DNA hydroxymethylation in macrophages

​Activated macrophages are found in the inflamed and hyperplasic synovial RA tissues. Macrophages are the main producers of high levels of pro-inflammatory cytokines such as TNFa and IL6. However, the mechanism of TNFa overexpression is still unknown.  Recent findings showed that the 5-methylcytosine (5-mC) modification of DNA can be converted to 5-hydroxymethylcytosine (5-hmC) through the activation of the family of Ten-Eleven-Translocation (TET1-3) enzymes. We investigated the 5-hmC modification in macrophages stimulated with lipopolysaccharide (LPS) and characterized the function of TET1-3 enzymes during inflammation. Undifferentiated monocytes have the lowest levels of 5-hmC. It increases when monocytes differentiated into macrophages. This is accompanied by increases of 5-hmC at the TNF locus. Differentiated macrophages are stronger responders than monocytes in pro-inflammatory cytokines. Furthermore, upon LPS, 5-hmC showed a time-depend increase in the TNFa promoter. It was higher in macrophages than monocytes. TET1 inhibition reduced the stimulatory capacity of macrophages; this is associated with incapacity of increase 5-hmC at the TNF locus. Thus, TET1 contributes to the activation of macrophages through the regulation of 5-hydroxymethylation in the promoter of TNFa. TET1 could be a promising target to study in macrophages from RA patients.

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Collaborators

Dr. Fangfang Sun and Prof. Shuang Ye, Department of Rheumatology, South Campus, Renji Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, China.

Financing

Baugarten Foundation, Zurich.

Publications