Histone deacetylase/acetylase activity in total synovial tissue derived from rheumatoid arthritis and osteoarthritis patients

Objective Rheumatoid arthritis (RA) is a chronic inflammatory disorder of unknown origin. Histone deacetylase (HDA) activity is considered to play a major role in the transcriptional regulation of proinflammatory genes. We undertook this study to investigate the balance of histone acetylase and HDA activity in synovial tissue from RA patients compared with that from patients with osteoarthritis (OA) and normal controls. Methods Activity of histone acetylases and HDAs was measured in nuclear extracts of total synovial tissue samples, which were obtained from RA and OA patients undergoing surgical joint replacement, and compared with the activity in synovial tissues from patients without arthritis. Tissue expression of HDAs 1 and 2 was quantified by Western blotting. In addition, immunohistochemistry was performed for HDA‐2. Results Mean ± SEM HDA activity in synovial tissue samples derived from patients with RA was measured as 1.5 ± 0.3 μmoles/μg, whereas the activity levels in OA (3.2 ± 0.7 μmoles/μg) and normal (7.1 ± 4.2 μmoles/μg) synovial tissue samples were significantly higher. Histone acetylase activity reached similar levels in RA and OA tissues and in normal tissues. The ratio of HDA activity to histone acetylase activity in RA synovial tissue was significantly reduced (12 ± 2%) compared with that in OA synovial tissue (26 ± 3%). The activity ratio in normal control samples was arbitrarily set at 100 ± 40%. In addition, the tissue expression of HDA‐1 and HDA‐2 proteins was clearly lower in RA samples than in OA samples. Conclusion The balance of histone acetylase/HDA activities is strongly shifted toward histone hyperacetylation in patients with RA. These results offer novel molecular insights into the pathogenesis of the disease that might be relevant to the development of future therapeutic approaches.