Differential regulation of human and murine P-selectin expression and function in vivo

Shiga toxin down-regulates ERG protein in endothelial cells and impairs angiogenesis

BACKGROUND

Shiga toxin (Stx) can activate inflammatory signaling, leading to vascular dysfunction and promotion of a pro-thrombotic tissue microenvironment. Stx can trigger the development of the enterohemorrhagic (childhood) hemolytic uremic syndrome (eHUS), a triad of thrombocytopenia, hemolytic anemia, and acute kidney injury, often requiring dialysis. Additional features may include damage to other organs, including the gastrointestinal tract, pancreas, brain and cardiovascular system; death occurs in 2-5 %. eHUS is a thrombotic microangiopathy; thus, endothelial cell (EC) injury and platelet fibrin thrombus formation in glomerular arterioles and in the arterioles of other affected organs are likely. To elucidate mechanisms of this microangiopathy, we examined in human ECs the regulation of the platelet adhesion proteins P-selectin and von Willebrand factor (VWF), along with the downregulation of erythroblast-transformation-specific transcription factor (ERG) a key regulator of angiogenesis and megakaryocyte development.

METHODS

VWF, P-selectin, and ERG levels were determined using immunofluorescence and Western blot in human umbilical endothelial cells (HUVECs). HUVECs were treated with tumor necrosis factor-alpha (TNF-α), Stx-1 or both, versus normal controls. Capillary morphogenesis on Matrigel was performed using HUVECs treated, for 22 h with TNF-α, Stx-1, or both, or treated 4 h with Stx-1 alone or in combination with TNF-α for 22 h.

RESULTS

Stx-1 significantly reduced ERG and VWF expression on HUVECs, but upregulated P-selectin expression. ERG levels decreased with Stx-1 alone or in combination with TNF-α, in the nuclear, perinuclear and cytoplasmatic regions. Stx-1 reduced capillary morphogenesis, while Stx-1-TNF-α combined treatment reduced capillary morphogenesis still further.

CONCLUSIONS

In the presence of Stx-1 or TNF-α or both treatments, ECs were activated, expressing higher levels of P-selectin and lower levels of VWF. Our findings, further, provide evidence that Stx-1 downregulates ERG, repressing angiogenesis in vitro.

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.

Targeting hematologic malignancies by inhibiting E-selectin: A sweet spot for AML therapy?

E-selectin, a cytoadhesive glycoprotein, is expressed on venular endothelial cells and mediates leukocyte localization to inflamed endothelium, the first step in inflammatory cell extravasation into tissue. Constitutive marrow endothelial E-selectin expression also supports bone marrow hematopoiesis via NF-κB-mediated signaling. Correspondingly, E-selectin interaction with E-selectin ligand (sialyl Lewisx) on acute myeloid leukemia (AML) cells leads to chemotherapy resistance in vivo. Uproleselan (GMI-1271) is a carbohydrate analog of sialyl Lewisx that blocks E-selectin binding. A Phase 2 trial of MEC chemotherapy combined with uproleselan for relapsed/refractory AML showed a median overall survival of 8.8 months and low (2%) rates of severe oral mucositis. Clinical trials seek to confirm activity in AML and mitigation of neutrophil-mediated adverse events (mucositis and diarrhea) after intensive chemotherapy. In this review we summarize E-selectin biology and the rationale for uproleselan in combination with other therapies for hematologic malignancies. We also describe uproleselan pharmacology and ongoing clinical trials.

Mitigating neutrophil trafficking and cardiotoxicity with DS-IkL in a microphysiological system of a cytokine storm

A feature of severe COVID-19 is the onset of an acute and intense systemic inflammatory response referred to as the "cytokine storm". The cytokine storm is characterized by high serum levels of inflammatory cytokines and the subsequent transport of inflammatory cells to damaging levels in vital organs (e.g., myocarditis). Immune trafficking and its effect on underlying tissues (e.g., myocardium) are challenging to observe at a high spatial and temporal resolution in mouse models. In this study, we created a vascularized organ-on-a-chip system to mimic cytokine storm-like conditions and tested the effectiveness of a novel multivalent selectin-targeting carbohydrate conjugate (composed of DS - dermatan sulfate and IkL - a selectin-binding peptide, termed DS-IkL) in blocking infiltration of polymorphonuclear leukocytes (PMN). Our data shows that cytokine storm-like conditions induce endothelial cells to produce additional inflammatory cytokines and facilitate infiltration of PMNs into tissue. Treatment of tissues with DS-IkL (60 μM) reduced PMN accumulation in the tissue by >50%. We then created cytokine storm-like conditions in a vascularized cardiac tissue-chip and found that PMN infiltration increases the spontaneous beating rate of the cardiac tissue, and this effect is eliminated by treatment with DS-IkL (60 μM). In summary, we demonstrate the utility of an organ-on-a-chip platform to mimic COVID-19 related cytokine storm and that blocking leukocyte infiltration with DS-IkL could be a viable strategy to mitigate associated cardiac complications.

The biology of E-selectin ligands in leukemogenesis

Both the cascade whereby a blood-borne cell enters a tissue and the anchoring of hematopoietic stem/progenitor cells (HSPCs) within bone marrow critically pivots on cell-cell interactions mediated by E-selectin binding to its canonical carbohydrate ligand, the tetrasaccharide termed "sialylated Lewis X" (sLeX). E-selectin, a member of the selectin class of adhesion molecules that is exclusively expressed by vascular endothelium, engages sLeX-bearing glycoconjugates that adorn mature leukocytes and HSPCs, as well as malignant cells, thereby permitting these cells to extravasate into various tissues. E-selectin expression is induced on microvascular endothelial cells within inflammatory loci at all tissues. However, conspicuously, E-selectin is constitutively expressed within microvessels in skin and marrow and, additionally, is inducibly expressed at these sites. Within the marrow, E-selectin receptor/ligand interactions promote lodgment of HSPCs and their malignant counterparts within hematopoietic growth-promoting microenvironments, collectively known as "vascular niches". Indeed, E-selectin receptor/ligand interactions have been reported to regulate both hematopoietic stem, and leukemic, cell proliferative dynamics. As such, signaling induced via engagement of E-selectin ligands is gaining interest as a critical mediator of homeostatic and malignant hematopoiesis, and this review will present current perspectives on the glycoconjugates mediating E-selectin receptor/ligand interactions and their currently defined role(s) in leukemogenesis.

Extracellular Vesicles in Sickle Cell Disease: A Promising Tool

Sickle cell disease (SCD) is the most common hemoglobinopathy worldwide. It is characterized by an impairment of shear stress-mediated vasodilation, a pro-coagulant, and a pro-adhesive state orchestrated among others by the depletion of the vasodilator nitric oxide, by the increased phosphatidylserine exposure and tissue factor expression, and by the increased interactions of erythrocytes with endothelial cells that mediate the overexpression of adhesion molecules such as VCAM-1, respectively. Extracellular vesicles (EVs) have been shown to be novel actors involved in SCD pathophysiological processes. Medium-sized EVs, also called microparticles, which exhibit increased plasma levels in this pathology, were shown to induce the activation of endothelial cells, thereby increasing neutrophil adhesion, a key process potentially leading to the main complication associated with SCD, vaso-occlusive crises (VOCs). Small-sized EVs, also named exosomes, which have also been reported to be overrepresented in SCD, were shown to potentiate interactions between erythrocytes and platelets, and to trigger endothelial monolayer disruption, two processes also known to favor the occurrence of VOCs. In this review we provide an overview of the current knowledge about EVs concentration and role in SCD.

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.

Narrative review of the systemic inflammatory reaction to cardiac surgery and cardiopulmonary bypass

Background

Data from large cardiac surgery registries have been depicting a downward trend of mortality and morbidities in the last 20 years. However, despite decades of medical evolution, cardiac surgery and cardiopulmonary bypass still provoke a systemic inflammatory response, which occasionally leads to worsened outcome. This article seeks to outline the mechanism of the phenomenon.

