A subgenomic segment of Theiler's murine encephalomyelitis virus RNA causes demyelination

Area of Science:

• Neurovirology
• Demyelinating Diseases
• Molecular Virology

Background:

• Theiler's murine encephalomyelitis virus (TMEV) infection in mice causes a persistent CNS infection and inflammatory demyelination, serving as a model for multiple sclerosis (MS).
• The precise roles of the virus and the immune system in TMEV-induced white matter disease pathogenesis remain incompletely understood, mirroring the complexity of MS.
• Clarifying the direct pathogenic contribution of the virus is crucial for understanding demyelinating diseases.

Purpose of the Study:

• To elucidate the direct pathogenic role of TMEV in demyelination using a novel transgenic approach.
• To investigate the impact of viral gene expression in myelin-producing cells (oligodendrocytes and Schwann cells).
• To differentiate between immune-mediated and direct viral pathogenic mechanisms in TMEV-induced disease.

Main Methods:

• Generation of a transgenic mouse model with tamoxifen (Tm)-inducible expression of a TMEV subgenomic RNA segment in oligodendrocytes and Schwann cells using Cre/loxP technology.
• Administration of Tm to young and aged transgenic mice to control the timing and location of viral RNA expression.
• Assessment of clinical signs, histopathology (demyelination, inflammation), and cellular abnormalities in the CNS and peripheral nerves.

Main Results:

• Tm-treated young transgenic mice exhibited progressive weakness, demyelination, and abnormalities in oligodendrocytes and Schwann cells without inflammation, confirming direct viral pathogenicity.
• Later-age Tm treatment resulted in milder disease, with evidence of peripheral nerve remyelination and focal fur depigmentation.
• Surviving mice showed persistent transgene expression, suggesting the viral segment can cause cellular dysfunction rather than immediate cell death, potentially mimicking persistent TMEV infection.

Conclusions:

• DA RNA or associated proteins are directly toxic to myelin-synthesizing cells, establishing a direct viral role in demyelination.
• The developed Cre/loxP transgenic system enables controlled, spatiotemporal expression of viral transgenes, facilitating the study of non-immune mechanisms in viral demyelination.
• This model is valuable for dissecting the mechanisms of demyelination induced by TMEV and potentially other viruses.