Differential Expression of Platelet‐Endothelial Cell Adhesion Molecule‐1 (PECAM‐1) in Murine Tissues

Targeting nanoparticles to the brain by exploiting the blood-brain barrier impermeability to selectively label the brain endothelium

Current strategies to direct therapy-loaded nanoparticles to the brain rely on functionalizing nanoparticles with ligands which bind target proteins associated with the blood-brain barrier (BBB). However, such strategies have significant brain-specificity limitations, as target proteins are not exclusively expressed at the brain microvasculature. Therefore, novel strategies which exploit alternative characteristics of the BBB are required to overcome nonspecific nanoparticle targeting to the periphery, thereby increasing drug efficacy and reducing detrimental peripheral side effects. Here, we present a simple, yet counterintuitive, brain-targeting strategy which exploits the higher impermeability of the BBB to selectively label the brain endothelium. This is achieved by harnessing the lower endocytic rate of brain endothelial cells (a key feature of the high BBB impermeability) to promote selective retention of free, unconjugated protein-binding ligands on the surface of brain endothelial cells compared to peripheral endothelial cells. Nanoparticles capable of efficiently binding to the displayed ligands (i.e., labeled endothelium) are consequently targeted specifically to the brain microvasculature with minimal "off-target" accumulation in peripheral organs. This approach therefore revolutionizes brain-targeting strategies by implementing a two-step targeting method which exploits the physiology of the BBB to generate the required brain specificity for nanoparticle delivery, paving the way to overcome targeting limitations and achieve clinical translation of neurological therapies. In addition, this work demonstrates that protein targets for brain delivery may be identified based not on differential tissue expression, but on differential endocytic rates between the brain and periphery.

Chrysin Attenuates VCAM-1 Expression and Monocyte Adhesion in Lipopolysaccharide-Stimulated Brain Endothelial Cells by Preventing NF-κB Signaling

Adhesion of leukocytes to endothelial cells plays an important role in neuroinflammation. Therefore, suppression of the expression of adhesion molecules in brain endothelial cells may inhibit neuroinflammation. Chrysin (5,7-dihydroxyflavone) is a flavonoid component of propolis, blue passion flowers, and fruits. In the present study, we examined the effects of chrysin on lipopolysaccharide (LPS)-induced expression of vascular cell adhesion molecule-1 (VCAM-1) in mouse cerebral vascular endothelial (bEnd.3) cells. In bEnd.3 cells, LPS increased mRNA expression of VCAM-1 in a time-dependent manner, and chrysin significantly decreased LPS-induced mRNA expression of VCAM-1. Chrysin also reduced VCAM-1 protein expression in a concentration-dependent manner. Furthermore, chrysin blocked adhesion of monocytes to bEnd.3 cells exposed to LPS. Nuclear factor-κB (NF-κB), p38 mitogen-activated protein kinase (MAPK), and c-Jun N-terminal kinase, which are all activated by LPS, were significantly inhibited by chrysin. These results indicate that chrysin inhibits the expression of VCAM-1 in brain endothelial cells by inhibiting NF-κB translocation and MAPK signaling, resulting in the attenuation of leukocyte adhesion to endothelial cells. The anti-inflammatory effects of chrysin suggest a possible therapeutic application of this agent to neurodegenerative diseases, such as multiple sclerosis, septic encephalopathy, and allergic encephalomyelitis.

The vascular endothelial growth factor (VEGF)-E encoded by orf virus regulates keratinocyte proliferation and migration and promotes epidermal regeneration

