Platelet-derived CXCL12 (SDF-1α): basic mechanisms and clinical implications

Effect of tocilizumab on endothelial and platelet-derived CXC-chemokines and their association with inflammation and myocardial injury in STEMI patients undergoing primary PCI

BACKGROUND

Tocilizumab improves myocardial salvage in ST-elevation myocardial infarction (STEMI) patients when administered before percutaneous coronary intervention (PCI). The mechanisms underlying ischemia-reperfusion injury remain unclear. In this sub-study, we investigated whether endothelial and platelet-derived CXC chemokines are involved, as they represent inflammatory mediators from two cell types relevant to myocardial infarction. Associations between these chemokines and neutrophils, C-reactive protein (CRP), troponin T (TnT), myocardial salvage index (MSI), microvascular obstruction (MVO), and infarct size.

METHODS

This is a sub-study of the ASSAIL-MI trial, a double-blind clinical trial that randomized 199 STEMI patients to receive either 280 mg tocilizumab (n = 101) or placebo (n = 98) intravenously before PCI. Blood samples were collected prior to infusion, at day 1-2, 3-7, and at 3 and 6 months. Heparin was administered before baseline in 150 patients, while 49 received it after. We measured CXC-chemokines CXCL4, CXCL5, CXCL6, CXCL7, and CXCL12 using immunoassays. Cardiac MRI was performed in the first week and at 6 months.

RESULTS

Tocilizumab did not significantly affect CXC-chemokines levels. Although some correlations were observed between chemokine levels and neutrophil counts and CRP, none of the CXC chemokines were associated with infarct size, MSI, MVO, or TnT levels. Notably, CXCL 12 levels increased in patients who received heparin before baseline, while other CXC-chemokines decreased significantly.

CONCLUSION

This study suggests that the beneficial effects of tocilizumab in STEMI patients are not due to changes in circulating endothelial or platelet-derived CXC-chemokines, compared to placebo. However, heparin significantly influences the levels of these chemokines.

Unlocking the intricacies: Exploring the complex interplay between platelets and ovarian cancer

Ovarian cancer, an aggressive malignancy of the female reproductive tract, is frequently linked to an elevated risk of thrombotic events. This association is manifested by a pronounced rise in platelet counts and activation levels. Current research firmly supports the pivotal role of platelets in the oncogenic processes of ovarian cancer, influencing tumor cell proliferation and metastasis. Platelets influence these processes through direct interactions with tumor cells or by secreting cytokines and growth factors that enhance tumor growth, angiogenesis, and metastasis. This review aims to thoroughly dissect the interactions between platelets and ovarian cancer cells, emphasizing their combined role in tumor progression and associated thrombotic events. Additionally, it summarizes therapeutic strategies targeting platelet-cancer interface which show significant promise. Such approaches could not only be effective in managing the primary ovarian tumor but also play a pivotal role in preventing metastasis and attenuating thrombotic complications associated with ovarian cancer.

One immune cell to bind them all: platelet contribution to neurodegenerative disease

Alzheimer's disease (AD) and related dementias (ADRD) collectively affect a significant portion of the aging population worldwide. The pathological progression of AD involves not only the classical hallmarks of amyloid beta (Aβ) plaque buildup and neurofibrillary tangle development but also the effects of vasculature and chronic inflammatory processes. Recently, platelets have emerged as central players in systemic and neuroinflammation. Studies have shown that patients with altered platelet receptor expression exhibit accelerated cognitive decline independent of traditional risk factors. Additionally, platelets from AD patients exhibit heightened unstimulated activation compared to control groups. Platelet granules contain crucial AD-related proteins like tau and amyloid precursor protein (APP). Dysregulation of platelet exocytosis contributes to disease phenotypes characterized by increased bleeding, stroke, and cognitive decline risk. Recent studies have indicated that these effects are not associated with the quantity of platelets present in circulation. This underscores the hypothesis that disruptions in platelet-mediated inflammation and healing processes may play a crucial role in the development of ADRD. A thorough look at platelets, encompassing their receptors, secreted molecules, and diverse roles in inflammatory interactions with other cells in the circulatory system in AD and ADRD, holds promising prospects for disease management and intervention. This review discusses the pivotal roles of platelets in ADRD.

Pim Kinase Inhibition Disrupts CXCR4 Signalling in Megakaryocytes and Platelets by Reducing Receptor Availability at the Surface

A key step in platelet production is the migration of megakaryocytes to the vascular sinusoids within the bone marrow. This homing is mediated by the chemokine CXCL12 and its receptor CXCR4. CXCR4 is also a positive regulator of platelet activation and thrombosis. Pim-1 kinase has been shown to regulate CXCR4 signalling in other cell types, and we have previously described how Pim kinase inhibitors attenuate platelet aggregation to CXCL12. However, the mechanism by which Pim-1 regulates CXCR4 signalling in platelets and megakaryocytes has yet to be elucidated. Using human platelets, murine bone marrow-derived megakaryocytes, and the megakaryocyte cell line MEG-01, we demonstrate that pharmacological Pim kinase inhibition leads to reduced megakaryocyte and platelet function responses to CXCL12, including reduced megakaryocyte migration and platelet granule secretion. Attenuation of CXCL12 signalling was found to be attributed to the reduced surface expression of CXCR4. The decrease in CXCR4 surface levels was found to be mediated by rapid receptor internalisation, in the absence of agonist stimulation. We demonstrate that pharmacological Pim kinase inhibition disrupts megakaryocyte and platelet function by reducing constitutive CXCR4 surface expression, decreasing the number of receptors available for agonist stimulation and signalling. These findings have implications for the development and use of Pim kinase inhibitors for the treatment of conditions associated with elevated circulating levels of CXCL12/SDF1α and increased thrombotic risk.

Effect of coffee, tea and alcohol intake on circulating inflammatory cytokines: a two sample-Mendelian randomization study

BACKGROUND

Despite the abundance of research examining the effects of coffee, tea, and alcohol on inflammatory diseases, there is a notable absence of conclusive evidence regarding their direct causal influence on circulating inflammatory cytokines. Previous studies have primarily concentrated on established cytokines, neglecting the potential impact of beverage consumption on lesser-studied but equally important cytokines.

METHODS

Information regarding the consumption of coffee, tea, and alcohol was collected from the UK Biobank, with sample sizes of 428,860, 447,485, and 462,346 individuals, respectively. Data on 41 inflammatory cytokines were obtained from summary statistics of 8293 healthy participants from Finnish cohorts.

RESULTS

The consumption of coffee was found to be potentially associated with decreased levels of Macrophage colony-stimulating factor (β = -0.57, 95% CI -1.06 ~ -0.08; p = 0.022) and Stem cell growth factor beta (β = -0.64, 95% CI -1.16 ~ -0.12; p = 0.016), as well as an increase in TNF-related apoptosis-inducing ligand (β = 0.43, 95% CI 0.06 ~ 0.8; p = 0.023) levels. Conversely, tea intake was potentially correlated with a reduction in Interleukin-8 (β = -0.45, 95% CI -0.9 ~ 0; p = 0.045) levels. Moreover, our results indicated an association between alcohol consumption and decreased levels of Regulated on Activation, Normal T Cell Expressed and Secreted (β = -0.24, 95% CI -0.48 ~ 0; p = 0.047), as well as an increase in Stem cell factor (β = 0.17, 95% CI 0.02 ~ 0.31; p = 0.023) and Stromal cell-derived factor-1 alpha (β = 0.20, 95% CI 0.04 ~ 0.36; p = 0.013).

CONCLUSION

Revealing the interactions between beverage consumption and various inflammatory cytokines may lead to the discovery of novel therapeutic targets, thereby facilitating dietary interventions to complement clinical disease treatments.

Platelet-Rich Fibrin Increases CXCL8 Expression in Gingival Fibroblasts

Platelet-rich fibrin (PRF), the coagulated plasma of fractionated blood, is widely used to support tissue regeneration in dentistry, and the underlying cellular and molecular mechanisms are increasingly being understood. Periodontal connective tissues steadily express CXCL8, a chemokine that attracts granulocytes and lymphocytes, supporting homeostatic immunity. Even though PRF is considered to dampen inflammation, it should not be ruled out that PRF increases the expression of CXCL8 in gingival fibroblasts. To test this hypothesis, we conducted a bioassay where gingival fibroblasts were exposed to PRF lysates and the respective serum. We show here that PRF lysates and, to a lesser extent, PRF serum increased the expression of CXCL8 by the gingival fibroblasts, as confirmed by immunoassay. SB203580, the inhibitor of p38 mitogen-activated protein kinase, reduced CXCL8 expression. Consistently, PRF lysates and, to a weaker range, the PRF serum also caused phosphorylation of p38 in gingival fibroblasts. Assuming that PRF is a rich source of growth factors, the TGF-β receptor type I kinase inhibitor SB431542 decreased the PRF-induced expression and translation of CXCL8. The findings suggest that PRF lysates and the respective serum drive CXCL8 expression by activating TGF-β and p38 signaling in gingival fibroblasts.

