Inflammation-induced TRPV4 channels exacerbate blood-brain barrier dysfunction in multiple sclerosis.

BACKGROUND: Blood-brain barrier (BBB) dysfunction and immune cell migration into the central nervous system (CNS) are pathogenic drivers of multiple sclerosis (MS). Ways to reinstate BBB function and subsequently limit neuroinflammation present promising strategies to restrict disease progression. However, to date, the molecular players directing BBB impairment in MS remain poorly understood. One suggested candidate to impact BBB function is the transient receptor potential vanilloid-type 4 ion channel (TRPV4), but its specific role in MS pathogenesis remains unclear. Here, we investigated the role of TRPV4 in BBB dysfunction in MS. MAIN TEXT: In human post-mortem MS brain tissue, we observed a region-specific increase in endothelial TRPV4 expression around mixed active/inactive lesions, which coincided with perivascular microglia enrichment in the same area. Using in vitro models, we identified that microglia-derived tumor necrosis factor-α (TNFα) induced brain endothelial TRPV4 expression. Also, we found that TRPV4 levels influenced brain endothelial barrier formation via expression of the brain endothelial tight junction molecule claudin-5. In contrast, during an inflammatory insult, TRPV4 promoted a pathological endothelial molecular signature, as evidenced by enhanced expression of inflammatory mediators and cell adhesion molecules. Moreover, TRPV4 activity mediated T cell extravasation across the brain endothelium. CONCLUSION: Collectively, our findings suggest a novel role for endothelial TRPV4 in MS, in which enhanced expression contributes to MS pathogenesis by driving BBB dysfunction and immune cell migration.

Endothelial-Derived Extracellular Vesicles Induce Cerebrovascular Dysfunction in Inflammation.

Blood-brain barrier (BBB) dysfunction is a key hallmark in the pathology of many neuroinflammatory disorders. Extracellular vesicles (EVs) are lipid membrane-enclosed carriers of molecular cargo that are involved in cell-to-cell communication. Circulating endothelial EVs are increased in the plasma of patients with neurological disorders, and immune cell-derived EVs are known to modulate cerebrovascular functions. However, little is known about whether brain endothelial cell (BEC)-derived EVs themselves contribute to BBB dysfunction. Human cerebral microvascular cells (hCMEC/D3) were treated with TNFα and IFNy, and the EVs were isolated and characterised. The effect of EVs on BBB transendothelial resistance (TEER) and leukocyte adhesion in hCMEC/D3 cells was measured by electric substrate cell-substrate impedance sensing and the flow-based T-cell adhesion assay. EV-induced molecular changes in recipient hCMEC/D3 cells were analysed by RT-qPCR and Western blotting. A stimulation of naïve hCMEC/D3 cells with small EVs (sEVs) reduced the TEER and increased the shear-resistant T-cell adhesion. The levels of microRNA-155, VCAM1 and ICAM1 were increased in sEV-treated hCMEC/D3 cells. Blocking the expression of VCAM1, but not of ICAM1, prevented sEV-mediated T-cell adhesion to brain endothelia. These results suggest that sEVs derived from inflamed BECs promote cerebrovascular dysfunction. These findings may provide new insights into the mechanisms involving neuroinflammatory disorders.

Profiling the unique protective properties of intracranial arterial endothelial cells.

