Objective To evaluate microRNA expression in synovial fluid (SF), plasma and leukocytes from patients with juvenile idiopathic arthritis (JIA). Methods MicroRNA expression in pooled JIA plasma and SF was assessed by absolute quantitative droplet digital (dd)PCR array. The results were validated in individual patient samples. MicroRNA content in leukocytes and extracellular vesicles was evaluated by real-time PCR in JIA blood and SF. Blood microRNA expression was compared with healthy controls. Principal component analysis was used to profile JIA plasma and SF microRNAs, and the potential biological consequences of microRNA dysregulation were investigated by pathway analysis. Results MiR-15a-5p and miR-409-3p levels were higher in JIA plasma than in healthy control plasma. JIA SF contained elevated levels of miR-21-5p, miR-27a-3p, miR-146b-5p, miR-155-5p and miR-423-5p, and decreased miR-192-5p and miR-451a, compared to JIA plasma. Extracellular vesicle analysis demonstrated variable encapsulation among selected microRNAs, with only miR-155-5p being represented substantially in extracellular vesicles. SF leukocytes also had higher expression of miR-21-5p, miR-27a-3p, miR-146b-5p and miR-155-5p, and lower expression of miR-409-3p and miR-451a, relative to blood. No differences were observed between JIA and healthy control blood leukocytes. Clusters of microRNAs were commonly altered in JIA joint fluid and leukocytes compared to JIA blood samples. In silico analysis predicted that differentially expressed microRNAs in JIA target the TGF-β pathway. Conclusion The expression of multiple microRNAs is dysregulated in JIA both locally and systemically, which may inhibit the TGF-β pathway. These findings advance our knowledge of JIA immunopathogenesis and may lead to the development of targeted therapies.

Background Juvenile Idiopathic Arthritis (JIA) is the most prevalent chronic pediatric rheumatic disorder. In joints of JIA patients, aggressive phenotypic changes in fibroblast-like synoviocytes (FLS) of the synovial lining play a key role in inflammation. MicroRNAs are dysregulated in rheumatoid arthritis and JIA, including miR-27a-3p. However, it is not understood if miR-27a-3p, enriched in JIA synovial fluid (SF) and leukocytes, alters FLS function. Methods Primary JIA FLS cells were transfected with a miR-27a-3p mimic or a negative control microRNA (miR-NC) and stimulated with pooled JIA SF or inflammatory cytokines. Viability and apoptosis were analyzed by flow cytometry. Proliferation was evaluated using a 3H-thymidine incorporation assay. Cytokine production was assessed by qPCR and ELISA. Expression of TGF-β pathway genes was determined using a qPCR array. Results MiR-27a-3p was constitutively expressed in FLS. Overexpression of miR-27a-3p caused increased interleukin-8 secretion in resting FLS, and interleukin-6 was elevated in SF-activated FLS compared to miR-NC. Furthermore, stimulation with pro-inflammatory cytokines augmented FLS proliferation in miR-27a-3p-transfected FLS relative to miR-NC. Expression of multiple TGF-β pathway genes was modulated by overexpression of miR-27a-3p. Conclusions MiR-27a-3p significantly contributes to FLS proliferation and cytokine production, making it a potential candidate for epigenetic therapy that targets FLS in arthritis.