Microscopic localization of active gelatinases in equine osteochondritis dissecans (OCD) cartilage.

This research article investigates the role of matrix metalloproteinase (MMP) activity in osteochondritis dissecans (OCD), a joint condition, in horses. It discusses the way gelatinase MMPs behave in cartilage and suggests they may contribute to the degradation of cartilage in OCD.

Methodology

• This study used articular cartilage collected from horses during autopsy. Eight samples were from normal joints, while six were from joints showing signs of OCD.
• The researchers identified the activities of gelatinase MMPs—enzymes implicated in cartilage degradation—in cartilage cross-sections, using in situ gelatin zymography. This is a technique that allows precise localisation of enzymatic activity in tissue samples.

Results

• Much higher gelatinase activity was found in the articular cartilage from joints with OCD. This activity was notably intense in the deep cartilage zone.
• The activity was limited to the pericellular area, which surrounds the cartilage cells, or chondrocytes.
• Vertical lines of gelatinase activity were also found in the OCD cartilage. These lines started in the deep zone and extended towards the articular surface.
• On the other hand, normal cartilage showed minimal gelatinolytic (degrading gelatin or collagen) activity, and this was not limited to any particular area of the cartilage.
• Gelatin zymograms (a form of electrophoresis allowing the visualization of the enzymatic activity) from the culture supernatants of isolated chondrocytes showed a higher production of two specific gelatinases (MMP-2 and MMP-9) in the cells derived from OCD cartilage.

Conclusions

• OCD lesions in the articular cartilage showed MMP activity, with a noteworthy concentration in the deep zones bordering the hardened subchondral bone structure.
• Given the role of MMPs in degrading cartilage’s extracellular matrix, this enzyme activity could explain why cartilage integrity is compromised in these deep zones in OCD cases.
• The vertical activity lines could indicate areas of mechanical weakness, which might lead to fissures and result in fragments of cartilage becoming detached and floating in the joint space—an outcome typical of OCD.