Cardiovascular disorders, like atherosclerosis and hypertension, are increasingly known to be associated with vascular cognitive impairment (VCI). In particular, intracranial atherosclerosis is one of the main causes of VCI, although plaque development occurs later in time and is structurally different compared to atherosclerosis in extracranial arteries. Recent data suggest that endothelial cells (ECs) that line the intracranial arteries may exert anti-atherosclerotic effects due to yet unidentified pathways. To gain insights into underlying mechanisms, we isolated post-mortem endothelial cells from both the intracranial basilar artery (BA) and the extracranial common carotid artery (CCA) from the same individual (total of 15 individuals) with laser capture microdissection. RNA sequencing revealed a distinct molecular signature of the two endothelial cell populations of which the most prominent ones were validated by means of qPCR. Our data reveal for the first time that intracranial artery ECs exert an immune quiescent phenotype. Secondly, genes known to be involved in the response of ECs to damage (inflammation, differentiation, adhesion, proliferation, permeability and oxidative stress) are differentially expressed in intracranial ECs compared to extracranial ECs. Finally, Desmoplakin (DSP) and Hop Homeobox (HOPX), two genes expressed at a higher level in intracranial ECs, and Sodium Voltage-Gated Channel Beta Subunit 3 (SCN3B), a gene expressed at a lower level in intracranial ECs compared to extracranial ECs, were shown to be responsive to shear stress and/or hypoxia. With our data we present a set of intracranial-specific endothelial genes that may contribute to its protective phenotype, thereby supporting proper perfusion and consequently may preserve cognitive function. Deciphering the molecular regulation of the vascular bed in the brain may lead to the identification of novel potential intervention strategies to halt vascular associated disorders, such as atherosclerosis and vascular cognitive dysfunction.

Inflammation-induced endothelial to mesenchymal transition promotes brain endothelial cell dysfunction and occurs during multiple sclerosis pathophysiology.

The blood-brain barrier (BBB) has a major role in maintaining brain homeostasis through the specialized function of brain endothelial cells (BECs). Inflammation of the BECs and loss of their neuroprotective properties is associated with several neurological disorders, including the chronic neuro-inflammatory disorder multiple sclerosis (MS). Yet, the underlying mechanisms of a defective BBB in MS remain largely unknown. Endothelial to mesenchymal transition (EndoMT) is a pathophysiological process in which endothelial cells lose their specialized function and de-differentiate into mesenchymal cells. This transition is characterized by an increase in EndoMT-related transcription factors (TFs), a downregulation of brain endothelial markers, and an upregulation of mesenchymal markers accompanied by morphological changes associated with cytoskeleton reorganization. Here, we postulate that EndoMT drives BEC de-differentiation, mediates inflammation-induced human BECs dysfunction, and may play a role in MS pathophysiology. We provide evidence that stimulation of human BECs with transforming growth factor (TGF)-ß1 and interleukin (IL)-1ß promotes EndoMT, a process in which the TF SNAI1, a master regulator of EndoMT, plays a crucial role. We demonstrate the involvement of TGF-ß activated kinase 1 (TAK1) in EndoMT induction in BECs. Finally, immunohistochemical analysis revealed EndoMT-associated alterations in the brain vasculature of human post-mortem MS brain tissues. Taken together, our novel findings provide a better understanding of the molecular mechanisms underlying BECs dysfunction during MS pathology and can be used to develop new potential therapeutic strategies to restore BBB function.

Angiopoietin like-4 as a novel vascular mediator in capillary cerebral amyloid angiopathy.

Increasing evidence suggests that vascular dysfunction in the brain is associated with early stages of Alzheimer's disease. Amyloid-ß deposition in the microvasculature of the brain, a process referred to as capillary cerebral amyloid angiopathy (capillary CAA), propagates vascular remodelling, which results in impaired function of the blood-brain barrier, reduced cerebral perfusion and increased hypoxia. While improving vascular function may be an attractive new way to fight capillary CAA, the underlying factors that mediate vascular alterations in Alzheimer's disease and capillary CAA pathogenesis remain largely unknown. Here we provide first evidence that angiopoietin like-4 (ANGPTL4), a hypoxia-induced factor, is highly expressed by reactive astrocytes in well characterized post-mortem tissues of patients with capillary CAA. Our in vitro studies reveal that ANGPTL4 is upregulated and secreted by human cortical astrocytes under hypoxic conditions and in turn stimulates endothelial cell migration and sprouting in a 3D spheroid model of human brain endothelial cells. Interestingly, plasma levels of ANGPTL4 are significantly increased in patients with vascular dementia compared to patients with subjective memory complaints. Overall, our data suggest that ANGPTL4 contributes to pathological vascular remodelling in capillary CAA and that detection of ANGPTL4 levels may improve current diagnostics. Ways of counteracting the detrimental effects of ANGPTL4 and thus promoting cerebral vascular function may provide novel treatment regimens to halt the progression of Alzheimer's disease.

