Fig. 4: Enhancing the UPR^mt with NR ameliorates DMM-induced OA in vivo.

a Safranin-O/fast green staining of the cartilage of mice in the different groups. Black arrowheads indicate articular cartilage degradation, yellow arrowheads indicate synovial hyperplasia, and red arrowheads indicate osteophytes. Scale bar, 200 μm. b Quantitative analysis of the OARSI score, c synovitis score, and d osteophyte maturity in the different groups of mice. *p < 0.05, **p < 0.01, ***p < 0.001; n = 6–8. e Micro-CT imaging of the morphological structure of the knee in mice in the different groups. Scale bar, 10 mm. f The volumes of the calcified meniscus and synovial tissue were quantified. **p < 0.01; n = 6–8. g TUNEL analysis of chondrocyte apoptosis in mouse knee cartilage. Green fluorescence indicates apoptotic cells, and blue fluorescence indicates normal chondrocytes. Scale bar, 100 μm; *p < 0.05, ***p < 0.001; n = 8–12. h Western blot analysis of MMP-13, Col2a1, ADAMTS-5, and Aggrecan expression in knee articular cartilage in the different groups. *p < 0.05 compared with the sham group; ^#p < 0.05 compared with the DMM group; NS not significant compared with the DMM group; n = 8–12. i Immunohistochemical staining of MMP-13 and Col2a1 in knee articular cartilage in the different groups. Scale bar, 100 μm; *p < 0.05 compared with the sham group; ^#p < 0.05 compared with the DMM group; NS not significant compared with the DMM group; n = 6.