Abstracts

RATIONALE: Patients with tuberous sclerosis complex (TSC) may develop a wide range of neurological abnormalities, including epilepsy, mental retardation, cortical dysplasias, and astrocytomas. Many of the abnormal neurological features of TSC could be due to a primary defect in astrocyte function. The objective of this study was to generate a mouse model of TSC-associated central nervous system abnormalities using an astrocyte-specific conditional knockout of the [italic]Tsc1[/italic] gene.
METHODS: Two independent lines of astrocyte-specific [italic]Tsc1[/italic] conditional knockout mice ([italic]Tsc1[/italic]^GFAP cKO mice) were generated using the Cre-LoxP system by expressing nuclear-targeted Cre recombinase under the control of the human glial fibrillary acidic protein (GFAP) promotor. [italic]Tsc1[/italic]^GFAP cKO mice were studied by video-EEG for characterization of seizures. Immunostaining for GFAP and conventional histological techniques were used to examine for glial and neuronal abnormalities.
RESULTS: At birth, [italic]Tsc1[/italic]^GFAP cKO mice appeared normal compared to wild type littermates. By two months of age, [italic]Tsc1[/italic]^GFAP cKO mice became less active, tended to assume a retracted posture, and exhibited paroxysmal movements resembling seizures. Video-EEG analysis confirmed that [italic]Tsc1[/italic]^GFAP cKO developed frequent clinical and electrographic seizures, usually characterized by tonic stiffening and clonus of the trunk or extremities without loss of upright posture. Electrographically, most seizures appeared to have simultaneous bilateral onset, but hippocampal depth recordings indicated focal onset for some seizures. Seizures were documented at one month of age, the earliest time point examined. By 3-4 months of age, seizures became extremely frequent, interictal EEG showed a burst-suppression pattern, and all mice died of an uncertain cause. GFAP immunostaining demonstrated significant increases in astrocyte numbers, as a result of increased cell proliferation, throughout the brain starting around 3 weeks of life and increasing progressively with age. Selective abnormalities of neuronal organization of hippocampal pyramidal neurons, primarily in the dentate hilar CA4 region, also developed and progressively worsened over a similar time course.
CONCLUSIONS: Selective inactivation of [italic]Tsc1[/italic] in astrocytes results in severe behavioral and neuropathological abnormalities, most likely involving both astrocytic and neuronal functions. The phenotype of this mouse model suggests that seizures and other neuronal abnormalities in TSC could be due to a primary defect of [italic]Tsc1[/italic] in astrocytes. Further work on [italic]Tsc1[/italic]^GFAP cKO mice should yield important insights into the mechanisms by which astrocytic dysfunction may lead to abnormal neuronal excitability and seizures (See accompanying abstract II).
[Supported by: Tuberous Sclerosis Alliance (DHG, HO, DJK, LB), NIH NS36996 (DHG), NIH NS31535 & NS24279 (DJK), NIH NRSA (EJU), NIH 5K12NS0169004 (MW)]