Overexpression of Complement in the Brain and HIV Neuropathogenesis

描述(由申请人提供)：补体成分在各种神经退行性疾病的大脑中升高，但它们在神经发病机制中的作用尚不清楚。最近的研究表明，C1q和C3在发育过程中参与突触重构，并在疾病过程中介导某些特定形式的突触损伤。与这些发现一致，我们发现C3在a)在HIV-1相关性痴呆期间在大脑中升高；b)在感染嵌合HIV-1的小鼠中；以及c)在原代培养的暴露于HIV-1的人和小鼠星形胶质细胞中。我们的初步数据还表明，HIV-1通过与IL-6的产生相关的NF：B依赖的途径间接诱导星形胶质细胞中的C3。根据在正常脑发育过程中突触重构需要C3的发现，我们假设在HIV感染期间大脑中C3的过度表达启动了异位突触重构和神经发病。在这一应用中，我们建议进行探索性研究，以验证这一假说的两个特定目的：1.我们将确定完整的HIV-1和TAT诱导星形胶质细胞C3的机制，重点是HIV-1诱导的IL-6作为媒介的潜在作用。2.我们将找到一种最适合于研究HIV-1或TAT诱导脑内C3和IL-6以及突触内活性补体沉积的HIV-1相关神经发病机制的小鼠模型。建议的探索性研究应该为详细研究补体及其潜在的诱导物HIV和IL-6在HIV介导的神经发病中的作用建立概念基础和实验工具。这些研究将包括在原代培养的星形胶质细胞中进行HIV和TAT的实验，并将评估现有的三种HIV神经发病的小动物模型，包括将感染HIV-1的同基因星形胶质细胞移植到小鼠脑内，将表达TAT的同基因星形胶质细胞移植到小鼠脑内，以及将嵌合HIV-1直接感染小鼠。每个系统都将使用野生型、C3基因敲除和IL-6基因敲除小鼠。该项目涉及的研究学科包括逆转录病毒学、分子生物学、神经生物学、神经病理学和动物研究。该项目解决了艾滋病毒相关的神经认知障碍这一日益严重的公共卫生问题。如果成功，这项工作中描述的小动物模型可能被用于转化性研究，旨在对抗补体和IL-6在大脑中潜在的神经退化行为的治疗方法。与公共卫生的相关性：艾滋病毒-1感染仍是一种世界性大流行。令人不安的是，美国的新感染发病率被低估了，而纽约的新感染发病率近年来实际上正在上升。因此，这一祸害仍然是一个严重的公共卫生挑战。这项应用解决了HIV-1感染者中持续存在的一种疾病，即神经认知障碍。神经系统功能障碍可由细胞直接死亡引起，但最近的研究也表明，神经功能损伤在HIV-1感染的大脑中的重要性。这项应用侧重于突触消除的机制，这种机制通常发生在发育中的大脑中，但可能在感染HIV-1期间被颠覆。这条途径需要补体成分C3的表达，补体C3是一种血清蛋白，在HIV-1感染期间在大脑中发现升高，如图所示。建议对原代星形胶质细胞过度表达的机制进行研究，星形胶质细胞是大脑中数量最多的细胞。为了了解这一过程对大脑的影响，将研究三种HIV-1神经发病模型的C3表达和突触消除的显著程度，这是导致神经退化的明确途径。如果成功，这一发展应用将为对抗HIV-1感染期间发生的神经元功能损害的一种新的、生理相关的途径提供重要的线索。

DESCRIPTION (provided by applicant): Complement components are elevated in the brain in a variety of neurodegenerative disorders but their contribution to neuropathogenesis is unknown. Recent studies indicate that C1q and C3 contribute to synaptic remodeling during development and mediate some specific forms of synaptic damage during disease. Consistent with these findings, we have shown that C3 is elevated a) in the brain during HIV-1-associated dementia; b) in mice infected with chimeric HIV-1; and c) in primary human and mouse astrocytes exposed to HIV-1 in culture. Our preliminary data also indicate that HIV-1 induces C3 in astrocytes indirectly through a NF-:B dependent pathway that correlates with production of interleukin 6 (IL-6). Based on the finding that synaptic remodeling during normal brain development requires C3, we hypothesize that C3 overexpression in the brain during HIV infection initiates ectopic synaptic remodeling and neuropathogenesis. In this application, we propose exploratory studies toward testing this hypothesis in two Specific Aims: 1. We will determine the mechanism of C3 induction in astrocytes by intact HIV-1 and Tat with focus on the potential role of HIV-1-induced IL-6 as a mediator. 2. We will identify a mouse model of HIV-1-associated neuropathogenesis that is most suitable for study of C3 and IL-6 induction by HIV-1 or Tat in the brain and the deposition of activated complement in synapses. The proposed exploratory studies should establish the conceptual basis and experimental tools for detailed investigation of the role of complement and its potential inducers HIV and IL-6 in HIV mediated neuropathogenesis. The studies will include experiments with HIV and Tat in primary astrocytes in culture and will evaluate three existing small animal models of HIV neuropathogenesis including transplant of HIV-1-infected syngeneic astrocytes into the mouse brain, transplant of Tat-expressing syngeneic astrocytes into the mouse brain, and direct infection of mice by chimeric HIV-1. Each system will employ wildtype, C3 knockout, and IL-6 knockout mice. Research disciplines involved in this project include retrovirology, molecular biology, neurobiology, neuropathology, and animal studies. The project addresses the growing public health problem of HIV-associated neurocognitive disorders. If successful, the small animal models characterized in this work may be employed for translational research on treatments designated to counter the potential neurodegenerative actions of complement and IL-6 in the brain. PUBLIC HEALTH RELEVANCE: HIV-1 infection continues as a world-wide pandemic. It is disturbing to learn that the incidence of new infections has been under-estimated in the United States and the rate is actually increasing over recent years in New York. Thus this scourge remains a serious Public Health challenge. This application addresses one disorder that persists among HIV-1-infected people, neurocognitive disorders. Nervous system dysfunction can arise from outright cell death, but recent studies also indicate the importance of neuronal functional impairment in the HIV-1- infected brain. This application focuses upon a mechanism of synapse elimination that normally takes place in the developing brain, but may be subverted during HIV-1 infection. This route entails expression of complement component C3, a serum protein found elevated in the brain during HIV-1 infection, as shown here. Proposed are studies on the mechanism of overexpression in primary astrocytes, the most numerous cell in the brain. Turning to understand the impact of this process in the brain, three mouse models of HIV-1 neuropathogenesis will be investigated for the salience of C3 expression and synaptic elimination, a clear path to neurodegeneration. If successful, this developmental application will provide significant leads to counter a new, physiologically relevant pathway of functional impairment of neurons that occurs during HIV-1 infection.