Approaches for Studying Autophagy in Caenorhabditis elegans

Cannabinoids and healthy ageing: the potential for extending healthspan and lifespan in preclinical models with an emphasis on Caenorhabditis elegans

There is a significant global upsurge in the number and proportion of older persons in the population. With this comes an increasing prevalence of age-related conditions which pose a major challenge to healthcare systems. The development of anti-ageing treatments may help meet this challenge by targeting the ageing process which is a common denominator to many health problems. Cannabis-like compounds (cannabinoids) are reported to improve quality of life and general well-being in human trials, and there is increasing preclinical research highlighting that they have anti-ageing activity. Moreover, preclinical evidence suggests that endogenous cannabinoids regulate ageing processes. Here, we review the anti-ageing effects of the cannabinoids in various model systems, including the most extensively studied nematode model, Caenorhabditis elegans. These studies highlight that the cannabinoids lengthen healthspan and lifespan, with emerging evidence that they may also hinder the development of cellular senescence. The non-psychoactive cannabinoid cannabidiol (CBD) shows particular promise, with mechanistic studies demonstrating it may work through autophagy induction and activation of antioxidative systems. Furthermore, CBD improves healthspan parameters such as diminishing age-related behavioural dysfunction in models of both healthy and accelerated ageing. Translation into mammalian systems provides an important next step. Moreover, looking beyond CBD, future studies could probe the multitude of other cannabis constituents for their anti-ageing activity.

Environmentally relevant concentrations of perfluorobutane sulfonate impair locomotion behaviors and healthspan by downregulating mitophagy in C. elegans

Perfluorobutane sulfonate (PFBS), a chemical compound within the group of per- and polyfluoroalkyl substances (PFAS), has been utilized as an alternative to perfluorooctane sulfonate (PFOS) recently. Previous research has indicated that PFBS might be linked to a range of health concerns. However, the potential impacts of environmentally relevant concentrations of PFBS (25 nM) on aging as well as the underlying mechanisms remained largely unexplored. In this study, we investigated the impact of PFBS exposure on aging and the associated mechanisms in Caenorhabditis elegans. Our findings indicated that exposure to PFBS impaired healthspan of C. elegans. Through bioinformatic screening analyses, we identified that the dysfunctions of pink-1 mediated mitophagy might play a critical role in PFBS induced aging. The results furtherly revealed that PFBS exposure led to elevated levels of reactive oxygen species (ROS) and mitophagy impairment through downregulating pink-1/pdr-1 pathway. Furthermore, the mitophagy agonist Urolithin A (UA) effectively reversed PFBS-induced mitophagy dysfunction and enhanced healthspan in C. elegans. Taken together, our study suggested that exposure to environmentally relevant concentrations of PFBS could accelerate aging by downregulating the pink-1 mediated mitophagy. Promoting mitophagy within cells could be a promising therapeutic strategy for delaying PFBS-induced aging.

Neuroprotective effect of erythropoietin on anesthesia-induced neurotoxicity through the modulation of autophagy in Caenorhabditis elegans

BACKGROUND

The anti-oxidative, anti-inflammatory, and anti-apoptotic effects of erythropoietin may provide neuroprotective effects. Erythropoietin also modulates autophagy signaling that may play a role in anesthesia-induced neurotoxicity (AIN). Herein, we investigated whether AIN can be attenuated by the neuroprotective effect of erythropoietin in the Caenorhabditis elegans (C. elegans).

METHODS

Synchronized worms were divided into the control, Iso, EPO, and EPO-Iso groups. The chemotaxis index (CI) was evaluated when they reached the young adult stage. The lgg-1::GFP-positive puncta per seam cell were used to determine the autophagic events. The erythropoietin-mediated pathway of autophagy was determined by measuring the genetic expression level of let-363, bec-1, atg-7, atg-5, and lgg-3.

RESULTS

Increased lgg-1::GFP puncta were observed in the Iso, EPO, and EPO-Iso groups. In the Iso group, only the let-363 level decreased significantly as compared to that in the control group (P = 0.009). bec-1 (P < 0.001), atg-5 (P = 0.012), and lgg-3 (P < 0.001) were expressed significantly more in the EPO-Iso group than in the Iso groups. Repeated isoflurane exposure during development decreased the CI. Erythropoietin could restore the decreased CI by isoflurane significantly in the EPO-Iso group.

CONCLUSIONS

Erythropoietin showed neuroprotective effects against AIN and modulated the autophagic pathway in C. elegans. This experimental evidence of erythropoietin-related neuroprotection against AIN may be correlated with the induced autophagic degradation process that was sufficient for handling enhanced autophagy induction in erythropoietin-treated worms.

