p38 MAPK and COX2 inhibition modulate human chondrocyte response to TGF-β

These studies compare actions of p38 MAPK inhibition and COX2 inhibition to modulate human arthritic chondrocyte responses to TGF-β and FCS under basal and IL-1 activated conditions. Chondrocytes isolated from arthritic human femoral condyle cartilage obtained at total knee replacement were grown to 80% confluence. Proteoglycan synthesis and proliferation were measured with and without IL-1 activation in the presence and absence of growth factors and with and without inhibition of p38 MAPK or COX2 activity. Experiments to evaluate TIMP-1 production under these conditions were done using cartilage organ cultures. Neither p38 MAPK inhibitors nor COX2 inhibition affected basal proliferation. However both inhibitors enhanced the proliferative response to TGF-β and FCS in IL-1 activated chondrocytes. TGF-β stimulated proteoglycan synthesis was decreased by p38 MAPK inhibition, however COX2 inhibition restored the response to TGF-β in IL-1 activated cells. In contrast, COX2 inhibition did not modulate TIMP-1 production while p38 MAPK inhibitors potentiated TGF-β stimulated production of TIMP-1 in IL-1 activated cartilage. p38 MAPK inhibition and COX2 inhibition have unique and similar abilities to counteract some of the effects of IL-1 on human chondrocyte/cartilage metabolism. Both will partially restore the proliferative response to growth factors. p38 MAPK inhibition blunts TGF-β stimulation of proteoglycan synthesis, but increases TIMP-1 synthesis. COX2 inhibition can restore the proteoglycan synthetic response to TGF-β, but has no effect on cartilage TIMP-1 production. Use of these inhibitors to minimize cartilage damage in arthritic and mechanically stressed joints should reflect these characteristics.