Methods

A thorough review of the literature has been performed. Criteria for considering studies for this non‐systematic review were as follows: observational and interventional studies investigating the systemic inflammatory response to cardiac surgery, experimental studies describing relevant molecular mechanisms, and essential review studies pertinent to the topic.

Results

The intrinsic variability of the inflammatory response to cardiac surgery, together with its heterogenous perception among clinicians, as well as the arduousness to early discriminate high‐responder patients from those who will not develop a clinically relevant reaction, concurred to hitherto unconclusive randomized controlled trials. Furthermore, peremptory knowledge about the pathophysiology of maladaptive inflammation following heart surgery is still lacking.

Conclusions

Systemic inflammation following cardiac surgery is a frequent entity that occasionally becomes clinically relevant. Specific genomic differences, age, and other preoperative factors influence the magnitude of the response, which elements display extreme redundancy and pleiotropism that the target of a single pathway cannot represent a silver bullet.

Thrombosis in COVID-19 infection: Role of platelet activation-mediated immunity

Background

Thrombosis plays an important role in the Coronavrus Disease 2019 (COVID-19) infection-related complications such as acute respiratory distress syndrome and myocardial infarction. Multiple factors such as oxygen demand injuries, endothelial cells injury related to infection, and plaque formation.

Main body

Platelets obtained from the patients may have severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA, showing that the increased activation potential recommends platelet can be hyper-activated in severely ill SARS-CoV-2 cases. Platelets contain multiple receptors that interact with specific ligands. Pathogen’s receptors such as Toll-like receptors (TLRs), NOD-like receptor, C-type lectin receptor family, glycoprotein (GP) such as GPαIIbβ3 and GPIbα which allow pathogens to interact with platelets. Platelet TLRs and NOD2 are involved in platelet activation and thrombosis. Accordingly, TLRs are critical receptors that could recognize various endogenous damage-associated molecular patterns and exogenous pathogen-associated molecular patterns (PAMPs). TLRs are considered as important components in the activation of innate immunity response against pathogenic and non-pathogenic components like damaged tissues. TLRs-1,-2,-4,-6,-7 expression on or within platelets has been reported previously. Various PAMPs were indicated to be capable of binding to platelet-TLRs and inducing both the activation and promotion of downstream proinflammatory signaling cascade.

Conclusion

It is possible that the increased TLRs expression and TLR-mediated platelets activation during COVID-19 may enhance vascular and coronary thrombosis. It may be hypothesized using TLRs antagonist and monoclonal antibody against P-selectin, as the marker of leukocyte recruitment and platelet activation, besides viral therapy provide therapeutic advances in fighting against the thrombosis related complications in COVID-19.

P-selectin antibody treatment after blunt thoracic trauma prevents early pulmonary arterial thrombosis without changes in viscoelastic measurements of coagulation

INTRODUCTION

Previously, in a murine model of blunt thoracic trauma, we provided evidence of primary pulmonary thrombosis associated with increased expression of the cell adhesion molecule, P-selectin. In this study, mice are treated with P-selectin blocking antibody after injury to investigate the clinical viability of this antibody for the prevention of pulmonary thrombosis. In addition, viscoelastic testing is performed to investigate if P-selectin inhibition has a detrimental impact on normal hemostasis.

METHODS

A murine model of thoracic trauma was used. Mice were divided into sham control and experimental injury groups. Thirty minutes after trauma, mice were treated with the following: P-selectin blocking antibody, isotype control antibody, low-dose heparin, high-dose heparin, or normal saline. At 90 minutes, whole blood was collected for characterization of coagulation by viscoelastic coagulation monitor (VCM Vet; Entegrion, Durham, NC). Mean clotting time, clot formation time, clot kinetics (α angle), and maximum clot firmness were compared between each treatment group.

RESULTS

Mice that received P-selectin antibody 30 minutes after blunt thoracic trauma had four- to fivefold less (p < 0.001) arterial fibrin accumulation than those that received the isotype control. In both sham and trauma groups, compared with vehicle (normal saline) alone, no statistical difference was noted in any coagulation parameters after injection with P-selectin antibody, isotype control, or low-dose heparin. In addition, blinded histopathological evaluation yielded no difference in hemorrhage scores between injured mice treated with P-selectin blocking antibody and those treated with isotype antibody control.

CONCLUSION

This study supports the clinical use of P-selectin blocking antibody for the prevention of pulmonary thrombosis by confirming its efficacy when given after a blunt thoracic trauma. In addition, we demonstrated that the administration of P-selectin antibody does not adversely affect systemic coagulation as measured by viscoelastic testing, suggesting that P-selectin antibody can be safely given during the acute posttraumatic period.

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 Role of Platelet Cell Surface P-Selectin for the Direct Platelet-Tumor Cell Contact During Metastasis Formation in Human Tumors

Mammalian platelets, devoid of nuclei, are the smallest cells in the blood stream. They are essential for hemostasis, but also transmit cell signals that are necessary for regenerative and generative processes such as inflammation, immunity and tissue repair. In particular, in malignancies they are also associated with cell proliferation, angiogenesis, and epithelial-mesenchymal transition. Platelets promote metastasis and resistance to anti-tumor treatment. However, fundamental principles of the interaction between them and target cells within tumors are complex and still quite obscure. When injected into animals or circulating in the blood of cancer patients, cancer cells ligate platelets in a timely manner closely related to platelet activation either by direct contact or by cell-derived substances or microvesicles. In this context, a large number of different surface molecules and transduction mechanisms have been identified, although the results are sometimes species-specific and not always valid to humans. In this mini-review, we briefly summarize the current knowledge on the role of the direct and indirect platelet-tumor interaction for single steps of the metastatic cascade and specifically focus on the functional role of P-selectin.

Hemodynamic regulation of perivalvular endothelial gene expression prevents deep venous thrombosis

Deep venous thrombosis (DVT) and secondary pulmonary embolism cause approximately 100,000 deaths per year in the United States. Physical immobility is the most significant risk factor for DVT, but a molecular and cellular basis for this link has not been defined. We found that the endothelial cells surrounding the venous valve, where DVTs originate, express high levels of FOXC2 and PROX1, transcription factors known to be activated by oscillatory shear stress. The perivalvular venous endothelial cells exhibited a powerful antithrombotic phenotype characterized by low levels of the prothrombotic proteins vWF, P-selectin, and ICAM1 and high levels of the antithrombotic proteins thrombomodulin (THBD), endothelial protein C receptor (EPCR), and tissue factor pathway inhibitor (TFPI). The perivalvular antithrombotic phenotype was lost following genetic deletion of FOXC2 or femoral artery ligation to reduce venous flow in mice, and at the site of origin of human DVT associated with fatal pulmonary embolism. Oscillatory blood flow was detected at perivalvular sites in human veins following muscular activity, but not in the immobile state or after activation of an intermittent compression device designed to prevent DVT. These findings support a mechanism of DVT pathogenesis in which loss of muscular activity results in loss of oscillatory shear-dependent transcriptional and antithrombotic phenotypes in perivalvular venous endothelial cells, and suggest that prevention of DVT and pulmonary embolism may be improved by mechanical devices specifically designed to restore perivalvular oscillatory flow.

