Role of host spingolipids against fungal infections

 描述（由申请人提供）： 本项目的目的是研究宿主鞘脂在控制病原真菌新生隐球菌（Cn）感染中的作用和机制。 一个迅速兴起的研究领域是研究鞘脂在传染病调节中的作用（1年综述）。尽管一些鞘脂与吞噬细胞的抗菌活性有关，但对宿主鞘脂对抗真菌感染的作用知之甚少。显示调节免疫应答的宿主鞘脂代谢酶之一是鞘磷脂合酶（SMS），由SMS 1和SMS 2基因编码。4 -6 SMS将磷酸胆碱部分从磷脂酰胆碱（PC）转移到神经酰胺，因此产生鞘磷脂（SM）和二酰基甘油（DAG）。7 -9非常有趣的是，由SMS调节的脂质与促炎应答的激活有关，这表明免疫细胞中SMS活性的调节可能在控制感染中起关键作用。 在我们初步和已发表的研究中10，11， 发现：1）SMS活性的抑制通过在不存在吞噬作用的情况下影响细胞外杀伤而深刻地损害吞噬细胞吞噬Cn细胞的能力; 2）SMS调节 高尔基体的DAG; 3）由SMS在高尔基体产生的DAG通过激活蛋白激酶D（PKD）调节蛋白分泌; 4）SMS或PKD的抑制阻断嗜中性粒细胞对Cn的细胞外杀伤和肽分泌（如防御素）;和5）中性粒细胞减少症显著加剧Cn感染。基于这些观察结果，我们假设SMS活性通过调节DAG-PKD介导的分泌途径在控制嗜中性粒细胞的细胞外杀伤中起关键作用（图1）。因此，我们提出以下目标：1）建立SMS对Cn的作用; 2）确定SMS调节Cn杀伤的机制。 本申请中提出的研究在不同水平上是重要的和新颖的：i）它们将建立用于真菌感染研究的新动物模型， 与目前的模型相比，它们在临床上与人类感染更相关; ii）它们将确定吞噬细胞在宿主对真菌感染的反应中的作用;和iii）它们将鉴定吞噬细胞对感染的反应的新调节剂，其可以被工程化以增强宿主免疫系统。

 DESCRIPTION (provided by applicant): The goal of this project is to study the role and mechanisms by which host sphingolipids are involved in controlling the infection caused by the pathogenic fungus Cryptococcus neoformans (Cn). A rapidly emerging area of research is the study of the role of sphingolipids in the regulation of infectious diseases (Reviewed in1). Although some sphingolipids have been linked to antibacterial activity of phagocytic cells,2,3 very little is known about the role of host sphingolipids against fungal infections. One of the host sphingolipid-metabolizing enzymes shown to regulate immune responses is sphingomyelin synthase (SMS), encoded by the SMS1 and SMS2 genes.4-6 SMS transfers a choline phosphate moiety from phosphatidylcholine (PC) to ceramide, therefore producing sphingomyelin (SM) and diacylglycerol (DAG).7-9 Very interestingly, the lipids regulated by SMS have been implicated in the activation of pro-inflammatory responses, suggesting that the regulation of SMS activity in immune cells may assume a critical role in controlling infections. In our preliminary and published studies10,11 we found that: 1) inhibition of SMS activity profoundly impairs the ability of phagocytic cells to kil Cn cells by affecting extracellular killing in absence of phagocytosis; 2) SMS regulates production of DAG at the Golgi; 3) DAG produced at the Golgi by SMS regulates protein secretion via activation of protein kinase D (PKD); 4) inhibition of SMS or PKD blocks extracellular killing of Cn and peptide secretion (such as defensins) by neutrophils; and 5) neutropenia significantly exacerbates Cn infection. Based on these observations, we hypothesize that SMS activity plays a key role in controlling the extracellular killing of neutrophils through the regulation of a DAG-PKD-mediated secretion pathway (Figure 1). Thus, we propose the following aims: 1) To establish the role of SMS against Cn; and 2) To determine the mechanism by which SMS regulates Cn killing. The studies proposed in this applications are significant and novel at different levels: i) they will establish novel animal models for the study of fungal infection that are more clinically relevant to the human infection than current models; ii) they will define the role of phagocytes in the host response to fungal infections; and iii) they will identify novel regulators of the phagocytes' response against the infection which can be engineered to boost the host immune system.