Bone Abstracts

Better quality of cartilage repair in developing skeleton is recognized. The associated repair factors may be important in osteoarthritis and those factors would be the targets for the management of osteoarthritis. Microarray analysis of cartilage repair in rat knee joint was therefore carried out. Surgical injury on the femoral cartilage of the right patello-femoral joint in the 3- and 8-week-old rats for 2 weeks was first made. The left side of joint cartilage was used as the sham control.

The results showed that cellular proliferation over the surgical injured cartilage in the 3-week-old rats was identified by histology, whereas not in the sham control side and 8-week-old joint cartilage. Primary cultures from the joint cartilage with 1×10⁵ cells to observe cell proliferation were performed. Fibroblastic morphology with increased growth rate in injured groups was seen. Then, the gene expression level in the sham control and injury groups by microarray analysis demonstrated some novel genes involvement in this process. The top five upregulated genes were asporin (log2 ratio 4.49), growth associated protein 43 (GAP-43) (4.43), tenascin N (4.36), C1q and tumor necrosis factor related protein 3 (4.06), and ADAM metallopeptidase (3.94).

Both asporin and GAP-43 upregulation were confirmed by real time polymerase chain reaction. Further functional verification by cartilage frozen sections in different time courses including 1, 2, 3, and 4 weeks was carried out, especially GAP-43. GAP-43 has been known as a nerve growth associated protein which involves on neurite outgrowth. Here, we novelly identified that GAP-43 was expressed strongly on 2 weeks cartilage repair period by immunofluorescence. The GAP-43 expression was correlated with the cyclooxygenase 2 expression during the repair process.

On present data, the upregulation of GAP-43 is novelly linked to the cartilage repair process. The target of GAP-43 in osteoarthritis pathogenesis may be value of further investigation.