The influence of surface mineral and osteopontin on the formation and function of murine bone marrow-derived osteoclasts.

The phosphorylated glycoprotein osteopontin (OPN) is involved in the regulation of biomineralization under normal and pathological conditions. Its actions include inhibiting apatite crystal growth and promoting the formation and function of mineral resorbing cells, including osteoclasts (OCL). The purpose of this study was to develop stable apatitic mineral surfaces and determine their influence on OCL formation and mineral resorption from bone marrow macrophages derived from OPN wild-type (OPN+/+) and OPN deficient (OPN-/-) mice. We demonstrated that these mineral coatings were stable and supported bone marrow-derived macrophage differentiation to OCL under our culture conditions. Macrophages harvested from OPN-/- mice had a greater capacity to form OCL than macrophages from OPN+/+ mice when allowed to differentiate on tissue culture plastic. In contrast, when allowed to differentiate on a mineral surface, no difference in OCL formation was observed. Interestingly, OPN+/+ OCL were more efficient at mineral dissolution than OPN-/- OCL, and this difference was observed regardless of differentiating surface. Our results suggest that mineralized substrates as well as ability to synthesize OPN both control OCL function in our model system. The exact nature of these effects may be dependent on variables related to mineral substrate presentation.