Enzyme replacement therapy of a novel humanized mouse model of globoid cell leukodystrophy

An inherited deficiency of β-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 6months after birth and death by 2years 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 40days 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 46days. 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. [Display omitted] •We construct a humanized mouse model of globoid cell leukodystrophy.•We inject recombinant human galactosylceramidase intravenously.•Enzyme is delivered across the blood–brain barrier to parenchymal brain cells.•Treatment reduces psychosine levels in the peripheral and central nervous system.•Enzyme replacement therapy has no effect on neuroinflammation and life span.