Structural basis for PECAM-1 homophilic binding

Podoplanin immunoexpression in odontogenic lesions: a systematic review, meta-analysis, and integrated bioinformatic analysis

BACKGROUND

Podoplanin (PDPN) is a transmembrane glycoprotein implicated in the pathogenesis of odontogenic lesions (OL). It is localized at the membrane and cytoplasmic level, and its interaction with other proteins could trigger cell proliferation, invasion and migration. The main objective of this systematic review is to explore the immunoexpression pattern of podoplanin in OL. In addition, as secondary objectives, we aimed to compare the immunostaining intensity of PDPN in OL, to analyze its interaction networks by bioinformatic analysis and to highlight its importance as a potential diagnostic marker useful in the pathogenesis of OL.

METHODS

The protocol was developed following PRISMA and Cochrane guidelines. The digital search was performed in the databases: PubMed/MEDLINE, ScienceDirect, Scopus, Web of Science and Google Schoolar from August 15, 2010 to June 15, 2023. We included cross-sectional and cohort studies that will analyze the pattern of PDPN immunoexpression in OL. Two investigators independently searched for eligible articles, selected titles and abstracts, analyzed full text, conducted data collection, and performed assessment of study quality and risk of bias. In addition, part of the results were summarized through a random-effects meta-analysis. STRING database was used for protein-protein interaction analysis.

RESULTS

Twenty-nine relevant studies were included. The ages of the subjects ranged from 2 to 89 years, with a mean age of 33.41 years. Twenty-two point two percent were female, 21.4% were male, and in 56.4% the gender of the participants was not specified. A total of 1,337 OL samples were analyzed for PDPN immunoexpression pattern. Ninety-four (7.03%) were dental follicles and germs, 715 (53.47%) were odontogenic cysts, and 528 (39.49%) were odontogenic tumors. Meta-analysis indicated that the immunostaining intensity was significantly stronger in odontogenic keratocysts compared to dentigerous cysts (SMD=3.3(CI=1.85-4.82, p=0.000*). Furthermore, bioinformatic analysis revealed that PECAM-1, TNFRF10B, MSN, EZR and RDX interact directly with PDPN and their expression in OL was demonstrated.

CONCLUSIONS

The results of the present systematic review support the unique immunoexpression of PDPN as a potential useful diagnostic marker in the pathogenesis of OL.

Elucidating the molecular basis of PECAM-1 and Tie2 interaction from binding dynamics and complex formation

BACKGROUND

Endothelial hyperpermeability-induced vascular dysfunction is a prevalent and significant characteristic in critical illnesses such as sepsis and other conditions marked by acute systemic inflammation. Platelet endothelial cell adhesion molecule-1 (PECAM-1) and Tie2 serve as transmembrane receptors within endothelial cells (ECs), playing pivotal roles not only in maintaining EC-EC junctions but also in influencing vasculogenesis, vessel homeostasis, and vascular remodeling.

OBJECTIVES

At present, the molecular basis of the PECAM-1-Tie2 interaction remains inadequately elucidated. In the study, recombinant soluble PECAM-1 (sPECAM-1) and Tie2 (sTie2) were expressed by Drosophila S2 and HEK293 expression systems, respectively. The interactions between sPECAM-1 and sTie2 were investigated using the Surface Plasmon Resonance (SPR) and size-exclusion chromatography methods. An immunofluorescence assay was used to detect the binding of sPECAM-1 and sTie2 on endothelial cells.

RESULTS

PECAM-1 was found to bind with sTie2 in a sodium and pH-dependent manner as confirmed by the ELISA, the D5-D6 domains of PECAM-1 might play a crucial role in binding with sTie2. Surface Plasmon Resonance (SPR) results showed that the full length of sPECAM-1 has the strongest binding affinity (KD = 48.4 nM) with sTie2, compared to sPECAM-1-D1-D4 and sPECAM-1-D1-D2. This result is consistent with that in the ELISA. In addition, size-exclusion chromatography demonstrated that sPECAM-1, sTie2, and Ang1 can form a ternary complex.

CONCLUSION

In this study, we determined that sPECAM-1 binds to sTie2 in a pH and sodium-dependent manner. The full length of sPECAM-1 has the strongest binding affinity, and the D5-D6 domains in sPECAM-1 play a crucial role in the interaction between sPECAM-1 and sTie2.

Camouflaging endovascular stents with an endothelial coat using CD31 domain 1 and 2 mimetic peptides

Objective

Implantation of an endovascular device disrupts the homeostatic CD31:CD31 interactions among quiescent endothelial cells (ECs), platelets, and circulating leukocytes. The aim of this study was to design an endothelial-mimetic coating of nitinol and cobalt-chromium (CoCr) surfaces and stents using synthetic CD31 peptides, to promote device endothelialization and pacific integration within the arterial wall.

Methods

Peptides mimicking the domains 1 (D1) and 2 (D2) of CD31 were synthetized and immobilized onto experimental nitinol and CoCr surfaces using a three-step, dip-coating, mussel-inspired protocol using copper-free click chemistry. Human aortic EC phenotype and endothelialization assessment using parallel scratch tests were carried out using five synthetic CD31 peptides coated on 4.8-mm nitinol and CoCr flat disks and were compared with control disks. The CD31 peptide exhibiting the best results in vitro was then immobilized on clinical-grade 3 × 40-mm self-expanding nitinol and 2.5 × 20.0-mm balloon-expandable CoCr stents. Such devices were implanted in native arteries of White New Zealand rabbits, and compared with control uncoated bare metal stents (BMS) and drug-eluting stents 7 and 30 days after implantation using resin cross-sections and scanning electron microscopy (n = 2-3 per group at each time point).

Results

Membrane-distal CD31 D1 and D2 peptides exhibited a distinct capability to foster a healthy endothelial phenotype and to promote endothelialization in vitro. By day 7 after implantation, CD31 nitinol and CoCr stents were evenly covered by wholesome ECs, devoid of thromboinflammatory signs, in contrast with both BMS and drug-eluting stents. Such results were consistent until day 30.

Conclusions

Membrane-distal CD31 biomimetic peptides seem to camouflage the device surface effectively, preventing local reactions and promoting rapid and seamless endovascular integration.

[Protective effect of FAK inhibitor PF-562271 against human umbilical vein endothelial cell injury induced by aging platelets]

OBJECTIVE

To investigate the protective effect of PF-562271, a FAK inhibitor, against aging platelet-induced injury in human umbilical vein endothelial cells (HUVECs).

METHODS

Cultured HUVECs were treated with vehicle, lipopolysaccharide (LPS), LPS+aging platelets, or LPS+aging platelets+PF-562271. The changes in protein expressions of FAK, pFAK and PECAM-1 in the treated cells were detected using Western blotting and immunofluorescence assay, and the level of reactive oxygen species (ROS) was detected with flow cytometry. The changes of barrier function of the cells were assessed with cell permeability test and transendothelial cell resistance test. RT-qPCR was used to analyze mRNA expressions of inflammatory factors, and pro-inflammatory cytokine levels in the culture supernatants was determined with enzyme-linked immunosorbent assay. Immunofluorescence assay was used to examine the effect of the ROS inhibitor vitamin C on PECAM-1 expression in the cells with different treatments.

RESULTS

Treatment of HUVECs with LPS and aging platelets significantly increased cellular protein expressions of FAK, pFAK and PECAM-1, which were effectively lowered by addition of PF-562271 (P < 0.05). LPS and aged platelets obviously enhanced ROS production in the cells, which was inhibited by the addition of PF-562271 (P < 0.001). PF-562271 significantly alleviated the damage of endothelial cell barrier function of the cells caused by LPS and aging platelets (P < 0.01). The expressions of TNF-α, IL-6 and IL-8 in HUVECs increased significantly after exposure to LPS and aging platelets, and were obviously lowered after treatment with PF-562271 (P < 0.05). Treatment with vitamin C significantly decreased the expression of PECAM-1 protein in the cells (P < 0.01).

CONCLUSION

The FAK inhibitor PF-562271 alleviates endothelial cell damage induced by LPS and aging platelets by lowering cellular oxidative stress levels and reducing inflammatory responses.

