Background/Purpose: Our current understanding of osteoarthritis (OA) comes mainly from late stage disease and this is partly due to when patients present with symptoms. It is therefore essential to find biomarkers indicative of OA development. One promising biomarker is circulating microRNAs, which were discovered to exist in an acellular form within the plasma and serum (1). Previous work has suggested that the level of microRNA Let7e is a potential predictor of severe hip and knee OA, with a negative correlation between expression and number of joint replacements (2). We found that microRNAs that are predicted to regulate BMP/TGFβ signalling pathways (miR24-3p and miR342-3p), are robustly expressed in the cartilage suggesting a role in the regulation of cartilage remodelling. Our current study was aimed at investigating the levels of cartilage associate candidate microRNAs in plasma of established OA.

Methods: RNA was extracted from the plasma of both end stage OA patients (mean age 69.6 years) at the point of joint replacement surgery and age/sex matched healthy controls (mean age 69.5 years) using the miRNeasy kit (Qiagen). Synovial fluid from OA patients and rheumatoid arthritis patients was extracted using the Qiagen kit. cDNA was synthesised with miScript RT kit (Qiagen). qPCR was carried out using miScript SYBR green (Qiagen) and miRNA specific primers (Qiagen). C.elegans miR-39 (Qiagen) was used as a spike in control for normalisation of RNA input.

Results: The circulating levels of miR24-3p (p <0.01), miR342-3p (p <0.05), miR-140 (p <0.05 ) and Let7e (p <0.05) were significantly decreased in OA patients (n=9) compared to healthy individuals (n=9). Evaluation of the synovial fluid showed that the levels of miR24-3p and miR342-3p were also decreased (p <0.01) in OA (n=9) compared to rheumatoid arthritis patients (n=4) suggesting a direct involvement in OA joint remodelling. Synovial fluid levels of miR-140 and Let7e were unchanged.

Conclusion: The 4 microRNAs, differentially expressed in the OA plasma, offer a potential signature that could be used as a convenient, easily accessible OA biomarker. This circulating signature is also partially reflected in the synovial fluid where miR24-3p and miR-342-3p are distinctively changed. Further studies are underway to evaluate the predictive potential of this signature in early OA.