Background Giant cell arteritis (GCA) is a common form of primary vasculitis characterised by dysfunctional vessels and inflammatory infiltration leading to luminal occlusion. Toll-Like receptor-2 (TLR2) has been implicated in the pathogenesis of GCA; however, the mechanisms involved have yet to be elucidated.
Objectives This study examines the mechanistic role of TLR2 activation in regulating the pro-inflammatory mechanisms in GCA.
Methods Temporal artery (TA) sections from patients positive and negative for GCA were assessed for TLR2 expression by immunohistology. Ex-vivo TA explant cultures were stimulated with Pam3CSK4 (TLR2 agonist) (1ug/ml) for 24 hrs. VEGF, Ang2, IL-6, IL-8 and MMP2/9 expression was quantified in cultured supernatants by ELISA and gelatin zymography. The effect of Pam3CSK4-induced GCA TA explant conditioned media on endothelial cell (dHMVEC) function was assessed by angiogenic assays. GCA TA explant myofibroblast outgrowth was assessed using matrigel assays (1-20 days)1. Finally the effect of GCA TA explant conditioned media on Human embryonic kidney (HEK)-TLR2 cells was quantified by NFκB luciferase reporter assays.
Results TLR2 expression was higher in positive versus negative TA sections. Pam3CSK4 significantly increased VEGF, IL-6 and IL-8 expression (all p<.0.05), with differential effects observed for Ang2 and MMP2/9 in TA explant cultures. Pam3CSK4-induced GCA TA conditioned media promoted dHMVEC tube formation (p<0.05). Pam3CSK4 induced myofibroblast outgrowths from GCA TA explants embedded in matrigel. Finally GCA TA conditioned media induced TLR2 activation through induction of NF-κB activation in HEK-TLR2 cells (p<0.05), confirming the presence of endogenous ligands for TLR2 at the site of inflammation in GCA.
Conclusions Using ex-vivo TA explant cultures, TLR2 activation induced angiogenic and invasive functional mechanisms in GCA. Furthermore activation of TLR2 by GCA TA conditioned media, suggests that TLR2 may represent a potential therapeutic target for GCA.
Lozano E, Segarra M, García-Matínez A, Hernández-Rodríguez J, Cid MC. (2008) Imatinib mesylate inhibits in vitro and ex vivo biological responses related to vascular occlusion in giant cell arteritis. Ann Rheum Dis., 67(11): 1581-8.
Disclosure of Interest A. Maher: None Declared, D. Molloy: None Declared, J. McCormick: None Declared, L. O’Neill: None Declared, D. Veale Grant/research support from: Abbott, Opsona, Pfizer, Roche, Consultant for: MSD, Pfizer, Roche, Speakers bureau: Janssen, MSD, Pfizer, UCB, C. Murphy: None Declared, U. Fearon: None Declared, E. Molloy: None Declared
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