Suppression of kindling epileptogenesis by adenosine releasing stem cell-derived brain implants

Abstract

Epilepsy therapy is largely symptomatic and no effective therapy is available to prevent epileptogenesis. We therefore analysed the potential of stem cell-derived brain implants and of paracrine adenosine release to suppress the progressive development of seizures in the rat kindling-model. Embryonic stem (ES) cells, engineered to release the inhibitory neuromodulator adenosine by biallelic genetic disruption of the adenosine kinase gene (Adk-/-), and respective wild-type (wt) cells, were differentiated into neural precursor cells (NPs) and injected into the hippocampus of rats prior to kindling. Therapeutic effects of NP-derived brain implants were compared with those of wt baby hamster kidney cells (BHK) and adenosine releasing BHK cell implants (BHK-AK2), which were previously shown to suppress seizures by paracrine adenosine release. Wild-type NP-graft recipients were characterized by an initial delay of seizure development, while recipients of adenosine releasing NPs displayed sustained protection from developing generalized seizures. In contrast, recipients of wt BHK cells failed to display any effects on kindling development, while recipients of BHK-AK2 cells were only moderately protected from seizure development. The therapeutic effect of Adk(-/-)-NPs was due to graft-mediated adenosine release, since seizures could transiently be provoked after blocking adenosine A1 receptors. Histological analysis of NP-implants at day 26 revealed cell clusters within the infrahippocampal cleft as well as intrahippocampal location of graft-derived cells expressing mature neuronal markers. In contrast, BHK and BHK-AK2 cell implants only formed cell clusters within the infrahippocampal cleft. We conclude that ES cell-derived adenosine releasing brain implants are superior to paracrine adenosine release from BHK-AK2 cell implants in suppressing seizure progression in the rat kindling-model. These findings may indicate a potential antiepileptogenic function of stem cell-mediated adenosine delivery.

The adenosine kinase hypothesis of epileptogenesis

“…However, despite the presence of the epileptogenesis triggering acute injury DPCPX-treated fb-Adk-def mice were resistant to subsequent epileptogenesis. Neither astrogliosis, nor upregulation of ADK, nor spontaneous seizures were found three weeks after CA3 injury (Li et al, 2007b). These studies demonstrate that epileptogenesis was prevented by reduced levels of ADK.…”

“…These cells were highly effective in reducing stroke-induced brain injury in a mouse model of middle cerebral artery occlusion (Pignataro et al, 2007c). In a more recent approach Adk −/− ES cell derived neural precursor cells were transplanted into the infrahippocampal cleft of rats one week prior to the onset of hippocampal kindling (Li et al, 2007b). In contrast to wild-type graft recipients and shamtreated control animals, Adk −/− graft recipients were characterized by a profound reduction of kindling induced epileptogenesis (Li et al, 2007b).…”

Genome Editing in Neuroepithelial Stem Cells to Generate Human Neurons with High Adenosine-Releasing Capacity

“…Initial experiments applied non‐neural cells, which resulted in strong but temporally limited antiepileptic activity 18, 19, 20. Using mouse ADK‐deficient embryonic stem cell‐derived neural cell populations, we demonstrated (a) strongly enhanced levels of secreted adenosine compared to cells derived from wild‐type controls 33, (b) short‐term protection of murine brains against experimental epileptogenesis upon grafting encapsulated ADK‐deficient cells into the ventricles of rats subjected to kindling 34, and (c) efficient suppression of kindling‐induced epileptogenesis and seizure severity upon direct transplantation of ADK −/− cells into the hippocampus of rats 21. However, translation of these findings to human cells was, for a long time, complicated by the fact that homologous recombination in human cells proved to be highly inefficient 35.…”

“…We previously showed that adenosine‐releasing murine embryonic stem cell‐derived neural cells are superior to adenosine‐releasing non‐neuronal baby hamster kidney cells in a rat model of epileptogenesis 21. This beneficial effect could be due to several reasons, including better provision of adenosine to the CNS tissue via axonal and dendritic extensions or an activity‐dependent release from neuronal cells.…”

“…In line with this idea, we have explored neural progenitors derived from ADK −/− murine embryonic stem cells. Following transplantation into a murine kindling model of epileptogenesis, transplanted cells significantly delayed epileptogenesis and were superior to non‐neuronal BHK‐AK2 hamster kidney cells 21.…”