Abstract

The role of chondrocyte metalloprotease (CMP) in mediating cartilage autolysis was studied. Proteoglycan (PG) release and synthesis by rabbit articular cartilage explants were measured. After a 1-day preculture in control medium, 3.3 X 10(-6) M retinoic acid (RET) treatment for 1 day stimulated PG release several fold. RET also caused a large decrease in PG synthesis that returned to the control level after a 3-day recovery period. The effect on PG synthesis was observed at serum levels of 5 and 0.05%. The effect of RET on PG release required protein synthesis, inasmuch as it was lost in cultures maintained in media without amino acids or in a low volume of media. Interleukin-1 (IL-1) and lipopolysaccharide (LPS) treatment for 2 days also stimulated PG release. More PG was released after RET than after IL-1 or LPS, and only RET produced an effect that was evident by day 1. The amount of CMP that produced the same size effect on PG release as these stimulators was below the detection level of PG protease assays. Three potent CMP inhibitors reduced RET-, IL-1- and LPS-stimulated PG release to control levels. These inhibitors did not block another action of RET on chondrocytes, namely the inhibition of PG synthesis by RET immediately after treatment. The inhibitors did not act by reducing cell viability, because recovery of the rate of PG synthesis 3 days post-treatment occurred in inhibitor-treated cultures. These studies suggest that CMP is involved in cartilage autolysis that is stimulated by RET and IL-1.