p38γ mitogen-activated protein kinase suppresses chondrocyte production of MMP-13 in response to catabolic stimulation

Objective: The signaling protein p38 mitogen-activated protein kinase is required for inflammatory signaling in chondrocytes that regulates matrix metalloproteinase (MMP) production. We sought to determine the role of specific p38 isoforms in chondrocyte catabolic signaling in response to IL-1 beta and fibronectin fragments (Fn-f). Methods: Human articular chondrocytes isolated from normal ankle cartilage from tissue donors or from osteoarthritic knee cartilage obtained during knee replacement were stimulated with IL-1 beta or Fn-f, with or without pretreatment with p38 inhibitors (SB203580 or BIRB796) or growth factors (IGF-1 and OP-1). p38 isoform phosphorylation was measured by antibody array and immunoblotting. MMP-13 expression was measured by real-time polymerase chain reaction (PCR), enzyme-linked immunosorbent assay (ELISA), and immunoblotting. Chondrocytes were transfected with plasmids expressing constitutively active (CA) p38 gamma or with adenovirus expressing dominant negative (DN) p38 gamma. Results: Stimulation of chondrocytes with either IL-1 beta or Fn-f led to enhanced phosphorylation of p38 alpha and p38 gamma, with little phosphorylation of p38 beta or p38 delta isoforms. p38 alpha localized to the nucleus and p38 gamma to the cytosol. Inhibition of both p38 alpha and p38 gamma with BIRB796 resulted in less inhibition of MMP-13 production in response to IL-1 beta or FN-f than did inhibition of only p38 alpha with SB203580. Transfection with CA p38 gamma resulted in decreased MMP-13 production while transduction with DN p38 gamma resulted in increased MMP-13 production. IGF-1 and OP-1 pretreatment inhibited p38 alpha phosphorylation but not p38y phosphorylation. Conclusions: p38 gamma is activated by catabolic stimulation of human articular chondrocytes, but interestingly suppresses MMP-13 production. Treatments that increase p38 gamma activation may be of therapeutic benefit in reducing chondrocyte production of MMP-13. (C) 2010 Osteoarthritis Research Society International. Published by Elsevier Ltd. All rights reserved.