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Immunoproteasome dysfunction augments alternative polarization of alveolar macrophages

ABSTRACT: The proteasome is a central regulatory hub for intracellular signaling by degrading numerous signaling mediators. Immunoproteasomes are specialized types of proteasomes known to be involved in shaping adaptive immune responses, but their role for innate immune signaling is elusive. Here, we analyzed immunoproteasome function for polarization of alveolar macrophages which are highly specialized tissue macrophages of the alveolar surface of the lung. Classical activation (M1 polarization) of primary alveolar macrophages by LPS/IFNγ transcriptionally induced all three immunoproteasome subunits LMP2, LMP7, and MECL-1. In contrast, IL-4 triggered alternative (M2) activation was accompanied by posttranscriptional upregulation of LMP2 and LMP7. Accordingly, immunoproteasome activity increased in M1 cells, and to some extent under M2 conditions. Analyzing the polarization capability from LMP7 deficient mice revealed no effect on the LPS/IFNγ triggered M1 profile, but uncovered a distorted M2 profile for IL-4 stimulated LMP7-/- alveolar macrophages as characterized by increased M2 marker gene expression and CCL17 cytokine release. This shift in immunoproteasome-dependent M2 polarization was accompanied by amplified AKT/STAT6 activation and IRF4 expression in LMP7-/- alveolar macrophages. IL-13 stimulation of LMP7 deficient cells induced a similar M2 skewed profile and IL4Rα protein expression was generally elevated in LMP7-/- alveolar macrophages, indicating that amplified IL4R signaling in immunoproteasome defective cells may contribute to augmented M2 polarization. Importantly, treatment with an LMP7-specific proteasome inhibitor recapitulated the findings of genetic LMP7 inactivation. Our results thus suggest a novel role of immunoproteasome function for regulating innate immune function of macrophages by limiting IL4R expression and signaling.

ORGANISM(S): Mus musculus

PROVIDER: GSE72000 | GEO | 2016/06/29

SECONDARY ACCESSION(S): PRJNA292698

REPOSITORIES: GEO

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Project description:Background: When exposed to specific stimuli, macrophages exhibit distinct activation programs, M1 and M2 polarization, that define macrophage function as inflammatory/immune effectors or anti-inflammatory/tissue remodeling cells, respectively. Due to their position on the lung epithelial surface, alveolar macrophages (AM) directly interact with environmental stimuli such as cigarette smoke, the major risk factor for the development of chronic obstructive pulmonary disease (COPD). Based on the current paradigm that, in response to smoking, AM contribute to both inflammatory and tissue remodeling processes in the lung relevant to the pathogenesis of COPD, we hypothesized that chronic exposure to cigarette smoking activates both the M1 and M2 polarization programs in AM. Methods and Findings: To assess this hypothesis, global transcriptional profiling with TaqMan confirmation and flow cytometry analysis was carried out on AM obtained by bronchoalveolar lavage of 24 healthy nonsmokers, 34 healthy smokers and 12 smokers with COPD to assess the expression of 41 M1 genes and 32 M2 genes in each group. Contrary to our expectations, while there was up-regulation of some genes typical for M2-related phenotypes, AM of healthy smokers exhibited substantial suppression of M1-related inflammatory/immune genes. These M1- and M2-related changes progressed with the development of smoking-induced lung disease, with AM of smokers with COPD exhibiting further down-regulation of M1-related genes accompanied with further up-regulation of some M2-related genes. Conclusion: The data demonstrates that the modifications of the AM transcriptome associated with smoking result in a unique phenotype characterized by reprogramming of AM towards M1-deactivated partially M2-polarized macrophages and suggests that, while AM likely contribute to smoking-induced tissue remodeling, the role of AM in the early pathogenesis of smoking-induced COPD in humans is not inflammatory. This concept is a departure from the conventional concept that AM-mediated inflammation participates in the early derangements of the lung induced by smoking, and suggests a novel paradigm for conceptualizing COPD and developing new approaches to prevent the development of smoking-induced lung disease. Comparison of gene expression in alveolar macrophages of normal non-smokers and normal smokers and smokers with COPD

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Immunoproteasome dysfunction augments alternative polarization of alveolar macrophages

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