Mitochondrial expression and function of GAS-1 in Caenorhabditis elegans

Paeoniflorin alleviates toxicity and accumulation of 6-PPD quinone by activating ACS-22 in Caenorhabditis elegans

6-PPD quinone (6-PPDQ) is extensively existed in various environments. In Caenorhabditis elegans, exposure to 6-PPDQ could cause multiple toxic effects. In the current study, we further used C. elegans to investigate the effect of paeoniflorin (PF) treatment on 6-PPDQ toxicity and accumulation and the underlying mechanism. Treatment with PF (25-100 mg/L) inhibited 6-PPDQ toxicity on reproduction capacity and locomotion behavior and in inducing reactive oxygen species (ROS) production. Additionally, PF (25-100 mg/L) alleviated the dysregulation in expression of genes governing oxidative stress caused by 6-PPDQ exposure. Moreover, PF (25-100 mg/L) inhibited the enhancement in intestinal permeability caused by 6-PPDQ exposure and the accumulation of 6-PPDQ in the body of nematodes. In 6-PPDQ exposed nematodes, PF (25-100 mg/L) increased expression of acs-22 encoding a fatty acid transporter. RNAi of acs-22 could inhibit the beneficial effect of PF against 6-PPDQ toxicity in decreasing reproductive capacity and locomotion behavior, in inducing intestinal ROS production, and in enhancing intestinal permeability. RNAi of acs-22 could also suppress the PF beneficial effect against 6-PPDQ accumulation in the body of nematodes. Therefore, our results demonstrate the function of PF treatment against 6-PPDQ toxicity and accumulation in nematodes by activating the ACS-22.

Validation of metaxin-2 deficient C. elegans as a model for MandibuloAcral Dysplasia associated to mtx-2 (MADaM) syndrome

MandibuloAcral Dysplasia associated to MTX2 gene (MADaM) is a recently described progeroid syndrome (accelerated aging disease) whose clinical manifestations include skin abnormalities, growth retardation, and cardiovascular diseases. We previously proposed that mtx-2-deficient C. elegans could be used as a model for MADaM and to support this, we present here our comprehensive phenotypic characterization of these worms using atomic force microscopy (AFM), transcriptomic, and oxygen consumption rate analyses. AFM analysis showed that young mtx-2-less worms had a significantly rougher, less elastic cuticle which becomes significantly rougher and less elastic as they age, and abnormal mitochondrial morphology. mtx-2 C. elegans displayed slightly delayed development, decreased pharyngeal pumping, significantly reduced mitochondrial respiratory capacities, and transcriptomic analysis identified perturbations in the aging, TOR, and WNT-signaling pathways. The phenotypic characteristics of mtx-2 worms shown here are analogous to many of the human clinical presentations of MADaM and we believe this validates their use as a model which will allow us to uncover the molecular details of the disease and develop new therapeutics and treatments.

You Don't Always Get What You Want!

BACKGROUND

Mutations in several genes of Caenorhabditis elegans confer altered sensitivities to volatile anesthetics. A mutation in one gene, gas-1(fc21), causes animals to be immobilized at lower concentrations of all volatile anesthetics than in the wild type, and it does not depend on mutations in other genes to control anesthetic sensitivity. gas-1 confers different sensitivities to stereoisomers of isoflurane, and thus may be a direct target for volatile anesthetics. The authors have cloned and characterized the gas gene and the mutant allele fc21.

METHODS

Genetic techniques for nematodes were as previously described. Polymerase chain reaction, sequencing, and other molecular biology techniques were performed by standard methods. Mutant rescue was done by injecting DNA fragments into the gonad of mutant animals and scoring the offspring for loss of the mutant phenotype.

RESULTS

The gas-1 gene was cloned and identified. The protein GAS-1 is a homologue of the 49-kd (IP) subunit of the mitochondrial NADH-ubiquinone-oxidoreductase (complex I of the respiratory chain). gas-1(fc21) is a missense mutation replacing a strictly conserved arginine with lysine.

CONCLUSIONS

The function of the 49-kd (IP) subunit of complex I is unknown. The finding that mutations in complex I increase sensitivity of C. elegans to volatile anesthetics may implicate this physiologic process in the determination of anesthetic sensitivity. The hypersensitivity of animals with a mutation in the gas-1 gene may be caused by a direct anesthetic effect on a mitochondrial protein or secondary effects at other sites caused by mitochondrial dysfunction.

CMTR-1 RNA methyltransferase mutations activate widespread expression of a dopaminergic neuron-specific mitochondrial complex I gene

The mitochondrial proteome is comprised of approximately 1,100 proteins,1 all but 12 of which are encoded by the nuclear genome in C. elegans. The expression of nuclear-encoded mitochondrial proteins varies widely across cell lineages and metabolic states,2,3,4 but the factors that specify these programs are not known. Here, we identify mutations in two nuclear-localized mRNA processing proteins, CMTR1/CMTR-1 and SRRT/ARS2/SRRT-1, which we show act via the same mechanism to rescue the mitochondrial complex I mutant NDUFS2/gas-1(fc21). CMTR-1 is an FtsJ-family RNA methyltransferase that, in mammals, 2'-O-methylates the first nucleotide 3' to the mRNA CAP to promote RNA stability and translation5,6,7,8. The mutations isolated in cmtr-1 are dominant and lie exclusively in the regulatory G-patch domain. SRRT-1 is an RNA binding partner of the nuclear cap-binding complex and determines mRNA transcript fate.9 We show that cmtr-1 and srrt-1 mutations activate embryonic expression of NDUFS2/nduf-2.2, a paralog of NDUFS2/gas-1 normally expressed only in dopaminergic neurons, and that nduf-2.2 is necessary for the complex I rescue by the cmtr-1 G-patch mutant. Additionally, we find that loss of the cmtr-1 G-patch domain cause ectopic localization of CMTR-1 protein to processing bodies (P bodies), phase-separated organelles involved in mRNA storage and decay.10 P-body localization of the G-patch mutant CMTR-1 contributes to the rescue of the hyperoxia sensitivity of the NDUFS2/gas-1 mutant. This study suggests that mRNA methylation at P bodies may control nduf-2.2 gene expression, with broader implications for how the mitochondrial proteome is translationally remodeled in the face of tissue-specific metabolic requirements and stress.

RNA: De-silencing to the rescue

The fate of transcribed RNA dictates cellular function. A new study finds that mutations in specific RNA processing machinery genes result in de-silencing of a transcript encoding a subunit of the mitochondrial electron transport chain and rescue of a mitochondrial respiratory complex I defect.

Potassium Leak Channels and Mitochondrial Complex I Interact in Glutamatergic Interneurons of the Mouse Spinal Cord

BACKGROUND

Volatile anesthetics induce hyperpolarizing potassium currents in spinal cord neurons that may contribute to their mechanism of action. They are induced at lower concentrations of isoflurane in noncholinergic neurons from mice carrying a loss-of-function mutation of the Ndufs4 gene, required for mitochondrial complex I function. The yeast NADH dehydrogenase enzyme, NDi1, can restore mitochondrial function in the absence of normal complex I activity, and gain-of-function Ndi1 transgenic mice are resistant to volatile anesthetics. The authors tested whether NDi1 would reduce the hyperpolarization caused by isoflurane in neurons from Ndufs4 and wild-type mice. Since volatile anesthetic behavioral hypersensitivity in Ndufs4 is transduced uniquely by glutamatergic neurons, it was also tested whether these currents were also unique to glutamatergic neurons in the Ndufs4 spinal cord.

METHODS

Spinal cord neurons from wild-type, NDi1, and Ndufs4 mice were patch clamped to characterize isoflurane sensitive currents. Neuron types were marked using fluorescent markers for cholinergic, glutamatergic, and γ-aminobutyric acid-mediated (GABAergic) neurons. Norfluoxetine was used to identify potassium channel type. Neuron type-specific Ndufs4 knockout animals were generated using type-specific Cre-recombinase with floxed Ndufs4.

RESULTS

Resting membrane potentials (RMPs) of neurons from NDi1;Ndufs4, unlike those from Ndufs4, were not hyperpolarized by 0.6% isoflurane (Ndufs4, ΔRMP -8.2 mV [-10 to -6.6]; P = 1.3e-07; Ndi1;Ndufs4, ΔRMP -2.1 mV [-7.6 to +1.4]; P = 1). Neurons from NDi1 animals in a wild-type background were not hyperpolarized by 1.8% isoflurane (wild-type, ΔRMP, -5.2 mV [-7.3 to -3.2]; P = 0.00057; Ndi1, ΔRMP, 0.6 mV [-1.7 to 3.2]; P = 0.68). In spinal cord slices from global Ndufs4 animals, holding currents (HC) were induced by 0.6% isoflurane in both GABAergic (ΔHC, 81.3 pA [61.7 to 101.4]; P = 2.6e-05) and glutamatergic (ΔHC, 101.2 pA [63.0 to 146.2]; P = 0.0076) neurons. In neuron type-specific Ndufs4 knockouts, HCs were increased in cholinergic (ΔHC, 119.5 pA [82.3 to 156.7]; P = 0.00019) and trended toward increase in glutamatergic (ΔHC, 85.5 pA [49 to 126.9]; P = 0.064) neurons but not in GABAergic neurons.

