Integrin alphaDbeta2, an adhesion receptor up-regulated on macrophage foam cells, exhibits multiligand-binding properties

Regulating Blood Clot Fibrin Films to Manipulate Biomaterial-Mediated Foreign Body Responses

The clinical efficacy of implanted biomaterials is often compromised by host immune recognition and subsequent foreign body responses (FBRs). During the implantation, biomaterials inevitably come into direct contact with the blood, absorbing blood protein and forming blood clot. Many studies have been carried out to regulate protein adsorption, thus manipulating FBR. However, the role of clot surface fibrin films formed by clotting shrinkage in host reactions and FBR is often ignored. Because of the principle of fibrin film formation being relevant to fibrinogen or clotting factor absorption, it is feasible to manipulate the fibrin film formation via tuning the absorption of fibrinogen and clotting factor. As biological hydroxyapatite reserved bone architecture and microporous structure, the smaller particle size may expose more microporous structures and adsorb more fibrinogen or clotting factor. Therefore, we set up 3 sizes (small, <0.2 mm; medium, 1 to 2 mm; large, 3 to 4 mm) of biological hydroxyapatite (porcine bone-derived hydroxyapatite) with different microporous structures to investigate the absorption of blood protein, the formation of clot surface fibrin films, and the subsequent FBR. We found that small group adsorbed more clotting factors because of more microporous structures and formed the thinnest and sparsest fibrin films. These thinnest and sparsest fibrin films increased inflammation and profibrosis of macrophages through a potential signaling pathway of cell adhesion-cytoskeleton-autophagy, leading to the stronger FBR. Large group adsorbed lesser clotting factors, forming the thickest and densest fibrin films, easing inflammation and profibrosis of macrophages, and finally mitigating FBR. Thus, this study deepens the understanding of the role of fibrin films in host recognition and FBR and demonstrates the feasibility of a strategy to regulate FBR by modulating fibrin films via tuning the absorption of blood proteins.

CCN1 upregulates IL-36 via AKT/NF-κB and ERK/CEBP β-mediated signaling pathways in psoriasis-like models

Psoriasis is a chronic skin disorder characterized by epidermal keratinocyte hyperproliferation and inflammatory infiltration. CCN1 (also termed CYR61 or cysteine-rich angiogenic inducer 61) is an extracellular matrix-associated protein that is involved in multiple physiological functions. In psoriasis, we recently demonstrated that the overexpression of CCN1 promoted keratinocyte proliferation and activation. Furthermore, CCN1 was highly expressed in psoriatic skin lesions from psoriasis vulgaris patients. Here, we dissect the underlying molecular mechanism in imiquimod (IMQ) and interleukin (IL)-23-induced psoriasis-like models. Our results demonstrate that CCN1 can significantly upregulate IL-36 production in the murine skin of IMQ and IL-23-induced psoriasis-like models. Injection of CCN1-neutralizing antibody improved epidermal acanthosis and significantly reduced IL-36 production in vivo. These results suggest that CCN1 can be a critical upstream pro-inflammatory factor in psoriasis. In primary normal human epidermal keratinocytes, we demonstrated that CCN1 can selectively induced the production of IL-36α and IL-36γ through the activation of the protein kinase B (AKT)/nuclear factor kappa light chain enhancer of activated B cells (NF-κB) and extracellular-regulated kinase (ERK)/CCAAT/enhancer binding protein β (CEBPβ) signaling pathways via integrin receptor α6β1 in vitro. Our results suggest that targeting CCN1 can be a potential therapeutic strategy for psoriasis.

Targeting integrin pathways: mechanisms and advances in therapy

Integrins are considered the main cell-adhesion transmembrane receptors that play multifaceted roles as extracellular matrix (ECM)-cytoskeletal linkers and transducers in biochemical and mechanical signals between cells and their environment in a wide range of states in health and diseases. Integrin functions are dependable on a delicate balance between active and inactive status via multiple mechanisms, including protein-protein interactions, conformational changes, and trafficking. Due to their exposure on the cell surface and sensitivity to the molecular blockade, integrins have been investigated as pharmacological targets for nearly 40 years, but given the complexity of integrins and sometimes opposite characteristics, targeting integrin therapeutics has been a challenge. To date, only seven drugs targeting integrins have been successfully marketed, including abciximab, eptifibatide, tirofiban, natalizumab, vedolizumab, lifitegrast, and carotegrast. Currently, there are approximately 90 kinds of integrin-based therapeutic drugs or imaging agents in clinical studies, including small molecules, antibodies, synthetic mimic peptides, antibody-drug conjugates (ADCs), chimeric antigen receptor (CAR) T-cell therapy, imaging agents, etc. A serious lesson from past integrin drug discovery and research efforts is that successes rely on both a deep understanding of integrin-regulatory mechanisms and unmet clinical needs. Herein, we provide a systematic and complete review of all integrin family members and integrin-mediated downstream signal transduction to highlight ongoing efforts to develop new therapies/diagnoses from bench to clinic. In addition, we further discuss the trend of drug development, how to improve the success rate of clinical trials targeting integrin therapies, and the key points for clinical research, basic research, and translational research.

Regulation of CD18 stability by SIGIRR-modulated ubiquitination: new insights into the relationship between innate immune response and acute lung injury

Inappropriate accumulation of alveolar macrophages (AMs) and subsequent excessive production of immune responses play critical roles in the pathogenesis of acute lung injury (ALI), but the core negative regulators governing innate signalling in AMs are ill defined. We have previously shown that single immunoglobin IL-1 receptor-related protein (SIGIRR), a negative regulator of IL-1 receptor and Toll-like receptor signalling, inhibits lipopolysaccharide (LPS)-induced inflammatory responses in AMs. To address the biological relevance of SIGIRR in vivo, we generated a murine ALI model via intratracheal instillation of LPS. Intriguingly, SIGIRR expression was observed to be decreased in resident and recruited macrophages during ALI. This decrease was associated with parallel induction in CD18 protein levels in LPS-challenged lung tissues. Through intranasal injection of SIGIRR lentiviral particles studies, we showed that the overexpression of SIGIRR attenuated recruitment of macrophages and neutrophils, decreased production of inflammatory cytokines and ameliorated pathological changes in lungs. Whilst exploring the basis for this phenotype, SIGIRR was found to be coexpressed with CD18 in AMs, and SIGIRR potentiated the instability of CD18 protein via enhancement of its ubiquitination and proteasome degradation. Conversely, by using CD18^-/- mice, we further observed that CD18 deletion completely abolished the therapeutic effects of overexpression of SIGIRR on LPS-induced ALI. Mover, overexpression of CD18 in AMs promoted adhesion to ECM components, enhanced TLR4-mediated inflammasome activation and thereby potentiated IL-1β production. These data collectively identify SIGIRR/CD18 as a key negative regulatory circuit maintaining innate immune homeostasis in AMs along the pathogenesis of ALI.

Modification of Extracellular Matrix by the Product of DHA Oxidation Switches Macrophage Adhesion Patterns and Promotes Retention of Macrophages During Chronic Inflammation

Oxidation of polyunsaturated fatty acids contributes to different aspects of the inflammatory response due to the variety of products generated. Specifically, the oxidation of DHA produces the end-product, carboxyethylpyrrole (CEP), which forms a covalent adduct with proteins via an ϵ-amino group of lysines. Previously, we found that CEP formation is dramatically increased in inflamed tissue and CEP-modified albumin and fibrinogen became ligands for α_Dβ₂ (CD11d/CD18) and α_Mβ₂ (CD11b/CD18) integrins. In this study, we evaluated the effect of extracellular matrix (ECM) modification with CEP on the adhesive properties of M1-polarized macrophages, particularly during chronic inflammation. Using digested atherosclerotic lesions and in vitro oxidation assays, we demonstrated the ability of ECM proteins to form adducts with CEP, particularly, DHA oxidation leads to the formation of CEP adducts with collagen IV and laminin, but not with collagen I. Using integrin α_Dβ₂-transfected HEK293 cells, WT and αD-/- mouse M1-polarized macrophages, we revealed that CEP-modified proteins support stronger cell adhesion and spreading when compared with natural ECM ligands such as collagen IV, laminin, and fibrinogen. Integrin α_Dβ₂ is critical for M1 macrophage adhesion to CEP. Based on biolayer interferometry results, the isolated α_D I-domain demonstrates markedly higher binding affinity to CEP compared to the "natural" α_Dβ₂ ligand fibrinogen. Finally, the presence of CEP-modified proteins in a 3D fibrin matrix significantly increased M1 macrophage retention. Therefore, CEP modification converts ECM proteins to α_Dβ₂-recognition ligands by changing a positively charged lysine to negatively charged CEP, which increases M1 macrophage adhesion to ECM and promotes macrophage retention during detrimental inflammation, autoimmunity, and chronic inflammation.

