DAF-16/FoxO in Caenorhabditis elegans and its role in metabolic remodeling

DAF-16, the only forkhead box transcription factors class O (FoxO) homolog in Caenorhabditis elegans, integrates signals from upstream pathways to elicit transcriptional changes in many genes involved in aging, development, stress, metabolism, and immunity. The major regulator of DAF-16 activity is the insulin/insulin-like growth factor 1 (IGF-1) signaling (IIS) pathway, reduction of which leads to lifespan extension in worms, flies, mice, and humans. In C. elegans daf-2 mutants, reduced IIS leads to a heterochronic activation of a dauer survival program during adulthood. This program includes elevated antioxidant defense and a metabolic shift toward accumulation of carbohydrates (i.e., trehalose and glycogen) and triglycerides, and activation of the glyoxylate shunt, which could allow fat-to-carbohydrate conversion. The longevity of daf-2 mutants seems to be partially supported by endogenous trehalose, a nonreducing disaccharide that mammals cannot synthesize, which points toward considerable differences in downstream mechanisms by which IIS regulates aging in distinct groups

The nutritional requirements of Caenorhabditis elegans

Animals require sufficient intake of a variety of nutrients to support their development, somatic maintenance and reproduction. An adequate diet provides cell building blocks, chemical energy to drive cellular processes and essential nutrients that cannot be synthesised by the animal, or at least not in the required amounts. Dietary requirements of nematodes, including Caenorhabditis elegans have been extensively studied with the major aim to develop a chemically defined axenic medium that would support their growth and reproduction. At the same time, these studies helped elucidating important aspects of nutrition-related biochemistry and metabolism as well as the establishment of C. elegans as a powerful model in studying evolutionarily conserved pathways, and the influence of the diet on health

Elevated trehalose levels in C. elegans daf-2 mutants increase stress resistance, not lifespan

The C. elegans insulin/IGF-1 (insulin-like growth factor 1) signaling mutant daf-2 recapitulates the dauer metabolic signature-a shift towards lipid and carbohydrate accumulation-which may be linked to its longevity and stress resistance phenotypes. Trehalose, a disaccharide of glucose, is highly upregulated in daf-2 mutants and it has been linked to proteome stabilization and protection against heat, cold, desiccation, and hypoxia. Earlier studies suggested that elevated trehalose levels can explain up to 43% of the lifespan extension observed in daf-2 mutants. Here we demonstrate that trehalose accumulation is responsible for increased osmotolerance, and to some degree thermotolerance, rather than longevity in daf-2 mutants. This indicates that particular stress resistance phenotypes can be uncoupled from longevity

International classroom studies of inclusive practices: Comparing teaching-learning processes

In B. Johnsen (Ed.), International Classroom Studies of Inclusive Practises : Comparing Teaching-Learning Processe

Accumulation of glycogen and upregulation of LEA-1 in C. elegans daf-2(e1370) support stress resistance, not longevity

DAF-16-dependent activation of a dauer-associated genetic program in the C. elegans insulin/IGF-1 daf-2(e1370) mutant leads to accumulation of large amounts of glycogen with concomitant upregulation of glycogen synthase, GSY-1. Glycogen is a major storage sugar in C. elegans that can be used as a short-term energy source for survival, and possibly as a reservoir for synthesis of a chemical chaperone trehalose. Its role in mitigating anoxia, osmotic and oxidative stress has been demonstrated previously. Furthermore, daf-2 mutants show increased abundance of the group 3 late embryogenesis abundant protein LEA-1, which has been found to act in synergy with trehalose to exert its protective role against desiccation and heat stress in vitro, and to be essential for desiccation tolerance in C. elegans dauer larvae. Here we demonstrate that accumulated glycogen is not required for daf-2 longevity, but specifically protects against hyperosmotic stress, and serves as an important energy source during starvation. Similarly, lea-1 does not act to support daf-2 longevity. Instead, it contributes to increased resistance of daf-2 mutants to heat, osmotic, and UV stress. In summary, our experimental results suggest that longevity and stress resistance can be uncoupled in IIS longevity mutants

