A8.13 Syndecan-4 Function is Essential for Matrix Remodelling Under Inflammatory Conditions, But Dispensable During Embryogenesis
Authors: Jessica Bertrand, Richard Stange, Heriburg Hidding, Frank Echtermeyer, Giovanna Nalesso, Lars Godmann, Melanie Timmen, Peter Bruckner, Francesco Dell’Accio, Michael J Raschke, Thomas Pap, Rita Dreier
Journal: Annals of the Rheumatic Diseases (2013)

<h3>Objective</h3> The heparan sulphate proteoglycan syndecan-4 (Sdc4) has been associated strongly with osteoarthritis, a disease that mimics key aspects of early cartilage remodelling during endochondral ossification, but its role in embryonic and adult bone formation remains unclear. Therefore, we used <i>Sdc4 <sup>-/-</sup></i> mice to analyse the distribution and functional role of Scd4 in endochondral ossification of mouse embryos and in adult fracture repair, which recapitulates endochondral ossification, but like osteoarthritis, involves an inflammatory component. <h3>Methods</h3> <i>Sdc4</i> promoter activity was analysed in <i>Sdc4 <sup>-/-</sup> /LacZ knock-in</i> animals using β-galactosidase stainings. E16.5 embyros were used for histological (alcian blue/alizarin red) and immunohistological (PCNA, Col10a1, ADAMTS-4, BC-3, Sdc2) staining and the calcified bone area was quantified using whole mount staining of these embryos. Histological (Masson-Goldner, alcian blue) and immunohistological (Col10a1, Sdc2, PCNA) staining at day 7, 14 and 28 fracture calli were performed. These experiments were repeated with anti-TNF treatment during fracture healing. Callus size and cartilage area were quantified using image J Chondrocytes were isolated from neonatal knee joints and embyronal cartilage. Proliferation was investigated using MTT assay. Gene expression analysis for Sdc-2, Sdc-4 with and without stimulation using TNFα and WNT3a was performed using quantitative RT-PCR. <h3>Results</h3> In <i>Sdc4 <sup>-/-</sup> /LacZ knock-in</i> animals, <i>Sdc4</i> promoter activity was detectable in all stages of chondrocyte differentiation during embryogenesis. <i>Sdc4</i> deficiency inhibited chondrocyte proliferation both in vivo and in vitro, but this did not lead to a growth phenotype at birth. In contrast to embryogenesis, fracture healing in adult mice was markedly delayed in <i>Sdc4 <sup>-/-</sup></i> animals and accompanied by increased callus formation. Analysing the discrepancy between the mild embryonic and the severe adult phenotype, we found a compensatory up-regulation of <i>Sdc2</i> in the developing cartilage of <i>Sdc4 <sup>-/-</sup></i> mice that was absent in adult tissue. Stimulation of chondrocytes with Wnt3a in vitro, led to an increased expression of <i>Sdc2</i>, while stimulation with TNFα resulted in an up-regulation of <i>Sdc4</i> but a decreased expression of <i>Sdc2</i>. In consequence treatment with a blocking anti-TNF antibody during fracture healing abolished the difference in callus size between wildtype and <i>sdc4 <sup>-/-</sup></i> mice. <h3>Conclusions</h3> We conclude that Sdc4 is functionally involved in endochondral ossification and that the loss of Sdc4 impairs adult fracture healing due to the inhibition of compensatory mechanisms under inflammatory conditions.