Combinatorial interventions in aging

Insight on the underlying mechanisms of aging will advance our ability to extend healthspan, treat age-related pathology and improve quality of life. Multiple genetic and pharmacological manipulations extend longevity in different species, yet monotherapy may be relatively inefficient, and we have limited data on the effect of combined interventions. Here we summarize interactions between age-related pathways and discuss strategies to simultaneously retard these in different organisms. In some cases, combined manipulations additively increase their impact on common hallmarks of aging and lifespan, suggesting they quantitatively participate within the same pathway. In other cases, interactions affect different hallmarks, suggesting their joint manipulation may independently maximize their effects on lifespan and healthy aging. While most interaction studies have been conducted with invertebrates and show varying levels of translatability, the conservation of pro-longevity pathways offers an opportunity to identify 'druggable' targets relevant to multiple human age-associated pathologies.

Stalking the link between reproduction and aging: After decades of research, it still remains a mystery whether and how reproduction drives the process of aging: After decades of research, it still remains a mystery whether and how reproduction drives the process of aging

The hypothesis that aging and number of offspring are linked with each other has attracted much attention and research, but evidence for it remains elusive.

The role of Aβ in Alzheimer's Disease as an Evolutionary Outcome of Optimized Innate Immune Defense

Alzheimer's Disease is a progressive manifestation of aging associated with accumulated Amyloid β. It remains frustratingly unclear why this protein accumulates and how it contributes to Alzheimer's Disease pathology. In one recent hypothesis, Amyloid β is suggested to function as an antimicrobial peptide in innate immune defense within the brain, where Amyloid β gains toxicity when it becomes abundant. This essay proposes an evolutionary explanation for why Amyloid β expression is regulated at an optimum based on its function as a defense and how this leads to disease. Among its potential physiological functions, Amyloid β confers benefits to reduce direct pathogen damage while this simultaneously entails cellular cost of defense. Optimal Amyloid β expression occurs when the gain in fitness from an incremental increase is balanced by the marginal cost of this increase. It proposes that natural selection acting upon the young favored systems to maintain Amyloid β at an optimal level through mechanisms that induce the defense and repress its expression. With age, the force of natural selection declines and permits mechanisms of negative feedback repression to degenerate. Consequently, Amyloid β is expressed beyond its optimum. Age also elevates cumulative pathogen exposure, reduces pathogen barriers and reactivates latent pathogens. The net effect is elevated, chronic induction of Amyloid β in the brain. The model recommends attention to innate immune negative regulation in the brain to discover ways to restore these functions toward a youthful state in the elderly.

Aging modulated by the Drosophila insulin receptor through distinct structure-defined mechanisms

Mutations of the Drosophila melanogaster insulin/IGF signaling system slow aging, while also affecting growth and reproduction. To understand this pleiotropy, we produced an allelic series of single codon substitutions in the Drosophila insulin receptor, InR. We generated InR substitutions using homologous recombination and related each to emerging models of receptor tyrosine kinase structure and function. Three mutations when combined as trans-heterozygotes extended lifespan while retarding growth and fecundity. These genotypes reduced insulin-stimulated Akt phosphorylation, suggesting they impede kinase catalytic domain function. Among these genotypes, longevity was negatively correlated with egg production, consistent with life-history trade-off theory. In contrast, one mutation (InR353) was located in the kinase insert domain, a poorly characterized element found in all receptor tyrosine kinases. Remarkably, wild-type heterozygotes with InR353 robustly extended lifespan without affecting growth or reproduction and retained capacity to fully phosphorylate Akt. The Drosophila insulin receptor kinase insert domain contains a previously unrecognized SH2 binding motif. We propose the kinase insert domain interacts with SH2-associated adapter proteins to affect aging through mechanisms that retain insulin sensitivity and are independent of reproduction.

Cough reflex sensitivity and fractional exhaled nitric oxide in children with asthma

Individual studies have suggested the utility of fractional exhaled nitric oxide (FeNO) measurement in detecting cough-variant asthma and eosinophilic bronchitis in patients with chronic cough. The aim of this study was to clarify a correlation of cough reflex sensitivity and fractional exhaled nitric oxide in asthmatic children. 25 children with asthma and 15 controls were submitted to cough reflex sensitivity measurement - capsaicin aerosol in doubling concentrations (from 0.61 to 1250 micromol/l) was inhaled by a single breath method. Concentrations of capsaicin causing two (C2) and five coughs (C5) were reported. Fractional exhaled nitric oxide (FeNO) measurement was included. Asthmatic children' (11 boys and 14 girls, mean age 9+/-1 years) and control group (unconfirmed diagnosis of asthma) (6 boys and 9 girls, mean age 8+/-1 years) were included into the study. FeNO vs. C2 in asthma (Spearman´s rank correlation: -0.146, p=0.49); FENO vs. C5 in asthma (Spearman´s rank correlation: -0.777, p=0.71). We found that there is no correlation between cough reflex sensitivity and fractional exhaled nitric oxide either in children with asthma or in the control group.

