Importance of primary capture and L-selectin-dependent secondary capture in leukocyte accumulation in inflammation and atherosclerosis in vivo

Panzerina lanata accelerates methicillin-resistant Staphylococcus aureus eradication by promoting migration and activation of neutrophils

Background

Panzerina lanata (Lanata) is generally used to treat pustule infection in Inner Mongolia folk medicine and is called "the holy medicine for pustule." However, the pharmacological mechanism of Lanata in treating pustule infection is still unclear.

Aims

This study aimed to investigate the therapeutic effects of Lanata on skin infection and explore the underlying mechanisms.

Methods

A skin wound methicillin-resistant Staphylococcus aureus (MRSA) infection mouse model was established to evaluate the healing effect of Lanata on infected wounds. In vitro assays were also conducted to determine the antibacterial activity of Lanata. Flow cytometry and immunohistochemistry were used to dynamically detect the number of neutrophils in the bone marrow, peripheral blood, and MRSA-infected wound. Protein expression in the infected wound skin was detected by a protein chip. Using an air pouch MRSA infection mouse model, the number of neutrophils, reactive oxygen species (ROS) level in neutrophils, and neutrophil extracellular trap (NET) formation were dynamically detected by flow cytometry and immunofluorescence. RNA-seq, RT-qPCR, flow cytometry, ELISA, and CXC chemokine receptor 2 (CXCR2) and P-selectin glycoprotein ligand-1 (PSGL-1) inhibitors were used to explore the mechanism of Lanata in regulating neutrophils.

Results

In vitro assays showed that Lanata had no direct antibacterial activity. In skin wound MRSA-infected mouse, Lanata promoted the rapid migration of neutrophils from the bone marrow via peripheral blood to the wound site to eradicate MRSA in the acute stage of infection and accelerate wound healing. Skin protein chip analysis showed that Lanata upregulated CXCR2 and PSGL-1 protein levels in skin wounds. Furthermore, analysis using the air pouch MRSA infection mouse model found that Lanata not only promoted the rapid migration of neutrophils from peripheral blood to the air pouch but also enhanced the activation of neutrophils, including the increase of ROS and the release of NETs, and upregulated the expression of CXCR2, PSGL-1, and myeloperoxidase (MPO) in neutrophils. Inhibition of CXCR2 and MPO significantly attenuated the effect of Lanata on promoting migration and activation of neutrophils.

Conclusion

Panzerina lanata resists MRSA infection by promoting migration and activation of neutrophils to rapidly eradicate MRSA.

Neutrophil diversity and function in health and disease

Neutrophils, the most abundant type of granulocyte, are widely recognized as one of the pivotal contributors to the acute inflammatory response. Initially, neutrophils were considered the mobile infantry of the innate immune system, tasked with the immediate response to invading pathogens. However, recent studies have demonstrated that neutrophils are versatile cells, capable of regulating various biological processes and impacting both human health and disease. Cytokines and other active mediators regulate the functional activity of neutrophils by activating multiple receptors on these cells, thereby initiating downstream signal transduction pathways. Dysfunctions in neutrophils and disruptions in neutrophil homeostasis have been implicated in the pathogenesis of numerous diseases, including cancer and inflammatory disorders, often due to aberrant intracellular signaling. This review provides a comprehensive synthesis of neutrophil biological functions, integrating recent advancements in this field. Moreover, it examines the biological roles of receptors on neutrophils and downstream signaling pathways involved in the regulation of neutrophil activity. The pathophysiology of neutrophils in numerous human diseases and emerging therapeutic approaches targeting them are also elaborated. This review also addresses the current limitations within the field of neutrophil research, highlighting critical gaps in knowledge that warrant further investigation. In summary, this review seeks to establish a comprehensive and multidimensional model of neutrophil regulation, providing new perspectives for potential clinical applications and further research.

Unleashing the biomimetic targeting potential of platelet-derived nanocarriers on atherosclerosis

Atherosclerosis, the primary mechanism underlying the development of many cardiovascular illnesses, continues to be one of the leading causes of mortality worldwide. Platelet (PLT), which are essential for maintaining body homeostasis, have been strongly linked to the onset of atherosclerosis at various stages due to their inherent tendency to bind to atherosclerotic lesions and show an affinity for plaques. Therefore, mimicking PLT's innate adhesive features may be necessary to effectively target plaques. PLT-derived nanocarriers have emerged as a promising biomimetic targeting strategy for treating atherosclerosis due to their numerous advantages. These advantages include excellent biocompatibility, minimal macrophage phagocytosis, prolonged circulation time, targeting capability for impaired vascular sites, and suitability as carriers for anti-atherosclerotic drugs. Herein, we discuss the role of PLT in atherogenesis and propose the design of nanocarriers based on PLT-membrane coating and PLT-derived vesicles. These nanocarriers can target multiple biological elements relevant to plaque development. The review also emphasizes the current challenges and future research directions for the effective utilization of PLT-derived nanocarriers in treating atherosclerosis.

Selectins in Biology and Human Disease: Opportunity in E-selectin Antagonism

Selectins are cell adhesion proteins discovered in the 1980s. As C-type lectins, selectins contain an essential calcium ion in the ligand-binding pocket and recognize the isomeric tetrasaccharides sialyl Lewisx (sLex) and sialyl Lewisa (sLea). Three selectins, E-selectin, P-selectin, and L-selectin, play distinct, complementary roles in inflammation, hematopoiesis, and tumor biology. They have been implicated in the pathology of diverse inflammatory disorders, and several selectin antagonists have been tested clinically. E-selectin plays a unique role in leukocyte activation, making it an attractive target for intervention, for example, in sickle cell disease (SCD). This review summarizes selectin biology and pathology, structure and ligand binding, and selectin antagonists that have reached clinical testing with an emphasis on E-selectin.

Dynamic thiol/disulfide homeostasis and myeloperoxidase levels in Gilbert's syndrome with mild hyperbilirubinemia

Aim

This study aimed to compare dynamic thiol/disulfide homeostasis and myeloperoxidase (MPO) levels in patients with Gilbert's syndrome (GS) and healthy controls.

Background

Thiol/disulfide homeostasis and MPO levels are both associated with increased progression of atherosclerosis.

Methods

The study included a total of 130 voluntary participants comprising 65 patients with GS and 65 healthy controls. These patients were selected randomly and dynamic thiol/disulfide homeostasis, MPO, complete blood count results, and biochemistry and lipid parameters were evaluated. Patients with known chronic diseases, medication usage, and acute infections were excluded from the study. Serum total thiol and native thiol levels were measured using the fully automated colorimetric method, while serum MPO levels were measured using the sandwich ELISA method.

Results

We found that patients with GS had significantly higher total thiol (352.3±38.6 vs. 317.9±47.9, p<0.001) and native thiol (386.6±42.6 vs. 348.0±51.1, p<0.001) and significantly lower disulfide (15.7±4.0 vs. 17.3±4.0, p=0.022) and MPO (130.7 vs. 166.3, p=0.006). In patients with bilirubin of <1 mg/dL, total thiol and native thiol levels were lower and disulfide, disulfide/native thiol (DNT) and disulfide/total thiol (DTT) ratios, and MPO levels were higher. Patients with bilirubin of <1 mg/dL also had higher total cholesterol.

