Pentchev et al. (1985) were prompted to study cholesterol esterification in Niemann-Pick disease because of the similar
phenotypic findings in a murine mutation affecting cholesterol esterification . They found esterification
to be normal in 6 type A and 8 type B Niemann-Pick cell lines. In striking contrast, all 24 type C Niemann-Pick cell lines
showed a major block in cholesterol esterification. Fluorescent microscopy showed that type C cells grown in fetal calf
serum store much unesterified cholesterol. The state of heterozygotes may help elucidate whether this is a primary defect.
The partial expression of the esterification defect (50% of normal) in heterozygous mice indicates that it is the primary fault.
NCBI Summary:
NPC1 was identified as the gene that when mutated, results in Niemann-Pick C disease. NPC1 encodes a putative integral membrane protein containing motifs consistent with a role in intracellular transport of cholesterol to post-lysosomal destinations.
General function
Comment
NPC1 is a member of a family of genes encoding membrane-bound proteins containing putative sterol sensing domains. By
use of a specific antipeptide antibody to human NPC1, Patel et al. (1999) investigated the cellular and subcellular
localization and regulation of NPC1 in monkey brain. By light and electron microscopic immunocytochemistry, NPC1 was
expressed predominantly in presynaptic astrocytic glial processes. At a subcellular level, NPC1 localized to vesicles with
the morphologic characteristics of lysosomes and to sites near the plasma membrane. Analysis of the temporal and spatial
pattern of neurodegeneration in the NPC mouse, a spontaneous mutant model of human NPC, 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 neurologic phenotype. Western blots of cultured human fibroblasts and monkey brain homogenates revealed
NPC1 as a 165-kD 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 NPC.
Given the vesicular localization of NPC1 and its proposed role in mediating retroendocytic trafficking of cholesterol and
other lysosomal cargo, these results suggested that disruption of NPC1-mediated vesicular trafficking in astrocytes may be
linked to neuronal degeneration in NPC.
Cellular localization
Cytoplasmic, lysosome
Comment
Ovarian function
Steroid metabolism
Comment
Niemann-Pick type C (NPC) disease is an inherited lipid storage disorder that affects the viscera and
central nervous system. A characteristic feature of NPC cells is the lysosomal accumulation of low
density lipoprotein-derived cholesterol.
Watari H, et al 1999 examined the ability of wild-type NPC1
and NPC1 mutants to correct the excessive lysosomal storage of low density lipoprotein-derived
cholesterol in a model cell line displaying the NPC cholesterol-trafficking defect (CT60 Chinese
hamster ovary cells). CT60 cells transfected with human wild-type NPC1 contained immunoreactive
proteins of 170 and 190 kDa localized to the lysosomal/endosomal compartment. Wild-type NPC1
protein corrected the NPC cholesterol-trafficking defect in the CT60 cells. Mutation of conserved
cysteine residues in the NPC1 N terminus to serine residues resulted in proteins targeted to lysosomal
membranes encircling cholesterol-laden cores, whereas deletion of the C-terminal 4-aa residues
containing the LLNF lysosome-targeting motif resulted in the expression of protein localized to the
endoplasmic reticulum. None of these mutant NPC1 proteins corrected the NPC cholesterol-trafficking
defect in CT60 cells.
