Amyloid beta-protein stimulates the expression of urokinase-type plasminogen activator (uPA) and its receptor (uPAR) in human cerebrovascular smooth muscle cells

Identification of vilazodone as a novel plasminogen activator inhibitor to overcome Alzheimer's disease through virtual screening, molecular dynamics simulation, and biological evaluation

Urokinase-type plasminogen activator (PLAU), a member of the S1 serine peptidase family in Clan PA, plays a crucial role in the conversion of plasminogen into active plasmin. However, the precise role of PLAU in the central nervous system remains incompletely elucidated, particularly, in relation to Alzheimer's disease (AD). In this study, we successfully identified that PLAU could promote cell senescence in neurons, indicating it as a potential target for AD treatment through a systematic approach, which included both bioinformatics analysis and experimental verification. Subsequently, a structure-based virtual screening approach was employed to identify a potential PLAU inhibitor from the Food and Drug Administration-approved drug database. After analyzing docking scores and thoroughly examining the receptor-ligand complex interaction modes, vilazodone emerges as a highly promising PLAU inhibitor. Additionally, molecular docking and molecular dynamics simulations were performed to generate a complex structure between the relatively stable inhibitor vilazodone and PLAU. Of note, vilazodone exhibited superior cytotoxicity against senescent cells, showing a senolytic activity through targeting PLAU and ultimately producing an anti-AD effect. These findings suggest that targeting PLAU could represent a promising therapeutic strategy for AD. Furthermore, investigating the inhibitory potential and structural modifications based on vilazodone may provide valuable insights for future drug development targeting PLAU in AD disorders.

Proximity extension assay in cerebrospinal fluid identifies neurofilament light chain as biomarker of neurodegeneration in sporadic cerebral amyloid angiopathy

BACKGROUND

Sporadic cerebral amyloid angiopathy (sCAA) is a disease characterised by the progressive deposition of the amyloid beta (Aβ) in the cerebral vasculature, capable of causing a variety of symptoms, from (mild) cognitive impairment, to micro- and major haemorrhagic lesions. Modern diagnosis of sCAA relies on radiological detection of late-stage hallmarks of disease, complicating early diagnosis and potential interventions in disease progression. Our goal in this study was to identify and validate novel biomarkers for sCAA.

METHODS

We performed a proximity extension assay (PEA) on cerebrospinal fluid (CSF) samples of sCAA/control participants (n = 34/51). Additionally, we attempted to validate the top candidate biomarker in CSF and serum samples (n = 38/26) in a largely overlapping validation cohort, through analysis with a targeted immunoassay.

RESULTS

Thirteen proteins were differentially expressed through PEA, with top candidate NFL significantly increased in CSF of sCAA patients (p < 0.0001). Validation analyses using immunoassays revealed increased CSF and serum NFL levels in sCAA patients (both p < 0.0001) with good discrimination between sCAA and controls (AUC: 0.85; AUC: 0.79 respectively). Additionally, the CSF: serum NFL ratio was significantly elevated in sCAA (p = 0.002).

DISCUSSION

Large-scale targeted proteomics screening of CSF of sCAA patients and controls identified thirteen biomarker candidates for sCAA. Orthogonal validation of NFL identified NFL in CSF and serum as biomarker, capable of differentiating between sCAA patients and controls.

Distinguishing Plasmin-Generating Microvesicles: Tiny Messengers Involved in Fibrinolysis and Proteolysis

A number of stressors and inflammatory mediators (cytokines, proteases, oxidative stress mediators) released during inflammation or ischemia stimulate and activate cells in blood, the vessel wall or tissues. The most well-known functional and phenotypic responses of activated cells are (1) the immediate expression and/or release of stored or newly synthesized bioactive molecules, and (2) membrane blebbing followed by release of microvesicles. An ultimate response, namely the formation of extracellular traps by neutrophils (NETs), is outside the scope of this work. The main objective of this article is to provide an overview on the mechanism of plasminogen reception and activation at the surface of cell-derived microvesicles, new actors in fibrinolysis and proteolysis. The role of microvesicle-bound plasmin in pathological settings involving inflammation, atherosclerosis, angiogenesis, and tumour growth, remains to be investigated. Further studies are necessary to determine if profibrinolytic microvesicles are involved in a finely regulated equilibrium with pro-coagulant microvesicles, which ensures a balanced haemostasis, leading to the maintenance of vascular patency.

Severe bleeding diathesis as onset of light-chain amyloidosis: combined excessive fibrinolysis and acquired von Willebrand disease in a young patient

Our report shows a case of primary light-chain amyloidosis in a young patient that reflects the potential severity of bleeding diathesis associated with this plasma cell dyscrasia and the difficulty of diagnosis when only hemorrhagic manifestations are present at the onset of disease. The patient presented with recurrent and severe muscular bleeding secondary to associated acquired von Willebrand disease and fibrinolysis dysfunction. Treatment with bortezomib-cyclophosphamide and sequential hematopoietic stem cell transplantation solved coagulation alterations. On the basis of our case, we review previous reports and discuss the potential mechanism of dysfunction of coagulation in light-chain amyloidosis.

Elevated expression of urokinase plasminogen activator in rodent models and patients with cerebral amyloid angiopathy

AIMS

The aim of this work is to study the association of urokinase plasminogen activator (uPA) with development and progression of cerebral amyloid angiopathy (CAA).

MATERIALS AND METHODS

We studied the expression of uPA mRNA by quantitative polymerase chain reaction (qPCR) and co-localisation of uPA with amyloid-β (Aβ) using immunohistochemistry in the cerebral vasculature of rTg-DI rats compared with wild-type (WT) rats and in a sporadic CAA (sCAA) patient and control subject using immunohistochemistry. Cerebrospinal fluid (CSF) uPA levels were measured in rTg-DI and WT rats and in two separate cohorts of sCAA and Dutch-type hereditary CAA (D-CAA) patients and controls, using enzyme-linked immunosorbent assays (ELISA).

RESULTS

The presence of uPA was clearly detected in the cerebral vasculature of rTg-DI rats and an sCAA patient but not in WT rats or a non-CAA human control. uPA expression was highly co-localised with microvascular Aβ deposits. In rTg-DI rats, uPA mRNA expression was highly elevated at 3 months of age (coinciding with the emergence of microvascular Aβ deposition) and sustained up to 12 months of age (with severe microvascular CAA deposition) compared with WT rats. CSF uPA levels were elevated in rTg-DI rats compared with WT rats (p = 0.03), and in sCAA patients compared with controls (after adjustment for age of subjects, p = 0.05 and p = 0.03). No differences in CSF uPA levels were found between asymptomatic and symptomatic D-CAA patients and their respective controls (after age-adjustment, p = 0.09 and p = 0.44). Increased cerebrovascular expression of uPA in CAA correlates with increased quantities of CSF uPA in rTg-DI rats and human CAA patients, suggesting that uPA could serve as a biomarker for CAA.

