Filipe Cabreiro

Absence of effects of Sir2 overexpression on lifespan in C. elegans and Drosophila

Overexpression of sirtuins (NAD+-dependent protein deacetylases) has been reported to increase lifespan in budding yeast (Saccharomyces cerevisiae), Caenorhabditis elegans and Drosophila melanogaster. Studies of the effects of genes on ageing are vulnerable to confounding effects of genetic background. Here we re-examined the reported effects of sirtuin overexpression on ageing and found that standardization of genetic background and the use of appropriate controls abolished the apparent effects in both C. elegans and Drosophila. In C. elegans, outcrossing of a line with high-level sir-2.1 overexpression abrogated the longevity increase, but did not abrogate sir-2.1 overexpression. Instead, longevity co-segregated with a second-site mutation affecting sensory neurons. Outcrossing of a line with low-copy-number sir-2.1 overexpression also abrogated longevity. A Drosophila strain with ubiquitous overexpression of dSir2 using the UAS-GAL4 system was long-lived relative to wild-type controls, as previously reported, but was not long-lived relative to the appropriate transgenic controls, and nor was a new line with stronger overexpression of dSir2. These findings underscore the importance of controlling for genetic background and for the mutagenic effects of transgene insertions in studies of genetic effects on lifespan. The life-extending effect of dietary restriction on ageing in Drosophila has also been reported to be dSir2 dependent. We found that dietary restriction increased fly lifespan independently of dSir2. Our findings do not rule out a role for sirtuins in determination of metazoan lifespan, but they do cast doubt on the robustness of the previously reported effects of sirtuins on lifespan in C. elegans and Drosophila.

Metformin Retards Aging in C. elegans by Altering Microbial Folate and Methionine Metabolism

Summary The biguanide drug metformin is widely prescribed to treat type 2 diabetes and metabolic syndrome, but its mode of action remains uncertain. Metformin also increases lifespan in Caenorhabditis elegans cocultured with Escherichia coli. This bacterium exerts complex nutritional and pathogenic effects on its nematode predator/host that impact health and aging. We report that metformin increases lifespan by altering microbial folate and methionine metabolism. Alterations in metformin-induced longevity by mutation of worm methionine synthase (metr-1) and S-adenosylmethionine synthase (sams-1) imply metformin-induced methionine restriction in the host, consistent with action of this drug as a dietary restriction mimetic. Metformin increases or decreases worm lifespan, depending on E. coli strain metformin sensitivity and glucose concentration. In mammals, the intestinal microbiome influences host metabolism, including development of metabolic disease. Thus, metformin-induced alteration of microbial metabolism could contribute to therapeutic efficacy—and also to its side effects, which include folate deficiency and gastrointestinal upset. PaperClip

Increased life span from overexpression of superoxide dismutase in Caenorhabditis elegans is not caused by decreased oxidative damage

The superoxide free radical (O2•−) has been viewed as a likely major contributor to aging. If this is correct, then superoxide dismutase (SOD), which removes O2•−, should contribute to longevity assurance. In Caenorhabditis elegans, overexpression (OE) of the major cytosolic Cu/Zn-SOD, sod-1, increases life span. But is this increase caused by enhanced antioxidant defense? sod-1 OE did not reduce measures of lipid oxidation or glycation and actually increased levels of protein oxidation. The effect of sod-1 OE on life span was dependent on the DAF-16/FoxO transcription factor (TF) and, partially, on the heat shock TF HSF-1. Similarly, overexpression of sod-2 (major mitochondrial Mn-SOD) resulted in life-span extension that was daf-16 dependent. sod-1 OE increased steady-state hydrogen peroxide (H2O2) levels in vivo. However, co-overexpression of catalase did not suppress the life-span extension, arguing against H2O2 as a cause of longevity. sod-1 OE increased hsp-4 expression, suggesting increased endoplasmic reticulum (ER) stress. Moreover, longevity was partially suppressed by inactivation of ire-1 and xbp-1, mediators of the ER stress response. This suggests that high levels of SOD-1 protein may challenge protein-folding homeostasis, triggering a daf-16- and hsf-1-dependent stress response that extends life span. These findings imply that SOD overexpression increases C. elegans life span, not by removal of O2•−, but instead by activating longevity-promoting transcription factors.

Repurposing metformin: an old drug with new tricks in its binding pockets

Improvements in healthcare and nutrition have generated remarkable increases in life expectancy worldwide. This is one of the greatest achievements of the modern world yet it also presents a grave challenge: as more people survive into later life, more also experience the diseases of old age, including type 2 diabetes (T2D), cardiovascular disease (CVD) and cancer. Developing new ways to improve health in the elderly is therefore a top priority for biomedical research. Although our understanding of the molecular basis of these morbidities has advanced rapidly, effective novel treatments are still lacking. Alternative drug development strategies are now being explored, such as the repurposing of existing drugs used to treat other diseases. This can save a considerable amount of time and money since the pharmacokinetics, pharmacodynamics and safety profiles of these drugs are already established, effectively enabling preclinical studies to be bypassed. Metformin is one such drug currently being investigated for novel applications. The present review provides a thorough and detailed account of our current understanding of the molecular pharmacology and signalling mechanisms underlying biguanide–protein interactions. It also focuses on the key role of the microbiota in regulating age-associated morbidities and a potential role for metformin to modulate its function. Research in this area holds the key to solving many of the mysteries of our current understanding of drug action and concerted effects to provide sustained and long-life health.

