Mitochondrial Oxidative Stress Impairs Energy Metabolism and Reduces Stress Resistance and Longevity ofC. elegans

Abstract

Introduction Mitochondria supply cellular energy and are key regulators of intrinsic cell death and consequently affect longevity. The nematode Caenorhabditis elegans is frequently used for lifespan assays. Using paraquat (PQ) as a generator of reactive oxygen species, we here describe its effects on the acceleration of aging and the associated dysfunctions at the level of mitochondria. Methods Nematodes were incubated with various concentrations of paraquat in a heat-stress resistance assay (37°C) using nucleic staining. The most effective concentration was validated under physiological conditions, and chemotaxis was assayed. Mitochondrial membrane potential (ΔΨm) was measured using rhodamine 123, and activity of respiratory chain complexes determined using a Clark-type electrode in isolated mitochondria. Energetic metabolites in the form of pyruvate, lactate, and ATP were determined using commercial kits. Mitochondrial integrity and structure was investigated using transmission electron microscopy. Live imaging after staining with fluorescent dyes was used to measure mitochondrial and cytosolic ROS. Expression of longevity- and mitogenesis-related genes were evaluated using qRT-PCR. Results PQ (5 mM) significantly increased ROS formation in nematodes and reduced the chemotaxis, the physiological lifespan, and the survival in assays for heat-stress resistance. The number of fragmented mitochondria significantly increased. The ∆Ψm, the activities of complexes I-IV of the mitochondrial respiratory chain, and the levels of pyruvate and lactate were significantly reduced, whereas ATP production was not affected. Transcript levels of genetic marker genes, atfs-1, atp-2, skn-1, and sir-2.1, were significantly upregulated after PQ incubation, which implicates a close connection between mitochondrial dysfunction and oxidative stress response. Expression levels of aak-2 and daf-16 were unchanged. Conclusion Using paraquat as a stressor, we here describe the association of oxidative stress, restricted energy metabolism, and reduced stress resistance and longevity in the nematode Caenorhabditis elegans making it a readily accessible in vivo model for mitochondrial dysfunction.

Caenorhabditis elegans as a Useful Model for Studying Aging Mutations

“…At the cellular level, the primary age-dependent changes in C. elegans generally include diminishing integrity of nuclei and increased relative size of the nucleoli; however, these changes may vary depending on the tissue types. Moreover, mitochondria undergo age-dependent structural and functional changes, including mitochondrial fusion and increased mitochondrial fragmentation, which is consistent with changes in mitochondrial DNA copy numbers and oxygen consumption rates ( 15 ). The capacity of the unfolded protein response of endoplasmic reticulum (ER UPR ) seems to be reduced in aged C. elegans .…”

IMPACT OF PHENOLIC ACIDS ON THE ENERGY METABOLISM AND LONGEVITY IN C. ELEGANS

“…Increasing evidence suggests a close relationship between mitochondrial function and longevity [6,33]. During oxidative phosphorylation electrons are able escape mitochondrial respiration, forming reactive oxygen species (ROS), which can cause cellular damage in form of lipid and DNA oxidation [34,35].…”

“…Over the last decades, growing evidence suggests mitochondrial function to play a key role during aging [3,4]. The "mitochondrial theory of aging", first proposed by Harman in 1956 [5], suggests the accumulation of reactive oxygen species (ROS) to cause oxidative damage, induce mitochondrial dysfunction and thus contribute to aging and the development of related diseases [6,7]. Although an imbalance of exaggerated ROS are associated with DNA mutations or oxidative damage to lipids and proteins [8], recent evidence suggests mild doses of stressors to be beneficial [9].…”

“…Mitochondria represent a unique organelle, conserved over long evolutionary distances and across species, making nematodes an ideal organism to investigate mitochondrial function [6,12]. According to a recent report mitochondria of nematodes even poses an cold-tolerance mechanism comparable to mammalian non-shivering thermogenesis, allowing mitochondria to generate heat rather than ATP [13].…”

Infertility induced by auxin in PX627 Caenorhabditis elegans does not affect mitochondrial functions and aging parameters

“…Consequential alterations in mitochondrial function, due to mtDNA depletion, can be linked to a number of human diseases, such as encephalopathy or myopathy [10]. Furthermore, there is a close relationship between mitochondrial function and longevity [11], making the use of FUdR an unfavourable option for investigations concerned with mitochondrial function, longevity, or their interconnection.…”