LRP and alphavbeta3 mediate tPA activation of smooth muscle cells

Role of Nasal Fibroblasts in Airway Remodeling of Chronic Rhinosinusitis: The Modulating Functions Reexamined

Chronic rhinosinusitis (CRS) is a multifactorial inflammatory disease of the nose and sinuses that affects more than 10% of the adult population worldwide. Currently, CRS is classified into endotypes according to the inflammatory response (Th1, Th2, and Th17) or the distribution of immune cells in the mucosa (eosinophilic and non-eosinophilic). CRS induces mucosal tissue remodeling. Extracellular matrix (ECM) accumulation, fibrin deposition, edema, immune cell infiltration, and angiogenesis are observed in the stromal region. Conversely, epithelial-to-mesenchymal transition (EMT), goblet cell hyperplasia, and increased epithelial permeability, hyperplasia, and metaplasia are found in the epithelium. Fibroblasts synthesize collagen and ECM, which create a structural skeleton of tissue and play an important role in the wound-healing process. This review discusses recent knowledge regarding the modulation of tissue remodeling by nasal fibroblasts in CRS.

The VWF/LRP4/αVβ3-axis represents a novel pathway regulating proliferation of human vascular smooth muscle cells

AIMS

Von Willebrand factor (VWF) is a plasma glycoprotein involved in primary haemostasis, while also having additional roles beyond haemostasis namely in cancer, inflammation, angiogenesis, and potentially in vascular smooth muscle cell (VSMC) proliferation. Here, we addressed how VWF modulates VSMC proliferation and investigated the underlying molecular pathways and the in vivo pathophysiological relevance.

METHODS AND RESULTS

VWF induced proliferation of human aortic VSMCs and also promoted VSMC migration. Treatment of cells with a siRNA against αv integrin or the RGT-peptide blocking αvβ3 signalling abolished proliferation. However, VWF did not bind to αvβ3 on VSMCs through its RGD-motif. Rather, we identified the VWF A2 domain as the region mediating binding to the cells. We hypothesized the involvement of a member of the LDL-related receptor protein (LRP) family due to their known ability to act as co-receptors. Using the universal LRP-inhibitor receptor-associated protein, we confirmed LRP-mediated VSMC proliferation. siRNA experiments and confocal fluorescence microscopy identified LRP4 as the VWF-counterreceptor on VSMCs. Also co-localization between αvβ3 and LRP4 was observed via proximity ligation analysis and immuno-precipitation experiments. The pathophysiological relevance of our data was supported by VWF-deficient mice having significantly reduced hyperplasia in carotid artery ligation and artery femoral denudation models. In wild-type mice, infiltration of VWF in intimal regions enriched in proliferating VSMCs was found. Interestingly, also analysis of human atherosclerotic lesions showed abundant VWF accumulation in VSMC-proliferating rich intimal areas.

CONCLUSION

VWF mediates VSMC proliferation through a mechanism involving A2 domain binding to the LRP4 receptor and integrin αvβ3 signalling. Our findings provide new insights into the mechanisms that drive physiological repair and pathological hyperplasia of the arterial vessel wall. In addition, the VWF/LRP4-axis may represent a novel therapeutic target to modulate VSMC proliferation.

Identification of SERPINE1 as a Regulator of Glioblastoma Cell Dispersal with Transcriptome Profiling

High mortality rates of glioblastoma (GBM) patients are partly attributed to the invasive behavior of tumor cells that exhibit extensive infiltration into adjacent brain tissue, leading to rapid, inevitable, and therapy-resistant recurrence. In this study, we analyzed transcriptome of motile (dispersive) and non-motile (core) GBM cells using an in vitro spheroid dispersal model and identified SERPINE1 as a modulator of GBM cell dispersal. Genetic or pharmacological inhibition of SERPINE1 reduced spheroid dispersal and cell adhesion by regulating cell-substrate adhesion. We examined TGFβ as a potential upstream regulator of SERPINE1 expression. We also assessed the significance of SERPINE1 in GBM growth and invasion using TCGA glioma datasets and a patient-derived orthotopic GBM model. SERPINE1 expression was associated with poor prognosis and mesenchymal GBM in patients. SERPINE1 knock-down in primary GBM cells suppressed tumor growth and invasiveness in the brain. Together, our results indicate that SERPINE1 is a key player in GBM dispersal and provide insights for future anti-invasive therapy design.

Low Density Receptor-Related Protein 1 Interactions With the Extracellular Matrix: More Than Meets the Eye

The extracellular matrix (ECM) is a biological substrate composed of collagens, proteoglycans and glycoproteins that ensures proper cell migration and adhesion and keeps the cell architecture intact. The regulation of the ECM composition is a vital process strictly controlled by, among others, proteases, growth factors and adhesion receptors. As it appears, ECM remodeling is also essential for proper neuronal and glial development and the establishment of adequate synaptic signaling. Hence, disturbances in ECM functioning are often present in neurodegenerative diseases like Alzheimer’s disease. Moreover, mutations in ECM molecules are found in some forms of epilepsy and malfunctioning of ECM-related genes and pathways can be seen in, for example, cancer or ischemic injury. Low density lipoprotein receptor-related protein 1 (Lrp1) is a member of the low density lipoprotein receptor family. Lrp1 is involved not only in ligand uptake, receptor mediated endocytosis and lipoprotein transport—functions shared by low density lipoprotein receptor family members—but also regulates cell surface protease activity, controls cellular entry and binding of toxins and viruses, protects against atherosclerosis and acts on many cell signaling pathways. Given the plethora of functions, it is not surprising that Lrp1 also impacts the ECM and is involved in its remodeling. This review focuses on the role of Lrp1 and some of its major ligands on ECM function. Specifically, interactions with two Lrp1 ligands, integrins and tissue plasminogen activator are described in more detail.

Pulsatile stretch as a novel modulator of amyloid precursor protein processing and associated inflammatory markers in human cerebral endothelial cells

Amyloid β (Aβ) deposition is a hallmark of Alzheimer’s disease (AD). Vascular modifications, including altered brain endothelial cell function and structural viability of the blood-brain barrier due to vascular pulsatility, are implicated in AD pathology. Pulsatility of phenomena in the cerebral vasculature are often not considered in in vitro models of the blood-brain barrier. We demonstrate, for the first time, that pulsatile stretch of brain vascular endothelial cells modulates amyloid precursor protein (APP) expression and the APP processing enzyme, β-secretase 1, eventuating increased-Aβ generation and secretion. Concurrent modulation of intercellular adhesion molecule 1 and endothelial nitric oxide synthase (eNOS) signaling (expression and phosphorylation of eNOS) in response to pulsatile stretch indicates parallel activation of endothelial inflammatory pathways. These findings mechanistically support vascular pulsatility contributing towards cerebral Aβ levels.

