The role of endothelial cells in cystic fibrosis.

Cystic fibrosis (CF) is an autosomal recessive disease caused by the loss of function of the cystic fibrosis transmembrane conductance regulator (CFTR) protein which primarily acts as a chloride channel. CFTR has mainly been studied in epithelial cells although it is also functional and expressed in other cell types including endothelial cells. The present review summarizes current knowledge on the role of the endothelium in CF. More specifically, this review highlights the role of endothelial cells in CF in acting as a semipermeable barrier, as a key regulator of angiogenesis, coagulation, the vascular tone and the inflammatory responses. It could contribute to different aspects of the disease including cardiovascular symptoms, excessive blood vessel formation, pulmonary and portal hypertension and CF-related diabetes. Despite the important role of vascular endothelium in many biological processes, it has largely been under investigated in CF.

Hypoxia determines survival outcomes of bacterial infection through HIF-1alpha dependent re-programming of leukocyte metabolism.

Hypoxia and bacterial infection frequently co-exist, in both acute and chronic clinical settings, and typically result in adverse clinical outcomes. To ameliorate this morbidity, we investigated the interaction between hypoxia and the host response. In the context of acute hypoxia, both S. aureus and S. pneumoniae infections rapidly induced progressive neutrophil mediated morbidity and mortality, with associated hypothermia and cardiovascular compromise. Preconditioning animals through longer exposures to hypoxia, prior to infection, prevented these pathophysiological responses and profoundly dampened the transcriptome of circulating leukocytes. Specifically, perturbation of HIF pathway and glycolysis genes by hypoxic preconditioning was associated with reduced leukocyte glucose utilisation, resulting in systemic rescue from a global negative energy state and myocardial protection. Thus we demonstrate that hypoxia preconditions the innate immune response and determines survival outcomes following bacterial infection through suppression of HIF-1α and neutrophil metabolism. The therapeutic implications of this work are that in the context of systemic or tissue hypoxia therapies that target the host response could improve infection associated morbidity and mortality.

Impact of placental growth factor deficiency on early mouse implant site angiogenesis.

Effects of placental growth factor (PGF), an angiokine product of fetal trophoblasts and maternal decidual cells, on early decidual angiogenesis are undefined. We used whole-mount immunofluorescence analyses to compare uterus and gestation day 4.5-9.5 mouse implantation sites that differed genetically in fetal or maternal PGF deficiency. Implant site number and embryonic development were similar in Pgf(-/-) and Pgf(+/+) females although Pgf(-/-) lymphatic vessels were anomalous. Correct, fine branching angiogenesis of anti-mesometrial vessels required both conceptus and maternal PGF; correct mesometrial branching angiogenesis depended solely upon conceptus PGF. Thus, PGF is non-redundant for optimizing branching angiogenesis in early decidua.

Vascular endothelial growth factor receptor 1 expression in nasal polyp tissue.

BACKGROUND: Edema represents a key feature of nasal polyp (NP) disease. Members of the vascular endothelial growth factor (VEGF) family may be involved, but the precise role of VEGF-A, VEGF-B, placental growth factor (PlGF), and their receptors VEGFR1 and VEGFR2 in NP edema formation remains elusive. OBJECTIVE: Exploring the expression of VEGF family members and their receptors and their correlation with clinical, radiological, and edema markers in NP. METHODS: The expression of VEGF-A, VEGF-B, PlGF, VEGFR1, and VEGFR2 was measured in NP (n = 23) and control tissue (n = 22) at mRNA and protein level. Edema was evaluated by measuring albumin levels and wet/dry ratios. Computed tomography (CT) scans were scored using the Lund-Mackay scoring system. IL-5 mRNA expression was determined by real-time RT-PCR. Cell suspensions from NP (n = 10) and control tissue (n = 12) were stimulated in vitro with IL-1ß or TNFα. RESULTS: mRNA expression of VEGFR1 and VEGF-B was significantly higher in NP compared with control tissue. Expression levels of VEGF-B and VEGFR1 significantly correlated with NP albumin content (VEGF-B: P = 0.0208; VEGFR1: P = 0.0293), CT scan scores (VEGF-B: P = 0.0075; VEGFR1: P = 0.0068), and IL-5 mRNA (VEGF-B: P = 0.0027; VEGFR1: P = 0.0001). In vitro stimulation of control and NP tissue cell suspensions with IL-1ß or TNFα significantly reduced the expression of VEGFR2 in control tissue, without altering VEGFR1 and VEGF-B expression. hVEGF-B induced nitric oxide production in NP macrophages (P < 0.05). CONCLUSION: Expression levels of VEGFR1 and VEGF-B correlate with edema and clinical markers of NP disease and therefore represent potential therapeutic targets.

