Background Cell-matrix interactions of synovial fibroblasts (SF) with cartilage components via β1 integrins are of importance not only for cartilage degradation, but also for the persistence of synovial inflammation during rheumatoid arthritis (RA). In this context, integrin α11β1 (ITGA11) is of special interest, because it is mainly expressed in cellular adhesive structures. The loss of ITGA11 leads to disturbed cell-collagen interactions, altered metalloproteinase synthesis and reduced cell proliferation.
Objectives The underlying mechanisms and the role of ITGA11 in inflammatory arthritis such as RA are of special interest, but currently unknown.
Methods Hind paws of 14-week-old wild type (wt) and hTNFtg mice, an established mouse model of RA were prepared, paraffin-embedded, sectioned and stained with a specific anti-ITGA11 antibody. Furthermore, wt and hTNFtg SF were isolated and seeded on various extracellular matrix substrates, including collagen I, fibronectin and ternary collagen complexes of articular cartilage followed by an analysis of the ITGA11 expression and its subcellular location by Western blotting and immunofluorescence. The migration capacity of wt, hTNFtg as well as SF isolated from ITGA11–/– mice was investigated in a modified scratch assay and by live cell imaging. To analyse the adhesive potential, a published cartilage attachment assay was performed, using isolated IL-1β pre-treated murine femoral head cartilage followed by incubation with wt, hTNFtg and ITGA11–/– SF.
Results In immunohistological stainigs and Western blot analyses, elevated ITGA11 levels were detected in hTNFtg SF as compared to wt SF. This was also confirmed by immunofluorescence, where hTNFtg SF showed an enrichment of focal adhesions with elevated and most prominent expression of ITGA11. ITGA11–/– SF showed a modified cytoskeleton and an altered cell morphology after cultivation on the different substrates. The most intriguing differences were detected when using the ternary collagen complexes of articular cartilage. Analyses of the functional assays showed an altered migration rate and adhesion capacity of ITGA11–/– SF in comparison to wt SF, as well in the modified scratch assay as in the cartilage attachment assay, even enforced by IL-1β stimulation.
Conclusions Our data demonstrate that integrin α11β1 is induced under inflammatory conditions such as in hTNFtg mice and contributes to the migratory and adhesive capacity of synovial fibroblasts. Therefore, integrin α11β1–/– may be an important target for therapeutic strategies in rheumatoid arthritis.
Disclosure of Interest None declared