Valproic acid suppresses lipopolysaccharide-induced cyclooxygenase-2 expression via MKP-1 in murine brain microvascular endothelial cells

Abstract

Inflammation and vascular perturbations are increasingly implicated in the pathogenesis of neurodegenerative diseases. Prevailing evidence suggests that valproic acid (VPA), an antiepileptic and mood stabilizer, exhibits not only neuro-protective effects, but also anti-inflammatory effects in neurodegenerative diseases. However, the underlying mechanism contributing to VPA's suppression of inflammatory responses remains unclear. In this study, we explored the inhibitory action of VPA on cyclooxygenase (COX)-2 expression in bEnd.3 mouse brain microvascular endothelial cells exposed to lipopolysaccharide (LPS), a pro-inflammatory stimulus. The LPS-induced increases in COX-2 protein level and COX-2 promoter-luciferase activity were significantly suppressed by VPA. VPA inhibited p38MAPK and JNK phosphorylation in LPS-stimulated bEnd.3 cells. Treatment of cells with a p38MAPK inhibitor (p38MAPK inhibitor III) or a JNK signaling inhibitor (JNK inhibitor II) significantly inhibited LPS-induced COX-2 expression. VPA inhibited LPS-induced NF-κB subunit p65 phosphorylation and κB-luciferase activity. LPS-increased p65 and C/EBPβ binding to the COX-2 promoter region was attenuated in the presence of VPA. In addition, VPA suppression of p38MAPK, JNK and p65 phosphorylation, and subsequent COX-2 expression was restored in cells transfected with mitogen-activated protein kinase phosphatase-1 (MKP-1) dominant negative (DN) mutant. VPA also caused increases in MKP-1 acetylation and MKP-1 phosphatase activity in bEnd.3 cells. In conclusion, VPA may cause MKP-1 activation to dephosphorylate p38MAPK and JNK, leading to decrease in p65 and C/EBPβ binding to the COX-2 promoter region and COX-2 down-regulation in LPS-stimulated bEnd.3 cells. The present study therefore supports the therapeutic value of VPA in alleviating brain inflammatory processes.

Keywords: Brain microvascular endothelial cells; Cyclooxygenase-2 (COX-2); Mitogen-activated protein kinase phosphatase-1 (MKP-1); Valproic acid (VPA).