Regulation of intestinal NPC1L1 expression by dietary fish oil and docosahexaenoic acid

Abstract

To address the effect of the n-3 fatty acid, docosahexaenoic acid (22:6), on proteins that play a role in cholesterol absorption, CaCo-2 cells were incubated with taurocholate micelles alone or micelles containing 22:6 or oleic acid (18:1). Compared with controls or 18:1, 22:6 did not interfere with the cellular uptake of micellar cholesterol. Apical cholesterol efflux was enhanced in cells incubated with 22:6. Cholesterol trafficking from the plasma membrane to the endoplasmic reticulum was decreased by 22:6. 22:6 decreased Niemann-Pick C1-Like 1 (NPC1L1) protein and mRNA levels without altering gene or protein expression of ACAT2, annexin-2, caveolin-1, or ABCG8. Peroxisome proliferatoractivated receptor d (PPARd) activation decreased NPC1L1 mRNA levels and cholesterol trafficking to the endoplasmic reticulum, suggesting that 22:6 may act through PPARd. Compared with hamsters fed a control diet or olive oil (enriched 18:1), NPC1L1 mRNA levels were decreased in duodenum and jejunum of hamsters ingesting fish oil (enriched 22:6). In an intestinal cell, independent of changes in ABCG8 expression, 22:6 increases the apical efflux of cholesterol. 22:6 interferes with cholesterol trafficking to the endoplasmic reticulum by the suppression of NPC1L1, perhaps through the activation of PPARd. Moreover, a diet enriched in n-3 fatty acids decreases the gene expression of NPC1L1 in duodenum and jejunum of hamster. Hypercholesterolemia is a significant risk factor for atherosclerosis. In addition to de novo cholesterol synthesis, cholesterol derived from the diet also contributes to the amount of cholesterol circulating in plasma (1). Moreover, reducing the intestinal absorption of dietary and biliary cholesterol will decrease plasma cholesterol levels (2). It is clear, therefore, that the intestine plays an important role in maintaining total body cholesterol homeostasis. During the past several years, numerous proteins, including ACAT2, caveolin-1, annexin-2, scavenger receptor class B type I, ABCG5, and ABCG8, have been implicated in facilitating/regulating cholesterol absorption by the intestinal absorptive cell (3-8). None of these proteins, however, has turned out to be the "putative" cholesterol transporter in the intestine, as individually these proteins are not essential for the uptake of luminal cholesterol by the absorptive cell (5, 7, 9-11). In the past few years, Altmann and his group (12-15) have described a plasma membrane transporter, Niemann-Pick C1-Like 1 (NPC1L1), which has been shown to play a critical role in the absorption of cholesterol by the intestine. Mice lacking NPC1L1 have a marked reduction in cholesterol absorption and do not get hypercholesterolemic in response to a high-cholesterol diet. The level of gene expression of NPC1L1 along the length of the small intestine in mice parallels the efficiency of cholesterol absorption, with the highest levels found in proximal intestine (duodenum and jejunum) and less expression found in distal intestine (ileum). NPC1L1 also contains an extrac...

NPC1L1 and SR‐BI are Involved in Intestinal Cholesterol Absorption from Small‐Size Lipid Donors

“…This clearly means that efficient intestinal CL absorption requires both mixed micelles and intestinal CL transporters. The main reason for this is that enterocytes have an apical brush-border membrane made of many microvilli where the CL transporters (NPC1L1 and SR-BI) are present in Caco-2 cells [1,10,11]. The space between the microvilli ranges from 5 to 20 nm.…”

“…However, its involvement in intestinal CL absorption is not fully understood and its cell surface and/or intracellular localization is still debated. While some reports indicate that NPC1L1 is located at the cell surface in animal enterocytes [7][8][9] and Caco-2 cells [1,10,11], others describe NPC1L1 as being an intracellular [12], endosomal protein [5]. Moreover, very recent studies have confirmed the presence of NPC1L1 in both regions [1,13,14].…”

Madin-Darby Canine Kidney II Cells: A Pharmacologically Validated System for NPC1L1-Mediated Cholesterol Uptake

“…We used binding of [ 3 H]AS to explore surface expression of NPC1L1 in the widely used CaCo-2 (Davies et al, 2005;During et al, 2005;Garmy et al, 2005;van der Veen et al, 2005;Duval et al, 2006;Sané et al, 2006;Alrefai et al, 2007;Field et al, 2007;Mathur et al, 2007;Yamanashi et al, 2007) and HepG2 (Davies et al, 2005;Yu et al, 2006) cells. However, we found that under basal conditions, there was not detectable surface expression of NPC1L1 in these cell lines.…”

“…Therefore, researchers have developed a variety of alternative systems, including brush-border membrane vesicles from enterocytes (Knöpfel et al, 2007;Labonté et al, 2007), cell lines heterologously expressing recombinant NPC1L1 (Davies et al, 2005;Iyer et al, 2005;Yu et al, 2006;Brown et al, 2007;Hawes et al, 2007), cell lines endogenously expressing NPC1L1, such as CaCo-2 (Davies et al, 2005;During et al, 2005;Garmy et al, 2005;van der Veen et al, 2005;Duval et al, 2006;Sané et al, 2006;Alrefai et al, 2007;Field et al, 2007;Mathur et al, 2007;Yamanashi et al, 2007) and HepG2 (Davies et al, 2005;Yu et al, 2006), and functional complementation in Caenorhabditis elegans (Smith and Levitan, 2007). By overexpressing NPC1L1 in McArdles RH7777 hepatoma cells (Yu et al, 2006) and CaCo-2 enterocyte-like cells (Yamanashi et al, 2007), it has been possible to establish assays with which to monitor a component of EZEsensitive cholesterol influx (Yu et al, 2006;Yamanashi et al, 2007).…”

TNF-α decreases ABCA1 expression and attenuates HDL cholesterol efflux in the human intestinal cell line Caco-2

“…nih.gov/). The sequences for the other primers have been described previously ( 30,31 ). The values were normalized using 18S rRNA as endogenous internal standard.…”