Author ORCID Identifier
https://orcid.org/0009-0002-5489-4663
Defense Date
2025
Document Type
Thesis
Degree Name
Master of Science
Department
Biomedical Engineering
First Advisor
Jennifer Puetzer
Second Advisor
Michael McClure
Third Advisor
Nastassja Lewinski
Abstract
Tendons are connective tissues that link muscle to bone, enabling joint movement and stability. Their structural integrity and mechanical function depend on large type I collagen fibers that run the length of the tissue. There is a clear link between increasing age and injuries in tendons. Many mechanisms have been suggested to contribute; however, due to the dominance of collagen in tendons, a prominent one is advanced glycation end-products (AGEs). AGEs accumulate in tendons with age, producing non-enzymatic crosslinks. These crosslinks stiffen the extracellular matrix, disrupt fibril sliding, impair tenocyte mechanotransduction, and ultimately contribute to reduced flexibility and higher injury risk. It has been suggested exercise can combat AGE accumulation, reducing age-related tendon injuries; however, in vivo investigations have yielded variable results.It is unknown whether exercise loading reduces AGEs by increasing matrix turnover, preventing AGE crosslink formation or whether loading can stimulate cells to breakdown existing AGEs. The objective of this thesis was to determine how tensile loading regulates AGE accumulation, breakdown, and tendon homeostasis in an ex vivo tendon model so to reduce AGEs and age-related injuries. We hypothesize that intermittent cyclic tensile loading can both prevent and reduce existing AGEs by stimulating tenocytes to turnover the matrix.
To do this, tail tendons were extracted from 7-8 week old Sprague Dawley rats and cultured in a CellScale tensile bioreactor for up to 4 weeks. Tendons were cultured in standard medium with or without 30 mM ribose to induce physiological AGEs. Then tendons were loaded with a cyclic tensile loading regime (5% strain at 1 Hz for 1 hour on-1 hr off-1 hr on, 3x a week) which we have previously established drives tissue maturation and mirrors cyclic muscle activity. In Aim 1, we first investigated if loading can prevent AGE formation by mechanically stimulating tendons while inducing AGEs. We found that cyclic load did indeed prevent AGE accumulation, suggesting exercise can help to minimize AGE accumulation. We repeated the study with frozen, devitalized tendons and found this effect was a cell-mediated process, as frozen tendons had significant increases in AGEs with and without load. We then investigated whether loading can drive cells to reduce existing AGEs by inducing AGEs and then loading tendons. We found little reduction in AGEs, and instead a negative response to load, with cells appearing to breakdown uncrosslinked collagen more than AGE crosslinked collagen, resulting in a net gain of AGEs. Collectively this work demonstrated that loading decreases AGE accumulation, but an optimal loading regime is still needed to potentially stimulate cells to reduce existing AGEs (Chapter 2).
Recent studies have shown that frequencies less than 1 Hz enable better cellular recovery between deformation cycles allowing for increased ECM synthesis and promote fibroblast alignment and integrin expression, which are key components of mechanosensing. Therefore, in Aim 2 we evaluated whether cyclic loading at decreased frequencies could better promote cells to reduce existing AGEs and we found that indeed they did minimize AGE accumulation compared to 1 Hz loading (Chapter 3). Overall, this thesis demonstrates that cyclic mechanical stimulation of tendons does minimize AGE accumulation via a cell driven process and that lower frequency stimulation may further help to reduce existing AGEs. This suggests that exercise can help mitigate AGEs, and activities such as stretching and weightlifting with slower repetitions may be more beneficial to reducing AGE and maintaining tendon health with age.
Rights
© 2025 Alex Samson
Is Part Of
VCU University Archives
Is Part Of
VCU Theses and Dissertations
Date of Submission
12-12-2025
Included in
Animal Experimentation and Research Commons, Animals Commons, Animal Structures Commons, Biological Engineering Commons, Biotechnology Commons, Cellular and Molecular Physiology Commons, Exercise Physiology Commons, Laboratory and Basic Science Research Commons, Sports Sciences Commons, Structural Biology Commons