A Noninvasive Approach to Evaluate Tumor Immune Microenvironment and Predict Outcomes in Hepatocellular Carcinoma

It is widely recognized that tumor immune microenvironment (TIME) plays a crucial role in tumor progression, metastasis, and therapeutic response. Despite several noninvasive strategies have emerged for cancer diagnosis and prognosis, there are still lack of effective radiomic-based model to evaluate TIME status, let alone predict clinical outcome and immune checkpoint inhibitor (ICIs) response for hepatocellular carcinoma (HCC). In this study, we developed a radiomic model to evaluate TIME status within the tumor and predict prognosis and immunotherapy response. A total of 301 patients who underwent magnetic resonance imaging (MRI) examinations were enrolled in our study. The intra-tumoral expression of 17 immune-related molecules were evaluated using co-detection by indexing (CODEX) technology, and we construct Immunoscore (IS) with the least absolute shrinkage and selection operator (LASSO) algorithm and Cox regression method to evaluate TIME. Of 6115 features extracted from MRI, five core features were filtered out, and the Radiomic Immunoscore (RIS) showed high accuracy in predicting TIME status in testing cohort (area under the curve = 0.753). More importantly, RIS model showed the capability of predicting therapeutic response to anti-programmed cell death 1 (PD-1) immunotherapy in an independent cohort with advanced HCC patients (area under the curve = 0.731). In comparison with previously radiomic-based models, our integrated RIS model exhibits not only higher accuracy in predicting prognosis but also the potential guiding significance to HCC immunotherapy.

Supplementary Information

The online version contains supplementary material available at 10.1007/s43657-023-00136-8.

Enhancing the Treatment of Uncontrolled Inflammation through the Targeted Delivery of TPCA-1-Loaded Nanoparticles

Uncontrolled inflammation is a pathological state that underlies many diseases. Despite the development of numerous anti-inflammatory agents, the treatment of uncontrolled inflammation remains a challenging task. We developed a targeted delivery system for [5-(p-fluorophenyl)-2-ureido]thiophene-3-carboxamide (TPCA-1), a potent inhibitor of the NF-κB signaling pathway. The system comprises TPCA-1-loaded nanoparticles (NPs) functionalized with a monoclonal antibody (mAb) that specifically binds to the break point of the IgD6 region of the platelet/endothelial cell adhesion molecule-1 (PECAM-1) extracellular segment that is overexposed on the injured endothelium and activated macrophages during the pathogenesis of inflammation. In vitro binding and cellular uptake experiments revealed that the mAb modification on NPs could significantly enhance uptake by both Raw264.7 and HUVEC compared with unmodified NPs. In studies conducted at the cellular level focusing on anti-inflammatory and antioxidant effects, this formulation was found to effectively inhibit M1 polarization of macrophages, downregulate the secretion of pro-inflammatory cytokines, and reduce the production of reactive oxygen species (ROS) and nitric oxide (NO). In an animal model of vascular endothelial injury with acute inflammation, these NPs were capable of delivering TPCA-1 to inflammatory lesions in a targeted manner. Compared with the free agent-treated group, the NP-treated group exhibited reduced infiltration of inflammatory cells. In conclusion, our study demonstrates that this targeted delivery of TPCA-1-loaded NPs represents a promising strategy for improved mitigation of uncontrolled inflammation.

CD31 as a probable responding and gate-keeping protein of the blood-brain barrier and the risk of Alzheimer's disease

Several studies have shown that an abnormal vascular-immunity link could increase Alzheimer's disease (AD) risk; however, the mechanism is unclear. CD31, also named platelet endothelial cell adhesion molecule (PECAM), is a surface membrane protein of both endothelial and immune cells and plays important roles in the interaction between the vascular and immune systems. In this review, we focus on research regarding CD31 biological actions in the pathological process that may contribute to AD based on the following rationales. First, endothelial, leukocyte and soluble forms of CD31 play multi-roles in regulating transendothelial migration, increasing blood-brain barrier (BBB) permeability and resulting in neuroinflammation. Second, CD31 expressed by endothelial and immune cells dynamically modulates numbers of signaling pathways, including Src family kinases, selected G proteins, and β-catenin which in turn affect cell-matrix and cell-cell attachment, activation, permeability, survival, and ultimately neuronal cell injury. In endothelia and immune cells, these diverse CD31-mediated pathways act as a critical regulator in the immunity-endothelia-brain axis, thereby mediating AD pathogenesis in ApoE4 carriers, which is the major genetic risk factor for AD. This evidence suggests a novel mechanism and potential drug target for CD31 in the background of genetic vulnerabilities and peripheral inflammation for AD development and progression.

Case report: BCL-2 and CD31 immunoexpression related to clinical and histopathological evaluation of renal dysplasia in a Welsh Corgi Puppy

A case of renal dysplasia (RD) in the Welsh Corgi dog has been reported. Clinically, the affected 3-month-old, female, Welsh Corgi dog showed unclear symptoms of chronic kidney disease. Grossly, both left and right kidneys revealed cystic hypoplasia. Histologically, the primary lesions included immature or fetal glomeruli/tubules, proliferative arterioles, persistent metanephric ducts, persistent mesenchyme, and atypical tubular epithelium were presented. A group of degenerative and inflammatory lesions consisting of interstitial nephritis, interstitial fibrosis, and mineralization of tubules were found. Immunohistochemically, the epithelial cells of immature (fetal) tubules had BCL-2 labeling whereas CD31 (PECAM-1) was labeled in the endothelial cells of the proliferative arterioles. The immunohistochemical findings were confirmed and consolidated with the routine histopathological findings. This study was the first demonstration of the clinical, histopathological, and immunohistochemical features of RD disease in a Welsh Corgi puppy.

Therapeutic Potential of Standardized Extract of Melilotus indicus (L.) All. and Its Phytochemicals against Skin Cancer in Animal Model: In Vitro, In Vivo, and In Silico Studies

Melilotus indicus (L.) All. is known to have anti-inflammatory and anticancer properties. The present study explored the in vivo skin carcinogenesis attenuating potential of ethanolic extract of M. indicus (L.) All. (Miet) in a 7,12-dimethylbenz[a]anthracene (DMBA)-induced skin cancer model. The ethanolic extract of the plant was prepared by a maceration method. HPLC analysis indicated the presence of quercetin in abundance and also various other phytoconstituents. DPPH radical scavenging assay results showed moderate antioxidant potential (IC50 = 93.55 ± 5.59 μg/mL). A topical acute skin irritation study showed the nonirritant nature of Miet. Data for the skin carcinogenic model showed marked improvement in skin architecture in Miet and its primary phytochemicals (quercetin and coumarin) treated groups. Miet 50% showed comparable effects with 5-fluorouracil. Significant (p < 0.05) anticancerous effects were seen in coumarin-quercetin combination-treated animals than in single agent (coumarin and quercetin alone)-treated animals. Chorioallantoic membrane (CAM) assay results showed the antiangiogenic potential of Miet. Treatment with Miet significantly down-regulated the serum levels of CEA (carcinoembryonic antigen) and TNF-α (Tumor necrosis factor-α). Data for the docking study indicated the binding potential of quercetin and coumarin with TNF-α, EGFR, VEGF, and BCL2 proteins. Thus, it is concluded that Miet has skin cancer attenuating potential that is proposed to be due to the synergistic actions of its bioactive molecules. Further studies to explore the effects of Miet and its bioactive molecules as an adjuvant therapy with low dose anticancer drugs are warranted, which may lead to a new area of research.

Activation of CD44 signaling in leader cells induced by tumor-associated macrophages drives collective detachment in luminal breast carcinomas

Collective detachment of cancer cells at the invading front could generate efficient metastatic spread. However, how cancer cell clusters shed from the leading front remains unknown. We previously reported that the dynamic expression of CD44 in breast cancers (BrCas) at collectively invading edges was associated with tumor-associated macrophages (TAMs). In this study, we first observed that the highly expressed CD44 (CD44^high) cancer cell clusters were located in the BrCa circulating vessels, accompanied by CD206⁺ TAMs. Next, we identified that the cancer cell clusters can be converted to an invasive CD44^high state which was induced by TAMs, thus giving rise to CD44-associated signaling mediated cohesive detachment. Then, we showed that disrupting CD44-signaling inhibited the TAMs triggered cohesive detaching using 3D organotypic culture and mouse models. Furthermore, our mechanistic study showed that the acquisition of CD44^high state was mediated by the MDM2/p53 pathway activation which was induced by CCL8 released from TAMs. Blocking of CCL8 could inhibit the signaling cascade which decreased the CD44-mediated cohesive detachment and spread. Our findings uncover a novel mechanism underlying collective metastasis in BrCas that may be helpful to seek for potential targets.

