Abstracts

Rationale: Temporal lobe epilepsy (TLE) is the most prevalent form of acquired epilepsy, and it is difficult to treat with current anti-seizure drugs. Thus, the development of new disease-modifying therapies is critical to treat and prevent seizures in high-risk groups. Although the precise mechanisms that lead to epilepsy remain unclear, evidence from experimental and clinical work suggests that brain inflammation is a significant contributor. Several viruses have been implicated in the development of TLE. Brain inflammation, induced by viral infection of the central nervous system (CNS), alters the excitatory and inhibitory balance among neurons and is a significant cause of acute seizures.

In our model, C57BL/6J mice infected intra-cranially (ic) with Theiler’s murine encephalomyelitis virus (TMEV) develop acute behavioral seizures between 3-10 days post-infection (dpi), which is coincident with CNS infiltration of peripheral macrophages. This acute seizure period is followed by a latent period, during which seizures are not observed. A significant portion of mice then goes on to exhibit spontaneous, recurrent limbic seizures and develop TLE. We previously demonstrated that macrophages are required for acute seizures to occur and that interleukin (IL)-6-producing macrophages play a key role in acute seizure development. We recently isolated infiltrating macrophages and resident microglia from the CNS of TMEV-infected mice and performed RNA-sequencing to determine the expression profiles of genes related to CNS infection/inflammation. We found, among other genes, that C-type Lectin Domain Family 4 Member E (Clec4e) is highly and specifically expressed by brain-infiltrating macrophages during neuroinflammation and acute seizures. CLEC4E was previously shown to be expressed by macrophages, and activation of this receptor is associated with inflammation and secretion of inflammatory cytokines, such as IL-6.

Methods: To determine the time course expression of Clec4e following TMEV-infection, C57BL/6J mice were ic infected with 4x10⁵ plaque-forming units of TMEV. Mice were euthanized at 2, 3, and 7 dpi (n=4/time point). PBS-injected mice were used as control (n=3). Hippocampus was obtained from each mouse, and RNA was isolated using RNeasy. RT-qPCR was used to measure mRNA levels of Clec4e expression.

Results: We found that the levels of Clec4e are highly increased at 2 and 3 dpi, when seizures are starting, compared to PBS-injected mice (p< 0.001). At the peak of seizure activity (day 7), we found a significant increase in Clelc4e expression level compared to days 2 and 3 (p< 0.001).