Vascular endothelial growth factor (VEGF)-A, a key regulator of cutaneous blood vessel formation, appears to have an additional role during wound healing, enhancing re-epithelialization. Orf virus, a zoonotic parapoxvirus, induces proliferative skin lesions that initiate in wounds and are characterized by extensive blood vessel formation, epidermal hyperplasia and rete ridge formation. The vascular changes beneath the lesion are largely due to viral-expressed VEGF-E. This study investigated using mouse skin models whether VEGF-E can induce epidermal changes such as that seen in the viral lesion. Injection of VEGF-E into normal skin increased the number of endothelial cells and blood vessels within the dermis and increased epidermal thickening and keratinocyte number. Injection of VEGF-E into wounded skin, which more closely mimics orf virus lesions, increased neo-epidermal thickness and area, promoted rete ridge formation, and enhanced wound re-epithelialization. Quantitative RT-PCR analysis showed that VEGF-E did not induce expression of epidermal-specific growth factors within the wound, but did increase matrix metalloproteinase (MMP)-2 and MMP-9 expression. In cell-based assays, VEGF-E induced keratinocyte migration and proliferation, responses that were inhibited by a neutralizing antibody against VEGF receptor (VEGFR)-2. These findings demonstrate that VEGF-E, both directly and indirectly, regulates keratinocyte function, thereby promoting epidermal regeneration.

Tumour metastasis as an adaptation of tumour cells to fulfil their phosphorus requirements

Inorganic phosphate (Pi) is a vital component of nucleotides, membrane phospholipids, and phosphorylated intermediates in cellular signalling. The Growth Rate Hypothesis (GRH) states that fast growing organisms should be richer in phosphorus (relatively low C:P and N:P cell content) than slow developing organisms as a result of high ribosome biogenesis. Cells that proliferate rapidly, such as cancer cells, require a high amount of ribosomes and other P-rich RNA components that are necessary to manufacture proteins. The GRH hypothesis may be applied to cancer predicting that tumour cells are richer in phosphorus than the surrounding tissue, and that they resort to metastasis in order to meet their nutrient demands. Considering that the cells most P-deprived should be located in the inner parts of the tumour we propose that changes in the membrane of these cells favour the detachment of the more peripheral cells.

Dual targeting improves microbubble contrast agent adhesion to VCAM-1 and P-selectin under flow

To improve ultrasound contrast agents targeted to the adhesion molecules P-selectin and VCAM-1 for the purpose of molecular imaging of atherosclerotic plaques, perfluorocarbon-filled phospholipid microbubble contrast agents were coupled by a polyethylene glycol-biotin-streptavidin bridge with mAb MVCAM.A(429), a sialyl Lewis(x) polymer (PAA-sLe(x)), or both (dual). Approximately three hundred thousand antibody molecules were coupled to the surface of each microbubble. Recombinant mouse P-selectin and/or VCAM-1 coated on flow chambers showed saturation of binding at approximately 15 ng/microl, resulting in 800 and 1200 molecules/microm(2) for P-selectin and VCAM-1, respectively. Dual substrates coated with equal concentrations of P-selectin and VCAM-1 had site densities between 50 and 60% of single substrates. When microbubbles were perfused through flow chambers at 5 x 10(6) microbubbles/ml (wall shear stress from 1.5 to 6 dyn/cm(2)) dual-targeted microbubbles adhered almost twice as efficiently as single-targeted microbubbles at 6 dyn/cm(2). The present study suggests that dual-targeted contrast agents may be useful for atherosclerotic plaque detection at physiologically relevant shear stresses.

Reactive hyperemia and BOLD MRI demonstrate that VEGF inhibition, age, and atherosclerosis adversely affect functional recovery in a murine model of peripheral artery disease

PURPOSE

To develop magnetic resonace imaging (MRI) methods for functional assessment of arteriogenesis in a murine model of peripheral artery disease to quantify the influences of vascular endothelial growth factor (VEGF), age, and atherosclerosis.

MATERIALS AND METHODS

Reactive hyperemia (RH), which was induced using a device designed for remote and transient occlusion of the aorta and vena cava, was measured by blood-oxygen-level-dependent MRI. Twenty-eight days after femoral artery ligation, peak height (PH) and time to peak (TTP) of the RH response was compared with sham-operated animals in 10-week-old C57Bl6, 9-month-old C57Bl6, and 9-month-old Ldlr(-/-)Apobec(-/-) mice. The contribution of VEGF to functional recovery was assessed in young mice. Angiogenesis was quantified using an anti-PECAM1 radioimmunoassay.

