A new study, by the Royal Veterinary College (RVC), which examined protein turnover rates in the tendons of rats, has found that tendons are a dynamic tissue with varying turnover rates of proteins – a discovery that may eventually provide greater understanding of how tendon disease and other connective tissue disorders can be treated.

With tendons connecting muscle to bone and providing an essential function in skeletal movement, it is crucial that tendon structure and its mechanical properties are maintained in order to sustain healthy function.

Previous research had shown that the interfascicular matrix, which forms part of the tendon and is the structure surrounding and separating fascicles - the main load-bearing structures of the tendon - allows sliding between fascicles, meaning that it may be prone to damage.

Building upon these findings, this study, led by Dr Chavaunne Thorpe, Versus Arthritis Career Development Fellow at the RVC, sought to establish if the turnover rate of proteins in the interfascicular matrix is greater than in the fascicles, which would help repair any damage.

Conducting this study, researchers fed rats labelled ‘heavy’ water to allow for the identification of newly synthesised proteins and collected separate samples from fascicles and interfascicular matrix regions of the rats’ Achilles tendons using laser-assisted microdissection. They used mass spectrometry and bioinformatics to calculate the turnover rates of individual proteins identified within the fascicles and interfascicular matrix.

The findings revealed highly variable turnover rates in tendon, with values ranging from a few days to several years, and significantly faster turnover of proteins in the interfascicular matrix. This key discovery challenges long-held beliefs that almost no protein turnover occurs in tendon and instead, provides the first step in understanding how altered protein turnover contributes to the development of tendon disease. Additionally, with alterations in protein turnover rates contributing to other musculoskeletal and connective tissue diseases, this study will also help target future research into how these diseases can most effectively be treated.

Dr Chavaunne Thorpe, Versus Arthritis Career Development Fellow at the RVC and author of the paper, said:
“Our results show that proteins within tendon are renewed much more rapidly than previously thought, with different rates of turnover in different regions of the tendon.

“These findings will help us to understand how the rate of protein renewal in tendon is affected by ageing or injury, and will allow future studies to identify potential targets for treatment of tendon disease and other prominent diseases which are caused by alterations in protein turnover rates.”

This study was funded by Versus Arthritis (grant number 21216).

The full paper will be available from 8am on 12 May 2020:
https://doi.org/10.7554/eLife.55262