Plasmin-mediated fibroblast growth factor-2 mobilisation supports smooth muscle cell proliferation in human saphenous vein

Epithelial-mesenchymal plasticity in kidney fibrosis

Epithelial-mesenchymal transition (EMT) is an important biological process contributing to kidney fibrosis and chronic kidney disease. This process is characterized by decreased epithelial phenotypes/markers and increased mesenchymal phenotypes/markers. Tubular epithelial cells (TECs) are commonly susceptible to EMT by various stimuli, for example, transforming growth factor-β (TGF-β), cellular communication network factor 2, angiotensin-II, fibroblast growth factor-2, oncostatin M, matrix metalloproteinase-2, tissue plasminogen activator (t-PA), plasmin, interleukin-1β, and reactive oxygen species. Similarly, glomerular podocytes can undergo EMT via these stimuli and by high glucose condition in diabetic kidney disease. EMT of TECs and podocytes leads to tubulointerstitial fibrosis and glomerulosclerosis, respectively. Signaling pathways involved in EMT-mediated kidney fibrosis are diverse and complex. TGF-β1/Smad and Wnt/β-catenin pathways are the major venues triggering EMT in TECs and podocytes. These two pathways thus serve as the major therapeutic targets against EMT-mediated kidney fibrosis. To date, a number of EMT inhibitors have been identified and characterized. As expected, the majority of these EMT inhibitors affect TGF-β1/Smad and Wnt/β-catenin pathways. In addition to kidney fibrosis, these EMT-targeted antifibrotic inhibitors are expected to be effective for treatment against fibrosis in other organs/tissues.

Receptor Tyrosine Kinase: Still an Interesting Target to Inhibit the Proliferation of Vascular Smooth Muscle Cells

Vascular smooth muscle cells (VSMCs) proliferation is a critical event that contributes to the pathogenesis of vascular remodeling such as hypertension, restenosis, and pulmonary hypertension. Increasing evidences have revealed that VSMCs proliferation is associated with the activation of receptor tyrosine kinases (RTKs) by their ligands, including the insulin-like growth factor receptor (IGFR), fibroblast growth factor receptor (FGFR), epidermal growth factor receptor (EGFR), vascular endothelial growth factor receptor (VEGFR), and platelet-derived growth factor receptor (PDGFR). Moreover, some receptor tyrosinase inhibitors (TKIs) have been found and can prevent VSMCs proliferation to attenuate vascular remodeling. Therefore, this review will describe recent research progress on the role of RTKs and their inhibitors in controlling VSMCs proliferation, which helps to better understand the function of VSMCs proliferation in cardiovascular events and is beneficial for the prevention and treatment of vascular disease.

Plasmin and Plasminogen System in the Tumor Microenvironment: Implications for Cancer Diagnosis, Prognosis, and Therapy

Simple Summary

In this review, we present a detailed discussion of how the plasminogen-activation system is utilized by tumor cells in their unrelenting attack on the tissues surrounding them. Plasmin is an enzyme which is responsible for digesting several proteins that hold the tissues surrounding solid tumors together. In this process tumor cells utilize the activity of plasmin to digest tissue barriers in order to leave the tumour site and spread to other parts of the body. We specifically focus on the role of plasminogen receptor—p11 which is an important regulatory protein that facilitates the conversion of plasminogen to plasmin and by this means promotes the attack by the tumour cells on their surrounding tissues.

Abstract

The tumor microenvironment (TME) is now being widely accepted as the key contributor to a range of processes involved in cancer progression from tumor growth to metastasis and chemoresistance. The extracellular matrix (ECM) and the proteases that mediate the remodeling of the ECM form an integral part of the TME. Plasmin is a broad-spectrum, highly potent, serine protease whose activation from its precursor plasminogen is tightly regulated by the activators (uPA, uPAR, and tPA), the inhibitors (PAI-1, PAI-2), and plasminogen receptors. Collectively, this system is called the plasminogen activation system. The expression of the components of the plasminogen activation system by malignant cells and the surrounding stromal cells modulates the TME resulting in sustained cancer progression signals. In this review, we provide a detailed discussion of the roles of plasminogen activation system in tumor growth, invasion, metastasis, and chemoresistance with specific emphasis on their role in the TME. We particularly review the recent highlights of the plasminogen receptor S100A10 (p11), which is a pivotal component of the plasminogen activation system.