Expression regulated by
Comment
Ovarian localization
Granulosa, Luteal cells
Comment
Watari H et al 2000 employed cytochemical and biochemical methods to
explore the expression, regulation, and function of the Niemann-Pick C1 protein
(NPC1) in human granulosa-lutein cells. NPC1 was localized in a subset of
lysosome-associated membrane glycoprotein 2 (LAMP-2)-positive vesicles. By
analyzing the sensitivity of NPC1 N-linked oligosaccharide chains to glycosidases
and neuraminidase, evidence was obtained for movement of nascent NPC1 from
the endoplasmic reticulum through the medial and trans compartments of the Golgi
apparatus prior to its appearance in cytoplasmic vesicles. NPC1 protein content
and the morphology and cellular distribution of NPC1-containing vesicles were
not affected by treatment of the granulosa-lutein cells with 8-Br-cAMP, which
stimulates cholesterol metabolism into progesterone. Incubation
of granulosa-lutein cells with low-density lipoprotein (LDL) in the presence of the
hydrophobic amine, U18666A, caused accumulation of free cholesterol in
granules, identified by filipin staining, that contained LAMP-2 and NPC1. These
granules also stained for neutral lipid with Nile red, reflecting accumulation of
LDL-derived cholesterol esters. LDL-stimulated progesterone synthesis was
completely blocked by U18666A, leaving steroid output at levels similar to those
of cells incubated in the absence of LDL. The hydrophobic amine also blocked the
LDL augmentation of 8-Br-cAMP-stimulated progesterone synthesis, reducing
steroid production to levels seen in cells stimulated with 8-Br-cAMP in the
absence of LDL. Steroidogenesis recovered after U18666A was removed from the
culture medium. U18666A treatment caused a 2-fold or more increase in NPC1
protein and mRNA levels, suggesting that disruption of NPC1's function activates
a compensatory mechanism resulting in increased NPC1 synthesis. It was conclude
that the NPC1 compartment plays an important role in the trafficking of
LDL-derived substrate in steroidogenic cells; that NPC1 expression is
up-regulated when NPC1 action is blocked; and that the NPC1 compartment can
be functionally separated from other intracellular pathways contributing substrate
for steroidogenesis.
Follicle stages
Antral, Preovulatory, Corpus luteum
Comment
Phenotypes
Mutations
2 mutations
Species: mouse
Mutation name: None
type: naturally occurring fertility: None Comment: Two independently derived mutant mouse colonies played a pivotal role in delineating the biochemical basis of NPC.
One was a BALB/c mouse presenting clinical and biochemical features of NPC (Pentchev et al., 1984) ; the other was
the C57BL/Ks mouse characterized as a sphingomyelinosis because of attenuated sphingomyelinase activity and excess
sphingomyelin accumulation (Miyawaki et al., 1986 .
Species: mouse
Mutation name: None
type: null mutation fertility: infertile - non-ovarian defect Comment:Gevry NY, et al reported that aberrant intracellular cholesterol transport disrupts pituitary and ovarian function.
Cholesterol is imported and processed to provide substrate for ovarian steroidogenesis. The Niemann-Pick type C-1 gene codes for a glycoprotein that processes low density lipoprotein (LDL)-imported cholesterol. Mutation of this gene causes marked impairment of export of LDL-derived cholesterol from endosomes, and consequent lysosomal accumulation of the sterol. The Balb/c npc(nih-/-) mouse line, bearing spontaneous mutation of the NPC-1 gene, provides a model for investigation of aberrant endosomal cholesterol transfer in the ovary. Female homozygote mutant mice are infertile, with underdeveloped ovarian follicles, reduced steroidogenesis, no ovulation and no corpora lutea. Mutant ovaries transplanted under wild type kidney capsules display both ovulation and formation of corpora lutea. Gonadotropin treatment induces ovulation and restores expression of steroidogenic proteins. Pituitary glands of mutants are hypoplastic, and prolactin expression is dramatically reduced compared with wild type mice. Both long and short splice variants of the dopamine-D2 receptors are overexpressed in the pituitary of Balb/c npc(nih-/-)mice. Chronic treatment of mutant mice with estradiol 17beta restores pituitary volume, prolactin expression and folliculogenetic capability. We conclude that inactivating mutation of Niemann Pick-C-1 perturbs the hypothalamic-pituitary-ovarian feedback loop. Reduced estrogens attenuate prolactin expression and alter gonadotropin secretion patterns and interfere with normal ovarian follicular development and ovulation.