Downregulated Platelet miR-1233-5p in Patients with Alzheimer's Pathologic Change with Mild Cognitive Impairment is Associated with Aβ-Induced Platelet Activation via P-Selectin

MicroRNAs (miRNAs) have been proposed as a promising biomarker for various diseases including Alzheimer's disease (AD). More attention has recently been focused on the diagnosis and treatment at earlier stage of mild cognitive impairment (MCI) for preventing its progression to AD. To identify potential pathologic markers for Aβ(+)MCI (Alzheimer's pathologic change with MCI), we investigated miRNA expression profiles in the platelets from patients with Aβ(+)MCI, in comparison with those from Aβ(-)MCI (Non-Alzheimer's pathologic change with MCI) and CNI (cognitively normal individuals). We found that let-7i-5p, miR-125a, miR-1233-5p, and miR-6787-5p were significantly downregulated, while miR-6880-5p expression was upregulated. Of these, only miR-1233-5p was significantly downregulated by Aβ treatment in both human platelets and their precursor megakaryocytes (MEG-01 cells). We explored the role of miRNAs by using miRNA mimics or inhibitors, and found that the diminished level of miR-1233-5p was associated with Aβ-induced increase in the expression of P-selectin and cell adhesion to fibronectin. Our results further indicated that Aβ-induced increase in platelet/MEG adhesion to fibronectin is likely mediated via P-selectin. In conclusion, this study suggests the downregulation of platelet-derived miR-1233-5p as a pathologic marker for Aβ(+)MCI.

Th1 Cells Rolling on Selectins Trigger DAP12-Dependent Signals That Activate Integrin αLβ2

During inflammation, both neutrophils and effector T cells use selectins to roll and integrins to arrest in postcapillary venules. In both cell types, chemokines can transduce signals that convert integrin αLβ2 to a high-affinity conformation, which interacts with ICAM-1 to mediate arrest. In neutrophils, selectins also trigger an immunoreceptor-like signaling cascade that converts integrin αLβ2 to an intermediate-affinity conformation, which interacts with ICAM-1 to slow rolling. It is not known whether selectins induce similar signaling events in T cells. Ag engagement causes phosphorylation of ITAMs on the TCR; these motifs recruit kinases and adaptors that lead to the activation of αLβ2. We found that mouse Th1 cells rolling on P- or E-selectin triggered signals that promoted αLβ2-dependent slow rolling on ICAM-1 in vitro and in vivo. The selectin signaling cascade resembled that used by the TCR, except that unexpectedly, Th1 cells employed the ITAM-bearing protein DAP12, which was not known to be expressed in these cells. Importantly, outside-in signaling through ligand-occupied αLβ2 also required DAP12. Cooperative selectin and chemokine signaling in Th1 cells promoted αLβ2-dependent slow rolling and arrest in vitro and in vivo and migration into Ag-challenged tissues in vivo. Our findings reveal an important function for DAP12 in Th1 cells and a new mechanism to recruit effector T cells to sites of inflammation.

Selectins and Immune Cells in Acute Myocardial Infarction and Post-infarction Ventricular Remodeling: Pathophysiology and Novel Treatments

The glycosciences aim to understand the impact of extracellular and intracellular carbohydrate structures on biological function. These glycans primarily fall into three major groups: lipid-linked carbohydrates that are referred to as glycosphingolipids or simply glycolipids; relatively short carbohydrate chains that are often O- or N-linked to proteins yielding common glycoproteins; and extended linear polymeric carbohydrate structures that are referred to as glycosaminoglycans (GAGs). Whereas, the impact of such carbohydrate structures has been extensively examined in cancer biology, their role in acute and chronic heart disease is less studied. In this context, a growing body of evidence indicates that glycans play an important role in immune mediated cell recruitment to damaged heart tissue to initiate wound healing and repair after injury. This is particularly important following ischemia and reperfusion that occurs in the heart in the setting of acute myocardial infarction. Here, immune system-mediated repair of the damaged myocardium plays a critical role in determining post-infarction ventricular remodeling, cardiac function, and patient outcome. Further, alterations in immune cell activity can promote the development of heart failure. The present review summarizes our current understanding of the phases of immune-mediated repair following myocardial infarction. It discusses what is known regarding glycans in mediating the recruitment of circulating immune cells during the early inflammatory stage of post-infarction repair, with focus on the selectin family of adhesion molecules. It offers future directions for research aimed at utilizing our knowledge of mechanisms underlying immune cell recruitment to either modulate leukocyte recruitment to the injured tissue or enhance the targeted delivery of biologic therapeutics such as stem cells in an attempt to promote repair of the damaged heart.

More Than Just a Removal Service: Scavenger Receptors in Leukocyte Trafficking

Scavenger receptors are a highly diverse superfamily of proteins which are grouped by their inherent ability to bind and internalize a wide array of structurally diverse ligands which can be either endogenous or exogenous in nature. Consequently, scavenger receptors are known to play important roles in host homeostasis, with common endogenous ligands including apoptotic cells, and modified low density lipoproteins (LDLs); additionally, scavenger receptors are key regulators of inflammatory diseases, such as atherosclerosis. Also, as a consequence of their affinity for a wide range of microbial products, their role in innate immunity is also being increasingly studied. However, in this review, a secondary function of a number of endothelial-expressed scavenger receptors is discussed. There is increasing evidence that some endothelial-expressed scavenger receptors are able to directly bind leukocyte-expressed ligands and subsequently act as adhesion molecules in the trafficking of leukocytes in lymphatic and vascular tissues. Here, we cover the current literature on this alternative role for endothelial-expressed scavenger receptors and also speculate on their therapeutic potential.

A cell-extrinsic ligand acquired by activated T cells in lymph node can bridge L-selectin and P-selectin

P-selectin expressed on activated endothelia and platelets supports recruitment of leukocytes expressing P-selectin ligand to sites of inflammation. While monitoring P-selectin ligand expression on activated CD8+ T cells in murine adoptive transfer models, we observed two distinct ligands on responding donor cells, the canonical cell-intrinsic P-selectin ligand PSGL-1 and a second undocumented P-selectin ligand we provisionally named PSL2. PSL2 is unusual among selectin ligands in that it is cell-extrinsic, loaded onto L-selectin expressed by activated T cells but not L-selectin on resting naïve CD8+ T cells. PSL2 display is highest on activated T cells responding in peripheral lymph nodes and low on T cells responding in spleen suggesting that the original source of PSL2 is high endothelial venules, cells known to produce L-selectin ligands. PSL2 is a ligand for both P-selectin and L-selectin and can physically bridge the two selectins. The L-selectin/PSL2 complex can mediate P-selectin-dependent adherence of activated T cells to immobilized P-selectin or to activated platelets, either independently or cooperatively with PSGL-1. PSL2's capacity to bridge between L-selectin on activated T cells and P-selectin reveals an undocumented and unanticipated activity of cell-extrinsic selectin ligands in mediating selectin-selectin connectivity. The timing and circumstances of PSL2 detection on T cells, together with its capacity to support adherence to P-selectin-bearing substrates, are consistent with P-selectin engagement of both PSGL1 and the L-selectin/PSL2 complex during T cell recruitment. Engagement of PSGL-1 and L-selectin/PSL2 would likely deliver distinct signals known to be relevant in this process.

A systems-approach reveals human nestin is an endothelial-enriched, angiogenesis-independent intermediate filament protein

The intermediate filament protein nestin is expressed during embryonic development, but considered largely restricted to areas of regeneration in the adult. Here, we perform a body-wide transcriptome and protein-profiling analysis to reveal that nestin is constitutively, and highly-selectively, expressed in adult human endothelial cells (EC), independent of proliferative status. Correspondingly, we demonstrate that it is not a marker for tumour EC in multiple malignancy types. Imaging of EC from different vascular beds reveals nestin subcellular distribution is shear-modulated. siRNA inhibition of nestin increases EC proliferation, and nestin expression is reduced in atherosclerotic plaque neovessels. eQTL analysis reveals an association between SNPs linked to cardiovascular disease and reduced aortic EC nestin mRNA expression. Our study challenges the dogma that nestin is a marker of proliferation, and provides insight into its regulation and function in EC. Furthermore, our systems-based approach can be applied to investigate body-wide expression profiles of any candidate protein.