The Role of CCN1 in Esophageal Adenocarcinoma: What We Have Learned From the Lab

Background: Esophageal cancer is one of the most common and deadliest cancers in the world, particularly esophageal adenocarcinoma. There has never been a special drug to treat it.Purpose: This article summarizes the work that we have done in our laboratory about the role of CCN1 in esophageal cancer and gives a new perspective of CCN1 biology.Research Design: This is a review article. Study Sample: The work was done using validated cell lines and fixed human tissue slides.Data Collection and Analysis: This is a review article, therefore, no data collection or analysis was involved.Results: CCN1 is a matricellular protein supporting adhesion, migration, and survival in normal cells, but in the esophageal cancer cells, it induces TRAIL-mediated apoptosis. CCN1 promotes TRAIL and its death receptor expression but downregulates the decoy receptors and survivin in a p53-dependant manner. It was thought that CCN1 relies on TNF to induce apoptosis, but our study found that these two molecules antagonize each other. CCN1 promotes TNFR1 cleavage and uses the soluble product to block TNF signaling, while TNF upregulates PGLYRP1 to overcome this obstacle because PGLYRP1 is a secreted protein that competes with TNF for TNFR1 binding. As a result, when CCN1 and TNF are present together in the vicinity of esophageal tumors, they cancel each other out.Conclusions: Based on our laboratory study, CCN1 has much potential to be a candidate for the treatment of esophageal cancer.

β2 Integrin CD11d/CD18: From Expression to an Emerging Role in Staged Leukocyte Migration

CD11d/CD18 is the most recently discovered and least understood β2 integrin. Known CD11d adhesive mechanisms contribute to both extravasation and mesenchymal migration – two key aspects for localizing peripheral leukocytes to sites of inflammation. Differential expression of CD11d induces differences in monocyte/macrophage mesenchymal migration including impacts on macrophage sub-set migration. The participation of CD11d/CD18 in leukocyte localization during atherosclerosis and following neurotrauma has sparked interest in the development of CD11d-targeted therapeutic agents. Whereas the adhesive properties of CD11d have undergone investigation, the signalling pathways induced by ligand binding remain largely undefined. Underlining each adhesive and signalling function, CD11d is under unique transcriptional control and expressed on a sub-set of predominately tissue-differentiated innate leukocytes. The following review is the first to capture the nearly three decades of CD11d research and discusses the emerging role of CD11d in leukocyte migration and retention during the progression of a staged immune response.

ITGB2 as a prognostic indicator and a predictive marker for immunotherapy in gliomas

PURPOSE

Glioma is the most common primary tumor in the brain, accounting for 81% of intracranial malignancies. Nowadays, cancer immunotherapy has become a novel and revolutionary treatment for patients with advanced, highly aggressive tumors. However, to date, there are no effective biomarkers to reflect the response of glioma patients to immunotherapy. In this study, we aimed to assess the clinical predictive value of ITGB2 in patients with glioma.

METHODS

The correlation between ITGB2 expression levels and glioma progression was explored and validated using data from CGGA, TCGA, GEO datasets, and patient samples from our hospital. Univariate and multivariate cox regression models were developed to determine the predictive role of ITGB2 on the prognosis of patients with glioma. The relationship between ITGB2 and immune activation was then analyzed. Finally, we predicted the immunotherapy response in both high and low ITGB2 expression subgroups.

RESULTS

ITGB2 was significantly elevated in gliomas with higher malignancy and predicted poor prognosis. In multivariate analysis, the hazard ratio for ITGB2 expression (low versus high) was 0.71 with 95% CI (0.59-0.85) (P < 0.001). Furthermore, we found that ITGB2 stratified glioma patients into high and low ITGB2 expression subgroups, exhibiting different clinical outcomes and immune activation status. At last, we demonstrated that glioma patients with high ITGB2 expression levels had better immunotherapy response.

CONCLUSIONS

This study demonstrated ITGB2 as a novel predictor for clinical prognosis and response to immunotherapy in gliomas. Assessing expression levels of ITGB2 is a promising method to discover patients that may benefit from immunotherapy.

Frontline Science: The expression of integrin αD β2 (CD11d/CD18) on neutrophils orchestrates the defense mechanism against endotoxemia and sepsis

Neutrophil-macrophage interplay is a fine-tuning mechanism that regulates the innate immune response during infection and inflammation. Cell surface receptors play an essential role in neutrophil and macrophage functions. The same receptor can provide different outcomes within diverse leukocyte subsets in different inflammatory conditions. Understanding the variety of responses mediated by one receptor is critical for the development of anti-inflammatory treatments. In this study, we evaluated the role of a leukocyte adhesive receptor, integrin αD β2 , in the development of acute inflammation. αD β2 is mostly expressed on macrophages and contributes to the development of chronic inflammation. In contrast, we found that αD -knockout dramatically increases mortality in the cecal ligation and puncture sepsis model and LPS-induced endotoxemia. This pathologic outcome of αD -deficient mice is associated with a reduced number of monocyte-derived macrophages and an increased number of neutrophils in their lungs. However, the tracking of adoptively transferred fluorescently labeled wild-type (WT) and αD-/- monocytes in WT mice during endotoxemia demonstrated only a moderate difference between the recruitment of these two subsets. Moreover, the rescue experiment, using i.v. injection of WT monocytes to αD -deficient mice followed by LPS challenge, showed only slightly reduced mortality. Surprisingly, the injection of WT neutrophils to the bloodstream of αD-/- mice markedly increased migration of monocyte-derived macrophage to lungs and dramatically improves survival. αD -deficient neutrophils demonstrate increased necrosis/pyroptosis. αD β2 -mediated macrophage accumulation in the lungs promotes efferocytosis that reduced mortality. Hence, integrin αD β2 implements a complex defense mechanism during endotoxemia, which is mediated by macrophages via a neutrophil-dependent pathway.

The Promiscuous Profile of Complement Receptor 3 in Ligand Binding, Immune Modulation, and Pathophysiology

The β2-integrin receptor family has a broad spectrum of physiological functions ranging from leukocyte adhesion, cell migration, activation, and communication to the phagocytic uptake of cells and particles. Among the members of this family, complement receptor 3 (CR3; CD11b/CD18, Mac-1, αMβ2) is particularly promiscuous in its functional profile and ligand selectivity. There are close to 100 reported structurally unrelated ligands for CR3, and while many ligands appear to cluster at the αMI domain, molecular details about binding modes remain largely elusive. The versatility of CR3 is reflected in its functional portfolio, which includes prominent roles in the removal of invaders and cell debris, induction of tolerance and synaptic pruning, and involvement in the pathogenesis of numerous autoimmune and chronic inflammatory pathologies. While CR3 is an interesting therapeutic target for immune modulation due to these known pathophysiological associations, drug development efforts are limited by concerns of potential interference with host defense functions and, most importantly, an insufficient molecular understanding of the interplay between ligand binding and functional impact. Here, we provide a systematic summary of the various interaction partners of CR3 with a focus on binding mechanisms and functional implications. We also discuss the roles of CR3 as an immune receptor in health and disease, as an activation marker in research and diagnostics, and as a therapeutic target.

Cyr61 promotes Schwann cell proliferation and migration via αvβ3 integrin

BACKGROUND

Schwann cells (SCs) play a crucial role in the repair of peripheral nerves. This is due to their ability to proliferate, migrate, and provide trophic support to axon regrowth. During peripheral nerve injury, SCs de-differentiate and reprogram to gain the ability to repair nerves. Cysteine-rich 61 (Cyr61/CCN1) is a member of the CCN family of matrix cell proteins and have been reported to be abundant in the secretome of repair mediating SCs. In this study we investigate the function of Cyr61 in SCs.

RESULTS

We observed Cyr61 was expressed both in vivo and in vitro. The promoting effect of Cyr61 on SC proliferation and migration was through autocrine and paracrine mechanisms. SCs expressed αvβ3 integrin and the effect of Cyr61 on SC proliferation and migration could be blocked via αvβ3 integrin. Cyr61 could influence c-Jun protein expression in cultured SCs.

CONCLUSIONS

In this study, we found that Cyr61 promotes SC proliferation and migration via αvβ3 integrin and regulates c-Jun expression. Our study contributes to the understanding of cellular and molecular mechanisms underlying SC's function during nerve injury, and thus, may facilitate the regeneration of peripheral nerves after injury.

