Role of VEGF in Promoting Osteoclastogenesis

Objectives: Osteoclastogenesis and subsequent alveolar bone resorption are necessary for tooth eruption. This osteoclastogenesis appears to be regulated by the dental follicle. One of the key molecules produced by the follicle is colony-stimulating factor (CSF-1) which promotes osteoclastogenesis by stimulating receptor activator of nuclear factor-kappa B (RANK) gene expression in osteoclast precursors. Although CSF-1 is maximally expressed at the time of the major burst of the osteoclasteogenesis (day 3) in the rat first mandibular molar, it is minimally expressed at the time of a minor burst of osteoclastogenesis at day 9 postnatally. However, vascular endothelial growth factor (VEGF) is maximally expressed at this later time and we hypothesize that it substitutes for CSF-1 to stimulate RANK expression. Thus, the objective of this study was to determine if VEGF can stimulate RANK expression in osteoclast precursors, as does CSF-1. Methods: Cell cultures from spleen and bone marrow were established from adult rats. The cells were incubated with CSF-1 or VEGF 10-40 ng/ml alone or in combination for 3-4 hours. Cell cultures without any treatment were used as controls. Total RNA was extracted from the cells and RANK gene expression was assessed using RT-PCR. Results: Either CSF-1 or VEGF causes up-regulation of RANK expression as compared to controls. The maximum effect of VEGF on enhancing RANK expression is at a concentration of 10 to 20 ng/ml. At this optimal concentration, the effect of VEGF on RANK expression was similar to that of CSF-1. RANK expression was higher in the treatment combination of CSF-1 and VEGF than in treatment with them alone. Conclusion: VEGF can substitute for CSF-1 to increase RANK gene expression. This up-regulation of RANK expression may be the means by which VEGF stimulates the minor burst of osteoclastogenesis seen prior to eruption. Supported by NIDCR grant DE08911-13 to G.E.W.