Atypical Neurogenesis, Astrogliosis, and Excessive Hilar Interneuron Loss Are Associated with the Development of Post-Traumatic Epilepsy

Abstract

Background: Traumatic brain injury (TBI) remains a significant risk factor for post-traumatic epilepsy (PTE). The pathophysiological mechanisms underlying the injury-induced epileptogenesis are under investigation. The dentate gyrus—a structure that is highly susceptible to injury—has been implicated in the evolution of seizure development. Methods: Utilizing the murine unilateral focal control cortical impact (CCI) injury, we evaluated seizure onset using 24/7 EEG video analysis at 2–4 months post-injury. Cellular changes in the dentate gyrus and hilus of the hippocampus were quantified by unbiased stereology and Imaris image analysis to evaluate Prox1-positive cell migration, astrocyte branching, and morphology, as well as neuronal loss at four months post-injury. Isolation of region-specific astrocytes and RNA-Seq were performed to determine differential gene expression in animals that developed post-traumatic epilepsy (PTE+) vs. those animals that did not (PTE−), which may be associated with epileptogenesis. Results: CCI injury resulted in 37% PTE incidence, which increased with injury severity and hippocampal damage. Histological assessments uncovered a significant loss of hilar interneurons that coincided with aberrant migration of Prox1-positive granule cells and reduced astroglial branching in PTE+ compared to PTE- mice. We uniquely identified Cst3 as a PTE+-specific gene signature in astrocytes across all brain regions, which showed increased astroglial expression in the PTE+ hilus. Conclusions: These findings suggest that epileptogenesis may emerge following TBI due to distinct aberrant cellular remodeling events and key molecular changes in the dentate gyrus of the hippocampus.

Transcriptomic alterations in cortical astrocytes following the development of post-traumatic epilepsy

“…Finally, we previously identified Cystatin 3 ( Cst3 ) , a highly expressed gene in astrocytes 16 , to be altered in the ipsilateral and contralateral hippocampus of PTE+ astrocytes via bulk RNA-seq of hippocampal astrocytes from PTE+ mice and further confirmed by immunohistochemistry 13 . We demonstrate that this is the only gene influenced across all brain regions in isolated astrocytes from PTE+ mice.…”

“…We assessed transcriptomic changes by performing RNA-Seq on astrocytes isolated from the ipsilateral and contralateral cortex of sham (n = 5) and severe CCI-injured (n = 15) mice at 4 months post-injury. Mice were stratified based on seizure development (PTE+ vs. PTE−), as previously reported 13 . In total, among the severe CCI-injured mice, five mice were PTE+ (33%) and ten mice were PTE− (67%).…”

“…Evidence suggests an important functional and structural basis of contralateral interictal activity in focal, unilateral epilepsy 14 . We next addressed associated changes in the contralateral cortical astrocytic transcriptome in our focal CCI model 13 . CCI injury showed changes in 421 genes compared to sham, and when comparing PTE+ versus PTE− injured-mice we observed 457 genes that were altered in astrocytes from animals that developed generalized seizures (Fig.…”

“…BioPac's AcqKnowledge software, version 4.0, was employed for continuous EEG data recording over the course of two months. The identification and incidence of seizure development was reported previously 13 .…”

Transcriptomic alterations in cortical astrocytes following the development of post-traumatic epilepsy

“…We assessed transcriptomic changes by performing RNA-seq on astrocytes isolated from the ipsilateral and contralateral cortex of sham and severe CCI-injured mice at four months post-injury. Mice were strati ed based on seizure development (PTE + vs PTE-), as previously described (11). Transcriptomic analysis was performed in conjunction with gene ontology pathway enrichment to detect differentially expressed genes (DEGs) and biological processes (BP) respectively.…”