LXR agonist increases apoE secretion from HepG2 spheroid, together with an increased production of VLDL and apoE-rich large HDL

Abstract

BackgroundThe physiological regulation of hepatic apoE gene has not been clarified, although the expression of apoE in adipocytes and macrophages has been known to be regulated by LXR.Methods and ResultsWe investigated the effect of TO901317, a LXR agonist, on hepatic apoE production utilizing HepG2 cells cultured in spheroid form, known to be more differentiated than HepG2 cells in monolayer culture. Spheroid HepG2 cells were prepared in alginate-beads. The secretions of albumin, apoE and apoA-I from spheroid HepG2 cells were significantly increased compared to those from monolayer HepG2 cells, and these increases were accompanied by increased mRNA levels of apoE and apoA-I. Several nuclear receptors including LXRα also became abundant in nuclear fractions in spheroid HepG2 cells. Treatment with TO901317 significantly increased apoE protein secretion from spheroid HepG2 cells, which was also associated with the increased expression of apoE mRNA. Separation of the media with FPLC revealed that the production of apoE-rich large HDL particles were enhanced even at low concentration of TO901317, and at higher concentration of TO901317, production of VLDL particles increased as well.ConclusionsLXR activation enhanced the expression of hepatic apoE, together with the alteration of lipoprotein particles produced from the differentiated hepatocyte-derived cells. HepG2 spheroids might serve as a good model of well-differentiated human hepatocytes for future investigations of hepatic lipid metabolism.

LDL Receptor and ApoE Are Involved in the Clearance of ApoM-associated Sphingosine 1-Phosphate

“…Analysis of Clearance of Lipoproteins Containing C 17 S1P and ApoM in Vivo-The conditional medium of apoM-overexpressing HepG2 cells (prepared as described previously (23)) or apoM-depleted HepG2 cells (prepared with siRNA against apoM (sc-61978, Santa Cruz Biotechnology)), the total volumes of which were 12 ml/dish, were concentrated to about 500 l/dish by centrifugation and purification using Amicon Ultara-15 (UFC901008, Millipore Co., Bedford, MA) (25). Then, 160 g of evaporated C 17 S1P (860641P, Avanti Polar Lipids, Alabaster, AL) was gently mixed with 2 ml of the condensed conditional medium.…”

Effect of fenofibrate and atorvastatin on VLDL apoE metabolism in men with the metabolic syndrome

“…Our data may be more consistent with the latter mechanism. Although hepatic apoE gene expression may be regulated via a liver X receptor (LXR)-mediated pathway ( 28 ), fenofi brate, in its carboxylic acid form, does not function as an LXR-antagonist ( 29 ). Therefore, we hypothesize that the decrease in VLDL apoE PR may be due to increased intracellular degradation of translated apoE prior to secretion ( 30 ).…”

Modulation of lipid metabolism with the overexpression of NPC1L1 in mouse liver

“…VI-A). Upregulation of hepatic apoE, which has been shown to be associated with increased ERL production in HepG2 spheroids when treated with a LXR agonist ( 18 ), was the other candidate; however, hepatic apoE protein and mRNA levels were unaltered (supplementary Fig. VI-B, C).…”

“…The supernatants were centrifuged at 444,000 g for 60 min, and the pellets were suspended in 50 mM Tris-HCl (pH7.5) solution containing 1% TritonX-100, 5 mM EDTA, 10 mM EGTA, and 1 mM PMSF. The nuclear fractions were prepared as described previously ( 18 ).…”