Autophagy and regulation of aquaporins in the kidneys

Aquaporins (AQPs) are water channel proteins that facilitate the transport of water molecules across cell membranes. To date, seven AQPs have been found to be expressed in mammal kidneys. The cellular localization and regulation of the transport properties of AQPs in the kidney have been widely investigated. Autophagy is known as a highly conserved lysosomal pathway, which degrades cytoplasmic components. Through basal autophagy, kidney cells maintain their functions and structure. As a part of the adaptive responses of the kidney, autophagy may be altered in response to stress conditions. Recent studies revealed that autophagic degradation of AQP2 in the kidney collecting ducts leads to impaired urine concentration in animal models with polyuria. Therefore, the modulation of autophagy could be a therapeutic approach to treat water balance disorders. However, as autophagy is either protective or deleterious, it is crucial to establish an optimal condition and therapeutic window where autophagy induction or inhibition could yield beneficial effects. Further studies are needed to understand both the regulation of autophagy and the interaction between AQPs and autophagy in the kidneys in renal diseases, including nephrogenic diabetes insipidus.

Differential production rates of cytosolic and transmembrane GFP reporters in C. elegans L3 larval uterine cells

Transgene driven protein expression is an important tool for investigating developmental mechanisms in C. elegans . Here, we have assessed protein production rates and levels in L3 larval uterine cells (UCs). Using ubiquitous promoter driven cytosolic and transmembrane tethered GFP, fluorescence recovery after photobleaching, and quantitative fluorescence analysis, we reveal that cytosolic GFP is produced at an ~two-fold higher rate than transmembrane tethered GFP and accumulates at ~five-fold higher levels in UCs. We also provide evidence that cytosolic GFP in the anchor cell, a specialized UC that mediates uterine-vulval connection, is more rapidly degraded through an autophagy-independent mechanism.

Chlorogenic acid delays the progression of Parkinson's disease via autophagy induction in Caenorhabditis elegans

OBJECTIVES

Parkinson's disease (PD) is the second most common neurodegenerative disease. Chlorogenic acid (CGA) is a polyphenolic substance derived from various medicinal plants. Although CGA is reported to have potential anti-PD effect, the beneficial effect and the underlying mechanism remain unclear. In this study, we aimed to further investigate the protective effect and clarify the mechanism of action of CGA in Caenorhabditis elegans (C. elegans) models of PD.

METHODS

Measurements of a-synuclein aggregation, movement disorders, and lipid, ROS and malondialdehyde (MDA) contents were observed in NL5901 nematodes. Determinations of dopamine (DA) neuron degeneration, food perception, and ROS content were performed in 6-OHDA-exposed BZ555 nematodes. The autophagy activation of CGA was monitored using DA2123 and BC12921 nematodes. Meanwhile, RNAi technology was employed to knockdown the autophagy-related genes and investigate whether the anti-PD effect of CGA was associated with autophagy induction in C. elegans.

RESULTS

CGA significantly reduced α-synuclein aggregation, improved motor disorders, restored lipid content, and decreased ROS and MDA contents in NL5901 nematodes. Meanwhile, CGA inhibited DA neuron-degeneration and improved food-sensing behavior in 6-OHDA-exposed BZ555 nematodes. In addition, CGA increased the number of GFP::LGG-1 foci in DA2123 nematodes and degraded p62 protein in BC12921 nematodes. Meanwhile, CGA up-regulated the expression of autophagy-related genes in NL5901 nematodes. Moreover, the anti-PD effect of CGA was closely related to autophagy induction via increasing the expression of autophagy-related genes, including unc-51, bec-1, vps-34, and lgg-1.

CONCLUSIONS

The present study indicates that CGA exerts neuroprotective effect in C. elegans via autophagy induction.

Crosstalk between cGAS-STING pathway and autophagy in cancer immunity

The cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway is critical in cancer immunity. Autophagy is a highly conserved process that is responsible for the degradation of cytoplasmic material and is involved in both innate and adaptive immunity. Recently, cGAS-STING and autophagy have been shown to be interconnected, which may influence the progression of cancer. Although cGAS-STING and autophagy have been shown to be interrelated in innate immunity, little has been reported about cancer immunity. As cancer immunity is key to treating tumors, it is essential to summarize the relationship and interactions between the two. Based on this, we systematically sorted out the recent findings of cGAS-STING and autophagy in cancer immunity and explored the interactions between cGAS-STING and autophagy, although these interactions have not been extensively studied. Lastly, we provide an outlook on how cGAS-STING and autophagy can be combined, with the hope that our research can help people better understand their potential roles in cancer immunity and bring light to the treatment of cancer.

Folium Hibisci Mutabilis extract, a potent autophagy enhancer, exhibits neuroprotective properties in multiple models of neurodegenerative diseases

BACKGROUND

Protein aggregates are considered key pathological features in neurodegenerative diseases (NDs). The induction of autophagy can effectively promote the clearance of ND-related misfolded proteins.

