| Summary: | Osteoarthritis (OA) is a degenerative joint disease that has no disease- modifying drug licenced for its treatment. Mechanical injury of cartilage is a principal risk factor in osteoarthritis (OA). Recent insights arising from our group demonstrate that mechano-sensitive intracellular signalling drives disease pathways. Cartilage injury is known to activate inflammatory signalling that leads to production of matrix-degrading proteases and consequent cartilage breakdown – a process our group has called mechanoflammation. Cartilage injury induces activation of transforming growth factor-β activated kinase 1 (TAK1), that further activates downstream extracellular signal regulated kinase (ERK), p38 and Jun N terminal kinase (JNK) mitogen-activated protein kinases (MAPKs). Our group has previously identified the role of apoptosis signal regulating kinase 1 (ASK1) and reactive oxygen species as key drivers of MAPKs on cartilage injury and downstream inflammatory gene regulation. My project sought to identify the role of ASK1 in the cartilage injury response. ASK1 was phosphorylated rapidly after cartilage injury, leading to the accumulation of ASK1 protein in the cell. Inhibition of ASK1 phosphorylation suppressed ASK1 accumulation, suggesting that phosphorylation was responsible for stabilising ASK1, most likely, by preventing its degradation. Degradation was through a proteosome- dependent mechanism as stabilisation of non-phosphorylated protein could be induced by pre-incubation with a proteosome inhibitor. IL1 and H2O2 stimulation of isolated primary chondrocytes activated MAPKs and NF-κB but did not appear to involve ASK1, although this needs repeating. Attempting to inhibit ASK1 in murine OA did not suppress cartilage degradation nor osteophyte formation. Giving mice a modified diet of oxidation-resistant compounds appeared to reduce injury-induced inflammatory gene regulation in vitro but increased cartilage damage in murine OA. My findings provide further insight into the role of ASK1 and other mechano-inflammatory pathways in articular cartilage and highlight the challenges of inhibiting them in vivo.
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