Mitochondrial regulation of neuronal presynapses in health and disease

A PhD project for the 2022 doctoral clinical fellows programme with Mike Devine (primary supervisor, Crick) and Selina Wray (UCL)

Project description

Selina Wray

Professor of Molecular Neuroscience, Neurodegenerative Diseases, UCL Queen Square Institute of Neurology

Fundamental to the success of complex multicellular life has been the evolution of the nervous system, because this enables organisms to respond to stimuli in a rapid and coordinated manner. However, nervous systems are expensive: the human brain comprises just 2% of the body's mass, yet utilises 20% of the body's energy.

This energy is needed to power synapses, where neurons communicate with each other. In order to process information, not all synapses are active simultaneously; therefore energy usage varies hugely between synapses within individual neurons, and at individual synapses over time. Additionally, neurotransmitter release at synapses is triggered by a rapid influx of Ca2+ ions in response to incoming action potentials, so synapses must quickly clear Ca2+ to stop neurotransmission and prepare for future release events. A key question in the field is how do neurons meet such spatiotemporally diverse energy and Ca2+ buffering requirements? 

Mitochondria are ideally suited to help, because they are a potent source of ATP (via oxidative phosphorylation) and they avidly take up local Ca2+ via the mitochondrial calcium uniporter. Crucially, they are also mobile: they move within neurons to where they are most needed. They frequently localise to presynapses where they support sustained synaptic transmission via provision of ATP [1]. But recently we and others have shown that presynaptic mitochondria can lower neurotransmission via buffering local Ca2+ [2]. So mitochondria play a dual role in shaping synaptic activity, which has potentially far reaching implications for diseases featuring a mismatch between energy demand and supply (such as stroke and epilepsy) and our recent studies suggest that this delicate balance of Ca2+ regulation and ATP provision breaks down in models of Parkinson's disease — a neurodegenerative disorder that currently has no cure.

We are also interested in whether all mitochondria within a neuron are equivalent, or whether specific subtypes of mitochondria exist in different subcellular locations. If the latter, are particular mitochondrial subtypes susceptible to disease? To tackle this, we have been using a novel nanotweezer to directly ‘biopsy’ and then compare individual mitochondria from different locations within live neurons, enabling us to study single mitochondria in unprecedented detail [3].

Potential projects

  1. establishing the role of presynaptic mitchondria in regulating synapses in midbrain dopaminergic neurons (the neurons most vulnerable in Parkinson’s) and whether they could contribute to the ‘silencing’ of these synapses [4],
  2. how mitochondria precisely localise at presynapses in order to appropriately buffer Ca2+,
  3. how presynaptic mitochondria interact with endoplasmic reticulum, which can itself buffer Ca2+ thereby tuning synaptic activity [5],
  4. studying subcellular mitochondrial heterogeneity within neurons via single mitochondrial biopsy.

Techniques include primary neuronal and slice culture, iPSC culture and neuronal differentiation, live synaptic imaging, 3D electron and superresolution microscopy, microfluidics, genomic and transcriptomic analysis, and nanobiopsy.

Medical relevance

The goal of the lab is to unpick the molecular mechanisms by which mitochondria govern synaptic transmission, and how this changes in neurological and psychiatric disease, with the aim of opening up new therapeutic avenues for these disorders.

The partner institution for this project is UCL.

References

  1. Devine, M.J. and Kittler, J.T. (2018) Mitochondria at the neuronal presynapse in health and disease. Nature Reviews Neuroscience 19:63-80
  2. Vaccaro, V., Devine, M.J., Higgs, N.F. and Kittler, J.T. (2017) Miro1-dependent mitochondrial positioning drives the rescaling of presynaptic Ca2+ signals during homeostatic plasticity. EMBO Reports 18:231-240
  3. Nadappuram, B.P., Cadinu, P., Barik, A., Ainscough, A.J., Devine, M.J., Kang, M., Gonzalez-Garcia, J., Kittler, J.T., Willison, K.R., Vilar, R., Actis, P., Wojciak-Stothard, B., Oh, S.H., Ivanov, A.P. and Edel, J.B. (2019) Nanoscale tweezers for single-cell biopsies. Nature Nanotechnology 14:80-88.
  4. Pereira, D.B., Schmitz, Y., Meszaros, J., Merchant, P., Hu. G., Li, S., Henke, A., Lizardi-Ortiz, J.E., Kzrpowicz Jr, R.J., Morgenstern, T.J., Sonders, M.S., Kanter, E., Rodriguez, P.C., Mosharov, E.V., Sames, D. and Sulzer, D. (2016) Fluorescent false neurotransmitter reveals functionally silent dopamine vesicle clusters in the striatum. Nature Neuroscience 19:578-86
  5. de Juan Sanz, J., Holt, G.T., Schreiter, E.R., de Juan, F., Kim, D.S. and Ryan, T.A. (2017) Axonal Endoplasmic Reticulum Ca2+ Content Controls Release Probability in CNS Nerve Terminals. Neuron 93:867-881