Mechanisms of the cell non-autonomous dietary restriction pathway

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PROJECT SUMMARY/ABSTRACT Our understanding of the molecular and genetic mechanisms of aging has grown exponentially in the past 25 years. Groundbreaking studies in invertebrate models such as the nematode Caenorhabditis elegans have been at the forefront of many breakthroughs, including the discovery of the first genes that control longevity. Despite these important studies, there are many aspects of the genetic and molecular mechanisms of aging that are still not well understood. One of these mechanisms is the cell non-autonomous control of aging by small subsets of cells (frequently neurons) in an organism. Multiple highly regarded publications have identified individual genes and neurons at the origin of signaling pathways that eventually modify genetic and metabolic responses in peripheral tissues. These studies provide substantial evidence that cell non- autonomous control of aging is common to multiple longevity pathways, but they lack in detail as to the specific signals, receptors, neural circuits, and downstream effectors involved. Our preliminary data show that the most well-studied longevity intervention, dietary restriction (DR), acts in part through a cell non-autonomous signaling pathway that is inhibited by the smell of food in C. elegans. We further find that DR and fasting each lead to induction of an intestinal protein, flavin-containing monooxygenase-2 (fmo-2), that is both necessary and sufficient to improve healthspan, stress resistance, and longevity. We also observe that induction of fmo-2 and extension of lifespan both depend on the serotonergic signaling and can be recapitulated by the serotonin antagonist drug, mianserin. This project will map the cell non-autonomous pathway initiated by removal of food that eventually leads to intestinal fmo-2 induction and extension of lifespan. Aim 1 will identify and epistatically relate the neurons involved in this neural circuit, answering important questions about which specific cell(s) initiate the signal, which cell(s) propagate the signal, and ultimately, which cell(s) integrate the signal into a system-wide response. The results will define a neural circuit led by food sensing and utilizing serotonin that may overlap with other longevity pathways. The second aim will focus on the signals involved in inter-neuronal and tissue to tissue communication by identifying small peptides, synaptic transport mechanisms, and receptors involved in the pathway. The resulting data will fill out the neural circuit model from aim 1 with the key signals and receptors beyond serotonin, and could lead to future studies designed to mimic/block these signals. The third aim will identify the major receptors and transcription factors necessary to induce fmo-2 in the intestine. We will use a forward genetic screen, a targeted RNAi approach, and existing ChIP-SEQ data to define the major intestinal genes involved with DR-mediated fmo-2 induction. Together, these aims will act independently and synergistically to provide an understanding of a major signaling network that modifies aging. Our ultimate goal is to exploit this knowledge of control mechanisms of aging to develop approaches that promote human health.