This study investigates the secretion of tau protein via exosomes in early Alzheimer's disease (AD). The researchers found that M1C cells, a neuroblastoma cell line expressing wild-type human tau, secrete exosome-associated tau that is selectively phosphorylated at Thr-181 (AT270), a biomarker for AD. This tau is enriched in exosome fractions of cerebrospinal fluid (CSF) from patients with mild AD (Braak stage 3) compared to non-AD controls and later stages of AD. The findings suggest that exosome-mediated tau secretion may play a significant role in the abnormal processing of tau and the elevated levels of CSF tau seen in early AD. The study also highlights the potential of tau secretion biomarkers as revolutionary diagnostic tools for AD.This study investigates the secretion of tau protein via exosomes in early Alzheimer's disease (AD). The researchers found that M1C cells, a neuroblastoma cell line expressing wild-type human tau, secrete exosome-associated tau that is selectively phosphorylated at Thr-181 (AT270), a biomarker for AD. This tau is enriched in exosome fractions of cerebrospinal fluid (CSF) from patients with mild AD (Braak stage 3) compared to non-AD controls and later stages of AD. The findings suggest that exosome-mediated tau secretion may play a significant role in the abnormal processing of tau and the elevated levels of CSF tau seen in early AD. The study also highlights the potential of tau secretion biomarkers as revolutionary diagnostic tools for AD.