The Activation and Regulation of β2 Integrins in Phagocytes and Phagocytosis

Phagocytes, which include neutrophils, monocytes, macrophages, and dendritic cells, protect the body by removing foreign particles, bacteria, and dead or dying cells. Phagocytic integrins are greatly involved in the recognition of and adhesion to specific antigens on cells and pathogens during phagocytosis as well as the recruitment of immune cells. β2 integrins, including αLβ2, αMβ2, αXβ2, and αDβ2, are the major integrins presented on the phagocyte surface. The activation of β2 integrins is essential to the recruitment and phagocytic function of these phagocytes and is critical for the regulation of inflammation and immune defense. However, aberrant activation of β2 integrins aggravates auto-immune diseases, such as psoriasis, arthritis, and multiple sclerosis, and facilitates tumor metastasis, making them double-edged swords as candidates for therapeutic intervention. Therefore, precise regulation of phagocyte activities by targeting β2 integrins should promote their host defense functions with minimal side effects on other cells. Here, we reviewed advances in the regulatory mechanisms underlying β2 integrin inside-out signaling, as well as the roles of β2 integrin activation in phagocyte functions.

Biomechanical Contributions to Macrophage Activation in the Tumor Microenvironment

Alterations in extracellular matrix composition and organization are known to promote tumor growth and metastatic progression in breast cancer through interactions with tumor cells as well as stromal cell populations. Macrophages display a spectrum of behaviors from tumor-suppressive to tumor-promoting, and their function is spatially and temporally dependent upon integrated signals from the tumor microenvironment including, but not limited to, cytokines, metabolites, and hypoxia. Through years of investigation, the specific biochemical cues that recruit and activate tumor-promoting macrophage functions within the tumor microenvironment are becoming clear. In contrast, the impact of biomechanical stimuli on macrophage activation has been largely underappreciated, however there is a growing body of evidence that physical cues from the extracellular matrix can influence macrophage migration and behavior. While the complex, heterogeneous nature of the extracellular matrix and the transient nature of macrophage activation make studying macrophages in their native tumor microenvironment challenging, this review highlights the importance of investigating how the extracellular matrix directly and indirectly impacts tumor-associated macrophage activation. Additionally, recent advances in investigating macrophages in the tumor microenvironment and future directions regarding mechano-immunomodulation in cancer will also be discussed.

Dendritic Cells as Targets for Biomaterial-Based Immunomodulation

Various subtypes of immunocytes react against implanted biomaterials to eliminate the foreign body object from the host's body. Among these cells, dendritic cells (DCs) play a key role in early immune response, later engaging lymphocytes through antigens presentation. Due to their capability to induce tolerogenic or immunogenic responses, DCs have been considered as key therapeutic targets for immunomodulatory products. For instance, tolerogenic DCs are applied in the treatment of autoimmune diseases, rejection of allograft transplantation, and implanted biomaterial. Due to the emerging importance of DCs in immunomodulatory biomaterials, this Review summarizes DCs' responses-such as adhesion, migration, and maturation-to biomaterials. We also review some examples of key molecules and their applications in DCs' immunoengineering. These evaluations would pave the way for designing advanced biomaterials and nanomaterials to modulate the immune system, applicable in tissue engineering, transplantation, and drug delivery technologies.

β2 Integrins-Multi-Functional Leukocyte Receptors in Health and Disease

β2 integrins are heterodimeric surface receptors composed of a variable α (CD11a-CD11d) and a constant β (CD18) subunit and are specifically expressed by leukocytes. The α subunit defines the individual functional properties of the corresponding β2 integrin, but all β2 integrins show functional overlap. They mediate adhesion to other cells and to components of the extracellular matrix (ECM), orchestrate uptake of extracellular material like complement-opsonized pathogens, control cytoskeletal organization, and modulate cell signaling. This review aims to delineate the tremendous role of β2 integrins for immune functions as exemplified by the phenotype of LAD-I (leukocyte adhesion deficiency 1) patients that suffer from strong recurrent infections. These immune defects have been largely attributed to impaired migratory and phagocytic properties of polymorphonuclear granulocytes. The molecular base for this inherited disease is a functional impairment of β2 integrins due to mutations within the CD18 gene. LAD-I patients are also predisposed for autoimmune diseases. In agreement, polymorphisms within the CD11b gene have been associated with autoimmunity. Consequently, β2 integrins have received growing interest as targets in the treatment of autoimmune diseases. Moreover, β2 integrin activity on leukocytes has been implicated in tumor development.

Integrin αDβ2 influences cerebral edema, leukocyte accumulation and neurologic outcomes in experimental severe malaria

Malaria is an infectious disease of major worldwide clinical importance that causes a variety of severe, or complicated, syndromes including cerebral malaria, which is often fatal. Leukocyte integrins are essential for host defense but also mediate physiologic responses of the innate and adaptive immune systems. We previously showed that targeted deletion of the α_D subunit (α_D^-/-) of the α_Dβ₂ integrin, which is expressed on key leukocyte subsets in mice and humans, leads to absent expression of the integrin heterodimer on murine macrophages and reduces mortality in mice infected with Plasmodium berghei ANKA (P. berghei ANKA). To further identify mechanisms involved in the protective effect of α_D deletion in this model of severe malaria we examined wild type C57BL/6 (WT) and α_D^-/- mice after P. berghei ANKA infection and found that vessel plugging and leukocyte infiltration were significantly decreased in the brains of α_D^-/- animals. Intravital microscopy demonstrated decreased rolling and adhesion of leukocytes in cerebral vessels of α_D^-/- mice. Flow cytometry analysis showed decreased T-lymphocyte accumulation in the brains of infected α_D^-/- animals. Evans blue dye exclusion assays demonstrated significantly less dye extravasation in the brains of α_D^-/- mice, indicating preserved blood-brain barrier integrity. WT mice that were salvaged from P. berghei ANKA infection by treatment with chloroquine had impaired aversive memory, which was not observed in α_D^-/- mice. We conclude that deletion of integrin α_Dβ₂ alters the natural course of experimental severe malaria, demonstrating previously unrecognized activities of a key leukocyte integrin in immune-inflammatory responses that mediate cerebral involvement.

Inhibition of integrin αDβ2-mediated macrophage adhesion to end product of docosahexaenoic acid (DHA) oxidation prevents macrophage accumulation during inflammation

A critical step in the development of chronic inflammatory diseases is the accumulation of proinflammatory macrophages in the extracellular matrix (ECM) of peripheral tissues. The adhesion receptor integrin α_Dβ₂ promotes the development of atherosclerosis and diabetes by supporting macrophage retention in inflamed tissue. We recently found that the end product of docosahexaenoic acid (DHA) oxidation, 2-(ω-carboxyethyl)pyrrole (CEP), serves as a ligand for α_Dβ₂ CEP adduct with ECM is generated during inflammation-mediated lipid peroxidation. The goal of this project was to identify a specific inhibitor for α_Dβ₂-CEP interaction that can prevent macrophage accumulation. Using a specially designed peptide library, Biacore-detected protein-protein interaction, and adhesion of integrin-transfected HEK 293 cells, we identified a sequence (called P5 peptide) that significantly and specifically inhibited α_D-CEP binding. In the model of thioglycollate-induced peritoneal inflammation, the injection of cyclic P5 peptide reduced 3-fold the macrophage accumulation in WT mice but had no effect in α_D-deficient mice. The tracking of adoptively transferred, fluorescently labeled WT and α_D ^-/- monocytes in the model of peritoneal inflammation and in vitro two-dimensional and three-dimensional migration assays demonstrated that P5 peptide does not affect monocyte transendothelial migration or macrophage efflux from the peritoneal cavity but regulates macrophage migration through the ECM. Moreover, the injection of P5 peptide into WT mice on a high-fat diet prevents macrophage accumulation in adipose tissue in an α_Dβ₂-dependent manner. Taken together, these results demonstrate the importance of α_Dβ₂-mediated macrophage adhesion for the accumulation of infiltrating macrophages in the inflamed ECM and propose P5 peptide as a potential inhibitor of atherogenesis and diabetes.

Molecular signatures for CCN1, p21 and p27 in progressive mantle cell lymphoma

Mantle cell lymphoma (MCL) is a comparatively rare non-Hodgkin's lymphoma characterised by overexpression of cyclin D1. Many patients present with or progress to advanced stage disease within 3 years. MCL is considered an incurable disease with median survival between 3 and 4 years. We have investigated the role(s) of CCN1 (CYR61) and cell cycle regulators in progressive MCL. We have used the human MCL cell lines REC1 < G519 < JVM2 as a model for disease aggression. The magnitude of CCN1 expression in human MCL cells is REC1 > G519 > JVM2 cells by RQ-PCR, depicting a decrease in CCN1 expression with disease progression. Investigation of CCN1 isoform expression by western blotting showed that whilst expression of full-length CCN1 was barely altered in the cell lines, expression of truncated forms (18-20 and 28-30 kDa) decreased with disease progression. We have then demonstrated that cyclin D1 and cyclin dependent kinase inhibitors (p21^CIP1and p27^KIP1) are also involved in disease progression. Cyclin D1 was highly expressed in REC1 cells (OD: 1.0), reduced to one fifth in G519 cells (OD: 0.2) and not detected by western blotting in JVM2 cells. p27^KIP1 followed a similar profile of expression as cyclin D1. Conversely, p21^CIP1 was absent in the REC1 cells and showed increasing expression in G519 and JVM2 cells. Subcellular localization detected p21^CIP1/ p27^KIP1 primarily within the cytoplasm and absent from the nucleus, consistent with altered roles in treatment resistance. Dysregulation of the CCN1 truncated forms are associated with MCL progression. In conjunction with reduced expression of cyclin D1 and increased expression of p21, this molecular signature may depict aggressive disease and treatment resistance.

