Gene delivery to the liver for inherited metabolic disorder provide the opportunity for specific treatment of two forms of glycogen storage disease (GSD). Glycogen accumulation due to single enzyme defects represents the prototype of metabolic storage disease. A detailed biochemical understanding and availability of mouse models for GSD Ia, and GSD II make these conditions excellent examples for correction for the metabolic defect in the liver by gene replacement therapy. In order to demonstrate the feasibility of this approach we propose to investigate the AAV-mediated delivery of the gene for glucose-6-phosphatase (G6P) and, acid alpha-glucosidase (GAA) in animal models of GSD I and II. The proposed study is designed to examine the ability of AAV to direct the sustained hepatic expression of G6P and GAA in murine models GSD. The vector has been shown to yield high-level, long-term expression of a number of therapeutic proteins without eliciting a clinically significant immune reaction. We have recently demonstrated high-efficacy gene transfer of GAA into embryonic tissues, cultured adult and neonatal rat cardiomyocytes, as well as, adult rat heart, and murine skeletal muscle in vivo using this approach. Substantial preliminary evidence in our lab and others demonstrates the utility of over-expression of therapeutic proteins in hepatic tissues. In principles, this system has the capacity to delivery the therapeutic protein to all tissues via secretion from the hepatic platform. Additionally, correct of G6P deficiency examines the important question of direct correction of a microsomal enzyme defect by hepatocyte transduction. We now propose to evaluate this potential by assessing the effectiveness and biological impact following AAV-mediated reconstitution of G6P and GAA in animal models off GSD. The effectiveness of several hepatic specific promoters will be tested in vitro using immortalize cell lines from the representative mouse models. One of the important considerations of systemic delivery of corrective vectors will be the ability to deliver the vector early, prior to detrimental effects of the metabolic defect in these diseases. To accomplish this we will examine the ability of AAV vectors to correct the systemic correction in these models. Assessment of successful gene transfer will be evaluated by new technologies using MR imaging and MR spectroscopy. The efficiency of processing and targeting of lysosomal enzymes will be examined by strategies which allow for the augmentation of the phosphotransferase enzyme involved in lysosomal enzyme secondary processing or by anti-sense of critical proteins which control lysosomal targeting and thereby result in a preference for the secretory pathway. These studies will yield important new information in establishing a clinically relevant treatment for these fatal diseases and add new understanding to the basic pathophysiology of GSD.
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