Aging Regulated Through a Stability Model of Insulin/Insulin Growth Factor Receptor Function

Mutations of the insulin-like receptor in Drosophila extend lifespan. New research suggests this receptor operates in two modes. The first extends lifespan while slowing reproduction and reducing growth. The second strongly extends lifespan without impairing growth or reproduction; it confers longevity assurance. The mutation that confers longevity assurance resides in the kinase insert domain, which contains a potential SH2 binding site for substrate proteins. We apply a recent model for the function of receptor tyrosine kinases to propose how insulin receptor structure can modulate aging. This concept hypothesizes that strong insulin-like ligands promote phosphorylation of high threshold substrate binding sites to robustly induce reproduction, which impairs survival as a consequence of trade-offs. Lower levels of receptor stimulation provide less kinase dimer stability, which reduces reproduction and extends lifespan by avoiding reproductive costs. Environmental conditions that favor diapause alter the expression of insulin ligands to further repress the stability of the interacting kinase domains, block phosphorylation of low threshold substrates and thus induce a unique molecular program that confers longevity assurance. Mutations of the insulin receptor that block low-phosphorylation site interactions, such as within the kinase insert domain, can extend lifespan while maintaining overall dimer stability. These flies are long-lived while maintaining reproduction and growth. The kinase insert domain of Drosophila provides a novel avenue from which to seek signaling of the insulin/insulin-like growth factor system of humans that modulate aging without impacting reproduction and growth, or incurring insulin resistance pathology.

Relationship between cough reflex sensitivity and body mass index in children with chronic cough - a pilot study

Obesity is characterized by chronic, low-grade systemic inflammation. Obesity may also be associated with chronic cough. The aim of this pilot study was to clarify relation of cough reflex sensitivity and body mass index (BMI) in children with chronic cough. Altogether 41 children having symptoms of chronic cough were submitted to cough reflex sensitivity measurement. We assessed the relation of cough reflex sensitivity (CKR) due to BMI. Cough reflex sensitivity was defined as the lowest capsaicin concentration which evoked two (C2) or five (C5) coughs. Capsaicin aerosol in doubling concentrations (from 0.61 to 1250 micromol/l) was inhaled by a single breath method (KoKo DigiDoser; nSpire heath Inc, Louisville, CO, USA), modified by the addition of an inspiratory flow regulator valve (RIFR; nSpire heath Inc, Louisville, CO, USA). BMI was calculated. Pulmonary function was within normal range. Concentrations of capsaicin causing two (C2) and five coughs (C5) were reported. Children (22 boys and 19 girls, mean age 6.8 years) cough reflex sensitivity (median, with the Inter-Quartile Range) for C2 was 19.5 (73.4) micromol/l; for C5 it was 78.1 (605.5) micromol/l. We have noticed statistically significant relation of the cough reflex sensitivity (C5) and body mass index (P<0.0001); however, the effect size was small, R2=0.03. Increase of body mass index in one unit is associated with -34.959 micromol/l decrease of C5. We did not find a statistically significant relation between C2 and BMI (P=0.41). The median value of CKR (C2) in boys is not statistically significantly different than the median value of CKR (C2) in girls (P-value 0.5). The median value of CKR (C5) in boys is not statistically significantly different than the median value of CKR (C5) in girls (P-value 0.5). Increase of body mass index in children suffering from chronic cough relates to decrease of cough reflex sensitivity (C5 value).

Extracellular matrix induced by steroids and aging through a G-protein-coupled receptor in a Drosophila model of renal fibrosis

Aldosterone is produced by the mammalian adrenal cortex to modulate blood pressure and fluid balance; however, excessive, prolonged aldosterone promotes fibrosis and kidney failure. How aldosterone triggers disease may involve actions independent of its canonical mineralocorticoid receptor. Here, we present a Drosophila model of renal pathology caused by excess extracellular matrix formation, stimulated by exogenous aldosterone and by insect ecdysone. Chronic administration of aldosterone or ecdysone induces expression and accumulation of collagen-like Pericardin in adult nephrocytes - podocyte-like cells that filter circulating hemolymph. Excess Pericardin deposition disrupts nephrocyte (glomerular) filtration and causes proteinuria in Drosophila, hallmarks of mammalian kidney failure. Steroid-induced Pericardin production arises from cardiomyocytes associated with nephrocytes, potentially reflecting an analogous role of mammalian myofibroblasts in fibrotic disease. Remarkably, the canonical ecdysteroid nuclear hormone receptor, Ecdysone receptor (EcR), is not required for aldosterone or ecdysone to stimulate Pericardin production or associated renal pathology. Instead, these hormones require a cardiomyocyte-associated G-protein-coupled receptor, Dopamine-EcR (DopEcR), a membrane-associated receptor previously characterized in the fly brain to affect behavior. DopEcR in the brain is known to affect behavior through interactions with the Drosophila Epidermal growth factor receptor (Egfr), referred to as dEGFR. Here, we find that the steroids ecdysone and aldosterone require dEGFR in cardiomyocytes to induce fibrosis of the cardiac-renal system. In addition, endogenous ecdysone that becomes elevated with age is found to foster age-associated fibrosis, and to require both cardiomyocyte DopEcR and dEGFR. This Drosophila renal disease model reveals a novel signaling pathway through which steroids may modulate mammalian fibrosis through potential orthologs of DopEcR.