Therapeutic potential of VEGF and VEGF-derived peptide in peripheral neuropathies.

Besides its prominent role in angiogenesis, the vascular endothelial growth factor (VEGF) also exerts important protective effects on neurons. In particular, mice expressing reduced levels of VEGF suffer from late-onset motor neuron degeneration, whereas VEGF delivery significantly delays motor neuron death in ALS mouse models, at least partly through neuroprotective effects. Additionally, VEGF protects dorsal root ganglion (DRG) neurons against paclitaxel-induced neurotoxicity. Here, we demonstrate that VEGF also protects DRG neurons against hyperglycemia-induced neuronal stress as a model of diabetes-induced peripheral neuropathy. Specifically, VEGF decreased expression of the stress-related gene activating transcription factor 3 (ATF3) in DRG neurons isolated from streptozotocin-induced diabetic mice (ex vivo) and in isolated DRG neurons exposed to high glucose concentrations (in vitro). In vivo, local VEGF application also protected against paclitaxel- and diabetes-induced neuropathies without causing side effects. A small synthetic VEGF mimicking pentadecapeptide (QK) exerted similar effects on DRG cultures: the peptide reduced ATF3 expression in vitro and ex vivo in paclitaxel- and hyperglycemia-induced models of neuropathy to a similar extent as the full-length recombinant VEGF protein. By using transgenic mice selectively overexpressing the VEGF receptor 2 in postnatal neurons, these neuroprotective effects were shown to be mediated through VEGF receptor 2. Overall, these results underscore the potential of VEGF and VEGF-derived peptides for the treatment of peripheral neuropathies.

Paracrine control of vascular innervation in health and disease.

Proper vascular regulation is of paramount importance for the control of blood flow to tissues. In particular, the regulation of peripheral resistance arteries is essential for several physiological processes, including control of blood pressure, thermoregulation and increase of blood flow to central nervous system and heart under stress conditions such as hypoxia. Arterial tone is regulated by the periarterial autonomic nervous plexus, as well as by endothelium-dependent, myogenic and humoral mechanisms. Underscoring the importance of proper vascular regulation, defects in these processes can lead to diseases such as hypertension, orthostatic hypotension, Raynaud's phenomenon, defective thermoregulation, hand-foot syndrome, migraine and congestive heart failure. Here, we review the molecular mechanisms controlling the development of the periarterial nerve plexus, retrograde and localized signalling at neuro-effector junctions, the molecular and cellular mechanisms of vascular regulation and adult plasticity and maintenance of periarterial innervation. We particularly highlight a newly discovered role for vascular endothelial growth factor in the structural and functional maintenance of arterial neuro-effector junctions. Finally, we discuss how defects in neuronal vascular regulation can lead to disease.

Potentiating role of Gas6 and Tyro3, Axl and Mer (TAM) receptors in human and murine platelet activation and thrombus stabilization.

BACKGROUND: Interaction of murine Gas6 with the platelet Gas6 receptors Tyro3, Axl and Mer (TAM) plays an important role in arterial thrombus formation. However, a role for Gas6 in human platelet activation has been questioned. OBJECTIVE: To determine the role of Gas6 in human and murine platelet activation and thrombus formation. METHODS AND RESULTS: Gas6 levels appeared to be 20-fold higher in human plasma than in platelets, suggesting a predominant role of plasma-derived Gas6. Human Gas6 synergizes with ADP-P2Y(12) by enhancing and prolonging the phosphorylation of Akt. Removal of Gas6 from plasma impaired ADP-induced platelet aggregation. Under flow conditions, absence of human Gas6 provoked gradual platelet disaggregation and integrin α(IIb) ß(3) inactivation. Recombinant human Gas6 reversed the effects of Gas6 removal. In mouse blood, deficiency in Gas6 or in one of the TAM receptors led to reduced thrombus formation and increased disaggregation, which was completely antagonized by external ADP. In contrast, collagen-induced platelet responses were unchanged by the absence of Gas6 in both human and mouse systems. CONCLUSIONS: The ADP-P2Y(12) and Gas6-TAM activation pathways synergize to achieve persistent α(IIb) ß(3) activation and platelet aggregation. We postulate a model of thrombus stabilization in which plasma Gas6, by signaling via the TAM receptors, extends and enhances the platelet-stabilizing effect of autocrine ADP, particularly when secretion becomes limited.

Antenatal fetal VEGF therapy to promote pulmonary maturation in a preterm rabbit model.

