背景:脑实质中的β-淀粉样蛋白(Aβ)沉积是阿尔茨海默病(AD)病理的淀粉样蛋白级联假说的关键起始步骤。此外,斑块相关小胶质细胞的功能障碍,也称为疾病相关小胶质细胞(DAM)已被报道加速Aβ沉积和认知障碍。我们先前的研究表明,间歇性低氧训练(IHT)通过上调DAM中的自噬改善AD病理,从而增强寡聚Aβ(oAβ)清除。考虑到oAβ内化是oAβ清除的初始阶段,这项研究集中在IHT机制中涉及DAM上调Aβ摄取。
方法:对8月龄APP/PS1小鼠或6月龄小胶质细胞液泡蛋白分选(VPS35)敲除小鼠在APP/PS1背景下(MGVPS35KO:APP/PS1)给药IHT28天。在IHT之后,评估小鼠的空间学习记忆能力.此外,通过估计神经纤维和突触密度来确定AD病理,Aβ斑块沉积,和Aβ在大脑中的负荷。构建Aβ暴露小胶质细胞模型,并对其进行IHT处理,以探讨相关机制。最后,使用荧光示踪技术测量髓样细胞2(TREM2)细胞内再循环和Aβ内化表达的触发受体.
结果:我们的结果显示IHT改善了认知功能和Aβ病理。特别是,IHT通过增强小胶质细胞TREM2的细胞内转运功能来增强Aβ内吞作用,从而有助于Aβ清除。此外,IHT特别上调DAM中的VPS35,TREM2细胞内再循环增强的主要原因。IHT对MGVPS35KO:APP/PS1小鼠脑Aβ病理失去改善作用。最后,DAM中VPS35上调的IHT机制是由转录因子EB(TFEB)对VPS35的转录调节介导的。
结论:IHT通过上调VPS35依赖的TREM2再循环来增强DAM中的Aβ内吞作用,从而促进oAβ的清除和Aβ病理的缓解。此外,TFEB对VPS35的转录调控表明小胶质细胞内吞作用与自噬之间存在密切联系。我们的研究进一步阐明了IHT改善AD病理的机制,并提供了支持IHT作为AD补充疗法的潜在应用的证据。
Beta-amyloid (Aβ) deposition in the brain parenchyma is a crucial initiating step in the amyloid cascade hypothesis of Alzheimer\'s disease (AD) pathology. Furthermore, dysfunction of plaque-associated microglia, also known as disease-associated microglia (DAM) has been reported to accelerate Aβ deposition and cognitive impairment. Our previous research demonstrated that intermittent hypoxia training (IHT) improved AD pathology by upregulating autophagy in DAM, thereby enhancing oligomeric Aβ (oAβ) clearance. Considering that oAβ internalization is the initial stage of oAβ clearance, this study focused on the IHT mechanism involved in upregulating Aβ uptake by DAM.
IHT was administered to 8-month-old APP/PS1 mice or 6-month-old microglial vacuolar protein sorting 35 (
VPS35) knockout mice in APP/PS1 background (MG
VPS35 KO: APP/PS1) for 28 days. After the IHT, the spatial learning-memory capacity of the mice was assessed. Additionally, AD pathology was determined by estimating the nerve fiber and synapse density, Aβ plaque deposition, and Aβ load in the brain. A model of Aβ-exposed microglia was constructed and treated with IHT to explore the related mechanism. Finally, triggering receptor expressed on myeloid cells 2 (TREM2) intracellular recycling and Aβ internalization were measured using a fluorescence tracing technique.
Our results showed that IHT ameliorated cognitive function and Aβ pathology. In particular, IHT enhanced Aβ endocytosis by augmenting the intracellular transport function of microglial TREM2, thereby contributing to Aβ clearance. Furthermore, IHT specifically upregulated VPS35 in DAM, the primary cause for the enhanced intracellular recycling of TREM2. IHT lost ameliorative effect on Aβ pathology in MG
VPS35 KO: APP/PS1 mice brain. Lastly, the IHT mechanism of
VPS35 upregulation in DAM was mediated by the transcriptional regulation of
VPS35 by transcription factor EB (TFEB).
IHT enhances Aβ endocytosis in DAM by upregulating VPS35-dependent TREM2 recycling, thereby facilitating oAβ clearance and mitigation of Aβ pathology. Moreover, the transcriptional regulation of VPS35 by TFEB demonstrates a close link between endocytosis and autophagy in microglia. Our study further elucidates the IHT mechanism in improving AD pathology and provides evidence supporting the potential application of IHT as a complementary therapy for AD.