Elevated monocyte-specific type I interferon signalling correlates positively with cardiac healing in myocardial infarct patients but interferon alpha application deteriorates myocardial healing in rats.

Monocytes are involved in adverse left ventricular (LV) remodelling following myocardial infarction (MI). To provide therapeutic opportunities we aimed to identify gene transcripts in monocytes that relate to post-MI healing and evaluated intervention with the observed gene activity in a rat MI model. In 51 MI patients treated by primary percutaneous coronary intervention (PCI), the change in LV end-diastolic volume index (EDVi) from baseline to 4-month follow-up was assessed using cardiovascular magnetic resonance imaging (CMR). Circulating monocytes were collected at day 5 (Arterioscler Thromb Vasc Biol 35:1066-1070, 2015; Cell Stem Cell 16:477-487, 2015; Curr Med Chem 13:1877-1893, 2006) after primary PCI for transcriptome analysis. Transcriptional profiling and pathway analysis revealed that patients with a decreased LV EDVi showed an induction of type I interferon (IFN) signalling (type I IFN pathway: P value < 0.001; false discovery rate < 0.001). We subsequently administered 15,000 Units of IFN-α subcutaneously in a rat MI model for three consecutive days following MI. Cardiac function was measured using echocardiography and infarct size/cardiac inflammation using (immuno)-histochemical analysis. We found that IFN-α application deteriorated ventricular dilatation and increased infarct size at day 28 post-MI. Moreover, IFN-α changed the peripheral monocyte subset distribution towards the pro-inflammatory monocyte subset whereas in the myocardium, the presence of the alternative macrophage subset was increased at day 3 post-MI. Our findings suggest that induction of type I IFN signalling in human monocytes coincides with adverse LV remodelling. In rats, however, IFN-α administration deteriorated post-MI healing. These findings underscore important but also contradictory roles for the type I IFN response during cardiac healing following MI.

Vascular Endothelial Growth Factor remains unchanged in cerebrospinal fluid of patients with Alzheimer's disease and vascular dementia.

BACKGROUND: Increasing evidence suggests that cerebral vascular dysfunction is associated with the early stages of Alzheimer's disease (AD). Vascular endothelial growth factor (VEGF) is one of the key players involved in the development and maintenance of the vasculature. Here, we hypothesized that VEGF levels in cerebrospinal fluid (CSF) may be altered in AD patients with vascular involvement, characterized by the presence of microbleeds (MB), and in vascular dementia (VaD) patients compared to controls. METHODS: VEGF levels were determined by electrochemilumiscence Meso Scale Discovery (MULTI-SPOT Assay System) in CSF from age-matched groups of controls with subjective cognitive decline (n = 21), AD without MB (n = 25), AD with MB (n = 25), and VaD (n = 21) patients. RESULTS: The average level of VEGF in the different groups was 2.8 ± 1 pg/ml CSF. Adjusted for age and gender, no significant differences were detected between groups (p > 0.5). However, we detected a significant correlation between the concentration of VEGF in the CSF and age (r = 0.22, p = 0.03). In addition, males (n = 54) revealed higher VEGF levels in their CSF compared to females (n = 38) (males = 3.08 ± 0.769 pg/ml (mean ± SD), females = 2.6 ± 0.59; p = 0.006), indicating a gender-related regulation. CONCLUSION: Our study suggests that VEGF levels in the CSF do not reflect the cerebral vascular alterations in either AD or VaD patients. The observed associations of VEGF with age and gender may indicate that VEGF reflects normal aging and that males and females may differ in their aging process.

Notch signaling is impaired during inflammation in a Lunatic Fringe-dependent manner.

