Proangiogenic function of CD40 ligand-CD40 interactions

CD40 Ligand-CD40 Interaction Is an Intermediary between Inflammation and Angiogenesis in Proliferative Diabetic Retinopathy

We aimed to investigate the role of the CD40-CD40 ligand (CD40L) pathway in inflammation-mediated angiogenesis in proliferative diabetic retinopathy (PDR). We analyzed vitreous fluids and epiretinal fibrovascular membranes from PDR and nondiabetic patients, cultures of human retinal microvascular endothelial cells (HRMECs) and Müller glial cells and rat retinas with ELISA, immunohistochemistry, flow cytometry and Western blot analysis. Functional tests included measurement of blood-retinal barrier breakdown, in vitro angiogenesis and assessment of monocyte-HRMEC adherence. CD40L and CD40 levels were significantly increased in PDR vitreous samples. We demonstrated CD40L and CD40 expression in vascular endothelial cells, leukocytes and myofibroblasts in epiretinal membranes. Intravitreal administration of soluble (s)CD40L in normal rats significantly increased retinal vascular permeability and induced significant upregulation of phospho-ERK1/2, VEGF, intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1). sCD40L induced upregulation of VEGF, MMP-9, MCP-1 and HMGB1 in cultured Müller cells and phospo-ERK1/2, p65 subunit of NF-ĸB, VCAM-1 and VEGF in cultured HRMECS. TNF-α induced significant upregulation of CD40 in HRMECs and Müller cells and VEGF induced significant upregulation of CD40 in HRMECs. sCD40L induced proliferation and migration of HRMECs. We provide experimental evidence supporting the involvement of the CD40L-CD40 pathway and how it regulates inflammatory angiogenesis in PDR.

SARS-CoV-2 infection- induced growth factors play differential roles in COVID-19 pathogenesis

Aims

Biologically active molecules cytokines and growth factors (GFs) are critical regulators of tissue injury/repair and emerge as key players in COVID-19 pathophysiology. However, specific disease stage of GFs dysregulation and, whether these GFs have associations with thromboembolism and tissue injury/repair in COVID-19 remain vague.

Main methods

GF profiling in hospitalized moderate (non-ICU) and critically ill (ICU) COVID-19 patients was performed through legendPlex assay.

Key findings

Investigation revealed profound elevation of VEGF, PDGFs, EGF, TGF-α, FGF-basic, and erythropoietin (EPO) in moderate cases and decline or trend of decline with disease advancement. We found strong positive correlations of plasma VEGF, PDGFs, and EPO with endothelial dysfunction markers P-selectin and sCD40L. Interestingly, the HGF and G-CSF were upregulated at the moderate stage and remained elevated at the severe stage of COVID-19. Moreover, strong negative correlations of PDGFs (r² = 0.238, P = 0.006), EPO (r² = 0.18, P = 0.01) and EGF (r² = 0.172, P = 0.02) and positive correlation of angiopoietin-2 (r² = 0.267, P = 0.003) with D-dimer, a marker of thromboembolism, was observed. Further, plasma PDGFs (r² = 0.199, P = 0.01), EPO (r² = 0.115, P = 0.02), and EGF (r² = 0.108, P = 0.07) exhibited negative correlations with tissue injury marker, myoglobin.

Significance

Taken together, unlike cytokines, most of the assessed GFs were upregulated at the moderate stage of COVID-19. The induction of GFs likely occurs due to endothelial dysfunction and may counter the adverse effects of cytokine storms which is reflected by inverse correlations of PDGFs, EPO, and EGF with thromboembolism and tissue injury markers. The findings suggest that the assessed GFs play differential roles in the pathogenesis of COVID-19.

Role of Lipid Accumulation and Inflammation in Atherosclerosis: Focus on Molecular and Cellular Mechanisms

Atherosclerosis is a chronic lipid-driven and maladaptive inflammatory disease of arterial intima. It is characterized by the dysfunction of lipid homeostasis and signaling pathways that control the inflammation. This article reviews the role of inflammation and lipid accumulation, especially low-density lipoprotein (LDL), in the pathogenesis of atherosclerosis, with more emphasis on cellular mechanisms. Furthermore, this review will briefly highlight the role of medicinal plants, long non-coding RNA (lncRNA), and microRNAs in the pathophysiology, treatment, and prevention of atherosclerosis. Lipid homeostasis at various levels, including receptor-mediated uptake, synthesis, storage, metabolism, efflux, and its impairments are important for the development of atherosclerosis. The major source of cholesterol and lipid accumulation in the arterial wall is proatherogenic modified low-density lipoprotein (mLDL). Modified lipoproteins, such as oxidized low-density lipoprotein (ox-LDL) and LDL binding with proteoglycans of the extracellular matrix in the intima of blood vessels, cause aggregation of lipoprotein particles, endothelial damage, leukocyte recruitment, foam cell formation, and inflammation. Inflammation is the key contributor to atherosclerosis and participates in all phases of atherosclerosis. Also, several studies have shown that microRNAs and lncRNAs have appeared as key regulators of several physiological and pathophysiological processes in atherosclerosis, including regulation of HDL biogenesis, cholesterol efflux, lipid metabolism, regulating of smooth muscle proliferation, and controlling of inflammation. Thus, both lipid homeostasis and the inflammatory immune response are closely linked, and their cellular and molecular pathways interact with each other.

Cytokine release syndrome in COVID-19: Innate immune, vascular, and platelet pathogenic factors differ in severity of disease and sex

COVID-19 rapidly emerged as a crippling public health crisis in the last few months, which has presented a series health risk. Understanding of the immune response and biomarker analysis is needed to progress toward understanding disease pathology and developing improved treatment options. The goal of this study is to identify pathogenic factors that are linked to disease severity and patient characteristics. Patients with COVID-19 who were hospitalized from March 17 to June 5, 2020 were analyzed for clinical features of disease and soluble plasma cytokines in association with disease severity and sex. Data from COVID-19 patients with acute illness were examined along with an age- and gender-matched control cohort. We identified a group of 16 soluble factors that were found to be increased in COVID-19 patients compared to controls, whereas 2 factors were decreased. In addition to inflammatory cytokines, we found significant increases in factors known to mediate vasculitis and vascular remodeling (PDGF-AA, PDGF-AB-BB, soluble CD40L (sCD40L), FGF, and IP10). Four factors such as platelet-derived growth factors, fibroblast growth factor-2, and IFN-γ-inducible protein 10 were strongly associated with severe disease and ICU admission. Th2-related factors (IL-4 and IL-13) were increased with IL-4 and sCD40L present at increased levels in males compared with females. Our analysis revealed networking clusters of cytokines and growth factors, including previously unknown roles of vascular and stromal remodeling, activation of the innate immunity, as well activation of type 2 immune responses in the immunopathogenesis of COVID-19. These data highlight biomarker associations with disease severity and sex in COVID-19 patients.

The Role of Macrophages in Aortic Dissection

Aortic dissection (AD) is a fatal disease that accounts for a large proportion of aortic-related deaths and has an incidence of about 3–4 per 100,000 individuals every year. Recent studies have found that inflammation plays an important role in the development of AD, and that macrophages are the hub of inflammation in the aortic wall. Aortic samples from AD patients reveal a large amount of macrophage infiltration. The sites of macrophage infiltration and activity vary throughout the different stages of AD, with involvement even in the tissue repair phase of AD. Angiotensin II has been shown to be an important factor in the stimulation of macrophage activity. Stimulated macrophages can secrete metalloproteinases, inflammatory factors and other substances to cause matrix destruction, smooth muscle cell apoptosis, neovascularization and more, all of which destroy the aortic wall structure. At the same time, there are a number of factors that regulate macrophages to reduce the formation of AD and induce the repair of torn aortic tissues. The aim of this review is to take a close look at the roles of macrophages throughout the course of AD disease.

