ingelheim, LVL Medical, Novartis, Roche, Bellorophon Therapeutics, Biogen, Fibrogen, Galecto Biotech, Gilead Sciences, Pharm-Olam, Pliant Therapeutics, Savara Pharmaceuticals/Serendex Pharmaceuticals, Consultant of: Actelion, AIRB, AstraZeneca, Bristol-Myers Squibb, Boehringer Ingelheim, Chiesi, Genzyme, GlazoSmithKline, LVL Medical, Mundipharma, Novartis, Pfizer, Roche, Sanofi, Patrick Jégo: None declared, Laurent Vernhet: None declared, Olivier Fardel: None declared, Valérie Lecureur: None declared

TNF-α and IL-10 Control CXCL13 Expression in Human Macrophages

The chemokine CXCL13 controls the normal organization of secondary lymphoid tissues and the neogenesis of ectopic lymphoid structures in nonlymphoid organs, particularly the lungs. The progression and severity of idiopathic pulmonary fibrosis (IPF), a fatal and irreversible interstitial lung disease, is predicted by the circulating blood concentrations of CXCL13. Although CXCL13 is produced by pulmonary tissues, it has not been determined which cells are involved. This study examines CXCL13 production by lung tissue macrophages from patients with IPF and the signaling pathways controlling CXCL13 gene expression in human alveolar macrophages (AM) and monocyte-derived macrophages (MoDM). CXCL13 is found in CD68- and CD206-positive AM from patients with IPF, and the CXCL13 gene is induced in these macrophages and MoDM when they are stimulated with LPS. We found that TNF-α and IL-10 control optimal CXCL13 gene expression in MoDM and possibly in AM by activating the NF-κB and JAK/STAT pathways, respectively. We also found that blood TNF-α and CXCL13 concentrations are significantly correlated in patients with IPF, suggesting that TNF-α contributes to CXCL13 production in humans. In conclusion, the results of this study demonstrate that AM from patients with IPF produces CXCL13 and that the NF-κB and JAK/STAT pathways are required to induce the expression of this major chemokine.

Crystalline Silica Impairs Efferocytosis Abilities of Human and Mouse Macrophages: Implication for Silica-Associated Systemic Sclerosis

Inhalation of crystalline silica (SiO2) is a risk factor of systemic autoimmune diseases such as systemic sclerosis (SSc) and fibrotic pulmonary disorders such as silicosis. A defect of apoptotic cell clearance (i.e., efferocytosis, a key process in the resolution of inflammation) is reported in macrophages from patients with fibrotic or autoimmune diseases. However, the precise links between SiO2 exposure and efferocytosis impairment remain to be determined. Answering to this question may help to better link innate immunity and fibrosis. In this study, we first aim to determine whether SiO2 might alter efferocytosis capacities of human and mouse macrophages. We secondly explore possible mechanisms explaining efferocytosis impairment, with a specific focus on macrophage polarization and on the RhoA/ROCK pathway, a key regulator of cytoskeleton remodeling and phagocytosis. Human monocyte-derived macrophages (MDM) and C57BL/6J mice exposed to SiO2 and to CFSE-positive apoptotic Jurkat cells were analyzed by flow cytometry to determine their efferocytosis index (EI). The effects of ROCK inhibitors (Y27632 and Fasudil) on EI of SiO2-exposed MDM and MDM from SSc patients were evaluated in vitro. Our results demonstrated that SiO2 significantly decreased EI of human MDM in vitro and mouse alveolar macrophages in vivo. In human MDM, this SiO2-associated impairment of efferocytosis, required the expression of the membrane receptor SR-B1 and was associated with a decreased expression of M2 polarization markers (CD206, CD204, and CD163). F-actin staining, RhoA activation and impairment of efferocytosis, all induced by SiO2, were reversed by ROCK inhibitors. Moreover, the EI of MDM from SSc patients was similar to the EI of in vitro- SiO2-exposed MDM and Y27632 significantly increased SSc MDM efferocytosis capacities, suggesting a likewise activation of the RhoA/ROCK pathway in SSc. Altogether, our results demonstrate that SiO2 exposure may contribute to the impairment of efferocytosis capacities of mouse and human macrophages but also of MDM in SiO2-associated autoimmune diseases and fibrotic disorders such as SSc; in this context, the silica/RhoA/ROCK pathway may constitute a relevant therapeutic target.

Potent repression of C-reactive protein (CRP) expression by the JAK1/2 inhibitor ruxolitinib in inflammatory human hepatocytes

OBJECTIVE AND DESIGN

To determine whether inflammatory hepatocytes may constitute primary targets for ruxolitinib, a Janus kinase (JAK) inhibitor, its effects towards expression of hepatic acute-phase proteins, especially C-reactive protein (CRP), were assessed.

MATERIALS

Ruxolitinib effects were analysed in primary human hepatocytes and human hepatoma HepaRG cells exposed to various inflammatory stimuli.