Distinct Migratory Properties of M1, M2, and Resident Macrophages Are Regulated by αDβ2 and αMβ2 Integrin-Mediated Adhesion

Chronic inflammation is essential mechanism during the development of cardiovascular and metabolic diseases. The outcome of diseases depends on the balance between the migration/accumulation of pro-inflammatory (M1) and anti-inflammatory (M2) macrophages in damaged tissue. The mechanism of macrophage migration and subsequent accumulation is still not fully understood. Currently, the amoeboid adhesion-independent motility is considered essential for leukocyte migration in the three-dimensional environment. We challenge this hypothesis by studying the contribution of leukocyte adhesive receptors, integrins α_Mβ₂, and α_Dβ₂, to three-dimensional migration of M1-polarized, M2-polarized, and resident macrophages. Both integrins have a moderate expression on M2 macrophages, while α_Dβ₂ is upregulated on M1 and α_Mβ₂ demonstrates high expression on resident macrophages. The level of integrin expression determines its contribution to macrophage migration. Namely, intermediate expression supports macrophage migration, while a high integrin density inhibits it. Using in vitro three-dimensional migration and in vivo tracking of adoptively-transferred fluorescently-labeled macrophages during the resolution of inflammation, we found that strong adhesion of M1-activated macrophages translates to weak 3D migration, while moderate adhesion of M2-activated macrophages generates dynamic motility. Reduced migration of M1 macrophages depends on the high expression of α_Dβ₂, since α_D-deficiency decreased M1 macrophage adhesion and improved migration in fibrin matrix and peritoneal tissue. Similarly, the high expression of α_Mβ₂ on resident macrophages prevents their amoeboid migration, which is markedly increased in α_M-deficient macrophages. In contrast, α_D- and α_M-knockouts decrease the migration of M2 macrophages, demonstrating that moderate integrin expression supports cell motility. The results were confirmed in a diet-induced diabetes model. α_D deficiency prevents the retention of inflammatory macrophages in adipose tissue and improves metabolic parameters, while α_M deficiency does not affect macrophage accumulation. Summarizing, β₂ integrin-mediated adhesion may inhibit amoeboid and mesenchymal macrophage migration or support mesenchymal migration in tissue, and, therefore, represents an important target to control inflammation.

Oxidative modifications of extracellular matrix promote the second wave of inflammation via β2 integrins

Early stages of inflammation are characterized by extensive oxidative insult by recruited and activated neutrophils. Secretion of peroxidases, including the main enzyme, myeloperoxidase, leads to the generation of reactive oxygen species. We show that this oxidative insult leads to polyunsaturated fatty acid (eg, docosahexaenoate), oxidation, and accumulation of its product 2-(ω-carboxyethyl)pyrrole (CEP), which, in turn, is capable of protein modifications. In vivo CEP is generated predominantly at the inflammatory sites in macrophage-rich areas. During thioglycollate-induced inflammation, neutralization of CEP adducts dramatically reduced macrophage accumulation in the inflamed peritoneal cavity while exhibiting no effect on the early recruitment of neutrophils, suggesting a role in the second wave of inflammation. CEP modifications were abundantly deposited along the path of neutrophils migrating through the 3-dimensional fibrin matrix in vitro. Neutrophil-mediated CEP formation was markedly inhibited by the myeloperoxidase inhibitor, 4-ABH, and significantly reduced in myeloperoxidase-deficient mice. On macrophages, CEP adducts were recognized by cell adhesion receptors, integrin αMβ2 and αDβ2 Macrophage migration through CEP-fibrin gel was dramatically augmented when compared with fibrin alone, and was reduced by β2-integrin deficiency. Thus, neutrophil-mediated oxidation of abundant polyunsaturated fatty acids leads to the transformation of existing proteins into stronger adhesive ligands for αMβ2- and αDβ2-dependent macrophage migration. The presence of a carboxyl group rather than a pyrrole moiety on these adducts, resembling characteristics of bacterial and/or immobilized ligands, is critical for recognition by macrophages. Therefore, specific oxidation-dependent modification of extracellular matrix, aided by neutrophils, promotes subsequent αMβ2- and αDβ2-mediated migration/retention of macrophages during inflammation.

Integrin αDβ2 (CD11d/CD18) Modulates Leukocyte Accumulation, Pathogen Clearance, and Pyroptosis in Experimental Salmonella Typhimurium Infection

β₂ integrins are critical in host defense responses to invading pathogens and inflammation. Previously, we reported that genetic deficiency of integrin α_Dβ₂ in mice altered outcomes in experimental systemic infections including accelerated mortality in animals infected with Salmonella enterica serovar Typhimurium. Here, we show that deficiency of α_Dβ₂ results in impaired accumulation of leukocytes in response to peritoneal infection by S. Typhimurium, impaired pathogen clearance in vivo, defective bacterial elimination by cultured peritoneal macrophages, and enhanced pyroptosis, a cell death process triggered by Salmonella. Salmonella-infected animals deficient in α_Dβ₂ had increased levels of peritoneal cytokines in addition to other markers of pyroptosis, which may contribute to inflammatory injury and increased mortality in the context of impaired bacterial killing. These observations indicate important contributions of leukocyte integrins to the host response in experimental Salmonella infection and reveal previous activities of α_Dβ₂ in bacterial infection.

The membrane-distal regions of integrin α cytoplasmic domains contribute differently to integrin inside-out activation

Functioning as signal receivers and transmitters, the integrin α/β cytoplasmic tails (CT) are pivotal in integrin activation and signaling. 18 α integrin subunits share a conserved membrane-proximal region but have a highly diverse membrane-distal (MD) region at their CTs. Recent studies demonstrated that the presence of α CTMD region is essential for talin-induced integrin inside-out activation. However, it remains unknown whether the non-conserved α CTMD regions differently regulate the inside-out activation of integrin. Using αIIbβ3, αLβ2, and α5β1 as model integrins and by replacing their α CTMD regions with those of α subunits that pair with β3, β2, and β1 subunits, we analyzed the function of CTMD regions of 17 α subunits in talin-mediated integrin activation. We found that the α CTMD regions play two roles on integrin, which are activation-supportive and activation-regulatory. The regulatory but not the supportive function depends on the sequence identity of α CTMD region. A membrane-proximal tyrosine residue present in the CTMD regions of a subset of α integrins was identified to negatively regulate integrin inside-out activation. Our study provides a useful resource for investigating the function of α integrin CTMD regions.

β2 Integrins As Regulators of Dendritic Cell, Monocyte, and Macrophage Function

Emerging evidence suggests that the β₂ integrin family of adhesion molecules have an important role in suppressing immune activation and inflammation. β₂ integrins are important adhesion and signaling molecules that are exclusively expressed on leukocytes. The four β₂ integrins (CD11a, CD11b, CD11c, and CD11d paired with the β₂ chain CD18) play important roles in regulating three key aspects of immune cell function: recruitment to sites of inflammation; cell-cell contact formation; and downstream effects on cellular signaling. Through these three processes, β₂ integrins both contribute to and regulate immune responses. This review explores the pro- and anti-inflammatory effects of β₂ integrins in monocytes, macrophages, and dendritic cells and how they influence the outcome of immune responses. We furthermore discuss how imbalances in β₂ integrin function can have far-reaching effects on mounting appropriate immune responses, potentially influencing the development and progression of autoimmune and inflammatory diseases. Therapeutic targeting of β₂ integrins, therefore, holds enormous potential in exploring treatment options for a variety of inflammatory conditions.

