Rescuing mitochondria in peril by targeting of a critical antioxidant protein

This project aims to advance our understanding of how mitochondria are able to retain their function under severe stress. Mitochondria are fundamental components of animal cells that are essential for proper cell metabolism and physiology. Mitochondrial dysfunction is linked to ageing, and to numerous human pathologies and so the maintenance of their normal function is very important.

The project will analyse how a critical antioxidant protein that normally resides in the cytoplasm is redirected into redox stressed mitochondria and how it is then able to ameliorate this stress. Protein import into mitochondria is essential for their construction. Most mitochondrial proteins (~10-15% of the human proteome) are synthesized in the cytosol and so must be imported following their synthesis. Under healthy conditions most of the import of most of these proteins is powered by the mitochondrial transmembrane energy gradient. Remarkably this antioxidant protein is imported by a system that does not require this energy gradient, which is just as well since that gradient is compromised under these severe redox stress conditions.

Our findings offer the first opportunity to explore the mechanism of this entirely new import pathway that is critical to defend cells against deleterious oxidative stress. Our interdisciplinary approach outlined in this project will further our understanding of mitochondrial protein import and cell stress mechanisms and it is likely to provide a novel paradigm for understanding the coordination of oxidative stress signalling in eukaryotic cells.

We have recently discovered that under severe redox stress mitochondria are able to import a protective antioxidant protein that is able to promote reactions that counteract this stress. This protein normally resides in the cytoplasm and is only redirected to the mitochondria under conditions of strong redox stress. Somehow this stress is detected and it results in the antioxidant protein being expressed from a novel start site that introduces a specific leader sequence that targets the protein to the mitochondria. Its import uses a novel uptake system that does not require the mitochondrial proton motive force. This project aims to fully characterise the molecular processes whereby it is imported and how it discharges its antioxidant function. Mitochondria are not only important for cellular energy metabolism but they also play a key role on apoptosis and their dysfunction is linked to many pathologies. Understanding mechanisms that can potentially save mitochondria from irreversible damage are therefore very important.

This proposal addresses a fundamental research question developing new concepts at the core of ideas emerging within the international cell biology and chemical biology community. The work is based on the study of a critical yet unexplored pathway of targeting an antioxidant protein into mitochondria in peril of irreversible loss of function due to severe oxidative stress. The research should stimulate thinking about the topics of plasticity of the mitochondrial protein import system under stress and compartment-specific discharge of stress defence mechanisms. It should help facilitate a paradigm shift in approach. These studies are based on recent findings by KT's group in expanding the capacity for protein targeting mechanisms into the mitochondrial IMS and how an antioxidant protein in the cytoplasm can relocate to the organelle under severe stress conditions. Mitochondrial function is central to life of all cells. As a consequence mitochondrial dysfunction is key to several devastating human diseases and ageing. The fundamental bioscience questions underpinning this research will apply to a very broad range of research audiences: cell biologists and biochemists, biomedical researchers and clinical scientists. This research project has the potential to have significant and wide-ranging impact. In addition to solving a fundamental biological question, our aim is to develop the chemistry required to produce new peptide tools that will be used to investigate protein-protein interactions that define the cellular architecture.

Longer term beneficiaries include the pharmaceuticals, healthcare agencies, patients and the general public. More immediate, academic and educational impacts will be delivered to researchers and students in this field. Specific communication channels:
1. Industry: We have made contacts with the Dundee Drug Discovery Unit and the University's knowledge exchange partnership with AstraZeneca, GLAZgo. With these industry partners we have identified clear pathways whereby once a potential target or technology is identified we will apply for company funded initiatives to develop an activity assay for future drug screens. Other University KE support mechanisms will be leveraged at various stages including research and business development managers, relevant events and communications channels.
2. Public: We have set up several communication channels via our website, and we will continuously update the college research and business development office as a means of dissemination to stakeholders. Outreach activities will be undertaken by the PI and the PDRA as public lectures incl. the Science Show-Off, Glasgow Science Festival, Glasgow Pint of Science and Science Showcase at the Hunterian Museum.

The new chemical biology tools we propose could impact a diverse range of beneficiaries including academics, the pharmaceutical industry and the general public. We plan to engage with beneficiaries in academia and the pharmaceutical industry through dissemination of our research results in high impact journals, at conferences (both home and abroad) and through professional networks (e.g. Protein-Protein Interaction Network). The general public will also be engaged with our research using news articles appearing on our website and through social networking sites

Dissemination to the immediate beneficiaries (academics at all levels) will be through publications, reviews on the state-of-the-art suitable for a wider audience incl. healthcare/pharmaceutical professionals and decision and policy makers, and presentations in international meetings (FEBS, EMBO, Gordon Conference) and invited talks in Academia and Industry. The PDRA and technician will benefit from tailored training and mentoring.