Expression of Osteoprotegerin (Osteoclastogenesis Inhibitory Factor) in Cultures of Human Dental Mesenchymal Cells and Epithelial Cells

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Abstract
Osteoprotegerin (OPG)/osteoclastogenesis inhibitory factor (OCIF) inhibits osteoclast differentiation, activity, and survival; therefore OPG/OCIF may regulate the resorption of dental hard tissues, such as alveolar bone, cementum, and dentin. To investigate this issue, reverse transcriptase-polymerase chain reaction using specific primers for OPG/OCIF was performed with total RNAs isolated from human gingival keratinocytes (HGKs), human gingival fibroblasts (HGFs), human periodontal ligament cells (HPDLs), and human pulp cells (HPCs) in culture. PCR products were found in HGFs, HPDLs, and HPCs, but not in HGKs, and the DNA sequence of these products was 100% identical to the reported sequence of the OPG gene. Northern blot analyses also showed that HGFs, HPDLs, and HPCs, but not HGKs, expressed OPG/OCIF transcripts of ∼2.5 kb. Interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) increased OPG/OCIF mRNA levels in a dose-and time-dependent manner in HPDL. After 12 h of treatment, IL-1β at 3 ng/ml and TNF-α at 3 ng/ml increased OPG/OCIF mRNA expression by 190% and 110%, respectively, with a maximal effect. The stimulatory effects of IL-1β and TNF-α were also seen in HPC. However, IL-6 and transforming growth factor-β had little effect on OPG/OCIF mRNA levels in HPDL. These findings suggest that OPG/OCIF synthesized by dental mesenchymal cells locally regulates the resorption of dental hard tissues through cytokines.