PROJECT SUMMARY/ABSTRACT Frontotemporal dementia (FTD) is an Alzheimer’s disease-related dementia and is the most frequent form of dementia in patients under 60 years old. Mutations in the MAPT gene encoding the neuronal protein tau, including the autosomal dominant MAPT R406W missense mutation, have been linked to FTD. Induced pluripotent stem cell (iPSC)-derived forebrain neuronal progenitor cells (NPCs) from MAPT R406W carriers have provided insight on FTD pathology in vitro. These cells display p-tau aggregation, fragmentation, impaired microtubule binding, and mitochondrial deficits. RNA sequencing of patient cells also revealed differentially expressed genes involved in calcium and synaptic signaling, lysosomal function, and neuronal development. Animal models that faithfully replicate FTD are needed to understand how neuronal cell tauopathy affects the organism, identify biomarkers, and test candidate new therapies. At the Wisconsin National Primate Research Center, 6 members of a family of rhesus macaques (aged 0.6 to 19 years) were identified as carriers of MAPT R406W. Preliminary evaluation of these animals identified behavioral and imaging features that resemble the human FTD phenotype. To take advantage of this resource, we generated iPSC lines from one male and one female mutation carrier. Based on the phenotype of the rhesus carriers and the 99% MAPT sequence homology between humans and rhesus, our overarching hypothesis is that rhesus iPSC-derived forebrain cortical NPCs will mirror the tau-related phenotype and transcriptomic signatures observed in cells from human MAPT R406W carriers. To test our hypothesis, we propose: Aim 1: To phenotypically characterize iPSC-derived forebrain cortical NPCs from MAPT R406W+/- rhesus macaques with direct comparison to human patient cells. Rhesus iPSCs will be CRISPR/Cas9-edited to correct the point mutation to serve as isogenic controls. Human MAPT R406W iPSCs and their isogenic controls will be obtained from collaborators at the Tau Consortium. Mutant and isogenic human and rhesus iPSCs will be patterned to forebrain cortical NPCs to study MAPT R406W-related pathology in vitro. Aim 2: To compare the gene expression profiles of iPSC-derived forebrain cortical NPCs from MAPT R406W+/- rhesus macaques and humans. Bulk cell RNA sequencing will be performed on mutant and isogenic forebrain cortical NPCs from both species to determine if there is a shared or divergent transcriptomic signature associated to MAPT R406W. Overall, these aims will establish the validity of the rhesus NPCs as an in vitro model of FTD. This study is highly translational as these cells could serve as an in vitro platform for screening novel therapies which will help reduce the number of monkeys used for in vivo preclinical testing before human clinical trials.