Conclusion

In these patients with GS, the thiol/disulfide balance shifted towards thiols and proinflammatory MPO levels were lower. When bilirubin was <1 mg/dL, disulfide, DNT and DTT ratios, and MPO were higher. Bilirubin levels affected all parameters of thiol/disulfide homeostasis and MPO levels independently of other risk factors. In light of our results, we suggest that mild hyperbilirubinemia in cases of GS has an anti-inflammatory and antioxidant effect and may be protective against atherosclerosis.

The effects of brominated flame retardants (BFRs) on pro-atherosclerosis mechanisms

Brominated flame-retardants (BFRs) are environmental endocrine disruptors, comprising several pollutants, which potentially affect the endocrine system and cause dysfunction and disease. Widespread BFR exposure may cause multisystem toxicity, including cardiovascular toxicity in some individuals. Studies have shown that BFRs not only increase heart rate, induce arrhythmia and cardiac hypertrophy, but also cause glycolipid metabolism disorders, vascular endothelial dysfunction, and inflammatory responses, all of which potentially induce pre-pathological changes in atherosclerosis. Experimental data indicated that BFRs disrupt gene expression or signaling pathways, which cause vascular endothelial dysfunction, lipid metabolism-related disease, inflammation, and possibly atherosclerosis. Considerable evidence now suggests that BFR exposure may be a pro-atherosclerotic risk factor. In this study, we reviewed putative BFR effects underpinning pro-atherosclerosis mechanisms, and focused on vascular endothelial cell dysfunction, abnormal lipid metabolism, pro-inflammatory cytokine production and foam cell formation. Consequently, we proposed a scientific basis for preventing atherosclerosis by BFRs and provided concepts for further research.

Selectin-Mediated Signaling-Shedding Light on the Regulation of Integrin Activity in Neutrophils

As a consequence of tissue injury or infection, neutrophils are recruited in a stepwise recruitment process from the bloodstream into the surrounding tissue. Selectins are a family of adhesion molecules comprised of L-, E-, and P-selectin. Differences in expression patterns, protein structure, and ligand binding characteristics mediate distinct functions of each selectin. Interactions of selectins and their counter-receptors mediate the first contact of neutrophils with the endothelium, as well as subsequent neutrophil rolling along the endothelial surface. For efficient neutrophil recruitment, activation of β₂-integrins on the cell surface is essential. Integrin activation can be elicited via selectin- as well as chemokine-mediated inside-out signaling resulting in integrin conformational changes and clustering. Dysregulation of selectin-induced integrin activation on neutrophils is involved in the development of severe pathological disease conditions including leukocyte adhesion deficiency (LAD) syndromes in humans. Here, we review molecular mechanisms involved in selectin-mediated signaling pathways in neutrophils and their impact on integrin activation, neutrophil recruitment, and inflammatory diseases.

Neutrophils in acute inflammation: current concepts and translational implications

Modulation of neutrophil recruitment and function is crucial for targeting inflammatory cells to sites of infection to combat invading pathogens while, at the same time, limiting host tissue injury or autoimmunity. The underlying mechanisms regulating recruitment of neutrophils, 1 of the most abundant inflammatory cells, have gained increasing interest over the years. The previously described classical recruitment cascade of leukocytes has been extended to include capturing, rolling, adhesion, crawling, and transmigration, as well as a reverse-transmigration step that is crucial for balancing immune defense and control of remote organ endothelial leakage. Current developments in the field emphasize the importance of cellular interplay, tissue environmental cues, circadian rhythmicity, detection of neutrophil phenotypes, differential chemokine sensing, and contribution of distinct signaling components to receptor activation and integrin conformations. The use of therapeutics modulating neutrophil activation responses, as well as mutations causing dysfunctional neutrophil receptors and impaired signaling cascades, have been defined in translational animal models. Human correlates of such mutations result in increased susceptibility to infections or organ damage. This review focuses on current advances in the understanding of the regulation of neutrophil recruitment and functionality and translational implications of current discoveries in the field with a focus on acute inflammation and sepsis.

Neutrophils-From Bone Marrow to First-Line Defense of the Innate Immune System

Neutrophils (polymorphonuclear cells; PMNs) form a first line of defense against pathogens and are therefore an important component of the innate immune response. As a result of poorly controlled activation, however, PMNs can also mediate tissue damage in numerous diseases, often by increasing tissue inflammation and injury. According to current knowledge, PMNs are not only part of the pathogenesis of infectious and autoimmune diseases but also of conditions with disturbed tissue homeostasis such as trauma and shock. Scientific advances in the past two decades have changed the role of neutrophils from that of solely immune defense cells to cells that are responsible for the general integrity of the body, even in the absence of pathogens. To better understand PMN function in the human organism, our review outlines the role of PMNs within the innate immune system. This review provides an overview of the migration of PMNs from the vascular compartment to the target tissue as well as their chemotactic processes and illuminates crucial neutrophil immune properties at the site of the lesion. The review is focused on the formation of chemotactic gradients in interaction with the extracellular matrix (ECM) and the influence of the ECM on PMN function. In addition, our review summarizes current knowledge about the phenomenon of bidirectional and reverse PMN migration, neutrophil microtubules, and the microtubule organizing center in PMN migration. As a conclusive feature, we review and discuss new findings about neutrophil behavior in cancer environment and tumor tissue.

Receptor Interacting Protein Kinases 1/3: The Potential Therapeutic Target for Cardiovascular Inflammatory Diseases

The receptor interacting protein kinases 1/3 (RIPK1/3) have emerged as the key mediators in cell death pathways and inflammatory signaling, whose ubiquitination, phosphorylation, and inhibition could regulate the necroptosis and apoptosis effectually. Recently, more and more studies show great interest in the mechanisms and the regulator of RIPK1/3-mediated inflammatory response and in the physiopathogenesis of cardiovascular diseases. The crosstalk of autophagy and necroptosis in cardiomyocyte death is a nonnegligible conversation of cell death. We elaborated on RIPK1/3-mediated necroptosis, pathways involved, the latest regulatory molecules and therapeutic targets in terms of ischemia reperfusion, myocardial remodeling, myocarditis, atherosclerosis, abdominal aortic aneurysm, and cardiovascular transplantation, etc.

Systematic Review and Meta-Analysis of the Effect of Statins on Circulating E-Selectin, L-Selectin, and P-Selectin

The pleiotropic effects of statins might involve preventing inflammatory cell adhesion to the endothelium, which is a critical step in the pathogenesis of atherosclerosis. We conducted a systematic review and meta-analysis of the effects of statins on the circulating cell adhesion molecules E-Selectin, L-Selectin, and P-Selectin. A literature search was conducted in PubMed, Web of Science, and Scopus, from inception to July 2021. Risk of bias and certainty of evidence were assessed using the Joanna Briggs Institute Critical Appraisal Checklist and GRADE, respectively. In 61 studies, statins significantly reduced P-selectin (standard mean difference, SMD = -0.39, 95% CI -0.55 to -0.22, p < 0.001; moderate certainty of evidence), L-selectin (SMD = -0.49, 95% CI -0.89 to -0.10, p = 0.014; very low certainty of evidence), and E-Selectin (SMD = -0.73, 95% CI -1.02 to -0.43, p < 0.001; moderate certainty of evidence), independently of baseline lipid profile and other study and patient characteristics. The corresponding pooled SMD values in sensitivity analysis were not substantially altered when individual studies were sequentially removed. Simvastatin had a significant lowering effect on both P-selectin and E-selectin. Therefore, statins significantly reduce circulating selectins. Further studies are required to investigate whether selectin lowering mediates cardiovascular risk reduction with these agents. (PROSPERO registration number: CRD42021282778).