Platelet-derived sTLT-1 is associated with platelet-mediated inflammation in coronary artery disease patients

The development of coronary artery disease (CAD) depends heavily on platelet activation, and inflammation plays a major role in all stages of atherosclerosis. Platelet-specific soluble triggering receptor expressed on myeloid cells like transcript 1 (sTLT-1) facilitate clot formation and have been linked to chronic inflammation. In this study, we explored the role of platelet-derived sTLT-1 in platelet-mediated inflammation in CAD patients. Plasma levels of sTLT-1 were measured using enzyme-linked immunosorbent assay in CAD patients (n = 163) and healthy controls (n = 99). Correlation analysis was performed to determine the circulatory sTLT-1 levels with platelet activation markers, immune cells, and inflammatory cytokines/chemokines. Increased plasma sTLT-1 levels were observed in CAD patients compared with those in healthy controls (p < 0.0001). A positive correlation was observed between sTLT-1 and platelet activation markers (P-selectin, PAC-1), CD14++ CD16- cells (classical monocytes), Natural killer T (NKT) cells, and platelet-immune cell aggregates with monocytes, neutrophils, dendritic cells, CD11c+ cells, and NKT cells. In contrast, a significant negative correlation was observed with CD8 cells. Furthermore, a significant positive correlation was observed between sTLT-1 and inflammatory markers (TNF-α, IL-1β, IL-2, IL-6, IL-12p70, IL-18, CXCL-12, and CCL-11). Logistic regression analysis identified sTLT-1 and triglycerides as predictors of CAD. Receiver operating characteristic curve (ROC) analysis showed that sTLT-1 had a higher sensitivity and specificity for predicting CAD. Our findings suggest that platelet activation induces the release of sTLT-1 into the circulation in CAD patients, which aggregates with immune cells and enhances inflammatory responses.

Circulating Cytokines and Venous Thromboembolism: A Bidirectional Two-Sample Mendelian Randomization Study

BACKGROUND

 Epidemiological evidence has linked circulating cytokines to venous thromboembolism (VTE). However, it remains uncertain whether these associations are causal due to confounding factors or reverse causality. We aim to explore the causality between circulating cytokines and VTE, encompassing deep vein thrombosis (DVT) and pulmonary embolism (PE).

METHODS

 In the current bidirectional Mendelian randomization (MR) study, instrumental variables of 41 circulating cytokines were obtained from the genome-wide association study meta-analyses (8,293 individuals). Summary statistics for the association of VTE (17,048 cases and 325,451 controls), DVT (8,077 cases and 295,014 controls), and PE (8,170 cases and 333,487 controls) were extracted from the FinnGen Study. A multivariable MR study was conducted to adjust for potential confounders. The inverse-variance weighted method was employed as the main analysis, and comprehensive sensitivity analyses were conducted in the supplementary analyses.

RESULTS

 The MR analysis indicated stromal cell-derived factor-1α was suggestively associated with a reduced risk of VTE (odds ratio [OR]: 0.90; 95% confidence interval [CI]: 0.81-0.99; p = 0.033) and DVT (OR: 0.85; 95% CI: 0.75-0.97; p = 0.015). In addition, suggestive association of granulocyte colony-stimulating factor with PE (OR: 1.20; 95% CI: 1.06-1.37; p = 0.005) was observed. Multivariable MR analysis showed that the effect of cytokines on VTE was partly mediated through hemoglobin A1c and systolic blood pressure. Reverse MR analysis revealed that VTE was linked to decreased levels of several cytokines.

CONCLUSION

 We provide suggestive genetic evidence supporting the bidirectional causal effect between circulating cytokines and VTE, highlighting the importance of targeting circulating cytokines to reduce the incidence of VTE.

Synergy by Ristocetin and CXCL12 in Human Platelet Activation: Divergent Regulation by Rho/Rho-Kinase and Rac

CXCL12, belonging to the CXC chemokine family, is a weak agonist of platelet aggregation. We previously reported that the combination of CXCL12 and collagen at low doses synergistically activates platelets via not CXCR7 but CXCR4, a specific receptor for CXCL12 on the plasma membrane. Recently, we reported that not Rho/Rho kinase, but Rac is involved in the platelet aggregation induced by this combination. Ristocetin is an activator of the von Willebrand factor that interacts with glycoprotein (GP) Ib/IX/V, which generates thromboxane A2 via phospholipase A2 activation, resulting in the release of the soluble CD40 ligand (sCD40L) from human platelets. In the present study, we investigated the effects of a combination of ristocetin and CXCL12 at low doses on human platelet activation and its underlying mechanisms. Simultaneous stimulation with ristocetin and CXCL12 at subthreshold doses synergistically induce platelet aggregation. A monoclonal antibody against not CXCR7 but CXCR4 suppressed platelet aggregation induced by the combination of ristocetin and CXCL12 at low doses. This combination induces a transient increase in the levels of both GTP-binding Rho and Rac, followed by an increase in phosphorylated cofilin. The ristocetin and CXCL12-induced platelet aggregation as well as the sCD40L release were remarkably enhanced by Y27362, an inhibitor of Rho-kinase, but reduced by NSC23766, an inhibitor of the Rac-guanine nucleotide exchange factor interaction. These results strongly suggest that the combination of ristocetin and CXCL12 at low doses synergistically induces human platelet activation via Rac and that this activation is negatively regulated by the simultaneous activation of Rho/Rho-kinase.

Platelet versus plasma CXCL14, coronary artery disease, and clinical outcomes

Background

Platelets express CXCL14, while platelet-derived CXCL14 induces monocyte chemotaxis and exerts an angiostatic effect on endothelial cells.

Objectives

This study investigated both platelet surface-associated and circulating levels of CXCL14 in patients with heart disease and associations of this chemokine with myocardial function and outcomes in patients with coronary artery disease (CAD).

Methods

This prospective study enrolled 450 patients with symptomatic heart disease. Platelet surface-associated and plasma CXCL14 levels were analyzed. All patients were followed up for 360 days for a primary composite outcome consisting of all-cause mortality, myocardial infarction, and/or ischemic stroke. Secondary outcomes consisted of the single events of all-cause mortality or myocardial infarction.

Results

Baseline platelet-associated but not circulating CXCL14 levels were significantly lower in patients with chronic coronary syndrome (mean fluorescence intensity logarithmized, 1.35 ± 0.35) when compared to those with acute coronary syndrome (1.47 ± 0.38) and without CAD (1.51 ± 0.40). Platelet CXCL14 levels were significantly lower (1.37 ± 0.37 vs 1.48 ± 0.39) and circulating CXCL14 levels were significantly higher (lg, 2.88 ± 0.20 pg/mL vs 2.82 ± 0.26 pg/mL) in patients with normal baseline left ventricular ejection fraction (LVEF) when compared to those with impaired LVEF. Low baseline circulating CXCL14 (hazard ratio, 2.33; 1.00-5.46) but not platelet CXCL14 was associated with worse outcome in patients with CAD.

Conclusion

Platelet-associated and circulating CXCL14 levels show differential regulation in patients with and without CAD. Although platelet-associated CXCL14 increased and circulating CXCL14 decreased with impairment of LVEF, only lower circulating CXCL14 upon admission was associated with worse prognosis in patients with CAD.

Platelets at the Vessel Wall in Non-Thrombotic Disease

Platelets are small, anucleate entities that bud from megakaryocytes in the bone marrow. Among circulating cells, platelets are the most abundant cell, traditionally involved in regulating the balance between thrombosis (the terminal event of platelet activation) and hemostasis (a protective response to tissue injury). Although platelets lack the precise cellular control offered by nucleate cells, they are in fact very dynamic cells, enriched in preformed RNA that allows them the capability of de novo protein synthesis which alters the platelet phenotype and responses in physiological and pathological events. Antiplatelet medications have significantly reduced the morbidity and mortality for patients afflicted with thrombotic diseases, including stroke and myocardial infarction. However, it has become apparent in the last few years that platelets play a critical role beyond thrombosis and hemostasis. For example, platelet-derived proteins by constitutive and regulated exocytosis can be found in the plasma and may educate distant tissue including blood vessels. First, platelets are enriched in inflammatory and anti-inflammatory molecules that may regulate vascular remodeling. Second, platelet-derived microparticles released into the circulation can be acquired by vascular endothelial cells through the process of endocytosis. Third, platelets are highly enriched in mitochondria that may contribute to the local reactive oxygen species pool and remodel phospholipids in the plasma membrane of blood vessels. Lastly, platelets are enriched in proteins and phosphoproteins which can be secreted independent of stimulation by surface receptor agonists in conditions of disturbed blood flow. This so-called biomechanical platelet activation occurs in regions of pathologically narrowed (atherosclerotic) or dilated (aneurysmal) vessels. Emerging evidence suggests platelets may regulate the process of angiogenesis and blood flow to tumors as well as education of distant organs for the purposes of allograft health following transplantation. This review will illustrate the potential of platelets to remodel blood vessels in various diseases with a focus on the aforementioned mechanisms.