RESULTS

Ruxolitinib was found to fully inhibit lipopolysaccharide (LPS)-induced CRP secretion and mRNA expression, at concentrations (IC₅₀ = 12.9 nM) achievable in human blood. It similarly repressed CRP up-regulation due to several Toll-like receptor agonists or pro-inflammatory cytokines [interleukin (IL) 1β, IL6 and tumour necrosis factor α] and counteracted LPS-mediated induction of serum amyloid A, fibrinogen, haptoglobin and serpin. Ruxolitinib was additionally found to block the activation of the IL6/JAK/signal transducer and activator of transcription (STAT) pathway triggered by LPS and whose inhibition by the neutralizing anti-IL6 receptor antibody tocilizumab prevented CRP induction.

CONCLUSION

Ruxolitinib can potently repress induction of CRP in inflammatory human hepatocytes, most likely through targeting the IL6/JAK/STAT signalling cascade. Hepatic production of acute-phase proteins during liver inflammation may, therefore, constitute a target for ruxolitinib.

A novel Staphylococcus aureus cis-trans type I toxin-antitoxin module with dual effects on bacteria and host cells

Bacterial type I toxin–antitoxin (TA) systems are widespread, and consist of a stable toxic peptide whose expression is monitored by a labile RNA antitoxin. We characterized Staphylococcus aureus SprA2/SprA2_AS module, which shares nucleotide similarities with the SprA1/SprA1_AS TA system. We demonstrated that SprA2/SprA2_AS encodes a functional type I TA system, with the cis-encoded SprA2_AS antitoxin acting in trans to prevent ribosomal loading onto SprA2 RNA. We proved that both TA systems are distinct, with no cross-regulation between the antitoxins in vitro or in vivo. SprA2 expresses PepA2, a toxic peptide which internally triggers bacterial death. Conversely, although PepA2 does not affect bacteria when it is present in the extracellular medium, it is highly toxic to other host cells such as polymorphonuclear neutrophils and erythrocytes. Finally, we showed that SprA2_AS expression is lowered during osmotic shock and stringent response, which indicates that the system responds to specific triggers. Therefore, the SprA2/SprA2_AS module is not redundant with SprA1/SprA1_AS, and its PepA2 peptide exhibits an original dual mode of action against bacteria and host cells. This suggests an altruistic behavior for S. aureus in which clones producing PepA2 in vivo shall die as they induce cytotoxicity, thereby promoting the success of the community.

Alteration of human macrophage phenotypes by the anti-fibrotic drug nintedanib

The tyrosine kinase inhibitor, Nintedanib (NTD), has been approved for the treatment of idiopathic pulmonary fibrosis (IPF). In cell-free systems, NTD was recently shown to inhibit kinase activity of the human recombinant colony-stimulating factor 1 (CSF1) receptor (CSF1R) which mediates major functions of pulmonary macrophages. In the present study, we have investigated the effects of NTD on the phenotype of human monocyte-derived macrophages controlled by CSF1 in order to identify its anti-inflammatory properties via CSF1R inhibition. NTD (0.01 to 1 μM) prevented the CSF1-induced phosphorylation of CSF1R and activation of the downstream signaling pathways. NTD, like the CSF1R inhibitor GW2580, significantly decreased the adhesion of macrophages and production of the chemokine ligand (CCL) 2. NTD also altered the polarization of macrophages to classical M1 and alternative M2a macrophages. It reduced the secretion of several pro-inflammatory and/or pro-fibrotic cytokines (IL-1β, IL-8, IL-10 and CXCL13) by M1 macrophages but did not prevent the expression of M1 markers. While NTD (50-200 nM) partially blocked the synthesis of M2a markers (CD11b, CD200R, CD206, and CD209), it did not reduce synthesis of the M2a pro-fibrotic cytokines CCL22 and PDGF-BB, and increased CCL18 release when used at its highest concentration (1 μM). The effects of NTD on macrophage polarization only was partially mimicked by GW2580, suggesting that the drug inhibits other molecules in addition to CSF1R. In conclusion, NTD alters the CSF1-controlled phenotype of human macrophages mainly by blocking the activation of CSF1R that thus constitutes a new molecular target of NTD, at least in vitro.

Induction of multidrug resistance-associated protein 3 expression by diesel exhaust particle extract in human bronchial epithelial BEAS-2B cells

Diesel exhaust particles (DEPs) are common environmental air pollutants known to impair expression and activity of drug detoxifying proteins, including hepatic ATP-binding cassette (ABC) drug transporters. The present study was designed to determine whether organic DEP extract (DEPe) may also target ABC drug transporters in bronchial cells. DEPe (10 μg/mL) was demonstrated to induce mRNA and protein expression of the multidrug resistance-associated protein (MRP) 3 in cultured bronchial epithelial BEAS-2B cells, whereas mRNA levels of other MRPs, multidrug resistance gene 1 or breast cancer resistance protein were unchanged, reduced or not detected. DEPe also increased MRP3 mRNA expression in normal human bronchial epithelial cells. Inhibition of the aryl hydrocarbon receptor (AhR) pathway by AhR antagonist or AhR silencing, as well as the silencing of nuclear-factor-E2-related factor 2 (Nrf2) repressed DEPe-mediated MRP3 induction. This underlines the implication of the AhR and Nrf2 signaling cascades in DEPe-mediated MRP3 regulation. DEPe was additionally demonstrated to directly inhibit MRP activity in BEAS-2B cells, in a concentration-dependent manner. Taken together, these data indicate that DEPs may impair expression and activity of MRPs, notably MRP3, in human bronchial cells, which may have consequences in terms of lung barrier and toxicity for humans exposed to diesel pollution.

