Dental cells express factors that regulate bone resorption.

Odontoblasts and osteoblasts produce similar highly mineralized extracellular matrices. In bone, osteoblasts/stromal cells regulate osteoclast (ocl) formation and bone resorption by producing factors like osteoprotegerin (OPG), osteoclast differentiating factor (ODF/RANKL), and macrophage colony-stimulating factor (M-CSF) that interact with hematopoietic ocl precursor cells. Using odontoblast and pulp cell lines, we detected a constitutive expression of OPG, RANKL, and M-CSF mRNA in both cell types. OPG and RANKL proteins were also detectable. In vivo, RANKL and OPG were localized to odontoblasts, ameloblasts, and pulp cells in developing mouse teeth by immunohistochemistry. In a coculture system, we found the dental cells to be inhibitory to ocl formation from spleen and bone marrow precursors, despite their production of osteoclast stimulatory factors. Our data indicate for the first time that dental cells express factors important in regulation of osteoclastogenesis and bone resorption. Since both stimulatory (RANKL, M-CSF) and inhibitory (OPG) factors are expressed, a balance between positive and negative factors may contribute to regulation of bone resorption.