Localization of Niemann-Pick C1 protein in astrocytes: Implications for neuronal degeneration in Niemann-Pick type C disease

Niemann-Pick type C disease (NP-C) is an inherited neurovisceral lipid stor age disorder characterized by progressive neurodegeneration, Most cases of NP C result from inactivating mutations of NPC1, a recently identified memb er of a family of genes encoding membrane-bound proteins containing putativ e sterol sensing domains. By using a specific antipeptide antibody to human NPC1, we have here investigated the cellular and subcellular localization and regulation of NPC1, By light and electron microscopic immunocytochemist ry of monkey brain, NPC1 was expressed predominantly in perisynaptic astroc ytic glial processes. At a subcellular level, NPC1 localized to vesicles wi th the morphological characteristics of lysosomes and to sites near the pla sma membrane. Analysis of the temporal and spatial pattern of neurodegenera tion in the NP-C mouse, a spontaneous mutant model of human NP-C, by amino- cupric-silver staining, showed that the terminal fields of axons and dendri tes are the earliest sites of degeneration that occur well before the appea rance of a neurological phenotype. Western blots of cultured human fibrobla sts and monkey brain homogenates revealed NPC1 as a 165-kDa protein. NPC1 l evels in cultured fibroblasts were unchanged by incubation with low density lipoproteins or oxysterols but were increased 2- to 3-foId by the drugs pr ogesterone and U-18666A, which block cholesterol transport out of lysosomes , and by the lysosomotropic agent NH4Cl. These studies show that NPC1 in br ain is predominantly a glial protein present in astrocytic processes closel y associated with nerve terminals, the earliest site of degeneration in NP- C, Given the vesicular localization of NPC1 and its proposed role in mediat ing retroendocytic trafficking of cholesterol and other lysosomal cargo, th ese results suggest that disruption of NPC1-mediated vesicular trafficking in astrocytes may be linked to neuronal degeneration in NP-C.