Cell Adhesion Molecules are Mediated by Photobiomodulation at 660 nm in Diabetic Wounded Fibroblast Cells

Diabetes affects extracellular matrix (ECM) metabolism, contributing to delayed wound healing and lower limb amputation. Application of light (photobiomodulation, PBM) has been shown to improve wound healing. This study aimed to evaluate the influence of PBM on cell adhesion molecules (CAMs) in diabetic wound healing. Isolated human skin fibroblasts were grouped into a diabetic wounded model. A diode laser at 660 nm with a fluence of 5 J/cm² was used for irradiation and cells were analysed 48 h post-irradiation. Controls consisted of sham-irradiated (0 J/cm²) cells. Real-time reverse transcription (RT) quantitative polymerase chain reaction (qPCR) was used to determine the expression of CAM-related genes. Ten genes were up-regulated in diabetic wounded cells, while 25 genes were down-regulated. Genes were related to transmembrane molecules, cell–cell adhesion, and cell–matrix adhesion, and also included genes related to other CAM molecules. PBM at 660 nm modulated gene expression of various CAMs contributing to the increased healing seen in clinical practice. There is a need for new therapies to improve diabetic wound healing. The application of PBM alongside other clinical therapies may be very beneficial in treatment.

Isolation and characterization of the primary epithelial breast cancer cells and the adjacent normal epithelial cells from Iranian women's breast cancer tumors

As an experimental model, most studies rely on established human cancer cell lines; however, some genetical or phenotypical differences exist between these cells and their original tumor. Therefore, primary cells isolated directly from tissue are believed to be more biologically relevant tools for studying human and animal biology. Here, we aimed to isolate primary epithelial cancer and normal cells from breast tumors of Iranian women, for the first time. Thus, we isolated the epithelial and fibroblast cells from biopsy samples of patients with breast cancer based on differential centrifugation followed by culture in selective media. Normal epithelial cells obtained from the tissue biopsy away from the core of the tumor, based on the pathological diagnosis. Flow cytometry analysis indicated the positive immunoreactivity of the isolated epithelial cells against CD24 and Epithelial Specific Antigen (ESA/EpCAM), while they displayed a concomitant low expression of CD44 and CD49f. In contrat to fibroblasts, the qPCR data indicated the expression of luminal intracellular cytokeratin (Ck18) in both normal and cancer epithelial cells, but there was no expression of myoepithelial/basal markers, CK5 and vimentin. The epithelial cancer cells were reactive to cytokeratin 19 (CK19) antibody, whereas the normal epithelial cells were not. The expression of calmodulin-like protein (CLP) was also lower in the cancer epithelial cells than in the normal ones. In conclusion, primary epithelial normal and cancer cells, in addition to the fibroblasts were isolated and characterized from breast tumor of Iranian patients; and CLP expression is suggested as a susceptibility marker for breast cancer screening.

T-lymphocyte homing: an underappreciated yet critical hurdle for successful cancer immunotherapy

Advances in cancer immunotherapy have offered new hope for patients with metastatic disease. This unfolding success story has been exemplified by a growing arsenal of novel immunotherapeutics, including blocking antibodies targeting immune checkpoint pathways, cancer vaccines, and adoptive cell therapy (ACT). Nonetheless, clinical benefit remains highly variable and patient-specific, in part, because all immunotherapeutic regimens vitally hinge on the capacity of endogenous and/or adoptively transferred T-effector (T_eff) cells, including chimeric antigen receptor (CAR) T cells, to home efficiently into tumor target tissue. Thus, defects intrinsic to the multi-step T-cell homing cascade have become an obvious, though significantly underappreciated contributor to immunotherapy resistance. Conspicuous have been low intralesional frequencies of tumor-infiltrating T-lymphocytes (TILs) below clinically beneficial threshold levels, and peripheral rather than deep lesional TIL infiltration. Therefore, a T_eff cell 'homing deficit' may arguably represent a dominant factor responsible for ineffective immunotherapeutic outcomes, as tumors resistant to immune-targeted killing thrive in such permissive, immune-vacuous microenvironments. Fortunately, emerging data is shedding light into the diverse mechanisms of immune escape by which tumors restrict T_eff cell trafficking and lesional penetrance. In this review, we scrutinize evolving knowledge on the molecular determinants of T_eff cell navigation into tumors. By integrating recently described, though sporadic information of pivotal adhesive and chemokine homing signatures within the tumor microenvironment with better established paradigms of T-cell trafficking under homeostatic or infectious disease scenarios, we seek to refine currently incomplete models of T_eff cell entry into tumor tissue. We further summarize how cancers thwart homing to escape immune-mediated destruction and raise awareness of the potential impact of immune checkpoint blockers on T_eff cell homing. Finally, we speculate on innovative therapeutic opportunities for augmenting T_eff cell homing capabilities to improve immunotherapy-based tumor eradication in cancer patients, with special focus on malignant melanoma.

Differential DARC/ACKR1 expression distinguishes venular from non-venular endothelial cells in murine tissues

BACKGROUND

Intravascular leukocyte recruitment in most vertebrate tissues is restricted to postcapillary and collecting venules, whereas capillaries and arterioles usually support little or no leukocyte adhesion. This segmental restriction is thought to be mediated by endothelial, rather than hemodynamic, differences. The underlying mechanisms are largely unknown, in part because effective tools to distinguish, isolate, and analyze venular endothelial cells (V-ECs) and non-venular endothelial cells (NV-ECs) have been unavailable. We hypothesized that the atypical chemokine receptor DARC (Duffy Antigen Receptor for Chemokines, a.k.a. ACKR1 or CD234) may distinguish V-ECs versus NV-ECs in mice.

METHODS

We generated a rat-anti-mouse monoclonal antibody (MAb) that specifically recognizes the erythroid and endothelial forms of native, surface-expressed DARC. Using this reagent, we characterized DARC expression and distribution in the microvasculature of murine tissues.

RESULTS

DARC was exquisitely restricted to post-capillary and small collecting venules and completely absent from arteries, arterioles, capillaries, veins, and most lymphatics in every tissue analyzed. Accordingly, intravital microscopy showed that adhesive leukocyte-endothelial interactions were restricted to DARC+ venules. DARC was detectable over the entire circumference of V-ECs, but was more concentrated at cell-cell junctions. Analysis of single-cell suspensions suggested that the frequency of V-ECs among the total microvascular EC pool varies considerably between different tissues.

CONCLUSIONS

Immunostaining of endothelial DARC allows the identification and isolation of intact V-ECs from multiple murine tissues. This strategy may be useful to dissect the mechanisms underlying segmental microvascular specialization in healthy and diseased tissues and to characterize the role of EC subsets in tissue-homeostasis, immune surveillance, infection, inflammation, and malignancies.

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.

Neutrophil adhesion is tightly regulated to enforce protective immunity, but it is unclear how mechanochemical processes such as catch bonds and slip bonds modulate neutrophils in vivo. Here the authors show that a point mutation in the adhesion molecule L-selectin alters mechanochemical regulation to affect neutrophil functions in mice.

An Analysis of Trafficking Receptors Shows that CD44 and P-Selectin Glycoprotein Ligand-1 Collectively Control the Migration of Activated Human T-Cells

Selectins guide the traffic of activated T-cells through the blood stream by mediating their tethering and rolling onto inflamed endothelium, in this way acting as beacons to help navigate them to sites of inflammation. Here, we present a comprehensive analysis of E-selectin ligands expressed on activated human T-cells. We identified several novel glycoproteins that function as E-selectin ligands. Specifically, we compared the role of P-selectin glycoprotein ligand-1 (PSGL-1) and CD43, known E-selectin ligands, to CD44, a ligand that has not previously been characterized as an E-selectin ligand on activated human T-cells. We showed that CD44 acts as a functional E-selectin ligand when expressed on both CD4⁺ and CD8⁺ T-cells. Moreover, the CD44 protein carries a binding epitope identifying it as hematopoietic cell E- and/or L-selectin ligand (HCELL). Furthermore, by knocking down these ligands individually or together in primary activated human T-cells, we demonstrated that CD44/HCELL, and not CD43, cooperates with PSGL-1 as a major E-selectin ligand. Additionally, we demonstrated the relevance of our findings to chronic autoimmune disease, by showing that CD44/HCELL and PSGL-1, but not CD43, from T-cells isolated from psoriasis patients, bind E-selectin.

