Broad screening test for sphingolipid-storage diseases

Abstract

Lipid-storage diseases are collectively important because they cause substantial morbidity and mortality, and because they may present as dementia, major psychiatric illness, developmental delay, or cerebral palsy. At present, no single assay can be used as an initial general screen for lipid-storage diseases. We used a fluorescent analogue of lactosylceramide, called N-[5-(5,7-dimethylborondipyrromethenedifluoride)-1-pentanoyl]D- lactosylsphingosine (BODIPY-LacCer), the emission of which changes from green to red wavelengths with increasing concentrations in membranes, to examine the intracellular distribution of the lipid within living cells. During a brief pulse-chase experiment, the fluorescent lipid accumulated in the lysosomes of fibroblasts from patients with Fabry's disease, GM1 gangliosidosis, GM2 gangliosidosis (Tay-Sachs and Sandhoff forms), metachromatic leucodystrophy, mucolipidosis type IV, Niemann-Pick disease (types A, B, and C), and sphingolipid-activator-protein-precursor (prosaposin) deficiency. In control cells, the lipid was mainly confined to the Golgi complex. In a masked study, replicate samples of 25 of 26 unique cell lines representing ten different lipid-storage diseases, and 18 of 20 unique cell lines representing controls were correctly identified; the sensitivity was 96.2% (95% CI 80.4-99.9) and the specificity 90.0% (68.3-98.8). This method may be useful as an initial general screen for lipid-storage diseases, and, with modification, could be used for large-scale automated screening of drugs to abrogate lysosomal storage in various lipidoses. The unexpected accumulation of BODIPY-LacCer in several biochemically distinct diseases raises important questions about common mechanisms of cellular dysfunction in these disorders.