Investigating immunophenotypic and transcriptional heterogeneity as biomarkers of pain centralization in rheumatoid arthritis

Over half of patients with rheumatoid arthritis (RA) report clinically meaningful pain, despite treatment with disease-modifying antirheumatic drugs (DMARDs). The prevalence of fibromyalgia, the prototypical centralized pain condition is 6-33% among RA patients, compared to 2-3% in the general population. In addition, we and others have shown that patients with RA, compared to healthy controls, have lower pressure pain thresholds in a widespread distribution, as well as abnormalities in other quantitative sensory testing (QST) measures of centralized pain. However, our ability to determine which patients will experience pain refractory to treatment is limited by our understanding of the mechanisms underlying RA-related pain centralization. There is a critical unmet need to elucidate these pathways and develop objective biomarkers to identify patients with pain centralization for enrollment into clinical trials. The objective of this high-risk, high-reward proposal is to generate cutting-edge insights into the relationship between peripheral blood mononuclear cells (PBMCs) and pain centralization in patients with RA. To test investigate potential immune biomarkers, we will use a two-step approach that leverages the capacity of: a) multi-parameter flow cytometry to discover associations between the immunophenotypic profiles of PBMCs and pain centralization and b) single-cell RNA-sequencing (scRNA-seq) to detect heterogeneity in gene expression among individual cells, with a particular interest in circulating monocytes. Our central hypothesis is that the composition and transcriptional heterogeneity of circulating immune cells will vary with centralized pain phenotype in RA patients. In Aim 1, we will determine the association between the immunophenotypic profile of PBMCs and pain centralization. We will enroll 50 RA patients with well-controlled joint inflammation but varying levels of systemic inflammation and pain to undergo QST to assess pain centralization and pro