Comparison of the Effect of Two Hyaluronic Acid Preparations on Fibroblast and Endothelial Cell Functions Related to Angiogenesis

Hyaluronic acid (HA) is used in substitutive and aesthetic medicine with various applications. Ultrapure absorbable HA (Bioregen^®) and a mix of reticulated and free low molecular weight HA (Regenyal Idea Bioexpander®) (both provided by Regenyal Laboratories Srl, San Benedetto del Tronto (AP), Italy) represent a reliable hydrating device and skin filler, useful for skin blemishes, lines and wrinkles, and lip widening, respectively. The commercial products are known for their safety, but data on the molecular, cellular, and tissue responses are lacking. We aimed to evaluate the bioavailability and the pro-angiogenic features of the products Bioregen^® and Bioexpander^® in vitro on cultured endothelial cells (ECs) and dermal fibroblasts in vivo when injected into experimental animals. When added to fibroblasts and ECs, Bioexpander^® induced cell migration. The two HA preparations were well tolerated, while a transient proangiogenic behavior of Bioexpander^®, when implanted subcutaneously in mice, was found. The neovascular response was evident in the first week with higher levels of VEGF and FGF-2 before undergoing regression. In conclusion, our data strengthen the safety of HA synthetic preparations both in vitro and in vivo. Even if a proangiogenic response is documented, it is modest and transient, leading to tissue recovery and absence of an inflammatory infiltrate.

A PPARγ-dependent miR-424/503-CD40 axis regulates inflammation mediated angiogenesis

Activation of the endothelium by pro-inflammatory stimuli plays a key role in the pathogenesis of a multitude of vascular diseases. Angiogenesis is a crucial component of the vascular response associated with inflammatory signaling. The CD40/CD40 ligand dyad in endothelial cells (EC) has a central role in promoting vascular inflammatory response; however, the molecular mechanism underlying this component of inflammation and angiogenesis is not fully understood. Here we report a novel microRNA mediated suppression of endothelial CD40 expression. We found that CD40 is closely regulated by miR-424 and miR-503, which directly target its 3′ untranslated region. Pro-inflammatory stimuli led to increased endothelial CD40 expression, at least in part due to decreased miR-424 and miR-503 expression. In addition, miR-424 and miR-503 reduced LPS induced EC sprouting, migration and tube formation. Moreover, we found that miR-424 and miR-503 expression is directly regulated by peroxisome proliferator-activated receptor gamma (PPARγ), whose endothelial expression and activity are decreased in response to inflammatory factors. Finally, we demonstrate that mice with endothelial-specific deletion of miR-322 (miR-424 ortholog) and miR-503 have augmented angiogenic response to LPS in a Matrigel plug assay. Overall, these studies identify a PPARγ-dependent miR-424/503-CD40 signaling axis that is critical for regulation of inflammation mediated angiogenesis.

Exposure to Fine Particulate Air Pollution Is Associated With Endothelial Injury and Systemic Inflammation

RATIONALE

Epidemiological evidence indicates that exposures to fine particulate matter air pollution (PM_2.5) contribute to global burden of disease, primarily as a result of increased risk of cardiovascular morbidity and mortality. However, mechanisms by which PM_2.5 exposure induces cardiovascular injury remain unclear. PM_2.5-induced endothelial dysfunction and systemic inflammation have been implicated, but direct evidence is lacking.

OBJECTIVE

To examine whether acute exposure to PM_2.5 is associated with endothelial injury and systemic inflammation.

METHODS AND RESULTS

Blood was collected from healthy, nonsmoking, young adults during 3 study periods that included episodes of elevated PM_2.5 levels. Microparticles and immune cells in blood were measured by flow cytometry, and plasma cytokine/growth factors were measured using multiplexing laser beads. PM_2.5 exposure was associated with the elevated levels of endothelial microparticles (annexin V⁺/CD41^-/CD31⁺), including subtypes expressing arterial-, venous-, and lung-specific markers, but not microparticles expressing CD62⁺. These changes were accompanied by suppressed circulating levels of proangiogenic growth factors (EGF [epidermal growth factor], sCD40L [soluble CD40 ligand], PDGF [platelet-derived growth factor], RANTES [regulated on activation, normal T-cell-expressed and secreted], GROα [growth-regulated protein α], and VEGF [vascular endothelial growth factor]), and an increase in the levels of antiangiogenic (TNFα [tumor necrosis factor α], IP-10 [interferon γ-induced protein 10]), and proinflammatory cytokines (MCP-1 [monocyte chemoattractant protein 1], MIP-1α/β [macrophage inflammatory protein 1α/β], IL-6 [interleukin 6], and IL-1β [interleukin 1β]), and markers of endothelial adhesion (sICAM-1 [soluble intercellular adhesion molecule 1] and sVCAM-1 [soluble vascular cellular adhesion molecule 1]). PM_2.5 exposure was also associated with an inflammatory response characterized by elevated levels of circulating CD14⁺, CD16⁺, CD4⁺, and CD8⁺, but not CD19⁺ cells.

CONCLUSIONS

Episodic PM_2.5 exposures are associated with increased endothelial cell apoptosis, an antiangiogenic plasma profile, and elevated levels of circulating monocytes and T, but not B, lymphocytes. These changes could contribute to the pathogenic sequelae of atherogenesis and acute coronary events.

CD40 in coronary artery disease: a matter of macrophages?

Coronary artery disease (CAD), also known as ischemic heart disease (IHD), is the leading cause of mortality in the western world, with developing countries showing a similar trend. With the increased understanding of the role of the immune system and inflammation in coronary artery disease, it was shown that macrophages play a major role in this disease. Costimulatory molecules are important regulators of inflammation, and especially, the CD40L-CD40 axis is of importance in the pathogenesis of cardiovascular disease. Although it was shown that CD40 can mediate macrophage function, its exact role in macrophage biology has not gained much attention in cardiovascular disease. Therefore, the goal of this review is to give an overview on the role of macrophage-specific CD40 in cardiovascular disease, with a focus on coronary artery disease. We will discuss the function of CD40 on the macrophage and its (proposed) role in the reduction of atherosclerosis, the reduction of neointima formation, and the stimulation of arteriogenesis.

Diagnostic utility of VEGF and soluble CD40L levels in serum of Alzheimer's patients

BACKGROUND

Non-invasive blood-based biomarkers are eagerly awaited for the diagnosis of Alzheimer's disease (AD). The present study aimed to evaluate the individual and combined diagnostic value of soluble CD40 ligand (sCD40L) and vascular endothelial growth factor (VEGF) for AD.

METHODS

Fifty patients with AD and forty gender and age-matched control participants with standardized clinical assessments and neuroimaging measures were enrolled. VEGF and sCD40L were qualified in 90 subjects using immunomagnetic beads assay.

RESULTS

To evaluate the individual and combined diagnostic value of sCD40L and VEGF for AD, receiver operating characteristic curves were generated and logistic regression analysis was conducted. The AUCs (area under ROCs) of sCD40L and VEGF and their corresponding 95% confidence interval (CI) were 0.824 (95% CI: 0.737-0.910) and 0.731 (95% CI: 0.622-0.839), respectively. Combined ROC analysis based on these 2 biomarkers revealed an elevated AUC of 0.858 (95% CI: 0.775-0.941), which indicates an additive effect in the diagnostic value of these two biomarkers.

