Plasminogen activator inhibitor-1 in cardiovascular cells: Rapid induction after injecting mice with kainate or adrenergic agents

Objectives: Plasminogen activator inhibitor-1 (PAI-1) is a major anti-fibrinolytic glycoprotein thought to promote vascular diseases. Recently we have shown that systemically injecting mice with kainate, an analog of the principal brain excitatory neurotransmitter glutamate, immediately induced PAI-1 mRNA in brain vascular cells which are not known to contain glutamate receptors. Here we further investigated whether: (a) kainate also increases PAI-1 gene expression in the cardiac vascular bed; (b) subunits of kainate/AMPA receptors could be expressed in cardiac and brain vascular cells; and (c) PAI-1 mRNA could be similarly induced by agonists of adrenergic receptors that are candidates to act downstream in kainate-activated pathways. Methods: We analyzed cardiac and brain cryosections for PAI-1 mRNA, as well as mRNAs encoding three receptor subunits, by in situ hybridization using ³⁵S-labeled specific riboprobes. PAI-1 activity was tested in cardiac homogenates using one-phase reverse zymography. Results: Prominent PAI-1 mRNA hybridization signals were induced in the vascular cells of the heart, and unexpectedly, also in cardiocytes, within 1-2 h after injection of kainate (i.p., 11-25 mg/kg body weight); the signals persisted for at least 8 h and disappeared after 24 h. In addition, PAI-1 activity increased (5 fold) 2-10 h after the treatment. In contrast, mRNAs encoding the kainate/AMPA receptor subunits could not be detected. The adrenergic agents adrenaline (3.5 mg/kg) and isoproterenol (200 mg/kg) exerted kainate-like effects in cardiovascular cells. Conclusions: These results revealed, for the first time, that PAI-1 gene expression can be enhanced locally in the cardiovascular system by a fast-acting neurological mechanism triggered by glutamate receptors, whose pathway and relation to catecholamines, which exerted similar effects, have yet to be resolved. These findings raised the possibility that excessive glutamate, or stress-related catecholamines, may increase the risk of stroke and myocardial infarction.