The Upregulation of Integrin αDβ2 (CD11d/CD18) on Inflammatory Macrophages Promotes Macrophage Retention in Vascular Lesions and Development of Atherosclerosis

Macrophage accumulation is a critical step during development of chronic inflammation, initiating progression of many devastating diseases. Leukocyte-specific integrin α_Dβ₂ (CD11d/CD18) is dramatically upregulated on macrophages at inflammatory sites. Previously we found that CD11d overexpression on cell surfaces inhibits in vitro cell migration due to excessive adhesion. In this study, we have investigated how inflammation-mediated CD11d upregulation contributes to macrophage retention at inflammatory sites during atherogenesis. Atherosclerosis was evaluated in CD11d^-/-/ApoE^-/- mice after 16 wk on a Western diet. CD11d deficiency led to a marked reduction in lipid deposition in aortas and isolated macrophages. Macrophage numbers in aortic sinuses of CD11d^-/- mice were reduced without affecting their apoptosis and proliferation. Adoptive transfer of fluorescently labeled wild-type and CD11d^-/- monocytes into ApoE^-/- mice demonstrated similar recruitment from circulation, but reduced accumulation of CD11d^-/- macrophages within the aortas. Furthermore, CD11d expression was significantly upregulated on macrophages in atherosclerotic lesions and M1 macrophages in vitro. Interestingly, expression of the related ligand-sharing integrin CD11b was not altered. This difference defines their distinct roles in the regulation of macrophage migration. CD11d-deficient M1 macrophages demonstrated improved migration in a three-dimensional fibrin matrix and during resolution of peritoneal inflammation, whereas migration of CD11b^-/- M1 macrophages was not affected. These results prove the contribution of high densities of CD11d to macrophage arrest during atherogenesis. Because high expression of CD11d was detected in several inflammation-dependent diseases, we suggest that CD11d/CD18 upregulation on proinflammatory macrophages may represent a common mechanism for macrophage retention at inflammatory sites, thereby promoting chronic inflammation and disease development.

Control of immune cell entry through the tumour vasculature: a missing link in optimising melanoma immunotherapy?

Metastatic melanoma remains a fatal disease to many worldwide, even after the breakthrough introduction of targeted therapies such as BRAF inhibitors and immune checkpoint blockade therapies such as CTLA-4 and PD-1 inhibitors. With advances in our understanding of this disease, as well as the increasing data gathered from patient studies, the significance of the host immune response to cancer progression and response to treatment is becoming clear. More specifically, the presence of intratumoral CD8⁺ cytotoxic T-cells correlates with better prognosis whereas the accumulation of monocytes/macrophages and neutrophils in the tumour is often associated with worse prognosis. Access and infiltration of circulating leukocytes into the tumour is governed by adhesion molecules and chemokines expressed by the endothelial cells of the vasculature. This review focuses on the adhesion molecules and chemokines which control the homing of CD8⁺ cytotoxic T-cells, monocytes and neutrophils to peripheral tissues, including tumours. We discuss the role of these leukocyte subsets in regulating melanoma growth, and detail the mechanisms used by tumours to selectively recruit or exclude these leukocytes for their own advantage. In doing so, we bring to light an underappreciated component of tumour biology which should be considered in combination with current treatments to selectively alter the leukocyte composition of tumours and ultimately enhance treatment outcome.

Integrin signaling in atherosclerosis

Atherosclerosis, a chronic lipid-driven inflammatory disease affecting large arteries, represents the primary cause of cardiovascular disease in the world. The local remodeling of the vessel intima during atherosclerosis involves the modulation of vascular cell phenotype, alteration of cell migration and proliferation, and propagation of local extracellular matrix remodeling. All of these responses represent targets of the integrin family of cell adhesion receptors. As such, alterations in integrin signaling affect multiple aspects of atherosclerosis, from the earliest induction of inflammation to the development of advanced fibrotic plaques. Integrin signaling has been shown to regulate endothelial phenotype, facilitate leukocyte homing, affect leukocyte function, and drive smooth muscle fibroproliferative remodeling. In addition, integrin signaling in platelets contributes to the thrombotic complications that typically drive the clinical manifestation of cardiovascular disease. In this review, we examine the current literature on integrin regulation of atherosclerotic plaque development and the suitability of integrins as potential therapeutic targets to limit cardiovascular disease and its complications.

Integrin αMβ2 is differently expressed by subsets of human osteoclast precursors and mediates adhesion of classical monocytes to bone

Bone-degrading osteoclasts are formed through fusion of their monocytic precursors. In the population of human peripheral blood monocytes, three distinct subsets have been identified: classical, intermediate and non-classical monocytes. We have previously shown that when the monocyte subsets are cultured on bone, significantly more osteoclasts are formed from classical monocytes than from intermediate or non-classical monocytes. Considering that this difference does not exist when monocyte subsets are cultured on plastic, we hypothesized that classical monocytes adhere better to the bone surface compared to intermediate and non-classical monocytes. To investigate this, the different monocyte subsets were isolated from human peripheral blood and cultured on slices of human bone in the presence of the cytokine M-CSF. We found that classical monocytes adhere better to bone due to a higher expression of the integrin αMβ2 and that their ability to attach to bone is significantly decreased when the integrin is blocked. This suggests that integrin αMβ2 mediates attachment of osteoclast precursors to bone and thereby enables the formation of osteoclasts.

Leukocyte arrest: Biomechanics and molecular mechanisms of β2 integrin activation

Integrins are a group of heterodimeric transmembrane receptors that play essential roles in cell-cell and cell-matrix interaction. Integrins are important in many physiological processes and diseases. Integrins acquire affinity to their ligand by undergoing molecular conformational changes called activation. Here we review the molecular biomechanics during conformational changes of integrins, integrin functions in leukocyte biorheology (adhesive functions during rolling and arrest) and molecules involved in integrin activation.

CD11c/CD18 Dominates Adhesion of Human Monocytes, Macrophages and Dendritic Cells over CD11b/CD18

Complement receptors CR3 (CD11b/CD18) and CR4 (CD11c/CD18) belong to the family of beta2 integrins and are expressed mainly by myeloid cell types in humans. Previously, we proved that CR3 rather than CR4 plays a key role in phagocytosis. Here we analysed how CD11b and CD11c participate in cell adhesion to fibrinogen, a common ligand of CR3 and CR4, employing human monocytes, monocyte-derived macrophages (MDMs) and monocyte-derived dendritic cells (MDDCs) highly expressing CD11b as well as CD11c. We determined the exact numbers of CD11b and CD11c on these cell types by a bead-based technique, and found that the ratio of CD11b/CD11c is 1.2 for MDDCs, 1.7 for MDMs and 7.1 for monocytes, suggesting that the function of CD11c is preponderant in MDDCs and less pronounced in monocytes. Applying state-of-the-art biophysical techniques, we proved that cellular adherence to fibrinogen is dominated by CD11c. Furthermore, we found that blocking CD11b significantly enhances the attachment of MDDCs and MDMs to fibrinogen, demonstrating a competition between CD11b and CD11c for this ligand. On the basis of the cell surface receptor numbers and the measured adhesion strength we set up a model, which explains the different behavior of the three cell types.

Integrin αDβ2 (CD11d/CD18) mediates experimental malaria-associated acute respiratory distress syndrome (MA-ARDS)

BACKGROUND

Malaria-associated acute respiratory distress syndrome (MA-ARDS) is a potentially lethal complication of clinical malaria. Acute lung injury in MA-ARDS shares features with ARDS triggered by other causes, including alveolar inflammation and increased alveolar-capillary permeability, leading to leak of protein-rich pulmonary oedema fluid. Mechanisms and physiologic alterations in MA-ARDS can be examined in murine models of this syndrome. Integrin αDβ2 is a member of the leukocyte, or β2 (CD18), sub-family of integrins, and emerging observations indicate that it has important activities in leukocyte adhesion, accumulation and signalling. The goal was to perform analysis of the lungs of mice wild type C57Bl/6 (a D (+/+) ) and Knockout C57Bl/6 (a D (-/-) ) with malaria-associated acute lung injury to better determine the relevancy of the murine models and investigate the mechanism of disease.

METHODS

C57BL/6 wild type (a D (+/+) ) and deficient for CD11d sub-unit (a D (-/-) ) mice were monitored after infection with 10(5) Plasmodium berghei ANKA. CD11d subunit expression RNA was measured by real-time polymerase chain reaction, vascular barrier integrity by Evans blue dye (EBD) exclusion and cytokines by ELISA. Protein and leukocytes were measured in bronchoalveolar lavage fluid (BALF) samples. Tissue cellularity was measured by the point-counting technique, F4/80 and VCAM-1 expression by immunohistochemistry. Respiratory function was analysed by non-invasive BUXCO and mechanical ventilation.

RESULTS

Alveolar inflammation, vascular and interstitial accumulation of monocytes and macrophages, and disrupted alveolar-capillary barrier function with exudation of protein-rich pulmonary oedema fluid were present in P. berghei-infected wild type mice and were improved in αDβ2-deficient animals. Key pro-inflammatory cytokines were also decreased in lung tissue from α D (-/-) mice, providing a mechanistic explanation for reduced alveolar-capillary inflammation and leak.

CONCLUSIONS

The results indicate that αDβ2 is an important inflammatory effector molecule in P. berghei-induced MA-ARDS, and that leukocyte integrins regulate critical inflammatory and pathophysiologic events in this model of complicated malaria. Genetic deletion of integrin subunit αD in mice, leading to deficiency of integrin αDβ2, alters lung inflammation and acute lung injury in a mouse model of MA-ARDS caused by P. berghei.