Tramadol regulates the activation of human platelets via Rac but not Rho/Rho-kinase

Tramadol is a useful analgesic which acts as a serotonin and noradrenaline reuptake inhibitor in addition to μ-opioid receptor agonist. Cytoplasmic serotonin modulates the small GTPase activity through serotonylation, which is closely related to the human platelet activation. We recently reported that the combination of subthreshold collagen and CXCL12 synergistically activates human platelets. We herein investigated the effect and the mechanism of tramadol on the synergistic effect. Tramadol attenuated the synergistically stimulated platelet aggregation (300 μM of tramadol, 64.3% decrease, p<0.05). Not morphine or reboxetine, but duloxetine, fluvoxamine and sertraline attenuated the synergistic effect of the combination on the platelet aggregation (30 μM of fluvoxamine, 67.3% decrease, p<0.05; 30 μM of sertraline, 67.8% decrease, p<0.05). The geranylgeranyltransferase inhibitor GGTI-286 attenuated the aggregation of synergistically stimulated platelet (50 μM of GGTI-286, 80.8% decrease, p<0.05), in which GTP-binding Rac was increased. The Rac1-GEF interaction inhibitor NSC23766 suppressed the platelet activation and the phosphorylation of p38 MAPK and HSP27 induced by the combination of collagen and CXCL12. Tramadol and fluvoxamine almost completely attenuated the levels of GTP-binding Rac and the phosphorylation of both p38 MAPK and HSP27 stimulated by the combination. Suppression of the platelet aggregation after the duloxetine administration was observed in 2 of 5 patients in pain clinic. These results suggest that tramadol negatively regulates the combination of subthreshold collagen and CXCL12-induced platelet activation via Rac upstream of p38 MAPK.

Mechanism of platelet activation and potential therapeutic effects of natural drugs

BACKGROUND

Cardiovascular disease is one of the most concerning chronic diseases in the world. Many studies have shown that platelet overactivation is a very important factor in the occurrence and development of cardiovascular diseases. At present, the widely used antiplatelet drugs have some defects, such as drug resistance and adverse reactions.

PURPOSE

The purpose of this article is to summarize the main mechanisms and pathways of platelet activation, the main targets of antiplatelet aggregation, and the antiplatelet aggregation components of natural drugs and their mechanisms of action to provide new research ideas for the development and application of antiplatelet drugs.

STUDY DESIGN AND METHODS

In this review, we systematically searched the PubMed, Google Scholar, Web of Science, and CNKI databases and selected studies based on predefined eligibility criteria. We then assessed their quality and extracted data.

RESULTS

ADP, AA, THR, AF, collagen, SDF-1α, and Ca²⁺ can induce platelet aggregation and trigger thrombosis. Natural drugs have a good inhibitory effect on platelet activation. More than 50 kinds of natural drugs and over 120 kinds of chemical compounds, including flavonoids, alkaloids, saponins, terpenoids, coumarins, and organic acids, have significantly inhibited platelet activation activity. The MAPK pathway, cGMP-PKG pathway, cAMP-PKA pathway, PI3K-AKT pathway, PTK pathway, PLC pathway, and AA pathway are the main mechanisms and pathways of platelet activation.

CONCLUSION

Natural drugs and their active ingredients have shown good activity and application prospects in anti-platelet aggregation. We hope that this review provides new research ideas for the development and application of antiplatelet drugs.

Improved biological performance of human cartilage-derived progenitors in platelet lysate xenofree media in comparison to fetal bovine serum media

Primary articular cartilage-derived cells are among the preferred contenders for cell-based therapy approaches for cartilage repair. Limited access to primary human cartilage tissue necessitates the process of in vitro cell expansion to obtain sufficient cells for therapeutic purposes. Therapeutic outcomes of such cell-based approaches become highly dependent on the quality of the in vitro culture-expanded cells. The objective of this study was to determine the differential biological effects of human platelet lysate (hPL) xeno-free defined media vs FBS containing traditional media on primary human cartilage-derived cells. Our goal in pursuing this work was to identify a preferred xenofree media alternative, that can be used as a platform for expansion of cells intended for clinical applications. Primary cartilage-derived cells obtained from five patients were simultaneously cultured in two expansion media's: (1) traditional (DMEM+10%FBS+1%P/S) and (2) defined xenofree (Nutristem® complete media+0.5%hPL). Connective tissue progenitors (CTPs) were assayed by standard colony forming unit assay, morphology, proliferation in early and late passages, expression of MSC associated cell-surface markers (CD73, CD90 and CD105) and trilineage differentiation (adipogenesis, osteogenesis and chondrogenesis) were considered for comparison of biological performance. Early biological performance of primary cartilage-derived cells was significantly improved in Nutristem® expansion media in comparison to traditional expansion media with respect to (1) Colony forming efficiency tended to be higher (p = 0.058) and (2) CTPs formed larger colonies with respect to total cells per colony and colony area (p < 0.01). In the culture expanded cell population, Nutristem® expansion media was superior to traditional expansion media with respect to: (1) overall proliferation rate through passages 1-4 (p = 0.027), (2) total cells harvested at end of passage 4 (p = 0.028) and (3) total positive stain area of CD73 (p = 0.006), CD90 (p = 0.001) and CD105 (p = 0.049). Nutristem®-hPL expanded cells when differentiated in respective xenofree serum-free defined MSCgo™ differentiated media's, also showed significant improvement in adipogenic, osteogenic and chondrogenic marker expression. Overall, we convincingly demonstrated that a low concentration of hPL in combination with defined xenofree media is an effective and economic growth supplement to culture expand primary cartilage-derived cells. It can be manufactured under cGMP conditions to improve clinical-grade cell products' quality for therapeutic applications.

Cobra Venom Factor Boosts Arteriogenesis in Mice

Arteriogenesis, the growth of natural bypass blood vessels, can compensate for the loss of arteries caused by vascular occlusive diseases. Accordingly, it is a major goal to identify the drugs promoting this innate immune system-driven process in patients aiming to save their tissues and life. Here, we studied the impact of the Cobra venom factor (CVF), which is a C3-like complement-activating protein that induces depletion of the complement in the circulation in a murine hind limb model of arteriogenesis. Arteriogenesis was induced in C57BL/6J mice by femoral artery ligation (FAL). The administration of a single dose of CVF (12.5 µg) 24 h prior to FAL significantly enhanced the perfusion recovery 7 days after FAL, as shown by Laser Doppler imaging. Immunofluorescence analyses demonstrated an elevated number of proliferating (BrdU+) vascular cells, along with an increased luminal diameter of the grown collateral vessels. Flow cytometric analyses of the blood samples isolated 3 h after FAL revealed an elevated number of neutrophils and platelet-neutrophil aggregates. Giemsa stains displayed augmented mast cell recruitment and activation in the perivascular space of the growing collaterals 8 h after FAL. Seven days after FAL, we found more CD68+/MRC-1+ M2-like polarized pro-arteriogenic macrophages around growing collaterals. These data indicate that a single dose of CVF boosts arteriogenesis by catalyzing the innate immune reactions, relevant for collateral vessel growth.

