Innate Immunity and Angiogenesis

VEGF in biological control

Vascular endothelial growth factor A (VEGF-A) belongs to a family of heparin binding growth factors that include VEGF-B, VEGF-C, VEGF-D, and placental-like growth factor (PLGF). First discovered for its ability to regulate vascular endothelial cell permeability, VEGF is a well-known angiogenic factor that is important for vascular development and maintenance in all mammalian organs. The development of molecular tools and pharmacological agents to selectively inhibit VEGF function and block angiogenesis and/or vascular permeability has led to great promise in the treatment of various cancers, macular degeneration, and wound healing. However, VEGF is also important in animals for the regulation of angiogenesis, stem cell and monocyte/macrophage recruitment, maintenance of kidney and lung barrier functions and neuroprotection. In addition to its role in regulating endothelial cell proliferation, migration, and cell survival, VEGF receptors are also located on many non-endothelial cells and act through autrocrine pathways to regulate cell survival and function. The following review will discuss the role of VEGF in physiological angiogenesis as well as its role in non-angiogenic processes that take place in adult organs.

Effect of tumor microenvironment modulation on the efficacy of oncolytic virus therapy

BACKGROUND

The tumor microenvironment is being increasingly recognized as an important determinant of tumor progression as well as of therapeutic response. We investigated oncolytic virus (OV) therapy-induced changes in tumor blood vessels and the impact of modulating tumor vasculature on the efficacy of oncolytic virus therapy.

METHODS

Rat glioma cells (D74/HveC) were implanted intracranially in immune-competent rats. Seven days later, the rats (groups of 3-7 rats) were treated with oncolytic virus (hrR3), and, 3 days later, brains were harvested for evaluation. Some rats were treated with angiostatic cRGD peptide 4 days before oncolytic virus treatment. Some rats were treated with cyclophosphamide (CPA), an immunosuppressant, 2 days before oncolytic virus treatment. Changes in tumor vascular perfusion were evaluated by magnetic resonance imaging of live rats and by fluorescence microscopy of tumor sections from rats perfused with Texas red-conjugated lectin immediately before euthanasia. Leukocyte infiltration in tumors was evaluated by anti-CD45 immunohistochemistry, and the presence of oncolytic virus in tumors was evaluated by viral titration. Changes in cytokine gene expression in tumors were measured by quantitative real-time polymerase chain reaction-based microarrays. Survival was analyzed by the Kaplan-Meier method. All statistical tests were two-sided.

RESULTS

Oncolytic virus treatment of experimental rat gliomas increased tumor vascular permeability, host leukocyte infiltration into tumors, and intratumoral expression of inflammatory cytokine genes, including interferon gamma (IFN-gamma). The increase in vascular permeability was suppressed in rats pretreated with cyclophosphamide. Compared with rats treated with hrR3 alone, rats pretreated with a single dose of cRGD peptide before hrR3 treatment had reduced tumor vascular permeability, leukocyte infiltration, and IFN-gamma protein levels (mean IFN-gamma level for hrR3 versus hrR3 + cRGD = 203 versus 65.6 microg/mg, difference = 137 microg/mg, 95% confidence interval = 72.7 to 202.9 microg/mg, P = .006); increased viral titers in tumor tissue; and longer median survival (21 days versus 17 days, P<.001).

CONCLUSIONS

A single dose of angiostatic cRGD peptide treatment before oncolytic virus treatment enhanced the antitumor efficacy of oncolytic virus.

Wnt5a-mediated non-canonical Wnt signalling regulates human endothelial cell proliferation and migration

Cell to cell interaction is one of the key processes effecting angiogenesis and endothelial cell function. Wnt signalling is mediated through cell-cell interaction and is involved in many developmental processes and cellular functions. In this study, we investigated the possible function of Wnt5a and the non-canonical Wnt pathway in human endothelial cells. We found that Wnt5a-mediated non-canonical Wnt signalling regulated endothelial cell proliferation. Blocking this pathway using antibody, siRNA or a down-stream inhibitor led to suppression of endothelial cell proliferation, migration, and monolayer wound closure. We also found that the mRNA level of Wnt5a is up-regulated when endothelial cells are treated with a cocktail of inflammatory cytokines. Our findings suggest non-canonical Wnt signalling plays a role in regulating endothelial cell growth and possibly in angiogenesis.

