Mori Kohji, Yokoyama Akiko, Yang Lihua, Yang Limin, Maeda Nobuji, Mitsuda Noriaki, Tanaka Junya
Department of Physiology, School of Medicine, Ehime University, Ehime 791-0295, Japan.
Exp Neurol. 2004 Feb;185(2):220-31. doi: 10.1016/j.expneurol.2003.10.010.
Apolipoprotein E (ApoE), one of the genetic risk factors for Alzheimer's disease, is considered to have a critical role in transporting lipids in the brain. In the present study, we investigated ApoE release in primary rat microglial cultures. Microglial cells released ApoE in response to L-Ser in culture medium, and ApoE-immunoreactivity was detected in granules in the cell periphery and in perinuclear structures. Immunocytochemical studies, immunoblotting, and reverse transcription-polymerase chain reaction (RT-PCR) results all supported the notion that microglial cells are the potential source of ApoE in the brain. L-Ser enhanced ApoE release in a concentration-dependent manner without upregulating ApoE mRNA expression. Astrocytes presumably enhanced production and release of ApoE by microglial cells through secretion of L-Ser. As revealed by gel chromatography, ApoE was secreted as a component of lipoproteins, and L-Ser enhanced release of cholesterol and triglycerides together with ApoE. Activation of microglial cells by lipopolysaccharides and serum resulted in an overall decrease of the ApoE release. These findings suggest that microglial cells are a significant source of lipoproteins containing ApoE in the brain under physiological conditions, and that L-Ser is an important mediator of the neuron-astrocyte-microglia network in the brain.
载脂蛋白E（ApoE）是阿尔茨海默病的遗传风险因素之一，被认为在大脑脂质运输中起关键作用。在本研究中，我们调查了原代大鼠小胶质细胞培养物中ApoE的释放情况。小胶质细胞在培养基中对L-丝氨酸作出反应而释放ApoE，并且在细胞周边的颗粒和核周结构中检测到ApoE免疫反应性。免疫细胞化学研究、免疫印迹和逆转录-聚合酶链反应（RT-PCR）结果均支持小胶质细胞是大脑中ApoE潜在来源的观点。L-丝氨酸以浓度依赖性方式增强ApoE释放，而不上调ApoE mRNA表达。星形胶质细胞可能通过分泌L-丝氨酸增强小胶质细胞ApoE的产生和释放。凝胶色谱显示，ApoE作为脂蛋白的一个组分被分泌，并且L-丝氨酸与ApoE一起增强胆固醇和甘油三酯的释放。脂多糖和血清激活小胶质细胞导致ApoE释放总体减少。这些发现表明，在生理条件下小胶质细胞是大脑中含ApoE脂蛋白的重要来源，并且L-丝氨酸是大脑中神经元-星形胶质细胞-小胶质细胞网络的重要介质。
