Exploiting Alzheimer's disease patient-derived stem cells to biochemically define tau and amyloid-beta oligomer toxic features and their downstream cellular effects

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Project Summary: Alzheimer's disease (AD) is an ever-growing socio-economic burden across the globe. Oligomerized amyloid-b peptide (Ab) and hyper-phosphorylated tau are the pathological hallmarks of the disease and a key piece of the neurodegenerative cascade that leads to symptoms. To develop effective oligomer targeting therapies, we must fully describe the biochemical attributes of the target. The objective of this grant is to link oligomer structural components to toxic bioactivity and delineate the steps in the AD neurodegenerative cascade. The central hypothesis is that by using AD patient derived induced pluripotent stem cells (iPSC) cultured as cerebrocortical organoids, we can recreate the AD niche closely enough to produce brain-like Ab and tau oligomers and to understand cell type specific responses to oligomer exposure. Our rationale is that the cell type in which a protein is made heavily impacts its function and so to fully recapitulate AD in vitro, you must model the human brain. Our AD patient derived iPSC model will capture the important genetic and tissue specific elements to support Ab/tau oligomerization and intercellular communication networks. Our specific aims will test the following hypotheses: (Aim 1) AD patient iPSC grown as cerebrocortical organoids recreate the AD niche and produce bioactive Ab and tau oligomers; (Aim 2) Through toxicity screening on iPSC derived neurons and glia independently, we will discover the primary and secondary cellular responders to Ab and tau oligomer exposure; (Aim 3) Not every cell is exposed to Ab and tau oligomers directly and yet there is wide spread degeneration. Subpopulation oligomer exposure in an AD-organoid will uncover the intercellular communication networks that causes this phenomenon. Upon conclusion, we will understand the structural components that make Ab and tau oligomers bioactive, what the main oligomer responding cell types are, and how intercellular communication upon oligomer exposure of some cells, effects all the cells in the niche. This contribution is significant because a new, reliable, and relevant source of Ab and tau oligomers is needed by the community for large scale studies. Currently used post-mortem brain tissue is scarce and due to the high lipid content, difficult to use as a source material. Further, by biochemically defining a bioactive Ab and tau oligomer, therapeutics can be designed to specifically target it. This research will also establish which cell types in the disease niche are the primary and secondary responders to Ab and tau oligomers. By examining oligomer response in both stem cell derived brain cell types in isolation and in the organoid niche, we will establish the steps in the neurotoxic AD cascade. The proposed research is innovative because we will illustrate a new use for patient derived stem cells as a reliable source for bioactive oligomers. This finding can be extrapolated to other diseases such as Parkinson's disease and its related a-synuclein protein aggregates. Additionally, we have designed a new use for RNA drop sequencing to multiplex oligomer uptake tracking and single cell transcriptomics through a nucleotide barcoding strategy.