SUR1-TRPM4 is expressed in human epilepsy and promotes neuron hyperactivity and seizures in rodents

One third of epilepsy patients do not achieve sufficient seizure freedom with current standard anti-seizure medications. Better understanding of the pathological mechanisms contributing to epileptogenesis is thus necessary to improve current therapies. SUR1-TRPM4 is a depolarizing ion channel minimally expressed in healthy brain that is upregulated de novo in neurons and glia after epileptogenic CNS injuries such as traumatic brain injury and stroke. However, its role in epilepsy is not well understood. Here, we demonstrate using immunofluorescent microscopy that SUR1-TRPM4 expression is elevated in neurons within electrographically sorted human epileptic brain compared to non-epileptic brain obtained after resection from six drug-resistant temporal lobe epilepsy patients. Additionally, we utilized immunofluorescence and co-immunoprecipitation to observe that SUR1-TRPM4 is upregulated within the hippocampus and temporal cortex in mice after PTZ kindling, a chronic model of rodent epilepsy. Pharmacologic inhibition of SUR1-TRPM4 using either the FDA-approved drug glyburide or 9-phenanthrol, as well as either constitutive or neuron-specific knock-out of this channel, attenuated chronic seizure development in this model. Exogenous overexpression of SUR1-TRPM4 by plasmid transfection in neurons in vitro increased neuronal hyperexcitability in response to low Mg2+ stimulation, while pharmacologic inhibition of endogenous TRPM4 attenuated neuronal population hyperexcitation. Collectively, our results reveal that elevated SUR1-TRPM4 expression found in human and rodent epileptic neurons promotes chronic seizures by increasing neuronal excitation. These findings directly support clinical investigation of SUR1-TRPM4 inhibitors as potential anti-seizure therapies in epilepsy patients and suggest further investigations into the contribution of SUR1-TRPM4 to seizures induced by specific epileptogenic insults, such as TBI, are warranted.