Tuberous sclerosis complex (TSC) is a dominant tumor suppressor disorder caused by mutations in either TSC1 or TSC2. TSC causes substantial neuropathology, often leading to autism spectrum disorders (ASDs) in up to 60% of patients. The anatomic and neurophysiologic links between these two disorders are not well understood. We have generated and characterized a novel TSC mouse model with Purkinje cell specific Tsc2 loss. These Tsc2f/-;Cre mice exhibit progressive Purkinje cell degeneration. Since loss of Purkinje cells is a well reported postmortem finding in patients with ASD, we conducted a series of behavior tests to asses if Tsc2f/-;Cre mice displayed autistic-like deficits. Tsc2f/-;Cre mice demonstrated increased repetitive behavior as assessed with marble burying activity. Using the three chambered apparatus to asses social behavior, we found that Tsc2f/-;Cre mice showed behavioral deficits, exhibiting no preference between a stranger mouse and an inanimate object, or between a novel and a familiar mouse. We also detected social deficits in Tsc2f/f;Cre mice, suggesting that Purkinje cell pathology is sufficient to induce ASD-like behavior. Importantly, social behavior deficits were prevented with rapamycin treatment. Altogether, these results demonstrate that loss of Tsc2 in Purkinje cells in a Tsc2-haploinsufficient background leads to autistic-like behavioral deficits. These studies provide compelling evidence that Purkinje cell loss and/or dysfunction may be an important link between TSC and ASD as well as a general anatomic phenomenon that contributes to the ASD phenotype.

Tuberous sclerosis complex (TSC) is an autosomal dominant, tumor predisposition disorder characterized by significant neurodevelopmental brain lesions, such as tubers and subependymal nodules. The neuropathology of TSC is often associated with seizures and intellectual disability. To learn about the developmental perturbations that lead to these brain lesions, we created a mouse model that selectively deletes the Tsc2 gene from radial glial progenitor cells in the developing cerebral cortex and hippocampus. These Tsc2 mutant mice were severely runted, developed post-natal megalencephaly and died between 3 and 4 weeks of age. Analysis of brain pathology demonstrated cortical and hippocampal lamination defects, hippocampal heterotopias, enlarged dysplastic neurons and glia, abnormal myelination and an astrocytosis. These histologic abnormalities were accompanied by activation of the mTORC1 pathway as assessed by increased phosphorylated S6 in brain lysates and tissue sections. Developmental analysis demonstrated that loss of Tsc2 increased the subventricular Tbr2-positive basal cell progenitor pool at the expense of early born Tbr1-positive post-mitotic neurons. These results establish the novel concept that loss of function of Tsc2 in radial glial progenitors is one initiating event in the development of TSC brain lesions as well as underscore the importance of Tsc2 in the regulation of neural progenitor pools. Given the similarities between the mouse and the human TSC lesions, this model will be useful in further understanding TSC brain pathophysiology, testing potential therapies and identifying other genetic pathways that are altered in TSC.

Tuberous sclerosis complex (TSC) is a neurodevelopmental disorder with variable expressivity. Heterozygous mutations in either of two genes, TSC1 (hamartin) or TSC2 (tuberin), are responsible for most cases. Hamartin and tuberin form a heterodimer that functions as a major cellular inhibitor of the mammalian target of rapamycin complex 1 (mTORC1) kinase. Genotype-phenotype studies suggest that TSC2 mutations are associated with a more severe neurologic phenotype, although the biologic basis for the difference between TSC1- and TSC2-based disease is unclear. Here we performed a study to compare and contrast the brain phenotypes of Tsc1 and Tsc2 single and double mutants. Using Tsc1 and Tsc2 floxed alleles and a radial glial transgenic Cre driver (FVB-Tg(GFAP-cre)25Mes/J), we deleted Tsc1 and/or Tsc2 in radial glial progenitor cells. Single and double mutants had remarkably similar phenotypes: early postnatal mortality, brain overgrowth, laminar disruption, astrogliosis, a paucity of oligodendroglia, and myelination defects. Double Tsc1/Tsc2 mutants died earlier than single mutants, and single mutants showed differences in the location of heterotopias and the organization of the hippocampal stratum pyramidale. The differences were not due to differential mTORC1 activation or feedback inhibition on Akt. These data provide further genetic evidence for individual hamartin and tuberin functions that may explain some of the genotype-phenotype differences seen in the human disease.

Tuberous sclerosis complex (TSC) is a neurogenetic disorder that often causes brain abnormalities leading to epilepsy, developmental delay, and autism. TSC is caused by inactivating mutations in either of the genes encoding the proteins hamartin (TSC1) and tuberin (TSC2). These proteins form a heterodimer that inhibits the mammalian target of rapamycin complex 1 (mTORC1) pathway, controlling translation and cell growth. Loss of either protein results in dysregulated mTORC1 activation, an important aspect of TSC pathogenesis. About thirty percent of TSC patients have cerebellar pathology that is poorly understood. To investigate the effects of TSC on the cerebellum, we created a mouse model in which the Tsc2 gene was selectively deleted from Purkinje cells starting at postnatal day 6 (P6). The loss of Tsc2 caused a progressive increase in Purkinje cell size and subsequent death from apoptosis. Purkinje cell loss was predominantly cell type specific and associated with motor deficits. Immunohistochemical analysis showed that both endoplasmic reticulum (ER) and oxidative stress were increased in Tsc2-null Purkinje cells. The cell death and ER stress phenotypes were rescued by treatment with the mTORC1 inhibitor rapamycin. To assess whether the murine Purkinje cell loss has a correlate to the human TSC, we analyzed postmortem cerebellum samples from TSC patients and detected Purkinje cell loss in half of the samples. Our results establish a critical role for the TSC complex in Purkinje cell survival by regulating ER and oxidative stress and reveal a novel aspect of TSC neuropathology.