Mitochondrial dysfunction confers resistance to multiple drugs 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.

CHCHD2 P14L, found in amyotrophic lateral sclerosis, exhibits cytoplasmic mislocalization and alters Ca2+ homeostasis

CHCHD2 and CHCHD10, linked to Parkinson's disease and amyotrophic lateral sclerosis-frontotemporal dementia (ALS), respectively, are mitochondrial intermembrane proteins that form a heterodimer. This study aimed to investigate the impact of the CHCHD2 P14L variant, implicated in ALS, on mitochondrial function and its subsequent effects on cellular homeostasis. The missense variant of CHCHD2, P14L, found in a cohort of patients with ALS, mislocalized CHCHD2 to the cytoplasm, leaving CHCHD10 in the mitochondria. Drosophila lacking the CHCHD2 ortholog exhibited mitochondrial degeneration. In contrast, human CHCHD2 P14L, but not wild-type human CHCHD2, failed to suppress this degeneration, suggesting that P14L is a pathogenic variant. The mitochondrial Ca2+ buffering capacity was reduced in Drosophila neurons expressing human CHCHD2 P14L. The altered Ca2+-buffering phenotype was also observed in cultured human neuroblastoma SH-SY5Y cells expressing CHCHD2 P14L. In these cells, transient elevation of cytoplasmic Ca2+ facilitated the activation of calpain and caspase-3, accompanied by the processing and insolubilization of TDP-43. These observations suggest that CHCHD2 P14L causes abnormal Ca2+ dynamics and TDP-43 aggregation, reflecting the pathophysiology of ALS.

In vitro evolution and whole genome analysis to study chemotherapy drug resistance in haploid human cells

In vitro evolution and whole genome analysis has proven to be a powerful method for studying the mechanism of action of small molecules in many haploid microbes but has generally not been applied to human cell lines in part because their diploid state complicates the identification of variants that confer drug resistance. To determine if haploid human cells could be used in MOA studies, we evolved resistance to five different anticancer drugs (doxorubicin, gemcitabine, etoposide, topotecan, and paclitaxel) using a near-haploid cell line (HAP1) and then analyzed the genomes of the drug resistant clones, developing a bioinformatic pipeline that involved filtering for high frequency alleles predicted to change protein sequence, or alleles which appeared in the same gene for multiple independent selections with the same compound. Applying the filter to sequences from 28 drug resistant clones identified a set of 21 genes which was strongly enriched for known resistance genes or known drug targets (TOP1, TOP2A, DCK, WDR33, SLCO3A1). In addition, some lines carried structural variants that encompassed additional known resistance genes (ABCB1, WWOX and RRM1). Gene expression knockdown and knockout experiments of 10 validation targets showed a high degree of specificity and accuracy in our calls and demonstrates that the same drug resistance mechanisms found in diverse clinical samples can be evolved, discovered and studied in an isogenic background.

SKN-1/Nrf2-dependent regulation of mitochondrial homeostasis modulates transgenerational toxicity induced by nanoplastics with different surface charges in Caenorhabditis elegans

The toxic effects of nanoplastics on transgenerational toxicity in environmental organisms and the involved mechanisms remain poorly comprehended. This study aimed to identify the role of SKN-1/Nrf2-dependent regulation of mitochondrial homeostasis in response to transgenerational toxicity caused by changes in nanoplastic surface charges in Caenorhabditis elegans (C. elegans). Our results revealed that compared with the wild-type control and PS exposed groups, exposure to PS-NH₂ or PS-SOOOH at environmentally relevant concentrations (ERC) of ≥ 1 μg/L caused transgenerational reproductive toxicity, inhibited mitochondrial unfolded protein responses (UPR) by downregulating the transcription levels of hsp-6, ubl-5, dve-1, atfs-1, haf-1, and clpp-1, membrane potential by downregulating phb-1 and phb-2, and promoted mitochondrial apoptosis by downregulating ced-4 and ced-3 and upregulating ced-9, DNA damage by upregulating hus-1, cep-1, egl-1, reactive oxygen species (ROS) by upregulating nduf-7 and nuo-6, ultimately resulting in mitochondrial homeostasis. Additionally, further study indicated that SKN-1/Nrf2 mediated antioxidant response to alleviate PS-induced toxicity in the P0 generation and dysregulated mitochondrial homeostasis to enhance PS-NH₂ or PS-SOOOH-induced transgenerational toxicity. Our study highlights the momentous role of SKN-1/Nrf2 mediated mitochondrial homeostasis in the response to nanoplastics caused transgenerational toxicity in environmental organisms.

Neurodegeneration-associated mitochondrial proteins, CHCHD2 and CHCHD10–what distinguishes the two?

Coiled-coil-helix-coiled-coil-helix domain containing 2 (CHCHD2) and Coiled-coil-helix-coiled-coil-helix domain containing 10 (CHCHD10) are mitochondrial proteins that are thought to be genes which duplicated during evolution and are the causative genes for Parkinson’s disease and amyotrophic lateral sclerosis/frontotemporal lobe dementia, respectively. CHCHD2 forms a heterodimer with CHCHD10 and a homodimer with itself, both of which work together within the mitochondria. Various pathogenic and disease-risk variants have been identified; however, how these mutations cause neurodegeneration in specific diseases remains a mystery. This review focuses on important new findings published since 2019 and discusses avenues to solve this mystery.

The Role of Mitochondria in Optic Atrophy With Autosomal Inheritance

Optic atrophy (OA) with autosomal inheritance is a form of optic neuropathy characterized by the progressive and irreversible loss of vision. In some cases, this is accompanied by additional, typically neurological, extra-ocular symptoms. Underlying the loss of vision is the specific degeneration of the retinal ganglion cells (RGCs) which form the optic nerve. Whilst autosomal OA is genetically heterogenous, all currently identified causative genes appear to be associated with mitochondrial organization and function. However, it is unclear why RGCs are particularly vulnerable to mitochondrial aberration. Despite the relatively high prevalence of this disorder, there are currently no approved treatments. Combined with the lack of knowledge concerning the mechanisms through which aberrant mitochondrial function leads to RGC death, there remains a clear need for further research to identify the underlying mechanisms and develop treatments for this condition. This review summarizes the genes known to be causative of autosomal OA and the mitochondrial dysfunction caused by pathogenic mutations. Furthermore, we discuss the suitability of available in vivo models for autosomal OA with regards to both treatment development and furthering the understanding of autosomal OA pathology.

