Synthetic viability: a novel approach to defining healthspan determinants

Ageing of the human body results in gradual loss of tissue and organ function, with consequent frailty and illness leading to poor quality of later life for many older people. This is a huge socioeconomic problem in much of the world today, as improvements in medicine over the past few decades have led to a significant increase in life expectancy but without concomitant increase in the time spent in good health (healthspan). Thus, research aimed at discovering ways of increasing healthspan in old age is rising to prominence, with work addressing the basic biology of ageing likely to underpin future medical advances. We plan to investigate regulation of organismal ageing and healthspan at the very fundamental level of the genes involved and the proteins they encode.

In this project, we will study the control of age-related decline in health in a tiny free-living worm, the nematode Caenorhabditis elegans. C. elegans is a very useful model organism for studying ageing because it has a short (2-3 week), well defined lifespan and healthspan that can be easily measured. Most importantly, the worm can be conveniently subjected to experimental manipulation at the genetic, cellular and whole organism level, allowing scientists to dissect the role that particular genes play in controlling ageing and healthspan, as well as the interactions between genes. Moreover, many previous studies have shown that factors important in worm ageing are equally important in man, i.e. they are conserved across evolution. Hence any discoveries made in the worm should have relevance to people. Treating the frailty and illness of older age might be possible by modulating the ageing process itself, but we need to first understand exactly how this works at the level of individual molecules.

Although many different cellular processes contribute to the decline of tissues and organs during ageing, mutations in single genes can completely change the rate of ageing. This is true of both worms and man. For instance, there is a human premature ageing syndrome, called Werner Syndrome (WS), in which affected individuals age at a highly accelerated rate, reaching "old age" by the age of 40 or so. The accelerated ageing in WS patients is caused by mutations in a single gene, the Werner gene (WRN). Significantly, the worm counterpart of this gene, wrn-1, is also involved in the control of ageing, with wrn-1 worm mutants similarly showing decreased lifespan and signs of accelerated ageing.

Because one of the major roles of WRN-1 is to help repair DNA when it becomes damaged, we are interested in how WRN-1 interacts with other proteins required to sense and respond to such damage, like p53 (encoded by the cep-1 gene in worms), an important human tumour suppressor gene. We have made the fundamental and crucially important observation that, while both wrn-1 and cep-1 single mutants have shortened lifespans, double mutant worms in which both wrn-1 and cep-1 are non-functional have a greatly extended lifespan and healthspan, living more than twice as long as normal worms, and staying healthier for much longer too.

We propose to use this observation as a springboard to identify new components of the healthspan and lifespan regulatory framework, to probe the effect of specific genes on healthy ageing and to understand the importance of the response to DNA damage and other forms of cellular stress in determining lifespan and healthspan. We will use well-established techniques for inactivating genes in various combinations as well as powerful new technologies that can highlight differences in gene expression patterns, enabling us to tease apart pathways of ageing. Overall, we hope to uncover new biochemical pathways important in determining healthspan, with important consequences for understanding and eventually treating frailty and disease in older people.

Understanding the molecular basis of ageing is prerequisite to modifying the ageing process to promote healthier old age. Biochemical pathways impacting on longevity and healthspan integrate stress, hormonal and nutritional signals to ensure appropriate biological outcomes. Given the complexity of ageing pathways, it is perhaps surprising that huge changes in the rate of ageing of an organism can be achieved by mutation of a single gene. For example, the human premature ageing Werner Syndrome (WS) is caused by mutation of the WRN gene, which has complex roles in DNA damage processing and telomere maintenance.

