Accelerated release of exosome-associated GM1 ganglioside (GM1) by endocytic pathway abnormality: another putative pathway for GM1-induced amyloid fibril formation

Authors

  • Kohei Yuyama,

    1. Department of Alzheimer’s Disease Research, National Institute for Longevity Sciences, National Center for Geriatrics and Gerontology, Obu, Japan
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  • Naoki Yamamoto,

    1. Department of Alzheimer’s Disease Research, National Institute for Longevity Sciences, National Center for Geriatrics and Gerontology, Obu, Japan
    2. Japan Society for the Promotion of Sciences (JSPS), Tokyo, Japan
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  • Katsuhiko Yanagisawa

    1. Department of Alzheimer’s Disease Research, National Institute for Longevity Sciences, National Center for Geriatrics and Gerontology, Obu, Japan
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Address correspondence and reprint requests to Katsuhiko Yanagisawa, Department of Alzheimer’s Disease Research, National Institute for Longevity Sciences, National Center for Geriatrics and Gerontology, 36-3 Gengo, Morioka, Obu 474-8522, Japan. E-mail: katuhiko@nils.go.jp

Abstract

Exosomes are extracellularly released small vesicles that are derived from multivesicular bodies formed via the endocytic pathway. We treated pheochromocytoma PC12 cells with chloroquine, an acidotropic agent, which potently perturbs membrane trafficking from endosomes to lysosomes. Chloroquine treatment increased the level of GM1 ganglioside in cell media only when the cells were exposed to KCl for depolarization, which is known to enhance exosome release from neurons. In the sucrose-density-gradient fractionation of cell media, GM1 ganglioside was exclusively recovered with Alix, a specific marker of exosomes, in the fractions with the density corrresponding to that of exosomes. Notably, amyloid-β assembly was markedly accelerated when incubated with the exosome fraction prepared from the culture media of PC12 cells treated with chloroquine and KCl. Furthermore, amyloid-β assembly was significantly suppressed by the co-incubation with an antibody specific to GM1-bound amyloid-β, an endogenous seed for amyloid formation of Alzheimer’s disease. Together with our previous finding that chloroquine treatment induces the accumulation of GM1 ganglioside in early endosomes, results of this study suggest that endocytic pathway abnormality accelerates the release of exosome-associated GM1 ganglioside following its accumulation in early endosomes. Furthermore, this study also suggests that extracellular amyloid fibril formation is induced by not only GM1 gangliosides accumulated on the surface of the cells but also those released in association with exosomes.

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