CD40 ligand binds to alpha5beta1 integrin and triggers cell signaling

Poorly Differentiated Hepatocellular Carcinoma Cells Avoid Apoptosis by Interacting with T Cells via CD40-CD40 Ligand Linkage

Hepatocellular carcinoma (HCC) is associated with increased soluble CD40 levels. This study aimed to investigate CD40's role in liver tumor progression. CD40 levels were examined in HCC patient tissues and various HCC cell lines, and their interaction with CD4+T cells was studied. RNA sequencing analysis was performed to explore the mechanisms of CD40 induction. Poorly differentiated HCC tumor tissues exhibited high membrane-bound CD40 expression, in contrast to nontumor areas. Poorly differentiated HCC cell lines showed high expression of membrane-bound CD40 with low CD40 promoter methylation, which was the opposite of that observed in the well-differentiated HCC cell lines. Solely modulating CD40 expression in HCC cells exerted no direct consequences on cell growth or appearance. Interestingly, the human hepatoma cell line HLF co-cultured with activated (CD40 ligand+) CD4+ T cells had increased CD40 levels and a modest 3.2% dead cells. The percentage of dead cells increased to 10.9% and underwent preneutralizing CD40 condition, whereas preblocking both CD40 and integrin α5β1 concomitantly caused only 1.9% cell death. RNA sequencing of co-cultured HLFs with activated CD4+ T cells revealed the up-regulation of interferon and immune-response pathways. Increased interferon-γ levels in the activated T-cell media stimulated the Janus kinase/signal transducer and activator of transcription 3 pathway, resulting in increased CD40 expression in HLF. Collectively, CD40 expression in poorly differentiated HCC cells prevented cell death by interacting with CD40 ligand in activated T cells. Targeting CD40 may represent a promising anticancer therapy.

CD40L Activates Platelet Integrin αIIbβ3 by Binding to the Allosteric Site (Site 2) in a KGD-Independent Manner and HIGM1 Mutations Are Clustered in the Integrin-Binding Sites of CD40L

CD40L is expressed in activated T cells, and it plays a major role in immune response and is a major therapeutic target for inflammation. High IgM syndrome type 1 (HIGM1) is a congenital functional defect in CD40L/CD40 signaling due to defective CD40L. CD40L is also stored in platelet granules and transported to the surface upon platelet activation. Platelet integrin αIIbβ3 is known to bind to fibrinogen and activation of αIIbβ3 is a key event that triggers platelet aggregation. Also, the KGD motif is critical for αIIbβ3 binding and the interaction stabilizes thrombus. Previous studies showed that CD40L binds to and activates integrins αvβ3 and α5β1 and that HIGM1 mutations are clustered in the integrin-binding sites. However, the specifics of CD40L binding to αIIbβ3 were unclear. Here, we show that CD40L binds to αIIbβ3 in a KGD-independent manner using CD40L that lacks the KGD motif. Two HIGM1 mutants, S128E/E129G and L155P, reduced the binding of CD40L to the classical ligand-binding site (site 1) of αIIbβ3, indicating that αIIbβ3 binds to the outer surface of CD40L trimer. Also, CD40L bound to the allosteric site (site 2) of αIIbβ3 and allosterically activated αIIbβ3 without inside-out signaling. Two HIMG1 mutants, K143T and G144E, on the surface of trimeric CD40L suppressed CD40L-induced αIIbβ3 activation. These findings suggest that CD40L binds to αIIbβ3 in a manner different from that of αvβ3 and α5β1 and induces αIIbβ3 activation. HIGM1 mutations are clustered in αIIbβ3 binding sites in CD40L and are predicted to suppress thrombus formation and immune responses through αIIbβ3.

Targeting integrin α5β1 in urological tumors: opportunities and challenges

Urological tumors, such as prostate cancer, renal cell carcinoma, and bladder cancer, have shown a significant rise in prevalence in recent years and account for a significant proportion of malignant tumors. It has been established that metastasis to distant organs caused by urological tumors is the main cause of death, although the mechanisms underlying metastasis have not been fully elucidated. The fibronectin receptor integrin α5β1 reportedly plays an important role in distant metastasis and is closely related to tumor development. It is widely thought to be an important cancer mediator by interacting with different ligands, mediating tumor adhesion, invasion, and migration, and leading to immune escape. In this paper, we expound on the relationship and regulatory mechanisms of integrin α5β1 in these three cancers. In addition, the clinical applications of integrin α5β1 in these cancers, especially against treatment resistance, are discussed. Last but not least, the possibility of integrin α5β1 as a potential target for treatment is examined, with new ideas for future research being proposed.

Cell targeting and immunostimulatory properties of a novel Fcγ-receptor-independent agonistic anti-CD40 antibody in rhesus macaques

Targeting CD40 by agonistic antibodies used as vaccine adjuvants or for cancer immunotherapy is a strategy to stimulate immune responses. The majority of studied agonistic anti-human CD40 antibodies require crosslinking of their Fc region to inhibitory FcγRIIb to induce immune stimulation although this has been associated with toxicity in previous studies. Here we introduce an agonistic anti-human CD40 monoclonal IgG1 antibody (MAB273) unique in its specificity to the CD40L binding site of CD40 but devoid of Fcγ-receptor binding. We demonstrate rapid binding of MAB273 to B cells and dendritic cells resulting in activation in vitro on human cells and in vivo in rhesus macaques. Dissemination of fluorescently labeled MAB273 after subcutaneous administration was found predominantly at the site of injection and specific draining lymph nodes. Phenotypic cell differentiation and upregulation of genes associated with immune activation were found in the targeted tissues. Antigen-specific T cell responses were enhanced by MAB273 when given in a prime-boost regimen and for boosting low preexisting responses. MAB273 may therefore be a promising immunostimulatory adjuvant that warrants future testing for therapeutic and prophylactic vaccination strategies.

Role of CD40(L)-TRAF signaling in inflammation and resolution—a double-edged sword

Cardiovascular diseases (CVD) and cardiovascular risk factors are the leading cause of death in the world today. According to the Global Burden of Disease Study, hypertension together with ischemic heart and cerebrovascular diseases is responsible for approximately 40% of all deaths worldwide. The major pathomechanism underlying almost all CVD is atherosclerosis, an inflammatory disorder of the vascular system. Recent large-scale clinical trials demonstrated that inflammation itself is an independent cardiovascular risk factor. Specific anti-inflammatory therapy could decrease cardiovascular mortality in patients with atherosclerosis (increased markers of inflammation). Inflammation, however, can also be beneficial by conferring so-called resolution, a process that contributes to clearing damaged tissue from cell debris upon cell death and thereby represents an essential step for recovery from, e.g., ischemia/reperfusion damage. Based on these considerations, the present review highlights features of the detrimental inflammatory reactions as well as of the beneficial process of immune cell-triggered resolution. In this context, we discuss the polarization of macrophages to either M1 or M2 phenotype and critically assess the role of the CD40L-CD40-TRAF signaling cascade in atherosclerosis and its potential link to resolution. As CD40L can bind to different cellular receptors, it can initiate a broad range of inflammatory processes that may be detrimental or beneficial. Likewise, the signaling of CD40L downstream of CD40 is mainly determined by activation of TRAF1-6 pathways that again can be detrimental or beneficial. Accordingly, CD40(L)-based therapies may be Janus-faced and require sophisticated fine-tuning in order to promote cardioprotection.