The hidden costs of dietary restriction: Implications for its evolutionary and mechanistic origins

Dietary restriction (DR) extends life span across taxa. Despite considerable research, universal mechanisms of DR have not been identified, limiting its translational potential. Guided by the conviction that DR evolved as an adaptive, pro-longevity physiological response to food scarcity, biomedical science has interpreted DR as an activator of pro-longevity molecular pathways. Current evolutionary theory predicts that organisms invest in their soma during DR, and thus when resource availability improves, should outcompete rich-fed controls in survival and/or reproduction. Testing this prediction in Drosophila melanogaster (N > 66,000 across 11 genotypes), our experiments revealed substantial, unexpected mortality costs when flies returned to a rich diet following DR. The physiological effects of DR should therefore not be interpreted as intrinsically pro-longevity, acting via somatic maintenance. We suggest DR could alternatively be considered an escape from costs incurred under nutrient-rich conditions, in addition to costs associated with DR.

Regulatory Roles of Drosophila Insulin-Like Peptide 1 (DILP1) in Metabolism Differ in Pupal and Adult Stages

The insulin/IGF-signaling pathway is central in control of nutrient-dependent growth during development, and in adult physiology and longevity. Eight insulin-like peptides (DILP1-8) have been identified in Drosophila, and several of these are known to regulate growth, metabolism, reproduction, stress responses, and lifespan. However, the functional role of DILP1 is far from understood. Previous work has shown that dilp1/DILP1 is transiently expressed mainly during the pupal stage and the first days of adult life. Here, we study the role of dilp1 in the pupa, as well as in the first week of adult life, and make some comparisons to dilp6 that displays a similar pupal expression profile, but is expressed in fat body rather than brain neurosecretory cells. We show that mutation of dilp1 diminishes organismal weight during pupal development, whereas overexpression increases it, similar to dilp6 manipulations. No growth effects of dilp1 or dilp6 manipulations were detected during larval development. We next show that dilp1 and dilp6 increase metabolic rate in the late pupa and promote lipids as the primary source of catabolic energy. Effects of dilp1 manipulations can also be seen in the adult fly. In newly eclosed female flies, survival during starvation is strongly diminished in dilp1 mutants, but not in dilp2 and dilp1/dilp2 mutants, whereas in older flies, only the double mutants display reduced starvation resistance. Starvation resistance is not affected in male dilp1 mutant flies, suggesting a sex dimorphism in dilp1 function. Overexpression of dilp1 also decreases survival during starvation in female flies and increases egg laying and decreases egg to pupal viability. In conclusion, dilp1 and dilp6 overexpression promotes metabolism and growth of adult tissues during the pupal stage, likely by utilization of stored lipids. Some of the effects of the dilp1 manipulations may carry over from the pupa to affect physiology in young adults, but our data also suggest that dilp1 signaling is important in metabolism and stress resistance in the adult stage.

Age-Dependent Changes in Transcription Factor FOXO Targeting in Female Drosophila

FOXO transcription factors have long been associated with longevity control and tissue homeostasis. Although the transcriptional regulation of FOXO have been previously characterized (especially in long-lived insulin mutants and under stress conditions), how normal aging impacts the transcriptional activity of FOXO is poorly understood. Here, we conducted a chromatin immunoprecipitation sequencing (ChIP-Seq) analysis in both young (2-week-old) and aged (5-week-old) wild-type female fruit flies, Drosophila melanogaster, to evaluate the dynamics of FOXO gene targeting during aging. Intriguingly, the number of FOXO-bound genes dramatically decreases with age (from 2617 to 224). Consistent to the reduction of FOXO binding activity, many genes targeted by FOXO in young flies are transcriptionally altered with age, either up-regulated (FOXO-repressing genes) or down-regulated (FOXO-activating genes) in adult head tissue. In addition, we show that many FOXO-bound genes in wild-type flies are unique from those in insulin receptor substrate chico mutants. Distinct from chico mutants, FOXO targets specific cellular processes (e.g., actin cytoskeleton) and signaling pathways (e.g., Hippo, MAPK) in young wild-type female flies. FOXO targeting on these pathways decreases with age. Interestingly, FOXO targets in aged flies are enriched in cellular processes like chromatin organization and nucleosome assembly. Furthermore, FOXO binding to core histone genes is well maintained at aged flies. Together, our findings provide new insights into dynamic FOXO targeting under normal aging and highlight the diverse and understudied regulatory mechanisms for FOXO transcriptional activity.