LDL receptor blockade reduces mortality in a mouse model of ischaemic stroke without improving tissue-type plasminogen activator-induced brain haemorrhage: towards pre-clinical simulation of symptomatic ICH

Background

Symptomatic intracerebral haemorrhage (sICH) following tissue-type plasminogen activator (rt-PA) administration is the most feared and lethal complication of thrombolytic therapy for ischaemic stroke, creating a significant obstacle for a broader uptake of this beneficial treatment. rt-PA also undermines cerebral vasculature stability in a multimodal process which involves engagement with LDL receptor-related protein 1 (LRP-1), potentially underlying the development of sICH.

Aims and methods

We aimed to simulate rt-PA-induced haemorrhagic transformation (HT) in a mouse model of stroke and to assess if it drives symptomatic neurological deterioration and whether it is attenuated by LDL receptor blockade. rt-PA (10 mg/kg) or its vehicle, with or without the LDL receptor antagonist, receptor-associated protein (RAP; 2 mg/kg), were intravenously injected at reperfusion after 0.5 or 4 h of middle cerebral artery occlusion (MCAo). Albumin and haemoglobin content were measured in the perfused mouse brains 24 h post MCAo as indications of blood–brain barrier (BBB) compromise and HT, respectively.

Results

rt-PA did not elevate brain albumin and haemoglobin levels in sham mice or in mice subjected to 0.5 h MCAo. In contrast, administration of rt-PA after prolonged MCAo (4 h) caused a marked increase in HT (but similar changes in brain albumin) compared to vehicle, mimicking the clinical shift from a safe to detrimental intervention. Interestingly, this HT did not correlate with functional deficit severity at 24 h, suggesting that it does not play a symptomatic role in our mouse stroke model. Co-administration of RAP with or without rt-PA reduced mortality and neurological scores but did not effectively decrease brain albumin and haemoglobin levels.

Conclusion

Despite the proven causative relationship between severe HT and neurological deterioration in human stroke, rt-PA-triggered HT in mouse MCAo does not contribute to neurological deficit or simulate sICH. Model limitations, such as the long duration of occlusion required, the type of HT achieved and the timing of deficit assessment may account for this mismatch. Our results further suggest that blockade of LDL receptors improves stroke outcome irrespective of rt-PA, blood–brain barrier breakdown and HT.

Endogenous plasminogen activators mediate progressive intracerebral hemorrhage after traumatic brain injury in mice

Persistent intracerebral hemorrhage (ICH) is a major cause of death and disability after traumatic brain injury (TBI) for which no medical treatment is available. Delayed bleeding is often ascribed to consumptive coagulopathy initiated by exposed brain tissue factor. We examined an alternative hypothesis, namely, that marked release of tissue-type plasminogen activator (tPA) followed by delayed synthesis and release of urokinase plasminogen activator (uPA) from injured brain leads to posttraumatic bleeding by causing premature clot lysis. Using a murine model of severe TBI, we found that ICH is reduced in tPA(-/-) and uPA(-/-) mice but increased in PAI-1(-/-) mice compared with wild-type (WT) mice. tPA(-/-), but not uPA(-/-), mice developed a systemic coagulopathy post-TBI. Tranexamic acid inhibited ICH expansion in uPA(-/-)mice but not in tPA(-/-) mice. Catalytically inactive tPA-S(481)A inhibited plasminogen activation by tPA and uPA, attenuated ICH, lowered plasma d-dimers, lessened thrombocytopenia, and improved neurologic outcome in WT, tPA(-/-), and uPA(-/-) mice. ICH expansion was also inhibited by tPA-S(481)A in WT mice anticoagulated with warfarin. These data demonstrate that protracted endogenous fibrinolysis induced by TBI is primarily responsible for persistent ICH and post-TBI coagulopathy in this model and offer a novel approach to interrupt bleeding.

LRP-1: functions, signaling and implications in kidney and other diseases

Low-density lipoprotein (LDL)-related protein-1 (LRP-1) is a member of LDL receptor family that is implicated in lipoprotein metabolism and in the homeostasis of proteases and protease inhibitors. Expression of LRP-1 is ubiquitous. Up-regulation of LRP-1 has been reported in numerous human diseases. In addition to its function as a scavenger receptor for various ligands, LRP-1 has been shown to transduce multiple intracellular signal pathways including mitogen-activated protein kinase (MAPK), Akt, Rho, and the integrin signaling. LRP-1 signaling plays an important role in the regulation of diverse cellular process, such as cell proliferation, survival, motility, differentiation, and transdifferentiation, and thus participates in the pathogenesis of organ dysfunction and injury. In this review, we focus on the current understanding of LRP-1 signaling and its roles in the development and progression of kidney disease. The role and signaling of LRP-1 in the nervous and cardiovascular systems, as well as in carcinogenesis, are also briefly discussed.

Plasmin-dependent modulation of the blood-brain barrier: a major consideration during tPA-induced thrombolysis?

Plasmin, the principal downstream product of tissue-type plasminogen activator (tPA), is known for its potent fibrin-degrading capacity but is also recognized for many non-fibrinolytic activities. Curiously, plasmin has not been conclusively linked to blood-brain barrier (BBB) disruption during recombinant tPA (rtPA)-induced thrombolysis in ischemic stroke. This is surprising given the substantial involvement of tPA in the modulation of BBB permeability and the co-existence of tPA and plasminogen in both blood and brain throughout the ischemic event. Here, we review the work that argues a role for plasmin together with endogenous tPA or rtPA in BBB alteration, presenting the overall controversy around the topic yet creating a rational case for an involvement of plasmin in this process.

In vivo analysis of Arg-Gly-Asp sequence/integrin α5β1-mediated signal involvement in embryonic enchondral ossification by exo utero development system

Enchondral ossification is a fundamental mechanism for longitudinal bone growth during vertebrate development. In vitro studies suggested that functional blockade with RGD peptides or with an antibody that interferes with integrin α5β1-ligand interactions inhibited pre-hypertrophic chondrocyte differentiation. The purpose of this study is to elucidate in vivo the roles of the integrin α5β1-mediated signal through the Arg-Gly-Asp (RGD) sequence in the cell-extracellular matrix (ECM) interaction in embryonic enchondral ossification by an exo utero development system. We injected Arg-Gly-Asp-Ser (RGDS) peptides and anti-integrin α5β1 antibody (α5β1 ab) in the upper limbs of mouse embryos at embryonic day (E) 15.5 (RGDS-injected limbs, α5β1 ab-injected limbs), and compared the effects on enchondral ossification with those found in the control limbs (Arg-Gly-Glu-Ser peptide-, mouse IgG-, or vehicle-injected, and no surgery) at E16.5. In the RGDS-injected limbs, the humeri were shorter and there were fewer BrdU-positive cells than in the control limbs. The ratios of cartilage length and area to those of the humerus were higher in the RGDS-injected limbs. The ratios of type X collagen to type 2 collagen mRNA and protein (Coll X/Coll 2) were significantly lower in the RGDS-injected limbs. In those limbs, TUNEL-positive cells were hardly observed, and the ratios of fractin to the Coll X/Coll 2 ratio were lower than in the control limbs. Furthermore, the α5β1 ab-injected limbs showed results similar to those of RGDS-injected limbs. The present in vivo study by exo utero development system showed that RGDS and α5β1 ab injection decreased chondrocyte proliferation, differentiation, and apoptosis in enchondral ossification, and suggested that the integrin α5β1-mediated ECM signal through the RGD sequence is involved in embryonic enchondral ossification.