Mechanisms of disease: Toll-like receptors in cardiovascular disease

The innate immune system detects highly conserved, relatively invariant structural motifs of pathogens. Toll-like receptors (TLRs) have been identified as the primary innate immune receptors. TLRs distinguish between different patterns of pathogens and activate a rapid innate immune response; however, TLRs can also be activated by host-derived molecules. In addition to being expressed in immune cells, TLRs are expressed in other tissues, such as those of the cardiovascular system. TLRs could, therefore, be a key link between cardiovascular disease development and the immune system. Indeed, evidence that TLR activation contributes to the development and progression of atherosclerosis, cardiac dysfunction in sepsis, and congestive heart failure, is convincing. Although much has been learned about TLR activation in cellular components of the cardiovascular system, the role individual TLR family members have in the pathophysiology of cardiovascular diseases and hence in clinical practice remains to be defined. Here we review the rapid progress that has been made in this field, which has improved our understanding of vascular as well as myocardial TLR function in basic and clinical science.

Crucial role of the protein C pathway in governing microvascular inflammation in inflammatory bowel disease

Endothelial protein C receptor (EPCR) and thrombomodulin (TM) are expressed at high levels in the resting microvasculature and convert protein C (PC) into its activated form, which is a potent anticoagulant and antiinflammatory molecule. Here we provide evidence that in Crohn disease (CD) and ulcerative colitis (UC), the 2 major forms of inflammatory bowel disease (IBD), there was loss of expression of endothelial EPCR and TM, which in turns caused impairment of PC activation by the inflamed mucosal microvasculature. In isolated human intestinal endothelial cells, administration of recombinant activated PC had a potent antiinflammatory effect, as demonstrated by downregulated cytokine-dependent cell adhesion molecule expression and chemokine production as well as inhibited leukocyte adhesion. In vivo, administration of activated PC was therapeutically effective in ameliorating experimental colitis as evidenced by reduced weight loss, disease activity index, and histological colitis scores as well as inhibited leukocyte adhesion to the inflamed intestinal vessels. The results suggest that the PC pathway represents a new system crucially involved in governing intestinal homeostasis mediated by the mucosal microvasculature. Restoring the PC pathway may represent a new therapeutic approach to suppress intestinal inflammation in IBD.

HIF-1 alpha expression is associated with an atheromatous inflammatory plaque phenotype and upregulated in activated macrophages

OBJECTIVE

Angiogenesis and inflammation are important features in atherosclerotic plaque destabilization. The transcription factor hypoxia-inducible factor-1 alpha (HIF-1 alpha) is a key regulator of angiogenesis and is also involved in inflammatory reactions. We studied HIF-1 alpha expression in different atherosclerotic plaque phenotypes.

METHODS AND RESULTS

HIF-1 alpha expression was observed in 18/37 (49%) carotid and in 9/15 (60%) femoral endarterectomy specimens. Expression of HIF-1 alpha was associated with the presence of a large extracellular lipid core (P=0.03) and macrophages (P=0.02). HIF-1 alpha co-localized with vascular endothelial growth factor (VEGF), an important downstream target of HIF-1 alpha. In addition, a strong association was observed between expression levels of HIF-1 alpha and VEGF (P=0.001). The average number of plaque microvessels was higher in plaques with no or minor HIF-1 alpha staining than in plaques with moderate or heavy HIF-1 alpha staining (P=0.03). In human macrophages, lipopolysaccharide activation induced HIF-1 alpha expression. In embryonic fibroblasts derived from wild-type mice, lipopolysaccharide activation induced an increase in HIF-1 alpha mRNA, whereas in Toll-like receptor 4 defective embryonic fibroblasts no effect was observed after lipopolysaccharide stimulation.

