A 'Mitochondria-Nucleus-Ribosome' Signaling Axis Controls Lifespan in Mit Mutants

The long-term goal of this study is to improve the health and well-being of older Americans. Our immediate goal is to examine how disruption of mitochondrial function is linked with the aging process. In recent years, it has become clear that defects in the electron transport chain of mitochondria, the key site of energy production in cells are linked with many age-related diseases - including heart disease, Type II diabetes, Parkinson Disease, Alzheimer's dementia, and cancer. 15% of the US population suffers from these chronic degenerative disorders. While it cannot yet be said that mitochondria cause these problems, it is clear that changes in mitochondria are involved, because their function is measurably altered. Perhaps most surprising has been the discovery of a number of mutants, across several species including mice, flies, nematodes and yeast, that paradoxically respond to mitochondrial electron transport chain dysfunction with increases in their lifespan. Investigation of this intriguing family of mutants is shedding new light on mitochondria and their role in aging.In this study, we will examine aging in the Caenorhabditis elegans Mit mutants, which are all long-lived and contain defective mitochondrial electron transport chain activity. We have uncovered evidence for a novel, three component signaling cascade in these mutants that links disruption of mitochondrial ETC activity with nuclear checkpoint signaling, blockade of cytoplasmic ribosomal translation, and lifespan control. This is a completely unexpected finding because these processes span three distinct cellular compartments. Our current study will define the cause and effects of this novel signaling cascade. We hypothesize that disruption of nucleotide synthesis in Mit mutants underlies activation of their nuclear checkpoint response. We have identified three checkpoint proteins that are activated in these animals, and now our preliminary data points toward a direct ribosomal target that potentially acts as a key longevity control point by regulating trafficking of nuclear-encoded proteins to the mitochondria. Our specific objectives will be determined if the biosynthesis of ribonucleotides is altered in Mit mutants. We will also determine if there is nuclear transcriptional stalling in these animals. Finally we will test whether our identified ribosomal target does indeed differentially act to control translation of nuclear-encoded mitochondrial ETC transcripts following checkpoint activation. We will address these questions through the use of powerful biochemical and genetic tools. We will use LC-MS/MS to quantify changes in nucleotide pools, quantitative PCR to determine if transcriptional stalling is occurring, and a combination of transgenic reporters, polysomal profiling and RNA Seq to determine if nuclear-encoded mitochondrial proteins are differentially prevented from being translated in Mit mutants. PUBLIC HEALTH RELEVANCE: The National Research Council, at the request of Congress, recently examined the long-term macroeconomic challenges faced by the US due to its shifting demographic from working-age people to retirees. It was concluded that unless household consumption is decreased, or workers retire later, the quality of life of future Americans is destined to decrease. This grant aims to investigate the fundamental mechanisms by which cells age, with the ultimate goal of increasing the healthspan of people into their elder years.