The Role of Integrins αMβ2 (Mac-1, CD11b/CD18) and αDβ2 (CD11d/CD18) in Macrophage Fusion

The subfamily of β2 integrins is implicated in macrophage fusion, a hallmark of chronic inflammation. Among β2 family members, integrin Mac-1 (αMβ2, CD11b/CD18) is abundantly expressed on monocyte/macrophages and mediates critical adhesive reactions of these cells. However, the role of Mac-1 in macrophage fusion leading to the formation of multinucleated giant cells remains unclear. Moreover, the role of integrin αDβ2 (CD11d/CD18), a receptor with recognition specificity overlapping that of Mac-1, is unknown. We found that multinucleated giant cells are formed in the inflamed mouse peritoneum during the resolution phase of inflammation, and their numbers were approximately twofold higher in wild-type mice than in Mac-1(-/-) mice. Analyses of isolated inflammatory peritoneal macrophages showed that IL-4-induced fusion of Mac-1-deficient cells was strongly reduced compared with wild-type counterparts. The examination of adhesive reactions known to be required for fusion showed that spreading, but not adhesion and migration, was reduced in Mac-1-deficient macrophages. Fusion of αDβ2-deficient macrophages was also significantly decreased, albeit to a smaller degree. Deficiency of intercellular adhesion molecule 1, a counter-receptor for Mac-1 and αDβ2, did not alter the fusion rate. The results indicate that both Mac-1 and αDβ2 support macrophage fusion with Mac-1 playing a dominant role and suggest that Mac-1 may mediate cell-cell interactions with a previously unrecognized counter-receptor(s).

Integrin αDβ2 (CD11d/CD18) is expressed by human circulating and tissue myeloid leukocytes and mediates inflammatory signaling

Integrin α(D)β(2) is the most recently identified member of the leukocyte, or β(2), subfamily of integrin heterodimers. Its distribution and functions on human leukocytes have not been clearly defined and are controversial. We examined these issues and found that α(D)β(2) is prominently expressed by leukocytes in whole blood from healthy human subjects, including most polymorphonuclear leukocytes and monocytes. We also found that α(D)β(2) is displayed by leukocytes in the alveoli of uninjured and inflamed human lungs and by human monocyte-derived macrophages and dendritic cells, indicating broad myeloid expression. Using freshly-isolated human monocytes, we found that α(D)β(2) delivers outside-in signals to pathways that regulate cell spreading and gene expression. Screening expression analysis followed by validation of candidate transcripts demonstrated that engagement of α(D)β(2) induces mRNAs encoding inflammatory chemokines and cytokines and secretion of their protein products. Thus, α(D)β(2) is a major member of the integrin repertoire of both circulating and tissue myeloid leukocytes in humans. Its broad expression and capacity for outside-in signaling indicate that it is likely to have important functions in clinical syndromes of infection, inflammation, and tissue injury.

Matricellular protein CCN1/CYR61: a new player in inflammation and leukocyte trafficking

Cystein-rich protein 61 (CYR61/CCN1) is a component of the extracellular matrix, which is produced and secreted by several cell types including endothelial cells, fibroblasts and smooth muscle cells. CCN1 has been implicated in leukocyte migration and the inflammatory process, but it is also involved in cardiovascular development and carcinogenesis. It exerts its functions through binding to multiple integrins present in many different cell types. This multiplicity in function is now known to contribute to the diverse array of cellular processes it can regulate. The expression of CCN1 is tightly regulated by cytokines and growth factors. However, CCN1 can directly modulate cell adhesion and migratory processes whilst simultaneously regulating the production of other cytokines and chemokines through paracrine and autocrine feedback loops. This complex functionality of CCN1 has highlighted the pivotal role this molecule can play in regulating the immunosurveillance process. Furthermore, CCN1 has now emerged as an important partner when targeting components of the infectious or chronic inflammatory disease processes such as atherosclerosis or rheumatoid arthritis. This review will focus on CYR61/CCN1 and its ability to control the migration of leukocytes, the production of cytokines and cell proliferation or senescence at the site of inflammation.

Potential role of kringle-integrin interaction in plasmin and uPA actions (a hypothesis)

We previously showed that the kringle domains of plasmin and angiostatin, the N-terminal four kringles (K1–4) of plasminogen, directly bind to integrins. Angiostatin blocks tumor-mediated angiogenesis and has great therapeutic potential. Angiostatin binding to integrins may be related to the antiinflammatory action of angiostatin. We reported that plasmin induces signals through protease-activated receptor (PAR-1), and plasmin-integrin interaction may be required for enhancing plasmin concentration on the cell surface, and enhances its signaling function. Angiostatin binding to integrin does not seem to induce proliferative signals. One possible mechanism of angiostatin's inhibitory action is that angiostatin suppresses plasmin-induced PAR-1 activation by competing with plasmin for binding to integrins. Interestingly, plasminogen did not interact with αvβ3, suggesting that the αvβ3-binding sites in the kringle domains of plasminogen are cryptic. The kringle domain of urokinase-type plasminogen activator (uPA) also binds to integrins. The uPA-integrin interaction enhances uPA concentrations on the cell surface and enhances plasminogen activation on the cell surface. It is likely that integrins bind to the kringle domain, and uPAR binds to the growth factor-like domain (GFD) of uPA simultaneously, making the uPAR-uPA-integrin ternary complex. We present a docking model of the ternary complex.

CCN1 Induces β-Catenin Translocation in Esophageal Squamous Cell Carcinoma through Integrin α11

Aims. Nuclear translocation of β-catenin is common in many cancers including esophageal squamous cell carcinoma (ESCC). As a mediator of Wnt signaling pathway, nuclear β-catenin can activate many growth-related genes including CCN1, which in turn can induce β-catenin translocation. CCN1, a matricellular protein, signals through various integrin receptors in a cell-dependent manner to regulate cell adhesion, proliferation, and survival. Its elevation has been reported in ESCC as well as other esophageal abnormalities such as Barrett's esophagus. The aim of this study is to examine the relationship between CCN1 and β-catenin in ESCC. Methods and Results. The expression and correlation between CCN1 and β-catenin in ESCC tissue were examined through immunohistochemistry and further analyzed in both normal esophageal epithelial cells and ESCC cells through microarray, functional blocking and in situ protein ligation. We found that nuclear translocation of β-catenin in ESCC cells required high level of CCN1 as knockdown of CCN1 in ESCC cells reduced β-catenin expression and translocation. Furthermore, we found that integrin α₁₁ was highly expressed in ESCC tumor tissue and functional blocking integrin α₁₁ diminished CCN1-induced β-catenin elevation and translocation. Conclusions. Integrin α₁₁ mediated the effect of CCN1 on β-catenin in esophageal epithelial cells.

Metalloproteinase-mediated Shedding of Integrin β2 promotes macrophage efflux from inflammatory sites

Macrophage exiting from inflammatory sites is critical to limit the local innate immune response. With tissue insult, resident tissue macrophages rapidly efflux to lymph nodes where they modulate the adaptive immune response, and inflammatory macrophages attracted to the site of injury then exit during the resolution phase. However, the mechanisms that regulate macrophage efflux are poorly understood. This study has investigated soluble forms of integrin β2 whose levels are elevated in experimental peritonitis at times when macrophages are exiting the peritoneum, suggesting that its proteolytic shedding may be involved in macrophage efflux. Both constitutive and inducible metalloproteinase-dependent shedding of integrin β2 from mouse macrophages are demonstrated. Soluble integrin β2 is primarily released as a heterodimeric complex with αM that retains its ability to bind its ligands intracellular adhesion molecule-1, fibrin, and collagen and thus may serve as a soluble antagonist. In a model of accelerated exiting, administration of a metalloproteinase inhibitor prevents macrophage efflux by 50% and impedes loss of macrophage integrin β2 from the cell surface. Exiting of peritoneal macrophages in mice lacking integrin β2 is accelerated, and antibody disruption of integrin β2-substrate interactions can reverse 50% of the metalloprotease inhibitor blockade of macrophage exiting. Thus, our study demonstrates the ability of metalloproteinase-mediated shedding of integrin β2 to promote macrophage efflux from inflammatory sites, and the release of soluble integrin heterodimers may also limit local inflammation.

CCN1/CYR61: the very model of a modern matricellular protein

CCN1 (CYR61) is a dynamically expressed, multifunctional matricellular protein that plays essential roles in cardiovascular development during embryogenesis, and regulates inflammation, wound healing and fibrogenesis in the adult. Aberrant CCN1 expression is associated with myriad pathologies, including various cancers and diseases associated with chronic inflammation. CCN1 promotes diverse and sometimes opposing cellular responses, which can be ascribed, as least in part, to disparate activities mediated through its direct binding to distinct integrins in different cell types and contexts. Accordingly, CCN1 promotes cell proliferation, survival and angiogenesis by binding to integrin α(v)β(3), and induces apoptosis and senescence through integrin α(6)β(1) and heparan sulfate proteoglycans. The ability of CCN1 to trigger the accumulation of a robust and sustained level of reactive oxygen species underlies some of its unique activities as a matrix cell-adhesion molecule. Emerging studies suggest that CCN1 might be useful as a biomarker or therapeutic target in certain diseases.