A Mutant Variant of E2F4 Triggers Multifactorial Therapeutic Effects in 5xFAD Mice

Alzheimer’s disease (AD) has a complex etiology, which requires a multifactorial approach for an efficient treatment. We have focused on E2 factor 4 (E2F4), a transcription factor that regulates cell quiescence and tissue homeostasis, controls gene networks affected in AD, and is upregulated in the brains of Alzheimer’s patients and of APP^swe/PS1^dE9 and 5xFAD transgenic mice. E2F4 contains an evolutionarily conserved Thr-motif that, when phosphorylated, modulates its activity, thus constituting a potential target for intervention. In this study, we generated a knock-in mouse strain with neuronal expression of a mouse E2F4 variant lacking this Thr-motif (E2F4DN), which was mated with 5xFAD mice. Here, we show that neuronal expression of E2F4DN in 5xFAD mice potentiates a transcriptional program consistent with the attenuation of the immune response and brain homeostasis. This correlates with reduced microgliosis and astrogliosis, modulation of amyloid-β peptide proteostasis, and blocking of neuronal tetraploidization. Moreover, E2F4DN prevents cognitive impairment and body weight loss, a known somatic alteration associated with AD. We also show that our finding is significant for AD, since E2F4 is expressed in cortical neurons from Alzheimer patients in association with Thr-specific phosphorylation, as evidenced by an anti-E2F4/anti-phosphoThr proximity ligation assay. We propose E2F4DN-based gene therapy as a promising multifactorial approach against AD.

Antimetastatic Potential of Quercetin Analogues with Improved Pharmacokinetic Profile: Pharmacoinformatic Preliminary Study

BACKGROUND

Urokinase-type plasminogen activator (uPA) system is a crucial pathway for tumor invasion and metastasis. Recently, multiple anticancer effects of quercetin have been described, including inhibitory activity against uPA. However, the clinical use of this flavonoid has been limited due to its low oral bioavailability.

OBJECTIVE

The objectives of the study were to assess the antimetastatic potential of quercetin analogues by analyzing their binding affinity for uPA and to select the compounds with improved pharmacological profiles.

METHODS

Binding affinities of structural analogues of quercetin to uPA receptor were determined by molecular docking analysis using Molegro Virtual Docker software, and molecular descriptors relevant for estimating pharmacological profile were calculated from ligand structures using computational models.

RESULTS

Among 44 quercetin analogues, only one quercetin analogue (3,6,2',4',5'-pentahydroxyflavone) was found to possess both higher aqueous solubility and membrane permeability, and a stronger affinity for uPA than quercetin, which makes it the potential lead compound for anticancer drug development. Like quercetin, this compound has five hydroxyl groups but is arranged differently, which contributes to the higher aqueous solubility and higher amphiphilic moment compared to quercetin. Since membrane permeability is not recognized as the limiting factor for quercetin absorption, analogues with higher aqueous solubility and retained or stronger uPA inhibitory activity should also be further experimentally validated for potential therapeutic use.

CONCLUSION

Identified quercetin analogues with better physicochemical and pharmacological properties have a high potential to succeed in later stages of research in biological systems as potential anticancer agents with antimetastatic activity.

Hemostasis components in cerebral amyloid angiopathy and Alzheimer's disease

Increased cerebrovascular amyloid-β (Aβ) deposition represents the main pathogenic mechanisms characterizing Alzheimer's disease (AD) and cerebral amyloid angiopathy (CAA). Whereas an increasing number of studies define the contribution of fibrin(ogen) to neurodegeneration, how other hemostasis factors might be pleiotropically involved in the AD and CAA remains overlooked. Although traditionally regarded as pertaining to hemostasis, these proteins are also modulators of inflammation and angiogenesis, and exert cytoprotective functions. This review discusses the contribution of hemostasis components to Aβ cerebrovascular deposition, which settle the way to endothelial and blood-brain barrier dysfunction, vessel fragility, cerebral bleeding, and the associated cognitive changes. From the primary hemostasis, the process that refers to platelet aggregation, we discuss evidence regarding the von Willebrand factor (vWF) and its regulator ADAMTS13. Then, from the secondary hemostasis, we focus on tissue factor, which triggers the extrinsic coagulation cascade, and on the main inhibitors of coagulation, i.e., tissue factor pathway inhibitor (TFPI), and the components of protein C pathway. Last, from the tertiary hemostasis, we discuss evidence on FXIII, involved in fibrin cross-linking, and on components of fibrinolysis, including tissue-type plasminogen activator (tPA), urokinase-type plasminogen activator (uPA) and its receptor uPA(R), and plasminogen activator inhibitor-1 (PAI-1). Increased knowledge on contributors of Aβ-related disease progression may favor new therapeutic approaches for early modifiable risk factors.

Plasminogen Activators in Neurovascular and Neurodegenerative Disorders

The neurovascular unit (NVU) is a dynamic structure assembled by endothelial cells surrounded by a basement membrane, pericytes, astrocytes, microglia and neurons. A carefully coordinated interplay between these cellular and non-cellular components is required to maintain normal neuronal function, and in line with these observations, a growing body of evidence has linked NVU dysfunction to neurodegeneration. Plasminogen activators catalyze the conversion of the zymogen plasminogen into the two-chain protease plasmin, which in turn triggers a plethora of physiological events including wound healing, angiogenesis, cell migration and inflammation. The last four decades of research have revealed that the two mammalian plasminogen activators, tissue-type plasminogen activator (tPA) and urokinase-type plasminogen activator (uPA), are pivotal regulators of NVU function during physiological and pathological conditions. Here, we will review the most relevant data on their expression and function in the NVU and their role in neurovascular and neurodegenerative disorders.

The plasminogen activating system in the pathogenesis of Alzheimer's disease

Dementia is a clinical syndrome that affects approximately 47 million people worldwide and is characterized by progressive and irreversible decline of cognitive, behavioral and sesorimotor functions. Alzheimer's disease (AD) accounts for approximately 60-80% of all cases of dementia, and neuropathologically is characterized by extracellular deposits of insoluble amyloid-β (Aβ) and intracellular aggregates of hyperphosphorylated tau. Significantly, although for a long time it was believed that the extracellular accumulation of Aβ was the culprit of the symptoms observed in these patients, more recent studies have shown that cognitive decline in people suffering this disease is associated with soluble Aβ-induced synaptic dysfunction instead of the formation of insoluble Aβ-containing extracellular plaques. These observations are translationally relevant because soluble Aβ-induced synaptic dysfunction is an early event in AD that precedes neuronal death, and thus is amenable to therapeutic interventions to prevent cognitive decline before the progression to irreversible brain damage. The plasminogen activating (PA) system is an enzymatic cascade that triggers the degradation of fibrin by catalyzing the conversion of plasminogen into plasmin via two serine proteinases: tissue-type plasminogen activator (tPA) and urokinase-type plasminogen activator (uPA). Experimental evidence reported over the last three decades has shown that tPA and uPA play a role in the pathogenesis of AD. However, these studies have focused on the ability of these plasminogen activators to trigger plasmin-induced cleavage of insoluble Aβ-containing extracellular plaques. In contrast, recent evidence indicates that activity-dependent release of uPA from the presynaptic terminal of cerebral cortical neurons protects the synapse from the deleterious effects of soluble Aβ via a mechanism that does not require plasmin generation or the cleavage of Aβ fibrils. Below we discuss the role of the PA system in the pathogenesis of AD and the translational relevance of data published to this date.

Molecular imaging of the urokinase plasminogen activator receptor: opportunities beyond cancer

The urokinase plasminogen activator receptor (uPAR) plays a multifaceted role in almost any process where migration of cells and tissue-remodeling is involved such as inflammation, but also in diseases as arthritis and cancer. Normally, uPAR is absent in healthy tissues. By its carefully orchestrated interaction with the protease urokinase plasminogen activator and its inhibitor (plasminogen activator inhibitor-1), uPAR localizes a cascade of proteolytic activities, enabling (patho)physiologic cell migration. Moreover, via the interaction with a broad range of cell membrane proteins, like vitronectin and various integrins, uPAR plays a significant, but not yet completely understood, role in differentiation and proliferation of cells, affecting also disease progression. The implications of these processes, either for diagnostics or therapeutics, have received much attention in oncology, but only limited beyond. Nonetheless, the role of uPAR in different diseases provides ample opportunity to exploit new applications for targeting. Especially in the fields of oncology, cardiology, rheumatology, neurology, and infectious diseases, uPAR-targeted molecular imaging could offer insights for new directions in diagnosis, surveillance, or treatment options.

