Dissecting the role of gut microbial-derived metabolites on epilepsy

Project Summary Epilepsy is a common neurological disorder, with a worldwide prevalence of over 65 million. There is general agreement that epilepsy is caused by hyperexcitable neuronal networks and most therapeutic strategies have focused on decreasing excitation by targeting neuronal synaptic proteins. Even with the available antiepileptic drugs, there is still no cure and 30% of patients are resistant to treatment. Historically, epilepsy has been viewed as driven solely by defects in brain processes; however, this brain-centric perspective neglects the fact that the function of the nervous system is affected by the metabolic state of the body. Current research recognizes that microorganisms influence the brain by modifying metabolic factors in the gut, the “gut-brain axis.” Most of the evidence thus far is correlative showing that changes in the gut microbiota can affect seizure outcomes. However, there is a gap in knowledge regarding specific mechanisms by which gut microbes contribute to seizure development that may offer novel approaches to treat epilepsy. Viral infection-induced epilepsy is the most common cause of epilepsy worldwide and is often difficult to model in rodents due to high mortality rates. However, the Theiler's murine encephalomyelitis virus (TMEV) is a low-mortality viral-induced model of temporal lobe epilepsy. Intracranial TMEV injection leads to hippocampal neuronal dysfunction, widespread cortical astrogliosis, and seizure-genesis peaking at 6 days post infection in ~50% of adult C57BL/6 mice. While central nervous system inflammation has been posited as a potential modulator of seizure phenotype development in TMEV infection, the molecular mechanism is unclear. Data obtained from this model surprisingly indicated that the majority of taxonomies underrepresented in TMEV-infected mice with seizure phenotypes contained genera associated with the production of the bacterial metabolite S-equol. These bacteria convert dietary daidzein into S-equol, which has been shown to activate large conductance Ca2+- and voltage-activated K+ (BK) channels. Activation of BK channels play an important role in controlling neuronal excitability and therefore represents a novel target for the treatment of epilepsy. This proposal will determine if depletion of the microbial-derived metabolite, S-equol, increase seizure occurrence in TMEV-injected mice. It further tests the hypothesis that S- equol-producing microbial species confer neuroprotection against seizure susceptibility and neuronal hyperexcitability following TMEV injection via activation of BK channels. This hypothesis will be tested using a combination of EEG and electrophysiology recordings, mass spectrometry and 16S RNA sequencing. To determine whether these findings are broadly applicable to other types of epilepsy we will examine three models of epilepsy, TMEV, kainic acid and a genetic epilepsy model. This work takes a critical step causally linking specific microbial shifts to neuronal excitability, seizures and epilepsy and will identify microbial metabolites that can be targeted for therapeutic intervention.