Ameloblastoma induces osteoclastogenesis: a possible role of ameloblastoma in expanding in the bone
Introduction
Ameloblastoma could have arisen from a tooth bud or dental lamina.1 Small and Waldron found 81% of ameloblastomas to have been in the mandible, and of these 70% were in the molar-ramus area.2 Ameloblastoma grows slowly and typically cause no symptoms until a swelling becomes noticeable. As the tumor enlarges it forms a hard, rounded swelling, but later thinning of the bone allows eggshell cracking to be elicited. If neglected further, the tumor can perforate the bone and, ultimately, spread into the soft tissues.1 However, regarding the mechanism in how this tumor expands in the bone, until the present time, is poorly understood.
Receptor activator of NFκB ligand (RANKL) is a regulator of bone remodeling and essential for the development and activation of osteoclasts.3, 4 Production of RANKL by activated T cells directly controls osteoclastogenesis and bone remodeling, which explains why autoimmune diseases, cancers, leukaemias, asthma, chronic viral infections, and periodontal disease result in systemic and local bone loss.5 Regarding to ameloblastoma, it has been reported that RANKL was expressed in all types of ameloblastomas, which might be a possible factor in regulating bone metabolism.6
Besides RANKL, tumor necrosis factor alpha (TNFα) plays an important role in stimulating osteoclastogenesis as well, which has been confirmed by numerous investigators.7, 8 Both RANKL and TNFα are required for osteoclastogenesis through a dual level of regulation of these factors, selective signaling of the precursor cells via the two different receptors, and synergism in the stimulation of NFκB and JNK signaling.9, 10 Investigation of TNFα in ameloblastoma has shown that TNFα also was expressed in various ameloblastoma.11, 12 Moreover TNFα was reported found in intracystic fluid of ameloblastoma as well.12
Since the RANKL and TNFα are present in ameloblastoma, we hypothesized that those ligands might provide ameloblastoma a potential in inducing osteoclastogenesis, which later could result space in bone for its expansion. For that purpose, in the present study, we investigated on the potential and mechanism of ameloblastoma in inducing osteoclastogenesis.
Section snippets
Preparation of ameloblastoma tissue and AM-1 cell lysates
For tissue preparation, freshly resected ameloblastoma tissues of 9 patients (5 males and 4 females) were collected. The ameloblastoma tissues were resected from mandible (7 cases) and maxilla (2 cases) and based on the World Health Organization International, Histological Typing of Odontogenic Tumours, 2nd ed., 3 were plexiform, 3 were follicular and 3 were basal ameloblastomas. Fresh ameloblastoma tissues were homogenized in lysis buffer containing 50 mM Hepes/NaOH (pH 7.2), 0.5 M NaCl, 5 mM
RANKL and TNFα were detected in ameloblastoma, AM-1 cells and precipitated-10×CM
All ameloblastoma tissues, AM-1 cells and precipitated-10×CM expressed RANKL (Fig. 1). Comparing to follicular and plexiform ameloblastomas, basal cell ameloblastoma had the highest protein level of RANKL. In precipitated-10×CM, the expression of RANKL was seen more clearly comparing to the one of TNFα (Fig. 1B).
Amount of RANKL, TNFα and OPG in 10×CM
From Bio-Rad Protein Assay, we found that the concentration of protein contained in 10×CM was 500 μg/ml. From the ELISA results, in 10×CM, we found that concentration of RANKL was ±871.95
Discussion
Previously we had shown a clear expression of TNFα in ameloblastoma by detection of immunohistochemistry and western blot.11 And in the present study, we confirmed the immunohistochemical expression of RANKL in ameloblastoma, by western blot analysis, in all types of ameloblastomas. Expression of RANKL and TNFα were also detected in 10×CM, suggesting that AM-1 cells produce and secrete RANKL and TNFα. RANKL had shown to play more important role than TNFα in inducing osteoclastogenesis, and
Acknowledgements
We thank Dr. Hidemitsu Harada for providing the AM-1 cells and Dr. Quanyong Tang for technical supports. This project was supported by Grant-in-Aid for Scientific Research from JSPS (No. P 03145).
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