Targeting Leukocyte Trafficking in Inflammatory Bowel Disease

In the last two decades, understanding of inflammatory bowel disease (IBD) immunopathogenesis has expanded considerably. Histopathological examination of the intestinal mucosa in IBD demonstrates the presence of a chronic inflammatory cell infiltrate. Research has focused on identifying mechanisms of immune cell trafficking to the gastrointestinal tract that may represent effective gut-selective targets for IBD therapy whilst avoiding systemic immunosuppression that may be associated with off-target adverse effects such as infection and malignancy. Integrins are cell surface receptors that can bind to cellular adhesion molecules to mediate both leukocyte homing and retention. In 2014, Vedolizumab (Entyvio^®) was the first anti-integrin (anti-α4ß7 monoclonal antibody) treatment to be approved for use in IBD. Several other anti-integrin therapies are currently in advanced stages of development, including novel orally administered small-molecule drugs. Drugs targeting alternative trafficking mechanisms such as mucosal addressin cellular adhesion molecule-1 and sphingosine-1-phosphate receptors are also being evaluated. Here, we summarise key established and emerging therapies targeting leukocyte trafficking that may play an important role in realising the goal of stratified precision medicine in IBD care.

Exploring the regulatory roles of circular RNAs in the pathogenesis of atherosclerosis

Circular RNAs (circRNAs) are a class of noncoding RNAs with a covalently closed loop structure. Recent evidence has shown that circRNAs can regulate gene transcription, alternative splicing, microRNA (miRNA) "molecular sponges", RNA-binding proteins and protein translation. Atherosclerosis is one of the leading causes of death worldwide, and more studies have indicated that circRNAs are related to atherosclerosis pathogenesis, including vascular endothelial cells, vascular smooth muscle cells, inflammation and lipid metabolism. In this review, we systematically summarize the biogenesis, characteristics and functions of circRNAs with a focus on their roles in the pathogenesis of atherosclerosis.

Contribution of ADAM17 and related ADAMs in cardiovascular diseases

A disintegrin and metalloproteases (ADAMs) are key mediators of cell signaling by ectodomain shedding of various growth factors, cytokines, receptors and adhesion molecules at the cellular membrane. ADAMs regulate cell proliferation, cell growth, inflammation, and other regular cellular processes. ADAM17, the most extensively studied ADAM family member, is also known as tumor necrosis factor (TNF)-α converting enzyme (TACE). ADAMs-mediated shedding of cytokines such as TNF-α orchestrates immune system or inflammatory cascades and ADAMs-mediated shedding of growth factors causes cell growth or proliferation by transactivation of the growth factor receptors including epidermal growth factor receptor. Therefore, increased ADAMs-mediated shedding can induce inflammation, tissue remodeling and dysfunction associated with various cardiovascular diseases such as hypertension and atherosclerosis, and ADAMs can be a potential therapeutic target in these diseases. In this review, we focus on the role of ADAMs in cardiovascular pathophysiology and cardiovascular diseases. The main aim of this review is to stimulate new interest in this area by highlighting remarkable evidence.

Targeting Neutrophil Adhesive Events to Address Vaso-Occlusive Crisis in Sickle Cell Patients

Neutrophils are essential to protect the host against invading pathogens but can promote disease progression in sickle cell disease (SCD) by becoming adherent to inflamed microvascular networks in peripheral tissue throughout the body. During the inflammatory response, leukocytes extravasate from the bloodstream using selectin adhesion molecules and migrate to sites of tissue insult through activation of integrins that are essential for combating pathogens. However, during vaso-occlusion associated with SCD, neutrophils are activated during tethering and rolling on selectins upregulated on activated endothelium that line blood vessels. Recently, we reported that recognition of sLex on L-selectin by E-selectin during neutrophil rolling initiates shear force resistant catch-bonds that facilitate tethering to endothelium and activation of integrin bond clusters that anchor cells to the vessel wall. Evidence indicates that blocking this important signaling cascade prevents the congestion and ischemia in microvasculature that occurs from neutrophil capture of sickled red blood cells, which are normally deformable ellipses that flow easily through small blood vessels. Two recently completed clinical trials of therapies targeting selectins and their effect on neutrophil activation in small blood vessels reveal the importance of mechanoregulation that in health is an immune adaption facilitating rapid and proportional leukocyte adhesion, while sustaining tissue perfusion. We provide a timely perspective on the mechanism underlying vaso-occlusive crisis (VOC) with a focus on new drugs that target selectin mediated integrin adhesive bond formation.

The Tumour Vasculature as a Target to Modulate Leucocyte Trafficking

Simple Summary

Tumour blood vessels, characterised by abnormal morphology and function, create an immunosuppressive tumour microenvironment via restricting the appropriate leucocyte subsets trafficking. Strategies to trigger phenotypic alteration in tumour vascular system to resemble normal vascular system, named vascular normalisation, promote effective trafficking of leucocytes into tumours through enhancing the interactions between leucocytes and endothelial cells. This review specifically demonstrates how targeting tumour blood vessels modulates the critical steps of leucocyte trafficking. Furthermore, selective regulation of leucocyte subsets trafficking in tumours can be achieved by vasculature-targeting strategies, contributing to improved immunotherapy and thereby delayed tumour progression.

Abstract

The effectiveness of immunotherapy against solid tumours is dependent on the appropriate leucocyte subsets trafficking and accumulating in the tumour microenvironment (TME) with recruitment occurring at the endothelium. Such recruitment involves interactions between the leucocytes and the endothelial cells (ECs) of the vessel and occurs through a series of steps including leucocyte capture, their rolling, adhesion, and intraluminal crawling, and finally leucocyte transendothelial migration across the endothelium. The tumour vasculature can curb the trafficking of leucocytes through influencing each step of the leucocyte recruitment process, ultimately producing an immunoresistant microenvironment. Modulation of the tumour vasculature by strategies such as vascular normalisation have proven to be efficient in facilitating leucocyte trafficking into tumours and enhancing immunotherapy. In this review, we discuss the underlying mechanisms of abnormal tumour vasculature and its impact on leucocyte trafficking, and potential strategies for overcoming the tumour vascular abnormalities to boost immunotherapy via increasing leucocyte recruitment.

Macrophage 3D migration: A potential therapeutic target for inflammation and deleterious progression in diseases

Macrophages are heterogeneous cells that have different physiological functions, such as chemotaxis, phagocytosis, endocytosis, and secretion of various factors. All physiological functions of macrophages are integral to homeostasis, immune defense and tissue repair. However, in several diseases, macrophages are recruited from the blood towards inflammatory sites. This process is called macrophage migration, which promotes deleterious disease progression. Macrophage migration is a key player in many inflammatory diseases, autoimmune diseases and cancers because it contributes to the accumulation of proinflammatory factors, the destruction of tissues and the development of tumors. Therefore, macrophage migration is proposed to be a potential therapeutic target. Macrophages migrate between two-dimensional (2D) and three-dimensional (3D) environments, implying that distinct migratory features and mechanisms are involved. Compared with the 2D migration of macrophages, 3D migration involves more complex variations in cellular morphology and dynamics. The structure of the extracellular matrix, a key factor, is modified in diseases that influence macrophage 3D migration. Macrophage 3D migration relates to disease pathology. Research that focuses on macrophage 3D migration is an emerging field and was reviewed in this article to indicate the molecular and cellular mechanisms of macrophage migration in 3D environments and to provide potential targets for controlling disease progression associated with this migration.

