Lysosomal function in neuronal development and synaptic activity

Cells have several different compartments within them each with specialised functions. These include the nucleus, which houses the genes, mitochondria, which generate energy and lysosomes which are recycling compartments. Having separate, specialised compartments allows the cell to keep the structural proteins and the enzymes needed for these functions concentrated in one place. Additionally in the case of lysosomes, compartmentalisation also allows the cell to partition potentially dangerous enzymes away from other parts of the cell. Lysosomes are used to digest and recycle proteins, lipids and cellular components that have reached the end of their working life. This function is relatively well understood but lysosomes have other functions that appear particularly important for the health and function of nerve cells (neurons) but which are less well understood. These including storing large quantities of calcium, required for signaling cellular events, and organising complexes of proteins to manage how cells respond to their environment. The first part of this project will study some of these processes to ask why neurons depend on lysosomal function.

One of the most powerful methods of identifying how cellular processes work is to ask what happens to the cell when that process is absent or dysfunctional. We can use this approach to understand lysosomal function in neurons by studying mutations in genes which we know cause lysosomal dysfunction in humans. There are more than fifty inherited diseases in which lysosomal function is impaired and in most of these there is nervous system pathology from a young age, including such things as developmental delay, seizures and neurodegeneration. We will study mutations in some of these genes to ask what happens to the nervous system and make inferences about the normal function of lysosomes. We will ask what happens to the electrical activity of neurons and look for changes to the structure of the nervous system as it develops in animals suffering lysosomal dysfunction. Then, in the second part of the project we will begin to look at some of the proteins in lysosomes and ask how they operate with other proteins to control lysosomal function in neurons.

The project will primarily use the fruit fly, Drosophila, to study lysosomal function. While flies may look very different to mammals, at the level of the cell their biology is very similar and many of the same molecules can be seen performing the same functions. This means lessons learned from the study of flies are usually relevant to the biology of higher animals and humans. We have very powerful tools to manipulate the genes of Drosophila and it is also small, easy and quick to breed in the laboratory. Flies have several of the genes that are mutated in human lysosomal diseases so we can use the genetic tools to manipulate these genes in the nervous system of the fly to generate lysosomal dysfunction and ask what are the consequences for function.

Neurons are particularly dependent on lysosomal function. This is clear because there is early-onset neurological pathology, including developmental delay or seizures, in many of the lysosomal storage disorders, where lysosomal dysfunction occurs. How lysosomes regulate neuronal function is not known. Lysosomes are predominantly located close to the cell body in neurons and are physically separated from distal synapses so the mechanism through which they influence synaptic function is a particularly interesting problem of cell biology.

To develop an understanding of lysosomal function in neurons, this project will describe what happens to neural development and synaptic activity when lysosomes are dysfunctional. We will use mutations in lysosomal storage disorder genes to generate lysosomal dysfunction in the fruit fly, Drosophila, and perform a multi-gene survey to determine what happens to neural development in each case. We will then ask what effects each lysosomal mutation has on the electrical properties of synapses and on behaviour

To identify the molecular mechanisms underpinning the neural phenotypes we will firstly look for changes to lysosomal calcium homeostasis and ask how these affect synapse activity. Then, we will examine two cellular processes that require lysosomal activity - autophagy and TORC signaling - and ask how they are affected in each mutant. Finally, we will map protein interactions at the lysosomal membrane to identify the protein complexes regulating lysosomal function then validate key interactions in vivo in Drosophila.

1. Academic impact
This project will investigate the consequences for neural development, homeostasis and function of lysosomal dysfunction. It will primarily have academic impact. If successful, we aim to publish our results in high quality, peer-reviewed, open access journals with high visibility in the fields of neurobiology, cell biology and development and to present at scientific conferences. This will inform and instruct our colleagues' research into related aspects of neurobiology, neurophysiology, cell and developmental biology and lysosomal biology. We will increase the knowledge economy in general.

2. Long-term societal impact
In the longer term, our research will impact upon researchers interested in the large group of inherited syndromes known as the lysosomal storage disorders (LSDs). The more than 50 disorders in the group have lysosomal dysfunction as a common feature and are collectively the most common form of inherited neurological disorders with an incidence as high as 1 in 8000 live births in Western Europe. Our research is focussed on the basic cell biology of lysosomes but our findings should help to explain why neural pathology occurs in many of the LSDs. In turn, our findings will inform future translational studies searching for new avenues and targets to intervene in these disorders.

3. Training impact
This project will have an impact on the training of a junior post-doctoral fellow. By the end of the project (s)he will have received high-quality training in numerous research disciplines, in project and time management, in publication writing and, due to the requirement to work in a team, (s)he will have stronger collaborative and communication skills. All of these skills are transferable and they will benefit personally, as will the community more generally when they move to subsequent positions, be they in or outside of science. As a junior PI, I will also benefit greatly from the experience of managing my first Research Council project grant. By improving my planning, project management and collaboration skills I will improve my research output, which will benefit the both the University of Birmingham and the UK scientific community more generally.