Prada I, Ongania G Naum, Buonsanti C, Panina-Bordignon P, Meldolesi J
Department of Neuroscience, Vita-Salute San Raffaele University and San Raffaele Scientific Institute, via Olgettina 58, 20132 Milan, Italy.
Neuroscience. 2006 Jul 21;140(4):1139-48. doi: 10.1016/j.neuroscience.2006.03.058. Epub 2006 May 3.
Cell biology of triggering receptor expressed in myeloid cells 2, a receptor expressed in brain cells (microglia and possibly neurons and oligodendrocytes) which is responsible for a neurological and psychiatric genetic disease, polycystic lipomembranous osteodysplasia with sclerosing leukoencephalopathy otherwise called the Nasu-Hakola disease, is still largely unknown. Using immortalized mouse N9 microglial cells we demonstrate that triggering receptor expressed in myeloid cells 2 is mostly distributed intracellularly in two pools: a deposit in the Golgi complex and a population of exocytic vesicles, distinct from endosomes and lysosomes, which is continuously translocated to, and recycled from the cell surface. Results with ionomycin and gamma-interferon, showing rapid and slow increases, respectively, of triggering receptor expressed in myeloid cells 2 surface density, documented that the exocytosis of the receptor-rich vesicles is regulated. Pulse labeling in the cold of surface triggering receptor expressed in myeloid cells 2 with its antibody (or Fab fragment) followed by chase at 37 degrees C showed internalization, with recovery of the antibody in endosomes and lysosomes. However, part of the receptor/antibody complex, internalized for up to 30 min chase, was recycled to the cell surface within 2 min of ionomycin stimulation, together with a fraction of the total biotinylated surface protein chased in parallel. The internalized receptor appears therefore to get access to exocytic organelles distinct from lysosomes which may resemble the exocytic vesicles of resting cells. These results document that, in microglial cells, the surface density of the triggering receptor expressed in myeloid cells 2 and thus, presumably, the response to its activation, is continuously adapted and can be greatly increased, even at rapid rate, as a function of cell activation.
髓样细胞表达的触发受体2的细胞生物学研究，该受体在脑细胞（小胶质细胞，可能还有神经元和少突胶质细胞）中表达，与一种神经和精神遗传疾病——多囊性脂膜性骨发育异常伴硬化性白质脑病（又称那须-哈科拉病）有关，目前在很大程度上仍不清楚。我们利用永生化的小鼠N9小胶质细胞证明，髓样细胞表达的触发受体2主要分布在细胞内的两个池：一个沉积在高尔基体复合体中，另一个是胞吐小泡群体，与内体和溶酶体不同，它不断转运到细胞表面并从细胞表面回收。离子霉素和γ干扰素的实验结果分别显示了髓样细胞表达的触发受体2表面密度的快速和缓慢增加，证明了富含受体的小泡的胞吐作用是受调控的。用其抗体（或Fab片段）对表面的髓样细胞表达的触发受体2进行冷脉冲标记，然后在37℃下追踪，显示其内化，抗体在内体和溶酶体中回收。然而，部分内化长达30分钟追踪的受体/抗体复合物，在离子霉素刺激后2分钟内与一部分平行追踪的总生物素化表面蛋白一起被循环回细胞表面。因此，内化的受体似乎可以进入不同于溶酶体的胞吐细胞器，这些细胞器可能类似于静息细胞的胞吐小泡。这些结果表明，在小胶质细胞中，髓样细胞表达的触发受体2的表面密度，因此大概还有对其激活的反应，会不断调整，并且即使在细胞激活时，也能以快速的速度大幅增加。
