196. AAV-Mediated Gene Replacement Therapy in Mouse Model of Tuberous Sclerosis

Abstract

Tuberous sclerosis complex (TSC) is an autosomal dominant disorder due to mutations in either TSC1 or TSC2 that affects many organs with hamartomas and tumors. TSC-associated brain lesions include cortical heterotopias, tubers, subependymal nodules, and decreased myelination. Neurologic manifestations include epilepsy, hydrocephalus, mental retardation and autism. Here, we describe a new mouse model of TSC brain lesions in which complete loss of Tsc1 is achieved in multiple cell types in the brain in a stochastic pattern starting from the time of birth. Injection of an adeno-associated virus (AAV) vector encoding Cre recombinase into the cerebral ventricles of mice homozygous for a floxed Tsc1 conditional allele on P0 led to reduced survival, and pathologic findings of enlarged neurons, cortical heterotopias, subependymal nodules, and hydrocephalus. Although several other models of TSC brain disease exist, this model is unique in that the pathology reflects a variety of TSC-associated brain lesions involving different numbers and types of cells in different animals. This model provides a valuable and unique addition for therapeutic assessment.In addition, we have assessed the benefit of gene therapy in a related mouse model of Tsc1 in which the encoded gene product, hamartin is lost in most brain neurons at embryonic day 12. An adeno-associated virus (AAV) vector expressing a tagged form of hamartin was injected into the cerebral ventricles of newborn pups with the genotype Tsc1cc (homozygous for a conditional floxed Tsc1 allele) Syn-Cre+ (with Cre under the synapsin promoter). The AAV rh8 serotype gave widespread delivery of the tagged hamartin to brain cells. Treated mice showed an improvement in survival, from a mean of 22 days in non-injected Tsc1ccSynIcre+ mice to 52 days in hamartin AAV vector-injected, with improved weight gain and normalized behavior. Pathologic studies showed a reduction in neuron enlargement in comparison to untreated mutant littermates. Hence, we show that gene therapy is an effective approach in this mouse model of TSC. Our strategy for delivery has the advantage of single application, and AAV vectors are known to have minimal to nil toxicity in clinical trials for other neurologic conditions.