Novel Functions of Integrins as Receptors of CD154: Their Role in Inflammation and Apoptosis

CD154, an inflammatory mediator also known as CD40 ligand, has been identified as a novel binding partner for some members of the integrin family. The αIIbβ3, specifically expressed on platelets, was the first integrin to be described as a receptor for CD154 after CD40. Its interaction with soluble CD154 (sCD154) highly contributes to thrombus formation and stability. Identifying αIIbβ3 opened the door for investigating other integrins as partners of CD154. The αMβ2 expressed on myeloid cells was shown capable of binding CD154 and contributing as such to cell activation, adhesion, and release of proinflammatory mediators. In parallel, α5β1 communicates with sCD154, inducing pro-inflammatory responses. Additional pathogenic effects involving apoptosis-preventing functions were exhibited by the CD154–α5β1 dyad in T cells, conferring a role for such interaction in the survival of malignant cells, as well as the persistence of autoreactive T cells. More recently, CD154 receptors integrated two new integrin members, αvβ3 and α4β1, with little known as to their biological significance in this context. This article provides an overview of the novel role of integrins as receptors of CD154 and as critical players in pro-inflammatory and apoptotic responses.

The Inhibition of CD40/CD154 Costimulatory Signaling in the Prevention of Renal Transplant Rejection in Nonhuman Primates: A Systematic Review and Meta Analysis

The prevention of allograft transplant rejection by inhibition of the CD40/CD40L costimulatory pathway has been described in several species. We searched pubmed for studies reporting the prevention of kidney transplant rejection in nonhuman primates utilizing either anti CD40 or anti CD40L (CD154) treatment. Inclusion of data required treatment with anti CD40 or anti CD154 as monotherapy treatment arms, full text available, studies conducted in nonhuman primate species, the transplant was renal transplantation, sufficient duration of treatment to assess long term rejection, and the reporting of individual graft survival or survival duration. Eleven publications were included in the study. Rejection free survival was calculated using the Kaplan-Meier (KM) life test methods to estimate the survival functions. The 95% CI for the medians was also calculated. A log-rank test was used to test the equality of the survival curves between control and treatment arms (CD40 and CD154). The hazard ratio for CD154 compared to CD40 and 95% CI was calculated using a Cox proportional-hazards model including treatment as the covariate to assess the magnitude of the treatment effect. Both anti CD40 and anti CD154 treatments prevented acute and long term graft rejection. The median (95% CI) rejection free survival was 131 days (84,169 days) in the anti CD40 treated animals and 352 days (173,710 days) in the anti CD154 treated animals. Median survival in the untreated animals was 6 days. The inhibition of transplant rejection was more durable in the anti CD154 group compared to the anti CD40 group after cessation of treatment. The median (95% CI) rejection free survival after cessation of treatment was 60 days (21,80 days) in the anti CD40 treated animals and 230 days (84,552 days) in the anti CD154 treated animals.

Characterization of the Role of Integrin α5β1 in Platelet Function, Hemostasis, and Experimental Thrombosis

Objective  Integrins are key regulators of various platelet functions. The pathophysiological importance of most platelet integrins has been investigated, with the exception of α5β1, a receptor for fibronectin. The aim of this study was to characterize the role of α5β1 in megakaryopoiesis, platelet function, and to determine its importance in hemostasis and arterial thrombosis.

Approach and Results  We generated a mouse strain deficient for integrin α5β1 on megakaryocytes and platelets (PF4Cre-α5 ^−/− ). PF4Cre-α5 ^−/− mice were viable, fertile, and presented no apparent signs of abnormality. Megakaryopoiesis appears unaltered as evidence by a normal megakaryocyte morphology and development, which is in agreement with a normal platelet count. Expression of the main platelet receptors and the response of PF4Cre-α5 ^−/− platelets to a series of agonists were all completely normal. Adhesion and aggregation of PF4Cre-α5 ^−/− platelets under shear flow on fibrinogen, laminin, or von Willebrand factor were unimpaired. In contrast, PF4Cre-α5 ^−/− platelets displayed a marked decrease in adhesion, activation, and aggregation on fibrillar cellular fibronectin and collagen. PF4Cre-α5 ^−/− mice presented no defect in a tail-bleeding time assay and no increase in inflammatory bleeding in a reverse passive Arthus model and a lipopolysaccharide pulmonary inflammation model. Finally, no defects were observed in three distinct experimental models of arterial thrombosis based on ferric chloride-induced injury of the carotid artery, mechanical injury of the abdominal aorta, or laser-induced injury of mesenteric vessels.

Conclusion  In summary, this study shows that platelet integrin α5β1 is a key receptor for fibrillar cellular fibronectin but is dispensable in hemostasis and arterial thrombosis.

CD40L modulates transcriptional signatures of neutrophils in the bone marrow associated with development and trafficking

Neutrophils are produced in the BM in a process called granulopoiesis, in which progenitor cells sequentially develop into mature neutrophils. During the developmental process, which is finely regulated by distinct transcription factors, neutrophils acquire the ability to exit the BM, properly distribute throughout the body, and migrate to infection sites. Previous studies have demonstrated that CD40 ligand (CD40L) influences hematopoiesis and granulopoiesis. Here, we investigate the effect of CD40L on neutrophil development and trafficking by performing functional and transcriptome analyses. We found that CD40L signaling plays an essential role in the early stages of neutrophil generation and development in the BM. Moreover, CD40L modulates transcriptional signatures, indicating that this molecule enables neutrophils to traffic throughout the body and to migrate in response to inflammatory signals. Thus, our study provides insights into the complex relationships between CD40L signaling and granulopoiesis, and it suggests a potentially novel and nonredundant role of CD40L signaling in neutrophil development and function.

CD154 Resistant to Cleavage from Intracellular Milieu and Cell Surface Induces More Potent CD40-Mediated Responses

In addition to the membrane-bound form, CD154 also exists as a soluble molecule originating from an intracellular and membrane cleavage. We have previously shown that CD154 cleavage from T cell surface is mediated by CD40 and involves the action of ADAM10/ADAM17 enzymes. In the aim of defining the importance of CD154 maintained on cell surface, we generated a CD154 mutated at the cleavage site. Our data show that the double mutation of E112 and M113 residues of CD154 abolishes its spontaneous release and the CD40-mediated cleavage from cell surface but does not affect its binding to CD40. We also demonstrated that both the release of CD154 from the intracellular milieu and its CD40-mediated cleavage from cell surface are highly dependent on ADAM10/ADAM17 enzymes. The CD154-EM mutant was shown capable of inducing a more prominent apoptotic response in susceptible B cell lines than the wild-type (WT) form of the molecule. In addition, human B cells cultured in the presence of the CD154-EM mutant exhibited upregulated proliferative responses compared with the CD154-WT. The CD154-EM mutant was also shown to trigger differentiation of human B cells, reflected by an increased Ig production, more significantly than CD154-WT. Thus, our data strongly suggest that cleavage-resistant CD154 is a more prominent stimulant than the cleavable form of the molecule. Therefore, a maintained expression of CD154 on cell membrane and a disturbed cleavage of the molecule could be a mechanism by which CD154 is involved in some pathological conditions and should be revisited.

The Roles of Integrin α5β1 in Human Cancer

Cell adhesion to the extracellular matrix has important roles in tissue integrity and human health. Integrins are heterodimeric cell surface receptors that are composed by two non-covalently linked alpha and beta subunits that mainly participate in the interaction of cell-cell adhesion and cell-extracellular matrix and regulate cell motility, adhesion, differentiation, migration, proliferation, etc. In mammals, there have been eighteen α subunits and 8 β subunits and so far 24 distinct types of αβ integrin heterodimers have been identified in humans. Integrin α5β1, also known as the fibronectin receptor, is a heterodimer with α5 and β1 subunits and has emerged as an essential mediator in many human carcinomas. Integrin α5β1 alteration is closely linked to the progression of several types of human cancers, including cell proliferation, angiogenesis, tumor metastasis, and cancerogenesis. In this review, we will introduce the functions of integrin α5β1 in cancer progression and also explore its regulatory mechanisms. Additionally, the potential clinical applications as a target for cancer imaging and therapy are discussed. Collectively, the information reviewed here may increase the understanding of integrin α5β1 as a potential therapeutic target for cancer.

