Ring neurons in the Drosophila central complex act as a rheostat for sensory modulation of aging.

Sensory perception modulates aging, yet we know little about how. An understanding of the neuronal mechanisms through which animals orchestrate biological responses to relevant sensory inputs would provide insight into the control systems that may be important for modulating lifespan. Here, we provide new awareness into how the perception of dead conspecifics, or death perception, which elicits behavioral and physiological effects in many different species, affects lifespan in the fruit fly, Drosophila melanogaster. Previous work demonstrated that cohousing Drosophila with dead conspecifics decreases fat stores, reduces starvation resistance, and accelerates aging in a manner that requires both sight and the serotonin receptor 5-HT2A. In this manuscript, we demonstrate that a discrete, 5-HT2A-expressing neural population in the ellipsoid body (EB) of the Drosophila central complex, identified as R2/R4 neurons, acts as a rheostat and plays an important role in transducing sensory information about the presence of dead individuals to modulate lifespan. Expression of the insulin-responsive transcription factor foxo in R2/R4 neurons and insulin-like peptides dilp3 and dilp5, but not dilp2, are required, with the latter likely altered in median neurosecretory cells (MNCs) after R2/R4 neuronal activation. These data generate new insights into the neural underpinnings of how perceptive events may impact aging and physiology across taxa.

Light modulates Drosophila lifespan via perceptual systems independent of circadian rhythms.

Across taxa, sensory perception modulates aging in response to important ecological cues, including food, sex, and danger. The range of sensory cues involved, and their mechanism of action, are largely unknown. We therefore sought to better understand how one potential cue, that of light, impacts aging in Drosophila melanogaster. In accordance with recently published data, we found that flies lived significantly longer in constant darkness. Extended lifespan was not accompanied by behavioral changes that might indirectly slow aging such as activity, feeding, or fecundity, nor were circadian rhythms necessary for the effect. The lifespans of flies lacking eyes or photoreceptor neurons were unaffected by light kept at normal housing conditions, and transgenic activation of these same neurons was sufficient to phenocopy the effects of environmental light on lifespan. The relationship between light and lifespan was not correlated with its intensity, duration, nor the frequency of light-dark transitions. Furthermore, high-intensity light reduced lifespan in eyeless flies, indicating that the effects we observed were largely independent of the known, non-specific damaging effects associated with light. Our results suggest that much like other environmental cues, light may act as a sensory stimulus to modulate aging.

The serotonin receptor 5-HT2A modulates lifespan and protein feeding in Drosophila melanogaster.

The conserved neurotransmitter serotonin has been shown to be an important modulator of lifespan in specific nutritional contexts; however, it remained unclear how serotonin signaling influences lifespan under normal conditions. Here, we show that serotonin signaling through the 5-HT2A receptor influences lifespan, behavior, and physiology in Drosophila. Loss of the 5-HT2A receptor extends lifespan and induces a resistance to changes in dietary protein that are normally detrimental to lifespan. 5-HT2A -/- null mutant flies also display decreased protein feeding and protein content in the body. Therefore, serotonin signaling through receptor 5-HT2A is likely recruited to promote motivation for protein intake, and chronic reduction of protein-drive through loss of 5-HT2A signaling leads to a lower protein set-point adaptation, which influences physiology, decreases feeding, and increases lifespan. Our findings reveal insights into the mechanisms by which organisms physiologically adapt in response to perceived inability to satisfy demand.

Yeast volatiles double starvation survival in Drosophila.

Organisms make decisions based on the information they gather from their environment, the effects of which affect their fitness. Understanding how these interactions affect physiology may generate interventions that improve the length and quality of life. Here, we provide evidence that exposure to live yeast volatiles during starvation significantly extends survival, increases activity, and slows the rate of triacylglyceride (TAG) decline independent of canonical sensory perception. We demonstrate that ethanol (EtOH) is one of the active components in yeast volatiles that influences these phenotypes and that EtOH metabolites mediate dynamic mechanisms to promote Drosophila survival. Silencing R4d neurons reverses the ability of high EtOH concentrations to promote starvation survival, and their activation promotes EtOH metabolism. The transcription factor foxo promotes EtOH resistance, likely by protection from EtOH toxicity. Our results suggest that food-related cues recruit neural circuits and modulate stress signaling pathways to promote survival during starvation.

