Expression of osteoprotegerin (osteoclastogenesis inhibitory factor) in cultures of human dental mesenchymal cells and epithelial cells

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, ceme ntum, and dentin, To investigate this issue, reverse transcriptase-polymera se chain reaction using specific primers for OPG/OCIF was performed,vith to tal RNAs isolated from human gingival keratinocytes (HGKs), human gingival fibroblasts (HGFs), human periodontal ligament cells (HPDLs), and human pul p 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% identica l to the reported sequence of the OPG gene. Northern blot analyses also sho wed tl;at HGFs, HPDLs, and HPCs, but not HGKs, expressed OPG/OCIF transcrip ts of similar to 2.5 kb. Interleukin-1 beta (IL-1 beta) and tumor necrosis factor-alpha (TNF-alpha) increased OPG/OCIF mRNA levels in a dose-and time- dependent manner in HPDL. After 12 h of treatment, IL-1 beta at 3 ng/ml and TNF-alpha at 3 ng/ml increased OPG/OCIF mRNA expression by 190% and 110%, respectively,,vith a maximal effect. The stimulatory effects of IL-1 beta a nd TNF-alpha were also seen in HPC. However, IL-6 and transforming growth f actor-beta had little effect on OPG/OCIF mRNA levels in HPDL. These finding s suggest that OPG/OCIF synthesized by dental mesenchymal cells locally reg ulates the resorption of dental hard tissues through cytokines.