This section highlights the role of PAI-1 in apoptosis in pathophysiological settings of tumors and atherosclerosis. When the human prostate cancer cell line PC-3, and the human promyelocytic leukemia cell line HL were treated with recombinant wild-type WT PAI-1, induced and spontaneous apoptosis were diminished. This inhibition of apoptosis by PAI-1 was reversed by the presence of a neutralizing antibody that accelerated the conformational change of active PAI-1 to inactive PAI Similarly, treatment of cells with latent PAI-1 did not inhibit apoptosis, thus suggesting that the reactive site loop may be required for the apoptosis inhibiting function.

Inhibition of apoptosis by an exogenous source of PAI-1 could very well mimic the tumor environment where PAI-1 is secreted in the tumor vasculature by surrounding stromal cells, and potentially increasing the aggressiveness of the tumor, thus giving credence to the reported observations of PAI-1 as a prognostic marker of poor overall survival In contrast, tumor cells transfected to express high levels of PAI-1, acting as tumor-host PAI-1, behave differently, conferring anti-angiogenic properties 36 , 51 , These differences in PAI-1 expressing and PAIdeficient fibrosarcoma cells have been attributed to differences in cell proliferation, and that PAI-1 expressed by the tumor cells protects the tumors from apoptosis.

The inconsistent nature of PAI-1 surfaced when rPAI-1 did not induce apoptotic death or, control the growth and metastasis of implanted human colon cancer xenografts in nude mice. On the other hand, intraperitoneal infusion of rPAI-2 diminished the size of the primary tumor and enhanced the tumor apoptotic index A similar anti-cancer activity of PAI-2 was observed due to enhanced apoptosis in metastatic prostate cancer cells However, stable transfection of the human prostate cancer PC3 cells that conditionally expressed active PAI-1 regulated by doxycycline resulted in dramatic inhibition of angiogenesis as observed by CD31 staining, when these cells were injected in nude mice.

The PAIinduced diminished angiogenesis was ascribed to an early wave of apoptosis in tumor EC with a concomitant decrease in cell proliferation. The induction of EC apoptosis by PAI-1 was found to be vitronectin-dependent, which served as an adhesion matrix during angiogenesis At the time of a pathological condition, such as cancer progression, PAI-1 levels are dramatically increased.

Tumorigenicity and angiogenic phenotype of these transfected cell lines were observed when injected in either WT or PAI-1 deficient mice to allow investigation on the effect of PAI-1 on newly established tumor vasculature in early stages of tumor progression. Furthermore, recapitulation of PAI-1 inducing EC apoptosis, which is dependent on vitronectin, was observed in vitro when microvascular EC co-cultured with PC3 cells, stably transfected to express PAI-1 exclusively, underwent apoptosis when plated in the presence of vitronectin Similarly, PAI-1 could inhibit EC tube formation in the presence of vitronectin but not in the presence of fibronectin These in vitro experiments were performed utilizing rPAI-1 at high concentrations of 40— nM.

However, it should be noted that this mechanism of PAImediated tumor apoptosis by a vitronectin-dependent mechanism might be possible in an environment where the tumor is established and angiogenesis is still active. In such a scenario the EC detach and launch to re-adhere to vitronectin, which is inhibited due to the presence of high levels of PAI-1 in the tumor microenvironment.

Since tumor growth is dependent on neovascularization, this would result in an inability of the tumor to sustain further growth. Induction of apoptosis was mediated by the caspase-3 pathway and the apoptotic cells were associated with foam cells as observed in atherosclerotic vessel sections, thus re-enforcing the importance of apoptotic and anti-adhesive mechanism in tissue remodeling during neointima formation Instead it stimulated migration of EC from vitronectin towards fibronectin, promoting cell migration away from the vitronectin-rich perivascular spaces towards fibronectin-rich tumor tissues.

Thus, a lack of adhesion alone is not sufficient to induce apoptosis by PAI-1 suggesting that other mechanisms may be involved In this case, lack of host PAI-1 did not sustain tumor growth and survival potentially due to a lack of the ability to disrupt EC adhesion from the surrounding vitronectin and promote motility, thereby preventing neovascularization. It appears from the studies of Balsara et, 63 and Chen et al, 58 that either an exogenous source of PAI-1, in case of in vitro EC studies or tumor cells overexpressing PAI-1 is effectively able to induce apoptosis and control growth of tumor vasculature.

