GLYCOLIPID METABOLISM AND MOTOR NEURON DISEASE

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Amyotrophic lateral sclerosis (ALS) is a devastating, progrssive degenerative disease of motor neurons (typically manifesting itself in middle age), which results in muscle wasting, paralysis and death. Since very little is known about the cause or precise pathogenesis of ALS, we propose to test the hypothesis that the disease can result from abnormal glycosphingolipid (GSL) (ganglioside) metabolism. We will structurally characterize the 3 major abnormal gangliosides already detected in all 9 ALS spinal cords thus far examined, but absent from non-ALS spinal cords, and will extend the search to ALS muscle and motor neuron-rich regions of the brain, including both gangliosides and neutral hexosamine-containing glycolipids. Structural analysis will require a combination of thin-layer chromatography, specific glycosidases, GLS-mass-spectrometry and specific monoclonal antibodies. Comparison will be made with GSL from unaffected brain regions. Fibroblasts from patients with various types of GM2-gangliosidosis, including a 25 year-old patient with a previously undescribed specific deficiency of N-acetyl-B-D-glucosaminidase B (Hex B) and typical ALS-like symptoms will be assayed for ability to degrade these gangliosides. Polyclonal antibodies to Hex B Alpha- or Beta-chains will be used to determine if Hex B is undersynthesized in these cells and if Heb B or a novel isoenzyme predominates in motor neurons. Finally, all 100 or more ALS patients seen at the University of Chicago ech year will be tested for Hex A and B levels and isoenzyme patterns. Our long-term objective is to show that abnormal accumulation of certain hexosamine-containing gangliosides in ALS motor neurons results in the type of neuronal degeneration seen in lysosomal storage diseases or a failure in motor neuron sprouting, which leads to progressive loss of neuromotor function. Such a finding would form the basis for ALS therapy.