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

Ditte Køster,Hermann Eibel,Martin R Jakobsen,Johanne Hovgaard Egedal,Bent Deleuran,Malene Hvid,Søren Lomholt,Elena Neumann,Tue Wenzel Kragstrup,Ulf Müller-Ladner,Morten Aagaard Nielsen

doi:10.1038/s41598-021-01692-7

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.

Highlights

Fibroblast-like synoviocytes (FLS) play an important pathological role in persistent inflammatory joint diseases such as rheumatoid arthritis (RA)
Fibroblast‐like synoviocytes derived from synovial fluid are phenotypically homogeneous and different from non‐pathological fibroblasts at passage 4
In support of the uniform population of passage 4 sfRA-FLS, we detected similar levels of NFκB-related pathway proteins across different RA donors (Fig. 1d). These results indicate that sfRA-FLS cultures at passage 4 are morphologically, and phenotypically homogeneous, and functionally active by releasing several inflammatory cytokines dominated by MCP-1 and IL-6 without exogenous stimulation

Summary

Introduction

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. The podoplanin (PDPN)+ Thymocyte differentiation antigen-1 (THY1)+ CD34− subset of RA-FLS located in the sublining layer undergoes a dramatic expansion and is associated with increased disease activity in R A10. These P DPN+THY1+CD34− sublining layer RA-FLS display a unique pathogenic phenotype which is linked to HLA-DR expression[11]. The accessibility of these pathological RA-FLS is limited and no alternative commercial cell line is currently a vailable[19,20]

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