An integrated functional and transcriptomic analysis reveals that repeated exposure to diesel exhaust induces sustained mitochondrial and cardiac dysfunctions

Diesel exhaust (DE) contributes to air pollution, an important risk factor for cardiovascular diseases. However, the mechanisms by which DE exposure induces cardiovascular dysfunction remain unknown and there is still debate on the contribution of the primary particulate matter (PM) fraction compared to the gaseous phase. Although the mitochondria play a key role in the events leading to cardiovascular diseases, their role in DE-induced cardiovascular effects has not been investigated. The aim of this study was to highlight cardiac and mitochondrial events that could be disrupted following acute and/or repeated DE exposures and the contribution of gaseous pollutants to these effects. To address this question, Wistar rats were exposed to DE generated under strictly controlled and characterized conditions and extracted upstream or downstream of the diesel particulate filter (DPF). Evaluation of the cardiac function after acute DE exposure showed a disturbance in echocardiographic parameters, which persisted and worsened after repeated exposures. The presence of the DPF did not modify the cardiovascular dysfunction revealing an important implication of the gas phase in this response. Surprisingly, redox parameters were not altered by DE exposures while an alteration in mitochondrial oxidative capacity was observed. Exploration of the mitochondrial function demonstrated a more specific alteration in complex I of the respiratory chain after repeated exposures, which was further confirmed by transcriptional analysis of left ventricular (LV) tissue. In conclusion, this work provides new insights into cardiovascular effects induced by DE, demonstrating a cardiac mitochondrial impairment associated with the gaseous phase. These effects suggest deleterious consequences in terms of cardiac function for vulnerable populations with underlying energy deficit such as patients with heart failure or the elderly.

Efferocytosis capacities of blood monocyte-derived macrophages in systemic sclerosis

A defect in the apoptotic cell clearance (efferocytosis) by phagocytic cells may participate in autoimmunity and chronic inflammation. The mechanisms leading to the emergence of autoimmunity in systemic sclerosis (SSc) are still to be determined. In this study, the efferocytosis capacities of blood monocyte-derived macrophages (MDM) from patients with SSc were evaluated. Blood monocytes obtained from patients with SSc and healthy donors (HD) were differentiated in vitro into macrophages. The capacities of MDM to engulf CFSE+ apoptotic Jurkat human T lymphocytes were compared between SSc MDM and HD using flow cytometry. The expression of classical engulfing receptors in SSc MDM and HD MDM was also evaluated and their involvement in the modulation of efferocytosis was confirmed using a siRNA approach. The mean phagocytic index (PI) reflecting efferocytosis capacities of SSc MDM (PI = 19.3 ± 3.0; n = 21) was significantly decreased in comparison with the PI of HD MDM (PI = 35.9 ± 3.0; n = 31; P < 0.001). In comparison with HD, SSc MDM exhibited a downregulated expression of scavenger receptor (SR)-B1, SR-A1 and integrin β5 (ITGβ5). In HD MDM, the extinction of these receptors was followed by a reduction of efferocytosis only for the repression of ITGβ5, suggesting a possible selective role of this integrin in the impaired efferocytosis observed in SSc. As efferocytosis may be at the crossroads of inflammation, autoimmunity and fibrosis, in showing impaired efferocytosis capacities of blood MDM in SSc, our study offers new pathogenesis considerations for the involvement of macrophages in the autoimmune processes driving this disorder.

Comparative study of diesel and biodiesel exhausts on lung oxidative stress and genotoxicity in rats

The contribution of diesel exhaust to atmospheric pollution is a major concern for public health, especially in terms of occurrence of lung cancers. The present study aimed at addressing the toxic effects of a repeated exposure to these emissions in an animal study performed under strictly controlled conditions. Rats were repeatedly exposed to the exhaust of diesel engine. Parameters such as the presence of a particle filter or the use of gasoil containing rapeseed methyl ester were investigated. Various biological parameters were monitored in the lungs to assess the toxic and genotoxic effects of the exposure. First, a transcriptomic analysis showed that some pathways related to DNA repair and cell cycle were affected to a limited extent by diesel but even less by biodiesel. In agreement with occurrence of a limited genotoxic stress in the lungs of diesel-exposed animals, small induction of γ-H2AX and acrolein adducts was observed but not of bulky adducts and 8-oxodGuo. Unexpected results were obtained in the study of the effect of the particle filter. Indeed, exhausts collected downstream of the particle filter led to a slightly higher induction of a series of genes than those collected upstream. This result was in agreement with the formation of acrolein adducts and γH2AX. On the contrary, induction of oxidative stress remained very limited since only SOD was found to be induced and only when rats were exposed to biodiesel exhaust collected upstream of the particle filter. Parameters related to telomeres were identical in all groups. In summary, our results point to a limited accumulation of damage in lungs following repeated exposure to diesel exhausts when modern engines and relevant fuels are used. Yet, a few significant effects are still observed, mostly after the particle filter, suggesting a remaining toxicity associated with the gaseous or nano-particular phases.

