The β-propensity of Tau determines aggregation and synaptic loss in inducible mouse models of tauopathy

Neurofibrillary lesions are characteristic for a group of human diseases, named tauopathies, which are characterized by prominent intracellular accumulations of abnormal filaments formed by the microtubule-associated protein Tau. The tauopathies are accompanied by abnormal changes in Tau protein, including pathological conformation, somatodendritic mislocalization, hyperphosphorylation, and aggregation, whose interdependence is not well understood. To address these issues we have created transgenic mouse lines in which different variants of full-length Tau are expressed in a regulatable fashion, allowing one to switch the expression on and off at defined time points. The Tau variants differ by small mutations in the hexapeptide motifs that control the ability of Tau to adopt a beta-structure conformation and hence to aggregate. The "pro-aggregation" mutant Delta K280, derived from one of the mutations observed in frontotemporal dementias, aggregates avidly in vitro, whereas the "anti-aggregation" mutant Delta K280/PP cannot aggregate because of two beta-breaking prolines. In the transgenic mice, the pro-aggregation Tau induces a pathological conformation and pre-tangle aggregation, even at low expression levels, the antiaggregation mutant does not. This illustrates that abnormal aggregation is primarily controlled by the molecular structure of Tau in vitro and in the organism. Both variants of Tau become mislocalized and hyperphosphorylated independently of aggregation, suggesting that localization and phosphorylation are mainly a consequence of increased concentration. These pathological changes are reversible when the expression of Tau is switched off. The pro-aggregation Tau causes a strong reduction in spine synapses.