A Novel Experimental Approach for In Vivo Analyses of the Salivary Gland Microvasculature

Microvascular dysfunction plays a fundamental role in the pathogenesis of salivary gland disorders. Restoring and preserving microvascular integrity might therefore represent a promising strategy for the treatment of these pathologies. The mechanisms underlying microvascular dysfunction in salivary glands, however, are still obscure, partly due to the unavailability of adequate in vivo models. Here, we present a novel experimental approach that allows comprehensive in vivo analyses of the salivary gland microvasculature in mice. For this purpose, we employed different microscopy techniques including multi-photon in vivo microscopy to quantitatively analyze interactions of distinct immune cell subsets in the submandibular gland microvasculature required for their infiltration into the surrounding parenchyma and their effects on microvascular function. Confocal microscopy and multi-channel flow cytometry in tissue sections/homogenates complemented these real-time analyses by determining the molecular phenotype of the participating cells. To this end, we identified key adhesion and signaling molecules that regulate the subset- and tissue-specific trafficking of leukocytes into inflamed glands and control the associated microvascular leakage. Hence, we established an experimental approach that allows in vivo analyses of microvascular processes in healthy and diseased salivary glands. This enables us to delineate distinct pathogenetic factors as novel therapeutic targets in salivary gland diseases.

The aorta can act as a site of naïve CD4+ T-cell priming

AIMS

Aortic adaptive immunity plays a role in atherosclerosis; however, the precise mechanisms leading to T-cell activation in the arterial wall remain poorly understood.

METHODS AND RESULTS

Here, we have identified naïve T cells in the aorta of wild-type and T-cell receptor transgenic mice and we demonstrate that naïve T cells can be primed directly in the vessel wall with both kinetics and frequency of T-cell activation found to be similar to splenic and lymphoid T cells. Aortic homing of naïve T cells is regulated at least in part by the P-selectin glycosylated ligand-1 receptor. In experimental atherosclerosis the aorta supports CD4+ T-cell activation selectively driving Th1 polarization. By contrast, secondary lymphoid organs display Treg expansion.

CONCLUSION

Our results demonstrate that the aorta can support T-cell priming and that naïve T cells traffic between the circulation and vessel wall. These data underpin the paradigm that local priming of T cells specific for plaque antigens contributes to atherosclerosis progression.

Comprehensive analysis of circRNA expression pattern and circRNA-miRNA-mRNA network in the pathogenesis of atherosclerosis in rabbits

Atherosclerosis is a chronic and multifactorial inflammatory disease and is closely associated with cardiovascular and cerebrovascular diseases. circRNAs can act as competing endogenous RNAs to mRNAs and function in various diseases. However, there is little known about the function of circRNAs in atherosclerosis. In this study, three rabbits in the case group were fed a high-fat diet to induce atherosclerosis and another three rabbits were fed a normal diet. To explore the biological functions of circRNAs in atherosclerosis, we analyzed the circRNA, miRNA and mRNA expression profiles using RNA-seq. Many miRNAs, mRNAs and circRNAs were identified as significantly changed in atherosclerosis. We next predicted miRNA-target interactions with the miRanda tool and constructed a differentially expressed circRNA-miRNA-mRNA triple network. A gene ontology enrichment analysis showed that genes in the network were involved in cell adhesion, cell activation and the immune response. Furthermore, we generated a dysregulated circRNA-related ceRNAs network and found seven circRNAs (ocu-cirR-novel-18038, -18298, -15993, -17934, -17879, -18036 and -14389) were related to atherosclerosis. We found these circRNAs also functioned in cell adhesion, cell activation and the immune response. These results show that the crosstalk between circRNAs and their competing mRNAs might play crucial roles in the development of atherosclerosis.

Adventitial Cell Atlas of wt (Wild Type) and ApoE (Apolipoprotein E)-Deficient Mice Defined by Single-Cell RNA Sequencing

Objective- Vascular adventitia encompasses progenitors and is getting recognized as the major site of inflammation in early stage of atherosclerosis. However, the cellular atlas of the heterogeneous adventitial cells, the intercellular communication, the cellular response of adventitia to hyperlipidemia, and its contribution to atherosclerosis have been elusive. Approach and Results- Single-cell RNA sequencing was applied to wt (wild type) and ApoE (apolipoprotein E)-deficient aortic adventitia from 12-week-old C57BL/6J mice fed on normal laboratory diet with early stage of atherosclerosis. Unbiased clustering analysis revealed that the landscape of adventitial cells encompassed adventitial mesenchyme cells, immune cells (macrophages, T cells, and B cells), and some types of rare cells, for example, neuron, lymphatic endothelial cells, and innate lymphoid cells. Seurat clustering analysis singled out 6 nonimmune clusters with distinct transcriptomic profiles, in which there predominantly were stem/progenitor cell-like and proinflammatory population (Mesen II). In ApoE-deficient adventitia, resident macrophages were activated and related to increased myeloid cell infiltration in the adventitia. Cell communication analysis further elucidated enhanced interaction between a mesenchyme cluster and inflammatory macrophages in ApoE-deficient adventitia. In vitro transwell assay confirmed the proinflammatory role of SCA1+ (stem cell antigen 1 positive) Mesen II population with increased CCL2 (chemokine [C-C motif] ligand 2) secretion and thus increased capacity to attract immune cells in ApoE-deficient adventitia. Conclusions- Cell atlas defined by single-cell RNA sequencing depicted the heterogeneous cellular landscape of the adventitia and uncovered several types of cell populations. Furthermore, resident cell interaction with immune cells appears crucial at the early stage of atherosclerosis.

The emerging role of neutrophils as modifiers of recovery after traumatic injury to the developing brain

The innate immune response plays a critical role in traumatic brain injury (TBI), contributing to ongoing pathogenesis and worsening long-term outcomes. Here we focus on neutrophils, one of the "first responders" to TBI. These leukocytes are recruited to the injured brain where they release a host of toxic molecules including free radicals, proteases, and pro-inflammatory cytokines, all of which promote secondary tissue damage. There is mounting evidence that the developing brain is more vulnerable to injury that the adult brain. This vulnerability to greater damage from TBI is, in part, attributed to relatively low antioxidant reserves coupled with an early robust immune response. The latter is reflected in enhanced sensitivity to cytokines and a prolonged recruitment of neutrophils into both cortical and subcortical regions. This review considers the contribution of neutrophils to early secondary pathogenesis in the injured developing brain and raises the distinct possibility that these leukocytes, which exhibit phenotypic plasticity, may also be poised to support wound healing. We provide a basic review of the development, life cycle, and granular contents of neutrophils and evaluate their potential as therapeutic targets for early neuroprotection and functional recovery after injury at early age. While neutrophils have been broadly studied in neurotrauma, we are only beginning to appreciate their diverse roles in the developing brain and the extent to which their acute manipulation may result in enduring neurological recovery when TBI is superimposed upon brain development.