The Warburg Effect and lactate signaling augment Fgf-MAPK to promote sensory-neural development in the otic vesicle

Recent studies indicate that many developing tissues modify glycolysis to favor lactate synthesis (Agathocleous et al., 2012; Bulusu et al., 2017; Gu et al., 2016; Oginuma et al., 2017; Sá et al., 2017; Wang et al., 2014; Zheng et al., 2016), but how this promotes development is unclear. Using forward and reverse genetics in zebrafish, we show that disrupting the glycolytic gene phosphoglycerate kinase-1 (pgk1) impairs Fgf-dependent development of hair cells and neurons in the otic vesicle and other neurons in the CNS/PNS. Fgf-MAPK signaling underperforms in pgk1- / - mutants even when Fgf is transiently overexpressed. Wild-type embryos treated with drugs that block synthesis or secretion of lactate mimic the pgk1- / - phenotype, whereas pgk1- / - mutants are rescued by treatment with exogenous lactate. Lactate treatment of wild-type embryos elevates expression of Etv5b/Erm even when Fgf signaling is blocked. However, lactate’s ability to stimulate neurogenesis is reversed by blocking MAPK. Thus, lactate raises basal levels of MAPK and Etv5b (a critical effector of the Fgf pathway), rendering cells more responsive to dynamic changes in Fgf signaling required by many developing tissues.

Smooth muscle cells of human veins show an increased response to injury at valve sites

OBJECTIVE

Venous valves are essential but are prone to injury, thrombosis, and fibrosis. We compared the behavior and gene expression of smooth muscle cells (SMCs) in the valve sinus vs nonvalve sites to elucidate biologic differences associated with vein valves.

METHODS

Tissue explants of fresh human saphenous veins were prepared, and the migration of SMCs from explants of valve sinus vs nonvalve sinus areas was measured. Proliferation and death of SMCs were determined by staining for Ki67 and terminal deoxynucleotidyl transferase dUTP nick end labeling. Proliferation and migration of passaged valve vs nonvalve SMCs were determined by cell counts and using microchemotaxis chambers. Global gene expression in valve vs nonvalve intima-media was determined by RNA sequencing.

RESULTS

Valve SMCs demonstrated greater proliferation in tissue explants compared with nonvalve SMCs (19.3% ± 5.4% vs 6.8% ± 2.0% Ki67-positive nuclei at 4 days, respectively; mean ± standard error of the mean, five veins; P < .05). This was also true for migration (18.2 ± 2.7 vs 7.5 ± 3.0 migrated SMCs/explant at 6 days, respectively; 24 veins, 15 explants/vein; P < .0001). Cell death was not different (39.6% ± 16.1% vs 41.5% ± 16.0% terminal deoxynucleotidyl transferase dUTP nick end labeling-positive cells, respectively, at 4 days, five veins). Cultured valve SMCs also proliferated faster than nonvalve SMCs in response to platelet-derived growth factor subunit BB (2.9 ± 0.2-fold vs 2.1 ± 0.2-fold of control, respectively; P < .001; n = 5 pairs of cells). This was also true for migration (6.5 ± 1.2-fold vs 4.4 ± 0.8-fold of control, respectively; P < .001; n = 7 pairs of cells). Blockade of fibroblast growth factor 2 (FGF2) inhibited the increased responses of valve SMCs but had no effect on nonvalve SMCs. Exogenous FGF2 increased migration of valve but not of nonvalve SMCs. Unlike in the isolated, cultured cells, blockade of FGF2 in the tissue explants did not block migration of valve or nonvalve SMCs from the explants. Thirty-seven genes were differentially expressed by valve compared with nonvalve intimal-medial tissue (11 veins). Peptide-mediated inhibition of SEMA3A, one of the differentially expressed genes, increased the number of migrated SMCs of valve but not of nonvalve explants.

CONCLUSIONS

Valve compared with nonvalve SMCs have greater rates of migration and proliferation, which may in part explain the propensity for pathologic lesion formation in valves. Whereas FGF2 mediates these effects in cultured SMCs, the mediators of these stimulatory effects in the valve wall tissue remain unclear but may be among the differentially expressed genes discovered in this study. One of these genes, SEMA3A, mediates a valve-specific inhibitory effect on the injury response of valve SMCs.