CONCLUSIONS

We identified the feasibility of a blood-based biomarker approach in AD diagnostics though the results warrant validation in large-scale studies. A combination of sCD40L and VEGF could be a useful diagnostic biomarker for future clinical trials with AD and may act as a suitable add-on biomarker to the panel of markers already existing for AD.

Immune impairments in multiple myeloma bone marrow mesenchymal stromal cells

In multiple myeloma (MM), bone marrow mesenchymal stromal cells (BM-MSCs) play an important role in pathogenesis and disease progression by supporting myeloma cell growth and immune escape. Previous studies have suggested that direct and indirect interactions between malignant cells and BM-MSCs result in constitutive abnormal immunomodulatory capacities in MM BM-MSCs. The aim of this study was to investigate the mechanisms that underlie these MM BM-MSCs abnormalities. We demonstrated that MM BM-MSCs exhibit abnormal expression of CD40/40L, VCAM1, ICAM-1, LFA-3, HO-1, HLA-DR and HLA-ABC. Furthermore, an overproduction of IL-6 (1,806 ± 152.5 vs 719.6 ± 18.22 ng/mL; p = 0.035) and a reduced secretion of IL-10 (136 ± 15.02 vs 346.4 ± 35.32 ng/mL; p = 0.015) were quantified in culture medium when MM BM-MSCs were co-cultured with T lymphocytes compared to co-cultures with healthy donor (HD) BM-MSCs. An increased Th17/Treg ratio was observed when T cells were co-cultured with MM BM-MSCs compared to co-cultures with HD BM-MSCs (0.955 vs 0.055). Together, these observations demonstrated that altered immunomodulation capacities of MM BM-MSCs were linked to variations in their immunogenicity and secretion profile. These alterations lead not only to a reduced inhibition of T cell proliferation but also to a shift in the Th17/Treg balance. We identified factors that are potentially responsible for these alterations, such as IL-6, VCAM-1 and CD40, which could also be associated with MM pathogenesis and progression.

Chronic allograft rejection: a fresh look

PURPOSE OF REVIEW

New developments suggest that the graft itself and molecules expressed within the graft microenvironment dictate the phenotype and evolution of chronic rejection.

RECENT FINDINGS

Once ischemia-reperfusion injury, cellular and humoral immune responses target the microvasculature, the associated local tissue hypoxia results in hypoxia-inducible factor 1α-dependent expression of pro-inflammatory and proangiogenic growth factors including vascular endothelial growth factor (VEGF) as a physiological response to injury. Local expression of VEGF can promote the recruitment of alloimune T cells into the graft. mTOR/Akt signaling within endothelial cells regulates cytokine- and alloantibody-induced activation and proliferation and their proinflammatory phenotype. Inhibition of mTOR and/or Akt results in an anti-inflammatory phenotype and enables the expression of coinhibitory molecules that limit local T cell reactivation and promotes immunoregulation. Semaphorin family molecules may bind to neuropilin-1 on regulatory T cell subsets to stabilize functional responses. Ligation of neuropilin-1 on Tregs also inhibits Akt-induced responses suggesting common theme for enhancing local immunoregulation and long-term graft survival.

SUMMARY

Events within the graft initiated by mTOR/Akt-induced signaling promote the development of chronic rejection. Semaphorin-neuropilin biology represents a novel avenue for targeting this biology and warrants further investigation.

Anti-VEGF antibody enhances the antitumor effect of CD40

As its central immunomodulatory effects, CD40 induces interleukin (IL)-12-dependent antitumor immune responses; as its local protumor effects, CD40 induces the expression of vascular endothelial growth factor (VEGF) that promotes tumor angiogenesis and growth. Therefore, using a previously established tumor model in mouse, we examined if the antitumor functions of CD40 are self-limited by VEGF induction. We observed that as the tumor mass grew during day 6 to day 18, VEGF expression in the tumor peaked with concomitant decrease in expressions of CD40 and IL-12 but not of IL-10. Among the angiogenic factors, VEGF-B, VEGFR-1, VEGFR-2, angiopoietin-1 and Tie2 expressions decreased, whereas the expressions of angiopoietin-2 and angiopoietin-3 increased with tumor growth. As significant changes in the expressions of these factors were observed on day 6, we treated the tumor-bearing mice with the agonistic anti-CD40 antibody or neutralizing anti-VEGF antibody-alone or in combination-from the fifth day after the injection of tumor cells. The anti-VEGF antibody significantly enhanced the antitumor effects of the anti-CD40 antibody, as observed through increased survival of the mice, accompanied by reduced angiogenesis and angiopoietin-2 expression but higher T-cell proliferation in response to tumor antigens, increased interferon-γ production and tumor cell cytotoxicity and higher levels of tumor antigen-specific serum IgM, IgG1 and IgG2a, indicating B-cell activation. Thus, our data show for the first time that the combined treatment with an agonistic anti-CD40 antibody and a neutralizing anti-VEGF antibody, which increases antitumor immune response or reduces local angiogenesis, respectively, is a novel antitumor strategy.

The relationship between intervention in the CD40 signal pathway and choroidal neovascularization

Age-related macular degeneration, pathologic myopia, ocular trauma, and other eye diseases can cause choroidal neovascularization (CNV). In recent years, photodynamic therapy (PDT), anti-vascular endothelial growth factor (anti-VEGF) medications, laser treatment, and other measures against CNV have been gradually applied in the clinical setting and in some cases have achieved good results. However, the pathogenesis of CNV has not been fully elucidated. The costimulatory system made up of cluster of differentiation 40 protein (CD40) and its ligand (CD40L) is an important signal transduction pathway among immune cells. The activation of CD40 can also stimulate the secretion of a variety of angiogenic growth factors (eg, VEGF) and basic fibroblast growth factors that might lead to CNV. The high level expression of CD40 and CD40L has been detected in CNV diseases. Interference with the CD40 signaling pathway may become a new target for CNV treatment. We review the relationship between CD40, CD40L, and CNV.

The multitasking role of macrophages in Stanford type A acute aortic dissection

OBJECTIVES

The aim of the study was to determine whether the release by macrophages of matrix metalloproteinase (MMP)-12 and vascular endothelial growth factor (VEGF) - leading to inflammation, matrix degradation and neoangiogenesis - represents an effective pathway that underlies aortic wall remodeling in Stanford type A acute aortic dissection (AAD).

METHODS

Twenty-one consecutive patients with no genetic predisposition, with Stanford type A AAD were selected. In each patient, the levels of serum VEGF, MMP-12, serum interleukin (IL)-6, IL-8 and monocyte chemoattractant protein (MCP)-1 were evaluated using enzyme-linked immunosorbent assay. Ascending aortic specimens were collected for immunohistochemical identification of any presence of inflammatory infiltrate, VEGF and CD31 expression.

RESULTS

A significant increase in serum VEGF (p = 0.044), MMP-12 (p = 0.007), IL-6 (p = 0.0001), IL-8 (p = 0.0001) and MCP-1 (p = 0.0001) levels was observed in the AAD group compared to the control group. Furthermore, all AAD samples were positive for VEGF in the tunica media and showed vessel growth and immune-inflammatory infiltrate. A large number of cases (62.79%) showed inflammation at the edge of the dissection and approximately half (51.42%) showed neovessels growing at the edge of the dissection.

CONCLUSIONS

The results suggest that VEGF-mediated angiogenesis and matrix degradation play a role in AAD. Finally, we believe that MMP-12 should be considered a marker of AAD.

