Local injection of abaloparatide promotes mandibular condyle lengthening in adolescent rats via enhancing chondrogenesis and ossification

Background Mandibular condylar hypoplasia negatively affects patient's facial appearance and dentofacial function. Objective To investigate the effect of local injection of the drug abaloparatide (ABL), an analogue of parathyroid hormone related protein (PTHrP), on promoting lengthening of the mandibular condyle. Methods Thirty adolescent male Sprague–Dawley rats were randomly divided into two groups, which received the injection of ABL or normal saline (the control) every 3 days in the temporomandibular joint (TMJ) cavity. Cone‐beam computed tomography and immunohistochemistry assays were performed at 2, 4 and 6 weeks since the injection. Mandibular condylar chondrocytes (MCC) and pre‐osteoblasts were treated with ABL or PBS, followed by the CCK‐8 detection, IC50, real‐time PCR assay, Western Blot and immunofluorescence staining. Results In vivo, compared with the control, the ABL group significantly increased the mandibular condylar process length (by 1.34 ± 0.59 mm at 6 weeks), the thickness of the cartilage layer, and enhanced the matrix synthesis. The ABL group had significant up‐regulation of SOX 9, COL II, PTHrP and PTH1R, down‐regulation of COL X in the cartilage, up‐regulation of RUNX 2, and unchanged osteoclastogenesis in the subchondral bone. In vitro, the intra‐TMJ injection of ABL promoted the MCC proliferation, with up‐regulated expression of chondrogenic genes, and enhanced osteogenic differentiation of the pre‐osteoblasts. Conclusions Intra‐TMJ injection of abaloparatide promotes mandibular condyle lengthening in the adolescent rats via enhancing chondrogenesis in the mandibular condylar cartilage and ossification in the subchondral bone. ABL promoted lengthening of the mandibular condylar process (Co‐Mf) and enhanced thickening of the mandibular condylar cartilage layers. The possible mechanism is that ABL promoted chondrogenesis by up‐regulating SOX 9.