Use of gliptins reduces levels of SDF-1/CXCL12 in bullous pemphigoid and type 2 diabetes, but does not increase autoantibodies against BP180 in diabetic patients

The use of dipeptidyl peptidase 4 (DPP4) inhibitors, (also known as gliptins), is associated with an increased risk of bullous pemphigoid (BP), an autoimmune blistering skin disease. To explore the mechanism behind gliptin-associated BP we investigated circulating autoantibodies against the major BP autoantigen BP180 in serum samples from patients with type 2 diabetes (T2D) with preceding gliptin medication (n = 136) or without (n = 136). Sitagliptin was the most frequently prescribed gliptin (125/136 patients). Using an ELISA assay, we showed that IgG autoantibodies against the immunodominant NC16A domain of BP180 were found in 5.9% of gliptin treated and in 6.6% of non-gliptin treated T2D patients. We found that 28% of gliptin treated patients had IgG autoantibodies recognizing the native full-length BP180 in ELISA, but among non-gliptin treated the seropositivity was even higher, at 32%. Further ELISA analysis of additional serum samples (n = 57) found no major changes in the seropositivity against BP180 during a follow-up period of about nine years. In immunoblotting, full-length BP180 was recognized by 71% of gliptin treated and 89% of non-gliptin treated T2D patients, but only by 46% of the age-and sex-matched controls. The chemokine stromal derived factor-1(SDF-1/CXCL12) is one of the major substrates of DPP4. Immunostainings showed that the expression of SDF-1 was markedly increased in the skin of BP patients, but not affected by prior gliptin treatment. We found that the use of gliptins decreased the serum level of SDF-1α in both BP and T2D patients. Our results indicate that the autoantibodies against the linear full-length BP180 are common in patients with T2D, but seropositivity is unaffected by the use of sitagliptin.

Targeting CXCR4 to suppress glioma-initiating cells and chemoresistance in glioma

Glioma initiating cells (GICs), also known as glioma stem cells, display the capacity to recapitulate the functional diversity within the tumor. Despite the great progress achieved over the last decades, defining the key molecular regulators of GICs has represented a major obstacle in this field. In our study, data from The Cancer Genome Atlas database illustrated a relationship between C-X-C motif chemokine receptor 4 (CXCR4) expression and the survival of glioma patients. Mechanistically, we further indicated that CXCR4 mediated the upregulation of Kruppel like factor 5 (KLF5), a zinc-finger-containing transcription factor, to facilitate the proliferation of GICs. What's more, CXCR4 also enhanced the chemoresistance through KLF5/Bcl2-like 12 (BCl2L12) in glioma. The elevated expression of KLF5 and BCL2L12 induced by CXCR4 was dependent on phosphoinositide 3-kinases (PI3K)/serine/threonine kinase (AKT) signaling. Importantly, combined application of temozolomide and a CXCR4 inhibitor efficiently reversed CXCR4 mediated drugs resistance and improved anticancer effects in vivo. Collectively, our findings confirmed that CXCR4 promoted GICs proliferation via the KLF5/BCL2L12 dependent pathway, which may enrich the understanding of GICs and help drive the design of efficacious therapeutic strategies.

An Insight into Recent Advances on Platelet Function in Health and Disease

Platelets play a variety of roles in vascular biology and are best recognized as primary hemostasis and thrombosis mediators. Platelets have a large number of receptors and secretory molecules that are required for platelet functionality. Upon activation, platelets release multiple substances that have the ability to influence both physiological and pathophysiological processes including inflammation, tissue regeneration and repair, cancer progression, and spreading. The involvement of platelets in the progression and seriousness of a variety of disorders other than thrombosis is still being discovered, especially in the areas of inflammation and the immunological response. This review represents an integrated summary of recent advances on the function of platelets in pathophysiology that connects hemostasis, inflammation, and immunological response in health and disease and suggests that antiplatelet treatment might be used for more than only thrombosis.

The Role of CXC Chemokines in Cardiovascular Diseases

Cardiovascular disease (CVD) is a class of diseases with high disability and mortality rates. In the elderly population, the incidence of cardiovascular disease is increasing annually. Between 1990 and 2016, the age-standardised prevalence of CVD in China significantly increased by 14.7%, and the number of cardiovascular disease deaths increased from 2.51 million to 3.97 million. Much research has indicated that cardiovascular disease is closely related to inflammation, immunity, injury and repair. Chemokines, which induce directed chemotaxis of reactive cells, are divided into four subfamilies: CXC, CC, CX3C, and XC. As cytokines, CXC chemokines are similarly involved in inflammation, immunity, injury, and repair and play a role in many cardiovascular diseases, such as atherosclerosis, myocardial infarction, cardiac ischaemia-reperfusion injury, hypertension, aortic aneurysm, cardiac fibrosis, postcardiac rejection, and atrial fibrillation. Here, we explored the relationship between the chemokine CXC subset and cardiovascular disease and its mechanism of action with the goal of further understanding the onset of cardiovascular disease.

Targeting platelet-derived CXCL12 impedes arterial thrombosis

The prevention and treatment of arterial thrombosis continue to be clinically challenging, and understanding the relevant molecular mechanisms in detail may facilitate the quest to identify novel targets and therapeutic approaches that improve protection from ischemic and bleeding events. The chemokine CXCL12 augments collagen-induced platelet aggregation by activating its receptor CXCR4. Here we show that inhibition of CXCR4 attenuates platelet aggregation induced by collagen or human plaque homogenate under static and arterial flow conditions by antagonizing the action of platelet-secreted CXCL12. We further show that platelet-specific CXCL12 deficiency in mice limits arterial thrombosis by affecting thrombus growth and stability without increasing tail bleeding time. Accordingly, neointimal lesion formation after carotid artery injury was attenuated in these mice. Mechanistically, CXCL12 activated via CXCR4 a signaling cascade involving Bruton's tyrosine kinase (Btk) that led to integrin αIIbβ3 activation, platelet aggregation, and granule release. The heterodimeric interaction between CXCL12 and CCL5 can inhibit CXCL12-mediated effects as mimicked by CCL5-derived peptides such as [VREY]4. An improved variant of this peptide, i[VREY]4, binds to CXCL12 in a complex with CXCR4 on the surface of activated platelets, thereby inhibiting Btk activation and preventing platelet CXCL12-dependent arterial thrombosis. In contrast to standard antiplatelet therapies such as aspirin or P2Y12 inhibition, i[VREY]4 reduced CXCL12-induced platelet aggregation and yet did not prolong in vitro bleeding time. We provide evidence that platelet-derived CXCL12 is involved in arterial thrombosis and can be specifically targeted by peptides that harbor potential therapeutic value against atherothrombosis.

Perspectives on Vascular Regulation of Mechanisms Controlling Selective Immune Cell Function in the Tumor Immune Response

The vasculature plays a major role in regulating the tumor immune cell response although the underlying mechanisms explaining such effects remain poorly understood. This review discusses current knowledge on known vascular functions with a viewpoint on how they may yield distinct immune responses. The vasculature might directly influence selective immune cell infiltration into tumors by its cell surface expression of cell adhesion molecules, expression of cytokines, cell junction properties, focal adhesions, cytoskeleton and functional capacity. This will alter the tumor microenvironment and unleash a plethora of responses that will influence the tumor’s immune status. Despite our current knowledge of numerous mechanisms operating, the field is underexplored in that few functions providing a high degree of specificity have yet been provided in relation to the enormous divergence of responses apparent in human cancers. Further exploration of this field is much warranted.

Atypical Roles of the Chemokine Receptor ACKR3/CXCR7 in Platelet Pathophysiology

The manifold actions of the pro-inflammatory and regenerative chemokine CXCL12/SDF-1α are executed through the canonical GProteinCoupledReceptor CXCR4, and the non-canonical ACKR3/CXCR7. Platelets express CXCR4, ACKR3/CXCR7, and are a vital source of CXCL12/SDF-1α themselves. In recent years, a regulatory impact of the CXCL12-CXCR4-CXCR7 axis on platelet biogenesis, i.e., megakaryopoiesis, thrombotic and thrombo-inflammatory actions have been revealed through experimental and clinical studies. Platelet surface expression of ACKR3/CXCR7 is significantly enhanced following myocardial infarction (MI) in acute coronary syndrome (ACS) patients, and is also associated with improved functional recovery and prognosis. The therapeutic implications of ACKR3/CXCR7 in myocardial regeneration and improved recovery following an ischemic episode, are well documented. Cardiomyocytes, cardiac-fibroblasts, endothelial lining of the blood vessels perfusing the heart, besides infiltrating platelets and monocytes, all express ACKR3/CXCR7. This review recapitulates ligand induced differential trafficking of platelet CXCR4-ACKR3/CXCR7 affecting their surface availability, and in regulating thrombo-inflammatory platelet functions and survival through CXCR4 or ACKR3/CXCR7. It emphasizes the pro-thrombotic influence of CXCL12/SDF-1α exerted through CXCR4, as opposed to the anti-thrombotic impact of ACKR3/CXCR7. Offering an innovative translational perspective, this review also discusses the advantages and challenges of utilizing ACKR3/CXCR7 as a potential anti-thrombotic strategy in platelet-associated cardiovascular disorders, particularly in coronary artery disease (CAD) patients post-MI.

Cell Therapy for Anal Sphincter Incontinence: Where Do We Stand?