Early-life mitochondrial DNA damage results in lifelong deficits in energy production mediated by redox signaling in Caenorhabditis elegans

The consequences of damage to the mitochondrial genome (mtDNA) are poorly understood, although mtDNA is more susceptible to damage resulting from some genotoxicants than nuclear DNA (nucDNA), and many environmental toxicants target the mitochondria. Reports from the toxicological literature suggest that exposure to early-life mitochondrial damage could lead to deleterious consequences later in life (the “Developmental Origins of Health and Disease” paradigm), but reports from other fields often report beneficial (“mitohormetic”) responses to such damage. Here, we tested the effects of low (causing no change in lifespan) levels of ultraviolet C (UVC)-induced, irreparable mtDNA damage during early development in Caenorhabditis elegans. This exposure led to life-long reductions in mtDNA copy number and steady-state ATP levels, accompanied by increased oxygen consumption and altered metabolite profiles, suggesting inefficient mitochondrial function. Exposed nematodes were also developmentally delayed, reached smaller adult size, and were rendered more susceptible to subsequent exposure to chemical mitotoxicants. Metabolomic and genetic analysis of key signaling and metabolic pathways supported redox and mitochondrial stress-response signaling during early development as a mechanism for establishing these persistent alterations. Our results highlight the importance of early-life exposures to environmental pollutants, especially in the context of exposure to chemicals that target mitochondria.

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Early life mtDNA damage led to lifelong deficits in mitochondrial function.

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C. elegans developed slowly and were sensitive to chemical exposures as adults.

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Redox signaling is a mechanism that establishes these persistent alterations.

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Data are consistent with the Developmental Origins of Health and Disease model.

Mitochondrial CHCHD2: Disease-Associated Mutations, Physiological Functions, and Current Animal Models

Rare mutations in the mitochondrial protein coiled-coil-helix-coiled-coil-helix domain containing 2 (CHCHD2) are associated with Parkinson's disease (PD) and other Lewy body disorders. CHCHD2 is a bi-organellar mediator of oxidative phosphorylation, playing crucial roles in regulating electron flow in the mitochondrial electron transport chain and acting as a nuclear transcription factor for a cytochrome c oxidase subunit (COX4I2) and itself in response to hypoxic stress. CHCHD2 also regulates cell migration and differentiation, mitochondrial cristae structure, and apoptosis. In this review, we summarize the known disease-associated mutations of CHCHD2 in Asian and Caucasian populations, the physiological functions of CHCHD2, how CHCHD2 mutations contribute to α-synuclein pathology, and current animal models of CHCHD2. Further, we discuss the necessity of continued investigation into the divergent functions of CHCHD2 and CHCHD10 to determine how mutations in these similar mitochondrial proteins contribute to different neurodegenerative diseases.

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.

Genome-wide RNAi screen for regulators of UPRmt in Caenorhabditis elegans mutants with defects in mitochondrial fusion

Mitochondrial dynamics plays an important role in mitochondrial quality control and the adaptation of metabolic activity in response to environmental changes. The disruption of mitochondrial dynamics has detrimental consequences for mitochondrial and cellular homeostasis and leads to the activation of the mitochondrial unfolded protein response (UPRmt), a quality control mechanism that adjusts cellular metabolism and restores homeostasis. To identify genes involved in the induction of UPRmt in response to a block in mitochondrial fusion, we performed a genome-wide RNAi screen in Caenorhabditis elegans mutants lacking the gene fzo-1, which encodes the ortholog of mammalian Mitofusin, and identified 299 suppressors and 86 enhancers. Approximately 90% of these 385 genes are conserved in humans, and one third of the conserved genes have been implicated in human disease. Furthermore, many have roles in developmental processes, which suggests that mitochondrial function and the response to stress are defined during development and maintained throughout life. Our dataset primarily contains mitochondrial enhancers and non-mitochondrial suppressors of UPRmt, indicating that the maintenance of mitochondrial homeostasis has evolved as a critical cellular function, which, when disrupted, can be compensated for by many different cellular processes. Analysis of the subsets 'non-mitochondrial enhancers' and 'mitochondrial suppressors' suggests that organellar contact sites, especially between the ER and mitochondria, are of importance for mitochondrial homeostasis. In addition, we identified several genes involved in IP3 signaling that modulate UPRmt in fzo-1 mutants and found a potential link between pre-mRNA splicing and UPRmt activation.

Fluorizoline-induced apoptosis requires prohibitins in nematodes and human cells

We previously showed that fluorizoline, a fluorinated thiazoline compound, binds to both subunits of the mitochondrial prohibitin (PHB) complex, PHB1 and PHB2, being the expression of these proteins required for fluorizoline-induced apoptosis in mouse embryonic fibroblasts. To investigate the conservation of this apoptotic mechanism, we studied the effect of PHB downregulation on fluorizoline activity on two human cell lines, HEK293T and U2OS. Then, we asked whether PHBs mediate the effect of fluorizoline in a multicellular organism. Interestingly, reduced levels of PHBs in the human cells impaired the induction of apoptosis by fluorizoline. We observed that fluorizoline has a detrimental dose-dependent effect on the development and survival of the nematode model Caenorhabditis elegans. Besides, such effects of fluorizoline treatment in living nematodes were absent in PHB mutants. Finally, we further explored the apoptotic pathway triggered by fluorizoline in human cell lines. We found that the BH3-only proteins NOXA, BIM and PUMA participate in fluorizoline-induced apoptosis and that the induction of NOXA and PUMA is dependent on PHB expression.

