Fragile lifespan expansion by dietary mitohormesis in C. elegans

2,4,6-trinitrotoluene causes mitochondrial toxicity in Caenorhabditis elegans by affecting electron transport

As a typical energetic compound widely used in military activities, 2,4,6-trinitrotoluene (TNT) has attracted great attention in recent years due to its heavy pollution and wide distribution in and around the training facilities, firing ranges, and demolition sites. However, the subcellular targets and the underlying toxic mechanism of TNT remain largely unknown. In this study, we explored the toxic effects of TNT biological reduction on the mitochondrial function and homeostasis in Caenorhabditis elegans (C. elegans). With short-term exposure of L4 larvae, 10-1000 ng/mL TNT reduced mitochondrial membrane potential and adenosine triphosphate (ATP) content, which was associated with decreased expression of specific mitochondrial complex involving gas-1 and mev-1 genes. Using fluorescence-labeled transgenic nematodes, we found that fluorescence expression of sod-3 (muls84) and gst-4 (dvls19) was increased, suggesting that TNT disrupted the mitochondrial antioxidant defense system. Furthermore, 10 ng/mL TNT exposure increased the expression of the autophagy-related gene pink-1 and activated mitochondrial unfolded protein response (mt UPR), which was indicated by the increased expression of mitochondrial stress activated transcription factor atfs-1, ubiquitin-like protein ubl-5, and homeobox protein dve-1. Our findings demonstrated that TNT biological reduction caused mitochondrial dysfunction and the development of mt UPR protective stress responses, and provided a basis for determining the potential risks of energetic compounds to living organisms.

The Native Microbiome Member Chryseobacterium sp. CHNTR56 MYb120 Induces Trehalose Production via a Shift in Central Carbon Metabolism during Early Life in C. elegans

Aging is the system-wide loss of homeostasis, eventually leading to death. There is growing evidence that the microbiome not only evolves with its aging host, but also directly affects aging via the modulation of metabolites involved in important cellular functions. The widely used model organism C. elegans exhibits high selectivity towards its native microbiome members which confer a range of differential phenotypes and possess varying functional capacities. The ability of one such native microbiome species, Chryseobacterium sp. CHNTR56 MYb120, to improve the lifespan of C. elegans and to promote the production of Vitamin B6 in the co-colonizing member Comamonas sp. 12022 MYb131 are some of its beneficial effects on the worm host. We hypothesize that studying its metabolic influence on the different life stages of the worm could provide further insights into mutualistic interactions. The present work applied LC-MS untargeted metabolomics and isotope labeling to study the impact of the native microbiome member Chryseobacterium sp. CHNTR56 MYb120 on the metabolism of C. elegans. In addition to the upregulation of biosynthesis and detoxification pathway intermediates, we found that Chryseobacterium sp. CHNTR56 MYb120 upregulates the glyoxylate shunt in mid-adult worms which is linked to the upregulation of trehalose, an important metabolite for desiccation tolerance in older worms.

The unfolded protein response reverses the effects of glucose on lifespan in chemically-sterilized C. elegans

Metabolic diseases often share common traits, including accumulation of unfolded proteins in the endoplasmic reticulum (ER). Upon ER stress, the unfolded protein response (UPR) is activated to limit cellular damage which weakens with age. Here, we show that Caenorhabditis elegans fed a bacterial diet supplemented high glucose at day 5 of adulthood (HGD-5) extends their lifespan, whereas exposed at day 1 (HGD-1) experience shortened longevity. We observed a metabolic shift only in HGD-1, while glucose and infertility synergistically prolonged the lifespan of HGD-5, independently of DAF-16. Notably, we identified that UPR stress sensors ATF-6 and PEK-1 contributed to the longevity of HGD-5 worms, while ire-1 ablation drastically increased HGD-1 lifespan. Together, we postulate that HGD activates the otherwise quiescent UPR in aged worms to overcome ageing-related stress and restore ER homeostasis. In contrast, young animals subjected to HGD provokes unresolved ER stress, conversely leading to a detrimental stress response.