CONCLUSIONS

In atherosclerotic plaque, the transcription factor HIF-1 alpha is associated with an atheromatous inflammatory plaque phenotype and with VEGF expression. HIF-1 alpha expression is upregulated in activated macrophages under normoxic conditions.

Inflammation and the mucosal microcirculation in inflammatory bowel disease: the ebb and flow

PURPOSE OF REVIEW

Inflammatory bowel disease pathogenesis involves the interplay of multiple biological factors, among which nonimmune cells, including the endothelium, represent a crucial component of disease pathogenesis.

RECENT FINDINGS

Endothelial cells play a key role in chronic inflammation through multiple and disparate activities. The mucosal microvasculature in inflammatory bowel disease is dysfunctional, overexpresses inflammatory molecules and undergoes intense angiogenesis, failing to exert its physiological antiinflammatory and anticoagulant activities.

SUMMARY

The mucosal microcirculation is abnormal in inflammatory bowel disease and represents a novel component of disease pathogenesis; targeting the various abnormalities of the inflammatory bowel disease microcirculation may lead to new forms of therapeutic intervention.

Immune regulation by microvascular endothelial cells: directing innate and adaptive immunity, coagulation, and inflammation

An effective immune response depends not only on the proper activation, regulation, and function of immune cells, but also on their distribution and retention in diverse tissue microenvironments where they encounter a number of stimuli and other cell types. These activities are mediated by endothelial cells, which form specialized microcirculatory networks used by immune cells under both physiological and pathological circumstances. Endothelial cells represent a highly heterogeneous population of cells with the ability to interact with and modulate the function of immune cells. This review is focused on the role of microvascular endothelial cells in innate and adaptive immunity, inflammation, coagulation, angiogenesis, and the therapeutic implications of targeting endothelial cells in selected autoimmune and chronic inflammatory disorders.

Masquerader: High Mobility Group Box-1 and Cancer

Since its identification a third of a century ago, the high-mobility group box-1 (HMGB1) protein has been linked to varied diverse cellular processes, including release from necrotic cells and secretion by activated macrophages engulfing apoptotic cells. Initially described as solely chromatin-associated, HMGB1 was additionally discovered in the cytoplasm of several types of cultured mammalian cells 6 years later. In addition to its intracellular role, HMGB1 has been identified extracellularly as a putative leaderless cytokine and differentiation factor. In the years since its discovery, HMGB1 has also been implicated in disease states, including Alzheimer's, sepsis, ischemia-reperfusion, arthritis, and cancer. In cancer, overexpression of HMGB1, particularly in conjunction with its receptor for advanced glycation end products, has been associated with the proliferation and metastasis of many tumor types, including breast, colon, melanoma, and others. This review focuses on current knowledge and speculation on the role of HMGB1 in the development of cancer, metastasis, and potential targets for therapy.

Gene therapy progress and prospects: therapeutic angiogenesis for ischemic cardiovascular disease

During the past decade, both in vitro and in vivo studies have provided new insights into the cellular and molecular mechanisms that govern angiogenesis and arteriogenesis. However, therapeutic angiogenesis clinical trials using recombinant protein or gene therapy formulations of single angiogenic growth factors have yielded at best only modest success to date. Among the second generation of angiogenic agents are therapeutic transgenes that enhance expression of two or more proangiogenic cytokines. These include synthetic constructs that mimic that activity of endogenous transcriptional regulators and other upstream, regulatory factors that have the potential to induce formation of morphologically and physiologically functional vessels. These agents are now beginning to be evaluated in clinical trials for patients with advanced ischemic cardiac and peripheral vascular disease.

