New Model for Human Neuron Research That Simulates the Propagation of Tau Protein Aggregates Within the Brain

Recently, a team of researchers from Weill Cornell Medical College designed a human neuron model that addresses the shortcomings of previous models of its kind, simulates the spread of Tau protein aggregates in neurons of the brain in a matter of weeks, and helps to identify potential therapeutic targets that may stop the spread of Tau protein.

In this article, Creative Biolabs introduces this innovative model that helps scientists find new therapeutic targets that may block tau protein propagation. As a top service provider in the field of neural research, we also provide services related to neural modeling.

Introduction to Tau Proteinopathy

Tau proteinopathies, as age-related neurodegenerative disorders characterized by Tau protein aggregation but with unclear pathogenesis, mainly include Alzheimer's disease as well as subtypes of frontotemporal lobar degeneration such as Pick's disease, corticobasal ganglia degeneration and other disease types.

Among these, the Tau protein is encoded by a single MAPT gene and is selectively spliced by exon 10 to produce six isoforms, including isoforms containing three (3R) or four (4R) microtubule-binding repeat sequences. The three subtypes of Tauopathies, 3R, 4R, and 3R/4R hybrid Tauopathies, in turn, display distinct Tau protein filamentous structures under cryo-electron microscopy.

Therefore, Tau protein filaments in Alzheimer's disease (3R/4R), Pick's disease (3R), and corticobasal ganglia degeneration (4R) also differ structurally.

Scientists in related fields have now demonstrated that many of the MAPT mutations that cause familial cases of frontotemporal lobar degeneration alter the 3R-4R ratio. Moreover, several mutations, including P301 S/L, are located in exon 10 and are therefore 4R-specific.

iPSC-Derived Neurons for Mimicking Tau Proteinopathies

Human iPSC-derived neurons play an irreplaceable role in modeling neurological diseases such as Tau proteinosis. Combined with CRISPR-Cas9 technology, iPSC-derived neuron platform enables isogenic control for precise CNS disease modeling, along with functional genomics for identifying disease modifiers. There are also some drawbacks.

• iPSC-derived neurons can only express very low levels of 4R Tau even after prolonged culture, making them unsuitable for modeling 4R Tau proteopathies.
• The low levels of exon 10-containing Tau similarly limit their relevance in modeling frontotemporal lobe degeneration mutations in the dominant family located in exon 10.
• It is also very difficult to reproduce robust Tau protein aggregation in human iPSC-derived neurons.

Although researchers did not observe insoluble Tau aggregates in MAPT-P301L or MAPT-IVS10+16 iPSC neurons, limited Tau inclusions could be observed after 120 days. The reason for this phenomenon may be the lack of 4R Tau in iPSC-derived neurons.

Based on these findings, a research group group has established a robust and scalable human neuronal model that enables human iPSC-derived neuronal cell lines to express 4R Tau as well as 4R Tau carrying the P301S MAPT mutation (4R-P301S) when differentiated into neurons.

Innovative Human Neuron Models of Tau Protein Propagation - 4R-P301S

The researchers noted that the model they developed for tau protein propagation in human neurons overcomes the limitations of previous models and reveals new therapeutic targets for drug development.

The team used CRISPR technology to modify the genome of human stem cells, prompting them to express tau proteins associated with the aging brain. They found that the model simulated the propagation of tau proteins within neurons within a few weeks. To stop the tau protein from spreading, the team used CRISPR technology to inactivate 1,000 genes to determine their role in tau protein propagation. It turned out that 500 of these genes had a significant impact on tau protein abundance. Here's how it was done:

Fig. 1 Human iPSC 4R tauopathy model.¹

• By inoculating Tau protofibers, they found that 4R-P301S neurons exhibited progressive spreading of tau protein aggregates, abnormal neuronal activity, and dysfunction of the endolysosomal pathway.
• Using CRISPRi technology to screen for genes associated with the pathobiology of Tau, more than 500 genetic modifiers were identified that can influence inoculation-induced Tau propagation. These included genes in the reverse transporter protein VPS29 and the UFMylation cascade reaction.
• Inhibition of the UFMylation cascade in vitro and in vivo suppresses Tau propagation in neurons.

Overall, the model provides an effective platform for identifying novel therapeutic strategies for 4R Tau proteinopathies.

Methods and Techniques Used in Model Building

• iPSC technology and CRISPR/Cas9 gene editing technology - They engineered hiPSC lines to express 4R Tau and 4R Tau carrying the P301S MAPT mutation (4R-P301S) when differentiated into neurons.
• Characterization techniques for human iPSC-derived neurons - They mainly characterized the generated neurons with karyotype confirmation, pluripotency marker staining, and immunostaining.
• Neuronal activity monitor - They transduced seeded 4R-P301S neurons with a new generation of genetically encoded calcium sensors. Neuronal activity was monitored by measuring calcium transients through changes in fluorescence relative to basal fluorescence.
• CRISPRi screening technique - 4R-P301S-dCas9 iPSC were transduced using a customized lentiviral CRISPRi sgRNA library targeting genes involved in Tau pathology based on a genome-wide CRISPRi screen for modifiers at the level of Tau oligomers in human iPSC-derived neurons.

In summary, the team developed and characterized a human 4R iPSC platform that exhibits seeding-induced tau proliferation and identified known and novel genetic modifiers. We anticipate that this cell model will serve as a powerful platform to unravel the underlying mechanisms of 4R tau proteinopathies and identify novel targets for drug development. Creative Biolabs can help our customers unlock the potential of iPSC-derived neuron models to facilitate the rapid advancement of neuroscience research.

Reference

1. Parra Bravo, Celeste, et al. "Human iPSC 4R tauopathy model uncovers modifiers of tau propagation." bioRxiv (2023): 2023-06.

For Research Use Only. Not For Clinical Use.