Protective Effects of Transient Glucose Exposure in Adult C. elegans

C. elegans are used to study molecular pathways, linking high glucose levels (HG) to diabetic complications. Persistent exposure of C. elegans to a HG environment induces the mitochondrial formation of reactive oxygen species (ROS) and advanced glycation endproducts (AGEs), leading to neuronal damage and decreased lifespan. Studies suggest that transient high glucose exposure (TGE) exerts different effects than persistent exposure. Thus, the effects of TGE on ROS, AGE-formation and life span were studied in C. elegans. Four-day TGE (400 mM) as compared to controls (0mM) showed a persistent increase of ROS (4-days 286 ± 40 RLUs vs. control 187 ± 23 RLUs) without increased formation of AGEs. TGE increased body motility (1-day 0.14 ± 0.02; 4-days 0.15 ± 0.01; 6-days 0.16 ± 0.02 vs. control 0.10 ± 0.02 in mm/s), and bending angle (1-day 17.7 ± 1.55; 3-days 18.7 ± 1.39; 6-days 20.3 ± 0.61 vs. control 15.3 ± 1.63 in degree/s) as signs of neuronal damage. Lifespan was increased by 27% (21 ± 2.4 days) after one-day TGE, 34% (22 ± 1.2 days) after four-days TGE, and 26% (21 ± 1.4 days) after six-days TGE vs. control (16 ± 1.3 days). These experiments suggest that TGE in C. elegans has positive effects on life span and neuronal function, associated with mildly increased ROS-formation. From the perspective of metabolic memory, hormetic effects outweighed the detrimental effects of a HG environment.

Strategies to protect against age-related mitochondrial decay: Do natural products and their derivatives help?

Mitochondria serve vital roles critical for overall cellular function outside of energy transduction. Thus, mitochondrial decay is postulated to be a key factor in aging and in age-related diseases. Mitochondria may be targets of their own decay through oxidative damage. However, treating animals with antioxidants has been met with only limited success in rejuvenating mitochondrial function or in increasing lifespan. A host of nutritional strategies outside of using traditional antioxidants have been devised to promote mitochondrial function. Dietary compounds are under study that induce gene expression, enhance mitochondrial biogenesis, mitophagy, or replenish key metabolites that decline with age. Moreover, redox-active compounds may now be targeted to mitochondria which improve their effectiveness. Herein we review the evidence that representative dietary effectors modulate mitochondrial function by stimulating their renewal or reversing the age-related loss of key metabolites. While in vitro evidence continues to accumulate that many of these compounds benefit mitochondrial function and/or prevent their decay, the results using animal models and, in some instances human clinical trials, are more mixed and sometimes even contraindicated. Thus, further research on optimal dosage and age of intervention are warranted before recommending potential mitochondrial rejuvenating compounds for human use.

Acetyl-CoA Metabolism and Histone Acetylation in the Regulation of Aging and Lifespan

Acetyl-CoA is a metabolite at the crossroads of central metabolism and the substrate of histone acetyltransferases regulating gene expression. In many tissues fasting or lifespan extending calorie restriction (CR) decreases glucose-derived metabolic flux through ATP-citrate lyase (ACLY) to reduce cytoplasmic acetyl-CoA levels to decrease activity of the p300 histone acetyltransferase (HAT) stimulating pro-longevity autophagy. Because of this, compounds that decrease cytoplasmic acetyl-CoA have been described as CR mimetics. But few authors have highlighted the potential longevity promoting roles of nuclear acetyl-CoA. For example, increasing nuclear acetyl-CoA levels increases histone acetylation and administration of class I histone deacetylase (HDAC) inhibitors increases longevity through increased histone acetylation. Therefore, increased nuclear acetyl-CoA likely plays an important role in promoting longevity. Although cytoplasmic acetyl-CoA synthetase 2 (ACSS2) promotes aging by decreasing autophagy in some peripheral tissues, increased glial AMPK activity or neuronal differentiation can stimulate ACSS2 nuclear translocation and chromatin association. ACSS2 nuclear translocation can result in increased activity of CREB binding protein (CBP), p300/CBP-associated factor (PCAF), and other HATs to increase histone acetylation on the promoter of neuroprotective genes including transcription factor EB (TFEB) target genes resulting in increased lysosomal biogenesis and autophagy. Much of what is known regarding acetyl-CoA metabolism and aging has come from pioneering studies with yeast, fruit flies, and nematodes. These studies have identified evolutionary conserved roles for histone acetylation in promoting longevity. Future studies should focus on the role of nuclear acetyl-CoA and histone acetylation in the control of hypothalamic inflammation, an important driver of organismal aging.