Compromised Mitochondrial Protein Import Acts as a Signal for UPRmt

The induction of the mitochondrial unfolded protein response (UPR^mt) results in increased transcription of the gene encoding the mitochondrial chaperone HSP70. We systematically screened the C. elegans genome and identified 171 genes that, when knocked down, induce the expression of an hsp-6 HSP70 reporter and encode mitochondrial proteins. These genes represent many, but not all, mitochondrial processes (e.g., mitochondrial calcium homeostasis and mitophagy are not represented). Knockdown of these genes leads to reduced mitochondrial membrane potential and, hence, decreased protein import into mitochondria. In addition, it induces UPR^mt in a manner that is dependent on ATFS-1 but that is not antagonized by the kinase GCN-2. We propose that compromised mitochondrial protein import signals the induction of UPR^mt and that the mitochondrial targeting sequence of ATFS-1 functions as a sensor for this signal.

Autophagy compensates for defects in mitochondrial dynamics

Compromising mitochondrial fusion or fission disrupts cellular homeostasis; however, the underlying mechanism(s) are not fully understood. The loss of C. elegans fzo-1MFN results in mitochondrial fragmentation, decreased mitochondrial membrane potential and the induction of the mitochondrial unfolded protein response (UPRmt). We performed a genome-wide RNAi screen for genes that when knocked-down suppress fzo-1MFN(lf)-induced UPRmt. Of the 299 genes identified, 143 encode negative regulators of autophagy, many of which have previously not been implicated in this cellular quality control mechanism. We present evidence that increased autophagic flux suppresses fzo-1MFN(lf)-induced UPRmt by increasing mitochondrial membrane potential rather than restoring mitochondrial morphology. Furthermore, we demonstrate that increased autophagic flux also suppresses UPRmt induction in response to a block in mitochondrial fission, but not in response to the loss of spg-7AFG3L2, which encodes a mitochondrial metalloprotease. Finally, we found that blocking mitochondrial fusion or fission leads to increased levels of certain types of triacylglycerols and that this is at least partially reverted by the induction of autophagy. We propose that the breakdown of these triacylglycerols through autophagy leads to elevated metabolic activity, thereby increasing mitochondrial membrane potential and restoring mitochondrial and cellular homeostasis.

ROS-based lethality of Caenorhabditis elegans mitochondrial electron transport mutants grown on Escherichia coli siderophore iron release mutants

Caenorhabditis elegans consumes bacteria, which can supply essential vitamins and cofactors, especially for mitochondrial functions that have a bacterial ancestry. Therefore, we screened the Keio Escherichia coli knockout library for mutations that induce the C. elegans hsp-6 mitochondrial damage response gene, and identified 45 E. coli mutations that induce hsp-6::gfp We tested whether any of these E. coli mutations that stress the C. elegans mitochondrion genetically interact with C. elegans mutations in mitochondrial functions. Surprisingly, 4 E. coli mutations that disrupt the import or removal of iron from the bacterial siderophore enterobactin were lethal in combination with a collection of C. elegans mutations that disrupt particular iron-sulfur proteins of the electron transport chain. Bacterial mutations that fail to synthesize enterobactin are not synthetic lethal with these C. elegans mitochondrial mutants; it is the enterobactin-iron complex that is lethal in combination with the C. elegans mitochondrial mutations. Antioxidants suppress this inviability, suggesting that reactive oxygen species (ROS) are produced by the mutant mitochondria in combination with the bacterial enterobactin-iron complex.

KLF-1 orchestrates a xenobiotic detoxification program essential for longevity of mitochondrial mutants

Most manipulations that extend lifespan also increase resistance to various stress factors and environmental cues in a range of animals from yeast to mammals. However, the underlying molecular mechanisms regulating stress resistance during aging are still largely unknown. Here we identify Krüppel-like factor 1 (KLF-1) as a mediator of a cytoprotective response that dictates longevity induced by reduced mitochondrial function. A redox-regulated KLF-1 activation and transfer to the nucleus coincides with the peak of somatic mitochondrial biogenesis that occurs around a transition from larval stage L3 to D1. We further show that KLF-1 activates genes involved in the xenobiotic detoxification programme and identified cytochrome P450 oxidases, the KLF-1 main effectors, as longevity-assurance factors of mitochondrial mutants. Collectively, these findings underline the importance of the xenobiotic detoxification in the mitohormetic, longevity assurance pathway and identify KLF-1 as a central factor in orchestrating this response.

Respiratory analysis as a tool to detect physiological changes in Anisakis larvae subjected to stress

Human infection due to eating fish parasitized by live Anisakis larvae in the third stage is considered an important health problem, and the application of treatments to ensure their mortality in the fish products is crucial to prevent the risk of infection. Mobility is used to assess viability, but mobile larvae may not always be infective and immobile larvae may be erroneously considered as non-viable. The objective was to establish whether the analysis of respiratory activity by means of the oxygen consumption rate (OCR) of Anisakis could be used to identify subtle differences between larvae that were still considered viable in terms of their mobility but had been subjected to thermal and/or chemical stress. The metabolic modulators FCCP [carbonyl cyanide 4-(trifluoromethoxy) phenylhydrazone] and sodium azide were used and the basal, maximum, spare and residual respiration rates calculated. Results showed that maximum respiratory capacity of larvae subjected to freezing significantly decreased immediately after thawing, but after some acclimatization, they recovered their capacity fully. However, when these larvae were stored at 4.6 °C, their mitochondria became dysfunctional faster than those of untreated larvae. OCR also showed that mitochondria of larvae were affected by incubation at 37 °C in NaCl or gastric juice. To conclude, OCR of Anisakis in the presence of metabolic modulators can help to identify subtle changes that occur in the larva. These measurements could be used to characterize larvae subjected to various stresses so that a broader picture of Anisakis pathogenic potential can be gained.

