Expression of COX-2 in platelet-monocyte interactions occurs via combinatorial regulation involving adhesion and cytokine signaling

Platelet formation and activation are influenced by neuronal guidance proteins

Platelets are anucleate blood cells derived from megakaryocytes. They link the fundamental functions of hemostasis, inflammation and host defense. They undergo intracellular calcium flux, negatively charged phospholipid translocation, granule release and shape change to adhere to collagen, fibrin and each other, forming aggregates, which are key to several of their functions. In all these dynamic processes, the cytoskeleton plays a crucial role. Neuronal guidance proteins (NGPs) form attractive and repulsive signals to drive neuronal axon navigation and thus refine neuronal circuits. By binding to their target receptors, NGPs rearrange the cytoskeleton to mediate neuron motility. In recent decades, evidence has indicated that NGPs perform important immunomodulatory functions and influence platelet function. In this review, we highlight the roles of NGPs in platelet formation and activation.

Thromboinflammatory challenges in stroke pathophysiology

Despite years of encouraging translational research, ischemic stroke still remains as one of the highest unmet medical needs nowadays, causing a tremendous burden to health care systems worldwide. Following an ischemic insult, a complex signaling pathway emerges leading to highly interconnected thrombotic as well as neuroinflammatory signatures, the so-called thromboinflammatory cascade. Here, we thoroughly review the cell-specific and time-dependent role of different immune cell types, i.e., neutrophils, macrophages, T and B cells, as key thromboinflammatory mediators modulating the neuroinflammatory response upon stroke. Similarly, the relevance of platelets and their tight crosstalk with a variety of immune cells highlights the relevance of this cell-cell interaction during microvascular dysfunction, neovascularization, and cellular adhesion. Ultimately, we provide an up-to-date overview of therapeutic approaches mechanistically targeting thromboinflammation currently under clinical translation, especially focusing on phase I to III clinical trials.

Papain ameliorates monocyte-platelet aggregate formation-mediated inflammatory responses in monocytes by upregulating miRNA-146a transcription

BACKGROUND

MicroRNA-146a (miRNA-146a) is a nuclear factor κB (NF-κB)-inducible and inflammation-sensitive miRNA, while papain elicits anti-inflammatory effects by inhibiting monocyte-platelet aggregate (MPA)-mediated NF-κB pathway activation in monocytes. This study aimed to demonstrate the underlying effects of papain on MPA formation-initiated miRNA-146a expression and subsequent action in monocytes.

METHODS

THP-1 cells were exposed to papain, miRNA-146a mimic and inhibitor, NF-κB inhibitor (BAY11-7082), and platelets. Flow cytometry was used to measure the MPA formation-initiated monocyte activation. Levels of miRNA-146a, cyclooxygenase 2 (COX-2) mRNA and protein, and monocyte chemoattractant protein 1 (MCP-1) were analyzed in monocytes by RT-PCR, western blot, and ELISA.

RESULTS

The NF-κB inhibitor and miRNA-146a mimics upregulated miRNA-146a expression but suppressed subsequent monocyte activation and expression of COX-2 and MCP-1. Following exposure to papain, the enhanced miRNA-146a transcription induced by MPA-formation was found along with significant inhibition of monocyte activation in a dose-dependent manner. However, the inhibitory tendency was significantly reversed by miRNA-146a inhibitors. Expression of COX-2 mRNA and protein, as well as MCP-1, was inhibited in monocytes by papain, whereas miRNA-146a inhibitors promoted COX-2 and MCP-1 expression.

CONCLUSION

Our findings suggest that papain can inhibit MPA formation-mediated expression of inflammatory mediators in activated monocytes by upregulating miRNA-146a transcription.

Is there a relationship between morphological and functional platelet changes and depressive disorder?

BACKGROUND

Blood platelets, due to shared biochemical and functional properties with presynaptic serotonergic neurons, constituted, over the years, an attractive peripheral biomarker of neuronal activity. Therefore, the literature strongly focused on the investigation of eventual structural and functional platelet abnormalities in neuropsychiatric disorders, particularly in depressive disorder. Given their impact in biological psychiatry, the goal of the present paper was to review and critically analyze studies exploring platelet activity, functionality, and morpho-structure in subjects with depressive disorder.

METHODS

According to the PRISMA guidelines, we performed a systematic review through the PubMed database up to March 2020 with the search terms: (1) platelets in depression [Title/Abstract]"; (2) "(platelets[Title]) AND depressive disorder[Title/Abstract]"; (3) "(Platelet[Title]) AND major depressive disorder[Title]"; (4) (platelets[Title]) AND depressed[Title]"; (5) (platelets[Title]) AND depressive episode[Title]"; (6) (platelets[Title]) AND major depression[Title]"; (7) platelet activation in depression[All fields]"; and (8) platelet reactivity in depression[All fields]."

RESULTS

After a detailed screening analysis and the application of specific selection criteria, we included in our review a total of 106 for qualitative synthesis. The studies were classified into various subparagraphs according to platelet characteristics analyzed: serotonergic system (5-HT2A receptors, SERT activity, and 5-HT content), adrenergic system, MAO activity, biomarkers of activation, responsivity, morphological changes, and other molecular pathways.

CONCLUSIONS

Despite the large amount of the literature examined, nonunivocal and, occasionally, conflicting results emerged. However, the findings on structural and metabolic alterations, modifications in the expression of specific proteins, changes in the aggregability, or in the responsivity to different pro-activating stimuli, may be suggestive of potential platelet dysfunctions in depressed subjects, which would result in a kind of hyperreactive state. This condition could potentially lead to an increased cardiovascular risk. In line with this hypothesis, we speculated that antidepressant treatments would seem to reduce this hyperreactivity while representing a potential tool for reducing cardiovascular risk in depressed patients and, maybe, in other neuropsychiatric conditions. However, the problem of the specificity of platelet biomarkers is still at issue and would deserve to be deepened in future studies.

Platelet-leukocyte aggregates - a predictor for acute kidney injury after cardiac surgery

Background

Acute kidney injury (AKI) is one of the most common complications after cardiac surgery. However, effective biomarker used for early diagnosis of AKI has not been identified. Platelet-leukocyte aggregates (PLAs) participate in inflammation and coagulation, leading to vascular lesions and tissue destruction. We designed a prospective study to assess whether PLAs can serve as a good biomarker for early diagnosis of AKI after cardiac surgery.

Methods

Patients with rheumatic heart disease scheduled to undergo valve replacement surgery were enrolled. Blood samples were collected at five timepoints as follows: (a) At baseline. (b) At the end of extracorporeal circulation. (c) Arrival at intensive care unit (ICU). (d) Four-hours after the admission to ICU. (e) Twenty hours after the admission to ICU. After collection, the samples were immediately used for PLAs measurement by flow cytometry.

Results

A total of 244 patients were registered, and 15 of them were diagnosed with AKI according to the serum creatinine of KDIGO guidelines. The PLAs levels in AKI group were significantly increased 20 h after surgery (two-way repeated measure analysis of variance, p < 0.01) compared with that at baseline. Patients whose preoperative PLAs were higher than 6.8% showed increased risk of developing AKI (multivariate logistic regression; p = 0.01; adjusted odds ratio, 1.05; 95% confidence interval, 1.01–1.09).

Conclusion

PLAs is an independent risk factor for AKI after valve replacement among patients with rheumatic heart disease.

Platelet-leukocyte interactions in the pathogenesis of viral infections

Evolving evidence demonstrates that platelets have major roles in viral syndromes through previously unrecognized viral sensing and effector functions. Activated platelets and increased platelet-leukocyte aggregates are observed in clinical and experimental viral infections. The mechanisms and outcomes of platelet-leukocyte interactions depend on the interacting leukocyte as well as on the pathogen and pathological conditions. In this review, we discuss the mechanisms involved in platelet interactions with leukocytes and its functions during viral infections. We focus on the contributions of human platelet-leukocyte interactions to pathophysiological and protective responses during viral infections of major global health relevance, including acquired immunodeficiency syndrome (AIDS), dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS), influenza pneumonia, and COVID-19.