Novel Blood-Derived Extracellular Vesicle-Based Biomarkers in Alzheimer's Disease Identified by Proximity Extension Assay

Easily accessible biomarkers for Alzheimer's dementia (AD) are lacking and established clinical markers are limited in applicability. Blood is a common biofluid for biomarker discoveries, and extracellular vesicles (EVs) may provide a matrix for exploring AD related biomarkers. Thus, we investigated proteins related to neurological and inflammatory processes in plasma and EVs. By proximity extension assay (PEA), 182 proteins were measured in plasma and EVs from patients with AD (n = 10), Mild Cognitive Impairment (MCI, n = 10), and healthy controls (n = 10). Plasma-derived EVs were enriched by 20,000× g, 1 h, 4 °C, and confirmed using nanoparticle tracking analysis (NTA), western blotting, and transmission electron microscopy with immunolabelling (IEM). Presence of CD9+ EVs was confirmed by western blotting and IEM. No group differences in particle concentration or size were detected by NTA. However, significant protein profiles were observed among subjects, particularly for EVs. Several proteins and their ratios could distinguish cognitively affected from healthy individuals. For plasma TGF-α│CCL20 (AUC = 0.96, 95% CI = 0.88-1.00, p = 0.001) and EVs CLEC1B│CCL11 (AUC = 0.95, 95% CI = 0.86-1.00, p = 0.001) showed diagnostic capabilities. Using PEA, we identified protein profiles capable of distinguishing healthy controls from AD patients. EVs provided additional biological information related to AD not observed in plasma alone.

Urokinase-Type Plasminogen Activator Protects Cerebral Cortical Neurons from Soluble Aβ-Induced Synaptic Damage

Soluble amyloid β (Aβ)-induced synaptic dysfunction is an early event in the pathogenesis of Alzheimer's disease (AD) that precedes the deposition of insoluble Aβ and correlates with the development of cognitive deficits better than the number of plaques. The mammalian plasminogen activation (PA) system catalyzes the generation of plasmin via two activators: tissue-type (tPA) and urokinase-type (uPA). A dysfunctional tPA-plasmin system causes defective proteolytic degradation of Aβ plaques in advanced stages of AD. In contrast, it is unknown whether uPA and its receptor (uPAR) contribute to the pathogenesis of this disease. Neuronal cadherin (NCAD) plays a pivotal role in the formation of synapses and dendritic branches, and Aβ decreases its expression in cerebral cortical neurons. Here we show that neuronal uPA protects the synapse from the harmful effects of soluble Aβ. However, Aβ-induced inactivation of the eukaryotic initiation factor 2α halts the transcription of uPA mRNA, leaving unopposed the deleterious effects of Aβ on the synapse. In line with these observations, the synaptic abundance of uPA, but not uPAR, is decreased in the frontal cortex of AD patients and 5xFAD mice, and in cerebral cortical neurons incubated with soluble Aβ. We found that uPA treatment increases the synaptic expression of NCAD by a uPAR-mediated plasmin-independent mechanism, and that uPA-induced formation of NCAD dimers protects the synapse from the harmful effects of soluble Aβ oligomers. These data indicate that Aβ-induced decrease in the synaptic abundance of uPA contributes to the development of synaptic damage in the early stages of AD.SIGNIFICANCE STATEMENT Soluble amyloid β (Aβ)-induced synaptic dysfunction is an early event in the pathogenesis of cognitive deficits in Alzheimer's disease (AD). We found that neuronal urokinase-type (uPA) protects the synapse from the deleterious effects of soluble Aβ. However, Aβ-induced inactivation of the eukaryotic initiation factor 2α decreases the synaptic abundance of uPA, leaving unopposed the harmful effects of Aβ on the synapse. In line with these observations, the synaptic expression of uPA is decreased in the frontal cortex of AD brains and 5xFAD mice, and uPA treatment abrogates the deleterious effects of Aβ on the synapse. These results unveil a novel mechanism of Aβ-induced synaptic dysfunction in AD patients, and indicate that recombinant uPA is a potential therapeutic strategy to protect the synapse before the development of irreversible brain damage.

Copper accumulation and the effect of chelation treatment on cerebral amyloid angiopathy compared to parenchymal amyloid plaques

Accumulation of fibrillar amyloid β-protein (Aβ) in parenchymal plaques and in blood vessels of the brain, the latter condition known as cerebral amyloid angiopathy (CAA), are hallmark pathologies of Alzheimer's disease (AD) and related disorders. Cerebral amyloid deposits have been reported to accumulate various metals, most notably copper and zinc. Here we show that, in human AD, copper is preferentially accumulated in amyloid-containing brain blood vessels compared to parenchymal amyloid plaques. In light of this observation, we evaluated the effects of reducing copper levels in Tg2576 mice, a transgenic model of AD amyloid pathologies. The copper chelator, tetrathiomolybdate (TTM), was administered to twelve month old Tg2576 mice for a period of five months. Copper chelation treatment significantly reduced both CAA and parenchymal plaque load in Tg2576 mice. Further, copper chelation reduced parenchymal plaque copper content but had no effect on CAA copper levels in this model. These findings indicate that copper is associated with both CAA deposits and parenchymal amyloid plaques in humans, but less in Tg2576 mice. TTM only reduces copper levels in plaques in Tg2576 mice. Reducing copper levels in the brain may beneficially lower amyloid pathologies associated with AD.

The uPAR System as a Potential Therapeutic Target in the Diseased Eye

Dysregulation of vascular networks is characteristic of eye diseases associated with retinal cell degeneration and visual loss. Visual impairment is also the consequence of photoreceptor degeneration in inherited eye diseases with a major inflammatory component, but without angiogenic profile. Among the pathways with high impact on vascular/degenerative diseases of the eye, a central role is played by a system formed by the ligand urokinase-type plasminogen activator (uPA) and its receptor uPAR. The uPAR system, although extensively investigated in tumors, still remains a key issue in vascular diseases of the eye and even less studied in inherited retinal pathologies such as retinitis pigmantosa (RP). Its spectrum of action has been extended far beyond a classical pro-angiogenic function and has emerged as a central actor in inflammation. Preclinical studies in more prevalent eye diseases characterized by neovascular formation, as in retinopathy of prematurity, wet macular degeneration and rubeosis iridis or vasopermeability excess as in diabetic retinopathy, suggest a critical role of increased uPAR signaling indicating the potentiality of its modulation to counteract neovessel formation and microvascular dysfunction. The additional observation that the uPAR system plays a major role in RP by limiting the inflammatory cascade triggered by rod degeneration rises further questions about its role in the diseased eye.

