Delay of migrating leukocytes by the basement membrane deposited by endothelial cells in long-term culture

Crosslinking of membrane CD13 in human neutrophils mediates phagocytosis and production of reactive oxygen species, neutrophil extracellular traps and proinflammatory cytokines

Aminopeptidase N, or CD13, is a cell membrane ectopeptidase highly expressed in myeloid cells. Through its enzymatic activity, CD13 regulates the activity of several bioactive peptides, such as endorphins and enkephalins, chemotactic peptides like MCP-1 and IL-8, angiotensin III, bradikinin, etc. In recent years, it has been appreciated that independently of its peptidase activity, CD13 can activate signal transduction pathways and mediate effector functions such as phagocytosis and cytokine secretion in monocytes and macrophages. Although neutrophils are known to express CD13 on its membrane, it is currently unknown if CD13 can mediate effector functions in these cells. Here, we show that in human neutrophils CD13 can mediate phagocytosis, which is dependent on a signaling pathway that involves Syk, and PI3-K. Phagocytosis mediated by CD13 is associated with production of reactive oxygen species (ROS). The level of phagocytosis and ROS production mediated by CD13 are similar to those through FcγRIII (CD16b), a widely studied receptor of human neutrophils. Also, CD13 ligation induces the release of neutrophil extracellular traps (NETs) as well as cytokine secretion from neutrophils. These results support the hypothesis that CD13 is a membrane receptor able to activate effector functions in human neutrophils.

Human Multipotent Mesenchymal Stromal Cell–Derived Extracellular Vesicles Enhance Neuroregeneration in a Rat Model of Sciatic Nerve Crush Injury

Peripheral nerve injury remains a serious problem for medicine, with no effective method of treatment at the moment. The most prominent example of this problem is neonatal brachial plexus palsy, which results from the stretching of the brachial plexus nerves in the birth or perinatal period. Multipotent mesenchymal cells (MSCs) and the extracellular vesicles (EVs) they produce are known to have a marked neuroprotective effect in central nervous system injuries. We suggested that the use of MSCs-derived EVs may be an effective approach to the regeneration of peripheral nerves after injury. Sciatic nerve injury was modeled in rats via crushing, and then a gel containing MSCs–EVs was applied to the injured area. After 15 and 30 days, a histological, physiological, and functional assessment of nerve, dorsal root ganglia (DRG), and innervated muscles’ recovery was performed. Transplantation of EVs to the area of sciatic nerve injury significantly reduced muscle atrophy as compared to the control group. Functional recovery of the innervated muscles, as measured by the extensor postural thrust test, was revealed 30 days after the surgery. We associate the obtained results with EVs-induced neuroprotective mechanisms, which were expressed in a decrease in apoptotic neuronal death and an increase in regeneration-associated proteins NF-200 and GAP-43, as well as in DRG and damaged nerve. We suggest that the therapeutic scheme we used is efficient for the treatment of acute peripheral nervous system injuries and can be transferred to the clinics. However, additional studies are required for a more detailed analysis of neuroprotection mechanisms.

Microvascular Mimetics for the Study of Leukocyte-Endothelial Interactions

Introduction

The pathophysiological increase in microvascular permeability plays a well-known role in the onset and progression of diseases like sepsis and atherosclerosis. However, how interactions between neutrophils and the endothelium alter vessel permeability is often debated.

Methods

In this study, we introduce a microfluidic, silicon-membrane enabled vascular mimetic (μSiM-MVM) for investigating the role of neutrophils in inflammation-associated microvascular permeability. In utilizing optically transparent silicon nanomembrane technology, we build on previous microvascular models by enabling in situ observations of neutrophil-endothelium interactions. To evaluate the effects of neutrophil transmigration on microvascular model permeability, we established and validated electrical (transendothelial electrical resistance and impedance) and small molecule permeability assays that allow for the in situ quantification of temporal changes in endothelium junctional integrity.

Results

Analysis of neutrophil-expressed β₁ integrins revealed a prominent role of neutrophil transmigration and basement membrane interactions in increased microvascular permeability. By utilizing blocking antibodies specific to the β₁ subunit, we found that the observed increase in microvascular permeability due to neutrophil transmigration is constrained when neutrophil-basement membrane interactions are blocked. Having demonstrated the value of in situ measurements of small molecule permeability, we then developed and validated a quantitative framework that can be used to interpret barrier permeability for comparisons to conventional Transwell™ values.

