Department of Molecular Neurobiology, School of Pharmacy, Tokyo University of Pharmacy and Life Sciences, Hachioji, Tokyo, Japan.
PLoS One. 2011;6(11):e27544. doi: 10.1371/journal.pone.0027544. Epub 2011 Nov 15.
Phospholipase D4 (PLD4) is a recently identified protein that is mainly expressed in the ionized calcium binding adapter molecule 1 (Iba1)-positive microglia in the early postnatal mouse cerebellar white matter. Unlike PLD1 and PLD2, PLD4 exhibits no enzymatic activity for conversion of phosphatidylcholine into choline and phosphatidic acid, and its function is completely unknown. In the present study, we examined the distribution of PLD4 in mouse cerebellar white matter during development and under pathological conditions. Immunohistochemical analysis revealed that PLD4 expression was associated with microglial activation under such two different circumstances. A primary cultured microglia and microglial cell line (MG6) showed that PLD4 was mainly present in the nucleus, except the nucleolus, and expression of PLD4 was upregulated by lipopolysaccharide (LPS) stimulation. In the analysis of phagocytosis of LPS-stimulated microglia, PLD4 was co-localized with phagosomes that contained BioParticles. Inhibition of PLD4 expression using PLD4 specific small interfering RNA (siRNA) in MG6 cells significantly reduced the ratio of phagocytotic cell numbers. These results suggest that the increased PLD4 in the activation process is involved in phagocytosis of activated microglia in the developmental stages and pathological conditions of white matter.
磷脂酶 D4(PLD4)是一种新鉴定的蛋白,主要表达于离子钙结合衔接分子 1(Iba1)阳性的小胶质细胞,位于出生后早期小鼠小脑白质。与 PLD1 和 PLD2 不同,PLD4 没有将磷脂酰胆碱转化为胆碱和磷脂酸的酶活性,其功能完全未知。在本研究中,我们研究了 PLD4 在发育中和病理条件下在小鼠小脑白质中的分布。免疫组织化学分析显示,PLD4 的表达与这两种不同情况下小胶质细胞的激活有关。原代培养的小胶质细胞和小胶质细胞系(MG6)显示,PLD4 主要存在于细胞核中,除核仁外,PLD4 的表达可被脂多糖(LPS)刺激上调。在分析 LPS 刺激的小胶质细胞的吞噬作用时,PLD4 与含有 BioParticles 的吞噬体共定位。在 MG6 细胞中用 PLD4 特异性小干扰 RNA(siRNA)抑制 PLD4 表达,显著降低了吞噬细胞数量的比例。这些结果表明,在发育阶段和白质的病理条件下,激活过程中增加的 PLD4 参与了活化小胶质细胞的吞噬作用。