title: The Wnt Inhibitor Sclerostin Is Up-regulated by Mechanical Unloading in Osteocytes in Vitro.
abstract: Although bone responds to its mechanical environment, the cellular and molecular mechanisms underlying the response of the skeleton to mechanical unloading are not completely understood. Osteocytes are the most abundant but least understood cells in bones and are thought to be responsible for sensing stresses and strains in bone. Sclerostin, a product of the SOST gene, is produced postnatally primarily by osteocytes and is a negative regulator of bone formation. Recent studies show that SOST is mechanically regulated at both the mRNA and protein levels. During prolonged bed rest and immobilization, circulating sclerostin increases both in humans and in animal models, and its increase is associated with a decrease in parathyroid hormone. To investigate whether SOST/sclerostin up-regulation in mechanical unloading is a cell-autonomous response or a hormonal response to decreased parathyroid hormone levels, we subjected osteocytes to an in vitro unloading environment achieved by the NASA rotating wall vessel system. To perform these studies, we generated a novel osteocytic cell line (Ocy454) that produces high levels of SOST/sclerostin at early time points and in the absence of differentiation factors. Importantly, these osteocytes recapitulated the in vivo response to mechanical unloading with increased expression of SOST (3.4 ± 1.9-fold, p < 0.001), sclerostin (4.7 ± 0.1-fold, p < 0.001), and the receptor activator of nuclear factor κΒ ligand (RANKL)/osteoprotegerin (OPG) (2.5 ± 0.7-fold, p < 0.001) ratio. These data demonstrate for the first time a cell-autonomous increase in SOST/sclerostin and RANKL/OPG ratio in the setting of unloading. Thus, targeted osteocyte therapies could hold promise as novel osteoporosis and disuse-induced bone loss treatments by directly modulating the mechanosensing cells in bone.
authors.affiliation: From the Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114, Harvard-MIT Institute for Medical Engineering and Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139.
authors.forename: Jordan M
authors.initials: JM
authors.lastname: Spatz
authors.affiliation: From the Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114.
authors.forename: Marc N
authors.initials: MN
authors.lastname: Wein
authors.affiliation: NorthWest Academic Centre, The University of Melbourne, St. Albans, Victoria 3065, Australia, and.
authors.forename: Jonathan H
authors.initials: JH
authors.lastname: Gooi
authors.affiliation: From the Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114.
authors.forename: Yili
authors.initials: Y
authors.lastname: Qu
authors.affiliation: From the Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114.
authors.forename: Jenna L
authors.initials: JL
authors.lastname: Garr
authors.affiliation: From the Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114.
authors.forename: Shawn
authors.initials: S
authors.lastname: Liu
authors.affiliation: From the Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114.
authors.forename: Kevin J
authors.initials: KJ
authors.lastname: Barry
authors.affiliation: From the Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114.
authors.forename: Yuhei
authors.initials: Y
authors.lastname: Uda
authors.affiliation: From the Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114.
authors.forename: Forest
authors.initials: F
authors.lastname: Lai
authors.affiliation: From the Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114.
authors.forename: Christopher
authors.initials: C
authors.lastname: Dedic
authors.affiliation: Harvard-MIT Institute for Medical Engineering and Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, Bioengineering Department, Institut Quimic de Sarria, Ramon Llull University, 08017 Barcelona, Spain.
authors.forename: Mercedes
authors.initials: M
authors.lastname: Balcells-Camps
authors.affiliation: From the Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114.
authors.forename: Henry M
authors.initials: HM
authors.lastname: Kronenberg
authors.affiliation: Amgen Inc., Thousand Oaks, California 91320.
authors.forename: Philip
authors.initials: P
authors.lastname: Babij
authors.affiliation: From the Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114, pdivieti@bu.edu.
authors.forename: Paola Divieti
authors.initials: PD
authors.lastname: Pajevic
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D001696:Biomechanical Phenomena; D002460:Cell Line; D006023:Glycoproteins / Q000235:genetics* / Q000378:metabolism; D006112:Gravitation; D036341:Intercellular Signaling Peptides and Proteins; D051379:Mice; D010011:Osteocytes / Q000737:chemistry / Q000378:metabolism*; D053245:RANK Ligand / Q000235:genetics / Q000378:metabolism; D015854:Up-Regulation; D051153:Wnt Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D006023:Glycoproteins; D036341:Intercellular Signaling Peptides and Proteins; D053245:RANK Ligand; C486030:Sost protein, mouse; D051153:Wnt Proteins
keywords: Wnt pathway; bone; cell biology; cell line; cell sorting; mechanical unloading; osteocyte; sclerostin; shear stress