title: VEGF Receptor 2 (VEGFR2) Activation Is Essential for Osteocyte Survival Induced by Mechanotransduction.
abstract: Mechanical loading plays a key role in bone formation and maintenance. While unloading induces osteocyte apoptosis and bone loss in vivo, mechanical stimuli prevents osteocyte death through a mechanism involving β-catenin accumulation and ERK nuclear translocation. Vascular endothelial growth factor (VEGF) has a crucial role in bone formation, but its interaction with osteocytes is not completely understood. Of interest, VEGF receptor 2 (VEGFR2) has recently been shown to mediate the mechanical response of endothelial cells. The present study aimed to evaluate the putative role of the VEGF system in osteocyte mechanosensing. We show that either short (10 min) mechanical stimulus by pulsatile fluid flow (FF) (10 dyn/cm(2), 8 Hz) or exogenous VEGF165 (6 ng/ml) similarly stimulated cell viability, ERK phosphorylation, and β-catenin membrane translocation. A VEGFR2 antagonist (SU5416) or transfection with specific VEGFR2 siRNAs (siVEGFR2) decreased these events. FF for 10 min increased VEGFR2 phosphorylation at both Tyr-1059 and Tyr-1175; an effect that was mimicked by VEGF165 but was unaffected by a VEGF neutralizing antibody. Subsequently (at 6 h), this mechanical stimulus induced VEGF gene overexpression, which was prevented by siVEGFR2 transfection. Depletion of the structural protein caveolin-1 by using siRNA technology impaired FF-induced VEGFR2 phosphorylation. In conclusion, these in vitro findings point to caveolin-1-dependent VEGFR2 activation as an important mechanism whereby mechanical stimuli promote osteocyte viability.
authors.affiliation: Instituto de Medicina Molecular Aplicada (IMMA), Facultad de Medicina, Universidad CEU San Pablo, Madrid, Spain.
authors.forename: Luis F
authors.initials: LF
authors.lastname: de Castro
authors.affiliation: Instituto de Investigación Sanitaria (IIS)-Fundación Jiménez Díaz and Red Temática de Investigación Cooperativa en Envejecimiento y Fragilidad (RETICEF), Madrid, Spain.
authors.forename: Marta
authors.initials: M
authors.lastname: Maycas
authors.affiliation: Instituto de Medicina Molecular Aplicada (IMMA), Facultad de Medicina, Universidad CEU San Pablo, Madrid, Spain.
authors.forename: Beatriz
authors.initials: B
authors.lastname: Bravo
authors.affiliation: Instituto de Investigación Sanitaria (IIS)-Fundación Jiménez Díaz and Red Temática de Investigación Cooperativa en Envejecimiento y Fragilidad (RETICEF), Madrid, Spain.
authors.forename: Pedro
authors.initials: P
authors.lastname: Esbrit
authors.affiliation: Instituto de Medicina Molecular Aplicada (IMMA), Facultad de Medicina, Universidad CEU San Pablo, Madrid, Spain.
authors.forename: Arancha
authors.initials: A
authors.lastname: Gortazar
mesh_terms: D000818:Animals; D051242:Caveolin 1 / Q000378:metabolism*; D002465:Cell Movement / Q000502:physiology; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D042783:Endothelial Cells / Q000378:metabolism*; D004730:Endothelium, Vascular / Q000166:cytology; D004789:Enzyme Activation; D040542:Mechanotransduction, Cellular / Q000502:physiology*; D051379:Mice; D018919:Neovascularization, Physiologic / Q000187:drug effects / Q000502:physiology; D010011:Osteocytes / Q000166:cytology / Q000378:metabolism*; D040301:Vascular Endothelial Growth Factor Receptor-2 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D051176:beta Catenin / Q000378:metabolism
chemical_list: C495267:CTNNB1 protein, mouse; C495541:Cav1 protein, mouse; D051242:Caveolin 1; D051176:beta Catenin; C000592875:Kdr protein, mouse; D040301:Vascular Endothelial Growth Factor Receptor-2