Loss of liver FA binding protein significantly alters hepatocyte plasma membrane microdomains

Avery L. McIntosh; Barbara P. Atshaves; Stephen M. Storey; Kerstin K. Landrock; Danilo Landrock; Gregory G. Martin; Ann B. Kier; Friedhelm Schroeder

doi:10.1194/jlr.M019919

Loss of liver FA binding protein significantly alters hepatocyte plasma membrane microdomains[S]

^*Department of Physiology and Pharmacology, Texas A&M University Texas Veterinary Medical Center, College Station, TX 77843; and
^§Department of Pathobiology, Texas A&M University Texas Veterinary Medical Center, College Station, TX 77843; and
^†Department of Biochemistry & Molecular Biology, Michigan State University, East Lansing, MI 48824

Abstract

Although lipid-rich microdomains of hepatocyte plasma membranes serve as the major scaffolding regions for cholesterol transport proteins important in cholesterol disposition, little is known regarding intracellular factors regulating cholesterol distribution therein. On the basis of its ability to bind cholesterol and alter hepatic cholesterol accumulation, the cytosolic liver type FA binding protein (L-FABP) was hypothesized to be a candidate protein regulating these microdomains. Compared with wild-type hepatocyte plasma membranes, L-FABP gene ablation significantly increased the proportion of cholesterol-rich microdomains. Lack of L-FABP selectively increased cholesterol, phospholipid (especially phosphatidylcholine), and branched-chain FA accumulation in the cholesterol-rich microdomains. These cholesterol-rich microdomains are important, owing to enrichment therein of significant amounts of key transport proteins involved in uptake of cholesterol [SR-B1, ABCA-1, P-glycoprotein (P-gp), sterol carrier binding protein (SCP-2)], FA transport protein (FATP), and glucose transporters 1 and 2 (GLUT1, GLUT2) insulin receptor. L-FABP gene ablation enhanced the concentration of SCP-2, SR-B1, FATP4, and GLUT1 in the cholesterol-poor microdomains, with functional implications in HDL-mediated uptake and efflux of cholesterol. Thus L-FABP gene ablation significantly impacted the proportion of cholesterol-rich versus -poor microdomains in the hepatocyte plasma membrane and altered the distribution of lipids and proteins involved in cholesterol uptake therein.

Footnotes

↵1 To whom correspondence should be addressed. e-mail: fschroeder{at}cvm.tamu.edu.
Abbreviations:

L-FABP

liver type FA binding protein

FATP

FA transport protein 4

CLSM

confocal laser-scanning microscopy

GLUT1

glucose transporter 1

GLUT2

glucose transporter 2

IR

insulin receptor

MDR

multidrug resistant

NBD-cholesterol

22-(N-(7-Nitrobenz-2-Oxa-1,3-Diazol-4-yl)Amino)-23,24-Bisnor-5-Cholen-3β-Ol

P-gp

P-glycoprotein

PC

phosphatidylcholine

PE

phosphatidylethanolamine

PI

phosphatidylinositol

PS

phosphatidylserine

SCP-2

sterol carrier binding protein

SR-B1

scavenger receptor class B member 1
This work was supported in part by United States Public Health Service, National Institutes of Health, Grants GM-31651 and DK-41402 (F.S., A.B.K.) and DK-70965 (B.P.A.). Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the National Institutes of Health or other granting agencies.
↵[S] The online version of this article (available at http://www.jlr.org) contains supplementary data in the form of two tables.