The blood-brain barrier (BBB) assures brain homeostasis through the specialized function of brain endothelial cells (BECs). Dysfunction of the BBB due to inflammatory processes is associated with several neurological disorders, including multiple sclerosis (MS). Understanding the mechanisms that underlie these processes may ultimately lead to new therapeutic strategies to restore BBB function, thereby fighting disease progression. In this study, we demonstrate for the first time a critical role of the Notch signaling pathway in the function of the BBB under resting and inflammatory conditions. Inhibition of the Notch signaling, either by a γ-secretase inhibitor or by genetic ablation of endothelial NOTCH, led to BBB dysfunction in vitro as evidenced by reduced transendothelial electrical resistance (TEER), altered localization and loss of endothelial junction molecules and enhanced macromolecular permeability. Inflamed BECs showed impaired Notch signaling as indicated by reduced level of the downstream targets HES-1 and HES-5. Notably, barrier function was further reduced when the Notch signaling was inhibited under inflammatory conditions, suggesting an additive effect of the Notch signaling and inflammation in BECs. In contrast, inducible overexpression of Notch-intracellular domain 1 (NICD1) rescued the detrimental effect caused by inflammation. Furthermore, we provide evidence that inflammation reduced the expression of the glycosyltransferase Lunatic Fringe (LFNG), a known positive regulator of Notch glycosylation and signaling, thereby leading to disrupted barrier function of BECs. Together, our data demonstrate the functional importance of the conserved Notch signaling pathway in control of the brain endothelial barrier and shed light on the role of LFNG in the regulation of Notch glycosylation and signaling in the adult brain vasculature in both health and disease.

Delayed Microvascular Shear Adaptation in Pulmonary Arterial Hypertension. Role of Platelet Endothelial Cell Adhesion Molecule-1 Cleavage.

RATIONALE: Altered pulmonary hemodynamics and fluid flow-induced high shear stress (HSS) are characteristic hallmarks in the pathogenesis of pulmonary arterial hypertension (PAH). However, the contribution of HSS to cellular and vascular alterations in PAH is unclear. OBJECTIVES: We hypothesize that failing shear adaptation is an essential part of the endothelial dysfunction in all forms of PAH and tested whether microvascular endothelial cells (MVECs) or pulmonary arterial endothelial cells (PAECs) from lungs of patients with PAH adapt to HSS and if the shear defect partakes in vascular remodeling in vivo. METHODS: PAH MVEC (n = 7) and PAH PAEC (n = 3) morphology, function, protein, and gene expressions were compared with control MVEC (n = 8) under static culture conditions and after 24, 72, and 120 hours of HSS. MEASUREMENTS AND MAIN RESULTS: PAH MVEC showed a significantly delayed morphological shear adaptation (P = 0.03) and evidence of cell injury at sites of nonuniform shear profiles that are critical loci for vascular remodeling in PAH. In clear contrast, PAEC isolated from the same PAH lungs showed no impairments. PAH MVEC gene expression and transcriptional shear activation were not altered but showed significant decreased protein levels (P = 0.02) and disturbed interendothelial localization of the shear sensor platelet endothelial cell adhesion molecule-1 (PECAM-1). The decreased PECAM-1 levels were caused by caspase-mediated cytoplasmic cleavage but not increased cell apoptosis. Caspase blockade stabilized PECAM-1 levels, restored endothelial shear responsiveness in vitro, and attenuated occlusive vascular remodeling in chronically hypoxic Sugen5416-treated rats modeling severe PAH. CONCLUSIONS: Delayed shear adaptation, which promotes shear-induced endothelial injury, is a newly identified dysfunction specific to the microvascular endothelium in PAH. The shear response is normalized on stabilization of PECAM-1, which reverses intimal remodeling in vivo.

Expression of Nitric Oxide-Transporting Aquaporin-1 Is Controlled by KLF2 and Marks Non-Activated Endothelium In Vivo.

