A plant virus manipulates the long-winged morph of insect vectors.

Wing dimorphism of insect vectors is a determining factor for viral long-distance dispersal and large-area epidemics. Although plant viruses affect the wing plasticity of insect vectors, the potential underlying molecular mechanisms have seldom been investigated. Here, we found that a planthopper-vectored rice virus, rice stripe virus (RSV), specifically induces a long-winged morph in male insects. The analysis of field populations demonstrated that the long-winged ratios of male insects are closely associated with RSV infection regardless of viral titers. A planthopper-specific and testis-highly expressed gene, Encounter, was fortuitously found to play a key role in the RSV-induced long-winged morph. Encounter resembles malate dehydrogenase in the sequence, but it does not have corresponding enzymatic activity. Encounter is upregulated to affect male wing dimorphism at early larval stages. Encounter is closely connected with the insulin/insulin-like growth factor signaling pathway as a downstream factor of Akt, of which the transcriptional level is activated in response to RSV infection, resulting in the elevated expression of Encounter. In addition, an RSV-derived small interfering RNA directly targets Encounter to enhance its expression. Our study reveals an unreported mechanism underlying the direct regulation by a plant virus of wing dimorphism in its insect vectors, providing the potential way for interrupting viral dispersal.

Queen bee gut microbiota extends honeybee lifespan by inhibiting insulin signaling.

Queen and worker bees are natural models for aging research, as their lifespans vary considerably independent of genetic variation. Investigating the reasons why queens live longer than workers is of great significance for research on the universal processes of aging in animals. The gut microbiome has received attention as a vital regulator of host health, while its precise role in honeybee aging needs further investigation. The effects and mechanisms behind the relationship between gut microbiota and worker lifespan were measured by transplanting queen bee gut bacteria (QG) and worker bee gut bacteria (WG) into microbiota-free (MF) workers. The transplantation of QG to MF bees significantly extended the workers' lifespans compared with MF and WG bees. Untargeted metabolomics identified 49 lifespan-related differential metabolites, and Kyoto Encyclopedia of Genes and Genomes analysis of these revealed three lifespan-related metabolic pathways: insulin/insulin-like growth factor signaling, immune, and ketone body metabolism pathways. Further verification showed that QG inhibited the expression of insulin-like peptides (ILPs), and the expression of ILPs was lower in natural queens than in natural workers. QG transplantation also stimulated the expression of antioxidant genes and lowered oxidative damage products in natural queen bees. However, gut microbiota transplantation failed to mimic the immune properties and ketone body metabolism profiles of natural queens and workers. Concisely, QG could increase the antioxidant capacity to extend lifespan by inhibiting insulin signaling. These findings may help determine the mechanisms behind queen longevity and provide further insights into the role of gut symbionts. IMPORTANCE: Queen and worker bees share the same genetic background but have vastly different lifespans. The gut microbiome regulates host health, suggesting that differences in lifespan between queen and worker bees could be related to gut bacteria. Herein, we used an innovative method to transplant gut microbiota from adult queen or worker bees to microbiota-free bees. The transplantation of queen gut microbiota to microbiota-free bees extended their lifespan. Insulin/insulin-like growth factor signaling, a highly conserved metabolic pathway related to lifespan, displayed identical expression profiles in natural queen bees and microbiota-free bees transplanted with queen microbiota. This finding significantly expands our understanding of the relationships between intestinal bacteria, host health, and the biology of aging.

The insulin signaling pathway in Drosophila melanogaster: A nexus revealing an "Achilles' heel" in DDT resistance.

