title: Activation of autophagy by FOXO3 regulates redox homeostasis during osteogenic differentiation.
abstract: Bone remodeling is a continuous physiological process that requires constant generation of new osteoblasts from mesenchymal stem cells (MSCs). Differentiation of MSCs to osteoblast requires a metabolic switch from glycolysis to increased mitochondrial respiration to ensure the sufficient energy supply to complete this process. As a consequence of this increased mitochondrial metabolism, the levels of endogenous reactive oxygen species (ROS) rise. In the current study we analyzed the role of forkhead box O3 (FOXO3) in the control of ROS levels in human MSCs (hMSCs) during osteogenic differentiation. Treatment of hMSCs with H2O2induced FOXO3 phosphorylation at Ser294 and nuclear translocation. This ROS-mediated activation of FOXO3 was dependent on mitogen-activated protein kinase 8 (MAPK8/JNK) activity. Upon FOXO3 downregulation, osteoblastic differentiation was impaired and hMSCs lost their ability to control elevated ROS levels. Our results also demonstrate that in response to elevated ROS levels, FOXO3 induces autophagy in hMSCs. In line with this, impairment of autophagy by autophagy-related 7 (ATG7) knockdown resulted in a reduced capacity of hMSCs to regulate elevated ROS levels, together with a reduced osteoblast differentiation. Taken together our findings are consistent with a model where in hMSCs, FOXO3 is required to induce autophagy and thereby reduce elevated ROS levels resulting from the increased mitochondrial respiration during osteoblast differentiation. These new molecular insights provide an important contribution to our better understanding of bone physiology.
authors.affiliation: a Center for Molecular Medicine , University Medical Center Utrecht , Utrecht , The Netherlands.|b Regenerative Medicine Center , Uppsalalaan 8, Utrecht , The Netherlands.
authors.forename: M C
authors.initials: MC
authors.lastname: Gómez-Puerto
authors.affiliation: a Center for Molecular Medicine , University Medical Center Utrecht , Utrecht , The Netherlands.
authors.forename: L P
authors.initials: LP
authors.lastname: Verhagen
authors.affiliation: a Center for Molecular Medicine , University Medical Center Utrecht , Utrecht , The Netherlands.|b Regenerative Medicine Center , Uppsalalaan 8, Utrecht , The Netherlands.
authors.forename: A K
authors.initials: AK
authors.lastname: Braat
authors.affiliation: c Department of Surgery and Cancer , Imperial College London, Hammersmith Hospital Campus , London , UK.
authors.forename: E W-F
authors.initials: EW
authors.lastname: Lam
authors.affiliation: a Center for Molecular Medicine , University Medical Center Utrecht , Utrecht , The Netherlands.|b Regenerative Medicine Center , Uppsalalaan 8, Utrecht , The Netherlands.
authors.forename: P J
authors.initials: PJ
authors.lastname: Coffer
authors.affiliation: a Center for Molecular Medicine , University Medical Center Utrecht , Utrecht , The Netherlands.|b Regenerative Medicine Center , Uppsalalaan 8, Utrecht , The Netherlands.
authors.forename: M J
authors.initials: MJ
authors.lastname: Lorenowicz
mesh_terms: D001343:Autophagy / Q000187:drug effects; D002454:Cell Differentiation / Q000187:drug effects; D000071316:Forkhead Box Protein O3 / Q000378:metabolism*; D006706:Homeostasis / Q000187:drug effects; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D059630:Mesenchymal Stem Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D010012:Osteogenesis / Q000187:drug effects; D010084:Oxidation-Reduction / Q000187:drug effects; D018384:Oxidative Stress / Q000187:drug effects; D017382:Reactive Oxygen Species / Q000378:metabolism
chemical_list: C499517:FOXO3 protein, human; D000071316:Forkhead Box Protein O3; D017382:Reactive Oxygen Species; D006861:Hydrogen Peroxide; D020928:Mitogen-Activated Protein Kinases
keywords: FOXO3; autophagy; human mesenchymal stem cells (hMSCs); mitogen-activated protein kinase 8 (MAPK8/JNK); osteoblasts; reactive oxygen species (ROS)