Luján H D, Mowatt M R, Byrd L G, Nash T E
Laboratory of Parasitic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892-0425, USA.
Proc Natl Acad Sci U S A. 1996 Jul 23;93(15):7628-33. doi: 10.1073/pnas.93.15.7628.
Giardia lamblia, like most human intestinal parasitic protozoa, sustains fundamental morphological and biochemical changes to survive outside the small intestine of its mammalian host by differentiating into an infective cyst. However, the stimulus that triggers this differentiation remains totally undefined. In this work, we demonstrate the induction of cyst formation in vitro when trophozoites are starved for cholesterol. Expression of cyst wall proteins was detected within encystation-specific secretory vesicles 90 min after the cells were placed in lipoprotein-deficient TYI-S-33 medium. Four cloned lines derived from two independent Giardia isolates were tested, and all formed cysts similarly. Addition of cholesterol, low density or very low density lipoproteins to the lipoprotein-deficient culture medium, inhibited the expression of cyst wall proteins, the generation of encystation-specific vesicles, and cyst wall biogenesis. In contrast, high density lipoproteins, phospholipids, bile salts, or fatty acids had little or no effect. These results indicate that cholesterol starvation is necessary and sufficient for the stimulation of Giardia encystation in vitro and, likely, in the intestine of mammalian hosts.
与大多数人类肠道寄生原生动物一样，蓝氏贾第鞭毛虫通过分化形成感染性包囊，在其哺乳动物宿主的小肠外生存时会发生基本的形态和生化变化。然而，触发这种分化的刺激因素仍然完全不清楚。在这项研究中，我们证明了滋养体在缺乏胆固醇的情况下饥饿时，体外会诱导包囊形成。将细胞置于缺乏脂蛋白的TYI-S-33培养基中90分钟后，在包囊化特异性分泌小泡中检测到包囊壁蛋白的表达。对来自两个独立贾第虫分离株的四个克隆系进行了测试，所有克隆系形成包囊的情况相似。向缺乏脂蛋白的培养基中添加胆固醇、低密度或极低密度脂蛋白，会抑制包囊壁蛋白的表达、包囊化特异性小泡的产生以及包囊壁的生物合成。相比之下，高密度脂蛋白、磷脂、胆汁盐或脂肪酸几乎没有影响。这些结果表明，胆固醇饥饿对于体外刺激贾第虫包囊化是必要且充分的，并且可能在哺乳动物宿主的肠道中也是如此。