Tryptophan Metabolism in Caenorhabditis elegans Links Aggregation Behavior to Nutritional Status

Caenorhabditis elegans uses aggregation pheromones to communicate its nutritional status and recruit fellow members of its species to food sources. These aggregation pheromones include the IC-ascarosides, ascarosides modified with an indole-3-carbonyl (IC) group on the 4'-position of the ascarylose sugar. Nothing is known about the biosynthesis of the IC modification beyond the fact that it is derived from tryptophan. Here, we show that C. elegans produces endogenously several indole-containing metabolites, including indole-3-pyruvic acid (IPA), indole-3-acetic acid (IAA; auxin), and indole-3-carboxylic acid, and that these metabolites are intermediates in the biosynthetic pathway from tryptophan to the IC group. Stable isotope-labeled IPA and IAA are incorporated into the IC-ascarosides. Importantly, we show that flux through the biosynthetic pathway is affected by the activity of the pyruvate dehydrogenase complex (PDC). Knockdown of the PDC by RNA interference leads to an accumulation of upstream metabolites and a reduction in downstream metabolites in the pathway. Our results show that production of aggregation pheromones is linked to PDC activity and that aggregation behavior may reflect a favorable metabolic state in the worm. Lastly, we show that treatment of  C. elegans with indole-containing metabolites in the pathway induces the biosynthesis of the IC-ascarosides. Because the natural environment of C. elegans is rotting plant material, indole-containing metabolites in this environment could potentially stimulate pheromone biosynthesis and aggregation behavior in the worm. Thus, there may be important links between tryptophan metabolism in C. elegans and in plants and bacteria that enable interkingdom signaling.

Mitochondrial fusion, fission, and mitochondrial toxicity

Mitochondrial dynamics are regulated by two sets of opposed processes: mitochondrial fusion and fission, and mitochondrial biogenesis and degradation (including mitophagy), as well as processes such as intracellular transport. These processes maintain mitochondrial homeostasis, regulate mitochondrial form, volume and function, and are increasingly understood to be critical components of the cellular stress response. Mitochondrial dynamics vary based on developmental stage and age, cell type, environmental factors, and genetic background. Indeed, many mitochondrial homeostasis genes are human disease genes. Emerging evidence indicates that deficiencies in these genes often sensitize to environmental exposures, yet can also be protective under certain circumstances. Inhibition of mitochondrial dynamics also affects elimination of irreparable mitochondrial DNA (mtDNA) damage and transmission of mtDNA mutations. We briefly review the basic biology of mitodynamic processes with a focus on mitochondrial fusion and fission, discuss what is known and unknown regarding how these processes respond to chemical and other stressors, and review the literature on interactions between mitochondrial toxicity and genetic variation in mitochondrial fusion and fission genes. Finally, we suggest areas for future research, including elucidating the full range of mitodynamic responses from low to high-level exposures, and from acute to chronic exposures; detailed examination of the physiological consequences of mitodynamic alterations in different cell types; mechanism-based testing of mitotoxicant interactions with interindividual variability in mitodynamics processes; and incorporating other environmental variables that affect mitochondria, such as diet and exercise.

Increased mitochondrial fusion allows the survival of older animals in diverse C. elegans longevity pathways

Mitochondria are dynamic organelles that undergo fusion and fission events. Mitochondrial dynamics are required for mitochondrial viability and for responses to changes in bioenergetic status. Here we describe an insulin-signaling and SCFLIN-23-regulated pathway that controls mitochondrial fusion in Caenorhabditis elegans by repressing the expression of the mitochondrial proteases SPG-7 and PPGN-1. This pathway is required for mitochondrial fusion in response to physical exertion, and for the associated extension in lifespan. We show that diverse longevity pathways exhibit increased levels of elongated mitochondria. The increased mitochondrial fusion is essential for longevity in the diverse longevity pathways, as inhibiting mitochondrial fusion reduces their lifespans to wild-type levels. Our results suggest that increased mitochondrial fusion is not a major driver of longevity, but rather is essential to allow the survival of older animals beyond their normal lifespan in diverse longevity pathways.Mitochondria can undergo shape changes as a result of fusion and fission events. Here the authors describe how insulin signalling regulates mitochondrial fusion in C. elegans, and show that mitochondrial fusion is necessary, but not sufficient, for longevity of worms with mutations that increase lifespan.

Clk1-regulated aerobic glycolysis is involved in glioma chemoresistance

Chemoresistance remains a major challenge for the treatment of glioma. In this study, we investigated the role of Clock 1 (Clk1), which encodes an enzyme that is necessary for ubiquinone biosynthesis in glioma chemoresistance in vitro. The results showed that Clk1 was highly expressed in GL261 mouse glioma cells which were most sensitive to 1,3Bis (2-chloroethyl) 1 nitrosourea (BCNU) while was low expressed in BCNU resistant cells such as glioma cancer stem cells, T98G, U87MG and U251 glioma cells. Knockdown of Clk1 in GL261 glioma cells significantly reduced BCNU- or cisplatin-induced cell apoptosis, whereas the proliferative activity and the expression of multidrug resistance-related genes including MDR1, O6-methylguanine-DNA methyltransferase, and GSTP1 were not changed. When Clk1 was re-expressed in Clk1 knockdown GL261 glioma cells, the BCNU sensitivity was restored. The mechanistic study revealed that knockdown of Clk1 in GL261 glioma cells increased aerobic glycolysis including high glucose consumption, lactate production, and up-regulation of glycolysis-associated genes. Inhibition of glycolysis can reverse the chemoresistance elicited by Clk1 knockdown in GL261 cells. Moreover, knockdown of Clk1 induced HIF-1α expression in GL261 glioma cells which was found to be mediated by AMP-activated protein kinase (AMPK)/mechanistic target of rapamycin (mTOR) signaling pathway. Both metformin and rapamycin reversed the chemoresistance of Clk1 knockdown GL261 glioma cells. Over-expression of Clk1 significantly increased the sensitivity of T98G or U251 human glioblastoma cells to BCNU which was accompanied by decreased lactate secretion, decreased expression of HIF-1α, AMPK activation, and inhibition of mTOR pathway. Inhibition of glycolysis or activation of AMPK did not alter Clk1 expression in variant glioma cell lines suggesting that aerobic glycolysis is not an upstream event of Clk1 expression in glioma cells. Taken together, our results revealed, for the first time, that mitochondrial Clk1 regulated chemoresistance in glioma cells through AMPK/mTOR/HIF-1α mediated glycolysis pathway.

