Authors :
Presenting Author: Mitchell Moyer, BS – University of Maryland
Muznabanu Bachani, BS – Neurosurgery – University of Maryland; Vladimir Gerzanich, MD, PhD – Neurosurgery – University of Maryland; Svetlana Ivanova, BS – Neurosurgery – University of Maryland; Jemima Owotade, BS – Neurosurgery – University of Maryland; Alexander Ksendzovsky, MD, PhD – Neurosurgery – University of Maryland; J. Marc Simard, MD, PhD – Neurosurgery – University of Maryland
Rationale:
Current anti-seizure medications are insufficient for managing seizures in epilepsy patients, as they are associated with significant side effects and over one third of patients are resistant to current anti-convulsants. One promising disease-specific target for reducing seizures is SUR1-TRPM4, a sodium conducting ion channel not significantly expressed in healthy brain that upregulates
de novo in neurons after status epilepticus and in seizure-related pathologies such as stroke. SUR1-TRPM4 upregulation has been successfully targeted to reduce stroke pathology through preclinical studies and clinical trials. Here we investigated whether SUR1-TRPM4 upregulation in neurons contributes to chronic seizure susceptibility in epilepsy.
Methods:
SUR1-TRPM4 expression was examined by immunohistochemistry (IHC) in resected brain tissues from epilepsy patients electrographically sorted within each patient as either normal or epileptic using intracranial electrode recordings, as well as in brains from mice undergoing pentylenetetrazol (PTZ) kindling (35mg/kg IP every 2 days for 10 doses) compared to sham controls. SUR1-TRPM4 signals were co-localized to cell type markers for neurons (NeuN) or astrocytes (GFAP). To assess whether SUR1-TRPM4 contributes to chronic seizures, the effects of TRPM4 inhibition were studied
in vivo and
in vitro . An adapted PTZ kindling model was used to assess differences in chronic seizure threshold between global TRPM4 knock-out (KO) and littermate wildtype controls (WT). PTZ doses were started at 15mg/kg and escalated by 5mg/kg every three doses until seizures were seen in either group, after which that dose (25mg/kg) was used for the remainder of the experiment. To assess the underlying mechanism that SUR1-TRPM4 expression promotes seizures through neuron population hyperexcitability, rat cortical cultures were recorded with microelectrode array (MEA) and treated with either low Mg
2+ or control aCSF daily for two hours for seven days to induce seizure-like hyperactivity and co-treated with either TRPM4 inhibitor CBA (10μM) or vehicle.
Results:
Compared to controls, cellular counts co-expressing SUR1-TRPM4 were increased in neurons within epileptic tissues resected from patients (p< 0.05, paired t-test) and in PTZ kindled brains (p< 0.05, unpaired t-test). Furthermore, TRPM4 KO significantly attenuates (p< 0.05, logistical regression analysis) the development of seizures induced by PTZ kindling and pharmacological inhibition of SUR1-TRPM4
in vitro reduces (p< 0.01, 2-way ANOVA) neuronal population hyperactivity induced by low Mg
2+.
Conclusions:
These findings suggest that SUR1-TRPM4 is overexpressed in neurons within seizure-specific tissue from epilepsy patients. Furthermore, this channel is upregulated in mouse PTZ kindling and TRPM4 KO in this model reduces seizure susceptibility.
In vitro data suggest SUR1-TRPM4 contributes to seizure development through neuronal population hyperexcitability. Overall, this work suggests SUR1-TRPM4 is a clinically relevant biomarker and potential therapeutic target to manage seizures in epilepsy patients.
Funding: N/A