Phenotypic and functional characterization of synovial fluid-derived fibroblast-like synoviocytes in rheumatoid arthritis

Abstract

Fibroblast-like synoviocytes (FLS) play an important pathological role in persistent inflammatory joint diseases such as rheumatoid arthritis (RA). These cells have primarily been characterized in the RA synovial membrane. Here we aim to phenotypically and functionally characterize cultured synovial fluid-derived FLS (sfRA-FLS). Paired peripheral blood mononuclear cells (PBMC) and sfRA-FLS from patients with RA were obtained and monocultures of sfRA-FLS and autologous co-cultures of sfRA-FLS and PBMC were established. The in situ activated sfRA-FLS were CD34-, CD45-, Podoplanin+, Thymocyte differentiation antigen-1+. SfRA-FLS expressed uniform levels of NFкB-related pathway proteins and secreted several pro-inflammatory cytokines dominated by IL-6 and MCP-1. In a co-culture model with autologous PBMC, the ICAM-1 and HLA-DR expression on sfRA-FLS and secretion of IL-1β, IL-6, and MCP-1 increased. In vivo, human sfRA-FLS were cartilage invasive both at ipsilateral and contralateral implantation site. We conclude that, sfRA-FLS closely resemble the pathological sublining layer FLS subset in terms of surface protein expression, cytokine production and leukocyte cross-talk potential. Further, sfRA-FLS are comparable to tissue-derived FLS in their capabilities to invade cartilage at implantation sites but also spread tissue destruction to a distant site. Collectively, sfRA-FLS can serve as a an easy-to-obtain source of pathological sublining FLS in RA.

The synovial fluid fibroblast-like synoviocyte: A long-neglected piece in the puzzle of rheumatoid arthritis pathogenesis

“…These results demonstrate that SF-FLS from patients with RA share phenotypic characteristics with a pathogenic subset of sublining RA-FLS (19). However, Neidhart et al showed by flow cytometry the presence of common markers between SF-FLS and intimal lining FLS during RA including the intimal lining marker CD55 (16).…”

“…SF-FLS can be isolated from synovial fluid and grown in culture for several prolonged passages. SF is generally aspirated from the knee, wrist or elbow during an RA flare-up (16- 19,31). Centrifugation of SF gives a cell pellet, and some cells are able to adhere to tissue culture dishes.…”

“…The prevalence of positive cultures varies from a study to another. Generally, SF-FLS are obtained from 60% to 80% of SF from RA patients during the disease flare-up (16, 18,19). Neidhart et al demonstrated that the presence of RA FLS in SF can be affected by many clinical factors (16).…”

“…In order to phenotypically characterize the SF-FLS of patients with RA, Koster et al used three surface markers: podoplanin (PDPN), THY1 and CD34 (19). After a few passages, the SF-FLS cultures consist of primarily PDPN+ THY1 + CD34 − cells.…”

“…Interestingly, different FLS subsets with distinct functions have been characterized in the synovial tissue (13-15). In addition to tissue-resident cells, FLS have also been found in the synovial fluid (SF) of patients with RA (16- 19).…”