Adhesion Molecule Profile and the Effect of Anti-VLA-4 mAb Treatment in Experimental Autoimmune Encephalomyelitis, a Mouse Model of Multiple Sclerosis

In the course of multiple sclerosis (MS) and its animal model, experimental autoimmune encephalomyelitis (EAE), the infiltration of lymphocytes and other inflammatory cells across the blood–brain barrier is associated with interactions between adhesion molecules expressed by infiltrating cells and vascular endothelium. Monoclonal antibodies (mAb) against the α4 subunit of α4-β1 integrin (VLA-4) show beneficial effects in both MS and EAE. (1) Background: The aim of this study was to examine the expression of selected adhesion molecules: VLA-4, VCAM-1, LFA-1, ICAM-1 and PECAM-1 in the successive phases of EAE and the effect of anti-VLA-4 mAb treatment on that expression. (2) Methods: EAE was induced in C57BL/6 mice by immunization with MOG_35–55 peptide. The animals were killed in three successive phases of the disease: onset (day 13), peak (day 18) and chronic (day 28). Frozen sections of the lumbar spinal cord were examined by quantitative immunofluorescence microscopy. The expression of the studied molecules was quantified as the percentage of the cross-sectioned spinal cord lesion area occupied by immunopositive structures. (3) Results: The expression of the studied molecules showed two temporal patterns: (1) an increase in the onset phase, a maximum in the peak phase and a decrease in the chronic phase, which corresponded to the temporal pattern of the clinical score, the number of lesions and the inflammation level (ICAM-1, LFA-1 and PECAM-1), and (2) an increase in the peak phase and no significant change or further increase in the chronic phase (VCAM-1, VLA-4). Among the molecules studied, ICAM-1 and LFA-1 exhibited the highest expression levels in the peak phase of EAE. Anti-VLA-4 mAb inhibited the expression of not only VLA-4 but also other adhesion molecules. (4) Conclusions: The interactions of adhesion molecules governing the migration of leukocytes across the blood–brain barrier change in the successive phases of EAE. The therapeutic mechanism of anti-VLA-4 mAb treatment seems to include a complex influence on a variety of adhesion molecules expressed by infiltrating cells and vascular endothelium.

Neuroinflammation creates an immune regulatory niche at the meningeal lymphatic vasculature near the cribriform plate

Meningeal lymphatics near the cribriform plate undergo lymphangiogenesis during neuroinflammation to drain excess fluid. Here, we hypothesized that lymphangiogenic vessels may acquire an altered phenotype to regulate immunity. Using single-cell RNA sequencing of meningeal lymphatics near the cribriform plate from healthy and experimental autoimmune encephalomyelitis in the C57BL/6 model, we report that neuroinflammation induces the upregulation of genes involved in antigen presentation such as major histocompatibility complex class II, adhesion molecules including vascular cell adhesion protein 1 and immunoregulatory molecules such as programmed cell death 1 ligand 1, where many of these changes are mediated by interferon-γ. The inflamed lymphatics retain CD11c+ cells and CD4 T cells where they capture and present antigen, creating an immunoregulatory niche that represents an underappreciated interface in the regulation of neuroinflammation. We also found discontinuity of the arachnoid membrane near the cribriform plate, which provides unrestricted access to the cerebrospinal fluid. These findings highlight a previously unknown function of local meningeal lymphatics in regulating immunity that has only previously been characterized in draining lymph nodes.

Atomic Level Dissection of the Platelet Endothelial Cell Adhesion Molecule 1 (PECAM-1) Homophilic Binding Interface: Implications for Endothelial Cell Barrier Function

OBJECTIVE

PECAM-1 (platelet endothelial cell adhesion molecule 1) is a 130 kDa member of the immunoglobulin (Ig) gene superfamily that is expressed on the surfaces of platelets and leukocytes and concentrated at the intercellular junctions of confluent endothelial cell monolayers. PECAM-1 Ig domains 1 and 2 (IgD1 and IgD2) engage in homophilic interactions that support a host of vascular functions, including support of leukocyte transendothelial migration and the maintenance of endothelial junctional integrity. The recently solved crystal structure of PECAM-1 IgD1 and IgD2 revealed a number of intermolecular interfaces predicted to play important roles in stabilizing PECAM-1/PECAM-1 homophilic interactions and in formation and maintenance of endothelial cell-cell contacts. We sought to determine whether the protein interfaces implicated in the crystal structure reflect physiologically important interactions. Approach and Results: We assessed the impact of single amino acid substitutions at the interfaces between opposing PECAM-1 molecules on homophilic binding and endothelial cell function. Substitution of key residues within the IgD1-IgD1 and IgD1-IgD2 interfaces but not those within the smaller IgD2-IgD2 interface, markedly disrupted PECAM-1 homophilic binding and its downstream effector functions, including the ability of PECAM-1 to localize at endothelial cell-cell borders, mediate the formation of endothelial tubes, and restore endothelial barrier integrity.

CONCLUSIONS

Taken together, these results validate the recently described PECAM-1 IgD1/IgD2 crystal structure by demonstrating that specific residues visualized within the IgD1-IgD1 and IgD1-IgD2 interfaces of opposing molecules in the crystal are required for functionally important homophilic interactions. This information can now be exploited to modulate functions of PECAM-1 in vivo.

Mechanobiology of Microvascular Function and Structure in Health and Disease: Focus on the Coronary Circulation

The coronary microvasculature plays a key role in regulating the tight coupling between myocardial perfusion and myocardial oxygen demand across a wide range of cardiac activity. Short-term regulation of coronary blood flow in response to metabolic stimuli is achieved via adjustment of vascular diameter in different segments of the microvasculature in conjunction with mechanical forces eliciting myogenic and flow-mediated vasodilation. In contrast, chronic adjustments in flow regulation also involve microvascular structural modifications, termed remodeling. Vascular remodeling encompasses changes in microvascular diameter and/or density being largely modulated by mechanical forces acting on the endothelium and vascular smooth muscle cells. Whereas in recent years, substantial knowledge has been gathered regarding the molecular mechanisms controlling microvascular tone and how these are altered in various diseases, the structural adaptations in response to pathologic situations are less well understood. In this article, we review the factors involved in coronary microvascular functional and structural alterations in obstructive and non-obstructive coronary artery disease and the molecular mechanisms involved therein with a focus on mechanobiology. Cardiovascular risk factors including metabolic dysregulation, hypercholesterolemia, hypertension and aging have been shown to induce microvascular (endothelial) dysfunction and vascular remodeling. Additionally, alterations in biomechanical forces produced by a coronary artery stenosis are associated with microvascular functional and structural alterations. Future studies should be directed at further unraveling the mechanisms underlying the coronary microvascular functional and structural alterations in disease; a deeper understanding of these mechanisms is critical for the identification of potential new targets for the treatment of ischemic heart disease.

Mechanosensitive molecular interactions in atherogenic regions of the arteries: development of atherosclerosis

A terrible disease of the cardiovascular system, atherosclerosis, develops in the areas of bends and branches of arteries, where the direction and modulus of the blood flow velocity vector change, and consequently so does the mechanical effect on endothelial cells in contact with the blood flow. The review focuses on topical research studies on the development of atherosclerosis – mechanobiochemical events that transform the proatherogenic mechanical stimulus of blood flow – low and low/oscillatory arterial wall shear stress in the chains of biochemical reactions in endothelial cells, leading to the expression of specific proteins that cause the progression of the pathological process. The stages of atherogenesis, systemic risk factors for atherogenesis and its important hemodynamic factor, low and low/oscillatory wall shear stress exerted by blood flow on the endothelial cells lining the arterial walls, have been described. The interactions of cell adhesion molecules responsible for the development of atherosclerosis under low and low/oscillating shear stress conditions have been demonstrated. The activation of the regulator of the expression of cell adhesion molecules, the transcription factor NF-κB, and the factors regulating its activation under these conditions have been described. Mechanosensitive signaling pathways leading to the expression of NF-κB in endothelial cells have been described. Studies of the mechanobiochemical signaling pathways and interactions involved in the progression of atherosclerosis provide valuable information for the development of approaches that delay or block the development of this disease. Key words: atherogenesis; shear stress; transcription factor NF-κB; RelA expression; mechanosensitive receptors; cell adhesion molecules; signaling pathways; mechanotransduction.

