Rationale: Bioactive lipid mediators, derived from membrane lipid precursors, are released into the airway and airspace where they bind high-affinity cognate receptors and may mediate asthma pathogenesis. Lysophosphatidic acid (LPA), a bioactive lipid mediator generated by the enzymatic activity of extracellular autotaxin (ATX), binds LPA receptors, resulting in an array of biological actions on cell proliferation, migration, survival, differentiation, and motility, and therefore could mediate asthma pathogenesis.Objectives: To define a role for the ATX-LPA pathway in human asthma pathogenesis and a murine model of allergic lung inflammation. Methods: We investigated the profiles of LPA molecular species and the level of ATX exoenzyme in bronchoalveolar lavage fluids of human patients with asthma subjected to subsegmental bronchoprovocation with allergen. We interrogated the role of the ATX-LPA pathway in allergic lung inflammation using a murine allergic asthma model in ATX-LPA pathway-specific genetically modified mice. Measurements and Main Results: Subsegmental bronchoprovocation with allergen in patients with mild asthma resulted in a remarkable increase in bronchoalveolar lavage fluid levels of LPA enriched in polyunsaturated 22:5 and 22:6 fatty acids in association with increased concentrations of ATX protein. Using a triple-allergen mouse asthma model, we showed that ATX-overexpressing transgenic mice had a more severe asthmatic phenotype, whereas blocking ATX activity and knockdown of the LPA 2 receptor in mice produced a marked attenuation of Th2 cytokines and allergic lung inflammation. Conclusions: The ATX-LPA pathway plays a critical role in the pathogenesis of asthma. These preclinical data indicate that targeting the ATX-LPA pathway could be an effective antiasthma treatment strategy.Keywords: asthma; lysophosphatidic acid; autotaxin; allergic airway inflammation supplied the ATX inhibitor, GWJ-23. V.A., E.K., and I.N. were involved in discussions related to animal dosage. A.J.M. and S.S.S. provided breeding pairs of ATX-Tg and ATX 1/2 mice. S.J.A. managed the inflammatory cell purification core lab for the SBP-AG protocol, designed experiments, interpreted data, coordinated regular scientific research meetings for the project, and edited the manuscript. V.N. conceptualized the study, designed mouse experiments, interpreted data, provided genetically modified mice, and wrote part of and edited the manuscript. J.W.C. obtained the SBP-AG IRB and IND approval, supervised mouse experiments and performance of the human SBP-AG protocol, designed experiments, interpreted and analyzed data, and edited the manuscript. All authors contributed to data discussion and review of the manuscript.Correspondence and requests for reprints should be addressed to John W. What This Study Adds to the FieldThe enzyme autotaxin (ATX) and two of its LPA products, LPA 22:5 and LPA 22:6, are markedly and selectively increased in the bronchoalveolar lavage fluid of human patients with asthma in response to airway allergen ch...

Although alveolar macrophages (AMs) from patients with asthma are known to be functionally different from those of healthy individuals, the mechanism by which this transformation occurs has not been fully elucidated in asthma. The goal of this study was to define the mechanisms that control AM phenotypic and functional transformation in response to acute allergic airway inflammation. The phenotype and functional characteristics of AMs obtained from human subjects with asthma after subsegmental bronchoprovocation with allergen was studied. Using macrophagedepleted mice, the role and trafficking of AM populations was determined using an acute allergic lung inflammation model. We observed that depletion of AMs in a mouse allergic asthma model attenuates Th2-type allergic lung inflammation and its consequent airway remodeling. In both human and mouse, endobronchial challenge with allergen induced a marked increase in monocyte chemotactic proteins (MCPs) in bronchoalveolar fluid, concomitant with the rapid appearance of a monocyte-derived population of AMs. Furthermore, airway allergen challenge of allergic subjects with mild asthma skewed the pattern of AM gene expression toward high levels of the receptor for MCP1 (CCR2/ MCP1R) and expression of M2 phenotypic proteins, whereas most proinflammatory genes were highly suppressed. CCL2/MCP-1 gene expression was prominent in bronchial epithelial cells in a mouse allergic asthma model, and in vitro studies indicate that bronchial epithelial cells produced abundant MCP-1 in response to house dust mite allergen. Thus, our study indicates that bronchial allergen challenge induces the recruitment of blood monocytes along a chemotactic gradient generated by allergen-exposed bronchial epithelial cells.

