Background Giant cell arteritis (GCA) is a common form of primary vasculitis characterised by dysfunctional vessels and inflammatory infiltration leading to luminal occlusion. It is now evident that these processes may be altered by a class of small non-coding RNAs or microRNA (miRNA), which exert their biological function through suppression of specific target genes. Abnormal miRNA expression has been demonstrated in cancer and chronic inflammatory arthritis, however to date miRNA have not been examined in GCA.
Objectives This study examines expression and regulation of miRNA in GCA.
Methods Temporal artery (TA) sections from patients positive and negative for GCA were assessed by immunohistology. Peripheral blood mononuclear cells (PBMC) from GCA positive (n=10), GCA negative (n=2) and healthy controls (n=4) were collected and expression of miR-155, miR-146a, miR-125a-3p/-5p and miR-323-3p were quantified using the Qiagen miRNA isolation kit (Qiagen) and Taqman PCR. To examine possible factors involved in regulating miRNA expression, GCA positive PBMC were cultured with candidate stimuli including Toll-like receptor (TLR) ligands- Pam3CSK4 (1 ng/ml), LPS (100 ng/ml) and pro-inflammatory cytokines- IL-1β (1 ng/ml) and TNFα (10 ng/ml). Total RNA was isolated and individual miRNA quantified by Taqman assay. In parallel IL-6, IL-8 and IL-10 were quantified in cultured supernatants by ELISA.
Results Increased miR-155 levels were demonstrated in GCA positive PBMC compared to healthy controls and GCA negative PBMC (p<0.05). No difference in expression of miR-125a-5p or miR-146a was observed. MiR-323-3p and miR-125a-3p were undetectable in all samples. Pam3CSK4 and IL-1β significantly induced miR-155 and miR-146 (p<0.05), while TNFα induced miR-146a expression (P<0.05) with no effect observed for LPS. In parallel, Pam3CSK4 and/or IL-1β significantly induced IL-6, IL-8 and IL-10 protein expression. Finally in silico analysis was used to identify putative microRNA targets which included IL-6R, IL-6 gp130 and TRAF3.
Conclusions This study demonstrates for the first time increased expression and regulation of miRNA in patients positively diagnosed for GCA suggesting potential therapeutic regulation for the treatment of GCA.
Disclosure of Interest S. Wade: None declared, M. Connolly: None declared, L. O'Neill: None declared, J. Mc Cormick: None declared, D. Veale Grant/research support: Abbvie,MSD,Pfizer,Roche, Consultant for: Pfizer,Roche, Speakers bureau: Abbott, MSD,Pfzier, Roche, C. Murphy: None declared, E. Molloy: None declared, U. Fearon: None declared