Session Information
Session Type: Abstract Submissions (ACR)
Background/Purpose: Rheumatoid arthritis (RA) is a chronic and progressive autoinflammatory disorder characterized by the infiltration of inflammatory cells, including B-cells, T-cells and macrophages, in the synovial membrane ultimately leading to cartilage destruction and bone erosion. Clinical disease activity in RA correlates strongly with macrophage numbers in synovial tissue and expression of macrophage-derived cytokines. Bruton’s tyrosine kinase (Btk), a downstream target of phosphatidylinositol 3-kinase, is important not only in B cell activation, but also mediates immune complex-dependent activation of monocytes. Pharmacological inhibition of Btk effectively suppresses pathology in murine models of arthritis, but potential roles for Btk in the pathology of RA have not been examined.
Methods: Expression of Btk was detected by immunohistochemistry combined with digital image analysis in synovial tissue from 19 RA and 15 PsA patients, naïve to treatment with biologicals. Immunofluorescent double labelling confocal microscopy was performed to identify which cell types express Btk in RA synovial tissue, and validating qRT-PCR and immunoblotting experiments were performed on isolated relevant cell populations. Effects of a specific Btk inhibitor, RN486, on activation-dependent IL-6 production by human macrophages (n=8) and RA synovial tissue explant cultures (n=6) were assessed by ELISA. The influence of RN486 on macrophage expression of genes related to angiogenesis, cellular adhesion, tissue remodelling and innate immune responses was determined using low density qPCR arrays.
Results: Btk was expressed at equivalent levels in patients with RA and PsA, and no relationship was observed between expression levels and patient clinical characteristics (CRP, ESR, DAS28, RF-positivity). In RA, but not PsA, there was a significant relationship between Btk expression and numbers of synovial macrophages (R= 0.57, p< 0.01), T cells (R= 0.64, p< 0.005) and fibroblast-like synoviocytes (FLS) (R= 0.56, p< 0.05) but not B cells, plasma cells, or endothelial cells. qPCR and immunoblotting experiments confirmed that Btk was expressed in B cells, monocytes, and macrophages, but not T cells or RA FLS. RN486 (1μM) inhibited macrophage IL-6 production in response to Fc receptor stimulation (40% inhibition, p< 0.01) and anti-CD40 antibodies (50%, p< 0.05), but not TNFα or LPS stimulation. qPCR analysis of human macrophages demonstrated that RN486 inhibited by more than 2-fold 12 of 21 genes induced by IgG, 11 of 52 genes induced by CD40 stimulation, and 6 of 25 genes induced by RA SF in 3 independent experiments. RN486 also inhibited spontaneous IL-6 production by cultured RA synovial explants (65%, p< 0.01).
Conclusion: Our data demonstrate that Btk is expressed in RA synovial tissue and suggest that macrophages would be the prominent synovial targets of strategies aimed at inhibiting Btk in RA. As Btk activity is needed to drive macrophage activation in response to multiple stimuli relevant to RA, and drives IL-6 production in RA synovial tissue, pharmacological targeting of Btk may be of therapeutic benefit in the treatment of RA.
Disclosure:
L. M. Hartkamp,
None;
I. E. van Es,
None;
J. S. Fine,
Hoffmann-La Roche, Inc.,
3,
Hoffmann-La Roche, Inc.,
1;
M. Smith,
Hoffmann-La Roche, Inc.,
3,
Hoffmann-La Roche, Inc.,
1;
J. Woods,
Hoffmann-La Roche, Inc.,
3,
Hoffmann-La Roche, Inc.,
1;
S. Narula,
Hoffmann-La Roche, Inc.,
3,
Hoffmann-La Roche, Inc.,
1;
J. DeMartino,
Hoffmann-La Roche, Inc.,
3,
Hoffmann-La Roche, Inc.,
1;
P. P. Tak,
GlaxoSmithKline,
3;
K. A. Reedquist,
Hoffmann-La Roche, Inc.,
2.
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ACR Meeting Abstracts - https://acrabstracts.org/abstract/brutons-tyrosine-kinase-inhibition-suppresses-inflammatory-cytokine-production-and-affects-gene-expression-in-human-macrophages-and-ra-synovial-tissue-explants/