Inhibition of atherogenesis by the COP9 signalosome subunit 5 in vivo

Constitutive photomorphogenesis 9 (COP9) signalosome 5 (CSN5), an isopeptidase that removes neural precursor cell-expressed, developmentally down-regulated 8 (NEDD8) moieties from cullins (thus termed "deNEDDylase") and a subunit of the cullin-RING E3 ligase-regulating COP9 signalosome complex, attenuates proinflammatory NF-κB signaling. We previously showed that CSN5 is up-regulated in human atherosclerotic arteries. Here, we investigated the role of CSN5 in atherogenesis in vivo by using mice with myeloid-specific Csn5 deletion. Genetic deletion of Csn5 in Apoe^-/- mice markedly exacerbated atherosclerotic lesion formation. This was broadly observed in aortic root, arch, and total aorta of male mice, whereas the effect was less pronounced and site-specific in females. Mechanistically, Csn5 KO potentiated NF-κB signaling and proinflammatory cytokine expression in macrophages, whereas HIF-1α levels were reduced. Inversely, inhibition of NEDDylation by MLN4924 blocked proinflammatory gene expression and NF-κB activation while enhancing HIF-1α levels and the expression of M2 marker Arginase 1 in inflammatory-elicited macrophages. MLN4924 further attenuated the expression of chemokines and adhesion molecules in endothelial cells and reduced NF-κB activation and monocyte arrest on activated endothelium in vitro. In vivo, MLN4924 reduced LPS-induced inflammation, favored an antiinflammatory macrophage phenotype, and decreased the progression of early atherosclerotic lesions in mice. On the contrary, MLN4924 treatment increased neutrophil and monocyte counts in blood and had no net effect on the progression of more advanced lesions. Our data show that CSN5 is atheroprotective. We conclude that MLN4924 may be useful in preventing early atherogenesis, whereas selectively promoting CSN5-mediated deNEDDylation may be beneficial in all stages of atherosclerosis.

P-Selectin preserves immune tolerance in mice and is reduced in human cutaneous lupus

Mice deficient in P-Selectin presented altered immunity/tolerance balance. We have observed that the absence of P-Selectin promotes splenomegaly with reduced naïve T cell population, elevated activated/effector T cell subset, increased germinal center B and Tfh populations and high production of autoreactive antibodies. Moreover, 1.5-3-month-old P-selectin KO mice showed reduced IL-10-producing leukocytes in blood and a slightly reduced Treg population in the skin. With aging and, coinciding with disease severity, there is an increase in the IL17⁺ circulating and dermal T cell subpopulations and reduction of dermal Treg. As a consequence, P-Selectin deficient mice developed a progressive autoimmune syndrome showing skin alterations characteristic of lupus prone mice and elevated circulating autoantibodies, including anti-dsDNA. Similar to human SLE, disease pathogenesis was characterized by deposition of immune complexes in the dermoepidermal junction and renal glomeruli, and a complex pattern of autoantibodies. More important, skin biopsies of cutaneous lupus erythematosus patients did not show increased expression of P-Selectin, as described for other inflammatory diseases, and the number of vessels expressing P-Selectin was reduced.

Endotoxaemia-augmented murine venous thrombosis is dependent on TLR-4 and ICAM-1, and potentiated by neutropenia

Venous thromboembolism is a major cause of death during and immediately post-sepsis. Venous thrombosis (VT) is mediated by cell adhesion molecules and leukocytes, including neutrophil extracellular traps (NETs). Sepsis, or experimentally, endotoxaemia, shares similar characteristics and is modulated via toll like receptor 4 (TLR4). This study was undertaken to determine if endotoxaemia potentiates early stasis thrombogenesis, and secondarily to determine the role of VT TLR4, ICAM-1 and neutrophils (PMNs). Wild-type (WT), ICAM-1^-/- and TLR4^-/- mice underwent treatment with saline or LPS (10 mg/kg i. p.) alone, or followed by inferior vena cava (IVC) ligation to generate stasis VT. In vivo microscopy of leukocyte trafficking was performed in non-thrombosed mice, and tissue and plasma were harvested during early VT formation. Pre-thrombosis, circulating ICAM-1 was elevated and increased leukocyte adhesion and rolling occurred on the IVC of LPS-treated mice. Post-thrombosis, endotoxaemic mice formed larger, platelet-poor thrombi. Endotoxaemic TLR4^-/- mice did not have an augmented thrombotic response and exhibited significantly decreased circulating ICAM-1 compared to endotoxaemic WT controls. Endotoxaemic ICAM-1^-/- mice had significantly smaller thrombi compared to controls. Hypothesising that PMNs localised to the inflamed endothelium were promoting thrombosis, PMN depletion using anti-Ly6G antibody was performed. Paradoxically, VT formed without PMNs was amplified, potentially related to endotoxaemia induced elevation of PAI-1 and circulating FXIII, and decreased uPA. Endotoxaemia enhanced early VT occurs in a TLR-4 and ICAM-1 dependent fashion, and is potentiated by neutropenia. ICAM-1 and/or TLR-4 inhibition may be a unique strategy to prevent sepsis-associated VT.

Altered expression of glial markers, chemokines, and opioid receptors in the spinal cord of type 2 diabetic monkeys

Neuroinflammation is a pathological condition that underlies diabetes and affects sensory processing. Given the high prevalence of pain in diabetic patients and crosstalk between chemokines and opioids, it is pivotal to know whether neuroinflammation-associated mediators are dysregulated in the central nervous system of diabetic primates. Therefore, the aim of this study was to investigate whether mRNA expression levels of glial markers, chemokines, and opioid receptors are altered in the spinal cord and thalamus of naturally occurring type 2 diabetic monkeys (n=7) compared with age-matched non-diabetic monkeys (n=6). By using RT-qPCR, we found that mRNA expression levels of both GFAP and IBA1 were up-regulated in the spinal dorsal horn (SDH) of diabetic monkeys compared with non-diabetic monkeys. Among all chemokines, expression levels of three chemokine ligand-receptor systems, i.e., CCL2-CCR2, CCL3-CCR1/5, and CCL4-CCR5, were up-regulated in the SDH of diabetic monkeys. Moreover, in the SDH, seven additional chemokine receptors, i.e., CCR4, CCR6, CCR8, CCR10, CXCR3, CXCR5, and CXCR6, were also up-regulated in diabetic monkeys. In contrast, expression levels of MOP, KOP, and DOP, but not NOP receptors, were down-regulated in the SDH of diabetic monkeys, and the thalamus had fewer changes in the glial markers, chemokines and opioids. These findings indicate that neuroinflammation, manifested as glial activation and simultaneous up-regulation of multiple chemokine ligands and receptors, seems to be permanent in type 2 diabetic monkeys. As chemokines and opioids are important pain modulators, this first-in-primate study provides a translational bridge for determining the functional efficacy of spinal drugs targeting their signaling cascades.

Significant variations in alternative splicing patterns and expression profiles between human-mouse orthologs in early embryos

Human and mouse orthologs are expected to have similar biological functions; however, many discrepancies have also been reported. We systematically compared human and mouse orthologs in terms of alternative splicing patterns and expression profiles. Human-mouse orthologs are divergent in alternative splicing, as human orthologs could generally encode more isoforms than their mouse orthologs. In early embryos, exon skipping is far more common with human orthologs, whereas constitutive exons are more prevalent with mouse orthologs. This may correlate with divergence in expression of splicing regulators. Orthologous expression similarities are different in distinct embryonic stages, with the highest in morula. Expression differences for orthologous transcription factor genes could play an important role in orthologous expression discordance. We further detected largely orthologous divergence in differential expression between distinct embryonic stages. Collectively, our study uncovers significant orthologous divergence from multiple aspects, which may result in functional differences and dynamics between human-mouse orthologs during embryonic development.

