Inhibition of germline proliferation during C. elegans dauer development requires PTEN, LKB1 and AMPK signalling

In C. elegans, reduced insulin-like signalling induces developmental quiescence, reproductive delay and lifespan extension. We show here that the C. elegans orthologues of LKB1 and AMPK cooperate during conditions of reduced insulin-like signalling to establish cell cycle quiescence in the germline stem cell population, in addition to prolonging lifespan. The inactivation of either protein causes aberrant germline proliferation during diapause-like ;dauer' development, whereas the loss of AMPK uncouples developmental arrest from lifespan extension. Reduced TGF-beta activity also triggers developmental quiescence independent of the insulin-like pathway. Our data suggest that these two signalling pathways converge on the C. elegans PTEN orthologue to coordinate germline proliferation with somatic development during dauer formation, via the regulation of AMPK and its upstream activator LKB1, rather than through the canonical insulin-like signalling cascade. In humans, germline mutations in TGF-beta family members, PTEN or LKB1 result in related tumour-predisposing syndromes. Our findings establish a developmental relationship that may underscore their shared, characteristic aetiology.     

Role of insulin-like signalling in Drosophila lifespan

Regulation of lifespan by the insulin/insulin-like growth factor-like signalling (IIS) pathway has been conserved during evolution from the nematode worm to the mouse. In the insect Drosophila, regulation of lifespan by the IIS pathway was established by data showing that many mutations in single genes encoding IIS components result in an increase in lifespan. Recently, however, the focus has shifted from studying the effects of single gene mutations with ubiquitous effects to finding interventions that alter IIS in specific tissues and at specific stages in the life history of the fruitfly, in order to elucidate the signalling pathways at work and the mechanisms by which alterations in the IIS pathway can extend lifespan.     

The miR-58 microRNA family is regulated by insulin signaling and contributes to lifespan regulation in Caenorhabditis elegans

microRNAs regulate diverse biological processes such as development and aging by promoting degradation or inhibiting translation of their target mRNAs. In this study, we have found that the miR-58 family microRNAs regulate lifespan in C.elegans. Intriguingly, members of the miR-58 family affect lifespan differently, sometimes in opposite directions, and have complex genetic interactions. The abundances of the miR-58 family miRNAs are up-regulated in the long-lived daf-2 mutant in a daf-16-dependent manner, indicating that these miRNAs are effectors of insulin signaling in C. elegans. We also found that miR-58 is regulated by insulin signaling and partially required for the lifespan extension mediated by reduced insulin signaling,germline ablation, dietary restriction, and mild mitochondrial dysfunction. We further identified the daf-21, ins-1, and isw-1 mRNAs as endogenous targets of miR-58. Our study shows that miRNAs function in multiple lifespan extension mechanisms,and that the seed sequence is not the dominant factor defining the role of a miRNA in lifespan regulation.     

Comparison of physiological functions of antagonistic insulin-like peptides,INS-23 and INS-18, in Caenorhabditis elegans

In Caenorhabditis elgans, insulin-like peptides have significant roles in modulating larval diapause and adult lifespan via the insulin/IGF-1 signaling (IIS) pathway. Although 40 insulin-like peptides (ILPs) have been identified, it remains unknown how ILPs act as either agonists or antagonists for their sole receptor, DAF-2. Here we found 1) INS-23 functions as an antagonistic ILP to promote larval diapause through the IIS pathway like a DAF-2 antagonist, INS-18, 2) INS-23 and INS-18 have similar biochemical functions. In addition, our molecular modeling suggests that INS-23 and INS-18 have characteristic insertions in the B-domain, which are crucial for the recognition of the insulin receptor, when compared with DAF-2 agonists. These characteristic insertions in the B-domain of INS-23 and INS-18 would modulate their intermolecular interactions with the DAF-2 receptor, which may lead these molecules to act as antagonistic ligands. Our study provides new insight into the function and structure of ILPs.     

