Site-Dependence of Mechanosensitivity in Isolated Osteocytes

It is proposed that osteocytes embedded in mineralized bone matrix play a role in mechanosensory system during bone remodeling for mechanical adaptation. Various experimental and computer simulation approaches have revealed that the osteocytes sense the mechanical stimulus such as deformation/force and microdamages in bone matrix generated by mechanical loading, and also still have continued discussion. In this study, for interest to morphological character of osteocytes, we investigated site-dependence of mechanosensitivity in the osteocytes through observation of calcium response to applied local deformation. We developed a quantitative method using a microneedle and microparticles to apply local deformation to an isolated chick osteocyte, and analyzed intracellular calcium dynamics to the applied deformation. As the results, the applied local deformation induced calcium response at the vicinity of the stimulated point and caused its diffusive wave propagation to whole intracellular region in a single osteocyte. Furthermore, the large deformation was necessary at the cell body to induce calcium response, while a relatively small deformation was sufficient at the cell process, suggesting that the mechanosensitivity at the cell process was higher than that at the cell body. These results suggest that the cell shape with processes contributes to the mechanism of cellular response to mechanical stimulus in osteocytes, and that the site-dependent mechanosensitivity depends on cell shape in a single osteocyte.