The long-term objective of this project is to develop and analyze authentic brain models of TSC in the mouse, so that we can better understand the pathogenesis of TSC in the brain and develop effective therapeutic approaches. Tuberous sclerosis (TSC) is an autosomal dominant tumor suppressor gene syndrome, characterized by development of distinctive benign tumors (hamartomas) and malformations (hamartias) in multiple organ systems. The brain lesions (cortical tubers, subependymal nodules, and cerebral white matter migration tracts) account for the most severe manifestations in most patients, including seizures, mental retardation, and autism and other developmental disorders. The long-term objective of this project is to develop and analyze authentic brain models of TSC in the mouse, so that we can better understand the pathogenesis of TSC in the brain and develop effective therapeutic approaches. We have created a floxed Tsc1 conditional allele, which is a critical reagent for this study. In the first aim, we will complete an analysis of mice in which we have engineered complete loss of Tsc1 in the majority of cortical and hippocampal neurons. These mice are severely affected with both spontaneous and inducible seizure activity, a neurologic wasting syndrome, with ectopic and dysplastic neurons in both the cortex and hippocampus, and a myelination defect; all without genetic modification of astrocytes or astrogliosis. This model displays a marked therapeutic response to rapamycin/RAD001 treatment with increase in median survival from 35d to > 100d. We will examine cortical layer organization through use of specific antibodies and BrdU birthdating, assess neurotransmitter-receptor and transcription factor expression alterations, and assess the response to interrupted rapamycin/RAD001 treatment in this model. In the second aim, we will explore a second brain model of TSC, using a regulable neural progenitor cell specific promoter in the form of the rtTA-tet-on system. Detailed studies of cortical development, seizure predilection, and response to rapamycin/RAD001 will be performed. In the third aim, we will explore the specificity of a set of novel brain enhancers for the cortex, and select one or more of them for use in generating a novel inducible brain model of TSC, using the cre recombinase-estrogen receptor (Cre-ER) system. Through these approaches, we will be able to modulate the amount of recombination in neural progenitor cells, leading to variable fractions of cells lacking Tsc1 during various stages of brain development. In this way, we expect to generate mice which have cortical regions resembling those seen in patient cortical tubers, which will be a resource for detailed study of the pathogenesis of TSC brain lesions. TSC affects about 40,000 individuals in the US, and the majority of those have serious neurologic abnormalities including seizure disorders. An understanding of how these abnormalities develop in these patients will provide the opportunity for drug and other treatment. Study of an accurate mouse model of this disease will enable this understanding.