CONCLUSIONS

Bypassing complex I by overexpression of NDi1 eliminates increases in potassium currents induced by isoflurane in the spinal cord. The isoflurane-induced potassium currents in glutamatergic neurons represent a potential downstream mechanism of complex I inhibition in determining minimum alveolar concentration.

EDITOR’S PERSPECTIVE

Hypoxia and intra-complex genetic suppressors rescue complex I mutants by a shared mechanism

The electron transport chain (ETC) of mitochondria, bacteria, and archaea couples electron flow to proton pumping and is adapted to diverse oxygen environments. Remarkably, in mice, neurological disease due to ETC complex I dysfunction is rescued by hypoxia through unknown mechanisms. Here, we show that hypoxia rescue and hyperoxia sensitivity of complex I deficiency are evolutionarily conserved to C. elegans and are specific to mutants that compromise the electron-conducting matrix arm. We show that hypoxia rescue does not involve the hypoxia-inducible factor pathway or attenuation of reactive oxygen species. To discover the mechanism, we use C. elegans genetic screens to identify suppressor mutations in the complex I accessory subunit NDUFA6/nuo-3 that phenocopy hypoxia rescue. We show that NDUFA6/nuo-3(G60D) or hypoxia directly restores complex I forward activity, with downstream rescue of ETC flux and, in some cases, complex I levels. Additional screens identify residues within the ubiquinone binding pocket as being required for the rescue by NDUFA6/nuo-3(G60D) or hypoxia. This reveals oxygen-sensitive coupling between an accessory subunit and the quinone binding pocket of complex I that can restore forward activity in the same manner as hypoxia.

A drug-like molecule engages nuclear hormone receptor DAF-12/FXR to regulate mitophagy and extend lifespan

Autophagy-lysosomal function is crucial for maintaining healthy lifespan and preventing age-related diseases. The transcription factor TFEB plays a key role in regulating this pathway. Decreased TFEB expression is associated with various age-related disorders, making it a promising therapeutic target. In this study, we screened a natural product library and discovered mitophagy-inducing coumarin (MIC), a benzocoumarin compound that enhances TFEB expression and lysosomal function. MIC robustly increases the lifespan of Caenorhabditis elegans in an HLH-30/TFEB-dependent and mitophagy-dependent manner involving DCT-1/BNIP3 while also preventing mitochondrial dysfunction in mammalian cells. Mechanistically, MIC acts by inhibiting ligand-induced activation of the nuclear hormone receptor DAF-12/FXR, which, in turn, induces mitophagy and extends lifespan. In conclusion, our study uncovers MIC as a promising drug-like molecule that enhances mitochondrial function and extends lifespan by targeting DAF-12/FXR. Furthermore, we discovered DAF-12/FXR as a previously unknown upstream regulator of HLH-30/TFEB and mitophagy.

Comparative oxidative damages induced by silver nanoparticles with different sizes and coatings in Caenorhabditis elegans

Silver nanoparticles (AgNPs) are widely used in many commercial and medical products. Serious concerns are paid on their adverse potentials to the environment and human health. In this study, toxic effects and oxidative stress induced by AgNPs with different sizes and coatings (20 nm AgNPs, 20 nm polyvinylpyrrolidone (PVP) -AgNPs and 50 nm AgNPs) in Caenorhabditis elegans (C. elegans) were investigated. The toxic effects including the shortened lifespan and decreased frequency of head thrashes and body bends of C. elegans were induced in a dose-dependent manner by AgNPs. The reactive oxygen species (ROS) production and the oxidative stress-related indicators including malondialdehyde (MDA) and glutathione (GSH) in nematodes were changed after exposure to three kinds of AgNPs. These effects were the most obvious in a 20 nm PVP-AgNPs exposure group. AgNPs could also induce the expression of genes related to oxidative stress in nematodes. In addition, the up-regulation of mtl-1 and mtl-2 in nematodes might reduce the oxidative damage caused by AgNPs, by using transgenic strains CF2222 and CL2120 nematodes. Metallothionein (MT), an antioxidant, could relieve the oxidative damage caused by AgNPs. These results suggested that 20 nm PVP-AgNPs with a smaller particle size and better dispersion have stronger toxic effects and the oxidative damage to nematodes. Mtl-1 and mtl-2 might be involved in alleviating the oxidative damage caused by AgNPs. Our findings provide clues for the safety evaluation and mechanism information of metal nanoparticles.

Effects of tri-n-butyl phosphate (TnBP) on neurobehavior of Caenorhabditis elegans

As an emerging flame retardant, organic phosphate flame retardants have been extensively used worldwide. The aim of this study is to determine the effects of TnBP on neurobehavior of Caenorhabditis elegans (C. elegans) and its mechanisms. L1 larvae of wild-type nematodes (N2) were exposed to TnBP of 0, 0.1, 1, 10, and 20 mg/L for 72 hours. Then, we observed that the body length and body width were inhibited, the head swings were increased, the pump contractions and chemical trend index were reduced, the production of reactive oxygen species (ROS) was increased, and the expression of mitochondrial oxidative stress related genes (mev-1 and gas-1) and P38 MAPK signal pathway-related genes (pmk-1, sek-1, and nsy-1) was altered. After reporter gene strains BZ555, DA1240, and EG1285 were exposed to TnBP of 0, 0.1, 1, 10, and 20 mg/L for 72 hours, the synthesis of dopamine, glutamate, and Gamma-Amino Butyric Acid (GABA) was increased. In addition, the pmk-1 mutants (KU25) led to the sensitivity of C. elegans to TnBP in terms of head swings. The results showed that TnBP had harmful effects on the neurobehavior of C. elegans, oxidative stress might be one of the mechanisms of its neurotoxicity, and P38 MAPK signal pathway might play an important regulatory role in this process. The results revealed the potential adverse effects of TnBP on the neurobehavior of C. elegans.

Ecotoxicity induced by total, water soluble and insoluble components of atmospheric fine particulate matter exposure in Caenorhabditis elegans

Although PM_2.5 could cause toxicity in environmental organisms, the toxicity difference of PM_2.5 under different solubilities is still poorly understood. To acquire a better knowledge of the ecotoxicity of PM_2.5 under different solubilities, the model animal Caenorhabditis elegans (C. elegans) was exposed to Total-PM_2.5, water insoluble components of PM_2.5 (WIS-PM_2.5) and water soluble components of PM_2.5 (WS-PM_2.5). The physiological (growth, locomotion behavior, and reproduction), biochemical (germline apoptosis, and reactive oxygen species (ROS) production) indices, and the related gene expression were examined. According to the findings, acute exposure to these three components caused adverse physiological effects on growth and locomotion behavior, and significantly induced germline apoptosis or ROS production. In contrast, prolonged exposure showed stronger adverse effects than acute exposure. Additionally, the results of multiple toxicological endpoints showed that the toxicity effects of WIS-PM_2.5 are more intense than WS-PM_2.5, which means that insoluble components contributed more to the toxicity of PM_2.5. Prolonged exposure to 1000 mg/L WS-PM_2.5, WIS-PM_2.5, and Total-PM_2.5 dramatically altered the expression of stress-related genes, which further indicated that apoptosis, DNA damage and oxidative stress play a crucial part in toxicity induced by PM_2.5.

Dichloroacetate and thiamine improve survival and mitochondrial stress in a C. elegans model of dihydrolipoamide dehydrogenase deficiency

Dihydrolipoamide dehydrogenase (DLD) deficiency is a recessive mitochondrial disorder caused by depletion of DLD from α-ketoacid dehydrogenase complexes. Caenorhabditis elegans animal models of DLD deficiency generated by graded feeding of dld-1(RNAi) revealed that full or partial reduction of DLD-1 expression recapitulated increased pyruvate levels typical of pyruvate dehydrogenase complex deficiency and significantly altered animal survival and health, with reductions in brood size, adult length, and neuromuscular function. DLD-1 deficiency dramatically increased mitochondrial unfolded protein stress response induction and adaptive mitochondrial proliferation. While ATP levels were reduced, respiratory chain enzyme activities and in vivo mitochondrial membrane potential were not significantly altered. DLD-1 depletion directly correlated with the induction of mitochondrial stress and impairment of worm growth and neuromuscular function. The safety and efficacy of dichloroacetate, thiamine, riboflavin, 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR), l-carnitine, and lipoic acid supplemental therapies empirically used for human DLD disease were objectively evaluated by life span and mitochondrial stress response studies. Only dichloroacetate and thiamine showed individual and synergistic therapeutic benefits. Collectively, these C. elegans dld-1(RNAi) animal model studies demonstrate the translational relevance of preclinical modeling of disease mechanisms and therapeutic candidates. Results suggest that clinical trials are warranted to evaluate the safety and efficacy of dichloroacetate and thiamine in human DLD disease.

