Cellular fibronectin containing extra domain A promotes arterial thrombosis in mice through platelet Toll-like receptor 4

Myocardial ischemia-reperfusion injury released cellular fibronectin containing domain A (CFN-EDA): A destructive positive loop amplifying arterial thrombosis formation and exacerbating myocardial reperfusion injury

Previous research has identified intravascular platelet thrombi in regions affected by myocardial ischemia-reperfusion (MI/R) injury and neighbouring areas. However, the occurrence of arterial thrombosis in the context of MI/R injury remains unexplored. This study utilizes intravital microscopy to investigate carotid artery thrombosis during MI/R injury in rats, establishing a connection with the presence of prothrombotic cellular fibronectin containing extra domain A (CFN-EDA) protein. Additionally, the study examines samples from patients with coronary artery disease (CAD) both before and after coronary artery bypass grafting (CABG). Levels of CFN-EDA significantly increase following MI with further elevation observed following reperfusion of the ischemic myocardium. Thrombotic events, such as thrombus formation and growth, show a significant increase, while the time to complete cessation of blood flow in the carotid artery significantly decreases following MI/R injury induced by ferric chloride. The acute infusion of purified CFN-EDA protein accelerates in-vivo thrombotic events in healthy rats and significantly enhances in-vitro adenosine diphosphate and collagen-induced platelet aggregation. Treatment with anti-CFN-EDA antibodies protected the rat against MI/R injury and significantly improved cardiac function as evidenced by increased end-systolic pressure-volume relationship slope and preload recruitable stroke work compared to control. Similarly, in a human study, plasma CFN-EDA levels were notably elevated in CAD patients undergoing CABG. Post-surgery, these levels continued to rise over time, alongside cardiac injury biomarkers such as cardiac troponin and B-type natriuretic peptide. The study highlights that increased CFN-EDA due to CAD or MI initiates a destructive positive feedback loop by amplifying arterial thrombus formation, potentially exacerbating MI/R injury.

Targeting Neutrophil α9 Improves Functional Outcomes After Stroke in Mice With Obesity-Induced Hyperglycemia

BACKGROUND

Obesity-induced hyperglycemia is a significant risk factor for stroke. Integrin α9β1 is expressed on neutrophils and stabilizes adhesion to the endothelium via ligands, including Fn-EDA (fibronectin containing extra domain A) and tenascin C. Although myeloid deletion of α9 reduces susceptibility to ischemic stroke, it is unclear whether this is mediated by neutrophil-derived α9. We determined the role of neutrophil-specific α9 in stroke outcomes in a mice model with obesity-induced hyperglycemia.

METHODS

α9Neu-KO (α9fl/flMRP8Cre+) and littermate control α9WT (α9fl/flMRP8Cre-) mice were fed on a 60% high-fat diet for 20 weeks to induce obesity-induced hyperglycemia. Functional outcomes were evaluated up to 28 days after stroke onset in mice of both sexes using a transient (30 minutes) middle cerebral artery ischemia. Infarct volume (magnetic resonance imaging) and postreperfusion thrombo-inflammation (thrombi, fibrin, neutrophil, phospho-nuclear factor kappa B [p-NFκB], TNF [tumor necrosis factor]-α, and IL [interleukin]-1β levels, markers of neutrophil extracellular traps) were measured post 6 or 48 hours of reperfusion. In addition, functional outcomes (modified Neurological Severity Score, rota-rod, corner, and wire-hanging test) were measured for up to 4 weeks.

RESULTS

Stroke upregulated neutrophil α9 expression more in obese mice (P<0.05 versus lean mice). Irrespective of sex, deletion of neutrophil α9 improved functional outcomes up to 4 weeks, concomitant with reduced infarct, improved cerebral blood flow, decreased postreperfusion thrombo-inflammation, and neutrophil extracellular traps formation (NETosis) (P<0.05 versus α9WT obese mice). Obese α9Neu-KO mice were less susceptible to thrombosis in FeCl3 injury-induced carotid thrombosis model. Mechanistically, we found that α9/cellular fibronectin axis contributes to NETosis via ERK (extracellular signal-regulated kinase) and PAD4 (peptidyl arginine deiminase 4), and neutrophil α9 worsens stroke outcomes via cellular fibronectin-EDA but not tenascin C. Obese wild-type mice infused with anti-integrin α9 exhibited improved functional outcomes up to 4 weeks (P<0.05 versus vehicle).

CONCLUSIONS

Genetic ablation of neutrophil-specific α9 or pharmacological inhibition improves long-term functional outcomes after stroke in mice with obesity-induced hyperglycemia, most likely by limiting thrombo-inflammation.

Development potential of extracellular matrix hydrogels as hemostatic materials

The entry of subcutaneous extracellular matrix proteins into the circulation is a key step in hemostasis initiation after vascular injury. However, in cases of severe trauma, extracellular matrix proteins are unable to cover the wound, making it difficult to effectively initiate hemostasis and resulting in a series of bleeding events. Acellular-treated extracellular matrix (ECM) hydrogels are widely used in regenerative medicine and can effectively promote tissue repair due to their high mimic nature and excellent biocompatibility. ECM hydrogels contain high concentrations of extracellular matrix proteins, including collagen, fibronectin, and laminin, which can simulate subcutaneous extracellular matrix components and participate in the hemostatic process. Therefore, it has unique advantages as a hemostatic material. This paper first reviewed the preparation, composition and structure of extracellular hydrogels, as well as their mechanical properties and safety, and then analyzed the hemostatic mechanism of the hydrogels to provide a reference for the application and research, and development of ECM hydrogels in the field of hemostasis.

Fibronectin extra domain a limits liver dysfunction and protects mice during acute inflammation

Background and aim

The primary transcript of fibronectin (FN) undergoes alternative splicing to generate different isoforms, including FN containing the Extra Domain A (FN_EDA+), whose expression is regulated spatially and temporarily during developmental and disease conditions including acute inflammation. The role of FN_EDA+ during sepsis, however, remains elusive.

Methods

Mice constitutively express the EDA domain of fibronectin (EDA^+/+); lacking the FN EDA domain (EDA^-/-) or with a conditional ablation of EDA + inclusion only in liver produced FN (alb-CRE⁺EDA floxed mice) thus expressing normal plasma FN were used. Systemic inflammation and sepsis were induced by either LPS injection (70 mg/kg) or by cecal ligation and puncture (CLP) Neutrophils isolated from septic patients were tested for neutrophil binding ability.

Results

We observed that EDA^+/+ were protected toward sepsis as compared to EDA^-/- mice. Also alb-CRE⁺EDA floxed mice presented reduced survival, thus indicating a key role for EDA in protecting toward sepsis. This phenotype was associated with improved liver and spleen inflammatory profile. Ex vivo experiments showed that neutrophils bind to a larger extent to an FN_EDA + coated surface as compared to FN, thus potentially limiting their over-reactivity.

Conclusions

Our study demonstrates that the inclusion of the EDA domain in fibronectin dampens the nflammatoryi consequences of sepsis.

Role of neutrophil extracellular traps in inflammatory evolution in severe acute pancreatitis

ABSTRACT

Severe acute pancreatitis (SAP) is a life-threatening acute abdominal disease with two peaks of death: the first in the early stage, characterized by systemic inflammatory response-associated organ failure; and the second in the late stage, characterized by infectious complications. Neutrophils are the main immune cells participating in the whole process of SAP. In addition to the traditional recognition of neutrophils as the origination of chemokine and cytokine cascades or phagocytosis and degranulation of pathogens, neutrophil extracellular traps (NETs) also play an important roles in inflammatory reactions. We reviewed the role of NETs in the occurrence and development of SAP and its fatal complications, including multiple organs injury, infected pancreatic necrosis, and thrombosis. This review provides novel insights into the involvement of NETs throughout the entire process of SAP, showing that targeting NETs might be a promising strategy in SAP treatment. However, precision therapeutic options targeting NETs in different situations require further investigation.

PD-L1 blockade liberates intrinsic antitumourigenic properties of glycolytic macrophages in hepatocellular carcinoma

OBJECTIVE

Patients with increased PD-L1⁺ host cells in tumours are more potent to benefit from antiprogrammed death-1/programmed death ligand-1 (PD-L1) treatment, but the underlying mechanism is still unclear. We aim to elucidate the nature, regulation and functional relevance of PD-L1⁺ host cells in hepatocellular carcinoma (HCC).

