ELEVATED LEVELS OF PLASMINOGEN-ACTIVATOR INHIBITOR TYPE-1 IN ATHEROSCLEROTIC AORTA

Purpose: Plasminogen activator inhibitor type 1 (PAI-1) inhibits the p lasminogen activators that convert plasminogen to plasmin. In addition to initiating fibrinolysis, plasmin activates tissue matrix metallopr oteinases, which cause degradation of the extracellular matrix (ECM) i n the arterial wall, Elevated levels of PAI-1 ultimately decrease plas min formation and may lead to an accumulation of ECM and arteriosclero sis. Methods: PAI-1 was studied by four methods in atherosclerotic (an eurysmal and occlusive) and normal (organ donor) aorta: (1) PAI-1 secr etion by tissue explant supernatants, including time course and inhibi tion studies; (2) tissue PAT-I by protein extraction; (3) PAT-I mRNA w as quantitated by Northern analysis using glyceraldehyde-3-phosphate d ehydrogenase to normalize for RNA loading; and (4) in situ hybridizati on was used to localize the cells that produced PAI-1 mRNA. Results: S upernatant PAI-1 levels at 48 hours were 776 +/- 352 ng/ml in 11 ather osclerotic aortas and 248 +/- 98 ng/ml in 8 normal aortas (p < 0.005). Tissue PAI-1 levels per 100 mg of tissue were 99 +/- 58 ng in 11 athe rosclerotic aortas and 38 +/- 20 ng in 5 normal aortas (p < 0.05). PAI -1 mRNA levels by Northern analysis were 0.91 +/- 0.49 in seven athero sclerotic aortas and 0.44 +/- 0.27 in five normal aortas. Supernatant time-course experiments revealed that PAI-1 increased over time. Inhib itor studies revealed that PAT-I decreased to approximately one third of control values when cycloheximide or actinomycin D were added to th e media, indicating that active synthesis of PAI-1 had occurred. In-si tu hybridization localized PAI-1 mRNA predominately to endothelial cel ls and a few scattered vascular smooth muscle and inflammatory cells. Subgroup analysis revealed no statistically significant differences be tween aneurysmal and occlusive PAI-1 levels in any of the experiments. Conclusion: PAI-1 secretion, as measured by tissue explant supernatan ts, and total tissue PAI-1 in the protein extracts were significantly increased in atherosclerotic aorta. This elevation was also observed i n the mRNA,which suggests that the increase is controlled at the level of transcription. PAT-I mRNA was localized to endothelial, vascular s mooth muscle, and inflammatory cells. We conclude that elevated levels of PAI-1 exist in diseased aorta. These elevated levels may lead to a n accumulation of ECM, thereby contributing to the arteriosclerosis fo und in aortic occlusive and aneurysmal disease.