Background/Purpose:

Idiopathic inflammatory arthritis (IA) is a T-cell driven chronic condition characterized an imbalance in cell proliferation and apoptosis leading to significant synovial hyperplasia and degradation of the underlying cartilage and bone. The exact etiology of IA is still poorly understood with studies aimed at delineating the molecular pathways driving loss of immunological tolerance to the body’s self-antigens. Naturally, there is a compelling need to identify markers of aberrant immune pathways which may advance current insights into the molecular mechanisms of IA and serve as clinical markers for disease monitoring and treatment responses. Using mass spectrometry (MS), we aim to provide a detailed analysis of the proteome and peptidome of IA synovial fluid (SF).

Methods:

SF samples were collected from 10 patients satisfying the 1987 ACR classification criteria for rheumatoid arthritis (RA), 10 patients satisfying CASPAR classification criteria for psoriatic arthritis (PsA) and 10 controls. Samples were investigated under label-free MS-based methods. Proteomic fractions underwent reduction, alkylation, and trypsin digestion while peptidomic fractions were desalted using solid-phase extraction. All samples were subjected to liquid-chromatography tandem MS followed by data extraction using MaxQuant v.1.5.2.8.

Results:

Holistic proteome mining identified a total of 419 unique proteins across all 30 SF samples, with a false discovery rate of <1.0%. Non-parametric statistical tests identified 144 IA SF-derived proteins with significant differential expression relative to the control group. Application of filtering criteria resulted in a preliminary list of 5 IA-specific candidate biomarkers, of which MMP3 and neutrophil defensin 3 have been previously investigated. Intracohort comparison of RA and PsA SF proteomes identified 4 novel RA-specific candidates and 2 PsA-specific candidates. Peptidomic profiling of IA SF identified 288 unique peptides arising from 51 unique protein precursors across all SF samples. Differential expression analyses identified peptide fragments of fibrinopeptide A (FpA), a derivative of fibrinogen alpha chain, to be significantly upregulated in IA SF. FpA peptides were predicted to have antimicrobial peptide activity according to a bioinformatic tool. Moreover, KEGG analysis identified Staphylococcus aureus infection as a significantly enriched pathway. Taken together, our peptidomic findings underscore the potential for peptides to elucidate mechanistic pathways related to the etiopathogenesis of IA, including the possible interplay of the microbiome and immune system responses.

Conclusion:

Chronic inflammation in IA is orchestrated by a complex network of signaling pathways which are expected to be represented in the protein and peptide expression patterns of SF. The use of high resolution MS facilitates the discovery of key modulators of disease which may ultimately, enable the development of novel therapeutic interventions and minimally-invasive biomarker panels. Verification and validation of chosen candidates in a new set of SF and serum samples, respectively, are currently ongoing.

« Back to 2018 ACR/ARHP Annual Meeting

ACR Meeting Abstracts - https://acrabstracts.org/abstract/resolving-the-synovial-fluid-proteome-and-peptidome-for-disease-specific-mediators-of-inflammatory-arthritis/