Overexpression of Indian hedgehog partially rescues short stature homeobox 2-overexpression-associated congenital dysplasia of the temporomandibular joint in mice

Effect of condylar chondrocyte exosomes on condylar cartilage osteogenesis in rats under tensile stress

Background: Functional orthoses are commonly used to treat skeletal Class II malocclusion, but the specific mechanism through which they do this has been a challenging topic in orthodontics. In the present study, we aimed to explore the effect of tensile stress on the osteogenic differentiation of condylar chondrocytes from an exosomal perspective. Methods: We cultured rat condylar chondrocytes under resting and tensile stress conditions and subsequently extracted cellular exosomes from them. We then screened miRNAs that were differentially expressed between the two exosome extracts by high-throughput sequencing and performed bioinformatics analysis and osteogenesis-related target gene prediction using the TargetScan and miRanda softwares. Exosomes cultured under resting and tensile stress conditions were co-cultured with condylar chondrocytes for 24 h to form the Control-Exo and Force-Exo exosome groups, respectively. Quantitative real time PCR(RT-qPCR) and western blotting were then used to determine the mRNA and protein expression levels of Runx2 and Sox9 in condylar chondrocytes. Results: The mRNA and protein expression levels of Runx2 and Sox9 in the Force-Exo group were significantly higher than those in the Control-Exo group (p < 0.05). The differential miRNA expression results were consistent with our sequencing results. Bioinformatics analysis and target gene prediction results showed that the main biological processes and molecular functions involved in differential miRNA expression in exosomes under tensile stress were biological processes and protein binding, respectively. Kyoto Gene and Genome Data Bank (KEGG) pathway enrichment analysis showed significant enrichment of differentially expressed miRNAs in the mTOR signaling pathway. The differentially expressed miRNAs were found to target osteogenesis-related genes. Conclusion: These results suggest that stimulation of rat condylar chondrocytes with tensile stress can alter the expression levels of certain miRNAs in their exosomes and promote their osteogenic differentiation. Exosomes under tensile stress culture conditions thus have potential applications in the treatment of Osteoarthritis (OA).

The inhibitory roles of Ihh downregulation on chondrocyte growth and differentiation

The proliferative rate of chondrocytes affects bone elongation. Chondrocyte hypertrophy is required for endochondral bone formation as chondrocytes secrete factors required for osteoblast differentiation and maturation. Previous studies have demonstrated that the Indian hedgehog (Ihh) signaling pathway is a key regulator of skeletal development and homeostasis. The aim of the present study was to investigate the function of Ihh in chondrocyte proliferation and differentiation, as well as the underlying mechanisms. Ihh was knocked down in mouse chondrocyte cells using short hairpin RNA. Chondrocyte apoptosis and cell cycle arrest were assessed using flow cytometry and the results indicated that knockdown of Ihh significantly inhibited cell growth (P<0.05) and increased apoptosis (P<0.001) compared with negative control cells. Downregulation of Ihh also resulted in cell cycle arrest at G1 to S phase in chondrocytes. It was also observed that knockdown of Ihh decreased alkaline phosphatase activity and mineral deposition of chondrocytes. The inhibitory roles of Ihh downregulation on chondrocyte growth and differentiation may be associated with the transforming growth factor-β/mothers against decapentaplegic and osteoprotegerin/receptor activator of nuclear factor κB ligand signaling pathway. The results of the present study suggest that chondrocyte-derived Ihh is essential for maintaining bone growth plates and that manipulation of Ihh expression or its signaling components may be a novel therapeutic technique for the treatment of skeletal diseases, including achondroplasia.

Observing the development of the temporomandibular joint in embryonic and post-natal mice using various staining methods

The temporomandibular joint (TMJ) is a specialized synovial joint that is essential for the movement and function of the mammalian jaw. The TMJ develops from two mesenchymal condensations, and is composed of the glenoid fossa that originates from the otic capsule by intramembranous ossification, the mandibular condyle of the temporal bone and a fibrocartilagenous articular disc derived from a secondary cartilaginous joint by endochondral ossification. However, the development of the TMJ remains unclear. In the present study, the formation and development of the mouse TMJ was investigated between embryonic day 13.5 and post-natal day 180 in order to elucidate the morphological and molecular alterations that occur during this period. TMJ formation appeared to proceed in three stages: Initiation or blastema stage; growth and cavitation stage; and the maturation or completion stage. In order to investigate the activity of certain transcription factors on TMJ formation and development, the expression of extracellular matrix (ECM), sex determining region Y-box 9, runt-related transcription factor 2, Indian hedgehog homolog, Osterix, collagen I, collagen II, aggrecan, total matrix metalloproteinase (MMP), MMP-9 and MMP-13 were detected in the TMJ using in situ and/or immunohistochemistry. The results indicate that the transcription factors, ECM and MMP serve critical functions in the formation and development of the mouse TMJ. In summary, the development of the mouse TMJ was investigated, and the molecular regulation of mouse TMJ formation was partially characterized. The results of the present study may aid the systematic understanding of the physiological processes underlying TMJ formation and development in mice.