ABSTRACT Niemann-Pick disease type C (NPC) is an invariably fatal autosomal recessive lipid storage disorder affecting all ages. Patients develop a clinically heterogeneous phenotype that includes severe, progressive neurodegeneration, hepatomegaly, and early death. NPC is commonly caused by loss-of-function mutations in the NPC1 gene (95% of cases), encoding a multipass transmembrane glycoprotein required for exporting unesterified cholesterol from late endosomes and lysosomes. Despite our emerging understanding of the role of NPC1 in intracellular cholesterol trafficking, a diagnosis of NPC remains particularly bleak. There are currently no FDA-approved disease modifying therapies and patients most often die in childhood, reflecting both gaps in our current knowledge of disease pathogenesis and a significant unmet medical need. Our long-term goal is to contribute toward the development of disease-modifying therapies for NPC patients. The next step in attaining this goal is to pursue the overall objective of this application: to define critical targets in CNS disease pathogenesis that can be exploited by drug development efforts. Our central hypothesis is that NPC1 deficiency causes toxicity in both neurons and oligodendrocytes that underlies NPC neuropathology. Moreover, we hypothesize that this toxicity can be rescued by novel therapeutic strategies aimed at reducing the intracellular lipid storage that is characteristic of the disease or by correcting the misfolding of mutant NPC1 protein. These notions are based upon robust preliminary data supporting our model of NPC pathogenesis and the use of innovative therapeutic approaches to rescue disease phenotypes. We will use genetic, biochemical, histological, and phenotypic analyses to: establish the extent to which neuronal lipid storage and toxicity are rescued by optimized synthetic HDL nanoparticles (Aim 1); determine the role of oligodendrocyte lineage cells in NPC neuropathology (Aim 2); and establish effects of proteostasis regulators in humanized NPC1 model systems (Aim 3). These studies are expected to establish that targeting intracellular lipid storage using optimized sHDLs and modulating mutant NPC1 proteostasis will ameliorate disease phenotypes. Moreover, we expect to demonstrate an important, yet under-studied role for oligodendrocyte lineage cells in NPC neuropathology.