Elucidating the mechanism of macrophage death during infection with the AIDS-associated opportunistic pathogen Histoplasma capsulatum

项目摘要 荚膜组织胞浆菌（Hc）是一种未充分研究的真菌病原体，可导致致命的疾病， 免疫力低下的艾滋病患者我们的长期研究目标是深入了解 Hc用于杀死感染的免疫细胞的机制，最终导致对Hc的理解和 治疗HIV感染者的HC感染。HC是一种土壤真菌， 美国、中南美洲、非洲以及世界其他地区。其被引入 哺乳动物宿主吸入，随后被巨噬细胞吞噬。与大多数微生物不同，Hc 在巨噬细胞吞噬体内存活并复制。Hc在吞噬体内的强劲增殖是 随后宿主细胞死亡，从而允许活的真菌细胞从巨噬细胞中逃脱， 随后几轮的吞噬作用和细胞内增殖。缺乏细胞介导免疫的个体 反应更容易发展为严重的播散性疾病，Hc感染的艾滋病患者 长期接受抗真菌治疗，有时甚至是终生的。 我们最近发现，Hc利用分泌的效应子Cbp 1来触发整合应激， 在宿主巨噬细胞中的ISR反应，导致细胞内真菌复制后宿主细胞死亡。的ISR 是一种细胞内信号级联反应，触发翻译延伸的α亚基磷酸化 因子eIF 2以及诱导促凋亡转录因子CHOP响应于多种 压力我们已经证明，CHOP是宿主对Hc感染的敏感性所必需的。 感染这些数据现在正在PLoS Pathogens出版。据我们所知，这些是第一个数据， 表明ISR参与了宿主对真菌病原体的反应。然而，我们仍然对 cbp 1如何诱导ISR在这里，我们建议建立在强大的初步数据来定义机制， 在HC感染期间Cbp 1依赖性ISR诱导的后果。我们将：（1）研究 Cbp 1如何诱导ISR;（2）阐明在HC感染期间Cbp 1是否单独作用以诱导ISR和/或宿主- 细胞死亡，或其他Hc效应物是否参与;（3）确定eIF 2 α的机制和作用 磷酸化，启动ISR的中心信号事件，响应于HC感染。这些研究 将探索真核病原体控制巨噬细胞生存能力的新策略， 发展我们对细胞内微生物病原体的一般原理的理解， 细胞压力并导致疾病。鉴于艾滋病患者对多种细胞内 病原体，这些一般原则的建立可能是特别相关的背景下， 开发治疗策略（如ISR抑制），用于艾滋病相关的机会性感染， 其他病原体。

Project Summary Histoplasma capsulatum (Hc) is an understudied fungal pathogen that causes fatal disease in immunocompromised individuals with AIDS. Our long-term research goal is to gain insight into the pathogenic mechanisms used by Hc to kill infected immune cells, ultimately resulting in improved understanding and treatment of Hc infections in HIV-infected individuals. Hc is a soil fungus that is endemic in the Midwestern United States, Central and South America, Africa, and other regions of the world. It is introduced into mammalian hosts by inhalation and is subsequently phagocytosed by macrophages. Unlike most microbes, Hc survives and replicates within the macrophage phagosome. Robust proliferation of Hc within the phagosome is followed by host-cell death, thus allowing live fungal cells to escape from the macrophage and undergo subsequent rounds of phagocytosis and intracellular proliferation. Individuals who lack a cell-mediated immune response are more likely to develop severe disseminated disease, and AIDS patients with Hc infection are subjected to prolonged, sometimes lifelong, anti-fungal therapy. We recently discovered that Hc utilizes the secreted effector Cbp1 to trigger an integrated stress response (ISR) in host macrophages, resulting in host cell death after intracellular fungal replication. The ISR is an intracellular signaling cascade that triggers phosphorylation of the α-subunit of the translation elongation factor eIF2 as well as induction of the pro-apoptotic transcription factor CHOP in response to a variety of stresses. We have shown that CHOP is required for host sensitivity to Hc infection in the mouse model of infection. These data are now in press at PLoS Pathogens. To our knowledge, these are the first data that implicate the ISR in the host response to fungal pathogens. However, we still have very little understanding of how Cbp1 induces the ISR. Here we propose to build on robust preliminary data to define the mechanism and consequences of Cbp1-dependent ISR induction during Hc infection. We will: (1) investigate the mechanism of how Cbp1 induces the ISR; (2) elucidate if Cbp1 acts alone during Hc infection to induce the ISR and/or host- cell death, or whether other Hc effectors are involved; and (3) determine the mechanism and role of eIF2α phosphorylation, the central signaling event that initiates the ISR, in response to Hc infection. These studies will explore new strategies used by eukaryotic pathogens to control the viability of macrophages, ultimately developing our understanding of general principles deployed by intracellular microbial pathogens to trigger cellular stress and cause disease. Given the susceptibility of AIDS patients to a variety of intracellular pathogens, the establishment of these general principles may be particular relevant in the context of developing therapeutic strategies (such as ISR inhibition) for AIDS-related opportunistic infections with Hc and other like pathogens.