Oncostatin M in combination with tumour necrosis factor α induces a chondrocyte membrane associated aggrecanase that is distinct from ADAMTS aggrecanase-1 or-2

Objective: To determine whether oncostatin M (OSM) + tumour necrosis factor alpha (TNF alpha) induces aggrecanase activity in chondrocyte membranes, to determine the effects of transforming growth factor beta 1 (TGF beta 1), interleukin 4 (IL4), and tissue inhibitor of metalloproteinases (TIMPs) on this activity, and to determine whether this activity is due to a known ADAMTS aggrecanase. Methods: Aggrecanase activity and ability of agents to prevent membrane associated aggrecanase activity were assessed by Western blotting. Expression of known aggrecanases was measured by real time polymerase chain reaction in bovine nasal and human articular chondrocytes. Results: Chondrocyte membrane associated aggrecanase activity and increased mRNA expression of ADAMTS-1, -4, -5, and -9, but not ADAMTS-4 or -15, were enhanced after stimulation by OSM+TNF alpha in bovine chondrocytes. This activity was inhibited by TIMP-3. In human chondrocytes, OSM+TNF alpha also enhanced ADAMTS-1 and -4 expression, but not that of other ADAMTSs. TNF alpha alone induced ADAMTS- 9 expression, whereas OSM addition caused suppression. Both TGFb1 and IL4 blocked membrane associated aggrecanase activity and decreased OSM+TNF alpha-induced expression of ADAMTS- 9 in bovine and human chondrocytes. IL4 down regulated ADAMTS- 4 mRNA, whereas TGFb1 increased this expression in both bovine and human chondrocytes. Conclusions: OSM+TNF alpha up regulates membrane associated aggrecanase activity and several ADAMTS aggrecanase mRNAs in chondrocytes. The chondroprotective effects of IL4 and TIMP-3 suggest that they may have therapeutic benefit for aggrecanolysis, whereas the differential inhibitory effects of TGFb1 may limit its therapeutic potential. Induced membrane associated aggrecanase activity is distinct from known soluble ADAMTS aggrecanases and merits further investigation.