Collagen fibril morphology and mechanical properties of the Achilles tendon in two inbred mouse strains

Abstract

The relationship between collagen fibril morphology and the functional behavior of tendon tissue has been investigated in numerous experimental studies. Several of these studies suggest that larger fibril radius is a primary determinant of higher tendon stiffness and strength; others have shown that factors apart from fibril radius (such as fibril-fibril interactions) may be critical to improved tendon strength. In the present study, we investigate these factors in two inbred mouse strains that are widely used in skeletal structure-function research: C57BL ⁄ 6J (B6) and C3H ⁄ HeJ (C3H). The aim was to establish a quantitative baseline that will allow one to assess how regulation of tendon extracellular matrix architecture affects tensile mechanical properties. We specifically focused on collagen fibril structure and glycosaminoglycan (GAG) content -the two primary constituents of tendon by dry weight -and their potential functional interactions. For this purpose, Achilles tendons from both groups were tested to failure in tension. Tendon collagen morphology was analyzed from transmission electron microscopy images of tendon sections perpendicular to the longitudinal axis. Our results showed that the two inbred strains are macroscopically similar, but C3H mice have a higher elastic modulus (P < 0.05). Structurally, C3H mice showed a larger collagen fibril radius compared to B6 mice (96 ± 7 nm and 80 ± 10 nm respectively). Tendons from C3H mice also showed smaller specific fibril surface (0.015 ± 0.001 nm nm )2 vs.0.017 ± 0.003 nm nm )2 in the B6 tendons, P < 0.05), and accordingly a lower concentration of GAGs (0.60 ± 0.07 lg mg )1 vs. 0.83 ± 0.11 lg mg )1, P < 0.05). As in other studies of tendon structure and function, larger collagen fibril radius appears to be associated with stiffer tendon, but this functional difference could also be attributed to reduced potential surface area exchange between fibrils and the surrounding proteoglycan-rich matrix, in which the hydrophilic GAG side chains may promote inter-fibril sliding. This study provides an architectural and functional baseline for a comparative murine model that can be used to investigate the genetic regulation of tendon biomechanics.

Turnover of fibrillar collagen in soft biological tissue with application to the expansion of abdominal aortic aneurysms

“…The PG-based cross-linking was supported by numerous experimental studies showing that PGs play a direct role in inter-fibril load sharing [40][41][42][43][44][45][46], and this has also been verified through theoretical investigations [47][48][49]. However, it was also noted that the biomechanical role of PGs is discussed controversially, and some data indicate minimal, if any, PG contribution to tensile properties of the tissue [47,50,51].…”

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

“…Tail tendon explant models arguably provide the most reproducible and human-relevant in vitro models of tendon physiology that are available [75][76][77][78][79]. Regarding mechanical properties, rodent fascicles range in elastic modulus from several hundred MPa to over 1 GPa, depending on the anatomical location of tissue harvest, as well as the age, breed, sex, and/or diet of the animal [80][81][82][83][84]. The failure properties of isolated tail tendon fascicles reflect those of whole tendon, with failure stresses on the order of 80 MPa and failure strains of approximately 10% [72].…”

Potential of collagen cross-linking therapies to mediate tendon mechanical properties

“…5,19 Simple biochemical correlations of native cross-link content with tendon mechanical properties are rather weak, 7,13,28,67 reflecting the likely confounding influence of other dominant structural or compositional factors. 56 The essential functional role of cross-linking in collagen fibril stability and whole tissue integrity, however, is clearly demonstrated in the severely compromised connective tissues of animals subjected to dietary inhibition of lysyl oxidase, which results in collagen fibrils and tendons with reduced strength. 29,50 The importance of cross-links to fibril integrity has been indicated theoretically 70 and demonstrated experimentally 45,50 by balancing molecular slip and stretch under load.…”

“…27,68 The major contributors to increased structural stiffness are larger tendon cross-section, increased collagen content, and alterations in the structural arrangement of collagen fibrils. 27,56 The relative density, total number, and morphologies of collagen fibrils are thus correlated to tendon function, but the mechanical properties of the individual collagen fibrils largely drive whole tendon behavior. This is regulated by proper formation of covalent collagen cross-links.…”