Mitochondria-originated redox signalling regulates KLF-1 to promote longevity in Caenorhabditis elegans

Alternations of redox metabolism have been associated with the extension of lifespan in roundworm Caenorhabditis elegans, caused by moderate mitochondrial dysfunction, although the underlying signalling cascades are largely unknown. Previously, we identified transcriptional factor Krüppel-like factor-1 (KLF-1) as the main regulator of cytoprotective longevity-assurance pathways in the C. elegans long-lived mitochondrial mutants. Here, we show that KLF-1 translocation to the nucleus and the activation of the signalling cascade is dependent on the mitochondria-derived hydrogen peroxide (H2O2) produced during late developmental phases where aerobic respiration and somatic mitochondrial biogenesis peak. We further show that mitochondrial-inducible superoxide dismutase-3 (SOD-3), together with voltage-dependent anion channel-1 (VDAC-1), is required for the life-promoting H2O2 signalling that is further regulated by peroxiredoxin-3 (PRDX-3). Increased H2O2 release in the cytoplasm activates the p38 MAPK signalling cascade that induces KLF-1 translocation to the nucleus and the activation of transcription of C. elegans longevity-promoting genes, including cytoprotective cytochrome P450 oxidases. Taken together, our results underline the importance of redox-regulated signalling as the key regulator of longevity-inducing pathways in C. elegans, and position precisely timed mitochondria-derived H2O2 in the middle of it

Prediction of biological age by morphological staging of sarcopenia in Caenorhabditis elegans

Sarcopenia encompasses a progressive decline in muscle quantity and quality. Given its close association with ageing, it may represent a valuable healthspan marker. The commonalities with human muscle structure and facile visualization possibilities make Caenorhabditis elegans an attractive model for studying the relationship between sarcopenia and healthspan. However, classical visual assessment of muscle architecture is subjective and has low throughput. To resolve this, we have developed an image analysis pipeline for the quantification of muscle integrity in confocal microscopy images from a cohort of ageing myosin::GFP reporter worms. We extracted a variety of morphological descriptors and found a subset to scale linearly with age. This allowed establishing a linear model that predicts biological age from a morphological muscle signature. To validate the model, we evaluated muscle architecture in long-lived worms that are known to experience delayed sarcopenia by targeted knockdown of the daf-2 gene. We conclude that quantitativ e microscopy allows for staging sarcopenia in C . elegans and may foster the development of image-based screens in this model organism to identif y modulators that mitigate age-related muscle frailty and thus improve healthspan

Laser-induced remote release in vivo in C. elegans from novel silver nanoparticles-alginate hydrogel shells

Non-destructive, controllable, remote light-induced release inside cells enables studying time- and space-specific processes in biology. In this work we demonstrate the remote release of tagged proteins in Caenorhabditis elegans (C. elegans) worms using a near-infrared laser light as a trigger from novel hydrogel shells functionalized with silver nanoparticles responsive to laser light. A new type of hydrogel shells was developed capable of withstanding prolonged storage in the lyophilized state to enable the uptake of the shell by worms, which takes place on an agar plate under standard culture conditions. Uptake of the shells by C. elegans was confirmed using confocal laser scanning microscopy, while release from alginate shells in C. elegans and the laser effect on the shells on a substrate in air was followed using fluorescence microscopy. In addition, Raman microscopy was used to track the localization of particles to avoid the influence of autofluorescence. Hierarchical cluster spectral analysis is used to extract information about the biochemical composition of an area of a nematode containing the hydrogel shells, whose Raman signal is enhanced by the SERS (Surface Enhanced Raman Scattering) effect due to hot spots formed by silver nanoparticles present in the shells. The in vivo release demonstrated here can be used to study intestinal microbiota and probiotic compounds as well as a possible future strategy for gene delivery in the worms, other insects and other organisms