The flow-responsive transcription factor Krüppel-like factor 2 (KLF2) maintains an anti-coagulant, anti-inflammatory endothelium with sufficient nitric oxide (NO)-bioavailability. In this study, we aimed to explore, both in vitro and in human vascular tissue, expression of the NO-transporting transmembrane pore aquaporin-1 (AQP1) and its regulation by atheroprotective KLF2 and atherogenic inflammatory stimuli. In silico analysis of gene expression profiles from studies that assessed the effects of KLF2 overexpression in vitro and atherosclerosis in vivo on endothelial cells, identifies AQP1 as KLF2 downstream gene with elevated expression in the plaque-free vessel wall. Biomechanical and pharmaceutical induction of KLF2 in vitro is accompanied by induction of AQP1. Chromosome immunoprecipitation (CHIP) confirms binding of KLF2 to the AQP1 promoter. Inflammatory stimulation of endothelial cells leads to repression of AQP1 transcription, which is restrained by KLF2 overexpression. Immunohistochemistry reveals expression of aquaporin-1 in non-activated endothelium overlying macrophage-poor intimae, irrespective whether these intimae are characterized as being plaque-free or as containing advanced plaque. We conclude that AQP1 expression is subject to KLF2-mediated positive regulation by atheroprotective shear stress and is downregulated under inflammatory conditions both in vitro and in vivo. Thus, endothelial expression of AQP1 characterizes the atheroprotected, non-inflamed vessel wall. Our data provide support for a continuous role of KLF2 in stabilizing the vessel wall via co-temporal expression of eNOS and AQP1 both preceding and during the pathogenesis of atherosclerosis.

IFN-ß affects the angiogenic potential of circulating angiogenic cells by activating calpain 1.

Circulating angiogenic cells (CACs) are monocyte-derived cells with endothelial characteristics, which contribute to both angiogenesis and arteriogenesis in a paracrine way. Interferon-ß (IFN-ß) is known to inhibit these divergent processes in animals and patients. We hypothesized that IFN-ß might act by affecting the differentiation and function of CACs. CACs were cultured from peripheral blood mononuclear cells and phenotypically characterized by surface expression of monocytic and endothelial markers. IFN-ß significantly reduced the number of CACs by 18-64%. Apoptosis was not induced by IFN-ß, neither in mononuclear cells during differentiation, nor after maturation to CACs. Rather, IFN-ß impaired adhesion to, and spreading on, fibronectin, which was dependent on α5ß1 (VLA-5)-integrin. IFN-ß affected the function of VLA-5 in mature CACs, leading to rounding and detachment of cells, by induction of calpain 1 activity. Cell rounding and detachment was completely reversed by inhibition of calpain 1 activity in mature CACs. During in vitro capillary formation, CAC addition and calpain 1 inhibition enhanced sprouting of endothelial cells to a comparable extent, but were not sufficient to rescue tube formation in the presence of IFN-ß. We show that the IFN-ß-induced reduction of the numbers of in vitro differentiated CACs is based on activation of calpain 1, resulting in an attenuated adhesion to extracellular matrix proteins via VLA-5. In vivo, this could lead to inhibition of vessel formation due to reduction of the locally recruited CAC numbers and their paracrine angiogenic factors.

Galectin-2 induces a proinflammatory, anti-arteriogenic phenotype in monocytes and macrophages.

Galectin-2 is a monocyte-expressed carbohydrate-binding lectin, for which increased expression is genetically determined and associated with decreased collateral arteriogenesis in obstructive coronary artery disease patients. The inhibiting effect of galectin-2 on arteriogenesis was confirmed in vivo, but the mechanism is largely unknown. In this study we aimed to explore the effects of galectin-2 on monocyte/macrophage phenotype in vitro and vivo, and to identify the receptor by which galectin-2 exerts these effects. We now show that the binding of galectin-2 to different circulating human monocyte subsets is dependent on monocyte surface expression levels of CD14. The high affinity binding is blocked by an anti-CD14 antibody but not by carbohydrates, indicating a specific protein-protein interaction. Galectin-2 binding to human monocytes modulated their transcriptome by inducing proinflammatory cytokines and inhibiting pro-arteriogenic factors, while attenuating monocyte migration. Using specific knock-out mice, we show that galectin-2 acts through the CD14/toll-like receptor (TLR)-4 pathway. Furthermore, galectin-2 skews human macrophages to a M1-like proinflammatory phenotype, characterized by a reduced motility and expression of an anti-arteriogenic cytokine/growth factor repertoire. This is accompanied by a switch in surface protein expression to CD40-high and CD206-low (M1). In a murine model we show that galectin-2 administration, known to attenuate arteriogenesis, leads to increased numbers of CD40-positive (M1) and reduced numbers of CD206-positive (M2) macrophages surrounding actively remodeling collateral arteries. In conclusion galectin-2 is the first endogenous CD14/TLR4 ligand that induces a proinflammatory, non-arteriogenic phenotype in monocytes/macrophages. Interference with CD14-Galectin-2 interaction may provide a new intervention strategy to stimulate growth of collateral arteries in genetically compromised cardiovascular patients.

