Author ORCID Identifier:
Date of Graduation
7-2026
Document Type
Thesis
Degree Name
Master of Science in Human Environmental Science (MS)
Degree Level
Graduate
Department
General Human Environmental Sciences
Advisor/Mentor
Fiddler, Joanna
Committee Member
Greene, Nicholas
Second Committee Member
Thallapuranam, Suresh
Keywords
Energy metabolism; Ferritin; Hemoglobin; Iron deficiency; Mitochondria; Skeletal muscle
Abstract
Iron deficiency is the most common nutritional deficiency worldwide. Although severe iron depletion is known to disrupt mitochondrial energy metabolism, current models may not reflect earlier, physiologically relevant stages. The role of iron status in altered work capacity in females, particularly in skeletal muscle energy metabolism, remains unclear. This study provides a cell-culture and mouse model approach to evaluating mitochondrial energy metabolism in physiologically relevant stages of iron depletion, including adequate, marginally depleted, and severely depleted stages of iron status. Using C57Bl/6 female mice and C2C12 and Hepa1-6 cells, this study modeled adequate, marginally depleted, and severely depleted iron status levels. Both models were evaluated using several approaches to determining molecular signatures and flux measures of mitochondrial energy metabolism, and the mouse model was also evaluated for metabolic phenotype and whole-body outcomes. At low levels of iron depletion, mitochondrial respiration increased in C2C12 cells and was maintained in Hepa1-6 cells. At the highest level of iron depletion, however, mitochondrial respiration decreased in both cell lines. Furthermore, there were cell-type-dependent changes in membrane potential, protein expression of mitochondrial electron transport chain (ETC) complex subunits and proteins involved in the ISC or heme synthesis pathways. Shifts in iron requiring protein expression occurred prior to transferrin receptor increases in both cell lines. In female mice, whole body metabolic phenotyping exhibits increased respiratory exchange ratio (RER) and total energy expenditure (TEE) over 24 hours with iron depletion. At the skeletal muscle level, respiratory control ratio (RCR), a proxy measure of mitochondrial coupling efficiency, is correlated with ferritin, but not hemoglobin. Furthermore, the capacity of complex I respiration increased in early depletion, yet there was no change in ATP-linked respiration in response to pyruvate and malate. These findings exhibit whole-body metabolic perturbations in response to lowered iron status, suggesting that iron depletion increases energy expenditure and reliance on carbohydrate over fat oxidation. The role of skeletal muscle in these alterations is not yet defined; however, mitochondrial oxidation of pyruvate and malate is not significantly altered in this model, while the capacity of complexes I and II increased in early iron depletion. These outcomes may support a carbohydrate-oxidizing phenotype. Further, skeletal muscle mitochondrial coupling efficiency was better predicted by ferritin level than hemoglobin. The cell-culture model also showed skeletal-muscle-cell-specific compensatory increases in mitochondrial oxidative phosphorylation. The myoblast line exhibits increased mitochondrial ATP-linked respiration only in early iron depletion, despite decreased mitochondrial content. This may be the result of decreased allocation of proton motive force to membrane uncoupling and increased overall membrane potential, allowing for greater flow into ATP-assembly. Liver cells maintain mitochondrial respiration in early iron depletion despite loss of membrane potential. Further, there are early alterations to heme and iron sulfur cluster biosynthesis enzymes and utilizing proteins which occur before transferrin receptor increases, revealing subtle alterations prior to the sensitivity of the cellular iron status marker. Overall, these outcomes address metabolic perturbations that models of severe iron depletion do not capture and uphold the necessity of physiologically based models of nutritional deficiencies.
Citation
Zirbel, A. L. (2026). Iron Depletion and Mitochondrial Function: Defining Iron Status and Metabolic Outcomes in Mouse Skeletal Muscle. Graduate Theses and Dissertations Retrieved from https://scholarworks.uark.edu/etd/6408
