Mesenchymal Stem Cell Mechanobiology and Tendon Regeneration
Youngstrom, Daniel W.
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Tendon function is essential for quality of life, yet the pathogenesis and healing of tendinopathy remains poorly understood compared to other musculoskeletal disorders. The aim of regenerative medicine is to replace traditional tissue and organ transplantation by harnessing the developmental potential of stem cells to restore structure and function to damaged tissues. The recently discovered interdependency of cell phenotype and biophysical environment has created a paradigm shift in cell biology. This dissertation introduces a dynamic in vitro model for tendon function, dysfunction and development, engineered to characterize the mechanobiological relationships dictating stem cell fate decisions so that they may be therapeutically exploited for tendon healing. Cells respond to mechanical deformation via a complex set of behaviors involving force-sensitive membrane receptor activity, changes in cytoskeletal contractility and transcriptional regulation. Effective ex vivo model systems are needed to emulate the native environment of a tissue and to translate cell-matrix forces with high fidelity. A naturally-derived decellularized tendon scaffold (DTS) was invented to serve as a biomimetic tissue culture platform, preserving the structure and function of native extracellular matrix. DTS in concert with a newly designed dynamic mechanical strain system comprises a tendon bioreactor that is able to emulate the three-dimensional topography, extracellular matrix proteins, and mechanical strain that cells would experience in vivo. Mesenchymal stem cells seeded on decellularized tendon scaffolds subject to cyclic mechanical deformation developed strain-dependent alterations in phenotype and measurably improved tissue mechanical properties. The relative tenogenic efficacies of adult stem cells derived from bone marrow, adipose and tendon were then compared in this system, revealing characteristics suggesting tendon-derived mesenchymal stem cells are predisposed to differentiate toward tendon better than other cell sources in this model. The results of the described experiments have demonstrated that adult mesenchymal stem cells are responsive to mechanical stimulation and, while exhibiting heterogeneity based on donor tissue, are broadly capable of tenocytic differentiation and tissue neogenesis in response to specific ultrastructural and biomechanical cues. This knowledge of cellular mechanotransduction has direct clinical implications for how we treat, rehabilitate and engineer tendon after injury.
- Doctoral Dissertations