Survival strategies of Plasmodium berghei exoerythrocytic forms (EEF) in hepatocytes

细胞内寄生虫的存活取决于它们规避宿主细胞凋亡的能力。以啮齿动物寄生虫伯氏疟原虫为模型系统，研究了疟原虫在肝细胞内从孢子体进入到分裂子体释放的生存策略。在我们正在进行的研究过程中，我们可以证明在感染的前两天，寄生虫保护宿主细胞免于凋亡，而在第三天，它在形成分裂子时诱导细胞凋亡。计划研究寄生物依赖的促凋亡和抗凋亡宿主信号通路的调控，以及在分裂过程中导致宿主细胞剧烈变化的分子事件。本建议的另一个目标是肝细胞中分裂子形成的特征。该项目的这一部分是基于我们的观察，即寄生的肝细胞在细胞凋亡之前会在上清液中短暂地四舍五入并漂浮。漂浮的感染细胞可以很容易地从未感染的贴壁细胞中分离出来，这首次为详细研究肝脏来源的疟原虫提供了可能性。设想鉴定和特异性抑制所需的寄生虫蛋白的分裂子存活。除了更一般的方法来识别这些寄生虫蛋白质，我们将重点关注寄生虫蛋白酶，它在肝细胞释放分裂子时参与宿主细胞膜的破坏。

Survival of intracellular parasites depends on their ability to circumvent apoptosis of the host cell. Using the rodent parasite Plasmodium berghei as a model system we investigate survival strategies of Plasmodium parasites in hepatocytes from entry of sporozoites to the release of merozoites. In course of our ongoing studies we could show that during the first two days of infection the parasite protects the host cell from apoptosis, where as it induces apoptosis on the third day upon formation of merozoites. It is planned to study parasite dependent regulation of pro- and anti-apoptotic host signalling pathways as well as the molecular events leading to the dramatic changes in the host cell during merogony. Another goal of this proposal is the characterisation of merozoite formation in hepatocytes. This part of the project is based on our observation that parasitised hepatic cells round off and float in the supernatant briefly before they undergo apoptosis. Floating infected cells can easily be separated from non-infected adherent cells offering for the first time the possibility to study liver-derived Plasmodium parasites in detail. The identification and specific inhibition of parasite proteins needed for merozoite survival is envisaged. Apart from a more gereal approach to identify those parasite proteins we will focus on parasite proteases which are involved in the destruction of host cell membranes during the release of merozoites from hepatocytes.