Macrophage-intrinsic regulators of tissue type 2 in ammation
Julia Esser-von Bieren, Center of Allergy and Environment (ZAUM), Technical University of Munich (TUM) and Helmholtz Center Munich
Caspar Ohnmacht, Center of Allergy and Environment (ZAUM), Technical University of Munich (TUM) and Helmholtz Center Munich
Expression of transglutaminase 2 (brown staining) in airway tissue of house dust mite allergic patients and potential crosstalk between macrophage-intrinsic TG2 and AhR in type 2 inflammation: Whilst allergens or endogenous tissue factors (e.g. IL-4, retinoic acid) trigger TG2 expression, thus contributing to the initiation of type 2 inflammation, other factors (e.g. tryptophan metabolites) may activate the AhR system to counter-regulate type 2 inflammation. Both TG2 and the AhR system may regulate type 2 immune responses via modulating the lipid mediator metabolism in macrophages. A potential crosstalk between the AhR and TG2 has been reported for other disease settings, but has not been investigated in type 2 immune responses. Pathways or mediators with predominantly anti-inflammatory roles in airway allergy are shown in green, whilst red indicates pro-inflammatory roles.
Tissue damage or allergen exposure triggers type 2 inflammation with macrophages representing key sentinels of these challenges. Macrophages also govern type 2 immune responses both in allergy and during helminth infection. Whilst in helminth infection, the alternative (M2) activation of macrophages is protective, the mechanisms determining macrophage function in allergy remain obscure. The aim of the proposed project is thus to scrutinize macrophage-intrinsic regulators of type 2 inflammation in the context of allergy. First, we propose to study the role of the enzyme transglutaminase 2 (TG2) in macrophage polarization and function during house dust mite (HDM) allergy in humans and mice. We have observed that TG2 is strongly induced in the airways of HDM-allergic patients and in HDM-sensitized mice. Our preliminary data further suggest that macrophages are the major source of TG2 in HDM-induced allergy. To identify a potential functional role of TG2 in human airway allergy, we will study effector functions of isolated patient airway macrophages in the presence or absence of TG2 inhibitors. This will be complemented with in vitro experiments using siRNA knockdown or CRISPR/Cas9 mediated ablation of TG2 in monocyte- or induced pluripotent stem cell- (iPS) derived macrophages. In particular, we will assess the impact of macrophage-intrinsic TG2 ablation on macrophage polarization, mediator production and eosinophil or ILC2 activation. Using myeloid specific TG2 deficient mice (TG2fl/fl LysMCre), we will then explore the role of macrophage-intrinsic TG2 in HDM-induced allergic airway inflammation in vivo. Furthermore, we have observed that genetic ablation of the arylhydrocarbon receptor (AhR) or one of its downstream targets, the cytochrome P450 enzyme CYP1B1, increases allergic airway inflammation in two different murine models of allergic airway inflammation. We thus propose to explore the AhR pathway as a second macrophage-intrinsic regulator of type 2 inflammation. To identify the key cell types involved in AhR-mediated regulation of allergic airway inflammation, airway cells (including macrophages) will be sort-purified and analyzed for AhR and AhR target gene expression. The role of the AhR pathway in macrophage polarization and function will then be studied in vitro and ex vivo in macrophages isolated from tissues (lung, peritoneum, bone marrow) of AhR- or three different CYP1-deficient mouse strains. As both TG2 and the AhR pathway are known to regulate the metabolism of lipid mediators, we will analyze lipid mediator profiles of TG2- and AhR/CYP1-deficient macrophages and assess the contribution of individual mediators to allergic airway inflammation in the absence of macrophage-intrinsic TG2 or the AhR pathway both in vitro and ex vivo. Taken together, our work will provide new insights in to the roles of macrophages in allergy and advance our current understanding about the regulation of type 2 inflammation.
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