Drosophila insulin-like peptide dilp1 increases lifespan and glucagon-like Akh expression epistatic to dilp2

Insulin/IGF signaling (IIS) regulates essential processes including development, metabolism, and aging. The Drosophila genome encodes eight insulin/IGF‐like peptide (dilp) paralogs, including tandem‐encoded dilp1 and dilp2. Many reports show that longevity is increased by manipulations that decrease DILP2 levels. It has been shown that dilp1 is expressed primarily in pupal stages, but also during adult reproductive diapause. Here, we find that dilp1 is also highly expressed in adult dilp2 mutants under nondiapause conditions. The inverse expression of dilp1 and dilp2 suggests these genes interact to regulate aging. Here, we study dilp1 and dilp2 single and double mutants to describe epistatic and synergistic interactions affecting longevity, metabolism, and adipokinetic hormone (AKH), the functional homolog of glucagon. Mutants of dilp2 extend lifespan and increase Akh mRNA and protein in a dilp1‐dependent manner. Loss of dilp1 alone has no impact on these traits, whereas transgene expression of dilp1 increases lifespan in dilp1 − dilp2 double mutants. On the other hand, dilp1 and dilp2 redundantly or synergistically interact to control circulating sugar, starvation resistance, and compensatory dilp5 expression. These interactions do not correlate with patterns for how dilp1 and dilp2 affect longevity and AKH. Thus, repression or loss of dilp2 slows aging because its depletion induces dilp1, which acts as a pro‐longevity factor. Likewise, dilp2 regulates Akh through epistatic interaction with dilp1. Akh and glycogen affect aging in Caenorhabditis elegans and Drosophila. Our data suggest that dilp2 modulates lifespan in part by regulating Akh, and by repressing dilp1, which acts as a pro‐longevity insulin‐like peptide.

Ecdysone Elicits Chronic Renal Impairment via Mineralocorticoid-Like Pathogenic Activities

BACKGROUND/AIMS

Ecdysteroids are steroidal insect molting hormones that also exist in herbs. Ecdysteroid-containing adaptogens have been popularly used to improve well-being and by bodybuilders for muscle growth. However, the use of ecdysone in mammals is also associated with kidney growth and enlargement, indications of disturbed kidney homeostasis. The underlying pathogenic mechanism remains to be clarified.

METHODS

Virtual screening tools were employed to identify compounds that are homologous to ecdysone and to predict putative ecdysone-interacting proteins. The kidney effect of ecdysone was examined in vitro and in vivo and compared with that of aldosterone. Cellular apoptosis was estimated by terminal deoxynucleotidyl transferase dUTP nick end labeling. Cell motility was assessed by scratch-wound cell migration assay. Blood urea nitrogen was measured to evaluate renal function. Western immunblot analysis was employed to determine the expression profile of interested proteins.

RESULTS

Computational molecular structure analysis revealed that ecdysone is highly homologous to aldosterone. Moreover, virtual screening based on compound-protein interaction profiles identified the Mineralocorticoid Receptor (MR) to potentially interact with ecdysone. Accordingly, to assess potential biological functions of ecdysone in mammals, ecdysone was applied to mineralocorticoid-sensitive inner medullar collecting duct cells. Ecdysone induced mesenchymal accumulation of extracellular matrix and epithelial dedifferentiation characterized by de novo expression of α-smooth muscle actin. In addition, ecdysone elicited cellular apoptosis and retarded cell motility, akin to the effect of aldosterone. In vivo, daily treatment of mice with ecdysone increased cell apoptosis in the kidney, impaired renal function and elicited early signs of renal fibrogenesis, marked by deposition of collagen and fibronectin in tubulointerstitium, reminiscent of the action of aldosterone. The MR signaling pathway is likely responsible for the cellular and pathobiological effects of ecdysone, as evidenced by strong ecdysone-induced MR nuclear translocation in renal tubular cells both in vitro and in vivo, while blockade of MR by concomitant spironolactone treatment largely abolished the detrimental effects of ecdysone.

CONCLUSION

Our findings suggest that ecdysone induces mineralocorticoid-dependent activities that impair renal function and elicit renal injury.

Unraveling the Molecular Mechanism of Immunosenescence in Drosophila

A common feature of the aging process is a decline in immune system performance. Extensive research has sought to elucidate how changes in adaptive immunity contribute to aging and to provide evidence showing that changes in innate immunity have an important role in the overall decline of net immune function. Drosophila is an emerging model used to address questions related to immunosenescence via research that integrates its capacity for genetic dissection of aging with groundbreaking molecular biology related to innate immunity. Herein, we review information on the immunosenescence of Drosophila and suggest its possible mechanisms that involve changes in insulin/IGF(insulin-like growth factor)-1 signaling, hormones such as juvenile hormone and 20-hydroxyecdysone, and feedback system degeneration. Lastly, the emerging role of microbiota on the regulation of immunity and aging in Drosophila is discussed.

Dehydration triggers ecdysone-mediated recognition-protein priming and elevated anti-bacterial immune responses in Drosophila Malpighian tubule renal cells

Background

Drosophila is a powerful model for the study of factors modulating innate immunity. This study examines the effect of water-loss dehydration on innate immune responsiveness in the Drosophila renal system (Malpighian tubules; MTs), and how this leads to elevated host defense and contributes to immunosenescence.

Results

A short period of desiccation-elevated peptidoglycan recognition protein-LC (PGRP-LC) expression in MTs, increased antimicrobial peptide (AMP) gene induction, and protected animals from bacterial infection. We show that desiccation increased ecdysone synthesis in MTs, while inhibition of ecdysone synthesis or ecdysone receptor expression, specifically within MTs, prevented induction of PGRP-LC and reduced protection from bacterial infection. Additionally, aged flies are constitutively water-stressed and have elevated levels of ecdysone and PGRP-LC. Conversely, adults aged at high relative humidity show less water loss and have reduced expression of PGRP-LC and AMPs.

