The galactocerebrosidase enzyme contributes to the maintenance of a functional hematopoietic stem cell niche.
ABSTRACT The balance between survival and death in many cell types is regulated by small changes in the intracellular content of bioactive sphingolipids. Enzymes that either produce or degrade these sphingolipids control this equilibrium. The findings here described indicate that the lysosomal galactocerebrosidase (GALC) enzyme, defective in globoid cell leukodystrophy, is involved in the maintenance of a functional hematopoietic stem/progenitor cell (HSPC) niche by contributing to the control of the intracellular content of key sphingolipids. Indeed, we show that both insufficient and supraphysiologic GALC activity-by inherited genetic deficiency or forced gene expression in patients' cells and in the disease model-induce alterations of the intracellular content of the bioactive GALC downstream products ceramide and sphingosine, and thus affect HSPC survival and function and the functionality of the stem cell niche. Therefore, GALC and, possibly, other enzymes for the maintenance of niche functionality and health tightly control the concentration of these sphingolipids within HSPCs.
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ABSTRACT: Glycosphingolipids are ubiquitous components of mammalian cell membranes, and defects in their catabolism by lysosomal enzymes cause a diverse array of diseases. Deficiencies in the enzyme β-galactocerebrosidase (GALC) cause Krabbe disease, a devastating genetic disorder characterized by widespread demyelination and rapid, fatal neurodegeneration. Here, we present a series of high-resolution crystal structures that illustrate key steps in the catalytic cycle of GALC. We have captured a snapshot of the short-lived enzyme-substrate complex illustrating how wild-type GALC binds a bona fide substrate. We have extensively characterized the enzyme kinetics of GALC with this substrate and shown that the enzyme is active in crystallo by determining the structure of the enzyme-product complex following extended soaking of the crystals with this same substrate. We have also determined the structure of a covalent intermediate that, together with the enzyme-substrate and enzyme-product complexes, reveals conformational changes accompanying the catalytic steps and provides key mechanistic insights, laying the foundation for future design of pharmacological chaperones.Proceedings of the National Academy of Sciences 12/2013; 110(51). DOI:10.1073/pnas.1311990110 · 9.81 Impact Factor
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ABSTRACT: Globoid cell leukodystrophy (Krabbe disease) is a neurological disorder of infants caused by genetic deficiency of the lysosomal enzyme β-galactosylceramidase leading to accumulation of the neurotoxic metabolite 1-β-d-galactosylsphingosine (psychosine) in the central nervous system. Angiogenesis plays a pivotal role in the physiology and pathology of the brain. Here, we demonstrate that psychosine has anti-angiogenic properties by causing the disassembling of endothelial cell actin structures at micromolar concentrations as found in the brain of patients with globoid cell leukodystrophy. Accordingly, significant alterations of microvascular endothelium were observed in the post-natal brain of twitcher mice, an authentic model of globoid cell leukodystrophy. Also, twitcher endothelium showed a progressively reduced capacity to respond to pro-angiogenic factors, defect that was corrected after transduction with a lentiviral vector harbouring the murine β-galactosylceramidase complementary DNA. Finally, RNA interference-mediated β-galactosylceramidase gene silencing causes psychosine accumulation in human endothelial cells and hampers their mitogenic and motogenic response to vascular endothelial growth factor. Accordingly, significant alterations were observed in human microvasculature from brain biopsy of a globoid cell leukodystrophy case. Together these data demonstrate that β-galactosylceramidase deficiency induces significant alterations in endothelial neovascular responses that may contribute to central nervous system and systemic damages that occur in globoid cell leukodystrophy.Brain 09/2013; 136(Pt 9):2859-75. DOI:10.1093/brain/awt215 · 10.23 Impact Factor
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ABSTRACT: During the last few years microRNAs (miRNAs) have emerged as key mediators of post-transcriptional and epigenetic regulation of gene expression. MiRNAs targets, identified through gene expression profiling and studies in animal models, depict a scenario where miRNAs are fine-tuning metabolic pathways and genetic networks in both plants and animals. MiRNAs have shown to be differentially expressed in brain areas and alterations of miRNAs homeostasis have been recently correlated to pathological conditions of the nervous system, such as cancer and neurodegeneration. Here, we review and discuss the most recent insights into the involvement of miRNAs in the neurodegenerative mechanisms and their correlation with significant neurodegenerative disorders.06/2013; 4(2):244-63. DOI:10.3390/genes4020244