Utility of Platelet Endothelial Cell Adhesion Molecule 1 in the Platelet Activity Assessment in Mouse and Human Blood

In our previous study, we introduced the platelet endothelial cell adhesion molecule 1 (PECAM-1)/thrombus ratio, which is a parameter indicating the proportion of PECAM-1 in laser-induced thrombi in mice. Because PECAM-1 is an antithrombotic molecule, the higher the PECAM-1/thrombus ratio, the less activated the platelets. In this study, we used an extracorporeal model of thrombosis (flow chamber model) to verify its usefulness in the assessment of the PECAM-1/thrombus ratio in animal and human studies. Using the lipopolysaccharide (LPS)-induced inflammation model, we also evaluated whether the PECAM-1/thrombus ratio determined in the flow chamber (without endothelium) differed from that calculated in laser-induced thrombosis (with endothelium). We observed that acetylsalicylic acid (ASA) decreased the area of the thrombus while increasing the PECAM-1/thrombus ratio in healthy mice and humans in a dose-dependent manner. In LPS-treated mice, the PECAM-1/thrombus ratio decreased as the dose of ASA increased in both thrombosis models, but the direction of change in the thrombus area was inconsistent. Our study demonstrates that the PECAM-1/thrombus ratio can more accurately describe the platelet activation status than commonly used parameters such as the thrombus area, and, hence, it can be used in both human and animal studies.

Raphanus Sativus Seeds OilArrested In Vivo Inflammation and Angiogenesis Through Down-Regulation of TNF-a

BACKGROUND

Raphanus sativus is traditionally used as an anti-inflammatory agent.

OBJECTIVES

The current study was designed to explore the in vivo anti-inflammatory and antiangiogenic properties of Raphanus sativus seeds oil.

METHODS

Cold press method was used for the extraction of oil (RsSO) and was characterised using GC-MS techniques. Three in vitro antioxidant assays (DPPH, ABTS, and FRAP) were performed to explore antioxidant potential of RsSO. Disc diffusion methods were used to study in vitro antimicrobial properties. In vivo anti-inflammatory properties were studied in both acute and chronic inflammation models. In ovo chicken, a chorioallantoic membrane assay was performed to study antiangiogenic effects. Molecular mechanisms were identified using serum TNF-α ELISA kit and docking tools.

RESULTS

GC-MS analysis of RsSO revealed the presence of hexadecanoic and octadecanoic acid. Findings of DPPH, ABTS, and FRAP models indicated relatively moderate radical scavenging properties of RsSO. Oil showed antimicrobial activity against a variety of strains tested. Data of inflammation models showed significant (p < 0.05) anti-inflammatory effects of RsSO in both acute and chronic models. 500 mg/kg RsSO halted inflammation development significantly better (p < 0.05) as compared with lower doses. Histopathological evaluations of paws showed minimal infiltration of inflammatory cells in RsSO-treated animals. Findings of TNF-α ELSIA and docking studies showed that RsSO has the potential to downregulate the expression of TNF-α, iNOS, ROS, and NF-κB, respectively. Moreover, RsSO showed in vivo antiangiogenic effects.

CONCLUSION

Data of the current study highlight that Raphanus sativus seeds oil has anti-inflammatory, and antiangiogenic properties and can be used as an adjunct to standard NSAIDs therapy to reduce its dose and side effects.

Targeting platelet inhibition receptors for novel therapies: PECAM-1 and G6b-B

While current oral antiplatelet therapies benefit many patients, they deregulate the hemostatic balance leaving patients at risk of systemic side-effects such as hemorrhage. Dual antiplatelet treatment is the standard approach, combining aspirin with P2Y₁₂ blockers. These therapies mainly target autocrine activation mechanisms (TxA₂, ADP) and, more recently, the use of thrombin or thrombin receptor antagonists have been added to the available approaches. Recent efforts to develop new classes of anti-platelet drugs have begun to focus on primary platelet activation pathways such as through the immunoreceptor tyrosine-based activation motif (ITAM)-containing collagen receptor GPVI/FcRγ-chain complex. There are already encouraging results from targeting GPVI, with reduced aggregation and smaller arterial thrombi, without major bleeding complications, likely due to overlapping activation signaling pathways with other receptors such as the GPIb-V-IX complex. An alternative approach to reduce platelet activation could be to inhibit this signaling pathway by targeting the inhibitory pathways intrinsic to platelets. Stimulation of endogenous negative modulators could provide more specific inhibition of platelet function, but is this feasible? In this review, we explore the potential of the two major platelet immunoreceptor tyrosine-based inhibitory motif (ITIM)-containing inhibitory receptors, G6b-B and PECAM-1, as antithrombotic targets.

L-selectin regulates human neutrophil transendothelial migration

The migration of circulating neutrophils towards damaged or infected tissue is absolutely critical to the inflammatory response. L-selectin is a cell adhesion molecule abundantly expressed on circulating neutrophils. For over two decades, neutrophil L-selectin has been assigned the exclusive role of supporting tethering and rolling – the initial stages of the multi-step adhesion cascade. Here, we provide direct evidence for L-selectin contributing to neutrophil transendothelial migration (TEM). We show that L-selectin co-clusters with PECAM-1 – a well-characterised cell adhesion molecule involved in regulating neutrophil TEM. This co-clustering behaviour occurs specifically during TEM, which serves to augment ectodomain shedding of L-selectin and expedite the time taken for TEM (TTT) to complete. Blocking PECAM-1 signalling (through mutation of its cytoplasmic tail), PECAM-1-dependent adhesion or L-selectin shedding, leads to a significant delay in the TTT. Finally, we show that co-clustering of L-selectin with PECAM-1 occurs specifically across TNF- but not IL-1β-activated endothelial monolayers – implying unique adhesion interactomes forming in a cytokine-specific manner. To our knowledge, this is the first report to implicate a non-canonical role for L-selectin in regulating neutrophil TEM.

Highlighted Article: Neutrophil L-selectin co-clusters with PECAM-1 in cis during transendothelial migration (TEM). Clustering neutrophil PECAM-1 activates p38 MAPK and JNK to regulate L-selectin shedding, which in turn expedites TEM.

Plump endothelial cells integrated into pre-existing venules contribute to the formation of 'mother' and 'daughter' vessels in pyogenic granuloma: possible role of galectin-1, -3 and -8

INTRODUCTION

Pyogenic granuloma (PG) is a reactive inflammatory vascular lesion of the skin and mucous membranes, characterised by the presence of enlarged venules and seamed and seamless capillaries with plump endothelial cells (EC), and numerous macrophages. EC activation upregulates the synthesis of galectins and induces their translocation to the EC surface promoting angiogenesis and lymphangiogenesis, particularly galectin-1 (Gal-1), Gal-3 and Gal-8. However, the presence and distribution of Gal-1, -3 and -8, as well as their implications in the pathogenesis of PG, has not been considered.

MATERIALS AND METHODS

Eight biopsies from patients diagnosed with PG were selected. The presence of PECAM-1/CD31, IL-1β, VEGF-C, VEGFR-2, VEGFR-3, integrin β1, CD44, fibronectin and Gal-1, -3 and -8 was assessed by immunofluorescence staining using confocal laser scanning microscopy.

RESULTS AND DISCUSSION

Immunostaining revealed that these molecules were present in the enlarged venules with plump ECs, in some macrophages and other immune cells. We propose that macrophages release VEGF-A and VEGF-C inducing VEGFR-2/VEGFR-3 expression and activation, leading macrophages to transdifferentiate into plump ECs that might integrate into pre-existing venules, contributing to the formation of enlarged venules with transluminal bridges and capillaries. EC activation, induced by certain cytokines, has been shown to stimulate galectin expression and changes in the cellular localisation through association and activation of specific EC surface glycoproteins. Therefore, it is plausible that Gal-1, -3 and -8, acting in a concerted manner, could be mediating the transdifferentiation of macrophages into plump ECs and facilitating their migration and incorporation into the new vessels.