Increased proliferation and decreased apoptosis of VSMC is a distinguishing hallmark of restenosis 64 — 66 accompanied by increased synthesis of PAI-1 in patients with type 1 diabetes 67 — 69 suggesting that increased PAI-1 expression could affect VSMC apoptosis. These findings are in consonance with the fibrosarcoma studies of Romer et al described earlier Decreased apoptosis was due to a decrease in caspase-3 activity, and when exogenous PAI-1 was added to VSMC lysates or directly to recombinant caspase-3, inhibition of caspase-3 activity was observed.

The proteolytically inactive PAI-1 HL-HL could neither bind to caspase-3 nor inhibit caspase-3 activity suggesting that the inhibitory activity of PAI-1 is essential for its anti-apoptotic activity The serpin CrmA Cytokine Response Modifier A binds to caspase-1 modulating host inflammatory responses 73 , and the PI9 Proteinase Inhibitor 9 serpin interacts with caspases-1, -4, and -8 This could have significant physiological implications where CrmA could be required to completely inhibit an inflammatory response.

In contrast, inhibition of caspase activity in a more controlled manner would be beneficial. Though not much is known about inhibition of caspase-3 activity by interaction with PAI-1 it is possible that intracellular PAI-1 can bind to caspase-3 or pro-caspase-3 attenuating apoptosis. Fibroblasts and myofibroblasts are key cells involved in wound closure and reepithelialization and undergo physiologic apoptosis during wound repair, the absence of which could cause tissue fibrosis 67 , High levels of PAI-1 prevented extracellular proteolysis resulting in accumulation of extracellular matrix components, such as fibronectin, thereby promoting progressive tissue fibrosis.

Although the precise mechanism as to how PAI-1 regulates apoptosis in fibroblast cells is unknown, it has been shown to be associated with pericellular proteolysis of fibronectin. Therefore, PAI-1 plays a central role in protecting cells against plasminogen-induced apoptosis.

The significance of these findings allows for mechanistic insights regarding the pivotal role of PAI-1 in vascular remodeling, whereby increased expression of PAI-1 in diabetic patients may promote increased accumulation of VSMC in response to a vessel wall injury. This highlights the conflicting effects of PAI-1, which may be a reflection of variation in experimental scenarios that may be dependent on cell types and the challenge models that are employed.

In the central nervous system the tPA-plasmin system has been known to play a significant role in synaptic plasticity, remodeling 82 , 83 , and in regulation of neuronal survival in response to excitoxicity 84 , However, PAI-1 although secreted by astrocytes does not behave as the prototypic inhibitor of the neural protease cascade but rather functions as a neuroprotective agent 86 , 87 , and high levels of PAI-1 in cerebrospinal fluids 88 , 89 , and the central nervous system could also serve as an index of neurological diseases 90 — There is some evidence of a role for PAI-1 in regulating neuronal apoptosis.

When PC neurons were grown in medium containing PAI-1 obtained from astrocyte-derived conditioned medium, the neurons maintained their morphology and survived. Eventually, the formation of the apoptosome composed of cytochrome c, Apaf-1, and procaspase-9 results in upregulation of caspase-3 activity. Similar results were observed when an anti-PAI-1 neutralizing antibody was added to the neuronal medium.

Anti-apoptotic characteristics were restored to the neurons when recombinant PAI-1 was added to the culture medium. Interestingly, neural plasminogen activation activity was not affected by the presence or absence of PAI Thus reinforcing that PAI-1 is not the primary inhibitor of the neural plasminogen system, and that it plays an important role in regulating survival of neurons The pro-survival function of PAI-1 was found to be due to activation of c-jun and ERK pathways, which was preceded by the activation of the nerve growth factor receptor, Trk A Table 1 summarizes the pro- and anti-apoptotic activities of PAI-1 in different cell types.

PAI-1, whether indigenously present P or absent A in the cells or added as recombinant protein r-PAI-1 can affect apoptosis differently. This anomalous property of PAI-1 may depend on the origin of PAI-1, its ability to interact with vitronectin, or on the cell type and experimental setting.

It is evident that PAI-1 is a functionally promiscuous protein, not only acting as a primary inhibitor of uPA and tPA, but also involved in modulating cell proliferation, migration, and apoptosis 58 , 60 , 62 , 93 , PAI-1 expression is tightly regulated and under normal conditions PAI-1 is present as a trace protein in plasma.

