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As the demographics of the modern world skew older, understanding and mitigating the effects of aging is increasingly important within biomedical research. Recent studies in model organisms demonstrate that the aging process is frequently modified by an organism’s ability to perceive and respond to changes in its environment. Many well-studied pathways that influence aging involve sensory cells, frequently neurons, that signal to peripheral tissues and promote survival during the presence of stress. Importantly, this activation of stress response pathways is often sufficient to improve health and longevity even in the absence of stress. Here, we review the current landscape of research highlighting the importance of cell non-autonomous signaling in modulating aging from C. elegans to mammals. We also discuss emerging concepts including retrograde signaling, approaches to mapping these networks, and development of potential therapeutics.

An organism’s ability to perceive and respond to changes in its environment is crucial for its health and survival. Here we reveal how the most well-studied longevity intervention, dietary restriction, acts in-part through a cell non-autonomous signaling pathway that is inhibited by the presence of attractive smells. Using an intestinal reporter for a key gene induced by dietary restriction but suppressed by attractive smells, we identify three compounds that block food odor effects in C. elegans , thereby increasing longevity as dietary restriction mimetics. These compounds clearly implicate serotonin and dopamine in limiting lifespan in response to food odor. We further identify a chemosensory neuron that likely perceives food odor, an enteric neuron that signals through the serotonin receptor 5-HT1A/SER-4, and a dopaminergic neuron that signals through the dopamine receptor DRD2/DOP-3. Aspects of this pathway are conserved in D. melanogaster . Thus, blocking food odor signaling through antagonism of serotonin or dopamine receptors is a plausible approach to mimic the benefits of dietary restriction. This report finds that dietary restriction, the most extensively studied anti-aging intervention, can be mimicked by blocking food odour signaling and identifies a neural network of food perception that functions through serotonin and dopamine.

Stabilization of the hypoxia-inducible factor 1 (HIF-1) increases life span and health span in nematodes through an unknown mechanism. We report that neuronal stabilization of HIF-1 mediates these effects in Caenorhabditis elegans through a cell nonautonomous signal to the intestine, which results in activation of the xenobiotic detoxification enzyme flavincontaining monooxygenase-2 (FMO-2). This prolongevity signal requires the serotonin biosynthetic enzyme TPH-1 in neurons and the serotonin receptor SER-7 in the intestine. Intestinal FMO-2 is also activated by dietary restriction (DR) and is necessary for DR-mediated life-span extension, which suggests that this enzyme represents a point of convergence for two distinct longevity pathways. FMOs are conserved in eukaryotes and induced by multiple life span–extending interventions in mice, which suggests that these enzymes may play a critical role in promoting health and longevity across phyla.

Flavin containing monooxygenases (FMOs) are promiscuous enzymes known for metabolizing a wide range of exogenous compounds. In C. elegans , fmo-2 expression increases lifespan and healthspan downstream of multiple longevity-promoting pathways through an unknown mechanism. Here, we report that, beyond its classification as a xenobiotic enzyme, fmo-2 expression leads to rewiring of endogenous metabolism principally through changes in one carbon metabolism (OCM). These changes are likely relevant, as we find that genetically modifying OCM enzyme expression leads to alterations in longevity that interact with fmo-2 expression. Using computer modeling, we identify decreased methylation as the major OCM flux modified by FMO-2 that is sufficient to recapitulate its longevity benefits. We further find that tryptophan is decreased in multiple mammalian FMO overexpression models and is a validated substrate for FMO-2. Our resulting model connects a single enzyme to two previously unconnected key metabolic pathways and provides a framework for the metabolic interconnectivity of longevity-promoting pathways such as dietary restriction. FMOs are well-conserved enzymes that are also induced by lifespan-extending interventions in mice, supporting a conserved and important role in promoting health and longevity through metabolic remodeling. Flavin containing monooxygenase 2 (FMO-2) is known to increase lifespan under dietary restriction through incompletely understood mechanisms. Here the authors report that FMO-2 modifies tryptophan and methionine metabolic pathways to enhance stress resistance and slow aging in C. elegans .

