Regulation of antioxidant gene expression, oxidative stress resistance and ageing by peroxiredoxins

Our cells are unavoidably exposed to harmful reactive oxygen species (ROS) which are produced as unwanted bi-products of normal metabolism. Exposure to sunlight, drugs and environmental chemicals, such as heavy metals, also lead to increased ROS-levels in cells. ROS cause cellular damage (oxidative stress) that is an important cause of ageing and of many diseases, such as cancer. Our cells contain protective antioxidant proteins which detoxify ROS, limiting this cellular damage. Oxidative stress stimulates the increased production of antioxidants. Peroxiredoxins are one such group of antioxidant proteins which protect against oxidative stress and have been shown to have roles in cancer. Peroxiredoxins are found in different tissues and have several different activities. Using genetic studies in the nematode worm Caenorhabditis elegans we will examine how peroxiredoxins in different tissues protect against oxidative stress and ageing. This work will also identify genes required for increasing antioxidant levels in response to oxidative stress. The power of genetic studies C.elegans to yield important insight into fundamental biological processes in humans is widely recognised. For example, two Nobel Prizes for Medicine have been recently awarded for advances made through studies in C.elegans. In addition to their genetic amenability, these worms have a number of features which make them ideally suited to our studies. For instance, their short lifespan of only a few weeks will allow us to rapidly determine whether genes we identify affect ageing. Indeed we will be able to examine whether these genes are involved in known lifespan-increasing mechanisms. Importantly, genes we identify are extremely likely to have counterparts in human which may be important in protecting against cancer, bacterial infections and ageing-associated diseases. Ultimately, these studies may suggest future strategies to manipulate levels of oxidative stress protective proteins that might be used to prevent ageing and age related diseases.

Oxidative stress-induced damage is a cause of ageing and a component of many human diseases. Peroxiredoxins (Prx) are conserved antioxidant enzymes with important roles in protecting against oxidative stress. The short lifespan and amenability to genetic manipulation render the nematode worm Caenorhabditis elegans an excellent model for studies of stress-signalling/responses and ageing. We have found that, PRDX-2, the C.elegans orthologue of the tumour suppressor Prx1, is required for peroxide stress resistance and normal longevity but, unexpectedly, loss of the antioxidant PRDX-2 increases the resistance of C.elegans to heavy metal-induced oxidative stress. The aim of the research is to dissect how PRDX-2 produces these diverse effects on oxidative stress resistance and ageing.
Objectives:
[1] Is PRDX-2 required for the long-life and enhanced stress resistance associated with loss of Insulin/IGF-like signalling, calorific restriction, mitochondrial defects or loss of germ cell proliferation? Genetic studies in C.elegans have identified loss of function mutants that independently increase stress resistance and extend lifespan. We will combine long-lived mutant alleles with the short-lived prdx-2 mutant allele to determine which of these longevity-promoting signals requires PRDX-2.
[2] In which cell type/s is PRDX-2 expression required to (i)promote longevity (ii)reduce heavy metal stress resistance? Intestinal expression of PRDX-2 restores hydrogen peroxide resistance but does not rescue the shortened lifespan or elevated heavy metal resistance of a prdx-2 mutant. PRDX-2 is expressed in a variety of cell-types. We will generate transgenic C.elegans expressing PRDX-2 in particular cells and use these to dissect the role that the cellular expression pattern of PRDX-2 plays in heavy metal resistance and longevity.
[3] Which genes are required for the increased expression of a stress-induced reporter gene in the prdx-2 mutant and how does loss of expression of these genes affect stress resistance and lifespan? Like mammals, C.elegans contain stress-activated MAPK signalling pathways that are important for the expression of genes required for oxidative stress resistance and innate immunity. Using prdx-2 mutant C.elegans, we have uncovered the existence of other signalling pathway/s regulating expression of a stress-induced reporter gene. We will use an RNAi screen of the C.elegans genome to identify genes required for oxidative stress-induced gene expression in prdx-2 mutant C.elegans and characterise their role/s in stress responses and ageing.
Together these studies will identify new regulators of antioxidant gene expression and provide important insight into how Prx tumour suppressors affect stress responses and ageing in the context of a whole animal.