OBJECTIVE

In this study, we aimed to screen natural autophagy enhancers from traditional Chinese medicines (TCMs) presenting potent neuroprotective potential in multiple ND models.

METHODS

The autophagy enhancers were broadly screened in our established herbal extract library using the transgenic Caenorhabditis elegans (C. elegans) DA2123 strain. The neuroprotective effects of the identified autophagy enhancers were evaluated in multiple C. elegans ND models by measuring Aβ-, Tau-, α-synuclein-, and polyQ40-induced pathologies. In addition, PC-12 cells and 3 × Tg-AD mice were employed to further validate the neuroprotective ability of the identified autophagy enhancers, both in vitro and in vivo. Furthermore, RNAi bacteria and autophagy inhibitors were used to evaluate whether the observed effects of the identified autophagy enhancers were mediated by the autophagy-activated pathway.

RESULTS

The ethanol extract of Folium Hibisci Mutabilis (FHME) was found to significantly increase GFP::LGG-1-positive puncta in the DA2123 worms. FHME treatment markedly inhibited Aβ, α-synuclein, and polyQ40, as well as prolonging the lifespan and improving the behaviors of C. elegans, while siRNA targeting four key autophagy genes partly abrogated the protective roles of FHME in C. elegans. Additionally, FHME decreased the expression of AD-related proteins and restored cell viability in PC-12 cells, which were canceled by cotreatment with 3-methyladenine (3-MA) or bafilomycin A1 (Baf). Moreover, FHME ameliorated AD-like cognitive impairment and pathology, as well as activating autophagy in 3 × Tg-AD mice.

CONCLUSION

FHME was successfully screened from our natural product library as a potent autophagy enhancer that exhibits a neuroprotective effect in multiple ND models across species through the induction of autophagy. These findings offer a new and reliable strategy for screening autophagy inducers, as well as providing evidence that FHME may serve as a possible therapeutic agent for NDs.

Neuroprotective Capability of Narcissoside in 6-OHDA-Exposed Parkinson's Disease Models through Enhancing the MiR200a/Nrf-2/GSH Axis and Mediating MAPK/Akt Associated Signaling Pathway

We assessed the antioxidant potential of narcissoside from Sambucus nigra flowers (elderflowers) in Parkinson's disease models in vitro and in vivo. The results showed that narcissoside lessened the 6-hydroxydopamine (6-OHDA)-induced increase in reactive oxygen species (ROS) and apoptosis in SH-SY5Y cells. In the 6-OHDA-exposed Caenorhabditis elegans model, narcissoside reduced degeneration of dopaminergic neurons and ROS generation, and also improved dopamine-related food-sensitive behavior and shortened lifespan. Moreover, NCS increased total glutathione (GSH) by increasing the expression of the catalytic subunit and modifier subunit of γ-glutamylcysteine ligase in cells and nematodes. Treatment with a GSH inhibitor partially abolished the anti-apoptotic ability of narcissoside. Furthermore, narcissoside diminished the 6-OHDA-induced phosphorylation of JNK and p38, while rising activities of ERK and Akt in resisting apoptosis. The antioxidant response element (ARE)-luciferase reporter activity analysis and electromobility gel shift assay showed that narcissoside promotes the transcriptional activity mediated by Nrf2. Finally, we found that narcissoside augmented the expression of miR200a, a translational inhibitor of the Nrf2 repressor protein Keap1. Downregulation of Nrf2 and miR200a by RNAi and anti-miR200a, respectively, reversed the neuroprotective ability of narcissoside. In summary, narcissoside can enhance the miR200a/Nrf2/GSH antioxidant pathway, alleviate 6-OHDA-induced apoptosis, and has the neuroprotective potential.

Protein import motor complex reacts to mitochondrial misfolding by reducing protein import and activating mitophagy

Mitophagy is essential to maintain mitochondrial function and prevent diseases. It activates upon mitochondria depolarization, which causes PINK1 stabilization on the mitochondrial outer membrane. Strikingly, a number of conditions, including mitochondrial protein misfolding, can induce mitophagy without a loss in membrane potential. The underlying molecular details remain unclear. Here, we report that a loss of mitochondrial protein import, mediated by the pre-sequence translocase-associated motor complex PAM, is sufficient to induce mitophagy in polarized mitochondria. A genome-wide CRISPR/Cas9 screen for mitophagy inducers identifies components of the PAM complex. Protein import defects are able to induce mitophagy without a need for depolarization. Upon mitochondrial protein misfolding, PAM dissociates from the import machinery resulting in decreased protein import and mitophagy induction. Our findings extend the current mitophagy model to explain mitophagy induction upon conditions that do not affect membrane polarization, such as mitochondrial protein misfolding.

Mitophagy activation is mediated by mitochondrial depolarization. Here, the authors show that mitochondrial protein misfolding can activate mitophagy in a depolarization-independent manner mediated by a protein import reduction.

