Impact d’un épisode asphyxique périnatal associé à des convulsions sur le développement des interneurones corticaux : rôle de l’adenosine monophosphate-activated protein kinase (AMPK)

Hypoxia-­‐ischemia encephalopathy causes thousands of victims each year around the world. Children surviving such hypoxia-­‐ischemia insults are at risk of developing disabling neurological problems such as cerebral palsy, epilepsy or cognitive problems. Animal models have improved our knowledge about the underlying mechanisms causing cerebral injury, but it is still too incomplete to be able to prevent neurological problems. This project aims to understand the impact of a perinatal asphyxic insult associated with seizures as well as the activation of adenosine monophosphate-­‐activated protein kinase (AMPK) on developing inhibitory GABAergic networks in mouse. With the objective to study the fate of inhibitory cells, called interneurons, following a perinatal asphyxia insult associated with seizures in transgenic animals, we took advantage of a new hypoxia model allowing us to induce seizures in mice. Cells expressing parvalbumin (PV) and cells expressing somatostatin (SOM) were studied as together they represent about 60% of all cortical interneurons. A stereological study showed no cell death within those two interneuron populations in the hippocampus of adult hypoxic mice. However, the cortex of hypoxic mice showed zones with complete or strongly lacking PV cells, whereas SOM cells were not affected. A transgenic mouse line allowed us to show that PV holes are the reflection of two things 1) a decrease in PV cells and 2) immaturity of surviving PV cells. Because PV cells a selectively affected in the first part of our study, we wanted to study the molecular mechanisms underlying this vulnerability. AMPK is a metabolic energy sensor that orchestrates the recovery of energy in cells undergoing energy depletion by modulating cellular pathways involved in protein synthesis and membrane excitability. It is possible that the activation of AMPK following a perinatal asphyxic insult associated with seizures is detrimental for developing GABAergic networks and modifies the establishment of perisomatic innervation of PV cells on excitatory pyramidal cells. We have studied this hypothesis in an organotypic system by overexpressing the wild-­‐type (WT) form and the dominant negative (DN) form of AMPK iv α 2 sub-­‐unit in individual PV cells. We have observed that during the synaptic formation phase (equivalent post-­‐natal day EP 10-­‐18), overexpressing WT AMPK disorganises synapse stabilisation. Moreover, abolishing AMPK activity with the transfection of AMPK DN seems to increase the number of perisomatic synapses made by PV cells onto pyramidal cells, and seems to have the inverse effect during the synaptic maturation phase (EP 18-­‐24). GABAergic neurotransmission plays many roles in the brain, from interneurons birth to adulthood, and a dysfunction in GABAergic neurotransmission has been associated with many neurological diseases such as schizophrenia, autism and epilepsy. GABAergic networks maturation mainly happens postnatally and is highly dependent on neural activity and sensory experience. Our results reveal that the heavy energetic burden caused by an asphyxic insult can cause selective PV cells death and interfere with their maturation. AMPK activation following an asphyxic insult could be one mechanism interfering with PV cells maturity by disorganising their pattern of innervation onto pyramidal cells. We think that these GABAergic networks alterations could contribute to the neurological problems associated to a hypoxic insult.

Keyphrases: AMPK, Perinatal asphyxia, Development, Organotypic culture