A Novel Fibre Composite System to Investigate Tenocyte Metabolism Under Physiological and Pathological Loading Conditions.

Abstract

Tendons are crucial for locomotion, transferring forces from muscle to bone. They are subjected to high forces, and possess highly specialised hierarchical structures to function efficiently. Tendinopathies are debilitating tendon disorders common in both athletes and non-athletes. The unclear aetiology of tendinopathies has led to limited, generalised treatment, with poor regenerative outcomes for patients. Tendinopathies are thought to be instigated by changes in the local cellular environment, with tendon overuse generating matrix microdamage, which increases cellular shear. Shear is potentially an important mechanotransduction cue, but no mechanism is available to investigate this directly. To address this need, a fibre composite system based on polyethylene glycol (PEG) was developed, consisting of cell seeded PEG-peptide fibres encapsulated in a PEG matrix. Composites were developed to mimic the cell mechanical environment in tendons, creating shear-tension ratios equivalent to those seen physiologically (40% of applied strain transferred to the fibres; the remaining 60% as fibre shearing within the matrix). High shear-low tension (~25% tension, ~75% shear) and low shear-high tension (~60% tension, ~40% shear) environments were also developed to investigate non-physiological conditions. Broad spectrum gene expression analysis was performed to determine how different shear-tension ratios affect the behaviour of tenocytes derived from healthy and tendinopathic human tendons. Tendinopathic tenocytes appeared more mechano-sensitive than healthy tenocytes (shear-tension mediated changes in versican, IL-8, TIMP-3, MMP-3 and MMP-13 expression) and showed a distinct basal profile similar to that observed in tendinopathic tissue (lower MMP-3 and higher MMP-13 expression). Further investigation with bovine tenocytes found changing the cell attachment peptide in fibres from RGD to DGEA increased the sensitivity of tenocytes to the local shear-tension environment (shear-mediated changes in scleraxis, MMP-2 and COL-3 expression). This suggests tenocytes are more responsive when attached to collagen-like materials, and consequently that specific integrins are involved in sensing the local shear-tension environment.