title: Rac1 GTPase silencing counteracts microgravity-induced effects on osteoblastic cells.
abstract: Bone cells exposed to real microgravity display alterations of their cytoskeleton and focal adhesions, two major mechanosensitive structures. These structures are controlled by small GTPases of the Ras homology (Rho) family. We investigated the effects of RhoA, Rac1, and Cdc42 modulation of osteoblastic cells under microgravity conditions. Human MG-63 osteoblast-like cells silenced for RhoGTPases were cultured in the automated Biobox bioreactor (European Space Agency) aboard the Foton M3 satellite and compared to replicate ground-based controls. The cells were fixed after 69 h of microgravity exposure for postflight analysis of focal contacts, F-actin polymerization, vascular endothelial growth factor (VEGF) expression, and matrix targeting. We found that RhoA silencing did not affect sensitivity to microgravity but that Rac1 and, to a lesser extent, Cdc42 abrogation was particularly efficient in counteracting the spaceflight-related reduction of the number of focal contacts [-50% in silenced, scrambled (SiScr) controls vs. -15% for SiRac1], the number of F-actin fibers (-60% in SiScr controls vs. -10% for SiRac1), and the depletion of matrix-bound VEGF (-40% in SiScr controls vs. -8% for SiRac1). Collectively, these data point out the role of the VEGF/Rho GTPase axis in mechanosensing and validate Rac1-mediated signaling pathways as potential targets for counteracting microgravity effects.
authors.affiliation: Institute National de la Santé et de la Recherche Médicale (INSERM), Unité 1059, Laboratoire de Biologie Intégrée du Tissu Osseux, Université de Lyon, St-Etienne, France; alain.guignandon@univ-st-etienne.fr.
authors.forename: Alain
authors.initials: A
authors.lastname: Guignandon
authors.affiliation: Institute National de la Santé et de la Recherche Médicale (INSERM), Unité 1059, Laboratoire de Biologie Intégrée du Tissu Osseux, Université de Lyon, St-Etienne, France;
authors.forename: Céline
authors.initials: C
authors.lastname: Faure
authors.affiliation: Laboratory of Connective Tissues Biology, Groupe Interdisciplinaire de Génoprotéomique Appliqué (GIGA), Université de Liège, Sart Tilman, Belgium; and.
authors.forename: Thibaut
authors.initials: T
authors.lastname: Neutelings
authors.affiliation: Institute National de la Santé et de la Recherche Médicale (INSERM), Unité 1059, Laboratoire de Biologie Intégrée du Tissu Osseux, Université de Lyon, St-Etienne, France;
authors.forename: Aline
authors.initials: A
authors.lastname: Rattner
authors.affiliation: Laboratory of Connective Tissues Biology, Groupe Interdisciplinaire de Génoprotéomique Appliqué (GIGA), Université de Liège, Sart Tilman, Belgium; and.
authors.forename: Pierre
authors.initials: P
authors.lastname: Mineur
authors.affiliation: Institute National de la Santé et de la Recherche Médicale (INSERM), Unité 1059, Laboratoire de Biologie Intégrée du Tissu Osseux, Université de Lyon, St-Etienne, France;
authors.forename: Marie-Thérèse
authors.initials: MT
authors.lastname: Linossier
authors.affiliation: Institute National de la Santé et de la Recherche Médicale (INSERM), Unité 1059, Laboratoire de Biologie Intégrée du Tissu Osseux, Université de Lyon, St-Etienne, France;
authors.forename: Norbert
authors.initials: N
authors.lastname: Laroche
authors.affiliation: Laboratory of Connective Tissues Biology, Groupe Interdisciplinaire de Génoprotéomique Appliqué (GIGA), Université de Liège, Sart Tilman, Belgium; and.
authors.forename: Charles
authors.initials: C
authors.lastname: Lambert
authors.affiliation: Laboratory of Connective Tissues Biology, Groupe Interdisciplinaire de Génoprotéomique Appliqué (GIGA), Université de Liège, Sart Tilman, Belgium; and.
authors.forename: Christophe
authors.initials: C
authors.lastname: Deroanne
authors.affiliation: Laboratory of Connective Tissues Biology, Groupe Interdisciplinaire de Génoprotéomique Appliqué (GIGA), Université de Liège, Sart Tilman, Belgium; and.
authors.forename: Betty
authors.initials: B
authors.lastname: Nusgens
authors.affiliation: European Space Research and Technology Center (ESTEC), Human Spaceflight and Operations (HSO), Biological Science Unit (BSU), Noordwijk, The Netherlands.
authors.forename: René
authors.initials: R
authors.lastname: Demets
authors.affiliation: Laboratory of Connective Tissues Biology, Groupe Interdisciplinaire de Génoprotéomique Appliqué (GIGA), Université de Liège, Sart Tilman, Belgium; and.
authors.forename: Alain
authors.initials: A
authors.lastname: Colige
authors.affiliation: Institute National de la Santé et de la Recherche Médicale (INSERM), Unité 1059, Laboratoire de Biologie Intégrée du Tissu Osseux, Université de Lyon, St-Etienne, France;
authors.forename: Laurence
authors.initials: L
authors.lastname: Vico
mesh_terms: D000199:Actins / Q000378:metabolism; D002468:Cell Physiological Phenomena; D002478:Cells, Cultured; D003599:Cytoskeleton / Q000378:metabolism; D018466:Gravity Sensing; D006801:Humans; D040542:Mechanotransduction, Cellular; D008870:Microtubules / Q000378:metabolism; D010006:Osteoblasts / Q000166:cytology / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics*; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D013026:Space Flight; D042461:Vascular Endothelial Growth Factor A / Q000235:genetics / Q000378:metabolism; D014893:Weightlessness; D020764:cdc42 GTP-Binding Protein / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D020830:rac1 GTP-Binding Protein / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D020742:rhoA GTP-Binding Protein / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*
chemical_list: D000199:Actins; C107953:RAC1 protein, human; D012333:RNA, Messenger; D034741:RNA, Small Interfering; C467484:VEGFA protein, human; D042461:Vascular Endothelial Growth Factor A; C066737:RHOA protein, human; D020764:cdc42 GTP-Binding Protein; D020830:rac1 GTP-Binding Protein; D020742:rhoA GTP-Binding Protein
keywords: Cdc42; MG-63; RhoA; VEGF; spaceflight