Tissue plasminogen activator activates NF-κB through a pathway involving annexin A2/CD11b and integrin-linked kinase

NF-κB activation is central to the initiation and progression of inflammation, which contributes to the pathogenesis of CKD. Tissue plasminogen activator (tPA) modulates the NF-κB pathway, but the underlying mechanism remains unknown. We investigated the role of tPA signaling in macrophage NF-κB activation and found that tPA activated NF-κB in a time- and dose-dependent manner. tPA also induced the expression of the NF-κB-dependent chemokines IP-10 and MIP-1α. The protease-independent action of tPA required its membrane receptor, annexin A2. tPA induced the aggregation and interaction of annexin A2 with integrin CD11b, and ablation of CD11b or administration of anti-CD11b neutralizing antibody abolished the effect of tPA. Knockdown of the downstream effector of CD11b, integrin-linked kinase, or disruption of its engagement with CD11b also blocked tPA-induced NF-κB signaling. In vivo, tPA-knockout mice had reduced NF-κB signaling, fewer renal macrophages, and less collagen deposition than their counterparts. Taken together, these data suggest that tPA activates the NF-κB pathway in macrophages through a signaling pathway involving annexin A2/CD11b-mediated integrin-linked kinase.

Combination therapy with glucagon and a novel plasminogen activator inhibitor-1-derived peptide enhances protection against impaired cerebrovasodilation during hypotension after traumatic brain injury through inhibition of ERK and JNK MAPK

OBJECTIVE

Outcome of traumatic brain injury (TBI) is impaired by hypotension and glutamate, and TBI-associated release of endogenous tissue plasminogen activator (tPA) impairs cerebral autoregulation. Glucagon decreases central nervous system glutamate, lessens neuronal cell injury, and improves neurological score in mice after TBI. Glucagon partially protects against impaired cerebrovasodilation during hypotension after TBI in piglets by upregulating cAMP which decreases release of tPA. Pial artery dilation during hypotension is due to release of cAMP-dependent dilator prostaglandins (PG), such as PGE2 and PGI2. TBI impairs PGE2 and PGI2-mediated pial artery dilation, which contributes to disturbed cerebral autoregulation post-insult, by upregulating mitogen-activated protein kinase (MAPK). This study was designed to investigate relationships between tPA, prostaglandins, and MAPK as a mechanism to improve the efficacy of glucagon-mediated preservation of cerebrovasodilation during hypotension after TBI.

METHODS

Lateral fluid percussion brain injury (FPI) was induced in piglets equipped with a closed cranial window. ERK and JNK MAPK concentrations in cerebrospinal fluid were quantified by enzyme-linked immunosorbent assay.

RESULTS

Cerebrospinal fluid JNK MAPK was increased by FPI, but blunted by glucagon and the novel plasminogen activator inhibitor-1-derived peptide (PAI-1DP), Ac-RMAPEEIIMDRPFLYVVR-amide. FPI modestly increased, while glucagon and PAI-1DP decreased ERK MAPK. PGE2, PGI2, N-methyl-D-aspartate, and hypotension-induced pial artery dilation was blunted after FPI, partially protected by glucagon, and fully protected by glucagon+PAI-1DP, glucagon+JNK antagonist SP600125 or glucagon+ERK inhibitor U 0126.

DISCUSSION

Glucagon+PAI-1DP act in concert to protect against impairment of cerebrovasodilation during hypotension after TBI via inhibition of ERK and JNK MAPK.

Pivotal role of RanBP9 in integrin-dependent focal adhesion signaling and assembly

Accumulation of the amyloid β (Aβ) peptide derived from the amyloid precursor protein (APP) plays a central role in the pathogenesis of Alzheimer's disease (AD). We previously reported that the scaffolding protein RanBP9 is markedly increased in AD brains and promotes Aβ generation by scaffolding APP/BACE1/LRP complexes together and accelerating APP endocytosis. Because APP, LRP, and RanBP9 all physically interact with β-integrins, we investigated whether RanBP9 alters integrin-dependent cell adhesion and focal adhesion signaling. Here, we show that RanBP9 overexpression dramatically disrupts integrin-dependent cell attachment and spreading in NIH3T3 and hippocampus-derived HT22 cells, concomitant with strongly decreased Pyk2/paxillin signaling and talin/vinculin localization in focal adhesion complexes. Conversely, RanBP9 knockdown robustly promotes cell attachment, spreading, and focal adhesion signaling and assembly. Cell surface biotinylation and endocytosis assays reveal that RanBP9 overexpression and RanBP9 siRNA potently reduces and increases surface β1-integrin and LRP by accelerating and inhibiting their endocytosis, respectively. Primary hippocampal neurons derived from RanBP9-transgenic mice also demonstrate severely reduced levels of surface β1-integrin, LRP, and APP, as well as neurite arborization. Therefore, these data indicate that RanBP9 simultaneously inhibits cell-adhesive processes and enhances Aβ generation by accelerating APP, LRP, and β1-integrin endocytosis.

Low Molecular Weight Antagonists of Plasminogen Activator Inhibitor-1: Therapeutic Potential in Cardiovascular Disease

Plasminogen activator inhibitor-1 (PAI-1; SERPINE1) is the major physiologic regulator of the plasmin-based pericellular proteolytic cascade, a modulator of vascular smooth muscle cell (VSMC) migration and a causative factor in cardiovascular disease and restenosis, particularly in the context of increased vessel transforming growth factor- β1 (TGF-β1) levels. PAI-1 limits conversion of plasminogen to plasmin (and, thereby, fibrin degradation) by inhibiting its protease targets urokinase and tissue-type plasminogen activators (uPA, tPA). PAI-1 also has signaling functions and binds to the low density lipoprotein receptor-related protein 1 (LRP1) to regulate LRP1-dependent cell motility that, in turn, contributes to neointima formation. PAI-1/uPA/uPA receptor/LRPI/integrin complexes are endocytosed with subsequent uPAR/LRP1/integrin redistribution to the leading edge, initiating an "adhesion-detachment-readhesion" cycle to promote cell migration. PAI-1 also interacts with LRP1 in a uPA/uPAR-independent manner triggering Jak/Stat1 pathway activation to stimulate cell motility. PAI-1 itself is a substrate for extracellular proteases and exists in a "cleaved" form which, while unable to interact with uPA and tPA, retains LRP1-binding and migratory activity. These findings suggest that there are multiple mechanisms through which inhibition of PAI-1 may promote cardiovascular health. Several studies have focused on the design, synthesis and preclinical assessment of PAI-1 antagonists including monoclonal antibodies, peptides and low molecular weight (LMW) antagonists. This review discusses the translational impact of LMW PAI-1 antagonists on cardiovascular disease addressing PAI-1-initiated signaling, PAI-1 structure, the design and characteristics of PAI-1-targeting drugs, results of in vitro and in vivo studies, and their clinical implications.

tPA contributes to impaired NMDA cerebrovasodilation after traumatic brain injury through activation of JNK MAPK

OBJECTIVE

N-methyl-D-aspartate (NMDA)-induced pial artery dilation (PAD) is reversed to vasoconstriction after fluid percussion brain injury (FPI). Tissue type plasminogen activator (tPA) is up-regulated and the tPA antagonist, EEIIMD, prevents impaired NMDA PAD after FPI. Mitogen-activated protein kinase (MAPK), a family of at least three kinases, ERK, p38, and JNK, is also up-regulated after traumatic brain injury (TBI). We hypothesize that tPA impairs NMDA-induced cerebrovasodilation after FPI in a MAPK isoform-dependent mechanism.