RESULTS

In young animals, angiogenesis was maximal 7 days after ligation, whereas functional recovery took 28 days. Inhibition of VEGF eliminated the angiogenesis seen at 7 days and reduced RH (PH, P < 0.05). At day 28, RH was altered in old (TTP, P < 0.05) and atherosclerotic (PH, P < 0.05; TTP, P < 0.05) animals. RH was different in young, old, and atherosclerotic sham animals. Old and atherosclerotic mice showed reduced angiogenesis.

CONCLUSION

The method presented herein can provide a sensitive assay for the functional assessment of arteriogenesis and highlights the contribution of VEGF, age, and atherosclerosis to this process.

Differential roles of ICAM-1 and VCAM-1 in leukocyte-endothelial cell interactions in skin and brain of MRL/faslpr mice

MRL/fas(lpr) mice, which undergo a systemic autoimmune disease with similarities to systemic lupus erythematosus (SLE), display reduced pathology and prolonged survival if rendered deficient in ICAM-1. However, it remains unclear whether this is a result of the ability of ICAM-1 to promote the immune response or mediate leukocyte recruitment. Therefore, the aim of these studies was to compare the role of ICAM-1 in the elevated leukocyte-endothelial interactions, which affect MRL/fas(lpr) mice. Intravital microscopy was used to compare leukocyte rolling and adhesion in postcapillary venules in the dermal and cerebral (pial) microcirculations of wild-type (ICAM+/+) and ICAM-1-deficient (ICAM-1-/-) MRL/fas(lpr) mice. In the dermal microcirculation of 16-week MRL/fas(lpr) mice, leukocyte adhesion was increased relative to nondiseased MRL+/+ mice. However, this increase was abolished in ICAM-1-/- MRL/fas(lpr) mice. ICAM-1 deficiency was also associated with reduced dermal pathology. In contrast, in the pial microcirculation, the elevation in leukocyte adhesion observed in ICAM+/+ MRL/fas(lpr) mice also occurred in ICAM-1-/- MRL/fas(lpr) mice. VCAM-1 expression was detectable in both vascular beds, but higher levels were detected in the pial vasculature. Furthermore, VCAM-1 blockade significantly reduced leukocyte adhesion and rolling in the cerebral microcirculation of ICAM-1-/- MRL/fas(lpr) mice. Therefore, ICAM-1 was critical for leukocyte adhesion in the skin but not the brain, where VCAM-1 assumed the major function. Given the ongoing development of anti-adhesion molecule therapies and their potential in inflammatory diseases such as SLE, these data indicate that implementation of these therapies in SLE should take into account the potential for tissue-specific functions of adhesion molecules.

Myocardial hypertrophy in the absence of external stimuli is induced by angiogenesis in mice

Although studies have suggested a role for angiogenesis in determining heart size during conditions demanding enhanced cardiac performance, the role of EC mass in determining the normal organ size is poorly understood. To explore the relationship between cardiac vasculature and normal heart size, we generated a transgenic mouse with a regulatable expression of the secreted angiogenic growth factor PR39 in cardiomyocytes. A significant change in adult mouse EC mass was apparent by 3 weeks following PR39 induction. Heart weight; cardiomyocyte size; vascular density normalization; upregulation of hypertrophy markers including atrial natriuretic factor, beta-MHC, and GATA4; and activation of the Akt and MAP kinase pathways were observed at 6 weeks post-induction. Treatment of PR39-induced mice with the eNOS inhibitor L-NAME in the last 3 weeks of a 6-week stimulation period resulted in a significant suppression of heart growth and a reduction in hypertrophic marker expression. Injection of PR39 or another angiogenic growth factor, VEGF-B, into murine hearts during myocardial infarction led to induction of myocardial hypertrophy and restoration of myocardial function. Thus stimulation of vascular growth in normal adult mouse hearts leads to an increase in cardiac mass.

Magnetic resonance angiography reveals therapeutic enlargement of collateral vessels induced by VEGF in a murine model of peripheral arterial disease

PURPOSE

To quantify spontaneous and therapeutic arteriogenesis in vivo in a murine model of peripheral arterial disease using magnetic resonance angiography.