The Molecular Aspects of Disturbed Platelet Activation through ADP/P2Y12 Pathway in Multiple Sclerosis

Epidemiological studies confirm a high risk of ischemic events in secondary-progressive multiple sclerosis (SP MS) patients, directly associated with an increased level of pro-thrombotic activity of platelets. Our work aimed to verify potential molecular abnormalities of the platelet P2Y₁₂ receptor expression and functionality as a cause of an increased risk of thromboembolism observed in the course of MS. We have demonstrated an enhanced platelet reactivity in response to adenosine diphosphate (ADP) in SP MS relative to controls. We have also shown an increased mRNA expression for the P2RY12 gene in both platelets and megakaryocytes, as well as enhanced density of these receptors on the platelet surface. We postulate that one of the reasons for the elevated risk of ischemic events observed in MS may be a genetically or phenotypically reinforced expression of the platelet P2Y₁₂ receptor. In order to analyze the effect of the PAR1 (protease activated receptor type 1) signaling pathway on the expression level of P2Y₁₂, we also analyzed the correlation parameters between P2Y₁₂ expression and the markers of platelet activation in MS induced by selective PAR1 agonist (thrombin receptor activating peptide-6, TRAP-6). Identifying the molecular base responsible for the enlarged pro-thrombotic activity of platelets in SP MS could contribute to the implementation of prevention and targeted treatment, reducing the development of cardiovascular disorders in the course of the disease.

Platelets in dengue infection: more than a numbers game

Dengue virus (DENV) infection is responsible for the development of dengue illness, which can be either asymptomatic, present mild manifestations or evolve to severe dengue. Thrombocytopenia is an important characteristic during DENV infection, being observed both in mild and severe dengue, although the lowest platelet counts are encountered during severe cases. This review gathers information regarding several mechanisms that have been related to alterations in platelet number and function, leading to thrombocytopenia but also platelet-mediated immune and inflammatory response. On this regard, we highlight that the decrease in platelet counts may be due to bone marrow suppression or consumption of platelets at the periphery. We discuss the infection of hematopoietic progenitors and stromal cells as mechanisms involved in bone marrow suppression. Concerning peripheral consumption of platelets, we addressed the direct infection of platelets by DENV, adhesion of platelets to leukocytes and vascular endothelium and platelet clearance mediated by anti-platelet antibodies. We also focused on platelet involvement on the dengue immunity and pathogenesis through translation and secretion of viral and host factors and through platelet-leukocyte aggregates formation. Hence, the present review highlights important findings related to platelet activation and thrombocytopenia during dengue infection, and also exhibits different mechanisms associated with decreased platelet counts.Graphical abstract:Schematic mechanistic representation of platelet-mediated immune responses and thrombocytopenia during dengue infection. (A) DENV-infected platelets secrete cytokines and chemokines and also adhere to activated vascular endothelium. Platelets aggregate with leukocytes, inducing the secretion of NETs and inflammatory mediators by neutrophils and monocytes, respectively. (B) DENV directly infects stromal cells and hematopoietic precursors, including megakaryocytes, which compromises megakaryopoiesis. Both central and peripheric mechanisms contribute to DENV-associated thrombocytopenia.

Platelet-Monocyte Aggregates: Understanding Mechanisms and Functions in Sepsis

ABSTRACT

Platelets have been shown to play an important immunomodulatory role in the pathogenesis of various diseases through their interactions with other immune and nonimmune cells. Sepsis is a major cause of death in the United States, and many of the mechanisms driving sepsis pathology are still unresolved. Monocytes have recently received increasing attention in sepsis pathogenesis, and multiple studies have associated increased levels of platelet-monocyte aggregates observed early in sepsis with clinical outcomes in sepsis patients. These findings suggest platelet-monocyte aggregates may be an important prognostic indicator. However, the mechanisms leading to platelet interaction and aggregation with monocytes, and the effects of aggregation during sepsis are still poorly defined. There are few studies that have really investigated functions of platelets and monocytes together, despite a large body of research showing separate functions of platelets and monocytes in inflammation and immune responses during sepsis. The goal of this review is to provide insights into what we do know about mechanisms and biological meanings of platelet-monocyte interactions, as well as some of the technical challenges and limitations involved in studying this important potential mechanism in sepsis pathogenesis. Improving our understanding of platelet and monocyte biology in sepsis may result in identification of novel targets that can be used to positively affect outcomes in sepsis.

Aspirin for prevention of colorectal cancer in the elderly: friend or foe?

Cancer is the leading cause of death among men and women aged 60-79 years. Colorectal cancer is the third most common cancer in males and the second most common in females, with about 0.8 million deaths worldwide per year. Individuals older than 50 years account for 20-50% of colonic adenomas. Several measures have been proposed to decrease colorectal cancer risks, such as an increase in dietary fiber, use of aspirin, and physical activity. Nonsteroidal anti-inflammatory drugs have been proposed as protective agents against the development of colorectal cancer and colorectal adenomas. Aspirin was the first pharmacological agent endorsed by the United States Preventive Services Task Force screening for colorectal cancer chemoprevention. Although studies have shown up to 40% colorectal cancer risk reduction in individuals at average risk, data regarding this benefit are inconsistent. Several recent studies show that prophylactic use of aspirin in elderly subjects may not be beneficial in preventing the occurrence of colorectal cancers. Given the risks associated with aspirin, such as non-fatal and fatal bleeding events, aspirin's role should be redefined, especially in individuals at risk of bleeding. This review provides a discussion of the recent studies on the role of aspirin use in elderly individuals at risk of colorectal cancer.

Activated Platelets Convert CD14+CD16- Into CD14+CD16+ Monocytes With Enhanced FcγR-Mediated Phagocytosis and Skewed M2 Polarization

Monocytes are important cellular effectors of innate immune defense. Human monocytes are heterogeneous and can be classified into three distinct subsets based on CD14 and CD16 expression. The expansion of intermediate CD14⁺CD16⁺ monocytes has been reported in chronic inflammatory diseases including rheumatoid arthritis (RA). However, the mechanism underlying induction of CD16 and its role in monocytes remains poorly understood. Here, we demonstrate that activated platelets are important for induction of CD16 on classical CD14⁺CD16^- monocytes by soluble factors such as cytokines. Cytokine neutralization and signaling inhibition assays reveal that sequential involvement of platelet-derived TGF-β and monocyte-derived IL-6 contribute to CD16 induction on CD14⁺CD16^- monocytes. Activated platelet-induced CD16 on monocytes participates in antibody-dependent cellular phagocytosis (ADCP) and its level is positively correlated with phagocytic activity. CD14⁺CD16^- monocytes treated with activated platelets preferentially differentiate into M2 macrophages, likely the M2c subset expressing CD163 and MerTK. Lastly, the amount of sCD62P, a marker of activated platelets, is significantly elevated in plasma of RA patients and positively correlates with clinical parameters of RA. Our findings suggest an important role of activated platelets in modulating phenotypical and functional features of human monocytes. This knowledge increases understanding of the immunological role of CD14⁺CD16⁺ cells in chronic inflammatory diseases.