METHODS

Lateral FPI was induced in newborn pigs. The closed cranial window technique was used to measure pial artery diameter and to collect cerebrospinal fluid (CSF). ERK, p38, and JNK MAPK concentrations in CSF were quantified by ELISA.

RESULTS

CSF JNK MAPK was increased by FPI, increased further by tPA, but blocked by JNK antagonists SP600125 and D-JNKI1. FPI modestly increased p38 and ERK isoforms of MAPK. NMDA-induced PAD was reversed to vasoconstriction after FPI, whereas dilator responses to papaverine were unchanged. tPA, in post-FPI CSF concentration, potentiated NMDA-induced vasoconstriction while papaverine dilation was unchanged. SP 600125 and D-JNKI1, blocked NMDA-induced vasoconstriction and fully restored PAD. The ERK antagonist U 0126 partially restored NMDA-induced PAD, while the p38 inhibitor SB203580 aggravated NMDA-induced vasoconstriction observed in the presence of tPA after FPI.

DISCUSSION

These data indicate that tPA contributes to impairment of NMDA-mediated cerebrovasodilation after FPI through JNK, while p38 may be protective. These data suggest that inhibition of the endogenous plasminogen activator system and JNK may improve cerebral hemodynamic outcome post-TBI.

PAI-1: An Integrator of Cell Signaling and Migration

Cellular migration, over simple surfaces or through complex stromal barriers, requires coordination between detachment/re-adhesion cycles, involving structural components of the extracellular matrix and their surface-binding elements (integrins), and the precise regulation of the pericellular proteolytic microenvironment. It is now apparent that several proteases and protease inhibitors, most notably urokinase plasminogen activator (uPA) and plasminogen activator inhibitor type-1 (PAI-1), also interact with several cell surface receptors transducing intracellular signals that significantly affect both motile and proliferative programs. These events appear distinct from the original function of uPA/PAI-1 as modulators of the plasmin-based proteolytic cascade. The multifaceted interactions of PAI-1 with specific matrix components (i.e., vitronectin), the low-density lipoprotein receptor-related protein-1 (LRP1), and the uPA/uPA receptor complex have dramatic consequences on the migratory phenotype and may underlie the pathophysiologic sequalae of PAI-1 deficiency and overexpression. This paper focuses on the increasingly intricate role of PAI-1 as a major mechanistic determinant of the cellular migratory phenotype.

Urokinase plasminogen activator regulates pulmonary arterial contractility and vascular permeability in mice

The concentration of urokinase plasminogen activator (uPA) is elevated in pathological settings such as acute lung injury, where pulmonary arterial contractility and permeability are disrupted. uPA limits the accretion of fibrin after injury. Here we investigated whether uPA also regulates pulmonary arterial contractility and permeability. Contractility was measured using isolated pulmonary arterial rings. Pulmonary blood flow was measured in vivo by Doppler and pulmonary vascular permeability, according to the extravasation of Evans blue. Our data show that uPA regulates the in vitro pulmonary arterial contractility induced by phenylephrine in a dose-dependent manner through two receptor-dependent pathways, and regulates vascular contractility and permeability in vivo. Physiological concentrations of uPA (≤1 nM) stimulate the contractility of pulmonary arterial rings induced by phenylephrine through the low-density lipoprotein receptor-related protein receptor. The procontractile effect of uPA is independent of its catalytic activity. At pathophysiological concentrations, uPA (20 nM) inhibits contractility and increases vascular permeability. The inhibition of vascular contractility and increase of vascular permeability is mediated through a two-step process that involves docking to N-methyl-d-aspartate receptor-1 (NMDA-R1) on pulmonary vascular smooth muscle cells, and requires catalytic activity. Peptides that specifically inhibit the docking of uPA to NMDA-R, or the uPA variant with a mutated receptor docking site, abolished both the effects of uPA on vascular contractility and permeability, without affecting its catalytic activity. These data show that uPA, at concentrations found under pathological conditions, reduces pulmonary arterial contractility and increases permeability though the activation of NMDA-R1. The selective inhibition of NMDAR-1 activation by uPA can be accomplished without a loss of fibrinolytic activity.

Signaling through LRP1: Protection from atherosclerosis and beyond

The low-density lipoprotein receptor-related protein (LRP1) is a multifunctional cell surface receptor that belongs to the LDL receptor (LDLR) gene family and that is widely expressed in several tissues. LRP1 consists of an 85-kDa membrane-bound carboxyl fragment (β chain) and a non-covalently attached 515-kDa (α chain) amino-terminal fragment. Through its extracellular domain, LRP1 binds at least 40 different ligands ranging from lipoprotein and protease inhibitor complex to growth factors and extracellular matrix proteins. LRP-1 has also been shown to interact with scaffolding and signaling proteins via its intracellular domain in a phosphorylation-dependent manner and to function as a co-receptor partnering with other cell surface or integral membrane proteins. LRP-1 is thus implicated in two major physiological processes: endocytosis and regulation of signaling pathways, which are both involved in diverse biological roles including lipid metabolism, cell growth/differentiation processes, degradation of proteases, and tissue invasion. The embryonic lethal phenotype obtained after target disruption of the LRP-1 gene in the mouse highlights the biological importance of this receptor and revealed a critical, but yet undefined role in development. Tissue-specific gene deletion studies also reveal an important contribution of LRP1 in vascular remodeling, foam cell biology, the central nervous system, and in the molecular mechanisms of atherosclerosis.

tPA activates LDL receptor-related protein 1-mediated mitogenic signaling involving the p90RSK and GSK3beta pathway

In renal fibrosis, interstitial fibroblasts have an increased proliferative phenotype, and the numbers of interstitial fibroblasts closely correlate with the extent of kidney damage. The mechanisms underlying proliferation and resulting expansion of the interstitium remain largely unknown. Here we define the intracellular signaling events by which tissue plasminogen activator (tPA) promotes renal interstitial fibroblast proliferation. tPA promoted the proliferation of renal interstitial fibroblasts independent of its protease activity. The mitogenic effect of tPA required Tyr(4507) phosphorylation of the cytoplasmic tail of its receptor LDL receptor-related protein 1. tPA triggered sequential proliferative signaling events involving Erk1/2, p90RSK, GSK3β phosphorylation, and cyclin D1 induction. Blockade of Erk1/2 activation or knockdown of p90RSK suppressed tPA-induced GSK3β phosphorylation, cyclin D1 expression, and fibroblast proliferation. In contrast, expression of constitutively active Mek1 mimicked tPA in inducing GSK3β phosphorylation and cyclin D1 expression. Ectopic overexpression of an uninhibitable GSK3β mutant eliminated tPA-induced cyclin D1 expression. In the murine obstruction model, tPA deficiency reduced renal GSK3β phosphorylation and induction of PCNA and FSP-1. These findings show that tPA induces Tyr(4507) phosphorylation of LDL receptor-related protein 1, which in turn leads to the downstream phosphorylation of Erk1/2, p90RSK, and GSK3β, followed by the induction of cyclin D1 in murine interstitial fibroblasts. This study implicates tPA as a mitogen that promotes interstitial fibroblast proliferation, leading to expansion of these cells.

