Intermittent Parathyroid Hormone [1-34] Augments Chondrogenesis of the Mandibular Condylar Cartilage of the Temporomandibular Joint

Objective: To characterize the long-term effects of intermittent parathyroid hormone (I-PTH) on the mandibular condylar cartilage (MCC) and subchondral bone of the temporomandibular joint, in vivo and in vitro. Materials and Methods: For the in vivo experiments, sixteen 10-week-old mice were divided into 2 groups: (1) I-PTH (n = 8)—subcutaneous daily injection of PTH; (2) control group (n = 8)—subcutaneous daily injection of saline solution. Experiments were carried out for 4 weeks. Mice were injected with calcein, alizarin complexone, and cell proliferation marker before euthanasia. For the in vitro experiments, primary chondrocyte cultures from the MCC of eight 10-week-old mice were treated with I-PTH for 14 days. Results: There was a significant increase in bone volume, tissue density, mineral deposition, osteoclastic activity, cell proliferation in the cartilage, and cartilage thickness in the I-PTH-treated mice when compared with the control group. In addition, immunohistochemistry in cartilage revealed that I-PTH administration led to an increase in expression of vascular endothelial growth factor and to a decreased expression of sclerostin, matrix metallopeptidase 13, and aggreganase-1 (ADAM-TS4). Quantitative polymerase chain reaction analysis of the I-PTH-treated chondrocytes revealed significantly decreased relative expression of collagen type X (Col10a1), alkaline phosphatase (Alp), and Indian Hedgehog (Ihh) and remarkable increased expression of Sox9, fibroblast growth factor 2 (Fgf2), and proteoglycan 4 (Prg4). Conclusion: I-PTH administration causes anabolic effects at the subchondral region of the mandibular condyle while triggers anabolic and protective effects at the MCC.