The role of photobiomodulation on gene expression of cell adhesion molecules in diabetic wounded fibroblasts in vitro

Cell adhesion molecules (CAMs) are cell surface glycoproteins that facilitate cell-cell contacts and adhesion with the extracellular matrix (ECM). Cellular adhesion is affected by various disease conditions, such as diabetes mellitus (DM) and inflammation. Photobiomodulation (PBM) stimulates biological processes and expression of these cellular molecules. The aim of this experimental work was to demonstrate the role of PBM at 830nm on CAMs in diabetic wounded fibroblast cells. Isolated human skin fibroblast cells were used. Normal (N-) and diabetic wounded (DW-) cells were irradiated with a continuous wave diode laser at 830nm with an energy density of 5J/cm(2). Real time reverse transcriptase polymerase chain reaction (RT-PCR) was used to determine the relative gene expression of 39 CAMs 48h post-irradiation. Normalized expression levels from irradiated cells were calculated relative to non-irradiated control cells according to the 2^(-ΔΔCt) method. Thirty-one genes were significantly regulated in N-cells (28 were genes up-regulated and three genes down-regulated), and 22 genes in DW-cells (five genes were up-regulated and 17 genes down-regulated). PBM induced a stimulatory effect on various CAMs namely cadherins, integrins, selectins and immunoglobulins, and hence may be used as a complementary therapy in advancing treatment of non-healing diabetic ulcers. The regulation of CAMs as well as evaluating the role of PBM on the molecular effects of these genes may expand knowledge and prompt further research into the cellular mechanisms in diabetic wound healing that may lead to valuable clinical outcomes.

P-Selectin Expressed by a Human SELP Transgene Is Atherogenic in Apolipoprotein E-Deficient Mice

OBJECTIVE

During inflammation, P-selectin expressed on activated endothelial cells and platelets mediates rolling adhesion of leukocytes. Atherosclerosis-prone mice crossed with P-selectin-deficient (Selp(-/-)) mice develop smaller lesions. Cytokines, such as tumor necrosis factor-α, increase Selp transcripts and augment atherosclerosis in mice. However, they decrease SELP transcripts in humans, challenging assumptions that human P-selectin is atherogenic. We used mice expressing a human SELP transgene to examine the atherogenic role of P-selectin.

APPROACH AND RESULTS

We crossed apolipoprotein E-deficient (Apoe(-/-)) mice with Selp(-/-) mice or transgenic mice expressing the entire human SELP gene (TgSELP(+/-)). Aortas developed larger, macrophage-rich atheromas in Apoe(-/-)Selp(-/-)TgSELP(+/-) mice than in Apoe(-/-)Selp(-/-) mice after 8 or 16 weeks on a Western diet. Confocal microscopy of Apoe(-/-)Selp(-/-)TgSELP(+/-) aortas revealed staining for human P-selectin in endothelial cells overlying atheromas but not in lesional macrophages. We also observed staining for human P-selectin in aortic endothelial cells of 3- to 4-week-old Apoe(-/-)Selp(-/-)TgSELP(+/-) weanlings before atheromas developed. Furthermore, human SELP transcripts were ≈3-fold higher in aortas of Apoe(-/-)Selp(+/-)TgSELP(+/-) weanlings than in Selp(+/-)TgSELP(+/-) weanlings, whereas murine Selp and Sele transcripts were equivalent in weanlings of both genotypes. Human SELP transcripts in aortas of Apoe(-/-)Selp(+/-)TgSELP(+/-) mice remained nearly constant during 16 weeks on a Western diet, whereas murine Selp and Sele transcripts progressively increased. Bone marrow transplantation in Apoe(-/-)Selp(-/-) and Apoe(-/-)Selp(-/-)TgSELP(+/-) mice demonstrated that both platelets and endothelial cells must express human P-selectin to promote atherogenesis.

CONCLUSIONS

P-selectin expressed by human SELP is atherogenic in Apoe(-/-) mice, suggesting that P-selectin contributes to atherogenesis in humans.

Fulfilling Koch's postulates in glycoscience: HCELL, GPS and translational glycobiology

Glycoscience-based research that is performed expressly to address medical necessity and improve patient outcomes is called "translational glycobiology". In the 19th century, Robert Koch proposed a set of postulates to rigorously establish causality in microbial pathogenesis, and these postulates can be reshaped to guide knowledge into how naturally-expressed glycoconjugates direct molecular processes critical to human well-being. Studies in the 1990s indicated that E-selectin, an endothelial lectin that binds sialofucosylated carbohydrate determinants, is constitutively expressed on marrow microvessels, and investigations in my laboratory indicated that human hematopoietic stem cells (HSCs) uniquely express high levels of a specialized glycoform of CD44 called "hematopoietic cell E-/L-selectin ligand" (HCELL) that functions as a highly potent E-selectin ligand. To assess the role of HCELL in directing HSC migration to marrow, a method called "glycosyltransferase-programmed stereosubstitution" (GPS) was developed to custom-modify CD44 glycans to enforce HCELL expression on viable cell surfaces. Human mesenchymal stem cells (MSCs) are devoid of E-selectin ligands, but GPS-based glycoengineering of CD44 on MSCs licenses homing of these cells to marrow in vivo, providing direct evidence that HCELL serves as a "bone marrow homing receptor". This review will discuss the molecular basis of cell migration in historical context, will describe the discovery of HCELL and its function as the bone marrow homing receptor, and will inform on how glycoengineering of CD44 serves as a model for adapting Koch's postulates to elucidate the key roles that glycoconjugates play in human biology and for realizing the immense impact of translational glycobiology in clinical medicine.

Glycosphingolipids on Human Myeloid Cells Stabilize E-Selectin-Dependent Rolling in the Multistep Leukocyte Adhesion Cascade

OBJECTIVE

Recent studies suggest that the E-selectin ligands expressed on human leukocytes may differ from those in other species, particularly mice. To elaborate on this, we evaluated the impact of glycosphingolipids expressed on human myeloid cells in regulating E-selectin-mediated cell adhesion.

APPROACH AND RESULTS

A series of modified human cell lines and primary neutrophils were created by targeting UDP-Glucose Ceramide Glucosyltransferase using either lentivirus-delivered shRNA or CRISPR-Cas9-based genome editing. Enzymology and mass spectrometry confirm that the modified cells had reduced or abolished glucosylceramide biosynthesis. Glycomics profiling showed that UDP-Glucose Ceramide Glucosyltransferase disruption also increased prevalence of bisecting N-glycans and reduced overall sialoglycan expression on leukocyte N- and O-glycans. Microfluidics-based flow chamber studies demonstrated that both the UDP-Glucose Ceramide Glucosyltransferase knockouts and knockdowns display ≈60% reduction in leukocyte rolling and firm adhesion on E-selectin bearing stimulated endothelial cells, without altering cell adhesion to P-selectin. Consistent with the concept that the glycosphingolipids support slow rolling and the transition to firm arrest, inhibiting UDP-Glucose Ceramide Glucosyltransferase activity resulted in frequent leukocyte detachment events, skipping motion, and reduced diapedesis across the endothelium. Cells bearing truncated O- and N-glycans also sustained cell rolling on E-selectin, although their ability to be recruited from free fluid flow was diminished.

CONCLUSIONS

Glycosphingolipids likely contribute to human myeloid cell adhesion to E-selectin under fluid shear, particularly the transition of rolling cells to firm arrest.