Insecticide resistance is an ongoing challenge in agriculture and disease vector control. Here, we demonstrate a novel strategy to attenuate resistance. We used genomics tools to target fundamental energy-associated pathways and identified a potential "Achilles' heel" for resistance, a resistance-associated protein that, upon inhibition, results in a substantial loss in the resistance phenotype. Specifically, we compared the gene expression profiles and structural variations of the insulin/insulin-like growth factor signaling (IIS) pathway genes in DDT-susceptible (91-C) and -resistant (91-R) Drosophila melanogaster (Drosophila) strains. A total of eight and seven IIS transcripts were up- and down-regulated, respectively, in 91-R compared to 91-C. A total of 114 nonsynonymous mutations were observed between 91-C and 91-R, of which 51.8% were fixed. Among the differentially expressed transcripts, phosphoenolpyruvate carboxykinase (PEPCK), down-regulated in 91-R, encoded the greatest number of amino acid changes, prompting us to perform PEPCK inhibitor-pesticide exposure bioassays. The inhibitor of PEPCK, hydrazine sulfate, resulted in a 161- to 218-fold decrease in the DDT resistance phenotype (91-R) and more than a 4- to 5-fold increase in susceptibility in 91-C. A second target protein, Glycogen synthase kinase 3ß (GSK3ß-PO), had one amino acid difference between 91-C and 91-R, and the corresponding transcript was also down-regulated in 91-R. A GSK3ß-PO inhibitor, lithium chloride, likewise reduced the resistance but to a lesser extent than did hydrazine sulfate for PEPCK. We demonstrate the potential role of IIS genes in DDT resistance and the potential discovery of an "Achilles' heel" against pesticide resistance in this pathway.

Peroxisome proliferator-activated receptor γ regulates genes involved in insulin/insulin-like growth factor signaling and lipid metabolism during adipogenesis through functionally distinct enhancer classes.

The nuclear receptor peroxisome proliferator-activated receptor (PPAR) is a transcription factor whose expression is induced during adipogenesis and that is required for the acquisition and control of mature adipocyte functions. Indeed, PPAR induces the expression of genes involved in lipid synthesis and storage through enhancers activated during adipocyte differentiation. Here, we show that PPAR also binds to enhancers already active in preadipocytes as evidenced by an active chromatin state including lower DNA methylation levels despite higher CpG content. These constitutive enhancers are linked to genes involved in the insulin/insulin-like growth factor signaling pathway that are transcriptionally induced during adipogenesis but to a lower extent than lipid metabolism genes, because of stronger basal expression levels in preadipocytes. This is consistent with the sequential involvement of hormonal sensitivity and lipid handling during adipocyte maturation and correlates with the chromatin structure dynamics at constitutive and activated enhancers. Interestingly, constitutive enhancers are evolutionary conserved and can be activated in other tissues, in contrast to enhancers controlling lipid handling genes whose activation is more restricted to adipocytes. Thus, PPAR utilizes both broadly active and cell type-specific enhancers to modulate the dynamic range of activation of genes involved in the adipogenic process.

Local requirement of the Drosophila insulin binding protein imp-L2 in coordinating developmental progression with nutritional conditions.

In Drosophila, growth takes place during the larval stages until the formation of the pupa. Starvation delays pupariation to allow prolonged feeding, ensuring that the animal reaches an appropriate size to form a fertile adult. Pupariation is induced by a peak of the steroid hormone ecdysone produced by the prothoracic gland (PG) after larvae have reached a certain body mass. Local downregulation of the insulin/insulin-like growth factor signaling (IIS) activity in the PG interferes with ecdysone production, indicating that IIS activity in the PG couples the nutritional state to development. However, the underlying mechanism is not well understood. In this study we show that the secreted Imaginal morphogenesis protein-Late 2 (Imp-L2), a growth inhibitor in Drosophila, is involved in this process. Imp-L2 inhibits the activity of the Drosophila insulin-like peptides by direct binding and is expressed by specific cells in the brain, the ring gland, the gut and the fat body. We demonstrate that Imp-L2 is required to regulate and adapt developmental timing to nutritional conditions by regulating IIS activity in the PG. Increasing Imp-L2 expression at its endogenous sites using an Imp-L2-Gal4 driver delays pupariation, while Imp-L2 mutants exhibit a slight acceleration of development. These effects are strongly enhanced by starvation and are accompanied by massive alterations of ecdysone production resulting most likely from increased Imp-L2 production by neurons directly contacting the PG and not from elevated Imp-L2 levels in the hemolymph. Taken together our results suggest that Imp-L2-expressing neurons sense the nutritional state of Drosophila larvae and coordinate dietary information and ecdysone production to adjust developmental timing under starvation conditions.

