Fig. 1

OA development, indicated as cartilage changes, osteophyte formation, and changes in the synovial lining cell layer with age. A Comparison of representative knee joints in 3- and 9-month-old SAMP8 using safranin-O staining. The 9-month-old mice had severe cartilage degradation extending to the subchondral bone and osteophyte formation (*) in the medial cartilage edge compared with the 3-month-olds. B H&E staining of synovium shown in the left and right vertical rectangle in A, respectively. The synovial lining cell layer in 9-month-old mice increased compared with that in 3-month-old mice. C, D Safranin-O staining of the representative cartridge changes in the control and SAMP8. Histological observations in the tibial plateau were performed, shown in the right horizontal rectangle in A. SAMP8 had irregular and reduced safranin-O staining on the cartilage surface in the tibial plateau that gradually increased with age. E Changes in the modified Mankin score. F Changes in the OARSI score. G Changes in the osteophyte formation scores. H Changes in the synovial lining cell layer score. The data from 7- and 9-month-old SAMR1 were used as a control. *p < 0.05, **p < 0.01. Scale bars = 500 μm (A), 50 μm (B), 200 μm (C, D). (n = 6–7 per age group)