Caenorhabditis elegans as a Model for the Effects of Phytochemicals on Mitochondria and Aging

The study of aging is an important topic in contemporary research. Considering the demographic changes and the resulting shifts towards an older population, it is of great interest to preserve youthful physiology in old age. For this endeavor, it is necessary to choose an appropriate model. One such model is the nematode Caenorhabditis elegans (C. elegans), which has a long tradition in aging research. In this review article, we explore the advantages of using the nematode model in aging research, focusing on bioenergetics and the study of secondary plant metabolites that have interesting implications during this process. In the first section, we review the situation of aging research today. Conventional theories and hypotheses about the ongoing aging process will be presented and briefly explained. The second section focuses on the nematode C. elegans and its utility in aging and nutrition research. Two useful genome editing methods for monitoring genetic interactions (RNAi and CRISPR/Cas9) are presented. Due to the mitochondria's influence on aging, we also introduce the possibility of observing bioenergetics and respiratory phenomena in C. elegans. We then report on mitochondrial conservation between vertebrates and invertebrates. Here, we explain why the nematode is a suitable model for the study of mitochondrial aging. In the fourth section, we focus on phytochemicals and their applications in contemporary nutritional science, with an emphasis on aging research. As an emerging field of science, we conclude this review in the fifth section with several studies focusing on mitochondrial research and the effects of phytochemicals such as polyphenols. In summary, the nematode C. elegans is a suitable model for aging research that incorporates the mitochondrial theory of aging. Its living conditions in the laboratory are optimal for feeding studies, thus enabling bioenergetics to be observed during the aging process.

Dietary-derived vitamin B12 protects Caenorhabditis elegans from thiol-reducing agents

BACKGROUND

One-carbon metabolism, which includes the folate and methionine cycles, involves the transfer of methyl groups which are then utilised as a part of multiple physiological processes including redox defence. During the methionine cycle, the vitamin B12-dependent enzyme methionine synthetase converts homocysteine to methionine. The enzyme S-adenosylmethionine (SAM) synthetase then uses methionine in the production of the reactive methyl carrier SAM. SAM-binding methyltransferases then utilise SAM as a cofactor to methylate proteins, small molecules, lipids, and nucleic acids.

RESULTS

We describe a novel SAM methyltransferase, RIPS-1, which was the single gene identified from forward genetic screens in Caenorhabditis elegans looking for resistance to lethal concentrations of the thiol-reducing agent dithiothreitol (DTT). As well as RIPS-1 mutation, we show that in wild-type worms, DTT toxicity can be overcome by modulating vitamin B12 levels, either by using growth media and/or bacterial food that provide higher levels of vitamin B12 or by vitamin B12 supplementation. We show that active methionine synthetase is required for vitamin B12-mediated DTT resistance in wild types but is not required for resistance resulting from RIPS-1 mutation and that susceptibility to DTT is partially suppressed by methionine supplementation. A targeted RNAi modifier screen identified the mitochondrial enzyme methylmalonyl-CoA epimerase as a strong genetic enhancer of DTT resistance in a RIPS-1 mutant. We show that RIPS-1 is expressed in the intestinal and hypodermal tissues of the nematode and that treating with DTT, β-mercaptoethanol, or hydrogen sulfide induces RIPS-1 expression. We demonstrate that RIPS-1 expression is controlled by the hypoxia-inducible factor pathway and that homologues of RIPS-1 are found in a small subset of eukaryotes and bacteria, many of which can adapt to fluctuations in environmental oxygen levels.

CONCLUSIONS

This work highlights the central importance of dietary vitamin B12 in normal metabolic processes in C. elegans, defines a new role for this vitamin in countering reductive stress, and identifies RIPS-1 as a novel methyltransferase in the methionine cycle.

Isoflurane inhibition of endocytosis is an anesthetic mechanism of action

The mechanisms of volatile anesthetic action remain among the most perplexing mysteries of medicine. Across phylogeny, volatile anesthetics selectively inhibit mitochondrial complex I, and they also depress presynaptic excitatory signaling. To explore how these effects are linked, we studied isoflurane effects on presynaptic vesicle cycling and ATP levels in hippocampal cultured neurons from wild-type and complex I mutant (Ndufs4(KO)) mice. To bypass complex I, we measured isoflurane effects on anesthetic sensitivity in mice expressing NADH dehydrogenase (NDi1). Endocytosis in physiologic concentrations of glucose was delayed by effective behavioral concentrations of isoflurane in both wild-type (τ [unexposed] 44.8 ± 24.2 s; τ [exposed] 116.1 ± 28.1 s; p < 0.01) and Ndufs4(KO) cultures (τ [unexposed] 67.6 ± 16.0 s; τ [exposed] 128.4 ± 42.9 s; p = 0.028). Increasing glucose, to enhance glycolysis and increase ATP production, led to maintenance of both ATP levels and endocytosis (τ [unexposed] 28.0 ± 14.4; τ [exposed] 38.2 ± 5.7; reducing glucose worsened ATP levels and depressed endocytosis (τ [unexposed] 85.4 ± 69.3; τ [exposed] > 1,000; p < 0.001). The block in recycling occurred at the level of reuptake of synaptic vesicles into the presynaptic cell. Expression of NDi1 in wild-type mice caused behavioral resistance to isoflurane for tail clamp response (EC₅₀ Ndi1(-) 1.27% ± 0.14%; Ndi1(+) 1.55% ± 0.13%) and halothane (EC₅₀ Ndi1(-) 1.20% ± 0.11%; Ndi1(+) 1.46% ± 0.10%); expression of NDi1 in neurons improved hippocampal function, alleviated inhibition of presynaptic recycling, and increased ATP levels during isoflurane exposure. The clear alignment of cell culture data to in vivo phenotypes of both isoflurane-sensitive and -resistant mice indicates that inhibition of mitochondrial complex I is a primary mechanism of action of volatile anesthetics.

Sanguinarine promotes healthspan and innate immunity through a conserved mechanism of ROS-mediated PMK-1/SKN-1 activation

The longevity of an organism is influenced by both genetic and environmental factors. With respect to genetic factors, a significant effort is being made to identify pharmacological agents that extend lifespan by targeting pathways with a defined role in the aging process. Sanguinarine (San) is a benzophenanthridine alkaloid that exerts a broad spectrum of properties. In this study, we utilized Caenorhabditis elegans to examine the mechanisms by which sanguinarine influences aging and innate immunity. We find that 0.2 μM sanguinarine extends healthspan in C. elegans. We further show that sanguinarine generates reactive oxygen species (ROS), which is followed by the activation of PMK-1/SKN-1pathway to extend healthspan. Intriguingly, sanguinarine increases resistance to pathogens by reducing the bacterial burden in the intestine. In addition, we also find that sanguinarine enhances innate immunity through PMK-1/SKN-1 pathway. Our data suggest that sanguinarine may be a viable candidate for the treatment of age-related disorders.

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Sanguinarine extends healthspan in C. elegans

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Sanguinarine-induced ROS activates the PMK-1/SKN-1 pathway to extend healthspan

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Sanguinarine increases resistance to pathogens by reducing the bacterial burden

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Sanguinarine enhances innate immunity through PMK-1/SKN-1 pathway

Study on the reproductive toxicity and mechanism of tri-n-butyl phosphate (TnBP) in Caenorhabditis elegans

Tri-n-butyl phosphate (TnBP), a typical alkyl organophosphate ester is widely used as an emerging flame retardant for polybrominated diphenyl ethers alternatives, but the potential toxicity and mechanism are unclear. In this study, the reproductive toxicity of TnBP and its related mechanisms were explored using the Caenorhabditis elegans (C. elegans) model. After TnBP (100-1000 μg/L) exposure, brood size and the number of fertilized eggs in the uterus in C. elegans were significantly reduced, the relative area of gonad arm and the number of total germline cells in C. elegans were significantly reduced, germ cell apoptosis and germ cell DNA damage in C. elegans were significantly increased, the level of ROS in C. elegans was significantly increased. Furthermore, TnBP exposure caused abnormal gene expressions of cell apoptosis (ced-9, ced-4 and ced-3), DNA damage (hus-1, clk-2, cep-1 and egl-1) and oxidative stress (mev-1 and gas-1). TnBP exposure can lead to reproductive ability decreased and gonad development impaired in C. elegans, the mechanism of TnBP reduced reproductive ability may be related to germ cell apoptosis, germ cell DNA damage and oxidative stress. Environmental exposure to TnBP may have potential reproductive toxicity.

