Murine coronavirus neurovirulence: role of type I interferon response

描述(申请人提供)：中枢神经系统(CNS)的病毒感染可引起摧毁宿主的急性和慢性疾病。这项建议旨在研究宿主的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方面的程度和有效性，以及病毒对抗干扰素反应的机制。小鼠感染小鼠冠状病毒，即小鼠肝炎病毒(MHV)，为研究病毒引起的脑炎和多发性硬化症(MS)等慢性脱髓鞘疾病提供了一个方便而引人注目的模型。使用一组表现出不同取向和毒力水平的病毒株和突变体，我们以前证明了MHV神经毒力的程度取决于病毒和宿主因素的组合，包括I型干扰素反应(主要是干扰素/干扰素)，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，已有报道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ISGs在大脑中的基本表达水平较低，而这些ISGs对于检测病毒入侵和抗病毒反应至关重要。因此，中枢神经系统可能不太准备对病毒入侵做出快速反应。此外，MHV还编码多种I型干扰素拮抗剂，最著名的是NS2蛋白，它拮抗干扰素诱导的强大的抗病毒2‘，5’-寡腺苷合成酶-核糖核酸酶L(OAS-RNASE)途径。此外，高神经毒力的JHM.WU株还能拮抗干扰素的诱导。基于这些发现，我们建议使用神经毒力较弱的A59毒株以及JHM.WU来检验以下总体假设：中枢神经系统中的干扰素信号可以有效地限制神经毒力MHV在体内的传播。同时，MHV具有通过细胞特异性干扰素拮抗作用来抑制I型干扰素应答的能力。病毒-宿主的平衡将取决于感染的组织和细胞类型，以及影响干扰素反应的病毒株特异性蛋白。目的如下：1)利用A59和JHM.WU以及I型干扰素受体表达缺陷的小鼠，特别是巨噬细胞/小胶质细胞、神经外胚层细胞或神经元，在体内确定限制神经毒力MHV感染的细胞类型；2)研究OAS-RNASEL通路在限制MHV诱导的急、慢性中枢神经系统感染病理中的有效性；3)定位基因并研究JHM.WU的I型干扰素拮抗作用和高神经毒力的机制。了解限制病毒致病的免疫机制和中枢神经系统细胞类型，并表征神经毒力MHV逃避宿主I型干扰素反应的策略，可能有助于开发更好的疗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型干扰素信号可能有助于开发或完善I型IFN的治疗应用，目前I型IFN用于治疗多发性硬化和丙型肝炎。

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.