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致病真菌新生隐球菌(CN)感染中的作用和机制。一个迅速兴起的研究领域是鞘磷脂在调节传染病中的作用(综述1)。虽然一些鞘脂与吞噬细胞的抗菌活性有关，但2，3对宿主鞘脂抗真菌感染的作用知之甚少。由SMS1和SMS2基因编码的鞘磷脂合成酶(SMS)是调节免疫反应的宿主鞘磷脂代谢酶之一。4-6 SMS将磷脂酰胆碱(PC)中的胆碱磷酸部分转移到神经酰胺，从而产生鞘磷脂(SM)和二酰甘油(DAG)。7-9非常有趣的是，由SM调节的脂类参与了促炎反应的激活，这表明免疫细胞中SM活性的调节可能在控制感染中发挥关键作用。在我们的初步研究和已发表的研究中，我们 发现：1)抑制sms的活性，通过在没有吞噬作用的情况下影响细胞外杀伤，从而深刻地削弱吞噬细胞杀伤CN细胞的能力；2)sms调节 在高尔基体产生的DAG；3)由SMS在高尔基体产生的DAG通过激活蛋白激酶D(PKD)来调节蛋白质的分泌；4)抑制SMS或PKD阻止中性粒细胞对CN的细胞外杀伤和多肽分泌(如防御素)；以及5)中性粒细胞减少显著加剧CN感染。基于这些观察，我们假设SMS活性通过调节DAG-PKD介导的分泌途径在控制细胞外对中性粒细胞的杀伤中发挥关键作用(图1)。因此，我们提出了以下目标：1)确定Sms对CN的作用；2)确定Sms调节CN杀伤的机制。这些申请中提出的研究在不同层面上具有重要意义和新颖性：i)它们将为研究真菌感染建立新的动物模型， 与目前的模型相比，它们在临床上与人类感染更相关；ii)它们将定义吞噬细胞在宿主对真菌感染的反应中的作用；以及iii)它们将确定吞噬细胞对感染的反应的新调节因子，这些调节因子可以被改造成增强宿主免疫系统。

 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.