Platelet-Derived Growth Factor Receptor-β Regulates Vascular Smooth Muscle Cell Phenotypic Transformation and Neuroinflammation After Intracerebral Hemorrhage in Mice

OBJECTIVE

Platelet-derived growth factor-BB activates platelet-derived growth factor receptor-β and promotes vascular smooth muscle cell phenotypic transformation. Elevated levels of non-muscle myosin IIB (SMemb) are found in secretory smooth muscle cells along with inflammatory mediators, such as intercellular adhesion molecule-1, which can amplify neutrophil infiltration into the brain. In the present study, we investigated the role of platelet-derived growth factor-BB/platelet-derived growth factor receptor-β following intracerebral hemorrhage-induced brain injury in mice, with emphasis on its ability to promote vascular smooth muscle cell phenotypic transformation followed by increased intercellular adhesion molecule-1 expression and elevated neutrophil infiltration in the vicinity of the hematoma. We also determined the extent to which plasmin from the hematoma influences the platelet-derived growth factor-BB/platelet-derived growth factor receptor-β system subsequent to intracerebral hemorrhage.

DESIGN

Controlled in vivo laboratory study.

SETTING

Animal research laboratory.

SUBJECTS

One hundred and fifty six eight-week-old male CD1 mice.

INTERVENTIONS

Brain injury was induced by autologous arterial blood or plasmin injection into mouse brains. Small interfering RNA targeting platelet-derived growth factor receptor-β was administered 24 hours before intracerebral hemorrhage. A platelet-derived growth factor receptor antagonist, Gleevec, was administered following intracerebral hemorrhage. A mitogen-activated protein kinase-activated protein kinase 2 inhibitor (KKKALNRQLGVAA) was delivered with platelet-derived growth factor-BB in naïve animals. Platelet-derived growth factor-BB was injected with a plasmin inhibitor (ε-aminocaproic acid) in intracerebral hemorrhage mice. Plasmin-injected mice were given platelet-derived growth factor receptor-β small interfering RNA 24 hours before the operation. Neurological deficits, brain edema, western blots, and immunofluorescence were evaluated.

MEASUREMENTS AND MAIN RESULTS

Platelet-derived growth factor receptor-β small interfering RNA attenuated SMemb and intercellular adhesion molecule-1 expression and neutrophil infiltration at 24 hours post injury and reduced neurological deficits and brain edema at 24 and 72 hours following intracerebral hemorrhage. The platelet-derived growth factor receptor antagonist, Gleevec, reduced SMemb and intercellular adhesion molecule-1 expression. Platelet-derived growth factor receptor-β activation led to increased expression of intercellular adhesion molecule-1 and was reversed by KKKALNRQLGVAA in naïve mice. Plasmin inhibition suppressed platelet-derived growth factor receptor-β activation and neutrophil infiltration, whereas exogenous platelet-derived growth factor-BB increased platelet-derived growth factor receptor-β activation, regardless of plasmin inhibition. Platelet-derived growth factor receptor-β small interfering RNA decreased the expression of intercellular adhesion molecule-1 by plasmin injection.

CONCLUSION

The platelet-derived growth factor-BB/platelet-derived growth factor receptor-β system contributes to neuroinflammation through vascular smooth muscle cell phenotypic transformation near the hematoma via the p38 mitogen-activated protein kinase/mitogen-activated protein kinase-activated protein kinase 2 pathway following intracerebral hemorrhage. Plasmin is hypothesized to be upstream of the proposed neuroinflammatory system. The therapeutic intervention targeting the platelet-derived growth factor-BB/platelet-derived growth factor receptor-β is a novel strategy to prevent plasmin-induced brain injury following intracerebral hemorrhage.

Peptides with 6-Aminohexanoic Acid: Synthesis and Evaluation as Plasmin Inhibitors

Fifteen new peptide derivatives of ɛ-aminocaproic acid (EACA) containing the known fragment –Ala–Phe–Lys– with an affinity for plasmin were synthesised in the present study. The synthesis was carried out a solid phase. The following compounds were synthesised: H–Phe–Lys–EACA–X, H–d-Ala–Phe–Lys–EACA–X, H–Ala–Phe–Lys–EACA–X, H–d-Ala–Phe–EACA–X and H–Ala–Phe–EACA–X, where X = OH, NH₂ and NH–(CH₂)₅–NH₂. All peptides, except for those containing the sequence H–Ala–Phe–EACA–X, displayed higher inhibitory activity against plasmin than EACA. The most active and selective inhibitor of plasmin was the compound H–d-Ala–Phe–Lys–EACA–NH₂ which inhibited the amidolytic activity of plasmin (IC₅₀ = 0.02 mM), with the antifibrinolytic activity weaker than EACA. The resulting peptides did not affect the viability of fibroblast cells, colon cancer cell line DLD-1, breast MCF-7 and MDA-MB-231 cell lines.