Distinct Properties of Human M-CSF and GM-CSF Monocyte-Derived Macrophages to Simulate Pathological Lung Conditions In Vitro: Application to Systemic and Inflammatory Disorders with Pulmonary Involvement

Macrophages play a central role in the pathogenesis of inflammatory and fibrotic lung diseases. However, alveolar macrophages (AM) are poorly available in humans to perform in vitro studies due to a limited access to broncho-alveolar lavage (BAL). In this study, to identify the best alternative in vitro model for human AM, we compared the phenotype of AM obtained from BAL of patients suffering from three lung diseases (lung cancers, sarcoidosis and Systemic Sclerosis (SSc)-associated interstitial lung disease) to human blood monocyte-derived macrophages (MDMs) differentiated with M-CSF or GM-CSF. The expression of eight membrane markers was evaluated by flow cytometry. Globally, AM phenotype was closer to GM-CSF MDMs. However, the expression levels of CD163, CD169, CD204, CD64 and CD36 were significantly higher in SSc-ILD than in lung cancers. Considering the expression of CD204 and CD36, the phenotype of SSc-AM was closer to MDMs, from healthy donors or SSc patients, differentiated by M-CSF rather than GM-CSF. The comparative secretion of IL-6 by SSc-MDMs and SSc-AM is concordant with these phenotypic considerations. Altogether, these results support the M-CSF MDM model as a relevant in vitro alternative to simulate AM in fibrotic disorders such as SSc.

Repression of interferon β-regulated cytokines by the JAK1/2 inhibitor ruxolitinib in inflammatory human macrophages

Ruxolitinib is a Janus kinase (JAK) 1/2 inhibitor, currently used in the treatment of myeloproliferative neoplasms. It exerts potent anti-inflammatory activity, but the involved molecular and cellular mechanisms remain poorly understood. In order to gain insights about this point, ruxolitinib effects towards expression of main inflammatory cytokines were studied in human macrophages, which constitute a key-cell type implicated in inflammation. Analysis of mRNA expression of cytokines (n=84) by PCR array indicated that, among those induced by the pro-inflammatory stimulus lipopolysaccharide (LPS) (n=44), 61.4% (n=27) were repressed by 5μM ruxolitinib. The major inflammatory cytokines, interleukin (IL) 6 and tumor necrosis factor α, were notably down-regulated by ruxolitinib at both the mRNA and protein level. Other repressed cytokines included IL27 and the chemokines CCL2, CXCL9, CXCL10 and CXCL11, but not IL1β. The interferon (IFN) β/JAK/signal transducer and activator of transcription (STAT) pathway, well-activated by LPS in human macrophages as demonstrated by increased secretion of IFNβ, STAT1 phosphorylation, and up-regulation of reference IFNβ-responsive genes, was concomitantly blocked by the JAK inhibitor. Most of cytokines targeted by ruxolitinib were shown to be regulated by IFNβ in a JAK-sensitive manner. In addition, counteracting the IFNβ/JAK/STAT cascade using a blocking monoclonal antibody directed against IFNβ receptor resulted in a similar profile of cytokine repression to that observed in response to the JAK inhibitor. Overall, these data provide evidence for ruxolitinib-mediated repression of inflammatory cytokines in human macrophages through inhibition of the LPS/IFNβ/JAK/STAT signalling pathway, which probably contributes to the anti-inflammatory effects of the JAK inhibitor.

Granulometry, microbial composition and biological activity of dusts collected in French dairy farms

BACKGROUND

Dairy working increases the prevalence of lower airway respiratory diseases, especially COPD and asthma. Epidemiological studies have reported that chronic inhalation of organic dusts released during specific daily tasks could represent a major risk factor for development of these pathologies in dairy workers. Knowledge on size, nature and biological activity of such organic dusts remain however limited.

OBJECTIVE

To compare size distribution, microbial composition and cellular effects of dusts liberated by the spreading of straw bedding in five French dairy farms located in Brittany.

RESULTS

Mechanized distribution of straw bedding generated a cloud of inhalable dusts in the five dairy farms' barns. Thoracic particles having a 3-7.5µm size constituted 58.9-68.3% of these dusts. Analyses of thoracic dusts by next generation sequencing showed that the microbial dust composition differed between the five French farms, although Actinobacteria, Bacteroidetes, Firmicutes and Proteobacteria represent more than 97.5% of the bacterial phyla detected in each sample. Several bacteria genera comprising of human pathogenic species, such as Pseudomonas, Staphylococcus, Thermoactinomyces or Saccharopolyspora were identified. Cladosporium and Alternaria fungal genera, which are potent environmental determinants of respiratory symptoms, were detected in dusts collected in the five farms and their levels reached 15.5-51.1% and 9-24.7% of assignable fungal sequences in each sample, respectively. Finally, all dust samples significantly and strongly increased the expression of the pro-inflammatory TNF-α, IL-1β, IL-6 and IL-8 cytokines at both mRNA and protein levels in human monocyte-derived macrophages. Their effects were dose-dependent and detectable from 1µg/ml. The intensity of the macrophage responses however differed according to the samples.

