Circular RNA circNFKB1 promotes osteoarthritis progression through interacting with ENO1 and sustaining NF-kappa B signaling

Inflammatory cytokines-induced activation of the nuclear factor kappa B (NF-kappa B) pathway plays a critical role in the pathogenesis of osteoarthritis (OA). Circular RNA (circRNA) has been identified as important epigenetic factor in numerous diseases. However, the biological roles of inflammation-related circRNAs in regulating OA pathogenesis remain elusive. Here, we revealed circRNA expression profiles in human primary chondrocytes with interleukin-1 beta (IL-1 beta) stimulation by circRNA sequencing. We identified a highly upregulated circRNA, termed as circNFKB1 in inflamed chondrocytes and osteoarthritic cartilage. As a circRNA derived from exon 2-5 of NFKB1, circNFKB1 is located in both cytoplasm and nucleus of chondrocytes. Furthermore, knockdown of circNFKB1 inhibited extracellular matrix (ECM) catabolism and rescued IL-1 beta impaired ECM anabolism whereas ectopic expression of circNFKB1 significantly promoted chondrocytes degradation in vitro. Moreover, intraarticular injection of adenovirus-circNFKB1 in mouse joints triggered spontaneous cartilage loss and OA development. Mechanistically, circNFKB1 interacted with alpha-enolase (ENO1), regulated the expression of its parental gene NFKB1 and sustained the activation of NF-kappa B signaling pathway in chondrocytes. Therefore, this study highlights a novel ENO1-interacting circNFKB1 in OA pathogenesis, and provides valuable insights into understanding the regulatory mechanism of NF-kappa B signaling in chondrocytes and a promising therapeutic target for the treatment of OA.