Citri Reticulatae Semen extract promotes healthy aging and neuroprotection via autophagy induction in Caenorhabditis elegans

Nutrition intervention has emerged as a potential strategy to delay aging and promote healthy longevity. Citri Reticulatae Semen (CRS) has diverse beneficial effects and has been used for thousands of years to treat pain. However, the health benefits of CRS in prolonging healthspan and improving aging-related diseases and the exact mechanisms remain poorly characterized. In this study, Caenorhabditis elegans (C. elegans) was used as a model organism to study the anti-aging and healthspan promoting activities of 75% ethanol extract of CRS (CRSE). The results showed that treatment with CRSE at 1000 μg/mL significantly extended the lifespan of worms by 18.93% without detriment to healthspan and fitness, as evidenced by the delayed aging-related phenotypes and increased body length and width and reproductive output. In addition, CRSE treatment enhanced the ability of resistance under heat, oxidative, and pathogenic bacterial stress. Consistently, heat shock proteins and antioxidant enzyme-related and pathogenesis-related (PR) genes were up-regulated by CRSE treatment. Furthermore, CRSE supplementation also improved α-synuclein, 6-OHDA, and polyQ40-induced pathologies in transgenic C. elegans models of Parkinson's disease (PD) and Huntington's disease (HD). The mechanistic study demonstrated that CRSE induced autophagy in worms, while the RNAi knockdown of 4 key autophagy-related genes including lgg-1, bec-1, vps-34, and unc-51 remarkably abrogated the beneficial effects of CRSE on the extending of lifespan and healthspan and neuroprotection, demonstrating that CRSE exerts beneficial effects via autophagy induction in worms. Together, our current findings provide new insights into the practical application of CRS for the prevention of aging and aging-related diseases.

Xanthotoxin induced photoactivated toxicity, oxidative stress and cellular apoptosis in Caenorhabditis elegans under ultraviolet A

Xanthotoxin (XAT) is widely present in many kinds of plants. Caenorhabditis elegans, a typical model organism, was used to study the effects of XAT on C. elegans developmental toxicity, neurotoxicity, reproductive toxicity induced under ultraviolet A (UVA), oxidative stress and apoptosis in C. elegans. The results showed that after XAT exposure treatment, the hatchability of C. elegans decreased significantly as the concentration increased; the body length and width increased markedly, the external morphology was swollen; the brood sizes had been decreased; and the frequencies of head thrashes and body bend decreased significantly. At 80 and 100 mg/L, XAT reduced the activities of mitochondrial complex enzymes I and III, resulting in the excessive production of ROS, and inhibited SOD and CAT so that the ROS could not be eliminated over time. ROS accumulation in the bodies further caused the contents of MDA, protein carbonyl and lipofuscin to increase significantly, the mitochondrial membrane potential to be severely damaged, apoptosis to occur, and the apoptosis genes ced-3 and ced-4 to be significantly upregulated. Thus, XAT showed photoactivated toxicity to C. elegans under UVA, which will help people to make full and rational use of plants containing XAT.

Endurance of extremely prolonged nutrient prevention across kingdoms of life

Numerous observations demonstrate that microorganisms can survive very long periods of nutrient deprivation and starvation. Moreover, it is evident that prolonged periods of starvation are a feature of many habitats, and many cells in all kingdoms of life are found in prolonged starvation conditions. Bacteria exhibit a range of responses to long-term starvation. These include genetic adaptations such as the long-term stationary phase and the growth advantage in stationary phase phenotypes characterized by mutations in stress-signaling genes and elevated mutation rates. Here, we suggest using the term "endurance of prolonged nutrient prevention" (EPNP phase), to describe this phase, which was also recently described in eukaryotes. Here, we review this literature and describe the current knowledge about the adaptations to very long-term starvation conditions in bacteria and eukaryotes, its conceptual and structural conservation across all kingdoms of life, and point out possible directions that merit further research.

Early-life and chronic exposure to di(2-ethylhexyl) phthalate enhances amyloid-β toxicity associated with an autophagy-related gene in Caenorhabditis elegans Alzheimer's disease models

The widespread use of di(2-ethylhexyl) phthalate (DEHP) has resulted in its ubiquitous presence in the environment, which has led to serious health concerns. One of these concerns is its possible link to Alzheimer's disease (AD), which is the most common neurodegenerative disease in aged individuals. This study investigated whether early-life and chronic exposure to DEHP affects AD via the toxicity of amyloid-β (Aβ), which has been implicated in the pathogenesis of AD, using Caenorhabditis elegans AD models (strains CL4176 and CL2006). We show that early-life DEHP exposure increased Aβ toxicity in C. elegans strains CL4176 and CL2006. Early-life and chronic exposure to DEHP also significantly increased intracellular ROS levels and Aβ deposition in aged CL2006 nematodes. Moreover, it was found that DEHP-induced Aβ toxicity does not require transcription factors DAF-16 or SKN-1, while early-life and chronic exposure to DEHP significantly increased the accumulation of lysosome-related organelles and the mRNA levels of the autophagy-related gene bec-1 in aged CL2006 nematodes. Our findings suggest that early-life and chronic exposure to DEHP enhances Aβ toxicity, which may be associated with the autophagy-lysosomal degradation pathway in C. elegans.