Serum concentrations and clinical significance of soluble CD40 ligand in patients with multiple myeloma

Multiple myeloma (MM) is a disease of plasma cells that express the CD40 receptor. Binding of the CD40 by its natural ligand, CD40 ligand (CD40L), produces growth arrest and/or apoptosis in MM. To evaluate serum levels of soluble CD40L (sCD40L) in MM patients and to correlate them with markers of disease activity and angiogenesis, such as vascular endothelial growth factor (VEGF), hepatocyte growth factor (HGF), interleukin-6 (IL-6), proliferation marker Ki-67 proliferation index (Ki-67 PI) and bone marrow plasma cell infiltration, fifty-eight MM patients were studied in diagnosis and 43 of them after completion of treatment. Serum levels of sCD40L, VEGF, HGF and IL-6 were measured by ELISA, whereas Ki-67 PI and bone marrow plasma cell infiltration were measured by immunohistochemistry. Pre-treatment levels of sCD40L in MM patients were higher compared to controls and to their levels after effective treatment. Treatment regimen did not affect the degree of reduction of sCD40L levels, whereas patient in partial remission had increased levels compared to those with better response. Significant differences were found among disease stages. There were also positive correlations between CD40L with HGF, VEGF, IL-6 and Ki-67 PI. Elevated serum sCD40L is found in patients with advanced MM stage and can be reduced after effective treatment. Increased levels of this mediator are correlated with angiogenic cytokines, providing evidences that CD40L/CD40 interactions play a significant role in the mechanisms of angiogenesis in MM patients.

TRAF6 inhibits proangiogenic signals in endothelial cells and regulates the expression of vascular endothelial growth factor

TNF-family molecules induce the expression Vascular Endothelial Growth Factor (VEGF) in endothelial cells (EC) and elicit signaling responses that result in angiogenesis. However, the role of TNF-receptor associated factors (TRAFs) as upstream regulators of VEGF expression or as mediators of angiogenesis is not known. In this study, HUVEC were cotransfected with a full-length VEGF promoter-luciferase construct and siRNAs to TRAF 1, -2, -3, -5, -6, and promoter activity was measured. Paradoxically, rather than inhibiting VEGF expression, we found that knockdown of TRAF6 resulted in a 4-6-fold increase in basal VEGF promoter activity compared to control siRNA-transfected EC (P<0.0001). In addition, knockdown of TRAF 1, -2, -3 or -5 resulted in a slight increase or no change in VEGF promoter activation. Using [(3)H]thymidine incorporation assays as well as the in vitro wound healing assay, we also found that basal rates of EC proliferation and migration were increased following TRAF6 knockdown; and this response was inhibited by the addition of a blocking anti-VEGF antibody into cell cultures. Using a limited protein array to gain insight into TRAF6-dependent intermediary signaling responses, we observed that TRAF6 knockdown resulted in an increase in the activity of Src family kinases. In addition, we found that treatment with AZD-0530, a pharmacological Src inhibitor, reduced the regulatory effect of TRAF6 knockdown on VEGF promoter activity. Collectively, these findings define a novel pro-angiogenic signaling response in EC that is regulated by TRAF6.

Synergistic CD40 signaling on APCs and CD8 T cells drives efficient CD8 response and memory differentiation

The role of CD4 help during CD8 response and memory differentiation has been clearly demonstrated in different experimental models. However, the exact mechanisms of CD4 help remain largely unknown and preclude replacement therapy to develop. Interestingly, studies have shown that administration of an agonist aCD40ab can substitute CD4 help in vitro and in vivo, whereas the targets of this antibody remain elusive. In this study, we address the exact role of CD40 expression on APCs and CD8 T cells using aCD40ab treatment in mice. We demonstrate that aCD40 antibodies have synergetic effects on APCs and CD8 T cells. Full efficiency of aCD40 treatment requires CD40 expression on both populations: if one of these cell populations is CD40-deficient, the CD8 T cell response is impaired. Most importantly, direct CD40 signaling on APCs and CD8 T cells affects CD8 T cell differentiation differently. In our model, CD40 expression on APCs plays an important but dispensable role on CD8 T cell expansion and effector functions during the early phase of the immune response. Conversely, CD40 on CD8 T cells is crucial and nonredundant for their progressive differentiation into memory cells. Altogether, these results highlight that CD40-CD40L-dependent and independent effects of CD4 help to drive a complete CD8 T cell differentiation.

The role of costimulatory receptors of the tumour necrosis factor receptor family in atherosclerosis

Atherosclerosis is a chronic inflammatory disease that is mediated by both the innate and adaptive immune responses. T lymphocytes, that together with B cells are the cellular effectors of the adaptive immune system, are currently endowed with crucial roles in the development and progression of atherosclerosis. Costimulatory receptors are a class of molecules expressed by T lymphocytes that regulate the activation of T cells and the generation of effector T-cell responses. In this review we present the roles of costimulatory receptors of the tumour necrosis factor receptor (TNFR) superfamily in atherosclerosis and discuss the implications for future therapies that could be used to specifically modulate the immune response of pathogenic T cells in this disease.

Microparticles, Vascular Function, and Atherothrombosis

Membrane-shed submicron microparticles (MPs) are released after cell activation or apoptosis. High levels of MPs circulate in the blood of patients with atherothrombotic diseases, where they could serve as a useful biomarker of vascular injury and a potential predictor of cardiovascular mortality and major adverse cardiovascular events. Atherosclerotic lesions also accumulate large numbers of MPs of leukocyte, smooth muscle cell, endothelial, and erythrocyte origin. A large body of evidence supports the role of MPs at different steps of atherosclerosis development, progression, and complications. Circulating MPs impair the atheroprotective function of the vascular endothelium, at least partly, by decreased nitric oxide synthesis. Plaque MPs favor local inflammation by augmenting the expression of adhesion molecule, such as intercellular adhesion molecule -1 at the surface of endothelial cell, and monocyte recruitment within the lesion. In addition, plaque MPs stimulate angiogenesis, a key event in the transition from stable to unstable lesions. MPs also may promote local cell apoptosis, leading to the release and accumulation of new MPs, and thus creating a vicious circle. Furthermore, highly thrombogenic plaque MPs could increase thrombus formation at the time of rupture, together with circulating MPs released in this context by activated platelets and leukocytes. Finally, MPs also could participate in repairing the consequences of arterial occlusion and tissue ischemia by promoting postischemic neovascularization.

The sequential expression of CD40 and Icam2 defines progressive steps in the formation of blood precursors from the mesoderm germ layer

During embryogenesis, the hematopoietic program is specified from the mesodermal germ layer through the formation of hemangioblast. This precursor gives rise to a hemogenic endothelium that later on matures to generate primitive and definitive hematopoietic precursors. A lack of specific cell surface markers to identify cells with discrete developmental potential is a major hurdle in the quest to further understand the cellular and molecular program governing blood formation. In the present study, we identify CD40 and Icam2, two markers typically associated with the adult immunological compartment, as expressed at the earliest stages of blood specification both in vitro and in vivo. Using in vitro serum-free culture conditions that support the efficient and directed differentiation of embryonic stem cells, we show that the sequential expression of CD40 and Icam2 delineate a transition in the acquisition of the blood potential from hemangioblast to hemogenic endothelium leading to the formation of primitive and definitive hematopoietic progenitors. CD40 is transiently expressed at the onset of blood development and marks first the hemangioblast then the hemogenic endothelium but is no longer expressed on fully committed hematopoietic precursors within the fetal liver. In contrast, Icam2 is first expressed on the hemogenic endothelium and its expression persists on fetal liver hematopoietic progenitors. Taken together, our data identify novel cell surface markers allowing us to further refine our understanding of the events marking progressive hematopoietic commitment from the mesoderm germ layer.

