Novel role of circRSU1 in the progression of osteoarthritis by adjusting oxidative stress

Osteoarthritis (OA), characterized as an end-stage syndrome caused by risk factors accumulated with age, significantly impacts quality of life in the elderly. Circular RNAs (circRNAs) are receiving increasing attention regarding their role in OA progression and development; however, their role in the regulation of age-induced and oxidative stress-related OA remains unclear. Methods: Herein, we explored oxidative stress in articular cartilage obtained from patients of different ages. The presence of circRSU1 was detected using RNA sequencing of H(2)O(2)-stimulated primary human articular chondrocytes (HCs), and validated in articular cartilage and HCs using fluorescence in situ hybridization (FISH) staining. miR-93-5p and mitogen-activated protein kinase kinase kinase 8 (MAP3K8) were identified as interactive circRSU1 partners based on annotation and target prediction databases, and their associations were identified through dual-luciferase reporter analysis. The effect of the circRSU1-miR-93-5p-MAP3K8 axis on HCs was confirmed using western blot, quantitative real-time PCR (qRT-PCR), enzyme-linked immunosorbent assay (ELISA), immunofluorescence, and reactive oxygen species (ROS) analyses. CircRSU1 and its mutant were ectopically expressed in mice to assess their effects in destabilization of the medial meniscus (DMM) in mice. Results: We found a marked upregulation of circRSU1 in H(2)O(2)-treated HCs and OA articular cartilage from elderly individuals. circRSU1 was induced by IL-1β and H(2)O(2) stimulation, and it subsequently regulated oxidative stress-triggered inflammation and extracellular matrix (ECM) maintenance in HCs, by modulating the MEK/ERK1/2 and NF-κB cascades. Ectopic expression of circRSU1 in mouse joints promoted the production of ROS and loss of ECM, which was rescued by mutation of the mir-93-5p target sequence in circRSU1. Conclusion: We identified a circRSU1-miR-93-5p-MAP3K8 axis that modulates the progression of OA via oxidative stress regulation, which could serve as a potential target for OA therapy.