Phosphorylation of Truncated Tau Promotes Abnormal Native Tau Pathology and Neurodegeneration

Abnormal posttranslational modifications of tau play important roles in mediating neurodegeneration in tauopathies including Alzheimer's disease. Both phosphorylation and truncation are implicated in the pathogenesis of tauopathies. However, whether phosphorylation aggravates truncated tau-induced pathology and neurodegeneration remains elusive. Here, we construct different tau fragments cleaved by delta secretase, with either phosphorylation or non-phosphorylation mimic mutations, and evaluate the contributions of phosphorylation to truncated tau-induced pathological and behavioral alterations in vitro and in vivo through biochemical methods including detergent insoluble tau extraction, western blot, immunofluorescence, flow cytometry, and behavior tests. Our results show that the self-aggregation of phospho-truncated tau is significantly influenced by the domain it contains. N-terminal inhibits, proline-rich domain promotes, and C-terminus have no impact on phospho-truncated tau aggregation. Phosphorylation of truncated tau1-368, which contains the microtubule-binding repeat domain and the proline-rich domain, induces endogenous tau phosphorylation and aggregation. In vivo, phospho-tau1-368 but not non-phospho-tau1-368 leads to a decrease in body weight of C57BL/6 J mice. Intriguingly, although tau1-368-induced anxiety behavior in C57BL/6 J mice is phosphorylation-independent, the recognition memory of mice is impaired by phospho-tau1-368, but not by non-phospho-tau1-368. Immunofluorescence staining shows that overexpressing phospho-tau1-368 results in neuronal loss and gliosis in the hippocampus, while the transmission of tau1-368 is phosphorylation-independent as revealed by the flow cytometry results in vitro and immunofluorescence staining in vivo. Our findings indicate that phosphorylation of truncated tau significantly fosters endogenous tau pathology and neurodegeneration.