Inhibitory mechanism of bone formation in ameloblastoma

• Main Authors: Hitoshi Nagatsuka, Sathi Gul san Ara, Naoki Katase, Ryo Tamamura, Hidetsugu Tsujigiwa
• Format: Conference Proceeding
• Language: eng ; jpn
• ISSN: 1341-7649

Ameloblastoma is the second most common encountered benign but locally invasive odontogenic tumor. Typically ameloblastoma begins insidiously as a central lesion of bone, which is slowly destructive, and ultimately shows expansive growth within the bone. Radiological examination shows multilocular or cystic type appearance suggesting that it occurs not only due to enhanced bone resorption but also due to impaired bone formation. Secreted frizzled related proteins (sFRPs) family, the negative regulators of Wnt signaling pathway, a major signaling pathway in osteoblasts have recently been identified. It has a great effect on both suppressed bone formation inhibition of tumor cell apoptosis. In ameloblastoma it already been reported that sFRP- 2 was strongly expressed by both stromal and tumor cells and may suppressed new bone formation. However, even though it was hypothesized that stromal cells is responsible for decrease bone formation, there is no investigation was performed to find out any direct role of these proteins secreted from tumor cells in the suppressed bone that could be a collaborative mechanism in tumor progression. A pre-osteoblastic cell line KUSA/A1 cells cultured in conditioned medium of an ameloblastoma- derived cell line (AM- 1CM) was used in the study. Alkaline phosphatase (ALP) activity, alizarin red staining, mineral quantification and MTS assay was performed. Wnt- canonical pathway is a major pathway for osteoblast, antagonists of this pathway, sFRP- 1, 2 and 3 were detected by immunohistochemistry and western blot analysis. Immunodepletion of sFRP- 2 from AM- 1CM was also done and evaluated by alizarin red staining and mineral quantification analysis. Results showed that, KUSA/A1 cells cultured in AM- 1CM showed high cell proliferation, low ALP activity without mineralized matrix deposition. sFRP- 2 was strongly expressed in ameloblastoma tissue and AM- 1 cells in compared to sFRP- 1 and sFRP- 3. After sFRP- 2 depletion, the KUSA/A1 cells cultured in AM- 1CM showed diffuse mineralization. In this study, it was confirmed that ameloblastoma cells have a great role in decreased bone formation by secreting sFRP- 2 in cell culture model. Though, sFRP- 2 has great effect on tumor progression, inhibition of sFRP- 2's anti-bone formation activity and cell proliferative activity may reduce the invasive property of ameloblastoma and possibility of recurrence rate.