title: Midkine-deficiency delays chondrogenesis during the early phase of fracture healing in mice.
abstract: The growth and differentiation factor midkine (Mdk) plays an important role in bone development and remodeling. Mdk-deficient mice display a high bone mass phenotype when aged 12 and 18 months. Furthermore, Mdk has been identified as a negative regulator of mechanically induced bone formation and it induces pro-chondrogenic, pro-angiogenic and pro-inflammatory effects. Together with the finding that Mdk is expressed in chondrocytes during fracture healing, we hypothesized that Mdk could play a complex role in endochondral ossification during the bone healing process. Femoral osteotomies stabilized using an external fixator were created in wildtype and Mdk-deficient mice. Fracture healing was evaluated 4, 10, 21 and 28 days after surgery using 3-point-bending, micro-computed tomography, histology and immunohistology. We demonstrated that Mdk-deficient mice displayed delayed chondrogenesis during the early phase of fracture healing as well as significantly decreased flexural rigidity and moment of inertia of the fracture callus 21 days after fracture. Mdk-deficiency diminished beta-catenin expression in chondrocytes and delayed presence of macrophages during early fracture healing. We also investigated the impact of Mdk knockdown using siRNA on ATDC5 chondroprogenitor cells in vitro. Knockdown of Mdk expression resulted in a decrease of beta-catenin and chondrogenic differentiation-related matrix proteins, suggesting that delayed chondrogenesis during fracture healing in Mdk-deficient mice may be due to a cell-autonomous mechanism involving reduced beta-catenin signaling. Our results demonstrated that Mdk plays a crucial role in the early inflammation phase and during the development of cartilaginous callus in the fracture healing process.
authors.affiliation: Institute of Orthopaedic Research and Biomechanics, University Medical Center Ulm, Ulm, Germany.
authors.forename: Melanie
authors.initials: M
authors.lastname: Haffner-Luntzer
authors.affiliation: Institute of Orthopaedic Research and Biomechanics, University Medical Center Ulm, Ulm, Germany.
authors.forename: Aline
authors.initials: A
authors.lastname: Heilmann
authors.affiliation: Institute of Orthopaedic Research and Biomechanics, University Medical Center Ulm, Ulm, Germany.
authors.forename: Anna Elise
authors.initials: AE
authors.lastname: Rapp
authors.affiliation: Institute of Orthopaedic Research and Biomechanics, University Medical Center Ulm, Ulm, Germany.
authors.forename: Simon
authors.initials: S
authors.lastname: Beie
authors.affiliation: Department of Osteology and Biomechanics, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.
authors.forename: Thorsten
authors.initials: T
authors.lastname: Schinke
authors.affiliation: Department of Osteology and Biomechanics, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Amling
authors.affiliation: Institute of Orthopaedic Research and Biomechanics, University Medical Center Ulm, Ulm, Germany.
authors.forename: Anita
authors.initials: A
authors.lastname: Ignatius
authors.affiliation: Institute of Orthopaedic Research and Biomechanics, University Medical Center Ulm, Ulm, Germany.
authors.forename: Astrid
authors.initials: A
authors.lastname: Liedert
mesh_terms: D000818:Animals; D002454:Cell Differentiation / Q000235:genetics; D002478:Cells, Cultured; D020219:Chondrogenesis / Q000235:genetics*; D016207:Cytokines / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D017102:Fracture Healing / Q000235:genetics*; D055785:Gene Knockdown Techniques; D051379:Mice; D008810:Mice, Inbred C57BL; D000078792:Midkine; D010012:Osteogenesis / Q000235:genetics*; D034622:RNA Interference; D051176:beta Catenin / Q000378:metabolism
chemical_list: D016207:Cytokines; D051176:beta Catenin; D000078792:Midkine