Elevation of Plasmin-α2-plasmin Inhibitor Complex Predicts the Diagnosis of Systemic AL Amyloidosis in Patients with Monoclonal Protein

Objective The complication of systemic immunoglobulin light chain (AL) amyloidosis in patients with monoclonal immunoglobulin affects the prognosis, but amyloid deposition in tissues is sometimes difficult to detect due to bleeding tendencies and preferential distributions. However, fibrinolysis is known to be exacerbated in patients with systemic AL amyloidosis specifically. We therefore explored new biomarkers for predicting a diagnosis of systemic AL amyloidosis focusing on coagulation and fibrinolysis markers. Methods We reviewed the clinical features and treatment outcomes of patients with serum monoclonal protein, including primary systemic AL amyloidosis and multiple myeloma (MM), treated at our hospital between January 2008 and December 2014. Results Among several biomarkers, only the serum level of plasmin-α2-plasmin inhibitor complex (PIC) in patients with systemic AL amyloidosis (n=26) at the diagnosis was significantly higher than in patients with MM without AL amyloidosis (n=26) (mean±standard deviation, 3.69±2.82 μg/mL vs. 1.23±0.97 μg/mL, p<0.01). The cut-off for predicting a diagnosis of systemic AL amyloidosis in patients with serum monoclonal protein was 1.72 μg/mL with 84.6% sensitivity and 80.8% specificity. Hepatic involvement resulted in a significantly higher PIC level than no involvement in patients with systemic AL amyloidosis. The serum PIC level was also associated with the hematological response of systemic AL amyloidosis. Conclusion PIC is a useful biomarker for the diagnosis and management of patients with systemic AL amyloidosis.

The influence of the amyloid ß-protein and its precursor in modulating cerebral hemostasis

Ischemic and hemorrhagic strokes are a significant cause of brain injury leading to vascular cognitive impairment and dementia (VCID). These deleterious events largely result from disruption of cerebral hemostasis, a well-controlled and delicate balance between thrombotic and fibrinolytic pathways in cerebral blood vessels and surrounding brain tissue. Ischemia and hemorrhage are both commonly associated with cerebrovascular deposition of amyloid ß-protein (Aß). In this regard, Aß directly and indirectly modulates cerebral thrombosis and fibrinolysis. Further, major isoforms of the Aß precursor protein (AßPP) function as a potent inhibitor of pro-thrombotic proteinases. The purpose of this review article is to summarize recent research on how cerebral vascular Aß and AßPP influence cerebral hemostasis. This article is part of a Special Issue entitled: Vascular Contributions to Cognitive Impairment and Dementia, edited by M. Paul Murphy, Roderick A. Corriveau and Donna M. Wilcock.

Shedding of soluble platelet-derived growth factor receptor-β from human brain pericytes

Platelet-derived growth factor receptor-β (PDGFRβ) is expressed in the brain by vascular mural cells-brain capillary pericytes and arterial vascular smooth muscle cells (VSMCs). Recent evidence shows that blood-brain barrier (BBB) disruption and increased permeability, especially in the hippocampus, positively correlates with elevated levels of soluble PDGFRβ (sPDGFRβ) in cerebrospinal fluid (CSF) in patients with mild dementia. To determine which vascular cell type(s) contributes to increased sPDGFRβ in CSF, we compared PDGFRβ expression and sPDGFRβ shedding in response to injury in early passage primary cultures of human brain pericytes, brain arterial VSMCs, and brain endothelial cells. PDGFRβ protein was undetectable in endothelial cells, but was found both in pericytes and VSMCs. PDGFRβ relative protein abundance was by 4.2-fold (p<0.05) higher in pericytes compared to VSMCs. Hypoxia (1% O2) or amyloid-β peptide (25 μM) compared to normoxia (21% O2) both increased over 48 h shedding of sPDGFRβ and its levels in the culture medium from pericytes cultures, but not from VSMCs cultures, by 4.3-fold and 4.6-fold, respectively, compared to the basal sPDGFRβ levels in the medium (1.43±0.15 ng/ml). This was associated with the corresponding loss of cell-associated PDGFRβ from pericytes and no change in cellular levels of PDGFRβ in VSMCs. Thus, sPDGFRβ is a biomarker of pericyte injury, and elevated sPDGFRβ levels in biofluids in patients with dementia and/or other neurodegenerative disorders likely reflects pericyte injury, which supports the potential for sPDGFRβ to be developed and validated as a biomarker of brain pericyte injury and BBB dysfunction.

Vascular contributions to cognitive impairment and dementia including Alzheimer's disease

Scientific evidence continues to demonstrate the linkage of vascular contributions to cognitive impairment and dementia such as Alzheimer's disease. In December, 2013, the Alzheimer's Association, with scientific input from the National Institute of Neurological Disorders and Stroke and the National Heart, Lung and Blood Institute from the National Institutes of Health, convened scientific experts to discuss the research gaps in our understanding of how vascular factors contribute to Alzheimer's disease and related dementia. This manuscript summarizes the meeting and the resultant discussion, including an outline of next steps needed to move this area of research forward.

Impacts of aging and amyloid-β deposition on plasminogen activators and plasminogen activator inhibitor-1 in the Tg2576 mouse model of Alzheimer's disease

Plasminogen activators (PAs), which convert plasminogen into the fibrinolytic protease plasmin, may initiate the degradation of amyloid-β (Aβ) to suppress the amyloid pathogenesis. In that way, tissue plasminogen activator (tPA)-mediated plasmin activation could maintain a low level of Aβ deposition to delay the pathogenesis of Alzheimer's disease (AD). In a previous study, we reported that tPA/plasmin proteolytic activity is attenuated throughout the brain during aging or with Aβ accumulation but clustered intense around the amyloid plaques in AD brain. The present study demonstrates that the altered proteolytic activity primarily results from the competition between the expressions of tPA and plasminogen activator inhibitor-1 (PAI-1) in the brains of Tg2576 Aβ-transgenic mice, as revealed by immunohistochemistry and immunoblot assays. Compared with that in the brains of younger Tg2576 mice, tPA protein is generally reduced throughout the brain in older Tg2576 mice but elevated near amyloid plaques. In contrary, PAI-1 expression increases during aging or Aβ deposition with its clusters surrounding amyloid plaques. No significant alteration in the expression of urokinase plasminogen activator (uPA) is detected. These results suggest reciprocal feedback influences between tPA, PAI-1 and Aβ during aging and amyloid pathogenesis in AD brain; tPA-mediated plasmin activity is declined throughout the brain causing Aβ deposition during aging, and the Aβ deposits locally attract the cluster of tPA and/or PAI-1 around their deposits to competitively determine tPA/plasmin-mediated Aβ proteolysis.

Extracellular proteolytic pathophysiology in the neurovascular unit after stroke

The NINDS Stroke Progress Review Group recommended a shift in emphasis from a purely neurocentric view of cell death towards a more integrative approach whereby responses in all brain cells and matrix are considered. The neurovascular unit (fundamentally comprising endothelium, astrocyte, and neuron) provides a conceptual framework where cell-cell and cell-matrix signaling underlies the overall tissue response to stroke and its treatments. Here, we briefly review recent data on extracellular proteolytic dysfunction in the neurovascular unit after a stroke. The breakdown of neurovascular matrix initiates blood-brain barrier disruption with edema and/or hemorrhage. Endothelial dysfunction amplifies inflammatory responses. Perturbation of cell-matrix homeostasis triggers multiple cell death pathways. Interactions between the major classes of extracellular proteases from the plasminogen and matrix metalloprotease families may underlie processes responsible for some of the hemorrhagic complications of thrombolytic stroke therapy. Targeting the proteolytic imbalance within the neurovascular unit may provide new approaches for improving the safety and efficacy of thrombolytic reperfusion therapy for stroke.