Soluble CD40 ligand impairs the function of peripheral blood angiogenic outgrowth cells and increases neointimal formation after arterial injury

BACKGROUND

Recent work has revealed an essential involvement of soluble CD40 ligand (sCD40L) in inflammation and atherosclerosis. We investigated whether sCD40L functionally affects peripheral blood-derived angiogenic early outgrowth cells (EOCs) and neointimal remodeling after arterial injury.

METHODS AND RESULTS

Besides myeloid and endothelial markers, cultured human EOCs strongly expressed CD40 mRNA and protein. EOC adhesion to fibronectin, fibrinogen, intercellular adhesion molecule-1, and vascular cell adhesion molecule-1 under flow conditions, as well as their transmigration toward stromal cell-derived factor-1alpha, was dose-dependently reduced after preincubation with recombinant human sCD40L for 24 hours. Integrin expression was unaffected by sCD40L, implying that integrin adhesiveness was attenuated. Surface-immobilized CD40L supported much lower adhesion of EOCs than fibronectin. Treatment of EOCs with sCD40L increased superoxide anion production and decreased viability and proliferation. Notably, CD40(-/-) mice displayed reduced neointima and improved re-endothelialization after carotid wire injury compared with wild-type mice, and therapeutic infusion of control EOCs but not EOCs pretreated with sCD40L attenuated neointimal growth after wire injury in nude mice. Furthermore, neointimal growth was more markedly diminished by infusion of spleen-derived CD40(-/-) mouse EOCs than by that of wild-type EOCs. Preincubation of wild-type EOCs but not CD40(-/-) EOCs with sCD40L before their infusion markedly aggravated neointimal formation. Treatment with sCD40L attenuated luminal incorporation of EOCs and accelerated neointimal progression.

CONCLUSIONS

Endothelial dysfunction due to persistently elevated plasma levels of sCD40L may be attributable to an impairment of EOC function. Hence, in the context of arterial injury, therapeutic blockade of sCD40L may provide a novel strategy for accelerating endothelial regeneration and attenuating neointimal remodeling.

Memory T cells in Rhesus macaques

The Rhesus macaque (Macaca mulatta) is one of the best studied species of Old World monkeys. DNA sequencing of the entire Rhesus macaque genome, completed in 2007, has demonstrated that humans and macaques share about 93% of their nucleotide sequence. Rhesus macaques have been widely used for medical research including drug testing, neurology, behavioral and cognitive science, reproduction, xenotransplantation and genetics. Because of the Rhesus macaque's sensitivity to bacteria, parasites and viruses that cause similar disease in humans, these animals represent an excellent model to study infectious diseases. The recent pandemic of HIV and the discovery of SIV, a lentivirus genetically related to HIV Type 1 that causes AIDS in Rhesus macaques, have prompted the development of reagents that can be used to study innate and adaptive immune responses in macaques at the single cell level. This review will focus on the distribution of memory cells in the different immunologic compartments of Rhesus macaques. In addition, the strategies available to manipulate memory cells in Rhesus macaques to understand their trafficking and function will be discussed. Emphasis is placed on studies of memory cells in macaques infected with SIV because many studies are available. Lastly, we highlight the usefulness of the Rhesus macaque model in studies related to the aging of the immune system.

CD40-induced signaling in human endothelial cells results in mTORC2- and Akt-dependent expression of vascular endothelial growth factor in vitro and in vivo

We have examined CD40-dependent signals in endothelial cells (EC) mediating the expression of vascular endothelial growth factor (VEGF) and VEGF-induced angiogenesis. We treated confluent cultures of EC with soluble CD40L (sCD40L), and by Western blot found a marked increase in the phosphorylation of Akt, 4EBP-1, and S6K1, compared with untreated cells. EC were transfected with a full-length VEGF promoter-luciferase construct and cultured in the absence or presence of rapamycin and sCD40L. We found that rapamycin, which blocks mTORC1 and mTORC2 signaling, inhibited sCD40L-mediated transactivation of VEGF. In addition, by Western blot, we found that the transfection of EC with small interfering RNA (siRNA) to rictor (to inhibit mTORC2), and not raptor (to inhibit mTORC1), inhibited sCD40L-dependent protein expression of VEGF. In additions, we found that basal levels of phosphorylated Akt as well as VEGF were increased in EC transfected with the raptor siRNA. Also, rapamycin failed to inhibit VEGF promoter activation, as well as VEGF protein expression in EC transfected with a constitutively active construct of Akt, further demonstrating that mTORC1 is not necessary for CD40- and Akt-induced expression of VEGF. Finally, we injected human CD40L-transfected fibroblasts or mock transfectants into human skin on SCID mice. We found that the injection of CD40L transfectants, but not mock cells, resulted in VEGF expression and mediated a marked angiogenesis reaction, and this response was reduced in mice treated with rapamycin. Together, these observations indicate that mTORC2 and Akt facilitate CD40-inducible expression of VEGF in EC, which is of clinical importance in tumor growth and the progression of chronic inflammatory diseases.

CD40 ligand+ microparticles from human atherosclerotic plaques stimulate endothelial proliferation and angiogenesis a potential mechanism for intraplaque neovascularization

OBJECTIVES

Our goal was to demonstrate that microparticles (MPs) are the endogenous signal leading to neovessel formation through CD40 ligation in human atherosclerotic plaques.

BACKGROUND

Vulnerable atherosclerotic plaques prone to rupture are characterized by an increased number of vasa vasorum and frequent intraplaque hemorrhage. Although inflammatory cytokines, growth factors, or CD40/CD40 ligand (CD40L) are possible candidates, the mechanism of atherosclerotic plaque neovascularization remains unknown. Atherosclerotic plaques contain large amounts of membrane-shed submicron MPs released after cell activation or apoptosis.

METHODS

Microparticles were isolated from endarterectomy specimens surgically obtained from 26 patients and characterized by phosphatidylserine exposure and specific markers of cellular origin.

RESULTS

Plaque MPs increased both endothelial proliferation assessed by (3)H-thymidine incorporation and cell number and stimulated in vivo angiogenesis in Matrigel (BD Biosciences, San Diego, California) assays performed in wild-type and BalbC/Nude mice, whereas circulating MPs had no effect. Microparticles from symptomatic patients expressed more CD40L and were more potent in inducing endothelial proliferation, when compared with asymptomatic plaque MPs. Most of CD40L+ MPs (93%) isolated from human plaques were of macrophage origin. Microparticle-induced endothelial proliferation was impaired by CD40L or CD40-neutralizing antibodies and abolished after endothelial CD40-ribonucleic acid silencing. In addition, the proangiogenic effect of plaque MPs was abolished in Matrigel assays performed in the presence of CD40L-neutralizing antibodies or in CD40-deficient mice.

CONCLUSIONS

These results demonstrate that MPs isolated from human atherosclerotic lesions express CD40L, stimulate endothelial cell proliferation after CD40 ligation, and promote in vivo angiogenesis. Therefore, MPs could represent a major determinant of intraplaque neovascularization and plaque vulnerability.

High-sensitivity C-reactive protein and soluble CD40 ligand as indices of inflammation and platelet activation in 880 patients with nonvalvular atrial fibrillation: relationship to stroke risk factors, stroke risk stratification schema, and prognosis

BACKGROUND AND PURPOSE

There is now considerable evidence that atrial fibrillation is associated with an inflammatory state. We tested the hypothesis that plasma levels of C-reactive protein (CRP; an index of inflammation) and soluble CD40 ligand (an index of platelet activation, with links to inflammation) could be related to 3 established stroke risk stratification schema (SPAF, CHADS(2), and NICE), recognized stroke risk factors or other cardiovascular disease, and prognosis.