Flavin-Containing Monooxygenases are conserved xenobiotic-detoxifying enzymes. Recent studies have revealed endogenous functions of FMOs in regulating longevity in Caenorhabditis elegans and in regulating aspects of metabolism in mice. To explore the cellular mechanisms of FMO’s endogenous function, here we demonstrate that all five functional mammalian FMOs may play similar endogenous roles to improve resistance to a wide range of toxic stresses in both kidney and liver cells. We further find that stress-activated c-Jun N-terminal kinase activity is enhanced in FMO-overexpressing cells, which may lead to increased survival under stress. Furthermore, FMO expression modulates cellular metabolic activity as measured by mitochondrial respiration, glycolysis, and metabolomics analyses. FMO expression augments mitochondrial respiration and significantly changes central carbon metabolism, including amino acid and energy metabolism pathways. Together, our findings demonstrate an important endogenous role for the FMO family in regulation of cellular stress resistance and major cellular metabolic activities including central carbon metabolism.

Caenorhabditis elegans is an instrumental research model used to advance our knowledge in areas including development, metabolism, and aging. However, research on metabolism and/or other measures of health/aging are confounded by the nematode’s food source in the lab, live E. coli bacteria. Commonly used treatments, including ultraviolet irradiation and antibiotics, are successful in preventing bacterial replication, but the bacteria can remain metabolically active. The purpose of this study is to develop a metabolically inactive food source for the worms that will allow us to minimize the confounding effects of bacterial metabolism on worm metabolism and aging. Our strategy is to use a paraformaldehyde (PFA) treated E. coli food source and to determine its effects on worm health, metabolism and longevity. We initially determine the lowest possible concentrations of PFA necessary to rapidly and reproducibly kill bacteria. We then measure various aspects of worm behavior, healthspan and longevity, including growth rate, food attraction, brood size, lifespan and metabolic assessments, such as oxygen consumption and metabolomics. Our resulting data show that worms eat and grow well on these bacteria and support the use of 0.5% PFA-killed bacteria as a nematode food source for metabolic, drug, and longevity experiments.Beydoun, Choi et al. develop a metabolically inactive food source for C. elegans worms that minimizes the confounding effects of bacterial metabolism on worm metabolism and aging. They find that worms eat and grow well on a paraformaldehyde (PFA)-treated E. coli food source, recommending the use of 0.5% PFA-killed bacteria as a nematode food source for metabolic experiments.

Flavin-containing monooxygenases (FMOs) are a conserved family of xenobiotic enzymes upregulated in multiple longevity interventions, including nematode and mouse models. Previous work supports that promotes longevity, stress resistance, and healthspan by rewiring endogenous metabolism. However, there are five FMOs and five mammalian FMOs, and it is not known whether promoting longevity and health benefits is a conserved role of this gene family. Here, we report that expression of promotes lifespan extension and paraquat stress resistance downstream of both dietary restriction and inhibition of mTOR. We find that overexpression of in just the hypodermis is sufficient for these benefits, and that this expression significantly modifies the transcriptome. By analyzing changes in gene expression, we find that genes related to calcium signaling are significantly altered downstream of expression. Highlighting the importance of calcium homeostasis in this pathway, overexpressing animals are sensitive to thapsigargin, an ER stressor that inhibits calcium flux from the cytosol to the ER lumen. This calcium/ interaction is solidified by data showing that modulating intracellular calcium with either small molecules or genetics can change expression of and/or interact with to affect lifespan and stress resistance. Further analysis supports a pathway where modulates calcium homeostasis downstream of activating transcription factor-6 ( ), whose knockdown induces and requires expression. Together, our data identify as a longevity-promoting gene whose actions interact with known longevity pathways and calcium homeostasis.

