The role of diet and gastrointestinal microbes in animal ageing and metabolism

There is much evidence that in general, diet affects ageing. Diet also impacts many major diseases and there is a multibillion-dollar industry that produces dietary supplements with the goal of improving human health. There are a vast number of constituents of the human diet, so assessing the effect of each them on ageing is a monumental task. Studying ageing in laboratory animals allows for quicker and better-controlled experiments. The tiny nematode worm, Caenorhabditis elegans, with a lifespan of only a few weeks, is a well-established lab animal for investigating the biology of ageing. The lifespan of the worm can be extended considerably by the disruption of some genes in the worm, several of which have clear human counterparts. For example disruption of genes similar to those needed to respond to insulin in humans, causes the worm to live longer. Experiments in mice have shown that this finding is also relevant to mammals. The digestive tracts of animals are populated by numerous microbes, mainly bacteria and these microbes assist nutrition in many ways. As well as assisting uptake of nutrients, gut bacteria produce compounds such as essential amino acids and vitamins that can't be made by the animal host. It has been suggested that changes in gut microbes can cause obesity. In the lab we maintain C. elegans on a single species of live bacteria, a harmless strain of E. coli, derived from the human intestine. This strain provides food but needs to be alive to provide good nutrition. We have discovered a mutant strain of E. coli, which when fed to worms makes them live considerably longer. We have found that the reason why this mutant causes the animals to live longer is a decrease in the synthesis of folic acid. Folic acid is needed in all cells for a variety of purposes, especially for cell growth, but folic acid is only made in microbes and plants so animals have to rely on their diet. Our experiments show that the lifespan of the worms eating the mutant bacteria is extended because they are receiving less folic acid than worms on the normal bacteria. In addition, the fact that the bacteria have less folic acid to support their own metabolism also contributes to the slowed ageing of the worms that eat them. We don't yet understand how reduced folic acid causes this effect but we know that is not because extra folic acid is toxic. E. coli is probably the best studied organism there is, because for over 60 years it has been used to understand the basic workings and metabolism of cells. E. coli has around 4000 genes and there is a collection of 3909 strains in which a single gene has been disrupted from each strain in the collection. The aim of this proposal is to feed worms on each of these mutant strains and look for long-lived worms and worms that grow slowly. We expect to find several E. coli mutants that increase worm lifespan and/or affect nutrition. Firstly, we should find mutants that disrupt genes related to folic acid metabolism. The identity of these genes will help us understand how the folic acid effect works. Secondly, we should also find new mutants that cause C. elegans to live longer and we will use the accumulated knowledge of C. elegans ageing and E. coli metabolism to understand how these mutants work. We will combine mutants to see if we can make the animals live longer still. We will also use mutants of C. elegans that affect ageing to understand how the animal responds to changes caused by E. coli mutants. Together these studies reveal fundamental relationships between diet, lifespan and intestinal microbes. Our findings can be followed up in higher animals such as mice, hopefully leading to pharmaceutical and dietary interventions for humans both to slow ageing and decrease obesity. The results of this study will also stimulate discussion and help our understanding of a topic that concerns us all: What to eat to live to a healthy old age?

Diet has a strong effect on ageing and health but the key constituents are not defined and mechanisms not understood. Studies of diet are confounded by intestinal microbes, which aid nutrition and have been implicated in conditions such as obesity. The nematode C. elegans, with a short lifespan, is a well-established model for the biology of ageing. In the lab, C. elegans is maintained solely on the bacteria E. coli, which must be alive for full nutrition. We have discovered an E. coli mutant that increases C. elegans lifespan. We have shown that the lifespan increase is caused by both decreased folate supply to animal as well as decreased folate-dependent bacterial metabolism. On less nutritious media the mutant also slows animal growth, implicating folate-dependent metabolism in aiding host nutrition. Others have found a separate class of mutants that increases C. elegans lifespan that probably works by decreasing respiration. The aim of the proposal is to screen a collection of all viable single gene knockouts of E. coli for strains that increase C. elegans lifespan and/or slow C. elegans development. Firstly, we should find mutants that disrupt genes involved in folic acid metabolism, increasing our understanding of this effect. Similarly we should discover respiration mutants if that hypothesis is correct. We will categorise novel mutants to understand if they affect folates, respiration or novel pathways. We will also test for other possibilities such as decreased pathogenesis. We will measure folate levels and develop methods for other key metabolites. We will make double mutants to understand interactions between pathways and use known C. elegans mutants to understand the animal response. Together these studies will reveal fundamental relationships between diet, lifespan and intestinal microbes, and provide preliminary data for further studies including mathematical models, studies in mouse models and industrial collaborations.

Who will benefit from this research? Industry: The pharmaceutical industry The nutrition industry The pet food industry The process industry The agricultural industry The public: Industry-associated wealth and job creation Quality of life of an ageing population Relief for sufferers of obesity and metabolic syndrome Pet owners Scientific awareness Ability to make informed choices about 'anti-ageing' compounds Public policy makers in relation to food fortification and other public health nutritional interventions The Health Service and elderly care providers Bioscience skill base How will they benefit from this research? One of the aims of this project to uncover new compounds to be used to either slow ageing or combat obesity, therefore producing new products for the pharmaceutical, nutrition and pet food industries. Other potential benefits include providing new biological solutions for the process industry (which has a strong base in NE England) and increasing efficient of animal nutrition in the agricultural industry. New products will lead to increased wealth and job creation, either by boosting existing companies or by the formation of spin outs. If the ageing process could be slowed it would increase the health in old age. Tackling obesity would also increase the health of the general public. Pet owners would welcome the means to increase the lifespan of their pets. Dissemination of our work through the media and the internet will increase the knowledge of the general public. We will stage events to enable the public to understand the scientific process from the eyes of real in-the-lab researchers and help inform decision-making about products and foods that claim to be anti-ageing. In the US, grained is fortified with folic acid as a health measure to prevent birth defects and a similar measure is being considered in the UK. Our research on folates will help inform this decision and contribute to the debate about similar public health measures. If we can improve the health and quality of life of old people, it would greatly relieve pressure on the health service and care providers. Students and researchers in the research group will be equipped with new skills that are rare in the UK. What will be done to ensure these groups have the opportunity to benefit from this research? 1. Intellectual property will be protected with the help of the Durham University Technology Transfer Office (TTO). We already in discussion about filing a patent relating to this work. Where applicable, the TTO will also help to commercialise and license IP. 2. We will communicate with potential industry partners through previous contacts, and the BBSRC DRINC and Healthy Ageing Industry and Technology Club. 3. We will collaborate with academic partners to translate findings to mouse models. Positive results will make findings more attractive to industry. 4. Results will be published in high impact journals and Durham University's awarded-winning media team will be employed to disseminate findings to the general public via the media. We will also use internet-based media to discuss our findings. 5. We will work with organizations such as 'The People Speak', Durham University Public outreach, and the Centre for Life, Newcastle to organize events to engage the public and show how science works. 6. Public health policy makers will be contacted via relevant clinical academic partners. 7. Health benefits should follow from translation of findings from mammalian models to clinic as well as research and development by pharmaceutical companies. 8. This project involves skills that are only available in a few labs in the UK. Personnel funded by the project as well as postgraduate and undergraduate students will be trained to increase the skills base of the UK, particularly in the North East region. We will also transfer skills to academic or industrial partners where relevant.