Decreased NADPH levels may impair C. elegans mitochondrial function during aging

Abstract

With aging there is increased hydrogen peroxide (H2O2) release from mitochondria causing oxidative damage. H2O2 detoxification systems include catalase as well as the peroxiredoxin and glutathione systems that both require NADPH, with parallel systems for each operating in the cytoplasm and mitochondria. For detoxification, H2O2 is converted to water by peroxiredoxins (PRDXs) or glutathione peroxidases (GPXs). During this process glutathione, PRDX, and thioredoxin become oxidized, and glutathione reductase (GSR) or thioredoxin reductase (TRXR) oxidize NADPH to NADP+ to reduce the antioxidants back to their active forms. The NADP+ must then be recycled back to NADPH by one of several enzymes including cytoplasmic glucose-6-phosphate dehydrogenase (G6PD) or 6-phosphogluconate dehydrogenase (PGD) or mitochondrial malic enzyme 3 (ME3) or isocitrate dehydrogenase (IDH2). NADP+ is generated from NAD+ by two NAD kinase (NADK) genes. NADPH levels decline with aging, but whether this contributes to the rate of aging is not yet known. Here, we use the nematode C. elegans to decrease NADPH levels to model aging and subsequently measure H2O2 levels and the oxygen consumption rate (OCR), a measure of mitochondrial function that declines with age. C. elegans genes nadk-1, nadk-2, gspd-1 (G6PD), T25B9.9 (PGD), men-1 (ME3) and idh-2 were individually knocked down to decrease NADPH levels. We also measured H2O2 and mitochondrial function in C. elegans trxr-1, trxr-2, prdx-2, prdx-3, and gsr-1 antioxidant mutants with and without decreasing NADPH levels. While decreasing NADPH levels in wild-type worms increased H2O2 as expected, decreasing NADPH levels in some antioxidant mutants unexpectedly decreased H2O2, suggesting the activation of a transcriptional stress response. So, mutants for antioxidant stress response transcription factors skn-1 (Nrf2), daf-16 (FOXO), or hsf-1 were used to determine the mechanism. The results from these experiments will aid in the understanding of the roles of NADPH and H2O2 in human aging and aging-related diseases.

Start Time

16-4-2025 9:00 AM

End Time

16-4-2025 11:30 AM

Presentation Type

Poster

Presentation Category

Science, Technology and Engineering

Student Type

Graduate Student - Doctoral

Faculty Mentor

Patrick Bradshaw

Faculty Department

Biomedical Sciences

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Apr 16th, 9:00 AM Apr 16th, 11:30 AM

Decreased NADPH levels may impair C. elegans mitochondrial function during aging

With aging there is increased hydrogen peroxide (H2O2) release from mitochondria causing oxidative damage. H2O2 detoxification systems include catalase as well as the peroxiredoxin and glutathione systems that both require NADPH, with parallel systems for each operating in the cytoplasm and mitochondria. For detoxification, H2O2 is converted to water by peroxiredoxins (PRDXs) or glutathione peroxidases (GPXs). During this process glutathione, PRDX, and thioredoxin become oxidized, and glutathione reductase (GSR) or thioredoxin reductase (TRXR) oxidize NADPH to NADP+ to reduce the antioxidants back to their active forms. The NADP+ must then be recycled back to NADPH by one of several enzymes including cytoplasmic glucose-6-phosphate dehydrogenase (G6PD) or 6-phosphogluconate dehydrogenase (PGD) or mitochondrial malic enzyme 3 (ME3) or isocitrate dehydrogenase (IDH2). NADP+ is generated from NAD+ by two NAD kinase (NADK) genes. NADPH levels decline with aging, but whether this contributes to the rate of aging is not yet known. Here, we use the nematode C. elegans to decrease NADPH levels to model aging and subsequently measure H2O2 levels and the oxygen consumption rate (OCR), a measure of mitochondrial function that declines with age. C. elegans genes nadk-1, nadk-2, gspd-1 (G6PD), T25B9.9 (PGD), men-1 (ME3) and idh-2 were individually knocked down to decrease NADPH levels. We also measured H2O2 and mitochondrial function in C. elegans trxr-1, trxr-2, prdx-2, prdx-3, and gsr-1 antioxidant mutants with and without decreasing NADPH levels. While decreasing NADPH levels in wild-type worms increased H2O2 as expected, decreasing NADPH levels in some antioxidant mutants unexpectedly decreased H2O2, suggesting the activation of a transcriptional stress response. So, mutants for antioxidant stress response transcription factors skn-1 (Nrf2), daf-16 (FOXO), or hsf-1 were used to determine the mechanism. The results from these experiments will aid in the understanding of the roles of NADPH and H2O2 in human aging and aging-related diseases.