Modulation of the host cell cholesterol metabolism by Eimeria bovis

牛艾美耳球虫是牛的细胞内顶复寄生虫，是导致小牛严重出血性腹泻的牛球虫病的重要原因。已有的资料表明，E.牛清除宿主细胞胆固醇以保证其在细胞内发育成大裂殖体，其特征在于寄生虫在感染的宿主细胞内的巨大扩大和每个裂殖体I产生> 120.000个裂殖子。与弓形虫等其它球虫相比，E.牛感染同时上调了感染细胞中胆固醇的从头合成和低密度脂蛋白（LDL）的摄取，以保证寄生虫的成功发育，并且不仅通过乙酰辅酶A乙酰转移酶（ACAT）调节胆固醇酯化，而且还通过胆固醇-25-羟化酶（CH 25 H）增强胆固醇加工，这表明氧固醇也可能参与E.本研究的目的是研究修饰的LDL（乙酰化和氧化的LDL）与经典LDL相比以及各自的宿主细胞受体（LDLR、OLR 1）对E.牛的内皮宿主细胞。此外，我们打算通过功能测定分析CH 25 H和氧化甾醇在大裂体形成中的作用。除了植物甾醇外，对前体、代谢产物和终产物的细胞含量的生化分析将分别阐明细胞从头合成和细胞外摄取胆固醇在感染宿主细胞中的实际作用。此外，将进行生化实验以分析细胞裂解物中胆固醇酯化的等级，以估计ACAT活性对寄生虫增殖的影响。使用荧光胆固醇类似物，差异运输的细胞，从而导致差异的ACAT的可及性，将使我们能够分析胆固醇储存在感染的细胞，并获得信息的可用性的免费和酯化的胆固醇寄生虫复制。为了对E.牛触发的宿主细胞胆固醇代谢的调节，我们最后打算在E.牛感染的内皮细胞。

Eimeria bovis is an intracellular apicomplexan parasite of cattle and represents an important cause of bovine coccidiosis leading to severe haemorrhagic diarrhea in calves. Out previous data indicate that E. bovis scavenges host cell cholesterol to guarantee its intracellular development into macromeronts that is characterized by an enormous enlargement of the parasite within infected host cells and the production of > 120.000 merozoites per meront I. In contrast to other coccidians, such as Toxoplasma gondii, E. bovis infections simultaneously up-regulates both, de novo synthesis of cholesterol and uptake of low densitiy lipoprotein (LDL) in infected cells to guarantee successful development of the parasite and modulates not only cholesterol esterification via acetyl-CoA-acetyltransferase (ACAT) but additionally enhances cholesterol procession by cholesterol-25-hydroxylase (CH25H) indicating that oxysterols may also be involved in the replication process of E. bovis.The aim of this study is to investigate the impact of modified LDL (acetylated and oxidized LDL) in comparison to classical LDL and of respective host cell receptors (LDLR, OLR1) on successful replication of E. bovis in endothelial host cells. Furthermore, we intend to analyze the role of CH25H and of oxysterols in macromeront formation via functional assays. Biochemical analyses on the cell contents of precursors, metabolites and end-products in addition to phytosterols will elucidate the actual role of cellular de novo synthesis and extracellular up-take of cholesterol in infected host cells, respectively. In addition, biochemical experiments will be conducted to analyze the grade of cholesterol esterification in cell lysates in order to estimate the impact of ACAT activity on parasite proliferation. The use of fluorescent cholesterol analogs that are differentially transported in cells thus leading to differential accessibility for ACAT will allow us to analyze cholesterol storage in infected cells and to get information on the usability of free and esterified cholesterol for parasite replication. To get more new insights into E. bovis-triggered modulation of host cell cholesterol metabolism, we finally intend to conduct first experiments on the cholesterol transport in E. bovis-infected endothelial cells.