The effect of intermittent fasting on preventing obesity-related early aging from a molecular and cellular perspective.

Obesity is a global health concern owing to its association with numerous degenerative diseases and the fact that it may lead to early aging. Various markers of aging, including telomere attrition, epigenetic alterations, altered protein homeostasis, mitochondrial dysfunction, cellular senescence, stem cell disorders, and intercellular communication, are influenced by obesity. Consequently, there is a critical need for safe and effective approaches to prevent obesity and mitigate the onset of premature aging. In recent years, intermittent fasting (IF), a dietary strategy that alternates between periods of fasting and feeding, has emerged as a promising dietary strategy that holds potential in counteracting the aging process associated with obesity. This article explores the molecular and cellular mechanisms through which IF affects obesity-related early aging. IF regulates various physiological processes and organ systems, including the liver, brain, muscles, intestines, blood, adipose tissues, endocrine system, and cardiovascular system. Moreover, IF modulates key signaling pathways such as AMP-activated protein kinase (AMPK), sirtuins, phosphatidylinositol 3-kinase (PI3K)/Akt, mammalian target of rapamycin (mTOR), and fork head box O (FOXO). By targeting these pathways, IF has the potential to attenuate aging phenotypes associated with obesity-related early aging. Overall, IF offers promising avenues for promoting healthier lifestyles and mitigating the premature aging process in individuals affected by obesity.

Functional evaluation of the insulin/insulin-like growth factor signaling pathway in determination of wing polyphenism in pea aphid.

Wing polyphenism is a common phenomenon that plays key roles in environmental adaptation of insects. Insulin/insulin-like growth factor signaling (IIS) pathway is a highly conserved pathway in regulation of metabolism, development, and growth in metazoans. It has been reported that IIS is required for switching of wing morph in brown planthopper via regulating the development of the wing pad. However, it remains elusive whether and how IIS pathway regulates transgenerational wing dimorphism in aphid. In this study, we found that pairing and solitary treatments can induce pea aphids to produce high and low percentage winged offspring, respectively. The expression level of ILP5 (insulin-like peptide 5) in maternal head was significantly higher upon solitary treatment in comparison with pairing, while silencing of ILP5 caused no obvious change in the winged offspring ratio. RNA interference-mediated knockdown of FoxO (Forkhead transcription factor subgroup O) in stage 20 embryos significantly increased the winged offspring ratio. The results of pharmacological and quantitative polymerase chain reaction experiments showed that the embryonic insulin receptors may not be involved in wing polyphenism. Additionally, ILP4 and ILP11 exhibited higher expression levels in 1st wingless offspring than in winged offspring. We demonstrate that FoxO negatively regulates the wing morph development in embryos. ILPs may regulate aphid wing polyphenism in a developmental stage-specific manner. However, the regulation may be not mediated by the canonical IIS pathway. The findings advance our understanding of IIS pathway in insect transgenerational wing polyphenism.

Tangeretin promotes lifespan associated with insulin/insulin-like growth factor-1 signaling pathway and heat resistance in Caenorhabditis elegans.

Tangeretin is a polymethoxylated flavonoid naturally occurred in citrus fruits with many pharmacological activities, such as anti-inflammatory, antiproliferative, and neuroprotective properties. A previous study reported that tangeretin-enriched orange extract could prolong the lifespan in Caenorhabditis elegans. However, the antiaging effect of tangeretin remains uncertain. In this study, we used the model organism C. elegans to conduct a lifespan test, observed the aging-related functional changes of nematodes, the fluorescence changes of stress-related proteins (DAF-16 and HSP-16.2) and its response to stress assay, and monitored the effect of tangeretin on the mRNA expression levels. The results showed that tangeretin supplementation (30 and 100 µM) extended the mean lifespan, slowed aging-related functional declines, and increased the resistance against heat-shock stress. Furthermore, tangeretin upregulated the mRNA expression of daf-16, hsp-16.2, and hsp-16.49, promoted the nuclear localization of DAF-16, and enhanced the fluorescence intensity of HSP-16.2, while it had no effect on the lifespan of daf-2, age-1, and daf-16 mutants. The current findings suggest that tangeretin can significantly extend the lifespan and enhance heat stress tolerance in an insulin/insulin-like growth factor signaling dependent manner.

