ABSTRACT
An inherited deficiency of ß-galactosylceramidase (GALC) causes the lysosomal storage disease globoid cell leukodystrophy (GLD). The disease is characterized by the accumulation of the cytotoxic metabolite psychosine (galactosylsphingosine), causing rapid degeneration of myelinating cells. Most patients suffer from the infantile form of GLD with onset of disease between 3 and 6 months after birth and death by 2 years of age. The most widely used animal model of GLD, the twitcher mouse, presents with an even more rapid course of disease and death around 40 days of age. We have generated a novel "humanized" mouse model of GLD by inserting a human GALC cDNA containing an adult-onset patient mutation into the murine GALC gene. Humanized GALC mice exhibit pathological hallmarks of GLD including psychosine accumulation, neuroinflammation, CNS infiltration of macrophages, astrogliosis and demyelination. Residual GALC activities in mouse tissues are low and the mice display a median lifespan of 46 days. Due to the expression of the human transgene, the mice do not develop an immune response against rhGALC, rendering the animal model suitable for therapies based on human enzyme. Intravenously injected rhGALC was able to surmount the blood-brain barrier and was targeted to lysosomes of brain macrophages, astrocytes and neurons. High-dose enzyme replacement therapy started at postnatal day 21 reduced the elevated psychosine levels in the peripheral and central nervous system by 14-16%, but did not ameliorate neuroinflammation, demyelination and lifespan. These results may indicate that treatment must be started earlier before pathology occurs.
Subject(s)
Disease Models, Animal , Enzyme Replacement Therapy/methods , Galactosylceramidase/metabolism , Gene Expression Regulation/drug effects , Leukodystrophy, Globoid Cell/enzymology , Leukodystrophy, Globoid Cell/therapy , Age Factors , Animals , Animals, Newborn , Body Weight/genetics , Central Nervous System/enzymology , Cytokines/metabolism , Female , Galactosylceramidase/genetics , Gene Expression Regulation/genetics , Humans , Leukodystrophy, Globoid Cell/genetics , Leukodystrophy, Globoid Cell/pathology , Male , Mice , Mice, Inbred BALB C , Mice, Transgenic , Mutation/genetics , Myelin Sheath/metabolism , Nerve Tissue Proteins/metabolism , Psychosine/metabolismABSTRACT
Metachromatic leukodystrophy (MLD) is a lysosomal storage disease caused by a functional deficiency of the lysosomal enzyme arylsulfatase A. The prevailing late-infantile variant of MLD is characterized by widespread and progressive demyelination of the central nervous system (CNS) causing death during childhood. In order to gain insight into the pathomechanism of the disease and to identify novel therapeutic targets, we analyzed neuroinflammation in two mouse models reproducing a mild, nondemyelinating, and a more severe, demyelinating, variant of MLD, respectively. Microgliosis and upregulation of cytokine/chemokine levels were clearly more pronounced in the demyelinating model. The analysis of the temporal cytokine/chemokine profiles revealed that the onset of demyelination is preceded by a sustained elevation of the macrophage inflammatory protein (MIP)-1α followed by an upregulation of MIP-1ß, monocyte chemotactic protein (MCP)-1, and several interleukins. The tumor necrosis factor (TNF)-α remains unchanged. Treatment of the demyelinating mouse model with the nonsteroidal anti-inflammatory drug simvastatin reduced neuroinflammation, improved the swimming performance and ataxic gait, and retarded demyelination of the spinal cord. Our data suggest that neuroinflammation is causative for demyelination in MLD mice and that anti-inflammatory treatment might be a novel therapeutic option to improve the CNS function of MLD patients.
