Regulation of secretion of osteoprotegerin in rat dental follicle cells

Abstract

Tooth eruption requires alveolar bone resorption and formation, both of which appear to be regulated by the dental follicle. Osteoclastogenesis needed for this bone resorption appears to occur as a result of a reduction in the expression of the osteoprotegerin (OPG) gene in the dental follicle at a specific time. This reduction in expression is mediated in vitro in the follicle cells by colony-stimulating factor-1 (CSF-1) and parathyroid hormone-related protein (PTHrP). Using enzyme-linked immunosorbent assays and immunoblotting, this study shows that the reduction in expression of OPG after incubation of the dental follicle cells in either CSF-1 or PTHrP also results in a reduction in its secretion. We also show, by laser capture microdissection, that PTHrP is expressed in vivo in the stellate reticulum such that it could inhibit OPG expression via a paracrine effect on the follicle. Bone formation is enhanced by OPG secretion, and incubation of the follicle cells with bone morphogenetic protein-2 (BMP-2) enhances OPG secretion. Thus, a reduction in secretion of the OPG protein at defined times may promote the osteoclastogenesis and alveolar bone resorption needed for eruption, and enhancement of OPG secretion at other times may promote alveolar bone formation.

Bone formation as a potential motive force of tooth eruption in the rat molar

“…Previous studies in our laboratory have shown that the BMP-2 gene is expressed in the dental follicle of the rat first mandibular molar, with an initial increase at day 3, followed by a decrease in expression at days 5-7, and then an increase at day 9 (Wise et al, 2004). When one examines the gene expression of BMP-2 in the dental follicle regionally, coronal [1/2] versus basal [1/2], the gene expression of BMP-2 is higher in the basal one-half than in the coronal one-half at days 3 and 9 (Wise and Yao, 2006).…”

“…Such formation appears to be regulated by the dental follicle, especially the basal (apical) one-half of the follicle. Based on previous studies demonstrating BMP-2 chronological expression in the follicle (Wise et al, 2004) and its greater expression in the basal one-half of the follicle (Wise and Yao, 2006), BMP-2 is a candidate molecule for regulating the bone growth in the base of the alveolar socket. The other requirement for tooth eruption is bone resorption in the coronal region of the crypt to form an eruption pathway and this also is regulated by the dental follicle.…”

Laser Capture Microdissection in Dentistry

“…Absence of CSF-1 receptor was associated with shortened ameloblasts, loss of odontoblastic polarization, and dramatically reduced DMP-1 expression. csCSF-1 may act in an autocrine fashion in odontoblasts to regulate DMP-1 since odontoblasts express the CSF-1R and may be involved in mediating tooth matrix formation [6, 10]. …”

“…The detailed mechanisms of tooth eruption is yet to be clarified, mainly because many issues regarding growth factors, such as types of expressing cells, temporo-spacial changes of expression patterns, and results of growth factor interaction, remain fully understood, LCM is applicable to molecular profiling of tissue specimens, permitting correlation of cellular and molecular signatures with specific cell population, especially comparison of cellular elements within the tissue microenvironment or in the variety of cell types. Thus, LCM has been applied to the studies of tooth eruption including evaluation of the tissue surrounding unerupted tooth, dental follicle microenvironment, factors involved in tooth eruption process, time expression of growth factors, and/or cytokines and type of cells releasing growth factors to conclude mechanism of tooth eruption [5, 8–10, 26]. …”

“…In dentistry, this technology has been utilized in different research fields such as oral embryology [5–10], oral oncology [11–16], oral cell biology [7, 17–21], and tissue engineering including teeth [17, 22–24]. In this paper, we will focus on the presentation and discussion of existing literature that covers the dental researches using LCM, especially in the field of RNA analysis.…”