Dietary restriction is a potent non-genetic dietary manipulation that has been shown to extend lifespan and healthspan in almost all the species tested so far. Our understandings of molecular mechanisms of DR come primarily from studies of genetically amenable systems, including yeast, worms, and flies, where DR has been imposed by either diluting the food source or by using genetic mutations that reduce feeding efficiency. However, a major drawback of these approaches is that it remains substantially uncertain in determining the exact caloric intake of individual organisms under these DR paradigms. To address this issue, we have previously developed an alternative dietary paradigm, termed as dietary deprivation (DD), and found that it can extend lifespan in C. elegans compared to the control worms fed ad libitum (AL). Since this regimen involves complete removal of the food source, the problem of controlling food intake, which has hampered interpretation of past studies, is alleviated. Using this unambiguous method, we have investigated the genetic pathways necessary for lifespan extension by diet. We have conducted a genetic screen and have found that the heat shock response pathway is critical for DD response. The heat shock response pathway is evolutionarily conserved from the nematode to humans. A manuscript describing the findings in C. elegans is under preparation. We are currently investigating additional conserved pathways that potentially modulate the lifespan of worms under the DD condition. Uncovering the conserved mechanisms will advance our knowledge on the effects of diet on aging and longevity in mammals, including humans. Drosophila melanogaster is another powerful genetic system that has been utilized extensively to address many basic biological questions including aging and dietary restriction (DR). The conserved insulin-like signaling pathway has been shown to play an important role not only in nutrient metabolism but also in lifespan regulation. To investigate the effects and molecular mechanisms of dietary macronutrients on lifespan, we have measured lifespan of flies fed diets of various ratios of macronutritions, including protein and carbohydrates. We have found that dietary composition has profound effects on lifespan and the insulin-like signaling pathway interacts with dietary nutrients to modulate lifespan. A manuscript describing these results is under preparation. This study provides us a foundation to investigate mechanisms of dietary regulation in D. melanogaster. By taking advantage of availability of a large number of fly mutants in the public stock centers, we are investigating the genetic pathways involved in DR, which will provide insight on lifespan regulation. Numerous studies in rodents have indicated that DR can extend not only lifespan but also healthspan. Adiponectin is a small protein primarily produced by adipose tissues prior to its release into circulation. To investigate whether and how adiponectin plays a role in mediating the neuroprotection by DR, we have employed the primary hippocampal cell culture system in rats. We have demonstrated that adiponectin can protect cultured hippocampal neurons against kainic acid-induced (KA) cytotoxicity. Furthermore, we have found that the conserved AMPK pathway is involved in adiponectin-induced neuroprotection. A manuscript describing some results from this study has been accepted for publication in AGE (2010). Considering that DR increases adiponectin levels in mammals, our findings suggest that adiponectin plays an important regulatory role in mediating the beneficial effects of DR including neuroprotection. In summary, we have addressed several issues related to dietary regulation of lifespan in this project. By utilizing a unique and robust dietary regimen in C. elegans, we are dissecting molecular mechanisms of dietary regulation of lifespan. With D. melanogaster, we are studying mechanisms by which genes and which tissues are critical for lifespan extension by dietary restriction. Using the cellular model, we are investigating the signaling pathways involved in the beneficial effects of DR. This project will allow us identify the conserved pathways required for lifespan extension by DR, which will be valuable for understanding human aging and more importantly for developing efficient aging intervention strategies for humans.
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