LAY SUMMARY

In this study, immunostaining of pyogenic granuloma (PG) tissue sections showed immunoreactivity for PECAM-1/CD31, IL-1β, VEGF-C, VEGFR-2 and VEGFR-3, and galectin-1, -3 and -8 in enlarged venules with plump endothelial cells (EC), as well as in some macrophages and other immune cells. Interestingly, enlarged and thin-walled transient vessels lined by PECAM-1/CD31 and VEGFR-2 immunopositive ECs that form from pre-existing normal venules in response to VEGF-A (called 'mother' vessels [MV]) and that undergo intraluminal bridging evolving into various types of capillaries (called 'daughter' vessels [DV]) have been observed in benign and malignant tumours, in physiological and pathological angiogenesis as well as in vascular malformations, suggesting an important role for VEGF-A and VEGFR-2 in such a process. However, it is not only the mechanisms by which the MVs evolve in different types of DVs that remains to be elucidated, but also whether the cells that form intraluminal bridges proceed from locally activated ECs or whether they are derived from bone marrow precursors or from resident macrophages.Given that the formation of homodimers by Gal-1 and Gal-8 and pentamers by Gal-3 to generate gal-glycan lattices at the cell surface and in the extracellular space has been shown, it is possible that in PG tissue Gal-1, -3 and -8, through their binding partners, form a supramolecular structure at the surface of ECs and plump ECs, macrophages and in the extracellular space that might be mediating the transdifferentiation of macrophages into plump ECs and facilitating the migration and incorporation of these cells into the pre-existing venules, thus contributing to the formation of MVs and DVs.

PECAM-1 protects against DIC by dampening inflammatory responses via inhibiting macrophage pyroptosis and restoring vascular barrier integrity

Disseminated intravascular coagulation (DIC) is a frequent complication of sepsis that affects patient outcomes due to accompanying thrombo-inflammation and microvascular permeability changes. Platelet endothelial cell adhesion molecule-1 (PECAM-1), a cellular adhesion and signaling receptor that is expressed on both hematopoietic and endothelial cells, plays an important anti-inflammatory role in acute and chronic inflammatory disease models. Little is known, however, about role and mechanism of PECAM-1 in septic DIC. Here, we investigated whether PECAM-1 might play a protective role in hindering the development of septic DIC. Plasma levels of soluble PECAM-1 were markedly elevated in septic patients that developed DIC, with a correspondingly poorer outcome. PECAM-1 knockout exhibited more severe DIC and poorer outcome in the LPS induced- and cecal ligation and puncture-induced DIC model, which could be alleviated by tissue factor inhibitor. This phenomenon seemed to be equally linked to PECAM-1 expression by both endothelial and blood cells. Furthermore, PECAM-1 was found to exert its protective effect on developing septic DIC by the following 2 distinct mechanisms: the inhibition of macrophage pyroptosis and the acceleration of the restoration of the endothelial cell barrier. Taken together, these results implicate PECAM-1 as a potentially attractive target for the development of novel therapeutics to manage and treat septic DIC.

The manifold roles of sialic acid for the biological functions of endothelial glycoproteins

Vascular endothelia are covered with a dense glycocalix that is heavily sialylated. Sialylation of vascular glycoconjugates is involved in the regulation of cell-cell interactions, be it among endothelial cells at cell junctions or between endothelial and blood-borne cells. It also plays important roles in modulating the binding of soluble ligands and the signaling by vascular receptors. Here, we provide an overview over the sialylation-function relationships of glycoproteins expressed in the blood and lymphatic vasculature. We first describe cellular interactions in which sialic acid contributes in a stereospecific manner to glycan epitopes recognized by glycan-binding proteins. Our major focus is however on the rarely discussed examples of vascular glycoproteins whose biological functions are modulated by sialylation through other mechanisms.

Generation of Pecam1 endothelial specific dual reporter mouse model

Endothelial cells are specialized epithelium lining the interior surface of vessels and play fundamental roles in angiogenesis, vascular permeability, and immune response. To identify endothelial cells in vivo, we constructed a Pecam1^{nlacZ-H2B-GFP/+} knock-in mouse model in which the endothelial cells are labeled by nuclear LacZ (nlacZ) expression. When Pecam1^{nlacZ-H2B-GFP/+} mice are bred with germline Cre deleter mice, Pecam1^H2B-GFP/+ line is created with native nuclear GFP (H2B-GFP) expression in the endothelium of various organs. This dual reporter mouse provides us with a powerful genetic tool for definitive identification of endothelial cells and monitoring this important cell population throughout development, homeostasis, and disease conditions in mammals.

Serum CXCL13 and PECAM-1 can be used as diagnostic and prognostic markers in elderly patients with gastric cancer

PURPOSE

To investigate the application value of serum CXC Chemokine-13 (CXCL-13) and platelet endothelial cell adhesion molecule-1 (PECAM-1) in elderly patients with gastric cancer (GC).

METHODS

Ninety-eight elderly GC patients admitted to the Affiliated Hexian Memorial Hospital of Southern Medical University were selected as a research group, and 60 healthy subjects of the same age and in relatively good health who underwent physical examination at the same period were selected as a control group. Enzyme-linked immunosorbent assay (ELISA) was used to detect the levels of CXCL13 and PECAM-1 in serum. The clinical diagnosis and prognostic value of serum CXCL13 and PECAM-1 in elderly GC patients were analyzed.

RESULTS

The levels of CXCL13 and PECAM-1 in serum of the research group were significantly higher than those of the control group (P < 0.001). The AUC value of combined diagnosis of elderly GC patients by serum CXCL13 and PECAM-1 was 0.950, and that of combined evaluation of prognosis of patients was 0.849. Serum CXCL13 and PECAM-1 were significantly related to TNM staging, differentiation degree and tumor diameter in elderly GC patients (P < 0.05). High levels of CXCL13 and PECAM-1 were significantly associated with lower 5-year OS (P < 0.05).

CONCLUSION

Elderly GC patients with higher TNM staging, longer tumor diameters, high levels of CXCL13 and PECAM-1 had an increased risk of poor prognosis. Serum CXCL13 and PECAM-1 can be used as effective indicators for diagnosis and prognosis of elderly patients with GC, and can predict the 5-year OS in patients.

CD31 as a Therapeutic Target in Atherosclerosis

The potential of CD31 as a therapeutic target in atherosclerosis has been considered ever since its cloning in the 1990s, but the exact role played by this molecule in the biologic events underlying atherosclerosis has remained controversial, resulting in the stalling of any therapeutic perspective. Due to the supposed cell adhesive properties of CD31, specific monoclonal antibodies and recombinant proteins were regarded as blocking agents because their use prevented the arrival of leukocytes at sites of acute inflammation. However, the observed effect of those compounds likely resulted from the engagement of the immunomodulatory function of CD31 signaling. This was acknowledged only later though, upon the discovery of CD31's 2 intracytoplasmic tyrosine residues called immunoreceptor tyrosine inhibitory motifs. A growing body of evidence currently points at a therapeutic potential for CD31 agonists in atherothrombosis. Clinical observations show that CD31 expression is altered at the surface of leukocytes infiltrating unhealed atherothrombotic lesions and that the physiological immunomodulatory functions of CD31 are lost at the surface of blood leukocytes in patients with acute coronary syndromes. On the contrary, translational studies using candidate therapeutic molecules in laboratory animals have provided encouraging results: synthetic peptides administered to atherosclerotic mice as systemic drugs in the acute phases of atherosclerotic complications favor the healing of wounded arteries, whereas the immobilization of CD31 agonist peptides onto coronary stents implanted in farm pigs favors their peaceful integration within the coronary arterial wall.

Soluble platelet endothelial cell adhesion molecule 1 (sPECAM-1) improves diagnostic accuracy of D-Dimer in patients with suspected deep vein thrombosis (DVT)

D-Dimer has a high sensitivity but a low specificity for the diagnosis of deep vein thrombosis (DVT) which limits its implementation as a general screening parameter. There is a demand for additional biomarkers to improve its diagnostic accuracy. Soluble platelet endothelial cell adhesion molecule 1 (sPECAM-1) is generated at the site of venous thrombosis, thus, represents a promising biomarker. Patients with clinically suspected DVT (N = 159) were prospectively recruited and underwent manual compression ultrasonography (CCUS) to confirm or exclude DVT. The diagnostic value of D-Dimer, sPECAM-1 and the combination of both was assessed. sPECAM-1 levels were significantly higher in patients with DVT (N = 44) compared to patients without DVT (N = 115) (85.9 [76.1/98.0] ng/mL versus 68.0 [50.1/86.0] ng/mL; p < 0.001) with a diagnostic sensitivity of 100% and a specificity of 28.7% at the cut point > 50.2 ng/mL. sPECAM-1 improved the diagnostic accuracy of D-Dimer: the combination of both biomarkers yielded a ROC-AUC of 0.925 compared to 0.905 for D-Dimer alone and 0.721 for sPECAM-1 alone with a reduction of false-positive D-Dimer cases 72- > 43 (Δ =  − 31.9%). The discrimination mainly occurred in a subgroup of patients characterized by an inflammatory background (defined by c-reactive protein level > 1 mg/mL). sPECAM-1 represents a novel diagnostic biomarker for venous thrombosis. It does not qualify as a diagnostic biomarker alone but improves the diagnostic accuracy of D-Dimer in patients with suspected DVT.

