Background Systemic sclerosis (SSc) is characterised by fibroblast-mediated progressive skin fibrosis. Subsequent involvement of internal organs leads to severe impairments of their function and lung fibrosis represents the most common cause of death in SSc. Molecular mechanisms of the spreading of SSc are largely unknown. Recent results showed the migratory potential of rheumatoid arthritis (RA) synovial fibroblasts (SFs). Based on these results, the aim of this study was the analysis of migratory and adhesive properties of SSc dermal fibroblasts (DFs) and their role in SSc-spreading with focus on organ involvement.
Methods SScDFs (in part GFP-transfected) were injected intracutaneously into SCID mice. After 14–25 days, parts of the skin, internal organs and blood were analysed. Besides fluorescence analysis, immunohisto- and -cytochemistry was performed using species-specific antibodies to detect human cells. To avoid cross-reactivity of the antibodies, additional real time PCR analysis with primers for human β2-microglobulin was performed after RNA isolation out of the respective organs and subsequent reverse transcription.
To analyse and to compare the adhesive behaviour of SScDFs with fibroblasts from other diseases and origins, multi-well culture plates were coated with Matrigel® (MG), growth factor-reduced (GFR) MG, or remained untreated. Cellular adhesion of SScDFs (n = 5), RASFs (n = 5), RADFs (n = 5), SFs (n = 2) and DFs of healthy individuals (n = 4) was analysed.
Results SScDFs or human cDNA, respectively, were not detected in any internal organ by fluorescence analysis, immunohistochemistry or real time PCR. Human SScDFs and human cDNA were only detectable in the murine skin at the injection site.
Fibroblasts of SSc patients, healthy SFs and DFs showed an increased adhesion to GFR MG compared to MG (SSc: GFR MG: 8.5 fold, MG: 8.2 fold; healthy SFs: GFR MG: 6.6 fold, MG: 4 fold; healthy DFs: GFR MG: 10 fold, MG: 7.6 fold). In contrast a reduction of cellular adhesion of RASFs (GFR MG: 4 fold, MG: 5.4 fold) and RADFs (GFR MG: 4.4 fold, MG: 4.8 fold) to GFR MG was observed compared to MG.
Discussion According to present knowledge and in comparison to results obtained from RASFs, SScDFs do not show the ability to migrate from their application site to internal organs. Adhesive properties do not differ from healthy controls. Nevertheless, SScDFs are mediators of organ fibrosis, but it seems that there is no contribution of SScDFs to the spreading of the disease.