High-throughput small molecule screening reveals Nrf2-dependent and -independent pathways of cellular stress resistance.

Aging is the dominant risk factor for most chronic diseases. Development of antiaging interventions offers the promise of preventing many such illnesses simultaneously. Cellular stress resistance is an evolutionarily conserved feature of longevity. Here, we identify compounds that induced resistance to the superoxide generator paraquat (PQ), the heavy metal cadmium (Cd), and the DNA alkylator methyl methanesulfonate (MMS). Some rescue compounds conferred resistance to a single stressor, while others provoked multiplex resistance. Induction of stress resistance in fibroblasts was predictive of longevity extension in a published large-scale longevity screen in Caenorhabditis elegans, although not in testing performed in worms and flies with a more restricted set of compounds. Transcriptomic analysis and genetic studies implicated Nrf2/SKN-1 signaling in stress resistance provided by two protective compounds, cardamonin and AEG 3482. Small molecules identified in this work may represent attractive tools to elucidate mechanisms of stress resistance in mammalian cells.

Neuronal Mechanisms that Drive Organismal Aging Through the Lens of Perception.

Sensory neurons provide organisms with data about the world in which they live, for the purpose of successfully exploiting their environment. The consequences of sensory perception are not simply limited to decision-making behaviors; evidence suggests that sensory perception directly influences physiology and aging, a phenomenon that has been observed in animals across taxa. Therefore, understanding the neural mechanisms by which sensory input influences aging may uncover novel therapeutic targets for aging-related physiologies. In this review, we examine different perceptive experiences that have been most clearly linked to aging or age-related disease: food perception, social perception, time perception, and threat perception. For each, the sensory cues, receptors, and/or pathways that influence aging as well as the individual or groups of neurons involved, if known, are discussed. We conclude with general thoughts about the potential impact of this line of research on human health and aging.

Neuronal-specific proteasome augmentation via Prosß5 overexpression extends lifespan and reduces age-related cognitive decline.

Cognitive function declines with age throughout the animal kingdom, and increasing evidence shows that disruption of the proteasome system contributes to this deterioration. The proteasome has important roles in multiple aspects of the nervous system, including synapse function and plasticity, as well as preventing cell death and senescence. Previous studies have shown neuronal proteasome depletion and inhibition can result in neurodegeneration and cognitive deficits, but it is unclear if this pathway is a driver of neurodegeneration and cognitive decline in aging. We report that overexpression of the proteasome ß5 subunit enhances proteasome assembly and function. Significantly, we go on to show that neuronal-specific proteasome augmentation slows age-related declines in measures of learning, memory, and circadian rhythmicity. Surprisingly, neuronal-specific augmentation of proteasome function also produces a robust increase of lifespan in Drosophila melanogaster. Our findings appear specific to the nervous system; ubiquitous proteasome overexpression increases oxidative stress resistance but does not impact lifespan and is detrimental to some healthspan measures. These findings demonstrate a key role of the proteasome system in brain aging.

Sensory perception of dead conspecifics induces aversive cues and modulates lifespan through serotonin in Drosophila.

Sensory perception modulates health and aging across taxa. Understanding the nature of relevant cues and the mechanisms underlying their action may lead to novel interventions that improve the length and quality of life. We found that in the vinegar fly, Drosophila melanogaster, exposure to dead conspecifics in the environment induced cues that were aversive to other flies, modulated physiology, and impaired longevity. The effects of exposure to dead conspecifics on aversiveness and lifespan required visual and olfactory function in the exposed flies. Furthermore, the sight of dead flies was sufficient to produce aversive cues and to induce changes in the head metabolome. Genetic and pharmacologic attenuation of serotonergic signaling eliminated the effects of exposure on aversiveness and lifespan. Our results indicate that Drosophila have an ability to perceive dead conspecifics in their environment and suggest conserved mechanistic links between neural state, health, and aging; the roots of which might be unearthed using invertebrate model systems.