Novel inhibitors of leukocyte transendothelial migration

Leukocyte transendothelial migration is one of the most important step in launching an inflammatory immune response and chronic inflammation can lead to devastating diseases. Leukocyte migration inhibitors are considered as promising and potentially effective therapeutic agents to treat inflammatory and auto-immune disorders. In this study, based on previous trioxotetrahydropyrimidin based integrin inhibitors that suboptimally blocked leukocyte adhesion, twelve molecules with a modified scaffold were designed, synthesized, and tested in vitro for their capacity to block the transendothelial migration of immune cells. One of the molecules, namely, methyl 4-((2-(tert-butyl)-6-((2,4,6-trioxotetrahydropyrimidin-5(2H)-ylidene) methyl) phenoxy) methyl) benzoate, (compound 12), completely blocked leukocyte transendothelial migration, without any toxic effects on immune or endothelial cells (IC₅₀ = 2.4 µM). In vivo, compound 12 exhibited significant therapeutic effects in inflammatory bowel disease (IBD)/Crohn's disease, multiple sclerosis, fatty liver disease, and rheumatoid arthritis models. A detailed acute and chronic toxicity profile of the lead compound in vivo did not reveal any toxic effects. Such a type of molecule might therefore provide a unique starting point for designing a novel class of leukocyte transmigration blocking agents with broad therapeutic applications in inflammatory and auto-immune pathologies.

Development of A New Mouse Model for Intrahepatic Cholangiocellular Carcinoma: Accelerating Functions of Pecam-1

Due to the lack of suitable in-vivo models, the etiology of intrahepatic cholangiocellular carcinoma (ICC) is poorly understood. We previously showed the involvement of platelet endothelial cell adhesion molecule-1 (Pecam-1/CD31) in acute liver damage. Here, we developed a model of ICC using thioacetamide (TAA) in drinking water of wild-type (WT)-mice and Pecam-1-knock-out (KO)-mice. Gross inspection and microscopy revealed liver-cirrhosis and ICC in both groups after 22 weeks of TAA. The severity of cirrhosis and ICC (Ck-19-positive) was reduced in Pecam-1 KO mice (stage-4 cirrhosis in WT vs. stage-3 in KO mice). Tumor networks (accompanied by neutrophils) were predominantly located in portal areas, with signs of epithelial-to-mesenchymal transition (EMT). In serum, TAA induced an increase in hepatic damage markers, with lower levels in Pecam-1 null mice. With qPCR of liver, elevated expression of Pecam-1 mRNA was noted in WT mice, in addition to Icam-1, EpCam, cytokines, cMyc, and Mmp2. Thereby, levels of EpCAM, cytokines, cMyc, and Mmp2 were significantly lower in Pecam-1 null mice. Lipocalin-2 and Ccl5 were elevated significantly in both WT and Pecam-1 null mice after TAA administration. Also, EMT marker Wnt5a (not Twist-1) was increased in both groups after TAA. We present a highly reproducible mouse model for ICC and show protective effects of Pecam-1 deficiency.

Glycosylation in the Tumor Microenvironment: Implications for Tumor Angiogenesis and Metastasis

Just as oncogene activation and tumor suppressor loss are hallmarks of tumor development, emerging evidence indicates that tumor microenvironment-mediated changes in glycosylation play a crucial functional role in tumor progression and metastasis. Hypoxia and inflammatory events regulate protein glycosylation in tumor cells and associated stromal cells in the tumor microenvironment, which facilitates tumor progression and also modulates a patient's response to anti-cancer therapeutics. In this review, we highlight the impact of altered glycosylation on angiogenic signaling and endothelial cell adhesion, and the critical consequences of these changes in tumor behavior.

Mechanotransduction, immunoregulation, and metabolic functions of CD31 in cardiovascular pathophysiology

Biomechanical changes in the heart and vessels drive rapid and dynamic regulation of blood flow, a vital process for meeting the changing metabolic needs of the peripheral tissues at any given point in time. The fluid movement of the blood exerts haemodynamic stress upon the solid elements of the cardiovascular system: the heart, vessels, and cellular components of the blood. Cardiovascular diseases can lead to prolonged mechanical stress, such as cardiac remodelling during heart failure or vascular stiffening in atherosclerosis. This can lead to a significantly reduced or increasingly turbulent blood supply, inducing a shift in cellular metabolism that, amongst other effects, can trigger the release of reactive oxygen species and initiate a self-perpetuating cycle of inflammation and oxidative stress. CD31 is the most abundant constitutive co-signalling receptor glycoprotein on endothelial cells, which line the cardiovascular system and form the first-line of cellular contact with the blood. By associating with most endothelial receptors involved in mechanosensing, CD31 regulates the response to biomechanical stimuli. In addition, by relocating in the lipid rafts of endothelial cells as well as of cells stably interacting with the endothelium, including leucocytes and platelets, CD31–CD31 trans-homophilic engagement guides and restrains platelet and immune cell accumulation and activation and at sites of damage. In this way, CD31 is at the centre of mediating mechanical, metabolic, and immunological changes within the circulation and provides a single target that may have pleiotropic beneficial effects.

Allicin improves the function of cardiac microvascular endothelial cells by increasing PECAM-1 in rats with cardiac hypertrophy

OBJECTIVE

Cardiac microvascular damage is significantly associated with the development of cardiac hypertrophy (CH). Researchers found that allicin could inhibit CH, but the relationship between cardiac microvessel and the inhibition of allicin on CH has not been reported. We aimed to investigate the effect of allicin on the function of cardiac microvascular endothelial cells (CMECs) in CH rat.

MATERIALS AND METHODS

The hemodynamic parameters were measured by BL-420F biological function experimental system and the indicators of the ventricular structure and function were measured by echocardiographic system. MTT assay was performed to assess the cell viability. Nitrite detection was performed to detect nitric oxide content. The morphology and molecular characteristics were detected by electron micrographs, immunofluorescence, quantitative real-time polymerase chain reaction (qRT-PCR), western blot. Wound healing experiment, analysis of tube formation and shear adaptation were performed to assess CMECs migration ability, angiogenesis and shear-responsiveness respectively.

RESULT

Our findings have identified that microvascular density was decreased by observing the expression of platelet endothelial cell adhesion molecule-1 (PECAM-1) in CH rats. Interestingly, allicin improved the distribution and expression of PECAM-1. Meanwhile, allicin enhanced the migration and angiogenesis ability of CMECs, activated PECAM-1-PI3K-AKT-eNOS signaling pathway, however, the role of allicin was disappear after PECAM-1 was silenced. Allicin decreased the expression of caspase-3 and receptor interacting protein 3 (RIP3), inhibited necroptosis, and increased the levels of Angiopoietin-2 (Ang-2) and platelet-derived growth factor receptor-β (PDGFR-β). Under 10 dyn/cm² condition, allicin advanced the modification ability of CMECs's shear-adaptation by activating PECAM-1.

CONCLUSION

Allicin provided cardioprotection for CH rats by improving the function of CMECs through increasing the expression of PECAM-1.