METHODS

We studied 880 subjects with atrial fibrillation recruited from subjects receiving aspirin 325 mg/d (alone or combined with fixed inefficacious doses of warfarin) from the Stroke Prevention in Atrial Fibrillation (SPAF) III clinical trial. CRP and soluble CD40 ligand were measured by enzyme-linked immunosorbent assay.

RESULTS

With respect to the SPAF III stroke risk stratification criteria, those with moderate to high risk had the highest levels of CRP (Kruskal Wallis test, P<0.001), but those with the highest risk had the lowest levels of soluble CD40 ligand (P=0.01). Similarly, CRP levels increased in a positive fashion with increasing stroke risk with respect to the CHADS(2) and NICE risk stratification criteria, whereas soluble CD40 ligand levels were negatively associated with stroke risk. CRP levels were higher among those patients with raised body mass index, diabetes, hypertension, ischemic heart disease, peripheral vascular disease, and recent heart failure, but not those with thromboembolism. Patients were followed-up for a mean time of 453 (standard deviation, 229) days, and all-cause mortality (log rank test, P=0.001), and vascular events (P=0.05), but not stroke, were more common in patients with high CRP levels. Soluble CD40 ligand levels were not related to stroke, vascular events, or all-cause mortality.

CONCLUSIONS

Among atrial fibrillation patients, CRP was positively correlated to stroke risk and related to stroke risk factors and prognosis (mortality, vascular events). Soluble CD40 ligand levels were lowest in those at moderate to high risk of stroke and not related to prognosis. The use of CRP in risk stratification for atrial fibrillation merits further study.

Giving blood: a new role for CD40 in tumorigenesis

CD40 was initially identified as a receptor expressed by B cells that is crucial for inducing an effective adaptive immune response. CD40 was subsequently shown to be expressed by endothelial cells and to promote angiogenesis. New data now show that in tumor-prone transgenic mice, CD40-mediated neovascularization is essential for early stage tumorigenicity. This suggests, at least in this mouse model, that CD40 has an important role in the angiogenic process that is coupled to carcinogenesis, a finding that could lead to novel therapeutic opportunities.

Triggering CD40 on endothelial cells contributes to tumor growth

Inflammatory cells can either promote or inhibit tumor growth. Here we studied whether CD40, a key molecule for adaptive immune response, has any role in mammary carcinogenesis of BALB/NeuT transgenic tumor-prone mice. We transferred the HER2/neu oncogene into CD40-null background to obtain the CD40-KO/NeuT strain. CD40-KO/NeuT mice showed delayed tumor onset and reduced tumor multiplicity. BM (BM) transplantation experiments excluded a role of BM-derived cells in the reduced tumorigenicity associated with CD40 deficiency. Rather, CD40 expressed by endothelial cells (ECs) takes part to the angiogenic process. Accordingly, large vessels, well organized around the tumor lobular structures, characterize BALB/NeuT tumors, whereas tiny numerous vessels with scarce extracellular matrix are dispersed in the parenchyma of poorly organized CD40-KO/NeuT tumors.

Activated platelets, which may interact with and activate ECs, are a possible source of CD40L. Their localization within tumor vessels prompted the idea of treating BALB/NeuT and CD40-KO/NeuT mice chronically with the anti-platelet drug clopidogrel, known to inhibit platelet CD40L expression. Treatment of BALB/NeuT mice reduced tumor growth to a level similar to CD40-deficient mice, whereas CD40-KO/NeuT mice treated or not showed the same attenuated tumor outgrowth, indicating that activated platelets are the likely source of CD40L in this model. Collectively, these data point to a participation of CD40/CD40L in the angiogenic processes associated with mammary carcinogenesis of BALB/NeuT mice.

Vascular endothelial growth factor-induced signaling pathways in endothelial cells that mediate overexpression of the chemokine IFN-gamma-inducible protein of 10 kDa in vitro and in vivo

Vascular endothelial growth factor (VEGF), an angiogenesis factor, has recently been found to have potent proinflammatory properties in vivo. However, the mechanism by which it mediates inflammation is poorly understood. In this study, we have evaluated the function of VEGF on the induced expression and function of the T cell chemoattractant chemokine IFN-gamma-inducible protein of 10 kDa (IP-10). In vitro, we find that VEGF augments the effect of IFN-gamma on the induction of IP-10 mRNA and protein expression in endothelial cells. Moreover, we show that VEGF and IFN-gamma regulate the activation of the IP-10 promoter, and that the kinases PI3K, phosphoinositide-dependent kinase 1, and Akt act as intermediary signaling molecules for cytokine-inducible IP-10 transcriptional activation in endothelial cells. To examine whether VEGF is functional for IP-10 expression in vivo, Chinese hamster ovary cells that were designed to secrete VEGF were injected s.c. into the skin of nude mice and were found to mediate a time-dependent increase in IP-10 mRNA. This response was reduced in animals treated systemically with the PI3K inhibitor wortmannin. When the Chinese hamster ovary cells expressing VEGF plasmid were injected s.c. into C57BL/6 wild-type or CXCR3-/- mice, they elicited an inflammatory reaction in wild-type but not in CXCR3-/- mice. Collectively, these findings indicate that VEGF-induced augmentation of IP-10 expression is a major mechanism underlying its proinflammatory function.

Vascular endothelial growth factor antagonist modulates leukocyte trafficking and protects mouse livers against ischemia/reperfusion injury

Although hypoxia stimulates the expression of vascular endothelial growth factor (VEGF), little is known of the role or mechanism by which VEGF functions after ischemia and reperfusion (I/R) injury. In this report, we first evaluated the expression of VEGF in a mouse model of liver warm ischemia. We found that the expression of VEGF increased after ischemia but peaked between 2 and 6 hours after reperfusion. Mice were treated with a neutralizing anti-mouse VEGF antiserum (anti-VEGF) or control serum daily from day -1 (1 day before the initiation of ischemia). Treatment with anti-VEGF significantly reduced serum glutaminic pyruvic transaminase levels and reduced histological evidence of hepatocellular damage compared with controls. Anti-VEGF also markedly decreased T-cell, macrophage, and neutrophil accumulation within livers and reduced the frequency of intrahepatic apoptotic terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling-positive cells. Moreover, there was a reduction in the expression of pro-inflammatory cytokines (tumor necrosis factor-alpha and interferon-gamma), chemokines (interferon-inducible protein-10 and monocyte chemoattractant protein-1) and adhesion molecules (E-selectin) in parallel with enhanced expression of anti-apoptotic genes (Bcl-2/Bcl-xl and heme oxygenase-1) in anti-VEGF-treated animals. In conclusion, hypoxia-inducible VEGF expression by hepatocytes modulates leukocyte trafficking and leukocyte-induced injury in a mouse liver model of warm I/R injury, demonstrating the importance of endogenous VEGF production in the pathophysiology of hepatic I/R injury.

Abnormal soluble CD40 ligand and C-reactive protein concentrations in hypertension: relationship to indices of angiogenesis

BACKGROUND

Abnormal inflammation, platelets and angiogenesis are involved in the pathophysiology of cardiovascular disease (CVD).