Extracellular matrix modulates angiogenesis in physiological and pathological conditions

Angiogenesis is a multistep process driven by a wide range of positive and negative regulatory factors. Extracellular matrix (ECM) plays a crucial role in the regulation of this process. The degradation of ECM, occurring in response to an angiogenic stimulus, leads to degradation or partial modification of matrix molecules, release of soluble factors, and exposure of cryptic sites with pro- and/or antiangiogenic activity. ECM molecules and fragments, resulting from proteolysis, can also act directly as inflammatory stimuli, and this can explain the exacerbated angiogenesis that drives and maintains several inflammatory diseases. In this review we have summarized some of the more recent literature data concerning the molecular control of ECM in angiogenesis in both physiological and pathological conditions.

Smooth muscle cell hypertrophy, proliferation, migration and apoptosis in pulmonary hypertension

Pulmonary hypertension is a multifactorial disease characterized by sustained elevation of pulmonary vascular resistance (PVR) and pulmonary arterial pressure (PAP). Central to the pathobiology of this disease is the process of vascular remodelling. This process involves structural and functional changes to the normal architecture of the walls of pulmonary arteries (PAs) that lead to increased muscularization of the muscular PAs, muscularization of the peripheral, previously nonmuscular, arteries of the respiratory acinus, formation of neointima, and formation of plexiform lesions. Underlying or contributing to the development of these lesions is hypertrophy, proliferation, migration, and resistance to apoptosis of medial cells and this article is concerned with the cellular and molecular mechanisms of these processes. In the first part of the article we focus on the concept of smooth muscle cell phenotype and the difficulties surrounding the identification and characterization of the cell/cells involved in the remodelling of the vessel media and we review the general mechanisms of cell hypertrophy, proliferation, migration and apoptosis. Then, in the larger part of the article, we review the factors identified thus far to be involved in PH intiation and/or progression and review and discuss their effects on pulmonary artery smooth muscle cells (PASMCs) the predominant cells in the tunica media of PAs.

Cell surface remodeling by plasmin: a new function for an old enzyme

Plasmin, one of the most potent and reactive serine proteases, is involved in various physiological processes, including embryo development, thrombolysis, wound healing and cancer progression. The proteolytic activity of plasmin is tightly regulated through activation of its precursor, plasminogen, only at specific times and in defined locales as well as through inhibition of active plasmin by its abundant natural inhibitors. By exploiting the plasminogen activating system and overexpressing distinct components of the plasminogen activation cascade, such as pro-uPA, uPAR and plasminogen receptors, malignant cells can enhance the generation of plasmin which in turn, modifies the tumor microenvironment to sustain cancer progression. While plasmin-mediated degradation and modification of extracellular matrix proteins, release of growth factors and cytokines from the stroma as well as activation of several matrix metalloproteinase zymogens, all have been a focus of cancer research studies for decades, the ability of plasmin to cleave transmembrane molecules and thereby to generate functionally important cleaved products which induce outside-in signal transduction, has just begun to receive sufficient attention. Herein, we highlight this relatively understudied, but important function of the plasmin enzyme as it is generated de novo at the interface between cross-talking cancer and host cells.

Natural and engineered plasmin inhibitors: applications and design strategies

The serine protease plasmin is ubiquitously expressed throughout the human body in the form of the zymogen plasminogen. Conversion to active plasmin occurs through enzymatic cleavage by plasminogen activators. The plasminogen activator/plasmin system has a well-established function in the removal of intravascular fibrin deposition through fibrinolysis and the inhibition of plasmin activity; this has found widespread clinical use in reducing perioperative bleeding. Increasing evidence also suggests diverse, although currently less defined, roles for plasmin in a number of physiological and pathological processes relating to extracellular matrix degradation, cell migration and tissue remodelling. In particular, dysregulation of plasmin has been linked to cancer invasion/metastasis and various chronic inflammatory conditions; this has prompted efforts to develop inhibitors of this protease. Although a number of plasmin inhibitors exist, they commonly suffer from poor potency and/or specificity of inhibition that either results in reduced efficacy or prevents clinical use. Consequently, there is a need for further development of high-affinity plasmin inhibitors that maintain selectivity over other serine proteases. This review summarises clearly defined and potential applications for plasmin inhibition. The properties of naturally occurring and engineered plasmin inhibitors are discussed in the context of current knowledge regarding plasmin structure, specificity and function. This includes design strategies to obtain the potency and specificity of inhibition in addition to controlled temporal and spatial distribution tailored for the intended use.