Conclusions

Overall, our results demonstrate the potential of the μSiM-MVM in elucidating mechanisms involved in the pathogenesis of inflammatory disease, and provide evidence for a role for neutrophils in inflammation-associated endothelial barrier disruption.

Endocrine Regulation of Lymphocyte Trafficking In Vitro

Lymphocyte recruitment in inflammation can be influenced by many molecules including cytokines, chemokines, and adipokines. In our lab, we have examined the effects of the adipokines leptin and adiponectin on lymphocyte migration, and observed modulation of this process. Lymphocyte behavior can be assessed in the lab under static conditions, or can be studied under flow, simulating in vivo conditions. In this chapter, in vitro methods for analyzing adhesion and migration of lymphocytes isolated from blood are described in detail. In static adhesion and migration assays, lymphocytes are allowed to settle on top of endothelial cell monolayers cultured in plates for a desired period of time. In the flow-based assay, lymphocytes are perfused over the endothelium at a continuous rate through microchannels which are commercially available. Depending on the choice of method employed, the efficiency of lymphocytes to adhere to and migrate across the endothelial cell monolayer under different conditions can be evaluated. Static assays are less complex and are of higher throughput. However, these assays provide less detailed information regarding lymphocyte behaviors. On the other hand, the flow-based assays are more difficult to perform, but are more physiologically relevant due to the presence of flow and yield more detailed information about lymphocyte activities such as capture, immobilization, and migration in real-time.

The Aminopeptidase CD13 Induces Homotypic Aggregation in Neutrophils and Impairs Collagen Invasion

Aminopeptidase N (CD13) is a widely expressed cell surface metallopeptidase involved in the migration of cancer and endothelial cells. Apart from our demonstration that CD13 modulates the efficacy of tumor necrosis factor-α-induced apoptosis in neutrophils, no other function for CD13 has been ascribed in this cell. We hypothesized that CD13 may be involved in neutrophil migration and/or homotypic aggregation. Using purified human blood neutrophils we confirmed the expression of CD13 on neutrophils and its up-regulation by pro-inflammatory agonists. However, using the anti-CD13 monoclonal antibody WM-15 and the aminopeptidase enzymatic inhibitor bestatin we were unable to demonstrate any direct involvement of CD13 in neutrophil polarisation or chemotaxis. In contrast, IL-8-mediated neutrophil migration in type I collagen gels was significantly impaired by the anti-CD13 monoclonal antibodies WM-15 and MY7. Notably, these antibodies also induced significant homotypic aggregation of neutrophils, which was dependent on CD13 cross-linking and was attenuated by phosphoinositide 3-kinase and extracellular signal-related kinase 1/2 inhibition. Live imaging demonstrated that in WM-15-treated neutrophils, where homotypic aggregation was evident, the number of cells entering IL-8 impregnated collagen I gels was significantly reduced. These data reveal a novel role for CD13 in inducing homotypic aggregation in neutrophils, which results in a transmigration deficiency; this mechanism may be relevant to neutrophil micro-aggregation in vivo.

Transcriptome profiling reveals differential expression of interferon family induced by dengue virus 2 in human endothelial cells on tissue culture plastic and polyacrylamide hydrogel

A cell model is critical for studying the molecular mechanisms of dengue virus 2 (DENV-2) invasions and cell bioactivity can be easily affected by the substrate matrix. Tissue culture plastic (TCP) and polyacrylamide hydrogel (PAMH) are two kinds of matrices widely used for cells. The effects of different matrices on the cultured cells with DENV-2 invasion remain unknown. To address the issue, the effects of TCP and PAMH were explored in primary human umbilical vein endothelial cells (HUVECs) with DENV-2 invasion. HUVECs were assigned into four groups: group A (cultured on TCP), group B (cultured on PAMH), group C (cultured on TCP with DENV-2 invasion), and group D (cultured on PAMH with DENV-2 invasion). Flow cytometry was performed on HUVECs after 48-hr culture. Gene expression patterns were analyzed by gene microarray. The levels of interleukin-29 (IL-29) were measured by real-time qRT-PCR and ELISA. There were no cell apoptosis induced by DENV-2 in HUVECs cultured on TCP and PAMH (P > 0.05). After DENV-2 invasion, the up-regulated genes involve in the activities of oligoadenylate synthetase (OAS), interferon-related cytokine, and growth factors so on. The up-regulated pathways involve in the responses to DENV-2 and innate immunity. IL-29 was induced in the HUVECs on PAMH when compared with the cells on TCP (P < 0.05). Thus, different matrices cause different immune responses, which should be considered in the cell models for exploring the molecular mechanisms of DENV-induced diseases.

