A younger and an older hand together symbolise the lifelong changes in connective tissues that underpin healthy ageing.
A preliminary mouse study suggests that mimecan helps regulate how tendon strength and stiffness change during maturation.
Tendons are reinforced by collagen fibrils held within a hydrated extracellular matrix. Small molecules called proteoglycans help organise this matrix and regulate collagen fibril development.
Their importance continues to attract attention. Newton and colleagues reported in 2024 that reducing the proteoglycans decorin and biglycan in injured tendons from aged mice affected collagen fibril morphology, scar area, mechanical properties and gene expression during healing. Published in Journal of Orthopaedic Research (DOI:10.1002/jor.25931), their findings reinforce the need to understand the individual roles of different proteoglycans in tendon structure and function.
Against this background, a 2023 study examined another, less studied member of the same proteoglycan family: mimecan, also known as osteoglycin.
The study built on almost two decades of work by the research team on collagen reinforcement, tendon structure and age-dependent mechanical behaviour. It asked whether removing the mimecan gene would alter how tendon properties change from early life into maturity.
Researchers compared tail tendons from normal wild-type mice with those from mice lacking a functional mimecan gene. The animals were studied at one, four and eight months of age.
Small tendon fascicles were isolated and stretched until rupture using a custom micromechanical testing system. The researchers measured stiffness, yield strength, resilience, fracture strength, fracture strain and fracture toughness.
In the wild-type mice, several mechanical properties improved between one month and the later ages. The tendons generally became stronger, stiffer and able to absorb more energy.
This pattern was less pronounced in the mimecan-deficient tendons. When age and genotype were considered together, removing mimecan significantly affected tendon modulus, yield strength and fracture strength. The clearest differences between the two groups occurred at four months.
Across the age groups, tendons lacking mimecan were generally more compliant and showed lower yield and fracture strength. However, their overall diameter did not differ significantly from that of normal tendons. The measured changes therefore could not be explained simply by differences in tendon size.
The researchers also observed a shorter strain-softening region in tendons lacking mimecan. They proposed that this might reflect changes in the matrix between collagen fibrils, but the study did not directly determine the structural mechanism responsible.
The findings support a possible role for mimecan in regulating age-dependent tendon mechanical function. They do not establish how the molecule produces these effects, or whether the findings apply to human tendons.
The work was preliminary and involved a relatively small number of mice. It also examined changes from one to eight months rather than advanced old age. Direct imaging of collagen fibril ultrastructure was not included.
Further studies combining mechanical testing with microscopy and molecular analysis will be needed to determine how mimecan affects collagen fibrils and whether other proteoglycans compensate when it is absent.
Nevertheless, the study adds another piece to an increasingly important research question: how do the smaller components surrounding collagen influence the strength and mechanical development of connective tissues?
Paper details
The paper, “Age-dependent mechanical properties of tail tendons in wild-type and mimecan gene-knockout mice – A preliminary study”, was published in the Journal of the Mechanical Behavior of Biomedical Materials. DOI: 10.1016/j.jmbbm.2023.105672.
Authors and affiliations
The study was carried out by Craig Boote from Cardiff University; Q. Ma from Cardiff University; and Kheng-Lim Goh from Newcastle University, Newcastle University in Singapore and the Newcastle Research and Innovation Institute in Singapore.
For further details, contact Associate Professor Kheng-Lim Goh at [email protected].
