Lower HDAC6 mRNA expression and promoter hypomethylation are associated with RA susceptibility.

BACKGROUND/PURPOSE: Recent studies showed that Histone deacetylases 6 (HDAC6) inhibitors could improve arthritis in rheumatoid arthritis (RA) rodent models, whereas lower HDAC6 expression was observed in RA patients' synovial fibroblasts, raising the concerns to use HDAC6 inhibitors to treat RA patients. In the present study, we investigated the involvement of HDAC6 mRNA expression and promoter methylation in RA.

METHODS

The DNA and RNAs were extracted from the peripheral blood mononuclear cells (PBMCs) from 138 RA patients and 102 healthy controls. The pyrosequencing technique was used for promoter methylation analysis. The quantitative real-time polymerase chain reaction was used to determine the HDAC6 mRNA expression. The patients' clinical characteristics and disease biomarkers were recorded when blood sampling.

RESULTS

The HDAC6 mRNA expression was lower in the RA patients than controls (p = 0.001). The RA patients had significant hypomethylation of the HDAC6 promoter (p < 0.001). The HDAC6 promoter was hypo-methylated in the -229, -225, -144, and -142 CpG sites in RA patients (p < 0.05). Unexpectedly, promoter methylation and mRNA expression of the HDAC6 gene were positively associated (p < 0.001). The HDAC6 mRNA expression and promoter methylation status were associated with the risk of RA (p = 0.006 and 0.002, respectively). The inflammatory cytokines, TNF-α and IL-6, were significantly increased after HDAC6 knockdown in PMA-stimulated THP1 cells and SW982 cells (p < 0.05).

CONCLUSION

The HDAC6 mRNA expression and promoter methylation were lower in RA patients. Both HDAC6 mRNA expression level and promoter hypomethylation were associated the susceptibility of RA. HDAC6 inhibitors seem not proper for RA patients' treatment.