Inactivation of NPC1L1 Causes Multiple Lipid Transport Defects and Protects against Diet-induced Hypercholesterolemia
ABSTRACT NPC1L1, a recently identified relative of Niemann-Pick C1, was characterized to determine its subcellular location and potential
function(s). NPC1L1 was highly expressed in HepG2 cells and localized in a subcellular vesicular compartment rich in the small
GTPase Rab5. mRNA expression profiling revealed significant differences between mouse and man with highest expression found
in human liver and significant expression in the small intestine. In contrast, liver expression in mouse was extremely low
with mouse small intestine exhibiting the highest NPC1L1 expression. A mouse knock-out model of NPC1L1 was generated and revealed
that mice lacking a functional NPC1L1 have multiple lipid transport defects. Surprisingly, lack of NPC1L1 exerts a protective
effect against diet-induced hyperlipidemia. Further characterization of cell lines generated from wild-type and knock-out
mice revealed that in contrast to wild-type cells, NPC1L1 cells exhibit aberrant plasma membrane uptake and subsequent transport
of various lipids, including cholesterol and sphingolipids. Furthermore, lack of NPC1L1 activity causes a deregulation of
caveolin transport and localization, suggesting that the observed lipid transport defects may be the indirect result of an
inability of NPC1L1 null cells to properly target and/or regulate caveolin expression.
- SourceAvailable from: Saeed Alqahtani
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- "In human tissues, NPC1L1 is predominantly expressed in the liver with detectable levels in lung, heart, brain, pancreas, and kidney, ranging in expression from about 0.5% to 3% of liver expression (Davies et al., 2005). Whereas, in the small intestine, NPClL1 is expressed at 1–4% of its level in the liver with highest expression in the proximal segment (Davies et al., 2005). To our knowledge, our study is the first to discuss the relationship between orlistat and NPC1L1. "
ABSTRACT: The known mechanism by which orlistat decreases the absorption of dietary cholesterol is by inhibition of intestinal lipases. The aim of this study was to investigate the ability of orlistat to limit cholesterol absorption by inhibition of the cholesterol transport protein Niemann-Pick C1-like 1 (NPC1L1) as another mechanism of action. In situ rat intestinal perfusion studies were conducted to study the effect of orlistat on jejunal cholesterol absorption. Inhibition kinetic parameters were calculated from in vitro inhibition studies using Caco2 and NPC1L1 transfected cell lines. The in situ studies demonstrated that intestinal perfusion of orlistat (100µM) was able to reduce cholesterol absorption by three-fold when compared to control (i.e. in the absence of orlistat, P<0.01). In vitro studies using Caco2 cells demonstrated orlistat to reduce the cellular uptake of cholesterol by 30%. Additionally, orlistat reduced the cellular uptake of cholesterol in dose dependent manner in NPC1L1 transfected cell line with an IC50=1.2µM. Lineweaver-Burk plot indicated a noncompetitive inhibition of NPC1L1 by orlistat. Beside the already established mechanism by which orlistat reduces the absorption of cholesterol, we demonstrated for the first time that orlistat limits cholesterol absorption by the inhibition of NPC1L1 transport protein. Copyright © 2015. Published by Elsevier B.V.European journal of pharmacology 06/2015; 762. DOI:10.1016/j.ejphar.2015.05.060 · 2.53 Impact Factor
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- "Several studies demonstrate that NPC1L1 has substrate specificity on sterol absorption. In NPC1L1 deficient mice [5,19,20], ezetimibe treated mice  and patients with cholesterolemia or sitosterolemia [30,31], sterols are significantly decreased. In cell culture system, phytosterols show the decrease of NPC1L1 internalization and uptake compared to cholesterol [16,17]. "
ABSTRACT: Polytopic transmembrane protein, Niemann-Pick C1-Like 1 (NPC1L1) is localized at the apical membrane of enterocytes and the canalicular membrane of hepatocytes. It mediates intestinal cholesterol absorption and prevents extensive loss of cholesterol by transporting biliary cholesterol into hepatocytes. NPC1L1 is a molecular target of ezetimibe, an agent for hypercholesterolemia. Recently, NPC1L1 inhibition has been shown to prevent metabolic disorders such as fatty liver disease, obesity, diabetes, and atherosclerosis. In this review, the identification and characterization of NPC1L1, NPC1L1-dependent cholesterol transport, the relationship with pathogenesis of metabolic disease and its newly introduced function for virus entry are discussed.Diabetes & metabolism journal 08/2013; 37(4):240-8. DOI:10.4093/dmj.2013.37.4.240
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- "Obesity and deposition of lipid in visceral adipose tissue does not occur, likewise insulin resistance does not develop , . Once in the liver, fatty acids from chylomicron remnant absorption may directly contribute to pathogenesis and cholesterol will induce triglyceride and fatty acid production through LXR responsive genes – Our data demonstrating steatosis without inflammation in Ccr2−/− and Cd44−/− mice are likely the result of the lipid source being directly related to dietary absorption thereby negating the role of the immune system on hepatic lipid accumulation. We did not specifically examine hepatic lipids biochemically and cannot rule out the possibility that there are biochemical differences in hepatic lipid content, but our data do demonstrate that Ccr2−/− and Cd44−/− mediated protection may occur independently of histological protection from steatosis. "
ABSTRACT: Non-alcoholic fatty liver disease (NAFLD) is a common disease with a spectrum of presentations. The current study utilized a lithogenic diet model of NAFLD. The diet was fed to mice that are either resistant (AKR) or susceptible (BALB/c and C57BL/6) to hepatitis followed by molecular and flow cytometric analysis. Following this, a similar approach was taken in congenic mice with specific mutations in immunological genes. The initial study identified a significant and profound increase in multiple ligands for the chemokine receptor CCR2 and an increase in CD44 expression in susceptible C57BL/6 (B6) but not resistant AKR mice. Ccr2(-/-) mice were completely protected from hepatitis and Cd44(-/-) mice were partially protected. Despite protection from inflammation, both strains displayed similar histological steatosis scores and significant increases in serum liver enzymes. CD45(+)CD44(+) cells bound to hyaluronic acid (HA) in diet fed B6 mice but not Cd44(-/-) or Ccr2(-/-) mice. Ccr2(-/-) mice displayed a diminished HA binding phenotype most notably in monocytes, and CD8(+) T-cells. In conclusion, this study demonstrates that absence of CCR2 completely and CD44 partially reduces hepatic leukocyte recruitment. These data also provide evidence that there are multiple redundant CCR2 ligands produced during hepatic lipid accumulation and describes the induction of a strong HA binding phenotype in response to LD feeding in some subsets of leukocytes from susceptible strains.PLoS ONE 06/2013; 8(6):e65247. DOI:10.1371/journal.pone.0065247 · 3.23 Impact Factor