Kruppel-like factor 2 improves neovascularization capacity of aged proangiogenic cells.

AIMS: Coronary artery disease (CAD) patients have less circulating proangiogenic cells (PACs), formerly known as endothelial progenitor cells, which exhibit impaired neovascularization properties. Inverse correlations were also found between PAC function and risk factors like age. Krüppel-like factor 2 (KLF2) is expressed by mature endothelial cells (ECs), is induced by both shear stress and statins, and provokes endothelial functional differentiation. The aim of this study is to identify whether KLF2 can reverse negative effects of ageing on PAC function. METHODS AND RESULTS: We describe that progenitor cells in the bone marrow and PACs also express KLF2 at a comparable level to mature ECs and that senescence decreases KLF2 levels. To study the effects of ageing on KLF2 levels, we compared progenitor cells of 4 weeks and 16- to 18-month-old C57BL/6 mice. In addition to the three-fold reduction of circulating Sca1(+)/c-Kit(+)/Lin(-) progenitor cells and the 15% reduction of Sca1(+)/Flk1(+) endothelial-committed progenitor cells, the spleen-derived PACs and bone marrow-derived progenitor cells isolated from aged mice showed a lower level of KLF2 when compared with young mice. Lentiviral overexpression of KLF2 increased human PAC numbers and endothelial nitric oxide synthase expression by 60% during in vitro culture. Endothelial lineage-specific KLF2 overexpression in aged bone marrow-derived mononuclear cells strongly augments neovascularization in vivo in a murine hind-limb ischaemia model. CONCLUSION: These results imply that KLF2 is an attractive novel target to rejuvenate PACs before autologous administration to CAD patients.

KLF2-induced actin shear fibers control both alignment to flow and JNK signaling in vascular endothelium.

The shear stress-induced transcription factor Krüppel-like factor 2 (KLF2) confers antiinflammatory properties to endothelial cells through the inhibition of activator protein 1, presumably by interfering with mitogen-activated protein kinase (MAPK) cascades. To gain insight into the regulation of these cascades by KLF2, we used antibody arrays in combination with time-course mRNA microarray analysis. No gross changes in MAPKs were detected; rather, phosphorylation of actin cytoskeleton-associated proteins, including focal adhesion kinase, was markedly repressed by KLF2. Furthermore, we demonstrate that KLF2-mediated inhibition of Jun NH(2)-terminal kinase (JNK) and its downstream targets ATF2/c-Jun is dependent on the cytoskeleton. Specifically, KLF2 directs the formation of typical short basal actin filaments, termed shear fibers by us, which are distinct from thrombin- or tumor necrosis factor-alpha-induced stress fibers. KLF2 is shown to be essential for shear stress-induced cell alignment, concomitant shear fiber assembly, and inhibition of JNK signaling. These findings link the specific effects of shear-induced KLF2 on endothelial morphology to the suppression of JNK MAPK signaling in vascular homeostasis via novel actin shear fibers.

Endothelial CD81 is a marker of early human atherosclerotic plaques and facilitates monocyte adhesion.

AIMS: In a recent report, we established at the genome-wide level those genes that are specifically upregulated in the endothelium of atherosclerotic plaques in human arteries. As the transcriptome data revealed that mRNA for the tetraspanin family member CD81 is significantly and specifically upregulated in the endothelium overlying early atheroma, we set out to validate these results on the protein level, and investigate the functional consequences of CD81 upregulation. METHODS AND RESULTS: Immunohistochemical analysis in an independent set of donor arteries verified in the endothelium of early human atherosclerotic lesions the enhanced expression of CD81, which appears oxidative stress-dependent. Using lentiviral overexpression and silencing in human umbilical endothelial cells, we established in an in vitro flow adhesion assay that elevated endothelial CD81 is associated with increased monocyte adhesion to non-activated CD81-transduced endothelial cells, approaching the levels normally only attained after tumour necrosis factor alpha stimulation. The CD81 effect was dependent on both intracellular adhesion molecule 1 (ICAM-1) and vascular cell adhesion molecule 1 (VCAM-1), as it was abolished in the presence of a mixture of anti-ICAM-1 and anti-VCAM-1 antibodies. Flow cytometry revealed that increased CD81 levels did not increase total ICAM-1 and VCAM-1 surface expression. Instead, it concentrated the available adhesion molecules into membrane clusters, as indicated by confocal and electron microscopy. CD81 also colocalized with ICAM-1 and VCAM-1 in the adhesion rings around bound monocytes. CONCLUSION: Endothelial CD81 upregulated in early human atheroma has the potential to play a crucial role in the initial stages of atherosclerotic plaque formation by increasing monocyte adhesion prior to the full-blown inflammatory response.

