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 proliferator-activated receptor delta (PPARdelta) activation decreased NPC1L1 mRNA levels and cholesterol trafficking to the endoplasmic reticulum, suggesting that 22:6 may act through PPARdelta. 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 PPARdelta. Moreover, a diet enriched in n-3 fatty acids decreases the gene expression of NPC1L1 in duodenum and jejunum of hamster.
Highlights
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 cells incubated with micelles containing 18:1, cells incubated with 22:6 contained significantly less labeled cholesteryl esters, suggesting that compared with 18:1, 22:6 caused less plasma membrane cholesterol to influx to the endoplasmic reticulum
Compared with control cells incubated without the peroxisome proliferator-activated receptor y (PPARy) agonist, cells incubated with GW501516 contained 25% less labeled cholesteryl esters (P, 0.01; n 5 6 dishes), suggesting that PPARy activation interfered with the trafficking of plasma membrane cholesterol to the endoplasmic reticulum
Summary
The apical medium was replaced with 1 ml of cold DMEM containing 1% delipidated fetal calf serum and 2.5 mCi of [3H]cholesterol, and cells were incubated for 2 h at 4jC to label plasma membrane cholesterol. To address whether 22:6 alters the influx of plasma membrane cholesterol to the endoplasmic reticulum, cells were first incubated for 24 h with 5 mM taurocholate micelles with or without 0.25 mM 18:1 or 22:6. The amount of labeled cholesteryl esters was determined to estimate the amount of plasma membrane cholesterol reaching ACAT in the endoplasmic reticulum.
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