Promotion of angiogenesis in tissue engineering: developing multicellular matrices with multiple capacities

One of the aims of tissue engineering is to be able to develop multi-tissue organs in the future. This requires the optimization of conditions for the differentiation of multiple cell types and maintenance of the differentiated phenotype within complex engineered tissues. The goal of this study was to develop prototype tissue engineered matrices to support the simultaneous growth of different cell types with a particular focus on the angiogenic process. We examined two different matrix compositions for the promotion of blood vessel and tube formation. A fibrin-based matrix with the addition of a combination of growth factors supported vascular growth and the invasion of inflammatory cells. Using this fibrin matrix, in combination with a collagen-based hydrogel, a simple in vitro model of the cornea with adjacent sclera was developed that was complete with innervation and vascular structures. In addition, we showed that collagen-based matrices were effective in delivering mononuclear endothelial progenitor cells to ischemic tissue in vivo, and allowing these cells to incorporate into vascular structures. It is anticipated that with further development, these matrices have potential for use as delivery matrices for cell transplantation and for in vitro study purposes of multiple cell types.

Inflammation and cancer: is trophism the link?

The pathophysiological mechanisms of the inflammatory response can be common to wound repair and tumor development. We propose that this response evolves in three phases, the nervous or immediate phase, the immune or intermediate phase, and the endocrine or late phase. In wound repair and in these phases, the interstitial space successively presents edema due to ischemia-revascularization and nutrition by diffusion (nervous phase), infiltration by leukocytes, which would mediate the nutrition of damaged neighbor cells (immune phase) and by angiogenesis, nutrition mediated by the capillaries that favor regeneration or scarring (endocrine phase). At the same time, in tumor development, it is considered that the cancerous cell successively occupies the interstitial space, expressing three different phenotypes: the hypoxia-reperfusion phenotype, with anaerobic glycolisis, oxidative stress and edema (dormant stage); the immune phenotype that expresses the functions corresponding to leukocytes, including the hyperproduction of pro-inflammatory mediators, lymphangiogenesis, the invasion of lymph nodes (N stage) and systemic inflammatory response syndrome; and lastly, the endocrine phenotype, in which the appearance of both local (tumor or T stage) and systemic (metastasis or M stage) angiogenesis induce a growing disease.

Adenosine, an endogenous distress signal, modulates tissue damage and repair

Adenosine is formed inside cells or on their surface, mostly by breakdown of adenine nucleotides. The formation of adenosine increases in different conditions of stress and distress. Adenosine acts on four G-protein coupled receptors: two of them, A(1) and A(3), are primarily coupled to G(i) family G proteins; and two of them, A(2A) and A(2B), are mostly coupled to G(s) like G proteins. These receptors are antagonized by xanthines including caffeine. Via these receptors it affects many cells and organs, usually having a cytoprotective function. Joel Linden recently grouped these protective effects into four general modes of action: increased oxygen supply/demand ratio, preconditioning, anti-inflammatory effects and stimulation of angiogenesis. This review will briefly summarize what is known and what is not in this regard. It is argued that drugs targeting adenosine receptors might be useful adjuncts in many therapeutic approaches.

Resolution of LPS-induced airway inflammation and goblet cell hyperplasia is independent of IL-18

Background

The resolution of inflammatory responses in the lung has not been described in detail and the role of specific cytokines influencing the resolution process is largely unknown.

Methods

The present study was designed to describe the resolution of inflammation from 3 h through 90 d following an acute injury by a single intratracheal instillation of F344/N rats with LPS. We documented the inflammatory cell types and cytokines found in the bronchoalveolar lavage fluid (BALF), and epithelial changes in the axial airway and investigated whether IL-18 may play a role in the resolution process by reducing its levels with anti-IL-18 antibodies.

Results

Three major stages of inflammation and resolution were observed in the BALF during the resolution. The first stage was characterized by PMNs that increased over 3 h to 1 d and decreased to background levels by d 6–8. The second stage of inflammation was characterized by macrophage influx reaching maximum numbers at d 6 and decreasing to background levels by d 40. A third stage of inflammation was observed for lymphocytes which were elevated over d 3–6. Interestingly, IL-18 and IL-9 levels in the BALF showed a cyclic pattern with peak levels at d 4, 8, and 16 while decreasing to background levels at d 1–2, 6, and 12. Depletion of IL-18 caused decreased PMN numbers at d 2, but no changes in inflammatory cell number or type at later time points.

