Author ORCID Identifier:
Date of Graduation
5-2026
Document Type
Dissertation
Degree Name
Doctor of Philosophy in Engineering (PhD)
Degree Level
Graduate
Department
Biomedical Engineering
Advisor/Mentor
Quinn, Kyle
Committee Member
Chen, Jingyi
Second Committee Member
Rajaram, Narasimhan
Third Committee Member
Song, Younghye
Keywords
Aging; Autofluorescence; Cell Metabolism; Diabetes; Multiphoton Microscopy
Abstract
Advanced age is the leading risk factor for chronic diseases, and the expected aging of general population will present a significant burden to the healthcare system. Although aging can be described as a general loss of homeostasis at multiple levels, biomarkers of aging have largely focused on epigenetic clocks that lack direct links to clinical surrogate metrics of aging such as weak gait and grip strength. The focus on molecular or organismal level metrics of aging highlights a critical gap in knowledge and need for biomarkers at the cellular and tissue levels. Mitochondrial dysfunction has been considered a hallmark of aging, and longitudinal imaging approaches capable of quantifying mitochondrial dysfunction are needed to address gaps in our understanding of aging. Label-free multiphoton microscopy (MPM) offers a non-invasive approach that can be used to visualize cells and tissues in three dimensions. Specifically, MPM is sensitive to the autofluorescence of metabolic cofactors NADH and FAD and enables longitudinal assessment of cell metabolism. The goal of this dissertation was to identify optical biomarkers of aging in skin using in vivo MPM and to quantify the effects of associated diseases. Using young and aged mouse models, a suite of optical biomarkers sensitive to the effects of aging on skin metabolism and microstructure was developed. Keratinocytes in aged skin exhibited greater optical redox ratios, bound NADH fractions, and mitochondrial fractal dimensions (FD) suggesting reduced proliferation and a fragmented mitochondrial network. In addition, the dermis of aged skin demonstrated a fragmented collagen fiber network and lower fiber density. Using young and aged diabetic mouse models, the interaction effects of aging and diabetes on wound edge metabolism were evaluated using in vivo MPM over the course of 10 days. Aged wounds experienced shifts in their optical redox ratios in later days when compared to young controls suggesting delays in proliferation, while diabetic wounds demonstrated lower redox ratios suggesting greater inflammation. Aging and diabetes had an additive effect on increased NADH binding, and greater bound NADH lifetimes in aged wounds suggest greater binding to complex I and reduced proliferation. Lastly, mitochondrial function and structure was evaluated throughout the mammalian lifespan in standard and high-fat diet (HFD) mice. Optical redox ratios and mitochondrial FDs increased from 2 to 10 months of age, suggesting a progressive loss in proliferation and increased mitochondrial fragmentation as mice approach middle age, and later decreased as mice approached 22 months of age suggesting a shift towards glycolytic metabolism and a compensatory fusion at advanced age. Piecewise linear modeling of optical redox ratios and mitochondrial fractal dimensions highlighted differences between dietary groups and demonstrated associations between optical markers of metabolism and lifespan. This work demonstrates that in vivo MPM of skin can be used to develop optical biomarkers of aging and disease, and that these biomarkers may contribute to the effectiveness of next-generation indices of aging.
Citation
Rodriguez, M. R. (2026). Development and Evaluation of Optical Biomarkers of Skin Aging Through In Vivo Label-Free Multiphoton Microscopy. Graduate Theses and Dissertations Retrieved from https://scholarworks.uark.edu/etd/6231