No abstract

The transcription factor PU.1 is involved in regulation of macrophage differentiation and maturation. However, the role of PU.1 in alternatively activated macrophage (AAM) and asthmatic inflammation has yet been investigated. Here we report that PU.1 serves as a critical regulator of AAM polarization and promotes the pathological progress of asthmatic airway inflammation. In response to the challenge of DRA (dust mite, ragweed, and Aspergillus) allergens, conditional PU.1-deficient (PU/ER(T)(+/-)) mice displayed attenuated allergic airway inflammation, including decreased alveolar eosinophil infiltration and reduced production of IgE, which were associated with decreased mucous glands and goblet cell hyperplasia. The reduced asthmatic inflammation in PU/ER(T)(+/-) mice was restored by adoptive transfer of IL-4-induced wild-type (WT) macrophages. Moreover, after treating PU/ER(T)(+/-) mice with tamoxifen to rescue PU.1 function, the allergic asthmatic inflammation was significantly restored. In vitro studies demonstrate that treatment of PU.1-deficient macrophages with IL-4 attenuated the expression of chitinase 3-like 3 (Ym-1) and resistin-like molecule alpha 1 (Fizz-1), two specific markers of AAM polarization. In addition, PU.1 expression in macrophages was inducible in response to IL-4 challenge, which was associated with phosphorylation of signal transducer and activator of transcription 6 (STAT6). Furthermore, DRA challenge in sensitized mice almost abrogated gene expression of Ym-1 and Fizz-1 in lung tissues of PU/ER(T)(+/-) mice compared with WT mice. These data, all together, indicate that PU.1 plays a critical role in AAM polarization and asthmatic inflammation.

No abstract

Macrophages are a heterogeneous population of immune cells that are essential for the initiation and containment inflammation. There are 2 well-established populations of inflammatory macrophages: classically activated M1 and alternatively activated M2 macrophages. The FoxO family of transcription factors plays key roles in a number of cellular processes, including cell growth, metabolism, survival, and inflammation. In this study, we determined whether the expression of FoxO1 contributes polarization of macrophages toward the M2-like phenotype by enhancing IL-10 cytokine expression. We identified that FoxO1 is highly expressed in M-CSF-derived (M2-like) macrophage subsets, and this M2-like macrophages showed a preferential FoxO1 enrichment on the IL-10 promoter but not in GM-CSF-derived (M1-like) macrophages during classic activation by LPS treatment, which suggests that FoxO1 enhances IL-10 by binding directly to the IL-10 promoter, especially in BMMs. In addition, our data show that macrophages in the setting of hyperglycemia contribute to the macrophage-inflammatory phenotype through attenuation of the contribution of FoxO1 to activate IL-10 expression. Our data identify a novel role for FoxO1 in regulating IL-10 secretion during classic activation and highlight the potential for therapeutic interventions for chronic inflammatory conditions, such as atherosclerosis, diabetes, inflammatory bowel disease, and arthritis.

Akt (protein kinase B) is a serine/threonine protein kinase that regulates cell metabolism, survival and proliferation. Recent studies of the role of Akt in phagocytosis, intracellular bacterial infections, LPS tolerance, production of inflammatory cytokines and mediators, and migration during macrophage-mediated innate immunity strongly suggest a pivotal role for this enzyme in the functional activation of macrophages. Considering that a variety of inflammatory diseases, such as rheumatoid arthritis, atherosclerosis, diabetes, obesity, cancer and osteoporosis, are regulated by macrophage-mediated innate immunity, efforts should be more carefully focused on understanding the function of Akt in macrophage-mediated innate immunity. Although few studies have addressed this question, this review discusses recent findings that support an important role for Akt in macrophage-mediated innate immunity and underlines the need for trials to develop pharmaceutically useful drugs that target Akt for treatment of macrophage-mediated inflammatory diseases. The findings we review here suggest that a novel and safe Akt inhibitor with strong immunosuppressive and anti-inflammatory properties will be applied to various chronic inflammatory diseases in the near future.

The hydroxylated benzene metabolite hydroquinone (HQ) is mainly generated from benzene, an important industrial chemical, and is also a common dietary component. Although numerous reports have addressed the tumorigenesis-inducing effects of HQ, few papers have explored its molecular regulatory mechanism in immunological responses. In this study we characterized Akt (protein kinase B)-targeted regulation by HQ and its derivatives, in suppressing inflammatory responses using cellular, molecular, biochemical, and immunopharmacological approaches. HQ down-regulated inflammatory responses such as NO production, surface levels of pattern recognition receptors, and cytokine gene expression with IC 50 values that ranged from 5 to 10 M. HQ inhibition was mediated by blocking NF-B activation via suppression of its translocation pathway, which is composed of Akt, IB␣ kinase ␤, and IB␣. Of the targets in this pathway, HQ directly targeted and bound to the sulfhydryl group of Cys-310 of Akt and sequentially interrupted the phosphorylation of both Thr-308 and Ser-473 by mediation of ␤-mercaptoethanol, according to the liquid chromatography/ mass spectroscopy analysis of the interaction of HQ with an Aktderived peptide. Therefore, our data suggest that Akt and its target site Cys-310 can be considered as a prime molecular target of HQ-mediated immunosuppression and for novel antiAkt-targeted immunosuppressive drugs.