Authors :
Presenting Author: Xi Guo, PhD – University of Alabama at Birmingham
Susan Campbell, PhD – University of Alabama at Birmingham
Allison Galluci, PhD – Virginia Polytechnic and State University
Rationale:
Epilepsy is one of the most prevalent chronic neurological disorders globally. Among its many etiologies, central nervous system (CNS) infections represent a significant and under-addressed cause. Despite this, there are currently no anti-seizure medications specifically designed to target infection-induced epilepsy. Theiler’s murine encephalomyelitis virus (TMEV) is a well-established viral model that induces seizures in mice with relatively low mortality, making it a valuable tool for investigating infection-associated epileptogenesis(1). We previously demonstrated that TMEV-infected mice exhibiting seizures have reduced levels of gut bacteria that produce the metabolite S-equol(2). Moreover, ex vivo application of S-equol to cortical brain slices from these animals increased the threshold for action potential firing and reduced the number of action potentials, suggesting that S-equol suppresses neuronal excitability. However, the specific molecular targets and mechanisms underlying this effect remain unclear. This study aimed to identify the role of S-equol’s known targets in reducing neuronal hyperexcitability.
Methods:
C57BL/6 (Jax) mice were infected with TMEV and monitored for acute behavioral seizures from 3 to 7 days post-infection (dpi). Whole-cell patch-clamp recordings were performed on cortical neurons from 7–8 days post TMEV-infected mice with a seizure phenotype. Action potential number and threshold were assessed in the presence of S-equol alone and in combination with pharmacological inhibitors of S-equol’s known targets: G protein-coupled estrogen receptor 1 (GPR30/GPER1), large-conductance calcium-activated potassium (BK) channels, and estrogen receptor beta (ESRβ). Western blotting was used to assess the protein expression levels of these targets relative to sham-infected controls (PBS injected mice).
Results:
Western blot analysis showed no significant difference in ESRβ expression between TMEV seizure mice and controls. Electrophysiological recordings indicated that blocking ESRβ did not alter the S-equol-mediated effects on action potential threshold or number. Protein expression of BK channel alpha subunit was significantly reduced in TMEV seizure mice compared to controls. Electrophysiological recordings indicated that S-equol significantly increased action potential threshold, however, pharmacological blockade of BK channels with paxillin did not influence action potential properties in the presence of S-equol. Notably, GPR30/GPER1 protein expression was also decreased in TMEV seizure mice. Importantly, co-application of the GPR30/GPER1 antagonist G15 abolished the effects of S-equol on both action potential number and threshold.
Conclusions:
These findings suggest that S-equol’s suppressive effects on neuronal hyperexcitability are not mediated through ESRβ or BK channels in this model but instead involve GPR30/GPER1 signaling. Our results highlight a previously unrecognized mechanism of S-equol’s neuroprotective action in TMEV-induced seizures and underscore the complexity of its molecular targets, warranting further investigation.Funding:
NIH/NINDS R01NS128421