Novel plasminogen activator inhibitor-1-derived peptide protects against impairment of cerebrovasodilation after photothrombosis through inhibition of JNK MAPK

The sole FDA-approved treatment for acute stroke is recombinant tissue-type plasminogen activator (rtPA). However, rtPA aggravates the impairment of cerebrovasodilation induced by global hypoxia/ischemia; this impairment is attenuated by the preinjury treatment with the plasminogen activator inhibitor derivative EEIIMD. MAPK (a family of kinases, p38, and JNK) is upregulated after cerebral ischemia. In this study, we determined whether the novel plasminogen activator inhibitor-derived peptide, Ac-RMAPEEIIMDRPFLYVVR-amide, (PAI-1-DP) given 30 min before or 2 h after, focal central nervous system injury induced by photothrombosis would preserve responses to cerebrovasodilators and the role of p38 and JNK MAPK in such effects. Cerebrospinal fluid JNK and p38 levels were elevated by photothrombotic injury, an effect potentiated by rtPA. Cerebrovasodilation was blunted by photothrombosis and reversed to vasoconstriction by rtPA but restored to dilation by PAI-1-DP pre- and posttreatment. PAI-1-DP blocked JNK, but preserved p38 MAPK upregulation after photothrombosis. The JNK MAPK antagonist SP600125 prevented, and the p38 antagonist SB203580 potentiated, impaired cerebrovasodilation after photothrombosis. These data indicate that rtPA impairs cerebrovasodilation after injury by activating JNK, while p38 MAPK is protective, and that the novel peptide PAI-1-DP protects by inhibiting activation of JNK by rtPA. JNK MAPK inhibitors, including PAI-1-DP, may offer a novel approach to increase the benefit-to-risk ratio of thrombolytic therapy and enable its use in central nervous system ischemic disorders.

PAI-1-derived peptide EEIIMD prevents impairment of cerebrovasodilation by augmenting p38 MAPK upregulation after cerebral hypoxia/ischemia

Babies are frequently exposed to cerebral hypoxia and ischemia (H/I) during the perinatal period as a result of stroke, problems with delivery, or postdelivery respiratory management. The sole approved treatment for acute stroke is tissue type plasminogen activator. H/I impairs pial artery dilation (PAD) induced by hypercapnia and hypotension, the impairment aggravated by type plasminogen activator and attenuated by the plasminogen activator inhibitor-1-derived peptide EEIIMD. Mitogen-activated protein kinase (MAPK), a family of at least three kinases, ERK, p38, and JNK, is upregulated after H/I and ERK contribute to impaired cerebrovasodilation. This study determined the roles of p38 and JNK MAPK in the impairment of dilation post-H/I in pigs equipped with a closed cranial window and the relationship between alterations in MAPK isoforms and EEIIMD-mediated cerebrovascular protection. Cerebrospinal fluid-phosphorylated (activated) p38 MAPK, but not JNK MAPK, was increased after H/I, an effect potentiated by intravenous EEIIMD administered 1 h postinjury. PAD in response to hypercapnia and hypotension was blunted by H/I, but dilation was maintained by EEIIMD. PAD was further impaired by the p38 antagonist SB-203580 but unchanged by the JNK antagonist SP-600125. Isoproterenol-induced PAD was unchanged by H/I, EEIIMD, SB-203580, and SP-600125. These data indicate that postinjury treatment with EEIIMD attenuated impaired cerebrovasodilation post-H/I by upregulating p38 but not JNK. These data suggest that plasminogen activator inhibitor-1-based peptides and other approaches to upregulate p38 may offer a novel approach to increase the benefit-to-risk ratio of thrombolytic therapy for diverse central nervous system disorders associated with H/I.

Signaling, delivery and age as emerging issues in the benefit/risk ratio outcome of tPA For treatment of CNS ischemic disorders

Stroke is a leading cause of morbidity and mortality. While tissue-type plasminogen activator (tPA) remains the only FDA-approved treatment for ischemic stroke, clinical use of tPA has been constrained to roughly 3% of eligible patients because of the danger of intracranial hemorrhage and a narrow 3 h time window for safe administration. Basic science studies indicate that tPA enhances excitotoxic neuronal cell death. In this review, the beneficial and deleterious effects of tPA in ischemic brain are discussed along with emphasis on development of new approaches toward treatment of patients with acute ischemic stroke. In particular, roles of tPA-induced signaling and a novel delivery system for tPA administration based on tPA coupling to carrier red blood cells will be considered as therapeutic modalities for increasing tPA benefit/risk ratio. The concept of the neurovascular unit will be discussed in the context of dynamic relationships between tPA-induced changes in cerebral hemodynamics and histopathologic outcome of CNS ischemia. Additionally, the role of age will be considered since thrombolytic therapy is being increasingly used in the pediatric population, but there are few basic science studies of CNS injury in pediatric animals.

Constriction of carotid arteries by urokinase-type plasminogen activator requires catalytic activity and is independent of NH(2)-terminal domains

Urokinase-type plasminogen activator (uPA) is expressed at increased levels in stenotic, atherosclerotic human arteries. However, the biological roles of uPA in the artery wall are poorly understood. Previous studies associate uPA with both acute vasoconstriction and chronic vascular remodeling and attribute uPA-mediated vasoconstriction to the kringle - not the catalytic - domain of uPA. We used an in-vivo uPA overexpression model to test the hypothesis that uPA-induced vasoconstriction is a reversible vasomotor process that can be prevented - and uPA fibrinolytic activity preserved - by: 1) removing the growth factor and kringle domains; or 2) anchoring uPA to the endothelial surface. To test this hypothesis we constructed adenoviral vectors that express: wild-type rabbit uPA (AduPA); a uPA mutant lacking the NH(2)-terminal growth-factor and kringle domains (AduPAdel); a mutant lacking catalytic activity (AduPAS-->A), and a cell-surface anchored mutant (AdTMuPA). uPA mutants were expressed and characterised in vitro and in carotid arteries in vivo. uPAS-->A had no plasminogen activator activity. Activity was similar for uPA and uPAdel, whereas AdTMuPA had only cell-associated activity. AduPAS-->A arteries were not constricted. AduPA, AduPAdel, and AdTM-uPA arteries were constricted (approximately 30% smaller lumens; p< or =0.008 vs. AdNull arteries). Papaverine reversed constriction of AduPA arteries. uPA-mediated arterial constriction is a vasomotor process that is mediated by uPA catalytic activity, not by the NH(2)-terminal domains. Anchoring uPA to the endothelial surface does not prevent vasoconstriction. uPA catalytic activity, generated by artery wall cells, may contribute to lumen loss in human arteries. Elimination of uPA vasoconstrictor activity requires concomitant loss of fibrinolytic activity.