DESIGN

A total of untreated 184 HCC patients was enrolled randomly. C57BL/6 mice are given injection of Hepa1-6 cells to form autologous hepatoma. ELISpot, flow cytometry and real-time PCR are applied to analyse the phenotypic characteristics of PD-L1⁺ cells isolated directly from HCC specimens paired with blood samples or generated from ex vivo and in vitro culture systems. Immunofluorescence and immunohistochemistry are performed to detect the presence of immune cells on paraffin-embedded and formalin-fixed samples. The underlying regulatory mechanisms of metabolic switching are assessed by both in vitro and in vivo studies.

RESULTS

We demonstrate that PD-L1⁺ host macrophages, which constructively represent the major cellular source of PD-L1 in HCC tumours, display an HLA-DR^highCD86^high glycolytic phenotype, significantly produce antitumourigenic IL-12p70 and are polarised by intrinsic glycolytic metabolism. Mechanistically, a key glycolytic enzyme PKM2 triggered by hepatoma cell derived fibronectin 1, via a HIF-1α-dependent manner, concurrently controls the antitumourigenic properties and inflammation-mediated PD-L1 expression in glycolytic macrophages. Importantly, although increased PKM2⁺ glycolytic macrophages predict poor prognosis of patients, blocking PD-L1 on these cells eliminates PD-L1-dominant immunosuppression and liberates intrinsic antitumourigenic properties.

CONCLUSIONS

Selectively modulating the 'context' of glycolytic macrophages in HCC tumours might restore their antitumourigenic properties and provide a precise strategy for anticancer therapy.

Gut microbiota in ischemic stroke: Where we stand and challenges ahead

Gut microbiota is increasingly recognized to affect host health and disease, including ischemic stroke (IS). Here, we systematically review the current understanding linking gut microbiota as well as the associated metabolites to the pathogenesis of IS (e.g., oxidative stress, apoptosis, and neuroinflammation). Of relevance, we highlight that the implications of gut microbiota-dependent intervention could be harnessed in orchestrating IS.

A narrative review of circulating tumor cells clusters: A key morphology of cancer cells in circulation promote hematogenous metastasis

Circulating tumor cells (CTCs) that survive in the blood are playing an important role in the metastasis process of tumor. In addition, they have become a tool for tumor diagnosis, prognosis and recurrence monitoring. CTCs can exist in the blood as individual cells or as clumps of aggregated cells. In recent years, more and more studies have shown that clustered CTCs have stronger metastasis ability compared to single CTCs. With the deepening of studies, scholars have found that cancer cells can combine not only with each other, but also with non-tumor cells present in the blood, such as neutrophils, platelets, etc. At the same time, it was confirmed that non-tumor cells bound to CTCs maintain the survival and proliferation of cancer cells through a variety of ways, thus promoting the occurrence and development of tumor. In this review, we collected information on tumorigenesis induced by CTC clusters to make a summary and a discussion about them. Although CTC clusters have recently been considered as a key role in the transition process, many characteristics of them remain to be deeply explored. A detailed understanding of their vulnerability can prospectively pave the way for new inhibitors for metastasis.

Emerging roles of platelets in cancer biology and their potential as therapeutic targets

The main role of platelets is to control bleeding and repair vascular damage via thrombosis. They have also been implicated to promote tumor metastasis through platelet-tumor cell interactions. Platelet-tumor cell interactions promote tumor cell survival and dissemination in blood circulation. Tumor cells are known to induce platelet activation and alter platelet RNA profiles. Liquid biopsies based on tumor-educated platelet biomarkers can detect tumors and correlate with prognosis, personalized therapy, treatment monitoring, and recurrence prediction. Platelet-based strategies for cancer prevention and tumor-targeted therapy include developing drugs that target platelet receptors, interfere with the release of platelet particles, inhibit platelet-specific enzymes, and utilize platelet-derived “nano-platelets” as a targeted drug delivery platform for tumor therapy. This review elaborates on platelet-tumor cell interactions and the molecular mechanisms and discusses future research directions for platelet-based liquid biopsy techniques and platelet-targeted anti-tumor strategies.

Fibronectin Functions as a Selective Agonist for Distinct Toll-like Receptors in Triple-Negative Breast Cancer

The microenvironment of tumors is characterized by structural changes in the fibronectin matrix, which include increased deposition of the EDA isoform of fibronectin and the unfolding of the fibronectin Type III domains. The impact of these structural changes on tumor progression is not well understood. The fibronectin EDA (FnEDA) domain and the partially unfolded first Type III domain of fibronectin (FnIII-1c) have been identified as endogenous damage-associated molecular pattern molecules (DAMPs), which induce innate immune responses by serving as agonists for Toll-Like Receptors (TLRs). Using two triple-negative breast cancer (TNBC) cell lines MDA-MB-468 and MDA-MB-231, we show that FnEDA and FnIII-1c induce the pro-tumorigenic cytokine, IL-8, by serving as agonists for TLR5 and TLR2, the canonical receptors for bacterial flagellin and lipoprotein, respectively. We also find that FnIII-1c is not recognized by MDA-MB-468 cells but is recognized by MDA-MB-231 cells, suggesting a cell type rather than ligand specific utilization of TLRs. As IL-8 plays a major role in the progression of TNBC, these studies suggest that tumor-induced structural changes in the fibronectin matrix promote an inflammatory microenvironment conducive to metastatic progression.

Fibronectin containing alternatively spliced extra domain A interacts at the central and c-terminal domain of Toll-like receptor-4

Extra domain A of cellular fibronectin (FN-EDA) is known to cause insulin resistance, atherosclerosis, tissue fibrosis, ischemic stroke and exaggerated myocardial reperfusion injury through Toll-like receptor 4 (TLR4). However, the FN-EDA-TLR4 interacting site is not well established. Therefore, in-silico approaches have been used to study FN-EDA and TLR4 interactions at the interface. In the present study, molecular docking studies of FN-EDA with TLR4-myeloid differentiation factor 2 (MD2) heterodimer have been performed to unravel the FN-EDA-TLR4 interacting sequence. Furthermore, the modulatory role of FN-EDA adjacent domains FNIII(11) and FNIII(12) on its interaction with TLR4-MD2 was investigated. The results show that FN-EDA interacting sequence “SPEDGIRELF” selectively interacts with TLR4 directly near its central and C-terminal domain region. The regulatory domains, FN type III 11 facilitate and 12 impede the FN-EDA-TLR4 interaction. Furthermore, the molecular dynamic simulation studies confirmed that FN-EDA forms a stable complex with TLR4-MD2 heterodimer. In conclusion, FN-EDA interacts and forms a stable complex through its “SPEDGIRELF” sequence at the central and C-terminal domain region of TLR4. The revelation of FN-EDA and TLR4 interacting sites may help design novel therapeutics for drug discovery research.

Platelet Innate Immune Receptors and TLRs: A Double-Edged Sword

Platelets are hematopoietic cells whose main function has for a long time been considered to be the maintenance of vascular integrity. They have an essential role in the hemostatic response, but they also have functional capabilities that go far beyond it. This review will provide an overview of platelet functions. Indeed, stress signals may induce platelet apoptosis through proapoptotis or hemostasis receptors, necrosis, and even autophagy. Platelets also interact with immune cells and modulate immune responses in terms of activation, maturation, recruitment and cytokine secretion. This review will also show that platelets, thanks to their wide range of innate immune receptors, and in particular toll-like receptors, and can be considered sentinels actively participating in the immuno-surveillance of the body. We will discuss the diversity of platelet responses following the engagement of these receptors as well as the signaling pathways involved. Finally, we will show that while platelets contribute significantly, via their TLRs, to immune response and inflammation, these receptors also participate in the pathophysiological processes associated with various pathogens and diseases, including cancer and atherosclerosis.

