TABLE 1.

Pathways mediating physiological tau release from neurons.

Pathways	Forms of Tau	Characteristics	References
Non-vesicular secretion	Free form	Majority of Secreted tau is in free, non-vesicular form. Whether it is HSPG- dependent was not examined.	Dujardin et al., 2014
Non-exosome associated	Physiological tau, non-aggregating form	AMPA-mediated, calcium-dependent tau release enhanced with increased neuronal activity. Not clear if this pathway involves other vesicles.	Pooler et al., 2013
Ectosome	Dephosphorylated, full-length tau or C-terminus truncated	Found in mouse ISF samples, slightly switches to exosomal secretion when tau accumulates inside cells.	Dujardin et al., 2014; Cocucci and Meldolesi, 2015
Autophagy-based unconventional secretion	Total tau	Released into media without any stimulation in SHSY-5Y cells	Kang et al., 2019