Principal component analysis of routine blood test results with Parkinson's disease: A case-control study

This study aimed to explore the association of routine blood test values and blood cell ratios with the risk or severity of Parkinson's disease (PD). The medical records of 453 PD patients and 436 controls were retrospectively reviewed. The severity of PD was quantified by the modified Hoehn-Yahr (HY) scale. We performed principal component analysis (PCA) of significant values/ratios and used logistic regression analysis to explore the relationship between principal components (PCs) and the risk of PD. Spearman correlation and ordinal logistic regression analyses were performed to explore the relationship between indicators and the severity of PD. The PCA generated 9 PCs, which contributed to 90.86% of the total variance. Logistic regression analysis revealed positive associations of PC2 (a measure monocyte ratios) and PC6 (a measure of platelet ratios and volume) and negative associations of PC1 (a comprehensive measure of lymphocyte, eosinophil, neutrophil, and red blood cell values), PC4 (a measure of red blood cell values), and PC7 (a measure of red blood cell values and platelet volume) with the risk of PD. However, we observed no associations of variables with the severity of PD. In conclusion, PCA reduced the dimensionality of the data. Peripheral blood disorders may be associated with PD.

The efficacy of aspirin and metformin combination therapy in patients with rectal aberrant crypt foci: a double-blinded randomized controlled trial

Background

The incidence and mortality rates of colorectal cancer (CRC) continue to increase worldwide. Therefore, new preventive strategies are needed to lower the burden of this disease. Previous studies reported that aspirin could suppress the development of sporadic colorectal adenoma. In addition, metformin is a biguanide derivative that is long widely used for the treatment of diabetes mellitus and has recently been suggested to have a suppressive effect on carcinogenesis and cancer cell growth. Both drugs exhibit a chemopreventive effect, but their efficacy is limited.

Aberrant crypt foci (ACF), defined as lesions containing crypts that are larger in diameter and stain more darkly with methylene blue than normal crypts, are more prevalent in patients with cancer and adenomas, and considered a reliable surrogate biomarker of CRC. Thus, we designed a prospective trial as a preliminary study prior to a CRC chemoprevention trial to evaluate the chemopreventive effect of aspirin combined with metformin on colorectal ACF formation in patients scheduled for polypectomy.

Methods

This study is a double-blind randomized controlled trial that will be conducted in patients with both colorectal ACF and colorectal polyps scheduled for polypectomy. Eligible patients will be recruited for the study and the number of ACF in the rectum will be counted at the baseline colonoscopy. Then, the participants will be allocated to one of the following two groups; the aspirin plus placebo group or the aspirin plus metformin group. Patients in the aspirin plus placebo group will receive oral aspirin (100 mg) and placebo for 8 weeks, and those in the aspirin plus metformin group will receive oral aspirin (100 mg) and metformin (250 mg) for 8 weeks. After 8 weeks of administration, polypectomy will be performed to evaluate changes in the number of ACF, and the cell-proliferative activity in the normal colorectal mucosa and colorectal polyps.

Discussion

This is the first study proposed that will explore the effect of aspirin combined with metformin on the formation of colorectal ACF in humans.

Trial registration

This trial has been registered in the University Hospital Medical Information Network (UMIN) Clinical Trials Registry as UMIN000028259. Registered 17 July 2017.

Innate immune receptors in platelets and platelet-leukocyte interactions

Platelets are chief cells in hemostasis. Apart from their hemostatic roles, platelets are major inflammatory effector cells that can influence both innate and adaptive immune responses. Activated platelets have thromboinflammatory functions linking hemostatic and immune responses in several physiological and pathological conditions. Among many ways in which platelets exert these functions, platelet expression of pattern recognition receptors (PRRs), including TLR, Nod-like receptor, and C-type lectin receptor families, plays major roles in sensing and responding to pathogen-associated or damage-associated molecular patterns (PAMPs and DAMPs, respectively). In this review, an increasing body of evidence is compiled showing the participation of platelet innate immune receptors, including PRRs, in infectious diseases, sterile inflammation, and cancer. How platelet recognition of endogenous DAMPs participates in sterile inflammatory diseases and thrombosis is discussed. In addition, platelet recognition of both PAMPs and DAMPs initiates platelet-mediated inflammation and vascular thrombosis in infectious diseases, including viral, bacterial, and parasite infections. The study also focuses on the involvement of innate immune receptors in platelet activation during cancer, and their contribution to tumor microenvironment development and metastasis. Finally, how innate immune receptors participate in platelet communication with leukocytes, modulating leukocyte-mediated inflammation and immune functions, is highlighted. These cell communication processes, including platelet-induced release of neutrophil extracellular traps, platelet Ag presentation to T-cells and platelet modulation of monocyte cytokine secretion are discussed in the context of infectious and sterile diseases of major concern in human health, including cardiovascular diseases, dengue, HIV infection, sepsis, and cancer.

Dengue virus-activated platelets modulate monocyte immunometabolic response through lipid droplet biogenesis and cytokine signaling

Dengue is characterized as one of the most important arthropod-borne human viral diseases, representing a public health problem. Increased activation of immune cells is involved in the progression of infection to severe forms. Recently, our group demonstrated the contribution of platelet-monocyte interaction to inflammatory responses in dengue, adding to evolving evidence that platelets have inflammatory functions and can regulate different aspects of innate immune responses. Furthermore, stimuli-specific-activated platelets can promote phenotypic changes and metabolic reprogramming in monocytes. Thus, this study aimed to evaluate the roles of dengue virus (DENV)-activated platelets on immunometabolic reprogramming of monocytes in vitro, focusing on lipid droplet (LD) biogenesis. We demonstrated that platelets exposed to DENV in vitro form aggregates with monocytes and signal to LD formation and CXCL8/IL-8, IL-10, CCL2, and PGE₂ secretion. Pharmacologic inhibition of LD biogenesis prevents PGE₂ secretion, but not CXCL8/IL-8 release, by platelet-monocyte complexes. In exploring the mechanisms involved, we demonstrated that LD formation in monocytes exposed to DENV-activated platelets is partially dependent on platelet-produced MIF. Additionally, LD formation is higher in monocytes, which have platelets adhered on their surface, suggesting that beyond paracrine signaling, platelet adhesion is an important event in platelet-mediated modulation of lipid metabolism in monocytes. Together, our results demonstrate that activated platelets aggregate with monocytes during DENV infection and signal to LD biogenesis and the secretion of inflammatory mediators, which may contribute to dengue immunopathogenesis.

Extracorporeal Photochemotherapy: Mechanistic Insights Driving Recent Advances and Future Directions

Dendritic cells (DCs) are professional antigen-presenting cells, necessary for the initiation and maintenance of antigen-specific immunity and tolerance. Decades of research have been driven by hopes to harness the immunological capabilities of DCs and achieve physiological partnership with the immune system for therapeutic ends. Potential applications for DC-based immunotherapy include treatments for cancer, autoimmune disorders, and infectious diseases. However, DCs have poor availability in peripheral and lymphoid tissues and have poor survivability in culture, leading to the development of multiple strategies to generate and manipulate large numbers of DCs ex vivo. Among these is Extracorporeal Photopheresis (ECP), a widely used cancer immunotherapy. Recent advancements have uncovered that stimulation of monocyte-to-DC maturation via physiologic inflammatory signaling lies at the mechanistic core of ECP. Here, we describe the landscape of DC-based immunotherapy, the historical context of ECP, the current mechanistic understanding of ex vivo monocyte-to-DC maturation in ECP, and the implications of this understanding on making scientifically driven improvements to modern ECP protocols and devices.

Differential mRNA expression combined with network pharmacology reveals network effects of Liangxue Tongyu Prescription for acute intracerebral hemorrhagic rats

ETHNOPHARMACOLOGICAL RELEVANCE

Liangxue Tongyu Prescription (LTP) is a traditional Chinese medicine formula composed of 8 crude drugs that is widely used to treat acute intracerebral hemorrhage (AICH).

