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Epigenetic silencing of the human NOS2 gene: rethinking the role of nitric oxide in human macrophage inflammatory responses
Journal article   Peer reviewed

Epigenetic silencing of the human NOS2 gene: rethinking the role of nitric oxide in human macrophage inflammatory responses

Thomas J Gross, Karol Kremens, Linda S Powers, Brandi Brink, Tina Knutson, Frederick E Domann, Robert A Philibert, Mohammed M Milhem and Martha M Monick
The Journal of immunology (1950), Vol.192(5), pp.2326-2338
03/01/2014
DOI: 10.4049/jimmunol.1301758
PMCID: PMC3943971
PMID: 24477906

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Abstract

Macrophages, including alveolar macrophages, are primary phagocytic cells of the innate immune system. Many studies of macrophages and inflammation have been done in mouse models, in which inducible NO synthase (NOS2) and NO are important components of the inflammatory response. Human macrophages, in contrast to mouse macrophages, express little detectable NOS2 and generate little NO in response to potent inflammatory stimuli. The human NOS2 gene is highly methylated around the NOS2 transcription start site. In contrast, mouse macrophages contain unmethylated cytosine-phosphate-guanine (CpG) dinucleotides proximal to the NOS2 transcription start site. Further analysis of chromatin accessibility and histone modifications demonstrated a closed conformation at the human NOS2 locus and an open conformation at the murine NOS2 locus. In examining the potential for CpG demethylation at the NOS2 locus, we found that the human NOS2 gene was resistant to the effects of demethylation agents both in vitro and in vivo. Our data demonstrate that epigenetic modifications in human macrophages are associated with CpG methylation, chromatin compaction, and histone modifications that effectively silence the NOS2 gene. Taken together, our findings suggest there are significant and underappreciated differences in how murine and human macrophages respond to inflammatory stimuli.
Cell Line Inflammation - pathology Nitric Oxide - immunology DNA Methylation - immunology CpG Islands - immunology Macrophages - pathology Species Specificity Humans Gene Silencing - immunology Male DNA Methylation - genetics Inflammation - immunology Genetic Loci - immunology Animals Nitric Oxide Synthase Type II - genetics Nitric Oxide Synthase Type II - immunology Epigenesis, Genetic - immunology Nitric Oxide - genetics Inflammation - genetics Female Mice Macrophages - immunology

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