Conclusions

The Drosophila renal system is an important contributor to host defense and can modulate immune responses in an organ autonomous manner, responding to environmental changes such as desiccation. Desiccation primes immune responsiveness by elevating PGRP-LC expression specifically in MTs. In response to desiccation, ecdysone is produced in MTs and acts in a paracrine fashion to increase PGRP-LC expression, immune responsiveness, and improve host defense. This activity of the renal system may contribute to the immunosenescence observed in Drosophila.

Electronic supplementary material

The online version of this article (10.1186/s12915-018-0532-5) contains supplementary material, which is available to authorized users.

Drosophila Insulin-Like Peptides DILP2 and DILP5 Differentially Stimulate Cell Signaling and Glycogen Phosphorylase to Regulate Longevity

Insulin and IGF signaling (IIS) is a complex system that controls diverse processes including growth, development, metabolism, stress responses, and aging. Drosophila melanogaster IIS is propagated by eight Drosophila insulin-like peptides (DILPs), homologs of both mammalian insulin and IGFs, with various spatiotemporal expression patterns and functions. DILPs 1-7 are thought to act through a single Drosophila insulin/IGF receptor, InR, but it is unclear how the DILPs thereby mediate a range of physiological phenotypes. We determined the distinct cell signaling effects of DILP2 and DILP5 stimulation upon Drosophila S2 cells. DILP2 and DILP5 induced similar transcriptional patterns but differed in signal transduction kinetics. DILP5 induced sustained phosphorylation of Akt, while DILP2 produced acute, transient Akt phosphorylation. Accordingly, we used phosphoproteomic analysis to identify distinct patterns of non-genomic signaling induced by DILP2 and DILP5. Across all treatments and replicates, 5,250 unique phosphopeptides were identified, representing 1,575 proteins. Among these peptides, DILP2, but not DILP5, dephosphorylated Ser15 on glycogen phosphorylase (GlyP), and DILP2, but not DILP5, was subsequently shown to repress enzymatic GlyP activity in S2 cells. The functional consequences of this difference were evaluated in adult Drosophila dilp mutants: dilp2 null adults have elevated GlyP enzymatic activity relative to wild type, while dilp5 mutants have reduced GlyP activity. In flies with intact insulin genes, GlyP overexpression extended lifespan in a Ser15 phosphorylation-dependent manner. In dilp2 mutants, that are otherwise long-lived, longevity was repressed by expression of phosphonull GlyP that is enzymatically inactive. Overall, DILP2, unlike DILP5, signals to affect longevity in part through its control of phosphorylation to deactivate glycogen phosphorylase, a central modulator of glycogen storage and gluconeogenesis.

Total Solid-Phase Synthesis of Biologically Active Drosophila Insulin-Like Peptide 2 (DILP2)

In the fruit fly Drosophila melanogaster, there are eight insulin-like peptides (DILPs) with DILPs 1-7 interacting with a sole insulin-like receptor tyrosine kinase (DInR) while DILP8 interacts with a single G protein-coupled receptor (GPCR), Lgr3. Loss-of-function dilp mutation studies show that the neuropeptide DILP2 has a key role in carbohydrate and lipid metabolism as well as longevity and reproduction. A better understanding of the processes whereby DILP2 mediates its specific actions is required. Consequently we undertook to prepare DILP2 as part of a larger, detailed structure-function relationship study. Use of our well-established insulin-like peptide synthesis protocol that entails separate solid phase assembly of each of the A- and B-chains with selective cysteine S-protection followed by sequential S-deprotection and simultaneous disulfide bond formation produced DILP2 in good overall yield and high purity. The synthetic DILP2 was shown to induce significant DInR phosphorylation and downstream signalling, with it being more potent than human insulin. This peptide will be a valuable tool to provide further insights into its binding to the insulin receptor, the subsequent cell signalling and role in insect metabolism.

Reproduction regulates Drosophila nutrient intake through independent effects of egg production and sex peptide: Implications for aging

BACKGROUND: The ratio of protein to carbohydrate (P:C) consumed influences reproduction and lifespan, outcomes that are often maximized by different P:C intake.

OBJECTIVE: Determine if reproduction in female Drosophila drives elevated P:C intake. Distinguish whether such a preference is driven by egg production or from male-derived sex peptides in seminal fluid.

METHODS: Intake of protein and carbohydrate was measured in a diet-choice assay. Macronutrient intake was calculated for mated and unmated fertile females, mated and unmated sterile females, and both types of female when mated to wildtype males and to males lacking sex peptide.

RESULTS: Mated females have high P:C intake relative to unmated females and mated, sterile females. Fertile females mated to wildtype males and to males lacking sex peptide have high P:C intake, but sterile females have similar, low P:C intake when unmated and when mated to males lacking sex peptide.

CONCLUSIONS: The metabolic demands of egg production and sex peptides are individually sufficient to drive elevated P:C intake in adult female Drosophila. Reproductive state can thus modulate how animals consume macronutrients, which in turn can impact their health and aging.

