Molecular Mechanism of Leishmaniasis

总结：利什曼原虫引起人类疾病（利什曼病），临床症状从自愈性皮肤损伤到致命的内脏感染。对利什曼原虫致病机制的缺乏了解在全球范围内构成了严重的公共卫生风险，特别是对生活或旅行在流行地区的美国军事人员，他们的家人和游客。 作为了解利什曼原虫发病机制的分子机制的第一步，我们已经开始分析参与寄生虫生命周期的过程，从无毒到有毒的形式转化，并针对这些过程来控制寄生虫的生长。 利什曼原虫细胞器的独特结构和功能特征，如细胞骨架和鞭毛器，在利什曼原虫感染性中的作用仍然不清楚。 为了鉴定控制生长的基因，我们首次从L. donovani。中心蛋白是一种钙离子结合的细胞骨架蛋白，对中心体的复制和分离至关重要。 中心蛋白mRNA和蛋白质的水平是高的寄生虫在文化中的指数增长和下降到一个较低的水平，在稳定期。在寄生虫中N-末端缺失的中心蛋白的表达显著降低其生长速率，并且发现比对照细胞中显著更多的细胞被阻滞在G2/M期。这些研究表明，中心蛋白可能在利什曼原虫生长中发挥功能性作用。 程序性细胞死亡（PCD）是细胞生物学的重要组成部分，被认为不仅是为了调节多细胞生物体的生长和发育。然而，最近的研究，这表明PCD的存在，在单细胞生物体中，已经假定PCD在单细胞生物学中的功能作用。 据推测，为了促进和维持种群内的克隆性，锥虫必须发展出一种利他机制来控制生长。 本研究旨在探讨利什曼原虫是否存在PCD，以及抗利什曼原虫药物是否能诱导PCD，这将为开发抗利什曼原虫药物提供契机。在本研究中，我们已经证明了一些特点，程序性细胞死亡（PCD）的单细胞原生动物寄生虫杜氏利什曼原虫，内脏利什曼病的病原体。我们报告说，PCD开始在静止期培养的前鞭毛体和积极增长的无鞭毛体和前鞭毛体的文化治疗后，与抗利什曼原虫药物（喷托霉素和阿替霉素B）。然而，这两种细胞类型对抗利什曼原虫药物的反应不同。 因此，这些研究为理解利什曼原虫发病机制以及如何利用它来控制寄生虫生长提供了基础。

Summary: Leishmania parasite causes human disease (Leishmaniasis) with clinical symptoms ranging from self healing cutaneous lesions to fatal visceral infection. The lack of understanding of the mechanism by which Leishmania parasite causes disease poses a serious public health risk worldwide and in particular for U.S. military personnel their families and tourists either living or travelling in endemic areas. As a first step towards understanding the molecular mechanism of Leishmania pathogenesis, we have began to analyze the processes that are involved in parasite life cycle in transformation from an avirulent to virulent form and to target such processes to control growth of the parasite. The role of unique structural and functional features of organelles, like the cytoskeleton and the flagellar apparatus, in infectivity of Leishmania, is still obscure. In order to identify genes that control growth, we have isolated for the first time a gene encoding for centrin from L. donovani. Centrin is calcium binding cytoskeletal protein essential for centrosome duplication or segregation. The levels of centrin mRNA and protein were high during the exponential growth of the parasite in culture and declined to a low level in the stationary phase. Expression of N-terminal deleted centrin in the parasite significantly reduces its growth rate and it was found that significantly more cells are arrested in the G2/M stage than in control cells. These studies indicate that centrin may have a functional role in Leishmania growth. Programmed cell death (PCD) is an essential part of cell biology and is thought to have evolved not only to regulate growth and development in multicellular organisms. However, recent studies, which showed the existence of PCD in unicellular organisms, have postulated a functional role of PCD in the biology of unicellular organisms. It has been postulated that in order to promote and maintain clonality within the population, the Trypanosomatids must have developed an altruistic mechanism to control growth. We wanted to explore whether PCD exists in Leishmania and if so can antiLeishmanial drugs induce it. This will provide an opportunity to develop future antiLeishmanial drugs. In the present study we have demonstrated some features characterizing programmed cell death (PCD) in the unicellular protozoan parasite Leishmania donovani, the causative agent of visceral Leishmaniasis. We report that PCD is initiated in stationary phase cultures of promastigotes and both in actively growing cultures of axenic amastigotes and promastigotes upon treatment with anti Leishmanial drugs (Pentostam and amphotericin B). However, the two cell types respond to antiLeishmanial drugs differently. Therefore, these studies provide the basis for understanding the mechanism of Leishmania pathogenesis and how it can be exploited in order to control parasite growth.