Physical Activity Associates With Lower Systemic Inflammatory Gene Expression in Rheumatoid Arthritis

Abstract

Objective: While general population studies have shown inverse associations between physical activity and common inflammatory biomarkers, the effects of physical activity on inflammatory gene expression and signaling pathways in rheumatoid arthritis (RA) remain unknown. We aimed to determine whether physical activity independently associates with expression of inflammatory genes among people with RA.

Methods: This was a prospective observational study of adults with RA. Physical activity was measured by quantitative actigraphy over 7 consecutive days, and peripheral blood collected during the same time period was used for RNA sequencing followed by differential gene expression, pathway, and network analyses.

Results: Actigraphy and RNA sequencing data were evaluated in 35 patients. The cohort had a mean age of 56 (SD 12) years, and was 91% female, 31% White, 9% Black, 9% Asian, and 40% Hispanic. We found 767 genes differentially expressed (adjusted P < 0.1) between patients in the greatest vs lowest physical activity tertiles, after adjusting for sex, age, race, and ethnicity. The most active patients exhibited dose-dependent downregulation of several immune signaling pathways implicated in RA pathogenesis. These included CD40, STAT3, TREM-1, interleukin (IL)-17A, IL-8, Toll-like receptor, and interferon (IFN) signaling pathways. Upstream cytokine activation state analysis predicted reduced activation of tumor necrosis factor-α and IFN in the most active group. In sensitivity analyses, we adjusted for RA disease activity and physical function and found consistent results.

Conclusion: Patients with RA who were more physically active had lower expression of immune signaling pathways implicated in RA pathogenesis, even after adjusting for disease activity, suggesting that physical activity may confer a protective effect in RA.

Keywords: biomarkers; exercise; inflammation; interferon; interleukin.

Figure 1.. Differentially expressed (DE) genes in peripheral blood between RA patients in the highest and lowest tertiles of physical activity.

a) Volcano plot of DE genes depicting 365 genes up-regulated in the highest activity tertile and 402 down-regulated genes at an adjusted p-value < 0.1 with respect to the highest physical activity tertile. Genes related to immune signaling and translation are highlighted. b) Principal Component Analysis based on the DE genes demonstrates separation of patients based on tertile of physical activity. c) Ingenuity Pathway Analysis (IPA) based on differential gene expression analyses demonstrating expression of canonical signaling pathways by IPA activation Z-score. Top pathways by |Z| score and pathways related to immunity and inflammation with a |Z| > 1 depicted, with an overlap P value < 0.05. Values and related genes tabulated in (Supplementary Data X). d) Predicted activation state of upstream cytokines in the highest versus lowest physical activity tertiles. Cytokines with a |Z| > 2 plotted. Values and related genes tabulated in (Supplementary Data X).

Figure 2.. Connectivity and dose-dependent downregulation of proinflammatory genes based on physical activity tertile.

a) Network connectivity map of proinflammatory genes downregulated in the highest physical activity tertile, constructed using STRING v.11. Color bar represents the degree of connectivity based on the number of edges to which each node/gene is connected. Complete network connectivity table of all differentially expressed genes in Supplementary Data File 3. b) Boxplots depicting normalized expression of six representative immune genes correlated with physical activity tertile in a dose-dependent manner.