RNA‐Binding Proteins Musashi and Tau Aggresome in Alzheimer’s disease

Abstract

AbstractBackgroundTauopathies, such as Alzheimer’s disease (AD), are characterized by the accumulation of toxic tau oligomers in the brain and accumulation of proteinaceous inclusions stored in cellular structures called aggresomes. Recent studies suggest that AD also exhibits pathology related to RNA binding proteins (RBPs), including Musashi proteins. Our lab has previously discovered that Musashi 1 (MSI1) and Musashi 2 (MSI2) aggregate in human AD brains and we have also visualized co‐localization with tau oligomers, suggesting toxic direct crosstalk between tau and MSI proteins. With this discovery and the growing evidence indicating MSI proteins as contributors to AD pathology, through their loss of functions it is crucial to elucidate how the interactions between misfolded tau and MSI influence tau aggregation and perhaps formation of cellular aggresomes.MethodIn this study, we characterize which tau oligomeric species, including phosphorylated and ubiquitinated ones, interact with MSI within the human AD brain (Braak Stage V‐VI). We investigate the deposition and cellular location of MSI and tau aggregates in AD and age‐matched control human cortical brain tissues by biochemical, immunohistochemistry and co‐immunofluorescence assays. Using high‐resolution microscopy and imaging analysis we measured the differences in size and morphology of MSI/tau co‐aggregates.ResultInvestigation of these co‐aggregates showed specific accumulation in neurons as well as in glial cells (astrocytes and microglia). We performed biochemical assays using commercial and in‐house antibodies to qualitatively investigate MSI1, MSI2, and tau across in AD brains. Co‐IF was performed to investigate the spatial and quantitative distribution of MSI1, MSI2, and tau aggregates. MSI/tau aggregate morphological characterization was conducted to profile their size and shape in AD cortices.ConclusionFor the first time, we show that the presence and quantity of tau oligomeric species and MSI co‐aggregates vary across the AD brains, showing inter‐subjects’ variability in size and deposition density. We also identify that tau conformers with MSI1 and MSI2 form different co‐aggregates in size and morphology quantifying their colocalization in high‐resolution 3D imaging. Further investigations are warranted to determine the temporal and regional distribution of these tau species in association with MSI proteins as well as the mechanisms underlying their aggregation.