Studies on the regulation of transient lower esophageal sphincter relaxations (TLESRs) by acid in the esophagus and stomach

Transient lower esophageal sphincter relaxation (TLESR) is the major mechanism of gastroesophageal reflux, but the regulation of TLESR by stimuli in the esophagus is incompletely understood. We have recently reported that acid infusion in the esophagus substantially (by 75%) increased the number of meal-induced TLESR in healthy subjects. We concluded that the TLESR reflex triggered by gastric distention with meal was enhanced by the stimulation of esophageal nerves by acid. However, the possibilities that the acid infused into the esophagus acts after passing though lower esophageal sphincter in stomach to enhance TLESR, or that the acid directly initiates TLESR from the esophagus were not addressed. Here, we evaluated the effect of acid infusion into the proximal stomach on meal-induced TLESR (study 1) and the ability of acid infusion into the esophagus to initiate TLESR without prior meal (study 2). We analyzed TLESRs by using high-resolution manometry in healthy subjects in paired randomized studies. In study 1, we found that acid infusion into the proximal stomach did not affect TLESRs induced by standard meal. The number of meal-induced TLESRs following the acid infusion into the proximal stomach was similar to the number of meal-induced TLESRs following the control infusion. In study 2, we found that acid infusion into the esophagus without prior meal did not initiate TLESRs. We conclude that the increase in the meal-induced TLESRs by acid in the esophagus demonstrated in our previous study is not attributable to the action of acid in the stomach or to direct initiation of TLESR from the esophagus by acid. Our studies are consistent with the concept that the stimuli in the esophagus can influence TLESRs. The enhancement of TLESR by acid in the esophagus may contribute to pathogenesis of gastroesophageal reflux in some patients.

Nutritional Geometric Profiles of Insulin/IGF Expression in Drosophila melanogaster

Insulin/IGF signaling (IIS) in Drosophila melanogaster is propagated by eight Drosophila insulin-like peptides (dilps) and is regulated by nutrition. To understand how dietary protein and sugar affect dilp expression, we followed the analytical concepts of the Nutritional Geometric Framework, feeding Drosophila adults media comprised of seven protein-to-carbohydrate ratios at four caloric concentrations. Transcript levels of all dilps and three IIS-regulated genes were measured. Each dilp presented a unique pattern upon a bivariate plot of sugar and protein. Dilp2 expression was greatest upon diets with low protein-to-carbohydrate ratio regardless of total caloric value. Dilp5 expression was highly expressed at approximately a 1:2 protein-to-carbohydrate ratio and its level increased with diet caloric content. Regression analysis revealed that protein-to-carbohydrate ratio and the interaction between this ratio and caloric content significantly affects dilp expression. The IIS-regulated transcripts 4eBP and InR showed strikingly different responses to diet composition: 4eBP was minimally expressed except when elevated at low caloric diets. InR expression increased with protein level, independent of caloric content. Values of published life history traits measured on similar diets revealed correlations between egg production and the expression of dilp8 4eBP, while low protein-to-carbohydrate ratio diets associated with long lifespan correlated with elevated dilp2. Analyzing how nutient composition associates with dilp expression and IIS reveals that nutritional status is modulated by different combinations of insulin-like peptides, and these features variously correlate to IIS-regulated life history traits.

Mechanisms of the adenosine A2A receptor-induced sensitization of esophageal C fibers

Clinical studies indicate that adenosine contributes to esophageal mechanical hypersensitivity in some patients with pain originating in the esophagus. We have previously reported that the esophageal vagal nodose C fibers express the adenosine A2A receptor. Here we addressed the hypothesis that stimulation of the adenosine A2A receptor induces mechanical sensitization of esophageal C fibers by a mechanism involving transient receptor potential A1 (TRPA1). Extracellular single fiber recordings of activity originating in C-fiber terminals were made in the ex vivo vagally innervated guinea pig esophagus. The adenosine A2A receptor-selective agonist CGS21680 induced robust, reversible sensitization of the response to esophageal distention (10-60 mmHg) in a concentration-dependent fashion (1-100 nM). At the half-maximally effective concentration (EC50: ≈3 nM), CGS21680 induced an approximately twofold increase in the mechanical response without causing an overt activation. This sensitization was abolished by the selective A2A antagonist SCH58261. The adenylyl cyclase activator forskolin mimicked while the nonselective protein kinase inhibitor H89 inhibited mechanical sensitization by CGS21680. CGS21680 did not enhance the response to the purinergic P2X receptor agonist α,β-methylene-ATP, indicating that CGS21680 does not nonspecifically sensitize to all stimuli. Mechanical sensitization by CGS21680 was abolished by pretreatment with two structurally different TRPA1 antagonists AP18 and HC030031. Single cell RT-PCR and whole cell patch-clamp studies in isolated esophagus-specific nodose neurons revealed the expression of TRPA1 in A2A-positive C-fiber neurons and demonstrated that CGS21682 potentiated TRPA1 currents evoked by allylisothiocyanate. We conclude that stimulation of the adenosine A2A receptor induces mechanical sensitization of nodose C fibers by a mechanism sensitive to TRPA1 antagonists indicating the involvement of TRPA1.

