MeCP2 Regulates PTCH1 Expression Through DNA Methylation in Rheumatoid Arthritis.

Rheumatoid arthritis (RA) is a chronic autoimmune inflammatory disease, in which pathogenesis is not clear. Many research demonstrated that fibroblast-like synoviocytes (FLSs) play a key role in RA pathogenesis, join in the cartilage injury and hyperplasia of the synovium, and contribute to the release of inflammatory cytokines. We used adjuvant arthritis (AA) rats as RA animal models. The methyl-CpG-binding protein 2 (MeCP2) enables the suppressed chromatin structure to be selectively detected in AA FLSs. Overexpression of this protein leads to an increase of integral methylation levels. Some research has confirmed the hedgehog (Hh) signaling pathway plays an important role in RA pathogenesis; furthermore, patched 1 (PTCH1) is a negative fraction of Hh signaling pathway. We used 5-aza-2'-deoxycytidine (5-azadc) as DNA methylation inhibitor. In our research, we found MeCP2 reduced PTCH1 expression in AA FLSs; 5-azadc obstructed the loss of PTCH1 expression. 5-Azadc, treatment of AA FLSs, also blocks the release of inflammatory cytokines. In order to probe the potential molecular mechanism, we assumed the epigenetic participation in the regulation of PTCH1. Results demonstrated that PTCH1 hypermethylation is related to the persistent FLS activation and inflammation in AA rats. Knockdown of MeCP2 using small-interfering RNA technique added PTCH1 expression in AA FLSs. Our results indicate that DNA methylation may offer molecule mechanisms, and the reduced PTCH1 methylation level could regulate inflammation through knockdown of MeCP2. Graphical Abstract PTCH1 is an inhibitory protein of the Hedgehog signaling pathway. Increased expression of PTCH1 can inhibit the expression of Gli1 and Shh, thereby inhibiting the activation of Hedgehog signaling pathway. Inactivated Hedgehog signaling pathway inhibits the secretion of IL-6 and TNF-α. MeCP2 mediates hypermethylation of PTCH1 gene and decreases the expression of PTCH1 protein, thus activating Hedgehog signaling pathway and increasing secretion of IL-6 and TNF-α.

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