Globoid cell leukodystrophy (GLD) is a rapidly progress- ing pediatric neurodegenerative disease caused by missing or dysfunctional lysosomal enzyme galactosylceramidase

Journal of Lipid Research Volume 54, 2013 3303 Copyright © 2013 by the American Society for Biochemistry and Molecular Biology, Inc. Globoid cell leukodystrophy (GLD) is a rapidly progressing pediatric neurodegenerative disease caused by missing or dysfunctional lysosomal enzyme galactosylceramidase (GALC). Hallmarks of this disease include macrophage (globoid cell) infi ltration into the brain parenchyma, loss and dysfunction of myelin and oligodendrocytes, and axonal damage ( 1, 2 ). The GALC enzyme is responsible for cleaving the glycosydic linkage of galactosylceramide and galatosylsphingosine (psychosine or psy) ( 3 ). Although galactosylceramide can be degraded by other enzymes, psy cannot and subsequently accumulates to high levels in the brains of GALC-defi cient individuals ( 4 ). Psychosine is a highly cytotoxic lipid, capable of inducing cell death in a wide variety of cell types including, most relevantly to GLD, oligodendrocytes ( 5 ). Psychosine accumulation was postulated to be the pathogenic mechanism leading to GLD nearly 40 years ago ( 4, 6, 7 ). However, the mechanism of psychosine toxicity has remained elusive ( 8 ). Psychosine induces pleiotropic effects, including dysfunctions in several cellular pathways and compartments with no clear mechanistic connection between them ( 9–13 ). No unifi ed cause for these dysfunctions has been proposed. Given the wide-ranging nature of psy’s effects, it seems unlikely that psy toxicity is mediated through a single proteinbinding partner, such as a receptor. It is similarly unlikely that psy specifi cally binds many proteins independently. As an amphipathic molecule, psy would be expected to partition largely into cellular membranes. Indeed, White et al. ( 14 ) demonstrated that psy preferentially partitions into detergent-resistant membrane microdomains rich in cholesterol. Cholesterol has a chemical affi nity for sphingolipids such as psy ( 15 ); therefore, this association is not Abstract Globoid cell leukodystrophy (GLD) is a neurological disease caused by defi ciency of the lysosomal enzyme galactosylceramidase (GALC). In the absence of GALC, the cytotoxic glycosphingolipid, psychosine (psy), accumulates in the nervous system. Psychosine accumulation preferentially affects oligodendrocytes, leading to progressive demyelination and infi ltration of activated monocytes/macrophages into the CNS. GLD is characterized by motor defects, cognitive defi cits, seizures, and death by 2–5 years of age. It has been hypothesized that psychosine accumulation, primarily within lipid rafts, results in the pathogenic cascade in GLD. However, the mechanism of psychosine toxicity has yet to be elucidated. Therefore, we synthesized the enantiomer of psychosine ( ent -psy) to use as a probe to distinguish between protein-psy (stereo-specifi c enantioselective) or membranepsy (stereo-insensitive nonenantioselective) interactions. The enantiomer of psychosine has equal or greater toxicity compared with psy, suggesting that psy exerts its toxicity through a nonenantioselective mechanism. Finally, in this study we demonstrate that psy and ent -psy localize to lipid rafts, perturb natural and artifi cial membrane integrity, and inhibit protein Kinase C translocation to the plasma membrane. Although other mechanisms may play a role in disease, these data strongly suggest that psy exerts its effects primarily through membrane perturbation rather than through specifi c protein-psy interactions. —Hawkins-Salsbury, J.A., A.R. Parameswar, X. Jiang, P.H. Schlesinger, E. Bongarzone, D.S. Ory, A.V. Demchenko, and M.S. Sands. Psychosine, the cytotoxic sphingolipid that accumulates in globoid cell leukodystrophy, alters membrane architecture. J. Lipid Res. 2013 . 54: 3303–3311.