Alzheimer's disease biomarker discovery using in silico literature mining and clinical validation

Background

Alzheimer’s Disease (AD) is the most widespread form of dementia in the elderly but despite progress made in recent years towards a mechanistic understanding, there is still an urgent need for disease modification therapy and for early diagnostic tests. Substantial international efforts are being made to discover and validate biomarkers for AD using candidate analytes and various data-driven 'omics' approaches. Cerebrospinal fluid is in many ways the tissue of choice for biomarkers of brain disease but is limited by patient and clinician acceptability, and increasing attention is being paid to the search for blood-based biomarkers. The aim of this study was to use a novel in silico approach to discover a set of candidate biomarkers for AD.

Methods

We used an in silico literature mining approach to identify potential biomarkers by creating a summarized set of assertional metadata derived from relevant legacy information. We then assessed the validity of this approach using direct assays of the identified biomarkers in plasma by immunodetection methods.

Results

Using this in silico approach, we identified 25 biomarker candidates, at least three of which have subsequently been reported to be altered in blood or CSF from AD patients. Two further candidate biomarkers, indicated from the in silico approach, were choline acetyltransferase and urokinase-type plasminogen activator receptor. Using immunodetection, we showed that, in a large sample set, these markers are either altered in disease or correlate with MRI markers of atrophy.

Conclusions

These data support as a proof of concept the use of data mining and in silico analyses to derive valid biomarker candidates for AD and, by extension, for other disorders.

The Therapeutic Effect of DL-3-n-Butylphthalide in Rats with Chronic Cerebral Hypoperfusion through Downregulation of Amyloid Precursor Protein and Matrix Metalloproteinase-2

OBJECTIVE: To investigate the therapeutic effect of DL-3- n-butylphthalide (DL-NBP) in rats with chronic cerebral hypoperfusion. METHODS: Chronic cerebral hypoperfusion was modelled by bilateral permanent occlusion of common carotid arteries in Wistar rats. The therapeutic effect of DL-NBP in hypoperfused rats was evaluated using the Morris water maze task. The levels and deposition of matrix metalloproteinase (MMP) and the amyloid precursor protein β-amyloid 40 (Aβ40) were measured by Western blot analysis and immunohistochemistry in the cerebral cortex and hippocampus. RESULTS: Treatment with DL-NBP significantly improved the learning and memory ability of hypoperfused rats. Western blot analysis indicated that, in comparison with the sham-operated control group, protein levels of Aβ40 and MMP-2 were significantly increased in the cerebral cortex of hypoperfused rats, and treatment with DL-NBP prevented this hypoperfusion-induced increase in Aβ40 and MMP-2. Immunohistochemical analysis showed that Aβ40 and MMP-2 were deposited in venous endothelial cells at day 3 and in arterial endothelial cells at day 14 after hypoperfusion. CONCLUSION: This study indicated that DL-NBP has therapeutic effects on chronic cerebral hypoperfusion and provided a useful insight into the potential molecular mechanisms underlying the therapeutic effect of DL-NBP in chronic cerebral hypoperfusion.

Wild-type amyloid beta 1-40 peptide induces vascular smooth muscle cell death independently from matrix metalloprotease activity

Cerebral amyloid angiopathy (CAA) is an important cause of intracerebral hemorrhages in the elderly, characterized by amyloid-β (Aβ) peptide accumulating in central nervous system blood vessels. Within the vessel walls, Aβ-peptide deposits [composed mainly of wild-type (WT) Aβ(1-40) peptide in sporadic forms] induce impaired adhesion of vascular smooth muscle cells (VSMCs) to the extracellular matrix (ECM) associated with their degeneration. This process often results in a loss of blood vessel wall integrity and ultimately translates into cerebral ischemia and microhemorrhages, both clinical features of CAA. In this study, we decipher the molecular mechanism of matrix metalloprotease (MMP)-2 activation in WT-Aβ(1-40) -treated VSMC and provide evidence that MMP activity, although playing a critical role in cell detachment disrupting ECM components, is not involved in the WT-Aβ(1-40) -induced degeneration of VSMCs. Indeed, whereas this peptide clearly induced VSMC apoptosis, neither preventing MMP-2 activity nor hampering the expression of membrane type1-MMP, or preventing tissue inhibitors of MMPs-2 (TIMP-2) recruitment (two proteins evidenced here as involved in MMP-2 activation), reduced the number of dead cells. Even the use of broad-range MMP inhibitors (GM6001 and Batimastat) did not affect WT-Aβ(1-40) -induced cell apoptosis. Our results, in contrast to those obtained using the Aβ(1-40) Dutch variant suggesting a link between MMP-2 activity, VSMC mortality and degradation of specific matrix components, indicate that the ontogenesis of the Dutch familial and sporadic forms of CAAs is different. ECM degradation and VSMC degeneration would be tightly connected in the Dutch familial form while being two independent processes in sporadic forms of CAA.

Synaptic protein expression is regulated by a pro-oxidant diet in APPxPS1 mice

Dietary factors may play a role in Alzheimer's disease (AD) pathogenesis. In an effort to recapitulate some of the synaptic protein changes observed in the disease, AD transgenic and wild-type mice were fed either a normal or pro-oxidant diet for 3 months from three months of age. Pro-oxidant diet treatment resulted in altered expression of vesicular glutamate transporter-1 and glutamine synthetase, suggesting changes in glutamatergic synaptic function, and increased expression of urokinase plasminogen activator receptor, possibly reflecting oxidative stress.

Species-specific anticoagulant and mitogenic activities of murine protein S

BACKGROUND

The protein C pathway down-regulates thrombin generation and promotes cytoprotection during inflammation and stress. In preclinical studies using models of murine injury (e.g., sepsis and ischemic stroke), murine protein S may be required because of restrictive species specificity.

DESIGN AND METHODS

We prepared and characterized recombinant murine protein S using novel coagulation assays, immunoassays, and cell proliferation assays.

RESULTS

Purified murine protein S had good anticoagulant co-factor activity for murine activated protein C, but not for human activated protein C, in mouse or rat plasma. In human plasma, murine protein S was a poor co-factor for murine activated protein C and had no anticoagulant effect with human activated protein C, suggesting protein S species specificity for factor V in addition to activated protein C. We estimated that mouse plasma contains 22+/-1 microg/mL protein S and developed assays to measure activated protein C co-factor activity of the protein S in murine plasma. Activated protein C-independent anticoagulant activity of murine protein S was demonstrable and quantifiable in mouse plasma, and this activity was enhanced by exogenous murine protein S. Murine protein S promoted the proliferation of mouse and human smooth muscle cells. The potency of murine protein S was higher for mouse cells than for human cells and similarly, human protein S was more potent for human cells than for mouse cells.

CONCLUSIONS

The spectrum of bioactivities of recombinant murine protein S with mouse plasma and smooth muscle cells is similar to that of human protein S. However, in vitro and in vivo studies of the protein C pathway in murine disease models are more appropriately performed using murine protein S. This study extends previous observations regarding the remarkable species specificity of protein S to the mouse.

