Characterization of the early immunopathologic events in a murine model of globoid cell leukodystrophy

Globoid cell leukodystrophy (GLD or Krabbe's disease) is an autosomal recessive lysosomal storage disease with a prevalence of 1 in100,000 children affected each year. The disease is characterized by the lack of galactocerebrosidase and alternative catabolism of galactocerebroside into the toxic substance, psychosine. Psychosine is associated with creating large, distended, multinucleated macrophages, astrogliosis, oligodendroglial cell death and demyelination, and cytokine and chemokine upregulation. Much work has been done to characterize the terminal pathological appearance of GLD, but little has been done to demonstrate early pathological changes that occur in this disease.;The early pathological changes in GLD are the primary aim of this study. The histological evaluation of the brains of mice (twitcher mice) affected by this disease yielded the novel discovery of microglial nodules at 2 and 3 weeks of age with subsequent activation of surrounding astrocytes. This finding helps to answer previously raised questions about which cell types might be the primary reactors in GLD. Coinciding with the morphologic changes associated with microglial and macrophage activation, quantitative PCR for toll-like receptor (TLR) expression demonstrated a slight increase in TLR2 mRNA levels at 2 weeks of age and marked increases at 3 weeks of age. Using TLR2 reporter cells, we showed that psychosine-treated oligodendrocytes could induce the TLR2 signaling pathway. Finally, cytokine and chemokine levels were measured throughout the course of disease and showed that significant increases were not identified prior to the upregulation of TLR2.;The findings of this study are useful in identifying the mechanism and order of cellular activation that may help to better understand the pathogenesis of GLD. No study to date has sufficiently answered the question of how neural cells were activated and whether psychosine was responsible for the activation. Based on this study, the proposed order of events in Krabbe's disease are: 1) psychosine accumulates within the oligodendrocytes, 2) the oligodendrocytes begin to undergo apoptosis and release a DAMP with subsequent axonal demyelination, 3) macrophage activation through TLR2 and subsequent astroglial activation and cytokine and chemokine upregulation and release.