Fibrin degradation enhances vascular smooth muscle cell proliferation and matrix deposition in fibrin-based tissue constructs fabricated in vitro

Completely biological tissue replacements can be fabricated by entrapping cells in a molded fibrin gel. Over time, the fibrin is degraded and replaced with cell-produced extracellular matrix. However, the relationship between fibrin degradation and matrix deposition has not been elucidated. We developed techniques to quantify fibrin degradation products (FDP) and examine plasmin activity in the conditioned medium from fibrin-based constructs. Fibrin-based tissue constructs fabricated with vascular smooth muscle cells (vSMC) were cultured for 5 weeks in the presence of varied concentrations of the fibrinolysis inhibitor -aminocaproic acid and cellularity, and deposited collagen and elastin were measured weekly. These data revealed that increasing concentrations of -aminocaproic acid led to delayed and diminished FDP production, lower vSMC proliferation, and decreased collagen and elastin deposition. FDP were shown to have a direct biological effect on vSMC cultures and vSMC within the fibrin-based constructs. Supplementing construct cultures with 250 or 500μg/mL FDP led to 30% higher collagen deposition than the untreated controls. FDP concentrations as high as 250μg/mL were estimated to exist within the constructs, indicating that FDP generation during remodeling of the fibrin-based constructs exerted direct biological activity. These results help explain many of the positive outcomes reported with fibrin-based tissue constructs in the literature, as well as demonstrate the importance of regulating plasmin activity during their fabrication.

MMP-7 mediates cleavage of N-cadherin and promotes smooth muscle cell apoptosis

Aims

Vascular smooth muscle cell (VSMC) apoptosis can lead to thinning of the fibrous cap and plaque instability. We previously showed that cell–cell contacts mediated by N-cadherin reduce VSMC apoptosis. This study aimed to determine whether matrix-degrading metalloproteinase (MMP)-dependent N-cadherin cleavage causes VSMC apoptosis.

Methods and results

Induction of human VSMC apoptosis using different approaches, including 200 ng/mL Fas ligand (Fas-L) and culture in suspension, caused N-cadherin cleavage and resulted in the appearance of a C-terminal fragment of N-cadherin (∼35 kDa). Appearance of this fragment during apoptosis was inhibited by 47% with the broad-spectrum MMP inhibitor BB-94. We observed retarded cleavage of N-cadherin after treatment with Fas-L in aortic mouse VSMCs lacking MMP-7. Furthermore, VSMC apoptosis, measured by quantification of cleaved caspase-3, was 43% lower in MMP-7 knockout mouse VSMCs compared with wild-type VSMCs following treatment with Fas-L. Addition of recombinant active MMP-7 increased the amount of N-cadherin fragment by 82% and augmented apoptosis by 53%. The involvement of MMP-7 was corroborated using human cells, where a MMP-7 selective inhibitor reduced the amount of fragment formed by 51%. Importantly, we observed that treatment with Fas-L increased levels of active MMP-7 by 80%. Finally, we observed significantly increased cleavage of N-cadherin, MMP-7 activity, and apoptosis in human atherosclerotic plaques compared with control arteries, and a significant reduction in apoptosis in atherosclerotic plaques from MMP-7 knockout mice.

Conclusion

This study demonstrates that MMP-7 is involved in the cleavage of N-cadherin and modulates VSMC apoptosis, and may therefore contribute to plaque development and rupture.

Breast cancer cell surface annexin II induces cell migration and neoangiogenesis via tPA dependent plasmin generation

Annexin II, an abundant phospholipids binding cell surface protein, binds tPA and functions as a regulator of fibrinolysis. Annexin II also mediates angiogenesis and enhances tumor growth and metastasis. However, the mechanism supporting this role is not known. Using human breast cancer model we show that invasive human breast cancer cells (MDA-MB231) synthesize annexin II and tissue plasminogen activator (tPA). In vitro both annexin II and tPA interacts which in turn convert zymogen plasminogen to reactive enzyme plasmin. Cell surface produced plasmin inhibited the migration of MDA-MB231 cells. Silencing of annexin II gene in MDA-MB231 cells abolished tPA binding therefore inhibited tPA dependent plasmin generation. These annexin II suppressed MDA-MB231 cells showed reduced motility. Immunohistochemical analysis of prediagnosed clinical specimens showed abundant secretion of tPA and expression of annexin II on the surface of invasive human breast cancer cells which correlates with neovascularization of the tumor. Taken together, these data indicate that annexin II may regulate localized plasmin generation in breast cancer. This may be an early event switching breast cancer from the prevascular phase to the vascular phase and thus contributing to aggressive cancer with the possibility of metastasis. The data provide a mechanism explaining the role of annexin II in breast cancer progression and suggest that annexin II may be an attractive target for therapeutic strategies aimed to inhibit angiogenesis and breast cancer.