MATERIALS AND METHODS

Male, 8-12-week-old, C57/BL6 mice underwent femoral artery ligation; 21 days later, 2 mg/kg recombinant murine VEGF165, formulated for slow release, was injected into the ipsilateral gastrocnemius. The spontaneous (following ligation) and therapeutic (following vascular endothelial growth factor (VEGF)) formation of collateral vessels was quantified using 3D magnetic resonance angiography on a small-bore 4.7T system. Therapeutically induced angiogenesis and blood flow were quantified using an in situ anti-platelet endothelial cell adhesion molecule (PECAM) 1 radioimmunoassay and radiolabeled microsphere deposition, respectively.

RESULTS

Spontaneous arteriogenesis was visible in all animals five days after ligation. VEGF treatment doubled the arteriogenic response five days after treatment compared to vehicle (cross-sectional area of vessels: 0.96 vs. 0.46 mm2, P<0.01). VEGF also induced angiogenesis (PECAM1 levels 191% of vehicle, P<0.05) and increased blood flow specific to the injection site (57 vs. 7 mL/minute/100 g, P<0.05).

CONCLUSION

The presented methodology allowed in vivo quantification of spontaneous arteriogenesis in a murine model of peripheral arterial disease and demonstrated that therapeutic enlargement of collateral vessels is possible with VEGF.

Gamma glutamyl transpeptidase is a dynamic indicator of endothelial response to stroke

Gamma glutamyl transpeptidase (gammaGT) is enriched at the apical surface of the cerebral capillaries that constitute the blood-brain barrier (BBB). This study tested the effects of hypoxia and inflammation on gammaGT activity in mice after stroke induced by transient cerebral artery occlusion (tMCAO) and in cultured cerebral microvessel endothelial cells. In microvessel-enriched preparations from mice after tMCAO, gammaGT activity was higher than in the sham controls in both ipsilateral and contralateral hemispheres from 12 h to 5 days after stroke, but lower at later time points (10-15 days). To identify the roles of different cytotoxic and stimulatory signals in this event, we further studied the dynamic changes of gammaGT activity in rat brain endothelial (RBE4) cells. Tumor necrosis factor alpha and lipopolyssachride significantly increased gammaGT activity in a time-dependent manner, an effect not seen after re-oxygenation. Such endothelial activation correlated with reduced total cellular ATP production. Thus, hypoxia and inflammatory stimulation appeared to have opposite effects on endothelial function. With the co-existence of inflammation and hypoxia in the brain after ischemic stroke, dynamic changes of gammaGT activity reflect evolving changes of endothelial function.

Differential expression and regulation of murine CD40 in regional vascular beds

There is emerging evidence for a role of the CD40/CD40 ligand (CD40L) dyad as a signaling mechanism in different inflammatory conditions. The aims of this study were to 1) quantify the constitutive and induced expression of CD40 in different regional vascular beds of the mouse and 2) assess the role of CD40L as a modulator of vascular endothelial CD40 expression. The dual radiolabeled monoclonal antibody technique was used to quantify the expression of endothelial CD40 in control and LPS-challenged wild-type (WT) mice. Significant constitutive CD40 expression was detected in several vascular beds of WT mice with lung, kidney, and small intestine exhibiting the highest expression, whereas the liver and stomach showed no detectable baseline expression. LPS administration elicited two- to sevenfold increases in CD40 expression in several tissues (heart, kidney, and intestine) within 4 h, whereas other organs (brain) required up to 48 h to exhibit CD40 upregulation. CD40 expression was not detected in unstimulated or LPS-challenged CD40−/− mice. Constitutive expression of CD40 was profoundly reduced in unstimulated CD40L−/− mice, but the LPS-induced CD40 upregulation did not differ between CD40L−/− and WT mice. Depletion of platelets or T lymphocytes, the major CD40L-expressing cells in blood, also resulted in a profound reduction in basal CD40 expression. These findings demonstrate significant endothelial expression of CD40 under basal conditions in different vascular beds and increased CD40 expression after endothelial cell activation with LPS. Platelet- and T-lymphocyte-associated CD40L appears to play a major role in regulating the density of CD40 expression on vascular endothelial cells in vivo.