Platelet TLR4-ERK5 Axis Facilitates NET-Mediated Capturing of Circulating Tumor Cells and Distant Metastasis after Surgical Stress

Surgical removal of malignant tumors is a mainstay in controlling most solid cancers. However, surgical insult also increases the risk of tumor recurrence and metastasis. Tissue trauma activates the innate immune system locally and systemically, mounting an inflammatory response. Platelets and neutrophils are two crucial players in the early innate immune response that heals tissues, but their actions may also contribute to cancer cell dissemination and distant metastasis. Here we report that surgical stress-activated platelets enhance the formation of platelet-tumor cell aggregates, facilitating their entrapment by neutrophil extracellular traps (NET) and subsequent distant metastasis. A murine hepatic ischemia/reperfusion (I/R) injury model of localized surgical stress showed that I/R promotes capturing of aggregated circulating tumor cells (CTC) by NETs and eventual metastasis to the lungs, which are abrogated when platelets are depleted. Hepatic I/R also increased deposition of NETs within the lung microvasculature, but depletion of platelets had no effect. TLR4 was essential for platelet activation and platelet-tumor cell aggregate formation in an ERK5-GPIIb/IIIa integrin-dependent manner. Such aggregation facilitated NET-mediated capture of CTCs in vitro under static and dynamic conditions. Blocking platelet activation or knocking out TLR4 protected mice from hepatic I/R-induced metastasis with no CTC entrapment by NETs. These results uncover a novel mechanism where platelets and neutrophils contribute to metastasis in the setting of acute inflammation. Targeted disruption of the interaction between platelets and NETs holds therapeutic promise to prevent postoperative distant metastasis. SIGNIFICANCE: Targeting platelet activation via TLR4/ERK5/integrin GPIIb/IIIa signaling shows potential for preventing NET-driven distant metastasis in patients post-resection.

Cellular fibronectin promotes deep vein thrombosis in diet-induced obese mice

BACKGROUND

Overweight and obesity are significant risk factors for deep vein thrombosis (DVT). Cellular fibronectin containing extra domain A (Fn-EDA), an endogenous ligand for toll-like-receptor 4 (TLR4), contributes to thrombo-inflammation. The role of Fn-EDA in the modulation of DVT is not elucidated yet.

OBJECTIVE

To determine whether Fn-EDA promotes DVT in the context of diet-induced obesity.

METHODS

Wild-type (WT) and Fn-EDA-deficient mice were either fed control or high-fat (HF) diet for 12 weeks. DVT was induced by inferior vena cava (IVC) stenosis and evaluated after 48 hours. Cellular Fn-EDA levels in the plasma of venous thromboembolism (VTE) patients were measured by sandwich ELISA.

RESULTS

We found that cellular Fn-EDA levels were significantly elevated in VTE patients' plasma and positively correlated with body mass index. HF diet-fed WT mice exhibited increased DVT susceptibility compared with control diet-fed WT mice. In contrast, HF diet-fed Fn-EDA-deficient mice exhibited significantly reduced thrombus weight and decreased incidence (%) of DVT compared with HF diet-fed WT mice concomitant with reduced neutrophil content and citrullinated histone H3-positive cells (a marker of NETosis) in IVC thrombus. Exogenous cellular Fn-EDA potentiated NETosis in neutrophils stimulated with thrombin-activated platelets via TLR4. Genetic deletion of TLR4 in Fn-EDA+ mice (constitutively express Fn-EDA in plasma and tissues), but not in Fn-EDA-deficient mice, reduced DVT compared with respective controls.

CONCLUSION

These results demonstrate a previously unknown role of Fn-EDA in the DVT exacerbation, which may be an essential mechanism promoting DVT in the setting of diet-induced obesity.

NETosis as a Pathogenic Factor for Heart Failure

Heart failure threatens the lives of patients and reduces their quality of life. Heart failure, especially heart failure with preserved ejection fraction, is closely related to systemic and local cardiac persistent chronic low-grade aseptic inflammation, microvascular damage characterized by endothelial dysfunction, oxidative stress, myocardial remodeling, and fibrosis. However, the initiation and development of persistent chronic low-grade aseptic inflammation is unexplored. Oxidative stress-mediated neutrophil extracellular traps (NETs) are the main immune defense mechanism against external bacterial infections. Furthermore, NETs play important roles in noninfectious diseases. After the onset of myocardial infarction, atrial fibrillation, or myocarditis, neutrophils infiltrate the damaged tissue and aggravate inflammation. In tissue injury, damage-related molecular patterns (DAMPs) may induce pattern recognition receptors (PRRs) to cause NETs, but whether NETs are directly involved in the pathogenesis and development of heart failure and the mechanism is still unclear. In this review, we analyzed the markers of heart failure and heart failure-related diseases and comorbidities, such as mitochondrial DNA, high mobility box group box 1, fibronectin extra domain A, and galectin-3, to explore their role in inducing NETs and to investigate the mechanism of PRRs, such as Toll-like receptors, receptor for advanced glycation end products, cGAS-STING, and C-X-C motif chemokine receptor 2, in activating NETosis. Furthermore, we discussed oxidative stress, especially the possibility that imbalance of thiol redox and MPO-derived HOCl promotes the production of 2-chlorofatty acid and induces NETosis, and analyzed the possibility of NETs triggering coronary microvascular thrombosis. In some heart diseases, the deletion or blocking of neutrophil-specific myeloperoxidase and peptidylarginine deiminase 4 has shown effectiveness. According to the results of current pharmacological studies, MPO and PAD4 inhibitors are effective at least for myocardial infarction, atherosclerosis, and certain autoimmune diseases, whose deterioration can lead to heart failure. This is essential for understanding NETosis as a therapeutic factor of heart failure and the related new pathophysiology and therapeutics of heart failure.

Oxidative Stress in Ischemic Heart Disease

One of the novel interesting topics in the study of cardiovascular disease is the role of the oxidation system, since inflammation and oxidative stress are known to lead to cardiovascular diseases, their progression and complications. During decades of research, many complex interactions between agents of oxidative stress, oxidation, and antioxidant systems have been elucidated, and numerous important pathophysiological links to na number of disorders and diseases have been established. This review article will present the most relevant knowledge linking oxidative stress to vascular dysfunction and disease. The review will focus on the role of oxidative stress in endotheleial dysfunction, atherosclerosis, and other pathogenetic processes and mechanisms that contribute to the development of ischemic heart disease.

Targeting myeloid-cell specific integrin α9β1 inhibits arterial thrombosis in mice

Evidence suggests that neutrophils contribute to thrombosis via several mechanisms, including neutrophil extracellular traps (NETs) formation. Integrin α9β1 is highly expressed on neutrophils when compared with monocytes. It undergoes affinity upregulation on neutrophil activation, and stabilizes adhesion to the activated endothelium. The role of integrin α9 in arterial thrombosis remains unexplored. We generated novel myeloid cell-specific integrin α9-/- mice (α9fl/flLysMCre+) to study the role of integrin α9 in arterial thrombosis. α9fl/fl littermates were used as controls. We report that α9fl/flLysMCre+ mice were less susceptible to arterial thrombosis in ferric chloride (FeCl3) and laser injury-induced thrombosis models with unaltered hemostasis. Neutrophil elastase-positive cells were significantly reduced in α9fl/flLysMCre+ mice concomitant with reduction in neutrophil count, myeloperoxidase levels, and red blood cells in the FeCl3 injury-induced carotid thrombus. The percentage of cells releasing NETs was significantly reduced in α9fl/flLysMCre+ mouse neutrophils stimulated with thrombin-activated platelets. Furthermore, we found a significant decrease in neutrophil-mediated platelet aggregation and cathepsin-G secretion in α9fl/flLysMCre+ mice. Transfusion of α9fl/fl neutrophils in α9fl/flLysMCre+ mice restored thrombosis similar to α9fl/fl mice. Treatment of wild-type mice with anti-integrin α9 antibody inhibited arterial thrombosis. This study identifies the potential role of integrin α9 in modulating arterial thrombosis.

Focal TLR4 activation mediates disturbed flow-induced endothelial inflammation

AIMS

Disturbed blood flow at arterial branches and curvatures modulates endothelial function and predisposes the region to endothelial inflammation and subsequent development of atherosclerotic lesions. Activation of the endothelial Toll-like receptors (TLRs), in particular TLR4, contributes to vascular inflammation. Therefore, we investigate whether TLR4 can sense disturbed flow (DF) to mediate the subsequent endothelial inflammation.