VEGF release by MMP-9 mediated heparan sulphate cleavage induces colorectal cancer angiogenesis.

Angiogenesis is crucial for the progression of colorectal carcinomas in which the bioavailability of Vascular Endothelial Growth Factor (VEGF) plays a major role. VEGF bioavailability is regulated by proteolytic release or cleavage. In colorectal cancer patients, we observed a significant correlation between circulating VEGF and tumour tissue Matrix Metalloproteinase-9 (MMP-9) levels but not with MMP-2. Therefore, we evaluated the role of MMP-9 in regulating VEGF bioavailability and subsequent angiogenesis in 3-dimensional human cell culture models. MMP-9 treatment released VEGF dose-dependently from HT29 colon carcinoma spheroids, comparable to heparitinase, a known mediator of VEGF release. Conditioned medium from human neutrophils, containing high amounts of active MMP-9, released VEGF comparable to recombinant MMP-9, in contrast to myofibroblast medium. MMP-9 treated spheroids showed decreased extracellular levels of heparan sulphates, required for VEGF binding to the matrix, whereas the levels in the medium were increased. Western blot analysis revealed that VEGF(165) is the major isoform released by MMP-9 treatment. In vitro experiments indicated that MMP-9 is not capable to cleave VEGF(165) into smaller isoforms, like plasmin does. These data suggested that MMP-9 mediates release rather than the cleavage of larger VEGF isoforms. Medium from MMP-9 treated HT29 spheroids induced endothelial cell sprouting in an angiogenesis assay, comparable to the effect of recombinant VEGF(165). Anti-VEGF antibody treatment resulted in a strongly reduced number of sprouts. In conclusion, we have shown that neutrophil-derived MMP-9 is able to release biologically active VEGF(165) from the ECM of colon cancer cells by the cleavage of heparan sulphates.

SOX-18 controls endothelial-specific claudin-5 gene expression and barrier function.

Members of the claudin family constitute tight junction strands and are major determinants in specificity and selectivity of paracellular barriers. Transcriptional control of claudin gene expression is essential to establish individual claudin expression patterns and barrier properties. Using full genome expression profiling, we now identify sex-determining region Y-box (SOX)-18, a member of the SOX family of high-mobility group box transcription factors, as one of the most differentially induced genes during establishment of the endothelial barrier. We show that overexpression of SOX-18 and a dominant-negative mutant thereof, as well as SOX-18 silencing, greatly affect levels of claudin-5 (CLDN5). The relevance of an evolutionary conserved SOX-binding site in the CLDN5 promoter is shown using sequential promoter deletions, as well as point mutations. Furthermore, SOX-18 silencing abrogates endothelial barrier function, as measured by electric cell-substrate impedance sensing. Thus an obligatory role for SOX-18 in the regulation of CLDN5 gene expression in an endothelial-specific and cell density-dependent manner is established, as well as a crucial, nonredundant role for specifically SOX-18 in the formation of the endothelial barrier.

Distinctive expression of chemokines and transforming growth factor-beta signaling in human arterial endothelium during atherosclerosis.