Endothelial-derived FGF2 contributes to the progression of pulmonary hypertension in humans and rodents

Pulmonary hypertension (PH) is a progressive, lethal lung disease characterized by pulmonary artery SMC (PA-SMC) hyperplasia leading to right-sided heart failure. Molecular events originating in pulmonary ECs (P-ECs) may contribute to the PA-SMC hyperplasia in PH. Thus, we exposed cultured human PA-SMC to medium conditioned by P-EC from patients with idiopathic PH (IPH) or controls and found that IPH P-EC-conditioned medium increased PA-SMC proliferation more than control P-EC medium. Levels of FGF2 were increased in the medium of IPH P-ECs over controls, while there was no detectable difference in TGF-beta1, PDGF-BB, or EGF levels. No difference in FGF2-induced proliferation or FGF receptor type 1 (FGFR1) mRNA levels was detected between IPH and control PA-SMCs. Knockdown of FGF2 in P-EC using siRNA reduced the PA-SMC growth-stimulating effects of IPH P-EC medium by 60% and control P-EC medium by 10%. In situ hybridization showed FGF2 overproduction predominantly in the remodeled vascular endothelium of lungs from patients with IPH. Repeated intravenous FGF2-siRNA administration abolished lung FGF2 production, both preventing and nearly reversing a rat model of PH. Similarly, pharmacological FGFR1 inhibition with SU5402 reversed established PH in the same model. Thus, endothelial FGF2 is overproduced in IPH and contributes to SMC hyperplasia in IPH, identifying FGF2 as a promising target for new treatments against PH.

Antiplasmin activity of natural occurring polyphenols

The equilibrium between proteolytic enzymes and their cognate inhibitors is crucial in a number of physiological as well as pathological processes, including cancer, inflammatory processes and thrombosis. Therefore, both synthetic and natural small molecule inhibitors are object of extensive studies as drugs in the treatment of these pathologies. Two natural occurring polyphenolic compounds, representative of glycosylated and unglycosylated flavonoid structures, namely quercetin and rutin, were thereby tested as potential ligands of plasmin(ogen), a serine (pro)protease, whose role in tumor cell invasion and migration has been reported. Quercetin showed a ten folds higher affinity with plasmin with respect to rutin in terms of equilibrium dissociation constant, both compounds acting as in vitro moderate reversible inhibitors; additionally, quercetin and rutin prevented plasmin-incubated BB1 cells from releasing E-cadherin fragment to a different extent, respectively. Furthermore, a feasible mechanism of interaction was analyzed and discussed using a molecular modeling approach.

Urokinase-type plasminogen activator deficiency (uPA-KO) prevented carotid artery ligation-induced vascular remodeling in mice

It has been demonstrated that urokinase-type plasminogen activator (uPA) plays an important role in vascular remodeling. This study was designed to determine whether uPA deficiency (KO) affects carotid artery ligation-induced vessel remodeling and the interaction with angiotensin II (Ang II). Ligation of the left common carotid artery in 6-month-old wild-type (C57 black/6J) mice for 4 weeks induced a concentric remodeling with vessel wall thickening, characterized by cell proliferation in neointima, media, and adventitia, and with lumen narrowing without a significant enlargement of overall vessel dimension. Intima lesions were characterized by alpha-actin positive smooth muscle cell (SMC) proliferation in a matrix background. No detectable presence of MAC-3 positive macrophages existed in the vascular wall. The ligation-induced vascular neointimal formation and adventitial proliferation, but not lumen narrowing and media expansion, were completely prevented in age-matched uPA-KO mice. Chronic infusion of Ang II (1.44 mg/kg per day) via a subcutaneously implanted osmotic minipump did not significantly affect the gross morphology of the nonligated carotid artery from both wild-type and uPA-KO mice, but it enhanced ligation-induced vascular remodeling. However, in the presence of Ang II, uPA deficiency had no effects on ligation-induced mophermetric change, but it partially and significantly reduced cell proliferation. These data indicate that uPA may play a critical role in ligation-induced vessel remodeling. Ang II may activate other mechanisms independent of uPA to exacerbate ligation-induced vascular remodeling.