Tequila Regulates Insulin-Like Signaling and Extends Life Span in Drosophila melanogaster

The aging process is a universal phenomenon shared by all living organisms. The identification of longevity genes is important in that the study of these genes is likely to yield significant insights into human senescence. In this study, we have identified Tequila as a novel candidate gene involved in the regulation of longevity in Drosophila melanogaster. We have found that a hypomorphic mutation of Tequila (Teq(f01792)), as well as cell-specific downregulation of Tequila in insulin-producing neurons of the fly, significantly extends life span. Tequila deficiency-induced life-span extension is likely to be associated with reduced insulin-like signaling, because Tequila mutant flies display several common phenotypes of insulin dysregulation, including reduced circulating Drosophila insulin-like peptide 2 (Dilp2), reduced Akt phosphorylation, reduced body size, and altered glucose homeostasis. These observations suggest that Tequila may confer life-span extension by acting as a modulator of Drosophila insulin-like signaling.

Acid infusion into the esophagus increases the number of meal-induced transient lower esophageal sphincter relaxations (TLESRs) in healthy volunteers

BACKGROUND

Transient lower esophageal sphincter relaxation (TLESR) is the major mechanism of gastroesophageal reflux (GER) but the regulation of TLESR by stimuli in the esophagus is incompletely understood. If stimuli in the esophagus can influence TLESR, then such regulation may perpetuate or limit GER. We addressed the hypothesis that acid in the esophagus enhances TLESRs.

METHODS

We evaluated the effect of acid infusion into the distal esophagus on TLESRs evoked by a standard meal in a paired randomized study in healthy subjects. TLESRs were evaluated by using high resolution manometry (HRM).

KEY RESULTS

We found that acid in the esophagus enhanced meal-induced TLESRs. Compared to control infusion the number of TLESRs (median [interquartile range]) was increased during 2 h following the acid infusion (11 [9-14] vs 17 [12.5-20], p < 0.01). The average duration of individual TLESRs was not affected. The time-course analysis revealed that a robust increase in TLESRs occurred already in the first hour when the number of TLESRs nearly doubled (6 [5.5-7.5] vs 11 [7.5-12.5], p < 0.05). In contrast to the enhancement of TLESRs, the number of swallows was not changed.

CONCLUSIONS & INFERENCES

The acid infusion into the esophagus increases the number of meal-induced TLESRs in healthy subjects. Our results provide evidence for the concept that the stimuli in the esophagus can influence TLESRs. The regulation of TLESR by stimuli in the esophagus may contribute to pathogenesis of GER in some patients.

Nutrient control of Drosophila longevity

Dietary restriction (DR) extends the lifespan of many animals, including Drosophila melanogaster. Recent work with flies shows that longevity is controlled by the ratio of consumed protein relative to carbohydrates. Given that reduced insulin and/or insulin-like growth factor (IGF) and target of rapamycin (TOR) signaling increase Drosophila lifespan, these pathways are candidate mediators of DR. However, this idea has ambiguous experimental support. The Nutritional Geometric Framework (NGF), which dissects the impact of nutrient protein relative to carbohydrates, may provide an approach to resolving the roles for these pathways in DR. Nutrient sensing of protein and carbohydrate may occur in the fat body through signals to hypothalamic-like neurons in the fly brain and, thus, control secretion of insulin-like peptides that regulate longevity.

Transcriptional response to dietary restriction in Drosophila melanogaster

Dietary restriction (DR) extends lifespan in a wide variety of organisms. Although several genes and pathways associated with this longevity response have been identified, the specific mechanism through which DR extends lifespan is not fully understood. We have recently developed a novel methodology to screen for transcriptional changes in response to acutely imposed DR upon adult Drosophila melanogaster and identified groups of genes that switch their transcriptional patterns from a normal diet pattern to a restricted diet pattern, or 'switching genes'. In this current report we extend our transcriptional data analysis with gene set enrichment analysis to generate a pathway-centered perspective. The pattern of temporal behavior in response to the diet switch is strikingly similar within and across pathways associated with mRNA processing and protein translation. Furthermore, most genes within these pathways display an initial spike in activity within 6-8h from the diet switch, followed by a coordinated, partial down-regulation after 24h. We propose this represents a stereotypical response to DR, which ultimately leads to a mild but widespread inhibition of transcriptional and translational activity. Inhibition of the protein synthesis pathway has been observed in DR in other studies and has been shown to extend lifespan in several model organisms.

Activin signaling targeted by insulin/dFOXO regulates aging and muscle proteostasis in Drosophila

Reduced insulin/IGF signaling increases lifespan in many animals. To understand how insulin/IGF mediates lifespan in Drosophila, we performed chromatin immunoprecipitation-sequencing analysis with the insulin/IGF regulated transcription factor dFOXO in long-lived insulin/IGF signaling genotypes. Dawdle, an Activin ligand, is bound and repressed by dFOXO when reduced insulin/IGF extends lifespan. Reduced Activin signaling improves performance and protein homeostasis in muscles of aged flies. Activin signaling through the Smad binding element inhibits the transcription of Autophagy-specific gene 8a (Atg8a) within muscle, a factor controlling the rate of autophagy. Expression of Atg8a within muscle is sufficient to increase lifespan. These data reveal how insulin signaling can regulate aging through control of Activin signaling that in turn controls autophagy, representing a potentially conserved molecular basis for longevity assurance. While reduced Activin within muscle autonomously retards functional aging of this tissue, these effects in muscle also reduce secretion of insulin-like peptides at a distance from the brain. Reduced insulin secretion from the brain may subsequently reinforce longevity assurance through decreased systemic insulin/IGF signaling.