Beneficial Effects of Cyclic Ether 2-Butoxytetrahydrofuran from Sea Cucumber Holothuria scabra against Aβ Aggregate Toxicity in Transgenic Caenorhabditis elegans and Potential Chemical Interaction

The pathological finding of amyloid-β (Aβ) aggregates is thought to be a leading cause of untreated Alzheimer’s disease (AD). In this study, we isolated 2-butoxytetrahydrofuran (2-BTHF), a small cyclic ether, from Holothuria scabra and demonstrated its therapeutic potential against AD through the attenuation of Aβ aggregation in a transgenic Caenorhabditis elegans model. Our results revealed that amongst the five H. scabra isolated compounds, 2-BTHF was shown to be the most effective in suppressing worm paralysis caused by Aβ toxicity and in expressing strong neuroprotection in CL4176 and CL2355 strains, respectively. An immunoblot analysis showed that CL4176 and CL2006 treated with 2-BTHF showed no effect on the level of Aβ monomers but significantly reduced the toxic oligomeric form and the amount of 1,4-bis(3-carboxy-hydroxy-phenylethenyl)-benzene (X-34)-positive fibril deposits. This concurrently occurred with a reduction of reactive oxygen species (ROS) in the treated CL4176 worms. Mechanistically, heat shock factor 1 (HSF-1) (at residues histidine 63 (HIS63) and glutamine 72 (GLN72)) was shown to be 2-BTHF’s potential target that might contribute to an increased expression of autophagy-related genes required for the breakdown of the Aβ aggregate, thus attenuating its toxicity. In conclusion, 2-BTHF from H. scabra could protect C. elegans from Aβ toxicity by suppressing its aggregation via an HSF-1-regulated autophagic pathway and has been implicated as a potential drug for AD.

Autophagy facilitates mitochondrial rebuilding after acute heat stress via a DRP-1-dependent process

Acute heat stress (aHS) can induce strong developmental defects in Caenorhabditis elegans larva but not lethality or sterility. This stress results in transitory fragmentation of mitochondria, formation of aggregates in the matrix, and decrease of mitochondrial respiration. Moreover, active autophagic flux associated with mitophagy events enables the rebuilding of the mitochondrial network and developmental recovery, showing that the autophagic response is protective. This adaptation to aHS does not require Pink1/Parkin or the mitophagy receptors DCT-1/NIX and FUNDC1. We also find that mitochondria are a major site for autophagosome biogenesis in the epidermis in both standard and heat stress conditions. In addition, we report that the depletion of the dynamin-related protein 1 (DRP-1) affects autophagic processes and the adaptation to aHS. In drp-1 animals, the abnormal mitochondria tend to modify their shape upon aHS but are unable to achieve fragmentation. Autophagy is induced, but autophagosomes are abnormally elongated and clustered on mitochondria. Our data support a role for DRP-1 in coordinating mitochondrial fission and autophagosome biogenesis in stress conditions.

Host-commensal interaction promotes health and lifespan in Caenorhabditis elegans through the activation of HLH-30/TFEB-mediated autophagy

Gut homeostasis is maintained by the close interaction between commensal intestinal microbiota and the host, affecting the most complex physiological processes, such as aging. Some commensal bacteria with the potential to promote healthy aging arise as attractive candidates for the development of pro-longevity probiotics. Here, we showed that heat-inactivated human commensal Lactobacillus fermentum BGHV110 (BGHV110) extends the lifespan of Caenorhabditis elegans and improves age-related physiological features, including locomotor function and lipid metabolism. Mechanistically, we found that BGHV110 promotes HLH-30/TFEB-dependent autophagy to delay aging, as longevity assurance was completely abolished in the mutant lacking HLH-30, a major autophagy regulator in C. elegans. Moreover, we observed that BGHV110 partially decreased the content of lipid droplets in an HLH-30-dependent manner and, at the same time, slightly increased mitochondrial activity. In summary, this study demonstrates that specific factors from commensal bacteria can be used to exploit HLH-30/TFEB-mediated autophagy in order to promote longevity and fitness of the host.