OBJECTIVE

To test the hypothesis that concentrations of high sensitive C-reactive protein (CRP, an index of inflammation) and soluble CD40 ligand (sCD40L, an index of platelet activation) would be abnormal in hypertension, and in turn, be related to plasma indices of angiogenesis, the angiopoietins-1 and -2, and vascular endothelial growth factor (VEGF), in addition to the presence or absence of CVD.

METHODS

Using a cross-sectional approach, we measured plasma concentrations of CRP, sCD40L, VEGF, and angiopoietins-1 and -2 in 147 patients with hypertension (85 with a history of CVD event/s, 62 CVD event-free) and 68 age- and sex-matched healthy controls.

RESULTS

Concentrations of sCD40L (P = 0.039), CRP (P < 0.001), angiopoietin-1 (P < 0.001), angiopoietin-2 (P = 0.003) and VEGF (P < 0.001) were all greater amongst hypertensive patients than in controls. There were no significant differences in sCD40L and VEGF concentrations between hypertensive individuals with and without CVD events, but CRP and angiopoietin-1 concentrations were significantly greater amongst those with CVD events. On multiple regression analysis, sCD40L was associated with angiopoietin-2 (P = 0.01) and VEGF (P = 0.007) in hypertensive individuals, but no such associations were found within the healthy control group.

CONCLUSION

In patients with hypertension, sCD40L was associated with increased circulating markers of abnormal angiogenesis (angiopoietin-2, VEGF). The interaction between sCD40L and angiogenesis may contribute to the pathophysiology of CVD in hypertension.

Angiogenesis and endothelial cell repair in renal disease and allograft rejection

This review discusses the concept that the turnover and replacement of endothelial cells is a major mechanism in the maintenance of vascular integrity within the kidney. CD133+CD34+KDR+ endothelial cell progenitor cells emigrate from the bone marrow and differentiate into CD34+KDR+ expressing cells, which are present in high numbers within the circulation. These progenitor cells are available for recruitment into normal or inflamed tissues to facilitate endothelial cell repair. In several forms of renal disease, proinflammatory insults mediate oxidative stress, senescence, and sloughing of endothelial cells. A lack of growth factors or an inefficient recruitment of endothelial cell progenitors results in hypoxic tissue injury and accelerates the process of chronic renal failure. Augmentation of vascular repair by the provision of growth factors such as vascular endothelial growth factor or by the transfer of progenitor cells directly into the kidney can be protective and prevent ongoing interstitial damage. In allografts, persistent injury results in excessive turnover of graft vascular endothelial cells. Moreover, chronic damage elicits a response that is associated with the recruitment of both leukocytes and endothelial cell progenitors, facilitating an overlapping process of inflammation and angiogenesis. Because the angiogenesis reaction itself is proinflammatory, this process becomes self-sustaining. Collectively, these data indicate that angiogenesis and endothelial cell turnover are important in renal inflammatory processes and allograft rejection. Manipulation of the response may have therapeutic implications to protect against injury and chronic disease processes.

Identification of H-2Db-Specific CD8+ T-Cell Epitopes From Mouse VEGFR2 That Can Inhibit Angiogenesis and Tumor Growth

Vascular endothelial growth factor receptor 2 (VEGFR2/KDR) plays a crucial role in tumor-associated angiogenesis and vascularization. It has been established that monoclonal antibodies against VEGFR2 can inhibit angiogenesis. In this study, two naturally processed CD8 T-cell epitopes (VILTNPISM and FSNSTNDILI) were identified from murine KDR. Cytotoxic T lymphocytes targeting endothelial cells could be directly monitored by KDR2 and KDR3 Elispots or major histocompatibility complex class I tetramer staining. Immunization with these two peptides effectively reduced angiogenesis and inhibited tumor growth in mouse models. Thus, vaccination with KDR peptides alone or in combination with other anti-angiogenesis agents may afford a novel immunotherapy for inhibition of tumor growth.

Association of vascular endothelial growth factor gene polymorphisms with behcet disease in a Korean population

Vascular endothelial growth factor (VEGF) is important for angiogenesis and inflammation, both of which are codependent and contribute to the pathophysiology of Behcet disease (BD). The increased expressions of VEGF have been observed in the active stage and in the ocular inflammation of BD. Polymorphisms of the VEGF gene have been associated with chronic inflammatory disease including rheumatoid arthritis. We sought to investigate whether polymorphisms on the regulatory region of the VEGF gene are associated with susceptibility of Korean patients with BD. One hundred one native Korean patients with BD and 138 healthy unrelated controls were recruited. Genotype and allele frequencies of the four selected polymorphisms (-2578, -1154, -634, and 936) were not different between the BD group and controls. Among the BD patients, the frequency of the -634 CC genotype decreased in patients with uveitis (2.6% vs. 20.6%, adjusted OR = 0.100, 95% CI 0.011-0.875, p = 0.037), although it became insignificant after correction for multiple comparisons. These results indicate that the VEGF gene polymorphisms are not associated with BD in the Korean population, but they may be involved in the development of the ocular inflammation of BD.

Atherosclerotic plaque progression and vulnerability to rupture: angiogenesis as a source of intraplaque hemorrhage

Observational studies of necrotic core progression identify intraplaque hemorrhage as a critical factor in atherosclerotic plaque growth and destabilization. The rapid accumulation of erythrocyte membranes causes an abrupt change in plaque substrate characterized by increased free cholesterol within the lipid core and excessive macrophage infiltration. Neoangiogenesis is associated closely with plaque progression, and microvascular incompetence is a likely source of intraplaque hemorrhage. Intimal neovascularization is predominantly thought to arise from the adventitia, where there are a plethora of pre-existing vasa vasorum. In lesions that have early necrotic cores, the majority of vessels invading from the adventitia occur at specific sites of medial wall disruption. A breech in the medial wall likely facilitates the rapid in-growth of microvessels from the adventitia, and exposure to an atherosclerotic environment stimulates abnormal vascular development characterized by disorganized branching and immature endothelial tubes with "leaky" imperfect linings. This network of immature blood vessels is a viable source of intraplaque hemorrhage providing erythrocyte-derived phospholipids and free cholesterol. The rapid change in plaque substrate caused by the excessive accumulation of erythrocytes may promote the transition from a stable to an unstable lesion. This review discusses the potential role of intraplaque vasa vasorum in lesion instability as it relates to plaque rupture.

Autocrine VEGF mediates the antiapoptotic effect of CD154 on CLL cells

CD154 is an important regulator of chronic lymphocytic leukaemia (CLL)-cell survival. In CLL, high serum levels of VEGF are a feature of advanced disease, and we and others have previously shown that CLL cells produce and secrete this growth factor. Since CD154 stimulates VEGF production in other cell types, and VEGF is known to promote cell survival, we examined whether the cytoprotection of CLL cells by CD154 involves VEGF. We report for the first time that treatment of CLL cells with CD154 results in increased VEGF production and demonstrate involvement of NF-kappaB in this process. Moreover, we show that CD154-induced CLL-cell survival is reduced by anti-VEGF-neutralising antibody and by inhibiting VEGF receptor (VEGFR) signalling with SU5416. However, addition of exogenous VEGF alone or blocking secreted autocrine VEGF had little or no effect on CLL-cell survival. We therefore conclude that CLL-cell cytoprotection in the presence of CD154 requires combined signalling by both CD40 and VEGFR. This combined signalling and resulting cytoprotection were shown to involve NF-kappaB activation and increased survivin production. In conclusion, our findings identify autocrine VEGF as an important mediator of the antiapoptotic effect of CD40 ligation, and thus provide new insights into CLL-cell rescue by CD154 in lymphoreticular tissues.

