Synaptophysin interacts with synaptobrevin in membranes of adult small synaptic vesicles. The synaptophysin/synaptobrevin complex promotes synaptobrevin to built up functional SNARE complexes thereby modulating synaptic efficiency. Synaptophysin in addition is a cholesterol-binding protein.Depleting the membranous cholesterol content by filipin or b-methylcyclodextrin (b-MCD) decreased the solubility of synaptophysin in Triton X-100 with less effects on synaptobrevin. In small synaptic vesicles from rat brain the synaptophysin/ synaptobrevin complex was diminished upon b-MCD treatment as revealed by chemical cross-linking. Mice with a genetic mutation in the Niemann-Pick C1 gene developing a defect in cholesterol sorting showed significantly reduced amounts of the synaptophysin/synaptobrevin complex compared to their homo-or heterozygous littermates. Finally when using primary cultures of mouse hippocampus the synaptophysin/synaptobrevin complex was down-regulated after depleting the endogenous cholesterol content by the HMG-CoA-reductase inhibitor lovastatin. Alternatively, treatment with cholesterol up-regulated the synaptophysin/synaptobrevin interaction in these cultures. These data indicate that the synaptophysin/synaptobrevin interaction critically depends on a high cholesterol content in the membrane of synaptic vesicles. Variations in the availability of cholesterol may promote or impair synaptic efficiency by interfering with this complex.

The Wiskott-Aldrich syndrome (WAS) is an X-linked disorder characterized by thrombocytopenia, eczema, disorders in cell-mediated and humoral immunity, and a proclivity to lymphoproliferative disease. The gene responsible encodes a 53-kD proline-rich protein of unknown function (WASP). We produced a FLAG-WASP fusion protein that was used to immunize mice and produce mAbs against WASP. Using monoclonal anti-WASP in Western immunoblots, we have determined that WASP is present in the cytoplasmic but not nuclear fraction of normal human peripheral blood mononuclear cells, in normal human platelets, in T lymphocytes, non-T lymphocytes, and monocytes. The protein is produced in the B cell immunoblastic cell line DS-1, in normal EBV-transformed B cell lines, and in HEL92.

Niemann-Pick type C disease is an inherited neurovisceral storage disorder with intracellular accumulation of cholesterol. In affected brains, many ballooned neurons are seen. Considerable nerve cell loss of unknown pathogenesis leads to neurological deterioration and dementia. Chemical examination of brains has failed to demonstrate increased levels of cholesterol. Using filipin fluorometry of neuronal cells in tissue slices, we found massive accumulation of cholesterol in neurons in four out of five human Niemann-Pick type C cases including adult patients. Neurofibrillary tangles composed of aggregates of the otherwise highly soluble protein tau were present in three Niemann-Pick type C cases and were also immunologically identical to those associated with Alzheimer's disease. However, only a thin slab of spinal cord or a tiny piece of isocortex was available for examination in the two cases without tangles. In a further semi-quantitative analysis of 576 neurons, we determined higher cholesterol content in tangle-bearing neurons than in adjacent tangle-free neurons. The association of cholesterol accumulation with neurofibrillary degeneration in Niemann-Pick type C disease and Alzheimer's disease awakens interest in the role of impaired cholesterol metabolism in the development of neurofibrillary tangles in both diseases.