Residue-Specific Message Encoding in CD40-Ligand

CD40-Ligand (CD40L)-CD40 interaction regulates immune responses against pathogens, autoantigens, and tumor and transplantation antigens. Single amino acid mutations within the 115-155 amino acids stretch, which is responsible for CD40L functions, result in XIgM syndrome. We hypothesize that each of these amino acids of CD40L encodes specific message that, when decoded by CD40 signaling, induces a specific profile of functions. We observed that every single substitution in the XIgM-related amino acids in the 115-155 41-mer peptide in CD40L selectively altered CD40 signaling and effector functions-cytokine productions, HMGCoA reductase, ceramide synthase, inducible nitric oxide synthase and arginase expression, survival of B cells, and control of Leishmania infection and anti-leishmanial T cell response-suggesting residue-specific encoding of a distinct set of messages that collectively define CD40L pleiotropy, serve as a target for engineering the ligand to generate superagonists as immunotherapeutic, and implicate the evolutionary diversification of functions among the ligands in a protein superfamily.

Revisiting Platelets and Toll-Like Receptors (TLRs): At the Interface of Vascular Immunity and Thrombosis

While platelet function has traditionally been described in the context of maintaining vascular integrity, recent evidence suggests that platelets can modulate inflammation in a much more sophisticated and nuanced manner than previously thought. Some aspects of this expanded repertoire of platelet function are mediated via expression of Toll-like receptors (TLRs). TLRs are a family of pattern recognition receptors that recognize pathogen-associated and damage-associated molecular patterns. Activation of these receptors is crucial for orchestrating and sustaining the inflammatory response to both types of danger signals. The TLR family consists of 10 known receptors, and there is at least some evidence that each of these are expressed on or within human platelets. This review presents the literature on TLR-mediated platelet activation for each of these receptors, and the existing understanding of platelet-TLR immune modulation. This review also highlights unresolved methodological issues that potentially contribute to some of the discrepancies within the literature, and we also suggest several recommendations to overcome these issues. Current understanding of TLR-mediated platelet responses in influenza, sepsis, transfusion-related injury and cardiovascular disease are discussed, and key outstanding research questions are highlighted. In summary, we provide a resource—a “researcher’s toolkit”—for undertaking further research in the field of platelet-TLR biology.

CD154 inhibits death of T cells via a Cis interaction with the α5β1 integrin

CD154 plays a major role in the pathogenesis of several autoimmune and inflammatory diseases. In addition to CD40, soluble CD154 (sCD154) binds to other receptors namely αIIbβ3, αMβ2, α5β1 and αvβ3 integrins. We have previously reported that binding of sCD154 to α5β1 integrin expressed on several human T cell lines is capable of inhibiting Fas-induced cell death. In the current study, we show that such effect of the sCD154/α5β1 interaction is not restricted to the cell death response induced by Fas but could also be exhibited toward other death signals such as TRAIL and TNF- α. We also demonstrate that sCD154 is capable of inhibiting Fas-mediated death of human activated T cells, more importantly of CD4⁺ than CD8⁺ T ones. Our data also show that membrane-bound CD154 and α5β1 integrin expressed on the surface of distinct cells failed to influence cell death responses. However, when membrane-bound CD154 and α5β1 are expressed on the surface of same cell, their interaction was capable of down regulating cell death. CD154 was shown to co-localize with the α5β1 integrin on the surface of these cells. These data strongly suggest a cis-type of interaction between CD154 and α5β1 when both are expressed on the same cell surface, rather than a trans-interaction which usually implicates the ligand and its receptor each expressed on the surface of a distinct cell. Taken together, these findings add to the list of roles through which CD154 is contributing to the pathogenesis of autoimmune-inflammatory diseases, i.e. by protecting T cells from death and enhancing their survival.

The CD40-CD40L Dyad as Immunotherapeutic Target in Cardiovascular Disease

Chronic inflammation drives the development of atherosclerosis. Despite optimal treatment of classical cardiovascular risk factors, a substantial portion of the population has elevated inflammatory biomarkers and develops atherosclerosis-related complications, indicating that a residual inflammatory risk drives atherosclerotic cardiovascular disease in these patients. Additional anti-inflammatory therapeutic strategies are therefore required. The co-stimulatory molecule CD40 and its ligand CD40L (CD154) have a central role in the regulation of the inflammatory response during the development of atherosclerosis by modulating the interaction between immune cells and between immune cells and non-immune cells. In this review, we discuss the role of the CD40-CD40L dyad in atherosclerosis, and we discuss recent studies on the therapeutic potential of novel CD40-CD40L targeting strategies in cardiovascular medicine.

B Lymphocytes and Adipose Tissue Inflammation

The immune system plays an important role in obesity-induced adipose tissue inflammation and the resultant metabolic dysfunction, which can lead to hypertension, dyslipidemia, and insulin resistance and their downstream sequelae of type 2 diabetes mellitus and cardiovascular disease. While macrophages are the most abundant immune cell type in adipose tissue, other immune cells are also present, such as B cells, which play important roles in regulating adipose tissue inflammation. This brief review will overview B-cell subsets, describe their localization in various adipose depots and summarize our knowledge about the function of these B-cell subsets in regulating adipose tissue inflammation, obesity-induced metabolic dysfunction and atherosclerosis.

CD40L Priming of Platelets via NF-κB Activation is CD40- and TAK1-Dependent

Background

CD40 ligand (CD40L) is a thromboinflammatory molecule that predicts cardiovascular events. CD40L is a strong activator of nuclear factor kappa B (NF‐κB) in platelets that primes and enhances platelet activation in response to thrombotic stimuli. In addition to its classical receptor CD40, CD40L binds αIIbβ3, α5β1, and αMβ2 in various cell types. However, the function of the different CD40L receptors on platelets remains unexplored. The present study aims to identify the receptors of CD40L, involved in platelet NF‐κB activation, their downstream signaling and their implication in platelet aggregation.

Methods and Results

We showed that platelets express CD40, αIIbβ3, and α5β1 and release CD40L in response to sCD40L stimulation. sCD40L alone dose‐dependently induced platelet NF‐κB activation; this effect was absent in CD40^−/− mouse platelets and inhibited by the CD40 blockade, but was unaffected by the αIIbβ3 or α5β1 blockade in human platelets. sCD40L/CD40 axis activates transforming growth factor‐β‐activated kinase 1 upstream of NF‐κB. In functional studies, sCD40L alone did not affect platelet aggregation but potentiated the aggregation response in the presence of suboptimal doses of thrombin; this effect was abolished by CD40, transforming growth factor‐β‐activated kinase 1, and NF‐κB inhibitors.

Conclusions

CD40L primes platelets via signaling pathways involving CD40/transforming growth factor‐β‐activated kinase 1/NF‐κB, which predisposes platelets to enhanced activation and aggregation in response to thrombotic stimuli.