Effects of INSR genetic polymorphism on hippocampal volume and episodic memory in chinese type 2 diabetes.

AIMS: We aimed to investigate the effect of the type 2 diabetes-specific insulin/IGF signaling genetic variants on the hippocampal volume and their relationships with episodic memory in Chinese patients with type 2 diabetes. METHODS: Analysis of variance was used to evaluate the genotype-by-diagnosis interaction effect on hippocampal volume in Chinese participants (109 patients with type 2 diabetes, 116 healthy controls). Mediation analysis was performed to test whether the hippocampal volume would mediate the association between genotype and episodic memory in patients with type 2 diabetes. RESULTS: INSR (rs8101064) exhibited a significant genotype-by-diagnosis interaction effect on the bilateral hippocampal volumes (left, P = 0.020; right, P = 0.004, PFDR < 0.05). The T allele carriers exhibited smaller bilateral hippocampal volumes than the CC homozygotes in patients with type 2 diabetes (left, P = 0.004; right, P = 0.002). Mediation analysis revealed the significant mediation effect of the left hippocampal volume on the association between INSR (rs8101064) genetic polymorphism and the short- and long-term memory scores in patients with type 2 diabetes (short-term memory: 95% CI, -2.716, -0.266; long-term memory: 95% CI, -0.823, -0.103). CONCLUSIONS: Hyperglycemia exposure and INSR (rs8101064) genetic polymorphism had an interaction effect on the hippocampal volume, and the T allele of the INSR (rs8101064) may serve as a risk factor for the decreased hippocampal volume in Chinese patients with type 2 diabetes. The left hippocampal volume mediated the effect of INSR (rs8101064) genetic polymorphism on episodic memory in Chinese patients with type 2 diabetes, which provided a biological pathway for understanding how the INSR (rs8101064) genetic polymorphism affects episodic memory in type 2 diabetes.

Stage-Specific Plasticity in Ovary Size Is Regulated by Insulin/Insulin-Like Growth Factor and Ecdysone Signaling in Drosophila.

Animals from flies to humans adjust their development in response to environmental conditions through a series of developmental checkpoints, which alter the sensitivity of organs to environmental perturbation. Despite their importance, we know little about the molecular mechanisms through which this change in sensitivity occurs. Here we identify two phases of sensitivity to larval nutrition that contribute to plasticity in ovariole number, an important determinant of fecundity, in Drosophila melanogaster. These two phases of sensitivity are separated by the developmental checkpoint called "critical weight"; poor nutrition has greater effects on ovariole number in larvae before critical weight than after. We find that this switch in sensitivity results from distinct developmental processes. In precritical weight larvae, poor nutrition delays the onset of terminal filament cell differentiation, the starting point for ovariole development, and strongly suppresses the rate of terminal filament addition and the rate of increase in ovary volume. Conversely, in postcritical weight larvae, poor nutrition affects only the rate of increase in ovary volume. Our results further indicate that two hormonal pathways, the insulin/insulin-like growth factor and the ecdysone-signaling pathways, modulate the timing and rates of all three developmental processes. The change in sensitivity in the ovary results from changes in the relative contribution of each pathway to the rates of terminal filament addition and increase in ovary volume before and after critical weight. Our work deepens our understanding of how hormones act to modify the sensitivity of organs to environmental conditions, thereby affecting their plasticity.

The cell cycle- and insulin-signaling-inhibiting miRNA expression pattern of very small embryonic-like stem cells contributes to their quiescent state.

