Btk inhibition suppresses agonist-induced human macrophage activation and inflammatory gene expression in RA synovial tissue explants.
OBJECTIVE
Bruton's tyrosine kinase (Btk) is required for B lymphocyte and myeloid cell contributions to pathology in murine models of arthritis. Here, we examined the potential contributions of synovial Btk expression and activation to inflammation in rheumatoid arthritis (RA).


METHODS
Btk was detected by immunohistochemistry and digital image analysis in synovial tissue from biologically naive RA (n=16) and psoriatic arthritis (PsA) (n=12) patients. Cell populations expressing Btk were identified by immunofluorescent double labelling confocal microscopy, quantitative (q-) PCR and immunoblotting. The effects of a Btk-specific inhibitor, RN486, on gene expression in human macrophages and RA synovial tissue explants (n=8) were assessed by qPCR, ELISA and single-plex assays.


RESULTS
Btk was expressed at equivalent levels in RA and PsA synovial tissue, restricted to B lymphocytes, monocytes, macrophages and mast cells. RN486 significantly inhibited macrophage IL-6 production induced by Fc receptor and CD40 ligation. RN486 also reduced mRNA expression of overlapping gene sets induced by IgG, CD40 ligand (CD40L) and RA synovial fluid, and significantly suppressed macrophage production of CD40L-induced IL-8, TNF, MMP-1 and MMP-10, LPS-induced MMP-1, MMP-7 and MMP-10 production, and spontaneous production of IL-6, PDGF, CXCL-9 and MMP-1 by RA synovial explants.


CONCLUSIONS
Btk is expressed equivalently in RA and PsA synovial tissue, primarily in macrophages. Btk activity is needed to drive macrophage activation in response to multiple agonists relevant to inflammatory arthritis, and promotes RA synovial tissue cytokine and MMP production. Pharmacological targeting of Btk may be of therapeutic benefit in the treatment of RA and other inflammatory diseases.
Department of Experimental Immunology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands Department of Clinical Immunology and Rheumatology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
Linda M
LM
Hartkamp
Department of Inflammation Discovery, Hoffmann-La Roche, Inc., Nutley, New Jersey, USA.
Jay S
JS
Fine
Department of Experimental Immunology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands Department of Clinical Immunology and Rheumatology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
Inge E
IE
van Es
Department of Experimental Immunology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands Department of Clinical Immunology and Rheumatology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
Man Wai
MW
Tang
Department of Inflammation Discovery, Hoffmann-La Roche, Inc., Nutley, New Jersey, USA.
Michael
M
Smith
Department of Inflammation Discovery, Hoffmann-La Roche, Inc., Nutley, New Jersey, USA.
John
J
Woods
Department of Inflammation Discovery, Hoffmann-La Roche, Inc., Nutley, New Jersey, USA.
Satwant
S
Narula
Department of Inflammation Discovery, Hoffmann-La Roche, Inc., Nutley, New Jersey, USA.
Julie
J
DeMartino
Department of Clinical Immunology and Rheumatology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands GlaxoSmithKline, Stevenage, and University of Cambridge, Cambridge, UK.
Paul P
PP
Tak
Department of Experimental Immunology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands Department of Clinical Immunology and Rheumatology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
Kris A
KA
Reedquist
D000328:Adult; D000077329:Agammaglobulinaemia Tyrosine Kinase; D000368:Aged; D001172:Arthritis, Rheumatoid / Q000235:genetics / Q000378:metabolism*; D001402:B-Lymphocytes / Q000378:metabolism; D005260:Female; D015870:Gene Expression; D006801:Humans; D007150:Immunohistochemistry; D015850:Interleukin-6 / Q000378:metabolism; D007546:Isoquinolines / Q000494:pharmacology*; D008264:Macrophages / Q000187:drug effects; D008297:Male; D008407:Mast Cells / Q000378:metabolism; D018613:Microscopy, Confocal; D008875:Middle Aged; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors* / Q000187:drug effects / Q000378:metabolism; D013583:Synovial Membrane / Q000378:metabolism*
D015850:Interleukin-6; D007546:Isoquinolines; C000588993:RN486; D011505:Protein-Tyrosine Kinases; D000077329:Agammaglobulinaemia Tyrosine Kinase; C000625949:BTK protein, human
Chemokines; Cytokines; Inflammation; Rheumatoid Arthritis