Molecular Basis of Neuronal Autophagy in Ageing: Insights from Caenorhabditis elegans

Autophagy is an evolutionarily conserved degradation process maintaining cell homeostasis. Induction of autophagy is triggered as a response to a broad range of cellular stress conditions, such as nutrient deprivation, protein aggregation, organelle damage and pathogen invasion. Macroautophagy involves the sequestration of cytoplasmic contents in a double-membrane organelle referred to as the autophagosome with subsequent degradation of its contents upon delivery to lysosomes. Autophagy plays critical roles in development, maintenance and survival of distinct cell populations including neurons. Consequently, age-dependent decline in autophagy predisposes animals for age-related diseases including neurodegeneration and compromises healthspan and longevity. In this review, we summarize recent advances in our understanding of the role of neuronal autophagy in ageing, focusing on studies in the nematode Caenorhabditis elegans.

Endonuclease G promotes autophagy by suppressing mTOR signaling and activating the DNA damage response

Endonuclease G (ENDOG), a mitochondrial nuclease, is known to participate in many cellular processes, including apoptosis and paternal mitochondrial elimination, while its role in autophagy remains unclear. Here, we report that ENDOG released from mitochondria promotes autophagy during starvation, which we find to be evolutionally conserved across species by performing experiments in human cell lines, mice, Drosophila and C. elegans. Under starvation, Glycogen synthase kinase 3 beta-mediated phosphorylation of ENDOG at Thr-128 and Ser-288 enhances its interaction with 14-3-3γ, which leads to the release of Tuberin (TSC2) and Phosphatidylinositol 3-kinase catalytic subunit type 3 (Vps34) from 14-3-3γ, followed by mTOR pathway suppression and autophagy initiation. Alternatively, ENDOG activates DNA damage response and triggers autophagy through its endonuclease activity. Our results demonstrate that ENDOG is a crucial regulator of autophagy, manifested by phosphorylation-mediated interaction with 14-3-3γ, and its endonuclease activity-mediated DNA damage response.

Monitoring autophagic flux in Caenorhabditis elegans using a p62/SQST-1 reporter

Autophagy is a well-conserved self-degrading mechanism, which involves the elimination of unnecessary or damaged cellular constituents. Although extensively studied, many aspects regarding its tight regulation and its implication in health and disease remain elusive. The nematode Caenorhabditis elegans has been widely used as a simple multicellular model organism for studying the autophagic machinery per se, and uncover its multidimensional roles in the maintenance of cellular and organismal homeostasis. The current protocol describes the in vivo detection and biochemical analysis of the autophagic substrate SQST-1, as an indicator of autophagic flux in C. elegans.

Heme Induces BECN1/ATG5-Mediated Autophagic Cell Death via ER Stress in Neurons

Intracerebral hemorrhage (ICH) is a serious medical problem, and effective treatment is limited. Hemorrhaged blood is highly toxic to the brain, and heme, which is mainly released from hemoglobin, plays a vital role in neurotoxicity. However, the specific mechanism involved in heme-mediated neurotoxicity has not been well studied. In this study, we investigated the neurotoxicity of heme in neurons. Neurons were treated with heme, and cell death, autophagy, and endoplasmic reticulum (ER) stress were analyzed. In addition, the relationship between autophagy and apoptosis in heme-induced cell death and the downstream effects were also assessed. We showed that heme induced cell death and autophagy in neurons. The suppression of autophagy using either pharmacological inhibitors (3-methyladenine) or RNA interference of essential autophagy genes (BECN1 and ATG5) decreased heme-induced cell death in neurons. Moreover, the ER stress activator thapsigargin increased cell autophagy and the cell death ratio following heme treatment. Autophagy promoted heme-induced cell apoptosis and cell death through the BECN1/ATG5 pathway. Our findings suggest that heme potentiates neuronal autophagy via ER stress, which in turn induces cell death via the BECN1/ATG5 pathway. Targeting ER stress-mediated autophagy might be a promising therapeutic strategy for ICH.

Tissue-Specific Impact of Autophagy Genes on the Ubiquitin-Proteasome System in C. elegans

The ubiquitin–proteasome system (UPS) and the autophagy–lysosomal pathway (ALP) are the two main eukaryotic intracellular proteolytic systems involved in maintaining proteostasis. Several studies have reported on the interplay between the UPS and ALP, however it remains largely unknown how compromised autophagy affects UPS function in vivo. Here, we have studied the crosstalk between the UPS and ALP by investigating the tissue-specific effect of autophagy genes on the UPS at an organismal level. Using transgenic Caenorhabditis elegans expressing fluorescent UPS reporters, we show that the downregulation of the autophagy genes lgg-1 and lgg-2 (ATG8/LC3/GABARAP), bec-1 (BECLIN1), atg-7 (ATG7) and epg-5 (mEPG5) by RNAi decreases proteasomal degradation, concomitant with the accumulation of polyubiquitinated proteasomal substrates in a tissue-specific manner. For some of these genes, the changes in proteasomal degradation occur without a detectable alteration in proteasome tissue expression levels. In addition, the lgg-1 RNAi-induced reduction in proteasome activity in intestinal cells is not dependent on sqst-1/p62 accumulation. Our results illustrate that compromised autophagy can affect UPS in a tissue-specific manner, and demonstrate that UPS does not function as a direct compensatory mechanism in an animal. Further, a more profound understanding of the multilayered crosstalk between UPS and ALP can facilitate the development of therapeutic options for various disorders linked to dysfunction in proteostasis.