Regulation of airway contractility by plasminogen activators through N-methyl-D-aspartate receptor-1

Reactive airway disease is mediated by smooth muscle contraction initiated through several agonist-dependent pathways. Activation of type 1 N-methyl-D-aspartate receptors (NMDA-R1s) by plasminogen activators (PAs) has been linked to control of vascular tone, but their effect on airway smooth muscle contractility has not previously been studied to our knowledge. We observed that NMDA-R1s are expressed by human airway smooth muscle cells and constitutively inhibit the contraction of isolated rat tracheal rings in response to acetylcholine (Ach). Both tissue-type PA (tPA) and urokinase-type PA (uPA) bind to NMDA-R1 and reverse this effect, thereby enhancing Ach-induced tracheal contractility. Tracheal contractility initiated by Ach is reduced in rings isolated from tPA(-/-) and uPA(-/-) mice compared with their wild-type counterparts. The procontractile effect of uPA or tPA was mimicked and augmented by the nitric oxide synthase inhibitor, l-NAME. uPA and tPA further enhanced the contractility of rings denuded of epithelium, an effect that was inhibited by the NMDA-R antagonist, MK-801. Binding of PAs to NMDA-R1 and the subsequent activation of the receptor were inhibited by PA inhibitor type 1, by a PA inhibitor type 1-derived hexapeptide that recognizes the tPA and uPA docking domains, as well as by specific mutations within the docking site of tPA. These studies identify involvement of PAs and NMDA-R1 in airway contractility, and define new loci that could lead to the development of novel interventions for reactive airway disease.

Blood-brain barrier permeability and tPA-mediated neurotoxicity

Tissue type plasminogen activator (tPA) can induce neuronal apoptosis, disrupt the blood-brain barrier (BBB), and promote dilation of the cerebral vasculature. The timing, sequence and contributions of these and other deleterious effects of tPA and their contribution to post-ischemic brain damage after stroke, have not been fully elucidated. To dissociate the effects of tPA on BBB permeability, cerebral vasodilation and protease-dependent pathways, we developed several tPA mutants and PAI-1 derived peptides constructed by computerized homology modeling of tPA. Our data show that intravenous administration of human tPA to rats increases BBB permeability through a non-catalytic process that is associated with reversible neurotoxicity, brain damage, mortality and contributes significantly to its brief therapeutic window. Furthermore, our data show that inhibiting the effect of tPA on BBB function without affecting its catalytic activity, improves outcome and significantly extends its therapeutic window in mechanical as well as in thromboembolic models of stroke.

Red blood cells-coupled tPA prevents impairment of cerebral vasodilatory responses and tissue injury in pediatric cerebral hypoxia/ischemia through inhibition of ERK MAPK activation

Babies experience hypoxia (H) and ischemia (I) from stroke. The only approved treatment for stroke is fibrinolytic therapy with tissue-type plasminogen activator (tPA). However, tPA potentiates H/I-induced impairment of responses to cerebrovasodilators such as hypercapnia and hypotension, and blockade of tPA-mediated vasoactivity prevents this deleterious effect. Coupling of tPA to red blood cells (RBCs) reduces its central nervous system (CNS) toxicity through spatially confining the drug to the vasculature. Mitogen-activated protein kinase (MAPK), a family of at least three kinases, is upregulated after H/I. In this study we determined whether RBC-tPA given before or after cerebral H/I would preserve responses to cerebrovasodilators and prevent neuronal injury mediated through the extracellular signal-related kinase (ERK) MAPK pathway. Animals given RBC-tPA maintained responses to cerebrovasodilators at levels equivalent to pre-H/I values. cerebrospinal fluid and brain parenchymal ERK MAPK was elevated by H/I and this upregulation was potentiated by tPA, but blunted by RBC-tPA. U0126, an ERK MAPK antagonist, also maintained cerebrovasodilation post H/I. Neuronal degeneration in CA1 hippocampus after H/I was not improved by tPA, but was ameliorated by RBC-tPA and U0126. These data suggest that coupling of tPA to RBCs offers a novel approach toward increasing the benefit/risk ratio of thrombolytic therapy for CNS disorders associated with H/I.

Soluble urokinase receptor conjugated to carrier red blood cells binds latent pro-urokinase and alters its functional profile

Coupling plasminogen activators to carrier red blood cells (RBC) prolongs their life-time in the circulation and restricts extravascular side effects, thereby allowing their utility for short-term thromboprophylaxis. Unlike constitutively active plasminogen activators, single chain urokinase plasminogen activator (scuPA) is activated by plasmin proteolysis or binding to its receptor, uPAR. In this study we conjugated recombinant soluble uPAR (suPAR) to rat RBC, forming RBC/suPAR complex. RBC carrying suPAR circulated in rats similarly to naïve RBC and markedly prolonged the circulation time of suPAR. RBC/suPAR carrying approximately 3x10(4) suPAR molecules per RBC specifically bound up to 2x10(4) molecules of scuPA, retained approximately 75% of scuPA-binding capacity after circulation in rats and markedly altered the functional profile of bound scuPA. RBC carrying directly conjugated scuPA adhered to endothelial cells, while showing no appreciable fibrinolytic activity. In contrast, RBC/suPAR loaded with scuPA did not exhibit increased adhesion to endothelium, while effectively dissolving fibrin clots. This molecular design, capitalizing on unique biological features of the interaction of scuPA with its receptor, provides a promising modality to deliver a pro-drug for prevention of thrombosis.

Integrins as "functional hubs" in the regulation of pathological angiogenesis

It is well accepted that complex biological processes such as angiogenesis are not controlled by a single family of molecules or individually isolated signaling pathways. In this regard, new insight into the interconnected mechanisms that regulate angiogenesis might be gained by examining this process from a more global network perspective. The coordination of signaling cues from both outside and inside many different cell types is required for the successful completion of angiogenesis. Evidence is accumulating that the multifunctional integrin family of cell adhesion receptors represent an important group of molecules that play active roles in sensing, integrating, and distributing a diverse set of signals that regulate many cellular events required for angiogenesis. Given the ability of integrins to bind numerous extracellular ligands and transmit signals in a bi-directional fashion, we will discuss the multiple ways by which integrins may serve as a functional hub during pathological angiogenesis. In addition, we will highlight potential imaging and therapeutic strategies based on the expanding new insight into integrin function.

