Background/Aims: Evidence suggests that IL-6 affects bone mass by modulating osteocyte communication towards osteoclasts. However, the mechanism by which IL-6 enhances osteocyte-mediated osteoclastogenesis is unclear. We aimed to investigate the inflammatory factors in serum after orthodontic surgery and their relationship between osteocytes and osteoclasts. Methods: Serum was obtained from 10 orthognathic surgery patients, and inflammatory factors were detected by ELISA. We treated the osteocyte-like cell line MLO-Y4 with recombinant mouse IL-6 and IL-6 receptor (IL-6R), and used quantitative RT-PCR and Western blotting to explore Receptor activator of nuclear factor-κB ligand (RANKL) expression at both the mRNA and protein level. MLO-Y4 cells were co-cultured with osteoclast precursor cells, and the formation of osteoclasts was detected by tartrate-resistant acid phosphatase (TRAP) staining. To explore the role of JAK2 in the osteocyte-mediated osteoclastogenesis, AG490, a JAK2 inhibitor, was used to inhibit the JAK2-STAT3 pathway in osteocytes. Results: In our study, we found that IL-6 and RANKL were stimulated in serum 3-7 days after orthognathic surgery. Therefore, IL-6 and IL-6 receptor enhanced the expression of RANKL at both the mRNA and protein level in MLO-Y4. Furthermore, when MLO-Y4 cells were co-cultured with osteoclast precursor cells, it significantly stimulated osteoclastogenesis. Our study indicated that osteocytes could promote osteoclastic differentiation and the formation of TRAP-positive multinucleated cells after stimulation with IL-6 and IL-6R. Our results also indicated that treatment with IL-6 and IL-6R increased RANKL mRNA expression and the RANKL/OPG expression ratio. Meanwhile, the phosphorylation of Janus kinase 2 (JAK2) and Signal transducer and activator of transcription (STAT3) also correlated with RANKL levels. Furthermore, we investigated the effects of a specific JAK2 inhibitor, AG490, on the expression of RANKL in osteocyte-like MLO-Y4 cells and osteocyte-mediated osteoclastogenesis. The results showed that AG490 inhibited (p)-JAK2 and RANKL expression. Osteoclastic differentiation was decreased after pretreatment in MLO-Y4 with mouse IL-6/IL-6R and AG490; therefore, we concluded that IL-6 increased osteocyte-mediated osteoclastic differentiation by activating JAK2 and RANKL. Conclusion: The effects of IL-6/il-6R and AG490 on osteocyte-mediated osteoclastogenesis contribute to our understanding of the role of inflammatory factors in the interaction between osteocytes and osteoclast precursors. IL-6 and RANKL are key factors for bone remodelling after the orthodontic surgery, and their roles in bone remodelling may be fundamental mechanisms accelerating tooth movement by orthodontic surgery.
Osteocytes, entrapped within the mineralized bone matrix, has been found to have numerous functions such as acting as an orchestrator of bone remodeling through regulation of both osteoclast and osteoblast activity and also functioning as an endocrine cell. Due to a specialized morphology and surrounding structure, osteocytes are more tolerant to hypoxia during osteoporosis, fracture, osteoarthritis, and orthodontic-orthognathic combination therapy. Hypoxia-inducible factor-1α (HIF-1α) is one of the master regulators of hypoxia reactions, playing an important role in bone modeling, remodeling, and homeostasis. This study aimed to investigate the pivotal functional role of HIF-1α in osteocytes initiating of bone remodeling under hypoxia. In the present study, the osteoclasts formation induced by RAW264.7 was significantly promoted in conditioned media (CM) from osteocytic MLO-Y4 exposed to hypoxia in vitro. Therefore, hypoxic MLO-Y4 cells simulated by 100 μmol/L CoCl 2 or 2% O 2 stably expressed HIF-1α proteins and upregulated the expression of receptor activator of nuclear factor-κB ligand (RANKL) at both the messenger RNA (mRNA) and protein level. Furthermore, with the Knockdown of HIF-1α, the expression of RANKL mRNA and protein decreased after transient transfection. In addition, the phosphorylation of Janus kinase 2 (JAK2) and signal transducer and activator of transcription (STAT3) was also correlated with HIF-1α and RANKL levels under hypoxia. Then AG490, a JAK2 inhibitor, inhibited p-JAK2, p-STAT3 and RANKL expression. It was possible that AG490 disturbed the contact of HIF-1α and RANKL by JAK2/STAT3 pathway, influencing osteoclastogenesis. Our findings suggested that HIF-1α promoted the expression of RANKL by activating JAK2/STAT3 pathway in MLO-Y4 cells, and enhanced osteocyte-mediated osteoclastic differentiation in vitro. K E Y W O R D Shypoxia-inducible factor-1α, JAK2/STAT3 pathway, osteoclastogenesis, osteocyte, receptor activator of nuclear factor-κB
Fang (2021) Liquiritigenin exerts the anti-cancer role in oral cancer via inducing autophagy-related apoptosis through PI3K/AKT/mTOR pathway inhibition invitro and invivo,
Summary Objectives The accelerated tooth movement phenomenon after orthognathic surgery has been observed. However, the underlying mechanism remains unclear. There is no experimental study showing the effect of orthognathic surgery on orthodontic tooth movement of the opposing jaw. Therefore, the present study aimed at investigating if mandibular osteotomy enhances maxillary tooth movement and bone remodelling. Materials and methods Fifty-four male Sprague-Dawley rats were randomly divided into two groups: maxillary tooth movement (TM) and maxillary tooth movement + mandibular surgery (TM + MS). The orthodontic force was delivered to move the left maxillary first molar mesially. The surgical intervention was performed on the left mandible. Microcomputed tomography, histological analysis, enzyme-linked immunosorbent assay, and quantitative real-time polymerase chain reaction were used to assess changes at 3, 7, and 21 days after surgery. Results The mandibular osteotomy accelerates the rate of maxillary tooth movement with decreased bone volume fraction on the seventh day. Bone resorption was observed on the third and seventh day after mandibular osteotomy. It was found that serum interleukin-1β level increased significantly in the TM + MS group compared with the TM group, as well as the high expression level of cathepsin K and tumour necrosis factor receptor-associated factor 5 of the orthodontic tooth on the third and seventh day after mandibular osteotomy. Conclusion Data from the present study suggested that mandibular osteotomy accelerates maxillary osteoclast activity and post-operative tooth movement, providing evidence for accelerated tooth movement phenomenon after orthognathic surgery.
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