Rhamnetin Prevents Bradykinin-Induced Expression of Matrix Metalloproteinase-9 in Rat Brain Astrocytes by Suppressing Protein Kinase-Dependent AP-1 Activation

Bradykinin (BK) has been recognized as a stimulant for matrix metalloproteinase (MMP)-9 expression, contributing to neuroinflammation. Modulating the BK/MMP-9 pathway offers potential in the treatment of neuroinflammatory disorders. Rhamnetin (RNT), a flavonoid compound known for its antioxidant and anti-inflammatory effects, has shown promise. However, the specific mechanisms through which RNT inhibits BK-induced MMP-9 expression remain unclear. Therefore, this study aims to delve into the intricate mechanisms underlying this process. Here, we initially demonstrated that RNT effectively attenuated BK-induced MMP-9 expression and its associated cell migration in rat brain astrocyte-1 (RBA-1) cells. Further investigation revealed that BK-driven MMP-9 protein, mRNA, and promoter activity linked to cell migration relied on c-Src, Pyk2, EGFR, PDGFR, PI3K/Akt, JNK1/2, and c-Jun. This was validated by the inhibition of these effects through specific inhibitors, a finding substantiated by the introduction of siRNAs targeting these signaling molecules. Notably, the phosphorylated levels of these signaling components induced by BK were significantly reduced by their respective inhibitors and RNT, underscoring the inhibitory role of RNT in this process. These findings indicate that, in RBA-1 cells, RNT diminishes the heightened induction of MMP-9 triggered by BK through the inhibition of c-Src/Pyk2/PDGFR and EGFR/PI3K/Akt/JNK1/2-dependent AP-1 activation. This suggests that RNT holds promise as a potential therapeutic approach for addressing neuroinflammation in the brain.