DAMPs Synergize with Cytokines or Fibronectin Fragment on Inducing Chondrolysis but Lose Effect When Acting Alone

Figure 2

The synergism between HMGB1 and IL-1β was replicable in the 3rd experiment with bovine chondrocytes. Such synergism was also observed between DAMPs and TNF-α but to a lesser extent. However, DAMPs were unable to synergize with Fn-f on the upregulation of MMPs while the synergism between cytokines and Fn-f was observed. Moreover, DAMPs alone or in combination did not evoke secretion of MMPs from bovine chondrocytes, which was consistent with what was observed in previous two experiments. Passage 1 bovine chondrocytes were treated with DAMPs with or without Fn-f (a), with or without proinflammatory cytokines (TNF-α or IL-1β) (b) for 24 hrs. Culture medium was then examined for MMP expression with Western blotting. In addition, some cells were insulted with culture medium containing soluble substances released from injured cartilage which was bluntly impacted at 7 or 14 J/cm² and cultured for 1 day. After 24 hrs of incubation, culture medium was resolved by SDS-PAGE side by side with medium samples from cultures treated with HMGB1, or MTDs, or Fn-f, or TNF-α. Expression of MMP-3 was then examined with immunoblotting (c). U. C. = untreated control; U. I. = unimpacted control; I. = impacted.

(a)

(b)

(c)