DISSOCIATION BETWEEN BONE-RESORPTION AND BONE-FORMATION IN OSTEOPENICTRANSGENIC MICE

Bone mass is maintained constant in vertebrates through bone remodelin g (BR), BR is characterized by osteoclastic resorption of preexisting bone followed by ne novo bone formation by osteoblasts. This sequence of events and the fact that bone mass remains constant in physiologica l situation lead to the assumption that resorption and formation are r egulated by each other during BR, Recent evidence shows that cells of the osteoblastic lineage are involved in osteoclast differentiation. H owever, the existence of a functional link between the two activities, formation and resorption, has never been shown in vivo. To define the role of bone formation in the control of bone resorption, we generate d an inducible osteoblast ablation mouse model. These mice developed a reversible osteopenia, Functional analyses showed that in the absence of bone formation, bone resorption continued to occur normally, leadi ng to an osteoporosis of controllable severity, whose appearance could be prevented by an antiresorptive agent. This study establishes that bone formation and/or bone mass do not control the extent of bone reso rption in vivo.