Excessive fibrinolysis in AL-amyloidosis is induced by urokinae-type plasminogen activator from bone marrow plasma cells

Activation of fibrinolysis system and excessive fibrinolysis are observed in monoclonal antibody light chain (AL)-amyloidosis. However, the mechanisms by which activation of fibrinolysis occurs in AL-amyloidosis have not been fully elucidated. To determine whether urokinase type-plasminogen activator (uPA), an important activator of fibrinolytic system, contributes to the activation of fibrinolytic system in AL-amyloidosis, we immunohistologically examined uPA in bone marrow plasma cells. More than 90% of bone marrow plasma cells from five different AL-amyloidosis patients were uPA-positive as examined with immunohistochemical staining. All the bone marrow plasma cells from seven different patients with multiple myeloma were uPA-negative. A patient with AL-amyloidosis, who had bleeding diathesis and excessive fibrinolysis with hypofibrinogenemia, was treated with nafamostat mesilate, a potential inhibitor of uPA. After the administration of nafamostat mesilate, the bleeding diathesis disappeared, and excessive fibrinolysis and hypofibrinogenemia were improved. The present data suggested that uPA expressed in plasma cells may have contributed to the pathogenesis of excessive fibrinolysis.

Cerebral amyloid angiopathy: progressive disruption of the neurovascular unit

Cellular elements of the neurovascular unit are essential for the physiological functioning of brain vessels. If any of these vascular elements are disturbed the consequences can be dire. Cerebral amyloid angiopathy (CAA), a disorder caused by the accumulation of amyloid in cerebral vessels, provides a case study of progressive neurovascular unit dysfunction leading to failure of vascular reactivity, smooth muscle cell loss, and eventual frank breakdown of vessel integrity resulting in recurrent and sometimes fatal intracerebral hemorrhage.

Development of a Mammalian suspension culture for expression of active recombinant human urokinase-type plasminogen activator

The development of specific catalytic inhibitors for the serine protease urokinase-type plasminogen activator (uPA) has been hindered due to difficulties in producing sufficient amounts of active recombinant uPA that is catalytically equivalent to native uPA. The purpose of this study was to develop an efficient system for the expression of recombinant human uPA that exhibits comparable proteolytic activity to that of the native protein. Since post-translational modifications (e.g. glycosylations) of uPA are necessary for efficient proteolytic activity, we have used a mammalian cell line [Chinese hamster ovary (CHO)-S] to express recombinant human uPA. CHO-S cells were selected to stably express full-length recombinant human uPA containing a hexahistidine tag at its C-terminus to permit purification by nickel-based affinity chromatography. Secretion of recombinant uPA into the culture media was confirmed by immunoblotting and the presence of an N-linked glycosylation was confirmed by PNGase sensitivity. Enzymatic activity of purified recombinant uPA was demonstrated using zymography and quantitatively compared to native uPA by kinetic analysis using an uPA-specific substrate. Native uPA and the recombinant uPA demonstrated comparable K(m) values (55.7 and 39 muM, respectively). Furthermore, inhibition studies using benzamidine resulted in a K(i) of 195 muM for native uPA, while recombinant uPA had a K(i) of 112 muM. These data indicate that recombinant human uPA expressed by CHO-S cells is functionally comparable to native uPA.

Enhanced clearance of Abeta in brain by sustaining the plasmin proteolysis cascade

The amyloid hypothesis states that a variety of neurotoxic beta-amyloid (Abeta) species contribute to the pathogenesis of Alzheimer's disease. Accordingly, a key determinant of disease onset and progression is the appropriate balance between Abeta production and clearance. Enzymes responsible for the degradation of Abeta are not well understood, and, thus far, it has not been possible to enhance Abeta catabolism by pharmacological manipulation. We provide evidence that Abeta catabolism is increased after inhibition of plasminogen activator inhibitor-1 (PAI-1) and may constitute a viable therapeutic approach for lowering brain Abeta levels. PAI-1 inhibits the activity of tissue plasminogen activator (tPA), an enzyme that cleaves plasminogen to generate plasmin, a protease that degrades Abeta oligomers and monomers. Because tPA, plasminogen and PAI-1 are expressed in the brain, we tested the hypothesis that inhibitors of PAI-1 will enhance the proteolytic clearance of brain Abeta. Our data demonstrate that PAI-1 inhibitors augment the activity of tPA and plasmin in hippocampus, significantly lower plasma and brain Abeta levels, restore long-term potentiation deficits in hippocampal slices from transgenic Abeta-producing mice, and reverse cognitive deficits in these mice.

Reduced incidence of ischemic stroke in patients with severe factor XI deficiency

Inherited disorders of hemostasis are natural models for investigating mechanisms of thrombosis and development of antithrombotic therapy. Because mice with total factor XI deficiency are protected against ischemic stroke and do not manifest excessive bleeding, we investigated the incidence of ischemic stroke in patients with severe inherited factor XI deficiency. Incidence of ischemic stroke in 115 patients aged 45 years or more with severe factor XI deficiency (activity less than 15 U/dL) was compared with incidence in the Israeli population as estimated from a stroke survey of 1528 patients. Adjustment for major risk factors of stroke (hypertension, diabetes mellitus, hypercholesterolemia, current smoking) was based on comparison of their prevalence in the stroke survey to an Israeli health survey of 9509 subjects. Incidence of myocardial infarction in the factor XI cohort was also recorded. After adjustment for the 4 major risk factors of ischemic stroke, the expected incidence of ischemic stroke was 8.56 compared with one observed (P = .003). The reduced 1:115 incidence of ischemic stroke contrasted with a 19:115 incidence of myocardial infarction, similar to the expected incidence. Thus, severe factor XI deficiency probably is protective against ischemic stroke but not against acute myocardial infarction.

Plasminogen activation induced pericellular fibronectin proteolysis promotes fibroblast apoptosis

Apoptosis of fibroblasts/myofibroblasts is a critical event in the resolution of tissue repair responses; however, mechanisms for the regulation of (myo)fibroblast apoptosis/survival remain unclear. In this study, we demonstrate counter-regulatory interactions between the plasminogen activation system and transforming growth factor-beta1 (TGF-beta1) in the control of fibroblast apoptosis. Plasmin treatment induced fibroblast apoptosis in a time- and dose-dependent manner in association with proteolytic degradation of extracellular matrix proteins, as detected by the release of soluble fibronectin peptides. Plasminogen, which was activated to plasmin by fibroblasts, also induced fibronectin proteolysis and fibroblast apoptosis, both of which were blocked by alpha2-antiplasmin but not by inhibition of matrix metalloproteinase activity. TGF-beta1 protected fibroblasts from apoptosis induced by plasminogen but not from apoptosis induced by exogenous plasmin. The protection from plasminogen-induced apoptosis conferred by TGF-beta1 is associated with the up-regulation of plasminogen activator-1 (PAI-1) expression and inhibition of plasminogen activation. Moreover, lung fibroblasts from mice genetically deficient in PAI-1 lose the protective effect of TGF-beta1 against plasminogen-induced apoptosis. These findings support a novel role for the plasminogen activation system in the regulation of fibroblast apoptosis and a potential role of TGF-beta1/PAI-1 in promoting (myo)fibroblast survival in chronic fibrotic disorders.