Loss of function CHCHD10 mutations in cytoplasmic TDP-43 accumulation and synaptic integrity

Although multiple CHCHD10 mutations are associated with the spectrum of familial and sporadic frontotemporal dementia–amyotrophic lateral sclerosis (FTD–ALS) diseases, neither the normal function of endogenous CHCHD10 nor its role in the pathological milieu (that is, TDP-43 pathology) of FTD/ALS have been investigated. In this study, we made a series of observations utilizing Caenorhabditis elegans models, mammalian cell lines, primary neurons and mouse brains, demonstrating that CHCHD10 normally exerts a protective role in mitochondrial and synaptic integrity as well as in the retention of nuclear TDP-43, whereas FTD/ALS-associated mutations (R15L and S59L) exhibit loss of function phenotypes in C. elegans genetic complementation assays and dominant negative activities in mammalian systems, resulting in mitochondrial/synaptic damage and cytoplasmic TDP-43 accumulation. As such, our results provide a pathological link between CHCHD10-associated mitochondrial/synaptic dysfunction and cytoplasmic TDP-43 inclusions.

Mutations in CHCHD10 have been recently associated with frontotemporal dementia and amyotrophic lateral sclerosis. Here the authors study the functions of endogenous CHCHD10 in Caenorhabditis elegans, primary neurons, and mouse, and show that it normally protects mitochondria and synaptic integrity, and retains TDP-43 in the nucleus.

The mitochondrial protein CHCHD2 primes the differentiation potential of human induced pluripotent stem cells to neuroectodermal lineages

Human induced pluripotent stem cell (hiPSC) utility is limited by variations in the ability of these cells to undergo lineage-specific differentiation. We have undertaken a transcriptional comparison of human embryonic stem cell (hESC) lines and hiPSC lines and have shown that hiPSCs are inferior in their ability to undergo neuroectodermal differentiation. Among the differentially expressed candidates between hESCs and hiPSCs, we identified a mitochondrial protein, CHCHD2, whose expression seems to correlate with neuroectodermal differentiation potential of pluripotent stem cells. We provide evidence that hiPSC variability with respect to CHCHD2 expression and differentiation potential is caused by clonal variation during the reprogramming process and that CHCHD2 primes neuroectodermal differentiation of hESCs and hiPSCs by binding and sequestering SMAD4 to the mitochondria, resulting in suppression of the activity of the TGFβ signaling pathway. Using CHCHD2 as a marker for assessing and comparing the hiPSC clonal and/or line differentiation potential provides a tool for large scale differentiation and hiPSC banking studies.

A screening-based platform for the assessment of cellular respiration in Caenorhabditis elegans

Mitochondrial dysfunction is at the core of many diseases ranging from inherited metabolic diseases to common conditions that are associated with aging. Although associations between aging and mitochondrial function have been identified using mammalian models, much of the mechanistic insight has emerged from Caenorhabditis elegans. Mitochondrial respiration is recognized as an indicator of mitochondrial health. The Seahorse XF96 respirometer represents the state-of-the-art platform for assessing respiration in cells, and we adapted the technique for applications involving C. elegans. Here we provide a detailed protocol to optimize and measure respiration in C. elegans with the XF96 respirometer, including the interpretation of parameters and results. The protocol takes ∼2 d to complete, excluding the time spent culturing C. elegans, and it includes (i) the preparation of C. elegans samples, (ii) selection and loading of compounds to be injected, (iii) preparation and execution of a run with the XF96 respirometer and (iv) postexperimental data analysis, including normalization. In addition, we compare our XF96 application with other existing techniques, including the eight-well Seahorse XFp. The main benefits of the XF96 include the limited number of worms required and the high throughput capacity due to the 96-well format.

In Vivo Determination of Mitochondrial Function Using Luciferase-Expressing Caenorhabditis elegans: Contribution of Oxidative Phosphorylation, Glycolysis, and Fatty Acid Oxidation to Toxicant-Induced Dysfunction

Mitochondria are a target of many drugs and environmental toxicants; however, how toxicant-induced mitochondrial dysfunction contributes to the progression of human disease remains poorly understood. To address this issue, in vivo assays capable of rapidly assessing mitochondrial function need to be developed. Here, using the model organism Caenorhabditis elegans, we describe how to rapidly assess the in vivo role of the electron transport chain, glycolysis, or fatty acid oxidation in energy metabolism following toxicant exposure, using a luciferase-expressing ATP reporter strain. Alterations in mitochondrial function subsequent to toxicant exposure are detected by depleting steady-state ATP levels with inhibitors of the mitochondrial electron transport chain, glycolysis, or fatty acid oxidation. Differential changes in ATP following short-term inhibitor exposure indicate toxicant-induced alterations at the site of inhibition. Because a microplate reader is the only major piece of equipment required, this is a highly accessible method for studying toxicant-induced mitochondrial dysfunction in vivo. © 2016 by John Wiley & Sons, Inc.