Application of medical adhesive inhibits intimal hyperplasia involving the downregulation of ERK1/2 and eNOS levels

Vein graft remains the most broadly applied vascular material in coronary artery bypass surgery. However, the restenosis rate of the vein bridge following angioplasty is high. The present study investigated the effect of medical adhesive on vascular intimal hyperplasia, in addition to the signal transduction mechanism. A total of 36 New Zealand white rabbits were divided into three groups at random, including the normal group, the surgery group and the medical adhesive spray group. Following surgery for transplantation of the left external jugular vein to the ipsilateral common carotid artery for 4 weeks, the thickness and area of the intima and media of the vessel were measured on formalin‑fixed, paraffin wax‑embedded pathological sections using hematoxylin‑eosin staining, and alterations in the expression of proliferating cell nuclear antigen (PCNA), platelet endothelial cell adhesion molecule 1 (PECAM‑1), vascular cell adhesion protein 1 (VCAM‑1), extracellular signal‑regulated kinase (ERK)1/2, and endothelial nitric oxide synthase (eNOS) were detected by immunohistochemical staining, reverse transcription‑quantitative polymerase chain reaction analysis and western blotting. The levels of intimal hyperplasia in the medical adhesive spray group were markedly decreased compared with the surgery group. Consistently, PCNA, PECAM‑1 and VCAM‑1 were underexpressed in the medical adhesive spray group compared with the surgery group. ERK1/2 and eNOS were underexpressed in the medical adhesive spray group compared with the surgery group. Therefore, the application of medical adhesive may inhibit intimal hyperplasia, which may be associated with the restriction of the over‑distension of the vein graft by downregulating the ERK1/2 and eNOS levels, reducing injury to the vascular intima and inhibiting the signaling pathway involved in intimal hyperplasia.

Involvement of TIMP-1 in PECAM-1-mediated tumor dissemination

Platelet endothelial cell adhesion molecule-1 (PECAM-1) is expressed on the vascular endothelium and has been implicated in the late progression of metastatic tumors. The activity of PECAM-1 appears to be mediated by modulation of the tumor microenvironment (TME) and promotion of tumor cell proliferation, rather than through the stimulation of tumor angiogenesis. The present study aimed to extend those initial findings by indicating that the presence of functional PECAM-1 on the endothelium promotes a proliferative tumor cell phenotype in vivo, as well as in tumor cell (B16-F10 melanoma and 4T1 breast cancer cell lines) co-culture assays with mouse endothelial cells (ECs) or a surrogate EC line (REN-MP). The pro-proliferative effects were mediated by soluble endothelial-derived factors that were dependent on PECAM-1 homophilic ligand interactions, but which were independent of PECAM-1-dependent signaling. Further analysis of the conditioned media obtained from tumor/EC and tumor/REN-MP co-cultures identified TIMP metallopeptidase inhibitor-1 (TIMP-1) as a PECAM-1-regulated factor, the targeting of which in the tumor cell/REN-MP system inhibited tumor cell proliferation. In addition, TIMP-1 expression was decreased in metastatic tumors from the lungs of PECAM-1-null mice, thus providing evidence of the in vivo significance of co-culture studies. Taken together, these studies indicated that endothelial PECAM-1, through PECAM-1-dependent homophilic binding interactions, may induce release of TIMP-1 from the endothelium into the TME, thus leading to increased tumor cell proliferation.

Matrilysin/MMP-7 Cleavage of Perlecan/HSPG2 Complexed with Semaphorin 3A Supports FAK-Mediated Stromal Invasion by Prostate Cancer Cells

Interrupting the interplay between cancer cells and extracellular matrix (ECM) is a strategy to halt tumor progression and stromal invasion. Perlecan/heparan sulfate proteoglycan 2 (HSPG2) is an extracellular proteoglycan that orchestrates tumor angiogenesis, proliferation, differentiation and invasion. Metastatic prostate cancer (PCa) cells degrade perlecan-rich tissue borders to reach bone, including the basement membrane, vasculature, reactive stromal matrix and bone marrow. Domain IV-3, perlecan’s last 7 immunoglobulin repeats, mimics native proteoglycan by promoting tumoroid formation. This is reversed by matrilysin/matrix metalloproteinase-7 (MMP-7) cleavage to favor cell dispersion and tumoroid dyscohesion. Both perlecan and Domain IV-3 induced a strong focal adhesion kinase (FAK) dephosphorylation/deactivation. MMP-7 cleavage of perlecan reversed this, with FAK in dispersed tumoroids becoming phosphorylated/activated with metastatic phenotype. We demonstrated Domain IV-3 interacts with the axon guidance protein semaphorin 3A (Sema3A) on PCa cells to deactivate pro-metastatic FAK. Sema3A antibody mimicked the Domain IV-3 clustering activity. Direct binding experiments showed Domain IV-3 binds Sema3A. Knockdown of Sema3A prevented Domain IV-3-induced tumoroid formation and Sema3A was sensitive to MMP-7 proteolysis. The perlecan-Sema3A complex abrogates FAK activity and stabilizes PCa cell interactions. MMP-7 expressing cells destroy the complex to initiate metastasis, destroy perlecan-rich borders, and favor invasion and progression to lethal bone disease.

Glycosylation controls cooperative PECAM-VEGFR2-β3 integrin functions at the endothelial surface for tumor angiogenesis

Most of the angiogenesis inhibitors clinically used in cancer treatment target the vascular endothelial growth factor (VEGF)/VEGF receptor (VEGFR) pathway. However, the current strategies for treating angiogenesis have limited efficacy. The issue of how to treat angiogenesis and endothelial dysfunction in cancer remains a matter of substantial debate. Here we demonstrate a glycosylation-dependent regulatory mechanism for tumor angiogenesis. St6gal1^-/- mice, lacking the α2,6-sialylation enzyme, were shown to exhibit impaired tumor angiogenesis through enhanced endothelial apoptosis. In a previous study, St6gal1^-/- endothelial cells exhibited a reduction in the cell surface residency of platelet endothelial cell adhesion molecule (PECAM). In this study, we found that cooperative functionality of PECAM-VEGFR2-integrin β3 was disturbed in St6gal1^-/- mice. First, cell surface PECAM-VEGFR2 complexes were lost, and both VEGFR2 internalization and the VEGFR-dependent signaling pathway were enhanced. Second, enhanced anoikis was observed, suggesting that the absence of α2,6-sialic acid leads to dysregulated integrin signaling. Notably, ectopic expression of PECAM increased cell surface integrin-β3, indicating that the reduction of cell surface integrin-β3 involves loss-of-endothelial PECAM. The results suggest that the cell surface stability of these glycoproteins is significantly reduced by the lack of α2,6-sialic acid, leading to abnormal signal transduction. The present findings highlight that α2,6-sialylation is critically involved in endothelial survival by controlling the cell surface stability and signal transduction of angiogenic molecules, and could be a novel target for anti-angiogenesis therapy.

Negative regulators of platelet activation and adhesion

Platelets are small anucleated cells that constantly patrol the cardiovascular system to preserve its integrity and prevent excessive blood loss where the vessel lining is breached. Their key challenge is to form a hemostatic plug under conditions of high shear forces. To do so, platelets have evolved a molecular machinery that enables them to sense trace amounts of signals at the site of damage and to rapidly shift from a non-adhesive to a pro-adhesive state. However, this highly efficient molecular machinery can also lead to unintended platelet activation and cause clinical complications such as thrombocytopenia and thrombosis. Thus, several checkpoints are in place to tightly control platelet activation and adhesiveness in space and time. In this review, we will discuss select negative regulators of platelet activation, which are critical to maintain patrolling platelets in a quiescent, non-adhesive state and/or to limit platelet adhesion to sites of injury.

CRISPR-mediated deletion of the PECAM-1 cytoplasmic domain increases receptor lateral mobility and strengthens endothelial cell junctional integrity

AIMS

PECAM-1 is an abundant endothelial cell surface receptor that becomes highly enriched at endothelial cell-cell junctions, where it functions to mediate leukocyte transendothelial migration, sense changes in shear and flow, and maintain the vascular permeability barrier. Homophilic interactions mediated by the PECAM-1 extracellular domain are known to be required for PECAM-1 to perform these functions; however, much less is understood about the role of its cytoplasmic domain in these processes.

MAIN METHODS

CRISPR/Cas9 gene editing technology was employed to generate human endothelial cell lines that either lack PECAM-1 entirely, or express mutated PECAM-1 missing the majority of its cytoplasmic domain (∆CD-PECAM-1). The endothelial barrier function was evaluated by Electric Cell-substrate Impedance Sensing, and molecular mobility was assessed by fluorescence recovery after photobleaching.

KEY FINDINGS

We found that ∆CD-PECAM-1 concentrates normally at endothelial cell junctions, but has the unexpected property of conferring increased baseline barrier resistance, as well as a more rapid rate of recovery of vascular integrity following thrombin-induced disruption of the endothelial barrier. Fluorescence recovery after photobleaching analysis revealed that ∆CD-PECAM-1 exhibits increased mobility within the plane of the plasma membrane, thus allowing it to redistribute more rapidly back to endothelial cell-cell borders to reform the vascular permeability barrier.

