gms | German Medical Science

Objectives: Joint trauma triggers a degenerative process, which causes in >40% of patients posttraumatic osteoarthritis (PTOA). PTOA affects the whole joint and can lead to severe disability. A relevant factor in the early disease stage is trauma-induced articular cartilage damage associated with chondrocyte death and sGAG loss. Novel therapies aim to control initial disease events such as cell death. We hypothesized that post-traumatic chondrocyte death can be reduced by using a 'novel' cartilage homeostasis master regulator with the ability to fine-tune FGF-2 signaling termed CCN2, also known as connective tissue growth factor. The rationale was that trauma releases FGF-2 from the damaged matrix, which can activate MAP kinase signaling cascades implicated in cell viability. Thus, using recombinant CCN2 as an in vitro post-traumatic therapeutic agent for cartilage trauma promises to decrease chondrocyte death.

Methods: Human articular cartilage explants (4mm diameter, 300µm thickness) were generated from macroscopically intact osteoarthritic joint replacement tissues (n=7). Using an incubator-housed loading machine, we applied a single injurious compression down to 65% explant height within ½ second and subsequent release of the compression. Similarly injured explants were treated with soluble human recombinant CCN2 and non-injured disks served as controls. After initial dose-finding experiments, injured explants were treated with 150 ng/ml soluble recombinant CCN2 after injury. Chondrocyte viability was assessed at the surface and at 150 and 300 µm depths on days 1 and 4 (life dead, Invitrogen). Patient- and joint location-matched non-injured disks served as controls. sGAG explant content and loss into the medium were determined with the DMMB-Assay. Statistical analyses were performed with SigmaPlot (Systat) with p<0.05 as significance level.

Results and Conclusion: Cell death was significantly higher in injured than non-injured explants (p<0.05). The dose-finding experiments established 150ng/ml CCN2 and post-injurious incubation with soluble CNN2 led to a significant decrease of cell death, compared to injured explants without CCN2 at days 1, 3 and 4 (day 1: injury without CCN2: 17.6±1.6%, injury with CCN2: 11.2±0.8%, p=0.002; day 3: injury without CCN2: 18.9±1.3%, injury with CCN2: 11.9±.10%, p<0.001; day 4: injury without CCN2: 21.4±2.61.2%, injury with CCN2: 14.7±1.5%, p<0.001). sGAG loss into the medium was not significantly different between injured explants with and without CCN2 incubation.

This pilot study demonstrated that chondrocyte death after compressive injury can be alleviated using recombinant CCN2 as an in vitro post-traumatic therapeutic agent for cartilage trauma. Further experiments need to address open questions pertaining to the underlying signaling, the effects on catabolic, anabolic, and inflammatory processes affected by CCN2, and its efficacy in combination with other substances intended for post-traumatic therapies.