Medico

Pampliega et al. Journal of Neuroinflammation 2011, 8:63 http://www.jneuroinflammation.com/content/8/1/63

JOURNAL OF NEUROINFLAMMATION

RESEARCH

Open Access

Increased expression of cystine/glutamate antiporter in multiple sclerosis
Olatz Pampliega1,5, María Domercq2, Federico N Soria2, Pablo Villoslada3, Alfredo Rodríguez-Antigüedad4 and Carlos Matute1,2*

Abstract
Background:Glutamate excitotoxicity contributes to oligodendrocyte and tissue damage in multiple sclerosis (MS). Intriguingly, glutamate level in plasma and cerebrospinal fluid of MS patients is elevated, a feature which may be related to the pathophysiology of this disease. In addition to glutamate transporters, levels of extracellular glutamate are controlled by cystine/glutamate antiporter xc-, an exchangerthat provides intracellular cystine for production of glutathione, the major cellular antioxidant. The objective of this study was to analyze the role of the system xc- in glutamate homeostasis alterations in MS pathology. Methods: Primary cultures of human monocytes and the cell line U-937 were used to investigate the mechanism of glutamate release. Expression of cystine glutamate exchanger (xCT)was quantified by quantitative PCR, Western blot, flow cytometry and immunohistochemistry in monocytes in vitro, in animals with experimental autoimmune encephalomyelitis (EAE), the animal model of MS, and in samples of MS patients. Results and discussion: We show here that human activated monocytes release glutamate through cystine/ glutamate antiporter xc- and that the expression of thecatalytic subunit xCT is upregulated as a consequence of monocyte activation. In addition, xCT expression is also increased in EAE and in the disease proper. In the later, high expression of xCT occurs both in the central nervous system (CNS) and in peripheral blood cells. In particular, cells from monocyte-macrophage-microglia lineage have higher xCT expression in MS and in EAE, indicating that immuneactivation upregulates xCT levels, which may result in higher glutamate release and contribution to excitotoxic damage to oligodendrocytes. Conclusions: Together, these results reveal that increased expression of the cystine/glutamate antiporter system xcin MS provides a link between inflammation and excitotoxicity in demyelinating diseases.

Background Multiple sclerosis (MS) is a chronic,degenerative disease of the CNS, which is characterized by focal lesions with inflammation, demyelination, infiltration of immune cells, oligodendroglial death and axonal degeneration [1-3]. MS is typically considered as a primary inflammatory disease in the early, relapsing phase which progresses to a secondary, progressive stage that is characterized by a diminished inflammatory activity and globalbrain atrophy [4]. Oligodendroglial death and demyelination can occur through glutamate excitotoxicity [5,6], a phenomenon that takes place when an excessive amount of glutamate
* Correspondence: carlos.matute@ehu.es 1 Neurotek-UPV/EHU, Parque Tecnológico de Bizkaia, Zamudio, Bizkaia, Spain Full list of author information is available at the end of the article

overactivates ionotropic glutamatereceptors (iGluRs). Several observations have linked glutamate excitotoxicity with MS demyelination. First, experimental autoimmune encephalitis (EAE), an animal model for MS, is ameliorated by AMPA and kainate iGluR antagonists, improving oligodendrocyte loss and demyelination without affecting immune reaction [7-9]. And second, the infusion of glutamatergic agonists into rabbit optic nerve leadsto inflammation, oligodendrocyte loss, demyelination, and axonal damage, reminding these characteristics those typical lesions in MS [10]. Data supporting the excitotoxic hypothesis in MS include the report of higher glutamate levels in MS, both at CNS and peripheral blood. Glutamate is increased in cerebrospinal fluid (CSF) from MS patients with acute lesions, whereas in silent ones glutamate...