Project description:Atherosclerosis is a chronic inflammatory disease of the blood vessels, characterized by atherosclerotic lesion formation. Vascular Smooth Muscle Cells (VSMC), macrophages (MΦ), and dendritic cells (DC) play a crucial role in vascular inflammation and atherosclerosis. Interferon (IFN)α, IFNγ, and Toll-like receptor (TLR)4 activate pro-inflammatory gene expression and are pro-atherogenic. Gene expression regulation of many pro-inflammatory genes has shown to rely on Signal Integration (SI) between IFNs and TLR4 through combinatorial actions of the Signal Transducer and Activator of Transcription (STAT)1 complexes ISGF3 and γ-activated factor (GAF), and Nuclear Factor-κB (NFκB). Thus, IFN pre-treatment ("priming") followed by LPS stimulation leads to enhanced transcriptional responses as compared to the individual stimuli. To characterize the mechanism of priming-induced IFNα + LPS- and IFNγ + LPS-dependent SI in vascular cells as compared to immune cells, we performed a comprehensive genome-wide analysis of mouse VSMC, MΦ, and DC in response to IFNα, IFNγ, and/or LPS. Thus, we identified IFNα + LPS or IFNγ + LPS induced genes commonly expressed in these cell types that bound STAT1 and p65 at comparable γ-activated sequence (GAS), Interferon-stimulated response element (ISRE), or NFκB sites in promoter proximal and distal regions. Comparison of the relatively high number of overlapping ISRE sites in these genes unraveled a novel role of ISGF3 and possibly STAT1/IRF9 in IFNγ responses. In addition, similar STAT1-p65 co-binding modes were detected for IFNα + LPS and IFNγ + LPS up-regulated genes, which involved recruitment of STAT1 complexes preceding p65 to closely located GAS/NFκB or ISRE/NFκB composite sites already upon IFNα or IFNγ treatment. This STAT1-p65 co-binding significantly increased after subsequent LPS exposure and correlated with histone acetylation, PolII recruitment, and amplified target gene transcription in a STAT1-p65 co-bound dependent manner. Thus, co-binding of STAT1-containing transcription factor complexes and NFκB, activated by IFN-I or IFN-II together with LPS, provides a platform for robust transcriptional activation of pro-inflammatory genes. Moreover, our data offer an explanation for the comparable effects of IFNα or IFNγ priming on TLR4-induced activation in vascular and immune cells, with important implications in atherosclerosis.

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.

Project description:Diabetes is associated with accelerated atherosclerosis and macrovascular complications are a major cause of morbidity and mortality in this disease. Although our understanding of vascular pathology has lately greatly improved, the mechanism(s) underlying enhanced atherosclerosis in diabetes remain unclear. Endothelial cell dysfunction is emerging as a key component in the pathophysiology of cardiovascular abnormalities associated with diabetes. Although it has been established that endothelium plays a critical role in overall homeostasis of the vessels, vascular smooth muscle cells (vSMC) in the arterial intima have a relevant part in the development of atherosclerosis in diabetes. However, high glucose induced alterations in vSMC behaviour are not fully characterized. Several studies have reported that impaired nitric oxide (NO) synthesis and/or actions are often present in diabetes and endothelial dysfunction. Furthermore, although endothelial cells are by far the main site of vascular NO synthesis, vSMC do express nitric oxyde synthases (NOSs) and NO synthesis in vSMC might be important in vessel's function. Although it is known that vSMC contribute to vascular pathology in diabetes by their change from a quiescent state to an activated proliferative and migratory phenotype (termed phenotypic modulation), whether this altered phenotypic modulation might also involve alterations in the nitrergic systems is still controversial. Our recent data indicate that, in vivo, chronic hyperglycemia might induce an increased number of vSMC proliferative clones which persist in culture and are associated with increased eNOS expression and activity. However, upregulation of eNOS and increased NO synthesis occur in the presence of a marked concomitant increase of O(2-) production. Since NO bioavailabilty might not be increased in high glucose stimulated vSMC, it is tempting to hypothesize that the proliferative phenotype observed in cells from diabetic rats is associated with a redox imbalance responsible quenching and/or trapping of NO, with the consequent loss of its biological activity. This might provide new insight on the mechanisms responsible for accelerated atherosclerosis in diabetes.

Dataset Information

STAT1-dependent signal integration between IFN? and TLR4 in vascular cells reflect pro-atherogenic responses in human atherosclerosis.

Publications

STAT1-dependent signal integration between IFNγ and TLR4 in vascular cells reflect pro-atherogenic responses in human atherosclerosis.

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