β-Galactosylceramidase Deficiency Causes Bone Marrow Vascular Defects in an Animal Model of Krabbe Disease

Abstract: Krabbe disease (KD) is an autosomal recessive sphingolipidosis caused by the deficiency
of the lysosomal hydrolase β-galactosylceramidase (GALC). Oligodendroglia degeneration and
demyelination of the nervous system lead to neurological dysfunctions which are usually lethal by
two years of age. At present, the only clinical treatment with any proven efficacy is hematopoietic
stem-cell transplantation, which is more effective when administered in the neonatal period to
presymptomatic recipients. Bone marrow (BM) sinusoidal endothelial cells (SECs) play a pivotal
role in stem cell engraftment and reconstitution of hematopoiesis. Previous observations had shown
significant alterations of microvascular endothelial cells in the brain of KD patients and in Galc mutant
twitcher mice, an authentic model of the disease. In the present study, we investigated the vascular
component of the BM in the femurs of symptomatic homozygous twitcher mice at postnatal day
P36. Histological, immunohistochemical, and two-photon microscopy imaging analyses revealed
the presence of significant alterations of the diaphyseal BM vasculature, characterized by enlarged,
discontinuous, and hemorrhagic SECs that express the endothelial marker vascular endothelial
growth factor receptor-2 (VEGFR2) but lack platelet/endothelial cell adhesion molecule-1 (CD31)
expression. In addition, computer-aided image analysis indicates that twitcher CD31−/VEGFR2+ SECs
show a significant increase in lumen size and in the number and size of endothelial gaps compared
to BM SECs of wild type littermates. These results suggest that morphofunctional defects in the
BM vascular niche may contribute to the limited therapeutic efficacy of hematopoietic stem-cell
transplantation in KD patients at symptomatic stages of the disease.