METHODS AND RESULTS

En face staining of endothelium revealed that TLR4 expression, activation, and its downstream inflammatory markers were elevated in mouse aortic arch compared with thoracic aorta, which were absent in Tlr4mut mice. Similar results were observed in the partial carotid ligation model where TLR4 signalling was activated in response to ligation-induced flow disturbance in mouse carotid arteries, and such effect was attenuated in Tlr4mut mice. DF in vitro increased TLR4 expression and activation in human endothelial cells (ECs) and promoted monocyte-EC adhesion, which were inhibited in TLR4-knockdown ECs. Among endogenous TLR4 ligands examined as candidate mediators of DF-induced TLR4 activation, fibronectin containing the extra domain A (FN-EDA) expressed by ECs was increased by DF and was revealed to directly interact with and activate TLR4.

CONCLUSION

Our findings demonstrate the indispensable role of TLR4 in DF-induced endothelial inflammation and pinpoint FN-EDA as the endogenous TLR4 activator in this scenario. This novel mechanism of vascular inflammation under DF condition may serve as a critical initiating step in atherogenesis.

Smooth muscle cell-specific fibronectin-EDA mediates phenotypic switching and neointimal hyperplasia

Fibronectin-splice variant containing extra domain A (Fn-EDA) is associated with smooth muscle cells (SMCs) following vascular injury. The role of SMC-derived Fn-EDA in SMC phenotypic switching or its implication in neointimal hyperplasia remains unclear. Herein, using human coronary artery sections with a bare metal stent, we demonstrate the expression of Fn-EDA in the vicinity of SMC-rich neointima and peri-strut areas. In mice, Fn-EDA colocalizes with SMCs in the neointima of injured carotid arteries and promotes neointima formation in the comorbid condition of hyperlipidemia by potentiating SMC proliferation and migration. No sex-based differences were observed. Mechanistic studies suggested that Fn-EDA mediates integrin- and TLR4-dependent proliferation and migration through activation of FAK/Src and Akt1/mTOR signaling, respectively. Specific deletion of Fn-EDA in SMCs, but not in endothelial cells, reduced intimal hyperplasia and suppressed the SMC synthetic phenotype concomitant with decreased Akt1/mTOR signaling. Targeting Fn-EDA in human aortic SMCs suppressed the synthetic phenotype and downregulated Akt1/mTOR signaling. These results reveal that SMC-derived Fn-EDA potentiates phenotypic switching in human and mouse aortic SMCs and neointimal hyperplasia in the mouse. We suggest that targeting Fn-EDA could be explored as a potential therapeutic strategy to reduce neointimal hyperplasia.

Entecavir as a P2X7R antagonist ameliorates platelet activation and thrombus formation

Platelet activation is the primary cause of thrombosis. The P2X7 receptor (P2X7R) is a therapeutic target of thrombosis. However, it is still unknown whether P2X7R activation affects platelet thrombus. Our molecular docking results showed that entecavir as a P2X7R antagonist interacted perfectly with the human P2X7R (hP2X7R) in silico simulation studies. Furthermore, our experimental data revealed that entecavir could act as a P2X7R antagonist to exert cytoprotective effects against platelet activation via protecting mitochondrial function, improving lipid peroxidation and increasing antioxidant activity. Correlated with this, entecavir inhibited platelet aggregation, dense-granule secretion, P-selectin expression, integrin activation and Ca²⁺ increase. In experimental mouse model, entecavir could significantly inhibit arteriovenous thrombosis and prolong the bleeding time. Furthermore, we found that entecavir had no significant effect on prothrombin time (PT), activated partial thrombin time (APTT), thrombin time (TT), fibrinogen (FIB), mean platelet volume (MPV) and platelet counts (PLT). This study demonstrates that entecavir markedly prevents platelet activation and thrombosis through inhibiting P2X7R without affecting coagulation system. Therefore, entecavir may be a potential candidate for treating thrombosis disease.

Fibronectin extra domain A (FN-EDA) elevates intraocular pressure through Toll-like receptor 4 signaling

Elevated intraocular pressure (IOP) is a major risk factor for the development and progression of primary open angle glaucoma and is due to trabecular meshwork (TM) damage, which leads to impaired aqueous humor outflow. Here, we explore a novel molecular mechanism involved in glaucomatous TM damage. We investigated the role of an endogenous Toll-like receptor 4 (TLR4) ligand, fibronectin-EDA (FN-EDA), in TGFβ2-induced ocular hypertension in mice. We utilized transgenic mouse strains that either constitutively express only FN containing the EDA isoform or contain an EDA-null allele and express only FN lacking EDA, with or without a mutation in Tlr4, in our inducible mouse model of ocular hypertension by injection of Ad5.TGFβ2. IOP was measured over time and eyes accessed by immunohistochemistry for total FN and FN-EDA expression. Constitutively active EDA caused elevated IOP starting at 14 weeks of age. Ad5.TGFβ2 induced ocular hypertension in wildtype C57BL/6J mice and further amplified the IOP in constitutively active EDA mice. TLR4 null and EDA null mice blocked Ad5.TGFβ-induced ocular hypertension. Total FN and FN-EDA isoform expression increased in response to Ad5.TGFβ2. These data suggest that both TLR4 and FN-EDA contribute to TGFβ2 induced ocular hypertension.

Human fibronectin extra domain B as a biomarker for targeted therapy in cancer

The extracellular matrix protein fibronectin contains a domain that is rarely found in healthy adults and is almost exclusively expressed by newly formed blood vessels in tumours, particularly in solid tumours, different types of lymphoma and some leukaemias. This domain, called the extra domain B (ED‐B), thus has broad therapeutic potential. The antibody L19 has been developed to specifically target ED‐B and has shown therapeutic potential when combined with cytokines, such as IL‐2. In this review article, we discuss the preclinical research and clinical trials that highlight the potential of ED‐B targeting for the imaging and treatment of various types of cancer. ED‐B‐centred studies also highlight how proper patient stratification is of utmost importance for the successful implementation of novel antibody‐based targeted therapies.

Targeting Myeloid-Specific Integrin α9β1 Improves Short- and Long-Term Stroke Outcomes in Murine Models With Preexisting Comorbidities by Limiting Thrombosis and Inflammation

RATIONALE

Currently, there is no effective intervention available that can reduce brain damage following reperfusion. Clinical studies suggest a positive correlation between the increased influx of neutrophils and severity of brain injury following reperfusion. Integrin α9β1 is highly expressed on activated neutrophils and contributes to stable adhesion, but its role in stroke outcome has not been demonstrated to date.

OBJECTIVE

We sought to determine the mechanistic role of myeloid-specific α9β1 in the progression of ischemic stroke in murine models with preexisting comorbidities.

METHODS AND RESULTS

We generated novel myeloid-specific α9-deficient (α9-/-) wild type (α9fl/flLysMCre+/-), hyperlipidemic (α9fl/flLysMCre+/-Apoe-/-), and aged (bone marrow chimeric) mice to evaluate stroke outcome. Susceptibility to ischemia/reperfusion injury was evaluated at 1, 7, and 28 days following reperfusion in 2 models of experimental stroke: filament and embolic. We found that peripheral neutrophils displayed elevated α9 expression following stroke. Irrespective of sex, genetic deletion of α9 in myeloid cells improved short- and long-term stroke outcomes in the wild type, hyperlipidemic, and aged mice. Improved stroke outcome and enhanced survival in myeloid-specific α9-/- mice was because of marked decrease in cerebral thromboinflammatory response as evidenced by reduced fibrin, platelet thrombi, neutrophil, NETosis, and decreased phospho-NF-κB (nuclear factor-κB), TNF (tumor necrosis factor)-α, and IL (interleukin)-1β levels. α9-/- mice were less susceptible to FeCl3 injury-induced carotid artery thrombosis that was concomitant with improved regional cerebral blood flow following stroke as revealed by laser speckle imaging. Mechanistically, fibronectin containing extra domain A, a ligand for integrin α9, partially contributed to α9-mediated stroke exacerbation. Infusion of a specific anti-integrin α9 inhibitor into hyperlipidemic mice following reperfusion significantly reduced infarct volume and improved short- and long-term functional outcomes up to 28 days.

CONCLUSIONS

We provide genetic and pharmacological evidence for the first time that targeting myeloid-specific integrin α9β1 improves short- and long-term functional outcomes in stroke models with preexisting comorbidities by limiting cerebral thrombosis and inflammation.