Anal sphincter incontinence is a chronic disease, which dramatically impairs quality of life and induces high costs for the society. Surgery, considered as the best curative option, shows a disappointing success rate. Stem/progenitor cell therapy is pledging, for anal sphincter incontinence, a substitute to surgery with higher efficacy. However, the published literature is disparate. Our aim was to perform a review on the development of cell therapy for anal sphincter incontinence with critical analyses of its pitfalls. Animal models for anal sphincter incontinence were varied and tried to reproduce distinct clinical situations (acute injury or healed injury with or without surgical reconstruction) but were limited by anatomical considerations. Cell preparations used for treatment, originated, in order of frequency, from skeletal muscle, bone marrow or fat tissue. The characterization of these preparations was often incomplete and stemness not always addressed. Despite a lack of understanding of sphincter healing processes and the exact mechanism of action of cell preparations, this treatment was evaluated in 83 incontinent patients, reporting encouraging results. However, further development is necessary to establish the correct indications, to determine the most-suited cell type, to standardize the cell preparation method and to validate the route and number of cell delivery.

Preferential interaction of platelets with prostate cancer cells with stem cell markers

BACKGROUND

Prostate cancer (PCa) may be initiated by CD133+/CD44+ expressing stem cell-like cells (PCSC), which are also thought to drive metastasis. Platelets also contribute to metastasis via tumor cell-induced platelet aggregation (TCIPA), which in part enhances cancer cell invasion. Moreover, activated platelets secrete stromal derived growth factor-1α (SDF-1α) that can mobilize CSCs via the CXCR4 receptor. However, the potential reciprocal interactions between CSCs and platelets have not been investigated.

OBJECTIVE

To characterize the mechanisms behind PCSC-platelet interaction.

METHODS

Fluorescence Activated Cell Sorting was utilized to separate DU145 and PC3 PCa cells into CD133+/CD44+, CD133+/CD44-, CD44+/CD133-, and CD133-/CD44- subpopulations and to measure their CXCR4 surface expression. PCa subpopulation TCIPA experiments were performed using aggregometry and immunoblot was used to measure prothrombin. Platelet SDF-1α secretion was measured by ELISA. Modified-Boyden chamber assays were used to assess the role of SDF-1α:CXCR4 pathway in platelet-PCSC interactions.

RESULTS

DU145 and PC3 expressing both CD133 and CD44 stem cell markers accounted for only small fractions of total cells (DU145: CD133+/CD44+ 3.44 ± 1.45% vs. CD133+/CD44- 1.56 ± 0.45% vs. CD44+/CD133- 68.19 ± 6.25% vs. CD133-/CD44- 20.36 ± 4.51%). However, CD133+ subpopulations induced the greatest amount of aggregation compared to CD44+/CD133- and double-negative DU145, and this aggregation potency of CD133+ PCa cells corresponded with high levels of prothrombin expression. Additionally, CD133+ subpopulations expressed significantly higher level of CXCR4 compared to CD133-/CD44- and CD44+/CD133-. Disruption of SDF-1α:CXCR4 pathway reduced platelet-induced PCSC invasion.

CONCLUSIONS

CD133+/CD44+ and CD133+/CD44- PCSCs have highest platelet aggregation potency, which could be attributed to their increased prothrombin expression. Reciprocally, platelet-derived SDF-1α stimulates PCSC invasion.

Deletion of SDF-1 or CXCR4 regulates platelet activation linked to glucose metabolism and mitochondrial respiratory reserve

Stromal cell-derived factor 1 (SDF-1, also known as CXCL12) and its receptor CXCR4 have shown to play a role in the homing and engraftment of hematopoietic stem and progenitor cells. SDF-1 is highly expressed in platelets and involved in thrombosis formation. However, the exact roles of platelet-derived SDF-1 and CXCR4 in platelet activation and mitochondrial function have not been revealed yet. Deletion of Sdf-1 and Cxcr4 specifically in platelets decreased agonist-induced platelet aggregation and dramatically impaired thrombin-induced glucose uptake. In SDF-1-deficient and CXCR4-deficient platelets, intracellular ATP secretions were reduced when activated by the addition of thrombin. SDF-1 deficiency in platelets can impair the routine respiration during resting state and maximal capacity of the electron transfer system (ETS) during activated state. Mitochondrial respiration measurements in permeabilized platelets indicated an impaired function of the oxidative phosphorylation system in -SDF-1 or CXCR4-deficient platelets. These results suggested a novel role of the SDF-1/CXCR4 axis in modulating platelet energy metabolism and activation by regulating mitochondrial respiration, glucose uptake, and ATP production.

Soluble Platelet Release Factors as Biomarkers for Cardiovascular Disease

Platelets are the main players in thrombotic diseases, where activated platelets not only mediate thrombus formation but also are involved in multiple interactions with vascular cells, inflammatory components, and the coagulation system. Although in vitro reactivity of platelets provides information on the function of circulating platelets, it is not a full reflection of the in vivo activation state, which may be relevant for thrombotic risk assessment in various disease conditions. Therefore, studying release markers of activated platelets in plasma is of interest. While this type of study has been done for decades, there are several new discoveries that highlight the need for a critical assessment of the available tests and indications for platelet release products. First, new insights have shown that platelets are not only prominent players in arterial vascular disease, but also in venous thromboembolism and atrial fibrillation. Second, knowledge of the platelet proteome has dramatically expanded over the past years, which contributed to an increasing array of tests for proteins released and shed from platelets upon activation. Identification of changes in the level of plasma biomarkers associated with upcoming thromboembolic events allows timely and individualized adjustment of the treatment strategy to prevent disease aggravation. Therefore, biomarkers of platelet activation may become a valuable instrument for acute event prognosis. In this narrative review based on a systematic search of the literature, we summarize the process of platelet activation and release products, discuss the clinical context in which platelet release products have been measured as well as the potential clinical relevance.

The C5a/C5a receptor 1 axis controls tissue neovascularization through CXCL4 release from platelets

Platelets contribute to the regulation of tissue neovascularization, although the specific factors underlying this function are unknown. Here, we identified the complement anaphylatoxin C5a-mediated activation of C5a receptor 1 (C5aR1) on platelets as a negative regulatory mechanism of vessel formation. We showed that platelets expressing C5aR1 exert an inhibitory effect on endothelial cell functions such as migration and 2D and 3D tube formation. Growth factor- and hypoxia-driven vascularization was markedly increased in C5ar1^-/- mice. Platelet-specific deletion of C5aR1 resulted in a proangiogenic phenotype with increased collateralization, capillarization and improved pericyte coverage. Mechanistically, we found that C5a induced preferential release of CXC chemokine ligand 4 (CXCL4, PF4) from platelets as an important antiangiogenic paracrine effector molecule. Interfering with the C5aR1-CXCL4 axis reversed the antiangiogenic effect of platelets both in vitro and in vivo.In conclusion, we identified a mechanism for the control of tissue neovascularization through C5a/C5aR1 axis activation in platelets and subsequent induction of the antiangiogenic factor CXCL4.

Local application reduces number of needed EPC for beneficial effects on wound healing compared to systemic treatment in mice

Introduction

Stem cell transplantation is one of the most promising strategies to improve healing in chronic wounds as systemic administration of endothelial progenitor cells (EPC) enhances healing by promoting neovascularization and homing though a high amount of cells is needed. In the following study, we analysed whether local application can reduce the number of EPC needed achieving the same beneficial effect on wound healing.

Material and Methods

Wound healing after local or systemic treatment with EPC was monitored in vivo by creating standardized wounds on the dorsum of hairless mice measuring wound closure every second day. Systemic group received 2 × 10⁶ EPC i.v. and locally treated group 2 × 10⁵ EPC, locally injected. As control PBS injection was performed the same way. Expression of CD31, VEGF, CD90 and, SDF-1α was analysed immunohistochemically for evaluation of neovascularisation and amelioration of homing.

Results

Local (7.1 ± 0.45 SD) as well as systemic (6.1 ± 0.23 SD) EPC transplantation led to a significant acceleration of wound closure compared to controls (PBS local: 9.7 ± 0.5 SD, PBS systemic 10.9 ± 0.38 SD). Systemic application enhanced CD31 expression on day 6 after wounding and local EPC on 6 and 9 in comparison to control. VEGF expression was not significantly affected. Systemic and local EPC treatment resulted in a significantly enhanced SDF-1α and CD90 expression on all days investigated.

Conclusion

Local as well as systemic EPC treatment enhances wound healing. Moreover, beneficial effects are obtained with a tenfold decrease number of EPC when applied locally. Thus, local EPC treatment might be more convenient way to enhance wound healing as number of progenitor cells is limited.