Mechanisms underlying neonate-specific metabolic effects of volatile anesthetics

Volatile anesthetics (VAs) are widely used in medicine, but the mechanisms underlying their effects remain ill-defined. Though routine anesthesia is safe in healthy individuals, instances of sensitivity are well documented, and there has been significant concern regarding the impact of VAs on neonatal brain development. Evidence indicates that VAs have multiple targets, with anesthetic and non-anesthetic effects mediated by neuroreceptors, ion channels, and the mitochondrial electron transport chain. Here, we characterize an unexpected metabolic effect of VAs in neonatal mice. Neonatal blood β-hydroxybutarate (β-HB) is rapidly depleted by VAs at concentrations well below those necessary for anesthesia. β-HB in adults, including animals in dietary ketosis, is unaffected. Depletion of β-HB is mediated by citrate accumulation, malonyl-CoA production by acetyl-CoA carboxylase, and inhibition of fatty acid oxidation. Adults show similar significant changes to citrate and malonyl-CoA, but are insensitive to malonyl-CoA, displaying reduced metabolic flexibility compared to younger animals.

Combinatorial glucose, nicotinic acid and N-acetylcysteine therapy has synergistic effect in preclinical C. elegans and zebrafish models of mitochondrial complex I disease

Mitochondrial respiratory chain disorders are empirically managed with variable antioxidant, cofactor and vitamin 'cocktails'. However, clinical trial validated and approved compounds, or doses, do not exist for any single or combinatorial mitochondrial disease therapy. Here, we sought to pre-clinically evaluate whether rationally designed mitochondrial medicine combinatorial regimens might synergistically improve survival, health and physiology in translational animal models of respiratory chain complex I disease. Having previously demonstrated that gas-1(fc21) complex I subunit ndufs2-/-C. elegans have short lifespan that can be significantly rescued with 17 different metabolic modifiers, signaling modifiers or antioxidants, here we evaluated 11 random combinations of these three treatment classes on gas-1(fc21) lifespan. Synergistic rescue occurred only with glucose, nicotinic acid and N-acetylcysteine (Glu + NA + NAC), yielding improved mitochondrial membrane potential that reflects integrated respiratory chain function, without exacerbating oxidative stress, and while reducing mitochondrial stress (UPRmt) and improving intermediary metabolic disruptions at the levels of the transcriptome, steady-state metabolites and intermediary metabolic flux. Equimolar Glu + NA + NAC dosing in a zebrafish vertebrate model of rotenone-based complex I inhibition synergistically rescued larval activity, brain death, lactate, ATP and glutathione levels. Overall, these data provide objective preclinical evidence in two evolutionary-divergent animal models of mitochondrial complex I disease to demonstrate that combinatorial Glu + NA + NAC therapy significantly improved animal resiliency, even in the face of stressors that cause severe metabolic deficiency, thereby preventing acute neurologic and biochemical decompensation. Clinical trials are warranted to evaluate the efficacy of this lead combinatorial therapy regimen to improve resiliency and health outcomes in human subjects with mitochondrial disease.

Mitochondrial hydrogen peroxide positively regulates neuropeptide secretion during diet-induced activation of the oxidative stress response

Mitochondria play a pivotal role in the generation of signals coupling metabolism with neurotransmitter release, but a role for mitochondrial-produced ROS in regulating neurosecretion has not been described. Here we show that endogenously produced hydrogen peroxide originating from axonal mitochondria (mtH2O2) functions as a signaling cue to selectively regulate the secretion of a FMRFamide-related neuropeptide (FLP-1) from a pair of interneurons (AIY) in C. elegans. We show that pharmacological or genetic manipulations that increase mtH2O2 levels lead to increased FLP-1 secretion that is dependent upon ROS dismutation, mitochondrial calcium influx, and cysteine sulfenylation of the calcium-independent PKC family member PKC-1. mtH2O2-induced FLP-1 secretion activates the oxidative stress response transcription factor SKN-1/Nrf2 in distal tissues and protects animals from ROS-mediated toxicity. mtH2O2 levels in AIY neurons, FLP-1 secretion and SKN-1 activity are rapidly and reversibly regulated by exposing animals to different bacterial food sources. These results reveal a previously unreported role for mtH2O2 in linking diet-induced changes in mitochondrial homeostasis with neuropeptide secretion.

A C. elegans genome-wide RNAi screen for altered levamisole sensitivity identifies genes required for muscle function

At the neuromuscular junction (NMJ), postsynaptic ionotropic acetylcholine receptors (AChRs) transduce a chemical signal released from a cholinergic motor neuron into an electrical signal to induce muscle contraction. To identify regulators of postsynaptic function, we conducted a genome-wide RNAi screen for genes required for proper response to levamisole, a pharmacological agonist of ionotropic L-AChRs at the Caenorhabditis elegans NMJ. A total of 117 gene knockdowns were found to cause levamisole hypersensitivity, while 18 resulted in levamisole resistance. Our screen identified conserved genes important for muscle function including some that are mutated in congenital myasthenic syndrome, congenital muscular dystrophy, congenital myopathy, myotonic dystrophy, and mitochondrial myopathy. Of the genes found in the screen, we further investigated those predicted to play a role in endocytosis of cell surface receptors. Loss of the Epsin homolog epn-1 caused levamisole hypersensitivity and had opposing effects on the levels of postsynaptic L-AChRs and GABA_A receptors, resulting in increased and decreased abundance, respectively. We also examined other genes that resulted in a levamisole-hypersensitive phenotype when knocked down including gas-1, which functions in Complex I of the mitochondrial electron transport chain. Consistent with altered ATP synthesis impacting levamisole response, treatment of wild-type animals with levamisole resulted in L-AChR–dependent depletion of ATP levels. These results suggest that the paralytic effects of levamisole ultimately lead to metabolic exhaustion.

Nutritive Manganese and Zinc Overdosing in Aging C. elegans Result in a Metallothionein-Mediated Alteration in Metal Homeostasis

SCOPE

Manganese (Mn) and zinc (Zn) are not only essential trace elements, but also potential exogenous risk factors for various diseases. Since the disturbed homeostasis of single metals can result in detrimental health effects, concerns have emerged regarding the consequences of excessive exposures to multiple metals, either via nutritional supplementation or parenteral nutrition. This study focuses on Mn-Zn-interactions in the nematode Caenorhabditis elegans (C. elegans) model, taking into account aspects related to aging and age-dependent neurodegeneration.

METHODS AND RESULTS

Chronic co-exposure of C. elegans to Mn and Zn increases metal uptake, exceeding levels of single metal exposures. Supplementation with Mn and/or Zn also leads to an age-dependent increase in metal content, a decline in overall mRNA expression, and metal co-supplementation induced expression of target genes involved in Mn and Zn homeostasis, in particular metallothionein 1 (mtl-1). Studies in transgenic worms reveal that mtl-1 played a prominent role in mediating age- and diet-dependent alterations in metal homeostasis. Metal dyshomeostasis is further induced in parkin-deficient nematodes (Parkinson's disease (PD) model), but this did not accelerate the age-dependent dopaminergic neurodegeneration.

CONCLUSIONS

A nutritive overdose of Mn and Zn can alter interactions between essential metals in an aging organism, and metallothionein 1 acts as a potential protective modulator in regulating homeostasis.

