Expression of ionotropic glutamate receptor GLUR3 and effects of glutamate on MBP- and MOG-specific lymphocyte activation and chemotactic migration in multiple sclerosis patients.

The present study was aimed at confirming the presence of GluR3 on T lymphocytes and to assess the effect of glutamate on proliferative responses to myelin basic protein (MBP) and myelin oligodendrocyte glycoprotein (MOG) and chemotactic migration to CXCL12/stromal cellderived factor-1, RANTES, and MIP-1 alpha in 15 control subjects and 20 relapsing-remitting multiple sclerosis (MS) patients (10 in a stable clinical phase and 10 during relapse). T lymphocytes of control subjects and MS patients express both mRNA and protein of GluR3 receptors, as shown by RT-PCR and immunoblot analyses. An up-regulation was evident during relapse and in patients with neuroradiological evidence of disease activity. Glutamate and AMPA at concentrations of 10 nM to 10 [mu M were able to enhance T lymphocyte proliferation to MBP and MOG and the chernotactic migration of T cells both in controls and NIS patients. In the latter group, significantly higher proliferation values in response to glutamate were found in patients assessed during relapse and in those with gadoliniurn (Gd)+ enhancing lesions on MRI. Glutamate concentrations above 10 mu M appeared to be inhibitory on MBP and MOG-specific T-lymphocyte proliferation as well as chernotactic response in both patients and controls. Higher GluR3 expression and higher activating effect of glutarnate on T cells of MS patients during relapses and with evidence of disease activity on MRI suggests the involvement of glutamate-mediated mechanisms in the T-cell detrimental effects. In NIS patients, glutamate within physiological ranges in the cerebrospinal fluid and brain extracellular space might enhance myelin antigen-specific proliferation and chernotactic migration via activation of AMPA receptors, which can be relevant for myelin and neuronal damage in MS. Excess glutamate levels seem to induce an inhibitory effect on lymphocyte function, and therefore the detrimental effect of this excitatory amino acid in this case could be attributed to a direct toxicity on glial and neuronal cells. (0 2007 Published by Elsevier B.V.