Method: Whole mandibles were dissected from 3-week-old wild-type (WT) or DKO mice and incubated with or without 250 µg/ml BMP-2 for 2 days using an explant culture system. Expression levels of cartilage and bone related genes were analyzed using RT-PCR with RNA extracted from condyles that contained an intact cartilage/subchondral bone interface. Protein expression was examined by immunohistochemistry (IHC) of processed tissues. Osteoclast activity was estimated by TRAP staining and by TRAP mRNA expression levels as well as by measuring CTX-ll in the media of the cultured condyles.
Result: Aggrecan (Agn) and type II collagen mRNA were significantly up-regulated in WT samples treated with BMP-2 and this up-regulation was increased even further in the DKO, and the findings were confirmed by IHC. mRNA expression of several other genes was up-regulated in a similar manner including Sox9, Ihh, Noggin, Wisp1, Mt1-mmp, Rankl, Adamts4 and Trap. TRAP activity in WT condyles was increased by BMP-2 treatment and its relative levels were increased even further in the DKO condyles treated with BMP-2. The levels of CTX-ll released into the conditioned media also showed up-regulation by BMP-2 as with what was observed in TRAP activity.
Conclusion: The upregulation of both anabolic and catabolic genes in the WT and DKO TMJs treated with BMP-2 suggests that BMP-2 increases matrix turnover in the condyle and, further, that Bgn/Fmod could have protective roles in regulating this process.