Insulin signaling (IIS) regulates metabolism, growth, and environmental stress responses and influences longevity in multicellular organisms. IIS is triggered by insulin like peptides (ILPs) that are produced by specialized endocrine cells (pancreatic beta cells of vertebrates or insulin producing cells, IPCs, of Drosophila) according to nutritional and environmental cues. These cells systemically regulate a range of biological processes in several distinct ILP target tissues. To understand how the control of insulin production integrates multiple external and internal signals to mediate an appropriate systemic response is a high priority. Such understanding is required for rational approaches to treat and prevent metabolic diseases that are caused by insulin dysregulation. Preliminary studies by the applicant have shown that the stress-responsive Jun-N-terminal Kinase (JNK) signaling pathway represses ILP expression in IPCs of Drosophila melanogaster and thereby regulates IIS activity throughout the organism. These findings suggest the JNK pathway as a relay for metabolic effects of organismic stress. This idea will be pursued experimentally. New unpublished data by the applicant suggest that the regulation of ILP expression by JNK signaling in IPCs deteriorates as animals age, an effect that might cause or contribute to metabolic changes during aging. The experiments proposed in aim 1 will test the hypothesis that JNK-mediated repression of ILP expression is required to coordinate cellular responses to environmental stress systemically. The nature of potential environmental stress signals that elicit an IPC response will be explored, and the involvement of tissue- autonomous and humoral mechanisms of IIS repression in cellular responses to stress will be evaluated. Experiments in aim 2 will examine the relative contributions of systemic and tissue-autonomous repression of IIS activity by JNK to stress tolerance and longevity of the organism.
Aim 3 is designed to test whether age-dependent changes of JNK activity in IPCs contribute to the general deterioration of metabolic control in aging animals, and whether a restoration of normal JNK signaling in IPCs may delay such changes.
All aims are based on genetic approaches using Drosophila and include transcriptional and metabolic analysis, as well as demographic analysis of mortality in populations of different genotypes exposed to a variety of environmental conditions. The studies proposed here will assess the regulation of insulin production and physiology by stress signaling in an intact organism. Due to the evolutionary conservation of IIS and JNK signaling, as well as the functional analogy of IPCs and pancreatic beta cells, it can be expected that the insight generated by studies in Drosophila will help to understand this regulatory system, its components, and its physiological and pathological impact on metabolic homeostasis and aging in vertebrates.
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