Identification of Key Regulators for Resolution of Chronic Inflammatory Arthritis through a Systems Approach

Abstract

Background/Purpose: Collagen-induced arthritis(CIA), a representative animal model of chronic inflammatory arthritis, follows phases of induction, peak of inflammation and resolution. This study aims to identify the key regulator genes that change with time course in animal models of rheumatoid arthritis through dynamics analysis.

Methods: We first investigated gene expression profiles in the synovial tissues of mice with CIA at early, peak, resolution phase of arthritis using microarray analysis and identified differentially expressed genes (DEGs) associated with arthritis resolution. We built a resolution-associated network model describing interactions among these DEGs and then selected three hub-like genes from the network model, which can significantly contribute to regulating function of the resolution-associated network. We examined the level of gene expression in the synovial tissues and the function of selected genes in resolution of CIA.

Results: From time-course gene expression profiles of CIA synovial tissues, we identified 2237 resolution-related genes, and found that these genes were significantly associated with Toll-like receptor and T and B cell receptor signaling pathways. Network analysis of these resolution-related genes further selected three hub genes, Itgb1, RPS3 and YwhaZ, that can be predominantly responsible for arthritis resolution. These genes were highly expressed in independent synovial tissues at resolution phase. Particularly, the expression of Itgb1, RPS3 and YwhaZ was elevated in regulatory T cells and alternatively-activated macrophages (M2) that are involved in restoration of chronic inflammation. Moreover, recombinant Itgb1, RPS3, and YwhaZ dose-dependently reduced pro-inflammatory cytokine expression in peritoneal macrophages and splenocytes. To test a potential application of proteins from selected genes for detecting the arthritis resolution, the levels of proteins from the selected genes also were analyzed in mice serum and urine of patients with rheumatoid arthritis (RA). As a result, serum YwhaZ concentration was higher at resolution phase than at peak phase among the three proteins from selected genes. Additionally, YwhaZ concentrations in the urine of patients with rheumatoid arthritis were associated with the degree of treatment response; YwhaZ levels increased significantly after treatment in good response group (n=23) while the protein level before and after treatment were not different in moderate (n=12) or none (n=25) response group.

Conclusion: Our comprehensive analysis of gene profile contributing to arthritis resolution reveals novel anti-arthritic genes, tgb1, RPS3, and YwhaZ. We anticipate that tgb1, RPS3 and YwhaZ will be novel targets for predict the arthritis resolution and could be therapeutic targets for choric inflammatory arthritis.