Inhibition of CXCR2 attenuates bronchial angiogenesis in the ischemic rat lung

Midkine Controls Arteriogenesis by Regulating the Bioavailability of Vascular Endothelial Growth Factor A and the Expression of Nitric Oxide Synthase 1 and 3

Midkine is a pleiotropic factor, which is involved in angiogenesis. However, its mode of action in this process is still ill defined. The function of midkine in arteriogenesis, the growth of natural bypasses from pre-existing collateral arteries, compensating for the loss of an occluded artery has never been investigated. Arteriogenesis is an inflammatory process, which relies on the proliferation of endothelial cells and smooth muscle cells. We show that midkine deficiency strikingly interferes with the proliferation of endothelial cells in arteriogenesis, thereby interfering with the process of collateral artery growth. We identified midkine to be responsible for increased plasma levels of vascular endothelial growth factor A (VEGFA), necessary and sufficient to promote endothelial cell proliferation in growing collaterals. Mechanistically, we demonstrate that leukocyte domiciled midkine mediates increased plasma levels of VEGFA relevant for upregulation of endothelial nitric oxide synthase 1 and 3, necessary for proper endothelial cell proliferation, and that non-leukocyte domiciled midkine additionally improves vasodilation.

The data provided on the role of midkine in endothelial proliferation are likely to be relevant for both, the process of arteriogenesis and angiogenesis. Moreover, our data might help to estimate the therapeutic effect of clinically applied VEGFA in patients with vascular occlusive diseases.

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Leukocyte domiciled midkine is decisive for collateral endothelial cell proliferation in arteriogenesis.

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Midkine controls the bioavailability of VEGFA mediating endothelial Nos1 and Nos3 expression.

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Nos1 and Nos3, relevant for endothelial cell proliferation, can substitute for each other.

Arteriogenesis is a life and tissue saving process as it compensates for the loss of an occluded artery. Decoding the underlying molecular mechanisms is a prerequisite for the development of novel therapeutic options to treat patients with vascular occlusive diseases. Lautz et al. identified midkine to be responsible for the increased bioavailability of VEGFA during arteriogenesis, necessary and sufficient to promote endothelial cell proliferation. These data might help to estimate the therapeutic effect of clinically applied VEGFA. As the identified mechanisms might also apply for angiogenesis, they are likely to be of broader relevance, e.g. in terms of tumor treatment.

CXCR2 is involved in pulmonary intravascular macrophage accumulation and angiogenesis in a rat model of hepatopulmonary syndrome

Hepatopulmonary syndrome (HPS) is a lung complication in various liver diseases, with high incidence, poor prognosis and no effective non-surgical treatments in patients with hepatocirrhosis. Therefore, assessing HPS pathogenesis to explore proper therapy strategies is clinically relevant. In the present study, male Sprague–Dawley rats underwent sham operation or common bile duct ligation (CBDL). Two weeks post-surgery, the following groups were set up for 2 weeks of treatment: sham + normal saline, CBDL + CXCR2 antagonist SB225002, CBDL + tumour necrosis factor α (TNF-α) antagonist PTX and CBDL + normal saline groups. Liver and lung tissues were collected after mean arterial pressure (MAP) and portal venous pressure (PVP) measurements. Haematoxylin and eosin (H&E) staining (lung) and Masson staining (liver) were performed for pathological analyses. Finally, pulmonary tissue RNA and total protein were assessed for target effectors. The mRNA and protein levels of CXCR2 were significantly increased in the pulmonary tissue of CBDL rats. What's more, CXCR2 inhibition by SB225002 reduced the expression of CD68 and von Willebrand factor (vWf) in CBDL rats. Importantly, CXCR2 inhibition suppressed the activation of Akt and extracellular signal-regulated kinase (ERK) in CBDL rats. Antagonization of TNF-α with PTX down-regulated the expression of CXCR2. During HPS pathogenesis in rats, CXCR2 might be involved in the accumulation of pulmonary intravascular macrophages and angiogenesis, possibly by activating Akt and ERK, with additional regulation by TNF-α that enhanced pulmonary angiogenesis by directly acting on the pulmonary tissue. Finally, the present study may provide novel targets for the treatment of HPS.

