Osteoporosis is a disease characterized by the decrease in bone mass, whose underlying mechanism is an imbalanced bone remodeling including inadequate bone formation by osteoblasts or excessive bone resorption by osteoclasts.The osteoclast precursors, i.e.monocytes derived from hematopoietic stem cells, are generally recruited to the resorption sites and fuse into multi-nucleated osteoclasts.It has been well recognized that bone resorption occurs close to microdamages and this process is called as targeted bone remodeling.However, what factors of the micro-environment around a microdamage regulates this targeted remodeling remains largely unknown.Our recent studies were focused on the effect of mechanical micro-environment on the migration and fusion of osteoclast precursors.