Dentate gyrus granule cells (DGCs) are the principal excitatory neurons of the dentate gyrus, a critical hippocampal structure that serves as the gateway to the hippocampus proper. These small, densely packed neurons play essential roles in pattern separation, memory encoding, and epileptogenesis. In temporal lobe epilepsy (TLE), dentate granule cells undergo profound structural and functional remodeling that contributes to seizure generation and cognitive comorbidities. Understanding DGC pathology in TLE is crucial for developing novel therapeutic interventions.
| Taxonomy | ID | Name / Label |
|---|---|---|
| Cell Ontology (CL) | CL:0000120 | granule cell |
Dentate granule cells are among the smallest neurons in the hippocampus (8-12 μm soma diameter), characterized by a compact cell body, a single apical dendrite that extends into the molecular layer, and an axon (mossy fiber) that projects to CA3 pyramidal cells. In rodents, each dentate gyrus contains approximately 1 million granule cells, while the human dentate gyrus contains roughly 10-20 million. Granule cells are generated throughout life via adult hippocampal neurogenesis, a process that continues in the subgranular zone (SGZ) of the dentate gyrus. [1]
The molecular signature of dentate granule cells includes:
The dentate gyrus is located in the medial temporal lobe, forming the most superficial layer of the hippocampal formation. It consists of three layers:
Granule cell axons (mossy fibers) project to CA3 pyramidal cells and hilus mossy cells, forming the trisynaptic circuit of the hippocampus. [3]
In TLE, dentate granule cells undergo characteristic pathological changes:
Mossy Fiber Sprouting: A hallmark of TLE, where granule cell axons abnormally sprout collaterals that re-enter the dentate gyrus, forming recurrent excitatory circuits. This aberrant connectivity lowers the seizure threshold and contributes to epileptogenesis. Mossy fiber sprouting can be visualized using Timm staining or dynorphin immunohistochemistry. [4]
Granule Cell Hyperactivity: Granule cells in epileptic tissue exhibit increased excitability due to downregulation of potassium channels, alterations in GABAergic inhibition, and changes in glutamatergic receptor composition. This hyperexcitability is thought to initiate seizure activity.
Altered Neurogenesis: Adult neurogenesis is dramatically reduced in chronic TLE, while newly generated granule cells frequently show ectopic positioning in the hilus, disrupting normal circuitry. However, some studies suggest that seizure-induced neurogenesis may initially increase before declining. [5]
mtsRNA Dysregulation: Mitochondrial transfer RNA (mtsRNA) expression is altered in epileptic granule cells, suggesting epigenetic mechanisms contribute to the disease process.
The dentate gyrus is essential for pattern separation—the ability to form distinct representations of similar experiences. DGC dysfunction in TLE contributes to:
Several therapeutic approaches target dentate granule cell pathology in TLE:
| Treatment | Mechanism | Status |
|---|---|---|
| mTOR inhibitors (everolimus) | Reduce mossy fiber sprouting | Clinical trials |
| Antiseizure medications (levetiracetam) | Reduce granule cell excitability | Approved |
| Neurogenesis modulation | Enhance healthy neurogenesis | Preclinical |
| Deep brain stimulation | Modulate dentate circuit activity | Experimental |
Sorrells SF, Paredes MF, Velican A, et al. Human hippocampal neurogenesis drops sharply in children to undetectable levels in adults. Nature. 2018. ↩︎
Kempermann G, Song H, Gage FH. Neurogenesis in the adult hippocampus. Cold Spring Harbor Perspectives in Biology. 2015. ↩︎
Ambrosi CM, Khodadade D, Scott RC. The dentate gyrus as a filter for memory. Current Topics in Behavioral Neurosciences. 2014. ↩︎
Buckmaster PS. Does mossy fiber sprouting give rise to the epileptic state? Advances in Experimental Medicine and Biology. Advances in Experimental Medicine and Biology. 2014. ↩︎
Paradisi M, Ravegnani M, Carletti F, et al. Altered neurogenesis in a mouse model of temporal lobe epilepsy. Neurobiology of Disease. 2020. ↩︎