Mitonuclear genomics and aging

Our cells operate based on two distinct genomes that are enclosed in the nucleus and mitochondria. The mitochondrial genome presumably originates from endosymbiotic bacteria. With time, a large portion of the original genes in the bacterial genome is considered to have been lost or transferred to the nuclear genome, leaving a reduced 16.5 Kb circular mitochondrial DNA (mtDNA). Traditionally only 37 genes, including 13 proteins, were thought to be encoded within mtDNA, its genetic repertoire is expanding with the identification of mitochondrial-derived peptides (MDPs). The biology of aging has been largely unveiled to be regulated by genes that are encoded in the nuclear genome, whereas the mitochondrial genome remained more cryptic. However, recent studies position mitochondria and mtDNA as an important counterpart to the nuclear genome, whereby the two organelles constantly regulate each other. Thus, the genomic network that regulates lifespan and/or healthspan is likely constituted by two unique, yet co-evolved, genomes. Here, we will discuss aspects of mitochondrial biology, especially mitochondrial communication that may add substantial momentum to aging research by accounting for both mitonuclear genomes to more comprehensively and inclusively map the genetic and molecular networks that govern aging and age-related diseases.

Lactate and pyruvate promote oxidative stress resistance through hormetic ROS signaling

L-lactate was long considered a glycolytic by-product but is now being recognized as a signaling molecule involved in cell survival. In this manuscript, we report the role of L-lactate in stress resistance and cell survival mechanisms using neuroblastoma cells (SH-SY5Y) as well as the C. elegans model. We observed that L-lactate promotes cellular defense mechanisms, including Unfolded Protein Response (UPR) and activation of nuclear factor erythroid 2-related factor 2 (NRF2), by promoting a mild Reactive Oxygen Species (ROS) burst. This increase in ROS triggers antioxidant defenses and pro-survival pathways, such as PI3K/AKT and Endoplasmic Reticulum (ER) chaperones. These results contribute to the understanding of the molecular mechanisms involved in beneficial effects of L-lactate, involving mild ROS burst, leading to activation of unfolded protein responses and detoxification mechanisms. We present evidence that this hormetic mechanism induced by L-lactate protects against oxidative stress in vitro and in vivo. This work contributes to the identification of molecular mechanisms, which could serve as targets for future therapeutic approaches for cell protection and aging-related disorders.

Phytochemicals-induced hormesis protects Caenorhabditis elegans against α-synuclein protein aggregation and stress through modulating HSF-1 and SKN-1/Nrf2 signaling pathways

Mild stress activates the adaptive cellular response for the subsequent severe stress called hormesis. Hormetic stress plays a vital role to activate multiple stress-responsive genes for the benefit of an organism. In tropical regions of world, tubers of Dioscorea spp. has been extensively used in folk medicine and also consumed as food. In this study, we report that the phytochemicals of Dioscorea alata L., tubers extends the lifespan of nematode model Caenorhabditis elegans by hormetic mechanism. We showed that the low dose of tubers extract at 200 and 300 μg/mL extends the mean lifespan of wild-type worms, whereas higher doses are found to be toxic. Supplementation of tubers extract slightly increased the intracellular ROS in second-day adult worms and it might activate the adaptive stress response, which protects the worms from oxidative and thermal stress. Transgenic reporter gene expression assay showed that extract treatment enhanced the expression of stress protective genes such as hsp-16.2, hsp-6, hsp-60 and gst-4. Further studies proved that the transcription factors HSF-1 and SKN-1/Nrf2 were implicated in hormetic stress response of the worms. Moreover, pretreatment of extract reduced the high glucose-mediated lipid accumulation by enhancing the expression of glyoxalase-1. It was also found that the aggregation of Parkinson's related protein α-synuclein reduced in the transgenic strain NL5901 and extended its lifespan. Finally, our results concluded that the presences of hormetic dietary phytochemicals in tubers might drive the stress response in C. elegans via HSF-1 and SKN-1/Nrf2 signaling pathways.