Conclusion

These data suggest that IL-18 plays a role in enhancing the LPS-induced neutrophilic inflammation of the lung, but does not affect the resolution of inflammation.

Toll-like receptor 2 ligand mediates the upregulation of angiogenic factor, vascular endothelial growth factor and interleukin-8/CXCL8 in human rheumatoid synovial fibroblasts

Rheumatoid arthritis (RA) is characterized by infiltrations of inflammatory cells accompanied by neovascularization in the joint. We hypothesized that cell activation via the toll-like receptor (TLR) may be involved in the induction of angiogenic molecules, which are relevant to the pathogenesis of RA. RA fibroblast like synoviocytes (FLS) were stimulated with TLR-2 ligand bacterial peptidoglycan (PGN), TLR-4 ligand lipopolysaccharide (LPS) and various cytokines. Vascular endothelial growth factor (VEGF) and IL-8 were measured by ELISA in culture supernatants; mRNA levels were assessed by RT-PCR and real time PCR. The levels of TLR-2, VEGF and IL-8 were analyzed by dual immunohistochemistry in RA synovium and compared with osteoarthritis (OA). Regulation of MyD88, IRAK4, IRAK1, IRAK-M and TRAF-6 mRNA expression levels by PGN were analyzed by RT-PCR. Phosphorylation of I kappa B alpha was evaluated by western blotting. Levels of VEGF and IL-8 were upregulated in culture supernatants of RA FLS stimulated with PGN, similar to the levels of IL-1beta and IL-17 stimulation. Neutralization of TLR-2 with a blocking monoclonal antibody significantly reduced both VEGF and IL-8 levels (P<0.05), which reflected the functional relevance of TLR-2 activation to the induction of VEGF and IL-8 production. Downstream intracellular signaling following TLR-2 stimulation involved MyD88-IRAK-4-TRAF-6 pathways, resulting in NF-kappaB activation. Thus, TLR-2 activation in RA FLS by microbial constituents could be involved in the induction of VEGF and IL-8 and thereby promote inflammation either directly or via angiogenesis. This possibly contributes to the perpetuation of synovitis in patients with RA.

Update on advances in atherothrombosis

The study of atherothrombosis is a rapidly evolving field, and significant progress was achieved in various aspects of the disease during the past year. In the area of diagnostic imaging, MRI and multidetector CT were actively used to evaluate the characteristics of the arterial wall, including calcified and noncalcified lesions, and both in the coronary and extracoronary vascular territories. There was also extensive research into the application of imaging modalities to visualize cellular or molecular disease processes, known as molecular imaging. Considerable efforts were devoted to the identification of novel biomarkers that reflect different components of atherothrombosis, namely inflammation, thrombogenicity, oxidative stress and reparative ability, predicting the presence of early disease or the risk of clinical events. In the therapeutic arena, substantial evidence accumulated on the beneficial effects of several pharmacologic agents, most significantly statins. Finally, important advances were also made in the understanding of the roles of immunity and neovascularization in atherogenesis, including the development and progression of disease at different stages. Awareness of these recent advances and new lines of active research is fundamental for health professionals involved in the care of patients with atherothrombosis. In this Review we present an overview of data in these areas.

Angiopoietin-1 and vascular endothelial growth factor induce expression of inflammatory cytokines before angiogenesis

The purpose of this study was to identify novel transcriptional events occurring in the aortic wall before angiogenesis. We used a defined tissue culture system that takes advantage of the capacity of rat aortic rings to generate neovessels ex vivo in response to angiogenic factor stimulation. Total RNA isolated from aortic rings 18 h posttreatment with angiopoietin (Ang)-1 or vascular endothelial growth factor (VEGF) was used to probe oligonucleotide microarrays. Many genes were up- or downregulated by either Ang-1 or VEGF, with a subset being affected by treatment with both growth factors. Grouping of genes by biological function revealed that Ang-1 and VEGF both upregulated a host of immune-related genes including many inflammatory cytokines. A mixture of the Ang-1- and VEGF-induced cytokines stimulated the spontaneous angiogenic response of aortic rings and was synergistic with a low dose of recombinant VEGF. This effect was associated with enhanced recruitment of adventitial macrophages and dendritic cells in the angiogenic outgrowths. Thus Ang-1 and VEGF activate the innate immune system of the vessel wall, stimulating the production of proangiogenic inflammatory cytokines before the emergence of neovessels. This hitherto unreported feature of the angiogenic response might represent an important early component of the cellular and molecular cascade responsible for the angiogenic response of the aortic wall.