Activation of plasminogen into plasmin at the surface of endothelial microparticles: a mechanism that modulates angiogenic properties of endothelial progenitor cells in vitro

The regulation of plasmin generation on cell surfaces is of critical importance in the control of vascular homeostasis. Cell-derived microparticles participate in the dissemination of biological activities. However, their capacity to promote plasmin generation has not been documented. In this study, we show that endothelial microparticles (EMPs) from tumor necrosis factor alpha (TNFalpha)-stimulated endothelial cells served as a surface for the generation of plasmin. The generation of plasmin involved expression of urokinase-type plasminogen activator (uPA) and its receptor (uPAR) at the surface of EMPs and was further increased by their ability to bind exogenous uPA on uPAR. Plasminogen was activated at the surface of EMPs in a dose-dependent, saturable, and specific manner as indicated by the inhibition of plasmin formation by epsilon-amino-caproic acid (epsilon-ACA) and carboxypeptidase B. EMP-induced plasmin generation affects tube formation mediated by endothelial progenitor cells. However, low amounts of EMPs increased tube formation, whereas higher concentrations inhibited it. Prevention of these effects by inhibitors of either uPA or plasmin underscore the key role of EMP-induced plasmin generation. In conclusion, we demonstrated that EMPs act as vectors supporting efficient plasmin generation and dissemination, a new pathway in the regulation of endothelial proteolytic activities with potential involvement in inflammation, angiogenesis, and atherosclerosis.

Plasminogen activator inhibitor-1 impairs plasminogen activation-mediated vascular smooth muscle cell apoptosis

The role of plasminogen activator inhibitor-1 (PAI-1) in vascular smooth muscle cell (VSMC) apoptosis mediated by plasminogen activation was studied with the use of aorticVSMC derived from mice with deficiency of PAI-1 (PAI-1 (-/-) ), tissue-type (t-PA (-/-) ) or urokinase-type (u-PA (-/-) ) plasminogen activator or from wildtype (WT) mice with corresponding genetic background. Plasminogen incubated with confluent VSMC was activated in a concentration-dependent and saturable manner for all four cell types, with maximal activation rates that were comparable for WT, u-PA (-/-) and t-PA (-/-) cells, but about two-fold higher for PAI-1 (-/-) cells. Plasminogen activation was impaired by addition of the lysine analogue 6-aminohexanoic acid, and by addition of t-PA and u-PA neutralizing antibodies, suggesting that it depends on binding to cell surface COOH-terminal lysine residues, and on plasminogen activator activity. Morphological alterations consistent with apoptosis were observed much earlier in PAI-1 (-/-) than in WT VSMC. Without addition of plasminogen, the apoptotic index was similar for all four cell types, whereas after incubation with physiological plasminogen concentrations, it was greater in PAI-1 (-/-) VSMC, as compared to WT, t-PA (-/-) or u-PA (-/-) VSMC. Furthermore, the apoptotic rate paralleled the release of plasmin. Thus, plasmin-mediated apoptosis of VSMC occurs via plasminogen activation by either t-PA or u-PA and is impaired by PAI-1.

The urokinase-type plasminogen activator polymorphism PLAU_1 is a risk factor for APOE-ε4 non-carriers in the Italian Alzheimer’s disease population and does not affect the plasma Aβ(1–42) level

Sporadic Alzheimer's disease (AD) is the most frequent form of dementia in the elderly. A non-conservative polymorphism in the urokinase-type plasminogen activator gene (PLAU_1=RS2227564) has been analyzed, but data are conflicting on whether it is a risk factor for AD. To clarify whether this genetic variant modifies AD risk in the Italian population, we ran a case-control association study on 192 AD and 126 age-matched controls. We did not find any association between PLAU_1 genotype and AD in the whole AD population, but when we stratified our sample by APOE-epsilon4 status, we found a significant association between PLAU_1 genotype (C/T+T/T) and APOE-epsilon4 negative AD subjects (p=0.02, chi(2)-test). The PLAU_1 genotype did not appear to affect the plasma Abeta42 concentration. Our data support a role for PLAU_1 as an independent genetic risk factor for AD in the Italian population for those subjects who do not have the APOE-epsilon4 allele.

Serum response factor and myocardin mediate arterial hypercontractility and cerebral blood flow dysregulation in Alzheimer's phenotype

Cerebral angiopathy contributes to cognitive decline and dementia in Alzheimer's disease (AD) through cerebral blood flow (CBF) reductions and dysregulation. We report vascular smooth muscle cells (VSMC) in small pial and intracerebral arteries, which are critical for CBF regulation, express in AD high levels of serum response factor (SRF) and myocardin (MYOCD), two interacting transcription factors that orchestrate a VSMC-differentiated phenotype. Consistent with this finding, AD VSMC overexpressed several SRF-MYOCD-regulated contractile proteins and exhibited a hypercontractile phenotype. MYOCD overexpression in control human cerebral VSMC induced an AD-like hypercontractile phenotype and diminished both endothelial-dependent and -independent relaxation in the mouse aorta ex vivo. In contrast, silencing SRF normalized contractile protein content and reversed a hypercontractile phenotype in AD VSMC. MYOCD in vivo gene transfer to mouse pial arteries increased contractile protein content and diminished CBF responses produced by brain activation in wild-type mice and in two AD models, the Dutch/Iowa/Swedish triple mutant human amyloid beta-peptide (Abeta)-precursor protein (APP)- expressing mice and APPsw(+/-) mice. Silencing Srf had the opposite effect. Expression of SRF did not change in VSMC subjected to Alzheimer's neurotoxin, Abeta. Thus, SRF-MYOCD overexpression in small cerebral arteries appears to initiate independently of Abeta a pathogenic pathway mediating arterial hypercontractility and CBF dysregulation, which are associated with Alzheimer's dementia.

Plasminogen activation: a mediator of vascular smooth muscle cell apoptosis in atherosclerotic plaques

BACKGROUND

Apoptosis of vascular cells is considered to be a major determinant of atherosclerotic plaque vulnerability and potential rupture. Plasmin can be generated in atherosclerotic plaques and recent in vitro data suggest that plasminogen activation may trigger vascular smooth muscle cell (VSMC) apoptosis.

AIM

To determine whether plasminogen activation may induce aortic VSMC apoptosis ex vivo and in vivo.

METHODS AND RESULTS

Mice with single or combined deficiencies of apolipoprotein E (ApoE) and plasminogen activator inhibitor-1 (PAI-1) were used. Ex vivo incubation with plasminogen of isolated aortic tunica media from PAI-1-deficient mice induced plasminogen activation and VSMC apoptosis, which was inhibited by alpha2-antiplasmin. In vivo, levels of plasmin, active caspase 3 and VSMC apoptotic index were significantly higher in atherosclerotic aortas from mice with combined ApoE and PAI-1 deficiencies than in those from littermates with single ApoE deficiency. A parallel decrease in VSMC density was observed.

CONCLUSIONS

These data strongly suggest that plasminogen activation may contribute to VSMC apoptosis in atherosclerotic plaques.

Functional hierarchy of plasminogen kringles 1 and 4 in fibrinolysis and plasmin-induced cell detachment and apoptosis

Plasmin(ogen) kringles 1 and 4 are involved in anchorage of plasmin(ogen) to fibrin and cells, an essential step in fibrinolysis and pericellular proteolysis. Their contribution to these processes was investigated by selective neutralization of their lysine-binding function. Blocking the kringle 1 lysine-binding site with monoclonal antibody 34D3 fully abolished binding and activation of Glu-plasminogen and prevented both fibrinolysis and plasmin-induced cell detachment-induced apoptosis. In contrast, blocking the kringle 4 lysine-binding site with monoclonal antibody A10.2 did not impair its activation although it partially inhibited plasmin(ogen) binding, fibrinolysis and cell detachment. This remarkable, biologically relevant, distinctive response was not observed for plasmin or Lys-plasminogen; each antibody inhibited their binding and activation of Lys-plasminogen to a limited extent, and full inhibition of fibrinolysis required simultaneous neutralization of both kringles. Thus, in Lys-plasminogen and plasmin, kringles 1 and 4 act as independent and complementary domains, both able to support binding and activation. We conclude that Glu-/Lys-plasminogen and plasmin conformations are associated with transitions in the lysine-binding function of kringles 1 and 4 that modulate fibrinolysis and pericellular proteolysis and may be of biological relevance during athero-thrombosis and inflammatory states. These findings constitute the first biological link between plasmin(ogen) transitions and functions.