Worms need microbes too: microbiota, health and aging in Caenorhabditis elegans

Many animal species live in close association with commensal and symbiotic microbes (microbiota). Recent studies have revealed that the status of gastrointestinal tract microbiota can influence nutrition‐related syndromes such as obesity and type‐2 diabetes, and perhaps aging. These morbidities have a profound impact in terms of individual suffering, and are an increasing economic burden to modern societies. Several theories have been proposed for the influence of microbiota on host metabolism, but these largely remain to be proven. In this article we discuss how microbiota may be manipulated (via pharmacology, diet, or gene manipulation) in order to alter metabolism, immunity, health and aging in the host. The nematode Caenorhabditis elegans in combination with one microbial species is an excellent, defined model system to investigate the mechanisms of host–microbiota interactions, particularly given the combined power of worm and microbial genetics. We also discuss the multifaceted nature of the worm–microbe relationship, which likely encompasses predation, commensalism, pathogenicity and necromeny.

Anthranilate Fluorescence Marks a Calcium-Propagated Necrotic Wave That Promotes Organismal Death in C. elegans

Death of the nematode Caenorhabditis elegans involves a conserved necrotic cell death cascade which generates endogenous blue anthranilate fluorescence, allowing death to be visualized.

Manipulation of in vivo iron levels can alter resistance to oxidative stress without affecting ageing in the nematode C. elegans.

Highlights ► Here we test whether iron-catalyzed oxidative damage contributes to organismal ageing. ► We develop new methodologies to measure free iron in vivo in C. elegans. ► Moderate iron supplementation can increase oxidative damage without reducing lifespan. ► Iron chelation or increasing ferritin levels increase resistance to oxidative stress but do not increase lifespan. ► Our findings argue against the oxidative damage theory of ageing.

Host-Microbe Co-metabolism Dictates Cancer Drug Efficacy in C. elegans

Summary Fluoropyrimidines are the first-line treatment for colorectal cancer, but their efficacy is highly variable between patients. We queried whether gut microbes, a known source of inter-individual variability, impacted drug efficacy. Combining two tractable genetic models, the bacterium E. coli and the nematode C. elegans, we performed three-way high-throughput screens that unraveled the complexity underlying host-microbe-drug interactions. We report that microbes can bolster or suppress the effects of fluoropyrimidines through metabolic drug interconversion involving bacterial vitamin B6, B9, and ribonucleotide metabolism. Also, disturbances in bacterial deoxynucleotide pools amplify 5-FU-induced autophagy and cell death in host cells, an effect regulated by the nucleoside diphosphate kinase ndk-1. Our data suggest a two-way bacterial mediation of fluoropyrimidine effects on host metabolism, which contributes to drug efficacy. These findings highlight the potential therapeutic power of manipulating intestinal microbiota to ensure host metabolic health and treat disease.

Metformin joins forces with microbes

The gut microbiota is a key player regulating human physiology and can adjust its structure and metabolic activity in response to host health. A recent Nature paper by Forslund et al. (2015) reveals that microbiota adaptation to metformin treatment are responsible for the drugs therapeutic effects against type 2 diabetes.

Folate metabolite profiling of different cell types and embryos suggests variation in folate one-carbon metabolism, including developmental changes in human embryonic brain.

Folates act as co-factors for transfer of one-carbon units for nucleotide production, methylation and other biosynthetic reactions. Comprehensive profiling of multiple folates can be achieved using liquid chromatography tandem mass spectrometry, enabling determination of their relative abundance that may provide an indication of metabolic differences between cell types. For example, cell lines exposed to methotrexate showed a dose-dependent elevation of dihydrofolate, consistent with inhibition of dihydrofolate reductase. We analysed the folate profile of E. coli sub-types as well as cell lines and embryonic tissue from both human and mouse. The folate profile of bacteria differed markedly from those of all the mammalian samples, most notably in the greater abundance of formyl tetrahydrofolate. The overall profiles of mouse and human fibroblasts and mid-gestation mouse embryos were broadly similar, with specific differences. The major folate species in these cell types was 5-methyl tetrahydrofolate, in contrast to lymphoblastoid cell lines in which the predominant form was tetrahydrofolate. Analysis of embryonic human brain revealed a shift in folate profile with increasing developmental stage, with a decline in relative abundance of dihydrofolate and increase in 5-methyl tetrahydrofolate. These cell type-specific and developmental changes in folate profile may indicate differential requirements for the various outputs of folate metabolism.