<scp>CircCOG6</scp> Suppresses Proliferation and Differentiation of Chicken Chondrocytes in Tibial Dyschondroplasia by Targeting ACVRL1 Protein

Tibial dyschondroplasia (TD) is a chronic cartilage disorder commonly found in fast-growing broiler chickens, characterized by impaired tibial development and subsequent growth retardation, which collectively compromise poultry health and production efficiency. Circular RNAs (circRNAs), a class of non-coding RNAs with covalently closed loop structures, have recently garnered increasing attention in biological research. Growing evidence suggests that circRNAs are involved in the fine-tuned regulation of TD in broiler through competitive endogenous RNA (ceRNA) networks. However, the role of circRNA in TD pathogenesis via protein-binding mechanisms remains unclear. In our previous study, we identified circCOG6 (circ_0002951), a circular RNA derived from the COG6 gene, as significantly upregulated in a Thiram-induced TD model, indicating its potential critical role in TD onset and progression. In vitro functional assays revealed that overexpression of circCOG6 suppresses proliferation and differentiation of TD chondrocytes and promotes apoptosis. Mechanistically, through AGO2-RIP, RNA pull-down, and RIP experiments, we demonstrated that circCOG6 interacts with activin receptor type-1-like (ACVRL1) to inhibit chondrocyte proliferation and differentiation, promote apoptosis, and synergistically enhance BMP/Smad signaling activation, thereby contributing to TD pathogenesis. Furthermore, in vivo studies showed that intra-articular injection of adeno-associated virus carrying shRNA targeting circCOG6 (AAV-sh-circCOG6) alleviates TD lesions in a broiler chicken. In conclusion, this study is the first to elucidate a circRNA-mediated regulatory mechanism in broiler TD via RBP-binding protein interaction, thereby enriching the TD regulatory network and offering a potential therapeutic target for its treatment.