Niemann-Pick type C disease (NP-C) is an inherited neurovisceral lipid storage disorder characterized by progressive neurodegeneration. Most cases of NP-C result from inactivating mutations of NPC1, a recently identified member of a family of genes encoding membrane-bound proteins containing putative 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 immunocytochemistry of monkey brain, NPC1 was expressed predominantly in perisynaptic astrocytic glial processes. At a subcellular level, NPC1 localized to vesicles with the morphological characteristics of lysosomes and to sites near the plasma membrane. Analysis of the temporal and spatial pattern of neurodegeneration 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 dendrites are the earliest sites of degeneration that occur well before the appearance of a neurological phenotype. Western blots of cultured human fibroblasts and monkey brain homogenates revealed NPC1 as a 165-kDa protein. NPC1 levels in cultured fibroblasts were unchanged by incubation with low density lipoproteins or oxysterols but were increased 2-to 3-fold by the drugs progesterone and U-18666A, which block cholesterol transport out of lysosomes, and by the lysosomotropic agent NH 4 Cl. These studies show that NPC1 in brain is predominantly a glial protein present in astrocytic processes closely associated with nerve terminals, the earliest site of degeneration in NP-C. Given the vesicular localization of NPC1 and its proposed role in mediating retroendocytic trafficking of cholesterol and other lysosomal cargo, these results suggest that disruption of NPC1-mediated vesicular trafficking in astrocytes may be linked to neuronal degeneration in NP-C.

Epidermal transient receptor potential vanilloid 1 in idiopathic small nerve fibre disease, diabetic neuropathy and healthy human subjects Aims: The transient receptor potential vanilloid 1 (TRPV1) plays an important role in mediating pain and heat. In painful neuropathies, intraepidermal TRPV1 nerve fibre expression is low or absent, suggesting that pain generated is not directly related to sensory nerve fibres. Recent evidence suggests that keratinocytes may act as thermal receptors via TRPV1. The aim was to investigate epidermal TRPV1 expression in patients with neuropathic conditions associated with pain. Methods and results: In a prospective study of distal small nerve fibre neuropathy (DISN; n = 13) and diabetic neuropathy (DN; n = 12) intraepidermal nerve fibre density was assessed using the pan axonal marker PGP 9.5 and epidermal TPVR1 immunoreactivity compared with controls (n = 9). Intraepidermal nerve fibres failed to show TRPV1 immunoreactivity across all groups. There was moderate and strong TRPV1 reactivity of epidermal keratinocytes in 41.8% and 6% for DISN, 32.9% and 2.9% for DN and 25.4% and 5.1% for controls, respectively. Moderate keratinocyte TRPV1 expression was significantly increased in DISN compared with controls (P = 0.01). Conclusion: Our study suggests that in human painful neuropathies, epidermal TRPV1 expression is mainly in keratinocytes.

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