AB0044 ENDOTHELIAL CELL AND RHEUMATOID ARTHRITIS SYNOVIAL FIBROBLAST MIGRATION AND ADHESION ARE ALTERED BY ACTIVIN/FOLLISTATIN

Abstract

Background:Activin A and follistatin belong to an anti-inflammatory auto-regulatory cycle. Patients with rheumatoid arthritis (RA) have increased activin A levels in the synovial fluid and tissue. During inflammation, activin A is released systemically, then inducing its antagonist follistatin. This negative feedback is active in different cell types but not RA synovial fibroblasts (SF). Fibroblasts interact with endothelial cells in inflamed tissues inducing angiogenesis.Objectives:Evaluation of the role of activin A and follistatin on RASF and endothelial cell interactions.Methods:RA synovium was used for RASF isolation, HUVEC were commercially obtained. RASF and HUVEC were stimulated in mono- and coculture. Direct: RASF together with HUVEC; indirect: inserts with HUVEC separated by a membrane from RASF. Stimuli: activin A 15ng/ml, follistatin 500ng/ml, IL-1β 1ng/ml. Proliferation was analyzed by BrdU assay. RASF were Calcein-AM stained. Cells were transferred to 24-well plates after 18h stimulation. After adhesion for 1h, non-adherent cells were removed by shaking 3x for 5 min. Afterwards, fluorescent cells were quantified. For the flow-adhesion assay, HUVEC were cultured on rattail collagen coated capillary slides. HUVEC and RASF were stimulated for 4h with TNFα, TNFα+activin A or TNFα+follistatin. After stimulation, 2x10^6 RASF were resuspended in 20ml medium and sent through the capillaries. Two 1min videos were recorded (18.4ml/h, 30.5ml/h). Settings: TNFα-stimulated RASF on HUVEC stimulated wit TNFα or activin A+TNFα or follistatin+ TNFα. For migration assays, 2% FCS medium with 1x10^5 cells were placed in inserts (8µm membrane) into wells with 10% FCS (control: 2%FCS vs. 2%FCS) and stimulated with, IL-1, IL-1+activinA and IL-1+follistatin. After 16h, migrated cells were quantified. For scratch-assay 4x10^5 cells were cultured overnight, then cells were scratched and stimulated, afterwards 3 pictures per scratch were taken at start, after 10h and every 1.5h. Cells migrating into the scratch area were quantified.Results:IL-1 induced activin A in RASF and HUVEC in all settings. IL-1-induced activin A release was reduced by follistatin in HUVEC monoculture and both cocultures compared to IL-1 alone but not in RASF monoculture. IL-1-induced IL-6 release was reduced by activin A in HUVEC and indirect coculture but not in RASF monoculture and direct coculture. Follistatin did not alter IL-6 responses. IL-1 induced VEGF in RASF but not in HUVEC and was not altered by activin A. Short-term adhesion showed no significant influence of activin A or follistatin (n=4). Flow adhesion assay showed reduced adherence/rolling of RASF on HUVEC stimulated with TNFα and activin A (n=4). Migration assays showed that IL-1 decreased migration but without significant difference between the induced effects mediated by IL-1+activinA and IL-1+follistatin (n=4). Scratch assay showed increased migration in dicrect coculture with greater difference between stimulated and unstimulated cells in RASF monoculture and indirect coculture (n=4). Proliferation was not altered by activin A or follistatin.Conclusion:In direct and indirect coculture of HUVEC with RASF the effect on HUVEC was dominant leading to reduced IL-1-induced activin A release. However, the IL-1-induced IL-6 release in RASF or HUVECs was decreased by activin A in HUVEC monoculture and indirect coculture but not during cell-contact between both cell types. The direct interaction of RASF with HUVEC seems to prevent the reducing activin A effect on IL-6 release in HUVECs. Activin A seems to not to have an impact on short-term cell adhesion but first observations show, that activin A alters selectin-mediated adhesion under flow conditions. The migration assay shows that IL-1-induced effects on cell migration were enhanced by activin A and follistatin. Migration assay shows that IL-1-induced decrease on migration more prominent in indirect coculture and RASF monoculture than in direct coculture although in gap migration in the scratch assay was highest in direct coculture.Disclosure of Interests:None declared