Lung-marginated monocytes modulate pulmonary microvascular injury during early endotoxemia

RATIONALE

The role of monocytes in acute endotoxemia has been ascribed to systemic release of mediators within the central circulation. Little is known about the potential role of "marginated" monocytes in regulating microvascular inflammatory signaling.

OBJECTIVES

To investigate whether lung-marginated monocytes can locally activate pulmonary endothelial cells through cell contact-dependent interactions in early endotoxemia.

METHODS

Mice were challenged with LPS to produce acute endotoxemia and pulmonary vascular injury. Adoptive transfer of ex vivo LPS-stimulated donor leukocytes to recipient mice was also performed to evaluate cell-associated inflammatory signaling between monocytes and endothelial cells within the lung. Cell suspensions from excised lungs were analyzed by flow cytometry for expression of tumor necrosis factor alpha (TNF-alpha) on monocytes and cell adhesion molecules on endothelial cells.

RESULTS

Substantial numbers of monocytes rapidly marginated to the lungs after endotoxin challenge in mice, and lung-marginated monocytes expressed significantly higher levels of membrane TNF than circulating monocytes, due to higher TNF production by the marginated cells. Injection of activated wild-type donor leukocytes to wild-type or TNF receptor double knockout recipients demonstrated that lung-marginated monocytes can induce TNF-dependent upregulation of adhesion molecules on pulmonary endothelial cells. Injection of activated donor leukocytes from TNF knock-in mice that express uncleavable mutant membrane TNF also induced adhesion molecule upregulation in wild-type recipients without a systemic soluble TNF release.

CONCLUSIONS

These results reveal a previously unacknowledged role for lung-marginated monocytes in early endotoxemia, exerting local, cell-associated TNF signaling within the pulmonary microcirculation, contributing to the evolution of pulmonary vascular injury.

Topical vascular endothelial growth factor accelerates diabetic wound healing through increased angiogenesis and by mobilizing and recruiting bone marrow-derived cells

Diminished production of vascular endothelial growth factor (VEGF) and decreased angiogenesis are thought to contribute to impaired tissue repair in diabetic patients. We examined whether recombinant human VEGF(165) protein would reverse the impaired wound healing phenotype in genetically diabetic mice. Paired full-thickness skin wounds on the dorsum of db/db mice received 20 microg of VEGF every other day for five doses to one wound and vehicle (phosphate-buffered saline) to the other. We demonstrate significantly accelerated repair in VEGF-treated wounds with an average time to resurfacing of 12 days versus 25 days in untreated mice. VEGF-treated wounds were characterized by an early leaky, malformed vasculature followed by abundant granulation tissue deposition. The VEGF-treated wounds demonstrated increased epithelialization, increased matrix deposition, and enhanced cellular proliferation, as assessed by uptake of 5-bromodeoxyuridine. Analysis of gene expression by real-time reverse transcriptase-polymerase chain reaction demonstrates a significant up-regulation of platelet-derived growth factor-B and fibroblast growth factor-2 in VEGF-treated wounds, which corresponds with the increased granulation tissue in these wounds. These experiments also demonstrated an increase in the rate of repair of the contralateral phosphate-buffered saline-treated wound when compared to wounds in diabetic mice never exposed to VEGF (18 days versus 25 days), suggesting that topical VEGF had a systemic effect. We observed increased numbers of circulating VEGFR2(+)/CD11b(-) cells in the VEGF-treated mice by fluorescence-activated cell sorting analysis, which likely represent an endothelial precursor population. In diabetic mice with bone marrow replaced by that of tie2/lacZ mice we demonstrate that the local recruitment of bone marrow-derived endothelial lineage lacZ+ cells was augmented by topical VEGF. We conclude that topical VEGF is able to improve wound healing by locally up-regulating growth factors important for tissue repair and by systemically mobilizing bone marrow-derived cells, including a population that contributes to blood vessel formation, and recruiting these cells to the local wound environment where they are able to accelerate repair. Thus, VEGF therapy may be useful in the treatment of diabetic complications characterized by impaired neovascularization.

