CONICET | Buscador de Institutos y Recursos Humanos

The microtubule associated protein tau contains either three (3R) or four (4R) microtubule-binding repeats, due to the alternative splicing of exon 10 (E10) in the tau primary transcript. Both isoforms are found in equal amounts in the adult human brain. Several tauopathies were associated with alterations in the 3R:4R ratio, yet the physiological consequences of such imbalance remain elusive. Here we aimed to modulate tau isoforms balance to analyze functional deficits in mature neurons and to evaluate phenotypic rescue in the hTau mouse model of tauopathy. hTau mice overproduce 3R tau in the adult brain, and present cognitive and biochemical phenotypes. Methods: Lentiviral vectors were used to express molecules that modulate E10 inclusion/exclusion by RNA trans-splicing with the endogenous tau transcript, either in human neurons differentiated in vitro or into the hTau mouse brain. After trans-splicing, tau isoforms were quantified (qPCR and western blot). Morphological features and axonal transport dynamics were analyzed in human neurons after induction of tau imbalance. Phenotypic analysis of hTau mice included behavioral tasks, biochemical and electrophysiological studies.Results: Perturbations of the endogenous tau 3R:4R ratio impaired axonal transport in human mature neurons without altering neuronal morphology. Modulation of the 3R:4R ratio in the hTau brain rescued some behavioral and neurochemical phenotypes; improved cognitive deficit, restored neuronal firing patterns and reduced insoluble tau contents.Conclusion: These results highlight the (dys)functional consequences of tau 3R:4R imbalance and provide a proof of concept for the potential use of RNA reprogramming to correct tau mis-splicing in human tauopathies.