III-10, a newly synthesized flavonoid, induces cell apoptosis with the involvement of reactive oxygen species-mitochondria pathway in human hepatocellular carcinoma cells

Study of the mechanisms of apoptosis in tumor cells is an important field of tumor therapy and cancer molecular biology. We recently established that III-10, a new flavonoid with a pyrrolidinyl and a benzyl group substitution, exerted its anti-tumor effect via inducing differentiation of human U937 leukemia cells. In this study, we demonstrated that III-10 induced cell apoptosis in human hepatocellular carcinoma cells. The activation of caspase-3, caspase-9, and the increased expression ratio of Bax/Bcl-2 were detected in III-10-induced apoptosis. Z-VAD-FMK, a pan-caspase inhibitor, partly attenuated the apoptotic induction of III-10 on both HepG2 and BEL-7402 cells. Furthermore, the increase of intracellular reactive oxygen species levels and the reduction of mitochondria ΔΨm were also observed in BEL-7402 and HepG2 cells after the treatment of III-10. Pretreatment with NAC, a reactive oxygen species production inhibitor, partly attenuated the apoptosis induced by III-10 via blocking the reactive oxygen species generation. Our data also showed that III-10 induced the release of cytochrome c and AIF to cytosol followed after the reactive oxygen species accumulation. Moreover, the GSH levels and ATP generation were both inhibited after III-10 treatment. Besides, the MAPK, the downstream effect of reactive oxygen species accumulation including JNK could be activated by III-10, as well as the inactivation of ERK. Collectively, the generation of reactive oxygen species might play an crucial role in III-10-induced mitochondrial apoptosis pathway, provided more stubborn evidence for III-10 as a potent anticancer therapeutic candidate.

Caenorhabditis elegans as a Model System for Studying Drug Induced Mitochondrial Toxicity

Today HIV-1 infection is recognized as a chronic disease with obligatory lifelong treatment to keep viral titers below detectable levels. The continuous intake of antiretroviral drugs however, leads to severe and even life-threatening side effects, supposedly by the deleterious impact of nucleoside-analogue type compounds on the functioning of the mitochondrial DNA polymerase. For detailed investigation of the yet partially understood underlying mechanisms, the availability of a versatile model system is crucial. We therefore set out to develop the use of Caenorhabditis elegans to study drug induced mitochondrial toxicity. Using a combination of molecular-biological and functional assays, combined with a quantitative analysis of mitochondrial network morphology, we conclude that anti-retroviral drugs with similar working mechanisms can be classified into distinct groups based on their effects on mitochondrial morphology and biochemistry. Additionally we show that mitochondrial toxicity of antiretroviral drugs cannot be exclusively attributed to interference with the mitochondrial DNA polymerase.

Exploring the function of protein kinases in schistosomes: perspectives from the laboratory and from comparative genomics

Eukaryotic protein kinases are well conserved through evolution. The genome of Schistosoma mansoni, which causes intestinal schistosomiasis, encodes over 250 putative protein kinases with all of the main eukaryotic groups represented. However, unraveling functional roles for these kinases is a considerable endeavor, particularly as protein kinases regulate multiple and sometimes overlapping cell and tissue functions in organisms. In this article, elucidating protein kinase signal transduction and function in schistosomes is considered from the perspective of the state-of-the-art methodologies used and comparative organismal biology, with a focus on current advances and future directions. Using the free-living nematode Caenorhabditis elegans as a comparator we predict roles for various schistosome protein kinases in processes vital for host invasion and successful parasitism such as sensory behavior, growth and development. It is anticipated that the characterization of schistosome protein kinases in the context of parasite function will catalyze cutting edge research into host-parasite interactions and will reveal new targets for developing drug interventions against human schistosomiasis.

Regulation of synaptic nlg-1/neuroligin abundance by the skn-1/Nrf stress response pathway protects against oxidative stress

The Nrf family of transcription factors mediates adaptive responses to stress and longevity, but the identities of the crucial Nrf targets, and the tissues in which they function in multicellular organisms to promote survival, are not known. Here, we use whole transcriptome RNA sequencing to identify 810 genes whose expression is controlled by the SKN-1/Nrf2 negative regulator WDR-23 in the nervous system of Caenorhabditis elegans. Among the genes identified is the synaptic cell adhesion molecule nlg-1/neuroligin. We find that the synaptic abundance of NLG-1 protein increases following pharmacological treatments that generate oxidative stress or by the genetic activation of skn-1. Increasing nlg-1 dosage correlates with increased survival in response to oxidative stress, whereas genetic inactivation of nlg-1 reduces survival and impairs skn-1-mediated stress resistance. We identify a canonical SKN-1 binding site in the nlg-1 promoter that binds to SKN-1 in vitro and is necessary for SKN-1 and toxin-mediated increases in nlg-1 expression in vivo. Together, our results suggest that SKN-1 activation in the nervous system can confer protection to organisms in response to stress by directly regulating nlg-1/neuroligin expression.

Increased mitochondrial functions in human glioblastoma cells persistently infected with measles virus

Measles virus (MV) is known for its ability to cause an acute infection with a potential of development of persistent infection. However, knowledge of how viral genes and cellular factors interact to cause or maintain the persistent infection has remained unclear. We have previously reported the possible involvement of mitochondrial short chain enoyl-CoA hydratase (ECHS), which is localized at mitochondria, in the regulation of MV replication. In this study we found increased functions of mitochondria in MV-persistently infected cells compared with uninfected or acutely infected cells. Furthermore, impairment of mitochondrial functions by treatment with mitochondrial inhibitors such as ethidium bromide (EtBr) or carbonyl cyanide-p-trifluoromethoxyphenylhydrazone (FCCP) induced the cytopathic effects of extensive syncytial formation in persistently infected cells. These findings suggest that mitochondria are one of the subcellular organelles contributing to regulate persistent infection of MV. Recent studies showed mitochondria provide an integral platform for retinoic acid-inducible protein (RIG-I)-like cytosolic receptors (RLRs) signaling and participate in cellular innate antiviral immunity. Our findings not only reveal a role of mitochondria in RLR mediated antiviral signaling but also suggest that mitochondria contribute to the regulation of persistent viral infection.