AIM OF THE STUDY

To verify the efficacy of LTP on the survival time in the treatment of acute intracerebral hemorrhagic rats (AICHs), and to elucidate its network pharmacodynamic mechanism of multi-component, multi-target, and multi-signaling pathways.

MATERIALS AND METHODS

Survival analysis was used to evaluate the survival time of AICH rats induced by different doses of collagenase and the efficacy of three doses of LTP in the treatment of AICH rats. The Kaplan-Meier curves for survival time were produced and compared with the Log-rank test and Wilcoxon (Gehan) χ². Differential mRNA-seq combined with network pharmacology was used to disclose the network effect mechanism of LTP on AICH, and the obtained differential genes were mapped into the predictive empirical compound-target network model (ECT network model) and the empirical compound-target-pathogenesis (disease) network model (ECTP network model).

RESULTS

The median survival time of four different doses of LTP-treated groups (0.00 g/kg, 5.78 g/kg, 11.55 g/kg, 23.10 g/kg) for adult AICH rats by 0.18 U collagenase was 14 h, 37 h, 150 h, and 51 h respectively, and the 7-day survival rates were 33.3%, 41.7%, 50.0%, and 38.5%, of which the medium-dose group (MD) had a longer survival time and higher survival rate. Through further validation experiments, the MD group had a better efficacy trend with a median survival time of 168 h vs 23 h in the model control group (MC) (Wilcoxon Gehan Test, χ² = 3.478, P = 0.062). The transcriptomic analysis of mRNA showed that 583 significant differential genes were found between the MC and MD group and 7 key therapeutic targets regulated by 29 compounds in LTP on AICH were screened out by VCT and VCTP network model. These targets were involved in 5 regulatory models or pathways.

CONCLUSION

Our study confirmed the exact efficacy of the LTP in the treatment of AICH and revealed the potential pharmacodynamic components and mode of action of the LTP on AICH. Using differential transcriptome of mRNA combined with network pharmacology, we screened out 29 chemical compounds as the potential effective ingredients of LTP which acted on 7 targets of AICH involving 5 pathological pathways, mainly including repairing the brain function defect, improving neural function, protecting blood-brain barrier from damage, reducing inflammatory factors, and inhibiting apoptosis. The present study not only provides a new explanation for the 'multi-component, multi-target, multi-pathway' effects of the LTP on AICH but also screened out some major compounds of LTP and their potential targets which will facilitate the development of new drugs for AICH.

The role of aspirin in the prevention of ovarian, endometrial and cervical cancers

Drug repurposing is the application of an existing licenced drug for a new indication and potentially provides a faster and cheaper approach to developing new anti-cancer agents. Gynaecological cancers contribute significantly to the global cancer burden, highlighting the need for low cost, widely accessible therapies. A large body of evidence supports the role of aspirin as an anti-cancer agent, and a number of randomized trials are currently underway aiming to assess the potential benefit of aspirin in the treatment of cancer. This review summarizes the evidence underpinning aspirin use for the prevention of the development and recurrence of gynaecological cancers (ovarian, endometrial and cervical) and potential mechanisms of action.

Platelets Modulate IFN-γ Production against Candida albicans in Peripheral Blood Mononuclear Cells via Prostaglandins

Platelets are known to have immunomodulatory properties. They modulate immune responses of leukocytes against various pathogens, including fungi. Candida albicans can cause systemic infection in immunocompromised individuals that is associated with a high mortality and morbidity. In the current study, we explored the role of platelets in antifungal host defense against C. albicans PBMCs were stimulated with heat-killed (HK) C. albicans in the presence or absence of isolated washed platelets. Cytokines were quantified from culture supernatants by ELISA. Inhibition of platelet receptors and cytokine pathways were used to elucidate the mechanisms involved in platelet-leukocyte interaction. In the presence of platelets, PBMCs produced less IFN-γ upon stimulation with HK C. albicans This effect was dependent on the direct contact between platelets and leukocytes but was independent of the platelet GPIb and P-selectin receptors. The attenuation of IFN-γ was not a direct effect on T cells but was dependent on the presence of APC and T cells. Platelets did not modulate the Th-1-polarizing cytokines IL-12 and IL-18. The addition of PG (PGE₂) further diminished IFN-γ levels in PBMCs, and supplementation of cells with nonsteroidal anti-inflammatory drugs was able to restore the level of IFN-γ. Overall, we show that modulation of the Th1 response against C. albicans by platelets is dependent on PGs.

Ex vivo dendritic cell generation-A critical comparison of current approaches

Dendritic cells (DCs) are professional antigen-presenting cells, required for the initiation of naïve and memory T cell responses and regulation of adaptive immunity. The discovery of DCs in 1973, which culminated in the Nobel Prize in Physiology or Medicine in 2011 for Ralph Steinman and colleagues, initially focused on the identification of adherent mononuclear cell fractions with uniquely stellate dendritic morphology, followed by key discoveries of their critical immunologic role in initiating and maintaining antigen-specific immunity and tolerance. The medical promise of marshaling these key capabilities of DCs for therapeutic modulation of antigen-specific immune responses has guided decades of research in hopes to achieve genuine physiologic partnership with the immune system. The potential uses of DCs in immunotherapeutic applications include cancer, infectious diseases, and autoimmune disorders; thus, methods for rapid and reliable large-scale production of DCs have been of great academic and clinical interest. However, difficulties in obtaining DCs from lymphoid and peripheral tissues, low numbers and poor survival in culture, have led to advancements in ex vivo production of DCs, both for probing molecular details of DC function as well as for experimenting with their clinical utility. Here, we review the development of a diverse array of DC production methodologies, ranging from cytokine-based strategies to genetic engineering tools devised for enhancing DC-specific immunologic functions. Further, we explore the current state of DC therapies in clinic, as well as emerging insights into physiologic production of DCs inspired by existing therapies.

Predicting significance of COX-2 expression of peripheral blood monocyte in patients with coronary artery disease

Background

Cyclooxygenase-2 (COX-2) plays an important role in the monocyte-platelet aggregate (MPA)-medicated inflammatory response and possible coronary artery disease (CAD). This study aimed to assess the predicting significance of COX-2 expression in peripheral blood monocyte for CAD.

Methods

A total of 66 patients with CAD including stable angina (SA) and unstable angina (UA) were enrolled. The inflammatory indexes including white blood cell (WBC) count, high-sensitive C reactive protein (hs-CRP), serum monocyte chemoattractant protein-1 (MCP-1) and MPA levels were measured. The western-blotting assay and reverse transcription-polymerase chain reaction (RT-PCR) analysis were used to detect the COX-2 expression in peripheral blood monocytes. Furthermore, the correlation between COX-2 expression and MPA levels, and the association of COX-2 expression with CAD risk were assessed.

Results

The UA patients demonstrated higher levels of inflammatory indexes than the SA patients (P<0.001). Simultaneously, higher MPA levels and enhanced COX-2 expression were observed in the UA patients (P<0.01). The patients with enhanced COX-2 expression exhibited higher MPA than those without (P<0.01), and patients with increased MPA also demonstrated enhanced COX-2 expression (P<0.001). Moreover, the levels of COX-2 protein expression was positively related to the MPA formation rates (R²=0.4933, P<0.01), and enhanced COX-2 expression was independently associated with CAD risk [odds ratio (OR): 6.322, 95% confidence interval (CI): 4.544-8.978 ].

Conclusions

The COX-2 expression of peripheral blood monocytes can be used as an independent predictor for CAD.

