Mechanical overloading promotes chondrocyte senescence and osteoarthritis development through downregulating FBXW7

Abstract

ObjectivesTo investigate the role of mechanical stress in cartilage ageing and identify the mechanistic association during osteoarthritis (OA) progression.MethodsF-box and WD repeat domain containing 7 (FBXW7) ubiquitin ligase expression and chondrocyte senescence were examined in vitro, in experimental OA mice and in human OA cartilage. Mice with Fbxw7 knockout in chondrocytes were generated and adenovirus-expressing Fbxw7 (AAV-Fbxw7) was injected intra-articularly in mice. Destabilised medial meniscus surgery was performed to induce OA. Cartilage damage was measured using the Osteoarthritis Research Society International score and the changes in chondrocyte senescence were determined. mRNA sequencing was performed in articular cartilage from Fbxw7 knockout and control mice.ResultsMechanical overloading accelerated senescence in cultured chondrocytes and in mice articular cartilage. FBXW7 was downregulated by mechanical overloading in primary chondrocytes and mice cartilage, and decreased in the cartilage of patients with OA, aged mice and OA mice. FBXW7 deletion in chondrocytes induced chondrocyte senescence and accelerated cartilage catabolism in mice, as manifested by an upregulation of p16INK4A, p21 and Colx and downregulation of Col2a1 and ACAN, which resulted in the exacerbation of OA. By contrast, intra-articular injection of adenovirus expressing Fbxw7 alleviated OA in mice. Mechanistically, mechanical overloading decreased Fbxw7 mRNA transcription and FBXW7-mediated MKK7 degradation, which consequently stimulated JNK signalling. In particular, inhibition of JNK activity by DTP3, a MKK7 inhibitor, ameliorated chondrocyte senescence and cartilage degenerationConclusionsFBXW7 is a key factor in the association between mechanical overloading and chondrocyte senescence and cartilage ageing in the pathology of OA.

Correspondence on ‘Mechanical overloading promotes chondrocyte senescence and osteoarthritis development through downregulating FBXW7’ by Zhang et al

“…Thus, based on the published literature concerning both the mechanism of action of DTP3 and the role of JNK in cellular senescence, and our own experiments, there is a lack of evidence to support the conclusions made by Zhang et al 1 that the effects of DTP3 on OA development in mice that they observed are due to inhibition of JNK activation or that JNK promotes senescence. Possible explanations for the observed effects of DTP3 could be due to release of GADD45β from MKK7, which perhaps has an effect independent of MKK7 and JNK or an off-target effect of DTP3 in chondrocytes where another pathway is being altered.…”

“…The results shown in the manuscript by Zang et al 1 did not examine if DTP3 treatment inhibited JNK activity, as they proposed, by inhibition of MKK7-mediated JNK phosphorylation. This would require immunoblotting cell and/or tissue lysates with anti-phospho-JNK antibodies, a standard method used to verify inhibitors.…”

“…The recent publication in the Annals of Rheumatic Diseases by Zhang et al 1 ‘Mechanical overloading promotes chondrocyte senescence and osteoarthritis development through downregulating FBXW7’ includes conclusions that ‘inhibition of JNK activity ameliorated chondrocyte senescence and cartilage degeneration’ and ‘this study suggests that targeting FBXW7–MKK7–JNK signalling may be a novel therapeutic approach for osteoarthritis (OA) treatment’. We were surprised to see these conclusions since we found very different results in a recent study2 examining the role of JNK signalling in OA.…”

“…We were surprised to see these conclusions since we found very different results in a recent study2 examining the role of JNK signalling in OA. In that study, rather than using a chemical inhibitor that can have off-target effects, as was done in the Zhang et al study,1 we evaluated JNK knockout mice in both the DMM model of OA performed at 12 weeks of age and in the model of naturally occurring age-related OA at 18 months of age. We conducted a well-powered study with 15 mice per experimental group and extensive, blinded, histologic assessment of OA with outcome measures of cartilage damage, osteophytes and synovial hyperplasia, as well as histomorphometric measures of cartilage and subchondral bone.…”

“…The conflicting evidence that JNK signalling promoted senescence provided in the Zhang et al 1 paper was based solely on the use of a compound, DTP3, that the authors claimed to be an ‘MKK7 inhibitor’. MKK7 and MKK4 are the upstream kinases that phosphorylate and thus activate JNK.…”