Monfort J et al. - Opticin (a glycoprotein and class III member of the small leucine-rich proteoglycans family) is expressed and produced in human articular tissues. Opticin in OA cartilage is degraded in a process that could be mediated by MMP-13, and may predispose cartilage to degeneration, particularly at the surface. Methods
Aim was to investigate (1) whether opticin is expressed and produced in human articular tissues; (2) ability of the key metalloprotease involved in cartilage pathology
Opticin gene expression was investigated in normal and OA human chondrocytes, synovial fibroblasts, and subchondral bone osteoblasts by RT-PCR
Opticin protein production was determined by IHC
Opticin was isolated from human cartilage using guanidinium chloride extraction
Human MMP-13-induced opticin degradation was analyzed by Western blotting
Finally, the opticin MMP-13 cleavage site was determined
Results
Opticin was expressed in human chondrocytes, synovial fibroblasts and subchondral osteoblasts
Protein was identified in synovial membrane and cartilage
At the protein level, OA cartilage showed a slightly higher level of opticin
In the OA cartilage matrix, opticin was found to be degraded
Cartilage opticin could be cleaved by MMP-13 after only 2 h of incubation, indicating a preferential substrate vs other SLRPs for this enzyme
Microsequencing revealed a major cleavage site at the G104/L105LAAP and a minor at P109/A110NHPG upon MMP-13 exposure
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