Abstracts

Rationale: Decreased inhibitory neurotransmission in the hippocampus due to loss of a significant fraction of gamma-amino butyric acid positive (GABA-ergic) interneurons and their axon terminals is among the major reasons for manifestations of spontaneous recurrent seizures (SRS) and cognitive, memory and mood dysfunction in temporal lobe epilepsy (TLE). Indeed, previous studies using status epilepticus (SE) models of TLE have shown that grafting of fetal brain or embryonic stem cell (ESC) derived GABA-ergic interneuron progenitors into the hippocampus decreases the occurrences of SRS. Yet, the clinical application of fetal tissue/ESC derived GABA-ergic progenitors is problematic because of ethical issues. Therefore, we examined the potential of medial ganglionic eminence (MGE)-like GABA-ergic progenitors derived from a directed differentiation of human induced pluripotent stem cells (hiPSCs) for restraining SRS and related co-morbidities in a rat model of SE. Methods: We first generated MGE-like GABA-ergic progenitor cells (Nkx2.1+ cells) from hiPSCs by activating hedgehog-signaling pathway. Next, we stereotactically placed three grafts (each containing 100,000 live human MGE-like GABA-ergic progenitors) into each hippocampus of young male rats, seven days after an episode of SE induced through graded intraperitoneal injections of kainic acid. An additional cohort of rats that underwent similar SE was included as epilepsy-only controls. Animals belonging to both groups were examined with novel object recognition, object location, pattern separation and sucrose preference tests to discern cognitive, memory and mood function in the third month after SE, and three weeks of continuous electroencephalographic (EEG) recordings in the fourth month after SE. Results: Evaluation of EEG data revealed that animals receiving hiPSC derived MGE-like GABA-ergic progenitors displayed greatly reduced frequency and intensity of SRS, in comparison to epilepsy controls. The reductions were ~73% for the frequency of all SRS, ~79% for Stage-V SRS (the most severe form of SRS) and ~73% for the percentage of time spent in seizure activity. Behavioral tests revealed significant cognitive, memory and mood impairments in epilepsy-only controls but not in epileptic rats receiving GABA-ergic progenitor cell grafts. Furthermore, histological analyses and quantification of graft-derived cells revealed an excellent yield (~218 % of injected cells) and pervasive migration of graft-derived cells into all layers of the hippocampus. Detailed dual immunofluorescence studies using confocal microscopy revealed that majority of graft-derived differentiated into NeuN+ neurons (~80%) and GABA-ergic interneurons (~70%) while a smaller fractions of graft-derived cells differentiated into GFAP+ astrocytes (~5%). Conclusions: Grafting of hiPSC derived MGE-like progenitors cells shortly after SE greatly reduced the occurrence of SRS and thwarted cognitive, memory and mood impairments in the chronic phase after SE. Funding: Supported by Emerging Technology Funds from the State of Texas, and grants from the Department of Defense and the Department of Veterans Affairs to A.K.S.