Reaction between Osteoclasts and Osteocytes When They Encounter Each Other at the Bone Resorption Surface during Bone Modeling

Osteocytes are considered to be a candidate for key cells regulating bone metabolism, which consists of bone formation by osteoblasts and bone resorption by osteoclasts; however, the role of the osteocyte remains unclear. Osteocytes are released from the osteocytic lacunae when osteoclasts resorb the bone matrix during bone metabolism, bone modeling and remodeling; and a variety of proposals for the fate of the released osteocytes have been made. This variety suggests that osteoclasts can react differently to individual osteocytes during bone resorption and that this difference may provide a clue as to the role of osteocytes in the regulation of bone metabolism. So we recently conducted a precise investigation of the reaction of osteoclasts to osteocytes when these cell types encounter one another during bone resorption in the course of bone modeling, including the fate of the released osteocytes. Morphological observations made by LM and TEM revealed that osteoclasts engulfed some osteocytes but did not engulf others when releasing osteocytes from the osteocytic lacunae during bone modeling and suggested that the 3-dimensional relationship between osteocytes and osteoclasts when they encounter each other might be a key to decide the reaction of osteoclasts to osteocytes. This article reviews the reaction between osteoclasts and osteocytes when they encounter each other at the bone resorption surface during bone modeling based on our present study and previously published studies.