Improving healthspan, defined as the period where organisms live without frailty and/or disease, is a major goal of biomedical research. While healthspan measures in people are relatively easy to identify, developing robust markers of healthspan in model organisms has proven challenging. Studies using the nematode Caenorhabditis elegans have provided vital information on the basic mechanisms of aging; however, worm health is difficult to define, and the impact of interventions that increase lifespan on worm healthspan has been controversial. Here, we describe a marker of population healthspan in C. elegans that we term age-associated vulval integrity defects, or Avid, frequently described elsewhere as rupture or exploding. We connect the presence of this phenotype with temperature, reproduction, diet, and longevity. Our results show that Avid occurs in post-reproductive worms under common laboratory conditions at a frequency that correlates negatively with temperature; Avid is rare in worms kept at 25 °C and more frequent in worms kept at 15 °C. We describe the kinetics of Avid, link the phenotype to oocyte production, and describe how Avid involves the ejection of worm proteins and/or internal organ(s) from the vulva. Finally, we find that Avid is preventable by removing worms from food, suggesting that Avid results from the intake, digestion, and/or absorption of food. Our results show that Avid is a significant cause of death in worm populations maintained under laboratory conditions and that its prevention often correlates with worm longevity. We propose that Avid is a powerful marker of worm healthspan whose underlying molecular mechanisms may be conserved.

Genetically heterogeneous UM-HET3 mice born in 2020 were used to test possible lifespan effects of alpha-ketoglutarate (AKG), 2,4-dinitrophenol (DNP), hydralazine (HYD), nebivolol (NEBI), 16α-hydroxyestriol (OH_Est), and sodium thiosulfate (THIO), and to evaluate the effects of canagliflozin (Cana) when started at 16 months of age. OH_Est produced a 15% increase ( p  = 0.0001) in median lifespan in males but led to a significant (7%) decline in female lifespan. Cana, started at 16 months, also led to a significant increase (14%, p  = 0.004) in males and a significant decline (6%, p  = 0.03) in females. Cana given to mice at 6 months led, as in our previous study, to an increase in male lifespan without any change in female lifespan, suggesting that this agent may lead to female-specific late-life harm. We found that blood levels of Cana were approximately 20-fold higher in aged females than in young males, suggesting a possible mechanism for the sex-specific disparities in its effects. NEBI was also found to produce a female-specific decline (4%, p  = 0.03) in lifespan. None of the other tested drugs provided a lifespan benefit in either sex. These data bring to 7 the list of ITP-tested drugs that induce at least a 10% lifespan increase in one or both sexes, add a fourth drug with demonstrated mid-life benefits on lifespan, and provide a testable hypothesis that might explain the sexual dimorphism in lifespan effects of the SGLT2 inhibitor Cana.

Dietary restriction (DR) and hypoxia (low oxygen) extend lifespan in Caenorhabditis elegans through the induction of a convergent downstream longevity gene, fmo-2 . Flavin-containing monooxygenases (FMOs) are highly conserved xenobiotic-metabolizing enzymes with a clear role in promoting longevity in nematodes and a plausible similar role in mammals. This makes them an attractive potential target of small molecule drugs to stimulate the health-promoting effects of longevity pathways. Here, we utilize an fmo-2 fluorescent transcriptional reporter in C. elegans to screen a set of 80 compounds previously shown to improve stress resistance in mouse fibroblasts. Our data show that 19 compounds significantly induce fmo-2 , and 10 of the compounds induce fmo-2 more than twofold. Interestingly, 9 of the 10 high fmo-2 inducers also extend lifespan in C. elegans . Two of these drugs, mitochondrial respiration chain complex inhibitors, interact with the hypoxia pathway to induce fmo-2 , whereas two dopamine receptor type 2 (DRD2) antagonists interact with the DR pathway to induce fmo-2 , indicating that dopamine signaling is involved in DR-mediated fmo-2 induction. Together, our data identify nine drugs that each (1) increase stress resistance in mouse fibroblasts, (2) induce fmo-2 in C. elegans , and (3) extend nematode lifespan, some through known longevity pathways. These results define fmo-2 induction as a viable approach to identifying and understanding mechanisms of putative longevity compounds.