AIM: To assess the effects of fetal tracheal administration of VEGF on pulmonary maturation in a preterm rabbit model. METHODS: On day 26 (term=31days), fetal rabbits received recombinant rat VEGF (30microg in 70microL normal saline) or placebo (normal saline 70microL) intratracheally, with or without subsequent tracheal occlusion. Non-operated littermates served as internal controls. Fetuses were harvested on day 28 for morphometric study of the lungs or for mechanical ventilation and measurement of lung mechanics. In total, 96 fetuses from 42 does were used, 47 for ventilation and 49 for morphometry. RESULTS: In fetuses receiving intratracheal VEGF, an increase in immunoreactivity for Flk-1 was observed throughout the lung parenchyma. Tracheal occlusion (TO) adversely affected pulmonary mechanics as compared to un-occluded controls. That effect is partly reversed by intratracheal VEGF. Intratracheal injection of VEGF without tracheal occlusion improves lung mechanics but no more than what was observed in placebo injected controls. CONCLUSION: Antenatal intratracheal VEGF administration was associated with an increase in Flk-1 immunoreactivity. It also improves lung mechanics, however more so when the trachea is occluded. Without TO, the effects were comparable to placebo controls.

Meta-analysis of vascular endothelial growth factor variations in amyotrophic lateral sclerosis: increased susceptibility in male carriers of the -2578AA genotype.

BACKGROUND: Targeted delivery of the angiogenic factor, vascular endothelial growth factor (VEGF), to motor neurons prolongs survival in rodent models of amyotrophic lateral sclerosis (ALS), while mice expressing reduced VEGF concentrations develop motor neuron degeneration reminiscent of ALS, raising the question whether VEGF contributes to the pathogenesis of ALS. An initial association study reported that VEGF haplotypes conferred increased susceptibility to ALS in humans, but later studies challenged this initial finding. METHODS AND FINDINGS: A meta-analysis was undertaken to critically reappraise whether any of the three common VEGF gene variations (-2578C/A, -1154G/A and -634G/C) increase the risk of ALS. Over 7000 subjects from eight European and three American populations were included in the analysis. Pooled odds ratios were calculated using fixed-effects and random-effects models, and four potential sources of heterogeneity (location of disease onset, gender, age at disease onset and disease duration) were assessed. After correction, none of the genotypes or haplotypes was significantly associated with ALS. Subgroup analysis by gender revealed, however, that the -2578AA genotype, which lowers VEGF expression, increased the risk of ALS in males (OR = 1.46 males vs females; 95% CI = 1.19 to 1.80; p = 7.8 10E-5), even after correction for publication bias and multiple testing. CONCLUSIONS: This meta-analysis does not support the original conclusion that VEGF haplotypes increase the risk of ALS in humans, but the significant association of the low-VEGF -2578AA genotype with increased susceptibility to ALS in males reappraises the link between reduced VEGF concentrations and ALS, as originally revealed by the fortuitous mouse genetic studies.

Development of targeted angiogenic medicine.

Strategies to alter angiogenesis have been successfully translated from the bench to bedside. With an estimated number of more than 500 million patients worldwide potentially benefiting from it, it is a prime example of targeted therapy that is increasingly changing the face of clinical medicine. Most efforts to stimulate or inhibit angiogenesis in the past were focused on the key angiogenic factor vascular endothelial growth factor (VEGF), resulting in the approval by the Food and Drug Administration of several drugs for the treatment of cancer and ocular disease. However, mounting clinical evidence reveals that inhibition of VEGF causes resistance and class-specific side effects, while therapeutic angiogenesis by delivering VEGF protein is more challenging than anticipated in human patients. Hence, alternatives are needed, and modulation of oxygen-sensitive enzymes (prolyl hydroxylase domain proteins) and of hypoxia induced transcription factors has recently emerged as a potential novel strategy to treat cancer and ischemic diseases. Furthermore, placental growth factor is a disease-specific angiogenic target, whose inhibition reduces cancer growth without causing major side effects, while its delivery induces revascularization of ischemic tissues. In this review, we summarize recent developments and discuss questions that arise in the exciting, rapidly developing field of angiogenic medicine, including a brief description of its possible implications in neurodegenerative diseases.

Beneficial effects of prolonged systemic administration of PlGF on late outcome of post-ischaemic myocardial performance.