Inflammatory phenotyping identifies CD11d as a gene markedly induced in white adipose tissue in obese rodents and women

In severe obesity, white adipose tissue (WAT) inflammation and macrophage infiltration are thought to contribute to WAT and whole-body insulin resistance. Specific players involved in triggering and maintaining inflammation (i.e. those regulating adipokine release and WAT macrophage recruitment, retention, or function) remain to be fully elaborated, and the degree to which moderate obesity promotes WAT inflammation remains to be clarified further. Therefore, we characterized adiposity and metabolic phenotypes in adult male C57BL/6J mice fed differing levels of dietary fat (10, 45, and 60% of energy) for 12 wk, concurrent with determinations of WAT inflammation markers and mRNA expression of leukocyte-derived integrins (CD11b, CD11c, CD11d) involved in macrophage extravasation and tissue macrophage homing/retention. As expected, a lard-based, very high-fat diet (60% energy) significantly increased adiposity and glucose intolerance compared with 10% fat-fed controls, coincident with higher retroperitoneal (RP) WAT transcript levels for proinflammatory factors and macrophage markers, including TNFα and CD68 mRNA, which were ~3- and ~15-fold of control levels, respectively (P < 0.001). Mice fed the 45% fat diet had more moderate obesity, less glucose intolerance, and lower WAT macrophage/inflammatory marker mRNA abundances compared with 60% fat-fed mice; TNFα and CD68 mRNA levels were ~2- and ~5-fold of control levels (P < 0.01). Relative WAT expression of CD11d was massively induced by obesity to an extent greater than any other inflammatory marker (to >300-fold of controls in the 45 and 60% fat groups) (P < 0.0001) and this induction was WAT specific. Because we found that CD11d expression also increased in RP-WAT of Zucker obese rats and in the subcutaneous WAT of obese adult women, this appears to be a common feature of obesity. Observed correlations of WAT macrophage transcript marker abundances with body weight in lean to modestly obese mice raises an interesting possibility that the activities of at least some WAT macrophages are closely linked to the normal adipose remodeling that is a requisite for changes in WAT energy storage capacity.

The integrins Mac-1 and alpha4beta1 perform crucial roles in neutrophil and T cell recruitment to lungs during Streptococcus pneumoniae infection

Neutrophils and T cells play an important role in host protection against pulmonary infection caused by Streptococcus pneumoniae. However, the role of the integrins in recruitment of these cells to infected lungs is not well understood. In this study we used the twin approaches of mAb blockade and gene-deficient mice to investigate the relative impact of specific integrins on cellular recruitment and bacterial loads following pneumococcal infection. We find that both Mac-1 (CD11b/CD18) and α(4)β(1) (CD49d/CD29) integrins, but surprisingly not LFA-1 (CD11a/CD18), contribute to two aspects of the response. In terms of recruitment from the circulation into lungs, neutrophils depend on Mac-1 and α(4)β(1), whereas the T cells are entirely dependent on α(4)β(1). Second, immunohistochemistry results indicate that adhesion also plays a role within infected lung tissue itself. There is widespread expression of ICAM-1 within lung tissue. Use of ICAM-1(-/-) mice revealed that neutrophils make use of this Mac-1 ligand, not for lung entry or for migration within lung tissue, but for combating the pneumococcal infection. In contrast to ICAM-1, there is restricted and constitutive expression of the α(4)β(1) ligand, VCAM-1, on the bronchioles, allowing direct access of the leukocytes to the airways via this integrin at an early stage of pneumococcal infection. Therefore, integrins Mac-1 and α(4)β(1) have a pivotal role in prevention of pneumococcal outgrowth during disease both in regulating neutrophil and T cell recruitment into infected lungs and by influencing their behavior within the lung tissue itself.

αMβ₂ integrin activation prevents alternative activation of human and murine macrophages and impedes foam cell formation

RATIONALE

The alternative activation of monocytes by interleukin (IL)-13 and IL-4 is a significant component of the inflammatory response. The consequences of alternative activation in inflammatory diseases remain to be determined.

OBJECTIVE

In this report, we explored how integrins, receptors important for monocyte migration to inflammatory sites, regulate IL-13-mediated monocyte activation. We focused on the analysis of 2 proteins, which are upregulated during the alternative activation and are important for the development of atherosclerosis, an oxidative enzyme 15-lipoxygenase (15-LO) and a scavenger receptor CD36.

METHODS AND RESULTS

We found that adhesion of resting monocytes through β(2) integrins and inside-out activation of β(2) integrins by monocyte chemoattractant protein-1 did not change IL-13-stimulated 15-LO upregulation; however, preincubation of monocytes with the antibody MEM48, which generates full activation of β(2) integrins, significantly inhibited 15-LO mRNA and protein expression. In contrast, activation of β(1) integrins had no effect on 15-LO expression. Analysis of integrin clustering through α(M), α(L), α(X), and α(D) subunits demonstrated the pivotal role for integrin α(M)β(2) in inhibiting 15-LO expression. IL-13 treatment upregulates 15-LO-dependent CD36 expression on human monocytes; our studies showed that β(2) integrin activation and α(M) integrin clustering significantly inhibited IL-13-dependent CD36 mRNA and protein expression, as well as CD36-related foam cell formation. Moreover, IL-13 stimulation of α(M)-deficient peritoneal macrophages demonstrated an upregulated level of 15-LO induction, CD36 expression, and lipid accumulation as compared with wild-type controls.

CONCLUSIONS

The adhesion of monocytes/macrophages through activated integrin α(M)β(2) has a regulatory and potential atheroprotective function during the alternative activation of macrophages.

Mary Allen Engle Award: The glue of life--a career retrospective

The author was privileged to be an early contributor to the concept that cell adhesion molecules, the leukocyte (β2) integrins, play a pivotal role in the acute inflammatory process. For the author, this began with the development of a monoclonal antibody (anti-Mo1) that identified a differentiation antigen on the surface of human myeloid cells (including neutrophils, monocytes, and natural killer (NK) cells). Serendipitously, it was discovered that the Mo1 antigen was the heterodimeric glycoprotein (gp155,95) absent from the surface of neutrophils isolated from patients with adhesion defects in vitro and a syndrome characterized by chronic, life-threatening infections in vivo (a syndrome now termed leukocyte adhesion deficiency, type 1) (LAD-1). Collaborative efforts with other investigators (including members of the ACCA) revealed that patients with LAD-1 exhibited genetic mutations on chromosome 21 resulting in absent or diminished expression of a class of 4 surface adhesion molecules (now termed CD11a/CD18, CD11b/CD18, CD11c/CD18, and CD11d/CD18) known as the leukocyte or β2 family of integrins. Knowledge of the role of the β2 integrins in the acute inflammatory response led to the development of effective gene therapy strategies to treat LAD-1 in preclinical animal models and to the comprehensive testing of anti-integrin antibodies as anti-inflammatory agents to prevent organ damage as a complication of acute inflammation. This retrospective provides one illustration of the potential of bench-to-bedside research to generate new knowledge of clinical significance.

Thrombospondin-4 regulates vascular inflammation and atherogenesis

RATIONALE

Thrombospondin (TSP)-4 is an extracellular protein that has been linked to several cardiovascular pathologies. However, a role for TSP-4 in vascular wall biology remains unknown.

OBJECTIVE

We have examined the effects of TSP-4 gene (Thbs4) knockout on the development of atherosclerotic lesions in ApoE(-/-) mice.

METHODS AND RESULTS

Deficiency in TSP-4 reduced atherosclerotic lesions: at 20 weeks of age, the size of the aortic root lesions in Thbs4(-/-)/ApoE(-/-) mice was decreased by 48% in females and by 39% in males on chow diets; in mice on Western diets, lesions in the descending aorta were reduced by 30% in females and 33% in males. In ApoE(-/-) mice, TSP-4 was abundant in vessel areas prone to lesion development and in the matrix of the lesions themselves. TSP-4 deficiency reduced the number of macrophages in lesions in all groups by ≥ 2-fold. In addition, TSP-4 deficiency reduced endothelial cell activation (expression of surface adhesion molecules) and other markers of inflammation in the vascular wall (decreased production of monocyte chemoattractant protein-1 and activation of p38). In vitro, both the adhesion and migration of wild-type macrophages increased in the presence of purified recombinant TSP-4 in a dose-dependent manner (up to 7- and 4.7-fold, respectively). These responses led to p38-MAPkinase activation and were dependent on β(2) and β(3) integrins, which recognize TSP-4 as a ligand.

