A novel Drosophila platform to replace the use of mice and zebrafish for the study of ER-mitochondria interactions.

Lead Research Organisation: King's College London
Department Name: Clinical Neuroscience

Abstract

A rapidly ageing population and the associated burden of age-related disease are two of the major societal and financial challenges facing developed and developing countries. Understanding the molecular processes that underpin ageing is a fundamental biological question and a critical step in designing interventions that could increase healthy life expectancy (healthspan). It is particularly important to understand the processes that contribute to ageing of neurons, as ageing is a major risk factor for many neurodegenerative diseases.

The proposed project will advance our basic understanding of the cell biology of neuronal ageing by shedding light on the molecular mechanisms by which the communication between the ER and the mitochondria affects neuronal functionality over time. Communication between the two organelles regulates a number of processes, for instance calcium and phospholipids exchange, essential for proper cellular functions. The project will take advantage of a new platform that we developed to monitor ER-mitochondria interactions in Drosophila melanogaster as part of a long-term project aimed at studying the cell biology of neuronal ageing.

Studying the cell biology of neurons in adult animals requires intravital or ex vivo imaging approaches, which in vertebrate model organisms are technically challenging and time-consuming. Moreover, such studies require a significant number of animals and often use surgical procedures. Our imaging system affords non-invasive, detailed imaging of intracellular dynamic processes in ageing neurons of ageing fruit flies. This system exploits the accessibility to microscopic observation of sensory neurons in the adult wing of Drosophila. The relatively short lifespan of fruit flies makes longitudinal studies feasible and the sophisticated genetic tools available in this organism greatly facilitate functional studies. Our methodology represents a significant advance for the field, allowing imaging of live neurons in an intact adult nervous system to be coupled to powerful genetic tools. With this system, we have been able to make significant progress towards understanding how specific neuronal functions decline during ageing.

In our past work, we have discovered a remarkable age-dependent decline in the axonal transport of mitochondria in adult neurons of Drosophila. Reduced transport contributes to the broader decline of neuronal homeostasis that occurs during ageing while upregulation of this process appears to be beneficial in older neurons. Although these findings provide a strong association between mitochondrial motility and neuronal function, it is still unknown how modulation of transport mechanistically affects neuronal ageing phenotypes. An exciting possibility is that the interactions between the mitochondria and the ER would directly regulate mitochondrial transport and functions thus significantly impacting on neuronal ageing.

By transferring our technology into the laboratory of Dr Tito Cali at the University of Padova (Italy), this work will reduce the number of mice and zebrafish used to study ER-mitochondria communications and further expand the utility of our Drosophila model to maximise its 3Rs potential.

Technical Summary

Many functions essential for neuronal survival are regulated by specialised contact sites between two cellular compartments, the ER and the mitochondria. It has become increasingly clear that disrupting ER-mitochondria contacts sites is a mechanistic step in a number of neurodegenerative diseases. Restoring damaged ER-mitochondria associations is therefore an exciting therapeutic target to ameliorate neuronal functions in disease. However, it is not clear how to precisely modulate the association between the two compartments because the full repertoire of complexes that mediate ER-mitochondria interactions is yet to be discovered. Whether perturbing the physical connection between the two organelles can impact on the ageing process of neurons is still an open question.

The majority of studies to date have been performed in cultured cells and surprisingly little work has been done in model organisms or using in vivo approaches. This is a considerable limitation and it has prevented a full understanding of the ER-mitochondria axis and its implication in ageing and disease.

I have established a novel assay that allows imaging of live neurons in the intact nervous system of the adult Drosophila (PMID:26598558). Based on this assay, I recently developed a procedure suitable to image ER-mitochondria interaction and produced transgenic flies that harbour a new reporter of ER-mitochondria contact sites. By coupling this protocol to the powerful genetics of the fruit fly, we are able to specifically visualise and interfere with the ER-mitochondria interactions in vivo over the lifespan of the animal. Our new platform will also be crucial in future work aimed at discovering novel factors that affect ER-mitochondria interactions during ageing and in the diseases of the nervous system.

Publications

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