Cellular Fibronectin Containing Extra Domain A Causes Insulin Resistance via Toll-like Receptor 4

We determined the role of cellular fibronectin (CFN) containing the alternatively spliced extra domain A (FN-EDA) in causing insulin resistance (IR) through toll-like receptor 4 (TLR4). Circulating FN-EDA level was evaluated in mouse and rat IR models. Specific anti-FN-EDA antibody and TLR4 inhibitor were used to study its role in IR in mice. CFN protein was injected to evaluate TLR4 dependent effect of FN-EDA in IR. Furthermore, FN-EDA was estimated in blood plasma and correlated with demographic and clinical characteristics in healthy human participants (n = 38). High-fat diet feeding significantly increased circulating FN-EDA in both mouse (P = 0.03) and rat (P = 0.02) IR models. Antibody against FN-EDA protected mice from IR by increasing glucose disposal rate following glucose (P = 0.02) and insulin (P = 0.01) tolerance tests. CFN protein injection caused IR, however, TLR4 inhibitor protected the mice from CFN induced IR. Multivariate regression analysis predicted an independent positive correlation between circulating FN-EDA and fasting plasma glucose (P = 0.003) in healthy human participants. In conclusion, FN-EDA may cause IR through TLR4 by decreasing glucose disposal rate following glucose and insulin load. Targeting FN-EDA thus can be considered as a possible therapeutic strategy to delay prediabetes progression to diabetes.

Fn-EDA (Fibronectin Containing Extra Domain A) in the Plasma, but Not Endothelial Cells, Exacerbates Stroke Outcome by Promoting Thrombo-Inflammation

Background and Purpose- Cellular Fn-EDA (fibronectin containing extra domain A) is expressed in activated endothelial cells and elevated in circulation in patients with cardiovascular diseases. Although global deficiency of Fn-EDA in mice improves stroke outcome, the specific contribution of plasma versus endothelium Fn-EDA in stroke outcome is currently unknown. We investigated the role of plasma versus endothelial Fn-EDA in stroke exacerbation in the comorbid condition of hyperlipidemia. Methods- We generated novel plasma Fn-EDA^-/- ( Fn-EDA ^fl/fl Alb ^Cre) and endothelial Fn-EDA^-/- ( Fn-EDA ^fl/fl Tie2 ^Cre) strains on hyperlipidemic apolipoprotein E-deficient ( ApoE^-/-) background. By following the Stroke Therapy Academic Industry Roundtable guidelines, we evaluated stroke outcome in male and female mice. Susceptibility to ischemia/reperfusion injury was evaluated in 2 different models of stroke: intraluminal monofilament and embolic model on days 1, 3, and 7. Quantitative assessment of stroke outcome was evaluated by measuring infarct volume (by magnetic resonance imaging), cerebral blood flow (by laser speckle imaging), neurological and sensory-motor outcome, and postischemic thrombo-inflammation (platelet thrombi, fibrin, neutrophil, phospho-NFκB [nuclear factor κB], TNFα [tumor necrosis factor α], and IL1β [interleukin 1β]). Results- Stroke outcome was comparable in ApoE^-/- Fn-EDA ^fl/fl Tie2 ^Cre and control ApoE^-/- Fn-EDA ^fl/fl mice suggesting endothelial Fn-EDA does not contribute to stroke. ApoE^-/- Fn-EDA ^fl/fl Alb ^Cre mice exhibited significantly smaller infarcts and improved neurological and sensory-motor outcome at days 1, 3, and 7 in monofilament and embolic models of stroke. Improved stroke outcome was concomitant with enhanced survival, and decreased postischemic thrombo-inflammatory response ( P<0.05 versus ApoE^-/- Fn-EDA ^fl/fl). No sex-based differences were observed. Laser speckle imaging revealed significantly improved regional cerebral blood flow at 1 hour in ApoE^-/- Fn-EDA ^fl/fl Alb ^Cre mice suggesting plasma Fn-EDA promotes postischemic secondary thrombosis. Coinfusion of anti-Fn-EDA antibody with r-tPA (recombinant tissue-type plasminogen activator) in ApoE^-/- mice, 1 hour after embolization, improved stroke outcome with enhanced survival, and improved neurological outcome ( P<0.05 versus r-tPA). Conclusions- Genetic evidence suggests that plasma Fn-EDA exacerbates stroke outcome by promoting postischemic thrombo-inflammation. Interventions targeting plasma Fn-EDA may reduce brain damage after reperfusion.

New approaches for the assessment of platelet activation status in thrombus under flow condition using confocal microscopy

The goal of the study was the assessment of heterogeneous platelet activation status in thrombus. In a ferric(III) chloride (FeCl₃) thrombosis (intravital) model of C57BL/6 J mice, the area of irreversibly activated (phosphatidylserine (PS)-positive) platelets was assessed after 1-s exposure of a vessel to FeCl₃. In a laser-induced thrombosis (intravital) model of GFP mice, the area of the thrombus composed of PS-negative platelets was evaluated. The ratio of the area of PECAM-1 to the area of the thrombus was used as a marker to assess the activity of PS-negative platelets. In the in vitro flow chamber model, the thrombus area (PS-negative and PS-positive platelets) and the platelet activation index (ratio of the area of PS-positive platelets to the area of thrombus) were determined. To assess platelet activation status with these models, acetylsalicylic acid (ASA) and iloprost (Ilo) were used. In the FeCl₃ thrombosis, ASA (10 mg/kg, 100 mg/kg) decreased the area of PS-positive platelets. In the laser thrombosis, ASA (10 mg/kg) decreased the thrombus area, but the decrease in platelet activity was evident even at 3 mg/kg by an increased PECAM-1/thrombus ratio. In the flow chamber, ASA (0.02 mg/ml, 0.2 mg/ml) equally decreased the platelet activation index, whereas only at 0.2 mg/ml, it decreased the thrombus area. Ilo (3.6 ng/ml, 36 ng/ml) decreased the thrombus area but at 36 ng/ml increased the platelet activation index. We showed that intravital models and flow chamber provide a detailed assessment of platelet activation status and the mechanism of drug action.

RETRACTED: Tetramethylpyrazine alleviates lipopolysaccharide-induced damage in ATDC5 cells via down-regulating MyD88

This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/our-business/policies/article-withdrawal). This article has been retracted at the request of the Editor-in-Chief and the authors. Following the concerns raised about the background pattern of the Western Blots from Figures 7A and 7C, the authors have contacted the journal to request the retraction of the article as they were reportedly not confident of the accuracy of the data and the conclusions of the article. Given the comments of Dr Elisabeth Bik regarding this article “This paper belongs to a set of over 400 papers (as per February 2020) that share very similar Western blots with tadpole-like shaped bands, the same background pattern, and striking similarities in title structures, paper layout, bar graph design, and - in a subset - flow cytometry panels”, the journal requested the authors to provide the raw data. However, the authors were not able to fulfil this request and therefore the Editor-in-Chief decided to retract the article.

Modulators of platelet function in aging

Platelets are small, anucleated effector cells that play an important role in linking the hemostatic and inflammatory processes in the body. Platelet function is known to be altered under various inflammatory conditions including aging. A gain in platelet function during aging can increase the risk of thrombotic events, such as stroke and acute myocardial infarction. Anti-platelet therapy is designed to reduce risk of serious cerebrovascular and cardiovascular events, but the adverse consequences of therapy, such as risk for bleeding increases with aging as well. Age-associated comorbidities such as obesity, diabetes, and hyperlipidemia also contribute to increased platelet activity and thus can enhance the risk of thrombosis. Therefore, identification of unique mechanisms of platelet dysfunction in aging and in age-associated comorbidities is warranted to design novel antiplatelet drugs. This review outlines some of the current areas of research on aging-related mechanisms of platelet hyperactivity and addresses the clinical urgency for designing anti-platelet therapies toward novel molecular targets in the aging population.

Unraveling the Mechanobiology of Extracellular Matrix

Cells need to be anchored to extracellular matrix (ECM) to survive, yet the role of ECM in guiding developmental processes, tissue homeostasis, and aging has long been underestimated. How ECM orchestrates the deterioration of healthy to pathological tissues, including fibrosis and cancer, also remains poorly understood. Inquiring how alterations in ECM fiber tension might drive these processes is timely, as mechanobiology is a rapidly growing field, and many novel mechanisms behind the mechanical forces that can regulate protein, cell, and tissue functions have recently been deciphered. The goal of this article is to review how forces can switch protein functions, and thus cell signaling, and thereby inspire new approaches to exploit the mechanobiology of ECM in regenerative medicine as well as for diagnostic and therapeutic applications. Some of the mechanochemical switching concepts described here for ECM proteins are more general and apply to intracellular proteins as well.

