Research focus

Our scientific objective has been to disclose and understand the basic mechanism for maturation of GABAergic and Glutamatergic transmission and their interplay with neurotrophic factors. In 2007 we found a novel role for the vital protein in the maturation of GABAergic transmission the chloride cotransporter KCC2. We found a crucial role of this protein for the maturation of glutamatergic transmission through a non-chloride dependent mechanism. In 2012 we found that trauma induced GABAA depolarisation is important for instalment of the requirement for neurotrophic support of surviving neurons. During the last period we have tried to answer the following questions: 1) what are the detailed molecular mechanism for the developmental maturation of dendritic spines and glutamatergic synapses and their interdependence on the maturation of GABAergic transmission. 2) Is post-traumatic GABAA depolarization / neurotrophin interplay an important step in the epiletogenic mechanisms following trauma. To address this questions we have focused on the following objectives: in A) development 1) find interacting partners for KCC2 with importance in glutamatergic transmission maturation and dendritic spine development. 2) Address the importance of these interactions for dendritic spine dynamics and functional glutamatergic transmission. B) Trauma 3) Investigate the role of GABAA mediated depolarisation and chloride regulatory proteins in early structural and functional rearrangement of the dentate gyrus following status epilepticus.

Table of content

  • aPilocarpine-induced model of temporal lobe epilepsy
  • bControlled-cortical impact model of traumatism brain injury
  • cSubcellular KCC2 localization
a

Pilocarpine-induced model of temporal lobe epilepsy

Experimental paradigm (click to enlarge)

Temporal lobe epilepsy is the most prevalent epilepsy in industrialized countries. The research project focuses on understanding the role of chlorine homeostasis in epileptogenesis after epilepticus status. The hypothesis is based on the fact that molecular and cellular changes occurring very early after the inaugural crisis will lead to functional changes in the hippocampal network activity leading to changes in the toothed gyrus of the hippocampus . We show that the very early and short-term blocking of aberrant sprouting by bumetanide significantly prevents the onset and severity of seizures.

By combining immunhistochemistry, in utero electroporation, ex vivo recordings and telemetric EEG, we follow and characterize epileptic events.

 

 

Kourdougli et al., 2015 & 2017

b

Controlled-cortical impact model of traumatism brain injury

Experimental paradigm (click to enlarge)

Traumatic Brain Injury is the primary cause of consultation in an emergency department. Our project focuses on the development of major depressive syndromes occurring after several months in patients. The animal model gives us access to a cross-sectional study combining cellular approaches, the study of network activity.

Our studies highlight the onset of post-traumatic depressive syndromes through behavioral testing. Our study shows drastic changes in the properties of GABAergic neurotransmission, which lead to a profound disturbance of secondary neurogenesis at the level of the hippocampus.

Our approach combines electrophysiological, immunohistochemical and behavioral studies.

c

Subcellular KCC2 localization

(click to enlarge)

The proteins with deforming power are derived from a new family of recently discovered proteins which are capable of causing the deformation of the cell membrane thus regulating the morphology of the cell as well as its displacement power. MIM proteins for “missing in metastasis” and ABBA for “actin-bundling protein with BAIA P2 homology”, according to their English acronyms, are proteins having the particularity to bind to actin, which is a major constituent in Architecture. Once linked to actin these proteins will be able to create and modulate the movements of the plasma membrane and create structures called dendritic spines which are key elements in the propagation of electrical activity between neurons of the central nervous system (CNS) . Our recent studies show that these two proteins are not expressed in the same CNS cells and could have particular and different roles during embryogenesis in mice and humans. Mutations in these genes have been linked to very severe phenotypes in man in adulthood such as epilepsy. More remarkably, the exact role of these proteins during development and still unknown.

Our project focuses on understanding the role of these proteins during the early phases of cortical development.

Previous discoveries

One of the main features of TBI is neurodegeneration. TBI-induced neurodegeneration is a major risk factor for epilepsy but the mechanisms of post-traumatic epileptogenesis are poorly understood. A current view is that the brain reacts to pathological insults by activating developmental-like programs for survival, regeneration and replacement of damaged neurons. We have shown that only after injury, mature central neurons become dependent on brain-derived neurotrophic factor (BDNF) trophic support for survival. The reasons for this dependency are poorly studied. In recent works we described a novel mechanism explaining the neuroprotective action of BDNF after trauma relying on three different and complementary issues (Shulga et al., 2008; 2009):

The post-traumatic effect of GABAA receptors is set by the down-regulation of the K-Cl cotransporter (KCC2, a neuronal potassium/chloride extruder) and the functional presence of Na-K-Cl cotransporter NKCC1;

  • Post-traumatic GABA depolarization induces the u
  • Up-regulation of the death-promoting pan-neurotrophin receptor p75NTR;
  • BDNF trophic support counterbalances this death signaling and thus exerts a neuroprotective action.
  • Restoring early on the chloride homeostasis after TBI is helpfull to reduce secondary effect of the TBI such as depressive behavior and effect on secondary neurogenesis of the hippocampus.
(click to enlarge)

However the intrinsic mechanisms causing trauma-induced decrease of KCC2, BDNF requirement for neuronal survival and consequent rearrangement of post-traumatic network, leading to the removal of synaptic contacts responsible for de-afferentiation and reorganization of the synaptic network are not known. This delayed progressive reorganization may stand for the sequelae commonly observed in patients suffering from different forms of brain injury e.g. post-traumatic epilepsy (PTE). Indeed, epilepsy is a common outcome of TBI, but the mechanisms of post-traumatic epileptogenesis are still under investigation, and there are currently no working therapies for the treatment of the long-term sequelae of brain trauma.

Using in vitro and ex vivo approaches we demonstrated the importance of chloride homeostasis and synaptic imputs in epileptogenesis. Using a combination of molecular biology, electrophysiology, chloride recordings and image analysis, we discovered that the neuronal K-Cl cotransporter, KCC2, plays a key role in the developmental shift of GABAA-mediated neurotransmission from depolarizing to hyperpolarizing (Rivera et al., 1999), and showed that activity-dependent regulation of KCC2 expression requires BDNF signaling (Rivera et al., 2002).
Recent works have revealed a central role of CCCs in neuronal plasticity and disease mechanisms, particularly epilepsy and trauma (Pallud et al., 2014; Huberfeld et al., 2007) leading to the identification of novel interactions among growth factors and CCCs (de Koninck Y et al., 2007; Viemari et al., 2011) and highlighted the role of neuronal chloride regulation in signaling, development, plasticity and pathophysiology (Pallud et al., 2014; Vlachos et al., 2013; Nudo et al., 2013; Pellegrino et al., 2011; Payne et al., 2003; Blaesse et al., 2009; Rivera et al., 2005).

technical approaches

Field recordings

Chloride imaging

Immunostaining

Electron microscopy

Biochemistry

Cellular and molecular biology

Collaborations

INMED collaborations:

Yehezkiel Ben-Ari, PhD, CEO Neurochlore

Igor Medina, PhD

 

University of Helsinki:

Neuroscience center

Division of Pharmacology & Toxicology, Faculty of Pharmacy

 

Fundings

EraNet Neuron

FRM

Amidex (AMU)

Fondation des Gueules cassées

Contact and job proposal

The team welcomes students Level M1, M2, PhD student or post-doctoral fellow.
Applications should be sent by email to:

claudio.rivera@inserm.fr (post doc and PhD student)

christophe.pellegrino@inserm.fr (M1, M2 and PhD student)

Publications

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