An insulin-like signaling pathway is the most potent regulator of lifespan in C. elegans. The function of this pathway in mediating metabolism and aging is conserved in C. elegans, Drosophila, and mammals. Because so much of the insulin signaling pathway is conserved, the new components we discover in C. elegans will have broad relevance to mammalian insulin signaling and longevity control. Genetic analysis in C. elegans continues to identify components of the pathway that are likely to reveal human variation in insulin-like signaling, with medical significance for diabetes and the understanding of how insulin signaling and analogous hormonal pathways couple chronological age to many late onset diseases. Using RNAi to screen for defects in daf-2 pathway mediated longevity regulation, we identified a comprehensive genetic network necessary for the longevity response to low daf-2 insulin/IGF1 signaling (9). Similarly, our proteomic analysis of insulin signaling components in Aim 2 has identified other new and unstudied candidate genes to act in insulin signaling. The use of RNAi screens and proteomics in C. elegans is opportune for two reasons: first, the tissues where insulin signaling is key for metabolic control has changed dramatically over the past decade. No longer is an exploration of insulin signaling only in the liver or muscle or even pancreas definitive. Neural and adipose centers of insulin signaling have emerged (7). We have identified new protein components of insulin signaling from whole animal extracts, and our RNAi screens are done in the whole animal, so insulin signaling across tissues is surveyed. This is unlike mammalian insulin signaling functional genomics which may assay for insulin responses in tissue culture, but not in the physiological context of a whole organism. Aging and diabetes may be more physiological and endocrine, not easily modeled in cell culture. In this way, the C. elegans insulin signaling genetic system is better model system for human aging and human diabetes than human cell culture. Our full genome screens for lifespan regulatory processes have also revealed that the second most potent axis of longevity regulation surveys core components of cells, the ribosome, the mitochondrion, the cytoskeleton, and if deficits are detected, the pathway couples to an endocrine system of longevity control that is distinct from the insulin-like pathway. Our exploration of the endocrine system for surveillance and signaling of deficits in core cellular components promises to illuminate an entirely new axis of eukaryotic lifespan regulation. Variation in both these endocrine systems may underlie human lifespan variation as well as variation in metabolism and drug sensitivities.
An insulin-like signaling pathway regulates metabolism and aging in C. elegans, Drosophila, and mammals. Our genetic, proteomic, and functional genomic analysis in C. elegans continues to identify components of the pathway with medical significance for diabetes and the understanding of how insulin signaling and analogous hormonal pathways couple chronological age to many late onset diseases. We will also explore another endocrine pathway for longevity that is coupled to the surveillance of core cellular elements such as the ribosome and mitochondrion.
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