Hippocampal dentate granule cells in temporal lobe epilepsy: A morphometry and transcriptomic study

The dentate gyrus (DG) plays a critical role in hippocampal circuitry, providing a "gate-like" function to the downstream cornu ammonis (CA) sectors. Despite this critical role, pathologies in DG are less commonly described than those in the CA sectors in the diagnosis of mesial temporal lobe epilepsy (mTLE). To elucidate the role of the DG in mTLE, we analysed hippocampal sclerosis (HS), no-HS, non-TLE epilepsy control, and non-epilepsy control cohorts using morphometry and gene expression profiling techniques. Morphometry techniques analysed DG cell spacing, nucleus size, and nucleus circularity. Our data show distinct DG morphometry and RNA expression profiles between HS and No-HS. Dentate granule cells are more dispersed in patients with HS, and the DG shows an elevated expression of the complement system, apoptosis, and extracellular matrix remodelling-related RNA. We also observe an overall decrease in neurogenesis-related RNA in HS DG. Interestingly, regardless of the pathological diagnosis, the DG morphometry correlates with post-operative outcomes. Increased cell spacing is observed in the DG of mTLE cases that achieve seizure freedom post-operatively. This study reveals the possible prognostic value of DG morphometry, as well as supporting the notion that HS and no-HS TLE may be distinct disease entities with differing contributing mechanisms.