Circulating serum miR‐223‐3p and miR‐16‐5p as possible biomarkers of early rheumatoid arthritis

Summary Small non‐coding RNAs have emerged as possible biomarkers for various diseases including autoimmune diseases. A number of studies have demonstrated that the expression of specific microRNAs (miRNAs) is dysregulated in rheumatoid arthritis (RA). So far, all studies on miRNAs in RA patients have been performed using either microarray or reverse transcription–quantitative polymerase chain reaction (RT–qPCR) analyses. Compared to RT–qPCR and microarray analyses, next‐generation sequencing (NGS) allows the genome‐wide analysis of small RNAs and the differentiation between miRNAs that differ by a single nucleotide. The application of NGS to the analysis of small RNAs circulating in sera of RA patients has not been reported. This study provides a global overview of the circulating small RNAs in the sera of RA patients and healthy subjects and identifies differences between these groups using NGS. Several classes of small RNAs, including hY RNA‐derived fragments, tRNA‐derived fragments and miRNAs, were determined. Differentially expressed individual small RNAs were verified by RT‐qPCR. The levels of two miRNAs, miR‐223‐3p and miR‐16‐5p, were significantly lower in the sera from early RA patients than in those from established RA patients and healthy controls. In contrast, the serum level of miR‐16‐5p was higher in patients with established RA than in healthy control samples. These miRNAs may not only serve as biomarkers, but may also shed more light on the pathophysiology of RA.