Cooperative PSGL-1 and CXCR2 signaling in neutrophils promotes deep vein thrombosis in mice

Inflammation is a major contributor to deep vein thrombosis (DVT). Flow restriction of the inferior vena cava (IVC) in mice induces DVT like that in humans. In this model, P-selectin-dependent adhesion of neutrophils and monocytes leads to release of neutrophil extracellular traps (NETs) and expression of tissue factor. However, it is not known what signals cause myeloid cells to generate these procoagulant effectors. Using ultrasonography and spinning-disk intravital microscopy in genetically engineered mice, we found that engagement of P-selectin glycoprotein ligand-1 (PSGL-1) and the chemokine receptor CXCR2 on rolling neutrophils propagated signals that cooperated to induce β2 integrin-dependent arrest in flow-restricted IVCs. Unlike previous reports, PSGL-1 signaling in neutrophils did not require L-selectin, and it used tyrosine 145 rather than tyrosines 112 and 128 on the adaptor Src homology domain-containing leukocyte phosphoprotein of 76 kDa. PSGL-1 and CXCR2 signaling cooperated to increase the frequency and size of thrombi, in part by stimulating release of NETs. Unlike in neutrophils, blocking PSGL-1 or CXCR2 signaling in monocytes did not affect their recruitment into thrombi or their expression of tissue factor. Our results demonstrate that neutrophils cooperatively signal through PSGL-1 and CXCR2 to promote DVT.

Intravascular leukocyte migration through platelet thrombi: directing leukocytes to sites of vascular injury

Leukocytes recruitment to thrombi supports an intimate cellular interaction leading to the enhancement of pro-coagulant functions and pro-inflammatory responses at site of vascular injury. Recent observations of neutrophil extracellular traps (NETs) formation and its mutual reactions with platelet thrombi adds more clinical interest to the growing body of knowledge in the field of platelet-leukocyte crosstalk. However, having considered thrombus as a barrier between leukocytes and injured endothelium, the full inflammatory roles of these cells during thrombosis is still ill defined. The most recent observation of neutrophils migration into the thrombi is a phenomenon that highlights the inflammatory functions of leukocytes at the site of injury. It has been hypothesised that leukocytes migration might be associated with the conveyance of highly reactive pro-inflammatory and/or procoagulant mediators to sites of vascular injury. In addition, the evidence of neutrophils migration into arterial thrombi following traumatic and ischaemia-reperfusion injury highlights the already described role of these cells in atherosclerosis. Regardless of the mechanisms behind leukocyte migration, whether these migrated cells benefit normal homeostasis by their involvement in wound healing and vascular rebuilding or they increase unwilling inflammatory responses, could be of interest for future researches that provide new insight into biological importance of leukocyte recruitment to thrombi.

P-Selectin and ICAM-1 synergy in mediating THP-1 monocyte adhesion in hemodynamic flow is length dependent

The tightly orchestrated recruitment of monocytes, whose progeny are critical to the progression and resolution of various physiological and pathophysiological processes, is implicated in the time course, severity, and resolution of pathology. Using a microfluidic-based cell adhesion assay integrating spatiotemporal analyses and micropatterning of adhesive proteins, we interrogated the effects of adhesive molecule presentation length, which varies in vivo with disease and stage, on THP-1 monocyte cell rolling versus firm adhesion mediated by P-selectin and/or ICAM-1 in hemodynamic flow. Our results indicate that co-presentation of P-selectin and ICAM-1 substantially decreases the length of adhesive substrate required to sustain adhesion in flow and that P-selectin functions synergistically with ICAM-1 to substantially enhance THP-1 firm adhesion. This synergy was found to furthermore correlate with diminished cell rolling velocities and length-enhanced secondary cell capture. Our results suggest pathophysiological ramifications for local remodeling of the inflamed microvascular microenvironment in directing the efficiency of monocyte trafficking.

Innate Immune Basis for Rift Valley Fever Susceptibility in Mouse Models

Rift Valley fever virus (RVFV) leads to varied clinical manifestations in animals and in humans that range from moderate fever to fatal illness, suggesting that host immune responses are important determinants of the disease severity. We investigated the immune basis for the extreme susceptibility of MBT/Pas mice that die with mild to acute hepatitis by day 3 post-infection compared to more resistant BALB/cByJ mice that survive up to a week longer. Lower levels of neutrophils observed in the bone marrow and blood of infected MBT/Pas mice are unlikely to be causative of increased RVFV susceptibility as constitutive neutropenia in specific mutant mice did not change survival outcome. However, whereas MBT/Pas mice mounted an earlier inflammatory response accompanied by higher amounts of interferon (IFN)-α in the serum compared to BALB/cByJ mice, they failed to prevent high viral antigen load. Several immunological alterations were uncovered in infected MBT/Pas mice compared to BALB/cByJ mice, including low levels of leukocytes that expressed type I IFN receptor subunit 1 (IFNAR1) in the blood, spleen and liver, delayed leukocyte activation and decreased percentage of IFN-γ-producing leukocytes in the blood. These observations are consistent with the complex mode of inheritance of RVFV susceptibility in genetic studies.

P-, but not E- or L-, selectin-mediated rolling adhesion persistence in hemodynamic flow diverges between metastatic and leukocytic cells

The ability of leukocytic cells to engage selectins via rolling adhesion is critical to inflammation, but selectins are also implicated in mediating metastatic dissemination. Using a microfluidic- and flow-based cell adhesion chromatography experimental and analytical technique, we interrogated the cell-subtype differences in engagement and sustainment of rolling adhesion on P-, E-, and L-selectin-functionalized surfaces in physiological flow. Our results indicate that, particularly at low concentrations of P-selectin, metastatic but not leukocytic cells exhibit reduced rolling adhesion persistence, whereas both cell subtypes exhibited reduced persistence on L-selectin and high persistence on E-selectin, differences not revealed by flow cytometry analysis or reflected in the extent or velocity of rolling adhesion. Conditions under which adhesion persistence was found to be significantly reduced corresponded to those exhibiting the greatest sensitivity to a selectin-antagonist. Our results suggest that potentially therapeutically exploitable differences in metastatic and leukocytic cell subtype interactions with selectins in physiological flow are identifiable through implementation of functional assays of adhesion persistence in hemodynamic flow utilizing this integrated, flow-based cell adhesion chromatography analytical technique.

How neutrophils resist shear stress at blood vessel walls: molecular mechanisms, subcellular structures, and cell-cell interactions

Neutrophils are the first cells arriving at sites of tissue injury or infection to combat invading pathogens. Successful neutrophil recruitment to sites of inflammation highly depends on specific molecular mechanisms, fine-tuning the received information into signaling pathways and converting them into well-described recruitment steps. This review highlights the impact of vascular flow conditions on neutrophil recruitment and the multitude of mechanisms developed to enable this sophisticated process under wall shear stress conditions. The recruitment process underlies a complex interplay between adhesion and signaling molecules, as well as chemokines, in which neutrophils developed specific mechanisms to travel to sites of lesion in low and high shear stress conditions. Rolling, as the first step in the recruitment process, highly depends on endothelial selectins and their ligands on neutrophils, inducting of intracellular signaling and subsequently activating β₂ integrins, enabling adhesion and postadhesion events. In addition, subcellular structures, such as microvilli, tethers, and slings allow the cell to arrest, even under high wall shear stress. Thereby, microvilli that are pulled out from the cell body form tethers that develop into slings upon their detachment from the substrate. In addition to the above-described primary capture, secondary capture of neutrophils via neutrophil-neutrophil or neutrophil-platelet interaction promotes the process of neutrophil recruitment to sites of lesion. Thus, precise mechanisms based on a complex molecular interplay, subcellular structures, and cell-cell interactions turn the delicate process of neutrophil trafficking during flow into a robust response allowing effective neutrophil accumulation at sites of injury.