PECAM-directed delivery of catalase to endothelium protects against pulmonary vascular oxidative stress

Targeted delivery of drugs to vascular endothelium promises more effective and specific therapies in many disease conditions, including acute lung injury (ALI). This study evaluates the therapeutic effect of drug targeting to PECAM (platelet/endothelial cell adhesion molecule-1) in vivo in the context of pulmonary oxidative stress. Endothelial injury by reactive oxygen species (e.g., H2O2) is involved in many disease conditions, including ALI/acute respiratory distress syndrome and ischemia-reperfusion. To optimize delivery of antioxidant therapeutics, we conjugated catalase with PECAM antibodies and tested properties of anti-PECAM/catalase conjugates in cell culture and mice. Anti-PECAM/catalase, but not an IgG/catalase counterpart, bound specifically to PECAM-expressing cells, augmented their H2O2-degrading capacity, and protected them against H2O2 toxicity. Anti-PECAM/catalase, but not IgG/catalase, rapidly accumulated in the lungs after intravenous injection in mice, where it was confined to the pulmonary endothelium. To test its protective effect, we employed a murine model of oxidative lung injury induced by glucose oxidase coupled with thrombomodulin antibody (anti-TM/GOX). After intravenous injection in mice, anti-TM/GOX binds to pulmonary endothelium and produces H2O2, which causes lung injury and 100% lethality within 7 h. Coinjection of anti-PECAM/catalase protected against anti-TM/GOX-induced pulmonary oxidative stress, injury, and lethality, whereas polyethylene glycol catalase or IgG/catalase conjugates afforded only marginal protective effects. This result validates vascular immunotargeting as a prospective strategy for therapeutic interventions aimed at immediate protective effects, e.g., for augmentation of antioxidant defense in the pulmonary endothelium and treatment of ALI.

Vascular endothelial growth factor stimulates bone repair by promoting angiogenesis and bone turnover

Several growth factors are expressed in distinct temporal and spatial patterns during fracture repair. Of these, vascular endothelial growth factor, VEGF, is of particular interest because of its ability to induce neovascularization (angiogenesis). To determine whether VEGF is required for bone repair, we inhibited VEGF activity during secondary bone healing via a cartilage intermediate (endochondral ossification) and during direct bone repair (intramembranous ossification) in a novel mouse model. Treatment of mice with a soluble, neutralizing VEGF receptor decreased angiogenesis, bone formation, and callus mineralization in femoral fractures. Inhibition of VEGF also dramatically inhibited healing of a tibial cortical bone defect, consistent with our discovery of a direct autocrine role for VEGF in osteoblast differentiation. In separate experiments, exogenous VEGF enhanced blood vessel formation, ossification, and new bone (callus) maturation in mouse femur fractures, and promoted bony bridging of a rabbit radius segmental gap defect. Our results at specific time points during the course of healing underscore the role of VEGF in endochondral vs. intramembranous ossification, as well as skeletal development vs. bone repair. The responses to exogenous VEGF observed in two distinct model systems and species indicate that a slow-release formulation of VEGF, applied locally at the site of bone damage, may prove to be an effective therapy to promote human bone repair.

Meningitis-associated central nervous system complications are mediated by the activation of poly(ADP-ribose) polymerase

The present study assessed the role of PARP [poly(adenosine diphosphate-ribose) polymerase] activation in experimental pneumococcal meningitis. Mice with a targeted disruption of the PARP 1 gene were protected against meningitis-associated central nervous system complications including blood-brain barrier breaching and increase in intracranial pressure. This beneficial effect was paralleled by a significant reduction in meningeal inflammation, as evidenced by significantly lower cerebrospinal fluid leukocyte counts and interleukin-1beta, -6, and tumor necrosis factor-alpha concentrations in the brain (compared with infected wild-type mice). The reduction in inflammation and central nervous system complications was associated with an improved clinical status of infected, PARP 1-deficient mice. A similar protective effect was achieved by PARP inhibition using 3-aminobenzamide, the pharmacologic efficacy of which was confirmed by a marked attenuation of meningitis-induced poly(ADP)ribose formation. When the rat brain-derived endothelial cell line GP8.3 was cocultured with macrophages, exposure to pneumococci induced endothelial cell death and was paralleled by PARP activation and a reduction in the oxidized form of cellular nicotinamide adenine dinucleotide content. Treatment with 3-aminobenzamide significantly attenuated cellular nicotinamide adenine dinucleotide depletion and pneumococci-induced cytotoxicity. Thus, PARP activation seems to play a crucial role in the development of meningitis-associated central nervous system complications and pneumococci-induced endothelial injury. Inhibitors of PARP activation could provide a potential therapy of acute bacterial meningitis.

