Background/Purpose: Theta (θ) defensins are the only known macrocyclic peptides found in the Animal kingdom and are exclusively expressed in Old World monkeys. θ-defensins were discovered as antimicrobial effector molecules in rhesus macaque neutrophils, but later found to possess immune regulatory activity. Rhesus macaque theta defensin-1 (RTD-1), the prototype θ-defensin, down-regulates expression of pro-inflammatory cytokines by macrophages stimulated with TLR agonists, reduces lethality in bacteremic and severely septic mice and also dose-dependently inhibits MAP kinase and NF-κB pathways in LPS-stimulated monocytes and macrophages. We recently showed that systemic administration of RTD-1 to rats with established pristane-induced arthritis (PIA), a model of rheumatoid arthritis (RA) rapidly arrests and induces resolution of arthritis. Pathogenesis of RA involves inflammation of the synovium, joint erosion and the dysregulation of immune signaling and cytokine gene expression pathways. We hypothesized that RTD-1 regulates the gene expression and signaling pathways in inflamed synovial tissues.

Methods: PIA was induced in DA rats and RNA-seq analysis was performed on synovial tissue RNA harvested from naïve and diseased rats, and from rats with PIA that were treated with vehicle or RTD-1. Bioinformatics analysis was used to investigate changes in gene expression in treated and untreated animals. These changes in gene expression were validated by quantitative real time PCR. Ingenuity Pathway Analysis (IPA) was used to identify signaling pathway targets of RTD-1.

Results: RNA-seq analysis revealed differential expression of 258 and 107 synovial tissue genes by 3 days and 5 days of RTD-1 treatment respectively (False Discovery Rate p < 0.05; fold change > ±1.5-fold). qPCR analysis of 12 genes confirmed the RTD-1 regulation detected with RNA-seq. Bioinformatics analyses revealed that RTD-1 treatment modulates genes involved in leukocyte migration, extracellular matrix, rheumatoid arthritis, regulation of cytokine activity and in additional immune response pathways. Analysis of gene expression data by IPA identified, among others, inhibition of pathways stimulated by proinflammatory cytokines such as TNFα, IL-1β, IL-6 and activation of anti-inflammatory nuclear receptor pathways after 5 days of RTD-1 treatment, consistent with resolution of disease.

Conclusion: RTD-1 regulates genes and signaling pathways that are operative in RA and experimental arthritis and induces an anti-inflammatory gene signature in treated PIA rats. RTD-1 regulated genes and pathways include targets for FDA-approved treatments for RA underscoring the potential for RTD-1 as a future new treatment for RA.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/rhesus-theta-defensin-1-rtd-1-suppresses-disease-associated-genes-and-induces-anti-inflammatory-expression-signature-in-synovial-tissues-of-rat-model-of-rheumatoid-arthritis/