Dichloroacetate, an inhibitor of pyruvate dehydrogenase kinases, inhibits platelet aggregation and arterial thrombosis

Resting platelets rely on oxidative phosphorylation (OXPHOS) and aerobic glycolysis (conversion of glucose to lactate in the presence of oxygen) to generate adenosine triphosphate, whereas activated platelets exhibit a high level of aerobic glycolysis, suggesting the existence of metabolic flexibility in platelets. Mitochondrial pyruvate dehydrogenase kinases (PDK 1-4) play a pivotal role in metabolic flexibility by inhibiting pyruvate dehydrogenase complex. We determined whether metabolic reprogramming, diverting metabolism from aerobic glycolysis back to OXPHOS, would inhibit platelet function. PDKs activity in human and mouse platelets was inhibited with dichloroacetic acid (DCA), a potent inhibitor of all 4 forms of PDK. Human and mouse platelets pretreated with DCA exhibited decreased platelet aggregation to suboptimal doses of collagen, convulxin, thrombin, and adenosine diphosphate concomitant with decreased glucose uptake. Bioenergetics profile revealed that platelets pretreated with DCA exhibited decreased aerobic glycolysis in response to convulxin only. Furthermore, DCA inhibited ATP secretion, thromboxane A2 generation, and tyrosine phosphorylation of Syk and PLCγ2 in response to collagen or convulxin in human and mouse platelets (P < .05 vs vehicle treated). In the flow chamber assay, human and mouse blood pretreated with DCA formed smaller thrombi when perfused over collagen for 10 minutes at an arterial shear rate of 1500 s^-1 (P < .05 vs control). Wild-type mice pretreated with DCA were less susceptible to thrombosis in the FeCl₃-induced carotid and laser injury-induced mesenteric artery thrombosis models (P < .05 vs vehicle control), without altering hemostasis. Targeting metabolic plasticity with DCA may be explored as a novel strategy to inhibit platelet function.

Aerobic glycolysis fuels platelet activation: small-molecule modulators of platelet metabolism as anti-thrombotic agents

Platelets are critical to arterial thrombosis, which underlies myocardial infarction and stroke. Activated platelets, regardless of the nature of their stimulus, initiate energy-intensive processes that sustain thrombus, while adapting to potential adversities of hypoxia and nutrient deprivation within the densely packed thrombotic milieu. We report here that stimulated platelets switch their energy metabolism to aerobic glycolysis by modulating enzymes at key checkpoints in glucose metabolism. We found that aerobic glycolysis, in turn, accelerates flux through the pentose phosphate pathway and supports platelet activation. Hence, reversing metabolic adaptations of platelets could be an effective alternative to conventional anti-platelet approaches, which are crippled by remarkable redundancy in platelet agonists and ensuing signaling pathways. In support of this hypothesis, small-molecule modulators of pyruvate dehydrogenase, pyruvate kinase M2 and glucose-6-phosphate dehydrogenase, all of which impede aerobic glycolysis and/or the pentose phosphate pathway, restrained the agonist-induced platelet responses ex vivo. These drugs, which include the anti-neoplastic candidate, dichloroacetate, and the Food and Drug Administration-approved dehydroepiandrosterone, profoundly impaired thrombosis in mice, thereby exhibiting potential as anti-thrombotic agents.

Platelets, NETs and cancer

In addition to the central role of platelets in hemostasis, they contribute to pathological conditions such as inflammation and tumor progression. Aberrant expression and/or exposure of pro-coagulant factors in the tumor microenvironment induce platelet activation and subsequent release of growth factors from platelet granules. Cancer patients are commonly affected by thrombotic events, as a result of tumor-induced platelet activation. A novel player potentially contributing to cancer-associated thrombosis is the formation of neutrophil extracellular traps (NETs). NETs are composed of externalized DNA of nuclear or mitochondrial origin, bound to histones and granular proteases such as neutrophil elastase (NE) and myeloperoxidase (MPO). These extracellular traps help neutrophils to catch and kill pathogens such as bacteria, virus and fungi. It is now clear that NETs form also under conditions of sterile inflammation such as cancer and autoimmunity and can promote thrombosis. Recent data show that platelets play a key role in determining when and where NETs should form. This review will highlight our current insight in the role of platelets as regulators of NET formation, both during infection and sterile inflammation.

Deletion of Extra Domain A of Fibronectin Reduces Acute Myocardial Ischaemia/Reperfusion Injury in Hyperlipidaemic Mice by Limiting Thrombo-Inflammation

BACKGROUND

 Fibronectin splicing variant containing extra domain A (Fn-EDA), which is an endogenous ligand for Toll-like receptor 4 (TLR4), is present in negligible amounts in the plasma of healthy humans, but markedly elevated in patients with co-morbid conditions including diabetes and hyperlipidaemia, which are risk factors for myocardial infarction (MI). Very little is known about the role of Fn-EDA in the pathophysiology of acute MI under these co-morbid conditions.

MATERIALS AND METHODS

 We determined the role of Fn-EDA in myocardial ischaemia/reperfusion (I/R) injury in the hyperlipidaemic apolipoprotein E-deficient (ApoE^-/-) mice. Infarct size, plasma cardiac troponin I (cTnI) levels, intravascular thrombosis (CD41-positive), neutrophil infiltration (Ly6 B.2-positive), neutrophil extracellular traps (citrullinated H3-positive) and myocyte apoptosis (terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling-positive) were assessed in myocardial I/R injury model (1-hour ischaemia/23 hours of reperfusion).

RESULTS

 Irrespective of gender, Fn-EDA^-/-ApoE^-/- mice exhibited smaller infarct size and decreased cTnI levels concomitant with reduced post-ischaemic intra-vascular thrombi, neutrophils influx, neutrophil extracellular traps and myocyte apoptosis (p < 0.05 vs. ApoE^-/- mice). Genetic deletion of TLR4 attenuated myocardial I/R injury in ApoE^-/- mice (p < 0.05 vs. ApoE^-/- mice), but did not further reduce in Fn-EDA^-/- ApoE^-/- mice suggesting that Fn-EDA requires TLR4 to mediate myocardial I/R injury. Bone marrow transplantation experiments revealed that Fn-EDA exacerbates myocardial I/R injury through TLR4 expressed on the haematopoietic cells. Infusion of a specific inhibitor of Fn-EDA, 15 minutes post-reperfusion, into ApoE^-/- mice attenuated myocardial I/R injury.

CONCLUSION

 Fn-EDA exacerbates TLR4-dependent myocardial I/R injury by promoting post-ischaemic thrombo-inflammatory response. Targeting Fn-EDA may reduce cardiac damage following coronary artery re-canalization after acute MI.

Increased blood levels of cellular fibronectin in asthma: Relation to the asthma severity, inflammation, and prothrombotic blood alterations

BACKGROUND

Recently, we have reported that asthma is characterized by prothrombotic blood alterations, which were related to the low-grade inflammatory state. Inflammation, however, may also lead to vascular dysfunction. The aim of this study was to evaluate plasma levels of cellular fibronectin (cFN), a marker of vascular injury in asthmatics, and to analyze their impact on described previously prothrombotic blood alterations.

METHODS

In a cross-sectional study, we investigated 164 adult stable asthmatics and 72 matched controls. Plasma cFN was measured using an ELISA. Its relations to inflammation, thrombin generation, fibrinolytic capacity, expressed as clot lysis time (CLT), and platelet markers were evaluated.

RESULTS

Asthma was associated with 50.1% higher plasma cFN levels as compared with controls (p < 0.001, after adjustment for potential confounders). There was a positive association of cFN with asthma severity and inverse with the FEV₁/VC index (β = 0.2 [95%CI:0.13-0.28] and β = -0.15 [95%CI: -0.23 to -0.07], respectively). In asthmatics cFN positively correlated with high-sensitivity C-reactive protein (β = 0.24 [95%CI:0.16-0.32]), fibrinogen (β = 0.13 [95%CI:0.04-0.21]), interleukin-6 (β = 0.23 [95%CI:0.15-0.3]), platelet factor 4 (β = 0.14 [95%CI:0.06-0.21]), plasminogen (β = 0.11 [95%CI:0.04-0.19]) and CLT (β = 0.35 [95%CI:0.28-0.42]). In both groups cFN was related to the endogenous thrombin potential (ETP) (β = 0.51 [95%CI:0.44-0.57], and β = 0.17 [95%CI:0.07-0.27], respectively). Multiple regression models showed that cFN was the most potent independent predictor of both ETP and CLT in asthmatics.