Recent evidence indicates that an imbalance between cardiomyocyte hypertrophy and blood vessel growth in the remote myocardium may contribute to heart failure in ischaemic heart disease. It remains, however, largely unknown which angiogenic factors are capable of stimulating vessel growth in the remote myocardium after myocardial infarction (MI) and whether systemic, rather than local, administration of such factors suffices to ameliorate post-MI cardiac recovery. We therefore analysed the effect of systemic placental growth factor (PlGF) delivery on myocardial recovery post-MI in mice. MI was induced by permanent ligation of the left anterior descending coronary (LAD) artery in C57Bl6/J mice, followed by systemic injection of a PlGF adenovirus, resulting in elevated circulating levels of PlGF for 4 weeks. Functional and morphological analysis revealed that PlGF treatment induced cardiomyocyte hypertrophy and improved cardiac recovery at day 28 post-MI. PlGF stimulated angiogenesis in the infarct border and vessel enlargement in the remote myocardium. In this mouse model, capillary-to-cardiomyocyte ratios in the remote myocardium were maintained post-MI, but PlGF increased the vascular perfusion area in balance with the cardiomyocyte hypertrophy. Overall, systemic delivery of PlGF improves cardiac performance and promotes adaptive remodelling of the post-MI heart.

The clinical implications of sunitinib-induced hypothyroidism: a prospective evaluation.

Sunitinib is approved for the treatment of metastatic renal cell carcinoma (RCC) and imatinib-resistant or -intolerant gastrointestinal stromal tumours (GIST). Several studies have identified unexpected rates of thyroid dysfunction with sunitinib treatment. We performed a prospective observational study with the aim of more accurately defining the incidence and severity of hypothyroidism in RCC or GIST patients receiving sunitinib. Thyroid function was assessed at baseline and on days 1 and 28 of each treatment cycle. Thyroid antibodies were assessed at baseline and during follow-up if abnormal thyroid function tests were recorded. Sixteen patients (27%) developed sub- or clinical hypothyroidism and required hormone replacement and 20 patients (34%) showed at least one elevated thyroid-stimulating hormone not requiring therapeutic intervention. Twenty patients (34%) did not develop any biochemical thyroid abnormality. Thus, sunitinib can induce (sub-) clinical hypothyroidism, warranting close monitoring of thyroid function. We propose a new algorithm for managing this side effect in clinical practise.

Genetic loss of Gas6 induces plaque stability in experimental atherosclerosis.

The growth arrest-specific gene 6 (Gas6) plays a role in pro-atherogenic processes such as endothelial and leukocyte activation, smooth muscle cell migration and thrombosis, but its role in atherosclerosis remains uninvestigated. Here, we report that Gas6 is expressed in all stages of human and mouse atherosclerosis, in plaque endothelial cells, smooth muscle cells and macrophages. Gas6 expression is most abundant in lesions containing high amounts of macrophages, ie thin fibrous cap atheroma and ruptured plaque. Genetic loss of Gas6 does not affect the number and size of initial and advanced plaques in ApoE(-/-) mice, but alters its plaque composition. Compared to Gas6(+/+): ApoE(-/-) mice, initial and advanced plaques of Gas6(-/-): ApoE(-/-) mice contained more smooth muscle cells and more collagen and developed smaller lipid cores, while the expression of TGFbeta was increased. In addition, fewer macrophages were found in advanced plaques of Gas6(-/-): ApoE(-/-) mice. Hence, loss of Gas6 promotes the formation of more stable atherosclerotic lesions by increasing plaque fibrosis and by attenuating plaque inflammation. These findings identify a role for Gas6 in plaque composition and stability.

Transgenic tissue-type plasminogen activator expression improves host defense during Klebsiella pneumonia.

BACKGROUND: Severe pneumonia is associated with a local inhibition of fibrinolysis in the lung as reflected by strongly reduced pulmonary plasminogen activator activity. OBJECTIVES: To study the effect of elevation of local plasminogen activator activity during pneumonia caused by the common respiratory pathogen Klebsiella pneumoniae. METHODS: Female C57Bl/6 mice were inoculated intranasally with a replication-defective adenoviral vector expressing human tissue-type plasminogen activator or a control vector 24 h before intranasal infection with K. pneumoniae. RESULTS: Mice infected with Klebsiella via the airways developed overt pneumonia, which was accompanied by a downregulation of pulmonary tissue-type plasminogen activator levels at protein and mRNA levels. Pulmonary overexpression of human tissue-type plasminogen activator resulted in increased fibrinolytic activity in the lungs during pneumonia, as indicated by higher D-dimer levels and reduced fibrin deposition. Interestingly, overexpression of tissue-type plasminogen activator markedly improved host defense against pneumonia: mice treated with the tissue-type plasminogen activator vector displayed less bacterial growth and dissemination, attenuated distant organ injury and a reduced mortality. CONCLUSIONS: These data demonstrate that local elevation of plasminogen activator activity in the lungs improves host defense against severe gram-negative pneumonia and sepsis.

