Role of proinflammatory cytokines in the inhibition of hippocampal neurogenesis in mesial temporal lobe epilepsy

Background

In mesial temporal lobe epilepsy, reduced hippocampal neurogenesis correlates with severe impairment in declarative learning and memory. The proinflammatory cytokines interleukin 1β and high-mobility group box 1 (HMGB1) and their receptors have key roles in generating and perpetuating seizures. This study aimed to assess their potential role in inhibiting neurogenesis in patients with mesial temporal lobe epilepsy and whether any effect would be pharmacologically reversible as a possible mechanism to restore learning and memory deficits.

Methods

We generated three-dimensional (3D) stem-cell cultures (Hi-Spot, Capsant Neurotechnologies Ltd, UK), preserving the inflammatory microenvironment and key features of the in-vivo stem-cell niche, from sclerotic tissue obtained from patients undergoing surgery for epilepsy (n=23). Concentrations of interleukin 1β and HMGB1 and their receptors in sclerotic tissue were determined with PCR, western blot, ELISA, and immunohistochemistry and compared with normal cortical tissue. Neurogenesis in the presence or absence of interleukin 1β or HMGB1 antagonists was examined by quantifying the number of newly born neurons.

Findings

We expanded the use of air–liquid interphase technology previously used to generate Hi-Spots from the cortex of rats to generate 3D Hi-Spots from the adult human hippocampus. Using ELISA, we demonstrated that interleukin 1β concentrations were significantly elevated in sclerotic hippocampal Hi-Spots compared with control (mean 24·4 pg/mL [SD 2·3] vs 3·6 [1·4], p<0·01). Interleukin 1 receptor mRNA was four times higher than control with dense protein coexpression by nestine-positive neural stem cells. Blockade of interleukin 1 receptor increased the number of newly born neurons in sclerotic Hi-Spots (mean 14·23 cells per mm² [SD 1·13] vs 4·8 [0·7], p<0·01) and significantly decreased HMGB1 activity (5·5 ng/mL [0·25] vs 7·7 [0·29], p<0·01). Treatment with the HMGB1 antagonist BoxA increased the percentage of newly born neurons and completely reversed the antineurogenic effects of interleukin 1β, indicating possible crosstalk between interleukin 1β and HMGB1 in modulating hippocampal neurogenesis.

Interpretation

We provide a novel in-vitro molecular model that relies on the interleukin 1β–interleukin 1 receptor–HMGB1 axis. Whereas previous studies have elegantly shown that blockade of this axis renders epileptic animals free of seizures, our observations support the development of therapeutic interventions that counteract the microenvironment to promote hippocampal neurogenesis. This possibility could lead to pharmacological strategies to treat learning and memory deficits in mesial temporal lobe epilepsy.

Funding

Epilepsy Research UK.