Adhesion Molecules: Master Controllers of the Circulatory System

This manuscript will review our current understanding of cellular adhesion molecules (CAMs) relevant to the circulatory system, their physiological role in control of vascular homeostasis, innate and adaptive immune responses, and their importance in pathophysiological (disease) processes such as acute lung injury, atherosclerosis, and pulmonary hypertension. This is a complex and rapidly changing area of research that is incompletely understood. By design, we will begin with a brief overview of the structure and classification of the major groups of adhesion molecules and their physiological functions including cellular adhesion and signaling. The role of specific CAMs in the process of platelet aggregation and hemostasis and leukocyte adhesion and transendothelial migration will be reviewed as examples of the complex and cooperative interplay between CAMs during physiological and pathophysiological processes. The role of the endothelial glycocalyx and the glycobiology of this complex system related to inflammatory states such as sepsis will be reviewed. We will then focus on the role of adhesion molecules in the pathogenesis of specific disease processes involving the lungs and cardiovascular system. The potential of targeting adhesion molecules in the treatment of immune and inflammatory diseases will be highlighted in the relevant sections throughout the manuscript.

The roles of integrins in function of human neutrophils after their migration through endothelium into interstitial matrix

We investigated the changes in neutrophil phenotype and function after transendothelial migration, and the roles played by integrin receptors in their behaviour. Neutrophils were tracked microscopically as they migrated through endothelial cells into collagen gels, and were retrieved at desired times. When endothelial cells were treated with increasing doses of tumour necrosis factor-α, neutrophils not only migrated in greater number, but also to a greater depth in the gel. Apoptosis was barely detectable in neutrophils retrieved after 24h, and many remained viable and motile at 48h. Neutrophils retrieved after 1h had increased oxidative capacity and at 24h had similar capacity as freshly-isolated neutrophils. However, by then they had impaired ability to phagocytose bacteria. Compared to fresh neutrophils, total mRNA was halved by 24h, but while β2-integrin expression decreased, β1- and β3-integrin increased along with ICAM-1. Studies of integrin blockade indicated that while β2-integrins were needed to cross the endothelial barrier, no integrins were required for migration within the gel. β2-integrins also contributed to phagocytosis, but their binding was not required for prolonged survival. These results demonstrate a model for integrated analysis of neutrophil migration and function, and describe development of effector functions and the roles of integrins in human neutrophils for the first time.

Analyzing the effects of stromal cells on the recruitment of leukocytes from flow

Stromal cells regulate the recruitment of circulating leukocytes during inflammation through cross-talk with neighboring endothelial cells. Here we describe two in vitro "vascular" models for studying the recruitment of circulating neutrophils from flow by inflamed endothelial cells. A major advantage of these models is the ability to analyze each step in the leukocyte adhesion cascade in order, as would occur in vivo. We also describe how both models can be adapted to study the role of stromal cells, in this case mesenchymal stem cells (MSC), in regulating leukocyte recruitment. Primary endothelial cells were cultured alone or together with human MSC in direct contact on Ibidi microslides or on opposite sides of a Transwell filter for 24 hr. Cultures were stimulated with tumor necrosis factor alpha (TNFα) for 4 hr and incorporated into a flow-based adhesion assay. A bolus of neutrophils was perfused over the endothelium for 4 min. The capture of flowing neutrophils and their interactions with the endothelium was visualized by phase-contrast microscopy. In both models, cytokine-stimulation increased endothelial recruitment of flowing neutrophils in a dose-dependent manner. Analysis of the behavior of recruited neutrophils showed a dose-dependent decrease in rolling and a dose-dependent increase in transmigration through the endothelium. In co-culture, MSC suppressed neutrophil adhesion to TNFα-stimulated endothelium. Our flow based-adhesion models mimic the initial phases of leukocyte recruitment from the circulation. In addition to leukocytes, they can be used to examine the recruitment of other cell types, such as therapeutically administered MSC or circulating tumor cells. Our multi-layered co-culture models have shown that MSC communicate with endothelium to modify their response to pro-inflammatory cytokines, altering the recruitment of neutrophils. Further research using such models is required to fully understand how stromal cells from different tissues and conditions (inflammatory disorders or cancer) influence the recruitment of leukocytes during inflammation.