It is widely known that reduced insulin/IGF signaling slows aging in many contexts. This process requires the forkhead transcription factor (FOXO). FOXO modulates the expression of many genes, and the list of those associated with slow aging is impressive. But there are few data indicating the mechanisms or genes through which FOXO actually slows aging. Here, we identify a novel FOXO target, dawdle, the Activin-like ligand in fruit flies. We show that down-regulation of Activin signaling in muscle, but not in adipose tissue, leads to extended lifespan. In part it does so when it alleviates the negative transcriptional repression of its Smox transcription factor (a Smad transcription factor) upon a keystone autophagy gene, Atg8a. This double signaling cascade autonomously improves muscle performance (measured at cellular and functional levels) and nonautonomously extends lifespan as it reduces the secretion of insulin peptides from the brain. The work develops the emerging model for interacting autonomous-nonautonomous roles of insulin/IGF signaling as a systems integrative mechanism of aging control.

The effects of nasal irritant induced responses on breathing and cough in anaesthetized and conscious animal models

There is little evidence to support the down-regulation of coughing from the nose. The cough response to citric acid (CA) was studied in anesthetized and conscious guinea pigs after nasal pretreatment with saline, 1% DMSO, allylisothiocyanate (TRPA1 agonist) and allylisothiocyanate +AP-18 (TRPA1 antagonist). Cough was induced by adding citric acid (CA) to the tracheal perfusion in anaesthetized animals, or by inhaling 0.4M CA in conscious animals. The cough response was counted from the dose response curves, airflow traces and cough sound analysis. In conscious animals, nasal allylisothiocyanate induced reproducible, dose dependent nasal symptoms and a significant drop in respiratory rate. Cough induced by CA was suppressed after nasal allylisothiocyanate (p<0.05), and this effect was prevented by AP-18 (1mM). In anaesthetized animals, nasal allylisothiocyanate induced a significant drop in respiratory rate. Cough induced subsequently by CA was suppressed when compared to baseline and vehicle responses (p<0.05). The reasons for the suppression of CA induced cough by TRPA1 agonist applied to the nose are not clear and remain to be elucidated.

Juvenile hormone regulation of Drosophila aging

Background

Juvenile hormone (JH) has been demonstrated to control adult lifespan in a number of non-model insects where surgical removal of the corpora allata eliminates the hormone’s source. In contrast, little is known about how juvenile hormone affects adult Drosophila melanogaster. Previous work suggests that insulin signaling may modulate Drosophila aging in part through its impact on juvenile hormone titer, but no data yet address whether reduction of juvenile hormone is sufficient to control Drosophila life span. Here we adapt a genetic approach to knock out the corpora allata in adult Drosophila melanogaster and characterize adult life history phenotypes produced by reduction of juvenile hormone. With this system we test potential explanations for how juvenile hormone modulates aging.

Results

A tissue specific driver inducing an inhibitor of a protein phosphatase was used to ablate the corpora allata while permitting normal development of adult flies. Corpora allata knockout adults had greatly reduced fecundity, inhibited oogenesis, impaired adult fat body development and extended lifespan. Treating these adults with the juvenile hormone analog methoprene restored all traits toward wildtype. Knockout females remained relatively long-lived even when crossed into a genotype that blocked all egg production. Dietary restriction further extended the lifespan of knockout females. In an analysis of expression profiles of knockout females in fertile and sterile backgrounds, about 100 genes changed in response to loss of juvenile hormone independent of reproductive state.

Conclusions

Reduced juvenile hormone alone is sufficient to extend the lifespan of Drosophila melanogaster. Reduced juvenile hormone limits reproduction by inhibiting the production of yolked eggs, and this may arise because juvenile hormone is required for the post-eclosion development of the vitellogenin-producing adult fat body. Our data do not support a mechanism for juvenile hormone control of longevity simply based on reducing the physiological costs of egg production. Nor does the longevity benefit appear to function through mechanisms by which dietary restriction extends longevity. We identify transcripts that change in response to juvenile hormone independent of reproductive state and suggest these represent somatically expressed genes that could modulate how juvenile hormone controls persistence and longevity.

Ecdysone triggered PGRP-LC expression controls Drosophila innate immunity

Throughout the animal kingdom, steroid hormones have been implicated in the defense against microbial infection, but how these systemic signals control immunity is unclear. Here, we show that the steroid hormone ecdysone controls the expression of the pattern recognition receptor PGRP-LC in Drosophila, thereby tightly regulating innate immune recognition and defense against bacterial infection. We identify a group of steroid-regulated transcription factors as well as two GATA transcription factors that act as repressors and activators of the immune response and are required for the proper hormonal control of PGRP-LC expression. Together, our results demonstrate that Drosophila use complex mechanisms to modulate innate immune responses, and identify a transcriptional hierarchy that integrates steroid signalling and immunity in animals.