Theiler's virus-induced aoptosis: A mechanism for CNS virus persistence

描述（由申请方提供）：Theiler鼠脑脊髓炎病毒（TMEV）是一种高度细胞溶解性RNA病毒，可在易感小鼠品系中产生持续性中枢神经系统（CNS）感染和免疫介导的脱髓鞘。TMEV感染为多发性硬化提供了相关的实验动物模型。与其中宿主细胞存活的非溶细胞RNA病毒的持久性相反，其中感染细胞死亡的裂解RNA病毒的持久性需要连续的细胞间传播以维持感染。在这种情况下，病毒在其中持续存在的靶细胞理想地应该是可再生的。感染不应该是高生产力的;然而，病毒特异性宿主免疫应答可以控制更有生产力的感染。巨噬细胞是主要的病毒库，并提供了TMEV在小鼠CNS中持续存在的体外模型。TMEV感染的巨噬细胞经历细胞凋亡并限制病毒产生（<10 pfu/细胞），这与其他啮齿动物细胞（包括神经元和少突胶质细胞）中的感染相反，其中坏死细胞死亡与高病毒产量（200-500 pfu/细胞）相关。TMEV感染是诱导鼠巨噬细胞凋亡所必需的，因为吸附到细胞表面以引发感染的UV灭活病毒不会诱导凋亡。我们已经表明TMEV感染通过Bax介导的内在途径诱导细胞凋亡，并严重限制了小鼠巨噬细胞中感染性病毒的产生。我们的工作假设是TMEV诱导的细胞凋亡是一种宿主细胞特异性机制，提供了一种将病毒传播到未感染巨噬细胞的手段，这些巨噬细胞吞噬含有感染性病毒的凋亡残余物。为了了解TMEV感染如何触发小鼠巨噬细胞凋亡并限制感染性病毒的产生，提出了四个具体目标：1）完成上游信号的鉴定（顶侧）在M1-D巨噬细胞中TMEV病毒感染期间参与内在凋亡途径，并确定来自小鼠抗性和敏感品系的原代巨噬细胞中凋亡的潜在差异; 2）抑制感染小鼠的细胞凋亡以评估对TMEV CNS持久性、病毒特异性CD 4 + T细胞应答和脱髓鞘疾病的影响，并检查p53和Noxa缺陷的转基因小鼠对CNS持久性和脱髓鞘疾病的影响; 3）通过在哺乳动物细胞中表达TMEV非结构蛋白L和3CD来鉴定细胞凋亡的潜在病毒“触发物”，并确定衣壳蛋白缺失的TMEV复制子是否能诱导细胞凋亡;和4）研究与细胞凋亡发生相关的鼠巨噬细胞中感染性病毒损失的机制。 公共卫生相关性：多发性硬化症（MS）是一种自身免疫性疾病的概念被广泛接受为事实。虽然MS无疑是免疫介导的，但自身免疫机制尚未得到证实。间接证据表明MS中存在持续的病毒感染。此外，免疫介导的损伤可由病毒感染引起，其中宿主免疫应答针对病毒蛋白而不是自身蛋白（自身免疫）。Theiler的小鼠脑脊髓炎病毒（TMEV）在易感小鼠品系中产生持续性中枢神经系统感染和免疫介导的脱髓鞘，为MS提供相关的实验动物模型。TMEV持续性需要驱动脱髓鞘疾病过程，但这种快速杀死感染细胞的病毒如何能够使感染永久化尚不清楚。该提案解决了TMEV持续存在的机制，程序性细胞死亡也称为细胞凋亡，其减少病毒产生（可能是强毒病毒持续存在所需的）并且还促进细胞间病毒传播（在宿主免疫存在下持续存在所需的）。

DESCRIPTION (provided by applicant): Theiler's murine encephalomyelitis virus (TMEV) is a highly cytolytic RNA virus that produces persistent central nervous system (CNS) infection and immune-mediated demyelination in susceptible strains of mice. TMEV infection provides a relevant experimental animal model for multiple sclerosis. In contrast to persistence of non-cytolytic RNA viruses in which the host cell survives, persistence of lytic RNA viruses in which an infected cell dies requires continuous cell- to-cell spread in order to maintain the infection. In this circumstance, the target cell in which the virus persists ideally should be renewable. The infection should not be highly productive; however, virus-specific host immune responses may control a more productive infection anyway. Macrophages are the principal virus reservoir and provide an in vitro model for TMEV persistence in the mouse CNS. TMEV infected macrophages undergo apoptosis and restrict virus production (<10 pfu/cell), in contrast to infection in other rodent cells, including neurons and oligodendrocytes, where necrotic cell death is associated with high virus yields (200-500 pfu/cell). TMEV infection is required to induce apoptosis in murine macrophages since UV- inactivated virus adsorbed to the cell surface to initiate infection does not induce apoptosis. We have shown that TMEV infection induces apoptosis through the intrinsic pathway that is Bax- mediated and severely restricts infectious virus production in murine macrophages. Our working hypothesis is that TMEV-induced apoptosis is a host cell-specific mechanism providing a means of spreading virus to uninfected macrophages that phagocytose apoptotic remnants containing infectious virus. To understand how TMEV infection triggers apoptosis in murine macrophages and restricts infectious virus production, four specific aims are proposed: 1) finish the identification of upstream signals (apical to the mitochondrion) involved in the intrinsic apoptotic pathway during TMEV virus infection in M1-D macrophages and determine potential differences in apoptosis in primary macrophages from resistant and susceptible strains of mice; 2) inhibit apoptosis in infected mice to assess the effect on TMEV CNS persistence, virus-specific CD4+ T cell responses and demyelinating disease, and examine the effect in transgenic mice deficient in p53 and Noxa on CNS persistence and demyelinating disease; 3) identify potential virus "triggers" of apoptosis by expressing TMEV nonstructural proteins L and 3CD in mammalian cells, and determine whether TMEV replicons in which the capsid proteins are deleted can induce apoptosis; and 4) investigate the mechanism of loss of infectious virus in murine macrophages that is associated with onset of apoptosis. PUBLIC HEALTH RELEVANCE: The notion that multiple sclerosis (MS) is an autoimmune disease is widely accepted as fact. While MS is undoubtedly immune-mediated, an autoimmune mechanism remains unproven. Circumstantial evidence points to a persistent virus infection in MS. Moreover, immune- mediated damage can result from a virus infection in which the host immune response is directed to virus proteins rather than self proteins (autoimmunity). Theiler's murine encephalomyelitis virus (TMEV) produces a persistent central nervous system infection and immune-mediated demyelination in susceptible strains of mice, providing a relevant experimental animal model for MS. TMEV persistence is needed to drive the demyelinating disease process, but just how this virus that rapidly kills infected cells is able to perpetuate the infection is not known. This proposal addresses a mechanism of TMEV persistence, programmed cell death also termed apoptosis, which decreases virus production (may be required for persistence of virulent virus) and also fosters cell-to-cell virus spread (required for persistence in the presence of host immunity).