A high glucose diet induces autophagy in a HLH-30/TFEB-dependent manner and impairs the normal lifespan of C. elegans

SIRT1-NRF2-TFEB axis-mediated hepatic lipophagy alleviates the lipid deposition induced by high glucose in yellow catfish Pelteobagrus fulvidraco

Metabolic stress induces lipophagy, a crucial process in lipid catabolism, which is under the regulation of autophagy involving transcription factor EB (TFEB). However, the precise mechanisms underlying TFEB's control remain enigmatic. In this study, we focused on yellow catfish (Pelteobagrus fulvidraco) as the model to investigate lipophagy activation under high glucose-induced lipid deposition. We hypothesized that lipophagy mediates high glucose-induced lipid deposition and proposed the involvement of the SIRT1-NRF2-TFEB pathway in the activation of lipophagy. We found that there was a functional antioxidative responsive element (ARE) on the tfeb gene promoter; high glucose (HG) increased the nuclear translocation of nuclear factor E2-related factor 2 (NRF2) recruitment to the tfeb promoter; TFEB, whose expression is regulated by NRF2, mediated the HG-induced activation of lipophagy and lipolysis. Moreover, we found that HG increased the silencing information regulator 2 related enzymes 1 (SIRT1) expression, and that the SIRT1 mediates NRF2 translocation to the nucleus, increased TFEB expression and activated autophagy. In the glucose tolerance test, blood glucose increased rapidly and plateaued at 4-h glucose after injection and then declined until 48-h post-injection. Generally speaking, the transcript level and protein expression of SIRT1, NRF2, TFEB, microtubule-associated proteins 1A/1B light chain 3B (LC3B), and autophagy-related 6 (Beclin1) showed similar trend after glucose injection, and trends to increase and plateau at 4-h injection, then decline until 16-h post-injection, and finally increased until 48-h post-injection. These results indicated that the SIRT1-NRF2-TFEB axis-mediated lipophagy may be an adaptive response to glucose injection. Collectively, for the first time, we found that NRF2 was associated directly with TFEB-mediated transcriptional control of hepatic lipophagy, and that lipophagy helps to alleviate the HG-induced lipid deposition via SIRT1-NRF2-TFEB activation in yellow catfish.

Lipid lowering and anti-ageing effects of edible flowers of Viola x wittrockiana Gams in a Caenorhabditis elegans obese model

Life expectancy has increased considerably in the last decades, clearing the way for preventive medicine. The ingestion of healthy foods or ingredients to improve health is gaining attention and edible flowers entail a promising source of bioactive compounds. The aim of this work was to study the anti-ageing and anti-obesity properties of an extract obtained from an edible flower Viola x wittrockiana though in vitro and in vivo methodologies with Caenorhabditis elegans as a model. The capacity to inhibit the enzymes α-glucosidase and lipase as well as to prevent advance glycation end-product (AGE) formation was tested in vitro. Caenorhabditis elegans was used as an obesity in vivo model to assess the effects of the extract on fat accumulation, development, progeny and health span. Viola flowers showed lower IC50 values in the α-glucosidase assay than the reference drug acarbose and exerted a higher inhibition of AGE formation than the reference substance aminoguanidine; the extract also showed pancreatic lipase inhibiting properties. Moreover, the extract lowered fat storage of C. elegans in a dose-dependent manner, up to 90.37% at the highest tested dose, and improved health span biomarkers such as lipofuscin accumulation and progeny availability. Our results demonstrate, for the first time, the anti-obesogenic and anti-ageing activity of Viola x wittrockiana flowers and their potential use as functional foods and nutraceuticals.