Platelet Inflammatory Response to Stress

Blood platelets play a central hemostatic role, (i) as they repair vascular epithelial damage, and (ii) they play immune defense roles, as they have the capacity to produce and secrete various cytokines, chemokines, and related products. Platelets sense and respond to local dangers (infectious or not). Platelets, therefore, mediate inflammation, express and use receptors to bind infectious pathogen moieties and endogenous ligands, among other components. Platelets contribute to effective pathogen clearance. Damage-associated molecular patterns (DAMPs) are danger signals released during inflammatory stress, such as burns, trauma and infection. Each pathogen is recognized by its specific molecular signature or pathogen-associated molecular pattern (PAMP). Recent data demonstrate that platelets have the capacity to sense external danger signals (DAMPs or PAMPs) differentially through a distinct type of pathogen recognition receptor (such as Toll-like receptors). Platelets regulate the innate immune response to pathogens and/or endogenous molecules, presenting several types of “danger” signals using a complete signalosome. Platelets, therefore, use complex tools to mediate a wide range of functions from danger sensing to tissue repair. Moreover, we noted that the secretory capacity of stored platelets over time and the development of stress lesions by platelets upon collection, processing, and storage are considered stress signals. The key message of this review is the “inflammatory response to stress” function of platelets in an infectious or non-infectious context.

Platelet-Specific Deletion of Cyclooxygenase-1 Ameliorates Dextran Sulfate Sodium-Induced Colitis in Mice

Inflammatory bowel disease (IBD) is associated with an increased risk for thromboembolism, platelet activation, and abnormalities in platelet number and size. In colitis, platelets can extravasate into the colonic interstitium. We generated a mouse with a specific deletion of cyclooxygenase (COX)-1 in megakaryocytes/platelets [(COX-1 conditional knockout (cKO)] to clarify the role of platelet activation in the development of inflammation and fibrosis in dextran sodium sulfate (DSS)-induced colitis. The disease activity index was assessed, and colonic specimens were evaluated for histologic features of epithelial barrier damage, inflammation, and fibrosis. Cocultures of platelets and myofibroblasts were performed. We found that the specific deletion of COX-1 in platelets, which recapitulated the human pharmacodynamics of low-dose aspirin, that is, suppression of platelet thromboxane (TX)A₂ production associated with substantial sparing of the systemic production of prostacyclin, resulted in milder symptoms of colitis, in the acute phase, and almost complete recovery from the disease after DSS withdrawal. Reduced colonic accumulation of macrophages and myofibroblasts and collagen deposition was found. Platelet-derived TXA₂ enhanced the ability of myofibroblasts to proliferate and migrate in vitro, and these effects were prevented by platelet COX-1 inhibition or antagonism of the TXA₂ receptor. Our findings allow a significant advance in the knowledge of the role of platelet-derived TXA₂ in the development of colitis and fibrosis in response to intestinal damage and provide the rationale to investigate the potential efficacy of the antiplatelet agent low-dose aspirin in limiting the inflammatory response and fibrosis associated with IBD. SIGNIFICANCE STATEMENT: Inflammatory bowel disease (IBD) is characterized by the development of a chronic inflammatory response, which can lead to intestinal fibrosis for which currently there is no medical treatment. Through the generation of a mouse with specific deletion of cyclooxygenase-1 in megakaryocytes/platelets, which recapitulates the human pharmacodynamics of low-dose aspirin, we demonstrate the important role of platelet-derived thromboxane A₂ in the development of experimental colitis and fibrosis, thus providing the rationale to investigate the potential efficacy of low-dose aspirin in limiting the inflammation and tissue damage associated with IBD.

Platelets and extracellular vesicles in cancer: diagnostic and therapeutic implications

Several pieces of evidence support the role of activated platelets in the development of the chronic inflammation-related diseases, such as atherothrombosis and cancer, mainly via the release of soluble factors and microparticles (MPs). Platelets and MPs contain a repertoire of proteins and genetic material (i.e., mRNAs and microRNAs) which may be influenced by the clinical condition of the individuals. In fact, platelets are capable of up-taking proteins and genetic material during their lifespan. Moreover, the content of platelet-derived MPs can be delivered to other cells, including stromal, immune, epithelial, and cancer cells, to change their phenotype and functions, thus contributing to cancer promotion and its metastasization. Platelets and MPs can play an indirect role in the metastatic process by helping malignant cells to escape from immunological surveillance. Furthermore, platelets and their derived MPs represent a potential source for blood biomarker development in oncology. This review provides an updated overview of the roles played by platelets and MPs in cancer and metastasis formation. The possible analysis of platelet and MP molecular signatures for the detection of cancer and monitoring of anticancer treatments is discussed. Finally, the potential use of MPs as vectors for drug delivery systems to cancer cells is put forward.

Platelets in cancer development and diagnosis

Platelets are involved in the development and progression of cancer through several mechanisms. Platelet activation at the site of tissue damage contributes to the initiation of a cascade of events which promote tumorigenesis. In fact, platelets release a wide array of proteins, including growth and angiogenic factors, lipids and extracellular vesicles rich in genetic material, which can mediate the induction of phenotypic changes in target cells, such as immune, stromal and tumor cells, and promote carcinogenesis and metastasis formation. Importantly, the role of platelets in tumor immune escape has been described. These lines of evidence open the way to novel strategies to fight cancer based on the use of antiplatelet agents. In addition to their ability to release factors, platelets are able of up-taking proteins and genetic material present in the bloodstream. Platelets are like 'sentinels' of the disease state. The evaluation of proteomics and transcriptomics signature of platelets and platelet-derived microparticles could represent a new strategy for the development of biomarkers for early cancer detection and/or therapeutic drug monitoring in cancer chemotherapy. Owing to the ability of platelets to interact with cancer cells and to deliver their cargo, platelets have been proposed as a 'biomimetic drug delivery system' for anti-tumor drugs to prevent the occurrence of off-target adverse events associated with the use of traditional chemotherapy.

Papain Ameliorates the MPAs Formation-Mediated Activation of Monocytes by Inhibiting Cox-2 Expression via Regulating the MAPKs and PI3K/Akt Signal Pathway

Monocytes activation and subsequent inflammatory response mediated by monocyte-platelet aggregates (MPAs) formation play the key roles in the early pathogenesis of atherosclerosis (AS). Exploration of novel drugs to ameliorate MPAs formation-mediated monocytes activation would be helpful for the treatment of AS patients. Papain has definite pharmacological effects including antiplatelet, thrombolysis, and anti-inflammation. However, its effect on MPAs formation and the following monocytes activation remains vague. This study aimed to illustrate the underlying mechanisms of papain on MPAs formation-initiated monocytes activation in vitro. In this study, Papain, Cox-2 inhibitor (NS-398), and NF-κB agonist (TNF-α) were used as the treating agents, respectively. MPAs formation and activated monocytes were measured by flow cytometry (FCM). Cox-2 mRNA, MCP-1, and proteins of Cox-2 and NF-κB signal pathway were detected by qRT-PCR, ELISA, and western blotting, respectively. As we observed, papain exhibited the powerful inhibitory effects on thrombin-mediated MPAs formation and monocytes activation in a concentration-dependent manner as what Cox-2 inhibitor demonstrated. However, the inhibitory tendency was significantly reversed by TNF-α. We also discovered that both Cox-2 mRNA and protein expression as well as the release of MCP-1 of monocyte was inhibited by either papain or NS-398, but TNF-α stimulated Cox-2 expression and release of MCP-1. The results of western blotting assay indicated that thrombin-mediated proteins expression of MAPKs and PI3K/Akt signal pathway was inhibited by papain and NS-398. However, TNF-α notably abated the inhibitory effects of papain on the process of MPAs-initiated monocytes activation. Our findings suggest that papain can inhibit the MPAs formation-mediated activation of monocytes by inhibiting the MAPKs and PI3K/Akt signal pathway.

