title: Osteocytes as mechanosensors in the inhibition of bone resorption due to mechanical loading.
abstract: Bone has the ability to adjust its structure to meet its mechanical environment. The prevailing view of bone mechanobiology is that osteocytes are responsible for detecting and responding to mechanical loading and initiating the bone adaptation process. However, how osteocytes signal effector cells and initiate bone turnover is not well understood. Recent in vitro studies have shown that osteocytes support osteoclast formation and activation when co-cultured with osteoclast precursors. In this study, we examined the osteocytes' role in the mechanical regulation of osteoclast formation and activation. We demonstrated here that (1) mechanical stimulation of MLO-Y4 osteocyte-like cells decreases their osteoclastogenic-support potential when co-cultured with RAW264.7 monocyte osteoclast precursors; (2) soluble factors released by these mechanically stimulated MLO-Y4 cells inhibit osteoclastogenesis induced by ST2 bone marrow stromal cells or MLO-Y4 cells; and (3) soluble RANKL and OPG were released by MLO-Y4 cells, and the expressions of both were found to be mechanically regulated. Our data suggest that mechanical loading decreases the osteocyte's potential to induce osteoclast formation by direct cell-cell contact. However, it is not clear that osteocytes in vivo are able to form contacts with osteoclast precursors. Our data also demonstrate that mechanically stimulated osteocytes release soluble factors that can inhibit osteoclastogenesis induced by other supporting cells including bone marrow stromal cells. In summary, we conclude that osteocytes may function as mechanotransducers by regulating local osteoclastogenesis via soluble signals.
authors.affiliation: Department of Mechanical and Industrial Engineering, Institute of Biomaterials and Biomedical Engineering, University of Toronto, ON, Canada M53 3G8. youlidan@mie.utoront.ca
authors.forename: Lidan
authors.initials: L
authors.lastname: You
authors.forename: Sara
authors.initials: S
authors.lastname: Temiyasathit
authors.forename: Peling
authors.initials: P
authors.lastname: Lee
authors.forename: Chi Hyun
authors.initials: CH
authors.lastname: Kim
authors.forename: Padmaja
authors.initials: P
authors.lastname: Tummala
authors.forename: Wei
authors.initials: W
authors.lastname: Yao
authors.forename: Wade
authors.initials: W
authors.lastname: Kingery
authors.forename: Amanda M
authors.initials: AM
authors.lastname: Malone
authors.forename: Ronald Y
authors.initials: RY
authors.lastname: Kwon
authors.forename: Christopher R
authors.initials: CR
authors.lastname: Jacobs
mesh_terms: D000818:Animals; D001862:Bone Resorption / Q000378:metabolism; D002450:Cell Communication; D002454:Cell Differentiation; D002460:Cell Line; D018920:Coculture Techniques; D051379:Mice; D010011:Osteocytes / Q000166:cytology* / Q000378:metabolism; D053244:Osteoprotegerin / Q000235:genetics / Q000378:metabolism; D053245:RANK Ligand / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics; D015398:Signal Transduction; D012995:Solubility
chemical_list: D053244:Osteoprotegerin; D053245:RANK Ligand; D012333:RNA, Messenger