Michael Petrascheck

An antidepressant that extends lifespan in adult Caenorhabditis elegans.

The mechanisms that determine the lifespan of an organism are still largely a mystery. One goal of ageing research is to find drugs that would increase lifespan and vitality when given to an adult animal. To this end, we tested 88,000 chemicals for the ability to extend the lifespan of adult Caenorhabditis elegans nematodes. Here we report that a drug used as an antidepressant in humans increases C. elegans lifespan. In humans, this drug blocks neural signalling by the neurotransmitter serotonin. In C. elegans, the effect of the drug on lifespan is reduced or eradicated by mutations that affect serotonin synthesis, serotonin re-uptake at synapses, or either of two G-protein-coupled receptors: one that recognizes serotonin and the other that detects another neurotransmitter, octopamine. In vitro studies show that the drug acts as an antagonist at both receptors. Testing of the drug on dietary-restricted animals or animals with mutations that affect lifespan indicates that its effect on lifespan involves mechanisms associated with lifespan extension by dietary restriction. These studies indicate that lifespan can be extended by blocking certain types of neurotransmission implicated in food sensing in the adult animal, possibly leading to a state of perceived, although not real, starvation.

The metabolite α-ketoglutarate extends lifespan by inhibiting ATP synthase and TOR

Metabolism and ageing are intimately linked. Compared with ad libitum feeding, dietary restriction consistently extends lifespan and delays age-related diseases in evolutionarily diverse organisms. Similar conditions of nutrient limitation and genetic or pharmacological perturbations of nutrient or energy metabolism also have longevity benefits. Recently, several metabolites have been identified that modulate ageing; however, the molecular mechanisms underlying this are largely undefined. Here we show that α-ketoglutarate (α-KG), a tricarboxylic acid cycle intermediate, extends the lifespan of adult Caenorhabditis elegans. ATP synthase subunit β is identified as a novel binding protein of α-KG using a small-molecule target identification strategy termed drug affinity responsive target stability (DARTS). The ATP synthase, also known as complex V of the mitochondrial electron transport chain, is the main cellular energy-generating machinery and is highly conserved throughout evolution. Although complete loss of mitochondrial function is detrimental, partial suppression of the electron transport chain has been shown to extend C. elegans lifespan. We show that α-KG inhibits ATP synthase and, similar to ATP synthase knockdown, inhibition by α-KG leads to reduced ATP content, decreased oxygen consumption, and increased autophagy in both C. elegans and mammalian cells. We provide evidence that the lifespan increase by α-KG requires ATP synthase subunit β and is dependent on target of rapamycin (TOR) downstream. Endogenous α-KG levels are increased on starvation and α-KG does not extend the lifespan of dietary-restricted animals, indicating that α-KG is a key metabolite that mediates longevity by dietary restriction. Our analyses uncover new molecular links between a common metabolite, a universal cellular energy generator and dietary restriction in the regulation of organismal lifespan, thus suggesting new strategies for the prevention and treatment of ageing and age-related diseases.

A pharmacological network for lifespan extension in Caenorhabditis elegans

One goal of aging research is to find drugs that delay the onset of age‐associated disease. Studies in invertebrates, particularly Caenorhabditis elegans, have uncovered numerous genes involved in aging, many conserved in mammals. However, which of these encode proteins suitable for drug targeting is unknown. To investigate this question, we screened a library of compounds with known mammalian pharmacology for compounds that increase C. elegans lifespan. We identified 60 compounds that increase longevity in C. elegans, 33 of which also increased resistance to oxidative stress. Many of these compounds are drugs approved for human use. Enhanced resistance to oxidative stress was associated primarily with compounds that target receptors for biogenic amines, such as dopamine or serotonin. A pharmacological network constructed with these data reveal that lifespan extension and increased stress resistance cluster together in a few pharmacological classes, most involved in intercellular signaling. These studies identify compounds that can now be explored for beneficial effects on aging in mammals, as well as tools that can be used to further investigate the mechanisms underlying aging in C. elegans.

Organ Polarity in Arabidopsis. NOZZLE Physically Interacts with Members of the YABBY Family

Plant lateral organs exhibit proximal-distal and adaxial-abaxial polarity. In Arabidopsis, abaxial cell fate is regulated in part by putative transcription factors of the YABBY family, such as FILAMENTOUS FLOWER (FIL) and INNER NO OUTER (INO), by a mechanism that currently is not fully understood. NOZZLE (NZZ) encodes a plant-specific nuclear protein. Genetic evidence has shown that NZZ is involved in the positive feedback regulation of INO, thereby acting both as a temporal and spatial repressor of INO transcription. This mechanism allows the ovule primordium to complete its proximal-distal organization, prior to the onset of adaxial-abaxial development in the chalaza. During our study, we isolated FIL in a yeast two-hybrid screen using NZZ as bait. In vitro pull-down experiments confirmed the NZZ-FIL interaction. NZZ also bound INO and YABBY3, suggesting that NZZ generally interacts with YABBY proteins in vitro. The polar-charged region of NZZ was necessary and sufficient to bind to the zinc finger of INO and to interact with its C terminus carrying the high mobility group-like domain. We suggest that NZZ coordinates proximal-distal patterning and adaxial-abaxial polarity establishment in the developing ovule by directly binding to INO.

Proton Pump Inhibitors Accelerate Endothelial Senescence

RATIONALE Proton pump inhibitors (PPIs) are popular drugs for gastroesophageal reflux, which are now available for long-term use without medical supervision. Recent reports suggest that PPI use is associated with cardiovascular, renal, and neurological morbidity. OBJECTIVE To study the long-term effect of PPIs on endothelial dysfunction and senescence and investigate the mechanism involved in PPI-induced vascular dysfunction. METHODS AND RESULTS Chronic exposure to PPIs impaired endothelial function and accelerated human endothelial senescence by reducing telomere length. CONCLUSIONS Our data may provide a unifying mechanism for the association of PPI use with increased risk of cardiovascular, renal, and neurological morbidity and mortality.

