Flux of fatty acids through NPC1 lysosomes

Niemann-Pick type C (NPC) is an autosomal recessive lipid storage disorder characterized by lysosomal accumulation of cholesterol and gangliosides resulting from a defect in intracellular lipid trafficking. The NPC1 gene encodes a 1278-amino acid integral membrane protein involved in the sub-cellular trafficking of lipids. The exact biological function of NPC1 remains unclear. Recent evidence suggests that NPC1 is a eukaryotic member of the RND permease family of transport proteins, which when expressed in bacteria is capable of transporting fatty acids. The goal of this project was to assess the role of NPC1 in the transport of fatty acids in primary human fibroblasts using normal fibroblasts and fibroblasts from patients with three lysosomal storage diseases: NPC, mucolipidosis IV, and Sandhoff disease. If NPC1 is a fatty acid transporter, we expect to find fatty acid accumulation only in NPC fibroblasts. We used three experimental approaches to assess the role of NPC1 as a fatty acid transporter. First, we evaluated the accumulation versus metabolism of low density lipoprotein-derived oleic acid. Second, we assessed the amount of free fatty acid present after growth in lipoprotein-containing media. Third, we assessed the cellular accumulation of acriflavine, a fluorescent substrate for a number of resistance-nodulation-cell division permease transporters. Our results indicate that fatty acid flux through NPC1-deficient lysosomes is normal.