TLR2 Ligand Pam3CSK4 Regulates MMP-2/9 Expression by MAPK/NF-κB Signaling Pathways in Primary Brain Microvascular Endothelial Cells

Blood–brain barrier (BBB) destruction is associated with a variety of neurological diseases. Brain microvascular endothelial cells (BMECs) are the key constituent of BBB. Both matrix metalloproteinases-2/9 (MMP-2/9) and toll-like receptor-2 (TLR2) are coexpressed in BMECs and have been shown to play important roles in BBB breakdown. It is unknown whether TLR2 can regulate MMP-2/9 in BMECs. In this study, Pam3CSK4 was used to activate TLR2, and the expression of MMP-2/9 and tight junctions (TJs) in BBB was measured by quantitative real-time PCR and western blotting. Phosphoproteins were determined by western blotting. The inhibitors of mitogen-activated protein kinases (MAPKs) and NF-κB were used to identify the signaling pathways by which TLR2 regulates the expression of MMP-2/9 in BMECs. This study showed that Pam3CSK4 upregulated the mRNA and protein expression of MMP-9 and downregulated MMP-2 and TJ expression in BMECs simultaneously. Pam3CSK4 also induced the phosphorylation of MAPKs and NF-κB signaling pathways in BMECs. MMP-9 expression was found to decrease by pretreatment with inhibitors of ERK1/2 and JNK but not p38. However, the mRNA and protein expression of MMP-2 and MMP-9 increased after addition of a NF-κB inhibitor. Our results indicated that Pam3CSK4 was able to upregulate MMP-9 expression through ERK1/2 and JNK signaling pathways, but the NF-κB signaling pathway negatively regulated the effect of TLR2 on MMP-2 and MMP-9 expression in BMECs. The finding provides novel insight into the molecular mechanism of MMP-2/9 expression in BMECs.