Endothelin-1 enhances cell migration via matrix metalloproteinase-9 up-regulation in brain astrocytes

The bioactivity of endothelin-1 (ET-1) has been suggested in the development of CNS diseases, including disturbance of water homeostasis and blood-brain barrier integrity. Recent studies suggest that hypoxic&ischemic injury of the brain induces release of ET-1, behaving through a G-protein coupled ET receptor family. The deleterious effects of ET-1 on astrocytes may aggravate brain inflammation. Increased plasma levels of matrix metalloproteinases (MMPs), in particular MMP-9, have been observed in patients with neuroinflammatory disorders. However, the detailed mechanisms underlying ET-1-induced MMP-9 expression remain unknown. In this study, the data obtained with zymographic, western blotting, real-time PCR, and immunofluorescent staining analyses showed that ET-1-induced MMP-9 expression was mediated through an ET_B-dependent transcriptional activation. Engagement of G _i&o- and G_q-coupled ET_B receptor by ET-1 led to activation of p42&p44 MAPK and then activated transcription factors including Ets-like kinase, nuclear factor-kappa B, and activator protein-1 (c-Jun&c-Fos). These activated transcription factors translocated into nucleus and bound to their corresponding binding sites in MMP-9 promoter, thereby turning on MMP-9 gene transcription. Eventually, up-regulation of MMP-9 by ET-1 enhanced the migration of astrocytes. Taken together, these results suggested that in astrocytes, activation of Ets-like kinase, nuclear factor-kappa B, and activator protein-1 by ET_B-dependent p42&p44 MAPK signaling is necessary for ET-1-induced MMP-9 gene up-regulation. Understanding the mechanisms of MMP-9 expression and functional changes regulated by ET-1&ET_B system on astrocytes may provide rational therapeutic interventions for brain injury associated with increased MMP-9 expression.