Molecular Mechanisms Underlying the Epileptogenesis and Seizure Progression in Tuberous Sclerosis Complex 1 Deficient Mouse Models

The causes of epileptic seizures in individuals with tuberous sclerosis (TS), and indeed in many patients with seizures of many types, are poorly understood. TS results from mutations in one of two TS complex genes (TSC1 and TSC2), and these mutations result in the aberrant and continued activation of the mTOR protein. We have been able to mimic many aspects of the disease in genetic mouse models. We now propose to use these models to understand four basic questions related to epileptogenesis: (1) What is the role of mTOR hyperactivation in epileptogenesis in the developing brain? (2) What are the molecular mechanisms downstream of mTOR hyperactivation that trigger epileptogenesis in developing brains? (3) What are rational, long-term pharmacological treatments to prevent the development or progression of seizures? (4) What are biomarkers for epileptogenesis and the prognostic biomarkers for disease progression? We have established a TSC1-deficient mouse line in which spontaneous seizures begin at 2.5 months of age and progress into 7-8months. Brains of these mice show many of the pathological changes we see in the brains of human TS patients. This long time course of survival allows us to analyze the molecular changes the brain undergoes before and after the onset of seizures. We have also developed a second mouse model in which the Tsc1 gene is deleted only in neurons. These mice develop seizures early and then die shortly after seizure onset.

We propose three specific aims, utilizing systems biology/gene expression profiling, electrophysiological, biochemical, immunohistochemical, and behavioral studies. Studies will use adolescent and adult mice before and after the onset of first electrographic evidence of hyperactivity and then after the onset of behavioral seizures. Specific Aim 1: Determine the effect of TSC1 deletion on epileptogenesis and on the progress of seizures. Using electroencephalography and videotaping, these mice we will define the exact onset of seizures in both mouse lines. This knowledge will provide the time windows for trials of therapies that inhibit the hyperactivation of mTOR. Specific Aim 2: Characterize the signaling pathways downstream of mTOR hyperactivation that are involved in epileptogenesis and seizure progression, using ribosome profiling technique. Here we will use up-to-date molecular genetics and computer algorithms to characterize how the expression of genes in neurons and astrocytes change with the onset of seizures and then when seizures become chronic. Specific Aim 3: Determine the effects of mTOR inhibitor on the initiation and progression of seizures and on the molecular changes that accompany the initiation and progression of seizures. This will test the efficacy of potential treatments with mTOR inhibitors and identify molecular players that respond to or do not response to these drugs. We will examine the effects of rapamycin on the molecular changes associated with the EEG/seizure activity, with a focus on the molecular signatures that are significantly changed during epileptogenesis in our model mice. Our studies will identify molecular mechanisms downstream mTOR signaling that underlie epileptogenesis in TS and other forms of epilepsies and determine potential therapeutic targets downstream of mTOR. This could impact treatment strategies for epileptogenesis and the progression of epilepsy.