Prevention of Aneurysm Development and Rupture by Local Overexpression of Plasminogen Activator Inhibitor-1

Abstract

Background-Arterial aneurysms exhibit a loss of elastin and an increase in the plasminogen activators urokinase plasminogen activator (u-PA) and tissue plasminogen activator (t-PA). Because u-PA, t-PA, and plasmin have a limited proteolytic activity against elastin, the role of plasminogen activators in the aneurysmal disease is unclear. To investigate this question, we overexpressed plasminogen activator inhibitor-1 (PAI-1), an inhibitor of t-PA and u-PA, in a rat model of aortic aneurysm. Methods and Results-Guinea pig-to-rat aortic xenografts were seeded with syngeneic Fischer 344 rat smooth muscle cells retrovirally transduced with the rat PAI-1 gene (LPSN group) or the vector alone (LXSN group). Some grafts were not seeded with cells (NO group). Western blots showed increased PAI-1 in grafts from the LPSN group compared with LXSN and NO groups. All grafts in the NO group (nϭ8) and 40% in the LXSN group ruptured between days 4 and 14. At 4 weeks in the LXSN group, the remaining unruptured grafts (nϭ6) were aneurysmal (diameter increase Ն100%), whereas in the LPSN group (nϭ6) none of the grafts had ruptured or were aneurysmal. Elastin was preserved in the LPSN group. t-PA, the major PA expressed in the model, was decreased in the LPSN group compared with the other groups, as determined by zymography. Quantitative zymography showed decreased levels of two matrix metalloproteinases (MMPs), a 28-kD caseinase, and activated MMP-9 in the LPSN group. Conclusions-The blockade of plasminogen activators prevents formation of aneurysms and arterial rupture by inhibiting MMP activation. (Circulation. 1998;98:249-255.)

Overexpression of PAI-1 prevents the development of abdominal aortic aneurysm in mice

“…Carmeliet et al 11,29 demonstrated increased neointima formation after electrical or mechanical injury in PAI-1 À/À mice, which was prevented by overexpression of PAI. Consistent with these results, de Waard et al 30 reported an increase in neointima formation in PAI-1 À/À mice after carotid artery ligation; and Allaire et al 31 showed that local overexpression of PAI-1 prevented aneurysm development in a xenograft model. In contrast to these findings, Ploplis and Castellino 32 reported that copper-cuff-induced neointima formation was decreased in PAI-1 À/À mice compared to wild type controls and DeYoung et al 33 reported that overexpression of PAI-1 gene in the carotid artery enhanced neointima growth following balloon injury in rats.…”

“…This hypothesis is also in agreement with the observation made in the xenograft model, that pretreatment of the artery with PAI-1 gene blocked the development of aneurysm. 31 In more advanced aneurysmal lesions, the vascular wall remodeling may also influence local PAI-1 gene expression and distribution after viral delivery, affecting PAI-1 efficacy. Taken together, these observations suggest that the antiinflammatory properties of PAI-1 play an important role in preventing AAA formation and progression of early aneurysm lesions.…”

A Truncated Plasminogen Activator Inhibitor-1 Protein Induces and Inhibits Angiostatin (Kringles 1–3), a Plasminogen Cleavage Product

“…The polyacrylamide gels containing the electrophoresed samples were first washed in 2.5% Triton-X before an overnight incubation at 37°C in a 50 mM Tris-HCl buffer, pH 7.9. The gels were fixed in 40% methanol, 10% acetic acid and then stained in 10% Coomassie Blue for 1 h. The gel was destained in 10% methanol, 10% acetic acid to detect the regions of proteolysis (50,51).…”

Abdominal Aortic Aneurysm Rupture Is Associated With Increased Medial Neovascularization and Overexpression of Proangiogenic Cytokines

“…5 Proteolytic activities of MMPs have been implicated in aneurysm wall weakening and rupture. [5][6][7] Previous work have demonstrated that high levels of MMPs-8 and MMP-9 were localized to aneurysm rupture edge in humans 5 and experimental studies in rats have shown that inhibition of MMP activity by tissue inhibitor of MMP (TIMP)-1 prevented aneurysm rupture. 6 The MMP family is closely involved in the process of neovascularization 8 and play key proangiogenic roles such as the proteolytic degradation of extracellular matrix (ECM) to facilitate endothelial cell migration during angiogenesis, 9 detachment of pericytes from microvessels undergoing angiogenesis, release of ECMsequestered angiogenic growth factors, 10 exposure of cryptic proangiogenic integrin binding sites in the ECM, cleavage of vascular endothelial-cadherin endothelial cell-cell adhesions and generation of promigratory ECM fragments.…”