Background/Purpose:

Lyme arthritis (LA), caused by a tick-borne spirochete Borrelia burgdorferi, usually resolves appropriately with antibiotic treatment, called antibiotic-responsive LA. However, in some patients, arthritis persists for months or years after spirochetal killing with oral and IV antibiotic therapy, called antibiotic-refractory LA. Synovial lesions in these patients show marked synovial proliferation, inflammation, and vascularization, accompanied by pathogenic autoimmunity. MicroRNAs (miRs) regulate many biological processes including inflammation, immune responses, and cell proliferation, and are effective biomarkers that may reveal molecular mechanisms of disease. Our objective here was to identify extracellular miRs (ex-miRs) in synovial fluid (SF) that distinguish regulated (responsive) from dysregulated (refractory) immune responses in LA, thereby providing insights into underlying biological processes and potential diagnostic biomarkers to distinguish between  these disease courses.

Methods:

Using an unbiased systems approach, SF was screened for the expression of 372 ex-miRs commonly found in biofluids, using qPCR, in patients with responsive LA (n=6) or refractory LA (n=5), and for comparison, in those with rheumatoid arthritis (RA, n=4) or osteoarthritis (OA, n=4). A cluster analysis algorithm (Qiagen) was used to identify ex-miR signatures present in one or more patient groups. Statistically significant differences in miR expression between groups were determined by ANOVA (p<0.05).

Results:

In SF from patients with responsive or refractory LA or RA, miRs reflective of an inflammatory signature (miR-146a, miR-155) and a vascularization signature (miR-30fam) were significantly up-regulated compared with that of OA patients. Furthermore, up-regulation of the inflammatory ex-miR signature was more pronounced (~4-6-fold higher) in patients with refractory LA than in those with responsive LA, consistent with the greater expression of inflammatory cytokines in SF of refractory patients. However, the most novel finding in refractory LA was marked up-regulation of a cell proliferation signature, which included miR-223, miR-142, and miR-17-92fam, miRs associated with oncogenesis. For miR-223 and miR-142, two of the most abundant ex-miRs, the amounts were ~3-to-6-fold greater in refractory LA compared with that in responsive LA and OA, and similar to the levels observed in RA SF. Preliminary cell culture experiments suggest that some of these ex-miRs are transferred to fibroblast-like synoviocytes where they alter target gene expression.

Conclusion:

Cell proliferation ex-miR signatures were a key component that distinguished antibiotic-refractory LA or RA from antibiotic-responsive LA or OA. Thus, in antibiotic-responsive LA, a localized inflammatory response to B. burgdorferi infection is down-regulated appropriately, whereas in antibiotic-refractory LA, the greater inflammatory response in joints appears to activate marked synovial proliferation that persists after spirochetal killing. It will be important to determine whether miR-223 and miR-142 may be used as biomarkers to identify patients at risk for a refractory disease course.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/extracellular-micrornas-in-synovial-fluid-reveal-a-marked-proliferative-signature-in-patients-with-antibiotic-refractory-lyme-arthritis/