CONCLUSIONS

Our results strengthen the hypothesis that organic dusts released during the distribution of straw bedding are mainly constituted of thoracic particles which are small enough to deposit on lower bronchial epithelium of dairy farmers and induce inflammation.

Aryl hydrocarbon receptor-dependent up-regulation of the heterodimeric amino acid transporter LAT1 (SLC7A5)/CD98hc (SLC3A2) by diesel exhaust particle extract in human bronchial epithelial cells

The heterodimeric L-type amino acid transporter (LAT) 1/CD98hc is overexpressed in lung cancers with a poor prognosis factor. Factors that contribute to LAT1/CD98hc overexpression in lung cells remain however to be determined, but the implication of atmospheric pollution can be suspected. The present study was therefore designed to analyze the effects of diesel exhaust particle (DEP) extract (DEPe) on LAT1/CD98hc expression in bronchial epithelial BEAS-2B cells. Exposure to DEPe up-regulated LAT1 and CD98hc mRNA levels in a concentration-dependent manner, with DEPe EC50 values (around 0.2 μg/mL) relevant to environmental situations. DEPe concomitantly induced LAT1/CD98hc protein expression and LAT1-mediated leucine accumulation in BEAS-2B cells. Inhibition of the aryl hydrocarbon receptor (AhR) pathway through the use of a chemical AhR antagonist or the siRNA-mediated silencing of AhR expression was next found to prevent DEPe-mediated induction of LAT1/CD98hc, indicating that this regulation depends on AhR, known to be activated by major chemical DEP components like polycyclic aromatic hydrocarbons. DEPe exposure was finally shown to induce mRNA expression and activity of matrix metalloproteinase (MMP)-2 in BEAS-2B cells, in a CD98hc/focal adhesion kinase (FAK)/extracellular regulated kinase (ERK) manner, thus suggesting that DEPe-mediated induction of CD98hc triggers activation of the integrin/FAK/ERK signaling pathway known to be involved in MMP-2 regulation. Taken together, these data demonstrate that exposure to DEPe induces functional overexpression of the amino acid transporter LAT1/CD98hc in lung cells. Such a regulation may participate to pulmonary carcinogenic effects of DEPs, owing to the well-documented contribution of LAT1 and CD98hc to cancer development.

AhR-dependent secretion of PDGF-BB by human classically activated macrophages exposed to DEP extracts stimulates lung fibroblast proliferation

Lung diseases are aggravated by exposure to diesel exhaust particles (DEPs) found in air pollution. Macrophages are thought to play a crucial role in lung immune response to these pollutants, even if the mechanisms involved remain incompletely characterized. In the present study, we demonstrated that classically and alternative human macrophages (MΦ) exhibited increased secretion of PDGF-B in response to DEP extract (DEPe). This occurred via aryl hydrocarbon receptor (AhR)-activation because DEPe-induced PDGF-B overexpression was abrogated after AhR expression knock-down by RNA interference, in both M1 and M2 polarizing MΦ. In addition, TCDD and benzo(a)pyrene, two potent AhR ligands, also significantly increased mRNA expression of PDGF-B in M1 MΦ, whereas some weak ligands of AhR did not. We next evaluated the impact of conditioned media (CM) from MΦ culture exposed to DEPe or of recombinant PDGF-B onto lung fibroblast proliferation. The tyrosine kinase inhibitor, AG-1295, prevents phosphorylations of PDGF-Rβ, AKT and ERK1/2 and the proliferation of MRC-5 fibroblasts induced by recombinant PDGF-B and by CM from M1 polarizing MΦ, strongly suggesting that the PDGF-BB secreted by DEPe-exposed MΦ is sufficient to activate the PDGF-Rβ pathway of human lung fibroblasts. In conclusion, we demonstrated that human MΦ, whatever their polarization status, secrete PDGF-B in response to DEPe and that PDGF-B is a target gene of AhR. Therefore, induction of PDGF-B by DEP may participate in the deleterious effects towards human health triggered by such environmental urban contaminants.