A High‐Throughput Screen for Chemicals that Increase the Lifespan of Caenorhabditis elegans

One long‐term goal of aging research is to find drugs that can delay aging and the onset of age‐associated diseases. With this in mind, we screened 88,000 chemicals for the ability to increase the lifespan of Caenorhabditis elegans nematodes. We found that mianserin, a serotonin receptor antagonist used as an antidepressant in humans, can increase C. elegans lifespan when given only during adulthood. This effect is reduced or abolished by mutations that affect serotonin synthesis or serotonin reuptake at synapses. It also requires a serotonin receptor and an octopamine receptor, both of which are inhibited by the drug. Mianserin has no effect on the lifespan of animals with increased longevity due to dietary restriction or with a mutation that reduces food intake, indicating that the drug extends lifespan via mechanisms linked to dietary restriction. These studies indicate that lifespan can be increased by inhibiting certain kinds of neurotransmission previously implicated in food sensing, possibly by mimicking a physiological state associated with dietary restriction.

Measuring Food Intake and Nutrient Absorption in Caenorhabditis elegans

Caenorhabditis elegans has emerged as a powerful model to study the genetics of feeding, food-related behaviors, and metabolism. Despite the many advantages of C. elegans as a model organism, direct measurement of its bacterial food intake remains challenging. Here, we describe two complementary methods that measure the food intake of C. elegans. The first method is a microtiter plate-based bacterial clearing assay that measures food intake by quantifying the change in the optical density of bacteria over time. The second method, termed pulse feeding, measures the absorption of food by tracking de novo protein synthesis using a novel metabolic pulse-labeling strategy. Using the bacterial clearance assay, we compare the bacterial food intake of various C. elegans strains and show that long-lived eat mutants eat substantially more than previous estimates. To demonstrate the applicability of the pulse-feeding assay, we compare the assimilation of food for two C. elegans strains in response to serotonin. We show that serotonin-increased feeding leads to increased protein synthesis in a SER-7-dependent manner, including proteins known to promote aging. Protein content in the food has recently emerged as critical factor in determining how food composition affects aging and health. The pulse-feeding assay, by measuring de novo protein synthesis, represents an ideal method to unequivocally establish how the composition of food dictates protein synthesis. In combination, these two assays provide new and powerful tools for C. elegans research to investigate feeding and how food intake affects the proteome and thus the physiology and health of an organism.

Metabolic drift in the aging brain

Brain function is highly dependent upon controlled energy metabolism whose loss heralds cognitive impairments. This is particularly notable in the aged individuals and in age-related neurodegenerative diseases. However, how metabolic homeostasis is disrupted in the aging brain is still poorly understood. Here we performed global, metabolomic and proteomic analyses across different anatomical regions of mouse brain at different stages of its adult lifespan. Interestingly, while severe proteomic imbalance was absent, global-untargeted metabolomics revealed an energy metabolic drift or significant imbalance in core metabolite levels in aged mouse brains. Metabolic imbalance was characterized by compromised cellular energy status (NAD decline, increased AMP/ATP, purine/pyrimidine accumulation) and significantly altered oxidative phosphorylation and nucleotide biosynthesis and degradation. The central energy metabolic drift suggests a failure of the cellular machinery to restore metabostasis (metabolite homeostasis) in the aged brain and therefore an inability to respond properly to external stimuli, likely driving the alterations in signaling activity and thus in neuronal function and communication.

C. elegans S6K Mutants Require a Creatine-Kinase-like Effector for Lifespan Extension

Deficiency of S6 kinase (S6K) extends the lifespan of multiple species, but the underlying mechanisms are unclear. To discover potential effectors of S6K-mediated longevity, we performed a proteomics analysis of long-lived rsks-1/S6K C. elegans mutants compared to wild-type animals. We identified the arginine kinase ARGK-1 as the most significantly enriched protein in rsks-1/S6K mutants. ARGK-1 is an ortholog of mammalian creatine kinase, which maintains cellular ATP levels. We found that argk-1 is possibly a selective effector of rsks-1/S6K-mediated longevity and that overexpression of ARGK-1 extends C. elegans lifespan, in part by activating the energy sensor AAK-2/AMPK. argk-1 is also required for the reduced body size and increased stress resistance observed in rsks-1/S6K mutants. Finally, creatine kinase levels are increased in the brains of S6K1 knockout mice. Our study identifies ARGK-1 as a longevity effector in C. elegans with reduced RSKS-1/S6K levels.

The DrugAge database of aging-related drugs

Aging is a major worldwide medical challenge. Not surprisingly, identifying drugs and compounds that extend lifespan in model organisms is a growing research area. Here, we present DrugAge (http://genomics.senescence.info/drugs/), a curated database of lifespan‐extending drugs and compounds. At the time of writing, DrugAge contains 1316 entries featuring 418 different compounds from studies across 27 model organisms, including worms, flies, yeast and mice. Data were manually curated from 324 publications. Using drug–gene interaction data, we also performed a functional enrichment analysis of targets of lifespan‐extending drugs. Enriched terms include various functional categories related to glutathione and antioxidant activity, ion transport and metabolic processes. In addition, we found a modest but significant overlap between targets of lifespan‐extending drugs and known aging‐related genes, suggesting that some but not most aging‐related pathways have been targeted pharmacologically in longevity studies. DrugAge is freely available online for the scientific community and will be an important resource for biogerontologists.