SKN-1 regulates stress resistance downstream of amino catabolism pathways

Quiescent cell re-entry is limited by macroautophagy-induced lysosomal damage

To maintain tissue homeostasis, many cells reside in a quiescent state until prompted to divide. The reactivation of quiescent cells is perturbed with aging and may underlie declining tissue homeostasis and resiliency. The unfolded protein response regulators IRE-1 and XBP-1 are required for the reactivation of quiescent cells in developmentally L1-arrested C. elegans. Utilizing a forward genetic screen in C. elegans, we discovered that macroautophagy targets protein aggregates to lysosomes in quiescent cells, leading to lysosome damage. Genetic inhibition of macroautophagy and stimulation of lysosomes via the overexpression of HLH-30 (TFEB/TFE3) synergistically reduces lysosome damage. Damaged lysosomes require IRE-1/XBP-1 for their repair following prolonged L1 arrest. Protein aggregates are also targeted to lysosomes by macroautophagy in quiescent cultured mammalian cells and are associated with lysosome damage. Thus, lysosome damage is a hallmark of quiescent cells, and limiting lysosome damage by restraining macroautophagy can stimulate their reactivation.

Berberine Extends Lifespan in C. elegans Through Multi-Target Synergistic Antioxidant Effects

Aging is a process of gradual functional decline in complex physiological systems and is closely related to the occurrence of various diseases. Berberine, a bioactive alkaloid derived from Coptis chinensis (Huanglian), has emerged as a promising candidate for anti-aging interventions. This study comprehensively investigated the lifespan-extending effects and molecular mechanisms of berberine in C. elegans through integrated approaches including lifespan assays, locomotor activity analysis, oxidative stress challenges, and transcriptomic profiling. Furthermore, genetic models of mutant and transgenic worms were employed to delineate their interactions with the insulin/IGF-1 signaling (IIS) pathway. Our results demonstrate that berberine extended the mean lifespan of wild-type worms by 27%. By activating transcription factors such as DAF-16/FOXO, HSF-1, and SKN-1/NRF2, berberine upregulated antioxidant enzyme expression, reduced lipofuscin accumulation, and improved stress resistance. Transcriptomic analysis revealed significant changes in lipid metabolism-related genes, particularly in pathways involving fatty acid synthesis, degradation, and sphingolipid metabolism. These findings establish that berberine exerts multi-target anti-aging effects through coordinated activation of stress-responsive pathways and metabolic optimization, providing mechanistic insights for developing natural product-based geroprotective strategies.

AlphaFold2-Guided Functional Screens Reveal a Conserved Antioxidant Protein at ER Membranes

Oxidative protein folding in the endoplasmic reticulum (ER) is essential for all eukaryotic cells yet generates hydrogen peroxide (H2O2), a reactive oxygen species (ROS). The ER-transmembrane protein that provides reducing equivalents to ER and guards the cytosol for antioxidant defense remains unidentified. Here we combine AlphaFold2-based and functional reporter screens in C. elegans to discover a previously uncharacterized and evolutionarily conserved protein ERGU-1 that fulfills these roles. Deleting C. elegans ERGU-1 causes excessive H2O2 and transcriptional gene up-regulation through SKN-1, homolog of mammalian antioxidant master regulator NRF2. ERGU-1 deficiency also impairs organismal reproduction and behavioral responses to H2O2. Both C. elegans and human ERGU-1 proteins localize to ER membranes and form network reticulum structures. Human and Drosophila homologs of ERGU-1 can rescue C. elegans mutant phenotypes, demonstrating evolutionarily ancient and conserved functions. In addition, purified ERGU-1 and human homolog TMEM161B exhibit redox-modulated oligomeric states. Together, our results reveal an ER-membrane-specific protein machinery for peroxide detoxification and suggest a previously unknown and conserved mechanisms for antioxidant defense in animal cells.

Curcumin enhances the anti-obesogenic activity of orlistat through SKN-1/NRF2-dependent regulation of nutrient metabolism in Caenorhabditis elegans

BACKGROUND

Metabolic dysregulation, a defining feature of obesity, disrupts essential signalling pathways involved in nutrient sensing and mitochondria homeostasis. The nuclear factor erythroid 2-related factor 2 (NRF-2) serves as a pivotal regulator of the cellular stress response, and recent studies have implicated it in the pathogenesis of obesity, diabetes, and metabolic syndrome. Curcumin, a polyphenolic compound derived from turmeric, has been identified as a potent activator of NRF-2. Evidence suggests curcumin impacts obesity and metabolic disorders by modulating gut microbiota composition, increasing energy expenditure, and regulating lipid metabolism. Orlistat, an anti-obesity drug, inhibits fat absorption in the gastrointestinal tract, but its side effects limits its broader use.