Plasminogen activator inhibitor type 1 derived peptide, EEIIMD, diminishes cortical infarct but fails to improve neurological function in aged rats following middle cerebral artery occlusion

Age is a primary risk factor in stroke that is often overlooked in animal studies. We contend that using aged animals yields insight into aspects of stroke injury and recovery that are masked, or not elicited, in younger animals. In this study, we examined effects of co-administration of a plasminogen activator inhibitor type 1 derived peptide, Glu-Glu-Iso-Iso-Met-Asp (EEIIMD), with tissue plasminogen activator (tPA) on infarct volume and functional outcome in aged rats following a transient middle cerebral artery occlusion. Results of our study showed aged (18-20 months) rats treated with EEIIMD along with tPA had reduced cortical infarction volume. However, aged rats showed no improvement in total infarction volume, edema formation, or functional outcome as compared to aged rats administered only tPA. Young adult rats (3-4 months) treated with EEIIMD showed significant improvement in cortical and total infarction volumes, edema formation, and functional outcome. Striatal infarction volume was unaffected by EEIIMD treatment in both young adult and aged rats. These findings emphasize that physiological differences exist between young adult and aged rats and suggest that taking aging processes into account when assessing stroke may improve our ability to discern which therapeutics can be translated from bench to bedside.

uPA modulates the age-dependent effect of brain injury on cerebral hemodynamics through LRP and ERK MAPK

We hypothesized that urokinase plasminogen activator (uPA) contributes to age-dependent early hyperemia after fluid percussion brain injury (FPI) by activating extracellular signal-related kinase (ERK) mitogen-activated protein kinase (MAPK), leading to histopathologic changes in the underlying cortex. Both cerebrospinal fluid (CSF) uPA and phosphorylation of CSF ERK MAPK was increased at 1 min after FPI in newborn pigs, but was unchanged in juvenile pigs. uPA and phosphorylated ERK MAPK, detectable in sham piglet brain by immunohistochemistry, was markedly elevated and associated with histopathology 4 h after FPI in the newborn but there was minimal staining and histopathology in the juvenile. EEIIMD, a peptide derived from PA inhibitor-1 that does not affect proteolysis, blunted FPI-induced phosphorylation of ERK MAPK. FPI produced pial artery dilation and increased cerebral blood flow at 1 min after insult in the newborn, but not in the juvenile. Antilipoprotein-related protein (LRP) antibody, EEIIMD, a soluble uPA antagonist, and the ERK MAPK antagonist U 0126 inhibited FPI-associated hyperemia. These data indicate that uPA is upregulated after FPI and produces an age-dependent early hyperemia followed by histopathology through an LRP- and ERK MAPK-dependent pathway.

Urokinase plasminogen activator impairs SNP and PGE2 cerebrovasodilation after brain injury through activation of LRP and ERK MAPK

Pial artery dilation in response to prostaglandin (PG)E(2) and the nitric oxide (NO) releaser sodium nitroprusside (SNP) are blunted after fluid percussion brain injury (FPI), whereas responses to papaverine are unchanged. Urokinase plasminogen activator (uPA) and ERK mitogen-activated protein kinase (MAPK) are upregulated and contribute to the impairment of cerebrohemodynamics seen after FPI. PA vascular activity is mediated through the low-density lipoprotein receptor (LRP). Therefore, we investigated the role of uPA, LRP, and ERK MAPK in the impaired cerebrovasodilation response to PGE(2) and SNP after FPI. Lateral FPI (2 atm) was induced in anesthetized piglets equipped with a closed cranial window. Cerebrospinal fluid (CSF) ERK MAPK was quantified by enzyme-linked immunosorbent assay (ELISA). Pretreatment with soluble uPA receptor (suPAR), which antagonizes the vascular action of uPA, blunted the impairment of SNP and PGE(2)-mediated dilation seen after FPI. Pretreatment with the LRP antagonist RAP, a monoclonal antibody against LRP (Mab ag LRP) and the ERK MAPK antagonist, U 0126, all provided similar protection, whereas control immunoglobulin G (IgG) had no effect. Responses to papaverine were unchanged after FPI. Upregulation of ERK MAPK phosphorylation in CSF after FPI was blunted in animals pretreated with suPAR, RAP, MAb ag LRP, or U 0126, whereas control IgG had no effect. These data indicate that uPA contributes to the impairment of SNP and PGE(2)-mediated cerebrovasodilation seen after brain injury through activation of LRP and ERK MAPK.

Inhibition of integrin alphavbeta3 prevents urokinase plasminogen activator-mediated impairment of cerebrovasodilation after cerebral hypoxia/ischemia

Cerebral hypoxia (10 min) followed immediately by ischemia (20 min) (H/I) impairs cerebrovasodilation in response to hypercapnia and hypotension in the newborn pig; exogenous urokinase plasminogen activator (uPA) potentiates this effect, whereas the blockade of endogenous uPA-mediated vasoactivity prevents it completely. This study investigated the role of integrin alpha(V)beta(3) in the uPA-mediated impairment of cerebrovasodilation after H/I in piglets equipped with a closed cranial window. Pial artery dilation induced by hypercapnia (Pco(2), 75 mmHg) and hypotension (mean arterial blood pressure, decreased by 45%) was blunted after H/I, reversed to vasconstriction in piglets treated with uPA (10(-7) M), a concentration observed in cerebrospinal fluid after H/I, but reverted to a dilation no different than preinsult in piglets administered an anti-alpha(V)beta(3) antibody (10 ng/ml) in addition to uPA (26 +/- 1, 9 +/- 1, -10 +/- 3, and 22 +/- 3% for hypercapnia before H/I, after H/I, after H/I with uPA, and after H/I with combined uPA and anti-alpha(V)beta(3) antibody, respectively). Responses to isoproterenol were unchanged after H/I and combined uPA and anti-alpha(V)beta(3) antibody. Similar results were obtained for the combined administration of uPA with the alpha(V)beta(3) antagonist Arg-Gly-Asp-d-Phe-Val and Arg-Gly-Asp-Ser, but not for the inactive analog Arg-Gly-Asp-Glu-Ser acetate. These data show that the activation of the integrin alpha(V)beta(3) contributes to the uPA-mediated impairment of pial artery dilation after H/I. These data suggest that the inhibition of uPA and integrin signaling may preserve cerebrohemodynamic control after H/I.

Novel actions of tissue-type plasminogen activator in chronic kidney disease

Tissue-type plasminogen activator (tPA) is traditionally viewed as a simple serine protease whose main function is to convert plasminogen into biologically active plasmin. As a protease, tPA plays a crucial role in regulating blood fibrinolysis, in maintaining the homeostasis of extracellular matrix and in modulating the post-translational activation of growth factors. However, emerging evidence indicates that tPA also functions as a cytokine that transmits its signal across the cell membrane, initiates a diverse array of intracellular signaling, and dictates gene expression in the nuclei. tPA binds to the cell membrane LDL receptor-related protein 1 (LRP-1), triggers its tyrosine phosphorylation. As a cytokine, tPA plays a pivotal role in the pathogenesis of renal interstitial fibrosis through diverse mechanisms. It facilitates tubular epithelial to mesenchymal transition, potentiates myofibroblast activation, and protects renal interstitial fibroblasts/myofibroblasts from apoptosis. Together, growing evidence has implicated tPA as a fibrogenic cytokine that promotes the progression of kidney diseases. These new findings have radically changed our conception of tPA in renal fibrogenesis and represent a paradigm shift towards uncovering its cytokine function.

