Novel gene therapy strategies to correct a murine model of GM1 gangliosidosis with special emphasis on early and late disease phases

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GM1-gangliosidosis is a lysosomal storage disease, belonging to the sphingolipidoses, caused by ß-galactosidase (Glb1) deficiency due to mutations in the Glb1 gene. The disease develops due to lysosomal accumulation of the ganglioside-GM1 and other ß-galactosidase substrates in the central nervous system and other organs and tissues. Abnormal storage of sphingolipids trigger neuronal dysfunction, axonal transport impairment and loss of myelin. This rare disease occurs in humans and various animal species and depending on clinic and age of onset, different forms have been noticed. Therapy options for storage diseases, particularly GM1-gangliosidosis, are still insufficient and include substrate reduction and chaperone-based therapy, bone marrow transplantation, and enzyme replacement. These therapy approaches have only some beneficial effects and lack final cure. Gene therapy is a very effective treatment option when applied early enough. The objective of this proposed research is based on the hypothesis that gene therapy will prevent early onset and development of GM1-gangliosidosis. To verify this hypothesis, the effect of a gene therapy approach will be investigated in a recently generated and well-characterized mouse model of GM1-gangliosidosis. Diseased mice will receive a transplantation of primary hematopoietic stem/progenitor cells (HSPC) transduced with a lentiviral vector or a conditionally inducible Hoxb8-immortalized HSPC line containing an expression cassette with a codon-optimized Glb1 cDNA encoding for a functional murine ß-galactosidase. To prevent the onset of the disease, mice will be treated at the age 5 weeks (early stage of the disease) by an intravenous application of genetically modified HSPCs and monitored clinically, using a variety of neurological tests, for adverse and beneficial treatment related effects and pathological changes till 7 months of age or longer, depending on the clinic. The impact of the treatment will be substantiated by in vitro analysis of the ß-galactosidase activity using skin fibroblasts and, depending on the findings, brain cells. Furthermore, the transduction efficacy of the lentiviral vector and different promotors will be studied throughout the course of the experiment by various in vitro tests. Depending on the results of the peripheral intravenous application of HSPC transduced with a lentiviral vector, and, additionally, to improve delivery and migration into the brain, intracerebroventricular injection of these cells will be performed. Moreover the conditionally inducible Hoxb8-immortalized HSPC line will be applied intracerebroventricularly. This study will determine the efficacy and safety of a gene therapy in a rare disease such as GM1-gangliosidosis in an animal model. Moreover, it is directly linked to the development of new and hopefully effective treatment concepts for the human and canine GM1-gangliosidosis as well as other species, for which there is a high therapeutic need.