Gene therapy and enzyme replacement in a mouse model of late infantile neuronal ceroid lipofuscinosis

Late infantile neuronal ceroid lipofuscinosis (LINCL) is a pediatric neurodegenerative disease caused by mutations in CLN2, which encodes the lysosomal protease tripeptidyl peptidase 1 (TPP1). As there is no known therapy, patients suffer motor and cognitive decline, and premature death. Existing murine and canine models of LINCL are suitable for testing novel therapies. The goals of my thesis were to identify relevant neuropathological and behavioral phenotypes in the TPP1-deficient mouse model, and develop therapeutic strategies for rescuing those phenotypes.;In the TPP1-deficient mouse, we characterized reactive astrocytosis in the brain and identified degenerating neuron populations that may contribute to the motor deficits of the mouse. We also developed a sensitive behavioral assay that detects an age-dependent increase in resting tremor. These quantifiable phenotypes were then used to assess efficacy in an enzyme replacement study.;Intravenous enzyme replacement is beneficial for some lysosomal storage diseases, but not for those with central nervous system (CNS) involvement, as enzymes do not efficiently cross the blood brain barrier. The cerebrospinal fluid offers an alternative route of enzyme delivery to the CNS. We tested the efficacy of intraventricular enzyme delivery to the TPP1-deficient mouse and observed that infusion of recombinant TPP1 restored enzyme activity throughout the brain and rescued disease phenotypes in the mouse.;Finally, we developed gene therapy strategies for treating CNS disease. In addition to evaluating the gene transfer properties of several adeno-associated virus (AAV) serotypes in the mouse and dog LINCL models, we also took a novel approach in which we redirected the tissue tropism of AAV to the cerebral vasculature, which we hypothesized could be co-opted for enzyme delivery to the CNS. We used in vivo phage display to screen for peptides that bind to the vasculature of the TPP1-deficient mouse, then inserted these peptides into the AAV capsid. Importantly, the resulting virus expressed TPP1 from the cerebral vasculature following intravenous injection. These vectors are now being tested in ongoing efficacy studies.;In summary, our findings illustrate novel approaches to treating CNS disease and lay the foundation for future pre-clinical studies.