However, during a pathological condition, such as cancer, atherosclerosis, diabetes, and severe obesity PAI-1 levels are dramatically elevated The involvement of PAI-1 in angiogenesis is controversial and not fully understood. It regulates this process through binding of PAI-1 to vitronectin 60 or through inhibition of uPA and tPA where excess plasmin activity is abrogated leading to vessel stabilization 33 , Components of the plasminogen activators-plasmin system are also known to regulate apoptosis, however PAI-1 can be pro-apoptotic 61 , 63 , 87 , and anti-apoptotic 70 , 93 , 94 , Increased levels of PAI-1 in tumor pathologies prove to be beneficial to the tumor as it down-regulates apoptosis promoting a more aggressive phenotype and supporting the paradox that elevated PAI-1 levels correlate with poor patient prognosis.

Another advantage for cancer cells producing high levels of endogenous PAI-1 may be that they are less sensitive to chemotherapy treatment.

Hence, up-regulation of PAI-1 in cancer cells foster tumor growth and spread. From the above investigations it appears that down-regulation of PAI-1 would be beneficial for killing tumorigenic growth. Absence of PAI-1 in VSMC, an important component of an atherosclerotic plaque, increases the apoptotic index, which may be beneficial in preventing atherosclerotic plaque formation or restenosis.

These data provide mechanistic insights in terms of the pathogenic or protective role of PAI-1 in vascular remodeling. Figure 1 schematically portrays the possible mechanisms by which PAI-1 could be regulating apoptosis. Alhough PAI-1 is a secreted protein, any intracellular events occurring after PAI-1 is internalized and is able to interact with caspases or other apoptotic proteins should not be discounted.

Besides, interaction of PAI-1 with LRP may elicit recruitment of signaling intermediates that could regulate apoptosis via an unknown mechanism. There is a high probability that such a mechanism is possible when PAI-1 is added exogenously.

Excess PAI-1 synthesized in a diseased state is known to compete for binding with vitronectin causing detachment of EC.

Patient education: Ischemic stroke treatment Beyond the Basics. American Stroke Association. Why getting quick stroke treatment is important. Merck Manual Consumer Version. Ischemic stroke. Multicenter study of adverse events after intravenous tissue-type plasminogen activator treatment of acute ischemic stroke.

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Create a personalised ads profile. Review Questions Access free multiple choice questions on this topic. Comment on this article. References 1. Gravanis I, Tsirka SE. Tissue-type plasminogen activator as a therapeutic target in stroke. Expert Opin Ther Targets. J Stroke Cerebrovasc Dis. Tissue plasminogen activator: an evaluation of clinical efficacy in acute myocardial infarction.

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High rate of complete recanalization and dramatic clinical recovery during tPA infusion when continuously monitored with 2-MHz transcranial doppler monitoring.

Golembiewski J. TPA is only used for strokes caused by blood clots. When TPA is injected into a vein, it quickly travels through the blood to reach the clogged blood vessel, where it works by trying to dissolve the blood clot and to restore blood flow to the brain. This allows the brain to remain healthy before stroke damage can occur. Intravenous TPA has to be administered within the first few hours after a stroke begins. The start of a stroke is counted from the time that you first notice stroke symptoms.

After this very short window of a few hours after a stroke starts, you cannot receive TPA because it might cause more harm than good at that point. Clinical guidelines for the early treatment of stroke published jointly by the American Heart Association and American Stroke Association strongly recommend the use of TPA for eligible patients within three hours of symptom onset. Some of the eligibility criteria involved in the decision to use TPA include other heart conditions, blood glucose levels, blood pressure levels, and age.

Most of the time, patients do not ask for TPA. But emergency medical workers are trained to recognize a stroke and emergency rooms are equipped with the staff and provisions to administer TPA when it is necessary. Since its inception, TPA has been administered to many patients. The long-term and short-term effects of TPA have been carefully evaluated. Overall, in the right circumstances, TPA has been proven to be beneficial.

A comparison of stroke patients who did receive TPA vs. The sooner stroke patients receive TPA, the better the recovery. For every minute delay in TPA treatment, the poorer the outcome. Mobile stroke units in some cities can help stroke patients receive treatment faster. Because TPA is a powerful blood thinner, the main side effect is bleeding.