Reprogramming reactive astrocytes into GABAergic neurons: a new therapeutical approach of epilepsy – ReprogramEpi

For the project ReprogramEpi, we decided to reprogram reactive glial cells by inserting in their genome neurogenic genes able to instruct their stable conversion into induced neurons. These factors are transmitted to glial cells with viral vectors.

This innovative project could lead to high-impact results showing for the first time that complete glia-to-neuron conversion can be achieved in vivo in the epileptic hippocampus. We expect to show that glia-derived GABAergic neurons generated during epileptogenesis functionally integrate into hippocampal neuronal networks, modulate their activity, and ultimately reduce seizures in the MTLE mouse. This reprogramming strategy should have synergistic effects against seizures by combining the elimination of pro-epileptic astrocytes and the regeneration of lost inhibitory neurons.

This strategy may open new avenues for possible future therapeutic approaches for MTLE patients and probably patients with other types of intractable epilepsies. More globally, the conversion of glial cells into neurons could have important implications for various CNS pathologies associated with neuronal degeneration and reactive gliosis.

Several oral and poster communications were presented in various international meetings located in France but also in Greece, Sweden and Germany, since the beginning of our project ReprogramEpi.

Background: Direct cellular reprogramming of non-neuronal cells into neurons emerges as an innovative strategy to regenerate lost neurons for brain repair. We and others showed that non-neurogenic glial cells from the murine cerebral cortex can be reprogrammed into functional neurons, both in vitro and in vivo, by forced expression of neurogenic transcription factors. The next challenge in this field is to achieve in vivo reprogramming of somatic cells residing within an injured brain, in pathophysiological conditions, into fully functional neurons, that acquire a specific phenotype, functionally integrate into the existing neuronal networks and modulate their activity with beneficial effects.
Epilepsy is a major clinical problem and about 30% of epileptic patients suffer from seizures that cannot be controlled with currently available medications. In particular, Mesial-Temporal Lobe Epilepsy (MTLE), the most common form of intractable epilepsies, is characterized by recurrent focal seizures mainly occurring in the hippocampus. There is a crucial need to identify new therapies aiming at preventing epilepsy development and/or recurrent seizures during the chronic phase of the disease. MTLE is associated with a massive proliferation of astroglia in the hippocampus in close contact with the excitatory dentate granule cells primarily involved in the epileptic neuronal networks. There is an increasing body of evidence suggesting that astrocytes exert pro-epileptic effects. MTLE is also associated with a loss of GABAergic neurons in the epileptic hippocampus, which has been suggested to participate in the increased neuronal excitability responsible for seizures. Therefore, a procedure to limit the proliferation of astroglia and reintroduce new GABAergic neurons within hippocampal epileptic networks (via glia-to-neuron conversion) represents an innovative strategy to restore lost inhibitory transmission and ultimately reduce seizures.

Objectives: The present proposal aims at reprogramming hippocampal reactive glia into neurons in the context of epilepsy. Using a MTLE mouse model and human tissues resected from MTLE patients, the specific objectives of the project are:
• To reprogram in vivo the reactive glia from the mouse epileptic hippocampus into functional GABAergic interneurons
• To assess whether glia-derived GABAergic neurons can integrate into hippocampal neuronal networks, modulate their activity, and ultimately reduce epileptogenesis and/or recurrent seizures
• To reprogram in vitro glial cells isolated from hippocampal tissues surgically resected from human MTLE patients into GABAergic neurons.

Expected results and impact: This innovative project could lead to high-impact results showing for the first time that complete glia-to-neuron conversion can be achieved in vivo in the epileptic hippocampus. We expect to show that glia-derived GABAergic neurons generated during epileptogenesis functionally integrate into hippocampal neuronal networks, modulate their activity, and ultimately reduce seizures in the MTLE mouse. This reprogramming strategy should have synergistic effects against seizures by combining the elimination of pro-epileptic astrocytes and the regeneration of lost inhibitory neurons. Finally, this strategy may open new avenues for possible future therapeutic approaches for MTLE patients and probably patients with other types of intractable epilepsies. More globally, the conversion of glial cells into neurons could have important implications for various CNS pathologies associated with neuronal degeneration and reactive gliosis.