title: The role of the sphingosine-1-phosphate signaling pathway in osteocyte mechanotransduction.
abstract: Osteocytes are proposed to be the mechanosensory cells that translate mechanical loading into biochemical signals during the process of bone adaptation. The lipid mediator sphingosine-1-phosphate (S1P) has been reported to play a role in the mechanotransduction process of blood vessels and also in the dynamic control of bone mineral homeostasis. Nevertheless, the potential role of S1P in bone mechanotransduction has yet to be elucidated. In this study, we hypothesized that a S1P cascade is involved in the activation of osteocytes in response to loading-induced oscillatory fluid flow (OFF) in bone. MLO-Y4 osteocyte-like cells express the necessary components of a functional S1P cascade. To examine the involvement of S1P signaling in osteocyte mechanotransduction, we applied OFF (1 Pa, 1 Hz) to osteocyte-like MLO-Y4 cells under conditions where the S1P signaling pathway was modulated. We found that decreased endogenous S1P levels significantly suppressed the OFF-induced intracellular calcium response. Addition of extracellular S1P to MLO-Y4 cells enhanced the synthesis and release of prostaglandin E2 (PGE2) under static cells and amplified OFF-induced PGE2 release. The stimulatory effect of OFF on the gene expression levels of osteoprotegerin (OPG) and receptor activator for nuclear factor κB ligand (RANKL) was S1P dependent. Furthermore, the S1P2 receptor subtype was shown to be involved in OFF-induced PGE2 synthesis and release, as well as down-regulation of RANKL/OPG gene expression ratio. In summary, our data suggest that S1P cascade is involved in OFF-induced mechanotransduction in MLO-Y4 cells and that extracellular S1P exerts its effect partly through S1P2 receptors.
authors.affiliation: Institute of Biomaterials & Biomedical Engineering, University of Toronto, ON, Canada.
authors.forename: Jia-Ning
authors.initials: JN
authors.lastname: Zhang
authors.affiliation: Institute of Biomaterials & Biomedical Engineering, University of Toronto, ON, Canada.
authors.forename: Yan
authors.initials: Y
authors.lastname: Zhao
authors.affiliation: Institute of Biomaterials & Biomedical Engineering, University of Toronto, ON, Canada.
authors.forename: Chao
authors.initials: C
authors.lastname: Liu
authors.affiliation: Institute of Biomaterials & Biomedical Engineering, University of Toronto, ON, Canada.
authors.forename: Elizabeth S
authors.initials: ES
authors.lastname: Han
authors.affiliation: Division of Engineering Science, University of Toronto, ON, Canada.
authors.forename: Xue
authors.initials: X
authors.lastname: Yu
authors.affiliation: Department of Physiology, University of Toronto, ON, Canada.
authors.forename: Darcy
authors.initials: D
authors.lastname: Lidington
authors.affiliation: Department of Physiology, University of Toronto, ON, Canada. Electronic address: sts.bolz@utoronto.ca.
authors.forename: Steffen-Sebastian
authors.initials: SS
authors.lastname: Bolz
authors.affiliation: Institute of Biomaterials & Biomedical Engineering, University of Toronto, ON, Canada; Department of Mechanical and Industrial Engineering, University of Toronto, ON, Canada. Electronic address: youlidan@mie.utoronto.ca.
authors.forename: Lidan
authors.initials: L
authors.lastname: You
mesh_terms: D000818:Animals; D016723:Bone Remodeling / Q000502:physiology*; D002460:Cell Line; D005786:Gene Expression Regulation / Q000502:physiology; D008246:Lysophospholipids / Q000378:metabolism*; D040542:Mechanotransduction, Cellular / Q000502:physiology*; D051379:Mice; D010011:Osteocytes / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D049349:Receptors, Lysosphingolipid / Q000378:metabolism; D013110:Sphingosine / Q000031:analogs & derivatives* / Q000378:metabolism
chemical_list: D008246:Lysophospholipids; D049349:Receptors, Lysosphingolipid; C060506:sphingosine 1-phosphate; D013110:Sphingosine
keywords: Calcium; Mechanotransduction; Osteocyte; PGE(2); RANKL/OPG ratio; Sphingsosine-1-phosphate