title: The roles of Wnt signaling modulators Dickkopf-1 (Dkk1) and Dickkopf-2 (Dkk2) and cell maturation state in osteogenesis on microstructured titanium surfaces.
abstract: Osteoblast differentiation on tissue culture polystyrene (TCPS) requires Wnt/beta-catenin signaling, regulating modulators of the Wnt pathway like Dickkopf-1 (Dkk1) and Dkk2. Osteoblast differentiation is increased on microstructured titanium (Ti) surfaces compared to TCPS; therefore, we hypothesized that surface topography and hydrophilicity affect Dkk1 and Dkk2 expression and that their roles in osteoblast differentiation on Ti differs depending on cell maturation state. Human osteoblast-like MG63 cells, normal human osteoblasts (HOBs), and human mesenchymal stem cells (MSCs), as well as MG63 cells stably silenced for Dkk1 or Dkk2 were grown for 6 days on TCPS and Ti surfaces (PT [Ra<0.2 microm], SLA [Ra=4 microm], modSLA [hydrophilic-SLA]). Dkk1 and Dkk2 mRNA and protein increased on SLA and modSLA for all cell types, but exogenous rhDkk1 and rhDkk2 affected MSCs differently than MG63 cells and HOBs. Silencing Dkk1 reduced MG63 cell number on TCPS and PT, but increased differentiation on these substrates. Silencing Dkk2 reduced stimulatory effects of SLA and modSLA on osteoblast differentiation; Dkk2 but not Dkk1 restored these effects. Antibodies to Dkk1 or Dkk2 specifically blocked substrate-dependent changes caused by the proteins, demonstrating their autocrine action. This indicates major roles for Dkk1 and the canonical Wnt pathway in early-stage differentiation, and for Dkk2 and Wnt/Ca2+-dependent signaling in late-stage differentiation on microstructured and hydrophilic surfaces, during osseointegration.
authors.affiliation: Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology, 315 Ferst Drive NW, Atlanta, GA 30332-0363, USA.
authors.forename: Rene
authors.initials: R
authors.lastname: Olivares-Navarrete
authors.forename: Sharon
authors.initials: S
authors.lastname: Hyzy
authors.forename: Marco
authors.initials: M
authors.lastname: Wieland
authors.forename: Barbara D
authors.initials: BD
authors.lastname: Boyan
authors.forename: Zvi
authors.initials: Z
authors.lastname: Schwartz
mesh_terms: D019898:Autocrine Communication / Q000502:physiology; D002454:Cell Differentiation / Q000502:physiology; D002478:Cells, Cultured; D020868:Gene Silencing; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D059630:Mesenchymal Stem Cells / Q000166:cytology / Q000502:physiology; D016348:Osseointegration / Q000502:physiology; D010006:Osteoblasts / Q000166:cytology / Q000502:physiology*; D010012:Osteogenesis / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology*; D013499:Surface Properties; D014025:Titanium / Q000378:metabolism*; D051153:Wnt Proteins / Q000378:metabolism*
chemical_list: C501126:DKK1 protein, human; C498622:DKK2 protein, human; D036341:Intercellular Signaling Peptides and Proteins; D051153:Wnt Proteins; D014025:Titanium