title: Intranuclear Actin Structure Modulates Mesenchymal Stem Cell Differentiation.
abstract: Actin structure contributes to physiologic events within the nucleus to control mesenchymal stromal cell (MSC) differentiation. Continuous cytochalasin D (Cyto D) disruption of the MSC actin cytoskeleton leads to osteogenic or adipogenic differentiation, both requiring mass transfer of actin into the nucleus. Cyto D remains extranuclear, thus intranuclear actin polymerization is potentiated by actin transfer: we asked whether actin structure affects differentiation. We show that secondary actin filament branching via the Arp2/3 complex is required for osteogenesis and that preventing actin branching stimulates adipogenesis, as shown by expression profiling of osteogenic and adipogenic biomarkers and unbiased RNA-seq analysis. Mechanistically, Cyto D activates osteoblast master regulators (e.g., Runx2, Sp7, Dlx5) and novel coregulated genes (e.g., Atoh8, Nr4a3, Slfn5). Formin-induced primary actin filament formation is critical for Arp2/3 complex recruitment: osteogenesis is prevented by silencing of the formin mDia1, but not its paralog mDia2. Furthermore, while inhibition of actin, branching is a potent adipogenic stimulus, silencing of either mDia1 or mDia2 blocks adipogenic gene expression. We propose that mDia1, which localizes in the cytoplasm of multipotential MSCs and traffics into the nucleus after cytoskeletal disruption, joins intranuclear mDia2 to facilitate primary filament formation before mediating subsequent branching via Arp2/3 complex recruitment. The resulting intranuclear branched actin network specifies osteogenic differentiation, while actin polymerization in the absence of Arp2/3 complex-mediated secondary branching causes adipogenic differentiation. Stem Cells 2017;35:1624-1635.
authors.affiliation: Department of Medicine, University of North Carolina, Chapel Hill, North Carolina, USA.
authors.forename: Buer
authors.identifier: 0000-0002-0487-7817
authors.initials: B
authors.lastname: Sen
authors.affiliation: Department of Medicine, University of North Carolina, Chapel Hill, North Carolina, USA.|Department of Mechanical/Biomedical Engineering, Boise State University, Boise, Idaho, USA.
authors.forename: Gunes
authors.initials: G
authors.lastname: Uzer
authors.affiliation: Department of Orthopedic Surgery and Biochemistry and Molecular Biology, Mayo Clinic, Rochester, Minnesota, USA.
authors.forename: Rebekah M
authors.initials: RM
authors.lastname: Samsonraj
authors.affiliation: Department of Medicine, University of North Carolina, Chapel Hill, North Carolina, USA.
authors.forename: Zhihui
authors.initials: Z
authors.lastname: Xie
authors.affiliation: Department of Medicine, University of North Carolina, Chapel Hill, North Carolina, USA.
authors.forename: Cody
authors.initials: C
authors.lastname: McGrath
authors.affiliation: Department of Medicine, University of North Carolina, Chapel Hill, North Carolina, USA.
authors.forename: Maya
authors.initials: M
authors.lastname: Styner
authors.affiliation: Department of Orthopedic Surgery and Biochemistry and Molecular Biology, Mayo Clinic, Rochester, Minnesota, USA.
authors.forename: Amel
authors.initials: A
authors.lastname: Dudakovic
authors.affiliation: Department of Orthopedic Surgery and Biochemistry and Molecular Biology, Mayo Clinic, Rochester, Minnesota, USA.
authors.forename: Andre J
authors.initials: AJ
authors.lastname: van Wijnen
authors.affiliation: Department of Medicine, University of North Carolina, Chapel Hill, North Carolina, USA.|Department of Pharmacology, University of North Carolina, Chapel Hill, North Carolina, USA.
authors.forename: Janet
authors.initials: J
authors.lastname: Rubin
mesh_terms: D000199:Actins / Q000378:metabolism*; D050156:Adipogenesis / Q000187:drug effects; D000818:Animals; D002454:Cell Differentiation / Q000187:drug effects; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism*; D015638:Cytochalasin D / Q000494:pharmacology; D020868:Gene Silencing; D007211:Indoles / Q000494:pharmacology; D059630:Mesenchymal Stem Cells / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D010012:Osteogenesis / Q000187:drug effects; D047495:PPAR gamma / Q000378:metabolism; D058105:Polymerization
chemical_list: D000199:Actins; C543733:CK-0944666; D007211:Indoles; D047495:PPAR gamma; D015638:Cytochalasin D
keywords: Adipocyte; Arp2/3 complex; Branched actin network; CK666; Osteoblast; mDia1