Regulation of human hepatic drug transporter activity and expression by diesel exhaust particle extract

Diesel exhaust particles (DEPs) are common environmental air pollutants primarily affecting the lung. DEPs or chemicals adsorbed on DEPs also exert extra-pulmonary effects, including alteration of hepatic drug detoxifying enzyme expression. The present study was designed to determine whether organic DEP extract (DEPe) may target hepatic drug transporters that contribute in a major way to drug detoxification. Using primary human hepatocytes and transporter-overexpressing cells, DEPe was first shown to strongly inhibit activities of the sinusoidal solute carrier (SLC) uptake transporters organic anion-transporting polypeptides (OATP) 1B1, 1B3 and 2B1 and of the canalicular ATP-binding cassette (ABC) efflux pump multidrug resistance-associated protein 2, with IC50 values ranging from approximately 1 to 20 μg/mL and relevant to environmental exposure situations. By contrast, 25 μg/mL DEPe failed to alter activities of the SLC transporter organic cation transporter (OCT) 1 and of the ABC efflux pumps P-glycoprotein and bile salt export pump (BSEP), whereas it only moderately inhibited those of sodium taurocholate co-transporting polypeptide and of breast cancer resistance protein (BCRP). Treatment by 25 μg/mL DEPe was next demonstrated to induce expression of BCRP at both mRNA and protein level in cultured human hepatic cells, whereas it concomitantly repressed mRNA expression of various transporters, including OATP1B3, OATP2B1, OCT1 and BSEP. Such changes in transporter expression were found to be highly correlated to those caused by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a reference activator of the aryl hydrocarbon receptor (AhR) pathway. This suggests that DEPe, which is enriched in known ligands of AhR like polycyclic aromatic hydrocarbons, alters drug transporter expression via activation of the AhR cascade. Taken together, these data established human hepatic transporters as targets of organic chemicals containing in DEPs, which may contribute to their systemic effects through impairing hepatic transport of endogenous compound or drug substrates of these transporters.

Exposure to diesel exhaust particle extracts (DEPe) impairs some polarization markers and functions of human macrophages through activation of AhR and Nrf2

Macrophages (MΦ), well-known to play an important role in immune response, also respond to environmental toxic chemicals such as diesel exhaust particles (DEP). Potential effects of DEPs towards MΦ polarization, a key hall-mark of MΦ physiology, remain however poorly documented. This study was therefore designed to evaluate the effects of a reference DEP extract (DEPe) on human MΦ polarization. Human blood monocytes-derived MΦ were incubated with IFNγ+LPS or IL-4 to obtain M1 and M2 subtypes, respectively; a 24 h exposure of polarizing MΦ to 10 μg/ml DEPe was found to impair expression of some macrophagic M1 and M2 markers, without however overall inhibition of M1 and M2 polarization processes. Notably, DEPe treatment increased the secretion of the M1 marker IL-8 and the M2 marker IL-10 in both MΦ subtypes, whereas it reduced lipopolysaccharide-induced IL-6 and IL-12p40 secretion in M1 MΦ. In M2 MΦ, DEPe exposure led to a reduction of CD200R expression and of CCL17, CCL18 and CCL22 secretion, associated with a lower chemotaxis of CCR4-positive cells. DEPe activated the Nrf2 and AhR pathways and induced expression of their reference target genes such as Hmox-1 and cytochrome P-4501B1 in M1 and M2 MΦ. Nrf2 or AhR silencing through RNA interference prevented DEPe-related down-regulation of IL-6. AhR silencing also inhibited the down-secretion of IL-12p40 and CCL18 in M1- and M2-DEPe-exposed MΦ, respectively. DEPs are therefore likely to alter expression of some M1 and M2 markers in an AhR- and Nrf2-dependent manner; such regulations may contribute to deleterious immune effects of atmospheric DEP.

Impaired functions of macrophage from cystic fibrosis patients: CD11b, TLR-5 decrease and sCD14, inflammatory cytokines increase

BACKGROUND

Early in life, cystic fibrosis (CF) patients are infected with microorganisms. The role of macrophages has largely been underestimated in literature, whereas the focus being mostly on neutrophils and epithelial cells. Macrophages may however play a significant role in the initiating stages of this disease, via an inability to act as a suppressor cell. Yet macrophage dysfunction may be the first step in cascade of events leading to chronic inflammation/infection in CF. Moreover, reports have suggested that CFTR contribute to altered inflammatory response in CF by modification of normal macrophage functions.

OBJECTIVES

In order to highlight possible intrinsic macrophage defects due to impaired CFTR, we have studied inflammatory cytokines secretions, recognition of pathogens and phagocytosis in peripheral blood monocyte-derived macrophages from stable adult CF patients and healthy subjects (non-CF).

RESULTS

In CF macrophage supernatants, concentrations of sCD14, IL-1β, IL-6, TNF-α and IL-10 were strongly raised. Furthermore expression of CD11b and TLR-5 were sorely decreased on CF macrophages. Beside, no difference was observed for mCD14, CD16, CD64, TLR-4 and TLR1/TLR-2 expressions. Moreover, a strong inhibition of phagocytosis was observed for CF macrophages. Elsewhere CFTR inhibition in non-CF macrophages also led to alterations of phagocytosis function as well as CD11b expression.

CONCLUSIONS

Altogether, these findings demonstrate excessive inflammation in CF macrophages, characterized by overproduction of sCD14 and inflammatory cytokines, with decreased expression of CD11b and TLR-5, and impaired phagocytosis. This leads to altered clearance of pathogens and non-resolution of infection by CF macrophages, thereby inducing an exaggerated pro-inflammatory response.

