Deficient release of plasminogen activator inhibitor-1 from astrocytes triggers apoptosis in neuronal cells

Plasminogen activator inhibitor-1 (PAI-1) plays an important role in the pr ocesses of peripheral tissue remodeling and fibrinolysis through the regula tion of plasminogen activation. We found that cultured human astrocytes eff iciently released PAI-1, and that both mRNA expression and protein release of PAI-1 were suppressed by pretreatment of the cells with daunorubicin. To examine the role of PAI-1 in the nervous system, neuronally differentiated PC-12 cells (PC-12 neurons) were maintained in a PAI-1-deficient culture m edium derived from daunorubicin-pretreated astrocytes. The deficiency of PA I-I in the medium caused a significant reduction in Bcl-2 and Bcl-X-L mRNAs and an increase in Bcl-X-S and Bar mRNAs in PC-12 neurons at 3 h. The chan ges in balance between mRNA expressions of the anti- and pro-apoptotic Bcl- 2 family proteins caused caspase-3 activation following the release of cyto chrome c from mitochondria. Apoptotic morphological change and DNA fragment ation were also observed in the neuronal cells at 24 h. Addition of exogeno us PAI-1 protein to the inhibitor-deficient medium blocked the apoptotic ch anges in PC-12 neurons. However, addition of PAI-1 antibodies to control me dium caused similar apoptotic changes in PC-12 neurons. During the apc,ptot ic processes, plasminogen activator (PA) activity in the PAI-1-deficient me dium was as low as the control level. The present data suggest that PAI-1 h as physiological functions other than its role as PA inhibitor for the surv ival of neurons. (C) 2001 Elsevier Science B.V. All rights reserved.