Proteolysis of CCN1 by plasmin: functional implications

Plasmin is shown to play a crucial role in many pathophysiologic processes primarily through its ability to degrade extracellular matrix (ECM) and/or mobilizing growth factors that are sequestered in the ECM. Cysteine-rich 61 (CCN1) is a matricellular protein of which expression is up-regulated in cancer and various vascular diseases. The present study was undertaken to investigate whether plasmin liberates CCN1 from the ECM and whether the released growth factor modulates endothelial cell migration. Treatment of breast carcinoma cells (MDA-MB-231) with plasmin released a truncated form of CCN1 (28 kDa) into the overlying medium. Experiments with recombinant CCN1 confirmed that plasmin effectively cleaves CCN1. Thrombin and other clotting/fibrinolytic proteases are ineffective in cleaving CCN1. Further studies revealed that the conditioned medium of plasmin-treated carcinoma cells supports endothelial cell migration and that antibodies specific to CCN1 blocked this enhancing effect. These data were the first to show that plasmin can liberate a pluripotent matrix signaling protein, CCN1, from the ECM. Because both CCN1 and the components of the plasmin generation system are present in tumor cells and a variety of other cells, the proteolysis of CCN1 by plasmin may play a role in many pathophysiologic processes, including tumor cell-mediated angiogenesis.

Effect of tissue plasminogen activator on vascular smooth muscle cells

OBJECTIVE

Engineered overexpression of tissue plasminogen activator (tPA) in vascular cells has been proposed as a means to decrease intravascular thrombosis; however, tPA gene transfer has augmented intimal hyperplasia in vivo in some studies. The purpose of this study was to define in vitro the effect of tPA gene transfer on smooth muscle cells (SMCs).

METHODS

Human SMCs were retrovirally transduced with the tPA gene (SMCs/tPA).

RESULTS

In the absence of plasminogen, no statistical differences in proliferation, migration, and morphology were observed between SMCs/tPA and SMCs. In the presence of plasminogen, many differences became apparent. Matrix metalloproteinase-2 (MMP-2) activation was 10-fold higher in SMCs/tPA than in SMCs. This activation was inhibited by aprotinin, a plasmin inhibitor. Collagen degradation increased sevenfold in SMCs/tPA. SMCs/tPA contracted dramatically in the presence of plasminogen. This cell contraction, indicative of extracellular matrix degradation, was blocked by aprotinin and partially inhibited by MMP inhibitors. SMC/tPA-conditioned medium induced significantly more SMC proliferation. The migration of SMCs/tPA through a porous membrane significantly exceeded untransduced SMCs.

CONCLUSIONS

Over-expression of tPA in SMCs results in increased extracellular matrix degradation and can promote cell proliferation and migration. This effect is mediated via plasmin, which further activates MMP-2.

CLINICAL RELEVANCE

TPA has been clinically used as a thrombolytic agent in the treatment of acute thrombotic disorders. Transferring the tPA gene into vascular cells as a strategy of gene therapy has been proposed to enhance fibrinolytic capability and therefore inhibit thrombosis and restenosis after vascular interventions. The mechanism(s) by which tPA affects SMC proliferation and vascular remodeling has not been thoroughly characterized. This study unveils the relationship between thrombolytic activity and intimal hyperplasia by showing how the elevated expression of tPA affects the vascular remodeling. This study underscores that the overexpression of an enzyme thought beneficial to blood flow can potentially compromise blood flow by altering the biology of the cell engineered to express it. The results are important to the rational engineering of bioactive grafts with better patency. A new strategy to enhance the thrombolytic ability of a vascular surface without inducing excessive neointimal hyperplasia is proposed.

Transforming growth factor-beta is activated by plasmin and inhibits smooth muscle cell death in human saphenous vein

BACKGROUND

The effect of activation of endogenous transforming growth factor-beta (TGF-beta) on smooth muscle cell apoptosis was assessed in human saphenous vein.

METHODS

Segments of human saphenous vein, obtained at the time of bypass graft surgery, were cultured for 14 days. During this time, smooth muscle cells accumulated in the intima as a result of proliferation and migration, partly counterbalanced by apoptotic cell death.

RESULTS

Addition of exogenous TGF-beta(1) had no effect on smooth muscle cell proliferation or apoptosis. However, antibody neutralization of endogenous TGF-beta(1) caused significant increases in smooth muscle cell death in the media and intima without any change in proliferation. A plasmin inhibitor (alpha-N-acetyl-L-lysine methyl ester), a specific urokinase-type plasminogen activator (uPA) inhibitor (amiloride) and an anti-catalytic anti-uPA antibody all caused decreases in the tissue content of active TGF-beta and increases in smooth muscle cell death in the media and intima.