L-selectin mechanochemistry restricts neutrophil priming in vivo

Circulating neutrophils must avoid premature activation to prevent tissue injury. The leukocyte adhesion receptor L-selectin forms bonds with P-selectin glycoprotein ligand-1 (PSGL-1) on other leukocytes and with peripheral node addressin (PNAd) on high endothelial venules. Mechanical forces can strengthen (catch) or weaken (slip) bonds between biological molecules. How these mechanochemical processes influence function in vivo is unexplored. Here we show that mice expressing an L-selectin mutant (N138G) have altered catch bonds and prolonged bond lifetimes at low forces. Basal lymphocyte homing and neutrophil recruitment to inflamed sites are normal. However, circulating neutrophils form unstable aggregates and are unexpectedly primed to respond robustly to inflammatory mediators. Priming requires signals transduced through L-selectin N138G after it engages PSGL-1 or PNAd. Priming enhances bacterial clearance but increases inflammatory injury and enlarges venous thrombi. Thus, L-selectin mechanochemistry limits premature activation of neutrophils. Our results highlight the importance of probing how mechanochemistry functions in vivo.

MFG-E8-derived peptide attenuates adhesion and migration of immune cells to endothelial cells

Milk fat globule-epidermal growth factor-factor 8 (MFG-E8) plays an immunomodulatory role in inflammatory diseases. MFG-E8-derived short peptide (MSP68) greatly reduces neutrophil infiltration and injury in the lung during sepsis. In this study, we examined the effect of MSP68 on chemotaxis of various immune cells and its regulatory mechanism. Bone marrow-derived neutrophils (BMDNs) from C57BL/6 mice, human monocyte THP-1 cell line, and human T lymphocyte Jurkat cell line were used for adhesion and migration assays using a Transwell method in the presence of MSP68. Treatment with MSP68 significantly inhibited the BMDN and THP-1 cell but not Jurkat cell adhesion on the TNF-α-stimulated pulmonary artery endothelial cell (PAEC) monolayer dose-dependently. MSP68 also significantly reduced BMDN adhesion on VCAM-1-coated wells dose dependently. Surface plasmon resonance (SPR) analysis revealed that MSP68 efficiently recognized integrin α₄β₁ (receptor for VCAM-1) at the dissociation constant (K_D) of 1.53 × 10^-7 M. These findings implicate that MSP68 prevents neutrophil adhesion to the activated endothelial cells by interfering with the binding between integrin α₄β₁ on neutrophils and VCAM-1 on endothelial cells. Moreover, MSP68 significantly attenuated the migration of BMDN and THP-1 cells but not Jurkat cells to their chemoattractants. Pretreatment with MSP68 inhibited the transmigration of BMDNs across the PAECs toward chemoattractants, fMLP, MIP-2, and complement fragment 5a (C5a) dose-dependently. Finally, we identified that the activation of p38 MAPK in BMDNs by fMLP was inhibited by MSP68. Thus, MSP68 attenuates extravasation of immune cells through the endothelial cell lining into inflamed tissue, implicating MSP68 to be a novel, therapeutic agent for inflammatory diseases caused by excessive immune cell infiltration.

Caveolae: A Role in Endothelial Inflammation and Mechanotransduction?

Vascular inflammation and disease progression, such as atherosclerosis, are in part a consequence of haemodynamic forces generated by changes in blood flow. The haemodynamic forces, such as shear stress or stretch, interact with vascular endothelial cells, which transduce the mechanical stimuli into biochemical signals via mechanosensors, which can induce an upregulation in pathways involved in inflammatory signaling. However, it is unclear how these mechanosensors respond to shear stress and most significantly what cellular mechanisms are involved in sensing the haemodynamic stimuli. This review explores the transition from shear forces, stretch and pressure to endothelial inflammation and the process of mechanotransduction, specifically highlighting evidence to suggest that caveolae play as a role as mechanosensors.

Live cell imaging to understand monocyte, macrophage, and dendritic cell function in atherosclerosis

Ley et al. provide a review of the technology and accomplishments of dynamic imaging of myeloid cells in atherosclerosis.

Intravital imaging is an invaluable tool for understanding the function of cells in healthy and diseased tissues. It provides a window into dynamic processes that cannot be studied by other techniques. This review will cover the benefits and limitations of various techniques for labeling and imaging myeloid cells, with a special focus on imaging cells in atherosclerotic arteries. Although intravital imaging is a powerful tool for understanding cell function, it alone does not provide a complete picture of the cell. Other techniques, such as flow cytometry and transcriptomics, must be combined with intravital imaging to fully understand a cell's phenotype, lineage, and function.

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.

Regulation of L-selectin-dependent hydrodynamic shear thresholding by leukocyte deformability and shear dependent bond number

BACKGROUND

During inflammation leukocyte attachment to the blood vessel wall is augmented by capture of near-wall flowing leukocytes by previously adherent leukocytes. Adhesive interactions between flowing and adherent leukocytes are mediated by L-selectin and P-selectin Glycoprotein Ligand-1 (PSGL-1) co-expressed on the leukocyte surface and ultimately regulated by hydrodynamic shear thresholding.

OBJECTIVE

We hypothesized that leukocyte deformability is a significant contributory factor in shear thresholding and secondary capture.

METHODS

Cytochalasin D (CD) was used to increase neutrophil deformability and fixation was used to reduce deformability. Neutrophil rolling on PSGL-1 coated planar surfaces and collisions with PSGL-1 coated microbeads were analyzed using high-speed videomicroscopy (250 fps).

RESULTS

Increased deformability led to an increase in neutrophil rolling flux on PSGL-1 surfaces while fixation led to a decrease in rolling flux. Abrupt drops in flow below the shear threshold resulted in extended release times from the substrate for CD-treated neutrophils, suggesting increased bond number. In a cell-microbead collision assay lower flow rates were correlated with briefer adhesion lifetimes and smaller adhesive contact patches.

CONCLUSIONS

Leukocyte deformation may control selectin bond number at the flow rates associated with hydrodynamic shear thresholding. Model analysis supported a requirement for both L-selectin catch-slip bond properties and multiple bond formation for shear thresholding.

Tuberculosis and Cardiovascular Disease: Linking the Epidemics

The burden of tuberculosis and cardiovascular disease (CVD) is enormous worldwide. CVD rates are rapidly increasing in low- and middle-income countries. Public health programs have been challenged with the overlapping tuberculosis and CVD epidemics. Monocyte/macrophages, lymphocytes and cytokines involved in cellular mediated immune responses against Mycobacterium tuberculosis are also main drivers of atherogenesis, suggesting a potential pathogenic role of tuberculosis in CVD via mechanisms that have been described for other pathogens that establish chronic infection and latency. Studies have shown a pro-atherogenic effect of antibody-mediated responses against mycobacterial heat shock protein-65 through cross reaction with self-antigens in human vessels. Furthermore, subsets of mycobacteria actively replicate during latent tuberculosis infection (LTBI), and recent studies suggest that LTBI is associated with persistent chronic inflammation that may lead to CVD. Recent epidemiologic work has shown that the risk of CVD in persons who develop tuberculosis is higher than in persons without a history of tuberculosis, even several years after recovery from tuberculosis. Together, these data suggest that tuberculosis may play a role in the pathogenesis of CVD. Further research to investigate a potential link between tuberculosis and CVD is warranted.