Platelets Promote Brucella abortus Monocyte Invasion by Establishing Complexes With Monocytes

Brucellosis is an infectious disease elicited by bacteria of the genus Brucella. Platelets have been extensively described as mediators of hemostasis and responsible for maintaining vascular integrity. Nevertheless, they have been recently involved in the modulation of innate and adaptive immune responses. Although many interactions have been described between Brucella abortus and monocytes/macrophages, the role of platelets during monocyte/macrophage infection by these bacteria remained unknown. The aim of this study was to investigate the role of platelets in the immune response against B. abortus. We first focused on the possible interactions between B. abortus and platelets. Bacteria were able to directly interact with platelets. Moreover, this interaction triggered platelet activation, measured as fibrinogen binding and P-selectin expression. We further investigated whether platelets were involved in Brucella-mediated monocyte/macrophage early infection. The presence of platelets promoted the invasion of monocytes/macrophages by B. abortus. Moreover, platelets established complexes with infected monocytes/macrophages as a result of a carrier function elicited by platelets. We also evaluated the ability of platelets to modulate functional aspects of monocytes in the context of the infection. The presence of platelets during monocyte infection enhanced IL-1β, TNF-α, IL-8, and MCP-1 secretion while it inhibited the secretion of IL-10. At the same time, platelets increased the expression of CD54 (ICAM-1) and CD40. Furthermore, we showed that soluble factors released by B. abortus-activated platelets, such as soluble CD40L, platelet factor 4, platelet-activating factor, and thromboxane A₂, were involved in CD54 induction. Overall, our results indicate that platelets can directly sense and react to B. abortus presence and modulate B. abortus-mediated infection of monocytes/macrophages increasing their pro-inflammatory capacity, which could promote the resolution of the infection.

Platelets in Immune Response to Virus and Immunopathology of Viral Infections

Platelets are essential effector cells in hemostasis. Aside from their role in coagulation, platelets are now recognized as major inflammatory cells with key roles in the innate and adaptive arms of the immune system. Activated platelets have key thromboinflammatory functions linking coagulation to immune responses in various infections, including in response to virus. Recent studies have revealed that platelets exhibit several pattern recognition receptors (PRR) including those from the toll-like receptor, NOD-like receptor, and C-type lectin receptor family and are first-line sentinels in detecting and responding to pathogens in the vasculature. Here, we review the main mechanisms of platelets interaction with viruses, including their ability to sustain viral infection and replication, their expression of specialized PRR, and activation of thromboinflammatory responses against viruses. Finally, we discuss the role of platelet-derived mediators and platelet interaction with vascular and immune cells in protective and pathophysiologic responses to dengue, influenza, and human immunodeficiency virus 1 infections.

Cancer and platelet crosstalk: opportunities and challenges for aspirin and other antiplatelet agents

Platelets have long been recognized as key players in hemostasis and thrombosis; however, growing evidence suggests that they are also significantly involved in cancer, the second leading cause of mortality worldwide. Preclinical and clinical studies showed that tumorigenesis and metastasis can be promoted by platelets through a wide variety of crosstalk between platelets and cancer cells. For example, cancer changes platelet behavior by directly inducing tumor-platelet aggregates, triggering platelet granule and extracellular vesicle release, altering platelet phenotype and platelet RNA profiles, and enhancing thrombopoiesis. Reciprocally, platelets reinforce tumor growth with proliferation signals, antiapoptotic effect, and angiogenic factors. Platelets also activate tumor invasion and sustain metastasis via inducing an invasive epithelial-mesenchymal transition phenotype of tumor cells, promoting tumor survival in circulation, tumor arrest at the endothelium, and extravasation. Furthermore, platelets assist tumors in evading immune destruction. Hence, cancer cells and platelets maintain a complex, bidirectional communication. Recently, aspirin (acetylsalicylic acid) has been recognized as a promising cancer-preventive agent. It is recommended at daily low dose by the US Preventive Services Task Force for primary prevention of colorectal cancer. The exact mechanisms of action of aspirin in chemoprevention are not very clear, but evidence has emerged that suggests a platelet-mediated effect. In this article, we will introduce how cancer changes platelets to be more cancer-friendly and highlight advances in the modes of action for aspirin in cancer prevention. We also discuss the opportunities, challenges, and opposing viewpoints on applying aspirin and other antiplatelet agents for cancer prevention and treatment.

Potential of anti-inflammatory agents for treatment of atherosclerosis

Chronic inflammation is a central pathogenic mechanism of atherosclerosis induction and progression. Vascular inflammation is associated with accelerated onset of late atherosclerosis complications. Atherosclerosis-related inflammation is mediated by a complex cocktail of pro-inflammatory cytokines, chemokines, bioactive lipids, and adhesion molecules, and blocking the key pro-atherogenic inflammatory mechanisms can be beneficial for treatment of atherosclerosis. Therapeutic agents that specifically target some of the atherosclerosis-related inflammatory mechanisms have been evaluated in preclinical and clinical studies. The most promising anti-inflammatory compounds for treatment of atherosclerosis include non-specific anti-inflammatory drugs, phospholipase inhibitors, blockers of major inflammatory cytokines, leukotrienes, adhesion molecules, and pro-inflammatory signaling pathways, such as CCL2-CCR2 axis or p38 MAPK pathway. Ongoing studies attempt evaluating therapeutic utility of these anti-inflammatory drugs for treatment of atherosclerosis. The obtained results are important for our understanding of atherosclerosis-related inflammatory mechanisms and for designing randomized controlled studies assessing the effect of specific anti-inflammatory strategies on cardiovascular outcomes.

Platelets and matrix metalloproteinases

Matrix metalloproteinases (MMPs) and their inhibitors essentially contribute to a variety of pathophysiologies by modulating cell migration, tissue degradation and inflammation. Platelet-associated MMP activity appears to play a major role in these processes. First, platelets can concentrate leukocyte-derived MMP activity to sites of vascular injury by leukocyte recruitment. Second, platelets stimulate MMP production in e.g. leukocytes, endothelial cells, or tumour cells by direct receptor interaction or/and by paracrine pathways. Third, platelets synthesise and secrete a variety of MMPs including MMP-1, MMP-2, MMP-3, and MMP-14 (MT1-MMP), and potentially MMP-9 as well as the tissue inhibitors of metalloproteinase (TIMPs). This review focuses on platelet-derived and platelet-induced MMPs and their inhibitors.

Granzyme A in Human Platelets Regulates the Synthesis of Proinflammatory Cytokines by Monocytes in Aging

Dysregulated inflammation is implicated in the pathobiology of aging, yet platelet-leukocyte interactions and downstream cytokine synthesis in aging remains poorly understood. Platelets and monocytes were isolated from healthy younger (age <45, n = 37) and older (age ≥65, n = 30) adults and incubated together under autologous and nonautologous conditions. Synthesis of inflammatory cytokines by monocytes, alone or in the presence of platelets, was examined. Next-generation RNA-sequencing allowed for unbiased profiling of the platelet transcriptome in aging. Basal IL-8 and MCP-1 synthesis by monocytes alone did not differ between older and younger adults. However, in the presence of autologous platelets, monocytes from older adults synthesized greater IL-8 (41 ± 5 versus 9 ± 2 ng/ml, p < 0.0001) and MCP-1 (867 ± 150 versus 216 ± 36 ng/ml, p < 0.0001) than younger adults. Platelets from older adults were sufficient for upregulating the synthesis of inflammatory cytokines by monocytes. Using RNA-sequencing of platelets followed by validation via RT-PCR and immunoblot, we discovered that granzyme A (GrmA), a serine protease not previously identified in human platelets, increases with aging (∼9-fold versus younger adults, p < 0.05) and governs increased IL-8 and MCP-1 synthesis through TLR4 and caspase-1. Inhibiting GrmA reduced excessive IL-8 and MCP-1 synthesis in aging to levels similar to younger adults. In summary, human aging is associated with changes in the platelet transcriptome and proteome. GrmA is present and bioactive in human platelets, is higher in older adults, and controls the synthesis of inflammatory cytokines by monocytes. Alterations in the platelet molecular signature and signaling to monocytes may contribute to dysregulated inflammatory syndromes in older adults.