MicroRNAs mir-184 and let-7 alter Drosophila metabolism and longevity.

MicroRNAs (miRNAs) are small RNA molecules that regulate gene expression associated with many complex biological processes. By comparing miRNA expression between long-lived cohorts of Drosophila melanogaster that were fed a low-nutrient diet with normal-lived control animals fed a high-nutrient diet, we identified miR-184, let-7, miR-125, and miR-100 as candidate miRNAs involved in modulating aging. We found that ubiquitous, adult-specific overexpression of these individual miRNAs led to significant changes in fat metabolism and/or lifespan. Most impressively, adult-specific overexpression of let-7 in female nervous tissue increased median fly lifespan by ~22%. We provide evidence that this lifespan extension is not due to alterations in nutrient intake or to decreased insulin signaling.

Perceptive costs of reproduction drive ageing and physiology in male Drosophila.

Costs of reproduction are thought to result from natural selection optimizing organismal fitness within putative physiological constraints. Phenotypic and population genetic studies of reproductive costs are plentiful across taxa, but an understanding of their mechanistic basis would provide important insight into the diversity in life-history traits, including reproductive effort and ageing. Here, we dissect the causes and consequences of specific costs of reproduction in male Drosophila melanogaster. We find that key survival and physiological costs of reproduction arise from perception of the opposite sex, and they are reversed by the act of mating. In the absence of pheromone perception, males are free from reproductive costs on longevity, stress resistance and fat storage. The costs of perception and the benefits of mating are both mediated by evolutionarily conserved neuropeptidergic signalling molecules, as well as the transcription factor dFoxo. These results provide a molecular framework in which certain costs of reproduction arise as a result of self-imposed 'decisions' in response to perceptive neural circuits, which then orchestrate the control of life-history traits independently of physical or energetic effects associated with mating itself.

Mitochondrial thioredoxin reductase 2 is elevated in long-lived primate as well as rodent species and extends fly mean lifespan.

In a survey of enzymes related to protein oxidation and cellular redox state, we found activity of the redox enzyme thioredoxin reductase (TXNRD) to be elevated in cells from long-lived species of rodents, primates, and birds. Elevated TXNRD activity in long-lived species reflected increases in the mitochondrial form, TXNRD2, rather than the cytosolic forms TXNRD1 and TXNRD3. Analysis of published RNA-Seq data showed elevated TXNRD2 mRNA in multiple organs of longer-lived primates, suggesting that the phenomenon is not limited to skin-derived fibroblasts. Elevation of TXNRD2 activity and protein levels was also noted in liver of three different long-lived mutant mice, and in normal male mice treated with a drug that extends lifespan in males. Overexpression of mitochondrial TXNRD2 in Drosophila melanogaster extended median (but not maximum) lifespan in female flies with a small lifespan extension in males; in contrast, overexpression of the cytosolic form, TXNRD1, did not produce a lifespan extension.

The sensory system: More than just a window to the external world.

While the traditional importance of the sensory system lies in its ability to perceive external information about the world, emerging discoveries suggest that sensory perception has a greater impact on health and longevity than was previously appreciated. These effects are conserved across species. In this mini-review, we discuss the specific sensory cues that have been identified to significantly impact organismal physiology and lifespan. Ongoing work in the aging field has begun to identify the downstream molecules that mediate the broad effects of sensory signals. Candidates include FOXO, neuropeptide F (NPF), adipokinetic hormone (AKH), dopamine, serotonin, and octopamine. We then discuss the many implications that arise from our current understanding of the effects of sensory perception on health and longevity.

Drosophila life span and physiology are modulated by sexual perception and reward.

Sensory perception can modulate aging and physiology across taxa. We found that perception of female sexual pheromones through a specific gustatory receptor expressed in a subset of foreleg neurons in male fruit flies, Drosophila melanogaster, rapidly and reversibly decreases fat stores, reduces resistance to starvation, and limits life span. Neurons that express the reward-mediating neuropeptide F are also required for pheromone effects. High-throughput whole-genome RNA sequencing experiments revealed a set of molecular processes that were affected by the activity of the longevity circuit, thereby identifying new candidate cell-nonautonomous aging mechanisms. Mating reversed the effects of pheromone perception; therefore, life span may be modulated through the integrated action of sensory and reward circuits, and healthy aging may be compromised when the expectations defined by sensory perception are discordant with ensuing experience.

