Evidence against proteoglycan mediated collagen fibril load transmission and dynamic viscoelasticity in tendon

Abstract

Evidence against proteoglycan mediated collagen fibril load transmission and dynamic viscoelasticity in tendon Fessel, G; Snedeker, J G Fessel, G; Snedeker, J G (2009 The glycosaminoglycan (GAG) dermatan sulphate and chondroitin sulphate side-chains of small leucine-rich proteoglycans have been increasingly posited to act as molecular cross links between adjacent collagen fibrils and to directly contribute to tendon elasticity. GAGs have also been implicated in tendon viscoelasticity, supposedly affecting frictional loss during elongation or fluid flow through the extra cellular matrix.The current study sought to systematically test these theories of tendon structure-function by investigating the mechanical repercussions of enzymatic depletion of GAG complexes by chondroitinase ABC in a reproducible tendon structure-function model (rat tail fascicles). The extent of GAG removal (at least 93%) was verified by relevant spectrophotometric assays and transmission electron microscopy. Dynamic viscoelastic tensile tests on GAG depleted rat tail tendon fascicle were not mechanically different from controls in storage modulus (elastic behavior) over a wide range of strain-rates (0.05, 0.5, and 5% change in length per second) in either the linear or nonlinear regions of the material curve. Loss modulus (viscoelastic behavior) was only affected in the nonlinear region at the highest strain rate, and even this effect was marginal (19% increased loss modulus, p=0.035). Thus glycosaminoglycan chains of small leucine rich proteoglycans do not appear to mediate dynamic elastic behavior nor do they appear to regulate the dynamic viscoelastic properties in rat tail tendon fascicles.

Exogenous collagen cross‐linking recovers tendon functional integrity in an experimental model of partial tear

“…experimental model for tendon mechanics (rat tail tendon fascicle; RTTF) that has been established in our laboratory. [12][13][14] Next we verified the suitability of these cross-linking treatments in application to the equine superficial digital flexor tendon (SDFT), a clinically relevant, large animal, load-bearing tendon model. 15 Finally, we selected the best candidate crosslinking agent to test the hypothesis that exogenous collagen cross-linking can arrest tendon tear propagation.…”

“…However, the biochemical composition and ultra-structure of both tendons is similar. 12 A further limitation is that we did not assess collagen crosslinking density, however the clear color changes due to cross-linking indicated successful treatment (and tissue penetration) and the employed protocols are well described in the literature. 10 Finally, with regard to tendon strain measurements, except for the characterization of altered strains in the injury model, strains were based on grip-to-grip separation.…”

Tendon injury and repair – A perspective on the basic mechanisms of tendon disease and future clinical therapy

“…These supramolecular collagen structures range in diameter from tens to hundreds of nanometers, with lengths that can span centimeters [91]. The collagen fibril is an exquisite example of cellular mediated protein self-assembly [92,93] -with emergent mechanical properties that depend on the diameter of the collagen fibril [88], as regulated by small leucine-rich proteoglycans [60,[94][95][96][97][98][99][100]. The properties are also highly dependent on the extent of covalent collagen molecule cross-linking as regulated by the enzyme lysyl-oxidase [85,86,[101][102][103][104].…”

Ring-Mesh Model of Proteoglycan Glycosaminoglycan Chains in Tendon based on Three-dimensional Reconstruction by Focused Ion Beam Scanning Electron Microscopy

“…Although proteoglycans with keratan sulfate such as fibromodulin and lumican are also expressed in tendon, their distribution differs from that of decorin/biglycan (3,24,31), and the amount of keratan sulfate proteoglycans is very small when assessed by enzymatic GAG depletion using chondroitinase ABC (3). Thus, the majority of GAG chains observed in this study can be considered to be decorin GAG chains; although, small amounts of biglycan GAG chains may also be involved.…”

“…In the "shape module model" (3,11,14,16,17) in which two GAG chains of decorin form the antiparallel duplex, GAG chains will be observed between collagen fibrils (Fig. 5a).…”