RNA-editing enzyme ADAR1 attenuates rheumatoid arthritis via regulating fibroblast-like synoviocytes-derived exosomal...

Rheumatoid arthritis (RA) is a chronic debilitating autoimmune disorder and a predominant cause of potentially treatable functional disability. Adenosine deaminase acting on RNA 1 (ADAR1), as an RNA-editing enzyme, can regulate circular RNAs (circRNAs) and fibroblast-like synoviocytes (FLSs)-derived exosomal circFTO has been proposed as a contributor to RA. This study was dedicated to elaborate the role of ADAR1 in RA and the association between ADAR1 and circFTO. RT-qPCR examined circFTO, fat mass and obesity-associated protein (FTO), DExH-box helicase 9 (DHX9), ADAR1 and Quaking (QKI) expressions in RA-FLSs and human fibroblast-like synoviocytes (HFLSs), and circFTO expression in RA-FLSs- or HFLSs-derived exosomes. In severe combined immunodeficiency (SCID) mice engrafted with human cartilage and rheumatoid synovium tissue (SCID-HuRAg), the in vivo imaging technique was adopted to track the distribution and migration of RA-FLSs and HFLSs. H&E staining and Safranin-O staining measured the severity of RA and engrafted cartilage degradation. Immunohistochemistry assessed the expression of inflammation-, anabolic- and catabolic-related genes. Also, RT-qPCR examined the expressions of circFTO, miR-548a-3p, heterogeneous nuclear ribonucleoprotein A2B1 (hnRNPA2B1), anabolic- and catabolic-related genes. ADAR1 was lowly expressed in RA-FLSs and ADAR1 silencing reduced circFTO expression in RA-FLSs-derived exosomes. In vivo, RA-FLSs were widely distributed and the migration capability was enhanced compared with HFLSs. ADAR1 overexpression efficiently decreased arthritis severity, attenuated cartilage degradation and inflammatory response in SCID-HuRAg mice injected with RA-FLSs. Besides, ADAR1 could decrease circFTO and hnRNPA2B1 expressions while elevating miR-548a-3p expression, particularly in SCID-HuRAg mice injected with RA-FLSs. To summarize, our findings identify ADAR1 as a potential treatment target for RA at least partially via regulating circFTO.