Holmes, D.F., Tait, A., Hodson, N.W., Sherratt, M.J., and Kadler, K.E. (2010). Growth of collagen fibril seeds from embryonic tendon: fractured fibril ends nucleate new tip growth. J Mol Biol 399, 9-16. pubmed
Tendon injury is a widespread medical condition that causes lengthy periods of disability. It can take a variety of forms including rupture, acute sprain and chronic repetitive strain injury. All these injuries will involve extensive breakage to the collagen fibrils, which are the structures that give the tendon its mechanical strength.
Collagen fibrils are the principal tensile element of most vertebrate tissues. They occur in the extracellular matrix as spatially organised arrays, and each tissue has its own arrangement of the fibrils. For example in some tissues they are arranged longitudinally while in others they in an organised criss-cross arrangement (a bit like plywood). A major challenge is to explain how nucleation, growth and remodelling of collagen yield fibrils of tissue-specific diameter and length. In addition, understanding how collagen fibril matrices are repaired after mechanical damage, will have significant medical implications.
In this study, we discovered that collagen fibrils with broken ends can readily regrow, forming new tapered tips. We used electron microscopy of broken collagen fibrils seeded into collagen solution, to show that the broken ends of fibrils act as nucleation sites where new deposition of collagen is initiated. The regrowth process leads to an increase in both length and diameter of the damaged fibrils.
This growth property of collagen fibrils after breakage is expected to be a central aspect of the repair process that restores mechanical strength in both acute and chronic tendon injury. It could also be important in the maintenance of healthy tendon by helping to repair day-to-day micro-damage. If we can eventually find out how to control collagen fibril regrowth in tissues, this might help to repair damaged or diseased tendons in people.