Mitochondrial redox protein quality control in ageing

Mitochondria are fundamental components of animal cells that are essential for proper cell metabolism and physiology. To work properly mitochondria need to respond to stress and metabolic changes, adapt their protein content accordingly and adjust their function across the lifespan of an organism. Our project will address exactly these questions using simple yeast cells and fly models. Mitochondrial dysfunction is linked to ageing, and to numerous human pathologies and so the maintenance of their normal function is very important. Mitochondria produce small molecules called reactive oxygen species (ROS) which are important for signalling in the cell but at high levels become highly damaging. On the other hand, protein maintenance in mitochondria is subject to redox control but the details of this process are still elusive. In our project we will elucidate how a redox-dependent mechanism allows proper quality control of the proteins in mitochondria and how this in turns allows cell survival and proper development across the lifespan of an organism, particularly in the face of deleterious stresses. This is absolutely critical because maintaining a fine balance between redox proteins and ROS species makes all the difference for ROS being beneficial as signalling molecules in low levels or reverting to damaging agents for the cell at high levels.
We will first investigate the function of a reductive machinery that we recently found to be targeted to the intermembrane space (IMS) between the outer and inner mitochondrial membranes. This could impact on either ensuring correct folding of proteins in the IMS or efficient clearance in case where they are misfolded. Then, we will ascertain how the redox machinery in the IMS provides a surveillance mechanism to maintain a balanced redox state not just for proteins but also for small metabolite molecules that are made in mitochondria and need to be released out of mitochondria as critical signalling molecules for the rest of the cell. Finally, we will use fly models to investigate at a whole organism level the role of those quality control mechanisms that preserve protein redox homeostasis in the IMS on lifespan.
Our findings offer the first opportunity to explore a poorly characterised reductive pathway in mitochondria and its impact or redox homeostasis. This is critical to effectively defend cells against deleterious oxidative stress and sustain survival. The work is likely to provide a novel paradigm for understanding the coordination of protein redox control and oxidative stress signalling in eukaryotic cells and their effects on ageing.

Our aim is to elucidate the redox protein quality control processes in mitochondria and how they impact the ageing process. This knowledge is missing and is a prerequisite to fully understand how mitochondria can maintain a healthy redox balance that is critical for cell survival and stress resistance. This requires a knowledge of both oxidative and reductive pathways and an interplay of these with mitochondrial ROS (mtROS) to preserve mitochondrial fitness in response to deleterious stresses and metabolic alterations. This is particularly important in maintaining the redox reactions within boundaries that are beneficial for cell physiology and survival across the lifespan rather than detrimental due to cell damage

We will use a combined biochemistry, cell biology and redox biology approach bringing together the expertise of the two applicants using three model systems ie yeast, mammalian cultured cells and Drosophila. Our work program will (1) investigate how reductive machinery operates in the IMS in retention of folded protein retention or retrograde export and degradation, (2) Dissect the effects on the global IMS redox state and mitochondrial metabolite transport in signalling processes and (3) Investigate the redox protein quality control as a key determinant in organismal ageing using Drosophila.
The proposed work will transform our knowledge by developing key aspects of mitochondrial biology shedding new light on how an IMS redox quality control operates in response to stresses and metabolic alterations to sustain mitochondrial homeostasis across the lifespan.