Brumeanu Teodor-D, Preda-Pais Anca, Stoica Cristina, Bona Constantin, Casares Sofia
Department of Medicine, Division of Immunology, Uniformed Services University of Health Sciences, Bethesda, MD 20814, USA.
Mol Immunol. 2007 Jan;44(4):530-40. doi: 10.1016/j.molimm.2006.02.008. Epub 2006 Apr 4.
The GM gangliosides and cholesterol components of plasma membrane lipid rafts play an important role in the recruitment and signaling of protein receptors in eukaryotic cells. Herein, we have analyzed at the single-cell level the partitioning and intracellular trafficking of GM gangliosides and cholesterol in quiescent (CD4+CD69-) and CD3-activated (CD4+CD69+) thymic and splenic T cells. First, regardless the gender and the quiescent or activated status of T cells, the GM and cholesterol content in cytosol and plasma membrane as well as the expression levels of GM synthase, Sphingomyelin phosphodiestarase 2 and HMG Co-A reductase genes involved in GM and cholesterol synthesis were constantly lower in CD4 thymocytes than in CD4 splenocytes. Second, we detected variations in the balance between GM and cholesterol in plasma membrane depending on aging, and found that deprivation of cellular cholesterol does not necessarily affect the GM content in both quiescent CD4 thymocytes and splenocytes. Third, CD3 stimulation up-regulated the GM and little if any the cholesterol content in both thymic and splenic CD4 T cells, suggesting a cross talk between the CD3 signaling and GM but not cholesterol biosynthesis pathway. Fourth, partitioning and trafficking of GM to the plasma membrane depended on the transport of ceramide precursors from endoplasmic reticulum to Golgi network, as well as on the synthesis, glycosylation and vesicular assembly in trans-Golgi, and less on the cytoskeleton architecture in both quiescent and activated CD4 thymic and splenic T cells. Together, these findings suggest that the differential partitioning and intracellular trafficking of GM and cholesterol in thymic and splenic CD4 T cells may account for the stage of functional maturation.
质膜脂筏中的神经节苷脂GM和胆固醇成分在真核细胞中蛋白质受体的募集和信号传导中发挥着重要作用。在此，我们在单细胞水平分析了神经节苷脂GM和胆固醇在静止（CD4+CD69-）和CD3激活（CD4+CD69+）的胸腺和脾T细胞中的分配及细胞内运输情况。首先，无论T细胞的性别以及静止或激活状态如何，CD4胸腺细胞中细胞质和质膜中的GM和胆固醇含量，以及参与GM和胆固醇合成的GM合酶、鞘磷脂磷酸二酯酶2和HMG Co-A还原酶基因的表达水平，均持续低于CD4脾细胞。其次，我们检测到质膜中GM与胆固醇之间的平衡随衰老而变化，并且发现细胞胆固醇的剥夺不一定会影响静止的CD4胸腺细胞和脾细胞中的GM含量。第三，CD3刺激上调了胸腺和脾CD4 T细胞中的GM含量，而对胆固醇含量几乎没有影响，这表明CD3信号传导与GM生物合成途径之间存在相互作用，但与胆固醇生物合成途径无关。第四，GM向质膜的分配和运输依赖于神经酰胺前体从内质网到高尔基体网络的转运，以及反式高尔基体中的合成、糖基化和囊泡组装，而在静止和激活的CD4胸腺细胞和脾细胞中，较少依赖于细胞骨架结构。总之，这些发现表明，胸腺和脾CD4 T细胞中GM和胆固醇的差异分配及细胞内运输可能与功能成熟阶段有关。