Differential regulation of drug transporter expression by hepatocyte growth factor in primary human hepatocytes

Hepatocyte growth factor (HGF) is known to down-regulate expression of drug-detoxifying proteins such as cytochromes P450 (P450s) in human hepatocytes. The present study was designed to determine whether HGF may also impair expression of uptake and efflux drug transporters, which constitute important determinants of the liver detoxification pathway, such as P450s. Exposure of primary human hepatocytes to 20 ng/ml HGF for 48 h was found to down-regulate mRNA levels of major sinusoidal uptake transporters, including sodium taurocholate-cotransporting polypeptide (NTCP), organic anion-transporting polypeptide (OATP) 2B1, OATP1B1, organic cation transporter (OCT) 1, and organic anion transporter 2. HGF concomitantly reduced NTCP, OATP2B1, and OATP1B1 protein expression and NTCP, OATP, and OCT1 transport activities. With respect to efflux pumps, HGF decreased mRNA expression of the canalicular bile salt export pump, whereas that of the multidrug resistance (MDR) 1 gene was transiently increased. Moreover, Western blot analysis indicated that HGF up-regulated expressions of MDR1/P-glycoprotein and breast cancer resistance protein in human hepatocytes, whereas those of multidrug resistance gene-associated protein (MRP) 2 and MRP3 were unchanged. However, HGF prevented constitutive androstane receptor-related up-regulation of MRP2 occurring in phenobarbital-treated hepatocytes. Taken together, these data demonstrate that HGF differentially regulates transporter expression in human hepatocytes, i.e., it represses most of the sinusoidal uptake transporters, whereas expression of most of the efflux transporters is unchanged or increased. Such changes probably contribute to alterations of pharmacokinetics in patients with diseases associated with increased plasma levels of HGF such as fulminant hepatitis.

NPC1 repression contributes to lipid accumulation in human macrophages exposed to environmental aryl hydrocarbons

AIMS

Aryl hydrocarbons (AHs), such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and benzo(a)pyrene (BP), are environmental contaminants promoting the development of atherosclerosis-related cardiovascular diseases. In order to identify molecular mechanisms involved in these effects, we have analysed AH-mediated regulation of the lipid trafficking Niemann-Pick type C1 protein (NPC1) and its contribution to AH-induced macrophage lipid accumulation.

METHODS AND RESULTS

Exposure of primary human macrophages to TCDD and BP decreased NPC1 mRNA expression in a time-dependent manner. NPC1 protein expression and NPC1-related acid sphingomyelinase activity were reduced in parallel. NPC1 was also similarly down-regulated in mice exposed to BP. Moreover, TCDD and BP were demonstrated to trigger lipid accumulation in human macrophages, as assessed by Oil Red O and Nile Red staining and cholesterol determination. Such lipid loading occurred at least partly in endosomal/lysosomal compartments as demonstrated by immunolabelling of lipid vesicles by the lysosome-associated membrane protein 1. These cellular phenotypic effects were found to be similar to those triggered by knock-down of NPC1 expression using siRNAs and were counteracted by NPC1 overexpression, thus supporting the contribution of NPC1 to AH-mediated lipid accumulation in macrophages. Finally, both NPC1 down-expression and lipid accumulation in response to TCDD were found to be abolished through knock-down of the AH receptor (AHR), a ligand-activated transcription factor mediating many effects of AHs.

CONCLUSION

Our data have shown that contaminants such as TCDD and BP repress NPC1 expression in macrophages in an AHR-dependent manner, which likely contributes to macrophage lipid accumulation caused by these environmental chemicals. Thus, NPC1 appears to be a new molecular target regulated by environmental AHs and putatively involved in their deleterious cardiovascular effects.

Regulation of drug transporter expression in human hepatocytes exposed to the proinflammatory cytokines tumor necrosis factor-alpha or interleukin-6

Tumor necrosis factor (TNF)-alpha and interleukin (IL)-6 are proinflammatory cytokines known to alter expression of drug transporters in rodent liver. However, their effects toward human hepatic transporters remain poorly characterized. Therefore, this study was designed to analyze the effects of these cytokines on drug transporter expression in primary human hepatocytes. Exposure to 100 ng/ml TNF-alpha or 10 ng/ml IL-6 for 48 h was found to down-regulate mRNA levels of major sinusoidal influx transporters, including sodium-taurocholate cotransporting polypeptide (NTCP), organic anion-transporting polypeptide (OATP) 1B1, OATP1B3, OATP2B1, organic cation transporter (OCT) 1, and organic anion transporter 2. TNF-alpha and IL-6 concomitantly reduced NTCP and OATP1B1 protein expression and NTCP, OATP, and OCT1 transport activities. IL-6, but not TNF-alpha, was also found to decrease mRNA expression of the canalicular transporters multidrug resistance 1 gene, multidrug resistance gene-associated protein (MRP) 2, and breast cancer resistance protein (BCRP); it concomitantly decreased MRP2 and BCRP protein expression. TNF-alpha, unlike IL-6, markedly reduced bile salt export pump mRNA levels and increased BCRP protein expression. Expression of the sinusoidal MRP3 efflux pump was found to be up-regulated at protein level by both TNF-alpha and IL-6. Taken together, these data show that TNF-alpha and IL-6 similarly altered expression of sinusoidal drug transporters and rather differentially that of canalicular efflux transporters. Such pronounced changes in hepatic transporter expression are likely to contribute to both cholestasis and alterations of pharmacokinetics caused by inflammation in humans.

