Abstracts

Rationale: Temporal lobe epilepsy (TLE) is the most common form of epilepsy, characterized by focal hippocampal seizures, hippocampal sclerosis and gliosis, and cognitive deficits. Nearly half of TLE patients develop pharmacoresistance, diminishing their quality of life. Thus, uncovering the cellular and molecular mechanisms of TLE will provide valuable insights into the disorder and aid in the development of novel treatments. In this vein, we aim to uncover the role of STEP in the pathophysiology of TLE. STEP is a negative regulator excitatory synaptic transmission. STEP achieves this by dephosphorylating two major glutamate receptors, the NMDA and AMPA receptors, leading to their internalization. Recently, we reported that the pharmacological inhibition of STEP reduced kainic acid (KA)-induced seizures, hippocampal network excitability, and hippocampal neuron intrinsic excitability. These results implicate STEP in the regulation of neuronal excitability and seizures, prompting us to investigate its function in a model of TLE.

Methods: To elucidate the role of STEP in TLE, we administered repeated low-dose KA injections (5mg/kg, i.p.) to induce status epilepticus (SE) in C57Bl/6J (WT) and STEP knock-out (KO) mice. Following the onset of SE, behavioral seizures were scored for 2h using a modified Racine scale. After 2h, seizures were blocked with Diazepam (10mg/kg, i.p.) and mice were returned to the mouse colony for 7 days. Each mouse was sacrificed 7 days post-SE via transcardial fixation (4% PFA/PBS), and their brains were collected for immunohistochemical (IHC) experiments.

Results: Compared to WT mice, STEP KO mice displayed a more rapid onset to SE. STEP KO mice required fewer 5mg/kg KA injections and less time to reach SE. Interestingly, STEP KO mice more rapidly recovered from SE, displaying decreased seizure severity by 1h post-SE. Additionally, STEP KO mice had a lower cumulative seizure score and seizure-related mortality. Overall, these data demonstrate that the genetic ablation of STEP decreases seizure severity and prevents seizure-related death. We are currently performing IHC on STEP WT and KO tissues collected 7 days post-SE to assess neuronal death and gliosis within their hippocampi. Based on our seizure data, we anticipate a reduction of TLE-associated hippocampal sclerosis and gliosis in STEP KO mice.

Conclusions: The genetic ablation of STEP significantly reduces seizure severity and mortality following SE. We are currently performing IHC experiments to assess STEP’s role in regulating hippocampal sclerosis and gliosis. Overall, these data provide further evidence of STEP’s role in the regulation of seizure severity and underscore its potential as a promising therapeutic target.

Funding: This research was supported by the National Institutes of Health under awards NIH R01 NS083402, R01 NS097610, and R01 NS100019 (to H.J.C.); It was also supported by the University of Illinois Campus Research Board RB21053 (to H.J.C.); It was also supported by the University of Illinois Neuroscience Program Fellowship (H.A.N.).