Obvious morphologic changes in the mandible and condylar cartilage after triple botulinum toxin injections into the bilateral masseter.

INTRODUCTION: Nonsurgical treatments that can prevent or reduce the extent of the mandibular excess at an early stage are desirable. A single botulinum toxin (BTX) injection into the unilateral and bilateral masseter can regulate mandibular contour and condylar cartilage. However, BTX injection is frequency dependent when used in facelifts. This study aimed to evaluate the effect of BTX injection into the bilateral masseter at different frequencies on the mandibular contour and condylar cartilage. METHODS: In the present study, 24 female Sprague Dawley rats (4 weeks old) were divided into 3 groups: control, single injection, and triple injection. Contour measurement of the mandible was carried out by radiographic imaging. Microcomputerized tomography was performed to determine the change in bone volume in the subchondral bone. Hematoxylin and eosin staining was used to observe the morphologic changes of condylar cartilage. Immunohistochemistry was performed to detect the expression level of biomechanically sensitive factors, including transforming growth factor-ß1, parathyroid hormone-related protein, SRY-box 9, and type II collagen. RESULTS: Bone volume and/or total volume, trabecular number, and trabecular thickness of the mineralized cartilage and subchondral bone significantly decreased in the triple injection group when compared with the single injection group. Mandibular contour also diminished after increased BTX injection frequencies. Chondrocyte proliferation ability and the expression levels of transforming growth factor-ß1, parathyroid hormone-related protein, SRY-box 9, and type II collagen significantly decreased in all BTX injection groups and more in the triple injection group. CONCLUSIONS: Morphologic changes of the mandible and condylar cartilage become more obvious after increased BTX injection frequencies, suggesting that multiple BTX injections into the masseter of patients may relieve the severity of mandibular deformity at an early stage.

Regulatory role of primary cilia in oral and maxillofacial development and disease.

Primary cilia have versatile functions, such as receiving signals from the extracellular microenvironment, mediating signaling transduction, and transporting ciliary substances, in tissue and organ development and clinical disease pathogenesis. During early development (embryos within 10 weeks) in the oral and maxillofacial region, defects in the structure and function of primary cilia can result in severe craniofacial malformations. For example, mice with mutations in the cilia-related genes Kif3a and IFT88 exhibit midline expansion and cleft lip/palate, which occur due to abnormalities in the fusion of the single frontonasal prominence and maxillary prominences. In the subsequent development of the oral and maxillofacial region, we discussed the regulatory role of primary cilia in the development of the maxilla, mandible, Meckel cartilage, condylar cartilage, lip, tongue, and tooth, among others. Moreover, primary cilia are promising regulators in some oral and maxillofacial diseases, such as tumors and malocclusion. We also summarize the regulatory mechanisms of primary cilia in oral and maxillofacial development and related diseases, including their role in various signaling transduction pathways. For example, aplasia of submandibular glands in the Kif3a mutant mice is associated with a decrease in SHH signaling within the glands. This review summarizes the similarities and specificities of the role of primary cilia in tissue and organ development and disease progression in the oral and maxillofacial region, which is expected to contribute several ideas for the treatment of primary cilia-related diseases.

Piezo1 and IFT88 synergistically regulate mandibular condylar chondrocyte differentiation under cyclic tensile strain.

OBJECTIVE(S): Mandibular condyle chondrocytes (MCCs) are exposed to various mechanical environments. Primary cilia, as a carrier for ion channels, can sense mechanical signals. Intraflagellar transport protein 88 (IFT88) is crucial for the assembly and function of primary cilia. Piezo1 is a mechanically activated ion channel that mediates mechanical signal transduction. This study aimed to identify the possible synergistic effect between Piezo1 and IFT88 in MCC differentiation during mechanical conduction. MATERIALS AND METHODS: Confocal immunofluorescence staining was used to reveal the Piezo1 localization. Small interfering RNA (siRNA) technology was used to knock down the expression levels of Piezo1 and IFT88. The chondrogenic differentiation ability of MCCs was evaluated by Alcian blue staining, and the early differentiation ability was evaluated by Western blot of SOX9 and COL2A1. RESULTS: Confocal immunofluorescence results showed that Piezo1 localized in the root of primary cilia. Without cyclic tensile strain (CTS) stimuli, Alcian blue staining showed that Piezo1 knockdown had a marginal effect on the chondrogenic differentiation of MCCs, while IFT88 knockdown inhibited the chondrogenic differentiation. The protein levels of SOX9 and COL2A1 decreased significantly with CTS stimuli. However, these protein levels were restored when Piezo1 was knocked down. In addition, IFT88 knockdown decreased the protein level of Piezo1 with or without CTS. CONCLUSION: Piezo1 and IFT88 might play a synergistic role in regulating MCC differentiation under CTS stimuli.

Intraflagellar transport protein 88 interacts with polycystin 2 to regulate mechanosensitive hedgehog signaling in mandibular condylar chondrocytes.

OBJECTIVE: This study aimed to explore whether intraflagellar transport protein 88 (IFT88) was associated with polycystin 2 during mechanotransduction of mandibular condylar chondrocytes. METHODS: Rat mandibular condylar chondrocytes isolated from the condylar bone-cartilage junction were subjected to cyclic tensile strain (0.1 Hz, 10% elongation). Overexpression of IFT88 was achieved by lentiviral vector-mediated transfection. Knockdown of IFT88 and polycystin 2 was achieved by small interfering RNA (siRNA). The prevalence and length of cilia were reflected by immunofluorescence staining. The activities of hedgehog signaling were evaluated by western blot analysis. The interaction between polycystin 2 and IFT88 was evaluated by conducting a co-immunoprecipitation (co-IP) assay. RESULTS: Overexpression of IFT88 increased the length of cilia. Protein levels of polycystin 2, Indian hedgehog (Ihh), Patched 1 (Ptch1), Smoothened (Smo), and Glioma-associated oncogene homolog 1 (Gli1) were elevated in IFT88-overexpressing mandibular condylar chondrocytes under cyclic tensile strain. Knockdown of the protein level of IFT88 reduced the prevalence and length of cilia, and protein levels of polycystin 2, Ihh, Ptch1, Smo, and Gli1. A co-IP assay showed that IFT88 formed a complex with polycystin 2 under cyclic tensile strain. Knockdown of polycystin 2 decreased the protein levels of IFT88, Ihh, Ptch1, Smo, and Gli1 in mandibular condylar chondrocytes following cyclic tensile strain. CONCLUSION: These findings highlight the vital role of an interaction between IFT88 and polycystin 2 in mechanosensitive hedgehog signaling in mandibular condylar chondrocytes following cyclic tensile strain, which suggest that therapies regulating polycystin 2 may be considered for the disorders of temporomandibular joints.