The Drosophila Insulin Receptor Independently Modulates Lifespan and Locomotor Senescence

The Insulin/IGF-like signalling (IIS) pathway plays an evolutionarily conserved role in ageing. In model organisms reduced IIS extends lifespan and ameliorates some forms of functional senescence. However, little is known about IIS in nervous system ageing and behavioural senescence. To investigate this role in Drosophila melanogaster, we measured the effect of reduced IIS on senescence of two locomotor behaviours, negative geotaxis and exploratory walking. Two long-lived fly models with systemic IIS reductions (daGAL4/UAS-InR^DN (ubiquitous expression of a dominant negative insulin receptor) and d2GAL/UAS-rpr (ablation of insulin-like peptide producing cells)) showed an amelioration of negative geotaxis senescence similar to that previously reported for the long-lived IIS mutant chico. In contrast, exploratory walking in daGAL4/UAS-InR^DN and d2GAL/UAS-rpr flies declined with age similarly to controls. To determine the contribution of IIS in the nervous system to these altered senescence patterns and lifespan, the InR^DN was targeted to neurons (elavGAL4/UAS-InR^DN), which resulted in extension of lifespan in females, normal negative geotaxis senescence in males and females, and detrimental effects on age-specific exploratory walking behaviour in males and females. These data indicate that the Drosophila insulin receptor independently modulates lifespan and age-specific function of different types of locomotor behaviour. The data suggest that ameliorated negative geotaxis senescence of long-lived flies with systemic IIS reductions is due to ageing related effects of reduced IIS outside the nervous system. The lifespan extension and coincident detrimental or neutral effects on locomotor function with a neuron specific reduction (elavGAL4/UAS-InR^DN) indicates that reduced IIS is not beneficial to the neural circuitry underlying the behaviours despite increasing lifespan.     

Insulin receptor substrate and p55 orthologous adaptor proteins function in the Caenorhabditis elegans daf-2/insulin-like signaling pathway

An insulin-like signaling pathway regulates development and lifespan in Caenorhabditis elegans. Genetic screens that identified many components of the C. elegans insulin pathway did not identify homologs of insulin receptor substrates or the phosphoinositide 3-kinase (PI3K) adaptor/regulatory subunit, which are both required for signaling by mammalian insulin/insulin-like growth factor I pathways. The C. elegans genome contains one homolog of each protein. The C. elegans versions of insulin receptor substrate (IST-1) and PI3K p50/p55 (AAP-1) share moderate sequence similarity with their vertebrate and Drosophila counterparts. Genetic experiments show that ist-1 and aap-1 potentiate C. elegans insulin-like signaling, although they are not required for signaling in the pathway under most conditions. Worms lacking AAP-1 activity because of the mutation aap-1(m889) constitutively arrest development at the dauer larval stage when raised at high temperatures. aap-1 mutants also live longer than wild-type animals, a phenotype observed in other C. elegans mutants with defects in DAF-2 signaling. Interestingly, IST-1 appears to be required for signaling through a pathway that may act in parallel to AGE-1/PI3K.     

Ablation of insulin-producing cells prevents obesity but not premature mortality caused by a high-sugar diet in Drosophila

Ageing can be modulated by genetic as well as nutritional interventions. In female Drosophila melanogaster, lifespan is maximized at intermediate concentrations of sucrose as the carbohydrate source, and yeast as the protein source. Dampening the signal through the insulin/IGF signalling (IIS) pathway, by genetic ablation of median neurosecretory cells (mNSCs) that produce insulin-like peptides, extends lifespan and counteracts the detrimental effects of excess yeast. However, how IIS reduction impacts health on a high-sugar diet remains unclear. We find that, while the ablation of the mNSCs can extend lifespan and delay the age-related decline in the health of the neuromuscular system irrespective of the amount of dietary sugar, it cannot rescue the lifespan-shortening effects of excess sugar. On the other hand, ablation of mNSCs can prevent adult obesity resulting from excess sugar, and this effect appears independent from the canonical effector of IIS, dfoxo. Our study indicates that while treatments that reduce IIS have anti-ageing effects irrespective of dietary sugar, additional interventions may be required to achieve full benefits in humans, where excessive sugar consumption is a growing problem. At the same time, pathways regulated by IIS may be suitable targets for treatment of obesity.