Background Integrins are involved in regulating and controlling cellular proliferation, migration, tissue invasion, cytokine and MMP production – key mechanisms leading to joint destruction during rheumatoid arthritis (RA). In this context, integrin α11β1 (ITGA11) is of special interest, because it is mainly expressed in cellular adhesive structures of mesenchymal cells and its role in regulating cartilage degradation due to altered interactions of synovial fibroblasts with ECM components in inflammatory arthritis is still unknown.
Materials and methods ITGA11 expression levels in SF of wild type and arthritic hTNFtg mice were analysed by Western Blot (WB) and immunofluorescence as well as immunohistochemistry using paraffin-embedded hind paws. Furthermore, different extracellular matrix substrates and their influence on ITGA11 expression and its subcellular location as well as integrin down-stream signalling pathways such as FAK and src and interaction partners (eg, vinculin) were investigated using WB and immunofluorescence.
Next, we analysed isolated SF of ITGA11-/- mice in functional studies (proliferation assay, modified scratch assay and electric cell-substrate impedance sensing) to identify differences in migration and adhesion. To identify an effect of integrin α11β1 loss on expression levels of other β1 integrins e.g integrin α2β1, we performed WB and immunofluorescence analyses.
Results hTNFtg SF showed an enrichment of focal adhesions with increased and most prominent expression of ITGA11. Furthermore, ITGA11-/- SF showed a modified cytoskeleton arrangement compared to wt SF. Analyses of the functional assays showed a reduced proliferation rate of ITGA11-/- SF (−41,2% vs wt SF), an altered coating-dependent migration rate (−29,7% vs wt SF at 48 hours with fibronectin coating, −66% vs wt SF at 48 hours with collagen I coating) and adhesion capacity of ITGA11-/- SF in comparison to wt SF and an altered cell-cell and cell-matrix interaction. WB analyses showed only a slight increase of ITGA2 expression in ITGA11-/- SF compared to wt SF.
Conclusion Integrin α11β1 is induced under inflammatory conditions and contributes to the migratory and adhesive capacity of SF.