title: Mechanically induced osteogenic differentiation--the role of RhoA, ROCKII and cytoskeletal dynamics.
abstract: Many biochemical factors regulating progenitor cell differentiation have been examined in detail; however, the role of the local mechanical environment on stem cell fate has only recently been investigated. In this study, we examined whether oscillatory fluid flow, an exogenous mechanical signal within bone, regulates osteogenic, adipogenic or chondrogenic differentiation of C3H10T1/2 murine mesenchymal stem cells by measuring Runx2, PPARgamma and SOX9 gene expression, respectively. Furthermore, we hypothesized that the small GTPase RhoA and isometric tension within the actin cytoskeleton are essential in flow-induced differentiation. We found that oscillatory fluid flow induces the upregulation of Runx2, Sox9 and PPARgamma, indicating that it has the potential to regulate transcription factors involved in multiple unique lineage pathways. Furthermore, we demonstrate that the small GTPase RhoA and its effector protein ROCKII regulate fluid-flow-induced osteogenic differentiation. Additionally, activated RhoA and fluid flow have an additive effect on Runx2 expression. Finally, we show RhoA activation and actin tension are negative regulators of both adipogenic and chondrogenic differentiation. However, an intact, dynamic actin cytoskeleton under tension is necessary for flow-induced gene expression.
authors.affiliation: Bone and Joint R&D Center, VA Palo Alto Health Care System, 3801 Miranda Avenue, Palo Alto, CA 94304, USA. emily.arnsdorf@gmail.com
authors.forename: Emily J
authors.initials: EJ
authors.lastname: Arnsdorf
authors.forename: Padmaja
authors.initials: P
authors.lastname: Tummala
authors.forename: Ronald Y
authors.initials: RY
authors.lastname: Kwon
authors.forename: Christopher R
authors.initials: CR
authors.lastname: Jacobs
mesh_terms: D000199:Actins / Q000378:metabolism; D050156:Adipogenesis; D000818:Animals; D002454:Cell Differentiation; D002460:Cell Line; D020219:Chondrogenesis; D050659:Core Binding Factor Alpha 1 Subunit / Q000096:biosynthesis / Q000235:genetics; D003599:Cytoskeleton / Q000737:chemistry / Q000201:enzymology; D004790:Enzyme Induction; D045604:Extracellular Fluid; D018507:Gene Expression Regulation, Developmental; D059630:Mesenchymal Stem Cells / Q000166:cytology; D051379:Mice; D010012:Osteogenesis; D047495:PPAR gamma / Q000096:biosynthesis / Q000235:genetics; D055758:SOX9 Transcription Factor / Q000096:biosynthesis / Q000235:genetics; D013314:Stress, Mechanical; D015854:Up-Regulation; D020741:rho GTP-Binding Proteins / Q000096:biosynthesis*; D054460:rho-Associated Kinases / Q000096:biosynthesis*; D020742:rhoA GTP-Binding Protein
chemical_list: D000199:Actins; D050659:Core Binding Factor Alpha 1 Subunit; D047495:PPAR gamma; C493716:Runx2 protein, mouse; D055758:SOX9 Transcription Factor; C527933:Sox9 protein, mouse; C515855:Rock2 protein, mouse; D054460:rho-Associated Kinases; C526380:RhoA protein, mouse; D020741:rho GTP-Binding Proteins; D020742:rhoA GTP-Binding Protein