Role of NF-κB in Platelet Function

Platelets are megakaryocyte-derived fragments lacking nuclei and prepped to maintain primary hemostasis by initiating blood clots on injured vascular endothelia. Pathologically, platelets undergo the same physiological processes of activation, secretion, and aggregation yet with such pronouncedness that they orchestrate and make headway the progression of atherothrombotic diseases not only through clot formation but also via forcing a pro-inflammatory state. Indeed, nuclear factor-κB (NF-κB) is largely implicated in atherosclerosis and its pathological complication in atherothrombotic diseases due to its transcriptional role in maintaining pro-survival and pro-inflammatory states in vascular and blood cells. On the other hand, we know little on the functions of platelet NF-κB, which seems to function in other non-genomic ways to modulate atherothrombosis. Therein, this review will resemble a rich portfolio for NF-κB in platelets, specifically showing its implications at the levels of platelet survival and function. We will also share the knowledge thus far on the effects of active ingredients on NF-κB in general, as an extrapolative method to highlight the potential therapeutic targeting of NF-κB in coronary diseases. Finally, we will unzip a new horizon on a possible extra-platelet role of platelet NF-κB, which will better expand our knowledge on the etiology and pathophysiology of atherothrombosis.

Integrin Binding to the Trimeric Interface of CD40L Plays a Critical Role in CD40/CD40L Signaling

CD40L plays a major role in immune response and is a major therapeutic target for inflammation. Integrin α5β1 and CD40 simultaneously bind to CD40L. It is unclear if α5β1 and CD40 work together in CD40/CD40L signaling or how α5β1 binds to CD40L. In this article, we describe that the integrin-binding site of human CD40L is predicted to be located in the trimeric interface by docking simulation. Mutations in the predicted integrin-binding site markedly reduced the binding of α5β1 to CD40L. Several CD40L mutants defective in integrin binding were defective in NF-κB activation and B cell activation and suppressed CD40L signaling induced by wild-type CD40L; however, they still bound to CD40. These findings suggest that integrin α5β1 binds to monomeric CD40L through the binding site in the trimeric interface of CD40L, and this plays a critical role in CD40/CD40L signaling. Integrin αvβ3, a widely distributed vascular integrin, bound to CD40L in a KGD-independent manner, suggesting that αvβ3 is a new CD40L receptor. Several missense mutations in CD40L that induce immunodeficiency with hyper-IgM syndrome type 1 (HIGM1) are clustered in the integrin-binding site of the trimeric interface. These HIGM1 CD40L mutants were defective in binding to α5β1 and αvβ3 (but not to CD40), suggesting that the defect in integrin binding may be a causal factor of HIGM1. These findings suggest that α5β1 and αvβ3 bind to the overlapping binding site in the trimeric interface of monomeric CD40L and generate integrin-CD40L-CD40 ternary complex. CD40L mutants defective in integrins have potential as antagonists of CD40/CD40L signaling.

CD40L controls obesity-associated vascular inflammation, oxidative stress, and endothelial dysfunction in high fat diet-treated and db/db mice

Aims

CD40 ligand (CD40L) signaling controls vascular oxidative stress and related dysfunction in angiotensin-II-induced arterial hypertension by regulating vascular immune cell recruitment and platelet activation. Here we investigated the role of CD40L in experimental hyperlipidemia.

Methods and results

Male wild type and CD40L-/- mice (C57BL/6 background) were subjected to high fat diet for sixteen weeks. Weight, cholesterol, HDL, and LDL levels, endothelial function (isometric tension recording), oxidative stress (NADPH oxidase expression, dihydroethidium fluorescence) and inflammatory parameters (inducible nitric oxide synthase, interleukin-6 expression) were assessed. CD40L expression, weight, leptin and lipids were increased, and endothelial dysfunction, oxidative stress and inflammation were more pronounced in wild type mice on a high fat diet, all of which was almost normalized by CD40L deficiency. Similar results were obtained in diabetic db/db mice with CD40/TRAF6 inhibitor (6877002) therapy. In a small human study higher serum sCD40L levels and an inflammatory phenotype were detected in the blood and Aorta ascendens of obese patients (body mass index > 35) that underwent by-pass surgery.

Conclusion

CD40L controls obesity-associated vascular inflammation, oxidative stress and endothelial dysfunction in mice and potentially humans. Thus, CD40L represents a therapeutic target in lipid metabolic disorders which is a leading cause in cardiovascular disease.

Update of inflammatory proliferative retinopathy: Ischemia, hypoxia and angiogenesis

Diabetic retinopathy (DR) and retinopathy of prematurity (ROP) present two examples of proliferative retinopathy, characterized by the same stages of progression; ischemia of the retinal vessels, leads to hypoxia and to correct the problem there is the setting up of uncontrolled angiogenesis, which subsequently causes blindness or even detachment of the retina. The difference is the following; that DR initiated by the metabolic complications that are due to hyperglycemia, and ROP is induced by overexposure of the neonatal retina to oxygen. In this review, we will demonstrate the physiopathological mechanism of the two forms of proliferative retinopathy DR and ROP, in particular the role of the CD40/CD40L axis and IL-1 on vascular complications and onset of inflammation of the retina, the implications of their effects on the onset of pathogenic angiogenesis, thus understanding the link between platelets and retinal ischemia. In addition, what are the therapeutic targets that could slow its progression?

The Tumor Necrosis Factor Family: Family Conventions and Private Idiosyncrasies

The tumor necrosis factor (TNF) cytokine family and the TNF/nerve growth factor (NGF) family of their cognate receptors together control numerous immune functions, as well as tissue-homeostatic and embryonic-development processes. These diverse functions are dictated by both shared and distinct features of family members, and by interactions of some members with nonfamily ligands and coreceptors. The spectra of their activities are further expanded by the occurrence of the ligands and receptors in both membrane-anchored and soluble forms, by "re-anchoring" of soluble forms to extracellular matrix components, and by signaling initiation via intracellular domains (IDs) of both receptors and ligands. Much has been learned about shared features of the receptors as well as of the ligands; however, we still have only limited knowledge of the mechanistic basis for their functional heterogeneity and for the differences between their functions and those of similarly acting cytokines of other families.

Distinct CD40L receptors mediate inflammasome activation and secretion of IL-1β and MCP-1 in cultured human retinal pigment epithelial cells

CD40L signaling occurs in several diseases with inflammatory components, including ocular and retinal diseases. However, it has never been evaluated as a pathogenic mechanism in age-related macular degeneration (AMD) or as an inducer of inflammasome formation in any cell type. mRNA and protein levels of CD40, IL-1β, NALP1, NALP3, caspase-1, and caspase-5 were determined by RT-PCR, qPCR, and Western blot. CD40L receptor (CD40, α5β1, and CD11b) expression was determined by Western and immunofluorescent staining. IL-1β, IL-18, and MCP-1 secretions were determined by ELISA. NALP1 and NALP3 inflammasome formation were determined by Co-IP. Experiments were conducted on primary human retinal pigment epithelial (hRPE) cells from four different donors. Human umbilical vein endothelial (HUVEC) and monocytic leukemia (THP-1) cells demonstrated the general applicability of our findings. In hRPE cells, CD40L-induced NALP1 and NALP3 inflammasome activation, cleavage of caspase-1 and caspase-5, and IL-1β and IL-18 secretion. Interestingly, neutralizing CD11b and α5β1 antibodies, but not CD40, reduced CD40L-induced IL-1β secretion in hRPE cells. Similarly, CD40L treatment also induced HUVEC and THP-1 cells to secret IL-1β through CD11b and α5β1. Additionally, the CD40L-induced IL-1β secretion acted in an autocrine/paracrine manner to feed back and induce hRPE cells to secrete MCP-1. This study is the first to show that CD40L induces inflammasome activation in any cell type, including hRPE cells, and that this induction is through CD11b and α5β1 cell-surface receptors. These mechanisms likely play an important role in many retinal and non-retinal diseases and provide compelling drug targets that may help reduce pro-inflammatory processes.