Current methods in quantifying ROS and oxidative damage in Caenorhabditis elegans and other model organism of aging

Accumulation of oxidative damage has been proposed to be causal to aging as defined by the Free radical Theory of Aging, which has been subject to recent debate. However, a major hurdle in understanding the biological roles of reactive oxygen species (ROS) signaling and their oxidative damage has been the widely recognized methodological difficulties to measure oxidative damage and ROS in vivo. In this review we describe the various novel approaches that have recently been developed to overcome this challenge in the nematode Caenorhabditis elegans, which is a paradigm invertebrate model organism for studying aging and age-related disease given its short lifespan, easy genetics and transparency. In addition, we also discuss these methods in other important model organisms of aging, including the budding yeast Saccharomyces cerevisiae, the fruitfly Drosophila melanogaster and the mouse Mus musculus. After an introduction on the various ROS that can be encountered, we discuss approaches for the detection and quantification of ROS and ROS damage of DNA, lipids and proteins, highlighting examples from literature to demonstrate the applicability and caveats of each method. As will become clear, combinations of approaches have now become possible and will prove essential for thoroughly understanding the involvement of ROS and ROS damage in the biology of aging and disease.

Discovery of anthelmintic drug targets and drugs using chokepoints in nematode metabolic pathways

Parasitic roundworm infections plague more than 2 billion people (1/3 of humanity) and cause drastic losses in crops and livestock. New anthelmintic drugs are urgently needed as new drug resistance and environmental concerns arise. A “chokepoint reaction” is defined as a reaction that either consumes a unique substrate or produces a unique product. A chokepoint analysis provides a systematic method of identifying novel potential drug targets. Chokepoint enzymes were identified in the genomes of 10 nematode species, and the intersection and union of all chokepoint enzymes were found. By studying and experimentally testing available compounds known to target proteins orthologous to nematode chokepoint proteins in public databases, this study uncovers features of chokepoints that make them successful drug targets. Chemogenomic screening was performed on drug-like compounds from public drug databases to find existing compounds that target homologs of nematode chokepoints. The compounds were prioritized based on chemical properties frequently found in successful drugs and were experimentally tested using Caenorhabditis elegans. Several drugs that are already known anthelmintic drugs and novel candidate targets were identified. Seven of the compounds were tested in Caenorhabditis elegans and three yielded a detrimental phenotype. One of these three drug-like compounds, Perhexiline, also yielded a deleterious effect in Haemonchus contortus and Onchocerca lienalis, two nematodes with divergent forms of parasitism. Perhexiline, known to affect the fatty acid oxidation pathway in mammals, caused a reduction in oxygen consumption rates in C. elegans and genome-wide gene expression profiles provided an additional confirmation of its mode of action. Computational modeling of Perhexiline and its target provided structural insights regarding its binding mode and specificity. Our lists of prioritized drug targets and drug-like compounds have potential to expedite the discovery of new anthelmintic drugs with broad-spectrum efficacy.

The World Health Organization estimates that 2.9 million people are infected with parasitic roundworms, causing high-morbidity and mortality rates, developmental delays in children, and low productivity of affected individuals. The agricultural industry experiences drastic losses in crop and livestock due to parasitic worm infections. Therefore, there is an urgent need to identify new targets and drugs to fight parasitic nematode infection. This study identified metabolic chokepoint compounds that were either produced or consumed by a single reaction and elucidated the chokepoint enzyme that drives the reaction. If the enzyme that catalyzes that reaction is blocked, a toxic build-up of a compound or lack of compound necessary for subsequent reaction will occur, potentially causing adverse effects to the parasite organism. Compounds that target some of the chokepoint enzymes were tested in C. elegans and several compounds showed efficacy. One drug-like compound, Perhexiline, showed efficacy in two different parasitic worms and yielded expected physiological effects, indicating that this drug-like compound may have efficacy on a pan-phylum level through the predicted mode of action. The methodology to find and prioritize metabolic chokepoint targets and prioritize compounds could be applied to other parasites.

A cytoprotective perspective on longevity regulation

There are many mechanisms of lifespan extension, including the disruption of insulin/insulin-like growth factor 1 (IGF-1) signaling, metabolism, translation, and feeding. Despite the disparate functions of these pathways, inhibition of each induces responses that buffer stress and damage. Here, emphasizing data from genetic analyses in Caenorhabditis elegans, we explore the effectors and upstream regulatory components of numerous cytoprotective mechanisms activated as major elements of longevity programs, including detoxification, innate immunity, proteostasis, and oxidative stress response. We show that their induction underpins longevity extension across functionally diverse triggers and across species. Intertwined with the evolution of longevity, cytoprotective pathways are coupled to the surveillance of core cellular components, with important implications in normal and aberrant responses to drugs, chemicals, and pathogens.

Premature and accelerated aging: HIV or HAART?

Highly active antiretroviral therapy (HAART) has significantly increased life expectancy of the human immunodeficiency virus (HIV)-positive population. Nevertheless, the average lifespan of HIV-patients remains shorter compared to uninfected individuals. Immunosenescence, a current explanation for this difference invokes heavily on viral stimulus despite HAART efficiency in viral suppression. We propose here that the premature and accelerated aging of HIV-patients can also be caused by adverse effects of antiretroviral drugs, specifically those that affect the mitochondria. The nucleoside reverse transcriptase inhibitor (NRTI) antiretroviral drug class for instance, is known to cause depletion of mitochondrial DNA via inhibition of the mitochondrial specific DNA polymerase-γ. Besides NRTIs, other antiretroviral drug classes such as protease inhibitors also cause severe mitochondrial damage by increasing oxidative stress and diminishing mitochondrial function. We also discuss important areas for future research and argue in favor of the use of Caenorhabditis elegans as a novel model system for studying these effects.