Chronic exposure to di(2-ethylhexyl) phthalate (DEHP) weakens innate immunity and leads to immunosenescence in C. elegans

Di(2-ethylhexyl) phthalate (DEHP), a widespread contaminant, has numerous adverse impacts on human health and ecosystems. Chronic DEHP exposure has been found to accelerate aging; however, its potential threat to age-dependent innate immune decline remains unknown. This study aims to evaluate the effects of chronic DEHP exposure on innate immunosenescence in Caenorhabditis elegans. We show that the length of the exposure period significantly impacts DEHP-induced age-related declines, which is linked to immunosenescence and oxidative stress. We found that the DEHP-caused immunosenescence is accompanied with downregulation of an antimicrobial gene lys-7 as well as an enhancement of the nuclear translocation of HLH-30, an orthologue of mammalian transcription factor EB (TFEB). Moreover, DEHP exposure increases the expression of riok-1, a human RIO kinase homolog, which is associated with DEHP-induced HLH-30/TFEB translocation. Our findings suggest that early-life and chronic exposure to DEHP, mostly due to parent compound rather than its metabolite mono(2-ethylhexyl) phthalate (MEHP), may weaken the innate immunity in C. elegans and may enhance susceptibility to infections or promote immunosenescence in aged populations.

Caenorhabditis elegans as an emerging model in food and nutrition research: importance of standardizing base diet

As a model organism that has helped revolutionize life sciences, Caenorhabditis elegans has been increasingly used in nutrition research. Here we explore the tradeoffs between pros and cons of its use as a dietary model based primarily on literature review from the past decade. We first provide an overview of its experimental strengths as an animal model, focusing on lifespan and healthspan, behavioral and physiological phenotypes, and conservation of key nutritional pathways. We then summarize recent advances of its use in nutritional studies, e.g. food preference and feeding behavior, sugar status and metabolic reprogramming, lifetime and transgenerational nutrition tracking, and diet-microbiota-host interactions, highlighting cutting-edge technologies originated from or developed in C. elegans. We further review current challenges of using C. elegans as a nutritional model, followed by in-depth discussions on potential solutions. In particular, growth scales and throughputs, food uptake mode, and axenic culture of C. elegans are appraised in the context of food research. We also provide perspectives for future development of chemically defined nematode food ("NemaFood") for C. elegans, which is now widely accepted as a versatile and affordable in vivo model and has begun to show transformative potential to pioneer nutrition science.

The Regulation of MiTF/TFE Transcription Factors Across Model Organisms: from Brain Physiology to Implication for Neurodegeneration

The microphthalmia/transcription factor E (MiTF/TFE) transcription factors are responsible for the regulation of various key processes for the maintenance of brain function, including autophagy-lysosomal pathway, lipid catabolism, and mitochondrial homeostasis. Among them, autophagy is one of the most relevant pathways in this frame; it is evolutionary conserved and crucial for cellular homeostasis. The dysregulation of MiTF/TFE proteins was shown to be involved in the development and progression of neurodegenerative diseases. Thus, the characterization of their function is key in the understanding of the etiology of these diseases, with the potential to develop novel therapeutics targeted to MiTF/TFE proteins and to the autophagic process. The fact that these proteins are evolutionary conserved suggests that their function and dysfunction can be investigated in model organisms with a simpler nervous system than the mammalian one. Building not only on studies in mammalian models but also in complementary model organisms, in this review we discuss (1) the mechanistic regulation of MiTF/TFE transcription factors; (2) their roles in different regions of the central nervous system, in different cell types, and their involvement in the development of neurodegenerative diseases, including lysosomal storage disorders; (3) the overlap and the compensation that occur among the different members of the family; (4) the importance of the evolutionary conservation of these protein and the process they regulate, which allows their study in different model organisms; and (5) their possible role as therapeutic targets in neurodegeneration.

