The circUbqln1, regulated by XBP1s, interplays with 14–3–3ζ to inhibit collagen synthesis and promote osteoarthritis by controlling PRODH activity and proline metabolism

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IntroductionOsteoarthritis (OA) is a degenerative bone disease associated with ageing, characterized by joint pain, stiffness, swelling and deformation. Currently, pharmaceutical options for the clinical treatment of OA are very limited. Circular RNAs(cirRNAs) have garnered significant attention in OA and related drug development due to their unique RNA sequence characteristics.Therefore,exploring the role of cirRNAs in the occurrence and development of OA is of paramount importance for the development of effective medications for OA. ObjectivesTo identify a novel circRNA, circUbqln1, for treating osteoarthritis and elucidate its pathophysiological role and mechanisms in the treatment of OA. MethodsThe circUbqln1 expression and distribution were determined by qRT-PCR and FISH. XBP1 gene knockout(XBP1 cKO) spontaneous OA and DMM model and WT mouse CIOA model were used to explore the role of XBP1 and circUbqln1 in OA.Overexpression or knockdown of circUbqln1 lentivirus was used to observe the impacts of circUbqln1 on primary chondrocytes,C28/I2 and mice in vitro and in vivo.Chromatin immunoprecipitation,luciferase reporter assay,RNA pulldown,mass spectrometry,RNA immunoprecipitation,fluorescence in situ hybridization,and flow cytometry to explore the molecular mechanisms of circUbqln1. ResultsIt was found that cartilage-specific XBP1 cKO mice exhibited a faster OA progression compared to normal’s.Importantly,transcript factor XBP1s has the capacity to impede the biogenesis of circUbqln1,derived from Ubqln1. The circUbqln1 promotes cartilage catabolism and inhibits anabolism, therefore accelerates the occurrence of OA.Mechanismly,circUbqln1 can translocate to the chondrocyte nucleus with the assistance of phosphorylated 14–3–3ζ, upregulate the transcriptional activity of the proline dehydrogenase(Prodh) promoter and PRODH enzyme activity. Consequently, this leads to the promotion of proline degradation and the inhibition of collagen synthesis,ultimately culminating in the impairment of cartilage and its structural integrity. ConclusionCircUbqln1 plays a crucial role in the occurrence and development of OA, indicating that the inhibition of circUbqln1 holds promise as a significant approach for treating OA in the future.