The CD154-CD40 T-cell co-stimulation pathway in liver ischemia and reperfusion inflammatory responses

BACKGROUND

Ischemia-reperfusion (I/R) injury is a prime antigen-independent inflammatory factor in the dysfunction of liver transplants. The precise contribution of T cells in the mechanism of I/R injury remains to be elucidated. As the CD154-CD40 co-stimulation pathway provides essential second signal in the initiation and maintenance of T-cell-dependent immune responses, this study was designed to assess the role of CD154 signaling in the pathophysiology of liver I/R injury.

METHODS

A mouse model of partial 90-min warm hepatic ischemia followed by 6 hr of reperfusion was used. Three animal groups were studied: (1) wild-type (WT) mice treated with Ad-(-gal versus Ad-CD40 immunoglobulin; (2) untreated WT versus CD154 (MR1) monoclonal antibody-treated WT mice; and (3) untreated WT versus CD154 knockout mice.

RESULTS

The disruption of CD154 signaling in all three animal groups ameliorated otherwise fulminant liver injury, as evidenced by depressed serum glutamic oxaloacetic transaminase levels, compared with controls. These beneficial effects were accompanied by depressed hepatic T-cell sequestration, local decrease of vascular endothelial growth factor expression, inhibition of tumor necrosis factor-(and T-helper type 1 cytokine production, and induction of antiapoptotic (Bcl-2/Bcl-xl) but depression of proapoptotic (caspase-3) proteins.

CONCLUSIONS

By using in parallel a gene therapy approach, pharmacologic blockade, and genetically targeted mice, these findings document the benefits of disrupting CD154 to selectively modulate inflammatory responses in liver I/R injury. This study reinforces the key role of CD154-CD40 T-cell co-stimulation in the pathophysiology of liver I/R injury.

The CD40-induced signaling pathway in endothelial cells resulting in the overexpression of vascular endothelial growth factor involves Ras and phosphatidylinositol 3-kinase

Ligation of endothelial cell (EC) CD40 induces the expression of several proinflammatory cytokines as well as angiogenesis factors, including vascular endothelial growth factor (VEGF). Moreover, despite the reported importance of CD40 in cell-mediated immunity, little is known of the CD40-induced signaling pathways in EC. In this study, we have investigated the function of the Ras signaling pathway(s) for CD40-induced overexpression of VEGF. EC were transiently transfected with a full-length VEGF promoter-luciferase construct and a dominant-inhibitory mutant of Ras (Ras17N). Following transfection, ligation of CD40 with soluble CD40 ligand resulted in a significant increase in VEGF transcriptional activation, and the inhibitory mutant of Ras blocked this CD40-induced VEGF overexpression. Using EMSA and Western blot analysis, we demonstrated that CD40-dependent binding of nuclear protein(s) to the VEGF promoter and CD40-induced VEGF protein expression in EC were also inhibited by the Ras mutant. Immunoprecipitation studies revealed that ligation of CD40 on EC promoted an increased association of Ras with its effector molecules Raf, Rho, and phosphatidylinositol 3-kinase (PI3K). But, cotransfection of effector-loop mutants of Ras determined that only PI3K was functional for Ras-induced VEGF transcription. Also, wortmanin and a dominant-inhibitory mutant of PI3K inhibited CD40-induced overexpression of VEGF. Together these findings demonstrate that both Ras and PI3K are intermediaries in CD40-induced regulation of VEGF in EC. We believe our findings are of importance in several chronic inflammatory diseases, including atherosclerosis and allograft rejection associated with both CD40-CD40 ligand signaling as well as VEGF expression and function.

CD40-induced transcriptional activation of vascular endothelial growth factor involves a 68-bp region of the promoter containing a CpG island

Vascular endothelial growth factor (VEGF) is produced by several cell types in the kidney, and its expression is tightly regulated for the maintenance of normal renal physiology. Increases or decreases in its expression are associated with proteinuria and renal disease. Recently, we found that the expression of VEGF is markedly induced following interactions between CD40 ligand (CD40L) and CD40. Here, endothelial cells (EC) or Jurkat T cell lines were transiently transfected with luciferase reporter constructs under the control of the human VEGF promoter and were treated with human soluble CD40L (sCD40L). We identified a CD40-responsive 68-bp region (bp -50 to +18) of the promoter and 43 bp within this region (bp -25 to +18) that have 97% homology to a sequence of CpG dinucleotides. A computerized search revealed that the CpG region has putative binding domains for the transcriptional repressor protein methyl CpG binding protein-2 (MeCP2). In EMSA, we found that the 43-bp methylated sequence formed four complex(es) with nuclear extracts from untreated EC and reduced binding of at least one complex when nuclear lysates from sCD40L-activated EC (30 min) were used. Supershift analysis using anti-MeCP2 demonstrated that most of the complex(es) in both untreated and sCD40L-activated EC involved interactions between the 43-bp DNA and MeCP2. In addition, we found that other CpG binding proteins may also interact with this region of the promoter. Taken together, this is the first demonstration that CpG binding transcriptional repressor proteins including MeCP2 may be of importance in VEGF biology.

Lipoprotein lipase protects bovine endothelial cells from human NK cytotoxic activity

Human lipoprotein lipase (LPL), in a dose dependent fashion, significantly inhibited spontaneous human natural killer (NK) cells, but not lymphokine-activated killer (LAK) cytotoxic activity against bovine pulmonary endothelial cells. The effect was dependent on endothelial heparan sulfate (HS) sites, since heparitinase reverted it. When HS is added before LPL, NK and LAK cytotoxicity are markedly reduced. Endothelial and NK cell priming, with LPL and HS+LPL, significantly induced CD40 and CD154 expression, respectively. Furthermore, CD40 expression was inversely proportional to lytic units (R2 = 0.9, P < 0.001). Treating endothelial cells simultaneously with indomethacin, CD154 fusion protein, and Wortmanin prevented the CD40 effect increasing xenograft rejection. LPL and HS+LPL protect bovine endothelial cells from NK cytotoxicity by inducing CD40, CD154 expression, and secretion of soluble factors. The high, non-modulated expression of adhesion receptors and the low number of HS sites account for the minor effect of CD40 in LAK cytotoxic responses against bovine endothelial cells.

Proinflammatory functions of vascular endothelial growth factor in alloimmunity

Vascular endothelial growth factor (VEGF), an established angiogenesis factor, is expressed in allografts undergoing rejection, but its function in the rejection process has not been defined. Here, we initially determined that VEGF is functional in the trafficking of human T cells into skin allografts in vivo in the humanized SCID mouse. In vitro, we found that VEGF enhanced endothelial cell expression of the chemokines monocyte chemoattractant protein 1 and IL-8, and in combination with IFN-gamma synergistically induced endothelial cell production of the potent T cell chemoattractant IFN-inducible protein-10 (IP-10). Treatment of BALB/c (H-2d) recipients of fully MHC-mismatched C57BL/6 (H-2b) donor hearts with anti-VEGF markedly inhibited T cell infiltration of allografts and acute rejection. Anti-VEGF failed to inhibit T cell activation responses in vivo, but inhibited intragraft expression of several endothelial cell adhesion molecules and chemokines, including IP-10. In addition, whereas VEGF expression was increased, neovascularization was not associated with acute rejection, and treatment of allograft recipients with the angiogenesis inhibitor endostatin failed to inhibit leukocyte infiltration of the grafts. Thus, VEGF appears to be functional in acute allograft rejection via its effects on leukocyte trafficking. Together, these observations provide mechanistic insight into the proinflammatory function of VEGF in immunity.