The chemokine CXCL14 mediates platelet function and migration via direct interaction with CXCR4

AIMS

Beyond classical roles in thrombosis and haemostasis, it becomes increasingly clear that platelets contribute as key players to inflammatory processes. The involvement of platelets in these processes is often mediated through a variety of platelet-derived chemokines which are released upon activation and act as paracrine and autocrine factors. In this study, we investigate CXCL14, a newly described platelet chemokine and its role in thrombus formation as well as monocyte and platelet migration. In addition, we examine the chemokine receptor CXCR4 as a possible receptor for CXCL14 on platelets. Furthermore, with the use of artificially generated platelets derived from induced pluripotent stem cells (iPSC), we investigate the importance of CXCR4 for CXCL14-mediated platelet functions.

METHODS AND RESULTS

In this study, we showed that CXCL14 deficient platelets reveal reduced thrombus formation under flow compared with wild-type platelets using a standardized flow chamber. Addition of recombinant CXCL14 normalized platelet-dependent thrombus formation on collagen. Furthermore, we found that CXCL14 is a chemoattractant for platelets and mediates migration via CXCR4. CXCL14 promotes platelet migration of platelets through the receptor CXCR4 as evidenced by murine CXCR4-deficient platelets and human iPSC-derived cultured platelets deficient in CXCR4. We found that CXCL14 directly interacts with the CXCR4 as verified by immunoprecipitation and confocal microscopy.

CONCLUSIONS

Our results reveal CXCL14 as a novel platelet-derived chemokine that is involved in thrombus formation and platelet migration. Furthermore, we identified CXCR4 as principal receptor for CXCL14, an interaction promoting platelet migration.

Regenerative medicine for anal incontinence: a review of regenerative therapies beyond cells

INTRODUCTION AND HYPOTHESIS

Current treatment modalities for anal sphincter injuries are ineffective for many patients, prompting research into restorative and regenerative therapies. Although cellular therapy with stem cells and progenitor cells show promise in animal models with short-term improvement, there are additional regenerative approaches that can augment or replace cellular therapies for anal sphincter injuries. The purpose of this article is to review the current knowledge of cellular therapies for anal sphincter injuries and discusses the use of other regenerative therapies including cytokine therapy with CXCL12.

METHODS

A literature search was performed to search for articles on cellular therapy and cytokine therapy for anal sphincter injuries and anal incontinence.

RESULTS

The article search identified 337 articles from which 33 articles were included. An additional 12 referenced articles were included as well as 23 articles providing background information. Cellular therapy has shown positive results for treating anal sphincter injuries and anal incontinence in vitro and in one clinical trial. However, cellular therapy has disadvantages such as the source and processing of stem cells and progenitor cells. CXCL12 does not have such issues while showing promising in vitro results for treating anal sphincter injuries. Additionally, electrical stimulation and extracorporeal shock wave therapy are potential regenerative medicine adjuncts for anal sphincter injuries. A vision for future research and clinical applications of regenerative medicine for anal sphincter deficiencies is provided.

CONCLUSION

There are viable regenerative medicine therapies for anal sphincter injuries beyond cellular therapy. CXCL12 shows promise as a focus of therapeutic research in this field.

The Recombinant Protein Based on Trypanosoma cruzi P21 Interacts With CXCR4 Receptor and Abrogates the Invasive Phenotype of Human Breast Cancer Cells

Trypanosoma cruzi P21 is a protein secreted by the parasite that plays biological roles directly involved in the progression of Chagas disease. The recombinant protein (rP21) demonstrates biological properties, such as binding to CXCR4 receptors in macrophages, chemotactic activity of immune cells, and inhibiting angiogenesis. This study aimed to verify the effects of rP21 interaction with CXCR4 from non-tumoral cells (MCF-10A) and triple-negative breast cancer cells (MDA-MB-231). Our data showed that the MDA-MB-231 cells expressed higher levels of CXCR4 than did the non-tumor cell lines. Besides, cytotoxicity assays using different concentrations of rP21 showed that the recombinant protein was non-toxic and was able to bind to the cell membranes of both cell lineages. In addition, rP21 reduced the migration and invasion of MDA-MB-231 cells by the downregulation of MMP-9 gene expression. In addition, treatment with rP21 blocked the cell cycle, arresting it in the G1 phase, mainly in MDA-MB-231 cells. Finally, rP21 prevents the chemotaxis and proliferation induced by CXCL12. Our data showed that rP21 binds to the CXCR4 receptors in both cells, downregulates CXCR4 gene expression, and decreases the receptors in the cytoplasm of MDA-MB-231 cells, suggesting CXCR4 internalization. This internalization may explain the desensitization of the receptors in these cells. Thus, rP21 prevents migration, invasion, and progression in MDA-MB-231 cells.

Synergistic effect of collagen and CXCL12 in the low doses on human platelet activation

CXCL12, also known as stromal cell-derived factor-1, is a chemokine classified into CXC families, which exerts its function by binding to specific receptors called CXCR4 and CXCR7. Human platelets express CXCR4 and CXCR7 on the plasma membrane. It has been reported that CXCL12 potentiates to induce platelet aggregation in cooperation with agonists including collagen. However, the precise roles and mechanisms of CXCL12 in human platelet activation are not fully elucidated. In the present study, we investigated the effect of simultaneous stimulation with low doses of collagen and CXCL12 on the activation of human platelets. The simultaneous stimulation with collagen and CXCL12 induced the secretion of platelet-derived growth factor (PDGF)-AB and the release of soluble CD40 ligand (sCD40L) from human platelets in addition to their aggregation, despite the fact that the simultaneous stimulation with thrombin receptor-activating peptide (TRAP) or adenosine diphosphate (ADP), and CXCL12 had little effects on the platelet aggregation. The agonist of Glycoprotein (GP) Ⅵ convulxin and CXCL12 also induced platelet aggregation synergistically. The monoclonal antibody against CXCR4 but not CXCR7 suppressed the platelet aggregation induced by simultaneous stimulation with collagen and CXCL12. The phosphorylation of p38 mitogen-activated protein kinase (MAPK), but not p44/p42 MAPK, was induced by the simultaneous stimulation. In addition, the simultaneous stimulation with collagen and CXCL12 induced the phosphorylation of HSP27 and the subsequent release of phosphorylated-HSP27 from human platelets. SB203580, a specific inhibitor of p38 MAPK, attenuated the platelet aggregation, the phosphorylation of p38 MAPK and HSP27, the PDGF-AB secretion, the sCD40L release and the phosphorylated-HSP27 release induced by the simultaneous stimulation with collagen and CXCL12. These results strongly suggest that collagen and CXCL12 in low doses synergistically act to induce PDGF-AB secretion, sCD40L release and phosphorylated-HSP27 release from activated human platelets via p38 MAPK activation.

Molecular Drivers of Platelet Activation: Unraveling Novel Targets for Anti-Thrombotic and Anti-Thrombo-Inflammatory Therapy

Cardiovascular diseases (CVDs) are the leading cause of death globally-partly a consequence of increased population size and ageing-and are major contributors to reduced quality of life. Platelets play a major role in hemostasis and thrombosis. While platelet activation and aggregation are essential for hemostasis at sites of vascular injury, uncontrolled platelet activation leads to pathological thrombus formation and provokes thrombosis leading to myocardial infarction or stroke. Platelet activation and thrombus formation is a multistage process with different signaling pathways involved to trigger platelet shape change, integrin activation, stable platelet adhesion, aggregation, and degranulation. Apart from thrombotic events, thrombo-inflammation contributes to organ damage and dysfunction in CVDs and is mediated by platelets and inflammatory cells. Therefore, in the past, many efforts have been made to investigate specific signaling pathways in platelets to identify innovative and promising approaches for novel antithrombotic and anti-thrombo-inflammatory strategies that do not interfere with hemostasis. In this review, we focus on some of the most recent data reported on different platelet receptors, including GPIb-vWF interactions, GPVI activation, platelet chemokine receptors, regulation of integrin signaling, and channel homeostasis of NMDAR and PANX1.

Platelet Function in Cardiovascular Disease: Activation of Molecules and Activation by Molecules

Globally, one of the major causes of death is the cardiovascular disease (CVD), and platelets play an important role in thrombosis and atherosclerosis that led to death. Platelet activation can be done by different molecules, genes, pathways, and chemokines. Lipids activate platelets by inflammatory factors, and platelets are activated by receptors of peptide hormones, signaling and secreted proteins, microRNAs (miRNAs), and oxidative stress which also affect the platelet activation in older age. In addition, surface molecules on platelets can interact with other cells and chemokines in activated platelets and cause inflammation thrombosis events and CVD. However, these molecules activating platelets or being activated by platelets can be suggested as the markers to predict the clinical outcome of CVD and can be targeted to reduce thrombosis and atherosclerosis. However, hindering these molecules by other factors such as genes and receptors can reduce platelet activation and aggregation and targeting these molecules can control platelet interactions, thrombosis, and CVD. In addition, dual therapy with the receptor blockers and novel drugs results in better management of CVD patients. Overall, our review will emphasize on the molecules involved in the activation of platelets and on the molecules that are activated by platelets in CVD and discuss the molecules that can be blocked or targeted to reduce the thrombosis events and control CVD.