Effector T Cells and Ischemia-Induced Systemic Angiogenesis in the Lung

Lymphocytes have been shown to modulate angiogenesis. Our previous work showed that T regulatory (Treg) cell depletion prevented angiogenesis. In the present study, we sought to examine T-cell populations during lung angiogenesis and subsequent angiostasis. In a mouse model of ischemia-induced systemic angiogenesis in the lung, we examined the time course (0-35 d) of neovascularization and T-cell phenotypes within the lung after left pulmonary artery ligation (LPAL). T cells increased and reached a maximum by 10 days after LPAL and then progressively decreased, suggestive of a modulatory role during the early phase of new vessel growth. Because others have shown IFN-γ to be angiostatic in tumor models, we focused on this effector T-cell cytokine to control the magnitude of angiogenesis. Results showed that IFN-γ protein is secreted at low levels after LPAL and that mice required Treg depletion to see the full effect of effector T cells. Using Foxp3(DTR) and diphtheria toxin to deplete T regulatory cells, increased numbers of effector T cells (CD8(+)) and/or increased capacity to secrete the prominent angiostatic cytokine IFN-γ (CD4(+)) were seen. In vitro culture of mouse systemic and pulmonary microvascular endothelial cells with IFN-γ showed increased endothelial cell apoptosis. CD8(-/-) mice and IFN-γR(-/-) mice showed enhanced angiogenesis compared with wild-type mice, confirming that, in this model, IFN-γ limits the extent of systemic neovascularization in the lung.

Lung Angiogenesis Requires CD4(+) Forkhead Homeobox Protein-3(+) Regulatory T Cells

Angiogenesis in ischemic organs is modulated by immune cells. Systemic neovascularization of the ischemic lung requires macrophages, with chemokines playing a central role in new vessel growth. Because regulatory T (Treg) cells modulate tumor-induced neovascularization, we questioned whether this CD4(+) lymphocyte subset impacts blood vessel growth during ischemia. In a model of left lung ischemia, an increase in CD4(+) CD25(+) forkhead homeobox protein-3 (Foxp3)(+) cells was observed 3-5 days after the onset of ischemia in wild-type C57Bl/6 mice. Using transgenic mice where Foxp3(+) Treg cells can be depleted with diphtheria toxin (DT; Foxp3(DTR)), we unexpectedly found that Foxp3(+) Treg depletion led to markedly reduced lung angiogenesis (90% reduction from Foxp3(gfp) controls). Adoptive transfer studies using CD4(+) CD25(+) splenocytes from congenic CD45.1 mice into Foxp3(+) Treg-depleted mice showed an almost complete recovery of the angiogenic phenotype (80% of Foxp3(gfp) controls). A survey of lung gene expression of angiogenic (lipopolysaccharide-induced CXC chemokine [LIX], IL-6, IL-17) and angiostatic (IFN-γ, transforming growth factor-β, IL-10) cytokines showed Treg-dependent differences only in LIX (CXCL5) and IL-6. Protein confirmation demonstrated a significant reduction in LIX in Treg-deficient mice compared with controls 5 days after the onset of ischemia. Phenotyping other inflammatory cells in the lung by multicolor flow cytometry demonstrated a significantly reduced number of macrophages (major histocombatibility complex class II [MHCII](int), CD11C(+)) in Treg-deficient lungs compared with Treg-sufficient lungs. Treg cells are essential for maximal systemic angiogenesis after pulmonary ischemia. One likely mechanism responsible for the decrease in angiogenesis in Treg-depleted mice was the decline in the essential CXC chemokine, LIX.

