We provide first evidence of the differential expression of circulating miRNAs in early-stage vs late-stage knee OA-SF. Further, we provide source, release and genes/pathways regulated by identified miRNAs.

Purpose: Osteoarthritis (OA) is a degenerative joint disease characterized by the progressive breakdown of articular cartilage. While cartilage degradation remains the hallmark of OA, it is clear that all joint tissues contribute to the pathological process, however, the molecular mechanisms that drive these degenerative events remain poorly understood. This highlights the critical need to perform parallel molecular studies on articular cartilage and other OA-affected joint tissues, such as the synovium (SYN) and underlying subchondral bone (SCB). Intriguingly, an increasing number of miRNAs are being identified as novel regulators of OA disease initiation and progression, making them exciting candidates for therapeutic targets and diagnostic biomarkers. The purpose of this study is to investigate previously published candidate miRNAs, known to be dysregulated in human OA, and determine their role in extra-cartilaginous OA joint tissues. Methods: OA was induced in 10e12 week old male wild type mice by bilateral surgical destabilization of the medial meniscus (DMM). RNA from SCB from DMM and sham-operated mice was isolated by laser microdissection at 1 and 6 weeks post-surgery. RNA was also extracted from the SYN of the same mice. miRNA expression profiling of SCB and SYN was performed using Agilent miRNA microarrays. Histological measurements examining the severity of OA in the contralateral joint (including: SCB sclerosis; osteophyte size and maturity; anterior and posterior synovitis -panus presence and bone erosion, sub-synovial inflammatory cell infiltration, synoviocyte hyperplasia, and exudate) were scored by one observer blinded to surgical intervention. Results: There was no difference in SCB sclerosis between surgeries at 1 week but DMM > sham at 6 weeks (p ¼ 0.003), and DMM-6wk > DMM-1wk (p ¼ 0.04). There was no osteophyte development at 1 week but at 6 weeks they had formed in DMM only, being larger (p ¼ 0.002) and more mature (p ¼ 0.001) than sham. Anterior and posterior synovitis decreased with post-operative time after sham and DMM (1wk > 6wk, p < 0.01 for all comparisons). There was no difference between surgeries in the individual synovitis parameters in the anterior aspect of the joint at either time, other than more panus in DMM at 1 week (p ¼ 0.049). However, more severe joint inflammation in DMM compared with sham was evident by significantly higher synovitis scores in the posterior region of the joint (distant from the surgical incision) at both 1 and 6 weeks (p ¼ 0.01 and 0.03, respectively). miRNA expression analysis revealed 584 miRNAs to be differentially expressed between SYN and SCB samples (adj.p.value < 0.05). Moreover, 384 and 164 miRNAs were dysregulated between 1 and 6 week time points (adj.p.value < 0.05) in SYN and SCB, respectively. However, there were no changes in miRNA expression between DMM and sham mice at both 1 and 6 weeks post-surgery in either the SCB or SYN. Additionally, promising candidate miRNAs previously identified in human OA cartilage (for example, miR-140, miR-...