CONCLUSIONS

TSP-4 is abundant in atherosclerotic lesions and in areas prone to development of lesions and may influence the recruitment of macrophages by activating endothelial cells and directly interacting with macrophages to increase their adhesion and migration. Our observations suggest an important role for this matricellular protein in the local regulation of inflammation associated with atherogenesis.

RGD-dependent binding of TP508 to integrin alphavbeta3 mediates cell adhesion and induction of nitric oxide

TP508, a 23-amino acid RGD-containing synthetic peptide representing residues 508 to 530 of human prothrombin, mitigates the effects of endothelial dysfunction in ischaemic reperfusion injury. The objective of this study was to investigate whether TP508 binds to members of the integrin family of transmembrane receptors leading to nitric oxide synthesis. Immobilised TP508 supported adhesion of endothelial cells and alphavbeta3-expressing human embryonic kidney cells in a dose- and RGD-dependent manner. Soluble TP508 also inhibited cell adhesion to immobilised fibrinogen. The involvement of alphavbeta3 was verified with function-blocking antibodies and surface plasmon resonance studies. Adhesion of the cells to immobilised TP508 resulted in an induction of phosphorylated FAK and ERK1/2. In endothelial cells, TP508 treatment resulted in an induction of nitric oxide that could be inhibited by LM609, an alphavbeta3-specific, function-blocking monoclonal antibody. Finally, TP508 treatment of isolated rat aorta segments enhanced carbachol-induced vasorelaxation. These results suggest that TP508 elicits a potentially therapeutic effect through an RGD-dependent interaction with integrin alphavbeta3.

The extracellular domain of CD11d regulates its cell surface expression

A mAb targeting the CD11d subunit of the leukocyte integrin CD11d/CD18 decreases intraspinal inflammation and oxidative damage leading to improved neurological outcomes in rodent models of SCI. CD11d/CD18 is the fourth member of the beta2-integrin family. Current evidence indicates that CD11d/CD18 is regulated differently than other beta2-integrins, suggesting that CD11d(+) leukocytes play a distinct role in inflammation. Although the transcriptional control of CD11d expression has been evaluated, control of the intracellular distribution of CD11d has not been addressed. For this reason and as a result of the potential of CD11d as a therapeutic target for SCI and possibly other CNS injuries, we investigated the intracellular localization and surface expression of CD11d in cultured cells. CD11d and CD18 were fused at their C-termini with YFP and mRFP, respectively. Flow cytometry and confocal microscopy demonstrated that rCD11d-YFP is expressed on the cell surface of leukocyte cell lines expressing CD18. In contrast, in heterologous cell lines, CD11d-YFP is retained intracellularly in the TGN. Coexpression of CD11d-YFP and CD18-mRFP relieves this intracellular restriction and allows the CD11d/CD18 heterodimer to be surface-expressed. Based on domain-swapping experiments with CD25, the extracellular domain of CD11d is required and sufficient for the observed intracellular retention in heterologous cells. Furthermore, the transmembrane and C-terminus are also required for proper heterodimerization with CD18 and localization to the plasma membrane. These findings suggest that multiple CD11d domains play a role in controlling intracellular location and association with CD18.

Leukocyte-endothelial interactions in inflammation

At sites of inflammation, infection or vascular injury local proinflammatory or pathogen-derived stimuli render the luminal vascular endothelial surface attractive for leukocytes. This innate immunity response consists of a well-defined and regulated multi-step cascade involving consecutive steps of adhesive interactions between the leukocytes and the endothelium. During the initial contact with the activated endothelium leukocytes roll along the endothelium via a loose bond which is mediated by selectins. Subsequently, leukocytes are activated by chemokines presented on the luminal endothelial surface, which results in the activation of leukocyte integrins and the firm leukocyte arrest on the endothelium. After their firm adhesion, leukocytes make use of two transmigration processes to pass the endothelial barrier, the transcellular route through the endothelial cell body or the paracellular route through the endothelial junctions. In addition, further circulating cells, such as platelets arrive early at sites of inflammation contributing to both coagulation and to the immune response in parts by facilitating leukocyte-endothelial interactions. Platelets have thereby been implicated in several inflammatory pathologies. This review summarizes the major mechanisms and molecules involved in leukocyte-endothelial and leukocyte-platelet interactions in inflammation.

The role of integrin alpha D beta2 (CD11d/CD18) in monocyte/macrophage migration

Integrin alpha(D)beta(2) (CD11d/CD18) is a multiligand macrophage receptor with recognition specificity identical to that of the major myeloid cell-specific integrin alpha(M)beta(2) (CD11b/CD18, Mac-1). Despite its prominent upregulation on inflammatory macrophages, the role of alpha(D)beta(2) in monocyte and macrophage migration is unknown. In this study, we have generated model and natural cell lines expressing different densities of alpha(D)beta(2) and examined their migration to various extracellular matrix proteins. When expressed at a low density, alpha(D)beta(2) on the surface of recombinant HEK293 cells and murine IC-21 macrophages cooperates with beta(1)/beta(3) integrins to support cell migration. However, its increased expression on the alpha(D)beta(2)-expressing HEK293 cells and its upregulation by PMA on the IC-21 macrophages result in increased cell adhesiveness and inhibition of cell migration. Furthermore, ligation of alpha(D)beta(2) with anti-alpha(D) blocking antibodies restores beta(1)/beta(3)-driven cell migration by removing the excess alpha(D)beta(2)-mediated adhesive bonds. Consistent with in vitro data, increased numbers of inflammatory macrophages were recovered from the inflamed peritoneum of mice after the administration of anti-alpha(D) antibody. These results demonstrate that the density of alpha(D)beta(2) is critically involved in modulating macrophage adhesiveness and their migration, and suggest that low levels of alpha(D)beta(2) contribute to monocyte migration while alpha(D)beta(2) upregulation on differentiated macrophages may facilitate their retention at sites of inflammation.

Integrin alphaDbeta2 is dynamically expressed by inflamed macrophages and alters the natural history of lethal systemic infections

The leukocyte integrins have critical roles in host defense and inflammatory tissue injury. We found that integrin alphaDbeta2, a novel but largely uncharacterized member of this family, is restricted to subsets of macrophages and a small population of circulating leukocytes in wild-type mice in the absence of inflammatory challenge and is expressed in regulated fashion during cytokine-induced macrophage differentiation in vitro. alphaDbeta2 is highly displayed on splenic red pulp macrophages and mediates their adhesion to local targets, identifying key functional activity. In response to challenge with Plasmodium berghei, a malarial pathogen that models systemic infection and inflammatory injury, new populations of alphaD+ macrophages evolved in the spleen and liver. Unexpectedly, targeted deletion of alphaD conferred a survival advantage in P. berghei infection over a 30-day observation period. Mechanistic studies demonstrated that the increased survival of alphaD-/- animals at these time points is not attributed to differences in magnitude of anemia or parasitemia or to alterations in splenic microanatomy, each of which is a key variable in the natural history of P. berghei infection, and indicated that an altered pattern of inflammatory cytokines may contribute to the difference in mortality. In contrast to the outcome in malarial challenge, death of alphaD-/- animals was accelerated in a model of Salmonella sepsis, demonstrating differential rather than stereotyped roles for alphaDbeta2 in systemic infection. These studies identify previously unrecognized and unique activities of alphaDbeta2, and macrophages that express it, in host defense and injury.

Roles of integrin activation in eosinophil function and the eosinophilic inflammation of asthma

Eosinophilic inflammation is a characteristic feature of asthma. Integrins are highly versatile cellular receptors that regulate extravasation of eosinophils from the postcapillary segment of the bronchial circulation to the airway wall and airspace. Such movement into the asthmatic lung is described as a sequential, multistep paradigm, whereby integrins on circulating eosinophils become activated, eosinophils tether in flow and roll on bronchial endothelial cells, integrins on rolling eosinophils become further activated as a result of exposure to cytokines, eosinophils arrest firmly to adhesive ligands on activated endothelium, and eosinophils transmigrate to the airway in response to chemoattractants. Eosinophils express seven integrin heterodimeric adhesion molecules: alpha 4 beta 1 (CD49d/29), alpha 6 beta 1 (CD49f/29), alpha M beta 2 (CD11b/18), alpha L beta 2 (CD11a/18), alpha X beta 2 (CD11c/18), alpha D beta2 (CD11d/18), and alpha 4 beta 7 (CD49d/beta 7). The role of these integrins in eosinophil recruitment has been elucidated by major advances in the understanding of integrin structure, integrin function, and modulators of integrins. Such findings have been facilitated by cellular experiments of eosinophils in vitro, studies of allergic asthma in humans and animal models in vivo, and crystal structures of integrins. Here, we elaborate on how integrins cooperate to mediate eosinophil movement to the asthmatic airway. Antagonists that target integrins represent potentially promising therapies in the treatment of asthma.