ABSTRACT
Several theories have been proposed regarding pain transmission mechanisms in tooth. However, the exact signaling mechanism from odontoblasts to pulp nerves remains to be clarified. Recently, ATP-associated pain transmission has been reported, but it is unclear whether ATP is involved in tooth pain transmission. In the present study, we focused on the vesicular nucleotide transporter (VNUT), a transporter of ATP into vesicles, and examined whether VNUT was involved in ATP release from odontoblasts. We examined the expression of VNUT in rat pulp by RT-PCR and immunostaining. ATP release from cultured odontoblast-like cells with heat stimulation was evaluated using ATP luciferase methods. VNUT was expressed in pulp tissue, and the distribution of VNUT-immunopositive vesicles was confirmed in odontoblasts. In odontoblasts, some VNUT-immunopositive vesicles were colocalized with membrane fusion proteins. Additionally P2X3, an ATP receptor, immunopositive axons were distributed between odontoblasts. The ATP release by thermal stimulation from odontoblast-like cells was inhibited by the addition of siRNA for VNUT. These findings suggest that cytosolic ATP is transported by VNUT and that the ATP in the vesicles is then released from odontoblasts to ATP receptors on axons. ATP vesicle transport in odontoblasts seems to be a key mechanism for signal transduction from odontoblasts to axons in the pulp.
ABSTRACT
OBJECTIVE: During orthodontic tooth movement, bone resorption and inhibition of bone formation occur on the compressed side, thereby preventing ankylosis. Periodontal ligament (PDL) cells control bone metabolism and inhibition of bone formation on the compressed side by secreting bone-formation inhibitory factors such as asporin (ASPN) or sclerostin (encoded by SOST). The aim of this study was to identify the inhibitory factors of bone formation in PDL cells. DESIGN: In vitro, the changes in expression of ASPN and SOST and subsequent protein release in human PDL (hPDL) cells were assessed by semi-quantitative polymerase chain reaction (PCR), real-time PCR, and immunofluorescence in hPDL cells subjected to centrifugal force using a centrifuge (45, 90, 135, and 160 × g). In vivo, we applied a compressive force using the Waldo method in rats, and examined the distribution of ASPN or sclerostin by immunohistochemistry. RESULTS: In vitro, hPDL cells subjected to 90 × g for 24h demonstrated upregulated ASPN and downregulated SOST expressions, which were confirmed by immunofluorescent staining. In addition, the formation of mineralized tissue by human osteoblasts was significantly inhibited by the addition of medium from hPDL cells cultured during compressive force as well as the addition of equivalent amounts of ASPN peptide. In vivo, asporin-positive immunoreactive PDL cells and osteoclasts were found on the compressed side, whereas few sclerostin-positive PDL cells were observed. CONCLUSIONS: PDL cells subjected to an optimal compressive force induce the expression and release of ASPN, which inhibits bone formation during orthodontic tooth movement on the compressed side.
Subject(s)
Extracellular Matrix Proteins/metabolism , Osteogenesis/physiology , Periodontal Ligament/physiology , Adaptor Proteins, Signal Transducing , Animals , Bone Morphogenetic Proteins/biosynthesis , Bone Morphogenetic Proteins/metabolism , Cell Line , Cells, Cultured , Extracellular Matrix Proteins/biosynthesis , Gene Expression , Genetic Markers , Humans , Male , Osteoblasts/cytology , Osteoblasts/metabolism , Osteoclasts/cytology , Osteoclasts/metabolism , Periodontal Ligament/cytology , Periodontal Ligament/metabolism , Pressure , Rats , Rats, Sprague-Dawley , Stress, Mechanical , Tooth Movement TechniquesABSTRACT
BACKGROUND/PURPOSE: Bone resorption and inhibition of bone formation occur on the compressed side during orthodontic tooth movement. Bone formation inhibitory factors such as sclerostin (encoded by SOST) are secreted on the compressed side by periodontal ligament (PDL) cells. PDL cells control bone metabolism, and compressed PDL cells inhibit bone formation during orthodontic tooth movement. The aim of this study was to identify the inhibitory factors of bone formation in PDL cells. MATERIALS AND METHODS: Changes in SOST expression and subsequent protein release from human PDL (hPDL) cells were assessed using the real-time polymerase chain reaction (PCR), semiquantitative PCR, and immunofluorescence in hPDL cells subjected to centrifugal force (40g and 90g). To confirm the effects on bone formation, human alveolar bone-derived osteoblasts (hOBs) were grown with the addition of sclerostin peptide. In vivo, a compressive force was applied using the Waldo method in rats, and the distribution of sclerostin in PDL tissues was examined by immunohistochemistry. RESULTS: SOST expression was downregulated in vitro by centrifugation at 90g for 24 hours but upregulated by centrifugation at 40g based on real-time PCR, as was confirmed by immunofluorescence staining. The addition of sclerostin peptide significantly decreased the mineralized area in hOBs. However, slightly weakly sclerostin-positive PDL cells were observed on the compressed side in vivo. CONCLUSION: These results indicate that PDL cells subjected to light compressive force exhibit increased expression of SOST/sclerostin, which inhibits bone formation on the compressed side during orthodontic tooth movement.
