Nuclear Dysfunction in Alzheimer's and Related Dementia: The Role of Heteromeric aggregation of RNA-Binding Protein Musashi1 and Tau - Alzheimer's disease (AD), the most common form of dementia, affects millions globally. In AD and primary tauopathies, neuronal Tau misfolds and aggregates into intracellular neurofibrillary tangles, with mutations, post- translational modifications, and intermolecular interactions, promoting Tau oligomerization. Soluble Tau oligomers (TauO) are a highly toxic species and spread pathology across brain regions. Recent findings from our group and others reveal that AD, amyotrophic lateral sclerosis (ALS) and frontotemporal lobar dementia (FTLD) are characterized by the concurrence of multiple protein inclusions. Among these, several RNA-binding proteins (RBPs), such as TDP-43 and FUS, irreversibly self-aggregate and form heteromeric aggregates with Tau, though their pathogenic role in AD and AD-related disorders (ADRD) remains unclear. Our recent findings identified RBP Musashi1 (MSI1) as a key contributor to TauO-mediated toxicity in both AD and FTLD-Tau. In these pathologies, neuronal MSI1 displays elevated expression, mislocalization, self-aggregation, and hetero aggregation with TauO in the cytoplasm and nucleus. These findings underscore the critical role of nuclear activities and highlight the importance of RBPs/Tau co-pathologies in the progression of AD/ADRD. However, how pathogenic Tau drives nuclear dysfunction in AD remains unknown. We propose that, in AD, MSI1 and Tau oligomers form harmful heteromeric aggregates that disrupt nuclear functions, leading to alterations in chromatin structure and expression implicated in AD pathogenesis and progression. The primary outcome of this application is to comprehensively determine the pathological effects of MSI1 self- aggregation and its hetero aggregation with Tau in AD/ADRD. Building on our published data, we will determine the impact of these pathological aggregates on nuclear activities, which remains undetermined. In Aim1, our objective is to determine the impact of MSI1 alterations on Tau pathology using in vivo models. We will harness a MSI1 promoter-GFP reporter line combined with Tau pathology mouse models to trace MSI1 expression, self- aggregation and co-aggregation with Tau during disease progression. We will also use antisense oligonucleotides to knock-down MSI1 expression in vivo and assess its effects on Tau pathology. In parallel, computational/structural methods will provide insights into MSI1’s self-aggregation, and its co-aggregation with Tau in cellular compartments. In Aim2, our objective is to determine MSI1 and Tau pathogenic roles in nuclear dysfunctions in AD, and the subsequent impact on chromatin remodeling and gene expression alterations in AD, using proteomics, RNA-Seq, and ATAC-Seq, RIP and iCLIP to assess changes in MSI1 RNA binding properties in primary neurons. Our approach goes beyond the previous focus on cytoplasmatic toxicity by examining heteromeric aggregates at the nuclear level. By linking aggregation and nuclear pathology, our study seeks to advance the field by identifying altered nuclear structures and chromatin domains caused by homo- and hetero- aggregates of Tau in AD/ADRD, paving the way for innovative and mechanisms-based therapeutic opportunities.
