Blazek et al. demonstrate that treatment with IL-28A reduces inflammation in collagen-induced arthritis by restricting the recruitment of IL-1β+ neutrophils.

Ecdysteroids affect Drosophila ovarian stem cell niche formation and early germline differentiationEcdysteroids affect Drosophila ovarian stem cell niche formation and early germline differentiation. The steroid hormone ecdysone regulates germline development and stem cell niche establishment in the Drosophila ovary by modulating TGF-β signalling and cell adhesion.

Whereas the importance of macrophages in chronic inflammatory diseases is well recognized, there is an increasing awareness that neutrophils may also play an important role. In addition to the well-documented heterogeneity of macrophage phenotypes and functions, neutrophils also show remarkable phenotypic diversity among tissues. Understanding the molecular pathways that control this heterogeneity should provide abundant scope for the generation of more specific and effective therapeutics. We have shown that the transcription factor IFN regulatory factor 5 (IRF5) polarizes macrophages toward an inflammatory phenotype. IRF5 is also expressed in other myeloid cells, including neutrophils, where it was linked to neutrophil function. In this study we explored the role of IRF5 in models of acute inflammation, including antigen-induced inflammatory arthritis and lung injury, both involving an extensive influx of neutrophils. Mice lacking IRF5 accumulate far fewer neutrophils at the site of inflammation due to the reduced levels of chemokines important for neutrophil recruitment, such as the chemokine (C-X-C motif) ligand 1. Furthermore we found that neutrophils express little IRF5 in the joints and that their migratory properties are not affected by the IRF5 deficiency. These studies extend prior ones suggesting that inhibiting IRF5 might be useful for chronic macrophage-induced inflammation and suggest that IRF5 blockade would ameliorate more acute forms of inflammation, including lung injury.macrophages | neutrophils | IRF5 | acute inflammation | arthritis

SummaryInterferon Regulatory Factor 5 (IRF5) plays a major role in setting up an inflammatory macrophage phenotype, but the molecular basis of its transcriptional activity is not fully understood. In this study, we conduct a comprehensive genome-wide analysis of IRF5 recruitment in macrophages stimulated with bacterial lipopolysaccharide and discover that IRF5 binds to regulatory elements of highly transcribed genes. Analysis of protein:DNA microarrays demonstrates that IRF5 recognizes the canonical IRF-binding (interferon-stimulated response element [ISRE]) motif in vitro. However, IRF5 binding in vivo appears to rely on its interactions with other proteins. IRF5 binds to a noncanonical composite PU.1:ISRE motif, and its recruitment is aided by RelA. Global gene expression analysis in macrophages deficient in IRF5 and RelA highlights the direct role of the RelA:IRF5 cistrome in regulation of a subset of key inflammatory genes. We map the RelA:IRF5 interaction domain and suggest that interfering with it would offer selective targeting of macrophage inflammatory activities.

SUMMARY The MDM2 oncoprotein ubiquitinates and antagonizes p53 but may also carry out p53-independent functions. Here we report that MDM2 is required for the efficient generation of induced pluripotent stem cells (iPSCs) from murine embryonic fibroblasts, in the absence of p53. Similarly, MDM2 depletion in the context of p53 deficiency also promoted the differentiation of human mesenchymal stem cells and diminished clonogenic survival of cancer cells. Most of the MDM2-controlled genes also responded to the inactivation of the Polycomb Repressor Complex 2 (PRC2) and its catalytic component EZH2. MDM2 physically associated with EZH2 on chromatin, enhancing the trimethylation of histone 3 at lysine 27 and the ubiquitination of histone 2A at lysine 119 (H2AK119) at its target genes. Removing MDM2 simultaneously with the H2AK119 E3 ligase Ring1B/RNF2 further induced these genes and synthetically arrested cell proliferation. In conclusion, MDM2 supports the Polycomb-mediated repression of line-age-specific genes, independent of p53.

Macrophages are an integral part of the innate immune system and key players in pathogen clearance and tissue remodelling. Both functions are accomplished by a pivotal network of different macrophage subtypes, including proinflammatory M1 and anti-inflammatory M2 macrophages. Previously, our laboratory identified the transcription factor interferon regulatory factor 5 (IRF5) as the master regulator of the M1 macrophage polarisation. IRF5 was found to be highly expressed in human M1 compared to M2 macrophages. Furthermore, IRF5 dictates the expression of proinflammatory genes such as IL12b and IL23a whilst repressing anti-inflammatory genes like IL10. Here we show that murine bone marrow derived macrophages differentiated in vitro with GM-CSF are also characterised by high levels of IRF5 mRNA and protein and express proinflammatory cytokines upon LPS stimulation. These macrophages display characteristic expression of M1-marker MHC II but lack the M2-marker CD206. Significantly, we develop intracellular staining of IRF5- expressing macrophages and utilise it to recapitulate the in vitro results in an in vivo model of antigen-induced arthritis, emphasising their physiological relevance. Thus, we establish the species-invariant role of IRF5 in controlling the inflammatory macrophage phenotype both in vitro and in in vivo.

Interferon regulatory factor 5 (IRF5) is a key transcription factor involved in the control of the expression of pro-inflammatory cytokine and responses to infection, however its role in regulating pulmonary immune responses to allergen is unknown. We used genetic ablation, adenoviral vector-driven overexpression and adoptive transfer approaches to interrogate the role of IRF5 in pulmonary immunity and during challenge with the aero-allergen, house dust mite. Global IRF5 deficiency resulted in impaired lung function and extracellular matrix (ECM) deposition. IRF5 was also essential for effective responses to inhaled allergen, controlling airway hyper-responsiveness, mucus secretion and eosinophilic inflammation. Adoptive transfer of IRF5-deficient alveolar macrophages into the WT pulmonary milieu was sufficient to drive airway hyper-reactivity, at baseline or following antigen challenge. These data identify IRF5-expressing macrophages as a key component of the immune defence of the airways. Manipulation of IRF5 activity in the lung could therefore be a viable strategy for the redirection of pulmonary immune responses and thus, the treatment of lung disorders.

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