NPC1L1 inhibition disturbs lipid trafficking and induces large lipid droplet formation in intestinal absorptive epithelial cells

Abstract

Ezetimibe inhibits Niemann-Pick C1-like 1 (NPC1L1) protein, which mediates intracellular cholesterol trafficking from the brush border membrane to the endoplasmic reticulum, where chylomicron assembly takes place in enterocytes or in the intestinal absorptive epithelial cells. Cholesterol is a minor lipid component of chylomicrons; however, whether or not a shortage of cholesterol attenuates chylomicron assembly is unknown. The aim of this study was to examine the effect of NPC1L1 inhibition on trans-epithelial lipid transport, and chylomicron assembly and secretion in enterocytes. Caco-2 cells, an absorptive epithelial model, grown onto culture inserts were given lipid micelles from the apical side, and chylomicron-like triacylglycerol-rich lipoprotein secreted basolaterally were analyzed after a 24-h incubation period in the presence of ezetimibe up to 50 μM. The secretion of lipoprotein and apolipoprotein B48 were reduced by adding ezetimibe (30%, p<0.01 and 34%, p<0.05, respectively). Additionally, ezetimibe accelerated intracellular apoB protein degradation by approximately 2.8-fold and activated sterol regulatory element binding protein 2 by approximately 1.5-fold: These are indicators whether the cells are sensing cellular cholesterol shortage. Thus, ezetimibe appeared to limit cellular cholesterol mobilization required for lipoprotein assembly. In such conditions, large lipid droplet formation in Caco-2 cells and the enterocytes in mice were induced, implying that unprocessed triglyceride was sheltered in these compartments. Although ezetimibe did not reduce the post-prandial lipid surge appreciably in triolein-infused mice, the results of the present study indicated that NPC1L1-mediated supply chylomicron with cholesterol may participate in a novel regulatory mechanism for the efficient chylomicron assembly and secretion.