Elevated Serum Level of Interleukin 17 in a Population With Prehypertension

Cytokines play an important role in the pathogenesis of hypertension. The authors hypothesized that interleukin 17 (IL-17) might contribute to the prehypertensive state. This study evaluated the relationship between serum levels of IL-17 and prehypertension. A total of 394 participants were enrolled, after excluding for hypertension or treated hypertension, and divided into two groups (optimal blood pressure [BP] and prehypertension) based on the Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure classification of BP. Optimal BP was defined as systolic BP <120 mm Hg and diastolic BP <80 mm Hg. Prehypertension was defined as systolic BP of 120 to 139 mm Hg or diastolic BP of 80 to 89 mm Hg. IL-17A levels were determined by enzyme-linked immunosorbent assay. The mean serum IL-17 concentration in the prehypertension group was significantly higher than in the optimal BP group. The cohort was divided into quartiles Q1 (≤3.5 ng/L), Q2 (3.60 to 6.10 ng/L), Q3 (6.20 to 10.00 ng/L), and Q4 (≥10.10 ng/L) based on IL-17 levels. The Q2 to Q4 groups had increasing odds ratios for having prehypertension compared with the Q1 group. Elevated serum IL-17 was accompanied by a rise in systolic BP. Thus, increased serum IL-17 levels are associated with prehypertension.

Quantitative and multiplexed study of endothelial cell inflammation

Endothelial inflammation plays major roles in all phases of the atherosclerotic process, the leading cause of death by cardiovascular disease. Both innate immunity and endothelial adhesion molecules contribute to endothelial inflammation. In this work, we applied multiple antibodies (Abs) to measure changes in expression levels of six proteins in response to inflammatory stimulation. These six proteins include toll-like receptor 2 (TLR2) and toll-like receptor 4 (TLR4) representing innate immunity and four endothelial adhesion molecules such as vascular cell adhesion molecule-1 (VCAM-1), intercellular adhesion molecule-1 (ICAM-1), E-selectin, and P-selectin. We observed two different types of dynamic behaviors among these proteins upon inflammatory stimulation. Increased expression of toll-like receptor 2 (TLR2), P-selectin, E-selectin, and TLR4 peaked relatively early (after 4 h of stimulation) while VCAM-1, and ICAM-1 showed a more gradual and consistent increase in expression with stimulatory time. The magnitude of this increase was significantly greater for VCAM-1 and ICAM-1. The multiplexed detection developed in this study using fluorophore-conjugated primary Abs provides an approach for live cell and in vivo imaging of endothelium inflammation for quantitative characterization of multiple proteins within a network.

Statins as Pleiotropic Modifiers of Vascular Oxidative Stress and Inflammation

Cardiovascular disease (CVD) is the leading cause of morbidity and mortality in the industrialized world and in the future is expected to be the number one killer worldwide. The main cause underlying CVD is atherosclerosis. A key event in atherosclerosis initiation and progression is oxidative stress through the production of reactive oxygen species as well as endothelial dysfunction. Several pro- inflammatory and anti-inflammatory cytokines and proteins are involved in this process, complemented by activation of adhesion molecules that promote leukocyte rolling, tethering and infiltration into the sub-endothelial space. Statins represent the agent of choice since numerous clinical trials have verified that their pharmacological action extends beyond lipid lowering. Statins demonstrate direct anti-oxidant effects by scavenging free radicals and stimulating anti-oxidant enzymes while acting as regulators for cytokine, protein and adhesion molecule expression, all of which are involved in the atherosclerotic process. Statin use is considered one of the most efficient currently used interventions in managing CVD with the likely hood of remaining so in the near future.

Role of the endothelial surface layer in neutrophil recruitment

Neutrophil recruitment in most tissues is limited to postcapillary venules, where E- and P-selectins are inducibly expressed by venular endothelial cells. These molecules support neutrophil rolling via binding of PSGL-1 and other ligands on neutrophils. Selectins extend ≤ 38 nm above the endothelial plasma membrane, and PSGL-1 extends to 50 nm above the neutrophil plasma membrane. However, endothelial cells are covered with an ESL composed of glycosaminoglycans that is ≥ 500 nm thick and has measurable resistance against compression. The neutrophil surface is also covered with a surface layer. These surface layers would be expected to completely shield adhesion molecules; thus, neutrophils should not be able to roll and adhere. However, in the cremaster muscle and in many other models investigated using intravital microscopy, neutrophils clearly roll, and their rolling is easily and quickly induced. This conundrum was thought to be resolved by the observation that the induction of selectins is accompanied by ESL shedding; however, ESL shedding only partially reduces the ESL thickness (to 200 nm) and thus is insufficient to expose adhesion molecules. In addition to its antiadhesive functions, the ESL also presents neutrophil arrest-inducing chemokines. ESL heparan sulfate can also bind L-selectin expressed by the neutrophils, which contributes to rolling and arrest. We conclude that ESL has both proadhesive and antiadhesive functions. However, most previous studies considered either only the proadhesive or only the antiadhesive effects of the ESL. An integrated model for the role of the ESL in neutrophil rolling, arrest, and transmigration is needed.

L-selectin shedding is activated specifically within transmigrating pseudopods of monocytes to regulate cell polarity in vitro

L-selectin is a cell adhesion molecule that tethers free-flowing leukocytes from the blood to luminal vessel walls, facilitating the initial stages of their emigration from the circulation toward an extravascular inflammatory insult. Following shear-resistant adhesion to the vessel wall, L-selectin has frequently been reported to be rapidly cleaved from the plasma membrane (known as ectodomain shedding), with little knowledge of the timing or functional consequence of this event. Using advanced imaging techniques, we observe L-selectin shedding occurring exclusively as primary human monocytes actively engage in transendothelial migration (TEM). Moreover, the shedding was localized to transmigrating pseudopods within the subendothelial space. By capturing monocytes in midtransmigration, we could monitor the subcellular distribution of L-selectin and better understand how ectodomain shedding might contribute to TEM. Mechanistically, L-selectin loses association with calmodulin (CaM; a negative regulator of shedding) specifically within transmigrating pseudopods. In contrast, L-selectin/CaM interaction remained intact in nontransmigrated regions of monocytes. We show phosphorylation of L-selectin at Ser 364 is critical for CaM dissociation, which is also restricted to the transmigrating pseudopod. Pharmacological or genetic inhibition of L-selectin shedding significantly increased pseudopodial extensions in transmigrating monocytes, which potentiated invasive behavior during TEM and prevented the establishment of front/back polarity for directional migration persistence once TEM was complete. We conclude that L-selectin shedding directly regulates polarity in transmigrated monocytes, which affirms an active role for this molecule in driving later stages of the multistep adhesion cascade.

Multi-ethnic analysis reveals soluble L-selectin may be post-transcriptionally regulated by 3'UTR polymorphism: the Multi-Ethnic Study of Atherosclerosis (MESA)

L-Selectin is constitutively expressed on leukocytes and mediates their interaction with endothelial cells during inflammation. Previous studies on the association of soluble L-selectin (sL-selectin) with cardiovascular disease (CVD) are inconsistent. Genetic variants associated with sL-selectin levels may be a better surrogate of levels over a lifetime. We explored the association of genetic variants and sL-selectin levels in a race/ethnicity stratified random sample of 2,403 participants in the Multi-Ethnic Study of Atherosclerosis (MESA). Through a genome-wide analysis with additive linear regression models, we found that rs12938 on the SELL gene accounted for a significant portion of the protein level variance across all four races/ethnicities. To evaluate potential additional associations, elastic net models were used for variants located in the SELL/SELP/SELE genetic region and an additional two SNPs, rs3917768 and rs4987361, were associated with sL-selectin levels in African Americans. These variants accounted for a portion of protein variance that ranged from 4 % in Hispanic to 14 % in African Americans. To investigate the relationship of these variants with CVD, 6,317 subjects were used. No significant association was found between any of the identified SNPs and carotid intima-media thickness or presence of carotid plaque using linear and logistic regression, respectively. Similarly no significant results were found for coronary artery calcium or coronary heart disease events. In conclusion, we found that variants within the SELL gene are associated with sL-selectin levels. Despite accounting for a significant portion of the protein level variance, none of the variants was associated with clinical or subclinical CVD.