A critical role for both CD40 and VLA5 in angiotensin II-mediated thrombosis and inflammation

Angiotensin II (Ang-II)-induced hypertension is associated with accelerated thrombus formation in arterioles and leukocyte recruitment in venules. The mechanisms that underlie the prothrombotic and proinflammatory responses to chronic Ang-II administration remain poorly understood. We evaluated the role of CD40/CD40 ligand (CD40L) signaling in Ang-II-mediated microvascular responses and assessed whether and how soluble CD40L (sCD40L) contributes to this response. Intravital video microscopy was performed to analyze leukocyte recruitment and dihydrorhodamine-123 oxidation in postcapillary venules. Thrombus formation in cremaster muscle arterioles was induced by using the light/dye endothelial cell injury model. Wild-type (WT), CD40^-/-, and CD40L^-/- mice received Ang-II for 14 d via osmotic minipumps. Some mice were treated with either recombinant sCD40L or the VLA5 (very late antigen 5; α5β1) antagonist, ATN-161. Our results demonstrate that CD40^-/-, CD40L^-/-, and WT mice that were treated with ATN-161 were protected against the thrombotic and inflammatory effects of Ang-II infusion. Infusion of sCD40L into CD40^-/- or CD40L^-/- mice restored the prothrombotic effect of Ang-II infusion. Mice that were treated with ATN-161 and infused with sCD40L were protected against accelerated thrombosis. Collectively, these novel findings suggest that the mechanisms that underlie Ang-II-dependent thrombotic and inflammatory responses link to the signaling of CD40L via both CD40 and VLA5.-Senchenkova, E. Y., Russell, J., Vital, S. A., Yildirim, A., Orr, A. W., Granger, D. N., Gavins, F. N. E. A critical role for both CD40 and VLA5 in angiotensin II-mediated thrombosis and inflammation.

Platelets, inflammation and tissue regeneration

Blood platelets have long been recognised to bring about primary haemostasis with deficiencies in platelet production and function manifesting in bleeding while upregulated function favourises arterial thrombosis. Yet increasing evidence indicates that platelets fulfil a much wider role in health and disease. First, they store and release a wide range of biologically active substances including the panoply of growth factors, chemokines and cytokines released from α-granules. Membrane budding gives rise to microparticles (MPs), another active participant within the blood stream. Platelets are essential for the innate immune response and combat infection (viruses, bacteria, micro-organisms). They help maintain and modulate inflammation and are a major source of pro-inflammatory molecules (e.g. P-selectin, tissue factor, CD40L, metalloproteinases). As well as promoting coagulation, they are active in fibrinolysis; wound healing, angiogenesis and bone formation as well as in maternal tissue and foetal vascular remodelling. Activated platelets and MPs intervene in the propagation of major diseases. They are major players in atherosclerosis and related diseases, pathologies of the central nervous system (Alzheimers disease, multiple sclerosis), cancer and tumour growth. They participate in other tissue-related acquired pathologies such as skin diseases and allergy, rheumatoid arthritis, liver disease; while, paradoxically, autologous platelet-rich plasma and platelet releasate are being used as an aid to promote tissue repair and cellular growth. The above mentioned roles of platelets are now discussed.

Co-stimulatory molecules in and beyond co-stimulation – tipping the balance in atherosclerosis?

A plethora of basic laboratory and clinical studies has uncovered the chronic inflammatory nature of atherosclerosis. The adaptive immune system with its front-runner, the T cell, drives the atherogenic process at all stages. T cell function is dependent on and controlled by a variety of either co-stimulatory or co-inhibitory signals. In addition, many of these proteins enfold T cell-independent pro-atherogenic functions on a variety of cell types. Accordingly they represent potential targets for immune- modulatory and/or anti-inflammatory therapy of atherosclerosis. This review focuses on the diverse role of co-stimulatory molecules of the B7 and tumour necrosis factor (TNF)-superfamily and their downstream signalling effectors in atherosclerosis. In particular, the contribution of CD28/CD80/CD86/CTLA4, ICOS/ICOSL, PD-1/PDL-1/2, TRAF, CD40/CD154, OX40/OX40L, CD137/CD137L, CD70/CD27, GITR/GITRL, and LIGHT to arterial disease is reviewed. Finally, the potential for a therapeutic exploitation of these molecules in the treatment of atherosclerosis is discussed.

Interruption of classic CD40L-CD40 signalling but not of the novel CD40L-Mac-1 interaction limits arterial neointima formation in mice

The co-stimulatory immune molecule CD40L figures prominently in a variety of inflammatory conditions including arterial disease. Recently, we made the surprising finding that CD40L mediates atherogenesis independently of its classic receptor CD40 via a novel interaction with the leukocyte integrin Mac-1. Here, we hypothesised that selective blockade of the CD40L-Mac-1 interaction may also retard restenosis. We induced neointima formation in C57/BL6 mice by ligation of the left carotid artery. Mice were randomised to daily intraperitoneal injections of either cM7, a small peptide selectively inhibiting the CD40L-Mac-1 interaction, scM7, a scrambled control peptide, or saline for 28 days. Interestingly, cM7-treated mice developed neointima of similar size compared with mice receiving the control peptide or saline as assessed by computer-assisted analysis of histological cross sections. These data demonstrate that the CD40L-Mac-1 interaction is not required for the development of restenosis. In contrast, CD40-deficient mice subjected to carotid ligation in parallel, developed significantly reduced neointimal lesions compared with respective wild-type controls (2872 ± 843 µm² vs 35469 ± 11870 µm²). Flow cytometry in CD40-deficient mice revealed reduced formation of platelet-granulocyte and platelet-inflammatory monocyte-aggregates. In vitro, supernatants of CD40-deficient platelet-leukocyte aggregates attenuated proliferation and increased apoptosis of smooth muscle cells. Unlike in the setting of atherosclerosis, CD40L mediates neointima formation via its classic receptor CD40 rather than via its recently described novel interaction with Mac-1. Therefore, selective targeting of CD40L-Mac-1 binding does not appear to be a favorable strategy to fight restenosis.

CD40 signaling and hepatic steatosis: Unanticipated links

Obesity predisposes to an increased risk of nonalcoholic fatty liver disease (NAFLD). Hepatic steatosis is the key pathological feature of NAFLD and has emerged as a metabolic disorder in which innate and adaptive arms of the immune response play a central role in disease pathogenesis. Recent studies have revealed unexpected relationships between CD40 signaling and hepatic steatosis in high fat diet rodent models. CD154, the ligand of CD40, is a mediator of inflammation and controls several critical events of innate and adaptive immune responses. In the light of these reports, we discuss potential links between CD40 signaling and hepatic steatosis in NAFLD.

CD40L and Its Receptors in Atherothrombosis-An Update

CD40L (CD154), a member of the tumor necrosis factor superfamily, is a co-stimulatory molecule that was first discovered on activated T cells. Beyond its fundamental role in adaptive immunity-ligation of CD40L to its receptor CD40 is a prerequisite for B cell activation and antibody production-evidence from more than two decades has expanded our understanding of CD40L as a powerful modulator of inflammatory pathways. Although inhibition of CD40L with neutralizing antibodies has induced life-threatening side effects in clinical trials, the discovery of cell-specific effects and novel receptors with distinct functional consequences has opened a new path for therapies that specifically target detrimental properties of CD40L. Here, we carefully evaluate the signaling network of CD40L by gene enrichment analysis and its cell-specific expression, and thoroughly discuss its role in cardiovascular pathologies with a specific emphasis on atherosclerotic and thrombotic disease.

