Background Rheumatoid arthritis (RA) is a chronic polyarticular inflammatory disease, in which RA synovial fibroblasts (SF) play a key role. These cells are able to migrate long distances in vivo via the vasculature as previously shown in our SCID mouse migration model. Adipose tissue, as an endocrine organ, plays an important role in inflammatory processes. Some of its effects may be mediated by adipokines, which can also act as immunomodulatory factors. In RA, these adipokines have been shown to affect RASF and endothelial cells (EC). The interaction between RASF and EC may be a crucial process in the migration of RASF through the vasculature.
Objectives To investigate whether adipokines affect the adhesion of RASF to EC under flow conditions simulating the in vivo situation in blood vessels and to identify relevant adhesion molecules whose expression is altered by adipokines, glucocorticoids and methotrexate.
Methods RASF adhesion to EC was studied under flow conditions (flow rates: 18.4/30.5/60.5 ml/h) in a dynamic adhesion assay as flow conditions are required for selectins to be obtain their active conformation. The expression of selected adhesion molecules from RASF and EC was analyzed by real-time PCR. For this purpose, primary RASF and EC were stimulated with adiponectin (10 μg/ml), visfatin (100 ng/ml) and resistin (20 ng/ml), and “therapeutically” with methotrexate (1.5 μM) and the glucocorticoids prednisolone (1 μM) and dexamethasone (1 μM).
Results Using the dynamic adhesion assay to simulate the blood flow in vivo, RASF showed an increased adhesion to EC after stimulation with visfatin (+156%/+87%/+89%) and TNF-α (+61%/+18%+19%). Dexamethasone (-9%/-39%/-53%) and prednisolone (-31%/-64%/-53%) on the other hand decreased the adhesion of RASF to EC. The expression of integrin α2 was upregulated after stimulation with resistin (2.8-fold; n=7) and TNF-α (13-fold; n=6). Only TNF-α increased the expression of ICAM-1 (40-fold; n=5) in RASF, while both visfatin (2.9-fold; n=10) and TNF-α (59-fold; n=9) increased the expression of VCAM-1 in RASF. In EC, TNF-α upregulated the expression of ICAM-1 (47-fold; n=9), while adiponectin decreased it (-2.9-fold; n=5). The expression of VCAM-1 was slightly decreased after stimulation with adiponectin (-1.3-fold; n=5) in EC, whereas TNF-α led to a strong upregulation (235-fold; n=7). P- Selectin was down-regulated after stimulation with TNF-α (-8.6-fold; n=7) in EC.
Conclusions Under dynamic flow conditions, adipokines increase the adhesion of RASF to EC. Adhesion of RASF to EC most likely plays a role in the migration of RASF in vivo. The influence of adipokines on adhesion molecules and their strengthening effect on adhesion of RASF to EC could therefore enhance the migration of RASF and thus the spreading of RA to different joints. Glucocorticoids showed the opposite effect, which could explain some of the benefits observed in patients. The expression of adhesion molecules is influenced by adipokines. Yet, how they influence these expressions appears to differ between RASF and EC.
Disclosure of Interest None declared