Delineation of biochemical, molecular, and physiological changes accompanying bile acid pool size restoration in Cyp7a1(-/-) mice fed low levels of cholic acid.

Cholesterol 7α-hydroxylase (CYP7A1) is the initiating and rate-limiting enzyme in the neutral pathway that converts cholesterol to primary bile acids (BA). CYP7A1-deficient (Cyp7a1(-/-)) mice have a depleted BA pool, diminished intestinal cholesterol absorption, accelerated fecal sterol loss, and increased intestinal cholesterol synthesis. To determine the molecular and physiological effects of restoring the BA pool in this model, adult female Cyp7a1(-/-) mice and matching Cyp7a1(+/+) controls were fed diets containing cholic acid (CA) at modest levels [0.

Unesterified cholesterol accumulation in late endosomes/lysosomes causes neurodegeneration and is prevented by driving cholesterol export from this compartment.

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, which hydrolyzes C esters, and NPC1 (Niemann-Pick type C1). 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.

Quantitative role of LAL, NPC2, and NPC1 in lysosomal cholesterol processing defined by genetic and pharmacological manipulations.

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 unesterified 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.

Multiple mechanisms limit the accumulation of unesterified cholesterol in the small intestine of mice deficient in both ACAT2 and ABCA1.

Cholesterol homeostasis in the enterocyte is regulated by the interplay of multiple genes that ultimately determines the net amount of cholesterol reaching the circulation from the small intestine. The effect of deleting these genes, particularly acyl CoA:cholesterol acyl transferase 2 (ACAT2), on cholesterol absorption and fecal sterol excretion is well documented. We also know that the intestinal mRNA level for adenosine triphosphate-binding cassette transporter A1 (ABCA1) increases in Acat2(-/-) mice.

Weekly cyclodextrin administration normalizes cholesterol metabolism in nearly every organ of the Niemann-Pick type C1 mouse and markedly prolongs life.

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 mouse, s.

Cyclodextrin overcomes the transport defect in nearly every organ of NPC1 mice leading to excretion of sequestered cholesterol as bile acid.

A mutation in NPC1 leads to sequestration of unesterified cholesterol in the late endosomal/lysosomal compartment of every cell culminating in the development of pulmonary, hepatic, and neurodegenerative disease. Acute administration of 2-hydroxypropyl-beta-cyclodextrin (CYCLO) rapidly overcomes this transport defect in both the 7-day-old pup and 49-day-old mature npc1(-/-) mouse, even though this compound is cleared from the body and plasma six times faster in the mature mouse than in the neonatal animal. The liberated cholesterol flows into the cytosolic ester pool, suppresses sterol synthesis, down-regulates SREBP2 and its target genes, and reduces expression of macrophage-associated inflammatory genes.

ABCA1 plays no role in the centripetal movement of cholesterol from peripheral tissues to the liver and intestine in the mouse.

This study uses the mouse to explore the role of ABCA1 in the movement of this cholesterol from the peripheral organs to the endocrine glands for hormone synthesis and liver for excretion. The sterol pool in all peripheral organs was constant and equaled 2,218 and 2,269 mg/kg, respectively, in abca1(+/+) and abca1(-/-) mice. Flux of cholesterol from these tissues equaled the rate of synthesis plus the rate of LDL-cholesterol uptake and was 49.

Reversal of defective lysosomal transport in NPC disease ameliorates liver dysfunction and neurodegeneration in the npc1-/- mouse.

Niemann-Pick type C disease is largely attributable to an inactivating mutation of NPC1 protein, which normally aids movement of unesterified cholesterol (C) from the endosomal/lysosomal (E/L) compartment to the cytosolic compartment of cells throughout the body. This defect results in activation of macrophages in many tissues, progressive liver disease, and neurodegeneration. In the npc1(-/-) mouse, a model of this disease, the whole-animal C pool expands from 2,082 to 4,925 mg/kg body weight (bw) and the hepatic C pool increases from 132 to 1,485 mg/kg bw between birth and 49 days of age.

Central nervous system: cholesterol turnover, brain development and neurodegeneration.

The average amount of cholesterol in the whole animal equals approximately 2100 mg/kg body weight, and 15% and 23% of this sterol in the mouse and human, respectively, is found in the central nervous system. There is no detectable uptake across the blood-brain barrier of cholesterol carried in lipoproteins in the plasma, even in the newborn. However, high rates of de novo cholesterol synthesis in the glia and neurons provide the sterol necessary for early brain development.