The pursuit of precision mitochondrial medicine: Harnessing preclinical cellular and animal models to optimize mitochondrial disease therapeutic discovery

Mitochondria share extensive evolutionary conservation across nearly all living species. This homology allows robust insights to be gained into pathophysiologic mechanisms and therapeutic targets for the heterogeneous class of primary mitochondrial diseases (PMDs) through the study of diverse in vitro cellular and in vivo animal models. Dramatic advances in genetic technologies, ranging from RNA interference to achieve graded knock-down of gene expression to CRISPR/Cas-based gene editing that yields a stable gene knock-out or targeted mutation knock-in, have enabled the ready establishment of mitochondrial disease models for a plethora of individual nuclear gene disorders. These models are complemented and extended by the use of pharmacologic inhibitor-based stressors to characterize variable degrees, onset, duration, and combinations of acute on chronic mitochondrial dysfunction in individual respiratory chain enzyme complexes or distinct biochemical pathways within mitochondria. Herein is described the rationale for, and progress made in, "therapeutic cross-training," a novel approach meant to improve the validity and rigor of experimental conclusions when testing therapies by studying treatment effects in multiple, evolutionarily-distinct species, including Caenorhabditis elegans (invertebrate, worm), Danio rerio (vertebrate, zebrafish), Mus musculus (mammal, mouse), and/or human patient primary fibroblast cell line models of PMD. The goal of these preclinical studies is to identify lead therapies from candidate molecules or library screens that consistently demonstrate efficacy, with minimal toxicity, in specific subtypes of mitochondrial disease. Conservation of in vitro and in vivo therapeutic effects of lead molecules across species has proven extensive, where molar concentrations found to be toxic or efficacious in one species are often consistent with therapeutic effects at similar doses seen in other mitochondrial disease models. Phenotypic outcome studies in all models are prioritized at the level of survival and function, to reflect the ultimate goal of developing highly potent therapies for human mitochondrial disease. Lead compounds that demonstrate significant benefit on gross phenotypes may be further scrutinized in these same models to decipher their cellular targets, mechanism(s), and detailed biochemical effects. High-throughput, automated technologic advances will be discussed that enable efficient, parallel screening in a diverse array of mitochondrial disease disorders and overarching subclasses of compounds, concentrations, libraries, and combinations. Overall, this therapeutic cross-training approach has proven valuable to identify compounds with optimal potency and safety profiles among major biochemical subtypes or specific genetic etiologies of mitochondrial disease. This approach further supports rational prioritization of lead compounds, target concentrations, and specific disease phenotypes, outcomes, and subgroups to optimally inform the design of clinical trials that test their efficacy in human mitochondrial disease subjects.

Multiple metabolic changes mediate the response of Caenorhabditis elegans to the complex I inhibitor rotenone

Rotenone, a mitochondrial complex I inhibitor, has been widely used to study the effects of mitochondrial dysfunction on dopaminergic neurons in the context of Parkinson's disease. Although the deleterious effects of rotenone are well documented, we found that young adult Caenorhabditis elegans showed resistance to 24 and 48 h rotenone exposures. To better understand the response to rotenone in C. elegans, we evaluated mitochondrial bioenergetic parameters after 24 and 48 h exposures to 1 μM or 5 μM rotenone. Results suggested upregulation of mitochondrial complexes II and V following rotenone exposure, without major changes in oxygen consumption or steady-state ATP levels after rotenone treatment at the tested concentrations. We found evidence that the glyoxylate pathway (an alternate pathway not present in higher metazoans) was induced by rotenone exposure; gene expression measurements showed increases in mRNA levels for two complex II subunits and for isocitrate lyase, the key glyoxylate pathway enzyme. Targeted metabolomics analyses showed alterations in the levels of organic acids, amino acids, and acylcarnitines, consistent with the metabolic restructuring of cellular bioenergetic pathways including activation of complex II, the glyoxylate pathway, glycolysis, and fatty acid oxidation. This expanded understanding of how C. elegans responds metabolically to complex I inhibition via multiple bioenergetic adaptations, including the glyoxylate pathway, will be useful in interrogating the effects of mitochondrial and bioenergetic stressors and toxicants.

Anesthetic Hypersensitivity in a Case-Controlled Series of Patients With Mitochondrial Disease

BACKGROUND

Children with mitochondrial disease undergo anesthesia for a wide array of surgical procedures. However, multiple medications used for their perioperative care can affect mitochondrial function. Defects in function of the mitochondrial electron transport chain (ETC) can lead to a profound hypersensitivity to sevoflurane in children. We studied the sensitivities to sevoflurane, during mask induction and maintenance of general anesthesia, in children presenting for muscle biopsies for diagnosis of mitochondrial disease.

METHODS

In this multicenter study, 91 children, aged 6 months to 16 years, presented to the operating room for diagnostic muscle biopsy for presumptive mitochondrial disease. General anesthesia was induced by a slow increase of inhaled sevoflurane concentration. The primary end point, end-tidal (ET) sevoflurane necessary to achieve a bispectral index (BIS) of 60, was recorded. Secondary end points were maximal sevoflurane used to maintain a BIS between 40 and 60 during the case, and maximum and minimum heart rate and blood pressures. After induction, general anesthesia was maintained according to the preferences of the providers directing the cases. Primary data were analyzed comparing data from patients with complex I deficiencies to other groups using nonparametric statistics in SPSS v.27.

RESULTS

The median sevoflurane concentration to reach BIS of 60 during inductions (ET sevoflurane % [BIS = 60]) was significantly lower for patients with complex I defects (0.98%; 95% confidence interval [CI], 0.5-1.4) compared to complex II (1.95%; 95% CI, 1.2-2.7; P < .001), complex III (2.0%; 95% CI, 0.7-3.5; P < .001), complex IV (2.0%; 95% CI, 1.7-3.2; P < .001), and normal groups (2.2%; 95% CI, 1.8-3.0; P < .001). The sevoflurane sensitivities of complex I patients did not reach significance when compared to patients diagnosed with mitochondrial disease but without an identifiable ETC abnormality (P = .172). Correlation of complex I activity with ET sevoflurane % (BIS = 60) gave a Spearman's coefficient of 0.505 (P < .001). The differences in sensitivities between groups were less during the maintenance of the anesthetic than during induction.

CONCLUSIONS

The data indicate that patients with complex I dysfunction are hypersensitive to sevoflurane compared to normal patients. Hypersensitivity was less common in patients presenting with other mitochondrial defects or without a mitochondrial diagnosis.

Advances in mt-tRNA Mutation-Caused Mitochondrial Disease Modeling: Patients' Brain in a Dish

Mitochondrial diseases are a heterogeneous group of rare genetic disorders that can be caused by mutations in nuclear (nDNA) or mitochondrial DNA (mtDNA). Mutations in mtDNA are associated with several maternally inherited genetic diseases, with mitochondrial dysfunction as a main pathological feature. These diseases, although frequently multisystemic, mainly affect organs that require large amounts of energy such as the brain and the skeletal muscle. In contrast to the difficulty of obtaining neuronal and muscle cell models, the development of induced pluripotent stem cells (iPSCs) has shed light on the study of mitochondrial diseases. However, it is still a challenge to obtain an appropriate cellular model in order to find new therapeutic options for people suffering from these diseases. In this review, we deepen the knowledge in the current models for the most studied mt-tRNA mutation-caused mitochondrial diseases, MELAS (mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes) and MERRF (myoclonic epilepsy with ragged red fibers) syndromes, and their therapeutic management. In particular, we will discuss the development of a novel model for mitochondrial disease research that consists of induced neurons (iNs) generated by direct reprogramming of fibroblasts derived from patients suffering from MERRF syndrome. We hypothesize that iNs will be helpful for mitochondrial disease modeling, since they could mimic patient’s neuron pathophysiology and give us the opportunity to correct the alterations in one of the most affected cellular types in these disorders.

A salvage pathway maintains highly functional respiratory complex I

Regulation of the turnover of complex I (CI), the largest mitochondrial respiratory chain complex, remains enigmatic despite huge advancement in understanding its structure and the assembly. Here, we report that the NADH-oxidizing N-module of CI is turned over at a higher rate and largely independently of the rest of the complex by mitochondrial matrix protease ClpXP, which selectively removes and degrades damaged subunits. The observed mechanism seems to be a safeguard against the accumulation of dysfunctional CI arising from the inactivation of the N-module subunits due to attrition caused by its constant activity under physiological conditions. This CI salvage pathway maintains highly functional CI through a favorable mechanism that demands much lower energetic cost than de novo synthesis and reassembly of the entire CI. Our results also identify ClpXP activity as an unforeseen target for therapeutic interventions in the large group of mitochondrial diseases characterized by the CI instability.

Maintenance and quality control of the mitochondrial respiratory chain complexes responsible for bulk energy production are unclear. Here, the authors show that the mitochondrial protease ClpXP is required for the rapid turnover of the core N-module of respiratory complex I, which happens independently of other modules in the complex.

Potential of esterase DmtH in transforming plastic additive dimethyl terephthalate to less toxic mono-methyl terephthalate

Dimethyl terephthalate (DMT) is a primary ingredient widely used in the manufacture of polyesters and industrial plastics; its environmental fate is of concern due to its global use. Microorganisms play key roles in the dissipation of DMT from the environment; however, the enzymes responsible for the initial transformation of DMT and the possible altered toxicity due to this biotransformation have not been extensively studied. To reduce DMT toxicity, we identified the esterase gene dmtH involved in the initial transformation of DMT from the AOPP herbicide-transforming strain Sphingobium sp. C3. DmtH shows 24-41% identity with α/β-hydrolases and belongs to subfamily V of bacterial esterases. The purified recombinant DmtH was capable of transforming DMT to mono-methyl terephthalate (MMT) and potentially transforming other p-phthalic acid esters, including diallyl terephthalate (DAT) and diethyl terephthalate (DET). Using C. elegans as an assay model, we observed the severe toxicity of DMT in inducing reactive oxygen species (ROS) production, decreasing locomotion behavior, reducing lifespan, altering molecular basis for oxidative stress, and inducing mitochondrial stress. In contrast, exposure to MMT did not cause obvious toxicity, induce oxidative stress, and activate mitochondrial stress in nematodes. Our study highlights the usefulness of Sphingobium sp. C3 and its esterase DmtH in transforming p-phthalic acid esters and reducing the toxicity of DMT to organisms.