Glucose enrichment impair neurotransmission and induce Aβ oligomerization that cannot be reversed by manipulating O-β-GlcNAcylation in the C. elegans model of Alzheimer's disease

Amyloid beta (Aβ) plaques formation and impaired neurotransmission and neuronal behaviors are primary hallmarks of Alzheimer's disease (AD) that are further associated with impaired glucose metabolism in elderly AD's patients. However, the exact role of glucose metabolism on disease progression has not been elucidated yet. In this study, the effect of glucose on Aβ-mediated toxicity, neurotransmission and neuronal behaviors has been investigated using a C. elegans model system expressing human Aβ. In addition to regular diet, worms expressing Aβ were supplemented with different concentrations of glucose and glycerol and 5 mM 2-deoxyglucose to draw any conclusions. Addition of glucose to the growth medium delayed Aβ-associated paralysis, promoted abnormal body shapes and movement, unable to restore impaired acetylcholine neurotransmission, inhibited egg laying and hatching in pre-existing Aβ-mediated pathology. The harmful effects of glucose may associate with an increase in toxic Aβ oligomers and impaired neurotransmission. O-β-GlcNAcylation (O-GlcNAc), a well-known post-translational modification is directly associated with glucose metabolism and has been found to ameliorates the Aβ- toxicity. We reasoned that glucose addition might induce O-GlcNAc, thereby protect against Aβ. Contrary to our expectations, induced glucose levels were not protective. Increasing O-GlcNAc, either with Thiamet-G (TMG) or by suppressing the O-GlcNAcase (oga-1) gene does interfere with and, therefore, reduce Aβ- toxicity but not in the presence of high glucose. The effects of glucose cannot be effectively managed by manipulating O-GlcNAc in AD models of C. elegans. Our observations suggest that glucose enrichment is unlikely to be an appropriate therapy to minimize AD progression.

Pediococcus acidilactici CECT9879 (pA1c) Counteracts the Effect of a High-Glucose Exposure in C. elegans by Affecting the Insulin Signaling Pathway (IIS)

The increasing prevalence of metabolic syndrome-related diseases, including type-2 diabetes and obesity, makes it urgent to develop new alternative therapies, such as probiotics. In this study, we have used Caenorhabditis elegans under a high-glucose condition as a model to examine the potential probiotic activities of Pediococcusacidilactici CECT9879 (pA1c). The supplementation with pA1c reduced C. elegans fat accumulation in a nematode growth medium (NGM) and in a high-glucose (10 mM) NGM medium. Moreover, treatment with pA1c counteracted the effect of the high glucose by reducing reactive oxygen species by 20%, retarding the aging process and extending the nematode median survival (>2 days in comparison with untreated control worms). Gene expression analyses demonstrated that the probiotic metabolic syndrome-alleviating activities were mediated by modulation of the insulin/IGF-1 signaling pathway (IIS) through the reversion of the glucose-nuclear-localization of daf-16 and the overexpression of ins-6 and daf-16 mediators, increased expression of fatty acid (FA) peroxisomal β-oxidation genes, and downregulation of FA biosynthesis key genes. Taken together, our data suggest that pA1c could be considered a potential probiotic strain for the prevention of the metabolic syndrome-related disturbances and highlight the use of C. elegans as an appropriate in vivo model for the study of the mechanisms underlying these diseases.

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.

Effects of High Dietary Carbohydrate and Lipid Intake on the Lifespan of C. elegans

Health and lifespan are influenced by dietary nutrients, whose balance is dependent on the supply or demand of each organism. Many studies have shown that an increased carbohydrate–lipid intake plays a critical role in metabolic dysregulation, which impacts longevity. Caenorhabditis elegans has been successfully used as an in vivo model to study the effects of several factors, such as genetic, environmental, diet, and lifestyle factors, on the molecular mechanisms that have been linked to healthspan, lifespan, and the aging process. There is evidence showing the causative effects of high glucose on lifespan in different diabetic models; however, the precise biological mechanisms affected by dietary nutrients, specifically carbohydrates and lipids, as well as their links with lifespan and longevity, remain unknown. Here, we provide an overview of the deleterious effects caused by high-carbohydrate and high-lipid diets, as well as the molecular signals that affect the lifespan of C. elegans; thus, understanding the detailed molecular mechanisms of high-glucose- and lipid-induced changes in whole organisms would allow the targeting of key regulatory factors to ameliorate metabolic disorders and age-related diseases.

