Virus persistence in an animal model of multiple sclerosis requires virion attachment to sialic acid coreceptors

Chronic encephalomyelitis virus exhibits cellular tropism and evades pDCs by binding to sialylated integrins as the cell surface receptors

Theiler's murine encephalomyelitis virus (TMEV) causes a chronic demyelinating disease similar to multiple sclerosis in mice. Although sialic acids have been shown to be essential for TMEV attachment to the host, the surface receptor has not been identified. While type I interferons play a pivotal role in the elimination of the chronic infectious Daniel (DA) strain, the role of plasmacytoid dendritic cells (pDCs) is controversial. We herein found that TMEV binds to conventional DCs but not to pDCs. A glycomics analysis showed that the sialylated N-glycan fractions were lower in pDCs than in conventional DCs, indicating that pDCs are not susceptible to TMEV infection due to the low levels of sialic acid. TMEV capsid proteins contain an integrin recognition motif, and dot blot assays showed that the integrin proteins bind to TMEV and that the viral binding was reduced in the desialylated αX β2 . αX β2 protein suppressed TMEV replication in vivo, and TMEV co-localized with integrin αM at the cell membrane and TLR 3 in the cytoplasm, suggesting that αM serves as the viral attachment and entry. These results show that the chronic encephalomyelitis virus utilizes sialylated integrins as cell surface receptors, leading to cellular tropism to evade pDC activation.

An overall view of the most common experimental models for multiple sclerosis

Multiple sclerosis (MS) is a complex chronic disease with an unknown etiology. It is considered an inflammatory demyelinating and neurodegenerative disorder of the central nervous system (CNS) characterized, in most cases, by an unpredictable onset of relapse and remission phases. The disease generally starts in subjects under 40; it has a higher incidence in women and is described as a multifactorial disorder due to the interaction between genetic and environmental risk factors. Unfortunately, there is currently no definitive cure for MS. Still, therapies can modify the disease's natural history, reducing the relapse rate and slowing the progression of the disease or managing symptoms. The limited access to human CNS tissue slows down. It limits the progression of research on MS. This limit has been partially overcome over the years by developing various experimental models to study this disease. Animal models of autoimmune demyelination, such as experimental autoimmune encephalomyelitis (EAE) and viral and toxin or transgenic MS models, represent the most significant part of MS research approaches. These models have now been complemented by ex vivo studies, using organotypic brain slice cultures and in vitro, through induced Pluripotent Stem cells (iPSCs). We will discuss which clinical features of the disorders might be reproduced and investigated in vivo, ex vivo, and in vitro in models commonly used in MS research to understand the processes behind the neuropathological events occurring in the CNS of MS patients. The primary purpose of this review is to give the reader a global view of the main paradigms used in MS research, spacing from the classical animal models to transgenic mice and 2D and 3D cultures.

Mutation of the Theiler's virus leader protein zinc-finger domain impairs apoptotic activity in murine macrophages

The Theiler's murine encephalomyelitis virus (TMEV) leader (L) protein zinc-finger domain was mutated to study its role in cell death in infection of the murine macrophage cell line M1-D, revealing that an intact zinc-finger domain is required for full apoptotic activity. A functional L zinc-finger domain was also required for activation of p38 MAPK that results in phosphorylation and activation of p53, and in turn, alteration of the conformation of the anti-apoptotic proteins Puma and Mcl-1, leading to the release of pro-apoptotic Bax and apoptosis through the intrinsic pathway. TMEV infection also inhibits host protein synthesis, a stress shown by others to induce apoptosis. Since inhibition of host protein synthesis follows rather than precedes activation of MKK3/6 and p38, it seems less likely that it triggers apoptosis in infected cells. Finally, we showed that the levels of reactive oxygen species following infection were consistent with apoptotic rather than necrotic cell death. Thus, these experiments support an important role for the TMEV L protein zinc-finger domain in apoptosis in an infected murine macrophage line.

Differential usage of carbohydrate co-receptors influences cellular tropism of Theiler's murine encephalomyelitis virus infection of the central nervous system

Theiler's murine encephalomyelitis viruses (TMEV) are ubiquitous pathogens of mice, producing either rapidly fatal encephalitis (high-neurovirulence strains) or persistent central nervous system infection and inflammatory demyelination (low-neurovirulence strains). Although a protein entry receptor has not yet been identified, carbohydrate co-receptors that effect docking and concentration of the virus on the cell surface are known for both TMEV neurovirulence groups. Low-neurovirulence TMEV use alpha2,3-linked N-acetylneuramic acid (sialic acid) on an N-linked glycoprotein, whereas high-neurovirulence TMEV use the proteoglycan heparan sulfate (HS) as a co-receptor. While the binding of low-neurovirulence TMEV to sialic acid can be inhibited completely, only a third of the binding of high-neurovirulence TMEV to HS is inhibitable, suggesting that high-neurovirulence strains use another co-receptor or bind directly to the putative protein entry receptor. Four amino acids on the surface (VP2 puff B) of low-neurovirulence strains make contact with sialic acid through non-covalent hydrogen bonds. Since these virus residues are conserved in all TMEV strains, the capsid conformation of this region is probably responsible for sialic acid binding. A persistence determinant that maps within the virus coat using recombinant TMEV is also conformational in nature. Low-neurovirulence virus variants that do not bind to sialic acid fail to persist in the central nervous system of mice, indicating a role for sialic acid binding in TMEV persistence. Analysis of high-neurovirulence variants that do not bind HS demonstrates that HS co-receptor usage influences neuronal tropism in brain, whereas, the HS co-receptor use is not required for the infection of spinal cord anterior horn cells associated with poliomyelitis.

Theiler's virus persistence in the central nervous system of mice is associated with continuous viral replication and a difference in outcome of infection of infiltrating macrophages versus oligodendrocytes

Theiler's murine encephalomyelitis virus (TMEV) infection of mice, in which persistent central nervous system (CNS) infection induces Th1 CD4+ T cell responses to both virus and myelin proteins, provides a relevant experimental animal model for MS. During persistence, >10(9) TMEV genome equivalents per spinal cord are detectable by real-time reverse transcription-polymerase chain reaction (RT-PCR). Because of the short half-life of TMEV (<1 day), continual viral replication is needed to sustain these very high TMEV copy numbers. An essential role for macrophages in TMEV persistence has been documented and, although limited by host anti-viral immune responses, TMEV nonetheless spreads during persistence to infect other cells, particularly oligodendrocytes, in which the infection is productive and lytic. Virus factors influencing persistence of TMEV are expression of the out-of-frame L* protein and use of sialic acid co-receptors.