Figure 1

Proposed Model for Bone Remodeling. The remodeling process comprises four major distinct but overlapping stages: (1) initiation/activation of bone remodeling at a specific site; (2) predominant bone resorption phase with concurrent recruitment of MSC/osteoprogenitors; (3) predominant osteoblast differentiation and function (osteoid synthesis); and (4) mineralization of osteoid and completion of bone remodeling. HSC: hematopoietic stem cells; SCF: stem cell factor; CMP: common myeloid progenitor; GM-CSF: granulocyte-macrophage colony stimulating factor; GMP: granulocyte-macrophage progenitors; M-CSF: monocyte-macrophage colony stimulating factor; BRC: bone remodeling compartment; MSC: mesenchymal stem cells.