Enhanced generation of intraluminal vesicles in neuronal late endosomes in the brain of a Down syndrome mouse model with endosomal dysfunction
Enhanced generation of intraluminal vesicles in neuronal late endosomes in the brain of a Down syndrome mouse model with endosomal dysfunction
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DOI：
10.1002/dneu.22708
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发表时间：
2019-08-01
影响因子：
3
通讯作者：
Levy, Efrat
中科院分区：
文献类型：
--
作者：
D'Acunzo, Pasquale;Hargash, Tal;Levy, Efrat
唐氏综合征(DS)是由21号染色体三体引起的一种人类遗传病，以早期发育脑异常为特征。神经元内体通路功能障碍是DS和阿尔茨海默病的早期事件。最近，我们已经证明，与二体对照相比，人DS死后脑、三体小鼠模型ts[Rb(12.17(16))]2Cje(TS2)和DS成纤维细胞的外体分泌上调。在DS的脑中观察到高水平的Tetraspanin CD63，这是一种外切体生物发生的调节因子。部分阻断DS成纤维细胞的外切体分泌加剧了先前存在的早期内分泌体病变。因此，我们假设CD63表达增强诱导晚期内小体/多囊泡(MVB)产生管腔内小泡(ILV)，增加外体释放作为减轻DS内体异常的内源性机制。在这里，我们展示了一个高分辨率的电子显微镜分析的MVB在12个月大的TS2小鼠和二倍体对照小鼠的额叶皮质神经元。我们的定量分析显示，与对照组相比，TS2MVB更大、更丰富，每个神经元含有更多的ILV。对提纯的内体部分进行的Western印迹分析进一步证实了这些发现，与对照组相比，TS2小鼠大脑中含有内体标记的相同部分中的ILV蛋白水平更高。这些数据表明，上调ILVS的产生可能是通过内体-外体途径缓解内体调节失调的一个关键的稳态机制。
Down syndrome (DS) is a human genetic disease caused by trisomy of chromosome 21 and characterized by early developmental brain abnormalities. Dysfunctional endosomal pathway in neurons is an early event of DS and Alzheimer's disease. Recently, we have demonstrated that exosome secretion is upregulated in human DS postmortem brains, in the brain of the trisomic mouse model Ts[Rb(12.17(16))]2Cje (Ts2) and by DS fibroblasts as compared with disomic controls. High levels of the tetraspanin CD63, a regulator of exosome biogenesis, were observed in DS brains. Partially blocking exosome secretion by DS fibroblasts exacerbated a pre-existing early endosomal pathology. We thus hypothesized that enhanced CD63 expression induces generation of intraluminal vesicles (ILVs) in late endosomes/multivesicular bodies (MVBs), increasing exosome release as an endogenous mechanism to mitigate endosomal abnormalities in DS. Herein, we show a high-resolution electron microscopy analysis of MVBs in neurons of the frontal cortex of 12-month-old Ts2 mice and littermate diploid controls. Our quantitative analysis revealed that Ts2 MVBs are larger, more abundant, and contain a higher number of ILVs per neuron compared to controls. These findings were further corroborated biochemically by Western blot analysis of purified endosomal fractions showing higher levels of ILVs proteins in the same fractions containing endosomal markers in the brain of Ts2 mice compared to controls. These data suggest that upregulation of ILVs production may be a key homeostatic mechanism to alleviate endosomal dysregulation via the endosomal-exosomal pathway.