Leishmania promastigotes require lipophosphoglycan to actively modulate the fusion properties of phagosomes at an early step of phagocytosis
Leishmania promastigotes require lipophosphoglycan to actively modulate the fusion properties of phagosomes at an early step of phagocytosis
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DOI：
10.1046/j.1462-5822.2000.00037.x
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发表时间：
2000-04-01
影响因子：
3.4
通讯作者：
Desjardins, M
中科院分区：
文献类型：
--
作者：
Dermine, JF;Scianimanico, S;Desjardins, M
promastigotes利什曼原虫的脂磷聚糖（LPG）在昆虫和哺乳动物宿主的寄生虫生存中起着关键作用。有证据表明，液化石油气在巨噬细胞感染时降低吞噬体融合特性。然而，人们对这种分子的作用机制知之甚少。在目前的研究中，我们使用了一系列的利什曼原虫突变体，展示了修饰的LPG结构，以更精确地确定LPG如何调节吞噬体-内体融合。利用体内融合实验，在电子显微镜下测量溶质物质从内体转移到吞噬体的过程，我们进一步证明了LPG的重复Gal(β 1,4)Man（α 1- po4）单位是吞噬体融合改变的原因。LPG对吞噬小体融合的抑制作用对晚期内吞细胞器和溶酶体的抑制作用比早期内吞小体的抑制作用更强，这解释了promastigotes利什曼原虫如何避免在富含水解酶的腔室中降解。其他含有重复单元的分子，包括分泌的酸性磷酸酶，在抑制过程中被排除，因为在高度融合性吞噬体中存在分泌含有重复单元的糖缀合物的lpg缺陷突变体（lpg1(-)）。在L. major中，LPG的寡糖侧链对抑制过程没有贡献，因为缺乏LPG侧链的L. major突变体Spock对融合的阻断程度与野生型寄生虫相同。最后，尽管存在LPG，但从培养基中内化的死寄生虫在改变吞噬体-内体融合方面不如活寄生虫有效。然而，寄生物在吞噬体中被隔离后用活性染料杀死，对该细胞器的融合特性没有影响。综上所述，这些结果表明，显示全长细胞表面液化石油气的活原毛藻可以在吞噬作用早期积极影响巨噬细胞，产生具有较差融合性的吞噬体。
The lipophosphoglycan (LPG) of Leishmania promastigotes plays key roles in parasite survival in both insect and mammalian hosts. Evidence suggests that LPG decreases phagosome fusion properties at the onset of infection in macrophages. The mechanisms of action of this molecule are, however, poorly understood. In the present study, we used a panoply of Leishmania mutants displaying modified LPG structures to determine more precisely how LPG modulates phagosome-endosome fusion. Using an in vivo fusion assay measuring, at the electron microscope, the transfer of solute materials from endosomes to phagosomes, we provided further evidence that the repeating Gal(beta 1,4)Man(alpha 1-PO4) units of LPG are responsible for the alteration in phagosome fusion. The inhibitory effect of LPG on phagosome fusion was shown to be more potent towards late endocytic organelles and lysosomes than early endosomes, explaining how Leishmania promastigotes can avoid degradation in hydrolase-enriched compartments. The involvement of other repeating unit-containing molecules, including the secreted acid phosphatase, in the inhibition process was ruled out, as an LPG-defective mutant (lpg1(-)) which secretes repeating unit-containing glycoconjugates was present in highly fusogenic phagosomes. In L. major, oligosaccharide side-chains of LPG did not contribute to the inhibition process, as Spock, an L. major mutant lacking LPG side-chains, blocked fusion to the same extent as wild-type parasites. Finally, dead parasites internalized from the culture medium were not as efficient as live parasites in altering phagosome-endosome fusion, despite the presence of LPG. However, the killing of parasites with vital dyes after their sequestration in phagosomes had no effect on the fusion properties of this organelle. Collectively, these results suggest that living promastigotes displaying full-length cell surface LPG can actively influence macrophages at an early stage of phagocytosis to generate phagosomes with poor fusogenic properties.