Background Synovial fibroblasts (SF) are recognized to play a vital role in the pathogenesis of rheumatoid arthritis (RA). However, their pathogenic role in osteoarthritis (OA), remains unclear despite the fact that OA SF are activated and affected during the course of the disease. To characterize the dysregulated pathways in both RA and OA several gene expression studies have been conducted mainly using microarrays and by comparing RASF to OASF. However these studies rarely include a healthy control group and do not take into account joint anatomical location.

Objectives To measure changes in the expression of microRNA (miR) as well as mRNA and long non-coding RNA (lncRNA) in SF isolated from knees of RA and OA patients compared to healthy individuals.

Methods SF were cultured from RA (n=3) and OA (n=3) patients undergoing total knee replacement. Healthy knee SF (n=3) were cultured from biopsies of individuals with arthralgia but no clinical or histological signs of synovitis. Total RNA was extracted after SF were grown for 5–7 passages and RNA sequencing was performed with the Illumina HiSeq 2000 sequencing system. Changes with a false discovery rate adjusted p-value below 0.05 were considered significantly changed. Functional annotation clustering of mRNAs was done using Database for Annotation, Visualization, and Integrated Discovery (DAVID).

Results We found 31 mRNAs, 6 lncRNA and 3 miR (miR-7–5p; miR-181a-3p; miR-378a-3p) upregulated in OASF, but not RASF compared to healthy, and 14 mRNA, 3 lncRNA and 5 miR (miR-3118; miR-514a-3p; miR-585–5p; miR-615–3p; miR-615–5p) were downregulated in knee OASF specifically.15 mRNA, 11 lncRNA and 3 miR (miR-143–3p; miR-145–3p; miR-493–3p) were upregulated in knee RASF, but not OASF compared to healthy. In this RA group 7 mRNA, 4 lncRNA and 4 miR (miR-124–5p; miR-204–5p; miR-3065–5p; miR-4657) were specifically downregulated. 29 mRNA, 6 lncRNA and 8 miR were upregulated in RA as well as OASF and 9 mRNA, 2 lncRNA and 7 miR were downregulated. Pathway analysis in mRNAs that were upregulated specifically in OA included cell adhesion pathways mainly based on the regulation of protocadherins (PCDH1; PCDHAC2). Pathways that were restricted to RA were extracellular matrix related genes such as Fraser Extracellular Matrix Complex Subunit 1 (FRAS1). The Wnt signaling pathway was regulated in both diseases, e.g. by upregulation of R-Sponding 3 (RSPO3) which has previously found to be upregulated in RASF compared to healthy SF.

Conclusions Using a next generation sequencing approach we have identified pathways and non-coding transcripts that are specifically dysregulated in OASF or RASF in the knees. These data corroborate and further elucidate the role of synovial fibroblasts in RA pathogenesis. Furthermore this study clearly demonstrates the involvement of SF in the pathogenesis of OA and identifies differences in the pathways activated in knee OA and knee RA, respectively.

Disclosure of Interest None declared