Cycle 2 project 7

Project 7: Novel molecular targets in the battle against epilepsy: a role for the presynaptic signaling molecule STXBP1


PhD student: Margherita Farina, Italy
Home Institute: Amsterdam Neuroscience; Principle Investigator: Dr. Ruud Toonen / Prof. M. Verhage
Host Institute:Center for Neuroscience and Cell Biology (University of Coimbra), Coimbra; Principle Investigator: Dr. Ines Araujo / Prof. C.M. Carvalho

Executive Summary
Epilepsy is a devastating and poorly understood disease that affects 1–2{4f6e60e6953937a1ab815e93856ab9862da64473b2fafe2c234a4daba9520ef4} of the world population   making it one of the most common neurological disorders. Epilepsy is characterized by recurrent unprovoked seizures and is caused by disturbances in the delicate balance between excitation and inhibition in neural circuits.

To date the majority of genes associated with epilepsy involve ion channels and classical antiepileptic drugs (AEDs) mainly act on voltage-gated sodium channels. However, recent attention has focused on proteins that modulate neurotransmitter output at synapses as critical novel sites of action for AEDs (Lynch et al., 2004; Sills, 2010).

To understand how impaired neurotransmitter output contributes to the development of epileptic seizures and to identify new molecular targets for AEDs we will focus our attention on STXBP1. This synaptic protein is essential for synaptic transmission and a major modulator of SNARE-protein mediated vesicle release. STXBP1 is therefore considered to be one of the most important hubs controlling synaptic transmission. Importantly, de novo mutations in STXBP1 cause early infantile epilepsy (Hamdan et al., 2009; Saitsu et al., 2008). However, the underlying molecular mechanism is not known.
We will combine expertise at the Home Institute (molecular neurobiology, proteomics and electrophysiology) and the Exchange Institute (experts on epilepsy research) to test the hypothesis that changes in STXBP1 protein complex composition and/or level are associated with recurrent epileptic seizures and to elucidate the function of STXBP1 in epilepsy.

The FIRST OBJECTIVE is to identify changes in the STXBP1 protein complex composition at the synapse during the latent and chronic phase of epilepsy, using the pilocarpine temporal lobe epilepsy model in rats.

The Host Institute has identified the STXBP1 synaptic interactome. Interestingly, one major STXBP1 interactor is SV2A, the target of the antiepileptic drug levetiracetam (Lynch et al., 2004). This screen, which will be the first to be conducted that focuses on protein composition changes at the synapse, has the potential to generate novel targets to prevent or slow down the progression of epilepsy.

The SECOND OBJECTIVE is to characterize the effect of infantile epileptic encephalopathy (EIEE) causing mutations in STXBP1 on synaptic function. We will reintroduce these mutations on STXBP1 heterozygote background to closely mimic the human situation. As STXBP1 stability might be compromised by these mutations we will test STXBP1 levels and transport to synaptic sites, synapse development and maintenance, and neurotransmission in autaptic culture systems.
The THIRD OBJECTIVE is to test the hypothesis that a reduction STXBP1 protein levels results in network imbalance that will lead to the generation of epileptic seizures. For this we will use STXBP1 heterozygote animals generated in the Host Institute and perform behavioral screens using telemetric electroencephalographic (EEG) recordings in freely moving animals at the Exchange Institute.

This proposal will generate new insight in how synaptic protein composition is
changed during the development of epilepsy and will generate detailed knowledge on the function of disease associated mutations in STXBP1. Together, this may lead to new strategies for improving treatment of this disorder.

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