Osteoarthritis
Figure 4 FBXW7 overexpression in chondrocytes alleviates experimental OA in mice. (A) Quantitative PCR analysis of COL2A1 and MMP13 in mouse primary chondrocytes treated with or without adenovirus containing FBXW7 (Ad- Fbxw7 ) under 20% elongation strain loading for 24 hours. n=6 per time point. (B) Quantitative PCR analysis of COL2A1 and MMP13 in human primary chondrocytes treated with or without Ad- Fbxw7 under 20% elongation strain loading for 24 hours. n=6 per time point. (C) Representative images and quantitative analysis of FBXW7-positive chondrocytes in the cartilage of mice intra-articularly injected with AAV-NC or AAV- Fbxw7 after DMM surgery. n=10 per group. Scale bar: 50 µm. (D) Safranin O/ fast green staining of joints from AAV- Fbxw7 and Control mice at 8 weeks after DMM surgery and quantitative analysis of the OARSI scale. n=10 per group. Scale bar: 100 µm. AAV-NC versus AAV-Fbxw7: p<0.002, 95% CI 0.5397 to 1.460. (E) Immunofluorescence staining and quantification of COL2A1, Colx, MMP13, p16 INK4a , p21 and TUNEL in chondrocytes of AAV- Fbxw7 and Control mice at 8 weeks after DMM surgery. n=10 per group. Scale bar: 50 µm. Data are shown as mean±SD. Statistical analyses were conducted using one-way analysis of variance followed by Tukey’s multiple comparison test (A–C,E), or Kruskal-Wallis test followed by Dunn’s multiple comparisons test (OARSI score (D). Boxed area is enlarged in the bottom right corner. *P<0.05, **P<0.01. AAV- Fbxw7 , adenovirus expressing FBXW7; AAV-NC, negative control; Con, control; DMM, destabilisation of the medial meniscus; FBXW7, F-box and WD repeat domain containing 7; NS, not significant, OA, osteoarthritis; OARSI, Osteoarthritis Research Society International; TUNEL, terminal deoxynucleotidyl transferase dUTP nick end labelling.
from patients undergoing total knee artificial implants has been noted, 32 but the direct relationship between the ageing process and OA development is not completely understood. 33 In the current study, we found senescent chondrocytes accumulated with age and in human OA cartilage. The presence of senescent chondrocytes near the osteoarthritic lesions, but not in intact tissue, further suggests an association between chondrocyte senescence and OA development. Additionally, mechanical over- load stimulated both primary chondrocytes and cartilage ageing in mice, indicating the interaction between biomechanics and the biological context during OA. FBXW7 has emerged as one of the substrate-recognition subunits of an SKP1-Cullin1-F-box protein (SCF)-type ubiquitin
OA. We showed that mechanical overloading stimulated chon- drocyte senescence in vitro and in mice articular cartilage, and identified FBXW7 as a key factor in the association between biomechanics and chondrocyte senescence in OA pathology. Excessive mechanical loading downregulated FBXW7 and thereby reduced FBXW7-mediated MKK7 ubiquitination and degradation. MKK7 accumulation subsequently activated JNK signalling, which promoted chondrocyte senescence and conse- quently accelerated cartilage degeneration and OA development. Supplementation of FBXW7 or inhibition of MKK7–JNK is thus a potential therapeutic target for OA treatment (figure 6D). Increasing age is strongly correlated with cartilage degener- ation and the presence of senescent cells in cartilage isolated
Zhang H, et al . Ann Rheum Dis 2022; 81 :676–686. doi:10.1136/annrheumdis-2021-221513
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