Glycosyltransferases, glycosylation and atherosclerosis

Cardiovascular diseases arising from atherosclerosis are currently the leading cause of mortality worldwide. Leukocyte recruitment is a key step for the successful initiation of atherosclerosis and occurs predominantly in the inflamed endothelium. Leukocyte recruitment is mediated by a group of adhesive molecules and chemokine receptors, which are often glycosylated protein. Recent studies demonstrated that post-translational glycosylation by glycosyltransferases is necessary for adhesive molecules and chemokine receptors activities. Several glycosyltransferases, such as α2,3-sialyltransferases IV, α1,3-fucosyltransferases IV and VII, core 2 β1,6-N-acetylglucosaminyltransferase-I, are considered to participate in the synthesis of glycosylation for adhesive molecules and chemokine receptors, and the initiation of atherosclerotic lesions. In this review, we will discuss new data concerning the roles of different glycosyltransferases in atherogenesis. The knowledge of glycosyltransferases in atherogenesis offers the opportunity to develop novel therapeutic strategies.

L-selectin deficiency decreases aortic B1a and Breg subsets and promotes atherosclerosis

There is a significant recruitment of leucocytes into aortas during atherogenesis. L-selectin regulates leucocyte migration into secondary lymphoid and peripheral tissues and was proposed to play a role in leucocyte homing into aortas. Here, we determine the role of L-selectin in atherosclerosis. L-selectin-deficient Apoe-/- (Sell-/-Apoe-/-) mice had a 74% increase in plaque burden compared to Apoe-/- mice fed a chow diet for 50 weeks. Elevated atherosclerosis was accompanied by increased aortic leucocyte content, but a 50% reduction in aortic B cells despite elevated B cell counts in the blood. Follicular B cells represented 65%, whereas B1a and regulatory B cells (Breg) comprised 5% of aortic B cells. B1a and Breg cell subsets were reduced in Sell-/-Apoe-/- aortas with accompanied two-fold decrease in aortic T15 antibody and 1.2-fold decrease of interleukin-10 (IL-10) levels. L-selectin was required for B1 cell homing to the atherosclerotic aorta, as demonstrated by a 1.5-fold decrease in the migration of Sell-/-Apoe-/- vs Apoe-/- cells. Notably, we found a 1.6-fold increase in CD68hi macrophages in Sell-/-Apoe-/- compared to Apoe-/- aortas, despite comparable blood monocyte numbers and L-selectin-dependent aortic homing. L-selectin had no effect on neutrophil migration into aorta, but led to elevated blood neutrophil numbers, suggesting a potential involvement of neutrophils in atherogenesis of Sell-/-Apoe-/- mice. Thus, L-selectin deficiency increases peripheral blood neutrophil and lymphocyte numbers, decreases aortic B1a and Breg populations, T15 antibody and IL-10 levels, and increases aortic macrophage content of Sell-/-Apoe-/- mice. Altogether, these data provide evidence for an overall atheroprotective role of L-selectin.

Plasma and serum L-selectin and clinical and subclinical cardiovascular disease: the Multi-Ethnic Study of Atherosclerosis (MESA)

L-selectin has been suggested to play a role in atherosclerosis. Previous studies on cardiovascular disease (CVD) and serum or plasma L-selectin are inconsistent. The association of serum L-selectin (sL-selectin) with carotid intima-media thickness, coronary artery calcium, ankle-brachial index (subclinical CVD), and incident CVD was assessed in 2403 participants in the Multiethnic Study of Atherosclerosis. Regression analysis and the Tobit model were used to study subclinical disease; Cox proportional hazards regression, for incident CVD. Mean age was 63 ± 10 years and 47% were male. Mean sL-selectin was significantly different across ethnicities. Within each race/ethnicity, sL-selectin was associated with age and sex; among non-Hispanic whites and African Americans, it was associated with smoking status and current alcohol use. sL-selectin levels did not predict subclinical or clinical CVD after correction for multiple comparisons. Conditional logistic regression models were used to study the association of plasma L-selectin and CVD in 154 incident CVD cases, and 306 age-, sex-, and ethnicity-matched control subjects. The median follow-up time was 8.5 years. L-selectin levels in plasma were significantly lower than in serum and the overall concordance was low. Plasma levels were not associated with CVD. In conclusion, in this large, multiethnic population, soluble L-selectin levels did not predict clinical or subclinical CVD.

O-GlcNAcylation and Inflammation: A Vast Territory to Explore

O-GlcNAcylation is a reversible post-translational modification that regulates the activities of cytosolic and nuclear proteins according to glucose availability. This modification appears to participate in several hyperglycemia-associated complications. An important feature of metabolic diseases such as diabetes and obesity is the presence of a low-grade chronic inflammation that causes numerous complications. Hyperglycemia associated with the metabolic syndrome is known to promote inflammatory processes through different mechanisms including oxidative stress and abnormally elevated protein O-GlcNAcylation. However, the role of O-GlcNAcylation on inflammation remains contradictory. O-GlcNAcylation associated with hyperglycemia has been shown to increase nuclear factor κB (NFκB) transcriptional activity through different mechanisms. This could contribute in inflammation-associated diabetic complications. However, in other conditions such as acute vascular injury, O-linked N-acetyl glucosamine (O-GlcNAc) also exerts anti-inflammatory effects via inhibition of the NFκB pathway, suggesting a complex regulation of inflammation by O-GlcNAc. Moreover, whereas macrophages and monocytes exposed to high glucose for a long-term period developed a pro-inflammatory phenotype, the impact of O-GlcNAcylation in these cells remains unclear. A future challenge will be to clearly establish the role of O-GlcNAcylation in pro- and anti-inflammatory functions in macrophages.

Pro-inflammatory genetic markers of atherosclerosis

Atherosclerosis (AS) is a chronic, progressive, multifactorial disease mostly affecting large and medium-sized elastic and muscular arteries. It has formerly been considered a bland lipid storage disease. Currently, multiple independent pathways of evidence suggest this pathological condition is a peculiar form of inflammation, triggered by cholesterol-rich lipoproteins and influenced both by environmental and genetic factors. The Human Genome Project opened up the opportunity to dissect complex human traits and to understand basic pathways of multifactorial diseases such as AS. Population-based association studies have emerged as powerful tools for examining genes with a role in common multifactorial diseases that have a strong environmental component. These association studies often estimate the risk of developing a certain disease in carriers and non-carriers of a particular genetic polymorphism. Dissecting out the influence of pro-inflammatory genes within the complex pathophysiology of AS and its complications will help to provide a more complete risk assessment and complement known classical cardiovascular risk factors. The detection of a risk profile will potentially allow both the early identification of individuals susceptible to disease and the possible discovery of potential targets for drug or lifestyle modification; i.e. it will open the door to personalized medicine.