Insulin increases cholesterol uptake, lipid droplet content, and apolipoprotein B secretion in CaCo‐2 cells by upregulating SR‐BI via a PI3K, AKT, and mTOR‐dependent pathway

• Published in: Journal of cellular biochemistry Vol. 120; no. 2; pp. 1550 - 1559
• Main Authors: Fuentes, Marcela, Santander, Nicolás, Cortés, Víctor
• Format: Journal Article
• Language: English
• Published: United States Wiley Subscription Services, Inc 01-02-2019
• Subjects: 1-Phosphatidylinositol 3-kinase; AKT protein; Apolipoprotein B; Apolipoproteins; Biotinylation; CaCo‐2 cells; Cell surface; Cholesterol; Confocal microscopy; Enzyme-linked immunosorbent assay; Epithelium; Glucose; Immunofluorescence; Insulin; Intestine; Intracellular; Lipids; lipoprotein; Lipoproteins; Localization; Microscopy; Pharmacology; Proteins; Reverse transcription; scavenger receptor, class B, type I (SR‐BI); Scavenger receptors; Streptavidin; TOR protein; cholesterol; scavenger receptor, class B, type I (SR-BI); intestine; CaCo-2 cells; insulin; lipoprotein
• ISSN: 0730-2312; 1097-4644
• DOI: 10.1002/jcb.27410

The actions of insulin on intestinal cholesterol absorption and lipoprotein secretion are not well understood. Herein, we determined the effects of insulin on the levels of cholesterol transporter scavenger receptor, class B, type I (SR‐BI), cellular cholesterol uptake, intracellular lipid accumulation, and lipoprotein secretion in a cellular model of human intestinal epithelium. Methods: CaCo‐2 cells were cultured to postconfluency in Transwell filters and stimulated with glucose (25 mM) in the presence or absence of insulin (100 nM) at their basolateral surface. SR‐BI mRNA and protein levels were quantified by quantitative reverse transcription‐PCR and immunoblot, respectively. Polarized localization of SR‐BI was determined by cell surface proteins biotinylation and streptavidin precipitation. Activities of PI3K, AKT, mTOR, and SR‐BI were pharmacologically antagonized. Cholesterol uptake was assessed by NBD‐cholesterol incorporation. Apolipoprotein (apo) B concentration was quantified by ELISA. Subcellular localization of neutral lipids (BODIPY) and SR‐BI (immunofluorescence) was determined by confocal microscopy.
Results: In polarized CaCo‐2 cells, insulin increased SR‐BI at the mRNA and protein levels. SR‐BI was exclusively present at apical cell surface, as indicated by biotinylation and confocal microscopy analysis. Glucose did not modify SR‐BI abundance or subcellular localization. Effects of insulin on SR‐BI levels were abrogated by PI3K, AKT, or mTOR pharmacological antagonism. Cholesterol uptake, neutral lipid abundance, and apo B secretion were increased by insulin in CaCo‐2 cells, and these effects were prevented by SR‐BI pharmacological antagonism with block lipid transport‐1.
Conclusions: insulin promotes cholesterol uptake, intracellular lipid store, and apo B–containing lipoproteins secretion by SR‐BI‐dependent mechanisms in a model of human intestinal epithelium.
Insulin increases enterocytes lipid droplet accumulation and apolipoprotein B–containing lipoprotein secretion by scavenger receptor, class B, type I–dependent mechanisms