Developmental regulation of tau splicing is disrupted in stem cell-derived neurons from frontotemporal dementia patients with the 10 + 16 splice-site mutation in MAPT

Abstract

The alternative splicing of the tau gene, MAPT, generates six protein isoforms in the adult human central nervous system (CNS). Tau splicing is developmentally regulated and dysregulated in disease. Mutations in MAPT that alter tau splicing cause frontotemporal dementia (FTD) with tau pathology, providing evidence for a causal link between altered tau splicing and disease. The use of induced pluripotent stem cell (iPSC)-derived neurons has revolutionized the way we model neurological disease in vitro. However, as most tau mutations are located within or around the alternatively spliced exon 10, it is important that iPSC–neurons splice tau appropriately in order to be used as disease models. To address this issue, we analyzed the expression and splicing of tau in iPSC-derived cortical neurons from control patients and FTD patients with the 10 + 16 intronic mutation in MAPT. We show that control neurons only express the fetal tau isoform (0N3R), even at extended time points of 100 days in vitro. Neurons from FTD patients with the 10 + 16 mutation in MAPT express both 0N3R and 0N4R tau isoforms, demonstrating that this mutation overrides the developmental regulation of exon 10 inclusion in our in vitro model. Further, at extended time points of 365 days in vitro, we observe a switch in tau splicing to include six tau isoforms as seen in the adult human CNS. Our results demonstrate the importance of neuronal maturity for use in in vitro modeling and provide a system that will be important for understanding the functional consequences of altered tau splicing.

Modeling ALS and FTD with iPSC-derived neurons

“…The majority of MAPT mutations are missense mutations that cluster around the microtubule binding domain, suggesting that these mutations most likely perturb the ability of tau to bind to microtubules and cause neuronal dysfunction or even death. Several groups have reported the isolation of iPSC-derived neurons, including one with MAPT A152T mutation from a patient with progressive supranuclear palsy (PSP), one with MAPT N279K and MAPT V337M from FTDP-17 patients, and one with 10+16 splice site mutation in MAPT gene (Ehrlich et al, 2015; Fong et al, 2013; Sposito et al, 2015). The study by Fong and colleagues showed that MAPT A152T neurons exhibit distinct degenerative features, characterized by breaks, bends and bulges along neuronal processes and reduced neuronal survival (Fong et al, 2013).…”

“…Finally, it is well-recognized that different isoforms of tau can be generated via alternative splicing. Using iPSCs from controls and two patients with 10+16 splice-site mutation in MAPT , Sposito and colleagues show that control iPSC-derived neurons express 3R tau only during the first 100 days in culture (Sposito et al, 2015). Interestingly, prolonged culturing of control neurons switches the tau expression from 3R tau to a diverse complement of tau isoforms.…”

Recapitulating Amyloid ß and Tau Pathology in Human Neural Cell Culture Models—Clinical Implications

“…One of the challenges of replicating tauopathy in human iPSC-derived neurons is that wild-type human iPSC-derived neurons, despite longer differentiation (>100 days), do not fully express adult tau splicing isoforms 39–41 . The presence of select FTD tau mutations enhances the expression of adult 4-repeat tau splicing isoforms 39–41 .…”

“…The presence of select FTD tau mutations enhances the expression of adult 4-repeat tau splicing isoforms 39–41 . However, control wild-type neurons do not express adult tau isoforms in the same conditions 39–41 . This clearly limits the recapitulation of human tauopathy, in which 4-repeat tau plays an important role, in human iPSC-derived neurons without FTD tau mutations.…”

Rapid and efficient CRISPR/Cas9 gene inactivation in human neurons during human pluripotent stem cell differentiation and direct reprogramming

“…Our group and others have developed protocols to obtain specific subtypes of neurons from fibroblast direct reprogramming without passing through an induced pluripotent stem cell20212223242526. Direct reprogramming can represent an interesting alternative strategy for neuronal modeling2728 in particular for late-onset neurological diseases since hPSCs generate immature neurons that may need long time in culture to recapitulate the disease phenotype2930.…”