Anti-citrullinated protein antibodies suppress let-7a expression in monocytes from patients with rheumatoid arthritis and facilitate the inflammatory responses in rheumatoid arthritis.

We hypothesized that anti-citrullinated protein antibodies (ACPAs) could affect the expression of miRNAs in monocytes and contribute to the inflammatory responses in rheumatoid arthritis (RA). The expression profiles of 270 human miRNAs, co-cultured with ACPAs or human immunoglobulin G (IgG), were analyzed using real-time polymerase chain reaction. Ten miRNAs exhibited differential expression in U937 cells after co-cultured with ACPAs compared with human IgG. The expression levels of these miRNAs were investigated in monocytes from 21 ACPA-positive RA patients and 13 controls. Among these miRNAs, the expression levels of let-7a was decreased in monocytes from ACPA-positive RA patients. The expression levels of let-7a showed a negative correlation with positivity of rheumatoid factor in patients sampled. We found that transfection of U937 cells with let-7a mimic suppressed K-Ras protein expression. In the ACPA-mediated signaling pathway, transfection of U937 cells with let-7a mimic suppressed the ACPA-enhanced phosphorylation of c-Jun N-terminal kinase (JNK), extracellular signal-regulated kinase 1/2 (ERK1/2), and the expression and secretion of interleukin (IL)-1β. In conclusion, ACPA-mediated decreased let-7a expression in monocytes from ACPA-positive RA patients. Decreased let-7a expression was associated with the positivity of RF in ACPA-positive RA patients. The decreased expression of let-7a could facilitate the inflammatory pathway via enhanced ACPA-mediated phosphorylation of ERK1/2 and JNK and increased expression of IL-1β through an increase in the expression of Ras proteins.