Pathogenesis of vascular leak in dengue virus infection

Endothelial dysfunction leading to vascular leak is the hallmark of severe dengue. Vascular leak typically becomes clinically evident 3-6 days after the onset of illness, which is known as the critical phase. This critical phase follows the period of peak viraemia, and lasts for 24-48 hr and usually shows rapid and complete reversal, suggesting that it is likely to occur as a result of inflammatory mediators, rather than infection of the endothelium. Cytokines such as tumour necrosis factor-α, which are known to be elevated in the critical phase of dengue, are likely to be contributing factors. Dengue NS1, a soluble viral protein, has also been shown to disrupt the endothelial glycocalyx and thus contribute to vascular leak, although there appears to be a discordance between the timing of NS1 antigenaemia and occurrence of vascular leak. In addition, many inflammatory lipid mediators are elevated in acute dengue viral infection such as platelet activating factor (PAF) and leukotrienes. Furthermore, many other inflammatory mediators such as vascular endothelial growth factor and angiopoietin-2 have been shown to be elevated in patients with dengue haemorrhagic fever, exerting their action in part by inducing the activity of phospholipases, which have diverse inflammatory effects including generation of PAF. Platelets have also been shown to significantly contribute to endothelial dysfunction by production of interleukin-1β through activation of the NLRP3 inflammasome and also by inducing production of inflammatory cytokines by monocytes. Drugs that block down-stream immunological mediator pathways such as PAF may also be beneficial in the treatment of severe disease.

Adenosine-to-inosine RNA editing controls cathepsin S expression in atherosclerosis by enabling HuR-mediated post-transcriptional regulation

Adenosine-to-inosine (A-to-I) RNA editing, which is catalyzed by a family of adenosine deaminase acting on RNA (ADAR) enzymes, is important in the epitranscriptomic regulation of RNA metabolism. However, the role of A-to-I RNA editing in vascular disease is unknown. Here we show that cathepsin S mRNA (CTSS), which encodes a cysteine protease associated with angiogenesis and atherosclerosis, is highly edited in human endothelial cells. The 3' untranslated region (3' UTR) of the CTSS transcript contains two inverted repeats, the AluJo and AluSx⁺ regions, which form a long stem-loop structure that is recognized by ADAR1 as a substrate for editing. RNA editing enables the recruitment of the stabilizing RNA-binding protein human antigen R (HuR; encoded by ELAVL1) to the 3' UTR of the CTSS transcript, thereby controlling CTSS mRNA stability and expression. In endothelial cells, ADAR1 overexpression or treatment of cells with hypoxia or with the inflammatory cytokines interferon-γ and tumor-necrosis-factor-α induces CTSS RNA editing and consequently increases cathepsin S expression. ADAR1 levels and the extent of CTSS RNA editing are associated with changes in cathepsin S levels in patients with atherosclerotic vascular diseases, including subclinical atherosclerosis, coronary artery disease, aortic aneurysms and advanced carotid atherosclerotic disease. These results reveal a previously unrecognized role of RNA editing in gene expression in human atherosclerotic vascular diseases.

Platelets in Pulmonary Immune Responses and Inflammatory Lung Diseases

Platelets are essential for physiological hemostasis and are central in pathological thrombosis. These are their traditional and best known activities in health and disease. In addition, however, platelets have specializations that broaden their functional repertoire considerably. These functional capabilities, some of which are recently discovered, include the ability to sense and respond to infectious and immune signals and to act as inflammatory effector cells. Human platelets and platelets from mice and other experimental animals can link the innate and adaptive limbs of the immune system and act across the immune continuum, often also linking immune and hemostatic functions. Traditional and newly recognized facets of the biology of platelets are relevant to defensive, physiological immune responses of the lungs and to inflammatory lung diseases. The emerging view of platelets as blood cells that are much more diverse and versatile than previously thought further predicts that additional features of the biology of platelets and of megakaryocytes, the precursors of platelets, will be discovered and that some of these will also influence pulmonary immune defenses and inflammatory injury.

Selective induction of anti-inflammatory monocyte-platelet aggregates in a model of pulsatile blood flow at low shear rates

In patients with cardiovascular abnormalities or immunological disorders, an increased number of circulating leukocyte-platelet aggregates is observed. Leukocyte-platelet aggregates play an essential role in linking the hemostatic and immune systems. High shear stress and pro-coagulant and pro-inflammatory stimulants are known to activate platelets and promote the formation of aggregates. Pulsatile blood flow under low shear stress can also induce platelet activation in comparatively mild conditions. However, the effect of such events on leukocyte-platelet aggregates has not yet been investigated. To determine whether low shear stress affects the formation of aggregates, we established a simple "inverting rotation" method of inducing periodic changes in the direction of blood flow in combination with low shear stress. We demonstrated that after the inverting rotation treatment for 10-20 min more than 70% of monocytes selectively aggregated with platelets. The formation of monocyte-platelet complexes was inhibited by an anti-CD162 (PSGL-1) monoclonal antibody or a Ca(2+) chelator. The phagocytic activity of monocytes was augmented by inverting rotation, whereas phagocytosis mediated by granulocytes remained unaffected. Interestingly, the formation of monocyte-platelet complexes suppressed the production of pro-inflammatory cytokines such as interleukin (IL)-1β. At the same time, monocyte-platelet complexes augmented the expression of the anti-inflammatory cytokine IL-10. Our results suggest that platelet-bound monocytes show an anti-inflammatory phenotype under low shear stress conditions. Thus, our method provided new insights into the mechanisms of monocyte-platelet aggregate formation and regulation.

Aspirin and colorectal cancer: the promise of precision chemoprevention

Aspirin (acetylsalicylic acid) has become one of the most commonly used drugs, given its role as an analgesic, antipyretic and agent for cardiovascular prophylaxis. Several decades of research have provided considerable evidence demonstrating its potential for the prevention of cancer, particularly colorectal cancer. Broader clinical recommendations for aspirin-based chemoprevention strategies have recently been established; however, given the known hazards of long-term aspirin use, larger-scale adoption of an aspirin chemoprevention strategy is likely to require improved identification of individuals for whom the protective benefits outweigh the harms. Such a precision medicine approach may emerge through further clarification of aspirin's mechanism of action.

Interleukin 1β Regulation of the System xc- Substrate-specific Subunit, xCT, in Primary Mouse Astrocytes Involves the RNA-binding Protein HuR

System xc(-) is a heteromeric amino acid cystine/glutamate antiporter that is constitutively expressed by cells of the CNS, where it functions in the maintenance of intracellular glutathione and extracellular glutamate levels. We recently determined that the cytokine, IL-1β, increases the activity of system xc(-) in CNS astrocytes secondary to an up-regulation of its substrate-specific light chain, xCT, and that this occurs, in part, at the level of transcription. However, an in silico analysis of the murine xCT 3'-UTR identified numerous copies of adenine- and uridine-rich elements, raising the possibility that undefined trans-acting factors governing mRNA stability and translation may also contribute to xCT expression. Here we show that IL-1β increases the level of mRNA encoding xCT in primary cultures of astrocytes isolated from mouse cortex in association with an increase in xCT mRNA half-life. Additionally, IL-1β induces HuR translocation from the nucleus to the cytoplasm. RNA immunoprecipitation analysis reveals that HuR binds directly to the 3'-UTR of xCT in an IL-1β-dependent manner. Knockdown of endogenous HuR protein abrogates the IL-1β-mediated increase in xCT mRNA half-life, whereas overexpression of HuR in unstimulated primary mouse astrocytes doubles the half-life of constitutive xCT mRNA. This latter effect is accompanied by an increase in xCT protein levels, as well as a functional increase in system xc(-) activity. Altogether, these data support a critical role for HuR in mediating the IL-1β-induced stabilization of astrocyte xCT mRNA.