Damage on functional state of intestinal barrier by microgravity stress in nematode Caenorhabditis elegans

Due to short life cycle, nematode Caenorhabditis elegans is a suitable animal model for assessing the effect of long-term simulated microgravity treatment on organisms. We here investigated the effect of simulated microgravity treatment for 24-h on development and functional state of intestinal barrier in nematodes. Simulated microgravity treatment not only caused a broadened intestinal lumen, but also enhanced intestinal permeability. Intestinal overexpression of SOD-2, a mitochondrial Mn-SOD protein, prevented the damage on functional state of intestinal barrier by simulated microgravity and induced a resistance to toxicity of simulated microgravity, suggesting the crucial role of oxidative stress in inducing the damage on functional state of intestinal barrier in simulated microgravity treated nematodes. For the molecular basis of damage on functional state of intestinal barrier, we observed significant decrease in expressions of some genes (acs-22, erm-1, and hmp-2) required for maintenance of functional state of intestinal barrier in simulated microgravity treated nematodes. Our results highlight the potential of long-term simulated microgravity treatment in inducing intestinal damage in animals.

Nanopolystyrene at predicted environmental concentration enhances microcystin-LR toxicity by inducing intestinal damage in Caenorhabditis elegans

We employed nematode Caenorhabditis elegans to determine the combinational effect between nanopolystyrene at predicted environmental concentration and microcystin-LR (MC-LR). Prolonged exposure to nanopolystyrene (1 μg/L) increased MC-LR (0.1 μg/L) toxicity in reducing brood size and locomotion behavior and in inducing oxidative stress. Moreover, the adsorption of MC-LR by nanopolystyrene particles played an important role in inducing the enhancement in MC-LR toxicity by nanopolystyrene particles. Additionally, only exposure to resuspension of nanopolystyrene (1 μg/L) caused the increased intestinal permeability in MC-LR (0.1 μg/L) exposed nematodes. Our data indicates the potential of nanopolystyrene at predicted environmental concentration in enhancing MC-LR toxicity on environmental organisms.

Multi-omics identify xanthine as a pro-survival metabolite for nematodes with mitochondrial dysfunction

Aberrant mitochondrial function contributes to the pathogenesis of various metabolic and chronic disorders. Inhibition of insulin/IGF‐1 signaling (IIS) represents a promising avenue for the treatment of mitochondrial diseases, although many of the molecular mechanisms underlying this beneficial effect remain elusive. Using an unbiased multi‐omics approach, we report here that IIS inhibition reduces protein synthesis and favors catabolism in mitochondrial deficient Caenorhabditis elegans. We unveil that the lifespan extension does not occur through the restoration of mitochondrial respiration, but as a consequence of an ATP‐saving metabolic rewiring that is associated with an evolutionarily conserved phosphoproteome landscape. Furthermore, we identify xanthine accumulation as a prominent downstream metabolic output of IIS inhibition. We provide evidence that supplementation of FDA‐approved xanthine derivatives is sufficient to promote fitness and survival of nematodes carrying mitochondrial lesions. Together, our data describe previously unknown molecular components of a metabolic network that can extend the lifespan of short‐lived mitochondrial mutant animals.

Sex and Mitonuclear Adaptation in Experimental Caenorhabditis elegans Populations

To reveal phenotypic and functional genomic patterns of mitonuclear adaptation, a laboratory adaptation study with Caenorhabditis elegans nematodes was conducted in which independently evolving lines were initiated from a low-fitness mitochondrial electron transport chain (ETC) mutant, gas-1 Following 60 generations of evolution in large population sizes with competition for food resources, two distinct classes of lines representing different degrees of adaptive response emerged: a low-fitness class that exhibited minimal or no improvement compared to the gas-1 mutant ancestor, and a high-fitness class containing lines that exhibited partial recovery of wild-type fitness. Many lines that achieved higher reproductive and competitive fitness levels were also noted to evolve high frequencies of males during the experiment, consistent with adaptation in these lines having been facilitated by outcrossing. Whole-genome sequencing and analysis revealed an enrichment of mutations in loci that occur in a gas-1-centric region of the C. elegans interactome and could be classified into a small number of functional genomic categories. A highly nonrandom pattern of mitochondrial DNA mutation was observed within high-fitness gas-1 lines, with parallel fixations of nonsynonymous base substitutions within genes encoding NADH dehydrogenase subunits I and VI. These mitochondrial gene products reside within ETC complex I alongside the nuclear-encoded GAS-1 protein, suggesting that rapid adaptation of select gas-1 recovery lines was driven by fixation of compensatory mitochondrial mutations.

Using acs-22 mutant Caenorhabditis elegans to detect the toxicity of nanopolystyrene particles

In this study, we employed Caenorhabditis elegans with acs-22 mutation to examine the in vivo effect of functional deficit in intestinal barrier on toxicity and translocation of nanopolystyrene particles. Mutation of acs-22 leads to deficit in intestinal barrier. After prolonged exposure, nanopolystyrene particles at concentrations ≥1 μg/L could cause toxicity on acs-22 mutant nematodes. acs-22 mutation resulted in translocation of nanopolystyrene particles into targeted organs through intestinal barrier in nanopolystyrene particles (1 μg/L) exposed nematodes. After prolonged exposure, nanopolystyrene particles (1 μg/L) dysregulated expressions of some genes required for the control of oxidative stress and activated expression of Nrf signaling pathway. Therefore, under certain pathological conditions, our results suggest the potential toxicity of nanoplastic particles at predicted environmental concentration on organisms after long-term exposure.

Adaptive Evolution under Extreme Genetic Drift in Oxidatively Stressed Caenorhabditis elegans

A mutation-accumulation (MA) experiment with Caenorhabditis elegans nematodes was conducted in which replicate, independently evolving lines were initiated from a low-fitness mitochondrial electron transport chain mutant, gas-1. The original intent of the study was to assess the effect of electron transport chain dysfunction involving elevated reactive oxygen species production on patterns of spontaneous germline mutation. In contrast to results of standard MA experiments, gas-1 MA lines evolved slightly higher mean fitness alongside reduced among-line genetic variance compared with their ancestor. Likewise, the gas-1 MA lines experienced partial recovery to wildtype reactive oxygen species levels. Whole-genome sequencing and analysis revealed that the molecular spectrum but not the overall rate of nuclear DNA mutation differed from wildtype patterns. Further analysis revealed an enrichment of mutations in loci that occur in a gas-1-centric region of the C. elegans interactome, and could be classified into a small number of functional-genomic categories. Characterization of a backcrossed four-mutation set isolated from one gas-1 MA line revealed this combination to be beneficial on both gas-1 mutant and wildtype genetic backgrounds. Our combined results suggest that selection favoring beneficial mutations can be powerful even under unfavorable population genetic conditions, and agree with fitness landscape theory predicting an inverse relationship between population fitness and the likelihood of adaptation.

Genetic inhibition of an ATP synthase subunit extends lifespan in C. elegans

Mild inhibition of mitochondrial respiration leads to longevity. Disruption of mitochondrial respiratory components extends lifespan in Caenorhabditis elegans, but the effects appear to be complex and the underlying mechanism for lifespan regulation by mitochondrial respiratory genes is still not fully understood. Here, we investigated the role of Y82E9BR.3, a worm homolog of the ATP synthase subunit C, in modulating longevity in C. elegans. We found that the Y82E9BR.3 protein is localized in mitochondria and expressed in various tissues throughout development. RNAi knockdown of Y82E9BR.3 extends lifespan, decreases the accumulation of lipofuscin, and affects various physiological processes, including development delay, reproduction impairment and slow behavior. Further tissue-specific RNAi analysis showed that the intestine is a crucial organ for the longevity effects conferred by Y82E9BR.3 RNAi. Moreover, we demonstrated that lifespan extension by Y82E9BR.3 RNAi is associated with reduced mitochondrial function, as well as the suppression of complex I activity in mitochondria. Unexpectedly, Y82E9BR.3 RNAi knock down did not influence the whole-worm ATP level. Our findings first reveal the crucial role of Y82E9BR.3 in mitochondrial function and the underlying mechanism of how Y82E9BR.3 regulates lifespan in C. elegans.