Replacing the Promoter of the Murine Gene Encoding P-selectin with the Human Promoter Confers Human-like Basal and Inducible Expression in Mice

In humans and mice, megakaryocytes/platelets and endothelial cells constitutively synthesize P-selectin and mobilize it to the plasma membrane to mediate leukocyte rolling during inflammation. TNF-α, interleukin 1β, and LPS markedly increase P-selectin mRNA in mice but decrease P-selectin mRNA in humans. Transgenic mice bearing the entire human SELP gene recapitulate basal and inducible expression of human P-selectin and reveal human-specific differences in P-selectin function. Differences in the human SELP and murine Selp promoters account for divergent expression in vitro, but their significance in vivo is not known. Here we generated knockin mice that replace the 1.4-kb proximal Selp promoter with the corresponding SELP sequence (Selp(KI)). Selp(KI) (/) (KI) mice constitutively expressed more P-selectin on platelets and more P-selectin mRNA in tissues but only slightly increased P-selectin mRNA after injection of TNF-α or LPS. Consistent with higher basal expression, leukocytes rolled more slowly on P-selectin in trauma-stimulated venules of Selp(KI) (/) (KI) mice. However, TNF-α did not further reduce P-selectin-dependent rolling velocities. Blunted up-regulation of P-selectin mRNA during contact hypersensitivity reduced P-selectin-dependent inflammation in Selp(KI) (/-) mice. Higher basal P-selectin in Selp(KI) (/) (KI) mice compensated for this defect. Therefore, divergent sequences in a short promoter mediate most of the functionally significant differences in expression of human and murine P-selectin in vivo.

Synergistic actions of blocking angiopoietin-2 and tumor necrosis factor-α in suppressing remodeling of blood vessels and lymphatics in airway inflammation

Remodeling of blood vessels and lymphatics are prominent features of sustained inflammation. Angiopoietin-2 (Ang2)/Tie2 receptor signaling and tumor necrosis factor-α (TNF)/TNF receptor signaling are known to contribute to these changes in airway inflammation after Mycoplasma pulmonis infection in mice. We determined whether Ang2 and TNF are both essential for the remodeling on blood vessels and lymphatics, and thereby influence the actions of one another. Their respective contributions to the initial stage of vascular remodeling and sprouting lymphangiogenesis were examined by comparing the effects of function-blocking antibodies to Ang2 or TNF, given individually or together during the first week after infection. As indices of efficacy, vascular enlargement, endothelial leakiness, venular marker expression, pericyte changes, and lymphatic vessel sprouting were assessed. Inhibition of Ang2 or TNF alone reduced the remodeling of blood vessels and lymphatics, but inhibition of both together completely prevented these changes. Genome-wide analysis of changes in gene expression revealed synergistic actions of the antibody combination over a broad range of genes and signaling pathways involved in inflammatory responses. These findings demonstrate that Ang2 and TNF are essential and synergistic drivers of remodeling of blood vessels and lymphatics during the initial stage of inflammation after infection. Inhibition of Ang2 and TNF together results in widespread suppression of the inflammatory response.

Selectins: initiators of leucocyte adhesion and signalling at the vascular wall

The selectins are transmembrane, Ca(2+)-dependent lectins that mediate leucocyte rolling on vascular surfaces, the first adhesive step during inflammation and immune surveillance. Leucocytes express L-selectin, activated platelets express P-selectin, and activated endothelial cells express E- and P-selectin. Rolling involves force-regulated, rapidly reversible interactions of selectins with a limited number of glycosylated cell surface ligands. Rolling permits leucocytes to interact with immobilized chemokines that convert β2 integrins to high-affinity conformations, which mediate arrest, post-arrest adhesion strengthening, and transendothelial migration. However, rolling leucocytes also transduce signals through selectin ligands, the focus of this review. These signals include serial activation of kinases and recruitment of adaptors that convert integrins to intermediate-affinity conformations, which decrease rolling velocities. In vitro, selectin signalling enables myeloid cells to respond to suboptimal levels of chemokines and other agonists. This cooperative signalling triggers effector responses such as degranulation, superoxide production, chemokine synthesis, and release of procoagulant/proinflammatory microparticles. In vivo, selectin-mediated adhesion and signalling likely contributes to atherosclerosis, arterial and deep vein thrombosis, ischaemia-reperfusion injury, and other cardiovascular diseases.

Engineered nanoparticles: thrombotic events in cancer

Engineered nanoparticles are being increasingly produced for specific applications in medicine. Broad selections of nano-sized constructs have been developed for applications in diagnosis, imaging, and drug delivery. Nanoparticles as contrast agents enable conjugation with molecular markers which are essential for designing effective diagnostic and therapeutic strategies. Such investigations can also lead to a better understanding of disease mechanisms such as cancer-associated thrombosis which remains unpredictable with serious bleeding complications and high risk of death. Here we review the recent and current applications of engineered nanoparticles in diagnosis and therapeutic strategies, noting their toxicity in relation to specific markers as a target.

TNF-induced endothelial barrier disruption: beyond actin and Rho

The decrease of endothelial barrier function is central to the long-term inflammatory response. A pathological alteration of the ability of endothelial cells to modulate the passage of cells and solutes across the vessel underlies the development of inflammatory diseases such as atherosclerosis and multiple sclerosis. The inflammatory cytokine tumour necrosis factor (TNF) mediates changes in the barrier properties of the endothelium. TNF activates different Rho GTPases, increases filamentous actin and remodels endothelial cell morphology. However, inhibition of actin-mediated remodelling is insufficient to prevent endothelial barrier disruption in response to TNF, suggesting that additional molecular mechanisms are involved. Here we discuss, first, the pivotal role of Rac-mediated generation of reactive oxygen species (ROS) to regulate the integrity of endothelial cell-cell junctions and, second, the ability of endothelial adhesion receptors such as ICAM-1, VCAM-1 and PECAM-1, involved in leukocyte transendothelial migration, to control endothelial permeability to small molecules, often through ROS generation. These adhesion receptors regulate endothelial barrier function in ways both dependent on and independent of their engagement by immune cells, and orchestrate the crosstalk between leukocyte transendothelial migration and endothelial permeability during inflammation.

Neutrophil dependence of vascular remodeling after Mycoplasma infection of mouse airways

Vascular remodeling is a feature of sustained inflammation in which capillaries enlarge and acquire the phenotype of venules specialized for plasma leakage and leukocyte recruitment. We sought to determine whether neutrophils are required for vascular remodeling in the respiratory tract by using Mycoplasma pulmonis infection as a model of sustained inflammation in mice. The time course of vascular remodeling coincided with the influx of neutrophils during the first few days after infection and peaked at day 5. Depletion of neutrophils with antibody RB6-8C5 or 1A8 reduced neutrophil influx and vascular remodeling after infection by about 90%. Similarly, vascular remodeling after infection was suppressed in Cxcr2(-/-) mice, in which neutrophils adhered to the endothelium of venules but did not extravasate into the tissue. Expression of the venular adhesion molecule P-selectin increased in endothelial cells from day 1 to day 3 after infection, as did expression of the Cxcr2-receptor ligands Cxcl1 and Cxcl2. Tumor necrosis factor α (TNFα) expression increased more than sixfold in the trachea of wild-type and Cxcr2(-/-) mice, but intratracheal administration of TNFα did not induce vascular remodeling similar to that seen in infection. We conclude that neutrophil influx is required for remodeling of capillaries into venules in the airways of mice with Mycoplasma infection and that TNFα signaling is necessary but not sufficient for vascular remodeling.

A cell rolling cytometer reveals the correlation between mesenchymal stem cell dynamic adhesion and differentiation state

This communication presents quantitative studies of the dynamic adhesion behavior of mesenchymal stem cells (MSCs) enabled by the combination of cell-surface receptor-ligand interactions and three-dimensional hydrodynamic control by microtopography.

Danger signalling during cancer cell death: origins, plasticity and regulation

Accumulating data indicates that following anti-cancer treatments, cancer cell death can be perceived as immunogenic or tolerogenic by the immune system. The former is made possible due to the ability of certain anti-cancer modalities to induce immunogenic cell death (ICD) that is associated with the emission of damage-associated molecular patterns (DAMPs), which assist in unlocking a sequence of events leading to the development of anti-tumour immunity. In response to ICD inducers, activation of endoplasmic reticulum (ER) stress has been identified to be indispensable to confer the immunogenic character of cancer cell death, due to its ability to coordinate the danger signalling pathways responsible for the trafficking of vital DAMPs and subsequent anti-cancer immune responses. However, in recent times, certain processes apart from ER stress have emerged (e.g., autophagy and possibly viral response-like signature), which have the ability to influence danger signalling. In this review, we discuss the molecular nature, emerging plasticity in the danger signalling mechanisms and immunological impact of known DAMPs in the context of immunogenic cancer cell death. We also discuss key effector mechanisms modulating the interface between dying cancer cells and the immune cells, which we believe are crucial for the therapeutic relevance of ICD in the context of human cancers, and also discuss the influence of experimental conditions and animal models on these.

