HDAC4 partially blocks the effect of IL-1 beta on expression of catabolic events in human OA chondrocytes. Human OA chondrocytes were transfected with HDAC4 or control constructs for 48 h, then the cells were stimulated with or without IL-1 beta (5 ng/ ul) for 24 h. All transfections were performed in triplicate. * = P <0.05 versus the group of HDAC4 + IL-1 beta, # = P <0.05 versus the group of control vercor, ^ = P <0.05 versus the group of control vector + IL-1 beta. Real-time PCR showed that IL-1 beta significantly increased the mRNA levels of MMP-1, MMP3, MMP-13, iNOS, Cox2, ADAMTS-4 and -5 in the OA chondrocytes, respectively compared to those untreated controls. In addition, the mRNA levels of aggrecan, and type II collagen significantly decreased after stimulation with IL-1 beta (P <0.05). Overexpression of HDAC4 partly blocked the upregulation of MMP-1, MMP3, MMP-13, iNOS, Cox2, ADAMTS-4, and -5 induced by IL-1 beta. In the meanwhile, the mRNA levels of aggrecan, and type II collagen significantly increased in those cells transfected by HDAC4 (P <0.05) (n = 3). HDAC4, histone deacetylase 4; IL, interleukin; MMP, matrix metalloprotease; OA, osteoarthritis; Runx2, runt-related transcription factor-2.