Worms, Fat, and Death: Caenorhabditis elegans Lipid Metabolites Regulate Cell Death

Omics analysis unveils changes in the metabolome and lipidome of Caenorhabditis elegans upon polydopamine exposure

Polydopamine (PDA) is an insoluble biopolymer with a dark brown-black color that forms through the autoxidation of dopamine. Because of its outstanding biocompatibility and durability, PDA holds enormous promise for various applications, both in the biomedical and non-medical domains. To ensure human safety, protect health, and minimize environmental impacts, the assessment of PDA toxicity is important. In this study, metabolomics and lipidomics assessed the impact of acute PDA exposure on Caenorhabditis elegans (C. elegans). The findings revealed a pronounced perturbation in the metabolome and lipidome of C. elegans at the L4 stage following 24 hours of exposure to 100 µg/mL PDA. The changes in lipid composition varied based on lipid classes. Increased lipid classes included lysophosphatidylethanolamine, triacylglycerides, and fatty acids, while decreased species involved in several sub-classes of glycerophospholipids and sphingolipids. Besides, we detected 37 significantly affected metabolites in the positive and 8 in the negative ion modes due to exposure to PDA in C. elegans. The metabolites most impacted by PDA exposure were associated with purine metabolism, biosynthesis of valine, leucine, and isoleucine; aminoacyl-tRNA biosynthesis; and cysteine and methionine metabolism, along with pantothenate and CoA biosynthesis; the citrate cycle (TCA cycle); and beta-alanine metabolism. In conclusion, PDA exposure may intricately influence the metabolome and lipidome of C. elegans. The combined application of metabolomics and lipidomics offers additional insights into the metabolic perturbations involved in PDA-induced biological effects and presents potential biomarkers for the assessment of PDA safety.

Ether lipid biosynthesis promotes lifespan extension and enables diverse pro-longevity paradigms in Caenorhabditis elegans

Biguanides, including the world's most prescribed drug for type 2 diabetes, metformin, not only lower blood sugar, but also promote longevity in preclinical models. Epidemiologic studies in humans parallel these findings, indicating favorable effects of metformin on longevity and on reducing the incidence and morbidity associated with aging-related diseases. Despite this promise, the full spectrum of molecular effectors responsible for these health benefits remains elusive. Through unbiased screening in Caenorhabditis elegans, we uncovered a role for genes necessary for ether lipid biosynthesis in the favorable effects of biguanides. We demonstrate that biguanides prompt lifespan extension by stimulating ether lipid biogenesis. Loss of the ether lipid biosynthetic machinery also mitigates lifespan extension attributable to dietary restriction, target of rapamycin (TOR) inhibition, and mitochondrial electron transport chain inhibition. A possible mechanistic explanation for this finding is that ether lipids are required for activation of longevity-promoting, metabolic stress defenses downstream of the conserved transcription factor skn-1/Nrf. In alignment with these findings, overexpression of a single, key, ether lipid biosynthetic enzyme, fard-1/FAR1, is sufficient to promote lifespan extension. These findings illuminate the ether lipid biosynthetic machinery as a novel therapeutic target to promote healthy aging.

L-threonine promotes healthspan by expediting ferritin-dependent ferroptosis inhibition in C. elegans

The pathways that impact longevity in the wake of dietary restriction (DR) remain still ill-defined. Most studies have focused on nutrient limitation and perturbations of energy metabolism. We showed that the L-threonine was elevated in Caenorhabditis elegans under DR, and that L-threonine supplementation increased its healthspan. Using metabolic and transcriptomic profiling in worms that were fed with RNAi to induce loss of key candidate mediators. L-threonine supplementation and loss-of-threonine dehydrogenaseincreased the healthspan by attenuating ferroptosis in a ferritin-dependent manner. Transcriptomic analysis showed that FTN-1 encoding ferritin was elevated, implying FTN-1 is an essential mediator of longevity promotion. Organismal ferritin levels were positively correlated with chronological aging and L-threonine supplementation protected against age-associated ferroptosis through the DAF-16 and HSF-1 pathways. Our investigation uncovered the role of a distinct and universal metabolite, L-threonine, in DR-mediated improvement in organismal healthspan, suggesting it could be an effective intervention for preventing senescence progression and age-induced ferroptosis.

Ether lipid deficiency disrupts lipid homeostasis leading to ferroptosis sensitivity

Ferroptosis is an iron-dependent form of regulated cell death associated with uncontrolled membrane lipid peroxidation and destruction. Previously, we showed that dietary dihomo-gamma-linolenic acid (DGLA; 20: 3(n-6)) triggers ferroptosis in the germ cells of the model organism, Caenorhabditis elegans. We also demonstrated that ether lipid-deficient mutant strains are sensitive to DGLA-induced ferroptosis, suggesting a protective role for ether lipids. The vinyl ether bond unique to plasmalogen lipids has been hypothesized to function as an antioxidant, but this has not been tested in animal models. In this study, we used C. elegans mutants to test the hypothesis that the vinyl ether bond in plasmalogens acts as an antioxidant to protect against germ cell ferroptosis as well as to protect from whole-body tert-butyl hydroperoxide (TBHP)-induced oxidative stress. We found no role for plasmalogens in either process. Instead, we demonstrate that ether lipid-deficiency disrupts lipid homeostasis in C. elegans, leading to altered ratios of saturated and monounsaturated fatty acid (MUFA) content in cellular membranes. We demonstrate that ferroptosis sensitivity in both wild type and ether-lipid deficient mutants can be rescued in several ways that change the relative abundance of saturated fats, MUFAs and specific polyunsaturated fatty acids (PUFAs). Specifically, we reduced ferroptosis sensitivity by (1) using mutant strains unable to synthesize DGLA, (2) using a strain carrying a gain-of-function mutation in the transcriptional mediator MDT-15, or (3) by dietary supplementation of MUFAs. Furthermore, our studies reveal important differences in how dietary lipids influence germ cell ferroptosis versus whole-body peroxide-induced oxidative stress. These studies highlight a potentially beneficial role for endogenous and dietary MUFAs in the prevention of ferroptosis.

Iron overload and neurodegenerative diseases: What can we learn from Caenorhabditis elegans?

Iron (Fe) is an essential trace element required for several physiological processes. It plays important roles in mitochondrial function, synthesis, and metabolism of the neurotransmitter, as well as oxygen transport. However, excess Fe can cause toxicity. Particularly, Fe overload may result in neurotoxicity, contributing to the development and progression of neurodegenerative diseases, although the molecular mechanisms underlying Fe-induced neurodegeneration have yet to be entirely understood. Alternative (non-rodent) experimental models have been pointed as important approaches to elucidate molecular and physiological events mediating Fe-induced pathology. Among such alternative strategies, an advantageous experimental worm-model system, Caenorhabditis elegans ( C. elegans), has been used to investigate Fe-induced neurotoxicity and neurodegenerative disorders. Its genome has been fully sequenced, corroborating that it shares significant homology with mammalians, and has approximately 40% of human disease-related genes. As part of this review, we discuss studies using the C. elegans model to study molecular mechanisms such as oxidative stress, mitochondrial dysfunction, disturbed homeostasis, and its potential contribution to the study of metal-induced neurodegenerative diseases such as Parkinson’s disease (PD) and Alzheimer’s disease (AD).