Distribution of C16:0, C18:0, C24:1, and C24:0 sulfatides in central nervous system lipid rafts by quantitative ultra-high-pressure liquid chromatography tandem mass spectrometry.

Sulfated galactosylceramides (sulfatides) are glycosphingolipids associated with cholesterol- and sphingolipid-enriched membrane microdomains (lipid rafts) and are highly expressed in brain tissue. Although it is known that sulfatide species show heterogeneity in their fatty acid acyl group composition throughout brain development, their lipid raft distribution and biological relevance is poorly understood. We validated a fast and sensitive ultra-high-pressure liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) method to measure developmentally regulated sulfatide species (C16:0, C18:0, C24:1, and C24:0) in central nervous system (CNS) lipid rafts isolated without using detergent. Our UHPLC-MS/MS assay showed good accuracy and precision with a linear range of 5 to 1,000 nM for C18:0 and C24:1 sulfatides and 10 to 1,000 nM for C16:0 and C24:0 sulfatides. We applied this quantitative analysis to detergent-free lipid rafts isolated from wild-type mice and arylsulfatase A-deficient (ASA knockout) mice that accumulate sulfatides. All four sulfatide species were more abundant in raft membranes than in non-raft membranes, with a significant increase in lipid rafts isolated from ASA knockout mice. This is the first description of an analytical method to study these sulfatide species in raft and non-raft membranes and has the potential to be applied to preparations from other tissues.

Axonopathy is a compounding factor in the pathogenesis of Krabbe disease.

Loss-of-function of the lysosomal enzyme galactosyl-ceramidase causes the accumulation of the lipid raft-associated sphingolipid psychosine, the disruption of postnatal myelination, neurodegeneration and early death in most cases of infantile Krabbe disease. This work presents a first study towards understanding the progression of axonal defects in this disease using the Twitcher mutant mouse. Axonal swellings were detected in axons within the mutant spinal cord as early as 1 week after birth. As the disease progressed, more axonopathic profiles were found in other regions of the nervous system, including peripheral nerves and various brain areas. Isolated mutant neurons recapitulated axonal and neuronal defects in the absence of mutant myelinating glia, suggesting an autonomous neuronal defect. Psychosine was sufficient to induce axonal defects and cell death in cultures of acutely isolated neurons. Interestingly, axonopathy in young Twitcher mice occurred in the absence of demyelination and of neuronal apoptosis. Neuronal damage occurred at later stages, when mutant mice were moribund and demyelinated. Altogether, these findings suggest a progressive dying-back neuronal dysfunction in Twitcher mutants.

Autonomic denervation of lymphoid organs leads to epigenetic immune atrophy in a mouse model of Krabbe disease.

Lysosomal beta-galactosylceramidase deficiency results in demyelination and inflammation in the nervous system causing the neurological Krabbe disease. In the Twitcher mouse model of this disease, we found that neurological symptoms parallel progressive and severe lymphopenia. Although lymphopoiesis is normal before disease onset, primary and secondary lymphoid organs progressively degenerate afterward. This occurs despite preserved erythropoiesis and leads to severe peripheral lymphopenia caused by reduced numbers of T cell precursors and mature lymphocytes. Hematopoietic cell replacement experiments support the existence of an epigenetic factor in mutant mice reconcilable with a progressive loss of autonomic axons that hampers thymic functionality. We propose that degeneration of autonomic nerves leads to the irreversible thymic atrophy and loss of immune-competence. Our study describes a new aspect of Krabbe disease, placing patients at risk of immune-related pathologies, and identifies a novel target for therapeutic interventions.