title: The anaphylatoxin receptor C5aR is present during fracture healing in rats and mediates osteoblast migration in vitro.
abstract: BACKGROUND
  There is evidence that complement components regulate cytokine production in osteoblastic cells, induce cell migration in mesenchymal stem cells, and play a regulatory role in normal enchondral bone formation. We proved the hypothesis that complement might be involved in bone healing after fracture.
  
  
  METHODS
  We investigated the expression of the key anaphylatoxin receptor C5aR during fracture healing in rats by immunostaining after 1, 3, 7, 14, and 28 days. C5aR expression was additionally analyzed in human mesenchymal stem cells (hMSC) during osteogenic differentiation, in human primary osteoblasts, and osteoclasts by reverse transcriptase polymerase chain reaction and immunostaining. Receptor functionality was proven by the migratory response of cells to C5a in a Boyden chamber.
  
  
  RESULTS
  C5aR was expressed in a distinct spatial and temporal pattern in the fracture callus by differentiated osteoblast, chondroblast-like cells in cartilaginous regions, and osteoclasts. In vitro C5aR was expressed by osteoblasts, osteoclasts, and hMSC undergoing osteogenic differentiation. C5aR was barely expressed by undifferentiated hMSC but was significantly induced after osteogenic differentiation. C5aR activation by C5a induced strong chemotactic activity in osteoblasts, and in hMSC, which had undergone osteogenic differentiation, being abolished by a specific C5aR antagonist. In hMSC, C5a induced less migration reflecting their low level of C5aR expression.
  
  
  CONCLUSIONS
  Our in vitro and in vivo results demonstrated the presence of C5aR in bone forming osteoblasts and bone resorbing osteoclasts. It is suggested that C5aR might play a regulatory role in fracture healing in intramembranous and in enchondral ossification, one possible function being the regulation of cell recruitment.
authors: Institute of Orthopaedic Research and Biomechanics, Department of Traumatology, Hand-, Plastic-, and Reconstructive Surgery, Center of Surgery, University of Ulm, Ulm, Germany. anita.ignatius@uni-ulm.de
authors: Anita
authors: A
authors: Ignatius
authors: Christian
authors: C
authors: Ehrnthaller
authors: Rolf E
authors: RE
authors: Brenner
authors: Ludwika
authors: L
authors: Kreja
authors: Philipp
authors: P
authors: Schoengraf
authors: Patricia
authors: P
authors: Lisson
authors: Robert
authors: R
authors: Blakytny
authors: Stefan
authors: S
authors: Recknagel
authors: Lutz
authors: L
authors: Claes
authors: Florian
authors: F
authors: Gebhard
authors: John D
authors: JD
authors: Lambris
authors: Markus
authors: M
authors: Huber-Lang
mesh_terms: D000328:Adult; D000818:Animals; D002454:Cell Differentiation / Q000502:physiology; D002465:Cell Movement / Q000502:physiology*; D002478:Cells, Cultured; D017102:Fracture Healing / Q000502:physiology*; D006801:Humans; D008297:Male; D059630:Mesenchymal Stem Cells / Q000502:physiology; D010006:Osteoblasts / Q000502:physiology*; D010010:Osteoclasts / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D060888:Real-Time Polymerase Chain Reaction; D044087:Receptor, Anaphylatoxin C5a / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013997:Time Factors; D055815:Young Adult
chemical_list: D044087:Receptor, Anaphylatoxin C5a