This proposal presents a powerful new approach for modeling Alzheimer's Disease (AD) and AD-related diseases (ADRD), which enables discovery of important conceptual advances in our understanding of disease mechanisms. We use mixed cultures of human neurons and astrocytes developed from iPSCs from APP717V and isogenic control subjects. These are combined together into in 3D organoids, termed “asteroids”. Exposing the asteroids to propagated tau oligomers (oTau) causes the neurons develop tau pathology and neurodegeneration, creating a novel model for AD and ADRD, termed AstAD. The AstADs rapidly and progressively develop many components tauopathy, including oligomeric tau, phospho-tau, misfolded tau, fibrillar tau and neurodegeneration. Our studies with the AstAD model reveal that oTau disrupts ribosomal biology, selectively changing levels of key ribosomal proteins known to exert non-ribosomal functions directed at regulating the transcription factor HSF1, stress granules and the p53 pathway. These actions of oTau appear to induce of a harmful dysfunctional network of heat shock proteins (HSPs) and p53 mediated activation of cell death. However, selective dissociation of dysfunctional HSP complexes with the HSP90 inhibitor PU-H71, elicits a surprising, powerful reduction oTau pathology and neurodegeneration. Dysregulation of ribosomal protein levels has been observed in proteomic studies of AD, but the significance of ribosomal dysregulation has never been questioned. Our observations lead to the hypothesis that oTau dysregulates ribosomal biology in AstAD, producing deleterious patterns of ribosomal protein and HSP expression We will use the AstAD model to determine how ribosomal dysregulation induced by Aβ, oTau or Aβ/oTau affects neurons and astrocytes. We will also use the AstAD cultures to explore functions of neuron/glial interactions in disease, and determine how protective strategies directed against neurons, glia or both provide resilience. Aim 1 will determine the pattern of physiology, pathology and gene expression produced by Aβ, oTau, fibrillar tau or Aβ/oTau. We will examine the biology of ribosomes, HSPs and RNA translation in the AstAD model, as well as characterize key pathologies associated with AD and ADRD. Aim 2 will elucidate the complex biology of tauopathies among different types of human AD and ADRD cases by examining effects on the physiological, pathological and transcriptional responses in the AstAD cultures. We will induce neuropathology in AstAD by exposure to brain lysate, oTau or fibrillar tau produced from different types of tauopathies (AD, FTD-tau, PSP, CBD and PART) as well as comparison to FTD-TDP, which does not exhibit Aβ or tau pathology. Aim 3 will determine the roles of key ribosomal and HSPs in neurons or glia during the pathological response to Aβ and oTau. We will knockdown or over-express oTau-responsive ribosomal or HSP transcripts in neurons and/or astrocytes. We will then determine the patterns of physiological, pathological and transcriptional responses to these genetic modifications. This work will lead to novel mechanisms and therapeutic targets in AD and ADRD.

This grant application develops approaches to model Alzheimer's disease in small groups of human cells, termed Asteroids, that are composed of the most abundant cell types in the brain: neurons, astrocytes and microglia. We show that these Asteroids develop pathology similar to that occurring in the brains of Alzheimer patients, and use these Asteroids to discover the biological mechanisms underlying the disease process.