Reduced Expression of m6A Demethylases FTO and ALKBH5 in Monocytes from the Site of Inflammation in Patients with Juvenile Idiopathic Arthritis

N⁶-methyladenosine (m⁶A) has recently emerged as a post-transcriptional modulator governing cell-specific gene expression in innate immune cells, particularly in monocytes. Disruptions in m⁶A homeostasis, manifested as the altered expression of m⁶A-related proteins and m⁶A levels, have been implicated in autoimmune disorders. Perturbations in m⁶A dynamics within total Peripheral blood mononuclear cells (PBMCs) have shown strong correlations with disease severity in rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE). It remains unclear in which specific cell type(s) m⁶A homeostasis is disturbed, and also whether other rheumatic diseases such as juvenile idiopathic arthritis (JIA) show similar features. Here, we assess the involvement of m⁶A and m⁶A-regulatory proteins in JIA monocytes. Notably, the diminished expression of m⁶A-eraser proteins FTO and ALKBH5 was observed in JIA monocytes extracted from the inflamed joint. This resulted in increased m⁶A-methylated transcripts in monocytes from these patients. Correspondingly, we observed that culturing monocytes in the presence of synovial fluid from JIA inflamed joints reduced the expression of both <i>FTO</i> and <i>ALKBH5</i>. The knock-out of <i>FTO</i> in human monocytes of healthy controls increased monocyte activation, indicating the relevance of <i>FTO</i> and m⁶A in the context of JIA. These findings underscore the potential of <i>ALKBH5</i> and <i>FTO</i> expression as a biomarker in JIA and identify the m⁶A machinery as a potential therapeutic target for the treatment of JIA and possibly other autoimmune diseases in the future.