Development of MAPT S305 mutation human iPSC lines exhibiting elevated 4R tau expression and functional alterations in neurons and astrocytes

Due to the importance of 4R tau (with four microtubule-binding-repeat domains) in the pathogenicity of primary tauopathies, it has been challenging to model these diseases in induced pluripotent stem cell (iPSC)-derived neurons, which express very low levels of 4R tau. To address this, we have developed a panel of isogenic iPSC lines carrying MAPT splice-site mutations, S305S, S305I, or S305N, derived from four different donors. All mutations significantly increase 4R tau expression in iPSC neurons and astrocytes. Functional analyses of S305 mutant neurons reveal shared disruption in synaptic signaling and maturity but divergent effects on mitochondrial bioenergetics. In iPSC astrocytes, S305 mutations promote internalization of exogenous tau that may be a precursor to glial pathology. These lines recapitulate previously characterized tauopathy-relevant phenotypes and highlight functional differences between the wild-type 4R and the mutant 4R proteins in both neurons and astrocytes. As such, these lines enable a more complete understanding of pathogenic mechanisms underlying 4R tauopathies across different cell types. [Display omitted] •Characterization of 26 human iPSC clones with three different MAPT splicing mutations•S305 mutations efficiently increase 4R tau expression in iPSC neurons and astrocytes•Altered oxidative phosphorylation and spontaneous firing are observed in neurons•Inflammation and rapidly internalized exogenous tau are observed in astrocytes Bowles et al. introduce an isogenic panel of human iPSC lines spanning three MAPT S305 splicing mutations that cause familial FTD that express high levels of 4R tau early in neuronal differentiation. Transcriptomic and functional characterization reveal synaptic and mitochondrial dysfunction in neurons and inflammation and tau internalization in astrocytes.