Dysregulated post-transcriptional control of COX-2 gene expression in gestational diabetic endothelial cells

BACKGROUND AND PURPOSE

Hyperglycaemic memory describes the progression of diabetic complications during subsequent periods of improved glycaemia. We addressed the hypothesis that transient hyperglycaemia causes aberrant COX-2 expression in HUVEC in response to IL-1β through the induction of long-lasting epigenetic changes involving microRNA-16 (miR-16), a post-transcriptional modulator of COX-2 expression.

EXPERIMENTAL APPROACH

Studies were performed on HUVEC collected from women with gestational diabetes mellitus (GDM) (dHUVEC) and normal women (nHUVEC).

KEY RESULTS

In dHUVEC treated with IL-1β, the expression of COX-2 mRNA and protein was enhanced and generation of prostanoids increased (the most abundant was the promitogenic PGF_2α ). COX-2 mRNA was more stable in dHUVEC and this was associated with miR-16 down-regulation and c-Myc induction (a suppressor of miR expression). dHUVEC showed increased proliferation in response to IL-1β, which was prevented by a COX-2 inhibitor and PGF_2α receptor antagonist. Comparable changes in COX-2 mRNA, miR-16 and c-Myc detected in dHUVEC were produced in nHUVEC exposed to transient high glucose and then stimulated with IL-1β under physiological glucose levels; superoxide anion production was enhanced under these experimental conditions.

CONCLUSIONS AND IMPLICATIONS

Our results describe a possible mechanism operating in GDM that links the enhanced superoxide anion production and epigenetic changes, associated with hyperglycaemic memory, to endothelial dysfunction through dysregulated post-transcriptional control of COX-2 gene expression in response to inflammatory stimuli. The association of conventional therapy for glycaemic control with agents affecting inflammatory responses and oxidative stress might lead to a more effective prevention of the complications associated with GDM.

Platelets and Their Interactions with Other Immune Cells

Platelets are anucleate blood cells, long known to be critically involved in hemostasis and thrombosis. In addition to their role in blood clots, increasing evidence reveals significant roles for platelets in inflammation and immunity. However, the notion that platelets represent immune cells is not broadly recognized in the field of Physiology. This article reviews the role of platelets in inflammation and immune responses, and highlights their interactions with other immune cells, including examples of major functional consequences of these interactions.

HuR mediates the synergistic effects of angiotensin II and IL-1β on vascular COX-2 expression and cell migration

BACKGROUND AND PURPOSE

Angiotensin II (AngII) and IL-1β are involved in cardiovascular diseases through the induction of inflammatory pathways. HuR is an adenylate- and uridylate-rich element (ARE)-binding protein involved in the mRNA stabilization of many genes. This study investigated the contribution of HuR to the increased expression of COX-2 induced by AngII and IL-1β and its consequences on VSMC migration and remodelling.

EXPERIMENTAL APPROACH

Rat and human VSMCs were stimulated with AngII (0.1 μM) and/or IL-1β (10 ng · mL(-1)). Mice were infused with AngII or subjected to carotid artery ligation. mRNA and protein levels were assayed by quantitative PCR, Western blot, immunohistochemistry and immunofluorescence. Cell migration was measured by wound healing and transwell assays.

KEY RESULTS

In VSMCs, AngII potentiated COX-2 and tenascin-C expressions and cell migration induced by IL-1β. This effect of AngII on IL-1β-induced COX-2 expression was accompanied by increased COX-2 3' untranslated region reporter activity and mRNA stability, mediated through cytoplasmic HuR translocation and COX-2 mRNA binding. These effects were blocked by ERK1/2 and HuR inhibitors. VSMC migration was reduced by blockade of ERK1/2, HuR, COX-2, TXAS, TP and EP receptors. HuR, COX-2, mPGES-1 and TXAS expressions were increased in AngII-infused mouse aortas and in carotid-ligated arteries. AngII-induced tenascin-C expression and vascular remodelling were abolished by celecoxib and by mPGES-1 deletion.

CONCLUSIONS AND IMPLICATIONS

The synergistic induction of COX-2 by AngII and IL-1β in VSMCs involves HuR through an ERK1/2-dependent mechanism. The HuR/COX-2 axis participates in cell migration and vascular damage. HuR might be a novel target to modulate vascular remodelling.

Differential effects of platelets and platelet inhibition by ticagrelor on TLR2- and TLR4-mediated inflammatory responses

Platelets and platelet-monocyte interaction play an important role in inflammation. Both pro- and anti-inflammatory effects of platelet inhibition have been reported in animal models. This study aimed to investigate the effect of platelets and platelet inhibition by the new P2Y12 receptor antagonist ticagrelor on monocyte function, as assessed by cytokine responses to Toll-like Receptor (TLR) ligands. In a set of in vitro experiments, peripheral blood mononuclear cells (PBMC) incubated with the TLR2 ligand Pam3CSK4 produced less cytokines in the presence of platelets, whereas platelets increased the production of cytokines when PBMC were exposed to TLR4 ligand lipopolysaccharide (LPS). These effects of platelets were dependent on direct platelet-leukocyte aggregation and for the Pam3CSK4-induced response, on phagocytosis of platelets by monocytes. In a double blind, placebo-controlled crossover trial in healthy volunteers, a single oral dosage of 180 mg ticagrelor reduced platelet-monocyte complex (PMC) formation. This was associated with an increase in pro-inflammatory cytokines in blood exposed to Pam3CSK4, but a decrease in these cytokines in blood exposed to LPS. These findings show that platelets differentially modulate TLR2- and TLR4-mediated cytokine responses of PBMC. Through inhibition of platelet-leukocyte interaction, P2Y12 receptor antagonists may either exert a pro- or anti-inflammatory effect during infections depending on the TLR primarily involved.

Dissociation of SERPINE1 mRNA from the translational repressor proteins Ago2 and TIA-1 upon platelet activation

Platelets play an important role in haemostasis, as well as in thrombosis and coagulation processes. They harbour a wide variety of messenger RNAs (mRNAs), that can template de novo protein synthesis, and an abundant array of microRNAs, which are known to mediate mRNA translational repression through proteins of the Argonaute (Ago) family. The relationship between platelet microRNAs and proteins capable of mediating translational repression, however, remains unclear. Here, we report that half of platelet microRNAs is associated to mRNA-regulatory Ago2 protein complexes, in various proportions. Associated to these Ago2 complexes are platelet mRNAs known to support de novo protein synthesis. Reporter gene activity assays confirmed the capacity of the platelet microRNAs, found to be associated to Ago2 complexes, to regulate translation of these platelet mRNAs through their 3'UTR. Neither the microRNA repertoire nor the microRNA composition of Ago2 complexes of human platelets changed upon activation with thrombin. However, under conditions favoring de novo synthesis of Plasminogen Activator Inhibitor-1 (PAI-1) protein, we documented a rapid dissociation of the encoding platelet SERPINE1 mRNA from Ago2 protein complexes as well as from the translational repressor protein T-cell-restricted intracellular antigen-1 (TIA-1). These findings are consistent with a scenario by which lifting of the repressive effects of Ago2 and TIA-1 protein complexes, involving a rearrangement of proteinmRNA complexes rather than disassembly of Ago2microRNA complexes, would allow translation of SERPINE1 mRNA into PAI-1 in response to platelet activation.