Clinical implications of vulnerable plaque

In many individuals, the first indicator of atherosclerosis is an acute heart attack, which is often fatal. Despite innovations in medical therapy and interventional cardiology techniques, coronary artery disease continues to be the leading cause of death in the USA. There is great interest in identifying vulnerable plaques and vulnerable patients as a possible means to stem the tide against coronary artery disease. Improvements in diagnostic studies and development of novel imaging tools have opened the possibilities for significant advances in the management of vulnerable plaque. The result of improved risk stratification, by both noninvasive and invasive means, will be a better assessment of the risk/benefit relationships for the novel therapies that are needed to further reduce the morbidity and mortality of the disease. Correct identification of vulnerable plaque would permit the use of more effective systemic treatment and enable clinical trials to study the supplemental benefit from local treatments.

The inflammatory response recapitulates phylogeny through trophic mechanisms to the injured tissue

The post-traumatic local acute inflammatory response is described as a succession of three functional phases of possible trophic significance: 1. Nervous or immediate (ischemia-reperfusion); 2. Immune or intermediate (infiltration by inflammatory and bacterial cells) and 3. Endocrine or late (angiogenesis with regeneration and/or cicatrization). Each of these phases emphasizes the trophic role of the mechanisms in the damaged tissue. Hence, the nervous phase is predominated by nutrition by diffusion; in the immune phase trophism is mediated by inflammatory cells and bacteria and, finally, in the endocrine phase, the blood circulation and oxidative metabolism play the most significant nutritive role. Since these trophic mechanisms are of increasing complexity, progressing from anoxia to total specialization in the use of oxygen to obtain usable energy, it could be speculated that they represent the successive reappearance of the stages that take place during the evolution of life on Earth, from ancient times without oxygen. In this sense, the inflammatory response could recapitulate phylogeny through the successive expression of pathophysiologic mechanisms that have a trophic meaning to the injured tissue.

Angiogenesis in Atherogenesis

Atherogenesis is the pathobiological process, which underlies atherosclerotic cardiovascular disease and evolves in the 3 stages of initiation, progression, and complication to clinical significance. Of note, this process is associated with neovascularization, and it was not until recently that the implications of angiogenesis in atherogenesis were delineated. This article gives an updated overview on this topic and briefly reflects on the similarities with neovessel formation in carcinogenesis.

Dual role of VEGF-induced heme-oxygenase-1 in angiogenesis

Heme-oxygenase-1 (HO-1) is an inducible cytoprotective molecule that displays antioxidant, antiapoptotic, and antiinflammatory effects. In addition, HO-1 appears to have a complex role in angiogenesis. Recent in vivo studies report that vascular endothelial growth factor (VEGF) regulates HO-1 expression and activity in vascular endothelial cells (ECs) and that inhibition of HO-1 abrogates VEGF-induced endothelial activation and subsequent angiogenesis, while promoting VEGF-induced monocyte recruitment and inflammatory angiogenesis. HO-1 may also regulate the synthesis and activity of VEGF, resulting in a positive-feedback loop. In contrast, HO-1 activity has the opposite effect on lipopolysaccharide-driven inflammatory angiogenesis, inhibiting leukocyte invasion and preventing subsequent angiogenesis. In this review, we summarize the current understanding of the role of HO-1 in angiogenesis. We conclude that further investigation, using targeted molecular approaches specifically to alter HO-1 activity, are required to develop our understanding of the role of HO-1 and its products, carbon monoxide, biliverdin, bilirubin, and free iron in angiogenesis. We propose that during chronic inflammation, HO-1 has two roles, first an antiinflammatory action inhibiting leukocyte infiltration, and second, promotion of VEGF-driven noninflammatory angiogenesis, which facilitates tissue repair. Additional studies will help determine whether modulating the activity of HO-1 and/or its products has therapeutic potential in chronic inflammatory dise.

