Elsevier

Journal of Vascular Surgery

Volume 56, Issue 4, October 2012, Pages 1089-1097
Journal of Vascular Surgery

Basic research study
The role of urokinase plasminogen activator and plasmin activator inhibitor-1 on vein wall remodeling in experimental deep vein thrombosis

Presented in part at the Twenty-third Annual American Venous Forum Meeting, San Diego, Calif, February 25, 2011.
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Objective

Deep vein thrombosis (DVT) resolution instigates an inflammatory response, resulting in vessel wall damage and scarring. Urokinase-plasminogen activator (uPA) and its inhibitor, plasminogen activator inhibitor-1 (PAI-1), are integral components of the fibrinolytic system, essential for venous thrombosis (VT) resolution. This study determined the vein wall response when exposed to increased and decreased plasmin activity.

Methods

A mouse inferior vena cava (IVC) ligation model in uPA −/− or PAI-1 −/− and their genetic wild types (B6/SvEv and C57/BL6, respectively) was used to create stasis thrombi, with tissue harvest at either 8 or 21 days. Tissue analysis included gene expression of vascular smooth muscle cells (alpha smooth muscle actin [αSMA], SM22) and endothelial marker (CD31), by real-time polymerase chain reaction, enzyme-linked immunosorbent assay, matrix metalloproteinase (MMP)-2 and -9 activity by zymography, and vein wall collagen by picro-Sirius red histologic analysis. A P < .05 was considered significant.

Results

Thrombi were significantly larger in both 8-day and 21-day uPA −/− as compared with wild type (WT) and were significantly smaller in both 8-day and 21-day PAI-1 −/− as compared with WT. Correspondingly, 8-day plasmin levels were reduced in half in uPA −/− and increased three-fold in PAI-1 −/− when compared with respective WT thrombi (P < .05; n = 5-6). The endothelial marker CD31 was elevated two-fold in PAI-1 −/− mice at 8 days, but reduced 2.5-fold at 21 days in uPA −/− as compared with WT (P = .02; n = 5-6), suggesting less endothelial preservation. Vein wall vascular smooth muscle cell (VSMC) gene expression showed that 8-day and 21-day PAI-1 −/− mice had 2.3- and 3.8-fold more SM22 and 1.8- and 2.3-fold more αSMA expression than respective WT (P < .05; n = 5-7), as well as 1.8-fold increased αSMA (+) cells (P ≤ .05; n = 3-5). No significant difference in MMP-2 or -9 activity was found in the PAI-1 −/− mice compared with WT, while 5.4-fold more MMP-9 was present in 21-day WT than 21-day uPA −/− (P = .03; n = 5). Lastly, collagen was ∼two-fold greater at 8 days in PAI-1 −/− IVC as compared with WT (P = .03; n = 6) with no differences observed in uPA −/− mice.

Conclusions

In stasis DVT, plasmin activity is critical for thrombus resolution. Divergent vein wall responses occur with gain or loss of plasmin activity, and despite smaller VT, greater vein wall fibrosis was associated with lack of PAI-1.

Clinical Relevance

DVT resolution is dependent on many factors. Clinical studies suggest that slowly resolving extensive DVTs are associated with greater likelihood of post-thrombotic syndrome, and this is experimentally modeled by vein wall fibrosis and inflammation. The current study suggests a more complex relationship in that the plasmin-mediated events are central to thrombus resolution as well as to how the vessel wall responds. Surprisingly, a larger thrombus from a stasis model is not associated with greater vein wall damage. Thus, novel modalities such as PAI-1 inhibition may require supplemental anticoagulants for full efficacy.

Cited by (0)

Supported by HL083918 and HL092129.

Author conflict of interest: none.

The editors and reviewers of this article have no relevant financial relationships to disclose per the JVS policy that requires reviewers to decline review of any manuscript for which they may have a conflict of interest.