Metabolic wastes are extracellularly disposed by excretosomes, nanotubes and exophers in mouse HT22 cells through an autophagic vesicle clustering mechanism

Abstract

Neurodegenerative diseases are characterized by metabolic waste accumulations in neuronal cells. However, little is known about the mechanism of metabolic waste disposal. We showed that there is a constitutive waste excretion by nanotubes and structures called excretosomes in mouse neuronal HT22 cells under normal conditions and an exopher-type waste disposal under stressed conditions. Excretosomes and exophers are waste-enriched multivesicular bodies that are formed by autophagic vesicle clustering and fusions. Upon H2O2 treatment, metabolic waste marker intensified 1.4 to 3.4 fold. However, in dying H2O2-treated cells, glycolysis and stress response markers, alpha-Tubulin, Amyloid beta and alpha-Synuclein intensities reduced 30% to 80%. Amyloid beta, TAU and alpha-Synuclein associated with the autophagic vesicle clustering and fusion process and were excreted in large exophers by live oxidative-stressed cells before cell death with important implications for amyloid plaque, ghost tangle and Lewy body formation. H2O2 treatment also induced exophers containing nucleic acid materials and significantly increased the level of oxidative damage marker 8-OHdG. Oxidative stress-induced HT22 cell death could be due to the combinations of excretion failure, cytoskeleton disruption, defective glycolysis and DNA damage.