Background

Declining proteostasis with aging contributes to increased susceptibility to neurodegenerative diseases, including Alzheimer’s disease (AD). Emerging studies implicate impairment of the endosome-lysosome pathway as a significant factor in the pathogenesis of these diseases. Previously, we demonstrated that BAG3 regulates phosphorylated tau clearance. However, we did not fully define how BAG3 regulates endogenous tau proteostasis, especially in the early stages of disease progression.

Methods

Mass spectrometric analyses were performed to identify neuronal BAG3 interactors. Multiple biochemical assays were used to investigate the BAG3-HSP70-TBC1D10B (EPI64B)-RAB35-HRS regulatory networks. Live-cell imaging was used to study the dynamics of the endosomal pathway. Immunohistochemistry and immunoblotting were performed in human AD brains and in P301S tau transgenic mice with BAG3 overexpressed.

Results

The primary group of neuronal BAG3 interactors identified are involved in the endocytic pathway. Among them were key regulators of small GTPases, such as the RAB35 GTPase-activating protein TBC1D10B. We demonstrated that a BAG3-HSP70-TBC1D10B complex attenuates the ability of TBC1D10B to inactivate RAB35. Thus, BAG3 interacts with TBC1D10B to support the activation of RAB35 and recruitment of HRS, initiating endosomal sorting complex required for transport–mediated endosomal tau clearance. Furthermore, TBC1D10B shows significantly less colocalization with BAG3 in AD brains than in age-matched controls. Overexpression of BAG3 in P301S tau transgenic mice increased the colocalization of phosphorylated tau with the endosomal sorting complex required for transport III protein CHMP2B and reduced the levels of the mutant human tau.

Conclusions

We identified a novel BAG3-TBC1D10B-RAB35 regulatory axis that modulates endosomal sorting complex required for transport–dependent protein degradation machinery and tau clearance. Dysregulation of BAG3 could contribute to the pathogenesis of AD.

中文翻译：

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BAG3 对 RAB35 的调节介导运输/内溶酶体途径和 Tau 清除所需的内体分选复合物

背景

随着年龄的增长，蛋白质稳态下降会增加对神经退行性疾病的易感性，包括阿尔茨海默病 (AD)。新兴研究表明内体-溶酶体途径的损伤是这些疾病发病机制的一个重要因素。之前，我们证明 BAG3 调节磷酸化 tau 清除。然而，我们并没有完全定义 BAG3 如何调节内源性 tau 蛋白稳态，特别是在疾病进展的早期阶段。

方法

进行质谱分析来鉴定神经元 BAG3 相互作用因子。使用多种生化测定来研究 BAG3-HSP70-TBC1D10B (EPI64B)-RAB35-HRS 调控网络。活细胞成像用于研究内体途径的动力学。在人类 AD 大脑和 BAG3 过表达的 P301S tau 转基因小鼠中进行了免疫组织化学和免疫印迹。

结果

确定的主要神经元 BAG3 相互作用蛋白组参与内吞途径。其中包括小 GTP 酶的关键调节因子，例如 RAB35 GTP 酶激活蛋白 TBC1D10B。我们证明 BAG3-HSP70-TBC1D10B 复合物会减弱 TBC1D10B 灭活 RAB35 的能力。因此，BAG3 与 TBC1D10B 相互作用，支持 RAB35 的激活和 HRS 的募集，启动转运介导的内体 tau 清除所需的内体分选复合物。此外，与年龄匹配的对照组相比，TBC1D10B 在 AD 大脑中与 BAG3 的共定位显着减少。P301S tau 转基因小鼠中 BAG3 的过度表达增加了磷酸化 tau 与转运 III 蛋白 CHMP2B 所需的内体分选复合物的共定位，并降低了突变人 tau 的水平。

结论

我们发现了一种新型 BAG3-TBC1D10B-RAB35 调节轴，可调节运输依赖性蛋白质降解机制和 tau 清除所需的内体分选复合物。BAG3 的失调可能导致 AD 的发病机制。