Asthma is not only an airway disease, but also a vascular disease

Multiple studies have identified an expansion and morphological dysregulation of the bronchial vascular network in the airways of asthmatics. Increased number, size and density of blood vessels, as well as vascular leakage and plasma engorgement, have been reported in the airways of patients with all grades of asthma from mild to fatal. This neovascularisation is an increasingly commonly reported feature of airway remodelling; however, the pathophysiological impact of the increased vasculature in the bronchial wall and its significance to pulmonary function in asthma are unrecognised at this time. Multiple factors capable of influencing the development and persistence of the vascular network exist within asthmatic airway tissue. These include structural components of the altered extracellular matrix (ECM), imbalance of proteases and their endogenous inhibitors, release of active matrikines and the dysregulated levels of both soluble and matrix sequestered growth factors. This review will explore the features of the asthmatic airway which influence the development and persistence of the increased vascular network, as well as the effect of enhanced tissue perfusion on chronic inflammation and airway dynamics. The response of cells of the airways to the altered vascular profile and the subsequent influence on the features of airway remodelling will also be highlighted. We will explore the failure of current asthma therapeutics in "normalising" this vascular remodelling. Finally, we will summarize the outcomes of recent clinical trials which provide hope that anti-angiogenic therapies may be a potent asthma-resolving class of drugs and provide a new approach to asthma management in the future.

Role of CXCR2 and TRPV1 in functional, inflammatory and behavioural changes in the rat model of cyclophosphamide-induced haemorrhagic cystitis

BACKGROUND AND PURPOSE

Cyclophosphamide induces urotoxicity characterized by the development of cystitis, which involves bladder overactivity and inflammation. Here, we investigated the roles of chemokine receptor 2 (CXCR2) and transient receptor potential vanilloid 1 (TRPV1) channels in a rat model of cyclophosphamide-induced cystitis.

EXPERIMENTAL APPROACH

Cystitis induced by cyclophosphamide in rats was assessed by gross morphology, histology and immunohistochemistry of bladder tissue. mRNA for CXCR2 and TRPV1 channels were measured by RT-PCR. Nociceptive responses in paw and abdomen, along with cystometric measures were recorded.

KEY RESULTS

Cyclophosphamide, i.p., induced pain behaviour, bladder inflammation and voiding dysfunction. The CXCR2 antagonist, SB225002, the TRPV1 channel antagonist, SB366791 or their combination reduced the mechanical hypersensitivity of paw and abdominal area and nociceptive behaviour after cyclophosphamide. Cyclophosphamide-induced cystitis was characterized by haemorrhage, oedema, neutrophil infiltration and other inflammatory changes, which were markedly decreased by the antagonists. Up-regulation of CXCR2 and TRPV1 mRNA in the bladder after cyclophosphamide was inhibited by SB225002, SB366791 or their combination. Expression of CXCR2 and TRPV1 channels was increased in the urothelium after cyclophosphamide. Bladder dysfunction was shown by increased number of non-voiding contractions (NVCs) and bladder pressures and a reduction in bladder capacity (BC), voided volume (VV) and voiding efficiency (VE). SB225002 or its combination with SB366791 reduced bladder pressures, whereas SB225002, SB366791 or their combination increased BC, VV and VE, and also reduced the number of NVCs.

CONCLUSIONS AND IMPLICATIONS

CXCR2 and TRPV1 channels play important roles in cyclophosphamide-induced cystitis in rats and could provide potential therapeutic targets for cystitis.

Characterization of early neovascular response to acute lung ischemia using simultaneous (19)F/ (1)H MR molecular imaging

Angiogenesis is an important constituent of many inflammatory pulmonary diseases, which has been unappreciated until recently. Early neovascular expansion in the lungs in preclinical models and patients is very difficult to assess noninvasively, particularly quantitatively. The present study demonstrated that (19)F/(1)H MR molecular imaging with αvβ3-targeted perfluorocarbon nanoparticles can be used to directly measure neovascularity in a rat left pulmonary artery ligation (LPAL) model, which was employed to create pulmonary ischemia and induce angiogenesis. In rats 3 days after LPAL, simultaneous (19)F/(1)H MR imaging at 3T revealed a marked (19)F signal in animals 2 h following αvβ3-targeted perfluorocarbon nanoparticles [(19)F signal (normalized to background) = 0.80 ± 0.2] that was greater (p = 0.007) than the non-targeted (0.30 ± 0.04) and the sham-operated (0.07 ± 0.09) control groups. Almost no (19)F signal was found in control right lung with any treatment. Competitive blockade of the integrin-targeted particles greatly decreased the (19)F signal (p = 0.002) and was equivalent to the non-targeted control group. Fluorescent and light microscopy illustrated heavy decorating of vessel walls in and around large bronchi and large pulmonary vessels. Focal segmental regions of neovessel expansion were also noted in the lung periphery. Our results demonstrate that (19)F/(1)H MR molecular imaging with αvβ3-targeted perfluorocarbon nanoparticles provides a means to assess the extent of systemic neovascularization in the lung.

