Proliferation in Mandibular Condylar Cartilage is Stimulated by Hedgehog

In the growth plate, Indian hedgehog (ihh) is known to play a key role in regulating the proliferation of chondrocytes as well as their rate of differentiation into hypertrophic chondrocytes. The influence of ihh on the undifferentiated dividing cells of the mandibular condylar cartilage (MCC) has not been studied, although hedgehog inhibition has been shown to reduce proliferation in chick secondary cartilage (Buxton et al., Dev. 130: 4729-4739, 2002). Objective: The goal of this study was to assess whether hedgehog inhibition alters proliferation in MCC. Methods: Mandibular condyles with ramus bone harvested from E17 mice pups were placed in serum-free explant culture in media containing hedgehog blocking antibody 5E1 (dilution 1:10) or no inhibitor. After 16 h, the MCC was dissected from the adjacent bone and the RNA extracted for analysis using real-time RT-PCR. Tissue localization of proliferation in treated and non-treated explants was examined using BrdU immunohistochemistry. Results: Treated condyles showed a 2-3 fold decrease in gene expression for both ihh and its receptor Ptc. In addition, expression of cyclin D1 was decreased 7-fold in treated MCC. Sections from treated explants examined for BrdU immunohistochemistry exhibited a large decrease in the number of labeled cells in the prechondroblastic layer of the MCC. Conclusion: These data suggest that ihh may stimulate proliferation in the dividing prechondroblasts of the MCC. This study was supported by NIDCR grant DE015401 to RJH and Baylor Oral Health Foundation funds to DH.