Murine coronavirus neurovirulence: role of type I interferon response

描述（由申请人提供）：中枢神经系统（CNS）的病毒感染可导致破坏宿主的急性和慢性疾病。本研究旨在探讨宿主I型干扰素（IFN）反应在限制病毒在中枢神经系统复制和传播中的程度和有效性，以及病毒拮抗IFN反应的机制。小鼠冠状病毒小鼠肝炎病毒（MHV）感染小鼠，为研究病毒诱导的脑炎和慢性脱髓鞘疾病（如多发性硬化症（MS））提供了一个方便和令人信服的模型。利用一系列表现出不同倾向和毒力水平的病毒株和突变体，我们先前表明MHV神经毒力的程度取决于病毒和宿主因素的组合，包括I型IFN反应（主要是IFN-¿/¿），这是对病毒入侵的早期和关键反应。MHV感染多种中枢神经系统细胞类型，包括神经元和神经胶质细胞，这些细胞类型在多种病毒感染中枢神经系统时表达干扰素刺激基因（ISGs）。然而，与其他器官相比，这些对检测病毒入侵和抗病毒反应至关重要的isg的基础表达水平在大脑中较低。因此，中枢神经系统可能对病毒入侵的快速反应准备不足。MHV编码多种I型IFN拮抗剂也有助于病毒与宿主的相互作用，最值得注意的是ns2蛋白，它可以拮抗IFN诱导的强效抗病毒2',5'-低聚腺苷酸合成酶-核糖核酸酶L （OAS-RNaseL）途径。此外还有高度神经毒性的JHM。WU菌株拮抗IFN-诱导。基于这些发现，我们建议使用轻度神经毒性的A59菌株和JHM。WU验证了以下总体假设：中枢神经系统中的IFN-信号传导可以有效地限制MHV在体内的神经毒性传播。同时，MHV具有通过细胞型特异性IFN拮抗剂破坏I型IFN应答的能力。病毒-宿主平衡将取决于受感染的组织和细胞类型以及损害IFN-反应的病毒株特异性蛋白。提出以下目标：1)利用A59和JHM确定体内限制中枢神经系统中神经毒性MHV感染的细胞类型。WU与I型IFN受体表达不足的小鼠，特别是巨噬细胞/小胶质细胞、神经外胚层细胞或神经元；2)研究OAS-RNaseL通路在急性和慢性中枢神经系统感染中限制MHV诱导病理的有效性；3)定位基因并研究JHM.WU的I型IFN拮抗和高神经毒力的机制。了解限制病毒发病机制的免疫机制和中枢神经系统细胞类型，以及描述神经毒性MHV逃避宿主I型IFN反应的策略，可能有助于开发更好的治疗方法来治疗人类病毒诱导的脑炎。此外，了解中枢神经系统中的I型IFN信号传导可能有助于开发或改进I型IFN的治疗应用，目前用于治疗多发性硬化症和丙型肝炎。

DESCRIPTION (provided by applicant): Viral infections of the central nervous system (CNS) can cause both acute and chronic diseases that devastate the host. This proposal aims to investigate the extent and effectiveness of the host's type I interferon (IFN) response in restricting virus replication and spread in the CNS, and in addition, the mechanisms used by viruses to antagonize the IFN response. Infection of mice with the murine coronavirus, mouse hepatitis virus (MHV), offers a convenient and compelling model for studying virus-induced encephalitis and chronic demyelinating diseases such as multiple sclerosis (MS). Using a collection of viral strains and mutants that display different tropisms and virulence levels, we showed previously that the extent of MHV neurovirulence depends on a combination of viral and host factors, including the type I IFN response (primarily IFN-¿/¿), an early and crucial response to viral invasion. MHV infects several CNS cell types, including neurons and glial cells, cells types that have been reported to express interferon-stimulated genes (ISGs) during infection of the CNS with multiple viruses. However, the basal expression level of these ISGs, crucial for detection of viral invasion and antiviral response, is lower in the brain compared with other organs. Consequently, the CNS may be less prepared to quickly respond to viral invasion. Also contributing to the virus-host interactions, MHV encodes multiple type I IFN antagonists, most notably the ns2 protein that confers antagonism of the potent antiviral 2',5'-oligoadenylate synthetase-ribonuclease L (OAS-RNaseL) pathway that is induced by IFN. In addition the highly neurovirulent JHM.WU strain antagonizes IFN- ¿/¿ induction. Based on these findings, we propose to use the mildly neurovirulent A59 strain as well as JHM.WU to test the following overall hypothesis: IFN- ¿/¿ signaling in the CNS can effectively restrict neurovirulent MHV spread in vivo. At the same time MHV has the ability to compromise the type I IFN response through cell-type specific IFN antagonism. The virus-host balance will depend on the tissue and cell types infected and virus strain-specific proteins that compromise the IFN-¿/¿ response. The following aims are proposed: 1) Determine the cell types that restrict neurovirulent MHV infection in the CNS in vivo, using A59 and JHM.WU along with mice deficient in type I IFN receptor expression, specifically in macrophage/microglia, neuroectodermal cells or neurons; 2) Investigate the effectiveness of the OAS-RNaseL pathway in limiting MHV induced pathology during acute and chronic CNS infection and 3) Map the genes and investigate the mechanisms underlying type I IFN antagonism and high neurovirulence of JHM.WU. Understanding the immune mechanisms and the CNS cell types that limit viral pathogenesis and characterizing the strategies used by neurovirulent MHV to evade the host type I IFN response will likely aid in the development of better therapeutics to treat virus-induced encephalitis in humans. Moreover, understanding type I IFN signaling in the CNS may aid in developing or refining therapeutic applications for type I IFNs, which are currently used in treatment of MS and hepatitis C.