Regulation of neuronal energy production by SUMOylation

Neurones are highly complex energy intensive cells. Most energy is derived from glucose metabolism, therefore the regulation of glycolysis and mitochondrial function is vital for normal neuronal function. Remarkably, however, many details of how neurons activity-dependently regulate energy production remain poorly understood.

Many proteins critical for glycolysis and mitochondrial metabolism are post-translationally modified by Small Ubiquitin-like Modifier (SUMO). Moreover, we have identified that specific proteins required for mitochondrial integrity are also SUMOylated, and this plays pivotal roles in neuronal protective responses to ischaemia and oxidative stress. These findings demonstrate that protein SUMOylation is fundamentally important for the regulation of neuronal energy homeostasis, however the underpinning mechanisms have not been fully explored.

SUMOylation is the covalent attachment of an ~11kD protein (SUMO1, 2 or 3) to lysine residues in target proteins. It is a highly dynamic process, and deconjugation requires SUMO-specific proteases, of which the SENPs (SENP1-3, 5- 7) are the best characterised. Many aspects of how SUMOylation is selectively targeted to particular substrates and how their SUMOylation status is regulated are unknown. One attractive hypothesis is that deSUMOylation, rather than SUMOylation, may regulate substrate-specific SUMOylation. Consistent with this concept, SENPs are acutely regulated by changes in cellular redox states, which also play a role in regulating energy metabolism.

This project will investigate SUMO/SENP regulation of glycolytic and mitochondrial metabolism in neurones and clonal cell lines by examining the role of specific SENPs under control and metabolic stressed conditions. The student will use lentiviral-mediated ablation or enhancement of individual SENPs to examine the effects on neuronal metabolism and mitochondrial morphology. Metabolic analyses will be carried out using a state-of-the art Seahorse XFe24 analyser at UWE, which can simultaneously measure key metabolic parameters including mitochondrial oxygen consumption and glycolytic flux. In parallel, we will use confocal microscopy to examine mitochondrial morphology, and Western blotting to monitor known SUMO substrates and assign metabolic effects to individual SUMOylation events. We will also examine how specific metabolic challenges known to damage neurones in disease states (e.g. free radicals, reduced or raised glucose levels, exposure to saturated fatty acids) affect SENP levels and activity using techniques routine in the host labs.

This multi-disciplinary approach will allow the PhD student to extensively examine the role and regulation of protein SUMOylation in neuronal metabolism under different conditions, thus gaining insight into this critical process in neuronal function.