OBJECTIVES

The present study aims to investigate the potential synergetic effect of a hybrid combination between orlistat and curcumin. Additionally, we provide a detailed understanding of the molecular mechanisms through which this combination mitigates glucose-induced lipid accumulation in Caenorhabditis elegans, with a focus on the role of the skinhead 1 (SKN-1) transcription factor, an orthologue of NRF2.

METHODS

We assessed the lipid accumulation and the changes in skn-1 transcriptional activity in C. elegans using confocal GFP-based detection, alongside mRNA expression analysis of genes from lipid metabolism and oxidative stress response in wild-type, QV225 and LD1 strains. Furthermore, we evaluated locomotion, chemotaxis and mitochondrial dynamics to enhance our understanding of the proposed molecular-based model.

RESULTS

Our findings reveal that the orlistat/curcumin combination exerts an anti-obesogenic effect through SKN-1/NRF2-dependent regulation of conserved genes involved in carbohydrate and lipid metabolism in C. elegans. Moreover, the combination stimulates mitochondrial potential, further contributing to the observed synergistic effects.

CONCLUSION

The hybrid combination of orlistat and curcumin demonstrates significant anti-obesity activity by regulating nutrient-sensing pathways through SKN-1/NRF-2 modulation. This approach may allow for the reduction of orlistat dosage, thereby minimizing its adverse effects while maintaining its therapeutic efficacy.

Perception of a pathogenic signature initiates intergenerational protection

Transmission of immune responses from one generation to the next represents a powerful adaptive mechanism to protect an organism's descendants. Parental infection by the natural C. elegans pathogen Pseudomonas vranovensis induces a protective response in progeny, but the bacterial cues and intergenerational signal driving this response were previously unknown. Here, we find that animals activate a protective stress response program upon exposure to P. vranovensis-derived cyanide and that a metabolic byproduct of cyanide detoxification, β-cyanoalanine, acts as an intergenerational signal to protect progeny from infection. Remarkably, this mechanism does not require direct parental infection; rather, exposure to pathogen-derived volatiles is sufficient to enhance the survival of the next generation, indicating that parental surveillance of environmental cues can activate a protective intergenerational response. Therefore, the mere perception of a pathogen-derived toxin, in this case cyanide, can protect an animal's progeny from future pathogenic challenges.

Age-dependent heat shock hormesis to HSF-1 deficiency suggests a compensatory mechanism mediated by the unfolded protein response and innate immunity in young Caenorhabditis elegans

The transcription factor HSF-1 (heat shock factor 1) acts as a master regulator of heat shock response in eukaryotic cells to maintain cellular proteostasis. The protein has a protective role in preventing cells from undergoing ageing, and neurodegeneration, and also mediates tumorigenesis. Thus, modulating HSF-1 activity in humans has a promising therapeutic potential for treating these pathologies. Loss of HSF-1 function is usually associated with impaired stress tolerance. Contrary to this conventional knowledge, we show here that inactivation of HSF-1 in the nematode Caenorhabditis elegans results in increased thermotolerance at young adult stages, whereas HSF-1 deficiency in animals passing early adult stages indeed leads to decreased thermotolerance, as compared to wild-type. Furthermore, a gene expression analysis supports that in young adults, distinct cellular stress response and immunity-related signaling pathways become induced upon HSF-1 deficiency. We also demonstrate that increased tolerance to proteotoxic stress in HSF-1-depleted young worms requires the activity of the unfolded protein response of the endoplasmic reticulum and the SKN-1/Nrf2-mediated oxidative stress response pathway, as well as an innate immunity-related pathway, suggesting a mutual compensatory interaction between HSF-1 and these conserved stress response systems. A similar compensatory molecular network is likely to also operate in higher animal taxa, raising the possibility of an unexpected outcome when HSF-1 activity is manipulated in humans.

Disrupting the SKN-1 homeostat: mechanistic insights and phenotypic outcomes

The mechanisms that govern maintenance of cellular homeostasis are crucial to the lifespan and healthspan of all living systems. As an organism ages, there is a gradual decline in cellular homeostasis that leads to senescence and death. As an organism lives into advanced age, the cells within will attempt to abate age-related decline by enhancing the activity of cellular stress pathways. The regulation of cellular stress responses by transcription factors SKN-1/Nrf2 is a well characterized pathway in which cellular stress, particularly xenobiotic stress, is abated by SKN-1/Nrf2-mediated transcriptional activation of the Phase II detoxification pathway. However, SKN-1/Nrf2 also regulates a multitude of other processes including development, pathogenic stress responses, proteostasis, and lipid metabolism. While this process is typically tightly regulated, constitutive activation of SKN-1/Nrf2 is detrimental to organismal health, this raises interesting questions surrounding the tradeoff between SKN-1/Nrf2 cryoprotection and cellular health and the ability of cells to deactivate stress response pathways post stress. Recent work has determined that transcriptional programs of SKN-1 can be redirected or suppressed to abate negative health outcomes of constitutive activation. Here we will detail the mechanisms by which SKN-1 is controlled, which are important for our understanding of SKN-1/Nrf2 cytoprotection across the lifespan.

