Lipid Biofunction Section, Faculty of Advanced Life Science, Hokkaido University, Sapporo, Japan.
Division of Molecular Interaction, Institute for Genetic Medicine, Hokkaido University Graduate School of Life Science, Sapporo, Japan.
FASEB J. 2020 Dec;34(12):16022-16033. doi: 10.1096/fj.202001599R. Epub 2020 Oct 8.
Exosomes are extracellular vesicles that mediate the transport of intracellular molecules, including neurodegenerative agents. Exogenously administrated ceramides have been implicated in the acceleration of exosome production by neurons; however, the molecular machinery involved in this process is unknown. Here, we found that ceramides, especially those consisting of long fatty acids, were internalized into the endocytic pathway in neuroblastoma SH-SY5Y cells to induce exosome secretion through lysosome-associated protein transmembrane 4B (LAPTM4B). Knockdown of LAPTM4B inhibited the ceramide-mediated increase in exosome release completely. Fluorescence microscopy observations indicated that exogenous ceramides promote the transport of multivesicular bodies to the plasma membranes in a LAPTM4B-dependent manner. Similarly, inhibition of acid ceramidase, which tends to induce intracellular ceramide accumulation, increased exosome production by SH-SY5Y cells in a LAPTM4B-dependent manner. Furthermore, the level of amyloid-ß protein (Aß) was decreased in neuronal cells following treatment with exogenous ceramide or inhibition of acid ceramidase, and this effect was attributed to the LAPTM4B-dependent efflux of Aß-containing exosomes. Overall, these findings reveal the novel machinery involved in exosome secretion regulated by ceramides and LAPTM4B, and may contribute to efforts to ameliorate the cellular accumulation of neurodegenerative agents such as Aß.
外泌体是介导细胞内分子转运的细胞外囊泡，包括神经退行性疾病的致病因子。外源性神经酰胺的给药已被牵连到神经元中外泌体产生的加速中；然而，这一过程中涉及的分子机制尚不清楚。在这里，我们发现神经母细胞瘤 SH-SY5Y 细胞中的神经酰胺（特别是那些由长脂肪酸组成的神经酰胺）被内吞到内体途径中，通过溶酶体相关蛋白跨膜 4B（LAPTM4B）诱导外泌体分泌。LAPTM4B 的敲低完全抑制了神经酰胺介导的外泌体释放增加。荧光显微镜观察表明，外源性神经酰胺以 LAPTM4B 依赖的方式促进多泡体向质膜的转运。同样，抑制倾向于诱导细胞内神经酰胺积累的酸性神经酰胺酶，也以 LAPTM4B 依赖的方式增加 SH-SY5Y 细胞的外泌体产生。此外，神经元细胞中淀粉样蛋白-β 蛋白（Aβ）的水平在用外源性神经酰胺或抑制酸性神经酰胺酶处理后降低，这一效应归因于 Aβ 含量的外泌体通过 LAPTM4B 依赖性外排。总的来说，这些发现揭示了受神经酰胺和 LAPTM4B 调控的外泌体分泌的新机制，并可能有助于改善神经退行性疾病相关致病因子（如 Aβ）的细胞积累。