Combinational effect of titanium dioxide nanoparticles and nanopolystyrene particles at environmentally relevant concentrations on nematode Caenorhabditis elegans

The possible adverse effects of nanoplastics have received the great attention recently; however, their effects at environmentally relevant concentration on organisms are still largely unclear. We here employed Caenorhabditis elegans to investigate the combinational effects of titanium dioxide nanoparticles (TiO₂-NPs) and nanopolystyrene particles at environmentally relevant concentrations on organisms. In wild-type nematodes, prolonged exposure to nanopolystyrene particles (1 μg/L) could enhance the toxicity of TiO₂-NPs (1 μg/L) in decreasing locomotion behavior and in inducing intestinal reactive oxygen species (ROS) production. Meanwhile, combinational exposure to TiO₂-NPs (1 μg/L) and nanopolystyrene particles (1 μg/L) altered the molecular basis for oxidative stress in wild-type nematodes. Moreover, prolonged exposure to nanopolystyrene particles (0.1 μg/L) could further enhance the toxicity of TiO₂-NPs (1 μg/L) in decreasing locomotion behavior and in inducing intestinal ROS production in sod-3 mutant nematodes. Our data suggest the potential role of nanopolystyrene particles at environmentally relevant concentrations in enhancing the toxicity of ENMs in the environment.

Biosafety assessment of water samples from Wanzhou watershed of Yangtze Three Gorges Reservior in the quiet season in Caenorhabditis elegans

We here employed a model animal of Caenorhabditis elegans to perform toxicity assessment of original surface water samples collected from Three Gorges Reservoir (TGR) in the quiet season in Wanzhou, Chongqing. Using some sublethal endpoints, including lifespan, body length, locomotion behavior, brood size, and intestinal reactive oxygen species (ROS) induction, we found that the examined five original surface water samples could not cause toxicity on wild-type nematodes. Nevertheless, the surface water sample collected from backwater area induced the significant increase in expressions of genes (sod-2 and sod-3) encoding Mn-SODs in wild-type nematodes. Among the examined five original surface water samples, exposure to the original surface water sample collected from backwater area could further cause the toxicity in decreasing locomotion behavior and in inducing intestinal ROS production in sod-3 mutant nematodes. Moreover, the solid phase of surface water sample collected from backwater area might mainly contribute to the observed toxicity in sod-3 mutant nematodes. Our results are helpful for understanding the potential effects of surface water in the TGR region in the quiet season on environmental organisms.

Bioassay-guided isolation of three anthelmintic compounds from Warburgia ugandensis Sprague subspecies ugandensis, and the mechanism of action of polygodial

Parasitic helminths continue to pose problems in human and veterinary medicine, as well as in agriculture. Resistance to current anthelmintics has prompted the search for new drugs. Anthelmintic metabolites from medicinal plants could be good anthelmintic drug candidates. However, the compounds active against nematodes have not been identified in most medicinal plants with anthelmintic activity. In this study, we aimed to identify the active compounds against helminths in Warburgia ugandensis Sprague subspecies ugandensis (Canellaceae) and study the underlying mechanism of action. A bioassay-guided isolation of anthelmintic compounds from the plant was performed using a Caenorhabditis elegans (C. elegans) test model with a WMicrotracker instrument to monitor motility. Three active compounds were purified and identified by nuclear magnetic resonance and high resolution MS: warburganal (IC₅₀: 28.2 ± 8.6 μM), polygodial (IC₅₀: 13.1 ± 5.3 μM) and alpha-linolenic acid (ALA, IC₅₀: 70.1 ± 17.5 μM). A checkerboard assay for warburganal and ALA as well as polygodial and ALA showed a fractional inhibitory concentration index of 0.41 and 0.37, respectively, suggesting that polygodial and ALA, as well as warburganal and ALA, have a synergistic effect against nematodes. A preliminary structure-activity relationship study for polygodial showed that the α,β-unsaturated 1,4-dialdehyde structural motif is essential for the potent activity. None of a panel of C. elegans mutant strains, resistant against major anthelmintic drug classes, showed significant resistance to polygodial, implying that polygodial may block C. elegans motility through a mechanism which differs from that of currently marketed drugs. Further measurements showed that polygodial inhibits mitochondrial ATP synthesis of C. elegans in a dose-dependent manner (IC₅₀: 1.8 ± 1.0 μM). Therefore, we believe that the underlying mechanism of action of polygodial is probably inhibition of mitochondrial ATP synthesis. In conclusion, polygodial could be a promising anthelmintic drug candidate worth considering for further development.

Developmental basis for intestinal barrier against the toxicity of graphene oxide

BACKGROUND

Intestinal barrier is crucial for animals against translocation of engineered nanomaterials (ENMs) into secondary targeted organs. However, the molecular mechanisms for the role of intestinal barrier against ENMs toxicity are still largely unclear. The intestine of Caenorhabditis elegans is a powerful in vivo experimental system for the study on intestinal function. In this study, we investigated the molecular basis for intestinal barrier against toxicity and translocation of graphene oxide (GO) using C. elegans as a model animal.

RESULTS

Based on the genetic screen of genes required for the control of intestinal development at different aspects using intestine-specific RNA interference (RNAi) technique, we identified four genes (erm-1, pkc-3, hmp-2 and act-5) required for the function of intestinal barrier against GO toxicity. Under normal conditions, mutation of any of these genes altered the intestinal permeability. With the focus on PKC-3, an atypical protein kinase C, we identified an intestinal signaling cascade of PKC-3-SEC-8-WTS-1, which implies that PKC-3 might regulate intestinal permeability and GO toxicity by affecting the function of SEC-8-mediated exocyst complex and the role of WTS-1 in maintaining integrity of apical intestinal membrane. ISP-1 and SOD-3, two proteins required for the control of oxidative stress, were also identified as downstream targets for PKC-3, and functioned in parallel with WTS-1 in the regulation of GO toxicity.

CONCLUSIONS

Using C. elegans as an in vivo assay system, we found that several developmental genes required for the control of intestinal development regulated both the intestinal permeability and the GO toxicity. With the focus on PKC-3, we raised two intestinal signaling cascades, PKC-3-SEC-8-WTS-1 and PKC-3-ISP-1/SOD-3. Our results will strengthen our understanding the molecular basis for developmental machinery of intestinal barrier against GO toxicity and translocation in animals.

Toxicity evaluation of Wanzhou watershed of Yangtze Three Gorges Reservior in the flood season in Caenorhabditis elegans

Three Gorges Reservoir (TGR) in the upper stream of Yangtze River in China is a reservoir with the largest and the longest yearly water-level drop. Considering the fact that most of safety assessments of water samples collected from TGR region were based on chemical analysis, we here employed Caenorhabditis elegans to perform in vivo safety assessment of original surface water samples collected from TGR region in the flood season in Wanzhou, Chongqing. Among the examined five original surface water samples, only exposure to original surface water sample collected from backwater area could induce the significant intestinal ROS production, enhance the intestinal permeability, and decrease the locomotion behavior. Additionally, exposure to original surface water sample collected from backwater area altered the expressions of sod-2, sod-5, clk-1, and mev-1. Moreover, mutation of sod-2 or sod-5 was susceptible to the potential toxicity of original surface water sample collected from backwater area on nematodes. Together, our results imply that exposure to surface water sample from the backwater area may at least cause the adverse effects on intestinal function and locomotion behavior in nematodes.

N-acetylcysteine and vitamin E rescue animal longevity and cellular oxidative stress in pre-clinical models of mitochondrial complex I disease

Oxidative stress is a known contributing factor in mitochondrial respiratory chain (RC) disease pathogenesis. Yet, no efficient means exists to objectively evaluate the comparative therapeutic efficacy or toxicity of different antioxidant compounds empirically used in human RC disease. We postulated that pre-clinical comparative analysis of diverse antioxidant drugs having suggested utility in primary RC disease using animal and cellular models of RC dysfunction may improve understanding of their integrated effects and physiologic mechanisms, and enable prioritization of lead antioxidant molecules to pursue in human clinical trials. Here, lifespan effects of N-acetylcysteine (NAC), vitamin E, vitamin C, coenzyme Q10 (CoQ10), mitochondrial-targeted CoQ10 (MS010), lipoate, and orotate were evaluated as the primary outcome in a well-established, short-lived C. elegans gas-1(fc21) animal model of RC complex I disease. Healthspan effects were interrogated to assess potential reversal of their globally disrupted in vivo mitochondrial physiology, transcriptome profiles, and intermediary metabolic flux. NAC or vitamin E fully rescued, and coenzyme Q, lipoic acid, orotic acid, and vitamin C partially rescued gas-1(fc21) lifespan toward that of wild-type N2 Bristol worms. MS010 and CoQ10 largely reversed biochemical pathway expression changes in gas-1(fc21) worms. While nearly all drugs normalized the upregulated expression of the "cellular antioxidant pathway", they failed to rescue the mutant worms' increased in vivo mitochondrial oxidant burden. NAC and vitamin E therapeutic efficacy were validated in human fibroblast and/or zebrafish complex I disease models. Remarkably, rotenone-induced zebrafish brain death was preventable partially with NAC and fully with vitamin E. Overall, these pre-clinical model animal data demonstrate that several classical antioxidant drugs do yield significant benefit on viability and survival in primary mitochondrial disease, where their major therapeutic benefit appears to result from targeting global cellular, rather than intramitochondria-specific, oxidative stress. Clinical trials are needed to evaluate whether the two antioxidants, NAC and vitamin E, that show greatest efficacy in translational model animals significantly improve the survival, function, and feeling of human subjects with primary mitochondrial RC disease.

