Original Article
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World J Gastroenterol. Feb 14, 2014; 20(6): 1554-1564
Published online Feb 14, 2014. doi: 10.3748/wjg.v20.i6.1554
Regulation of hepatic EAAT-2 glutamate transporter expression in human liver cholestasis
Mustapha Najimi, Xavier Stéphenne, Christine Sempoux, Etienne Sokal
Mustapha Najimi, Xavier Stéphenne, Etienne Sokal, Université Catholique de Louvain, Institut de Recherche Expérimentale et Clinique (IREC), Laboratory of Pediatric Hepatology and Cell Therapy, Brussels 1200, Belgium
Christine Sempoux, Anatomo-pathology, Cliniques Universitaires St-Luc, Université Catholique de Louvain, Brussels 1200, Belgium
Author contributions: Najimi M performed the majority of experiments; Najimi M designed the study and wrote the manuscript; Stéphenne X participated in performing the in vivo experiments on rats; Stéphenne X, Sempoux C and Sokal E were involved in revising the manuscript; Sempoux C provided the human liver samples, supervised the immunohistochemistry analyses; Sokal E provided the financial support.
Correspondence to: Mustapha Najimi, PhD, Université Catholique de Louvain, Institut de Recherche Expérimentale et Clinique (IREC), Laboratory of Pediatric Hepatology and Cell Therapy, Avenue Mounier 52, Brussels 1200, Belgium. mustapha.najimi@uclouvain.be
Telephone: +32-2-7645283 Fax: +32-2-7645258
Received: April 23, 2013
Revised: September 9, 2013
Accepted: September 16, 2013
Published online: February 14, 2014
Abstract

AIM: To investigate the activity and expression of EAAT2 glutamate transporter in both in vitro and in vivo models of cholestasis.

METHODS: This study was conducted on human hepatoblastoma HepG2 cell cultures, the liver of bile duct ligated rats and human specimens from cholestatic patients. EAAT2 glutamate transporter activity and expression were analyzed using a substrate uptake assay, immunofluorescence, reverse transcription-polymerase chain reaction, and immunohistochemistry, respectively.

RESULTS: In HepG2 cells, cholestasis was mimicked by treating cells with the protein kinase C activator, phorbol 12-myristate 13-acetate. Under such conditions, EAAT2 transporter activity was decreased both at the level of substrate affinity and maximal transport velocity. The decreased uptake was correlated with intracellular translocation of EAAT2 molecules as demonstrated using immunofluorescence. In the liver of bile duct ligated rats, an increase in EAAT2 transporter protein expression in hepatocytes was demonstrated using immunohistochemistry. The same findings were observed in human liver specimens of cholestasis in which high levels of γ-glutamyl transpeptidase were documented in patients with biliary atresia and progressive familial intrahepatic cholestasis type 3.

CONCLUSION: This study demonstrates the alteration in glutamate handling by hepatocytes in liver cholestasis and suggests a potential cross-talk between glutamatergic and bile systems.

Keywords: Glutamate transport, Hepatocyte, Bile duct ligation, Cholestasis, Biliary atresia

Core tip: The aim of the current study was to demonstrate the role of glutamate transport, the most abundant intracellular hepatic amino acid, in liver cholestasis. The study was conducted in vitro using HepG2 cells as well as the livers of bile duct ligated rats and human cholestasis specimens. The principal data revealed that the activity and expression of EAAT2-mediated glutamate transport were altered both in vitro and in vivo. This supports the involvement of glutamate transporters, as an indirect liver response and/or as a direct hepatic target, in restoring intracellular pools of this amino acid which are probably altered after cholestasis.