Chemokine localization in bronchial angiogenesis

Angiogenesis in the lung involves the systemic bronchial vasculature and becomes prominent when chronic inflammation prevails. Mechanisms for neovascularization following pulmonary ischemia include growth factor transit from ischemic parenchyma to upstream bronchial arteries, inflammatory cell migration/recruitment through the perfusing artery, and paracrine effects of lung cells within the left bronchus, the niche where arteriogenesis takes place. We analyzed left lung bronchoalveolar lavage (BAL) fluid and left bronchus homogenates after left pulmonary artery ligation (LPAL) in rats, immediately after the onset of ischemia (0 h), 6 h and 24 h later. Additionally, we tested the effectiveness of dexamethasone on decreasing inflammation (0–24 h LPAL) and angiogenesis at early (3 d LPAL; bronchial endothelial proliferation) and late (14 d LPAL; blood flow) stages. After LPAL (6 h), BAL protein, total inflammatory cells, macrophages, and polymorphonuclear cells increased significantly. In parallel, pro-angiogenic CXC chemokines increased in BAL and the left main-stem bronchus (CXCL1) or only within the bronchus (CXCL2). Dexamethasone treatment reduced total BAL protein, inflammatory cells (total and polymorphonuclear cells), and CXCL1 but not CXCL2 in BAL. By contrast, no decrease was seen in either chemokine within the bronchial tissue, in proliferating bronchial endothelial cells, or in systemic perfusion of the left lung. Our results confirm the presence of CXC chemokines within BAL fluid as well as within the left mainstem bronchus. Despite significant reduction in lung injury and inflammation with dexamethasone treatment, chemokine expression within the bronchial tissue as well as angiogenesis were not affected. Our results suggest that early changes within the bronchial niche contribute to subsequent neovascularization during pulmonary ischemia.

Angiogenesis in the ischemic rat lung

The adult lung is perfused by both the systemic bronchial artery and the entire venous return flowing through the pulmonary arteries. In most lung pathologies, it is the smaller systemic vasculature that responds to a need for enhanced lung perfusion and shows robust neovascularization. Pulmonary vascular ischemia induced by pulmonary artery obstruction has been shown to result in rapid systemic arterial angiogenesis in man as well as in several animal models. Although the histologic assessment of the time course of bronchial artery proliferation in rats was carefully described by Weibel , mechanisms responsible for this organized growth of new vessels are not clear. We provide surgical details of inducing left pulmonary artery ischemia in the rat that leads to bronchial neovascularization. Quantification of the extent of angiogenesis presents an additional challenge due to the presence of the two vascular beds within the lung. Methods to determine functional angiogenesis based on labeled microsphere injections are provided.

IL-25 drives remodelling in allergic airways disease induced by house dust mite

Background

Overexpression of the transforming growth factor β family signalling molecule smad2 in the airway epithelium provokes enhanced allergen-induced airway remodelling in mice, concomitant with elevated levels of interleukin (IL)-25.

Objective

We investigated whether IL-25 plays an active role in driving this airway remodelling.

Methods

Anti-IL-25 antibody was given to mice exposed to either inhaled house dust mite (HDM) alone, or in conjunction with an adenoviral smad2 vector which promotes an enhanced remodelling phenotype.

Results

Blocking IL-25 in allergen-exposed mice resulted in a moderate reduction in pulmonary eosinophilia and levels of T helper type 2 associated cytokines, IL-5 and IL-13. In addition, IL-25 neutralisation abrogated peribronchial collagen deposition, airway smooth muscle hyperplasia and airway hyperreactivity in control mice exposed to HDM and smad2-overexpressing mice. IL-25 was shown to act directly on human fibroblasts to induce collagen secretion. Recruitment of endothelial progenitor cells to the lung and subsequent neovascularisation was also IL-25 dependent, demonstrating a direct role for IL-25 during angiogenesis in vivo. Moreover, the secretion of innate epithelial derived cytokines IL-33 and thymic stromal lymphopoietin (TSLP) was completely ablated.