Adenosine 5'-triphosphate and adenosine as endogenous signaling molecules in immunity and inflammation

Human health is under constant threat of a wide variety of dangers, both self and nonself. The immune system is occupied with protecting the host against such dangers in order to preserve human health. For that purpose, the immune system is equipped with a diverse array of both cellular and non-cellular effectors that are in continuous communication with each other. The naturally occurring nucleotide adenosine 5'-triphosphate (ATP) and its metabolite adenosine (Ado) probably constitute an intrinsic part of this extensive immunological network through purinergic signaling by their cognate receptors, which are widely expressed throughout the body. This review provides a thorough overview of the effects of ATP and Ado on major immune cell types. The overwhelming evidence indicates that ATP and Ado are important endogenous signaling molecules in immunity and inflammation. Although the role of ATP and Ado during the course of inflammatory and immune responses in vivo appears to be extremely complex, we propose that their immunological role is both interdependent and multifaceted, meaning that the nature of their effects may shift from immunostimulatory to immunoregulatory or vice versa depending on extracellular concentrations as well as on expression patterns of purinergic receptors and ecto-enzymes. Purinergic signaling thus contributes to the fine-tuning of inflammatory and immune responses in such a way that the danger to the host is eliminated efficiently with minimal damage to healthy tissues.

Vascular endothelial growth factor (VEGF) is associated with reduced severity of acute graft-versus-host disease and nonrelapse mortality after allogeneic stem cell transplantation

This study investigated whether or not there is a correlation between the changes in the serum levels of vascular endothelial growth factor (VEGF) and the outcome of allogeneic stem cell transplantation (allo-SCT). Eighty-five patients undergoing allo-SCT were prospectively studied. The serum VEGF levels were measured on days 0, +7 and +14 after transplantation. The VEGF levels decreased significantly on day +7 and recovered on day +14. The highest levels from day +7 through day +14 were categorized by cluster analysis, which were then correlated with the nonrelapse mortality (NRM). There was a significant correlation between a low VEGF level and the occurrence of severe acute graft-versus-host disease (GVHD) including grade III-IV (P=0.029). The 1-year probability of NRM in patients with a low VEGF level was 22.5% compared with 3.5% for those with a high VEGF level (P=0.024). Multivariate analysis revealed clinically defined infections (P=0.011), advanced disease (P=0.014) and a low VEGF cluster (P=0.05) to be significantly associated with the occurrence of NRM in the cohort. In conclusion, low VEGF levels after allo-SCT are associated with NRM with an exacerbated severity of acute GVHD. VEGF monitoring after a transplant might identify those patients at risk of severe transplant-related mortality.

Physiological roles for ecto-5'-nucleotidase (CD73)

Nucleotides and nucleosides influence nearly every aspect of physiology and pathophysiology. Extracellular nucleotides are metabolized through regulated phosphohydrolysis by a series of ecto-nucleotidases. The formation of extracellular adenosine from adenosine 5’-monophosphate is accomplished primarily through ecto-5’-nucleotidase (CD73), a glycosyl phosphatidylinositol-linked membrane protein found on the surface of a variety of cell types. Recent in vivo studies implicating CD73 in a number of tissue protective mechanisms have provided new insight into its regulation and function and have generated considerable interest. Here, we review contributions of CD73 to cell and tissue stress responses, with a particular emphasis on physiologic responses to regulated CD73 expression and function, as well as new findings utilizing Cd73-deficient animals.

