TABLE 2.

Pathways mediating pathological tau release from neurons.

Pathways	Forms of tau	Characteristics	References
Exosome	Total tau, pT181- tau, pS396-tau, fragmented tau lacking C-Terminus	Neuronal activity- and synaptic connectivity-dependent	Saman et al., 2011; Dujardin et al., 2014; Wang et al., 2017
Ectosome	Fragmented tau lacking C-Terminus	Slightly switches to exosomal secretion when tau accumulates inside cells.	Dujardin et al., 2014
Tunneling Nanotube	Exogenous tau monomers and fibrils	Filamentous-actin-containing membranous structures	Tardivel et al., 2016
HSPG- mediated direct translocation	Soluble full-length tau, phosphorylated, oligomeric	Secreted soluble tau utilized the same HSPG-mediated direct translocation mechanism to transcellularly enter the recipient cells and induced aggregation	Katsinelos et al., 2018; Merezhko et al., 2018
Autophagy-based unconventional secretion	Various forms of pTau	Nigericin induced	Kang et al., 2019