Abalone peptide increases stress resilience and cost-free longevity via SKN-1-governed transcriptional metabolic reprogramming in C. elegans

A major goal of healthy aging is to prevent declining resilience and increasing frailty, which are associated with many chronic diseases and deterioration of stress response. Here, we propose a loss-or-gain survival model, represented by the ratio of cumulative stress span to life span, to quantify stress resilience at organismal level. As a proof of concept, this is demonstrated by reduced survival resilience in Caenorhabditis elegans exposed to exogenous oxidative stress induced by paraquat or with endogenous proteotoxic stress caused by polyglutamine or amyloid-β aggregation. Based on this, we reveal that a hidden peptide ("cryptide")-AbaPep#07 (SETYELRK)-derived from abalone hemocyanin not only enhances survival resilience against paraquat-induced oxidative stress but also rescues proteotoxicity-mediated behavioral deficits in C. elegans, indicating its capacity against stress and neurodegeneration. Interestingly, AbaPep#07 is also found to increase cost-free longevity and age-related physical fitness in nematodes. We then demonstrate that AbaPep#07 can promote nuclear localization of SKN-1/Nrf, but not DAF-16/FOXO, transcription factor. In contrast to its effects in wild-type nematodes, AbaPep#07 cannot increase oxidative stress survival and physical motility in loss-of-function skn-1 mutant, suggesting an SKN-1/Nrf-dependent fashion of these effects. Further investigation reveals that AbaPep#07 can induce transcriptional activation of immune defense, lipid metabolism, and metabolic detoxification pathways, including many SKN-1/Nrf target genes. Together, our findings demonstrate that AbaPep#07 is able to boost stress resilience and reduce behavioral frailty via SKN-1/Nrf-governed transcriptional reprogramming, and provide an insight into the health-promoting potential of antioxidant cryptides as geroprotectors in aging and associated conditions.

Nuclear hormone receptor NHR-49 is an essential regulator of stress resilience and healthy aging in Caenorhabditis elegans

The genome of Caenorhabditis elegans encodes 284 nuclear hormone receptor, which perform diverse functions in development and physiology. One of the best characterized of these is NHR-49, related in sequence and function to mammalian hepatocyte nuclear factor 4α and peroxisome proliferator-activated receptor α. Initially identified as regulator of lipid metabolism, including fatty acid catabolism and desaturation, additional important roles for NHR-49 have since emerged. It is an essential contributor to longevity in several genetic and environmental contexts, and also plays vital roles in the resistance to several stresses and innate immune response to infection with various bacterial pathogens. Here, we review how NHR-49 is integrated into pertinent signaling circuits and how it achieves its diverse functions. We also highlight areas for future investigation including identification of regulatory inputs that drive NHR-49 activity and identification of tissue-specific gene regulatory outputs. We anticipate that future work on this protein will provide information that could be useful for developing strategies to age-associated declines in health and age-related human diseases.

The metabolic contribution of SKN-1/Nrf2 to the lifespan of Caenorhabditis elegans

BACKGROUND AND AIMS

SKN-1, a C. elegans transcription factor analogous to the mammalian NF-E2-related factor (Nrf2), has been known to promote oxidative stress resistance aiding nematodes' longevity. Although SKN-1's functions suggest its implication in lifespan modulation through cellular metabolism, the actual mechanism of how metabolic rearrangements contribute to SKN-1's lifespan modulation has yet to be well characterized. Therefore, we performed the metabolomic profiling of the short-lived skn-1-knockdown C. elegans.

METHODS

We analyzed the metabolic profile of the skn-1-knockdown worms with nuclear magnetic resonance (NMR) spectroscopy and liquid chromatography-tandem mass spectrometry (LC-MS/MS) and obtained distinctive metabolomic profiles compared to WT worms. We further extended our study with gene expression analysis to examine the expression level of genes encoding all metabolic enzymes.

RESULTS

A significant increase in the phosphocholine and AMP/ATP ratio, potential biomarkers of aging, was observed, accompanied by a decrease in the transsulfuration metabolites, NADPH/NADP⁺ ratio, and total glutathione (GSHt), which are known to be involved in oxidative stress defense. skn-1-RNAi worms also exhibited an impairment in the phase II detoxification system, confirmed by the lower conversion rate of paracetamol to paracetamol-glutathione. By further examining the transcriptomic profile, we found a decrease in the expression of cbl-1, gpx, T25B9.9, ugt, and gst, which are involved in GSHt and NADPH synthesis as well as in the phase II detoxification system.

CONCLUSION

Our multi-omics results consistently revealed that the cytoprotective mechanisms, including cellular redox reactions and xenobiotic detoxification system, contribute to the roles of SKN-1/Nrf2 in the lifespan of worms.