Abstract
5-Hydroxymethylcytosine (5-hmC) generated by ten-eleven translocation 1-3 (TET1-3) enzymes is an epigenetic mark present in many tissues with different degrees of abundance. IL-1β and TNF-α are the two major cytokines present in arthritic joints that modulate the expression of many genes associated with cartilage degradation in osteoarthritis. In the present study, we investigated the global 5-hmC content, the effects of IL-1β and TNF-α on 5-hmC content, and the expression and activity of TETs and isocitrate dehydrogenases in primary human chondrocytes. The global 5-hmC content was found to be ∼0.1% of the total genome. There was a significant decrease in the levels of 5-hmC and the TET enzyme activity upon treatment of chondrocytes with IL-1β alone or in combination with TNF-α. We observed a dramatic (10-20-fold) decrease in the levels of TET1 mRNA expression and a small increase (2-3-fold) in TET3 expression in chondrocytes stimulated with IL-1β and TNF-α. IL-1β and TNF-α significantly suppressed the activity and expression of IDHs, which correlated with the reduced α-ketoglutarate levels. Whole genome profiling showed an erasure effect of IL-1β and TNF-α, resulting in a significant decrease in hydroxymethylation in a myriad of genes including many genes that are important in chondrocyte physiology. Our data demonstrate that DNA hydroxymethylation is modulated by pro-inflammatory cytokines via suppression of the cytosine hydroxymethylation machinery. These data point to new mechanisms of epigenetic control of gene expression by pro-inflammatory cytokines in human chondrocytes.
Highlights
Cytosine hydroxymethylation in the genomic DNA controls gene expression
IL-1 and TNF-␣ Inhibit the Expression of TET1 mRNA in Human Primary Chondrocytes—We investigated whether there were any changes in expression levels of the ten-eleven translocation (TET) genes upon treatment with IL-1 and TNF-␣
Pro-inflammatory cytokines IL-1 and TNF-␣ are up-regulated in joints with osteoarthritis, and these cytokines play important roles in the progression of the disease by imparting physiological changes in several cell types, including the chondrocytes that are present in the ailing joints
Summary
Cytosine hydroxymethylation in the genomic DNA controls gene expression. Results: Treatment of primary chondrocytes with IL-1 alone or in conjunction with TNF-␣ inhibited TET1 and IDH expression and suppressed cytosine hydroxymethylation. Pro-inflammatory cytokines IL-1 and TNF-␣ are the two major factors that are up-regulated during joint diseases including osteoarthritis (OA) and rheumatoid arthritis High levels of these cytokines have been shown to modulate the expression of many genes in chondrocytes, resulting in the activation of catabolic mechanisms that cause the damage to articular cartilage. Several recent studies have shown significant demethylation at specific sites in the promoter regions of important genes involved in cartilage catabolism such as MMP13, ADAMTS-4, and IL-1 in OA chondrocytes compared with normal chondrocytes or in OA chondrocytes in response to cytokines (6 –10) These data demonstrate the involvement of epigenetic DNA modifications in cartilage degradation in OA. We determined whether pro-inflammatory cytokines IL-1 and TNF-␣ regulate gene expression in human chondrocytes by modulating the levels of 5-hmC. We investigated whether IL-1 and TNF-␣, alone or in combination, modulate the expression and activity of TET enzymes, gene expression of isocitrate dehydrogenases 1 and 2 (IDH1 and IDH2, respectively), total IDH enzyme activity, ␣-ketoglutarate (␣-KG) lev-
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