Inhibiting intestinal NPC1L1 activity prevents diet-induced increase in biliary cholesterol in Golden Syrian hamsters.

Niemann-Pick C1-like 1 (NPC1L1) facilitates the uptake of sterols into the enterocyte and is the target of the novel cholesterol absorption inhibitor, ezetimibe. These studies used the Golden Syrian hamster as a model to delineate the changes in the relative mRNA expression of NPC1L1 and other proteins that regulate sterol homeostasis in the enterocyte during and following cessation of ezetimibe treatment and also to address the clinically important question of whether the marked inhibition of cholesterol absorption alters biliary lipid composition. In hamsters fed a low-cholesterol, low-fat basal diet, the abundance of mRNA for NPC1L1 in the small intestine far exceeded that in other regions of the gastrointestinal tract, liver, and gallbladder.

GM2/GD2 and GM3 gangliosides have no effect on cellular cholesterol pools or turnover in normal or NPC1 mice.

These studies investigated the role of gangliosides in governing the steady-state concentration and turnover of unesterified cholesterol in normal tissues and in those of mice carrying the NPC1 mutation. In animals lacking either GM2/GD2 or GM3 synthase, tissue cholesterol concentrations and synthesis rates were normal in nearly all organs, and whole-animal sterol pools and turnover also were not different from control animals. Mice lacking both synthases, however, had small elevations in cholesterol concentrations in several organs, and the whole-animal cholesterol pool was marginally elevated.

Liver X receptor activation enhances cholesterol loss from the brain, decreases neuroinflammation, and increases survival of the NPC1 mouse.

Although cholesterol is a major component of the CNS, there is little information on how or whether a change in sterol flux across the blood-brain barrier might alter neurodegeneration. In Niemann-Pick type C (NPC) disease, a mutation in NPC1 protein causes unesterified cholesterol to accumulate in the lysosomal compartment of every cell, including neurons and glia. Using the murine model of this disease, we used genetic and pharmacologic approaches in an attempt to alter cholesterol homeostasis across the CNS.

Genetic variations and treatments that affect the lifespan of the NPC1 mouse.

Niemann-Pick type C (NPC) disease is a multisystem disorder caused primarily by a mutation in the npc1 gene. These studies evaluated the effect of genetic background, deletion of additional genes, and administration of several agents on the age at death in a murine model of this disorder. Such factors as differing strain background or genetic drift within a given background in the npc1(-/-) mouse significantly altered the age at death and the degree of organ disease.

Receptor-mediated and bulk-phase endocytosis cause macrophage and cholesterol accumulation in Niemann-Pick C disease.

These studies explored the roles of receptor-mediated and bulk-phase endocytosis as well as macrophage infiltration in the accumulation of cholesterol in the mouse with Niemann-Pick type C (NPC) disease. Uptake of LDL-cholesterol varied from 514 microg/day in the liver to zero in the central nervous system. In animals lacking LDL receptors, liver uptake remained about the same (411 microg/day), but more cholesterol was taken up in extrahepatic organs.

Lysosomal unesterified cholesterol content correlates with liver cell death in murine Niemann-Pick type C disease.

Niemann-Pick type C (NPC) disease is a multisystem disorder resulting from mutations in the NPC1 gene that encodes a protein involved in intracellular cholesterol trafficking. Significant liver dysfunction is frequently seen in patients with this disease. The current studies used npc1 mutant mice to investigate the association between liver dysfunction and unesterified cholesterol accumulation, a hallmark of NPC disease.

Cholesterol substrate pools and steroid hormone levels are normal in the face of mutational inactivation of NPC1 protein.

Mutational inactivation of NPC1 largely blocks the movement of LDL-derived cholesterol from the lysosome to the metabolically active, cytosolic pool of sterol that is the substrate for steroid hormone production. Such a block might, in theory, lead to deficiencies in circulating levels of testosterone, progesterone, and corticosterone. However, there are at least two other sources for cellular cholesterol, de novo synthesis and scavenger receptor class B type I-mediated uptake of HDL cholesteryl ester (CE).

Cholesterol accumulation and liver cell death in mice with Niemann-Pick type C disease.

Niemann-Pick type C (NPC) disease develops as a result of mutations in the NPC1 gene that encodes a protein involved in the net movement of unesterified cholesterol from the late endosomal/lysosomal compartment to the metabolically active pool of sterol in the cytosol of virtually every cell in the body. Although early publications emphasized the neurodegeneration occurring in children with this mutation, more recent clinical information suggests that serious liver disease also is an important part of this syndrome. These studies, therefore, were undertaken to characterize the liver dysfunction seen in mice with this same mutation.

