Human osteoclast-like cells are formed from peripheral blood mononuclear cells in a coculture with SaOS-2 cells transfected with the parathyroid hormone (PTH)/PTH-related protein receptor gene

Subclones of the human osteosarcoma cell line SaOS-2 were established by tr ansfecting with an expression vector containing the human PTH/PTH-related p rotein (PTHrP) receptor, and their abilities to support osteoclast-like mul tinucleated cell (OCL) formation were examined in coculture with mouse or h uman hemopoietic cells. Of four subclones examined, SaOS-2/4 and SaOS-4/3 b ound high levels of [I-125]-PTH and produced a significant amount of cAMP i n response to PTH. OCLs were formed in response to PTH in the cocultures of mouse bone marrow cells with either SaOS-2/4 cells or SaOS-4/3 cells. Huma n OCLs were also formed in response to PTH in the coculture of SaOS-4/3 cel ls and human peripheral blood mononuclear cells. Adding dexamethasone toget her with PTH greatly enhanced PTH-induced human OCL formation. Like mouse O CLs, human OCLs formed in response to PTH were tartrate-resistant acid phos phatase positive, expressed abundant calcitonin receptors and vitronectin r eceptors, and formed resorption pits on dentine slices. Other osteotropic f actors such as 1 alpha,25-dihydroxyviitamin D-3, prostaglandin E-2, and int erleukin 6 plus soluble interleukin 6 receptors failed to induce mouse and human OCLs in cocultures with SaOS-4/3 cells. Both mouse and human OCL form ation supported by SaOS-4/3 cells were inhibited by either adding an antibo dy against macrophage-colony stimulating factor or adding granulocyte/macro phage-colony stimulating factor. Thus, it is likely that human and mouse OC L formation supported by SaOS-4/3 cells are similarly regulated. These resu lts indicate that the target cells of PTH for inducing osteoclast formation are osteoblast/stromal cells but not osteoclast progenitor cells in the co culture. This coculture model will be useful for investigating the abnormal ities of osteoclast differentiation and function in human metabolic bone di seases.