Department of Physiology and Biophysics, University of California, Irvine, Irvine, United States.
Department of Neurobiology and Behavior, University of California, Irvine, Irvine, United States.
Elife. 2022 Feb 22;11:e73021. doi: 10.7554/eLife.73021.
The membrane protein TREM2 (Triggering Receptor Expressed on Myeloid cells 2) regulates key microglial functions including phagocytosis and chemotaxis. Loss-of-function variants of TREM2 are associated with increased risk of Alzheimer's disease (AD). Because abnormalities in Ca signaling have been observed in several AD models, we investigated TREM2 regulation of Ca signaling in human induced pluripotent stem cell-derived microglia (iPSC-microglia) with genetic deletion of TREM2. We found that iPSC-microglia lacking TREM2 (TREM2 KO) show exaggerated Ca signals in response to purinergic agonists, such as ADP, that shape microglial injury responses. This ADP hypersensitivity, driven by increased expression of P2Y and P2Y receptors, results in greater release of Ca from the endoplasmic reticulum stores, which triggers sustained Ca influx through Orai channels and alters cell motility in TREM2 KO microglia. Using iPSC-microglia expressing the genetically encoded Ca probe, Salsa6f, we found that cytosolic Ca tunes motility to a greater extent in TREM2 KO microglia. Despite showing greater overall displacement, TREM2 KO microglia exhibit reduced directional chemotaxis along ADP gradients. Accordingly, the chemotactic defect in TREM2 KO microglia was rescued by reducing cytosolic Ca using a P2Y receptor antagonist. Our results show that loss of TREM2 confers a defect in microglial Ca response to purinergic signals, suggesting a window of Ca signaling for optimal microglial motility.
膜蛋白 TREM2（髓样细胞触发受体 2）调节关键的小胶质细胞功能，包括吞噬作用和趋化性。TREM2 的功能丧失变体与阿尔茨海默病（AD）的风险增加有关。由于在几种 AD 模型中观察到钙信号异常，我们研究了 TREM2 在人类诱导多能干细胞衍生的小胶质细胞（iPSC-小胶质细胞）中的钙信号调节，该细胞中 TREM2 缺失。我们发现，缺乏 TREM2 的 iPSC-小胶质细胞（TREM2 KO）对嘌呤能激动剂（如 ADP）的反应表现出过度的钙信号，这些信号塑造了小胶质细胞的损伤反应。这种 ADP 超敏反应是由 P2Y 和 P2Y 受体表达增加驱动的，导致内质网储存的 Ca 释放增加，通过 Orai 通道触发持续的 Ca 内流，并改变 TREM2 KO 小胶质细胞的细胞迁移。使用表达遗传编码钙探针 Salsa6f 的 iPSC-小胶质细胞，我们发现细胞质 Ca 更能调节 TREM2 KO 小胶质细胞的迁移。尽管 TREM2 KO 小胶质细胞表现出更大的整体位移，但它们沿着 ADP 梯度的定向趋化作用减少。因此，使用 P2Y 受体拮抗剂降低细胞质 Ca 可挽救 TREM2 KO 小胶质细胞的趋化缺陷。我们的结果表明，TREM2 的缺失赋予了小胶质细胞对嘌呤能信号的钙反应缺陷，这表明钙信号存在一个最佳的小胶质细胞迁移窗口。
