Date: Monday, November 6, 2017
Session Type: ACR Poster Session B
Session Time: 9:00AM-11:00AM
Anti-citrullinated proteins antibodies (ACPAs) injected in mice induce IL-8 dependent bone loss and arthralgia, but no synovial changes. We hypothesized that additional stimulus, sensitizing the synovial compartment to ACPA effects, is needed for the transition from bone to synovial pathology.
Synovial biopsies were obtained from healthy volunteers and RA patients by arthroscopy. Synovial fibroblasts (SFs) were isolated from synovial tissue of RA patients by enzymatic digestion. Polyclonal ACPA and other non-ACPA IgGs were separated from peripheral blood of RA patients by affinity purification on a cyclic citrullinated peptide (CCP)-2 column. Monoclonal ACPAs were generated from synovial fluid single B-cells. SFs migration capacity was tested by scratch-assays in starved and non-starved cultures treated with ACPAs, with or without presence of IL-8. The results were evaluated by NIH ImageJ software. SF adhesion was analyzed by xCELLigence System Real-Time Cell Analyzer (ACEA bioscience). Peptidylarginine deiminases (PAD) expression and protein citrullination were evaluated by immunohistochemistry and immunofluorescence on SFs. Citrullination level of synovial biopsies were evaluated by biotinylated monoclonal ACPAs. The role of signaling pathways in the ACPA-mediated SF modulation was analyzed by using specific signal inhibitors and by monitoring protein phosphorylation using western blot.
Serum starvation of SFs increased citrullinated proteins and PAD expression. Starved but not non-starved SFs showed an increased mobility index following polyclonal ACPA stimulation to a mean±SD fold increase of 2.6±0.5. Similar effects were observed with monoclonal B09 but not C03, with a fold increase of the migration index of 1.8±0.4 for B09 antibody and 1.0±0.5 for C03 antibody. This effect was abolished by PAD inhibition as well as ACPA blocking with citrullinated but not native fibrinogen. Exogenous pro-inflammatory cytokines IL-8 and TNF induced PAD expression in SF and synergistically increased their mobility when added together with ACPA. Phosphorylation and inhibition studies of intracellular signaling pathways in starved SFs indicated an important role for PI3K-mediated signals in the ACPA-induced increase of SF mobility. Neither B09 nor C03 were binding to the non-inflammed healthy synovial tissues, while both B09 and C03 showed various degrees of binding to the inflammed RA synovial biopsies, with only B09 bidning the fibroblast cell population.
We demonstrated that some but not all ACPAs fail to activate SFs in basal conditions but have a pronounce effect on cellular stressed SF. Our findings offer a novel scenario on how a synovial insult (in this case the in vitro induced cellular stress) that will normally resolve unobserved, might be essential for the transition towards chronic synovial changes in the presence of ACPA.
To cite this abstract in AMA style:Sun M, Joshua V, Krishnamurthy A, Hensvold A, Liu Y, Catrina SB, Ospelt C, Malmström V, Steen J, Engström M, Wähämaa H, Rethi B, Catrina AI. ACPA Activate Challenged Synovial Fibroblasts through a PAD Dependent Mechanism: A Potential Explanation of the “Second Hit Model” in RA [abstract]. Arthritis Rheumatol. 2017; 69 (suppl 10). https://acrabstracts.org/abstract/acpa-activate-challenged-synovial-fibroblasts-through-a-pad-dependent-mechanism-a-potential-explanation-of-the-second-hit-model-in-ra/. Accessed December 15, 2019.
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