Dopamine and Glutamate Crosstalk Worsen the Seizure Outcome in TLE-HS Patients.

Abstract

Temporal lobe epilepsy (TLE), accompanied by hippocampal sclerosis (HS), is the most common form of drug-resistant epilepsy (DRE). Nearly 20% of the patients showed seizure recurrence even after surgery, and the reasons are yet to be understood. Dysregulation of neurotransmitters is evident during seizures, which can induce excitotoxicity. The present study focused on understanding the molecular changes associated with Dopamine (DA) and glutamate signaling and their possible impact on the persistence of excitotoxicity and seizure recurrence in patients with drug-resistant TLE-HS who underwent surgery. According to the International League against Epilepsy (ILAE) suggested classification for seizure outcomes, the patients (n = 26) were classified as class 1 (no seizures) and class 2 (persistent seizures) using the latest post-surgery follow-up data to understand the prevalent molecular changes in seizure-free and seizure-recurrence patient groups. Our study uses thioflavin T assay, western blot analysis, immunofluorescence assays, and fluorescence resonance energy transfer (FRET) assays. We have observed a substantial increase in the DA and glutamate receptors that promote excitotoxicity. Patients who had seizure recurrence showed a significant increase in (pNR2B, p < 0.009; and pGluR1, p < 0.01), protein phosphatase1γ (PP1γ; p < 0.009), protein kinase A (PKAc; p < 0.001) and dopamine-cAMP regulated phospho protein32 (pDARPP32T34; p < 0.009) which are critical for long-term potentiation (LTP), excitotoxicity compared to seizure-free patients and controls. A significant increase in D1R downstream kinases like PKA (p < 0.001), pCAMKII (p < 0.009), and Fyn (p < 0.001) was observed in patient samples compared to controls. Anti-epileptic DA receptor D2R was found to be decreased in ILAE class 2 (p < 0.02) compared to class 1. Since upregulation of DA and glutamate signaling supports LTP and excitotoxicity, we believe it could impact seizure recurrence. Further studies about the impact of DA and glutamate signaling on the distribution of PP1γ at postsynaptic density and synaptic strength could help us understand the seizure microenvironment in patients. Dopamine, Glutamate signal crosstalk. Diagram representing the PP1γ regulation by NMDAR negative feedback inhibition signaling (green circle-left) and D1R signal (red circle-middle) domination over PP1γ though increased PKA, pDARPP32T34, and supports pGluR1, pNR2B in seizure recurrent patients. D1R-D2R hetero dimer activation (red circle-right) increases cellular Ca2+ and pCAMKIIα activation. All these events lead to calcium overload in HS patients and excitotoxicity, particularly in patients experiencing recurrent seizures.