Cell morphology and collagen types in equine tendon scar.

The research investigates the difference between normal and injured (scarred) tendons in horses, highlighting that the scar tissue contains different types of collagen and cells which make it weaker than normal tissue.

Study Objective and Methods

• The study aims to compare the histological, or microscopic anatomical, characteristics in the scar tissue formed in the equine superficial flexor tendon following a partial rupture, to that of a normal tendon.
• This involves evaluating the difference in size, types of cells present, cell to matrix ratio and collagen concentration and types, between the scarred and normal tendon tissues.
• Observation techniques such as indirect immunofluorescence were used to further confirm the presence of different cell and collagen types in the tendon tissues.

Key Findings

• The cells in the repair tissue, known as repair fibroblasts, are larger than the cells (tenocytes) in the normal tendon. These repair fibroblasts also carry large vesicular nuclei which resemble the ‘myofibroblasts’ often found in scar tissues.
• Scarred zones of tendon have a higher cell to matrix ratio and a lower concentration of collagen compared to normal tendons.
• Additionally, the ability to extract collagen from scarred tendon tissue was greater than from normal tendon.
• Regarding collagen types, while a regular tendon is composed almost entirely of type I collagen, the scarred tendon had substantial quantities (20-30 per cent) of type III collagen in addition to type I.

Implications

• Results indicate that the tendon scar tissue is not derived from proliferating tenocytes but from mesenchymal cells that rest in peritendinous connective tissue or blood vessels.
• The presence of type III collagen, which differs from the type I collagen usually found in tendons, implies that the scarred tendon is likely to have less tensile strength than a normal one.
• This research can inform veterinary and medical procedures, as well as drug or therapy development to better manage and treat tendon injuries in both horses and potentially in humans.