CONCLUSIONS

These data suggest that the amount of TGF-beta in human saphenous vein is sufficient, when in the active form, to protect smooth muscle cells against apoptosis. Adding exogenous TGF-beta(1) has no beneficial effect, but decreasing the amount of active TGF-beta causes smooth muscle cells to undergo apoptosis. Plasmin, generated by uPA, appears to be an important activator of endogenous latent TGF-beta.

A novel mechanism of plasmin-induced mitogenesis in fibroblasts

The plasminogen activator/plasmin system is believed to play an important role in diverse pathophysiological processes, including wound healing, vascular remodeling and pulmonary fibrosis. Our recent studies show that plasmin upregulates the expression of Cyr61, a growth factor-like gene that has been implicated in cell proliferation and migration. In the present study, we investigated whether plasmin promotes fibroblast proliferation and, if so, determine the role of Cyr61 in the plasmin-induced response. Human lung fibroblasts were exposed to varying concentrations of plasmin and DNA synthesis was monitored by measuring the incorporation of 3H-thymidine into DNA. Plasmin increased DNA synthesis of fibroblasts in a dose-dependent manner. Protease-activated receptor-1 (PAR-1)-specific antibodies, but not PAR-2-specific antibodies, reduced the plasmin-induced DNA synthesis. Consistent with this, plasmin had no substantial effect on the DNA synthesis in PAR-1-deficient mouse fibroblasts. Plasmin activated both p38 and p44/42 MAPKs and specific inhibitors of these pathways inhibited the plasmin-induced DNA synthesis. Plasmin-induced increase in the DNA synthesis was completely abrogated by anti-Cyr61 antibodies. Interestingly, thrombin, which is a potent inducer of Cyr61, had only a minimal effect on fibroblast proliferation. Additional experiments suggested that plasmin cleaved cell/extracellular matrix-associated Cyr61 and the conditioned media from plasmin-treated cells could support the cell proliferation. Overall, these data suggest that plasmin promotes fibroblast proliferation by a novel pathway, involving two independent steps. In the first step, plasmin induces Cyr61 expression via activation of PAR-1, and in the second step, plasmin releases Cyr61 deposited in the extracellular matrix, thus making it accessible to act on cells.

Tumor growth and metastasis are not affected in thrombin-activatable fibrinolysis inhibitor-deficient mice

Many studies have indicated that the plasminogen activation system may have a prominent role in cancer. Activation of the zymogen plasminogen into the serine protease plasmin by plasminogen activator is mediated by carboxyterminal basic amino acids in fibrin, including lysines and arginines. Thrombin-activatable fibrinolysis inhibitor (TAFI) is a circulating carboxypeptidase B-type proenzyme that, after activation, removes carboxyterminal lysine or arginine residues in fibrin, resulting in decreased plasminogen activation and attenuated fibrinolysis. To determine directly whether TAFI is involved in primary tumor growth and metastasis formation, we examined the effects of TAFI deficiency on subcutaneous growth and experimentally or spontaneously induced pulmonary metastasis formation of different tumor cell types in mice. In all tumor models TAFI deficiency did not affect the formation and growth of primary and metastasized tumors.

The role of plasminogen in angiogenesis in vivo

Plasminogen, by virtue of its role in the degradation of extracellular matrix proteins and by facilitation of cell migration, may contribute to angiogenesis.

OBJECTIVE

the purpose of this study was to evaluate the contribution of plasminogen to angiogenesis in vivo.

METHODS

Angiogenesis was assessed in gene-targeted mice with deficiencies of plasminogen, urokinase plasminogen activator (uPA), and urokinase receptor (uPAR) in a mouse corneal model. In wild-type mice, female and young mice showed a trend toward increased angiogenesis compared to males and old mice. Because of this influence of age and gender on angiogenesis, young, female mice (6-13 weeks of age) were used for this study.

RESULTS

In response to angiogenic stimulation by basic fibroblast growth factor (bFGF), uPA deficient mice exhibited a decrease in new vessel formation as reflected by vessel length (0.47 in control vs. 0.33 mm in uPA-/- mice, P = 0.043), but new vessel formation was not altered (P = 0.107) in the uPAR deficient mice compared to control mice. A significantly decreased angiogenic response of new vessel formation to both vascular endothelial growth factor (VEGF) (P < 0.02) and bFGF (P < 0.007) was observed in Plg deficient (Plg-/-) mice (VEGF - 0.36 mm, bFGF - 0.67 mm) compared to Plg+/+ mice (VEGF - 0.56 mm, bFGF - 0.85 mm).

CONCLUSIONS

These results demonstrate the importance of plasminogen, as well as of uPA, in angiogenesis in vivo.