CONCLUSION

Presented study is the first to show increased plasma cellular fibronectin in asthma, which is associated with disease severity, inflammation, and prothrombotic blood alterations. This novel observation suggests a previously unknown modulator of prothrombotic plasma properties in asthmatics.

Time-dependent changes in extra-domain A-fibronectin concentration and relative amounts of fibronectin-fibrin complexes in plasma of patients with peripheral arterial disease after endovascular revascularisation

Fibronectin (FN) may be involved in time- and stage-dependent and inter-related controlled processes of inflammation, coagulation, and wound healing accompanying peripheral arterial disease (PAD). In the present study, FN and FN-containing extra-domain A (EDA-FN), macromolecular FN-fibrin complexes, and FN monomer were analysed in the plasma of 142 PAD patients, including 37 patients with restenosis, for 37 months after revascularisation. FN concentration increased significantly in the plasma of PAD patients within 7 to 12 months after revascularisation, whereas the high concentration of EDA-FN was maintained up to 24 months, significantly higher in the group 7 to 12 months after revascularisation with recurrence of stenosis and lower in the PAD groups 1 to 3 months and 4 to 6 months after revascularisation with comorbid diabetes and ulceration, respectively. The relative amounts of FN-fibrin complexes up to 1600 kDa and FN monomer were significantly higher, within intervals of 4 to 24 months and 4 to 6 months after revascularisation, respectively. Moreover, the relative amounts of 750 to 1600 kDa FN-fibrin complexes within 13 to 24 months after revascularisation were higher in comparison with those in the group without restenosis. In conclusion, high levels of EDA-FN and FN-fibrin complexes could have potential diagnostic value in the management of PAD patients after revascularisation, predicting restenosis risk.

Fibronectin Containing Extra Domain A Induces Plaque Destabilization in the Innominate Artery of Aged Apolipoprotein E-Deficient Mice

OBJECTIVE

Fibronectin containing extra domain A (Fn-EDA) is an endogenous ligand of TLR4 (toll-like receptor 4) and is abundant in the extracellular matrix of advanced atherosclerotic lesions in human and mice. Irrespective of sex, deletion of Fn-EDA reduces early atherosclerosis in apolipoprotein E-deficient (Apoe^-/-) mice. However, the contribution of Fn-EDA in advanced atherosclerosis remains poorly characterized. We determined the contribution of Fn-EDA in advanced atherosclerotic lesions of aged (1-year-old) Apoe^-/- mice.

APPROACH AND RESULTS

Plaque composition was determined in the innominate artery, a plaque instability site that is known to mimic several histological features of vulnerable human plaques. Female Apoe^-/-, Fn-EDA^-/-Apoe^-/-, TLR4^-/-Apoe^-/-, and Fn-EDA^-/-TLR4^-/-Apoe^-/- mice were fed a high-fat Western diet for 44 weeks. Fn-EDA^-/-Apoe^-/- mice exhibited reduced plaque size characterized by smaller necrotic cores, thick fibrous caps containing abundant vascular smooth muscle cells and collagen, reduced CD68/MMP9 (matrix metalloproteinase 9)-positive content, less accumulation of MMP-cleaved extracellular matrix aggrecan, and decreased vascular smooth muscle cell and macrophage apoptosis (P<0.05 versus Apoe^-/- mice). Together these findings suggest that Fn-EDA induces plaque destabilization. Deletion of TLR4 reduced histological features of plaque instability in Apoe^-/- mice but did not further reduce features of plaque destabilization in Fn-EDA^-/-Apoe^-/- mice, suggesting that TLR4 may contribute to Fn-EDA-induced plaque destabilization. Fn-EDA potentiated TLR4-dependent MMP9 expression in bone marrow-derived macrophages, suggesting that macrophage TLR4 may contribute to Fn-EDA-mediated plaque instability.

CONCLUSIONS

Fn-EDA induces histological features of plaque instability in established lesions of aged Apoe^-/- mice. The abundance of Fn-EDA in advanced atherosclerotic lesions may increase the risk of plaque destabilization.

Toll-Like Receptor 4 Signalling and Its Impact on Platelet Function, Thrombosis, and Haemostasis

Platelets are anucleated blood cells that participate in a wide range of physiological and pathological functions. Their major role is mediating haemostasis and thrombosis. In addition to these classic functions, platelets have emerged as important players in the innate immune system. In particular, they interact with leukocytes, secrete pro- and anti-inflammatory factors, and express a wide range of inflammatory receptors including Toll-like receptors (TLRs), for example, Toll-like receptor 4 (TLR4). TLR4, which is the most extensively studied TLR in nucleated cells, recognises lipopolysaccharides (LPS) that are compounds of the outer surface of Gram-negative bacteria. Unlike other TLRs, TLR4 is able to signal through both the MyD88-dependent and MyD88-independent signalling pathways. Notably, despite both pathways culminating in the activation of transcription factors, TLR4 has a prominent functional impact on platelet activity, haemostasis, and thrombosis. In this review, we summarise the current knowledge on TLR4 signalling in platelets, critically discuss its impact on platelet function, and highlight the open questions in this area.

Vascular Smooth Muscle Cells and Arterial Stiffening: Relevance in Development, Aging, and Disease

The cushioning function of large arteries encompasses distension during systole and recoil during diastole which transforms pulsatile flow into a steady flow in the microcirculation. Arterial stiffness, the inverse of distensibility, has been implicated in various etiologies of chronic common and monogenic cardiovascular diseases and is a major cause of morbidity and mortality globally. The first components that contribute to arterial stiffening are extracellular matrix (ECM) proteins that support the mechanical load, while the second important components are vascular smooth muscle cells (VSMCs), which not only regulate actomyosin interactions for contraction but mediate also mechanotransduction in cell-ECM homeostasis. Eventually, VSMC plasticity and signaling in both conductance and resistance arteries are highly relevant to the physiology of normal and early vascular aging. This review summarizes current concepts of central pressure and tensile pulsatile circumferential stress as key mechanical determinants of arterial wall remodeling, cell-ECM interactions depending mainly on the architecture of cytoskeletal proteins and focal adhesion, the large/small arteries cross-talk that gives rise to target organ damage, and inflammatory pathways leading to calcification or atherosclerosis. We further speculate on the contribution of cellular stiffness along the arterial tree to vascular wall stiffness. In addition, this review provides the latest advances in the identification of gene variants affecting arterial stiffening. Now that important hemodynamic and molecular mechanisms of arterial stiffness have been elucidated, and the complex interplay between ECM, cells, and sensors identified, further research should study their potential to halt or to reverse the development of arterial stiffness.

Monocyte adhesion to atherosclerotic matrix proteins is enhanced by Asn-Gly-Arg deamidation

Atherosclerosis arises from leukocyte infiltration and thickening of the artery walls and constitutes a major component of vascular disease pathology, but the molecular events underpinning this process are not fully understood. Proteins containing an Asn-Gly-Arg (NGR) motif readily undergo deamidation of asparagine to generate isoDGR structures that bind to integrin α_vβ₃ on circulating leukocytes. Here we report the identification of isoDGR motifs in human atherosclerotic plaque components including extracellular matrix (ECM) proteins fibronectin and tenascin C, which have been strongly implicated in human atherosclerosis. We further demonstrate that deamidation of NGR motifs in fibronectin and tenascin C leads to increased adhesion of the monocytic cell line U937 and enhanced binding of primary human monocytes, except in the presence of a α_vβ₃-blocking antibody or the α_v-selective inhibitor cilengitide. In contrast, under the same deamidating conditions monocyte-macrophages displayed only weak binding to the alternative ECM component vitronectin which lacks NGR motifs. Together, these findings confirm a critical role for isoDGR motifs in mediating leukocyte adhesion to the ECM via integrin α_vβ₃ and suggest that protein deamidation may promote the pathological progression of human atherosclerosis by enhancing monocyte recruitment to developing plaques.

