Regulation of neuronal energy production by SUMOylation

The human brain uses 20% of the body’s energy but makes up only 2% of its mass. The 100 billion neurones which make up the functional units of the brain require a constant supply of energy, mostly in the form of glucose, in order to maintain and regulate their membrane potential over their large surface area. Without the constant production of ATP by glycolytic and mitochondrial metabolism, normal brain functions fail, which is a major contributory factor in multiple neurological and neurodegenerative diseases. Surprisingly, however, the regulation of metabolism in neuronal cells is still poorly understood.

Several proteins that are critical for the regulation of glycolysis and mitochondrial metabolism are post-translationally modified by Small Ubiquitin-like Modifier (SUMO). SUMOylation is the covalent attachment of an ~11kD protein (SUMO1, 2 or 3) to lysine residues in target proteins. It is a highly dynamic reversible 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 tight regulation of deSUMOylation may be a critical determinant of the extent of SUMOylation of substrate proteins. Consistent with this concept, SENPs are acutely regulated by changes in cellular redox states, which also play a role in regulating energy metabolism.

We have previously identified a number of mitochondrial SUMO substrates and demonstrated that SUMOylation plays a crucial role in regulating mitochondrial morphology in both cell lines and primary neurones. Moreover, our preliminary data suggests that that neuronal glycolytic and mitochondrial metabolism are regulated by SUMOylation. A large body of evidence links SUMOylation to the regulation of normal neuronal function, including neurotransmitter release and memory formation. Moreover, dysfunctional SUMOylation contributes to the pathology of multiple diseases. Remarkably, however, the roles of SUMOylation in the regulation of neuronal metabolism have not been extensively investigated.

In close collaboration with Dr Kevin Wilkinson (Senior Research Associate, Henley laboratory, University of Bristol) this project will use molecular and cell biology techniques to manipulate SUMOylation in neuronal cell lines and primary neurones. We will investigate how altering global SUMOylation, or the SUMOylation status of individual target proteins, affects cell metabolism and function. The student will be trained in a wide variety of molecular biology techniques, Western blotting, cell culture, confocal microscopy and real-time metabolic analyses.

More specifically, the student 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. S/he will use lentiviral-mediated knock-down or overexpression 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, which can simultaneously measure key metabolic parameters including mitochondrial oxygen consumption and glycolytic flux. In parallel, s/he will use confocal microscopy to examine mitochondrial morphology, and Western blotting to monitor known SUMO substrates and assign metabolic effects to individual SUMOylation events. S/he 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 combination of techniques will allow us to fully investigate the role of SUMOylation in the regulation of neuronal metabolism, which will greatly advance our understanding of energy homeostasis in the brain. The data generated will provide new and important insights into how SUMOylation and deSUMOylation impact on energy production in healthy and stressed cells.