Functional characterisation of newly identified Alzheimer's Disease associated genes in human and invertebrate model systems

Alzheimer's disease is the most common form of dementia, a neurological disorder which causes profound loss of memory and cognitive ability. The symptoms of Alzheimer's disease are caused by progressive death of neuronal cells in the brain. The degeneration of neurons in the brains of people affected by Alzheimer's disease is accompanied by the build-up of 'amyloid' protein in the brain. As neurons die and amyloid protein accumulates, specialised 'microglia' cells - a type of immune cell that clears away waste material from the brain - become activated and may themselves further contribute to the death of neurons.
Alzheimer's disease is often found to be inherited within families. This observation suggests DNA genes encoded within an individual's genome may contribute to susceptibility of developing the disorder. In an effort to understand how genes can contribute to Alzheimer's disease, large 'genome wide association studies' (GWAS) have compared the DNA of tens of thousands of people with and without dementia. These studies have been remarkably insightful, identifying many dozens of genes that are linked to increased susceptibility of developing Alzheimer's disease. Understanding how these genes alter the health and function of neurons and microglia is one of the current challenges in the Alzheimer's Disease research field, particularly due to the rate of discovery of new susceptibility genes.
Our project will focus on a new list of genes linked to increased susceptibility to developing Alzheimer's disease. The European Alzheimer DNA BioBank (EADB) is the largest GWAS study to date - identifying 75 genes linked to Alzheimer's disease of which 42 are new discoveries. To rapidly test how these new genes might contribute to Alzheimer's disease, we are turning to a remarkably powerful experimental model system: fruit flies. Thought small, flies have a complex brain which can replicate many of the symptoms and pathologies of people living with Alzheimer's disease. Furthermore, the fly genome shares much similarity with the human genome, containing many of the genes linked to Alzheimer's disease. Using genetic manipulation of fruit flies we will test how the genes identified by the EADB study aggravate or suppress features of Alzheimer's disease, including changes in behaviour, lifespan and amyloid protein build up in the brain.
We will use these fly experiments to identifying genes from the EADB study that strongly modifying features of Alzheimer's disease pathology. To further our understanding of how these genes increase risk of humans developing Alzheimer's disease, we will next test the highest priority genes identified from our fly experiments in state-of-the-art cell cultures of human neurons and microglia. We will grow cell cultures of neurons and microglia that have been genetically engineered to replicate the changes in human genes identified by the EADB study. We will define how our prioritised Alzheimer's disease susceptibility genes alter the activity of neurons, using a combination of microscopy image analysis, molecular biology techniques and electrophysiological recording. For microglia, we will test how Alzheimer's disease susceptibility genes contribute to immunity responses and waste disposal activity of these specialised cells.
Our innovative project will bring together the expertise of human geneticists, fly biologists and human cell culture research teams to rapidly identify and understand how novel genes contribute to Alzheimer's disease. Ultimately we aim to better understand how these genes alter the function of neuron and glia cells to render people more vulnerable to developing Alzheimer's disease. Advancing our understanding of the genetics of Alzheimer's disease will support future studies into how we may exploit these genes to design novel therapeutics for the treatment of dementia.

Alzheimer's disease is a complex genetic condition with a strong hereditary component, characterised by dementia associated with incurable neurodegeneration. The European Alzheimer DNA BioBank (EADB) study brought together European GWAS consortia to conduct the largest GWAS to date, defining 75 genetic loci associated with increased susceptibly. 42 of these loci are novel, including genes with protein coding variants involved in the processing of APP, with expression data suggest an unexpected microglial role for these novel genes in APP processing. Using combined Drosophila phenotypic screening and human iPSC-neuron and glia cell culture models, we will identify priority novel genes from EADB study and dissect their contribution to disease relevant phenotypes. First, we will use fly models of AD to assess the contribution of all novel susceptibly genes to behavioural, survival and amyloid pathology associated phenotypes including highly sensitive immunoassays to define APP proteolytic cleavage products. We will use findings from our fly experiments to triage genes with the strongest disease modifying activity, which will be taken forwards for further characterisation in hiPSCs derived neurons and glia. Expression of triaged AD susceptibility genes will be disrupted by CRISPR/Cas9 gene editing, in isogenic hiPSCs expressing high or low levels of APP. We will differentiate hiPSCs to mature neurons, where contribution of AD susceptibility genes to electrophysiological function, Ca2+ signalling, and amyloid processing will be defined. Mutant hiPSCs will also be differentiated to microglia, with immune stimulated cytokine release, morphological phenotypes and phagocytic activity assessed. Our innovative fly-human study will identify AD susceptibility genes from the large EADB gene list to prioritise for future research, dissect the contribution of these genes to AD pathology and potentially identify targets for therapeutic intervention.