No abstract

While unesterified cholesterol (C) is essential for remodeling neuronal plasma membranes, its role in certain neurodegenerative disorders remains poorly defined. Uptake of sterol from pericellular fluid requires processing that involves two lysosomal proteins, lysosomal acid lipase (LAL) that hydrolyzes C esters and NPC1. In systemic tissues, inactivation of either protein led to sterol accumulation and cell death, but in the brain, inactivation of only NPC1 caused C sequestration and neurodegeneration. When injected into the CNS of the npc1-/- mouse, HP-β-CD, a compound known to prevent this C accumulation, diffused throughout the brain and was excreted with a T½ of 6.5 h. This agent caused suppression of C synthesis, elevation of C esters, suppression of SREBP2 target genes, and activation of LXR controlled genes. These findings indicated that HP-β-CD promoted movement of the sequestered C from lysosomes to the metabolically active pool of C in the cytosolic compartment of cells in the CNS. The ED50 for this agent in the brain was ∼0.5 mg/kg, and the therapeutic effect lasted more than 7 days. Continuous infusion of HP-β-CD into the ventricular system of npc1-/- animals between 3 and 7 weeks of age normalized the biochemical abnormalities and completely prevented the expected neurodegeneration. These studies support the concept that neurons continuously acquire C from interstitial fluid to permit plasma membrane turnover and remodeling. Inactivation of NPC1 leads to lysosomal C sequestration and neurodegeneration, but this is prevented by the continuous, direct administration of HP-β-CD into the CNS.

Niemann-Pick type C1 (NPC1) disease arises from a mutation inactivating NPC1 protein that normally moves unesterified cholesterol from the late endosomal/lysosomal complex of cells to the cytosolic compartment for processing. As a result, cholesterol accumulates in every tissue of the body causing liver, lung, and CNS disease. Treatment of the murine model of this disease, the npc1 Ϫ/Ϫ mouse, s.c. with ␤-cyclodextrin (4000 mg/kg) one time each week normalized cellular cholesterol metabolism in the liver and most other organs. At the same time, the hepatic dysfunction seen in the untreated npc1 Ϫ/Ϫ mouse was prevented. The severity of cerebellar neurodegeneration also was ameliorated, although not entirely prevented, and the median lifespan of the animals was doubled. However, in contrast to these other organs, lung showed progressive macrophage infiltration with development of lipoid pneumonitis. These studies demonstrated that weekly cyclodextrin administration overcomes the lysosomal transport defect associated with the NPC1 mutation, nearly normalizes hepatic and whole animal cholesterol pools, and prevents the development of liver disease. Furthermore, this treatment slows cerebellar neurodegeneration but has little or no effect on the development of progressive pulmonary disease. (Pediatr Res 68: 309-315, 2010)

Cholesteryl Ester Storage Disease (CESD) and Wolman disease are autosomal recessive later-onset and severe infantile disorders, respectively, which result from the deficient activity of lysosomal acid lipase (LAL). LAL is encoded by LIPA (10q23.31) and the most common mutation associated with CESD is an exon 8 splice junction mutation (c.894G>A; E8SJM), which expresses only ~3–5% of normally spliced LAL. However, the frequency of c.894G>A is unknown in most populations. To estimate the prevalence of CESD in different populations, the frequencies of the c.894G>A mutation were determined in 10,000 LIPA alleles from healthy African-American, Asian, Caucasian, Hispanic and Ashkenazi Jewish individuals from the greater New York metropolitan area and 6,578 LIPA alleles from African-American, Caucasian, and Hispanic subjects enrolled in the Dallas Heart Study. The combined c.894G>A allele frequencies from the two cohorts ranged from 0.0005 (Asian) to 0.0017 (Caucasian and Hispanic), which translated to carrier frequencies of 1 in 1,000 to ~1 in 300, respectively. No African-American heterozygotes were detected. Additionally, by surveying the available literature, c.894G>A was estimated to account for 60% (95% CI: 51%–69%) of reported mutations among multi-ethnic CESD patients. Using this estimate, the predicted prevalence of CESD in the Caucasian and Hispanic populations is ~0.8 per 100,000 (~1 in 130,000; 95% CI: ~1 in 90,000 to 1 in 170,000). Conclusion These data indicate that CESD may be under-diagnosed in the general Caucasian and Hispanic populations, which is important since clinical trials of enzyme replacement therapy for LAL deficiency are currently being developed. Moreover, future studies on CESD prevalence in African and Asian populations may require full-gene LIPA sequencing to determine heterozygote frequencies since c.894G>A is not common in these racial groups.

This article is available online at http://www.jlr.org Nearly all cells in the body, including neurons of the central nervous system (CNS), take up cholesteryl ester (CE) and/or unesterifi ed cholesterol (UC) carried in various lipoproteins from the surrounding pericellular fl uid by receptor-mediated and bulk-phase endocytosis ( 1, 2 ). The sterol in these particles is processed in the late endosomal/lysosomal (E/L) compartment of cells by the sequential action of at least three proteins, lysosomal acid lipase (LAL) ( 3 ), Niemann-Pick C2 (NPC2) ( 4 ), and Niemann-Pick C1 (NPC1) ( 5 ), before being exported into the cytosolic compartment. There it joins other UC, newly synthesized from acetyl-CoA, to provide a metabolically active pool of sterol critical for normal turnover of plasma membrane cholesterol. Because UC is a hydrophobic amphipath and potentially toxic to cells, the size of this metabolically active pool is tightly monitored by two systems, the sterol regulatory element binding proteins (SREBPs) ( 6 ) and the liver X receptors (LXRs) ( 7 ), which, in turn, regulate the expression of genes controlling the uptake, synthesis, degradation, and export of UC. In this manner, the size of the metabolically active pool is kept relatively small and constant even though rates of lipoprotein uptake and sterol synthesis may vary widely.Mutations in any one of these three proteins cause accumulation of CE (LAL, Wolman disease) or UC (NPC2 or NPC1, Niemann-Pick C disease) in every tissue, which leads to cell dysfunction and death, and to a variety of clinical syndromes including disease of the liver, lungs, and Abstract Lipoprotein cholesterol taken up by cells is processed in the endosomal/lysosomal (E/L) compartment by the sequential action of lysosomal acid lipase (LAL), Niemann-Pick C2 (NPC2), and Niemann-Pick C1 (NPC1). Inactivation of NPC2 in mouse caused sequestration of unesterifi ed cholesterol (UC) and expanded the whole animal sterol pool from 2,305 to 4,337 mg/kg. However, this pool increased to 5,408 and 9,480 mg/kg, respectively, when NPC1 or LAL function was absent. The transport defect in mutants lacking NPC2 or NPC1, but not in those lacking LAL, was reversed by cyclodextrin (CD), and the ED 50 values for this reversal varied from ‫ف‬ 40 mg/kg in kidney to >20,000 mg/kg in brain in both groups. This reversal occurred only with a CD that could interact with UC. Further, a CD that could interact with, but not solubilize, UC still overcame the transport defect. These studies showed that processing and export of sterol from the late E/L compartment was quantitatively different in mice lacking LAL, NPC2, or NPC1 function. In both npc2 Ϫ / Ϫ and npc1 Ϫ / Ϫ mice, the transport defect was reversed by a CD that interacted with UC, likely at the membrane/bulk-water interface, allowing sterol to move rapidly to the export site of the E/L compartment. Press, February 2, 2011 DOI 10.1194 Abbreviations: ALT, alanine aminotransferase ; AST, aspartate aminotransferase ; bw, body weight; CD, cyclodextrin; CE, c...