BONE-FORMATION BY MARROW OSTEOGENIC CELLS (MBA-15) IS NOT ACCOMPANIEDBY OSTEOCLASTOGENESIS AND GENERATION OF HEMATOPOIETIC SUPPORTIVE MICROENVIRONMENT

This study was aimed at elucidating the relationship between osteogeni c activity of marrow stromal cells and their ability to support hemato poiesis followed by the bone-remodeling process. We used the MBA-15 ce ll line, which expresses osteoblastic phenotype in vitro and forms bon e in diffusion chamber. We have compared bone formation and hematopoie tic responses elicited in vivo by these cells with the implantation of freshly isolated bone marrow cells (BMC) or demineralized tooth matri x (DTM). Both MBA-W cells and BMC, implanted under the kidney capsule, yielded intramembraneous bone, but DTM, implanted subcutaneously, eli cited endochondral bone. MBA-15 formed primary bone, mimicking only th e initial sequential stages of the ossification process. Neither histo logic signs of bone resorption and remodeling nor tartrate-resistant a cid phosphatase (TRAP)-positive cells and marrow formation were observ ed. Bone formation was monitored biochemically. Functions for hematopo ietic stem and committed cell content were measured by GM-CFU and BFU- E assays that confirmed the morphologic observations. In both BMC and DTM implantation, bone formation was followed by hematopoietic activit y, osteoclastogenesis, and remodeling. We conclude that MBA-15 osteopr ogenitor cells, despite their extensive bone formation ability, are un able to form a microenvironment supportive for hematopoiesis and osteo clastogenesis or to initiate bone remodeling.