Cia5a Regulates the Synovial Expression of Pro-inflammatory Cytokines, Proteases, and Nuclear Receptors

Abstract

Background: The Cia5a locus regulates disease severity and joint damage in pristane-induced arthritis (PIA). Synovial transcriptome differences between DA (severe disease) and DA.F344(Cia5a) congenic rats (mild disease) could facilitate the identification of the Cia5a gene and point to novel pathways involved in the regulation of arthritis severity and joint damage. Methods: RNA from DA (n=6) and DA.F344 (Cia5a) (n=8) synovial tissue collected 21 days post-PIA was used for cRNA transcription and labeling. Samples were hybridized to RatRef-12 BeadChips (21,922 genes), scanned on a BeadArray reader, and normalized using BeadStudio 2.0 (Illumina). Genes with a difference between DA and DA.F344 (Cia5a) of ≥1.5-fold and P value≤0.01 (t-test) were used for pathway detection analyses using IPA 5.5.1 (Ingenuity) and NCBI databases. Results: A total of 8029 genes were expressed in all DA.F344(Cia5a) and DA samples. A total of 1416 genes were significantly up-regulated in DA, including cytokines (Il18 and Ltb), cytokine receptors (Ifngr1, Ifngr2, and Il17ra), innate immunity mediators (Tlr2, Fcer1g, Fcgr3a, and Ncf1), proliferation and survival genes (Apaf1, Casp3, and Cdc2), and proteases (Mmp3, Mmp14, and Mmp19). A total of 1281 genes were up-regulated in synovial samples from DA.F344(Cia5a) congenics, including nuclear receptors (Pparg, Lxra, Lxrg, Rxrg, and Rora) and lipid metabolism genes. A total of 83 differentially expressed genes mapped to the Cia5a interval. Conclusions: F344 alleles at Cia5a are associated with significant reduction of inflammatory and proliferative gene expression signatures observed in DA, and with increased expression of anti-inflammatory nuclear receptors. These observations suggest a potential role for the Cia5a gene in maintaining synovial homeostasis and limiting the synovial inflammatory response that contributes to articular damage.