A new method to isolate large numbers of rabbit osteoclasts and osteoclast-like cells: application to the characterization of serum response element binding proteins during osteoclast differentiation.

We have developed a new method that allows the purification of large numbers of both authentic osteoclasts (OCs) and in vitro differentiated osteoclast-like cells (OCLs) from rabbits. We characterized the OCLs in terms of the expression of different phenotypic markers of OC differentiation and their ability to resorb bone. The method provides a system for performing biochemical and molecular studies of OC differentiation and function in a single species. We used this system to characterize the effect of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) on the expression of proteins that bind to the serum response element (SRE) of the c-fos promoter. We found that OCLs and OCs displayed similar SRE-binding activities, including the serum response factor (SRF). This pattern is established in a time-dependent and cell-specific manner in response to long-term treatment of rabbit bone marrow by 1,25(OH)2D3. Thus, 1,25(OH)2D3 can modulate SRF and/or SRF-related protein. This finding may contribute to understanding the role of c-Fos in the regulation of OC differentiation.