We have developed a genetically amenable model of Werner syndrome in C. elegans to study whole organism ageing. C. elegans wrn-1 mutants display decreased lifespan and accelerated ageing whereas worms overexpressing wrn-1 show increased lifespan and healthspan. Thus wrn-1 acts as a bona fide anti-gerontogene. Strikingly, double mutants in which both wrn-1 and the p53 homologue cep-1 are inactivated display massively extended lifespan and significantly compressed morbidity, even though both wrn-1 and cep-1 single mutants have shortened lifespans. We will exploit this "synthetic viability" phenotype in RNAi screens designed to identify novel healthspan determinants in both wrn-1 and cep-1 mutant backgrounds. We will investigate the molecular basis of cep-1; wrn-1 synthetic viability (and other synthetic viability interactions that we find) by analyzing the role of DAF-16 as well as other stress signalling pathways, e.g. via MAPK and TOR. In addition, we will deploy RNA-seq analysis to investigate gene expression differences in long-lived vs. short-lived mutants, following up candidate target genes in appropriate epistasis analyses.

Overall, our findings will provide important new insights into the biology of longevity and healthspan and we anticipate that this work will highlight new targets that may be amenable to manipulation to improve ageing outcomes.

The primary immediate beneficiaries will be the scientific community, as discussed in academic beneficiaries. The longer-term impact of this work is rooted in increasing our understanding of ageing and healthspan biology. Strategies to improve the health of older people have the potential to transform society, providing huge economic and social, as well as medical impact. The benefit of even a small decrease in human age-related morbidity through rational therapy is potentially huge, both in terms of cost savings to the NHS and in improved quality of later life for the older population. Thus this work relates to the BBSRC Priority area of World Class Underpinning Bioscience and is central to the specific BBSRC strategic priority of Ageing Research: Lifelong Health and Wellbeing.

Longer-term beneficiaries will include:

1) The commercial sector. Understanding pathways of ageing will underpin efforts to identify targets for development of small molecule therapies for common age-related morbidities, promoting healthy ageing. The new worm strains to be generated (with characterised ageing baselines) may also provide novel druggable platforms for unbiased small molecule screens to identify compounds to improve healthspan in later life. Where relevant, IP protection will be sought via ISIS Innovation (a wholly owned subsidiary of the University of Oxford) to protect potentially sensitive information and provide an attractive package to investors and pharma.

2) Policy makers. It is necessary for policy makers to appreciate the importance of basic research into the biology of ageing in underpinning successful drug discovery; information from this project should assist them in making sound cost/benefit judgements concerning scarce resources. In addition, this work falls within the remit of the 3Rs (replacement, refinement or reduction of vertebrate animals in research), an adopted strategy of all UK Research Councils and other research funding organizations. Establishing an invertebrate model system for investigating ageing and healthspan is thus likely to impact public policy on animal research by developing a suitable alternative. We will continue to engage with policy makers to emphasise the importance of blue skies and primary research on the biology of ageing as necessary to developing subsequent therapeutic strategies eg. through the Society of Biology, Age UK and via the BSRA and parallel international organisations.

3) Third Sector. We will provide ageing funders and charity fund-raisers with news on progress in ageing research to inform policy and for use in campaign material to stimulate giving, with potential knock-on effects of increasing capacity in ageing research in the UK though attracting additional funding.

4) The wider public. Increased public understanding of the science of ageing is a non-quantifiable but important benefit. We will communicate our findings to the public, targeting as diverse an audience as possible. The PI has a particularly high profile in science communication, being the 2013 Royal Institution Christmas Lecturer and actively engaged with public programmes both nationally (Cheltenham Science Festival 2014, Green Man Festival 2014) and internationally (Singapore A* programme/Ri public science lectures 2014). She gives many talks in schools, at public outreach events and through national and international media (BBC, UK press, Australian Broadcasting Corporation). Similarly, the Co-investigator is a well-known commentator on ageing research, with regular media involvement (BBC TV and radio, ITV, Science Media Centre, web resources such as http://www.rigb.org/advent/01 - (chromosome 5)), school visits and wider outreach activities including science festivals and public debates. These two scientists are therefore uniquely placed to exploit their public engagement profiles to maximize impact.