Degree Name
PhD (Doctor of Philosophy)
Program
Biomedical Sciences
Date of Award
12-2025
Committee Chair or Co-Chairs
Patrick Bradshaw
Committee Members
Chad Frasier, Justin Gass, Tyrone Genade, Diego Rodriguez Gil
Abstract
Aging is characterized by progressive mitochondrial dysfunction and increased oxidative stress. NADPH is the essential reducing cofactor for antioxidant defense systems and lipid biosynthesis, but its levels decline with age in some tissues, partly due to age-related reduction of its precursor, NAD+. However, the relationship between NADPH depletion and mitochondrial impairment remains poorly understood. These studies describe how NADPH availability impacts mitochondrial function and longevity using Caenorhabditis elegans as a model organism. To induce NADPH depletion, NADP(H)-synthesizing enzymes including cytoplasmic nadk-1 (NADK), mitochondrial nadk-2 (NADK2), cytoplasmic pentose phosphate pathway (PPP) enzymes gspd-1 (G6PD) or T25B9.9 (PGD), mitochondrial idh-2 (IDH2), or mitochondrial men-1 (ME3) were knocked down across multiple genetic backgrounds. Mitochondrial oxygen consumption rates (OCRs), reactive oxygen species (ROS) production, ATP levels, lipid peroxidation, glutathione (GSH) levels, and lifespan were measured. Either cytoplasmic or mitochondrial NADPH depletion significantly decreased mitochondrial OCR and worm ATP levels but increased ROS levels and a lipid oxidative damage marker. The cellular response to cytoplasmic NADPH depletion was highly context-dependent. In wild-type worms, nadk-1 or gspd-1 knockdown increased oxidative damage but did not significantly affect lifespan. However, when cytoplasmic NADPH depletion was combined with a deficiency in a specific antioxidant pathway, the effects greatly differed. In trxr-1 mutants lacking cytoplasmic thioredoxin reductase-1, NADPH depletion mildly shortened lifespan, indicating the cytoplasmic thioredoxin system is essential for longevity when NADPH becomes limiting, whereas, in worms deficient for gsr-1, encoding cytoplasmic and mitochondrial glutathione reductase, or in cytoplasmic catalase ctl-1 mutants, NADP(H) depletion surprisingly decreased ROS levels and greatly extended lifespan, due to the activation of compensatory antioxidant stress responses. These findings reveal that the main H2O2 detoxification pathways have differential requirements for NADPH during aging. Cytoplasmic thioredoxin reductase appears critical for longevity under NADPH limitation, while deficiencies in glutathione reductase or cytoplasmic catalase allow for the induction of compensatory responses. This work demonstrates that genetic background profoundly influences whether NADP(H) depletion induces a pro-longevity antioxidant response, possibly providing insight into why antioxidant supplementation often fails to improve health. Understanding these context-dependent mechanisms may inform targeted therapeutic strategies to maintain mitochondrial health and extend healthspan during aging.
Document Type
Dissertation - embargo
Recommended Citation
Jamerson, Leah, "Genetic Context Determines Mitochondrial and Longevity Outcomes of NAD+ Kinase Knockdown in Caenorhabditis elegans" (2025). Electronic Theses and Dissertations. Paper 4626. https://dc.etsu.edu/etd/4626
Copyright
Copyright by the authors.
