Development of Mouse Models and Gene Therapy for Gaucher Disease

Abstract: Gaucher disease (GD) patients cannot metabolize glycosphingolipids properly due to deficiency of the enzyme glucosylceramidase (GCase). The lack of animal model for GD has hindered comprehensive investigation of disease mechanisms and also the development of curative treatment strategies such as hematopoietic stem cell (HSC) targeted gene therapy. Previous GCase deficient mice have either been lethal (due to disruption of the skin-barrier) or viable but without relevant symptoms of GD. We applied conditional strategies to create two different mouse models of GD, importantly sparing GCase activity in the skin during fetal development. Using the cre/loxP system and the Mx1-cre mouse we could develop an inducible mouse model with pathology and symptoms similar to type 1 GD patients, including infiltration of disease-characteristic Gaucher cells in target tissues, splenomegaly and anemia. We further used this model to demonstrate that HSC targeted gene therapy can cure manifest type 1 GD. The unfortunate occurrence of leukemia in otherwise successful clinical gene therapy trials has called attention to safety and by using two different transplantation-assays we provide evidence that GD has the potential to successfully respond to reduced-risk gene therapy protocols. In the second model, the function of a GBA null allele could be restored in the skin through breeding onto the K14-cre mouse, in which cre expression is restricted to the basal layer of the epidermis. This model developed early onset and rapidly progressive neurodegeneration characteristic of the severe neuronopathic form of GD. In this model we also observed considerable microglia activation. Microglia activation has been demonstrated to play an important role in the pathogenesis of other neurodegenerative conditions. Using a second mouse model in which GCase deficiency was restricted to neurons and macroglia we could demonstrate that the GCase deficient miroglia have a modulating role on disease onset and progression but are not the primary determinant of the severe neurodegeneration. Taken together the work described in this thesis provide the essential tools and proof-of-principle basis to proceed towards enhanced understanding of pathological mechanisms as well as development of novel treatment-modalities including HSC targeted gene therapy.