Alzheimer's Disease (AD) is a devastating disorder for which effective disease-modifying treatments are yet to be identified. Recent evidence from our laboratory indicates that neural circuit dysfunction emerges very early in AD, preceding cognitive deficits and shaping subsequent disease progression, ultimately leading to neurodegeneration and dementia. Neural circuits in AD exhibit early neuronal hyperexcitability which transitions to hypoactivity in later disease, as a result of the pathological effects of Abeta and tau (the hallmark proteins that accumulate in AD), respectively. Mouse models have been crucial to dissecting these circuit-level changes with high spatiotemporal resolution while providing remarkable insights into potential pathological mechanisms and candidate therapeutic targets. Nevertheless, clinical translation of promising therapies in preclinical models (e.g., reduction/removal of Abeta) has so far proven unviable, highlighting the limitations of animal-models as well as the challenge in disambiguating human-disease relevant pathological alterations. Current research investigating changes in neural circuit function in AD is typically conducted in mice that carry mutations/transgenes or manifest proteinopathies which reproduce phenotypes observed in human disorders. Such experiments (often of moderate severity) are highly complex, invasive, and of low-throughput, as it is often necessary to perform surgeries and implant cranial apparatus and inject biosensors/implant electrodes to enable high-resolution in-vivo recordings. These challenges emphasise the need to identify and validate complimentary and alternative models that more faithfully recapitulate human brain circuits in AD and beneficially address the use of animal models in AD research.
Technical advances in patient-derived induced pluripotent stem cell (iPSC) methodologies have recently emerged that provide an auxiliary approach with which to model human disease that can be studied and modulated under tightly controlled experimental conditions. Notably, our collaborator on this proposal, Prof. Selina Wray at UCL, building on work funded by the NC3Rs (through CRACK-IT in 2013 on the Untangle project, https://nc3rs.org.uk/crackit/untangle), has successfully generated long-term viable and homogeneous cerebral organoids from familial AD and tauopathy patients which form complex neuronal circuits and permit the study of disease-relevant circuit-level changes in human-associated neural components. Here, we propose to uniquely integrate this expertise with that of the Busche Laboratory's in state-ofart structural and functional recording techniques to study neuronal circuits in AD (i.e., Neuropixels multi-channel electrophysiology, two-photon calcium imaging, 3D lightsheet microscopy). In so doing, we aim to leverage and combine the cutting-edge methods established by both groups to establish a radically novel platform to gain transformative insights into AD circuit function, promote clinical translation, and significantly reduce reliance on animal models.
Patient-derived iPSC cultures will have the complete disease-relevant genetic profile, and the proposed high-resolution recording techniques will permit the detailed investigation of disease mechanisms in relevant cell types and overlying circuits, and provide a novel opportunity to interrogate the early cellular and molecular changes that lead to the development of clinical AD. With the increasing recognition of the importance of early neural circuit dysfunction in AD, and a growing number of laboratories worldwide utilising animal models to understand the mechanistic underpinnings of neuronal circuitry in AD, we anticipate that validation of our organoid model will lead to a substantial replacement of 25% of existing animal work, not only in our laboratory but also, subsequently, in the ~20 laboratories worldwide (equating to ~300 animals/year) which study circuit dysfunction in AD.