Elastase treatment of tendon specifically impacts the mechanical properties of the interfascicular matrix

Abstract

The tendon interfascicular matrix (IFM) binds tendon fascicles together. As a result of its low stiffness behaviour under small loads, it enables non-uniform loading and increased overall extensibility of tendon by facilitating fascicle sliding. This function is particularly important in energy storing tendons, with previous studies demonstrating enhanced extensibility, recovery and fatigue resistance in the IFM of energy storing compared to positional tendons. However, the compositional specialisations within the IFM that confer this behaviour remain to be elucidated. It is well established that the IFM is rich in elastin, therefore we sought to test the hypothesis that elastin depletion (following elastase treatment) will significantly impact IFM, but not fascicle, mechanical properties, reducing IFM resilience in all samples, but to a greater extent in younger tendons, which have a higher elastin content. Using a combination of quasi-static and fatigue testing, and optical imaging, we confirmed our hypothesis, demonstrating that elastin depletion resulted in significant decreases in IFM viscoelasticity, fatigue resistance and recoverability compared to untreated samples, with no significant changes to fascicle mechanics. Ageing had little effect on fascicle or IFM response to elastase treatment. This study offers a first insight into the functional importance of elastin in regional specific tendon mechanics. It highlights the important contribution of elastin to IFM mechanical properties, demonstrating that maintenance of a functional elastin network within the IFM is essential to maintain IFM and thus tendon integrity. Statement of significance Developing effective treatments or preventative measures for musculoskeletal tissue injuries necessitates the understanding of healthy tissue function and mechanics. By establishing the contribution of specific proteins to tissue mechanical behaviour, key targets for therapeutics can be identified. Tendon injury is increasingly prevalent and c hronically debilitating, with no effective treatments available. Here, we investigate how elastin modulates tendon mechanical behaviour, using enzymatic digestion combined with local mechanical characterisation, and demonstrate for the first time that removing elastin from tendon affects the mechanical properties of the interfascicular matrix specifically, resulting in decreased recoverability and fatigue resistance. These findings provide a new level of insight into tendon hierarchical mechanics, important for directing development of novel therapeutics for tendon injury.

CD146 Delineates an Interfascicular Cell Sub-Population in Tendon That Is Recruited during Injury through Its Ligand Laminin-α4

“…Our previous work established that the IFM plays an important mechanical role in tendon, allowing for sliding between fascicles and providing the tendon with additional extensibility [ 1 , 2 , 3 ]. These properties are provided by structural proteins, including elastin and lubricin [ 4 , 5 , 6 , 7 ]. The production and replacement of these components by IFM resident cells is likely critical to maintain tendon function.…”

Structure-function specialisation of the interfascicular matrix in the human achilles tendon

“…However, by combining quantitative assays to determine whole tendon elastin content, and immunolocalisation to identify its spatial arrangement, we were able to establish that elastin was localised to the IFM, with a trend towards lower elastin content in the old Achilles compared to the old anterior tibial tendon. Previous research demonstrates a decline in elastin content in the energy storing equine SDFT with ageing [16] , and elastin depletion results in alterations in IFM mechanical properties, characterised by small changes in quasi-static mechanical properties, and a large reduction in fatigue resistance [46] . In our samples, a particularly large individual variation in elastin content in the middle-aged Achilles tendon was evident (Supplementary Fig.…”

The alteration of the structure and macroscopic mechanical response of porcine patellar tendon by elastase digestion

“…Elastin is an essential component affecting the viscoelastic properties of the tissue extracellular matrix and is crucial for tissue ductility ( Urbanczyk et al, 2020 ). Although elastase treatment significantly affects the hysteresis experiment of tissue ( Godinho et al, 2021 ), the existing research has not completely clarified the effect of elastin on the stress relaxation characteristics of viscoelastic tissue. The proximal patellar tendon is considered a common injury site ( Pearson and Hussain, 2014 ), but the influence of elastin on the mechanical properties and structure of its region has not been better explored.…”