Knowledge about the in vivo role of endothelium in chronic human atherosclerosis has mostly been derived by insights from mouse models. Therefore, we set out to establish by microarray analyses the gene expression profiles of endothelium from human large arteries, as isolated by laser microbeam microdissection, having focal atherosclerosis of the early or the advanced stage. Within individual arteries, the endothelial transcriptomes of the lesional and unaffected sides were compared pairwise, thus limiting genetic and environmental confounders. Specific endothelial signature gene sets were identified with changed expression levels in either early (n = 718) or advanced atherosclerosis (n = 403), relative to their paired plaque-free controls. Gene set enrichment analysis identified distinct sets of chemokines and differential enrichments of nuclear factor-kappaB-, p53-, and transforming growth factor-beta-related genes in advanced plaques. Immunohistochemistry validated the discriminative value of corresponding endothelial protein expression between early (fractalkine/CX3CL1, IP10/CCL10, TBX18) or advanced (BAX, NFKB2) stages of atherosclerosis and versus their plaque-free controls. The functional involvement of transforming growth factor-beta signaling in directing its downstream gene repertoire was substantiated by a consistent detection of activated SMAD2 in advanced lesions. Thus, we identified truly common, local molecular denominators of pathological changes to vascular endothelium, with a marked distinction of endothelial phenotype between early and advanced plaques.

Limited contribution of claudin-5-dependent tight junction strands to endothelial barrier function.

Members of the claudin family are involved in formation of barriers that control access to the paracellular space of epithelia. Likewise, endothelium-specific claudin-5 is involved in the function of the blood-brain barrier (BBB). Here, we assessed the role of claudin-5 in non-BBB endothelial barriers using lentiviral-driven overexpression and silencing of claudin-5 in its native environment of primary vascular endothelial cells. Effects were monitored using macromolecular tracers between 342Da and 40kDa. Measurements were made both in absence and presence of transmigrating leukocytes. Freeze-fracture preparations were analyzed for effects at the ultrastructural level. We show that overexpression of claudin-5 leads to formation of elaborate networks of junction strands, which are absent in untransduced endothelial cells. Concomitantly, a modest, non-size-selective enhancement of the barrier function was observed. In contrast, silencing of endogenous claudin-5 does not influence barrier function. The efficient sealing of the endothelium during diapedesis of monocytes or granulocytes is also claudin-5 independent. Collectively, these data provide evidence for a limited contribution of claudin-5 to the barrier function of human umbilical vein endothelial cells (HUVEC), implying that, unlike selective barriers in epithelia, the barrier of non-BBB endothelium seems largely independent of claudin-directed tight junction structures.

Spatial segregation of transport and signalling functions between human endothelial caveolae and lipid raft proteomes.

Lipid rafts and caveolae are biochemically similar, specialized domains of the PM (plasma membrane) that cluster specific proteins. However, they are morphologically distinct, implying different, possibly complementary functions. Two-dimensional gel electrophoresis preceding identification of proteins by MS was used to compare the relative abundance of proteins in DRMs (detergent-resistant membranes) isolated from HUVEC (human umbilical-vein endothelial cells), and caveolae immunopurified from DRM fractions. Various signalling and transport proteins were identified and additional cell-surface biotinylation revealed the majority to be exposed, demonstrating their presence at the PM. In resting endothelial cells, the scaffold of immunoisolated caveolae consists of only few resident proteins, related to structure [CAV1 (caveolin-1), vimentin] and transport (V-ATPase), as well as the GPI (glycosylphosphatidylinositol)-linked, surface-exposed protein CD59. Further quantitative characterization by immunoblotting and confocal microscopy of well-known [eNOS (endothelial nitric oxide synthase) and CAV1], less known [SNAP-23 (23 kDa synaptosome-associated protein) and BASP1 (brain acid soluble protein 1)] and novel [C8ORF2 (chromosome 8 open reading frame 2)] proteins showed different subcellular distributions with none of these proteins being exclusive to either caveolae or DRM. However, the DRM-associated fraction of the novel protein C8ORF2 (approximately 5% of total protein) associated with immunoseparated caveolae, in contrast with the raft protein SNAP-23. The segregation of caveolae from lipid rafts was visually confirmed in proliferating cells, where CAV1 was spatially separated from eNOS, SNAP-23 and BASP1. These results provide direct evidence for the previously suggested segregation of transport and signalling functions between specialized domains of the endothelial plasma membrane.