Author's School

School of Medicine

ORCID

https://orcid.org/0000-0003-3096-8429

Author's Department/Program

Movement Science

Language

English (en)

Date of Award

5-15-2026

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Chair and Committee

Gretchen A. Meyer

Committee Members

Michael D Harris, Jennifer Zellers, Farshid Guilak, Amit Pathak

Abstract

Mesenchymal stem cells (MSCs) are resident cells residing with many adult tissues such as adipose tissue and bone marrow that have the potency for multiple lineage differentiation as well as the capacity to secrete a litany of beneficial factors to maintain homeostasis and promote tissue repair. Since 1995, MSCs have been used therapeutically to treat a variety of conditions from osteoarthritis to heart disease to muscle pathologies. Great leaps have been made in improving MSC-based therapies through optimization of culture methods and select enrichment of cellular subpopulations. More recently, the physical microenvironment of tissue in vivo and culture conditions in vitro have been shown to greatly impact cellular phenotype, function, and therapeutic efficacy. This is regulated by cells sensing and responding to their environment through altered shape, phenotype, and secretome signature, a process now broadly referred to as mechanobiology. This dissertation seeks to further elucidate and harness the relationship between cellular microenvironment and function to further improve MSC-based therapies.

In Chapter 2, we explore whether adipose stem cells (ASCs) located within subacromial fat (SAF), located within the human rotator cuff, possess altered mechanosensitivity compared to gold-standard subcutaneous (SQ) ASCs and may serve as an alternative choice in fibrosis-treating therapies. In this endeavor we collected SQ and SAF adipose biopsies from those with and without torn rotator cuffs and isolated ASCs. We assessed mechanosensitivity and its impacts by measuring cellular size, actin stress fiber formation, focal adhesion formation, myofibroblastic conversion, and extracellular matrix (ECM) secretion, in which we observed SAF ASCs to characterized as significantly smaller with lower stress fiber formation, smallerfocal adhesions, and a lower propensity for myofibroblastic conversion and ECM synthesis. Due to this reduced sensitivity, the secretome of SAF ASCs was also significantly more supportive of myogenesis in vitro. Finally, we also demonstrate that SAF ASCs sourced from those with torn rotator cuffs still maintain resiliency to fibrotic environments and can be used therapeutically. Together, Chapter 2 successfully identifies an ASC source with altered mechanobiology that may prove advantageous in therapies with a fibrotic component.

In Chapter 3, we sought to further define relationships between muscle stem cells (MuSCs) function, MuSCs senescence, and muscle fibrosis in non-diabetic (ND) individuals with orthopedic injuries and those with Type II Diabetes Mellitus (DIA). In this, we report that ND and DIA muscles exhibit similar volumes of muscle pathology, nor differences in MuSC differentiation capacity, while ND MuSCs are significantly more proliferative and less senescent compared to DIA MuSCs. We also establish strong relationships between muscle fibrosis, MuSC dysfunction, and MuSC senescence in ND individuals, demonstrating that MuSCs from highly fibrotic are characterized by elevated senescence and greatly diminished functionality. Interestingly, we do not find these relationships to be present in DIA individuals, suggesting T2DM obscures these relationships. Together, Chapter 3 is the first human study to measure and draw within-sample relationships between muscle fibrosis, MuSC function, and MuSC senescence, and further solidifies relationships between tissue microenvironment and cellular function.

In Chapter 4, we return to ASCs and determine whether a 6-week resistance training (RT) intervention could beneficially remodel adipose tissue and enhance ASC therapeutic efficacy in young and aged mice. We found that 6-weeks of RT improved strength in both young and aged mice but did not impact muscle weights, adipose tissue weights, or body composition overall. Moreover, RT was largely unimpactful on remodeling adipose tissue, with no differences seen in adipocyte size, fibrosis, vascularity, or macrophage burden. Finally, RT did have a modest impact on the transcriptome of inguinal stromal vascular fraction (SVF), although this impact did not translate to ASCs in vitro phenotype, as we observed no differences in senescence, proliferation, or expression of beneficial paracrine signaling genes.

These findings contribute to the field’s understanding of how the mechanobiology of cells impacts their phenotype and therapeutic uses. Great progress has been made in MSC-based therapies, and further characterization and harnessing of MSC mechanobiology offers the next generation of therapeutic development. This dissertation first demonstrates that in SAF ASCs, reduced sensitivity to physical and chemical cues confers a more efficacious secretome and SAF ASCs may have a particular use in rotator cuff and fibrosis-treating therapies. Next, we refine understanding of relationships between muscle fibrosis, MuSC dysfunction, and MuSC senescence in humans, highlighting mechanisms through which muscle pathology may be improved. Finally, we attempt to prime ASCs in vivo by beneficially remodeling adipose tissue through a 6-week RT intervention, in which we demonstrate that a 6-week duration is insufficient to produce measurable improvements in ASC therapeutic efficacy. Overall, this dissertation further illustrates the role of mechanobiology in cellular function, phenotype, and therapies.

DOI

https://doi.org/10.48765/d2xt-n716

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