Conclusions

In addition to modulating acute inflammation, we now demonstrate a role for IL-25 in orchestrating airway remodelling. IL-25 also drives IL-33 and TSLP production in the lung. These data delineate a wider role for IL-25 in mediating structural changes to the lung following allergen exposure and implicate IL-25 as a novel therapeutic target for the treatment of airway remodelling in asthma.

Lung homing of endothelial progenitor cells in humans with asthma after allergen challenge

RATIONALE

Increased bronchial vascularity is a feature of asthma that can contribute to airflow obstruction and progressive decline in lung function. Angiogenesis is associated with the lung homing and in situ differentiation of endothelial progenitor cells (EPC) in mouse models of asthma. We have previously shown that inhibiting allergen (Ag)-induced recruitment of EPC in sensitized mice attenuated increased bronchial vascularity and development of airway hyperresponsiveness.

OBJECTIVES

We investigated the accumulation of EPC and formation of new blood vessels in the lungs of human subjects with asthma after Ag inhalation challenge.

METHODS

Consenting patients with mild atopic asthma (n = 13) with FEV1 ≥ 70%, methacholine PC20 ≤ 16 mg/ml, and a dual response to Ag were recruited. Sputum levels of EPC were determined by multigating flow cytometry, and lung vascularity was enumerated by immunostaining with von Willebrand factor.

MEASUREMENTS AND MAIN RESULTS

Sputum levels of EPC were determined by multigating flow cytometry and lung vascularity was enumerated by immunostaining with von Willebrand factor. There was a significant increase in sputum EPC levels 24 hours post Ag but not diluent challenge. Similarly, a significant increase in the number and diameter of blood vessels in lung biopsy tissue 24 hours post Ag was observed. In vitro culture of EPC demonstrated the capacity of these cells to differentiate into mature endothelial cells and form tubelike vessel structures. In sputum supernatants, there was a significant increase in CXCR2 agonists, IL-8, and Gro-α 24 hours post Ag. Only Gro-α stimulated a significant EPC migrational response in vitro.

CONCLUSIONS

Our data suggest that increased lung homing of EPC may promote bronchial vascularity in allergic asthmatic responses and that the recruitment of these progenitors maybe orchestrated by CXCR2 chemokines.

Effects of ischemia on lung macrophages

Angiogenesis after pulmonary ischemia is initiated by reactive O(2) species and is dependent on CXC chemokine growth factors, and its magnitude is correlated with the number of lavaged macrophages. After complete obstruction of the left pulmonary artery in mice, the left lung is isolated from the peripheral circulation until 5-7 days later, when a new systemic vasculature invades the lung parenchyma. Consequently, this model offers a unique opportunity to study the differentiation and/or proliferation of monocyte-derived cells within the lung. In this study, we questioned whether macrophage subpopulations were differentially expressed and which subset contributed to growth factor release. We characterized the change in number of all macrophages (MHCII(int), CD11C+), alveolar macrophages (MHCII(int), CD11C+, CD11B-) and mature lung macrophages (MHCII(int), CD11C+, CD11B+) in left lungs from mice immediately (0 h) or 24 h after left pulmonary artery ligation (LPAL). In left lung homogenates, only lung macrophages increased 24 h after LPAL (vs. 0 h; p<0.05). No changes in proliferation were seen in any subset by PCNA expression (0 h vs. 24 h lungs). When the number of monocytic cells was reduced with clodronate liposomes, systemic blood flow to the left lung 14 days after LPAL decreased by 42% (p<0.01) compared to vehicle controls. Furthermore, when alveolar macrophages and lung macrophages were sorted and studied in vitro, only lung macrophages secreted the chemokine MIP-2α (ELISA). These data suggest that ischemic stress within the lung contributes to the differentiation of immature monocytes to lung macrophages within the first 24 h after LPAL. Lung macrophages but not alveolar macrophages increase and secrete the proangiogenic chemokine MIP-2α. Overall, an increase in the number of lung macrophages appears to be critical for neovascularization in the lung, since clodronate treatment decreased their number and attenuated functional angiogenesis.