Dobutamine stress cine-MRI of cardiac function in the hearts of adult cardiomyocyte-specific VEGF knockout mice

A mouse model of non-necrotic vascular deficiency in the adult heart was studied using cine-magnetic resonance imaging (MRI) and other techniques. The mice lacked cardiomyocyte-derived vascular endothelial growth factor (VEGF) following a targeted knockout in the ventricular cardiomyocytes. Quantitative endothelial labeling showed that the capillary density was significantly reduced in the hearts of knockout mice. Gene expression patterns suggested that they were hypoxic. Semiautomated MR image analysis was employed to obtain both global and regional measurements of left ventricular function at 10 or more time points through the cardiac cycle. MRI measurements showed a marked reduction in ejection fraction both at rest and under low- and high-dose dobutamine stress. Regional wall thickness, thickening, and displacement were all attenuated in the knockout mice. A prolonged high-dose dobutamine challenge was monitored by MRI. A maximal response was sustained for 90 minutes, suggesting that it did not depend on endogenous glycogen stores.

A cardiac myocyte vascular endothelial growth factor paracrine pathway is required to maintain cardiac function

The role of the cardiac myocyte as a mediator of paracrine signaling in the heart has remained unclear. To address this issue, we generated mice with cardiac myocyte-specific deletion of the vascular endothelial growth factor gene, thereby producing a cardiomyocyte-specific knockout of a secreted factor. The hearts of these mice had fewer coronary microvessels, thinned ventricular walls, depressed basal contractile function, induction of hypoxia-responsive genes involved in energy metabolism, and an abnormal response to beta-adrenergic stimulation. These findings establish the critical importance of cardiac myocyte-derived vascular endothelial growth factor in cardiac morphogenesis and determination of heart function. Further, they establish an adult murine model of hypovascular nonnecrotic cardiac contractile dysfunction.

Quantification of murine endothelial cell adhesion molecules in solid tumors

Coordinated adhesive interactions between lymphocyte receptors and endothelial cell adhesion molecules (CAMs) are a prerequisite for effector cell entry into tumor stroma. Whereas the diminished leukocyte-endothelial cell interactions observed in tumor microvessels have been attributed to a reduced expression of endothelial CAMs, there is no quantitative data bearing on this issue. The dual-radiolabeled monoclonal antibody technique was used to quantify constitutive and tumor necrosis factor (TNF)-alpha-induced expression of intercellular adhesion molecule 1 (ICAM-1), vascular cell adhesion molecule 1 (VCAM-1), ICAM-2, P-selectin, E-selectin, and platelet-endothelial cell adhesion molecule 1 (PECAM-1) in different vascular beds of normal (C57Bl/6) and RM-1 tumor-bearing mice. When corrected for endothelial surface area, the constitutive expression of selectins in tumor vessels was higher than that observed in other vascular beds. Both constitutive and induced expression of endothelial CAMs in peripheral vascular beds did not differ between normal and tumor-bearing mice. Within the tumor, the magnitude of the upregulation of P-selectin, ICAM-1, and VCAM-1 after TNF-alpha was similar to that within other vascular beds. E-selectin expression in tumors was refractory to TNF-alpha, whereas PECAM-1 and ICAM-2 expression were significantly reduced. Our findings suggest that the presence of a solid tumor does not influence endothelial CAM expression in other vascular beds and that the higher density of selectins in nonstimulated tumor vessels may promote the recruitment of rolling leukocytes in this tissue.