BACKGROUND: Niemann-Pick type C1 disease (NPC1) is a rare progressive 
neurodegenerative disorder caused by mutations in the NPC1 gene. In this 
lysosomal storage disorder the intracellular transport and sequestration of 
several lipids like cholesterol is severely impaired, resulting in an 
accumulation of lipids in late endosomes and lysosomes. The neurological 
manifestation of the disease is caused by dysfunction and cell death in the 
central nervous system. Several animal models were used to analyze the impaired 
pathways. However, the underlying pathogenic mechanisms are still not completely 
understood and the genetic variability in humans cannot be reflected in these 
models. Therefore, a human model using patient-specific induced pluripotent stem 
cells provides a promising approach.
METHODS: We reprogrammed human fibroblasts from a NPC1 patient and a healthy 
control by retroviral transduction with Oct4, Klf4, Sox2 and c-Myc. The obtained 
human induced pluripotent stem cells (hiPSCs) were characterized by 
immunocytochemical analyses. Neural progenitor cells were generated and patch 
clamp recordings were performed for a functional analysis of derived neuronal 
cells. Filipin stainings and the Amplex Red assay were used to demonstrate and 
quantify cholesterol accumulation.
RESULTS: The hiPSCs expressed different stem cell markers, e.g. Nanog, Tra-1-81 
and SSEA4. Using the embryoid body assay, the cells were differentiated in cells 
of all three germ layers and induced teratoma in immunodeficient mice, 
demonstrating their pluripotency. In addition, neural progenitor cells were 
derived and differentiated into functional neuronal cells. Patch clamp 
recordings revealed voltage dependent channels, spontaneous action potentials 
and postsynaptic currents. The accumulation of cholesterol in different tissues 
is the main hallmark of NPC1. In this study we found an accumulation of 
cholesterol in fibroblasts of a NPC1 patient, derived hiPSCs, and neural 
progenitor cells, but not in cells derived from fibroblasts of a healthy 
individual. These findings were quantified by the Amplex Red assay, 
demonstrating a significantly elevated cholesterol level in cells derived from 
fibroblasts of a NPC1 patient.
CONCLUSIONS: We generated a neuronal model based on induced pluripotent stem 
cells derived from patient fibroblasts, providing a human in vitro model to 
study the pathogenic mechanisms of NPC1 disease.