General Genetic Strategies

It is difficult to study the genetics and molecular mechanisms of anesthesia in humans. Fortunately, the genetic approaches in model organisms can, and have, led to profound insights as to the targets of anesthetics. In turn, the organization of these putative targets into meaningful pathways has begun to elucidate the mechanisms of action of these agents. However, it is important to first appreciate the strengths, and limitations, of genetic approaches to understand the anesthetic action. Here we compare the commonly used genetic model organisms, various anesthetic endpoints, and different modes of genetic screens. Coupled with the more specific data presented in subsequent chapters, this chapter places those results in a framework with which to analyze the discoveries across organisms and eventually extend the resulting models to humans.

Long-term exposure to thiolated graphene oxide in the range of μg/L induces toxicity in nematode Caenorhabditis elegans

The in vivo toxicity and translocation of thiolated graphene oxide (GO-SH) are still largely unclear. We hypothesized that long-term exposure to GO-SH may cause the adverse effects on environmental organisms. We here employed in vivo assay system of Caenorhabditis elegans to investigate the possible toxicity and translocation of GO-SH after long-term exposure. In wild-type nematodes, we observed that prolonged exposure to GO-SH at concentrations>100μg/L resulted in the toxicity on functions of both primary targeted organs such as the intestine and secondary targeted organs such as the neurons and the reproductive organs. The severe accumulation of GO-SH was further detected in the body of wild-type nematodes. The translocation of GO-SH into secondary targeted organs such as reproductive organs through intestinal barrier might be associated with the enhancement in intestinal permeability in GO-SH exposed wild-type nematodes. Prolonged exposure to GO-SH (100μg/L) decreased the expression of gas-1 encoding a subunit of mitochondrial complex I, and mutation of gas-1 caused the formation of GO-SH toxicity at concentration>10μg/L and more severe accumulation of GO-SH in the body of animals. Therefore, our results confirm the possibility for prolonged exposure to GO-SH in inducing adverse effects on nematodes. Our data highlight the potential adverse effects of GO-SH in the range of μg/L on environmental organisms after long-term exposure.

Regulation of the Response of Caenorhabditis elegans to Simulated Microgravity by p38 Mitogen-Activated Protein Kinase Signaling

The in vivo function of p38 mitogen-activated protein kinase (MAPK) signaling in regulating the response to simulated microgravity is still largely unclear. Using Caenorhabditis elegans as an assay system, we investigated the in vivo function of p38 MAPK signaling in regulating the response of animals to simulated microgravity and the underlying molecular mechanism. Simulated microgravity treatment significantly increased the transcriptional expressions of genes (pmk-1, sek-1, and nsy-1) encoding core p38 MAPK signaling pathway and the expression of phosphorylated PMK-1/p38 MAPK. The pmk-1, sek-1, or nsy-1 mutant was susceptible to adverse effects of simulated microgravity. The intestine-specific activity of PMK-1 was required for its function in regulating the response to simulated microgravity, and the entire p38 MAPK signaling pathway could act in the intestine to regulate the response to simulated microgravity. In the intestine, SKN-1 and ATF-7, two transcriptional factors, were identified as downstream targets for PMK-1 in regulating the response to simulated microgravity. Therefore, the activation of p38 MAPK signaling may mediate a protection mechanism for nematodes against the adverse effects of simulated microgravity. Additionally, our results highlight the potential crucial role of intestinal cells in response to simulated microgravity in nematodes.

Molecular basis for oxidative stress induced by simulated microgravity in nematode Caenorhabditis elegans

Caenorhabditis elegans is an important in vivo assay system for toxicological studies. Herein, we investigated the role of oxidative stress and the underlying molecular mechanism for induced adverse effects of simulated microgravity. In nematodes, simulated microgravity treatment induced a significant induction of oxidative stress. Genes (mev-1, gas-1, and isp-1) encoding a molecular machinery for the control of oxidative stress were found to be dysregulated in simulated microgravity treated nematodes. Meanwhile, genes (sod-2, sod-3, sod-4, sod-5, aak-2, skn-1, and gst-4) encoding certain antioxidant defense systems were increased in simulated microgravity treated nematodes. Mutation of mev-1, gas-1, sod-2, sod-3, aak-2, skn-1, or gst-4 enhanced susceptibility to oxidative stress induced by simulated microgravity, whereas mutation of isp-1 induced a resistance to oxidative stress induced by simulated microgravity. Mutation of sod-2, sod-3, or aak-2 further suppressed the recovery effect of simulated microgravity toxicity in nematodes after simulated microgravity treatment for 1h. Moreover, administration of ascorbate could inhibit the adverse effects including the induction of oxidative stress in simulated microgravity treated nematodes. Mutation of any of the genes encoding metallothioneins or the genes of hsp-16.1, hsp-16.2 and hsp-16.48 encoding heat-shock proteins did not affect the induction of oxidative stress in simulated microgravity treated nematodes. Our results provide a molecular basis for the induction of oxidative stress in simulated microgravity treated organisms.

Regional knockdown of NDUFS4 implicates a thalamocortical circuit mediating anesthetic sensitivity

Knockout of the mitochondrial complex I protein, NDUFS4, profoundly increases sensitivity of mice to volatile anesthetics. In mice carrying an Ndufs4lox/lox gene, adeno-associated virus expressing Cre recombinase was injected into regions of the brain postulated to affect sensitivity to volatile anesthetics. These injections generated otherwise phenotypically wild type mice with region-specific, postnatal inactivation of Ndufs4, minimizing developmental effects of gene loss. Sensitivities to the volatile anesthetics isoflurane and halothane were measured using loss of righting reflex (LORR) and movement in response to tail clamp (TC) as endpoints. Knockdown (KD) of Ndufs4 in the vestibular nucleus produced resistance to both anesthetics for movement in response to TC. Ndufs4 loss in the central and dorsal medial thalami and in the parietal association cortex increased anesthetic sensitivity to both TC and LORR. Knockdown of Ndufs4 only in the parietal association cortex produced striking hypersensitivity for both endpoints, and accounted for half the total change seen in the global KO (Ndufs4(KO)). Excitatory synaptic transmission in the parietal association cortex in slices from Ndufs4(KO) animals was hypersensitive to isoflurane compared to control slices. We identified a direct neural circuit between the parietal association cortex and the central thalamus, consistent with a model in which isoflurane sensitivity is mediated by a thalamic signal relayed through excitatory synapses to the parietal association cortex. We postulate that the thalamocortical circuit is crucial for maintenance of consciousness and is disrupted by the inhibitory effects of isoflurane/halothane on mitochondria.

Cell Biology of the Mitochondrion

Mitochondria are best known for harboring pathways involved in ATP synthesis through the tricarboxylic acid cycle and oxidative phosphorylation. Major advances in understanding these roles were made with Caenorhabditiselegans mutants affecting key components of the metabolic pathways. These mutants have not only helped elucidate some of the intricacies of metabolism pathways, but they have also served as jumping off points for pharmacology, toxicology, and aging studies. The field of mitochondria research has also undergone a renaissance, with the increased appreciation of the role of mitochondria in cell processes other than energy production. Here, we focus on discoveries that were made using C. elegans, with a few excursions into areas that were studied more thoroughly in other organisms, like mitochondrial protein import in yeast. Advances in mitochondrial biogenesis and membrane dynamics were made through the discoveries of novel functions in mitochondrial fission and fusion proteins. Some of these functions were only apparent through the use of diverse model systems, such as C. elegans Studies of stress responses, exemplified by mitophagy and the mitochondrial unfolded protein response, have also benefitted greatly from the use of model organisms. Recent developments include the discoveries in C. elegans of cell autonomous and nonautonomous pathways controlling the mitochondrial unfolded protein response, as well as mechanisms for degradation of paternal mitochondria after fertilization. The evolutionary conservation of many, if not all, of these pathways ensures that results obtained with C. elegans are equally applicable to studies of human mitochondria in health and disease.