Structure, function and regulation of P-glycoprotein and its clinical relevance in drug disposition

1. P-glycoprotein (P-gp/MDR1), one of the most clinically important transmembrane transporters in humans, is encoded by the ABCB1/MDR1 gene. Recent insights into the structural features of P-gp/MDR1 enable a re-evaluation of the biochemical evidence on the binding and transport of drugs by P-gp/MDR1. 2. P-gp/MDR1 is found in various human tissues in addition to being expressed in tumours cells. It is located on the apical surface of intestinal epithelial cells, bile canaliculi, renal tubular cells, and placenta and the luminal surface of capillary endothelial cells in the brain and testes. 3. P-gp/MDR1 confers a multi-drug resistance (MDR) phenotype to cancer cells that have developed resistance to chemotherapy drugs. P-gp/MDR1 activity is also of great clinical importance in non-cancer-related drug therapy due to its wide-ranging effects on the absorption and excretion of a variety of drugs. 4. P-gp/MDR1 excretes xenobiotics such as cytotoxic compounds into the gastrointestinal tract, bile and urine. It also participates in the function of the blood-brain barrier. 5. One of the most interesting characteristics of P-gp/MDR1 is that its many substrates vary greatly in their structure and functionality, ranging from small molecules such as organic cations, carbohydrates, amino acids and some antibiotics to macromolecules such as polysaccharides and proteins. 6. Quite a number of single nucleotide polymorphisms have been found for the MDR1 gene. These single nucleotide polymorphisms are associated with altered oral bioavailability of P-gp/MDR1 substrates, drug resistance, and a susceptibility to some human diseases. 7. Altered P-gp/MDR1 activity due to induction and/or inhibition can cause drug-drug interactions with altered drug pharmacokinetics and response. 8. Further studies are warranted to explore the physiological function and pharmacological role of P-gp/MDR1.

Interleukin-8 induction by the environmental contaminant benzo(a)pyrene is aryl hydrocarbon receptor-dependent and leads to lung inflammation

Benzo(a)pyrene (BP) is an environmental contaminant known to favor airway inflammation likely through up-regulation of pro-inflammatory cytokines. The present study was designed to characterize its effects toward interleukin-8 (IL-8), a well-established pulmonary inflammatory cytokine. In primary human macrophages, BP was shown to induce IL-8 expression at both mRNA and secretion levels in a dose-dependent manner. Such an up-regulation was likely linked to aryl hydrocarbon receptor (AhR)-activation since BP-mediated IL-8 induction was reduced after AhR expression knock-down through RNA interference. Moreover, electrophoretic mobility shift assays (EMSAs) and chromatin immunoprecipitation experiments showed BP-triggered binding of AhR to a consensus xenobiotic responsive element (XRE) found in the human IL-8 promoter. Finally, BP administration to mice led to over-expression of keratinocyte chemoattractant (KC), the murine functional homologue of IL-8, in lung. It also triggered the recruitment of neutrophils in bronchoalveolar lavage (BAL) fluids, which was however fully abolished in the presence of a chemical antagonist of the KC/IL-8 receptors CXCR1/CXCR2, thus supporting the functional and crucial involvement of KC in BP-induced lung inflammation. Overall, these data highlight an AhR-dependent regulation of IL-8 in response to BP that likely contributes to the airway inflammatory effects of this environmental chemical.

AhR- and c-maf-dependent induction of beta7-integrin expression in human macrophages in response to environmental polycyclic aromatic hydrocarbons

In order to identify molecular targets of environmental polycyclic aromatic hydrocarbons (PAHs), we have analysed regulation of integrin (ITG) expression in PAH-exposed human macrophages. Among ITG subunits, beta7 ITG was found to be markedly up-regulated at both mRNA and protein levels in response to the prototypical PAH benzo(a)pyrene (BP). Knock-down of the transcription factor c-maf, known to control beta7 ITG expression, markedly impaired BP-mediated beta7 ITG induction. Moreover, chromatin immunoprecipitation and electrophoretic mobility shift assays showed BP-triggered binding of c-maf to a specific maf-responsive element found in beta7 ITG promoter. Such a binding, and also beta7 ITG induction, were however abolished in response to chemical inhibition of the aryl hydrocarbon receptor (AhR), to which PAHs bind. Taken together, these data establish beta7 ITG as a new molecular target of PAHs, whose up-regulation by these environmental contaminants most likely requires activation of co-operative pathways involving both AhR and c-maf.