Cytokine-induced Chromatin Modifications of the Type I Collagen Alpha 2 Gene during Intestinal Endothelial-to-Mesenchymal Transition

Abstract

Background Fibrosis of the intestine is currently an irreversible complication of Inflammatory Bowel Disease yet little is understood of the underlying pathogenesis and anti-fibrotic strategies remain elusive. To develop effective therapies, knowledge of the mechanism of transcription and excessive deposition of type I collagen - a hallmark of fibrosis, is needed. We have shown previously that endothelial-to-mesenchymal transition (EndoMT) contributes to the pool of intestinal fibrotic cells and that a cytokine cocktail (IL1-β, TNF-α and TGF-β) induces Collagen I alpha 2 (COL1A2) mRNA and protein. Methods Chromatin immunoprecipitation assays on pure cultures of human intestinal mucosal endothelial cells undergoing EndoMT were performed with antibodies to specific histone modifications and RNA polymerase II. RT-PCR was used to quantify the levels of Col1A2 and endothelial specific von Willebrand factor (vWF) mRNA. Results We show that cytokines induce selective chromatin modifications (histone 4 hyperacetylation and hypermethylation of histone 3) and phosphorylated RNA polymerase II at the COL1A2 promoter. Hypoacetylated and hypomethylated histone 3 was detected on the repressed vWF gene. Prolonged exposure to cytokines (16 days) retained hyperacetylation of select lysines in H4 on the COL1A2 promoter. Removal of cytokines after 16 days and continued culture for 10 days, showed persistent hyperacetylation at lysine 16 in histone H4. Conclusion This is the first study to show that COL1A2 gene expression is associated with cytokine-induced, temporally ordered and persistent chromatin modifications and suggests that these are important determinants of gene expression in EndoMT and intestinal fibrosis.

The Epithelial Danger Signal IL-1α Is a Potent Activator of Fibroblasts and Reactivator of Intestinal Inflammation

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Systems biology in inflammatory bowel diseases

“…b) IBD Chromatin State: In addition to DNA methylation, histone modifications play a critical role in gene regulation by affecting chromatin packaging. A recent study revealed that cytokines could induce chromatin modifications in COL1A2 gene in intestinal mucosal endothelial cells 31 . Global histone modifications have been extensively studied in cancer and neurodegenerative diseases but despite evidence on their role in inflammation, their genome-wide distribution and function in IBD is still unknown.…”