A robust and miniaturized screening platform to study natural products affecting metabolism and survival in Caenorhabditis elegans

In this study a robust, whole organism screening based on Caenorhabditis elegans is presented for the discovery of natural products (NP) with beneficial effects against obesity and age-related diseases. Several parameters of the elaborated workflow were optimized to be adapted for probing multicomponent mixtures combining knowledge from traditional medicine and NP chemistry by generating optimized small-scale extracts considering scarcity of the natural source, solubility issues, and potential assay interferences. The established miniaturized assay protocol allows for in vivo probing of small amounts of even complex samples (~ 1 mg) to test their ability to increase the nematodes' survival time and the suppression of fat accumulation assessed by Nile red staining as hall marks of "healthy aging". The workflow was applied on 24 herbal and fungal materials traditionally used against symptoms of the metabolic syndrome and revealed promising results for the extracts of Gardenia jasminoides fruits and the sclerotia from Inonotus obliquus. Tested at 100 µg/mL they were able to significantly reduce the Nile red fluorescence and extend the 50% survival rate (DT50) compared to the control groups. This phenotype-directed in vivo approach opens up new horizons for the selection of natural starting materials and the investigation of their active principles as fast drug discovery tool with predictive value for human diseases.

C. elegans to model autophagy-related human disorders

Autophagy is a highly conserved degradation process that clears damaged intracellular macromolecules and organelles in order to maintain cellular health. Dysfunctional autophagy is fundamentally linked to the development of various human disorders and pathologies. The use of the nematode Caenorhabditis elegans as a model system to study autophagy has improved our understanding of its regulation and function in organismal physiology. Here, we review the genetic, functional, and regulatory conservation of the autophagy pathway in C. elegans and we describe tools to quantify and study the autophagy process in this incredibly useful model organism. We further discuss how these nematodes have been modified to model autophagy-related human diseases and underscore the important insights obtained from such models. Altogether, we highlight the strengths of C. elegans as an exceptional tool to understand the genetic and molecular foundations underlying autophagy-related human diseases.

Molecular Nanomachines Can Destroy Tissue or Kill Multicellular Eukaryotes

Light-activated molecular nanomachines (MNMs) can be used to drill holes into prokaryotic (bacterial) cell walls and the membrane of eukaryotic cells, including mammalian cancer cells, by their fast rotational movement, leading to cell death. We examined how these MNMs function in multicellular organisms and investigated their use for treatment and eradication of specific diseases by causing damage to certain tissues and small organisms. Three model eukaryotic species, Caenorhabditis elegans, Daphnia pulex, and Mus musculus (mouse), were evaluated. These organisms were exposed to light-activated fast-rotating MNMs and their physiological and pathological changes were studied in detail. Slow rotating MNMs were used to control for the effects of rotation rate. We demonstrate that fast-rotating MNMs caused depigmentation and 70% mortality in C. elegans while reducing the movement as well as heart rate and causing tissue damage in Daphnia. Topically applied light-activated MNMs on mouse skin caused ulceration and microlesions in the epithelial tissue, allowing MNMs to localize into deeper epidermal tissue. Overall, this study shows that the nanomechanical action of light-activated MNMs is effective against multicellular organisms, disrupting cell membranes and damaging tissue in vivo. Customized MNMs that target specific tissues for therapy combined with spatial and temporal control could have broad clinical applications in a variety of benign and malignant disease states including treatment of cancer, parasites, bacteria, and diseased tissues.

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.

Caenorhabditis elegans as a Useful Model for Studying Aging Mutations

The Caenorhabditis elegans genome possesses homologs of about two-thirds of all human disease genes. Based on its physiological aging characteristics and superiority, the use of C. elegans as a model system for studies on aging, age-related diseases, mechanisms of longevity, and drug screening has been widely acknowledged in recent decades. Lifespan increasing mutations in C. elegans were found to delay aging by impinging several signaling pathways and related epigenetic modifications, including the insulin/IGF-1 signaling (IIS), AMP-activated protein kinase (AMPK), and mechanistic target of rapamycin (mTOR) pathways. Interestingly, dietary restriction (DR) has been shown to increase the lifespan of numerous metazoans and protect them from multiple age-related pathologies. However, the underlying molecular mechanisms are unclear. In recent decades, C. elegans has been used as a unique model system for high-throughput drug screening. Here, we review C. elegans mutants exhibiting increased in lifespan and age-dependent changes under DR, as well as the utility of C. elegans for drug screening. Thus, we provide evidence for the use of this model organism in research on the prevention of aging.