The Interaction of CD154 with the α5β1 Integrin Inhibits Fas-Induced T Cell Death

CD154, a critical regulator of the immune response, is usually associated with chronic inflammatory, autoimmune diseases as well as malignant disorders. In addition to its classical receptor CD40, CD154 is capable of binding other receptors, members of the integrin family, the αIIbβ3, αMβ2 and α5β1. Given the role attributed to integrins and particularly the β1 integrins in inhibiting apoptotic events in normal as well as malignant T cells, we were highly interested in investigating the role of the CD154/α5β1 interaction in promoting survival of malignant T cells contributing as such to tumor development and/or propagation. To support our hypothesis, we first show that soluble CD154 binds to the T-cell acute lymphoblastic leukemia cell line, Jurkat E6.1 in a α5β1-dependent manner. Binding of soluble CD154 to α5β1 integrin of Jurkat cells leads to the activation of key survival proteins, including the p38 and ERK1/2 mitogen-activated protein kinases (MAPKs), phosphoinositide 3 kinase (PI-3K), and Akt. Interestingly, soluble CD154 significantly inhibits Fas-mediated apoptosis in T cell leukemia-lymphoma cell lines, Jurkat E6.1 and HUT78 cells, an important hallmark of T cell survival during malignancy progression. These anti-apoptotic effects were mainly mediated by the activation of the PI-3K/Akt pathway but also involved the p38 and the ERK1/2 MAPKs cascades. Our data also demonstrated that the CD154-triggered inhibition of the Fas-mediated cell death response was dependent on a suppression of caspase-8 cleavage, but independent of de novo protein synthesis or alterations in Fas expression on cell surface. Together, our results highlight the impact of the CD154/α5β1 interaction in T cell function/survival and identify novel targets for the treatment of malignant disorders, particularly of T cell origin.

The Immune Landscape in Nonalcoholic Steatohepatitis

The liver lies at the intersection of multiple metabolic pathways and consequently plays a central role in lipid metabolism. Pathological disturbances in hepatic lipid metabolism are characteristic of chronic metabolic diseases, such as obesity-mediated insulin resistance, which can result in nonalcoholic fatty liver disease (NAFLD). Tissue damage induced in NAFLD activates and recruits liver-resident and non-resident immune cells, resulting in nonalcoholic steatohepatitis (NASH). Importantly, NASH is associated with an increased risk of significant clinical sequelae such as cirrhosis, cardiovascular diseases, and malignancies. In this review, we describe the immunopathogenesis of NASH by defining the known functions of immune cells in the progression and resolution of disease.

Blocking α5β1 Integrin Attenuates sCD40L-Mediated Platelet Activation

The soluble form of CD40L (sCD40L) is a platelet-derived mediator that links inflammation, hemostasis, and vascular dysfunction. Indeed, blockade of CD40L by neutralizing antibodies or genetic disruption in mice prevents atherosclerosis and atherothrombosis. Until recently, it was believed that CD40 and αIIbβ3 were the only receptors on platelets responsible for binding sCD40L, leading to platelet activation and initiation of thrombotic events. Recent findings showed α5β1 integrin as a novel platelet sCD40L receptor, with an unknown function. For the first time, using anti-α5β1 blocking antibodies, we show that sCD40L/α5β1 interaction leads to platelet activation as evaluated in the human whole blood. Establishing α5β1 integrin's role in platelet activation, and therefore thrombosis will help further shed light on the etiology of thrombotic disease.

T cells, osteoblasts, and osteocytes: interacting lineages key for the bone anabolic and catabolic activities of parathyroid hormone

Osteoimmunology is a field of research dedicated to the study of the interactions between the immune system and bone. Among the cells of the immune system that regulate bone turnover and the responsiveness of bone cells to calciothropic hormones are bone marrow T lymphocytes. T cells secrete osteoclastogenic cytokines such as RANKL and TNF-α, as well as factors that stimulate bone formation, one of which is Wnt10b. In addition, T cells regulate the differentiation and life span of stromal cells (SCs) and their responsiveness to parathyroid hormone (PTH) via costimulatory molecules expressed on their surface. The conditioning effect of T cells on SCs is inherited by the osteoblastic and osteocytic progeny of SCs. As a result, osteoblastic cells of T cell-deficient mice have functional characteristics different from corresponding cells of T cell-replete mice. These differences include the ratio of RANKL/OPG produced in response to continuous PTH treatment, and the osteoblastogenic response to intermittent PTH treatment. This article reviews the evidence indicating that the effects of PTH are mediated not only by osteoblasts and osteocytes but also by T cells.

Staphylococcal SSL5-induced platelet microparticles provoke proinflammatory responses via the CD40/TRAF6/NFκB signalling pathway in monocytes

Pathogens-induced platelet activation contributes to inflammation in cardiovascular diseases, but underlying mechanisms remain elusive. Staphylococcal superantigen-like protein 5 (SSL5) is a known activator of platelets. Here we examined whether SSL5 is implicated in Staphylococcus aureus (S. aureus)-induced inflammation and potential mechanisms involved. As expected, we show that SSL5 activates human platelets and induces generation of platelet microparticles (PMPs). Flow cytometry and scanning electron microscopy studies demonstrate that SSL5-induced PMPs (SSL5-PMPs) bind to monocytes, causing aggregate formation. In addition, SSL5-PMPs provoke monocyte expression and release of inflammatory mediators, including interleukin-1β (IL-1β), tumour necrosis factor-α (TNFα), monocyte chemoattractant protein-1 (MCP-1) and matrix metalloproteinase-9 (MMP-9) in a dose- and time-dependent manner. SSL5-PMPs also enhance MCP-1-induced monocyte migration. Blockade of CD40 and CD40 ligand (CD40L) interactions with neutralising antibodies significantly reduce monocyte release of inflammatory mediators and migration induced by SSL5-PMPs. SiRNA-mediated silencing of CD40 or TNF receptor (TNFR)-associated factor 6 (TRAF6) gene largely abrogates phosphorylation and nuclear translocation of NFκB (p65). In conclusion, SSL5 provokes the release of inflammatory mediators in monocytes, at least in part, via PMPs-mediated activation of the CD40/TRAF6/NFκB signalling pathway, though it normally inhibits leukocyte function. Our findings thus reveal a novel mechanism by which S. aureus induces inflammation.

Characterisation of the TNF superfamily members CD40L and BAFF in the small-spotted catshark (Scyliorhinus canicula)

The tumour necrosis factor superfamily (TNFSF) members CD40L and BAFF play critical roles in mammalian B cell survival, proliferation and maturation, however little is known about these key cytokines in the oldest jawed vertebrates, the cartilaginous fishes. Here we report the cloning of CD40L and BAFF orthologues (designated ScCD40L and ScBAFF) in the small-spotted catshark (Scyliorhinus canicula). As predicted both proteins are type II membrane-bound proteins with a TNF homology domain in their extracellular region and both are highly expressed in shark immune tissues. ScCD40L transcript levels correlate with those of TCRα and transcription of both genes is modulated in peripheral blood leukocytes following in vitro stimulation. Although a putative CD40L orthologue was identified in the elephant shark genome the work herein is the first molecular characterisation and transcriptional analysis of CD40L in a cartilaginous fish. ScBAFF was also cloned and its transcription characterised in an attempt to resolve the discrepancies observed between spiny dogfish BAFF and bamboo shark BAFF in previously published studies.