Matrix metalloproteinase-9 in cerebral-amyloid-angiopathy-related hemorrhage

Spontaneous intracerebral hemorrhage (ICH) is one of the most recognized complications of cerebral amyloid angiopathy (CAA), but little is known about the molecular pathogenesis of this life-threatening complication. In this review, we present preliminary evidence which suggests that the extracellular-matrix-degrading protease, matrix metalloproteinase-9 (MMP-9), may play a role in the development of spontaneous ICH resulting from CAA. The amyloid-beta peptide (Abeta) induced the synthesis, cellular release, and activation of MMP-9 in murine cerebral endothelial cells (CECs), resulting in increased extracellular matrix (ECM) degradation. Furthermore, in a mouse model of CAA (APPsw transgenic mice), MMP-9 immunoreactivity was observed in amyloid-laden cerebral vessels in aged APPsw mice but not in young APPsw or aged wild-type mice. More extensive MMP-9 immunostaining was present in amyloid-laden vessels with evidence of microhemorrhage. These results suggest that increased vascular MMP-9 expression, stimulated by Abeta, may play a role in the pathogenesis of spontaneous intracerebral hemorrhage (ICH) in patients with CAA.

Insulin-degrading Enzyme in Brain Microvessels

The accumulation of amyloid beta (Abeta) in the walls of small vessels in the cerebral cortex is associated with diseases characterized by dementia or stroke. These include Alzheimer's disease, Down syndrome, and sporadic and hereditary cerebral amyloid angiopathies (CAAs) related to mutations within the Abeta sequence. A higher tendency of Abeta to aggregate, a defective clearance to the systemic circulation, and insufficient proteolytic removal have been proposed as mechanisms that lead to Abeta accumulation in the brain. By using immunoprecipitation and mass spectrometry, we show that insulin-degrading enzyme (IDE) from isolated human brain microvessels was capable of degrading (125)I-insulin and cleaved Abeta-(1-40) wild type and the genetic variants Abeta A21G (Flemish), Abeta E22Q (Dutch), and Abeta E22K (Italian) at the predicted sites. In microvessels from Alzheimer's disease cases with CAA, IDE protein levels showed a 44% increase as determined by sandwich enzyme-linked immunosorbent assay and Western blot. However, the activity of IDE upon radiolabeled insulin was significantly reduced in CAA as compared with age-matched controls. These results support the notion that a defect in Abeta proteolysis by IDE contributes to the accumulation of this peptide in the cortical microvasculature. Moreover they raise the possibility that IDE inhibition or inactivation is a pathogenic mechanism that may open novel strategies for the treatment of cerebrovascular Abeta amyloidoses.

Amyloid Angiopathy-Related Vascular Cognitive Impairment

We review accumulating evidence that cerebrovascular amyloid deposition (cerebral amyloid angiopathy [CAA]) is an independent risk factor for cognitive dysfunction. The two population-based autopsy studies that have analyzed cognitive status during life as a function of CAA have each suggested deleterious effects of CAA on cognition even after controlling for age and Alzheimer disease pathology. We also review data from patients with CAA-related intracerebral hemorrhage (the one form of CAA that can be noninvasively recognized) suggesting associations of CAA with radiographic white matter abnormalities and cognitive impairment. These data highlight the importance of elucidating the effects of vascular amyloid on cerebrovascular function and of developing therapeutic strategies for this potentially widespread form of microvascular cognitive impairment.

Cerebral amyloid angiopathy and thrombolysis-related intracerebral haemorrhage

Intracerebral haemorrhage is a complication of thrombolytic therapy for acute myocardial infarction, pulmonary embolism, and ischaemic stroke. There is increasing evidence that cerebral amyloid angiopathy (CAA), which itself can cause haemorrhage (CAAH), may be a risk factor for thrombolysis-related intracerebral haemorrhage. CAAH and thrombolysis-related intracerebral haemorrhage share some clinical features, such as predisposition to lobar or superficial regions of the brain, multiple haemorrhages, increasing frequency with age, and an association with dementia. In vitro work showed that accumulation of amyloid-beta peptide causes degeneration of cells in the walls of blood vessels, affects vasoactivity, and improves proteolytic mechanisms, such as fibrinolysis, anticoagulation, and degradation of the extracellular matrix. In a mouse model of CAA there is a low haemorrhagic threshold after thrombolytic therapy compared with that in wild-type mice. To date only a small number of anecdotal clinicopathological relations have been reported; neuroimaging advances and further study of the frequency and role of CAA in patients with thrombolysis-related intracerebral haemorrhage are required.

Protease nexin-1 inhibits plasminogen activation-induced apoptosis of adherent cells

Degradation of adhesive glycoproteins by plasmin is implicated in cell migration. In this study, we further explored the role of plasminogen activation in cell adhesion and survival and show that uncontrolled plasminogen activation at the cell surface may induce cell detachment and apoptosis. We hypothesized that this process could be prevented in adherent cells by expression of protease nexin-1, a potent serpin able to inhibit thrombin, plasmin, and plasminogen activators. Using two- and three-dimensional culture systems, we demonstrate that Chinese hamster ovary fibroblasts constitutively express tissue-type plasminogen activator and efficiently activate exogenously added plasminogen in a specific and saturable manner (K(m) = 46 nm). The formation of plasmin results in proteolysis of fibronectin and laminin, which is followed by cell detachment and apoptosis. Protease nexin-1 expressed by transfected cells significantly inhibited the activity of plasmin and tissue-type plasminogen activator via the formation of inhibitory complexes and prevented cell detachment and apoptosis. In conclusion, protease nexin-1 may be an important anti-apoptotic factor for adherent cells. This cell model could be a useful tool to evaluate therapeutic agents such as serpins in vascular pathologies involving pericellular protease-protease inhibitor imbalance.

Pathogenic A beta induces the expression and activation of matrix metalloproteinase-2 in human cerebrovascular smooth muscle cells

Cerebral amyloid angiopathy (CAA) is a major pathological feature of Alzheimer's disease and related disorders. Human cerebrovascular smooth muscle (HCSM) cells, which are intimately associated with CAA, have been used as an in vitro model system to investigate pathologic interactions with amyloid beta protein (A beta). Previously we have shown that pathogenic forms of A beta induce several pathologic responses in HCSM cells including fibril assembly at the cell surface, increase in the levels of A beta precursor, and apoptotic cell death. Here we show that pathogenic A beta stimulates the expression and activation of matrix metalloproteinase-2 (MMP-2). Furthermore, we demonstrate that the increase in MMP-2 activation is largely caused by increased expression of membrane type-1 (MT1)-MMP expression, the primary MMP-2 activator. Finally, treatment with MMP-2 inhibitors resulted in increased HCSM cell viability in the presence of pathogenic A beta. Our findings suggest that increased expression and activation of MMP-2 may contribute to HCSM cell death in response to pathogenic A beta. In addition, these activities may also contribute to loss of vessel wall integrity in CAA resulting in hemorrhagic stroke. Therefore, further understanding into the role of MMPs in HCSM cell degeneration may facilitate designing therapeutic strategies to treat CAA found in AD and related disorders.