Background: Pathological destruction of blood-brain barrier (BBB) has been thought to be the initial key event in the process of developing multiple sclerosis (MS). The purpose of the present study was to clarify the possible molecular mechanisms responsible for the malfunction of BBB by sera from relapse-remitting MS (RRMS) and secondary progressive MS (SPMS) patients.
Methods: We evaluated the effects of sera from the patients in the relapse phase of RRMS (RRMS-R), stable phase of RRMS (RRMS-S) and SPMS on the expression of tight junction proteins and vascular cell adhesion protein-1 (VCAM-1), and on the transendothelial electrical resistance (TEER) in human brain microvascular endothelial cells (BMECs).
Results: Sera from the RRMS-R or SPMS patients decreased the claudin-5 protein expression and the TEER in BMECs. In RRMS-R, this effect was restored after adding an MMP inhibitor, and the MMP-2/9 secretion by BMECs was significantly increased after the application of patients' sera. In SPMS, the immunoglobulin G (IgG) purified from patients' sera also decreased the claudin-5 protein expression and the TEER in BMECs. The sera and purified IgG from all MS patients increased the VCAM-1 protein expression in BMECs.
Conclusions: The up-regulation of autocrine MMP-2/9 by BMECs after exposure to sera from RRMS-R patients or the autoantibodies against BMECs from SPMS patients can compromise the BBB. Both RRMS-S and SPMS sera increased the VCAM-1 expression in the BBB, thus indicating that targeting the VCAM-1 in the BBB could represent a possible therapeutic strategy for even the stable phase of MS and SPMS.