Tissue-type plasminogen activator as a therapeutic target in stroke

BACKGROUND

Ischemic stroke is a leading cause of morbidity and mortality worldwide and recombinant human tissue-type plasminogen activator (tPA) is the prominent therapeutic among very few therapeutics used in its treatment. Due to complications attributed to the drug, most notably transformation of ischemia to hemorrhage, tPA is only used in a small number of ischemic stroke cases, albeit significantly more often in specialized stroke centers.

OBJECTIVE

What are the mechanisms of tPA action and side effects in ischemic stroke, and can the knowledge about these mechanisms aid in making tPA a more efficacious and safe therapeutic or in developing alternative therapeutics?

METHODS

tPA use and alternative/combination therapies in acute ischemic stroke treatment are summarized. The review focuses on literature concerning tPA neurotoxicity and its implications for further development of tPA as a stroke therapeutic.

RESULTS/CONCLUSION

Exogenously administered recombinant tPA and endogenous tPA have both turned into promising therapeutic targets for the stroke patient.

Regulation of plasminogen activators in human thyroid follicular cells and their relationship to differentiated function

Human thyroid cells in culture take up and organify (125)I when cultured in TSH (acting through cAMP) and insulin. They also secrete urokinase (uPA) and tissue-type (tPA) plasminogen activators (5-100 IU/10(6)cells/day). TSH and insulin both decreased secreted PA activity (PAA), uPA and tPA protein and their mRNAs. Autocrine fibroblast growth factor increased secreted PAA and inhibited thyroid cell (125)I uptake. Epidermal growth factor (EGF) and the protein kinase C (PKC) activator, TPA significantly increased PAA and inhibited thyroid differentiated function, (TPA > EGF). For TPA, effects were rapid, increased PAA secretion and decreased (125)I uptake being seen at 4 h whereas for EGF, a 24 h incubation was required. qRT-PCR showed significantly increased mRNA expression of uPA with lesser effects on tPA. Aprotinin, which inhibits PAA, increased (125)I uptake but did not abrogate the effects of TPA and EGF. The MEKK inhibitor, PD98059 partially reversed the effects of EGF and TPA on PAA, and largely reversed the effects of EGF but not TPA on differentiated function. PKC inhibitors bisindoylmaleimide 1, and the specific PKCbeta inhibitor, LY379196 completely reversed the effects of TPA on (125)I uptake and PAA whereas EGF effects were unaffected. TPA inhibited follicle formation and this effect was blocked by LY379196 but not PD98059. We conclude that in thyroid cells, MAPK activation inversely correlates with (125)I uptake and directly correlates with PA expression, in contrast to the effects of cAMP. TPA effects on iodide metabolism, dissolution of follicles and uPA synthesis are mediated predominantly through PKCbeta whereas EGF exerts its effects through MAPK but not PKCbeta.

Recombinant Desmodus rotundus salivary plasminogen activator crosses the blood-brain barrier through a low-density lipoprotein receptor-related protein-dependent mechanism without exerting neurotoxic effects

BACKGROUND AND PURPOSE

Desmoteplase, a recombinant form of the plasminogen activator DSPAalpha1 from Desmodus rotundus, may offer improved clinical benefits for acute ischemic stroke treatment over the current therapy, recombinant tissue plasminogen activator (rtPA). Accumulating evidence suggests that clinical use of rtPA could be limited by unfavorable properties, including its ability to cross the blood-brain barrier (BBB), thus potentially adding to the pro-excitotoxic effect of endogenous tPA in cerebral parenchyma. Here, to investigate whether desmoteplase may display a safer profile than the structurally-related tPA, both agents were compared for their ability to cross the BBB and promote neurotoxicity.

METHODS

First, the passage of vascular DSPA and rtPA was investigated in vitro in a model of BBB, subjected or not to oxygen and glucose deprivation. Second, we studied DSPA- and rtPA-mediated effects in an in vivo paradigm of excitotoxic necrosis.

RESULTS

The rtPA and desmoteplase cross the intact BBB by LRP-mediated transcytosis. Under conditions of oxygen and glucose deprivation, translocation rates of both compounds increased; however, unlike rtPA, desmoteplase transport remained LRP-dependent. Additionally, neither intracerebral nor intravenous desmoteplase administration enhanced NMDA-induced excitotoxic striatal damage in vivo. Interestingly, intravenous but not intrastriatal coadministration of desmoteplase and rtPA reduced the pro-excitotoxic effect of rtPA.

CONCLUSIONS

We show that desmoteplase crosses the BBB but does not promote neuronal death. Moreover, intravenous administration of desmoteplase antagonizes the neurotoxicity induced by vascular rtPA. This action may be caused by competition of desmoteplase with rtPA for LRP binding at the BBB, thus effectively blocking rtPA access to the brain parenchyma.

The LDL receptor-related protein (LRP) family: an old family of proteins with new physiological functions

The low-density lipoprotein (LDL) receptor is the founding member of a family of seven structurally closely related transmembrane proteins (LRP1, LRP1b, megalin/LRP2, LDL receptor, very low-density lipoprotein receptor, MEGF7/LRP4, LRP8/apolipoprotein E receptor2). These proteins participate in a wide range of physiological processes, including the regulation of lipid metabolism, protection against atherosclerosis, neurodevelopment, and transport of nutrients and vitamins. While currently available data suggest that the role of the LDL receptor is limited to the regulation of cholesterol homeostasis by receptor-mediated endocytosis of lipoprotein particles, there is growing experimental evidence that the other members of the gene family have additional physiological functions as signal transducers. In this review, we focus on the latest discovered functions of two major members of this family, LRP1 and megalin/LRP2, and on the newly elucidated physiological role of a third member of the family, MEGF7/LRP4, which can also function as a modulator of diverse signaling pathways during development.

Neutralizing the neurotoxic effects of exogenous and endogenous tPA

The clinical use of tissue-type plasminogen activator (tPA) in the treatment of stroke is profoundly constrained by its serious side effects. We report that the deleterious effects of tPA on cerebral edema and intracranial bleeding are separable from its fibrinolytic activity and can be neutralized. A hexapeptide (EEIIMD) corresponding to amino acids 350-355 of plasminogen activator inhibitor type 1 (PAI-1) abolished the tPA-induced increase in infarct size and intracranial bleeding in both mechanical and embolic models of stroke in rats, and reduced brain edema and neuronal loss after traumatic brain injury in pigs. These experiments suggest mechanisms to reduce the neurotoxic effects of tPA without compromising its fibrinolytic activity, through the use of selective antagonists and new tPA formulations.