Intravital microscopy in historic and contemporary immunology

In this review, we discuss intravital microscopy of immune cells, starting from its historic origins to current applications in diverse organs. It is clear from a quantitative review of the literature that intravital microscopy is a key tool in both historic and contemporary immunological research, providing unique advances in our understanding of immune responses. We have chosen to focus this review on how intravital microscopy methodologies are used to image specific organs or systems and we present recent descriptions of fundamental immunological processes that could not have been achieved by other methods. The following target organs/systems are discussed in more detail: cremaster muscle, skin (ear and dorsal skin fold chamber), lymph node, liver, lung, mesenteric vessels, carotid artery, bone marrow, brain, spleen, foetus and lastly vessels of the knee joint.

Analysis of Soluble Molecular Fibronectin-Fibrin Complexes and EDA-Fibronectin Concentration in Plasma of Patients with Atherosclerosis

Atherosclerosis, a chronic vascular disease, leads to molecular events bound with interplaying processes of inflammation and coagulation. In the present study, fibronectin (FN), FN containing extra domain A (EDA-FN), frequency of occurrence, and relative amounts of soluble plasma FN-fibrin complexes were analyzed in 80 plasma samples of patients suspected of coronary artery disease based on clinical evaluation and changes in arteries found by computed tomographic coronary angiography. The study showed that in the plasma of the patients’ group with high risk of coronary artery disease EDA-FN concentration was significantly higher (3.5 ± 2.5 mg/L; P < 0.025) and the molecular FN-fibrin complexes of 1000 kDa and higher occurred more often than in the groups of patients with mild risk of coronary artery disease and the normal age-matched. The increased level of EDA-FN and occurrence of FN-fibrin complexes could have a potential diagnostic value in the diagnosis and management of patients with coronary artery disease.

P-selectin can promote thrombus propagation independently of both von Willebrand factor and thrombospondin-1 in mice

Essentials The main receptor for platelet glycoprotein (GP) Ibα is von Willebrand factor (VWF). P-selectin and thrombospondin-1 (TSP1) have been suggested as counter receptors for GPIbα. In a laser injury model, P-selectin promotes thrombus propagation independently of VWF and TSP1. In a laser injury model, thrombus persists in interleukin-4 receptor α/GPIbα-transgenic mice.

SUMMARY

Background P-selectin and thrombospondin-1 (TSP1) have been suggested as counter ligands that may mediate GPIbα-dependent thrombus growth independently of von Willebrand factor (VWF) in vitro. However, residual thrombus formation still persists in Vwf -/- Tsp1-/- mice, suggesting existence of other mechanisms that modulate thrombus propagation. Objective We determined whether P-selectin modulates thrombus propagation in injured arterioles independently of TSP1 and VWF. Methods CD-62P blocking antibody in Vwf -/- Tsp1-/- mice was used to inhibit P-selectin. We determined thrombus growth kinetics in two models of thrombosis: FeCl3 injury-induced and laser injury-induced thrombosis. Results In a 10% FeCl3 injury-induced thrombosis model, the initial platelet adhesion, time to form first thrombus, and non-occlusive residual thrombus growth kinetics were comparable between P-selectin-blocking antibody-treated Vwf -/- Tsp1-/- mice and control IgG-treated Vwf -/- Tsp1-/- mice. On the other hand, in a laser injury-induced thrombosis model, residual thrombus growth kinetics were significantly decreased in P-selectin-blocking antibody-treated Vwf -/- Tsp1-/- mice vs. control IgG-treated Vwf -/- Tsp1-/- mice. Because P-selectin has been suggested as a counter ligand for platelet GPIbα, we determined the role of GPIbα in a laser injury-induced thrombosis model. Surprisingly, in a laser injury model, unlike in a FeCl3 injury model, thrombus formation was not completely inhibited in IL4Rα/GPIbα-tg mice. Residual thrombus growth kinetics were comparable between P-selectin-blocking antibody-treated IL4Rα/GPIbα-tg mice and control IgG-treated IL4Rα/GPIbα-tg mice. Comparison of slopes over time showed that residual thrombus growth kinetics were comparable in P-selectin-blocking antibody-treated Vwf -/- Tsp1-/- and control IgG-treated IL4Rα/GPIbα-tg mice Conclusion In a laser injury-induced thrombosis model, P-selectin modulates thrombus propagation independently of VWF and TSP1.

The Role of TLR2, TLR4, and TLR9 in the Pathogenesis of Atherosclerosis

Toll-like receptors (TLRs) are key players in the pathogenesis of inflammatory conditions including coronary arterial disease (CAD). They are expressed by a variety of immune cells where they recognize pathogen-associated molecular patterns (PAMPs). TLRs recruit adaptor molecules, including myeloid differentiation primary response protein (MYD88) and TIRF-related adaptor protein (TRAM), to mediate activation of MAPKs and NF-kappa B pathways. They are associated with the development of CAD through various mechanisms. TLR4 is expressed in lipid-rich and atherosclerotic plaques. In TLR2^−/− and TLR4^−/− mice, atherosclerosis-associated inflammation was diminished. Moreover, TLR2 and TLR4 may induce expression of Wnt5a in advanced staged atheromatous plaque leading to activation of the inflammatory processes. TLR9 is activated by CpG motifs in nucleic acids and have been implicated in macrophage activation and the uptake of oxLDL from the circulation. Furthermore, TLR9 also stimulates interferon-α (INF-α) secretion and increases cytotoxic activity of CD4⁺ T-cells towards coronary artery tunica media smooth muscle cells. This review outlines the pathophysiological role of TLR2, TLR4, and TLR9 in atherosclerosis, focusing on evidence from animal models of the disease.

NETosis in Cancer - Platelet-Neutrophil Crosstalk Promotes Tumor-Associated Pathology

It has become increasingly clear that circulating immune cells in the body have a major impact on cancer development, progression, and outcome. The role of both platelets and neutrophils as independent regulators of various processes in cancer has been known for long, but it has quite recently emerged that the platelet-neutrophil interplay is yet a critical component to take into account during malignant disease. It was reported a few years ago that neutrophils in mice with cancer have increased propensity to form neutrophil extracellular traps (NETs) - web-like structures formed by externalized chromatin and secreted proteases. The initial finding describing this as a cell death-associated process has been followed by reports of additional mechanisms for NET formation (NETosis), and it has been shown that similar structures can be formed also without lysis and neutrophil cell death as a consequence. Furthermore, presence of NETs in humans with cancer has been verified in a few recent studies, indicating that tumor-induced NETosis is clinically relevant. Several reports have also described that NETs contribute to cancer-associated pathology, by promoting processes responsible for cancer-related death such as thrombosis, systemic inflammation, and relapse of the disease. This review summarizes current knowledge about NETosis in cancer, including the role of platelets as regulators of tumor-induced NETosis. It has been shown that platelets can serve as inducers of NETosis, and the platelet-neutrophil interface can therefore be an important issue to consider when designing therapies targeting cancer-associated pathology in the future.

Fibronectin maintains the balance between hemostasis and thrombosis

Fibronectin is a dimeric protein widely distributed in solid tissues and blood. This major extracellular matrix protein is indispensable for embryogenesis and plays crucial roles in many physiological and pathological processes. Fibronectin pre-mRNA undergoes alternative splicing to generate over 20 splicing variants, which are categorized as either plasma fibronectin (pFn) or cellular fibronectin (cFn). All fibronectin variants contain integrin binding motifs, as well as N-terminus collagen and fibrin binding motifs. With motifs that can be recognized by platelet integrins and coagulation factors, fibronectin, especially pFn, has long been suspected to be involved in hemostasis and thrombosis, but the exact function of fibronectin in these processes is controversial. The advances made using intravital microscopy models and fibronectin deficient and mutant mice have greatly facilitated the direct investigation of fibronectin function in vivo. Recent studies revealed that pFn is a vital hemostatic factor that is especially crucial for hemostasis in both genetic and anticoagulant-induced deficiencies of fibrin formation. pFn may also be an important self-limiting regulator to prevent hemorrhage as well as excessive thrombus formation and vessel occlusion. In addition to pFn, cFn is found to be prothrombotic and may contribute to thrombotic complications in various diseases. Further investigations of the role of pFn and cFn in thrombotic and hemorrhagic diseases may provide insights into development of novel therapeutic strategies (e.g., pFn transfusion) for the maintenance of the fine balance between hemostasis and thrombosis.