Murine Oct4(+), very small embryonic-like stem cells (VSELs), are a quiescent stem cell population that requires a supportive co-culture layer to proliferate and/or to differentiate in vitro. Gene expression studies have revealed that the quiescence of these cells is due to changes in expression of parentally imprinted genes, including genes involved in cell cycle regulation and insulin and insulin-like growth factor signaling (IIS). To investigate the role of microRNAs (miRNAs) in VSEL quiescence, we performed miRNA studies in highly purified VSELs and observed a unique miRNA expression pattern in these cells. Specifically, we observed significant differences in the expression of certain miRNA species (relative to a reference cell population), including (i) miRNA-25_1 and miRNA-19 b, whose downregulation has the effect of upregulating cell cycle checkpoint genes and (ii) miRNA-675-3 p and miRNA-675-5 p, miRNA-292-5 p, miRNA-184, and miRNA-125 b, whose upregulation attenuates IIS. These observations are important for understanding the biology of these cells and for developing efficient ex vivo expansion strategies for VSELs isolated from adult tissues.

Overexpression of phosphatase and tensin homolog improves fitness and decreases Plasmodium falciparum development in Anopheles stephensi.

The insulin/insulin-like growth factor signaling (IIS) cascade is highly conserved and regulates diverse physiological processes such as metabolism, lifespan, reproduction and immunity. Transgenic overexpression of Akt, a critical regulator of IIS, was previously shown to shorten mosquito lifespan and increase resistance to the human malaria parasite Plasmodium falciparum. To further understand how IIS controls mosquito physiology and resistance to malaria parasite infection, we overexpressed an inhibitor of IIS, phosphatase and tensin homolog (PTEN), in the Anopheles stephensi midgut. PTEN overexpression inhibited phosphorylation of the IIS protein FOXO, an expected target for PTEN, in the midgut of A. stephensi. Further, PTEN overexpression extended mosquito lifespan and increased resistance to P. falciparum development. The reduction in parasite development did not appear to be due to alterations in an innate immune response, but rather was associated with increased expression of genes regulating autophagy and stem cell maintenance in the midgut and with enhanced midgut barrier integrity. In light of previous success in genetically targeting the IIS pathway to alter mosquito lifespan and malaria parasite transmission, these data confirm that multiple strategies to genetically manipulate IIS can be leveraged to generate fit, resistant mosquitoes for malaria control.

Regulation of longevity and oxidative stress by nutritional interventions: role of methionine restriction.

Comparative studies indicate that long-lived mammals have low rates of mitochondrial reactive oxygen species production (mtROSp) and oxidative damage in their mitochondrial DNA (mtDNA). Dietary restriction (DR), around 40%, extends the mean and maximum life span of a wide range of species and lowers mtROSp and oxidative damage to mtDNA, which supports the mitochondrial free radical theory of aging (MFRTA). Regarding the dietary factor responsible for the life extension effect of DR, neither carbohydrate nor lipid restriction seems to modify maximum longevity. However protein restriction (PR) and methionine restriction (at least 80% MetR) increase maximum lifespan in rats and mice. Interestingly, only 7weeks of 40% PR (at least in liver) or 40% MetR (in all the studied organs, heart, brain, liver or kidney) is enough to decrease mtROSp and oxidative damage to mtDNA in rats, whereas neither carbohydrate nor lipid restriction changes these parameters. In addition, old rats also conserve the capacity to respond to 7weeks of 40% MetR with these beneficial changes. Most importantly, 40% MetR, differing from what happens during both 40% DR and 80% MetR, does not decrease growth rate and body size of rats. All the available studies suggest that the decrease in methionine ingestion that occurs during DR is responsible for part of the aging-delaying effect of this intervention likely through the decrease of mtROSp and ensuing DNA damage that it exerts. We conclude that lowering mtROS generation is a conserved mechanism, shared by long-lived species and dietary, protein, and methionine restricted animals, that decreases damage to macromolecules situated near the complex I mtROS generator, especially mtDNA. This would decrease the accumulation rate of somatic mutations in mtDNA and maybe finally also in nuclear DNA.