PROJECT SUMMARY (OVERALL) Understanding the pathophysiology of dementia is often confounded by the uncertain causal roles of observed pathological phenotypes, even when highly correlated with disease. Genetic findings overcome these limitations by providing a causal anchor from which to begin mechanistic studies. In this regard, the genetic association between chromosome 17q21.31 and increased risk for tauopathies, including Frontotemporal Dementia (FTD) and Progressive Supranuclear Palsy (PSP), is well-established and striking. Despite this well-replicated association, little is known regarding mechanisms driving the differences in risk between the two major haplotypes, H1 and H2. This is in large part because this complex locus encompasses a genomic inversion of 970 KB, leading to an approximately 1.5Mb region where strong LD has confounded the identification of causal variants and understanding of the gene regulatory mechanisms contributing to disease. Here, we capitalize on recent advances in genomics to comprehensively characterize the genetic mechanisms by which this region, and the multiple loci within it, impart disease risk, thus identifying new targets for future therapeutic development. Our central hypothesis is that haplotype and cell type specific differences in gene expression and regulation, resulting from the H1/H2 genomic inversion lead to differences in risk for sporadic Tauopathies and differences in the effects of MAPT mutations associated with inherited forms of FTD. To test this hypothesis, we propose a multi-site, interdisciplinary center composed of two highly synergistic projects (P1, P2) and 4 cores (Proteomics, Human Tissue Validation, Data, Admin) integrating a highly complementary group of investigators with a strong history of collaboration and data sharing to connect multiple levels of function: a) genotype to b) chromatin structure to c) RNA expression and d) splicing, to protein and e) cell biological consequences to elucidate disease mechanisms. P1 will apply cutting edge multi-OMICs approaches in human induced pluripotent stem cell (iPSC)-derived neural cells and human brain tissue to determine the molecular and cellular mechanisms associated with the H1 and H2 haplotypes in individuals of European and African descent. Predicted regulatory element variation between haplotypes will be validated using a pooled CRISPR screen in assembloids. P2 uses parallel approaches to dissect the genetic mechanisms, cell types and molecular pathways involved in dominant forms of FTD-tau, and their modulation by the H1 and H2 haplotypes. Project 2 will use similar approaches to test whether H1/H2-associated differences in gene expression and regulation modulate the impact of FTD-associated MAPT mutations on disease-associated phenotypes and validate the impact of key haplotype specific enhancer/repressor regions using pooled Crispr i/a screens. Data and results generated from these projects will be integrated with existing public...