The Endoplasmic Reticulum Stress Response in Neuroprogressive Diseases: Emerging Pathophysiological Role and Translational Implications

The endoplasmic reticulum (ER) is the main cellular organelle involved in protein synthesis, assembly and secretion. Accumulating evidence shows that across several neurodegenerative and neuroprogressive diseases, ER stress ensues, which is accompanied by over-activation of the unfolded protein response (UPR). Although the UPR could initially serve adaptive purposes in conditions associated with higher cellular demands and after exposure to a range of pathophysiological insults, over time the UPR may become detrimental, thus contributing to neuroprogression. Herein, we propose that immune-inflammatory, neuro-oxidative, neuro-nitrosative, as well as mitochondrial pathways may reciprocally interact with aberrations in UPR pathways. Furthermore, ER stress may contribute to a deregulation in calcium homoeostasis. The common denominator of these pathways is a decrease in neuronal resilience, synaptic dysfunction and even cell death. This review also discusses how mechanisms related to ER stress could be explored as a source for novel therapeutic targets for neurodegenerative and neuroprogressive diseases. The design of randomised controlled trials testing compounds that target aberrant UPR-related pathways within the emerging framework of precision psychiatry is warranted.

Lipid and Carbohydrate Metabolism in Caenorhabditis elegans

Lipid and carbohydrate metabolism are highly conserved processes that affect nearly all aspects of organismal biology. Caenorhabditis elegans eat bacteria, which consist of lipids, carbohydrates, and proteins that are broken down during digestion into fatty acids, simple sugars, and amino acid precursors. With these nutrients, C. elegans synthesizes a wide range of metabolites that are required for development and behavior. In this review, we outline lipid and carbohydrate structures as well as biosynthesis and breakdown pathways that have been characterized in C. elegans We bring attention to functional studies using mutant strains that reveal physiological roles for specific lipids and carbohydrates during development, aging, and adaptation to changing environmental conditions.

The role of dietary carbohydrates in organismal aging

Carbohydrates are essential nutrients that are used as a primary source of energy. Carbohydrate utilization should be properly controlled, as abnormal regulation of carbohydrate metabolism is associated with diseases, such as diabetes, cardiovascular diseases, and stroke. These metabolic syndromes have become a serious problem in developed countries, and there is an increased need for research examining the influence of carbohydrates on animal physiology. Diets enriched in glucose, a major carbohydrate, are also associated with accelerated aging in several model organisms, including yeast and Caenorhabditis elegans (C. elegans). Genetic factors that mediate the effects of high glucose diets on aging have been identified during the last decade, mostly through the use of C. elegans. In this review, we describe studies that determine the effects of carbohydrate-enriched diets on aging by focusing on the mechanisms through which evolutionarily conserved pathways mediate the lifespan-altering effects of glucose in C. elegans. These include the insulin/insulin-like growth factor-1, sterol-regulatory element-binding protein, and AMP-activated protein kinase signaling pathways. We also discuss the effects of various carbohydrates and carbohydrate-derived metabolites on aging in model organisms and cultured mammalian cells. Finally, we discuss how dietary carbohydrates influence health and aging in humans.

Metabolism and the UPR(mt)

During mitochondrial dysfunction or the accumulation of unfolded proteins within mitochondria, cells employ a transcriptional response known as the mitochondrial unfolded protein response (UPR(mt)) to promote cell survival along with the repair and recovery of defective mitochondria. Considerable progress has been made in understanding how cells monitor mitochondrial function and activate the response, as well as in identifying scenarios where the UPR(mt) plays a protective role, such as during bacterial infection, hematopoietic stem cell maintenance, or general aging. To date, much of the focus has been on the role of the UPR(mt) in maintaining or re-establishing protein homeostasis within mitochondria by transcriptionally inducing mitochondrial molecular chaperone and protease genes. In this review, we focus on the metabolic adaptations or rewiring mediated by the UPR(mt) and how this may contribute to the resolution of mitochondrial unfolded protein stress and cell-type-specific physiology.