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.

Function of Platelet Glycosphingolipid Microdomains/Lipid Rafts

Lipid rafts are dynamic assemblies of glycosphingolipids, sphingomyelin, cholesterol, and specific proteins which are stabilized into platforms involved in the regulation of vital cellular processes. The rafts at the cell surface play important functions in signal transduction. Recent reports have demonstrated that lipid rafts are spatially and compositionally heterogeneous in the single-cell membrane. In this review, we summarize our recent data on living platelets using two specific probes of raft components: lysenin as a probe of sphingomyelin-rich rafts and BCθ as a probe of cholesterol-rich rafts. Sphingomyelin-rich rafts that are spatially and functionally distinct from the cholesterol-rich rafts were found at spreading platelets. Fibrin is translocated to sphingomyelin-rich rafts and platelet sphingomyelin-rich rafts act as platforms where extracellular fibrin and intracellular actomyosin join to promote clot retraction. On the other hand, the collagen receptor glycoprotein VI is known to be translocated to cholesterol-rich rafts during platelet adhesion to collagen. Furthermore, the functional roles of platelet glycosphingolipids and platelet raft-binding proteins including G protein-coupled receptors, stomatin, prohibitin, flotillin, and HflK/C-domain protein family, tetraspanin family, and calcium channels are discussed.

Progenitor Cells Activated by Platelet Lysate in Human Articular Cartilage as a Tool for Future Cartilage Engineering and Reparative Strategies

Regenerative strategies for human articular cartilage are still challenging despite the presence of resident progenitor cell population. Today, many efforts in the field of regenerative medicine focus on the use of platelet derivatives due to their ability to reactivate endogenous mechanisms supporting tissue repair. While their use in orthopedics continues, mechanisms of action and efficacy need further characterization. We describe that the platelet lysate (PL) is able to activate chondro-progenitor cells in a terminally differentiated cartilage tissue. Primary cultures of human articular chondrocytes (ACs) and cartilage explants were set up from donor hip joint biopsies and were treated in vitro with PL. PL recruited a chondro-progenitors (CPCs)-enriched population from ex vivo cartilage culture, that showed high proliferation rate, clonogenicity and nestin expression. CPCs were positive for in vitro tri-lineage differentiation and formed hyaline cartilage-like tissue in vivo without hypertrophic fate. Moreover, the secretory profile of CPCs was analyzed, together with their migratory capabilities. Some CPC-features were also induced in PL-treated ACs compared to fetal bovine serum (FBS)-control ACs. PL treatment of human articular cartilage activates a stem cell niche responsive to injury. These facts can improve the PL therapeutic efficacy in cartilage applications.

Circulating angiogenic cells in glioblastoma: toward defining crucial functional differences in CAC-induced neoplastic versus reactive neovascularization

Background

In order to identify suitable therapeutic targets for glioma anti-angiogenic therapy, the process of neovascularization mediated by circulating angiogenic cells (CACs) needs to be scrutinized.

Methods

In the present study, we compared the expression of neovascularization-related genes by 3 circulating CAC subsets (hematopoietic progenitor cells [HPCs], CD34⁺, and KDR⁺ cells; internal controls: peripheral blood mononuclear cells and circulating endothelial cells) of treatment-naïve patients with glioblastoma (GBM) to those of patients undergoing reactive neovascularization (myocardial infarction (MI). CACs from umbilical cord (representing developmental neovascularization) and healthy subjects served as controls. Fluorescent-activated cell sorting was used to isolate CACs, RT-PCR to determine the expression levels of a panel of 48 neovascularization-related genes, and Luminex assays to measure plasma levels of 21 CAC-related circulating molecules.

Results

We found essential differences in gene expression between GBM and MI CACs. GBM CACs had a higher expression of proangiogenic factors (especially, KITL, CXCL12, and JAG1), growth factor and chemotactic receptors (IGF1R, TGFBR2, CXCR4, and CCR2), adhesion receptor monomers (ITGA5 and ITGA6), and matricellular factor POSTN. In addition, we found major differences in the levels of neovascularization-related plasma factors. A strong positive correlation between plasma MMP9 levels and expression of CXCR4 in the CAC subset of HPCs was found in GBM patients.

Conclusions

Our findings indicate that CAC-mediated neovascularization in GBM is characterized by more efficient CAC homing to target tissue and a more potent proangiogenic response than in physiologic tissue repair in MI. Our findings can aid in selecting targets for therapeutic strategies acting against GBM-specific CACs.

Platelet biology and functions: new concepts and clinical perspectives

Platelets - blood cells continuously produced from megakaryocytes mainly in the bone marrow - are implicated not only in haemostasis and arterial thrombosis, but also in other physiological and pathophysiological processes. This Review describes current evidence for the heterogeneity in platelet structure, age, and activation properties, with consequences for a diversity of platelet functions. Signalling processes of platelet populations involved in thrombus formation with ongoing coagulation are well understood. Genetic approaches have provided information on multiple genes related to normal haemostasis, such as those encoding receptors and signalling or secretory proteins, that determine platelet count and/or responsiveness. As highly responsive and secretory cells, platelets can alter the environment through the release of growth factors, chemokines, coagulant factors, RNA species, and extracellular vesicles. Conversely, platelets will also adapt to their environment. In disease states, platelets can be positively primed to reach a pre-activated condition. At the inflamed vessel wall, platelets interact with leukocytes and the coagulation system, interactions mediating thromboinflammation. With current antiplatelet therapies invariably causing bleeding as an undesired adverse effect, novel therapies can be more beneficial if directed against specific platelet responses, populations, interactions, or priming conditions. On the basis of these novel concepts and processes, we discuss several initiatives to target platelets therapeutically.

LIM-only protein FHL2 attenuates inflammation in vascular smooth muscle cells through inhibition of the NFκB pathway

Despite the advent of new-generation drug-eluting stents, in-stent restenosis remains a significant problem in patients with coronary artery disease. In- stent restenosis is defined as the gradual re-narrowing of a stented coronary artery lesion due to arterial damage with subsequent local inflammation of the vessel wall and excessive growth of the vascular smooth muscle cells (vSMCs). Four-and-a-half LIM-domain protein 2 (FHL2) is a scaffold protein involved in regulating vSMC function and inflammation. Previously we have demonstrated that FHL2 prevents vSMC proliferation in a murine carotid artery ligation model. However, the effect of FHL2 on the inflammatory response of the vSMCs is not investigated. Therefore, we studied the inflammatory response in the vessel wall of FHL2-deficient (-KO) mice after carotid artery ligation. We found that circulating cytokines and local macrophage infiltration in the ligated carotid vessels were increased in FHL2-KO mice after carotid artery ligation. Moreover, FHL2-KO vSMCs showed increased secretion of cytokines such as SDF-1α and RANTES, and enhanced activation of the NFκB pathway. Finally, we found that blocking the NFκB signalling pathway abrogated this pro-inflammatory state in FHL2-KO vSMCs. Taken together, our results demonstrate that FHL2 decreases the inflammatory response of vSMCs through inhibition of the NFkB-signalling pathway.

Stromal cell derived factor-1 and long-term prognosis in acute coronary syndrome

Aim: To explore long-term prognostic value of SDF-1 in acute coronary syndrome (ACS). Materials & methods: We included 254 patients with ACS. Plasma SDF-1 was measured and patients were classified into tertiles of SDF-1. Results: Multivariate analysis showed third tertile of SDF-1 as an independent predictor of all-cause death (HR: 2.5; 95% CI: 1.2-5.2; p = 0.011) and the composite of major adverse cardiovascular and cerebrovascular events (HR: 1.8; 95% CI: 1.1-3.1; p = 0.031). SDF-1 added to a clinical model can improve all-cause death prediction (net reclassification improvement 0.362; 95% CI: 0.423-0.681; p = 0.027). Conclusion: SDF-1 is an independent predictor of all-cause mortality and major adverse cardiovascular and cerebrovascular events in long-term follow-up of patients with ACS and adds prognostic information beyond traditional cardiovascular risks factors.