TFEB: A Emerging Regulator in Lipid Homeostasis for Atherosclerosis

Atherosclerosis, predominantly characterized by the disturbance of lipid homeostasis, has become the main causation of various cardiovascular diseases. Therefore, there is an urgent requirement to explore efficacious targets that act as lipid modulators for atherosclerosis. Transcription factor EB (TFEB), whose activity depends on post-translational modifications, such as phosphorylation, acetylation, SUMOylation, ubiquitination, etc., is significant for normal cell physiology. Recently, increasing evidence implicates a role of TFEB in lipid homeostasis, via its functionality of promoting lipid degradation and efflux through mediating lipophagy, lipolysis, and lipid metabolism-related genes. Furthermore, a regulatory effect on lipid transporters and lipid mediators by TFEB is emerging. Notably, TFEB makes a possible therapeutic target of atherosclerosis by regulating lipid metabolism. This review recapitulates the update and current advances on TFEB mediating lipid metabolism to focus on two intracellular activities: a) how cells perceive external stimuli and initiate transcription programs to modulate TFEB function, and b) how TFEB restores lipid homeostasis in the atherosclerotic process. In-depth research is warranted to develop potent agents against TFEB to alleviate or reverse the progression of atherosclerosis.

MiT/TFE Family of Transcription Factors: An Evolutionary Perspective

Response and adaptation to stress are critical for the survival of all living organisms. The regulation of the transcriptional machinery is an important aspect of these complex processes. The members of the microphthalmia (MiT/TFE) family of transcription factors, apart from their involvement in melanocyte biology, are emerging as key players in a wide range of cellular functions in response to a plethora of internal and external stresses. The MiT/TFE proteins are structurally related and conserved through evolution. Their tissue expression and activities are highly regulated by alternative splicing, promoter usage, and posttranslational modifications. Here, we summarize the functions of MiT/TFE proteins as master transcriptional regulators across evolution and discuss the contribution of animal models to our understanding of the various roles of these transcription factors. We also highlight the importance of deciphering transcriptional regulatory mechanisms in the quest for potential therapeutic targets for human diseases, such as lysosomal storage disorders, neurodegeneration, and cancer.

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.

Key Roles of MiT Transcription Factors in Innate Immunity and Inflammation

Microphthalmia/TFE (MiT) transcription factors (TFs), such as transcription factor EB (TFEB) and transcription factor E3 (TFE3), are emerging as key regulators of innate immunity and inflammation. Rapid progress in the field requires a focused update on the latest advances. Recent studies show that TFEB and TFE3 function in innate immune cells to regulate antibacterial and antiviral responses downstream of phagocytosis, interferon (IFN)-γ, lipopolysaccharide (LPS), and adenosine receptors. Moreover, overexpression of TFEB or TFE3 can drive inflammation in vivo, such as in atherosclerosis, while in other scenarios they can perform anti-inflammatory functions. MiT factors may constitute potential therapeutic targets for a broad range of diseases; however, to harness their therapeutic potential, sophisticated ways to manipulate MiT factor activity safely and effectively must be developed.

Metabolic regulation of lifespan from a C. elegans perspective

Decline of cellular functions especially cognitive is a major deficit that arises with age in humans. Harnessing the strengths of small and genetic tractable model systems has revealed key conserved regulatory biochemical and signaling pathways that control aging. Here, we review some of the key signaling and biochemical pathways that coordinate aging processes with special emphasis on Caenorhabditis elegans as a model system and discuss how nutrients and metabolites can regulate lifespan by coordinating signaling and epigenetic programs. We focus on central nutrient-sensing pathways such as mTOR and insulin/insulin-like growth factor signaling and key transcription factors including the conserved basic helix-loop-helix transcription factor HLH-30/TFEB.