Autophagy contributes to the feeding, reproduction, and mobility of Bursaphelenchus xylophilus at low temperatures

The pine wood nematode (PWN), Bursaphelenchus xylophilus, is the pathogen causing pine wilt disease (PWD), which is a devastating forest disease. At present, little is known about the defense mechanisms of the PWN, which limits PWD control. Although autophagy plays an important role in the physiological and pathological processes of eukaryotes, its significance in the PWN remains unknown. In this study, we prepared an anti-BxATG8 polyclonal antibody and identified two PWN autophagy marker proteins: BxATG8-I and BxATG8-II. By western blot analysis, we found that the ratio of BxATG8-II to BxATG8-I, which represents autophagic activity, was decreased significantly when samples were treated with the autophagy inhibitor 3-methyladenine. As such, we were able to successfully detect and quantify autophagic activity in the PWN. Thereafter, we investigated the effects of low and high temperatures on PWN growth and reproduction. The results revealed that feeding rate, reproduction rate, and mobility decreased at 15°C and increased at 35°C. By contrast, autophagic activity was high at 15°C and low at 35°C, suggesting that the PWN regulates autophagic activity in response to changes in temperature to maintain physiological homeostasis. When autophagy was inhibited at 15°C, feeding rate, reproductive rate, and mobility declined further, indicating that autophagy is crucial for PWN growth and reproduction at low temperature. These results indicate that autophagy in the PWN is an important response mechanism to temperature changes.

Tubeimoside-1, a triterpenoid saponin, induces cytoprotective autophagy in human breast cancer cells in vitro via Akt-mediated pathway

Autophagy, a form of cellular self-digestion by lysosome, is associated with various disease processes including cancers, and modulating autophagy has shown promise in the treatment of various malignancies. A number of natural products display strong antitumor activity, yet their mechanisms of action remain unclear. To gain a better understanding of how traditional Chinese medicine agents exert antitumor effects, we screened 480 natural compounds for their effects on autophagy using a high content screening assay detecting GFP-LC3 puncta in HeLa cells. Tubeimoside-1 (TBMS1), a triterpenoid saponin extracted from Bolbostemma paniculatum (Maxim) Franquet (Cucurbitaceae), was identified as a potent activator of autophagy. The activation of autophagy by TBMS1 was evidenced by increased LC3-II amount and GFP-LC3 dots, observation of autophagosomes under electron microscopy, and enhanced autophagic flux. To explore the mechanisms underlying TBMS1-activated autophagy, we performed cheminformatic analyses and surface plasmon resonance (SPR) binding assay that showed a higher likelihood of the binding between Akt protein and TBMS1. In three human breast cancer cell lines, we demonstrated that Akt-mTOR-eEF-2K pathway was involved in TBMS1-induced activation of autophagy, while Akt-mediated downregulations of Mcl-1, Bcl-xl, and Bcl-2 led to the activation of apoptosis of the breast cancer cells. Inhibition of autophagy enhanced the cytotoxic effect of TBMS1 via promoting apoptosis. Our results demonstrate the role and mechanism of TBMS1 in activating autophagy, suggesting that inhibition of cytoprotective autophagy may act as a therapeutic strategy to reinforce the activity of TBMS1 against cancers.

Natural variation in the roles of C. elegans autophagy components during microsporidia infection

Natural genetic variation can determine the outcome of an infection, and often reflects the co-evolutionary battle between hosts and pathogens. We previously found that a natural variant of the nematode Caenorhabditis elegans from Hawaii (HW) has increased resistance against natural microsporidian pathogens in the Nematocida genus, when compared to the standard laboratory strain of N2. In particular, HW animals can clear infection, while N2 animals cannot. In addition, HW animals have lower levels of initial colonization of Nematocida inside intestinal cells, compared to N2. Here we investigate how this natural variation in resistance relates to autophagy. We found that there is much better targeting of autophagy-related machinery to parasites under conditions where they are cleared. In particular, ubiquitin targeting to Nematocida cells correlates very well with their subsequent clearance in terms of timing, host strain and age, as well as species of Nematocida. Furthermore, clearance correlates with targeting of the LGG-2/LC3 autophagy protein to parasite cells, with HW animals having much more efficient targeting of LGG-2 to parasite cells than N2 animals. Surprisingly, however, we found that LGG-2 is not required to clear infection. Instead, we found that LGG-2/LC3 regulates Nematocida colonization inside intestinal cells. Interestingly, LGG-2/LC3 regulates intracellular colonization only in the HW strain, and not in N2. Altogether these results demonstrate that there is natural genetic variation in an LGG-2-dependent process that regulates microsporidia colonization inside intestinal cells, although not microsporidia clearance.