Genome wide screen for modifiers of A beta 42-induced neurodegeneration in Drosophila

Alzheimer’s disease (AD) is a progressive neurodegenerative disease. It is characterised by two neuropathological hallmarks: neurofibrillary tangles and extracellular plaques composed of amyloid beta peptides (Abeta). The Abeta peptides are generated by differential proteolytic cleavage of the transmembrane receptor Amyloid Precursor Protein (APP). The endoproteolysis is performed by the beta-site APP-cleaving enzyme (BACE) and gamma-secretases, consisting of Presenilin 1/2, Nicastrin, APH-1 and PEN-2. Both cleavage products Abeta40 and Abeta42 are found in plaques. However, Abeta42 is the predominant form found in plaques and is considered as the main amyloidogenic peptide as it forms fibrils more easily. To investigate the molecular mechanisms underlying Abeta42-induced neurodegeneration, I am using an established fly model for AD. Drosophila melanogaster expresses human Abeta42 fused to a secretion signal for extracellular localisation under the control of UAS/GAL4 dual activation system. The overexpression of Abeta42 in the nervous system of Drosophila melanogaster results in progressive structural and behavioural phenotypes such as locomotor deficits, age-dependent neurodegeneration in the brain and reduced lifespan. Importantly, eye-specific expression of Abeta42 causes a rough eye phenotype (REP) indicating Abeta42-induced toxicity. The REP provides a tool to identify enhancers and suppressors of Abeta42-induced neurodegeneration, as they alter the REP severity. Using this model, a genetic screen for modifiers of Abeta42-induced neurodegeneration was performed through utilisation of a genome-wide RNAi library. Only RNAi lines silencing fly genes with human homologs were included (n = 7593). The modifier screen yielded 45 RNAi lines silencing genes involved in degradation, vesicular transport, protein modification, mitochondrial function and gene regulation. They were analysed with respect to their ability to modulate characteristic phenotypes induced by tissue-specific overexpression of Abate42 to gain insight into functional aspects of modifier genes in the pathomechanisms in AD. Furthermore, a fly expressing both Tau protein and Abeta42 peptides in nervous tissue was established as a model for combined toxicity of both proteins. Using this approach the study focused on Abeta42-induced Tau toxicity and its effects on survival and AD-specific Tau pathology. Additionally, the model organisms established in this study could provide tools that help to understand disease-specific processes resulting in neuronal loss