Link between dietary restriction and TOR using D. melanogasterInhibition of the conserved nutrient-sensing TOR pathway extends life span in yeast, worms, flies and mice. Our data suggests that inhibition of cap-dependent protein translation via S6 kinase and eIF4E binding protein (4EBP) downstream of the TOR plays a key role in regulating life span extension by DR in D. melanogaster. To examine the mechanisms of lifespan extension upon DR, we have assayed genome-wide translational changes in Drosophila. A number of genes including nuclear encoded mitochondrial genes, showed increased ribosomal loading and enhanced overall activity upon DR. The translational repressor 4E-BP was found to be upregulated upon DR and mediated DR dependent changes in mitochondrial activity and lifespan extension. We are currently identifying and characterizing the downstream targets of the TOR pathway that mediate lifespan extension upon DR. We are also characterizing the mechanism of translation regulation of these differentially translated genes which involves their 5' UTR structure
Dietary restriction, TOR, HIF-1 and ER stress in C. elegansUsing C. elegans we have identified HIF-1 (hypoxia inducing factor) acting downstream of S6 Kinase to modulate IRE-1 (inositol requiring protein) dependent ER signaling pathways to mediate the effects of DR. In mammalian cells, TOR and the downstream S6 kinase (S6K) activate expression of hypoxia-inducible factor 1 (HIF-1), which is frequently up-regulated in various tumors. We found that a mutation in hif-1 increases lifespan only under rich nutrient conditions but not under DR or S6K mutant background. In the egl-9 mutant animals, where HIF-1 activity is elevated, lifespan extension by DR is abrogated. This phenotype was rescued by tissue-specific expression of egl-9 in the body wall muscle. We also observed that lifespan extension by hif-1 or DR depends on IRE-1 and is associated with lower levels of an ER stress marker. Our study has uncovered a novel link between HIF-1, ER signaling and aging. We hypothesize that HIF-1 acts via IRE-1 to inhibit the beneficial effects of DR in aging and age-related diseases by modulating protein and energy homeostasis. We are currently identifying the downstream targets of HIF-1 and IRE-1 using multiple approaches. These approaches will include genome wide transcription profiling, examination of known HIF-1 targets and genetic screens. We propose the aims below to understand the role of HIF-1, IRE-1 and its targets in maintaining cellular homeostasis and modulating aging and age-related functions.
Antagonistic pleiotropy, mRNA translation and agingThe antagonistic pleiotropy theory of aging proposes that aging takes place as natural selection favors genes that confer benefit early on life at the cost of deterioration later in life. This theory predicts that genes that impact on development would play a key role in shaping adult lifespan. To better understand the molecular mechanisms of antagonistic pleiotropy, we examined the genes identified to cause larval arrest from previous genome-wide RNAi screens. From a pool of 57 genes that lead to developmental arrest after inhibition using RNAi, we have identified 23 novel genes that extend lifespan in C. elegans when inactivated during adulthood. Many of these genes are involved in regulation of mRNA translation and mitochondrial functions. Genetic epistasis experiments indicate that the mechanisms of lifespan extension by inactivating the identified genes may be different from those of the insulin-like/IGF-1 and DR dependent pathways. Inhibition of many of these genes also results in increased stress resistance and decreased fecundity, suggesting that they may mediate the tradeoffs between somatic maintenance and reproduction. We are currently examining the mechanisms of antagonistic pleiotropic functions which may help understand the intrinsic link between organismal development and adult lifespan.
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