Overactivity in growth and its effects on rates of ageing

Caloric restriction (CR), which is the reduction of nutrient intake without change in nutrient composition or malnutrition, is one of the few known treatments that delay ageing in a wide variety of animals, from yeast to mammals. The down-regulation of nutrient-sensing genetic pathways, such as the highly conserved TOR kinase and insulin pathways, are thought to mediate the effects of CR. How exactly the activity of nutrient-sensing pathways leads to faster ageing is not known. A popular theory suggests that high metabolism results in the production of free radicals, which causes molecular damage. However, there is some evidence that contradicts the oxidative damage theory as the cause of ageing. This research will address the mechanisms of ageing using an alternative theoretical framework. According to a theory developed recently, ageing is the result of an unintended hyperfunction of a developmental program. Thus, growth that continues later in life could lead to pathology and eventual death. This theory can explain many of the paradoxes reported for the oxidative damage theory, as well as explain why CR delays ageing. Making an analogy with a car, instead of ageing due to "rusting", this new theory proposes that ageing is like a car that drives without any brakes and driver.

We propose to study a species of nematode (roundworm) that produces genetically identical siblings, but that show different lifespan; hermaphrodites of this nematode consistently live a third longer than females. The absence of genetic differences between genders will facilitate proper control experiments for the cause of differences in lifespan. Nematodes are ideal for studying ageing because they have a relatively short lifespan, and are easy to culture and to manipulate in the laboratory. We hypothesize that females of hermaphrodites of our nematode model are ageing at different rates because they accumulate age-related pathologies that are the result of hyperfunction at different times during adulthood. We will test this hypothesis by manipulating the ageing rates using gender-modifying treatments, gene expression and gene knock-out analysis.

Our model species provides a powerful system to study the mechanisms underlying ageing, because we can culture them at large numbers and genetically manipulate their genomes as well as genders. Recent research showed that nematodes, insects and mammals share some of the same mechanisms of ageing. Therefore, we anticipate that the results of this proposal will be applicable to other organisms.

The comparison of organisms that have naturally different ageing rates may lead to new insights into the causes of ageing. This research will make use of a nematode that shows plasticity in ageing. This nematode, referred by its strain name SB347, produces hermaphrodites that live a third longer than females. The advantage of this system is that we can convert one gender into another, thus being able to disentangle developmental trajectory and mode of reproduction from lifespan. SB347 has many of the features that made C. elegans a prominent model in ageing research: it can be easily cultured in the laboratory, has a short lifespan, and rapid reproduction with large progeny size. In our first aim, we will contrast the ageing process between hermaphrodites and females, and tease apart the possible developmental and physiological causes underlying the differences in ageing process. We will use microscopy and loss-of-function mutations to characterize the morphological and physiological changes that occur during ageing. In this aim, we will also investigate if the ageing process is compatible with the theory that ageing is the result of hyperfunction of developmental processes. We will study in details three types of changes that occur during ageing and that are related to reproduction (yolk, oocyte and pheromone production). In the second aim, we will test if the different modes of reproduction and different rates of calorie intake can explain differences in lifespan and ageing between the two genders. We will perform RT-qPCR, laser microsurgery and diet manipulations to investigate the role of the reproductive mode and diet in the lifespan.

This research will shed some light on possible causes for ageing that are broadly applicable to a wide range of organisms. Our novel approach, of using a species with phenotypic plasticity in ageing and of using a relatively new theoretical framework for explaining ageing, may provide fresh insights into the causes of ageing. This multidisciplinary project, involves state-of-the-art bioinformatics, genetics, genomics, biochemistry, laser microsurgery and organic chemistry research techniques.

The work has high potential for future links within industry. Screening of biological compounds in the relatively long-lived vertebrate systems are labor-intensive and very costly. In contrast, the short lifespan of nematodes, simplicity and wealth of knowledge about their biology make them attractive models for pharmacological research. For the particular species described in the present proposal, it is an ideal species to screen compounds that affect ageing in more than one gender. The current models, as C. elegans, usually test the effects of ageing in only one gender, the hermaphrodite, because males are rare. No such a problem is found in SB347.

The PI will continue participating in outreach programs to disseminate results of his research to the broad public. The PI has a track record of working the lay public in presentations in parks, open-day events, schools and television.