Good Fences Make Good Neighbors: Human Immunodeficiency Virus and Vascular Disease

Cardiovascular disease, venous thrombosis, and microvascular disease in people with HIV (PWH) is predicted to increase in an aging HIV-infected population. Endothelial damage and dysfunction is a risk factor for cardiovascular events in PWH and is characterized by impaired vascular relaxation and decreased nitric oxide availability. Vascular disease has been attributed to direct viral effects, opportunistic infections, chronic inflammation, effects of antiretroviral therapy, and underlying comorbid conditions, like hypertension and use of tobacco. Although biomarkers have been examined to predict and prognosticate thrombotic and cardiovascular disease in this population, more comprehensive validation of risk factors is necessary to ensure patients are managed appropriately. This review examines the pathogenesis of vascular disease in PWH and summarizes the biomarkers used to predict vascular disease in this population.

Co-culture of Platelets with Monocytes Induced M2 Macrophage Polarization and Formation of Foam Cells: Shedding Light on the Crucial Role of Platelets in Monocyte Differentiation

Objective

Far beyond hemostasis and thrombosis, significant evidence has indicated the critical role of platelets in atherosclerosis. SDF-1 is among the pro-inflammatory chemokines that are increased in platelets of patients with coronary artery disease (CAD). The goal of the current work is to identify the in vitro effect of platelets from either CAD patients or healthy volunteers on the induction of macrophages and foam cells.

Materials and Methods

The expression of SDF-1 on platelet surfaces in CAD patients and healthy volunteers was investigated using flow cytometry. We also evaluated the CXCR4/CXCR7 expression on monocytes from buffy coats of healthy volunteers. The effect of platelets from CAD patients and healthy volunteers on differentiation of monocytes and foam cell formation was evaluated using Oil Red O (ORO) staining. Flow cytometry and real-time PCR were also employed to evaluate surface markers and mRNA expression of genes involved in this process after co-culture of platelets with monocytes.

Results

Monocytes in co-culture with platelets acquired a spindleshape appearance and ORO-positive lipid droplets. In addition, platelets could induce CD163 expression, as an important marker of M2 macrophage, and upregulate the mRNA expression of the SRB, CD36, ACAT, LXR-α, and ABCA1 genes in monocytes. Notably, platelets of CAD patients with higher expression of SDF-1, increased the expression of genes encoding SRB and CD36 as compared to platelets of healthy volunteers.

Conclusion

Our results indicate that platelets from CAD patients could provoke monocyte differentiation into macrophages with an M2 phenotype, which in turn may participate in an atheroprotective process.

Platelet concentrate supernatants alter endothelial cell mRNA and protein expression patterns as a function of storage length

BACKGROUND

Platelet transfusions are safe but can nevertheless cause serious adverse reactions (SARs). This study investigated the effects of platelet biological response modifiers (BRMs) that accumulate during storage and are commonly associated with transfusion adverse reactions.

STUDY DESIGN AND METHODS

Endothelial cells (ECs), that is, EA.hy926, were exposed in vitro to supernatants of platelet components (PCs) that had been either implicated or not in SARs. The EC Biology RT² Profiler PCR Array was used at the same time to study 84 genes related to functions of ECs. Soluble cytokines and surface expression of EC markers were determined by Luminex/enzyme-linked immunosorbent assay technology and flow cytometry, respectively. Apoptosis and scratch wound assays were performed using IncuCyte technology.

RESULTS

In vitro exposure of EA.hy926 monolayers with Day 0, 1-2, and 3-4 stored PC supernatants resulted in decreases in surface expression of markers of ECs. There was differential production of soluble BRMs in the tested cell line. Exposure to the supernatants of PCs that had been implicated in SARs showed a significant difference in the expression of the EC surface markers. EC mediators also responded differently when exposed to PC supernatants of different storage times and PCs involved in SARs.

CONCLUSION

PC supernatants collected at Day 1-2 activate fewer cell lines of ECs compared with supernatants collected at Day 3-4. Moreover, PC supernatants involved in SARs appear to alter EC activation compared with the control and storage length.

The role of platelets in the development and progression of pulmonary arterial hypertension

Pulmonary arterial hypertension is a multifactorial disease characterized by vasoconstriction, vascular remodeling, inflammation and thrombosis. Although an increasing number of research confirmed that pulmonary artery endothelial cells, pulmonary artery smooth muscle cells as well as platelets have a role in the pulmonary arterial hypertension pathogenesis, it is still unclear what integrates these factors. In this paper, we review the evidence that platelets through releasing a large variety of chemokines could actively impact the pulmonary arterial hypertension pathogenesis and development. A recent publication revealed that not only an excess of platelet derived cytokines, but also a deficiency may be associated with pulmonary arterial hypertension development and progression. Hence, a simple platelet blockade may not be a correct action to treat pulmonary arterial hypertension. Our review aims to analyse the interactions between the platelets and different types of cells involved in pulmonary arterial hypertension pathogenesis. This knowledge could help to find novel therapeutic options and improve prognosis in this devastating disease.

Cancer metastasis versus stem cell homing: Role of platelets

One of the major obstacles in achieving a successful stem cell therapy is insufficient homing of transplanted cells. To overcome this obstacle, understanding the underlying mechanisms of stem cell homing is of obvious importance. Central to this review is the concept that cancer metastasis can be viewed as a role model to build up a comprehensive concept of stem cell homing. In this novel perspective, the prosurvival choices of the cancerous cells in the bloodstream, their arrest, extravasation, and proliferation at the secondary site can be exploited in favor of targeted stem cell homing. To date, tumor cells have been found to employ a wide variety of strategies to promote metastasis. One of these strategies is through their ability to activate platelets and subsequently activated platelets serve cancer cell survival and metastasis. Accordingly, in the first part of this review the roles of platelets in cancer metastasis as well as stem cell homing are discussed. Next, we provide some lessons learned from cancer metastasis in favor of developing strategies for improvement of stem cell homing with emphasis on the role of platelets. Based on direct or indirect evidence from metastasis, strategies such as manipulation of stem cells to enhance interaction with platelets, preconditioning-pretreatment of stem cells with platelets in vitro, and coinjection of both stem cells and platelets are proposed to improve stem cell homing.

Individualized antithrombotic therapy in high-risk cardiovascular patients

Recent guidelines suggest dual antiplatelet therapy (DAPT) after 'drug-eluting' stent (DES) implantation for 6 months in stable patients and for 12 months in patients after acute coronary syndrome. Serious complications after stent implantation include stent thrombosis, recurrent myocardial infarction, ischemic stroke, cardiovascular death and bleeding. These complications also occur beyond 1 year after coronary intervention. Thus, it is important to consider whether a prolonged DAPT (>12 months after percutaneous coronary intervention) is of benefit to lower thrombo-ischemic events in high-risk patients. This review addresses the results of recent randomized clinical studies (DAPT, ITALIC, OPTIDUAL and PEGASUS) and meta-analyses to support the author's view of which patient collectives might benefit from prolonged DAPT.

Increased platelet content of SDF-1alpha is associated with worse prognosis in patients with pulmonary prterial hypertension

Inflammatory processes and platelet activity play an important role in the pathophysiology of pulmonary arterial hypertension (PAH). Enhanced IL-6 signaling and higher concentration of stromal-derived factor alpha (SDF-1) have been previously shown to be linked with prognosis in PAH. We hypothesized that platelets of PAH patients have higher content of IL-6 and SDF-1 and thus are involved in disease progression. We enrolled into study 22 PAH patients and 18 healthy controls. Patients with PAH presented significantly higher plasma concentrations and platelet contents of IL-6, sIL-6R, and SDF-1 than healthy subjects (platelet content normalized to protein concentration: IL-6 (0.85*10^-10 [0.29 - 1.37] vs. 0.45*10^-10 [0.19-0.65], sIL-6R 1.54*10^-7 [1.32-2.21] vs. 1.14*10^-7 [1.01-1.28] and SDF-1 (2.72*10^-7 [1.85-3.23] vs. 1.70*10^-7 [1.43-2.60], all p < 0.05). Patients with disease progression (death, WHO class worsening, or therapy escalation, n = 10) had a significantly higher platelet SDF-1/total platelet protein ratio (3.68*10^-7 [2.45-4.62] vs. 1.69*10^-7 [1.04-2.28], p = 0.001), with no significant differences between plasma levels. Kaplan-Meier analysis revealed that patients with higher platelet SDF-1/total platelet protein ratio had more frequently deterioration of PAH in the follow-up (15.24 ± 4.26 months, log-rank test, p = 0.01). Concentrations of IL-6, sIL-6 receptor and SDF-1 in plasma and platelets are elevated in PAH patients. Higher content of SDF-1 in platelets is associated with poorer prognosis. Our study, despite of limitation due to small number of enrolled patients, suggests that activated platelets may be an important source of cytokines at the site of endothelial injury, but their exact role in the pathogenesis of PAH requires further investigation.