Signaling pathways of prohibitin and its role in diseases

Prohibitin (PHB), appearing to be a negative regulator of cell proliferation and to be a tumor suppressor, has been connected to diverse cellular functions including cell cycle control, senescence, apoptosis and the regulation of mitochondrial activities. It is a growth regulatory gene that has pleiotropic functions in the nucleus, mitochondria and cytoplasmic compartments. However, in different tissues/cells, the expression of PHB was different, such as that it was increased in most of the cancers, but its expression was reduced in kidney diseases. Signaling pathways might be very important in the pathogenesis of diseases. This review was performed to provide a relatively complete signaling pathways flowchart for PHB to the investigators who were interested in the roles of PHB in the pathogenesis of diseases. Here, we review the signal transduction pathways of PHB and its role in the pathogenesis of diseases.

Induction of cytoprotective pathways is central to the extension of lifespan conferred by multiple longevity pathways

Many genetic and physiological treatments that extend lifespan also confer resistance to a variety of stressors, suggesting that cytoprotective mechanisms underpin the regulation of longevity. It has not been established, however, whether the induction of cytoprotective pathways is essential for lifespan extension or merely correlated. Using a panel of GFP-fused stress response genes, we identified the suites of cytoprotective pathways upregulated by 160 gene inactivations known to increase Caenorhabditis elegans longevity, including the mitochondrial UPR (hsp-6, hsp-60), the ER UPR (hsp-4), ROS response (sod-3, gst-4), and xenobiotic detoxification (gst-4). We then screened for other gene inactivations that disrupt the induction of these responses by xenobiotic or genetic triggers, identifying 29 gene inactivations required for cytoprotective gene expression. If cytoprotective responses contribute directly to lifespan extension, inactivation of these genes would be expected to compromise the extension of lifespan conferred by decreased insulin/IGF-1 signaling, caloric restriction, or the inhibition of mitochondrial function. We find that inactivation of 25 of 29 cytoprotection-regulatory genes shortens the extension of longevity normally induced by decreased insulin/IGF-1 signaling, disruption of mitochondrial function, or caloric restriction, without disrupting normal longevity nearly as dramatically. These data demonstrate that induction of cytoprotective pathways is central to longevity extension and identify a large set of new genetic components of the pathways that detect cellular damage and couple that detection to downstream cytoprotective effectors.

Many mutations that increase animal lifespan also confer stress tolerance, suggesting that cytoprotective mechanisms underpin the regulation of longevity. It has not been established, however, whether the induction of individual cytoprotective pathways is essential for lifespan extension, or merely correlated. To establish whether the regulatory pathways for the induction of cytoprotective responses are key in the extension of lifespan, we performed an RNAi screen for gene inactivations that decouple the activation of cytoprotective pathways from xenobiotic stimuli that normally induce them. The screen identified 29 genes that constitute the regulatory cascades of the unfolded protein response, oxidative stress response, and detoxification. These upstream regulatory genes are critical to stress tolerance and the extension of lifespan conferred by decreased insulin/IGF-1 signaling, disruption of mitochondrial function, or caloric restriction, but have little effect on normal longevity.

Photothermal confocal spectromicroscopy of multiple cellular chromophores and fluorophores

Confocal fluorescence microscopy is a powerful biological tool providing high-resolution, three-dimensional (3D) imaging of fluorescent molecules. Many cellular components are weakly fluorescent, however, and thus their imaging requires additional labeling. As an alternative, label-free imaging can be performed by photothermal (PT) microscopy (PTM), based on nonradiative relaxation of absorbed energy into heat. Previously, little progress has been made in PT spectral identification of cellular chromophores at the 3D microscopic scale. Here, we introduce PTM integrating confocal thermal-lens scanning schematic, time-resolved detection, PT spectral identification, and nonlinear nanobubble-induced signal amplification with a tunable pulsed nanosecond laser. The capabilities of this confocal PTM were demonstrated for high-resolution 3D imaging and spectral identification of up to four chromophores and fluorophores in live cells and Caenorhabditis elegans. Examples include cytochrome c, green fluorescent protein, Mito-Tracker Red, Alexa-488, and natural drug-enhanced or genetically engineered melanin as a PT contrast agent. PTM was able to guide spectral burning of strong absorption background, which masked weakly absorbing chromophores (e.g., cytochromes in the melanin background). PTM provided label-free monitoring of stress-related changes to cytochrome c distribution, in C. elegans at the single-cell level. In nonlinear mode ultrasharp PT spectra from cyt c and the lateral resolution of 120 nm during calibration with 10-nm gold film were observed, suggesting a potential of PTM to break through the spectral and diffraction limits, respectively. Confocal PT spectromicroscopy could provide a valuable alternative or supplement to fluorescence microscopy for imaging of nonfluorescent chromophores and certain fluorophores.

Disruption of alternative NAD(P)H dehydrogenases leads to decreased mitochondrial ROS in Neurospora crassa

Mitochondria are a main providers of high levels of energy, but also a major source of reactive oxygen species (ROS) during normal oxidative metabolism. The involvement of Neurospora crassa alternative NAD(P)H dehydrogenases in mitochondrial ROS production was evaluated. The growth responses of a series of respiratory mutants to several stress conditions revealed that disrupting alternative dehydrogenases leads to an increased tolerance to the redox cycler paraquat, with a mutant devoid of the external NDE1 and NDE2 enzymes being significantly more resistant. The nde1nde2 mutant mitochondria show a significant decrease in ROS generation in the presence and absence of paraquat, regardless of the respiratory substrate used, and an intrinsic increase in catalase activity. Analysis of ROS production by a complex I mutant (nuo51) indicates that, as in other organisms, paraquat-derived ROS in Neurospora mitochondria occur mainly at the level of complex I. We propose that disruption of the external NAD(P)H dehydrogenases NDE1 and NDE2 leads to a synergistic effect diminishing ROS generation by the mitochondrial respiratory chain. This, in addition to a robust increase in scavenging capacity, provides the mutant strain with an improved ability to withstand paraquat treatment.