Smad3-Dependent Induction of Plasminogen Activator Inhibitor-1 in Astrocytes Mediates Neuroprotective Activity of Transforming Growth Factor-β1 against NMDA-Induced Necrosis

The intravenous injection of the serine protease, tissue-type plasminogen activator (t-PA), has shownto benefit stroke patients by promoting early reperfusion. However, it has recently been suggested that t-PA activity, in the cerebral parenchyma, may also potentiate excitotoxic neuronal death. The present study has dealt with the role of the t-PA inhibitor, PAI-1, in the neuroprotective activity of the cytokine TGF-β1 and focused on the transduction pathway involved in this effect. We demonstrated that PAI-1, produced by astrocytes, mediates the neuroprotective activity of TGF-β1 against N-methyl- d -aspartate (NMDA) receptor-mediated excitotoxicity. This t-PA inhibitor, PAI-1, protected neurons against NMDA-induced neuronal death by modulating the NMDA-evoked calcium influx. Finally, we showed that the activation of the Smad3-dependent transduction pathway mediates the TGF-β-induced up-regulation of PAI-1 and subsequent neuroprotection. Overall, this study underlines the critical role of the t-PA/PAI-1 axis in the regulation of glutamatergic neurotransmission.