Dynamic changes of territories 17 and 18 during EBV-infection of human lymphocytes.

Interphase chromosomes form distinct spatial domains called chromosome territories (CTs). The arrangement of CTs is non-random and correlated with cellular processes such as differentiation. The purpose of this study is to provide some behavior information of CTs during lymphocyte EBV-infection, which is thought to be a general extra-biological model. Three-dimensional fluorescence in situ hybridization (3D-FISH) was performed on human lymphocytes every 24 h over 96 h periods in EBV-infection. Chromosomes 17 and 18 were selected as target territories for similar size and different gene density. The data indicate that the radial position of territories 17 was altered with time, whereas territories 18 showed relative stable localization. The relative CT volume of CTs 18 to 17 also changed with infection. Our study is the first to examine the timely changes of chromatin positioning and folding in EBV-lymphocyte infection. Dynamic changes in position and folding status of target chromosomes reflected an impact of EBV infection on genome stability.

Transcriptional regulation of the novel Toll-like receptor Tlr13.

Little has been known about Tlr13 (Toll-like receptor 13), a novel member of the Toll-like receptor family. To elucidate the molecular basis of murine Tlr13 gene expression, the activity of the Tlr13 gene promoter was characterized. Reporter gene analysis and electrophoretic mobility shift assays demonstrated that Tlr13 gene transcription was regulated through three cis-acting elements that interacted with the Ets2, Sp1, and PU.1 transcription factors. Furthermore, our work suggests that these transcription factors may cooperate, culminating in maximal transcription of the Tlr13 gene. In contrast, NF-kappaB appeared to act as an inhibitor of Tlr13 transcription. Overexpression of Ets2 caused a strong increase in the transcriptional activity of the Tlr13 promoter; however, overexpression of NF-kappaB p65 dramatically inhibited it. Additionally, interferon-beta is capable of acting Tlr13 transcription, but the activated signaling of lipopolysaccharide/TLR4 and peptidoglycan/TLR2 strongly inhibited the Tlr13 gene promoter. Thus, these findings reveal the mechanism of Tlr13 gene regulation, thereby providing insight into the function of Tlr13 in the immune response to pathogen.

Proteolytic activities of human ADAMTS-5: comparative studies with ADAMTS-4.

Aggrecanases have been characterized as proteinases that cleave the Glu373-Ala374 bond of the aggrecan core protein, and they are multidomain metalloproteinases belonging to the ADAMTS (adamalysin with thrombospondin type 1 motifs) family. The first aggrecanases discovered were ADAMTS-4 (aggrecanase 1) and ADAMTS-5 (aggrecanase 2). They contain a zinc catalytic domain followed by non-catalytic ancillary domains, including a disintegrin domain, a thrombospondin domain, a cysteine-rich domain, and a spacer domain. In the case of ADAMTS-5, a second thrombospondin domain follows the spacer domain. We previously reported that the non-catalytic domains of ADAMTS-4 influence both its extracellular matrix interaction and proteolytic abilities. Here we report the effects of these domains of ADAMTS-5 on the extracellular matrix interaction and proteolytic activities and compare them with those of ADAMTS-4. Although the spacer domain was critical for ADAMTS-4 localization in the matrix, the cysteine-rich domain influenced ADAMTS-5 localization. Similar to previous reports of other ADAMTS family members, very little proteolytic activity was detected with the ADAMTS-5 catalytic domain alone. The sequential inclusion of each carboxyl-terminal domain enhanced its activity against aggrecan, carboxymethylated transferrin, fibromodulin, decorin, biglycan, and fibronectin. Both ADAMTS-4 and -5 had a broad optimal activity at pH 7.0-9.5. Aggrecanolytic activities were sensitive to the NaCl concentration, but activities on non-aggrecan substrates, e.g. carboxymethylated transferrin, were not affected. Although ADAMTS-4 and ADAMTS-5 had similar general proteolytic activities, the aggrecanase activity of ADAMTS-5 was at least 1,000-fold greater than that of ADAMTS-4 under physiological conditions. Our studies suggest that ADAMTS-5 is a major aggrecanase in cartilage metabolism and pathology.