Analysis of the effects of stromal cells on the migration of lymphocytes into and through inflamed tissue using 3-D culture models

Stromal cells may regulate the recruitment and behaviour of leukocytes during an inflammatory response, potentially through interaction with the endothelial cells (EC) and the leukocytes themselves. Here we describe new in vitro methodologies to characterise the effects of stromal cells on the migration of lymphocytes through endothelium and its underlying matrix. Three-dimensional tissue-like constructs were created in which EC were cultured above a stromal layer incorporating fibroblasts either as a monolayer on a porous filter or dispersed within a matrix of collagen type 1. A major advantage of these constructs is that they enable each step in leukocyte migration to be analysed in sequence (migration through EC and then stroma), as would occur in vivo. Migrated cells can also be retrieved from the constructs to identify which subsets traffic more effectively and how their functional responses evolve during migration. We found that culture of EC with dermal fibroblasts promoted lymphocyte transendothelial migration but not onward transit through matrix. A critical factor influencing the effect of fibroblasts on recruitment proved to be their proximity to the EC, with direct contact tending to disrupt migration. Comparison of the different approaches indicates that choice of an appropriate 3-D model enables the steps in lymphocyte entry into tissue to be studied in sequence, the regulatory mechanism to be dissected, and the effects of changes in stroma to be investigated.

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New models of tissue using endothelial cells, fibroblasts and collagen matrix

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Imaging of T-cell migration through tissue-like constructs

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Fibroblasts promote T-cell migration through endothelial cells.

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Fibroblasts contract collagen gel, restricting T-cell entry.

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In vitro tools to test agents with the potential to alter leukocyte recruitment

TIMP-2 targets tumor-associated myeloid suppressor cells with effects in cancer immune dysfunction and angiogenesis

Angiogenesis and inflammation are important therapeutic targets in non-small cell lung cancer (NSCLC). It is well known that proteolysis mediated by matrix metalloproteinases (MMPs) promotes angiogenesis and inflammation in the tumor microenvironment. Here, the effects of the MMP inhibitor TIMP-2 on NSCLC inflammation and angiogenesis were evaluated in TIMP-2-deficient (timp2-/-) mice injected subcutaneously (SC) with Lewis lung carcinoma cells and compared with the effects on tumors in wild-type mice. TIMP-2-deficient mice demonstrated increased tumor growth, enhanced expression of angiogenic marker αvβ3 in tumor and endothelial cells, and significantly higher serum vascular endothelial growth factor-A levels. Tumor-bearing timp2-/- mice showed a significant number of inflammatory cells in their tumors, upregulation of inflammation mediators, nuclear factor-kappaB, and Annexin A1, as well as higher levels of serum interleukin (IL)-6. Phenotypic analysis revealed an increase in myeloid-derived suppressor cell (MDSC) cells (CD11b+ and Gr-1+) that coexpressed vascular-endothelial-growth factor receptor 1 (VEGF-R1) and elevated MMP activation present in tumors and spleens from timp2-/- mice. Furthermore, TIMP-2-deficient tumors upregulated expression of the immunosuppressing genes controlling MDSC growth, IL-10, IL-13, IL-11, and chemokine ligand (CCL-5/RANTES), and decreased interferon-γ and increased CD40L. Moreover, forced TIMP-2 expression in human lung adenocarcinoma A-549 resulted in a significant reduction of MDSCs recruited into tumors, as well as suppression of angiogenesis and tumor growth. The increase in MDSCs has been linked to cancer immunosuppression and angiogenesis. Therefore, this study supports TIMP-2 as a negative regulator of MDSCs with important implications for the immunotherapy and/or antiangiogenic treatment of NSCLC.

On, around, and through: neutrophil-endothelial interactions in innate immunity

This manuscript will review our current understanding of neutrophilic polymorphonuclear leukocyte (neutrophil) interactions with the endothelium during immune and inflammatory responses, focusing on the molecular mechanisms regulating neutrophil adhesion to and migration through the endothelium in response to infection or tissue injury. This is a complex and dynamic area of research and one that has been the topic of several recent comprehensive reviews to which the interested reader is referred (64, 118, 131). By design, this review will begin with a brief review of some basic aspects of neutrophil biology and endothelial adhesion to provide a foundation. The remainder of the review will focus on selected areas of this complex field, specifically the role of the endothelial glycocalyx in regulating neutrophil adhesion and the mechanisms and consequences of migration of neutrophils between (paracellular) and through (transcellular) endothelial cells during egress from the vasculature.