WP1: To investigate different aspects of Aβ overproduction in AD patients and what causes neurodegeneration, we created several fly lines that recapitulated different aspects of this overproduction. Results: Length of Aβ was important in causing toxic effects and also secretion from neurons. This led to cognitive defects and reduced longevity. Subsequent immunostaining showed that plaque-like deposits of Aβ were not the cause of toxic effects.
WP2: We set out to determine if neuronal damage is localised to neurons that express Aβ or if non-secreting neighbouring neurons are also affected. We expressed toxic Aβ from subsets of neurons and assessed how expressing and non-expressing neighbouring neurons were affected. Results: Certain subsets of neurons are more susceptible to Aβ accumulation. Aβ was observed at distant neurons and, often these neurons had greater accumulation than some neurons that were actually producing and secreting the Aβ. These results support the observations that not all brain regions are affected equally in AD patients - some regions are more susceptible than others. It is unknown why different brain regions have varying levels of vulnerability. Now that we have replicated these findings in a model that is much easier and faster to genetically manipulate and image, we continue to aim to provide novel insight into this unknown.
WP3: We aimed to dissect the molecular mechanisms involved in these phenotypes. In addition to the plethora of genetic tools at our disposal, thanks to the genetic tractability of Drosophila, we also had the benefit of being able to feed the animals compounds as an alternative approach to investigate different pathways involved. Due to the timeframe of the project, we sped up our search of pathways by systematically worked through a large range of compounds by feeding them to the animals for several days and then assessing the effects on cognitive defects and longevity. We then developed RNAi fly lines and mutant lines for genes of interest identified through the screen. A list which grew longer as we gained novel insights from the compound screen. Results: Of particular interest to our research group, was the role of efferocytosis in our phenotype. We found that inhibition of this process could reduce the cognitive defects. The speed at which efferocytosis occurs has previously presented an immense challenge for researchers aiming to unravel this process, however, fortunately for us, over the past few years the fly embryo has emerged as a powerful model for studying this process in vivo. As such, we have started to develop a novel state-of-the-art understanding of the role that efferocytosis plays downstream of the overproduction of hAβ42 in the brain. Information which, as it stands, is close to peer-reviewed publication, but additionally, opens up a wealth of research for me to continue in my own lab when I secure the opportunity.
Overview
The project has found that the length of Aβ was important for causing toxic effects and also that it needed to be secreted from neurons. We also identified the importance of the Aβ being secreted, as there were no ill effects in our flies when the amyloid peptide was not secreted. We also discovered that certain types of neurons are more susceptible to Aβ accumulation, whether or not they produce this peptide themselves. Furthermore, we found that inhibition of efferocytosis could improve cognitive defects and have continued building a clear picture of how this process occurs using state-of-the-art equipment and techniques.
Exploitation and dissemination
Research was presented regularly at seminars in the university to a diverse audience [6 seminars], and internationally at the large neuroscience, Neuroscience 2022, and Drosophila, 62th ADRC, conferences [2 conferences]. We have established new collaborations both in the UK and the EU to assist in aspects of the project outside our field of expertise. Results are being compiled and developed for peer-review publication. No specific website has been developed for the project.
