title: EphrinB2 signaling in osteoblasts promotes bone mineralization by preventing apoptosis.
abstract: Cells that form bone (osteoblasts) express both ephrinB2 and EphB4, and previous work has shown that pharmacological inhibition of the ephrinB2/EphB4 interaction impairs osteoblast differentiation in vitro and in vivo. The purpose of this study was to determine the role of ephrinB2 signaling in the osteoblast lineage in the process of bone formation. Cultured osteoblasts from mice with osteoblast-specific ablation of ephrinB2 showed delayed expression of osteoblast differentiation markers, a finding that was reproduced by ephrinB2, but not EphB4, RNA interference. Microcomputed tomography, histomorphometry, and mechanical testing of the mice lacking ephrinB2 in osteoblasts revealed a 2-fold delay in bone mineralization, a significant reduction in bone stiffness, and a 50% reduction in osteoblast differentiation induced by anabolic parathyroid hormone (PTH) treatment, compared to littermate sex- and age-matched controls. These defects were associated with significantly lower mRNA levels of late osteoblast differentiation markers and greater levels of osteoblast and osteocyte apoptosis, indicated by TUNEL staining and transmission electron microscopy of bone samples, and a 2-fold increase in annexin V staining and 7-fold increase in caspase 8 activation in cultured ephrinB2 deficient osteoblasts. We conclude that osteoblast differentiation and bone strength are maintained by antiapoptotic actions of ephrinB2 signaling within the osteoblast lineage.
authors: St. Vincent's Institute of Medical Research, Fitzroy, Victoria, Australia; Department of Medicine, St. Vincent's Hospital, The University of Melbourne, Fitzroy, Victoria, Australia;
authors: Stephen
authors: S
authors: Tonna
authors: St. Vincent's Institute of Medical Research, Fitzroy, Victoria, Australia; Department of Medicine, St. Vincent's Hospital, The University of Melbourne, Fitzroy, Victoria, Australia;
authors: Farzin M
authors: FM
authors: Takyar
authors: St. Vincent's Institute of Medical Research, Fitzroy, Victoria, Australia; Department of Medicine, St. Vincent's Hospital, The University of Melbourne, Fitzroy, Victoria, Australia;
authors: Christina
authors: C
authors: Vrahnas
authors: St. Vincent's Institute of Medical Research, Fitzroy, Victoria, Australia;
authors: Blessing
authors: B
authors: Crimeen-Irwin
authors: St. Vincent's Institute of Medical Research, Fitzroy, Victoria, Australia;
authors: Patricia W M
authors: PW
authors: Ho
authors: St. Vincent's Institute of Medical Research, Fitzroy, Victoria, Australia;
authors: Ingrid J
authors: IJ
authors: Poulton
authors: St. Vincent's Institute of Medical Research, Fitzroy, Victoria, Australia;
authors: Holly J
authors: HJ
authors: Brennan
authors: St. Vincent's Institute of Medical Research, Fitzroy, Victoria, Australia;
authors: Narelle E
authors: NE
authors: McGregor
authors: St. Vincent's Institute of Medical Research, Fitzroy, Victoria, Australia;
authors: Elizabeth H
authors: EH
authors: Allan
authors: Griffith Health Institute and School of Medical Science, Griffith University, Gold Coast, Queensland, Australia.
authors: Huynh
authors: H
authors: Nguyen
authors: Griffith Health Institute and School of Medical Science, Griffith University, Gold Coast, Queensland, Australia.
authors: Mark R
authors: MR
authors: Forwood
authors: Faculty of Veterinary Science, The University of Melbourne, Parkville, Victoria, Australia; and.
authors: Liliana
authors: L
authors: Tatarczuch
authors: Faculty of Veterinary Science, The University of Melbourne, Parkville, Victoria, Australia; and.
authors: Eleanor J
authors: EJ
authors: Mackie
authors: St. Vincent's Institute of Medical Research, Fitzroy, Victoria, Australia; Department of Medicine, St. Vincent's Hospital, The University of Melbourne, Fitzroy, Victoria, Australia;
authors: T John
authors: TJ
authors: Martin
authors: St. Vincent's Institute of Medical Research, Fitzroy, Victoria, Australia; Department of Medicine, St. Vincent's Hospital, The University of Melbourne, Fitzroy, Victoria, Australia; nsims@svi.edu.au.
authors: Natalie A
authors: NA
authors: Sims
mesh_terms: D000818:Animals; D017304:Annexin A5 / Q000235:genetics / Q000378:metabolism; D017209:Apoptosis; D002113:Calcification, Physiologic; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D010006:Osteoblasts / Q000166:cytology / Q000378:metabolism*; D010012:Osteogenesis; D036183:Receptor, EphB2 / Q000235:genetics / Q000378:metabolism*; D036224:Receptor, EphB4 / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction
chemical_list: D017304:Annexin A5; C586311:Ephb2 protein, mouse; C086681:Ephb4 protein, mouse; D036183:Receptor, EphB2; D036224:Receptor, EphB4
keywords: bone matrix; bone strength; osteoclast; osteocyte