Platelets as immune cells in infectious diseases

Platelets have been shown to cover a broad range of functions. Besides their role in hemostasis, they have immunological functions and thus participate in the interaction between pathogens and host defense. Platelets have a broad repertoire of receptor molecules that enable them to sense invading pathogens and infection-induced inflammation. Consequently, platelets exert antimicrobial effector mechanisms, but also initiate an intense crosstalk with other arms of the innate and adaptive immunity, including neutrophils, monocytes/macrophages, dendritic cells, B cells and T cells. There is a fragile balance between beneficial antimicrobial effects and detrimental reactions that contribute to the pathogenesis, and many pathogens have developed mechanisms to influence these two outcomes. This review aims to highlight aspects of the interaction strategies between platelets and pathogenic bacteria, viruses, fungi and parasites, in addition to the subsequent networking between platelets and other immune cells, and the relevance of these processes for the pathogenesis of infections.

Elevated CXCL1 expression in gp130-deficient endothelial cells impairs neutrophil migration in mice

Neutrophils emigrate from venules to sites of infection or injury in response to chemotactic gradients. How these gradients form is not well understood. Some IL-6 family cytokines stimulate endothelial cells to express adhesion molecules and chemokines that recruit leukocytes. Receptors for these cytokines share the signaling subunit gp130. We studied knockout mice lacking gp130 in endothelial cells. Unexpectedly, gp130-deficient endothelial cells constitutively expressed more CXCL1 in vivo and in vitro, and even more upon stimulation with tumor necrosis factor-α. Mobilization of this increased CXCL1 from intracellular stores to the venular surface triggered β2 integrin-dependent arrest of neutrophils rolling on selectins but impaired intraluminal crawling and transendothelial migration. Superfusing CXCL1 over venules promoted neutrophil migration only after intravenously injecting mAb to CXCL1 to diminish its intravascular function or heparinase to release CXCL1 from endothelial proteoglycans. Remarkably, mice lacking gp130 in endothelial cells had impaired histamine-induced venular permeability, which was restored by injecting anti-P-selectin mAb to prevent neutrophil rolling and arrest. Thus, excessive CXCL1 expression in gp130-deficient endothelial cells augments neutrophil adhesion but hinders migration, most likely by disrupting chemotactic gradients. Our data define a role for endothelial cell gp130 in regulating integrin-dependent adhesion and de-adhesion of neutrophils during inflammation.

IL-17A potentiates TNFα-induced secretion from human endothelial cells and alters barrier functions controlling neutrophils rights of passage

Interleukin-17A (IL-17A) is an important pro-inflammatory cytokine that regulates leukocyte mobilization and recruitment. To better understand how IL-17A controls leukocyte trafficking across capillaries in the peripheral blood circulation, we used primary human dermal microvascular endothelial cells (HDMEC) to investigate their secretory potential and barrier function when activated with IL-17A and TNFα. Activation by TNFα and IL-17A causes phosphorylation of p38 as well as IκBα whereby NFκB subsequently becomes phosphorylated, a mechanism that initiates transcription of adhesion molecules such as E-selectin. Members of the neutrophil-specific GRO-family chemokines were significantly up-regulated upon IL-17A stimulation on the mRNA and protein level, whereas all tested non-neutrophil-specific chemokines remained unchanged in comparison. Moreover, a striking synergistic effect in the induction of granulocyte colony-stimulating factors (G-CSF) was elicited when IL-17A was used in combination with TNFα, and IL-17A was able to significantly augment the levels of TNFα-induced E-selectin and ICAM-1. In accordance with this observation, IL-17A was able to markedly increase TNFα-induced neutrophil adherence to HDMEC monolayers in an in vitro adhesion assay. Using a trans-well migration assay with an HDMEC monolayer as a barrier, we here show that pre-stimulating the endothelial cells with TNFα and IL-17A together enhances the rate of neutrophil transmigration compared to TNFα or IL-17A alone. These results show that IL-17A and TNFα act in cooperation to facilitate neutrophil migration across the endothelial cell barrier. In addition, the synergistic actions of IL-17A with TNFα to secrete G-CSF appear to be important for mobilizing neutrophils from the bone marrow to the blood stream.

Bacterial lipopolysaccharides stimulate production of XCL1, a calcium-dependent lipopolysaccharide-binding serum lectin, in Xenopus laevis

Xenopus laevis serum lectin XCL1 is a newly identified molecule of the XCGL (or X-lectin) family, a unique group of Ca(2+)-dependent lectins that have a fibrinogen-like domain. The XCL1 protein was purified from lipopolysaccharide (LPS)-stimulated frog sera by sequential affinity chromatography on heparin-acrylic beads and galactose-Sepharose. XCL1 comprises multiple oligomeric proteins consisting of 37-kDa subunit polypeptides, as revealed by sodium dodecyl sulfate-polyacrylamide electrophoresis (SDS-PAGE) and Western blot analyses using the monoclonal antibody (mAb) produced against the recombinant XCL1 polypeptide. In the presence of Ca(2+), the protein bound to Escherichia coli, Staphylococcus aureus, LPS and galactose and the bound XCL1 was competitively eluted using ribose and xylose, and the elution was as efficient as that using EDTA, whereas elution using hexoses, GalNAc or GlcNAc was less effective. In reverse transcription-polymerase chain reaction (RT-PCR) and Western blot analyses, XCL1 expression was ubiquitously detected in frog tissues, with relatively high levels in hematopoietic tissues including the spleen, liver and kidney. Intraperitoneal injection of E. coli, S. aureus or 100-300μg S-type LPS from various bacteria induced several-fold increases in serum XCL1 concentrations on day 3, and the elevated levels retained up to day 12. It also caused a remarkable increase of the splenic XCL1 expression on day 3, followed by a rapid decline to nearly nonstimulated control levels by day 7. The R-type LPS with shortened polysaccharide chains was less effective in inducing the serum XCL1 response, indicating that the sugar chains of LPS were important, if not essential, for the stimulation of XCL1 production. These results suggest that XCL1 is a pathogen recognition molecule involved in antimicrobial innate immunity in Xenopus.

Platelets lacking PIP5KIγ have normal integrin activation but impaired cytoskeletal-membrane integrity and adhesion

Three isoforms of phosphatidylinositol-4-phosphate 5-kinase (PIP5KIα, PIP5KIβ, and PIP5KIγ) can each catalyze the final step in the synthesis of phosphatidylinositol-4,5-bisphosphate (PIP2), which in turn can be either converted to second messengers or bind directly to and thereby regulate proteins such as talin. A widely quoted model speculates that only p90, a longer splice form of platelet-specific PIP5KIγ, but not the shorter p87 PIP5KIγ, regulates the ligand-binding activity of integrins via talin. However, when we used mice genetically engineered to lack only p90 PIP5KIγ, we found that p90 PIP5KIγ is not critical for integrin activation or platelet adhesion on collagen. However, p90 PIP5KIγ-null platelets do have impaired anchoring of their integrins to the underlying cytoskeleton. Platelets lacking both the p90 and p87 PIP5KIγ isoforms had normal integrin activation and actin dynamics, but impaired anchoring of their integrins to the cytoskeleton. Most importantly, they formed weak shear-resistant adhesions ex vivo and unstable vascular occlusions in vivo. Together, our studies demonstrate that, although PIP5KIγ is essential for normal platelet function, individual isoforms of PIP5KIγ fulfill unique roles for the integrin-dependent integrity of the membrane cytoskeleton and for the stabilization of platelet adhesion.