Elastin is Localised to the Interfascicular Matrix of Energy Storing Tendons and Becomes Increasingly Disorganised With Ageing

Abstract

Tendon is composed of fascicles bound together by the interfascicular matrix (IFM). Energy storing tendons are more elastic and extensible than positional tendons; behaviour provided by specialisation of the IFM to enable repeated interfascicular sliding and recoil. With ageing, the IFM becomes stiffer and less fatigue resistant, potentially explaining why older tendons become more injury-prone. Recent data indicates enrichment of elastin within the IFM, but this has yet to be quantified. We hypothesised that elastin is more prevalent in energy storing than positional tendons, and is mainly localised to the IFM. Further, we hypothesised that elastin becomes disorganised and fragmented, and decreases in amount with ageing, especially in energy storing tendons. Biochemical analyses and immunohistochemical techniques were used to determine elastin content and organisation, in young and old equine energy storing and positional tendons. Supporting the hypothesis, elastin localises to the IFM of energy storing tendons, reducing in quantity and becoming more disorganised with ageing. These changes may contribute to the increased injury risk in aged energy storing tendons. Full understanding of the processes leading to loss of elastin and its disorganisation with ageing may aid in the development of treatments to prevent age related tendinopathy.

Variations in internal structure, composition and protein distribution between intra‐ and extra‐articular knee ligaments and tendons

“…This has also been recently reported by Godinho et al. () who measured increased elastin equine SDFT IFM, which is suggested to play an important function in the elastic recoil ability of the energy‐storing SDFT IFM. In the current study, elastin was present either in between collagen fibre bundles or orientated along the fibres; it was found to co‐localise with both fibrillin‐1 and fibrillin‐2, where it was also in close proximity to both ACL and LDET cells.…”

“…This may be due to breed differences, as this study was conducted in ACLs from ex-racing greyhounds. The distribution of elastic fibres in the IFM may provide elastic recoil and offer stress protection of blood vessels and nerves in this region (Grant et al 2013;Godinho et al 2017) and play an important role in the microenvironment of both LDET and ACL cells.…”

Comparative multi‐scale hierarchical structure of the tail, plantaris, and Achilles tendons in the rat

“…2013b; Godinho et al. ) and animals with the interfascicular matrix, such as horses and human, develop naturally occurring age‐related tendinopathy (Patterson‐Kane et al. ), whereas rats do not appear to do so.…”

“…The absence of fascicles in rat tendons should impact a researcher's animal model choice; studies that are focused on the structure and mechanics of the interfascicular matrix should exclude rat models. Interestingly, agerelated tendinopathy is mostly attributed to the degeneration of interfascicular matrix (Thorpe et al 2013b;Godinho et al 2017) and animals with the interfascicular matrix, such as horses and human, develop naturally occurring age-related tendinopathy (Patterson-Kane et al 2012), whereas rats do not appear to do so. While this difference may be due to the animal's life-span and activity level, studies of age-related tendinopathy should be aware that rats lack fascicles, and thus interfascicular matrix.…”

The “other” 15–40%: The Role of Non‐Collagenous Extracellular Matrix Proteins and Minor Collagens in Tendon

“…Some of the stretch and recoil properties of tendon are attributed to elastin . Elastic fibers are also found in the interfascicular matrix (IFM), specifically in energy storing tendons and here, elastic fibers become disorganized during aging . Elastin haploinsufficiency in mice resulted in larger collagen fibrils in the Achilles tendon but not in the supraspinatus tendon .…”