Decreasing NADPH levels may impair C. elegans mitochondrial function during aging
Location
D.P. Culp Center Ballroom
Start Date
4-5-2024 9:00 AM
End Date
4-5-2024 11:30 AM
Poster Number
149
Name of Project's Faculty Sponsor
Patrick Bradshaw
Faculty Sponsor's Department
Biomedical Sciences
Competition Type
Competitive
Type
Poster Presentation
Presentation Category
Science, Technology and Engineering
Abstract or Artist's Statement
Aging is characterized by increased oxidative damage by hydrogen peroxide released from mitochondria. There are three cellular pathways that detoxify hydrogen peroxide- two of them require NADPH and operate via parallel systems in the cytoplasm and mitochondria. The third detoxification pathway is catalyzed by peroxisomal catalase. NADPH plays a vital role in antioxidant defense mechanisms by providing reducing equivalents to oxidized glutathione (pathway 1) and thioredoxin (pathway 2) for their recycling after they detoxify reactive oxygen species (ROS). Peroxiredoxin (PRDX) converts hydrogen peroxide to water and oxidized PRDX is reduced back to its active form by the NADPH-dependent thioredoxin system. NADPH is also used as a cofactor by cytoplasmic fatty acid synthase, which fuels the endogenous production of fatty acids. NADP+ is generated from NAD+ by NAD kinase (NADK) in both the cytoplasm and mitochondria, and the NADP+ is reduced to NADPH by several enzymes including cytoplasmic glucose-6-phosphate dehydrogenase (G6PD), the rate-limiting step of the pentose phosphate pathway (PPP), and by isocitrate dehydrogenase enzymes in the cytoplasm (IDH1) and the mitochondria (IDH2). The ratio of NADPH/NADP+ declines with aging, but whether this contributes to the rate of aging has yet to be established. Here, to model aging we use the nematode C. elegans to explore the consequences of decreased cytoplasmic NADPH levels on ROS accumulation and nematode oxygen consumption rate as a measure of mitochondrial function. C. elegans genes nadk-1, gspd-1, and idh-2, which are homologous to human genes NADK2, G6PD, and IDH2, respectively, were individually knocked down using RNA interference to decrease NADP(H) synthesis, and ROS levels and the oxygen consumption rate were then measured. C. elegans thioredoxin antioxidant pathway genes prdx-2 and trxr-1 are homologous to human genes PRDX1 (and PRDX2) and TXNRD1. ROS was measured in strains harboring individual mutations in prdx-2 and trxr-1 with and without decreased NADP+ via nadk-1 RNAi. The overall findings of these experiments indicate that the mitochondrial oxygen consumption rate is compromised by decreased NADP(H) levels. Therefore, loss of NADPH may occur upstream of mitochondrial dysfunction in the aging process, and restoring NADPH levels may be a viable anti-aging strategy that prevents mitochondrial dysfunction to slow the rate of aging and extend healthy lifespan.
Decreasing NADPH levels may impair C. elegans mitochondrial function during aging
D.P. Culp Center Ballroom
Aging is characterized by increased oxidative damage by hydrogen peroxide released from mitochondria. There are three cellular pathways that detoxify hydrogen peroxide- two of them require NADPH and operate via parallel systems in the cytoplasm and mitochondria. The third detoxification pathway is catalyzed by peroxisomal catalase. NADPH plays a vital role in antioxidant defense mechanisms by providing reducing equivalents to oxidized glutathione (pathway 1) and thioredoxin (pathway 2) for their recycling after they detoxify reactive oxygen species (ROS). Peroxiredoxin (PRDX) converts hydrogen peroxide to water and oxidized PRDX is reduced back to its active form by the NADPH-dependent thioredoxin system. NADPH is also used as a cofactor by cytoplasmic fatty acid synthase, which fuels the endogenous production of fatty acids. NADP+ is generated from NAD+ by NAD kinase (NADK) in both the cytoplasm and mitochondria, and the NADP+ is reduced to NADPH by several enzymes including cytoplasmic glucose-6-phosphate dehydrogenase (G6PD), the rate-limiting step of the pentose phosphate pathway (PPP), and by isocitrate dehydrogenase enzymes in the cytoplasm (IDH1) and the mitochondria (IDH2). The ratio of NADPH/NADP+ declines with aging, but whether this contributes to the rate of aging has yet to be established. Here, to model aging we use the nematode C. elegans to explore the consequences of decreased cytoplasmic NADPH levels on ROS accumulation and nematode oxygen consumption rate as a measure of mitochondrial function. C. elegans genes nadk-1, gspd-1, and idh-2, which are homologous to human genes NADK2, G6PD, and IDH2, respectively, were individually knocked down using RNA interference to decrease NADP(H) synthesis, and ROS levels and the oxygen consumption rate were then measured. C. elegans thioredoxin antioxidant pathway genes prdx-2 and trxr-1 are homologous to human genes PRDX1 (and PRDX2) and TXNRD1. ROS was measured in strains harboring individual mutations in prdx-2 and trxr-1 with and without decreased NADP+ via nadk-1 RNAi. The overall findings of these experiments indicate that the mitochondrial oxygen consumption rate is compromised by decreased NADP(H) levels. Therefore, loss of NADPH may occur upstream of mitochondrial dysfunction in the aging process, and restoring NADPH levels may be a viable anti-aging strategy that prevents mitochondrial dysfunction to slow the rate of aging and extend healthy lifespan.