Lung and vascular function during chronic severe pulmonary ischemia

Bronchial vascular angiogenesis takes place in a variety of lung inflammatory conditions such as asthma, cystic fibrosis, lung cancer, and chronic pulmonary thromboembolic disease. However, it is unclear whether neovascularization is predominantly appropriate and preserves lung tissue or whether it contributes further to lung pathology through edema formation and inflammation. In the present study we examined airway and lung parenchymal function 14 days after left pulmonary artery ligation. In rats as well as higher mammals, severe pulmonary ischemia results in bronchial vascular proliferation. Using labeled microspheres, we demonstrated an 18-fold increase in systemic blood flow to the ischemic left lung. Additionally, vascular remodeling extended to the tracheal venules, which showed an average 28% increase in venular diameter. Despite this increase in vascularity, airways resistance was not altered nor was methacholine responsiveness. Since these measurements include the entire lung, we suggest that the normal right lung, which represented 78% of the total lung, obscured the ability to detect a change. When functional indexes such as diffusing capacity, in situ lung volume, and vascular permeability of the left lung could be separated from right lung, significant changes were observed. Thus when comparing average left lung values of rats 14 days after left pulmonary artery ligation to left lungs of rats undergoing sham surgery, diffusing capacity of the left lung decreased by 72%, left lung volume decreased by 38%, and the vascular permeability to protein increased by 58%. No significant differences in inflammatory cell recruitment were observed, suggesting that acute ischemic inflammation had resolved. We conclude that despite the preservation of lung tissue, the proliferating bronchial neovasculature may contribute to a sustained decrement in pulmonary function.

Differential activity of pro-angiogenic CXC chemokines

We showed previously in a mouse model of lung ischemia-induced angiogenesis, enhanced expression of the three ELR+ CXC chemokines (KC, LIX, and MIP-2) and that blockade of the ligand receptor CXCR(2) limited neovascularization. The present study was undertaken to determine the relative abundance and angiogenic potential of the three CXC chemokines and whether RhoA activation explained the measured differences in potencies. We found that LIX showed the greatest absolute amount in the in vivo model 4 h after left pulmonary artery obstruction (LIX>KC>MIP-2; p<0.05). In vitro, LIX induced the greatest degree of arterial endothelial cell chemotaxis and KC was without effect. A significant increase (approximately 40%) in active RhoA was observed with both LIX and MIP-2 compared with vehicle control (p<0.05). On average, LIX induced the greatest amount of tube formation within pleural tissue in culture. Thus, the results of the present study suggest that among the three ELR+ CXC chemokines, LIX predominates in eliciting a pro-angiogenic phenotype.

CXCR2 mediates the recruitment of endothelial progenitor cells during allergic airways remodeling

Airway remodeling is a central feature of asthma and includes the formation of new peribronchial blood vessels, which is termed angiogenesis. In a number of disease models, bone marrow-derived endothelial progenitor cells (EPCs) have been shown to contribute to the angiogenic response. In this study we set out to determine whether EPCs were recruited into the lungs in a model of allergic airways disease and to identify the factors regulating EPC trafficking in this model. We observed a significant increase in the number of peribronchial blood vessels at day 24, during the acute inflammatory phase of the model. This angiogenic response was associated with an increase in the quantity of EPCs recoverable from the lung. These EPCs formed colonies after 21 days in culture and were shown to express CD31, von Willebrand factor, and vascular endothelial growth factor (VEGF) receptor 2, but were negative for CD45 and CD14. The influx in EPCs was associated with a significant increase in the proangiogenic factors VEGF-A and the CXCR2 ligands, CXCL1 and CXCL2. However, we show directly that, while the CXCL1 and CXCL2 chemokines can recruit EPCs into the lungs of allergen-sensitized mice, VEGF-A was ineffective in this respect. Further, the blockade of CXCR2 significantly reduced EPC numbers in the lungs after allergen exposure and led to a decrease in the numbers of peribronchial blood vessels after allergen challenge with no effect on inflammation. The data presented here provide in vivo evidence that CXCR2 is critical for both EPC recruitment and the angiogenic response in this model of allergic inflammation of the airways.