Asymmetrical regulation of scavenger receptor class B type I by apical and basolateral stimuli using Caco‐2 cells

Abstract

Cholesterol uptake and the mechanisms that regulate cholesterol translocation from the intestinal lumen into enterocytes remain for the most part unclear. Since scavenger receptor class B type I (SR-BI) has been suggested to play a role in cholesterol absorption, we investigated cellular SR-BI modulation by various potential effectors administered in both apical and basolateral sides of Caco-2 cells. With differentiation, Caco-2 cells increased SR-BI protein expression. Western blot analysis showed the ability of cholesterol and oxysterols in both cell compartments to reduce SR-BI protein expression. Among the n-3, n-6, and n-9 fatty acid families, only eicosapentaenoic acid was able to lower SR-BI protein expression on both sides, whereas apical alpha-linolenic acid decreased SR-BI abundance and basolateral arachidonic acid (AA) raised it. Epidermal growth factor and growth hormone, either in the apical or basolateral medium, diminished SR-BI cellular content, while insulin displayed the same effect only on the basolateral side. In the presence of proinflammatory agents (LPS, TNF-alpha, IFN-gamma), Caco-2 cells exhibited differential behavior. SR-BI was downregulated by lipopolysaccharide on both sides. Finally, WY-14643 fibrate diminished SR-BI protein expression when it was added to the apical medium. Biotinylation studies in response to selected stimuli revealed that regulatory modifications in SR-BI protein expression occurred for the most part at the apical cell surface irrespective of the effector location. Our data indicate that various effectors supplied to the apical and basolateral compartments may impact on SR-BI at the apical membrane, thus suggesting potential regulation of intestinal cholesterol absorption and distribution in various intracellular pools.

Emulsified lipids increase endotoxemia: possible role in early postprandial low-grade inflammation

“…This suggests that an intestinal absorption of LPS occurs during absorption of lipid species that are generated in the digestive tract during fat digestion, such as fatty acids and monoacylglycerols [38]. To study such intestinal absorption, Caco-2 cells are recognized as a valuable transport model system for the small intestinal epithelium [39,40] and have been widely used to study absorption of various lipophilic molecules [41][42][43][44]. In this respect, our results with Caco-2 cells incubated with LPS show that increased amount of fat in lipolytic products in the apical space, namely, fatty acids, result in increased LPS absorption rate.…”

Modulatory Role of PYY in Transport and Metabolism of Cholesterol in Intestinal Epithelial Cells

“…Furthermore, intestinal epithelial cells were capable of organizing their response to inflammatory signals and producing inflammatory mediators in a bidirectional, vectorial fashion [43]. Finally, we have recently shown that there is a discrete regulation of SR-BI from stimuli, originating from apical and basolateral media, such as n−3 and n−6 fatty acids, fibrate, cholesterol, 7-ketocholesterol, methyl β-cyclodextrin, lipopolysaccharide, tumor necrosis factor-α, interferon γ, insulin, growth hormone and epidermal growth factor [44]. It is the first time that vectorial response in link with PYY location has been treated.…”

Regulation of the proprotein convertase subtilisin/kexin type 9 in intestinal epithelial cells

“…This mixture was placed under a stream of nitrogen until the odor of acetone was no longer detectable. Micellar cholesterol was prepared as described previously (45). The mixed bile salt micelle, as a vehicle of cholesterol and 25-hydroxycholesterol, contained 4.8 mM sodium taurocholate and 0.3 mM monoolein.…”