Differential basolateral-apical distribution of scavenger receptor, class B, type I in cultured cells and the liver.

Stefanie Fruhwürth,Werner J Kovacs,Clemens Röhrl,Herbert Stangl,Simon Messner,Robert Bittman

doi:10.1007/s00418-014-1251-9

Stefanie Fruhwürth, Werner J Kovacs + Show 4 more

Open Access

https://doi.org/10.1007/s00418-014-1251-9

Copy DOI

Abstract

The high-density lipoprotein (HDL) receptor, scavenger receptor class B, type I (SR-BI), mediates selective cholesteryl ester uptake into the liver, which finally results in cholesterol secretion into the bile. Despite several reports, the distribution of hepatic SR-BI between the sinusoidal and canalicular membranes is still under debate. We present immunohistological data using specific markers showing that the bulk of SR-BI is present in sinusoidal membranes and, to a lesser extent, in canalicular membranes in murine and human liver sections. In addition, SR-BI was detected in preparations of rat liver canalicular membranes. We also compared the in vivo findings to HepG2 cells, a widely used in vitro hepatocyte model. Interestingly, SR-BI was enriched in bile canalicular-like (BC-like) structures in polarized HepG2 cells, which were cultivated either conventionally to form a monolayer or in Matrigel to form three-dimensional structures. Fluorescently labeled HDL was transported into close proximity of BC-like structures, whereas HDL labeled with the fluorescent cholesterol analog BODIPY-cholesterol was clearly detected within these structures. Importantly, similarly to human and mouse liver, SR-BI was localized in basolateral membranes in three-dimensional liver microtissues from primary human liver cells. Our results demonstrate that SR-BI is highly enriched in sinusoidal membranes and is also found in canalicular membranes. There was no significant basolateral–apical redistribution of hepatic SR-BI in fasting and refeeding experiments in mice. Furthermore, in vitro studies in polarized HepG2 cells showed explicit differences as SR-BI was highly enriched in BC-like structures. These structures are, however, functional and accumulated HDL-derived cholesterol. Thus, biological relevant model systems should be employed when investigating SR-BI distribution in vitro.Electronic supplementary materialThe online version of this article (doi:10.1007/s00418-014-1251-9) contains supplementary material, which is available to authorized users.

Highlights

The scavenger receptor class B, type I (SR-BI), a cell surface glycoprotein that binds high-density lipoprotein (HDL), low-density lipoprotein (LDL), very low-density lipoprotein (VLDL), modified LDL, and anionic phospholipid (Acton et al 1994, 1996; Rigotti et al 1995; Calvo et al 1997), mediates the last step in reverse cholesterol transport, namely the delivery of cholesteryl esters and other lipids from HDL to liver cells for disposal into the bile
These bile canalicular-like (BC-like) structures exhibited a strong co-localization of phalloidin and multidrug resistance protein 1 (MDR1), an efflux transporter localized to the apical canalicular membrane in the liver
SR-BI was enriched at the apical side of HepG2 cells (Fig. 1a, upper panel) and co-localization with phalloidin was regularly detected, indicating that SR-BI is in part localized at BC-like structures in HepG2 cells

Summary

Introduction

The scavenger receptor class B, type I (SR-BI), a cell surface glycoprotein that binds high-density lipoprotein (HDL), low-density lipoprotein (LDL), very low-density lipoprotein (VLDL), modified LDL, and anionic phospholipid (Acton et al 1994, 1996; Rigotti et al 1995; Calvo et al 1997), mediates the last step in reverse cholesterol transport, namely the delivery of cholesteryl esters and other lipids from HDL to liver cells for disposal into the bile This process, in which HDL- and LDL-derived cholesteryl esters are transferred to the cell without the concomitant degradation of the lipoprotein particle, is termed selective cholesteryl ester uptake (Acton et al 1996; Glass et al 1983, 1985; Stangl et al 1998, 1999; Swarnakar et al 1998). Hepatic SR-BI expression is regulated by dietary, hormonal, and pharmacological interventions; for reviews see (Kent and Stylianou 2011) (Landschulz et al 1996; Fluiter et al 1998; Serougne et al 1999)

Methods

Results

Conclusion