P4–061: Niemann–Pick type C as model to study amyloidogenesis

Niemann–Pick type C (NPC) disease is an inherited lysosomal storage disorder caused by mutations within the NPC1 or NPC2 genes. NPC1 encodes a cholesterol transporter in a late endosomal compartment, and NPC2 (also known as HE1) encodes a lysosomal cholesterol–binding protein. Late infantile and juvenile forms of NPC manifest as a neurological disease, characterized by cerebellar ataxia, bulbar dysfunction, and dementia. At the cellular level, NPC develops from a failure of cholesterol trafficking throughout the endosomal/lysosomal system, leading to accumulation of unesterified cholesterol in an aberrantly enlarged late endosome/lysosome organelle. Similar to Alzheimer's disease (AD), NPC presents a phenotype of aberrant amyloid precursor protein (APP) trafficking and increased Aβ generation within the endosomal system, and it has been proposed that this phenotype may be linked to abnormal lipid raft (LR) homeostasis, since LRs are the sites of generation of secreted Aβ, and NPC1 deficiency leads to increased association of endocytosed cholesterol with lipid rafts. To determine the role of cholesterol homeostasis in amyloidogenesis using Niemann–Pick type C as a model. We have used human skin fibroblasts from Niemann–Pick type C patients carrying NPC1 mutations as well as cortical neurons from an NPC mouse model deficient in NPC1 function to measure APP trafficking parameters and amyloid Aβ generation in the presence and absence of NPC1 function. We have found cholesterol–dependent differences in amyloidogenesis in cells with and without functional NPC1. We propose that the endosomal dysfunction and impaired intracellular cholesterol trafficking associated with NPC1 deficiency may lead to abnormal APP internalization via lipid rafts resulting in increased amyloidogenesis. We discuss our results in this context.