Altered proteolytic activities of ADAMTS-4 expressed by C-terminal processing.

ADAMTS-4 (a disintegrin and metalloprotease with thrombospondin motifs) is a multidomain metalloproteinase belonging to the reprolysin family. The enzyme cleaves aggrecan core protein at several sites. Here we report that the non-catalytic ancillary domains of the enzyme play a major role in regulating aggrecanase activity, with the C-terminal spacer domain masking the general proteolytic activity. Expressing a series of domain deletion mutants in mammalian cells and examining their aggrecan-degrading and general proteolytic activities, we found that full-length ADAMTS-4 of 70 kDa was the most effective aggrecanase, but it exhibited little activity against the Glu(373)-Ala(374) bond, the site originally characterized as a signature of aggrecanase activity. Little activity was detected against reduced and carboxymethylated transferrin (Cm-Tf), a general proteinase substrate. However, it readily cleaved the Glu(1480)-Gly(1481) bond in the chondroitin sulfate-rich region of aggrecan. Of the constructed mutants, the C-terminal spacer domain deletion mutant more effectively hydrolyzed both the Glu(373)-Ala(374) and Glu(1480)-Gly(1481) bonds. It also revealed new activities against Cm-Tf, fibromodulin, and decorin. Further deletion of the cysteine-rich domain reduced the aggrecanase activity by 80% but did not alter the activity against Cm-Tf or fibromodulin. Further removal of the thrombospondin type I domain drastically reduced all tested proteolytic activities, and very limited enzymatic activity was detected with the catalytic domain. Full-length ADAMTS-4 binds to pericellular and extracellular matrix, but deletion of the spacer domain releases the enzyme. ADAMTS-4 lacking the spacer domain has promiscuous substrate specificity considerably different from that previously reported for aggrecan core protein. Finding of ADAMTS-4 in the interleukin-1alpha-treated porcine articular cartilage primarily as a 46-kDa form suggests that it exhibits a broader substrate spectrum in the tissue than originally considered.

TIMP-3 inhibits aggrecanase-mediated glycosaminoglycan release from cartilage explants stimulated by catabolic factors.

Aggrecanases are considered to play a key role in the destruction of articular cartilage during the progression of arthritis. Here we report that the N-terminal inhibitory domain of tissue inhibitor of metalloproteinases 3 (N-TIMP-3), but not TIMP-1 or TIMP-2, inhibits glycosaminoglycan release from bovine nasal and porcine articular cartilage explants stimulated with interleukin-1alpha or retinoic acid in a dose-dependent manner. This inhibition is due to the blocking of aggrecanase activity induced by the catabolic factors. Little apoptosis of primary porcine chondrocytes is observed at an effective concentration of N-TIMP-3. These results suggest that TIMP-3 may be a candidate agent for use against cartilage degradation.

Biodemographic trajectories of age-specific reproliferation from stationary phase in the yeast Saccharomyces cerevisiae seem multiphasic.

Ageing is usually seen as a monotonic decline of functions and survival. However, recent studies reported that age-specific mortality rates increased and then leveled off or even declined at later ages in several species including humans. Preliminary data using the yeast, Saccharomyces cerevisiae, demonstrated an even more complicated, non-monotonic pattern of reproliferation after stationary phase (i.e. the ability of a cell to exit stationary phase and form a colony). In the present article, we conducted a study of the age-specific reproliferation rates of yeast populations. Stationary phase yeast cells were maintained in water and the reproliferation rates were estimated by the number of yeast able to exit stationary phase on rich growth media. We showed that the age-specific reproliferation rates in yeast seem to rise, fall and rise again. Furthermore, we observed this pattern in different experiments and in different genotypes and established that this pattern was not due to genetic heterogeneity of the populations.