Fujian Provincial Key Laboratory of Neurodegenerative Disease and Aging Research, Institute of Neuroscience, School of Medicine, Xiamen University, Xiamen, 361102, China.
Xiamen Key Laboratory of Chiral Drugs, School of Medicine, Xiamen University, Xiamen, 361102, China.
J Neuroinflammation. 2021 Dec 10;18(1):286. doi: 10.1186/s12974-021-02340-7.
TREM2 is a microglial receptor genetically linked to the risk for Alzheimer's disease (AD). The cerebrospinal fluid (CSF) levels of soluble TREM2 (sTREM2) have emerged as a valuable biomarker for the disease progression in AD and higher CSF levels of sTREM2 are linked to slower cognitive decline. Increasing sTREM2 in mouse models of amyloidosis reduces amyloid-related pathology through modulating microglial functions, suggesting a beneficial role of sTREM2 in microglia biology and AD pathology.
In the current study, we performed serial C- and N-terminal truncations of sTREM2 protein to define the minimal sequence requirement for sTREM2 function. We initially assessed the impacts of sTREM2 mutants on microglial functions by measuring cell viability and inflammatory responses. The binding of the sTREM2 mutants to oligomeric Aβ was determined by solid-phase protein binding assay and dot blot assay. We further evaluated the impacts of sTREM2 mutants on amyloid-related pathology by direct stereotaxic injection of sTREM2 proteins into the brain of 5xFAD mice.
We found that both sTREM2 fragments 41-81 and 51-81 enhance cell viability and inflammatory responses in primary microglia. However, the fragment 51-81 exhibited impaired affinity to oligomeric Aβ. When administrated to the 5xFAD mice brain, the sTREM2 fragment 41-81, but not 51-81, increased the number of plaque-associated microglia and reduced the plaque deposition. Interestingly, the fragment 41-81 was more efficient than the physiological form of sTREM2 in ameliorating Aβ-related pathology.
Our results indicate that the interaction of sTREM2 truncated variants with Aβ is essential for enhancing microglial recruitment to the vicinity of an amyloid plaque and reducing the plaque load. Importantly, we identified a 41-amino acid sequence of sTREM2 that is sufficient for modulating microglial functions and more potent than the full-length sTREM2 in reducing the plaque load and the plaque-associated neurotoxicity. Taken together, our data provide more insights into the mechanisms underlying sTREM2 function and the minimal active sTREM2 sequence represents a promising candidate for AD therapy.
TREM2 是一种与阿尔茨海默病（AD）风险相关的小胶质细胞受体。脑脊液（CSF）中可溶性 TREM2（sTREM2）的水平已成为 AD 疾病进展的有价值的生物标志物，并且较高的 CSF sTREM2 水平与认知能力下降较慢有关。在淀粉样蛋白病的小鼠模型中增加 sTREM2 通过调节小胶质细胞功能来减少淀粉样相关病理，这表明 sTREM2 在小胶质细胞生物学和 AD 病理中具有有益作用。
在目前的研究中，我们对 sTREM2 蛋白进行了 C 端和 N 端的连续截断，以确定 sTREM2 功能的最小序列要求。我们最初通过测量细胞活力和炎症反应来评估 sTREM2 突变体对小胶质细胞功能的影响。通过固相蛋白结合测定和斑点印迹测定来确定 sTREM2 突变体与寡聚体 Aβ 的结合。我们还通过直接立体定向注射 sTREM2 蛋白到 5xFAD 小鼠的大脑中来评估 sTREM2 突变体对淀粉样相关病理的影响。
我们发现，sTREM2 片段 41-81 和 51-81 都能增强原代小胶质细胞的细胞活力和炎症反应。然而，片段 51-81 对寡聚体 Aβ的亲和力受损。当给予 5xFAD 小鼠脑内注射时，sTREM2 片段 41-81，但不是 51-81，增加了斑块相关小胶质细胞的数量，并减少了斑块沉积。有趣的是，与 sTREM2 的生理形式相比，片段 41-81 更有效地改善了 Aβ相关病理。
我们的结果表明，sTREM2 截断变体与 Aβ 的相互作用对于增强小胶质细胞向淀粉样斑块附近的募集和减少斑块负荷是必不可少的。重要的是，我们确定了 sTREM2 的 41 个氨基酸序列，该序列足以调节小胶质细胞功能，并且在降低斑块负荷和斑块相关神经毒性方面比全长 sTREM2 更有效。总之，我们的数据提供了更多关于 sTREM2 功能的机制的见解，并且最小的活性 sTREM2 序列代表了治疗 AD 的有希望的候选物。
