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

XBP1s inhibited Ubqln1 promoter activity and circUbqln1 biogenesis. Deletion of XBP1 amplified the elevation in circUbqln1 expression, facilitating the translocation of circUbqln1 into the nucleus with the assistance of p14–3–3ζ, then promoted the expression and enzyme activity of PRODH, accelerated the degradation of proline into P5C, leading to decreased collagen fiber synthesis, ultimately accelerating OA progression.