Characterisation of lubricin in synovial fluid from horses with osteoarthritis.
Authors: Svala E, Jin C, Rüetschi U, Ekman S, Lindahl A, Karlsson N G, Skiöldebrand E
Journal: Equine veterinary journal
Summary
# Editorial Summary Lubricin, a critical glycoprotein responsible for boundary lubrication at the articular cartilage surface, undergoes structural changes in osteoarthritic joints that may compromise its protective function. Svala and colleagues analysed synovial fluid from normal equine joints and those with osteoarthritis or osteochondral fragments, alongside an in vitro inflammation model using interleukin-1β-stimulated cartilage explants, employing proteomics, western blotting and immunoassay to characterise lubricin's glycosylation profiles. Diseased joints displayed significantly altered O-glycan patterns: synovial fluid from osteoarthritic joints contained 53.8% monosialylated Core 1 O-glycans versus 49.5% in normal joints, with further increases to 57.3% in fragments cases, whilst disialylated glycans were reduced in fragment joints (21.2% versus 26.7% normally). The research identified a consistent C-terminal proteolytic cleavage site in lubricin across both clinical samples and inflamed cartilage cultures, suggesting degradation occurs regardless of inflammation stimulus. The reduced sialation (sialylation) of lubricin in diseased synovial fluid likely impairs its boundary lubricating capacity at the critical superficial cartilage layer, positioning this glycosylation shift as a potentially early osteoarthritic marker—information that could inform earlier diagnostic approaches and targeted interventions aimed at preserving synovial fluid quality and joint lubrication in at-risk horses.
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Practical Takeaways
- •Changes in lubricin glycosylation occur early in osteoarthritis development and may serve as a biochemical marker for detecting joint disease before structural lesions become apparent
- •Understanding lubricin degradation pathways could inform therapeutic strategies targeting joint surface protection and early intervention in at-risk horses
- •Synovial fluid analysis for lubricin glycosylation profiles may help differentiate normal joints from those with early degenerative changes in clinical practice
Key Findings
- •Synovial fluid from osteoarthritic joints contained significantly higher monosialylated Core 1 O-glycans (53.8–57.3%) compared to normal joints (49.5%), P ≤ 0.03
- •Normal joints showed higher disialylated Core 1 O-glycans (26.7%) than joints with osteochondral fragments (21.2%), P = 0.03
- •Identical C-terminal proteolytic cleavage site of lubricin was demonstrated both in vivo (synovial fluid) and in vitro (cartilage explants with and without IL-1β stimulation)
- •Reduced sialation of lubricin in diseased joints may impair boundary lubrication and represent an early event in osteoarthritis progression