Interaction of Macrophage Antigen 1 and CD40 Ligand Leads to IL-12 Production and Resistance in CD40-Deficient Mice Infected with Leishmania major

Although some studies indicate that the interaction of CD40 and CD40L is critical for IL-12 production and resistance to cutaneous leishmaniasis, others suggest that this pathway may be dispensable. In this article, we compared the outcome of Leishmania major infection in both CD40- and CD40L-deficient mice after treatment with rIL-12. We show that although CD40 and CD40L knockout (KO) mice are highly susceptible to L. major, treatment with rIL-12 during the first 2 wk of infection causes resolution of cutaneous lesions and control of parasite replication. Interestingly, although treated CD40 KO mice remained healed, developed long-term immunity, and were resistant to secondary L. major challenge, treated CD40L KO reactivated their lesion after cessation of rIL-12 treatment. Disease reactivation in CD40L KO mice was associated with impaired IL-12 and IFN-γ production and a concomitant increase in IL-4 production by cells from lymph nodes draining the infection site. We show that IL-12 production by dendritic cells and macrophages via CD40L-macrophage Ag 1 (Mac-1) interaction is responsible for the sustained resistance in CD40 KO mice after cessation of rIL-12 treatment. Blockade of CD40L-Mac-1 interaction with anti-Mac-1 mAb led to spontaneous disease reactivation in healed CD40 KO mice, which was associated with impaired IFN-γ response and loss of infection-induced immunity after secondary L. major challenge. Collectively, our data reveal a novel role of CD40L-Mac-1 interaction in IL-12 production, development, and maintenance of optimal Th1 immunity in mice infected with L. major.

T cell-expressed CD40L potentiates the bone anabolic activity of intermittent PTH treatment

T cells are known to potentiate the bone anabolic activity of intermittent parathyroid hormone (iPTH) treatment. One of the involved mechanisms is increased T cell secretion of Wnt10b, a potent osteogenic Wnt ligand that activates Wnt signaling in stromal cells (SCs). However, additional mechanisms might play a role, including direct interactions between surface receptors expressed by T cells and SCs. Here we show that iPTH failed to promote SC proliferation and differentiation into osteoblasts (OBs) and activate Wnt signaling in SCs of mice with a global or T cell-specific deletion of the T cell costimulatory molecule CD40 ligand (CD40L). Attesting to the relevance of T cell-expressed CD40L, iPTH induced a blunted increase in bone formation and failed to increase trabecular bone volume in CD40L(-/-) mice and mice with a T cell-specific deletion of CD40L. CD40L null mice exhibited a blunted increase in T cell production of Wnt10b and abrogated CD40 signaling in SCs in response to iPTH treatment. Therefore, expression of the T cell surface receptor CD40L enables iPTH to exert its bone anabolic activity by activating CD40 signaling in SCs and maximally stimulating T cell production of Wnt10b.

Role of CD154 in cancer pathogenesis and immunotherapy

Many factors and molecules have been investigated as potential players in the pathogenesis or immunosurveillance of cancer. Among these, CD154 has been recognized as a co-stimulatory molecule with high potential for treating cancer, in addition to its contribution in the development of the disease. CD154 was initially described for its pivotal role in T cell-dependent humoral responses via an interaction with its classical receptor, CD40. Subsequent studies showed that CD154 is also implicated in cell-mediated immunity and inflammation via an interaction with CD40 alone or in combination with newly identified receptors, members of the integrin family, leading to the development of chronic inflammatory and autoimmune diseases. In the current article, we present an overview of the role of CD154 as a potential etiological factor in tumors inducing proliferation of malignant cells, their rescue from apoptosis and their invasiveness. In addition, this review describes the immuno-regulatory functions of CD154 against cancer reflected by its stimulation of antigen-presenting cells and the subsequent activation of effector cells, its enhancement of malignant cells' immunogenicity, its modulation of immune settings around tumors, and its initiation of proliferation inhibiting effects in malignant cells. In vitro as well as in vivo studies are outlined and a particular attention is given to clinical studies and progress reached at this point. Findings reviewed herein will improve our knowledge of the role of the CD154 system in cancers from causative to immunotherapeutic functions, paving the way for the identification of new targets for prevention and/or treatment of malignant disorders.

New frontiers for platelet CD154

The role of platelets extends beyond hemostasis. The pivotal role of platelets in inflammation has shed new light on the natural history of conditions associated with acute or chronic inflammation. Beyond the preservation of vascular integrity, platelets are essential to tissue homeostasis and platelet-derived products are already used in the clinics. Unanticipated was the role of platelets in the adaptative immune response, allowing a renewed conceptual approach of auto-immune diseases. Platelets are also important players in cancer growth and dissemination. Platelets fulfill most of their functions through the expression of still incompletely characterized membrane-bound or soluble mediators. Among them, CD154 holds a peculiar position, as platelets represent a major source of CD154 and as CD154 contributes to most of these new platelet attributes. Here, we provide an overview of some of the new frontiers that the study of platelet CD154 is opening, in inflammation, tissue homeostasis, immune response, hematopoiesis and cancer.

EGFL7 is expressed in bone microenvironment and promotes angiogenesis via ERK, STAT3, and integrin signaling cascades

Angiogenesis plays a pivotal role in bone formation, remodeling, and fracture healing. The regulation of angiogenesis in the bone microenvironment is highly complex and orchestrated by intercellular communication between bone cells and endothelial cells. Here, we report that EGF-like domain 7 (EGFL7), a member of the epidermal growth factor (EGF) repeat protein superfamily is expressed in both the osteoclast and osteoblast lineages, and promotes endothelial cell activities. Addition of exogenous recombinant EGFL7 potentiates SVEC (simian virus 40-transformed mouse microvascular endothelial cell line) cell migration and tube-like structure formation in vitro. Moreover, recombinant EGFL7 promotes angiogenesis featuring web-like structures in ex vivo fetal mouse metatarsal angiogenesis assay. We show that recombinant EGFL7 induces phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2), signal transducer and activator of transcription 3 (STAT3), and focal adhesion kinase (FAK) in SVEC cells. Inhibition of ERK1/2 and STAT3 signaling impairs EGFL7-induced endothelial cell migration, and angiogenesis in fetal mouse metatarsal explants. Bioinformatic analyses indicate that EGFL7 contains a conserved RGD/QGD motif and EGFL7-induced endothelial cell migration is significantly reduced in the presence of RGD peptides. Moreover, EGFL7 gene expression is significantly upregulated during growth plate injury repair. Together, these results demonstrate that EGFL7 expressed by bone cells regulates endothelial cell activities through integrin-mediated signaling. This study highlights the important role that EGFL7, like EGFL6, expressed in bone microenvironment plays in the regulation of angiogenesis in bone.

Interaction of CD154 with different receptors and its role in bidirectional signals

In addition to its classical receptor, CD40, it is now well established that CD154 also binds αIIbβ3, α5β1, and αMβ2 integrins. Although these integrins are all members of the same family, they bind CD154 differently. The current investigation aims to analyze the interaction of CD154 with α5β1 and αMβ2 and investigate its role in bidirectional signals in various human cell lines. Results obtained herein indicate that the CD154 residues involved in the interaction with α5β1 are N151 and Q166, whereas those involved in αMβ2 binding are common to residues required for CD40, namely Y145 and R203. Soluble CD40/CD154 or αMβ2/CD154 complexes do not interfere with the binding of CD154 to α5β1-positive cells, but inhibit the binding of CD154 to CD40- or αMβ2-positive cells, respectively. Ligation of CD154 on CD154-positive cells with soluble CD40, αIIbβ3, α5β1, or αMβ2 stimulates intracellular signaling, including MAPK phosphorylation. Given that CD154 exists as a trimer, our data strongly suggest that CD154 may bind concomitantly to two receptors of the same or different family, and biologically activate cells expressing both receptors. The characterization of CD154/receptor interactions helps the identification of new therapeutic targets for the prevention and/or treatment of CD154-associated autoimmune and inflammatory diseases.