Neuro-vascular link: from genetic insights to therapeutic perspectives.

Understanding the molecular basis of the formation of blood vessels (angiogenesis) and nerves (neurogenesis) is of great medical relevance. It is well known that dysregulation of angiogenesis leads to tissue ischemia, cancer, inflammation and other disorders, while a dysfunction of the nerve system contributes to motorneuron disorders like amyotrophic lateral sclerosis (ALs) and other neurodegenerative diseases. The observations of Andreas Vesalius--Belgian anatomist of the 16th century--that patterning ofvessels and nerves show more than remarkable similarities, are currently revisited in exciting studies. Indeed, often, vessels and nerves even track alongside each other. Recent genetic studies revealed that vessels and nerves share many more common principles and signals for navigation, proliferation and survival than previously suspected. For instance, gene inactivation studies in mice and zebrafish showed that axon guidance signals regulate vessel navigation. Conversely, prototypic angiogenic factors such as VEGF control neurogenesis and regulate axon and neuron guidance, independently of their angiogenic activity. The next coming years promise to become an exciting journey to further unravel the molecular basis and explore the therapeutic potential of the neurovascular link.

Clinical and fundamental aspects of angiogenesis and anti-angiogenesis.

Insight into the fundamental physiological mechanisms of blood vessel development and neoformation has led to the discovery of multiple angiogenic growth factors and inhibitors. To date, at least 5 angiogenesis inhibitors are readily available for clinical use, mainly in the treatment of cancers and age-related macular degeneration. More inhibitors are yet to come and the indications for their clinical use are expected to broaden. Conversely, the use of angiogenic stimulators, although initially promising in animal models and in small uncontrolled pilot studies in patients with ischaemic heart disease or peripheral arterial occlusive disease, could thus far not show any convincing therapeutic improvement. Challenges still remain as to which angiogenic factor or combination of factors should be administered and in which form (protein versus gene), and what route and duration of administration should be used. Further clinical perspective might come from the recent identification of vascular endothelial growth factor (VEGF) as a modifier of the neurodegenerative disease amyotrophic lateral sclerosis (ALS), and as a promising therapy in the treatment of ALS in preclinical animal models. This review discusses the different clinical trials of angiogenic inhibitors and stimulators, preceded by some fundamental aspects of angiogenesis, giving the clinician a brief overview of the most relevant angiogenic topics.

Plasminogen activator inhibitor-1 production is pathogenetic in experimental murine diabetic renal disease.

AIMS/HYPOTHESIS: Plasminogen activator inhibitor-1 (PAI-1, also known as serpin peptidase inhibitor, clade E [nexin, plasminogen activator inhibitor type 1], member 1 [SERPINE1]) plays a pathogenetic role in renal fibrosis. It is upregulated in experimental and human diabetic nephropathy. These studies assessed the effect of PAI-1 deficiency and overproduction on renal disease in experimental diabetes. MATERIALS AND METHODS: Diabetes was induced by injection of streptozotocin in 6-week-old PAI-1-deficient mice, transgenic mice overexpressing Pai-1 and control mice. Animals were killed after 24 weeks of diabetes or after observation alone. RESULTS: Pai-1 mRNA was upregulated in kidneys from genetically normal mice with diabetes and in non-diabetic Pai-1 transgenic mice. PAI-1 was not further increased in kidneys from Pai-1 transgenic mice with diabetes. Diabetes-associated albuminuria and glomerular injury, as well as renal alpha-smooth muscle actin production, were ameliorated in diabetic PAI-1-deficient mice, an amelioration associated with attenuated increases in renal matrix metallopeptidase-2 expression and activity. Diabetic Pai-1 transgenic mice did not develop increased albuminuria or glomerular injury, but the tubulointerstitial area was modestly enhanced. In addition to the findings in diabetic mice, abnormalities also developed in 30-week-old PAI-1-deficient and Pai-1 transgenic mice without diabetes. PAI-1 deficiency resulted in increased tubulointerstitial area, TGFB1 protein and alpha-smooth muscle actin. Non-diabetic 30-week-old Pai-1 transgenic mice developed similar renal abnormalities and increased matrix metallopeptidase-2 activity, together with a modest increase in serum glucose and HbA(1c). CONCLUSIONS/INTERPRETATION: These results demonstrate that endogenous PAI-1 deficiency protects mice from glomerular injury in longer term diabetes and that endogenous PAI-1 maintains normal renal interstitial structure in ageing not associated with diabetes.