The extracellular adherence protein (Eap) of Staphylococcus aureus inhibits wound healing by interfering with host defense and repair mechanisms

Staphylococcus aureus is a major human pathogen interfering with host-cell functions. Impaired wound healing is often observed in S aureus-infected wounds, yet, the underlying mechanisms are poorly defined. Here, we identify the extracellular adherence protein (Eap) of S aureus to be responsible for impaired wound healing. In a mouse wound-healing model wound closure was inhibited in the presence of wild-type S aureus and this effect was reversible when the wounds were incubated with an isogenic Eap-deficient strain. Isolated Eap also delayed wound closure. In the presence of Eap, recruitment of inflammatory cells to the wound site as well as neovascularization of the wound were prevented. In vitro, Eap significantly reduced intercellular adhesion molecule 1 (ICAM-1)-dependent leukocyte-endothelial interactions and diminished the consequent activation of the proinflammatory transcription factor nuclear factor kappaB (NFkappaB) in leukocytes associated with a decrease in expression of tissue factor. Moreover, Eap blocked alphav-integrin-mediated endothelial-cell migration and capillary tube formation, and neovascularization in matrigels in vivo. Collectively, the potent anti-inflammatory and antiangiogenic properties of Eap provide an underlying mechanism that may explain the impaired wound healing in S aureus-infected wounds. Eap may also serve as a lead compound for new anti-inflammatory and antiangiogenic therapies in several pathologies.

Cutting Edge: Extracellular High Mobility Group Box-1 Protein Is a Proangiogenic Cytokine

The chromosomal high mobility group box-1 (HMGB1) protein acts as a proinflammatory cytokine when released in the extracellular environment by necrotic and inflammatory cells. In the present study, we show that HMGB1 exerts proangiogenic effects by inducing MAPK ERK1/2 activation, cell proliferation, and chemotaxis in endothelial cells of different origin. Accordingly, HMGB1 stimulates membrane ruffling and repair of a mechanically wounded endothelial cell monolayer and causes endothelial cell sprouting in a three-dimensional fibrin gel. In keeping with its in vitro properties, HMGB1 stimulates neovascularization when applied in vivo on the top of the chicken embryo chorioallantoic membrane whose blood vessels express the HMGB1 receptor for advanced glycation end products (RAGE). Accordingly, RAGE blockade by neutralizing Abs inhibits HMGB1-induced neovascularization in vivo and endothelial cell proliferation and membrane ruffling in vitro. Taken together, the data identify HMGB1/RAGE interaction as a potent proangiogenic stimulus.

The dying stem cell hypothesis: immune modulation as a novel mechanism for progenitor cell therapy in cardiac muscle

Stem cell transplantation after myocardial infarction has been claimed to restore cardiac function, but the underlying mechanism remains unclear. A minority of transplanted cells become adherent in heart tissue and contribute to neovascularization, whereas many donor cells die from apoptosis. We propose that apoptosis of transplanted cells modulates local tissue reactions. Apoptotic cells impact on immune reactivity by down-regulating innate and adaptive immunity, deactivating macrophages and dendritic cells, and stimulating regulatory T cells. This leads to reduced scar formation, repressed myocardial apoptosis, and improved cardiac outcome.

Cutting edge: proangiogenic properties of alternatively activated dendritic cells

Angiogenesis plays an important role in tissue remodeling and repair during the late phase of inflammation. In the present study, we show that human dendritic cells (DC) that matured in the presence of anti-inflammatory molecules such as calcitriol, PGE2, or IL-10 (alternatively activated DC) selectively secrete the potent angiogenic cytokine vascular endothelial growth factor (VEGF) isoforms VEGF165 and VEGF121. No VEGF production was observed in immature or classically activated DC. Also, the capacity to produce VEGF was restricted to the myeloid DC subset. When implanted in the chick embryo chorioallantoic membrane, alternatively activated DC elicit a marked angiogenic response, which is inhibited by neutralizing anti-VEGF Abs and by the VEGFR-2 inhibitor SU5416. Therefore, alternatively activated DC may contribute to the resolution of the inflammatory reaction by promoting VEGF-induced angiogenesis.