Project description:Macrophages are able to differentiate into classically polarized (M1) or alternatively polarized (M2) states upon encountering pro-inflammatory cytokines such as interferon (IFN) g or anti-inflammatory cytokines such as interleukin (IL) -4/IL-13, respectively. Moreover, macrophages are known to regulate lipid metabolism via multiple members of the nuclear hormone receptor family, including the retinoid X receptors (RXR). It has been also documented that cytokines are able to modulate macrophage responses to lipid signals but the nature of these interactions and the underlying mechanisms of these processes especially at the level of the chromatinized genome are not well understood. Previous work from our laboratory suggested that STAT6 is a facilitator of nuclear receptor mediated transcriptional activity acting at the genome level. This prompted us to investigate genome-wide DNA binding events and the development of cistromes in human CD14+ monocyte-derived macrophages upon exposure to IL-4. We determined the impact of IL-4 on the PU.1, RXR and STAT6 cistromes within the active enhancer regions marked by H3K27-acetylation using chromatin immunoprecipitation followed by deep sequencing and integrated bioinformatics analyses. We found that about 2/3rd of the IL-4 induced STAT6 peaks co-localized with RXR peaks. These STAT6/RXR co-peaks differed at least in part from the non-overlapping RXR peaks regarding the most enriched de novo transcription factor binding motifs. Interestingly, RXR-binding was not regulated at the STAT6/RXR co-bound enhancers following IL-4 stimulation, but differential enhancer interactions were observed between the IL-4/STAT6 and RXR signaling pathways acting in a gene selective manner. Our results suggest that there is a novel, so far uncharacterized cistromic crosstalk between RXR and STAT6 that is likely to contribute to the formation of the active enhancer repertoire, transcriptome and differential signal-specific gene regulation of polarized macrophages.

Project description:Atherosclerosis is a disease of large and medium-sized muscular arteries and is characterized by vascular inflammation and lipid-laden plaque formation within the intima of the vessel wall. Atherosclerosis is initiated by recruitment of blood leukocytes to the injured vascular endothelium and leads to altered contractility of Vascular Smooth Muscle Cells (VSMCs), acute and chronic luminal obstruction, abnormalities of blood flow and diminished oxygen supply to target organs. The pro-inflammatory pathways activated by Toll-like Receptors (TLRs), and Interferons (IFNs) have been identified as key components of atherogenesis. These pathways culminate in the activation of Signal Transducers and Activator of Transcription (STAT)1-containing complexes ISGF3 and GAF, and Nuclear factor-κB (NFκB) that coordinate expression of multiple chemokines, adhesion molecules, antiviral and antimicrobial proteins in vascular and immune cells. IFN-I and IFN-II participate in signaling cross-talk with TLR4 through combinatorial actions of ISGF3 and GAF with NF-kB leading to enhanced gene expression. Currently it is not clear how this signal integration is regulated at the genome-wide level and if similar mechanisms are activated by the different IFNs in vascular cells as compared to macrophages and dendritic cells. Therefore, we compared genome-wide transcriptional responses of mouse VSMCs, macrophages (BMDMs) and dendritic cells (DCs) in response to IFNα, IFNγ or LPS alone, or after combined treatment using RNA-seq. Consequently, commonly up-regulated genes in VSMCs, BMDMs and DCs could be identified after combined treatment with IFNα+LPS, as well as after combined treatment with IFNγ+LPS. Generally, in all three cell-types combined treatment with IFNα+LPS or IFNγ+LPS resulted in a synergistic increase in gene expression as compared to single treatments. Also, significant functional overlap could be observed between commonly upregulated genes in response to IFNα+LPS and IFNγ+LPS. Using ChIP-seq on chromatin from VSMCs, STAT1 and p65 bound IFNα+LPS and IFNγ+LPS up-regulated genes were identified, containing GAF/GAS, ISGF3/ISRE or NF-kB binding motifs located in promoter regions, but also to up- and downstream genomic regions. Comparing IFNα+LPS and IFNγ+LPS commonly upregulated genes identified a substantial overlap of ISRE-containing genes. Interestingly, STAT1 as part of ISGF3 was shown to bind the promoter of these ISRE-containing genes in response to IFNα as well as IFNγ. Moreover, different binding modes of STAT1-p65 co-binding were detected, including GAS-NFκB, ISRE-NFκB or GAS-ISRE-NFκB, shared by IFNα+LPS and IFNγ+LPS up-regulated genes. This cooperative involvement involved a STAT1-dependent role in the nearby recruitment of p65 already upon single IFNα or IFNγ treatment, via closely located GAS-NFĸB or ISRE-NFĸB binding sites in promoter regions. More important, this STAT1-p65 co-binding was significantly increased upon subsequent LPS exposure and resulted in amplified transcriptional activity of IFNα+LPS and IFNγ+LPS upregulated genes.

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Prior IL-4 exposure induces epigenetic reprograming enabling activated NF-kB p65 cistrome expansion, extreme synergistic gene activation and unique imuune response in macrophages

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