Deficiency of nNOS in adult-born dentate granule cells causes epilepsy

Objective: This study aimed to elucidate the molecular role of neuronal nitric oxide synthase (nNOS, encoded by Nos1) in adult-born dentate granule cells (DGCs) during temporal lobe epilepsy (TLE).

Methods: We used GFP-expressing retrovirus (RV) to analyze morphological changes in DGCs. Nos1 knockout (Nos1^-/-) mice were generated to assess whether nNOS deficiency would induce mossy fiber sprouting (MFS), affect neurogenesis, and observe the morphological changes of DGCs. Nos1 conditional knockout (nNOS cKO, Nos1^loxp/loxp) mice were generated, and pAAV-Nestin-Cre virus was used to selectively delete Nos1 in adult-born DGCs, followed by electroencephalogram examination.

Results: We found seizures induced ectopic location, hilar basal dendrites, and dendritic hypertrophy in DGCs. While nNOS deficiency did not induce abnormal MFS or affect neurogenesis, it caused a significant increase in somatic size, branch points, dendritic length, and spine density in adult-born DGCs. A notable increase in mushroom spine density was observed in the middle and outer 1/3 of the molecular layer. Selective deletion of Nos1 in adult-born DGCs induced epileptic spikes and spontaneous recurrent seizures. Single-nucleus RNA-seq analysis confirmed that newborn neurons in the TLE hippocampus showed reduced nNOS expression and distinct gene expression profiles, likely contributing to abnormal synaptic and dendritic development, as well as increased hippocampal excitability. Single-nucleus RNA-seq analysis further confirmed that newborn neurons in the TLE hippocampus exhibited reduced nNOS expression and distinct gene expression profiles, likely contributing to abnormal synaptic and dendritic development, as well as increased hippocampal excitability.

Significance: Our findings suggest that selective Nos1 knockout in adult-born DGCs contributes to epileptogenesis, and regulating nNOS expression may offer a novel therapeutic approach for treating TLE.

Plain language summary: Epilepsy is a brain disorder where nerve cells become overly active. We found that deleting a gene called Nos1 in adult-born DGCs of mice led to seizures. These cells also showed abnormal shapes and gene activity. Our results suggest that Nos1 helps maintain normal brain circuits and could be a new target to treat epilepsy.

adult‐born dentate granule cells; neuronal nitric oxide synthase; pilocarpine; temporal lobe epilepsy.