The signaling role of CD40 ligand in platelet biology and in platelet component transfusion

The CD40 ligand (CD40L) is a transmembrane molecule of crucial interest in cell signaling in innate and adaptive immunity. It is expressed by a variety of cells, but mainly by activated T-lymphocytes and platelets. CD40L may be cleaved into a soluble form (sCD40L) that has a cytokine-like activity. Both forms bind to several receptors, including CD40. This interaction is necessary for the antigen specific immune response. Furthermore, CD40L and sCD40L are involved in inflammation and a panoply of immune related and vascular pathologies. Soluble CD40L is primarily produced by platelets after activation, degranulation and cleavage, which may present a problem for transfusion. Soluble CD40L is involved in adverse transfusion events including transfusion related acute lung injury (TRALI). Although platelet storage designed for transfusion occurs in sterile conditions, platelets are activated and release sCD40L without known agonists. Recently, proteomic studies identified signaling pathways activated in platelet concentrates. Soluble CD40L is a good candidate for platelet activation in an auto-amplification loop. In this review, we describe the immunomodulatory role of CD40L in physiological and pathological conditions. We will focus on the main signaling pathways activated by CD40L after binding to its different receptors.

Immune functions of platelets

This review collects evidence about immune and inflammatory functions of platelets from a clinician's point of view. A focus on clinically relevant immune functions aims at stimulating further research, because the complexity of platelet immunity is incompletely understood and not yet translated into patient care. Platelets promote chronic inflammatory reactions (e.g. in atherosclerosis), modulate acute inflammatory disorders such as sepsis and other infections (participating in the host defense against pathogens), and contribute to exacerbations of autoimmune conditions (like asthma or arthritis). It would hence be obsolete to restrict a description of platelet functions to thrombosis and haemostasis--platelets clearly are the most abundant cells with immune functions in the circulation.

Roles of ligands from the TNF superfamily in B cell development, function, and regulation

Most ligands from the tumour necrosis factor (TNF) superfamily play very important roles in the immune system, and particularly so in B lymphocyte biology. TNF ligands are essential to many aspects of normal B cell biology from development in the bone marrow to maturation in the periphery as well as for activation and differentiation into germinal centre, memory or plasma cells. TNF ligands also influence other aspects of B cell biology such as their ability to present antigens or regulate immune responses. Importantly, inadequate regulation of many TNF ligands is associated with B cell disorders including autoimmunity and cancers. As a result, inhibitors of a number of TNF ligands have been tested in the clinic, with some becoming very successful approved treatments alleviating B cell-mediated pathologies.

Immunoglobulin class switch recombination deficiency type 1 or CD40 ligand deficiency: from bedside to bench and back again

The immunoglobulin class switch recombination deficiency or hyper-IgM syndrome is characterized by normal or elevated serum IgM and low serum levels of other immunoglobulins. Since the first reported patient with hyper-IgM, more than 200 patients with this phenotype resulted from CD40 ligand deficiency have been reported. However, in addition to this common finding, they presented with different manifestations like opportunistic infections, autoimmunity and malignancies each of them are worth a detailed look. In this review, we will focus on different underlying mechanisms of these presentations to review what we have learned from our patients. In the end, we will discuss different treatment options available for these patients using this knowledge.

CD154 is released from T-cells by a disintegrin and metalloproteinase domain-containing protein 10 (ADAM10) and ADAM17 in a CD40 protein-dependent manner

CD154 (CD40 ligand) is a type II transmembrane protein that belongs to the tumor necrosis factor superfamily. The soluble form of CD154 (sCD154), which results from the shedding of membrane-bound CD154, plays a key role in the production of proinflammatory cytokines and has been linked to various autoimmune and vascular disorders. Therefore, elucidating the mechanisms by which CD154 is released from the cell surface following its interaction with its various receptors is of primordial importance. Using co-culture experiments, we show that CD154 is shed predominantly upon its engagement with CD40. Indeed, only CD40 (both membrane-bound and soluble) and not α5β1 or αMβ2 is involved in the cleavage and release of CD154 from Jurkat E6.1 T-cells. Interestingly, CD154 is cleaved independently of the formation of cell surface CD40 homodimers and independently of its association into lipid rafts. In contrast, we found that the protein kinase C (PKC) signaling family and the matrix metalloproteinases ADAM10 and ADAM17 are intimately involved in this process. In conclusion, our data indicate that CD154 is released from T-cells by ADAM10 and ADAM17 upon CD40 ligation. These findings add significant insights into the mechanisms by which CD154 is down-regulated and may lead to the generation of novel therapeutic targets for the treatment of CD154-associated disorders.

Osteoimmunology and its implications for transplantation

Osteoimmunology is a field of research dedicated to the study of the interactions between the immune system, the hemopoietic system and bone. Among the cells of the immune system that regulate bone cells and the hemopoietic function are T lymphocytes. These cells secrete inflammatory cytokines that promote bone resorption, as well as Wnt ligands that stimulate bone formation. In addition, T cells regulate bone homeostasis by cross talking with BM stromal cells and osteoblastic cells via CD40 ligand (CD40L) and other costimulatory molecules. This article describes the immune cells relevant to bone and the hemopoietic function, reviews the role of lymphocytes as mediators of the effects of PTH and estrogen in bone and the hemopoietic system and discusses the implication of osteoimmunology for transplant medicine.

CD154: the atherosclerotic risk factor in rheumatoid arthritis?

Atherosclerosis, now regarded as a chronic inflammatory disease of the arterial wall, and its clinical manifestations have increasingly been associated with rheumatoid arthritis (RA), supporting the notion that autoimmune diseases and vascular disorders share common etiological features. Indeed, evidence pertaining to this matter indicates that inflammation and its multiple components are the driving force behind the pathogenesis of these disorders. Interestingly, CD154 and its receptors have emerged as major players in the development of RA and atherosclerosis, which raises the possibility that this axis may represent an important biological link between both complications. Indeed, CD154 signaling elicits critical inflammatory responses that are common to the pathogenesis of both diseases. Here, we provide an overview of the traditional and disease-related interrelations between RA and vascular abnormalities, while focusing on CD154 as a potential mediator in the development of atherosclerotic events in RA patients.

Requirement of transmembrane domain for CD154 association to lipid rafts and subsequent biological events

Interaction of CD40 with CD154 leads to recruitment of both molecules into lipid rafts, resulting in bi-directional cell activation. The precise mechanism by which CD154 is translocated into lipid rafts and its impact on CD154 signaling remain largely unknown. Our aim is to identify the domain of CD154 facilitating its association to lipid rafts and the impact of such association on signaling events and cytokine production. Thus, we generated Jurkat cell lines expressing truncated CD154 lacking the cytoplasmic domain or chimeric CD154 in which the transmembrane domain was replaced by that of transferrin receptor I, known to be excluded from lipid rafts. Our results show that cell stimulation with soluble CD40 leads to the association of CD154 wild-type and CD154-truncated, but not CD154-chimera, with lipid rafts. This is correlated with failure of CD154-chimera to activate Akt and p38 MAP kinases, known effectors of CD154 signaling. We also found that CD154-chimera lost the ability to promote IL-2 production upon T cell stimulation with anti-CD3/CD28 and soluble CD40. These results demonstrate the implication of the transmembrane domain of CD154 in lipid raft association, and that this association is necessary for CD154-mediated Akt and p38 activation with consequent enhancement of IL-2 production.