Palacpac Nirianne Marie Q, Hiramine Yasushi, Mi-ichi Fumika, Torii Motomi, Kita Kiyoshi, Hiramatsu Ryuji, Horii Toshihiro, Mitamura Toshihide
PRESTO, Japan Science and Technology Corporation, 4-1-8 Honcho Kawaguchi, Saitama 332-0012, Japan.
J Cell Sci. 2004 Mar 15;117(Pt 8):1469-80. doi: 10.1242/jcs.00988.
Triacylglycerol (TAG) serves as a major energy storage molecule in eukaryotes. In Plasmodium, however, this established function of TAG appears unlikely, despite detecting previously considerable amount of TAG associated with intraerythrocytic parasites, because plasmodial cells have very little capacity to oxidize fatty acids. Thus, it is plausible that TAG and its biosynthesis in Plasmodium have other functions. As a first step in understanding the biological significance of TAG and its biosynthesis to the intraerythrocytic proliferation of Plasmodium falciparum, we performed detailed characterization of TAG metabolism and trafficking in parasitized erythrocyte. Metabolic labeling using radiolabeled-oleic and palmitic acids in association with serum albumin, which have been shown to be among the serum essential factors for intraerythrocytic proliferation of P. falciparum, revealed that accumulation of TAG was strikingly pronounced from trophozoite to schizont, whereas TAG degradation became active from schizont to segmented schizont; the consequent products, free fatty acids, were released into the medium during schizont rupture and/or merozoite release. These results were further supported by visualization of lipid bodies through immunofluorescence and electron microscopy. At the schizont stages, there is some evidence that the lipid bodies are partly localized in the parasitophorous vacuole. Interestingly, the discrete formation and/or trafficking of lipid bodies are inhibited by brefeldin A and trifluoperazine. Inhibition by trifluoperazine hints at least that a de novo TAG biosynthetic pathway via phosphatidic acid contributes to lipid body formation. Indeed, biochemical analysis reveals a higher activity of acyl-CoA:diacylglycerol acyltransferase, the principal enzyme in the sn-glycerol-3-phosphate pathway for TAG synthesis, at trophozoite and schizont stages. Together, these results establish that TAG metabolism and trafficking in P. falciparum-infected erythrocyte occurs in a stage-specific manner during the intraerythrocytic cycle and we propose that these unique and dynamic cellular events participate during schizont rupture and/or merozoite release.
三酰甘油（TAG）是真核生物中主要的能量储存分子。然而，在疟原虫中，尽管之前检测到与红细胞内寄生虫相关的大量TAG，但TAG的这一既定功能似乎不太可能存在，因为疟原虫细胞氧化脂肪酸的能力非常低。因此，疟原虫中的TAG及其生物合成可能具有其他功能。作为了解TAG及其生物合成对恶性疟原虫红细胞内增殖的生物学意义的第一步，我们对受感染红细胞中TAG的代谢和运输进行了详细表征。使用放射性标记的油酸和棕榈酸与血清白蛋白进行代谢标记，血清白蛋白已被证明是恶性疟原虫红细胞内增殖的血清必需因子之一，结果显示，从滋养体到裂殖体，TAG的积累显著增加，而从裂殖体到分段裂殖体，TAG降解变得活跃；随后产生的游离脂肪酸在裂殖体破裂和/或裂殖子释放期间释放到培养基中。通过免疫荧光和电子显微镜对脂质体的观察进一步支持了这些结果。在裂殖体阶段，有证据表明脂质体部分定位于寄生泡中。有趣的是，布雷菲德菌素A和三氟拉嗪可抑制脂质体的离散形成和/或运输。三氟拉嗪的抑制作用至少表明，通过磷脂酸的从头TAG生物合成途径有助于脂质体的形成。事实上，生化分析显示，在滋养体和裂殖体阶段，TAG合成的sn-甘油-3-磷酸途径中的主要酶酰基辅酶A：二酰甘油酰基转移酶的活性较高。总之，这些结果表明，在恶性疟原虫感染的红细胞中，TAG的代谢和运输在红细胞内周期中以阶段特异性方式发生，我们认为这些独特而动态的细胞事件参与了裂殖体破裂和/或裂殖子释放过程。
