a, b, Wild-type mice underwent intra-articular injection of Ad-C or Ad-CYP7B1 and were killed three weeks later. Representative images of CYP7B1 immunostaining (a) and safranin-O staining (b). n = 9 mice per group. c, d, Sham- or DMM-operated mice underwent intra-articular injection of Ad-shControl or Ad-shCyp7b1, and were killed 8 or 12 weeks later. Representative immunostaining images of CYP7B1 in cartilage sections (c) and quantification of OA parameters (d). n = 10 mice for sham and 13 mice for DMM. e, Sham- or DMM-operated mice fed regular diet or HCD underwent intra-articular injection of Ad-shControl or Ad-shCyp7b1. The mice were killed four or six weeks after the operation, and OA parameters were quantified (n = 10 mice for sham and 11 mice for DMM). f, g, Pain assays. Sham- or DMM-operated mice underwent intra-articular injection of Ad-shControl or Ad-shCyp7b1 (n = 9 mice per group) and were subjected to von Frey (f) and hot-plate (g) assays. Means ± 95% CI with Mann–Whitney U test for OARSI grade, osteophyte maturity and von Frey assay; means ± s.e.m. with two-tailed t-test for SBP thickness and hot-plate assay (d–g). Exact P values (for P < 0.001) can be found in the accompanying Source Data. Scale bars, 25 μm.