IGF-1 Released During Osteoclastic Bone Resorption Induces Osteoblast Differentiation from Bone Marrow Stromal Cells

Homeostasis of skeletal tissues is maintained by a well-balanced regulation of bone formation and bone resorption (1;2). This process is called remodeling, in which osteoblasts are involved in the bone formation process and osteoclasts are essential for bone resorption. During the remodeling process, bone resorption by osteoclasts acts as a trigger to stimulate bone formation by osteoblasts, a step called coupling (3). However, the factor(s) that mediate bone formation signals from osteoclasts to osteoblasts are not wellunderstood. Several factors, such as TGF-β, have been reported as possible candidates (4), but no direct evidence exists thus far.