Niemann-Pick C1 expression is not regulated by the amount of cholesterol flowing through cells in the mouse.

The Niemann-Pick C1 (NPC1) protein functions to regulate the transport of cholesterol from late endosomes/lysosomes to other cellular compartments after lipoprotein uptake through the coated-pit pathway. The present study examines the relative expression of NPC1 mRNA and NPC1 protein in different tissues of the mouse in relation to the uptake of total cholesterol carried in chylomicron remnants (CMr-TC), low density lipoproteins (LDL-TC), cholesteryl ester carried in high density lipoproteins (HDL-CE), and cholesterol synthesis. Results from this study demonstrate that the highest relative expression of NPC1 is in the liver, which is also the tissue with the highest uptake of CMr-TC, LDL-TC, HDL-CE, and cholesterol synthesis.

Molecular, anatomical, and biochemical events associated with neurodegeneration in mice with Niemann-Pick type C disease.

In Niemann-Pick type C (NPC) disease, cholesterol associated with either apoE or apoB100 is taken up by cells in all tissues, including the central nervous system, through clathrin-coated pits and becomes trapped in late endosomes and lysosomes. This study defines the functional, biochemical, and molecular events that ensue as nerve cell death occurs. In mice homozygous for a mutation in NPC1, neuromuscular dysfunction begins at 5 weeks and death occurs at 13 weeks of age.

Delineation of molecular changes in intrahepatic cholesterol metabolism resulting from diminished cholesterol absorption.

The absorption of cholesterol by the small intestine is a major route for the net entry of cholesterol into the body and can therefore affect the plasma low density lipoprotein-cholesterol (LDL-C) concentration. These studies used ezetimibe, a potent inhibitor of cholesterol absorption, to delineate the biochemical and molecular changes in intrahepatic metabolism and biliary lipid secretion when there is a major reduction in chylomicron cholesterol delivery to the liver. In female LDL receptor (LDLR)-deficient (LDLR-/-) mice fed a basal diet containing ezetimibe (0-10 mg/day/kg body weight), cholesterol absorption was reduced up to 91%, fecal neutral sterol excretion was increased up to 4.

ACAT2 deficiency limits cholesterol absorption in the cholesterol-fed mouse: impact on hepatic cholesterol homeostasis.

Acyl CoA:cholesterol acyltransferase (ACAT) 2 is the major cholesterol-esterifying enzyme in mouse enterocytes and hepatocytes. Male ACAT2(+/+) and ACAT2(-/ -) mice were fed chow containing added cholesterol (0%-0.500% w/w) for 24 days.

Thematic review series: brain Lipids. Cholesterol metabolism in the central nervous system during early development and in the mature animal.

Unesterified cholesterol is an essential structural component of the plasma membrane of every cell. During evolution, this membrane came to play an additional, highly specialized role in the central nervous system (CNS) as the major architectural component of compact myelin. As a consequence, in the human the mean concentration of unesterified cholesterol in the CNS is higher than in any other tissue (approximately 23 mg/g).

Ontogenesis and regulation of cholesterol metabolism in the central nervous system of the mouse.

These studies characterized the ontogenesis and regulation of cholesterol turnover in the central nervous system (CNS) of mice. During the first 3 weeks after birth, the CNS grew rapidly and equaled 5% of body weight. The cholesterol pool in this tissue expanded at a rate of 0.

Sterol absorption by the small intestine.

Purpose Of Review: Cholesterol absorption is a selective process in that plant sterols and other non-cholesterol sterols are absorbed poorly or not at all. Recent research on the sterol efflux pumps adenosine triphosphate-binding cassette transporter G5 and adenosine triphosphate-binding cassette transporter G8 has not only provided an explanation for this selectivity, but also, together with the discovery of a new class of cholesterol absorption inhibitor, has yielded new insights into the mechanisms that potentially regulate the flux of cholesterol across the enterocyte. This review discusses these recent developments and their importance to the regulation of whole body cholesterol homeostasis.

Quantitation of two pathways for cholesterol excretion from the brain in normal mice and mice with neurodegeneration.

Although the pool of cholesterol in the adult central nervous system (CNS) is large and of constant size, little is known of the process(es) involved in regulation of sterol turnover in this pool. In 7-week-old mice, net excretion of cholesterol from the brain equaled 1.4 mg/day/kg body weight, and from the whole animal was 179 mg/day/kg.