SIGNIFICANCE

The PECAM-1 cytoplasmic domain plays a novel role in regulating the rate and extent of vascular permeability following thrombotic or inflammatory challenge.

Platelet Endothelial Cell Adhesion Molecule-1 and Oligodendrogenesis: Significance in Alcohol Use Disorders

Alcoholism is a chronic relapsing disorder with few therapeutic strategies that address the core pathophysiology. Brain tissue loss and oxidative damage are key components of alcoholism, such that reversal of these phenomena may help break the addictive cycle in alcohol use disorder (AUD). The current review focuses on platelet endothelial cell adhesion molecule 1 (PECAM-1), a key modulator of the cerebral endothelial integrity and neuroinflammation, and a targetable transmembrane protein whose interaction within AUD has not been well explored. The current review will elaborate on the function of PECAM-1 in physiology and pathology and infer its contribution in AUD neuropathology. Recent research reveals that oligodendrocytes, whose primary function is myelination of neurons in the brain, are a key component in new learning and adaptation to environmental challenges. The current review briefly introduces the role of oligodendrocytes in healthy physiology and neuropathology. Importantly, we will highlight the recent evidence of dysregulation of oligodendrocytes in the context of AUD and then discuss their potential interaction with PECAM-1 on the cerebral endothelium.

ITIM receptors: more than just inhibitors of platelet activation

Since their discovery, immunoreceptor tyrosine-based inhibition motif (ITIM)-containing receptors have been shown to inhibit signaling from immunoreceptor tyrosine-based activation motif (ITAM)-containing receptors in almost all hematopoietic cells, including platelets. However, a growing body of evidence has emerged demonstrating that this is an oversimplification, and that ITIM-containing receptors are versatile regulators of platelet signal transduction, with functions beyond inhibiting ITAM-mediated platelet activation. PECAM-1 was the first ITIM-containing receptor identified in platelets and appeared to conform to the established model of ITIM-mediated attenuation of ITAM-driven activation. PECAM-1 was therefore widely accepted as a major negative regulator of platelet activation and thrombosis for many years, but more recent findings suggest a more complex role for this receptor, including the facilitation of α_IIbβ₃-mediated platelet functions. Since the identification of PECAM-1, several other ITIM-containing platelet receptors have been discovered. These include G6b-B, a critical regulator of platelet reactivity and production, and the noncanonical ITIM-containing receptor TREM-like transcript-1, which is localized to α-granules in resting platelets, binds fibrinogen, and acts as a positive regulator of platelet activation. Despite structural similarities and shared binding partners, including the Src homology 2 domain-containing protein-tyrosine phosphatases Shp1 and Shp2, knockout and transgenic mouse models have revealed distinct phenotypes and nonredundant functions for each ITIM-containing receptor in the context of platelet homeostasis. These roles are likely influenced by receptor density, compartmentalization, and as-yet unknown binding partners. In this review, we discuss the diverse repertoire of ITIM-containing receptors in platelets, highlighting intriguing new functions, controversies, and future areas of investigation.

Mechanism of Collaborative Enhancement of Binding of Paired Antibodies to Distinct Epitopes of Platelet Endothelial Cell Adhesion Molecule-1

Monoclonal antibodies (mAbs) directed to extracellular epitopes of human and mouse Platelet Endothelial Cell Adhesion Molecule-1 (CD31 or PECAM-1) stimulate binding of other mAbs to distinct adjacent PECAM-1 epitopes. This effect, dubbed Collaborative Enhancement of Paired Affinity Ligands, or CEPAL, has been shown to enhance delivery of mAb-targeted drugs and nanoparticles to the vascular endothelium. Here we report new insights into the mechanism underlying this effect, which demonstrates equivalent amplitude in the following models: i) cells expressing a full length PECAM-1 and mutant form of PECAM-1 unable to form homodimers; ii) isolated fractions of cellular membranes; and, iii) immobilized recombinant PECAM-1. These results indicate that CEPAL is mediated not by interference in cellular functions or homophilic PECAM-1 interactions, but rather by conformational changes within the cell adhesion molecule induced by ligand binding. This mechanism, mediated by exposure of partially occult epitopes, is likely to occur in molecules other than PECAM-1 and may represent a generalizable phenomenon with valuable practical applications.

Endothelial functions of platelet/endothelial cell adhesion molecule-1 (CD31)

PURPOSE OF REVIEW

The purpose of this article is to describe the function of the vascular cell adhesion and signaling molecule, platelet/endothelial cell adhesion molecule-1 (PECAM-1), in endothelial cells, with special emphasis on its role in maintaining and restoring the vascular permeability barrier following disruption of the endothelial cell junction.

RECENT FINDINGS

In addition to its role as an inhibitory receptor in circulating platelets and leukocytes, PECAM-1 is highly expressed at endothelial cell-cell junctions, where it functions as an adhesive stress-response protein to both maintain endothelial cell junctional integrity and speed restoration of the vascular permeability barrier following inflammatory or thrombotic challenge.

SUMMARY

Owing to the unique ability of antibodies that bind the membrane proximal region of the extracellular domain to trigger conformational changes leading to affinity modulation and homophilic adhesion strengthening, PECAM-1 might be an attractive target for treating vascular permeability disorders.

Structural Basis for Human PECAM-1-Mediated Trans-homophilic Cell Adhesion

Cell adhesion involved in signal transduction, tissue integrity and pathogen infection is mainly mediated by cell adhesion molecules (CAM). One CAM member, platelet–endothelial-cell adhesion molecule-1 (PECAM-1), plays an important role in tight junction among endothelia cells, leukocyte trafficking, and immune response through its homophilic and heterophilic binding patterns. Both kinds of interactions, which lead to endogenous and exogenous signal transmission, are derived from extracellular immunoglobulin-like (IgL) domains and cytoplasmic immunoreceptor tyrosine-based inhibitory motifs (ITIMs) of PECAM-1. To date, the mechanism of trans-homophilic interaction of PECAM-1 remains unclear. Here, we present the crystal structure of PECAM-1 IgL1-2 trans-homo dimer. Both IgL 1 and 2 adopt the classical Ig domain conformation comprised of two layers of β-sheets possessing antiparallel β-strands with each being anchored by a pair of cysteines forming a disulfide bond. The dimer interface includes hydrophobic and hydrophilic interactions. The Small-Angle X-ray Scattering (SAXS) envelope of PECAM-1 IgL1-6 supported such a dimer formation in solution. Cell adhesion assays on wildtype and mutant PECAM-1 further characterized the structural determinants in cell junction and communication.

The Role of Sialylated Glycans in Human Platelet Endothelial Cell Adhesion Molecule 1 (PECAM-1)-mediated Trans Homophilic Interactions and Endothelial Cell Barrier Function

Platelet Endothelial Cell Adhesion Molecule 1 (PECAM-1) is a major component of the endothelial cell intercellular junction. Previous studies have shown that PECAM-1 homophilic interactions, mediated by amino-terminal immunoglobulin homology domain 1, contribute to maintenance of the vascular permeability barrier and to its re-establishment following inflammatory or thrombotic insult. PECAM-1 glycans account for ∼30% of its molecular mass, and the newly solved crystal structure of human PECAM-1 immunoglobulin homology domain 1 reveals that a glycan emanating from the asparagine residue at position 25 (Asn-25) is located within the trans homophilic-binding interface, suggesting a role for an Asn-25-associated glycan in PECAM-1 homophilic interactions. In support of this possibility, unbiased molecular docking studies revealed that negatively charged α2,3 sialic acid moieties bind tightly to a groove within the PECAM-1 homophilic interface in an orientation that favors the formation of an electrostatic bridge with positively charged Lys-89, mutation of which has been shown previously to disrupt PECAM-1-mediated homophilic binding. To verify the contribution of the Asn-25 glycan to endothelial barrier function, we generated an N25Q mutant form of PECAM-1 that is not glycosylated at this position and examined its ability to contribute to vascular integrity in endothelial cell-like REN cells. Confocal microscopy showed that although N25Q PECAM-1 concentrates normally at cell-cell junctions, the ability of this mutant form of PECAM-1 to support re-establishment of a permeability barrier following disruption with thrombin was significantly compromised. Taken together, these data suggest that a sialic acid-containing glycan emanating from Asn-25 reinforces dynamic endothelial cell-cell interactions by stabilizing the PECAM-1 homophilic binding interface.