Sessa Giuseppina, Podini Paola, Mariani Margherita, Meroni Alessandra, Spreafico Roberto, Sinigaglia Francesco, Colonna Marco, Panina Paola, Meldolesi Jacopo
Department of Neuroscience, DIBIT, Vita-Salute San Raffaele University and San Raffaele Institute, Via Olgettina 58, 20132 Milan, Italy.
Eur J Neurosci. 2004 Nov;20(10):2617-28. doi: 10.1111/j.1460-9568.2004.03729.x.
Together with its adaptor protein, the adaptor protein of 12 kDa also known as KARAP and TYROBP (DAP12), triggering receptor expressed in myeloid cells 2 (TREM2) is a stimulatory membrane receptor of the immunoglobulin/lectin-like superfamily, well known in myeloid cells. In humans, however, loss-of-function mutations of TREM2/DAP12 leave myeloid cells unaffected but induce an autosomal recessive disease characterized, together with bone cysts, by a spectrum of pathological lesions in the cortex, thalamus and basal ganglia with clinical symptoms of progressive dementia (polycystic lipomembraneous osteodysplasia with sclerosing leukoencephalopathy). Nothing was known about the role of TREM2/DAP12 in brain cell biology and physiology. By confocal immunocytochemistry we demonstrate that, in both human and mouse cerebral cortex, TREM2/DAP12, strongly expressed by microglia, is also present in a fraction of neurons but not in astrocytes and oligodendrocytes. In contrast, in the hippocampal cortex TREM2-expressing neurons are rare. Both in neurons and microglia the receptor appears to be located mostly intracellularly in a discrete compartment(s) partially coinciding with (or adjacent to) the Golgi complex/trans-Golgi network. Four nerve cell lines were identified as expressing the intracellular receptor system. In living human microglia CHME-5 and glioblastoma T98G cells, activation of TREM2 by its specific antibody induced [Ca2+]i responses, documenting its surface expression and functioning. Surface expression of TREM2, low in resting CHME-5 and T98G cells, increases significantly and transiently (60 min) when cells are stimulated by ionomycin, as revealed by both surface biotinylation and surface immunolabeling. Our results provide the first information about the expression, distribution (mostly intracellular) and functioning of TREM2/DAP12 system in nerve cells, a necessary step in the understanding of the cellular mechanisms affected in polycystic lipomembraneous osteodysplasia with sclerosing leukoencephalopathy.
触发受体表达于髓样细胞2（TREM2）与它的衔接蛋白（也称为KARAP和TYROBP（DAP12）的12 kDa衔接蛋白）一起，是免疫球蛋白/凝集素样超家族的一种刺激性膜受体，在髓样细胞中广为人知。然而，在人类中，TREM2/DAP12的功能丧失突变不会影响髓样细胞，但会引发一种常染色体隐性疾病，其特征除了骨囊肿外，还包括皮质、丘脑和基底神经节的一系列病理病变，并伴有进行性痴呆的临床症状（伴有硬化性白质脑病的多囊性脂膜性骨发育异常）。关于TREM2/DAP12在脑细胞生物学和生理学中的作用，此前一无所知。通过共聚焦免疫细胞化学，我们证明，在人类和小鼠的大脑皮质中，由小胶质细胞强烈表达的TREM2/DAP12也存在于一部分神经元中，但不存在于星形胶质细胞和少突胶质细胞中。相反，在海马皮质中，表达TREM2的神经元很少见。在神经元和小胶质细胞中，该受体似乎大多位于细胞内的一个离散区室中，部分与高尔基体/反式高尔基体网络重合（或相邻）。鉴定出四种神经细胞系表达细胞内受体系统。在活的人类小胶质细胞CHME-5和胶质母细胞瘤T98G细胞中，其特异性抗体激活TREM2会诱导[Ca2+]i反应，证明其表面表达和功能。如表面生物素化和表面免疫标记所示，TREM2在静息CHME-5和T98G细胞中的表面表达较低，当细胞受到离子霉素刺激时，其表面表达会显著且短暂地增加（60分钟）。我们的结果提供了关于TREM2/DAP12系统在神经细胞中的表达、分布（大多在细胞内）和功能的首个信息，这是理解伴有硬化性白质脑病的多囊性脂膜性骨发育异常中受影响的细胞机制的必要步骤。
